The Construction Process (a) Provide a smooth surface

The construction process begins when an owner, (b) Resist wear

either public or private, decides to enhance land with (c) Resist cracking despite upward water pressure or
permanent or semi-permanent structures and secures uneven soil settlement
financing for the project. Owners may fund projects (d) Keep moisture out
through construction loans, mortgages, tax revenues, (e) Resist corrosive attack from soil and water
bonds, or user fees. Once the need and funding are 3. Basement walls
established, the owner hires a design professional, such (a) Support the rest of the building
as an architect or engineer, to create working drawings (b) Resist lateral side pressure from the earth
and specifications detailing the project, including (c) Keep moisture out
materials and compliance with building codes and (d) Resist corrosive attack from soil and water
regulations. 4. Other floors and ceilings
Contractors then use these documents to prepare (a) Provide a smooth surface
bids or estimates. The two primary contract types are (b) Resist wear
lump sum and unit price. In lump sum contracts, the (c) Support furniture and people without sagging
contractor estimates all costs upfront, while unit price excessively or breaking
contracts allow for adjustments based on actual material (d) Provide a satisfactory appearance
quantities. Change orders are used to manage any (e) Clean easily
modifications to the project scope. (f) Insulate against noise transmission
Safety is a critical aspect of construction, governed by 5. Outside walls
OSHA regulations, and contractors must maintain safety (a) Support floors and roof
data sheets for materials used. Contractors also create (b) Resist lateral wind pressure
and update project schedules to manage resources (c) Provide a satisfactory appearance inside and out
effectively and ensure timely completion. (d) Insulate against noise and heat transmission
Materials used in construction can be basic or (e) Keep moisture out
manufactured, and assemblies may be fully or partially 6. Partitions
built in factories. Contractors must select materials that (a) Support floors and roof
meet technical specifications and submit them for (b) Provide a satisfactory appearance
designer approval. During construction, the owner is (c) Insulate against noise transmission
represented by the designer, who oversees contract 7. Roof
compliance and quality assurance, while inspectors and (a) Keep moisture out
independent testing laboratories ensure materials meet (b) Support snow and other weights
specifications. (c) Resist wind pressure and wind uplift
Overall, the construction process involves (d) Provide a satisfactory appearance
careful planning, financing, design, contracting, safety (e) Insulate against noise and heat transmission
management, and quality control, with various
stakeholders including owners, designers, contractors, Materials used in smaller buildings have become
and suppliers working collaboratively to achieve the somewhat standardized, but new materials are
project goals. continually being introduced to reduce costs and enhance
living conditions. Understanding these materials is
essential for their effective development and application.
Construction projects, whether building structures,
Need for Materials with Various Qualities paving streets, or laying pipelines, involve various
The construction industry requires materials for
components that must fulfill specific functions, often
a vast range of uses. The qualities these materials
requiring a wider range of materials than one might
possess are as varied as the strength and flexibility
expect.
required of an elevator cable or the warm, wood grain
As people's needs evolve, there is a demand for
appearance and smooth finish of a birch or maple
materials with new properties. For instance, lightweight
cabinet.
materials that can withstand higher temperatures are
The construction of a simple building, such as a
necessary for space exploration. Innovations may
house, requires selection of materials to perform the
involve special treatments for existing materials, such as
following tasks:
making wood fire-resistant, or the creation of entirely
1. Footing
new materials, like steel, which has enabled the
(a) Distribute the weight of the building to the soil
construction of longer-span bridges that were previously
(b) Resist cracking despite uneven soil settlement
unachievable with wood.
(c) Resist corrosive attack from soil and water
2. Basement floor
Selecting Materials Reusability and Recycling: Construction materials
The selection of construction materials is should be recyclable and reusable. Many materials, such
essential for creating satisfactory man-made objects, as concrete and steel, can be processed for reuse, and
requiring knowledge of materials and a systematic advancements in production technologies are reducing
selection process. Designers are responsible for choosing energy costs.
materials that meet performance requirements while Sustainable practices are increasingly adopted
adhering to budget constraints. They must consider globally, not only for resource conservation but also for
factors such as the service each component provides, their economic benefits, including job creation and lower
appearance, initial cost, maintenance expenses, and energy costs. In the U.S., the U.S. Green Buildings
expected lifespan. Maintenance includes cleaning, Council (USGBC) promotes sustainability through the
corrosion prevention, and repairs, and designers must Leadership in Energy and Environmental Design
balance original costs with maintenance expenses, as (LEED) certification program, which encourages
low initial costs can lead to higher long-term measurable sustainability in building projects. Many
maintenance. government agencies now require LEED certification,
Designers can either specify exact materials and private owners are also pursuing it for its cost-saving
(material specifications) or outline performance criteria advantages. Design and construction professionals may
(performance specifications). Material specifications can seek LEED accreditation to demonstrate expertise in
be open (allowing substitutions) or closed (no sustainable practices.
substitutions allowed), while performance specifications
leverage the builder's expertise in selecting economical
materials and may include bonus and penalty clauses Properties of Materials
based on performance metrics. Thermal Expansion
The material selection process typically involves All building materials undergo size changes with
three steps: analyzing the problem (performance, temperature fluctuations, contracting when cold and
lifespan, cost, and maintenance), comparing available expanding when hot. When uniformly heated, a material
materials against these criteria, and selecting the expands, with each unit length increasing by a specific
appropriate material type, size, shape, finish, and percentage. This expansion occurs in all directions and
installation method. This process often employs life varies by material. To predict the extent of expansion
cycle-cost analysis to determine the most economical and contraction, each material has a coefficient of
material or system over its useful life, particularly for expansion, which is a decimal indicating the increase in
materials subjected to heavy use, such as pavements or length per unit length for each degree of temperature
HVAC systems. The goal is to identify options that yield increase. While this coefficient can vary slightly with
the lowest overall costs throughout their lifespan. temperature, it is generally consistent within the typical
temperature ranges encountered.
Sustainability For example, the coefficient of expansion for
The concept of sustainability in building design wrought iron is 0.0000067 inches per inch per °F (or
and construction has emerged from the need to better 0.0000121 cm per cm per °C), meaning that for every
utilize material and energy resources, enhance the 1°F increase, each inch of wrought iron expands by
environment, and reduce costs while creating jobs. 0.0000067 inches. As temperatures decrease, the
Terms like "green building" and "environmentally dimensions contract at the same rate. When combining
friendly design" reflect this focus. Historically, buildings materials in a construction assembly, it is important that
were demolished at the end of their useful life, with they have similar coefficients of expansion, or
materials discarded in landfills, leading to resource provisions must be made to accommodate their differing
depletion and environmental damage. expansions. A common example is the use of steel
Sustainability aims to improve resource management reinforcement in concrete, where both materials have
without hindering new construction. Key principles comparable thermal expansion properties. Additionally,
include: long structural members may require expansion joints to
Efficient Resource Use: New and renovated buildings allow for significant changes in size due to temperature
should maximize the use of finite materials, energy, and variations.
labor, promoting longevity through careful material
selection and detailing.
Energy Efficiency: Buildings should operate in ways
that significantly reduce energy consumption and
greenhouse gas emissions. Material choices that enhance
natural ventilation and thermal control are essential.
 quantified as the maximum stress it can withstand before
failure, which occurs when the material can no longer
fulfill its intended purpose, either by breaking or
deforming excessively.
Deformation is the change in dimensions caused
by stress, and strain is the ratio of the change in
dimension to the original dimension, expressed as a
unitless ratio. The behavior of materials under stress can
be illustrated through examples like stretching or
Thermal Conductivity compressing rubber. The failure strength of a material is
Buildings must maintain a temperature that is determined by the stress at which it can no longer
warmer than the surrounding air in cold climates and perform its function, which can vary based on the
cooler in hot climates. Heat naturally flows from warmer material's application.
to cooler areas until temperatures equalize, and this heat Designers use knowledge of the stress that
transfer occurs through conduction in solid materials. causes failure to inform their designs, but structures are
Managing heat movement is crucial, as it incurs costs for not designed to operate at failure points. Instead, an
heating and cooling, and unwanted heat flow can be allowable stress is established, representing the
expensive. maximum stress that a material can safely endure
The rate of heat transfer through materials is without risking failure.
measured by thermal conductivity (U), expressed in The failure stress of a material is greater than its
British thermal units (Btu) per square foot per hour per allowable stress, with the ratio between the two known
°F difference in temperature. Insulation, which has a low as the safety factor. For example, if the failure stress is
U value, is used to reduce heat flow in large surfaces like twice the allowable stress, the safety factor is two.
walls and roofs. The U value is influenced by material Failure stress is typically determined through
density, and materials with dead air spaces are effective experimental testing, and allowable stresses are
insulators. Expanded plastic foam is a notable insulation published by organizations such as the American
material, consisting mostly of air or gas, while some Institute of Steel Construction and the American
structural materials like wood and lightweight concrete Concrete Institute. Designers aim to select materials and
also provide insulation due to their low U values. dimensions that keep actual stresses at or below
Thermal resistance, denoted as R, measures a allowable levels for economic efficiency.
material's resistance to heat flow, with R being the There are three types of stresses: compressive,
reciprocal of U. Higher R values indicate better tensile, and shearing, which depend on the direction of
insulating properties. Construction materials are the applied forces. Stress is calculated by dividing the
assigned R values based on their thickness or per inch. force by the original area it acts upon, and while tensile
For example, a 4-inch thick expanded polystyrene panel and compressive stresses are assumed to be uniformly
has an R value of 16. Calculating heat loss and cooling distributed, shearing stresses can vary across an area.
loads for large buildings is typically done by mechanical The original cross-sectional area is used for stress
engineers in collaboration with architects to design calculations, as it simplifies computations and reflects
effective heating, ventilation, and air conditioning the material's initial properties.
