Construction Materials: Aggregate Quiz

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Questions and Answers

What is one consequence of water soluble sulfates in natural aggregates?

Improves the workability of the mix

Causes expansion and deterioration of cement paste (correct)

Acts as a bonding agent between aggregates

Increases the strength of concrete

What defines a deleterious chemical reaction between aggregates and cement alkalies?

When the reaction is not extensive and does not produce gel material

When the reaction causes expansion and cracking of the concrete (correct)

When there is no observable expansion or cracking

When an increase in water-cement ratio is necessary

Which approach can help mitigate Alkali-aggregate reaction?

Using conventional cement with high sodium content

Increasing the volume of aggregates in the mix

Selecting reactive aggregate

Reducing the water-cement ratio (correct)

Which of the following is NOT one of the suggested methods to avoid Alkali-aggregate reactions?

Incorporating a higher percentage of water in the mix Signup and view all the answers

What leads to the formation of highly expansive gel material in concrete?

The reaction of reactive aggregates with cement alkalies Signup and view all the answers

What is the minimum size (d) for fine aggregate?

0 mm Signup and view all the answers

Which of the following aggregate types has a maximum size of 31.5 mm?

8/31.5 Signup and view all the answers

What does the fineness modulus (FM) represent in aggregate grading?

Average particle size Signup and view all the answers

Which of the following is NOT a method used to assess the quality of aggregates?

Compressive strength test Signup and view all the answers

What is the significance of a low Los Angeles coefficient in aggregate testing?

Reflects good resistance to fragmentation Signup and view all the answers

For what type of concrete is aggregate strength most critical?

High-strength concrete Signup and view all the answers

How is the specific surface area of an aggregate defined?

Surface area per unit mass Signup and view all the answers

Which of the following is an example of fine aggregate?

0/4 Signup and view all the answers

What defines fresh concrete?

Concrete that can be transported, placed, and compacted. Signup and view all the answers

Which of the following statements about aggregates is true?

Aggregates serve as a strong filler material in concrete. Signup and view all the answers

Which type of concrete has undergone setting but has not yet hardened significantly?

Green Concrete Signup and view all the answers

Which is a characteristic of recycled aggregates?

They are derived from previously used construction materials. Signup and view all the answers

What is the role of admixtures in concrete?

They reduce the water-cement ratio without affecting workability. Signup and view all the answers

Which step in concrete manufacturing involves combining aggregates with cement and water?

Mixing Signup and view all the answers

Natural aggregates are characterized by which of the following?

They are derived from minerals without further processing. Signup and view all the answers

What is the significance of curing in the concrete manufacturing process?

It helps to maintain moisture for proper hydration. Signup and view all the answers

What is the typical range of relative densities for most natural aggregates?

2.40 to 2.90 Signup and view all the answers

Which factor does NOT affect void content in aggregates?

Type of cement used Signup and view all the answers

What does void content in aggregates represent?

The space not occupied by solid matter Signup and view all the answers

What is the moisture content state where aggregates are neither absorbing nor contributing water?

Saturated surface dry (SSD) Signup and view all the answers

How does void content affect the mixing water and cement requirements?

Increases with higher void content Signup and view all the answers

Which aggregate type generally has a higher range for absorption levels?

Coarse aggregate Signup and view all the answers

What state is described as fully absorbent with zero moisture content?

Oven dry Signup and view all the answers

Which of these describes free water within aggregates?

Difference between SSD and wet state moisture content Signup and view all the answers

What is a characteristic of crushed stone compared to natural gravel?

Crushed stone tends to have a rough surface. Signup and view all the answers

Why should flaky and elongated aggregate particles be limited in concrete?

They lead to higher specific surface area and increase voids. Signup and view all the answers

What size is classified as fine aggregate according to the given standards?

D ≤ 4 mm Signup and view all the answers

Which of the following statements about rounded smooth aggregates is true?

They produce lower cement content in concrete mixtures. Signup and view all the answers

What is the main advantage of using manufactured or recycled aggregates?

They provide specific properties needed for certain applications. Signup and view all the answers

What role does surface texture play in aggregate properties?

Surface texture influences the bond strength in the concrete mix. Signup and view all the answers

What is a potential disadvantage of using flaky aggregate particles?

They may crush during manufacturing, increasing fines in the mixture. Signup and view all the answers

Which statement correctly describes the grading of natural gravel?

The grading of natural gravel is not controlled. Signup and view all the answers

What does dry bulk density represent in relation to aggregates?

The mass of 1 m³ of aggregates Signup and view all the answers

Which type of aggregate is classified as lightweight?

Aggregates with bulk density less than 1120 kg/m³ Signup and view all the answers

How is relative density (specific gravity) of aggregates defined?

The ratio of aggregate particle density to the density of distilled water Signup and view all the answers

In concrete mix design, what is the primary use of compacted dry bulk density?

To assess the mass/volume relationships for aggregates Signup and view all the answers

What is the approximate bulk density range for normal weight concrete aggregates?

