Concrete - Concrete is a mixture of cement (11%), fine Mass Concrete
aggregates (26%), coarse aggregates (41%) and water (16%) Roller-Compacted Concrete
and air (6%).
Chapter 2: Portland Cement
Concrete – most common material
Cement – described as a material used to bind the mineral
Activities of production of concrete: fragments called aggregates
Material
Selection William Joseph Aspidin – conceived cement (1824)
Proportioning
Isaac Charles Johnson – developed cement (1845)
Process
Mixing - Produced modern cement by
Transportation burning mixture of chalk, clay, and
Placement silica temp of 1400 – 1450 degrees
Compaction Celsius
Curing -
Lime and Gypsum were used as early as 2560 BC by the
Process – responsible for quality of concrete Egyptians in making Great Pyramids.
The basic ingredients of concrete: Pozzolanic cement – produced by combinig lime with volcanic
Cement – most important and costliest ingredient ash containing active silica and aluminum, at normal
Aggregate – give volume to the concrete temperature.
Water – indispensable because it is required for
reaction of hydration. Hydraulic cement – present day cement
Admixture – optional ingredient used only for
specific purpose Composition of Modern cement:
Calcareous material: Limestone of chalk
Fine Aggregate - this component can be natural sand or Argillaceous material: Clay/shale
crushed stone, and represents particles Siliceous material: Silica
smaller than 3/8". Generally, accounts for
30%-35% of the mixture. Manufacturing of cement:
Proportioning of raw material
Coarse Aggregate - May be either gravel or crushed stone. Grinding, intimate mixing
Makes up 40%-45% of the mixture, Burning in a large rotary kiln at 1400-1450 deg.
comprised of particles greater than 1/4".
Manufacturing Process:
Materials added to alter the properties of concrete including: Crushing and Proportioning
Air entrainment Raw milling & Blending
Set accelerators Pyro processing
Set retarders Burning and cooling
Water reducers Cement milling, Storage & Packing
Mineral admixtures
Limitations of Concrete:
Low tensile strength
Low ductility
Volume instability
Low strength-to-weight ratio
Progress in Concrete Technology:
Lightweight Concrete
High-Strength Concrete
High Workability or Flowing Concrete
Shrinkage Compensating Concrete
Fiber-Reinforced Concrete
Concrete Containing polymers
Heavyweight Concrete
HEAT OF HYDRATION - Heat of hydration is the heat Inherited Properties
generated when cement and water react. Chemical and mineral composition
Specific gravity
Chapter 3: Aggregates for Concrete Hardness
Strength
Classification of Aggregates Color etc.
According to origin of aggregates
According to weight of aggregates
Acquired Properties
Aggregate shape
According to origin of aggregates Rounded
Natural Mineral Aggregates - Sand, gravel, and Angular
crushed rock derived from natural
Elongated
sources.
Igneous Rocks Flaky
Sedimentary Rocks. Irregular
Metamorphic Rocks. Aggregate size
It reduces the cement
Synthetic Aggregates - Thermally processed
materials, i.e. expanded clays and requirement
shale. It reduces the water
- Aggregates made from industrial requirement
by-products, i.e. blast-furnace slag It reduces shrinkage of
& fly ash.
Recycled Aggregates - Made from municipal wastes
concrete
and recycled concrete from Surface texture
demolished buildings and Smooth texture
pavements. Rough texture
Water absorption
According to weight of aggregates Bone dry
Air dry
Normal Weight - Gravels, Sands, Normal
Crushed Stone, Bulk Specific Saturated surface dry
Gravity - 2.4 to 2.9, Bulk Moist
Density (of Bulk Unit
Weight) - 1520 to 1680 Phases of Concrete:
kg/m3, Most commonly
Paste phase
used.
Aggregate phase
Light Weight - Manufactured or Natural, Bulk Density
Less than 1120 kg/m3. Most commonly Characteristics of paste phase:
used in lightweight concrete, many must be It is weaker than aggregate
screened to get the desired size
It is vulnerable to most of the ill effects on
distribution, and some must be crushed.
concrete
Heavy Weight - Aggregates weighing more than 2080 It is more permeable than any of the
Kg/m3 are called heavyweight. mineral aggregates
It is susceptible to aggressive chemicals
Types of Aggregates
Significance of Gradation:
Coarse Aggregate (CA) - Retained over size Economy
4.75 mm. Consistency
Fine Aggregate (FA) - Passing Size 4.75 mm Strength
Shrinkage
Properties of Aggregates: Finish ability
Tests on Aggregates
Bulk Density (ASTM C 29)
Defined as the weight of the aggregate
particles that would fill a unit volume. The
term bulk is used since the volume is
occupied by both the aggregates and voids.
The typical bulk density used in making
normal concrete ranges from 1200 to 1750
Maximum Aggregate Size (MSA) - It is the smallest kg/m3.
sieve opening through which the The void contents range between 30% to
entire sample passes (or in practice 45% for coarse aggregate and 40% to 50%
only 5% retained on this sieve. for fine aggregate. Void content increases
with angularity and decreases with well
Nominal Max Size - the largest size particle presents graded aggregate.
significantly to affect concrete Relative Density (Specific Gravity)
properties. The relative density of an aggregate (ASTM
C 127 and C 128) is defined is the ratio of
Bulking of Sand – it is the property of sand by virtue its mass to the mass of an equal absolute
of which its apparent volume of water. It is used in certain computations
increases when some water is for mixture proportioning and control.
added to it. Most natural aggregates have relative
densities between 2.4 and 2.9 (2400 and
Quality of aggregates: 2900 kg/m3).
Deleterious material The relative density of an aggregate (ASTM
Salt contamination C 127 and C 128) is defined is the ratio of
Alkali reaction its mass to the mass of an equal absolute
of water. It is used in certain computations
Durability of Aggregates for mixture proportioning and control.
Most natural aggregates have relative
• Any lack of durability of the aggregate will have disastrous densities between 2.4 and 2.9 (2400 and
consequences for the concrete. 2900 kg/m3).
• Durability can be divided into physical and chemical causes.
• Physical durability – exposure to freezing and thawing,
wetting
and drying, physical wear.
• Chemical durability –various forms of cement –aggregate
reactions (alkali –silica attack).
Physical durability:
Soundness: if volume changes
accompanied with environmental changes
lead to the deterioration of concrete –
unsoundness.
Volume changes: alternate freezing and
thawing, repeated wetting and drying –
internal stresses –volume increase.
Volume changes: alternate freezing and
thawing, repeated wetting and drying –
internal stresses –volume increase.
Chemical Durability
alkali-aggregate reaction.