(HVAC) systems. Materials respond differently to stress: ductile
materials can be stretched into wires, malleable materials
Strength and Stress can be flattened, and brittle materials tend to break
All construction materials must withstand loads suddenly with little deformation. Testing for strength
or forces, which are categorized into dead loads and live typically involves applying a steadily increasing force
loads. Dead loads consist of the weight of structural until failure occurs, but real-world applications may
elements and permanent equipment, while live loads involve prolonged or repeated forces, leading to
include variable factors such as occupants, furniture, phenomena like creep (slow deformation over time) and
wind, and earthquakes. fatigue (failure after repeated stress cycles).
When a force is applied to an object, it is The endurance limit is the maximum stress a
assumed to spread uniformly over the object's internal material can withstand indefinitely without failing, while
area, although this is not entirely accurate. Stress is toughness measures a material's ability to absorb energy
defined as the force per unit area and is measured in before fracture, calculated as the area under the stress-
pounds per square inch (psi) or kilopounds per square strain curve. Resilience refers to a material's ability to
inch (Ksi). The strength of a material refers to its ability return to its original shape after deformation, with the
to resist force, which depends on the material's modulus of resilience representing the energy absorbed
properties, size, and shape. The strength of a material is
up to the elastic limit. Both toughness and resilience are under the same force, both materials are equally elastic
important for materials subjected to impact loads. within their elastic range if they return to their original
shape after the force is removed.
Plasticity, on the other hand, is the property that
allows a material to retain a new size or shape after
being deformed by a force. Many materials exhibit
complete elasticity up to a certain stress level known as
the elastic limit. Beyond this limit, materials undergo
permanent deformation, resulting in both recoverable
elastic strain and permanent plastic strain. Initially, strain
is entirely elastic until the elastic limit is reached, after
which any additional strain becomes plastic.
The yield point is the lowest stress at which
strain increases without an increase in stress, marking a
point of zero slope on the stress-strain curve. This point
is significant for materials like steel, although some
Modulus of Elasticity steels do not exhibit a clear yield point. The stress at
Strain is directly proportional to the stress that which excessive plastic deformation occurs is termed
causes it within a considerable range for many materials. yield strength. In cases where the proportional limit and
Beyond this range, additional stress increments lead to yield point are not clearly defined, an offset yield
greater strain increments, with the point at which this strength is determined by drawing a line parallel to the
change occurs known as the proportional limit. The elastic portion of the stress-strain curve at a specified
modulus of elasticity, or Young’s modulus, is defined as strain offset, typically 0.002.
the constant ratio of stress to strain (E = s/e) and is a Materials behave differently at varying
measure of a material's stiffness or resistance to temperatures; they tend to be stronger and more brittle at
deformation. Stiffer materials exhibit less deformation low temperatures and weaker and more ductile at high
under a given stress compared to less stiff materials. temperatures. However, these changes are often not
Different materials have distinct modulus of noticeable unless the temperature variations are extreme.
elasticity values; for example, A36 steel has a modulus
of 30 million psi, gray cast iron has 15 million psi, and Inspection and Testing
concrete is around 3 million psi, varying with its Inspection involves examining a product or
compressive strength. Some materials do not maintain a observing an operation to determine its quality, which
constant stress-strain relationship, making it difficult to may include measuring dimensions, weighing, or
define a modulus of elasticity for them. In such cases, an performing simple tests. While inspections can raise
approximate E value may be used for design purposes, questions that lead to further testing, tests involve
although it is only accurate at specific stress levels. applying measurable influences to materials and
The modulus of elasticity can be determined assessing their effects. For example, a common test
through testing, where a sample is subjected to measures a material's strength by applying a force until it
increasing stress while measuring the resulting strain. breaks or deforms.
This relationship is typically plotted to analyze the Inspections and tests can be categorized by purpose:
material's behavior. The standard method for tension Quality Assurance or Acceptance: These inspections
testing of metallic materials is outlined by the American and tests determine if materials meet specific
Society for Testing and Materials (ASTM) E8. The requirements for acceptance. Manufacturers, builders,
modulus of elasticity applies to both compressive and and owners conduct these checks on raw materials and
tensile stresses, and for most materials, the values are finished products.
similar in both cases. The relationship between shearing Quality Control: Periodic inspections and tests on
stress and shearing strain is represented by the modulus selected samples ensure ongoing product acceptability. If
of rigidity (Es), which is generally lower than the quality issues arise, corrective actions are taken.
modulus of elasticity. Research and Development: Inspections and tests are
performed to understand new products and evaluate
Elastic and Plastic Properties inspection procedures. Extensive testing is conducted
Elasticity is the property of a material that before new products are marketed.
allows it to return to its original size and shape after the For example, a company producing concrete
removal of a force. It is not measured by the amount of masonry units (CMUs) tests a new aggregate material
strain caused by stress but by how completely the before and during production to ensure quality.
material returns to its original form. For example, while Continuous inspections are performed on finished
a metal wire may not stretch as much as a rubber band
products, and a final inspection is conducted before There is often overlap between aggregates and
project completion. soil, as both originate from rock. Some naturally
Test results can vary due to material heterogeneity occurring sand and gravel can be used as aggregates
and the inherent variability in testing methods. To without processing, while most aggregates are processed
improve accuracy, larger sample sizes and proper soil. However, soil that remains in place as a foundation
random selection are recommended. The degree of for construction is not classified as aggregate, regardless
repeatability of tests should also be considered when of its composition.
interpreting results. Statistical methods can help
determine appropriate sample sizes to ensure they are Common Terms
representative of the whole material being tested. Terms related to concrete aggregates are defined in
ASTM C125, which provides standard definitions
Standards applicable to various types of aggregates. Key
Designers and builders often require specific definitions include:
properties in the materials they use, and they must Coarse Aggregate: Material predominantly retained on
clearly specify the degree of each property in a way that the No. 4 (4.76-mm) sieve.
both they and the supplier understand. It is essential for Fine Aggregate: Material passing the 3/8inch sieve,
the supplier to demonstrate that the materials meet these mostly passing the No. 4 sieve, and predominantly
specified properties. While unique tests can be created retained on the No. 200 (74-micron) sieve.
for specific applications, standard measuring and testing Gravel: Granular material predominantly retained on the
methods are typically available, allowing both parties to No. 4 sieve, resulting from the natural disintegration and
communicate effectively using common terminology and abrasion of rock or processing of weakly bound
reproducible methods. conglomerate.
Material specifications outline the required Sand: Granular material passing the No. 4 sieve and
properties and their acceptable limits, while testing predominantly retained on the No. 200 sieve, resulting
methods detail how to conduct tests and measure results. from the natural disintegration and abrasion of rock or
When materials are tested and meet the required processing of friable sandstone.
properties, they are considered compliant with the Bank Gravel: Gravel found in natural deposits, often
standards. mixed with fine materials like sand or clay.
Inspections often involve measurements, which Crushed Gravel: Gravel that has been artificially
can range from simple size checks, like measuring the crushed, with fragments having at least one fractured
diameter of a pipe, to more complex assessments, such face.
as determining the air content in concrete. For example, Crushed Stone: Material resulting from the artificial
the size of cracks in wood must be measured according crushing of rocks, boulders, or large cobblestones, with
to standard specifications, as different types of cracks all faces resulting from the crushing process.
require different measurement methods. Consistency in Crushed Rock: Material from the artificial crushing of
testing and inspection is crucial for accurate evaluation, all rock, with all faces resulting from the crushing or
ensuring that results can be compared reliably with past blasting process.
data. Blast-Furnace Slag: A nonmetallic product consisting
mainly of silicates and aluminosilicates of lime,
Aggregates developed in molten form alongside iron in a blast
Aggregates are naturally occurring particles of furnace.
various shapes, including sand, gravel, stones, and These definitions facilitate discussions about
crushed rock, as well as by-products from industrial concrete aggregates in construction and engineering
processes or mining. The term generally refers to contexts.
mineral particles derived from rock, which includes
materials like fieldstone, boulders, and crushed rock. Sources
Aggregate sizes can range from several inches to the The Earth's crust consists of solid rock known as
smallest grains of sand, with particles smaller than sand bedrock, which is covered by soil particles derived from
considered impurities, although they may be tolerated or it. Soil is classified by particle size into gravel, sand, silt,
removed depending on the intended use. and clay, with gravel being the largest and clay the
The road building industry is the largest smallest. Natural aggregates include sand, gravel, and
consumer of aggregates, using them as bases or cushions larger stones, as well as bedrock that has been reduced to
under traffic, in pavements, and as ballast for railroad particle size through natural processes or manufacturing.
tracks. Aggregates also serve as protective coatings and Aggregates originate from the weathering and
are used in water filtration to retain suspended solids erosion of parent rock, which are transported and
while allowing water to pass through. deposited in various forms, such as sand and gravel
banks. The processes of breaking, transporting, and and protect navigation channels. In some cases, when
depositing aggregates are ongoing, influenced by factors channels or harbors are deepened for shipping, the
like temperature changes that cause rock to crack and extracted aggregate can have commercial value.
fracture. As particles travel, they become smoother and
more rounded due to abrasion from rolling downhill or Land Sources
being carried by water or glacial ice. Aggregates are extracted from natural banks,
Glacial deposits consist of a mix of particle pits, or mines using equipment such as bucket loaders,
sizes, with till being dropped directly by glaciers and power shovels, draglines, and power scrapers. Before
outwash being carried further by meltwater, resulting in accessing the deposits, unsuitable soil and vegetation,
smoother and more uniform aggregates. The most known as overburden, must be removed through a
rounded particles are found near large bodies of water, process called stripping, typically done with bulldozers
where they are continuously washed by waves. and power scrapers. Once the overburden is cleared, the
surface is prepared for drilling.
