CONCRETE TECHNOLOGY (CEC 303) Engr. Dr. A. O.

Familusi

2.0 PROPERTIES OF AGGREGATE AND WATER MIXTURES

2.1 Grading Coarse Aggregate into Standard Diameter Sizes:

 Coarse aggregates are graded into standard sizes based on the diameter of the particles. Common
standard sizes include 3/8 inch, ½ inch, ¾ inch, 1 inch, 1 ½ inch, and 2 inches. The grading is typically
done using sieves with specific mesh sizes to separate the aggregates into different size fractions.

2.2 Determining the Relative Density of Coarse and Fine Aggregates:

 Relative density, also known as specific gravity, is the ratio of the density of a substance to the density
of a reference substance (usually water). The relative density of aggregates is determined using
specific tests such as the water displacement method or the pycnometer method.

2.3 Grading by Sieve Analysis - Fine and Coarse Aggregates:

 Sieve analysis is a method used to determine the particle size distribution of aggregates. For both fine
and coarse aggregates, samples are passed through a series of sieves with progressively smaller
openings. The amount of material retained on each sieve is measured, and a grading curve is plotted to
represent the particle size distribution.

2.4 Combining Aggregates to Meet Particular Grading Requirements:

 Aggregates can be combined in different proportions to achieve specific grading requirements for
concrete mixtures. The grading of aggregates influences the workability, strength, and durability of
concrete, so it's important to carefully control the proportions of different size fractions in the mix.

2.5 Lightweight Aggregates:

 Lightweight aggregates are materials used in concrete that have a lower density than traditional
aggregates. They are typically produced from natural materials such as expanded clay, shale, or slate,
or from industrial by-products such as fly ash or slag.

2.6 Properties of Lightweight Aggregates:

 Lightweight aggregates have several properties that make them advantageous for use in concrete,
including:
o Low density: Lightweight aggregates reduce the weight of concrete, making it suitable for
applications where weight is a concern, such as high-rise construction.
o Thermal insulation: Lightweight aggregates provide better thermal insulation properties
compared to traditional aggregates, resulting in energy savings and improved comfort in
buildings.
o Improved workability: Concrete containing lightweight aggregates often exhibits better
workability and ease of placement, leading to reduced labor costs and construction time.

2.7 Uses of Water in Concreting:

 Water plays several important roles in concrete:

o Hydration: Water is essential for the chemical reaction between cement and aggregates, known
as hydration, which forms the hardened concrete matrix.

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CONCRETE TECHNOLOGY (CEC 303) Engr. Dr. A. O. Familusi

o Workability: Water helps to lubricate the concrete mix, making it easier to place and compact
during construction.
o Curing: Water is used for curing concrete to maintain adequate moisture levels and promote
proper hydration of cement, ensuring the development of strength and durability.

2.8 Quality of Water for Bad and Good Concrete:

 Good quality water for concrete should be clean, free from impurities, and suitable for drinking. It should
not contain excessive amounts of dissolved salts, organic matter, or harmful chemicals. Poor quality
water, such as water containing high levels of chlorides, sulfates, or organic contaminants, can
adversely affect the setting time, strength, and durability of concrete.

2.9 Effects of Bad Water on the Strength of Concrete:

 Poor quality water used in concrete can lead to several detrimental effects on its strength and durability,
including:
o Delayed setting time: Certain impurities in water can interfere with the hydration process,
causing delays in setting and hardening of concrete.
o Reduced strength: High levels of chlorides or sulfates in water can react with the cement paste,
leading to the formation of expansive compounds that weaken the concrete.
o Increased permeability: Contaminants in water can increase the porosity and permeability of
concrete, allowing harmful substances to penetrate more easily and causing deterioration over
time.
o Corrosion of reinforcement: Chloride ions in water can accelerate the corrosion of steel
reinforcement within concrete, compromising its structural integrity and service life.

