Aggregate Characteristics and Properties Quiz

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Questions and Answers

What is a characteristic of crushed aggregate?

Round shapes with smooth surfaces

Low cement content

High workability

Good bond strength (correct)

What is the primary advantage of using the largest possible maximum size of aggregate?

Higher bonding properties

Reduction in water requirement (correct)

Greater drying shrinkage

Increased workability of concrete

What does a good grading of aggregate help achieve?

Reduced strength of the concrete

Higher water content requirement

Higher voids within the concrete

Increased economy and durability (correct)

What does the Fineness Modulus (FM) indicate?

The uniformity and fineness of aggregate Signup and view all the answers

What preliminary step is essential before conducting sieve analysis on aggregate?

Surface drying the sample Signup and view all the answers

What is the primary requirement for aggregates in terms of strength and durability?

Aggregates should be stronger than the required concrete strength. Signup and view all the answers

Which source does NOT classify as a type of aggregate?

Synthetic aggregates produced from chemical reactions. Signup and view all the answers

What type of aggregate is typically used for radiation shielding?

Heavy weight aggregates Signup and view all the answers

Which classification of aggregates is based on their specific gravity?

Heavy weight, normal weight, and light weight aggregates Signup and view all the answers

What is a key characteristic of light weight aggregates?

Specific gravity is less than 2. Signup and view all the answers

Which type of aggregate is composed primarily of aluminum oxide?

Argillaceous aggregates Signup and view all the answers

What is the primary purpose of well-graded aggregates in concrete mixtures?

To minimize paste and cement requirements. Signup and view all the answers

What is one potential disadvantage of using aggregates that contain impurities?

They could adversely affect the strength and durability. Signup and view all the answers

What is the formula used to calculate moisture content (MC)?

MC = 100 * (Weight of Sample - A) / A Signup and view all the answers

How is the Bulk Specific Gravity (SSD) calculated?

B / (B - C) Signup and view all the answers

What does the apparent specific gravity indicate?

The volume of the aggregate excluding voids Signup and view all the answers

What is the typical range of void content for coarse aggregates?

30-45% Signup and view all the answers

How does aggregate angularity affect void content?

Void content increases with increasing angularity Signup and view all the answers

What does porosity measure in the context of aggregates?

The volume of pores to total volume Signup and view all the answers

What effect does void content have on the cement paste requirement for concrete?

Increases proportionately with void content Signup and view all the answers

Which of the following is NOT related to the absorption characteristics of aggregates?

Cement paste thickness Signup and view all the answers

What is the purpose of quality control in concrete production?

To reduce variation in strength and consistency Signup and view all the answers

Which of the following is NOT a critical phase in concrete quality control?

Marketing and selling Signup and view all the answers

When should cement be tested initially for quality control?

Once for each source and subsequently every two months Signup and view all the answers

What is one of the purposes of conducting control tests on concrete ingredients?

To ensure ingredients are free from impurities Signup and view all the answers

Which quality control stage occurs first in concrete construction?

Quality control before concreting Signup and view all the answers

What should be done if large lumps are found in cement bags?

Reject the cement Signup and view all the answers

Which quality control measure helps to ensure desirable quality at every stage of work?

Integrating quality checks at all phases Signup and view all the answers

Which of the following does NOT affect the strength or consistency of concrete?

Color of the cement Signup and view all the answers

What does the Vebe time measure in the concrete testing process?

Time taken for concrete to be compacted flat Signup and view all the answers

In which condition is bleeding predominantly observed in concrete?

Highly wet mix Signup and view all the answers

What is the primary purpose of concrete compaction?

To expel entrapped air from the concrete Signup and view all the answers

What could happen if 1% of air is entrapped in concrete?

It causes a 5-6% reduction in concrete strength Signup and view all the answers

Which of the following is NOT a type of segregation in concrete?

Air pockets formation Signup and view all the answers

Which method is NOT used for compacting concrete?

Compaction by temperature regulation Signup and view all the answers

What can help reduce bleeding in concrete?

Proper proportioning and complete mixing Signup and view all the answers

What is a critical factor affecting the duration of vibration during concrete compaction?

The height of the layer being compacted Signup and view all the answers

What does a flow test indicate about concrete?

Its workability and cohesiveness Signup and view all the answers

What phenomenon occurs when excess water rises to the surface of freshly placed concrete?

Bleeding Signup and view all the answers

Why is moisture crucial for the curing of concrete?

It allows for the completion of chemical reactions for hardening Signup and view all the answers

Which of the following contributes to permeability in concrete?

Continuous bleeding channels Signup and view all the answers

What is one potential consequence of rapid water loss from curing concrete?

Surface cracks due to shrinkage Signup and view all the answers

Which factor does NOT affect the bleeding rate of concrete?

Size of coarse aggregate Signup and view all the answers

Which curing method is considered the most effective?

Water curing Signup and view all the answers

What is the main goal of curing concrete?

To ensure complete hydration and strength attainment Signup and view all the answers

Study Notes

Course Information

Course name: Construction Materials
Course code: CEng- 2205
Course instructors: Zerihun M., Elias L., Melimal W., & Heaven Y.

Chapter Three: Cementing Materials

Lecture note on: Concrete

Introduction

Concrete is a heterogeneous material made from binding material (cement), fine aggregate (sand), coarse aggregate (gravel), and water.
The properties of concrete depend on the characteristics of its ingredients and the proportions of the mixture.
Key considerations in mix proportioning include workability, strength, durability, and cost-effectiveness.