The type of deposit beneath the surface can often
be inferred from the landform, which can be studied
through aerial photographs or field trips. Test pits or
boreholes are created to collect samples for examination
and testing to assess their suitability for intended uses.
Certain glacial deposits may contain undesirable silt and
clay, while glacial outwash is preferred for its cleaner,
In rivers and streams, the size of particles carried is more uniform aggregates.
proportional to the flow velocity, which varies with If crushed rock is required, it must be blasted
slope and water quantity. This leads to the sorting of loose with explosives and then crushed to the desired
aggregates by size along the streambed, with larger size. This process yields uniform-sized particles, which
particles settling in slower-flowing sections. Glaciers are angular and rough, making them suitable for specific
also contribute to aggregate formation by scraping rock applications compared to the smoother, rounded shapes
from valley sides and depositing it as they melt. of naturally formed aggregates. Rock formations tend to
Aggregates are commonly extracted from former have consistent characteristics, providing a reliable
lake and stream beds, which may now be elevated due to supply of quality aggregate, whereas sand and gravel
geological movements. Historical glaciation periods deposits often contain a mix of inferior and acceptable
have left significant deposits of aggregate, particularly in particles due to their geological transport history.
the northern hemisphere, where glaciers once covered Bank-run aggregates typically contain a range of
vast areas and their meltwater streams deposited large sizes and are screened to separate them, with additional
quantities of gravel. These deposits are now valuable crushing as needed. However, if larger sizes are
sources of aggregates. required, crushed rock is preferred. Generally, crushed
rock sources offer more versatility, while natural banks
Methods of Extraction and Processing may be more economical for specific aggregate types.
Underwater Sources
Aggregates are extracted from lake and river Rock Types
bottoms using barge-mounted dredges, which employ Natural mineral aggregates, as described in
either a single scoop or an endless chain of scoops, as ASTM C294, are derived from three main types of rock
well as draglines. The process can disturb the bottom based on their origin: igneous, sedimentary, and
and cause some undesirable fine particles and metamorphic.
lightweight materials to wash away during extraction. Igneous Rock: Formed from molten material that cooled
Once loaded onto barges, the aggregates are transported and solidified. Its texture can vary from coarse grains to
to shore, where they are unloaded and stockpiled. glasslike smoothness, depending on the cooling rate.
Alternatively, aggregates can be pumped Common examples include granite (coarse-grained,
through pipes to a barge or directly to the shore, light-colored) and gabbro (coarse-grained, dark-colored),
accommodating sizes up to 6 inches or larger. To both widely used in construction. Basalt is a fine-grained
effectively locate valuable aggregates, knowledge of equivalent of gabbro, while diabase is intermediate in
stream flow and deposition characteristics is essential. grain size. Trap rock, which includes diabase and basalt,
Samples are examined for desired properties before is valued for its hardness and low abrasiveness.
equipment is deployed, and unsuitable materials may Lightweight aggregates can be produced from pumice
need to be removed to access the desired aggregates. and scoria, which are filled with bubbles.
The operating area is typically regulated by Sedimentary Rock: Formed from particles deposited by
government guidelines to maintain natural water flow water, wind, or glaciers, often showing stratification.
Conglomerate is formed from gravel, while sandstone Properties and Uses
and quartzite are formed from sand. Siltstone and The effectiveness of aggregates in engineering
claystone are softer rocks made from silt or clay, with and construction relies on various properties that can
shale being a harder claystone. While sedimentary rocks predict their performance. When selecting aggregates for
generally break along stratification lines, limestone and specific tasks, it is essential to consider local availability
dolomite, formed from marine remains, do not break into and design specifications accordingly, rather than
flat particles and can serve as satisfactory aggregates. imposing rigid requirements. For instance, states with
Metamorphic Rock: This type results from the abundant high-quality natural aggregates tend to have
alteration of igneous or sedimentary rock due to intense more stringent specifications.
heat and pressure. Metamorphic rocks are typically Key qualities that determine the usefulness of aggregate
dense but may form platy particles, which are particles include:
undesirable for aggregate use. Examples include marble Weight: Important for stability in applications like
(recrystallized limestone) and slate (hardened shale). riprap, erosion control, and retaining walls.
Gneiss and schist are common metamorphic rocks that Weathering Resistance: The ability to withstand
can be derived from granite and exhibit varying degrees repetitive freezing and thawing, known as soundness, is
of lamination. crucial for durability, especially for outdoor use.
Aggregates can come from various rock types, Compressive Strength: Necessary for aggregates used
and while identifying the parent rock can provide as bases to support structures or in concrete.
general characteristics, testing is necessary to confirm Particle Strength: Individual particles must resist
specific properties. Once the characteristics of a breaking, crushing, or pulling apart under load to prevent
geological formation are known, only spot checks are movement and failure.
needed for verification, as the rocks within a formation Abrasion Resistance: Aggregates should withstand
are typically formed under similar conditions. wear from rubbing and abrasion during processing and
in service, as insufficient resistance can lead to size and
shape changes.
Adhesion: The ability to bond with cementing agents is
vital for effective concrete mixtures.
Permeability: The capacity to allow water flow without
losing strength or displacing particles is important for
certain applications.
Aggregates are subjected to various stresses,
including tension and compression, particularly in
concrete structures. They also face abrasion from
handling and traffic, which can alter their size and
gradation. Therefore, selecting aggregates with the right
properties is essential for ensuring the longevity and
performance of construction materials.

Miscellaneous Uses
Riprap consists of various sizes of stone used to
protect natural or man-made earthworks from erosion
caused by water. The stones must be large enough to
withstand the force of flowing water without being
displaced. For example, along reservoir shores or dam
edges, aggregates ranging from baseball to basketball
size are typically placed in a belt from low to high water
levels. In areas with swiftly flowing streams, larger
stones are often fitted together like a stone wall to
provide stability along the banks.
Irregular, slablike broken rock is commonly
used and is often positioned with equipment like cranes
or backhoes. The primary requirements for effective
riprap are high weight and low cost. This rock material
helps prevent the erosion of fine soil particles along
shorelines, dam toes, and piers in waterways, thereby
maintaining the integrity of these structures.
 When riprap is insufficient due to steep banks or aggregate fails to resist the shearing stress, particles may
strong currents, gabions can be used to secure stones in be forced closer together or pushed aside, disrupting the
place. A gabion is a basket-like container made of heavy overall structure.
steel mesh, designed to hold fist-sized stones or larger. When aggregate particles are pushed closer together,
These structures can act as riprap or as retaining walls to the surface settles, which can be viewed as strain
stabilize earth banks and can be stacked to create taller resulting from imposed stress. To prevent harmful
barriers. Gabions are filled with stones either by hand or settlement, aggregates should be compacted before use,
machinery and are wired together to form a continuous, ensuring that significant settlement occurs beforehand.
flexible structure that can adapt to soil settlement and The only other way aggregates can settle is through
water currents without breaking. crushing, which typically only happens with soft or
Gabions are permeable, allowing water to flow brittle particles that should be avoided.
through and preventing pressure buildup behind the wall, In practice, good aggregates will move before they
which helps avoid collapse. They are cost-effective can be crushed, as horizontal displacement occurs under
when stones are readily available nearby, and their rustic lower forces than those required to crush the particles.
appearance can be more aesthetically pleasing than The key factor in this movement is shearing strength,
concrete or steel alternatives. which is determined by the load that can be supported
To manage water flow and sediment deposition, without significant horizontal movement. This horizontal
structures such as training walls, breakwaters, groins, or movement is resisted by friction and interlocking
jetties are built from loose stones or gabions. These low between particles.
walls guide water currents to deposit materials where The friction between particles depends on their
desired or remove them from unwanted areas. The surface roughness; rougher surfaces provide more
primary requirements for the materials used in these resistance to sliding. Interlocking resistance is influenced
applications are high unit weight and good weather by particle shape, being greatest for angular particles like
resistance, with natural stones being favored for their crushed rock and least for well-rounded particles like
low cost and availability. beach sand.