2.10 Clay and Silt Content

Determining the clay and silt content, as well as other impurities, in a soil sample typically involves a
combination of laboratory tests and experiments. Here's a general procedure you can follow:

1. Soil Sample Collection:

o Collect a representative soil sample from the location of interest using a soil auger or shovel.
Ensure the sample is free from debris and large stones.
2. Soil Sample Preparation:
o Air-dry the soil sample to remove excess moisture.
o Break down any aggregates or clumps by gently crushing the soil with a mortar and pestle or by
sieving through a mesh screen.
3. Particle Size Analysis:
o Perform a particle size analysis to determine the proportions of sand, silt, and clay in the soil
sample. This can be done using the hydrometer method or the sieve analysis method.
o For the hydrometer method, mix the soil sample with water and dispersing agent, then allow the
particles to settle. Measure the specific gravity of the suspension at various time intervals to
calculate the particle size distribution.
o For the sieve analysis method, sieve the soil sample through a series of sieves with different mesh
sizes. Weigh the fractions retained on each sieve to determine the particle size distribution.
4. Clay and Silt Content Calculation:
o Calculate the clay and silt content based on the particle size analysis results. Clay particles have a
diameter less than 0.002 mm, while silt particles have a diameter between 0.002 mm and 0.05
mm.

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CONCRETE TECHNOLOGY (CEC 303) Engr. Dr. A. O. Familusi

o Determine the percentage of clay and silt fractions in the soil sample based on the weight of
particles retained in the respective size ranges.
5. Other Impurities Analysis:
o Conduct additional tests to identify and quantify other impurities present in the soil sample, such
as organic matter, carbonate content, and soluble salts.
o Organic matter content can be estimated by loss on ignition method, where the soil sample is
heated to burn off organic matter, and the weight loss is measured.
o Carbonate content can be determined using acid digestion methods, where the soil sample is
treated with acid to dissolve carbonates, and the released carbon dioxide is measured.
o Soluble salts content can be measured by extracting the soil sample with water and analyzing the
conductivity or electrical conductivity of the extract.
6. Data Interpretation:
o Analyze the results of the experiments to assess the soil quality and suitability for various
applications.
o Compare the clay and silt content, as well as other impurities, to soil classification criteria and
standards to determine the soil type and potential uses or limitations.
7. Reporting:
o Prepare a report summarizing the experimental procedures, results, and findings, including
recommendations for soil management or remediation if necessary.

It's essential to follow standardized procedures and quality control measures during soil testing to ensure
accurate and reliable results. Additionally, consult relevant soil testing manuals or guidelines for specific
methods and protocols.

2.11 Different Types of Concrete Admixtures:

1. Accelerators: These admixtures are used to accelerate the setting and early strength development of
concrete, particularly in cold weather conditions or when rapid construction is required.
2. Plasticizers (or water reducers): Plasticizers are added to concrete to improve workability and reduce
the water content needed for a given consistency. They enhance the flow of concrete without
compromising its strength.
3. Retarders: Retarders are used to slow down the setting time of concrete, allowing for better workability
and placement over an extended period. They are useful in hot weather or when delays in placement
are anticipated.
4. Air entrainers: Air entraining agents are added to concrete to introduce microscopic air bubbles, which
improve the freeze-thaw resistance, durability, and workability of concrete. They are especially
important in climates with freeze-thaw cycles.
5. Colorants: Colorants are pigments or dyes added to concrete to impart color for decorative or aesthetic
purposes. They can be used to achieve a wide range of colors and effects in finished concrete
surfaces.
6. Water proofers: Waterproofing admixtures are used to reduce the permeability of concrete and prevent
water penetration. They help protect concrete structures from moisture-related damage and enhance
durability.

2.12 Compositions of Different Additives and Admixtures:

 The compositions of additives and admixtures vary depending on their specific function and chemical
properties. They may include organic or inorganic compounds, polymers, surfactants, and other
ingredients designed to achieve desired performance characteristics in concrete.