Functions of Component Materials

Cement: Reacts with water to form a plastic mass when fresh and a solid mass when hardened, acting as a binder.
Water: Enables the chemical reactions leading to setting and hardening. Also lubricates the mixture for easier placement.
Aggregate: The inert mineral filler material which the cement paste binds together and reduces volume changes. Aggregates also contribute to the concrete's durability.
Admixtures: Modify the properties of concrete (fresh or hardened) to meet specific needs.

Aggregates

Occupy 65-75% of the concrete volume.
Selection and proportioning of aggregates is crucial for the concrete's performance.
Importance in determining the physical, thermal, and at times, chemical properties of concrete.
Purposes:
- Form the inert mineral filler material that the cement paste binds together.
- Reduce volume changes from setting and moisture changes.
- Provide better durability.
- Provide economic advantages.
Important requirements in selecting aggregate:
- Good workability during placement.
- Sufficient strength and durability in the hardened state.
- Impurity-free.
- Resistance to chemical reactions with cement.
- Economical availability.
Classification of aggregates:
- Natural (Igneous, Sedimentary, Metamorphic).
- Artificial (Recycled).
- Based on weight (Light weight, Normal weight, Heavy weight).
- Based on size (Fine, Coarse).
- Based on chemical composition (Siliceous, Calcareous, Argillaceous).
- Based on condition (Crushed, Uncrushed).

Grading of Aggregate

Using the largest possible maximum aggregate size in a given set of conditions can reduce cement requirements, shrinkage, and water requirements.
The maximum size may be limited by section thickness, reinforcement spacing, clear cover, or work handling techniques.
Good grading is crucial for workable concrete (less void spaces). This ensures higher strength, greater durability, and reduced shrinkage.
Fineness Modulus (FM): Used to evaluate the fineness or coarseness and uniformity of the aggregate.

Advantages and Disadvantages of Concrete

Advantages: High compressive strength, high stiffness, easy to cast, low thermal and electrical conductivity, economical, durable, fire resistant, energy efficient, aesthetic properties.
Disadvantages: Low tensile strength, limited ductility, little resistance to cracking, volume instability, low strength-to-weight ratio, need for forms and shoring.

Water in Concrete

Essential for chemical reactions with cement, enabling setting and hardening.
Crucial for managing the workability of fresh concrete, improving plasticity.
Impure water (containing suspended solids, silt) can negatively impact concrete's durability, strength, and may cause accelerated corrosion of reinforcing steel.

Admixtures in Concrete

Admixtures are materials added to fresh concrete to modify its properties.
Chemical admixtures: Accelerators, retarders, water reducers, and air-entraining admixtures.
Mineral admixtures (Supplementary Cementing Materials): Fly ash, silica fume, and ground granulated blast-furnace slag. Their purpose is replacing part of the cement, lowering early strength but increasing ultimate strength, increasing durability, reducing cost.

Types of Concrete

Classified by density (Normal, Light, Heavy).
Classified by strength (Low, Medium, High).

Process of Manufacturing Concrete

Batching: Accurate measurement of materials (cement, aggregates, water). Different methods for batching exist, with weighing being more precise.
Mixing: Thorough mixing to achieve a homogenous concrete mixture with uniform color, consistency. Hand mixing is for smaller jobs, while machine mixing is for large-scale work.
Transporting: Ensuring concrete maintains its homogenous state during transport; proper methods (e.g., chutes, conveyors) needed.
Placing: Placement should place concrete in uniform layers, to minimize segregation and enhance homogeneity; should be done quickly and at correct levels.
Compacting: Removing entrapped air. Methods including hand tools, vibration, or pressure are used.
Curing: Maintaining moisture content to enable hydration and strength gains.

Properties of Fresh Concrete

Workability: An important property describing how easily it can be mixed, placed, consolidated, and finished. Key components including its compatibility, mobility, and stability.
Consistency: Degree of fluidity or mobility (e.g., stiff, plastic, flowing).
Factors affecting workability include the properties of the materials (water content, cement content, aggregate size/shape, grading, admixture), and the environmental conditions (temperature, time).

Properties of Hardened Concrete

Strength: Generally the compressive strength (a measure of the resistance to crushing). Key influence factors including: Water-Cement Ratio (lower is better), Cement content (more is better), Aggregate characteristics (size, shape, and grading), and curing (maintenance of moisture).
Durability: Concrete's ability to resist degradation by environmental factors or the internal deterioration causing premature failure.
Shrinkage: Volume changes occur due to moisture loss during drying (or setting). Plastic shrinkage (occurs during the plastic phase), and drying shrinkage (due to drying after initial set). Influences factors: water-cement ratio, aggregate content and properties, curing practices.
Creep: Time-dependent deformation of concrete under sustained load, increasing with time under constant stress.

Quality Control

Importance of consistent quality in concrete production and control at all construction stages.
Methods used to test concrete (destructive and non-destructive testing) include compression testing of concrete, rebound hammer tests, and ultrasound pulse velocity testing.
Quality control is ongoing throughout all stages: equipment, materials, procedures, and workmanship.

Mix Design Process

Selection of suitable materials.
Determining the precise proportions of the materials (cement, water, aggregates, admixtures) necessary to achieve the required strength, consistency, and workability.

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Description

Test your knowledge on the characteristics and properties of aggregates in construction. This quiz covers topics such as grading, fineness modulus, moisture content, and types of aggregates used in concrete. Prepare to enhance your understanding of this crucial aspect of civil engineering.