While the lifespan of stones in these structures is When a load is applied, such as from vehicle wheels,
generally long, they may experience abrasion, breakage, it acts on multiple particles, complicating the force
or washing away over time. Regular inspections of wire transmission process. The load is transmitted outward in
gabions for corrosion or wear are necessary, and when all directions, creating a larger area of influence as it
replacement is needed, the entire structure can be moves downward, rather than acting on a single particle.
replaced or a new one built over the existing one. If enough horizontal movement occurs at multiple
contact points, the aggregate can fail.
Aggregate and Strength Figure 2–11 depicts the failure of an aggregate road,
Aggregates cannot transmit tensile forces between which occurs when overloading causes particles to be
particles; instead, cementing agents combine with the displaced and ride over one another. Aggregate is used
particles to create a mass that can resist some tension. as a base to support heavy weights because it effectively
While it may seem that aggregates can transmit spreads concentrated forces over a larger area, reducing
compressive forces, they do not do so effectively. If flat- pressure on the underlying soil. To prevent the mixing of
surfaced particles were stacked vertically, they could soil and aggregate, which can weaken the base, a
theoretically transmit compressive forces like a geotextile fabric is often placed between them. While
structural column. However, in practice, aggregates are soil is generally weaker than aggregate, it behaves
arranged randomly, which affects how forces are similarly under load, failing in shear when overloaded
transmitted. and being more prone to excessive settlement.
When a concentrated load is applied to a particle of
aggregate, the force is distributed to surrounding
particles as it moves deeper into the aggregate mass.
This distribution occurs because the random
arrangement of particles causes the load to spread over a
larger area. The vertical load creates horizontal Aggregate is sourced from high-quality materials
components at the points of contact between particles, and transported to the construction site, where it is
leading to a tendency for the upper particle to slide over placed on existing soil, which may be significantly
or push aside the lower particle, resulting in shearing weaker than the aggregate. Figure 2–12a illustrates how
stress. a concentrated wheel load is distributed over the soil by
The ability of aggregates to resist this shearing stress an aggregate base, reducing stress on the soil in
is known as shearing strength, which arises from friction proportion to the square of the aggregate's depth. The
and interlocking between adjacent particles. If the radius of the pressure circle is determined by the depth
of the aggregate multiplied by the tangent of a specific Compaction refers to the densification of a material,
angle (θ). As the shearing strength of the aggregate resulting in an increased weight per unit volume. The
increases, the load is spread over a larger area, resulting density of a material is influenced by its gradation,
in a greater angle (θ). moisture content, and the compactive energy applied
Figure 2–12b depicts a concrete spread footing that during densification. Well-graded aggregates compact
transmits a structural column load through a crushed more easily than poorly graded ones. Optimal moisture
stone base to the soil. The pressure from the footing content (OMC) facilitates compaction, as water acts as a
spreads in all directions, becoming wider as it moves lubricant; aggregates below OMC lack sufficient
downward. While the footing acts as a solid unit and lubrication, while those above OMC have voids filled
does not transmit force like aggregate particles, its with incompressible water. For example, the OMC for
function is similar: to reduce pressure on the base, which well-graded run-of-bank gravel is about 7%, while sand-
in turn reduces pressure on the soil. The decision to use clay mixtures may require around 13%.
an aggregate cushion versus a larger footing is based on The actual OMC and maximum dry densities are
a cost comparison between the two options. determined through laboratory tests on aggregate
Loosely piled aggregate particles have low shearing samples. Compaction methods include static weight,
strength and can be easily displaced. To enhance their kneading, impact, or vibration, and the choice of
performance, aggregates are typically compacted into a equipment—such as sheepsfoot, vibratory, pneumatic, or
tighter structure, which increases friction and high-speed tamping foot—depends on the material being
interlocking before any permanent load is applied. compacted. Vibratory equipment is typically used for
Compaction reduces compressibility and increases shear gravels, while sheepsfoot or high-speed tamping
strength, with vibrations being more effective than equipment is preferred for sand-clay mixtures.
simply applying weight for achieving this compaction. Compaction enhances the strength of aggregates,
For example, when sand or gravel is compacted reduces settlement, and improves bearing capacity.
without vibration, only minimal compaction occurs. Specifications for aggregates used as subbase and base
However, when vibrations are introduced, a significant course materials often stipulate required maximum dry
reduction in material level is observed due to increased density or percentage compaction. Field dry density can
density. The density or unit weight of the aggregate can be measured using methods like the sand cone, balloon,
indicate its strength, with denser aggregates exhibiting or nuclear density gauge, allowing for the calculation of
greater strength. percentage compaction by comparing field results to
To further increase density, a mix of various particle laboratory-determined maximum dry densities.
sizes is beneficial, as smaller particles fill voids between Contractors often establish test strips to evaluate
larger ones, resulting in a well-graded aggregate. A compaction techniques for compliance with
strong base can be constructed using a wide range of specifications and to calculate production rates based on
aggregate sizes, achieving high density and strength the chosen methods and number of passes of the
while also being cost-effective. compaction equipment.
Aggregates are sorted into standard sizes through The formula for determining the compacted cubic
screening, and mixing different sizes helps prevent meters per hour is as follows:
segregation. Key factors that enhance the shearing
strength of aggregates include:
1. Well-graded aggregates are stronger than poorly
graded ones.
2. Larger maximum aggregate sizes contribute to
greater strength due to better interlocking.
3. Particles with more flat, broken faces provide
better interlocking, although flat particles
themselves can slide and reduce strength.
4. Compaction, especially through vibration,
increases shearing strength across all aggregate Pavement Base
types. Typical pavement construction consists of
5. Rough particle surfaces enhance strength by multiple layers designed to distribute concentrated wheel
increasing friction between particles. loads, preventing overload on the underlying soil or
Overall, these factors contribute to the density and foundation. The wearing surfaces, made of asphalt
strength of the aggregate base, which is crucial for its mixtures or Portland cement concrete, are discussed in
performance in construction applications. later chapters. The underlying soil can be natural or
imported fill, which is compacted with heavy equipment
Compaction before placing a base or subbase.
 The subbase is usually unprocessed, run-of-bank particles, however, can permit significant capillary rise,
material that meets specific performance standards, leading to ice lens formation.
while the base material is more carefully selected. In During spring thaw, ice lenses can trap water
flexible pavement (asphalt), the base and subbase beneath the surface course, preventing drainage and
support the load and distribute it through thin layers of weakening the base, which can cause surface breakage
asphalt concrete. In rigid pavement (Portland cement under traffic. Rainwater seepage can carry fine particles
concrete), the concrete slab is the primary load-bearing out of the base, further weakening it. While some
element, with the base designed mainly to protect against moisture is beneficial for cohesion, excessive capillary
moisture-related issues, such as frost heaving, standing water accumulation beneath a watertight surface can
water, and pumping, which can lead to pavement failure. weaken the base by depriving it of solid support.
To prevent water accumulation, the base must be To mitigate these issues, large-size aggregates
well-drained, using well-graded coarse aggregate with with large voids are preferred for road and runway bases,
minimal fines. For watertightness, a well-graded which are subject to moving loads and weather
aggregate with sufficient fine material to fill voids is conditions. The movement of traffic can loosen the
necessary. The base under rural or secondary roads aggregate bond, and factors like freezing, thawing, and
serves as the main load-bearing element, with the asphalt water movement can further weaken it. Unlike static
surface course protecting it from traffic abrasion and loads, bases for roads and runways require careful
rain. gradation to maximize particle contact and
The strength of the base aggregate is crucial for watertightness. Fine materials, known as binders, are
transferring loads to the foundation, requiring it to be necessary to fill voids and stabilize larger load-bearing
well-graded and compacted while allowing for drainage particles.
to prevent capillary water rise. Sometimes, a small The most effective base material often combines
amount of asphalt cement is mixed in to enhance particle processed aggregate with natural soil from the
cohesion without blocking voids. A base course without construction site, optimizing the use of local materials.
surfacing must withstand traffic and rain while Depending on the site conditions, the base may require
effectively supporting and transferring loads. For lightly varying amounts of aggregate, with the goal of
traveled roads, a properly constructed base may not maximizing the use of nearby soil while ensuring
require a protective covering. structural integrity.

Stabilizing Aggregate
The strength of aggregate can be enhanced by
adding measured amounts of clay, which provides
cohesion and acts as a cementing agent. This process,
known as stabilization, can also involve other substances
such as salts, lime, portland cement, and bituminous
cement. Salts like calcium chloride and sodium chloride
are commonly mixed with aggregates to improve
strength, typically in quantities of 1 to 2.5 pounds per
square yard or 2% of the aggregate's weight. When
mixed with moisture, these salts form a brine that
increases particle cohesion and allows for closer packing
during compaction, enhancing overall strength.