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CONCRETE TECHNOLOGY (CEC 303) Engr. Dr. A. O. Familusi

2.13 Uses of Additives and Admixtures:

 Additives and admixtures are used to modify the properties of fresh and hardened concrete to meet
specific performance requirements. They can enhance workability, durability, strength, and aesthetics
of concrete, as well as provide protection against environmental factors such as freezing and thawing,
chemical attack, and water ingress.

2.14 Selection of Additives and Admixtures for Appropriate Uses:

 The selection of additives and admixtures depends on factors such as project requirements,
environmental conditions, concrete mix design, and desired performance characteristics. Engineers and
concrete professionals must carefully evaluate the intended application and consult with suppliers to
choose the most suitable additives and admixtures for achieving the desired results. Proper dosage,
compatibility, and mixing procedures are also critical considerations for the effective use of additives
and admixtures in concrete.

3.0 CONCRETE MIX

3.1 Define Concrete:

Concrete is a composite material composed of cement (commonly Portland cement), aggregates (such as
sand, gravel, or crushed stone), water, and sometimes admixtures. When mixed together, these materials form
a plastic mixture that hardens and gains strength over time through a chemical reaction called hydration.
Concrete is widely used in construction for various structural and non-structural applications due to its strength,
durability, versatility, and ability to be molded into different shapes.

3.2 Different Mix Proportioning Methods:

 Mix proportioning refers to the process of determining the quantities of cement, aggregates, water, and
admixtures needed to produce concrete with desired properties. Mix proportions can be determined by
weight or volume:
o By Weight: Mix proportions are specified based on the weight of each ingredient. This method
provides greater accuracy and consistency in mix design, as variations in aggregate moisture
content are accounted for by weighing the materials.
o By Volume: Mix proportions are specified based on the volume of each ingredient. This method is
less accurate than by weight method because the volume of aggregates can vary depending on
factors such as particle shape, compaction, and moisture content.

3.3 Thermal Effects on Design Mixes; Prescribed and Design Mix:

 Thermal effects on design mixes refer to the influence of temperature on the properties of concrete
during mixing, placing, and curing. Temperature variations can affect the rate of hydration, setting time,
strength development, and durability of concrete. Prescribed mix refers to a concrete mixture specified
by a standard or code without considering specific project requirements, while design mix refers to a
custom-designed concrete mixture tailored to meet the specific performance criteria and project
conditions.

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CONCRETE TECHNOLOGY (CEC 303) Engr. Dr. A. O. Familusi

3.4 Influence of Voids in Fine and Coarse Aggregates on Mix Design:

 Voids in fine and coarse aggregates affect the workability, strength, and durability of concrete.
Excessive voids can increase the water demand, reduce the strength, and increase the permeability of
concrete. Properly graded aggregates with minimal voids help optimize the packing density and particle
distribution in the concrete mix, resulting in improved overall performance.

3.5 Influence of Voids on Concrete by Mix Experiments:

 Mix experiments can be conducted to evaluate the influence of voids on concrete properties. By
adjusting the proportions and grading of aggregates, the amount of voids can be controlled to study its
effects on workability, strength, durability, and other performance indicators. Experimentation helps
identify optimal mix designs that balance the requirements for workability, strength, and durability while
minimizing voids and potential defects.

3.6 Purpose of Mix Design:

 The purpose of mix design is to proportion concrete ingredients in such a way as to achieve the desired
properties and performance characteristics for a specific application or project. Mix design aims to
optimize factors such as strength, workability, durability, permeability, and economy while considering
project requirements, environmental conditions, and material properties.

3.7 Steps Needed to Get a Good Mix:

 The steps for obtaining a good concrete mix include:

1. Define project requirements and performance criteria.
2. Select suitable materials, including cement, aggregates, water, and admixtures.
3. Conduct preliminary mix trials to determine initial proportions and evaluate material properties.
4. Adjust mix proportions based on trial results to achieve desired properties and performance.
5. Conduct laboratory testing and analysis to validate mix design and optimize performance.
6. Document and record mix design details for quality control and consistency in production.
7. Monitor and adjust mix proportions as needed during production to maintain quality and
consistency in the finished concrete.

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