Stabilization with salt also helps reduce dust from
traffic abrasion, as the brine holds fine particles in place
better than untreated water, minimizing road damage and
dust clouds. Calcium chloride is hygroscopic, absorbing
moisture from the air to maintain a damp surface and
prevent dusting. Additionally, salt stabilization fills
Freezing water in the base or subbase of a voids with moisture, preventing the loss of fine particles.
pavement does not cause significant expansion, but Lime, in the form of quicklime or hydrated lime, is
when water is drawn up by capillary action and another stabilizing agent mixed with aggregates in
subsequently freezes, it can form larger ice lenses that quantities of 2 to 4 percent of the aggregate weight.
disrupt the surface. Coarse soils have large voids that Lime reacts with clay to form larger particles, improving
prevent capillary rise, while fine soils with sufficient gradation and reducing excessive swelling. It also
clay allow for slow capillary movement, which is chemically reacts with silica and alumina in the clay and
typically insufficient to form ice lenses. Silt-sized
aggregate to create cementing agents, similar to those particles) and gradation (distribution of sizes). While a
found in portland cement. few very large or small particles typically do not impact
While stabilization improves aggregate strength, it overall performance, the significant range of sizes is
differs from manufacturing concrete, which involves important for functionality.
mixing aggregates with a cement paste to form a To determine size and gradation, a set of sieves with
continuous material. The strength of concrete depends progressively smaller openings is used. A sample is
on the strength of the aggregates, the cementing agent, placed in the top sieve, and after shaking, particles settle
and the adhesion between them. Stabilization aims to according to size. The amount retained on each sieve is
enhance the properties of the aggregate without weighed, and the results can be used to assess the
transforming it into a different material. aggregate's gradation. Excessive fine particles or large
particles beyond the specified range are of concern.
Permeability and Filters Sieve analysis is standardized, with specific
Permeability measures how easily a fluid, typically procedures outlined in ASTM standards. The results can
water, flows through a material. Gravels exhibit high be plotted on a semilogarithmic graph, known as a
permeability, while sands and silts have lower gradation chart, which visually represents the size
permeability. The coefficient of permeability, denoted as distribution of the aggregate. The effective size of the
k, is measured in cm/s, and optimal permeability is aggregate, particularly for filtering applications, is
achieved with large, uniform-sized aggregates that create defined by the percentage of particles finer than a certain
large voids for easy water flow. However, filling these size.
voids with smaller particles is necessary for maximum Gradation can be classified as well-graded, uniform,
strength, meaning high permeability and strength cannot or gap-graded based on the distribution of particle sizes.
be achieved simultaneously. Well-graded aggregates have a balanced distribution,
Filters are designed to retain particles larger than a while uniform aggregates consist mostly of similar-sized
certain size while allowing water to flow through with particles, and gap-graded aggregates lack intermediate
minimal resistance. The effectiveness of a filter depends sizes. The uniformity coefficient, calculated by dividing
on the size and gradation of the aggregate used. The the D60 size by the D10 size, indicates how uniform the
voids in the filter must be smaller than the particles it is aggregate is.
meant to retain, yet large enough to permit water flow. Specifications for aggregate size and gradation are
Uniform gradation ensures consistent void sizes, while often provided as ranges of percentages passing through
non-uniform gradation can lead to ineffective filtering. designated sieve sizes. An aggregate is considered
Filters can become clogged over time, requiring acceptable if its gradation curve falls within these
maintenance such as cleaning or replacement. Different specified limits, which can be visually represented as an
types of filters serve various purposes, including holding envelope on a graph. This detailed representation helps
soil in place while allowing water to flow through, and ensure that the aggregate meets the necessary
removing suspended particles from water. For example, performance criteria for its intended use.
drinking water filters and sewage filters operate
differently, with the former requiring frequent cleaning
and the latter sometimes functioning indefinitely due to
microbial activity.
Filters are categorized into two types: those that
stabilize soil while allowing water to flow through, and
those that remove suspended particles from water. In
stormwater management, filters, often combined with
pond systems, are used to treat runoff water to meet
regulatory standards. Construction projects must adhere
to erosion control and stormwater management practices
based on the extent of soil disturbance, which may
include various filtering systems to remove fine particles
from runoff.

Tests
1. Size and Gradation
Particle sizes are crucial in aggregate applications,
but measuring them can be challenging due to the 2. Weight-Volume Relationships
irregular shapes and size variations within samples. Key The total volume of aggregate consists of solid
aspects include the range of sizes (smallest to largest particles and the voids between them, which is crucial
for applications like filters and roadbeds that require weight is measured, deducting the weight of the
specific dimensions. The volume of solid matter is wire basket. The submerged aggregate displaces
important, as all aggregate particles contain pores that a volume of water equal to its own volume,
can absorb water. For certain applications, such as including pores filled with water.
asphalt concrete, the volume of these pores is significant • Bulk specific gravity is calculated by dividing
because a portion is filled with liquid asphalt. In the oven-dry weight of the aggregate by the
contrast, in portland cement concrete, mixing water fills difference between the saturated, surface-dry
the pores completely. Lightweight aggregates can absorb weight and the submerged weight. This ratio
excessive water, potentially affecting the cement's reflects the weight of the aggregate (including
performance. pores) compared to an equal volume of water.
The volume of voids between coarse aggregate • Apparent specific gravity is calculated similarly,
particles is relevant for determining the correct amount but it uses the difference between the oven-dry
of fine aggregate needed, while the volume of pores is weight and the submerged weight, determining
less critical. Understanding the relationship between the ratio of the weight of solid aggregate
aggregate volume and weight is essential, as quantities (without pores) to an equal volume of water.
are typically ordered by weight but must occupy a • The key difference between bulk and apparent
specific volume. Various combinations of weight and specific gravity is that bulk specific gravity uses
volume can be used, including bulk volume (solids, the saturated, surface-dry volume, while
pores, and voids), saturated surface-dry volume (solids apparent specific gravity uses the volume of
and pores), and solid volume (solids only). solid matter only.
Different weight measurements include wet weight • Bulk specific gravity is typically based on oven-
(solids plus water), saturated surface-dry weight (solids dry weight unless specified otherwise, and it can
plus water filling pores), and oven-dry weight (solids also be determined using the saturated, surface-
only). The unit weight of aggregate is determined by dry weight, referred to as bulk SSD.
dividing the oven-dry weight by its bulk volume, • Absorption is calculated as the percentage of the
following ASTM C29 standards. Specific gravity (SG) is weight of water needed to fill the pores
the ratio of solid unit weight to the unit weight of water compared to the oven-dry weight of the
and is useful for calculations involving aggregate aggregate, using the difference between the
volume. saturated, surface-dry weight and the oven-dry
There are two types of specific gravity for weight.
aggregates: bulk specific gravity, which includes pores These calculations are essential for understanding
in the volume, and apparent specific gravity, which the properties of aggregates in construction applications.
considers only solid volume. Effective specific gravity is
used in asphalt concrete design, accounting for the b. Specific Gravity of Fine Aggregate
volume of pores not filled with asphalt. Methods for The procedure for determining the specific gravity (SG)
determining specific gravity and absorption for and absorption of fine aggregate involves the following
aggregates are outlined in ASTM C127 and ASTM C128 steps:
standards. • A representative sample of fine aggregate
weighing about 1000 g is dried to a constant
3. Specific Gravity weight, known as the oven-dry weight.
a. Specific Gravity of Coarse Aggregate • The oven-dried sample is soaked in water for 24
The procedure for determining the specific gravity and hours.
absorption of coarse aggregate involves several steps: • The wet aggregate is then dried until it reaches a
• A representative sample of coarse aggregate saturated, surface-dry (SSD) condition. This
(about 5 kg) is dried in an oven and weighed condition is assessed by placing the aggregate in
until two consecutive weighings show no weight a standard metal mold shaped like a frustum of a
loss. This final weight is recorded as the oven- cone and tamping it. The aggregate is considered
dry weight. SSD when it retains the mold shape; if it slumps
• The oven-dried sample is soaked in water for 24 upon removal, it indicates insufficient moisture
hours. for cohesion.
• After soaking, the aggregate is removed and • A 500 g sample of the SSD aggregate is placed
dried with a cloth until no water film remains, in a 500-cm³ container, which is then filled with
resulting in a saturated, surface-dry weight in water at a controlled temperature.
air. • The total weight of the full container is
• The aggregate is then submerged in water at a measured, which includes the weight of the
controlled temperature, and the submerged flask, the SSD aggregate, and the unknown
 weight of water. The weight of the water is Organic Impurities: Organic materials that can hinder
calculated by subtracting the known weights cement hardening, with limits set for fine aggregates
from the total weight. used in concrete. Testing involves comparing the color
of a solution containing the aggregate to a standard
• The contents are removed from the container, reference.
and the oven-dry weight of the aggregate is Reactive Aggregates: Aggregates containing minerals
determined. that react with alkalis in cement, causing expansion and
• The container is weighed when full of water. potential disintegration over time. Testing for reactivity
• The collected data allows for the computation of is complex and may involve chemical methods or
specific gravity. For bulk SG, the SSD weight of petrographic examinations.
the aggregate is used in the denominator, while Various ASTM standards outline testing
for apparent SG, the oven-dry weight is used. methods for these deleterious substances, ensuring that
The formula for SG is the oven-dry weight of aggregates meet the necessary quality for their intended
the aggregate divided by the weight of the applications. Proper testing and adherence to specified
container filled with water plus the weight of the limits are crucial for maintaining the integrity and
aggregate in air, minus the weight of the durability of concrete structures.
container filled with aggregate and water.
• Absorption is calculated as the weight of water 5. Miscellaneous Properties
needed to fill the particle pores divided by the Toughness, which refers to an aggregate's resistance
weight of solid matter, expressed as a to abrasion and impact, is assessed using tests such as
percentage. This is computed by dividing the the Deval test (ASTM D2 and ASTM D289) and the Los
difference between the SSD weight and the Angeles abrasion test (ASTM C131 and ASTM C535).
oven-dry weight by the oven-dry weight. The Deval test involves rotating aggregate with or
These steps provide essential data for understanding the without steel spheres, while the Los Angeles test uses
properties of fine aggregates in construction steel spheres and involves more rotations, providing a
applications. broader range of results in a shorter time. Toughness is
crucial for aggregates used in concrete mixing,
compaction, and road surfaces, as these processes can
lead to particle breakage and changes in gradation.
4. Deleterious Matter In the Deval test, the percentage of materialpassing
Excessive foreign material in aggregates can through a No. 12 sieve after abrasion indicates
negatively impact their performance, with acceptable susceptibility to wear. The Los Angeles test similarly
limits varying based on the intended use. For high- measures the weight of fine particles after a specified
quality applications like Portland cement concrete, number of rotations. A consistent loss of weight suggests
asphalt concrete, or filters, minimal foreign matter is uniform toughness, while a rapid initial loss followed by
allowed, while greater amounts are permissible for base a steady rate indicates the presence of weaker particles.
materials. ASTM C33 specifies allowable limits for six Soundness refers to an aggregate's resistance to
types of deleterious substances in aggregates used for disintegration due to weathering, including freeze-thaw
Portland cement concrete, including: cycles and chemical changes. ASTM C88 measures
Friable Particles: Easily crumbled materials that can soundness by immersing aggregates in sodium or
alter gradation by increasing fine particles. Limited to magnesium sulfate solutions, simulating weathering
3% for fine aggregates and 2-10% for coarse aggregates. effects. The weight of material passing through a sieve
Material Finer than No. 200 Sieve: Fine material that after several cycles indicates soundness, with a focus on
can coat larger particles, hindering cement adherence. resistance to freeze-thaw damage.
Limits are 3% for fine aggregates in abrasion-resistant Hydrophilic aggregates do not maintain adhesion to
concrete, 5% for other concrete, and 1% for coarse asphalt when wet, which can hinder their use in asphalt
aggregates. mixtures. ASTM D1664 tests for adhesion by coating
Soft Particles: Particles that can be easily scratched and aggregates with asphalt and submerging them in water to
may break down under abrasion, limited to 5% in coarse assess the amount of asphalt that strips away. Aggregates
aggregates for concrete subjected to wear. that lose more than 5% of their coating are considered
Lightweight Pieces: Particles with significantly lower unsuitable for use with asphalt without special treatment.
specific gravity that can cause surface issues in concrete.
Limits for coal and lignite are 0.5% for appearance- 6. Sampling
sensitive concrete and 1% otherwise; chert is limited to Aggregate tests and inspections must be conducted on
1% for severe exposure and 5% for mild exposure. representative samples that accurately reflect the
characteristics of the entire quantity being tested. A
representative sample should avoid segregation, which is expanded blast-furnace slag, clay, and diatomite), and
the separation of particles based on properties such as cinders from coal combustion (used only for masonry
size. ASTM D75 outlines proper sampling methods for units).
aggregates. The production of expanded slag involves cooling
Samples are needed for several purposes: molten slag with water, creating a frothy lightweight
• Preliminary Investigation: To assess a material. Other aggregates, like shales and slates, expand
potential source of supply, such as a rock significantly when heated, forming discrete air cells.
formation or aggregate deposit, before investing Diatomite, fly ash, perlite, and vermiculite are also used
in extraction and processing. as lightweight aggregates, with perlite and vermiculite
• Acceptance or Rejection of Supply: Buyers being particularly effective for insulation due to their
conduct inspections and tests to determine if a low density.
source meets their requirements, especially for Lightweight aggregates can stain concrete surfaces
large projects. due to iron compounds, and ASTM C641 provides
• Final Acceptance or Rejection: At the time of testing procedures for this tendency.
delivery, buyers perform inspections and tests to Heavy aggregates, which have higher specific
ensure the material conforms to specifications. gravities than typical aggregates, are used to create
• Quality Control: Suppliers test their products to heavy concrete for specialized applications, such as
maintain consistent quality during removal and radiation shielding or counterbalancing structures.
processing. Natural heavy minerals, steel punchings, and
When investigating natural deposits, test holes are ferrophosphorus are examples of heavy aggregates, with
made to examine the contents, and layered deposits may relevant specifications found in ASTM C638 and ASTM
require sampling across multiple layers. If pockets of C637. These aggregates provide enhanced density for
atypical aggregate are found, separate samples should be applications requiring resistance to water flow or nuclear
taken from each. radiation shielding.
For stockpiles, a representative sample should be
collected from various levels (top, middle, bottom) to
avoid segregation. In bins, samples should be taken in
increments while the aggregate is being discharged,
avoiding the first and last particles.
Collected samples are often combined to create a
larger representative sample, with each individual
sample proportionate to the total quantity. If variations in
characteristics are significant, each sample may be tested
separately.
Since combined samples can be too large for testing,
they must be reduced in size using methods like
quartering or a sampler splitter, ensuring that the
characteristics of the sample remain unchanged.

SPECIAL AGGREGATES
Lightweight aggregates are defined as those with a
unit weight not exceeding 70 lb/cu ft (1120 kg/m³) for
fine aggregates, 55 lb/cu ft (880 kg/m³) for coarse
aggregates, and 65 lb/cu ft (1040 kg/m³) for combined
aggregates. Specifications for lightweight aggregates for
structural use are outlined in ASTM C330 and ASTM
C331. The primary purpose of using lightweight
aggregates is to reduce the weight of concrete structures,
allowing for smaller and more cost-effective supporting
elements. They also lower transportation costs compared
to traditional heavier aggregates.
Three main types of lightweight aggregates are used
for strength-critical concrete: volcanic rocks (like
pumice and scoria), man-made particles (such as
 bulk cement sold by the barrel or ton, and bagged
cement weighing 94 lb. The manufacturing process
requires various technical skills, with engineers and
chemists ensuring product uniformity. Type I portland
cement contains specific oxides as detailed in the
accompanying tables.

Water-Cement Reaction
Hydration is the chemical reaction that occurs when
portland cement is mixed with water, completing after
28 days, depending on moisture availability. This
process leads to the setting of the cement, where it
transitions from a fluid paste to a stiff and hard state.
Proper setting time is crucial; if it sets too quickly, the
mixture becomes unworkable, while slow setting can
waste valuable construction time. Most portland cements
achieve initial set in about 3 hours and final set in about
7 hours. The addition of gypsum during grinding helps
control the setting time, preventing rapid setting that
would hinder workability.
False set refers to a temporary stiffening of the
Concrete mixture without significant heat generation, which can
be remedied by further mixing. In contrast, a flash set
Manufacture of Portland Cement indicates that hydration has occurred, and additional
The manufacture of portland cement involves raw mixing will not restore plasticity. Actual setting times
materials containing lime, silica, alumina, and iron, can vary based on environmental factors like
sourced differently depending on the manufacturing temperature and humidity.
location. The process begins with acquiring materials The compressive strength of cement is a key
like limestone, clay, and sand. Limestone is crushed to property, typically tested using standard 2-inch cubes.
approximately 5 inches in size, then further reduced to ¾ However, these tests do not predict concrete strength due
inch. The raw materials are stored and proportioned to the influence of various mixture variables. The heat
before being sent to the grinding mill. generated during hydration, known as the heat of
There are two main processes: the wet process, hydration, is also significant, with its total amount
which creates a slurry, and the dry process, which influenced by the cement's chemical composition and
produces a fine powder. Both processes feed into rotary other factors.
kilns where chemical changes occur. The material moves Concrete has a low tensile strength, approximately
through the kiln, reaching temperatures between 2400°F 11 percent of its compressive strength, which
(1316°C) and 2700°F (1482°C), where chemical necessitates the use of steel reinforcement in applications
reactions produce the basic components of portland where tensile strength is critical or where increased
cement. The resulting clinker is black or greenish-black compressive strength is needed. Reinforcing steel can
and rough in texture. take the form of welded wire mesh, deformed
After storage, the clinker is ground with about 2 to 3 reinforcing bars, or cable tendons. Steel's high strength-
percent gypsum to control setting time, enhancing the to-weight ratio and similar coefficient of thermal
concrete's shrinkage and strength properties. The final expansion to concrete make it an ideal reinforcement
product is distributed in bulk or packaged in bags, with material.
 Plain reinforced concrete is commonly used in These types cater to various construction requirements,
construction, where steel is positioned in forms before ensuring durability and performance in different
concrete is poured around it. Once cured, the concrete environments.
and steel bond together, functioning as a single unit. In
contrast, prestressed concrete involves applying a load to Mixing Water
the steel before placing the concrete, which, after curing, Water is essential in concrete production, serving
remains in compression when the load is removed. multiple roles such as washing aggregates, mixing, and
Posttensioned concrete allows for the application of curing. However, using impure water can lead to
loads to the steel after the concrete has cured. This contamination of aggregates, resulting in distressed
method involves leaving ducts in the concrete for steel concrete due to chemical reactions or poor bonding.
tendons, which can be adjusted based on actual structural Potable water is generally acceptable for mixing, and
loading conditions. Posttensioned concrete offers even seawater with a 3.5% salt content can be used,
versatility, as the loads on the steel can be modified although it may affect strength. Questionable water
according to the specific requirements of the structure. supplies can be utilized if mortar cubes meet ASTM C94
requirements.
Types of Portland Cement ASTM C150 Impurities in water can impact concrete properties,
The various types of portland cement serve causing issues like efflorescence, discoloration, and
specific construction needs based on their properties: corrosion of reinforcement. The total dissolved solids in
ASTM Type I (Normal): General-purpose cement for water should ideally be below 2000 ppm, as higher
standard construction, not suitable for sulfate attack or concentrations may adversely affect certain cements.
severe weather. Used in pavements, sidewalks, and Specific salts, such as sodium carbonate and bicarbonate,
buildings. can alter setting times and strength, while others like
ASTM Type II (Moderate Heat): Offers moderate sodium chloride and sulfate can be tolerated in higher
sulfate resistance and generates less heat during concentrations.
hydration, making it suitable for mass structures like Seawater can be used in non-reinforced concrete, but
piers and retaining walls. it poses corrosion risks in reinforced structures.
ASTM Type III (High-Early-Strength): Designed for Industrial wastewater and treated sewage may also be
rapid strength gain, ideal for projects requiring quick acceptable, but testing is necessary to ensure no harmful
form removal, and beneficial in cold weather to reduce impurities are present. Organic materials, acids, and
heating time. excessive sugar can negatively affect strength and setting
ASTM Type IV (Low Heat): Minimizes heat times, necessitating careful evaluation of water quality
generation, used in large mass placements like gravity before use in concrete.
dams where temperature rise is critical.
ASTM Type V (Sulfate-Resisting): Specifically for Aggregates
environments with high sulfate concentrations to prevent Aggregates constitute 60 to 80 percent of concrete's
severe sulfate attack. volume and significantly influence its properties.
Air-Entraining Portland Cements: Types IA, IIA, and Selecting the right aggregates is crucial for mix design
IIIA improve freeze-thaw resistance and scaling and cost-effectiveness. Ideal aggregates should be clean,
protection by incorporating air-entraining materials. hard, strong, and durable, free from contaminants like
White Portland Cement: Aesthetically pleasing cement clay or chemicals that could impair bonding. Soft or
for architectural applications, produced with low iron porous aggregates, such as shale, should be avoided due
and manganese for a white color. to poor weathering resistance. Common aggregates
Portland Blast-Furnace Slag Cements: Interground include sand, gravel, and crushed stone, which produce
with granulated blast-furnace slag, offering moderate normal-weight concrete, while expanded materials yield
heat and sulfate resistance. lightweight concrete.
Portland-Pozzolan Cements: Used for large hydraulic Key characteristics of aggregates include abrasion
structures, made by blending portland cement with resistance, freeze-thaw resistance, and alkali reactivity.
pozzolans like volcanic ash. The Los Angeles rattler test measures abrasion
Masonry Cements: Types I and II, designed for resistance, while freeze-thaw tests assess durability
masonry mortars with added workability and water under cyclic temperature changes. Although aggregates
retention. are often seen as inert, they can react with alkalis in
Special Portland Cements: Includes oil well cement for cement, necessitating testing for new sources.
high-pressure applications and waterproof cement to The shape and texture of aggregates affect water
reduce water penetration. requirements; rough or elongated particles require more
water than rounded ones. Proper gradation and
maximum aggregate size, determined by sieve analysis,
are essential for workability and uniformity. Smaller absorbed and surface moisture, must be monitored to
aggregates generally yield higher strengths, while gap- control batch weights and water content in concrete.
graded aggregates can enhance strength in stiff mixes Certified facilities typically use automated systems for
but require careful control to prevent segregation. this purpose.

Recycled Concrete Materials

The construction industry's shift towards
sustainability has led to an increased use of recycled
construction materials, which helps reduce landfill
waste, increases aggregate availability, and offers
economic benefits through life cycle cost analysis.
Recycled concrete material (RCM) is created by
crushing demolished concrete structures, such as curbs
and pavements. This can be done on-site with portable
crushers or at a central facility, where reinforcing steel is
removed using magnetic separators and manual methods.
On-site processing allows crushed concrete to be
reused as backfill and base material, reducing
transportation costs. At central facilities, RCM is graded,
washed, and stockpiled as coarse and fine aggregates,
which are then tested for potential use as substitutes for
natural aggregates in concrete and asphalt mixes. Quality
control is essential due to the variability in the initial
concrete.
Using recycled aggregates can contribute to earning
credits in the U.S. Green Building Council’s LEED
certification system. The bulk unit weight of aggregates
is determined by filling a known volume container and
weighing it, while specific gravity helps in concrete mix
design. Moisture content in aggregates, divided into
Admixtures
Admixtures are materials added to concrete or
mortar mixes to modify their properties, enhancing
performance for specific applications. They can improve
workability, reduce water content, increase durability,
alter setting times, impart color, maintain volume
stability, and enhance freeze-thaw resistance. Common
admixtures include air-entraining agents, accelerators,
retarders, and water reducers, each serving multiple
functions. For instance, air-entraining admixtures create
microscopic air voids that help protect concrete from
freeze-thaw damage.
The effectiveness of admixtures can vary based on
factors like cement type, aggregate shape, and
environmental conditions, making trial mixes essential
for determining appropriate dosages and compatibility.
Admixtures must meet specifications, and their costs,
including purchase and storage, should be considered in
the mix design.
Air-entraining agents improve durability against
freeze-thaw cycles, while accelerators like calcium
chloride speed up setting times, particularly in cold
weather. Retarders are used in warm conditions to
extend setting times, and superplasticizers increase
workability for challenging placements. Microsilica and
fly ash are pozzolanic materials that enhance strength
and durability by reacting with calcium hydroxide during
hydration. Fly ash can replace a portion of cement,
improving workability and reducing environmental
impact, although it may extend setting times and require
longer curing periods for strength development.
 techniques must be considered, as well as the need to
minimize cement content, the most expensive ingredient.
Workability is crucial, as different applications
require varying concrete consistencies. Trial batches are
often conducted to refine mix designs before production,
with adjustments made based on performance records.
ACI 211.1 provides a widely accepted framework for
mix design, emphasizing that successful proportioning
combines technical knowledge with practical judgment.

Concrete Manufacturing
Concrete mixing is primarily conducted using
specialized equipment designed for two main functions:
mixing the ingredients to produce concrete and agitating
already-mixed concrete. Mixing equipment can be
stationary, portable, truck-mounted, or crawler-mounted
for paving operations. Stationary mixers are often used
for large projects, such as dams or highway paving,
where concrete is produced centrally and transported to
the site.
Mixing times vary, typically requiring 1 minute for
the first cubic yard and 15 seconds for each additional
cubic yard, with specific guidelines set by ASTM C94
regarding drum revolutions. Ready-mix concrete is
produced using central mix, transit mix, or shrink mix
methods, with each method having distinct mixing and
delivery processes.
Quality control is crucial, as the final concrete
quality depends on both the mixing process and the
contractor's handling, placing, and curing practices. Trial
batches are often conducted to ensure the mix meets
project specifications. The use of certified materials
testing laboratories is common to monitor production
and compliance with standards. Admixtures, such as
water reducers, can enhance workability and reduce
cement content, contributing to more economical
concrete mixes. Overall, effective concrete mixing
requires careful consideration of equipment, methods,
Proportioning Concrete Ingredients and quality control measures to ensure the desired
Duff Abrams introduced the water-cement ratio performance and durability of the final product.
(w/c) concept in 1918, establishing its inverse
relationship with concrete strength. Lowering the w/c Testing Concrete
ratio enhances concrete durability and reduces Testing concrete samples is crucial to ensure they
permeability. The term has evolved to water- accurately represent the concrete placed. According to
cementitious material ratio (w/cm) to account for ASTM C172, samples should be taken from multiple
pozzolans like fly ash and microsilica. A typical intervals within 15 minutes of mixing, after all water and
guideline suggests that reducing the w/c ratio by 0.01 admixtures have been added. A minimum composite
increases 28-day strength by 100 psi. For high-strength sample size of 1 cubic foot is recommended for cylinder
concrete (w/c ratios of 0.30 to 0.35), water reducers are tests, while smaller samples can be used for routine tests
necessary to maintain workability. like slump and temperature.
Concrete mix design, or proportioning, involves Workability, a key requirement for fresh concrete,
determining the optimal material quantities to achieve refers to how easily it can be mixed, transported, placed,
economical and workable concrete that meets strength and finished without segregation. The slump test
and service requirements. This can range from simple measures consistency and fluidity, with a 3% change in
ratios to more complex ACI 211.1 procedures. Factors water content affecting the slump by about 1 inch. The
such as mixing methods, transportation, and finishing
ASTM C143 outlines the procedure for conducting
slump tests.
Air content is also critical, as it affects durability and
strength. Various methods, including ASTM C173
(volumetric), ASTM C231 (pressure), and ASTM C138
(gravimetric), are used to measure air content. The unit
weight of fresh concrete is determined using a standard
cylindrical measure, which helps assess air content and
strength.
Yield calculations ensure the volume of concrete
produced matches expectations, aiding in quality control
and resolving disputes. Additionally, the temperature of
the concrete is monitored, as it influences setting times
and strength development, with specific temperature
limits often set for hot and cold weather placements. Nondestructive Test Methods
ASTM C1064 provides guidelines for measuring Nondestructive test methods are essential for
concrete temperature accurately. determining the in-place strength of concrete in the
construction industry. These tests are particularly useful
Compressive Strength Tests when renovating buildings to assess the strength of
Compressive strength is a critical property of existing concrete or during construction to monitor
hardened concrete, defined as its maximum resistance to concrete strength for safe removal of formwork and
axial loading, measured in pounds per square inch (psi). shoring. The most commonly used nondestructive testing
Designers select a desired compressive strength, which methods include:
is then reduced by a safety factor to ensure structural • Rebound Hammer: Measures surface hardness
integrity. Testing for compressive strength is typically to estimate strength.
conducted at 28 days, following ASTM standards, with • Penetration Probe: Assesses resistance to
ASTM C31 outlining the procedure for creating test penetration to infer strength.
cylinders. • Pullouts: Evaluates the force required to pull a
Standard test cylinders are 6 inches in diameter and steel insert from the concrete.
12 inches high, filled in three layers and rodded or • Ultrasound: Uses sound waves to detect
vibrated as necessary. Proper curing conditions are internal flaws and estimate strength.
essential, with specific temperature ranges required for Each of these methods has its limitations and
different strength levels. Concrete strengths are requires empirical correlations to standard compressive
evaluated at 7 and 28 days, but the traditional testing strength tests to ensure accurate assessments.
timeline has raised concerns about its effectiveness in
fast-paced construction environments. Accelerated Concrete Formwork
testing methods are being explored to provide earlier Formwork is a temporary structure that contains
strength assessments. fresh concrete until it gains sufficient strength to support
Acceptance testing follows ASTM C94 or ACI 318 itself. The entire system, including forms, supports,
criteria, requiring that the average strength of multiple hardware, and bracing, is referred to as formwork, which
cylinders meets or exceeds specified values. Statistical can account for 35 to 65 percent of concrete construction
measures, such as the coefficient of variation, help costs. Effective formwork design must meet three key
assess the uniformity of concrete production. Proper requirements: economy, quality, and safety.
control of materials and testing procedures is crucial to Economical form design involves careful material
ensure reliable results, and discrepancies may necessitate selection, fabrication, and construction techniques, as
additional testing by a secondary laboratory. well as the ability to reuse and adapt forms for different
applications. Designers can help reduce costs by
standardizing column sizes and adjusting concrete
strength and reinforcement requirements throughout the
structure.
Accurate construction of formwork is crucial for
ensuring the correct size, shape, finish, and alignment of
structural elements. The formwork must be strong
enough to withstand deflection and rigid enough to
prevent bulging and leakage, which could lead to costly
refinishing.
 Safety is also a critical consideration, as the proportions, design strength, and the size and shape of
formwork must support the weight of fresh concrete, the concrete structure.
equipment, and labor. Formwork design must adhere to In hot weather, the maximum placement temperature
structural loading requirements and be carried out by is generally set at 90°F (32.2°C). To achieve this, pre-
qualified professionals who produce stamped chilled aggregates or shaved ice may be used. Preventing
construction drawings for contractors to follow. moisture loss after placement is critical, and methods
such as wind screens, fog misting, evaporation-retarding
Placement of Concrete chemicals, and additional curing water can be employed.
During the testing of fresh concrete, various methods Curing methods include waterproof papers, plastic films,
of placement are employed, ranging from simple chutes liquid curing compounds, and wet coverings like burlap
and wheelbarrows to advanced conveyor and pump or sand.
systems. Care must be taken to prevent segregation, In cold weather, maintaining internal heat is crucial,
which can negatively impact the quality of the hardened which can be achieved using insulating blankets or
concrete. external heat sources like salamanders or space heaters.
The concrete pump is a versatile method that Care must be taken to vent fuel-burning heaters properly
transports plastic concrete through pipelines without to avoid carbonation, which can weaken the concrete
altering its characteristics, typically covering distances surface.
of 300 to 1000 feet horizontally and 100 to 300 feet Each concrete project is unique, so specifications
vertically. The pump's capacity can range from 10 to should be carefully reviewed to determine the
over 250 cubic yards per hour, and the maximum appropriate curing methods for hot or cold weather
aggregate size should not exceed 40% of the pipe conditions.
diameter. Proper lubrication of the pump lines with a
mortar mix is essential before pumping begins.
Conveyor belts have also been used for transporting
plastic concrete, with modern systems capable of
moving up to 300 cubic yards per hour. The design of
the conveyor system must ensure continuous delivery of
fresh concrete without excessive construction joints.
Concrete testing should ideally occur both at the
discharge point and after the concrete has traveled
through the system to ensure accurate results. To control
cracking, joints must be placed in the concrete, including
contraction joints, isolation joints, and construction
joints, each serving specific purposes.
After placement, the concrete must be consolidated
to eliminate voids, using vibrators to ensure proper
density. Over-vibration should be avoided to prevent
segregation. Self-compacting concrete (SCC) is an
innovative mix that flows easily and fills forms without
the need for vibration.
The finishing of concrete surfaces can vary, with
options including wood float, broom, and hard-troweled
finishes, depending on the application. Slipform pavers
are commonly used for finishing concrete pavements.
Overall, careful attention to placement, consolidation,
and finishing techniques is crucial for achieving high-
quality concrete structures.
Precast Concrete Products
Curing Concrete Precast concrete products are construction items
Proper curing is essential for concrete to achieve its manufactured off-site and delivered ready for
design strength, enhance resistance to freeze-thaw installation. These products include pipes, catch basins,
cycles, and improve watertightness and wear resistance. septic systems, beams, columns, and floor units. The
Curing ensures the continued hydration of cement, manufacturing process involves stringent quality control
which requires maintaining moisture and favorable measures similar to those used in site-cast concrete to
temperatures for an adequate duration. The necessary ensure the use of quality materials.
curing time depends on factors such as cement type, mix Precast concrete pipes are classified by their
production methods. Cast concrete pipes, typically 48
inches or larger in diameter, are reinforced with steel
rebar and wire mesh and cured using steam or moist
methods. Centrifugally spun pipes, 42 inches or less in
diameter, are produced using high-speed rotation to
compact the concrete. Tamped and packer head pipes are
nonreinforced and made by compacting dry concrete into
molds. Lined cylinder prestressed concrete pipes are
used for high-pressure water systems and involve
multiple stages of production, including core creation,
steel wrapping, and mortar coating.
Precast structural elements like beams and columns
are produced in casting beds with external vibrators.
These elements are often made using high-early-strength
cement and heated curing to achieve strengths of 3000
psi or more within 24 hours. The forms are reused in a
24-hour cycle, and the finished products are stored on-
site for delivery.
Quality control is crucial for both precast and site-
cast concrete to ensure durability and minimize
maintenance. Common field problems include issues
with fresh concrete characteristics, such as excessive
bleeding, segregation, and rapid or slow setting. These
problems can be mitigated by adjusting mix proportions,
controlling water content, and using proper vibration
techniques. Other issues like shrinkage cracks, hairline
surface cracking, and dusting can be addressed through
proper joint spacing, curing methods, and surface
finishing techniques.
The checklist provided in Table 4-15 offers detailed
causes and preventive measures for various concrete-
related problems, including those specific to flat slabs,
wall surfaces, and cylinder tests. For instance, shrinkage
cracks in slabs can be prevented by adequate joint
spacing and immediate curing, while honeycombing in
walls can be reduced by proper vibration and mix
adjustments. Cylinder test issues often stem from
nonstandard testing procedures or low-strength mixes,
which can be corrected by following ASTM C 31
standards and confirming mix proportions.
Overall, understanding concrete technology and
adhering to standardized practices are essential for
producing high-quality concrete structures with long
service lives. Addressing common field problems
through careful attention and quality control measures
ensures the durability and performance of concrete
products.
Pervious Concrete
Pervious concrete mixes consist of coarse aggregate,
small amounts of fine aggregate, water, and cementitious
materials. The mortar paste binds the aggregate particles
together while leaving interconnected voids, typically
comprising 15 to 25 percent of the hardened concrete.
This void system enables rapid water drainage through
the concrete into the underlying granular subbase, where
it can be collected for treatment or allowed to percolate
into the soil. Flow rates for pervious concrete generally
range between 3 to 5 gallons per square foot per minute,
depending on the void content.
Compared to conventional concrete, pervious
concrete has lower strength due to its low mortar content
and high void system. However, with proper design, it
can achieve suitable strengths for applications such as
pavements, parking areas, driveways, and sidewalks.
The benefits of pervious concrete are significant,
including:
• Reduction of the heat island effect: Pervious
concrete reduces heat stored in pavements,
helping to mitigate urban heat islands.
• Pollution control: The pore structure of
pervious concrete supports bacteria and fungi
that break down hydrocarbons in runoff,
improving water quality.
• Stormwater management: It reduces the need
for retention ponds, increasing buildable area
and managing stormwater runoff effectively.