1200 kg/m³ to 1750 kg/m³ Signup and view all the answers

Which property of aggregates is NOT typically classified under physical properties?

Chemical composition Signup and view all the answers

What does void content refer to in the context of aggregates?

The amount of empty spaces between aggregate particles Signup and view all the answers

The application of concrete aggregates with a bulk density greater than 2100 kg/m³ is primarily for which purpose?

Radiation shielding and counterbalancing Signup and view all the answers

Study Notes

Concrete Technology (CES 251s) Fall 2024

Course instructor: Dr. Hesham A. Sokairge
Contact: [email protected]

Course Contents

Concrete Constituents: Aggregates, Cement, Water, Admixtures
Concrete Properties: Fresh Concrete, Hardened Concrete
Concrete Mix Design

Introduction

Concrete Definition: A composite material fundamentally consisting of a binding medium (hydraulic cement and water) encompassing embedded aggregate particles (coarse and fine).
Concrete States:
- Fresh Concrete: Possesses sufficient workability for transportation, placement, and compaction.
- Green Concrete: Undergone setting but not hardened significantly.
- Hardened Concrete: Developed sufficient strength to endure anticipated loads without failure.
Concrete Manufacturing Processes: Batching, Mixing, Transporting, Placement (Casting), Compacting (Consolidating), Finishing, Curing.
Ready-mixed concrete manufacturing: Details of the process, including different systems, were shown.

Aggregates for Concrete

Aggregate Definition: Granular materials (sand, gravel, crushed stone) used with a cementing medium to produce concrete or mortar.
Role of aggregates in concrete: Strong filler with relatively low cost compared to cementitious materials; major constituent resisting abrasion and localized impact; affects limiting volumetric changes due to restraint from aggregate and dilution effect.
Classification of Aggregates:
- Source: Natural, Manufactured, Recycled
  - Natural Aggregates: Sand, Gravel, Crushed Stone (processed)
  - Manufactured Aggregates: LECA (Lightweight Aggregate), Slag, Fly ash
  - Recycled Aggregates: Crushed concrete, Crushed masonry, Crushed glass
- Size: Coarse Aggregate (D > 4 mm, d ≥ 2 mm), Fine Aggregate (D ≤ 4 mm), All-in Aggregate (mixture of coarse and fine aggregates), Filler Aggregates (smaller than 0.063 mm).
- Shape: Rounded (gravel, sand), Angular (crushed stone), Flaky (small thickness compared to other dimensions), Elongated (length large compared to other dimensions).
- Surface Texture: Smooth, Rough, Porous
Shape and surface texture:
- Avoiding flaky and elongated aggregates (limiting to 25% of mass); high specific surface area increases voids, cement content, and decreases workability.
- Rounded smooth aggregates decrease water content demand and improve durability, with limited bond strength.
Table (3): Approximate Free-Water Contents (kg/m³) required to give various workability levels based on slump (mm) and vebe time (s), with the max size of aggregate (mm) and concrete type.
Table (2): Approximate Compressive Strengths (N/mm²) of concrete mixes made with free-water/cement ratio of 0.5, classifying by cement strength class and type of aggregate (uncrushed and crushed).
Bulk Density: Light weight (less than 1120 kg/m³), Normal weight (1120-1920 kg/m³), Heavy weight (over 2100 kg/m³)
Relative density (Specific gravity): Ratio of aggregate density to distilled water density at a stated temperature; used in concrete mix proportions computations. Types of aggregates relative density.
Void Content: Space between particles not occupied by solid matter in aggregate; calculated using dry bulk density.
Physical Properties (continued):
- Absorption and moisture content: Moisture content of aggregates at SSD state; influence total water content of concrete. Coarse aggregate absorption typical (0.2%-4%); fine aggregate absorption typical (0.2%-2%). Water absorbed by aggregates isn't included in mix design water.
- Bulking of fine aggregate: Increase in volume of moist fine aggregate due to surface tension in the moisture; moisture content (4-6%) influences the volume of fine aggregates.
- Clay and Fines Content: Fines (particle size < 0.063 mm), adhere to aggregates, impact bond strength. ECP 203 limits on clay and fine content. How to avoid problems due to clay and fines.
- Aggregate Size and Grading: Particle size distribution; sieve analysis process to divide aggregate into particle fractions; standard sieves; different sieve sets for coarse and all-in aggregates, fine aggregates, and fillers. ECP203 limits and percentages for coarse aggregate maximum/minimum and fine aggregate maximum/minimum size.
Mechanical Properties:
- Strength: Aggregate strength rarely influences conventional concrete strength, but significant in high-strength concrete; compressive strength ranging.
- Resistance to Fragmentation: Resistance to abrasion or impact, important in industrial floors and pavements; Los Angeles abrasion test measures this property. ECP203 limits for Los Angeles coefficients.
Chemical properties:
- Salt Contamination: Soluble salts (chlorides) affect embedded steel via efflorescence or corrosion; sulfates attack aluminates and calcium hydroxide leading to expansion and deterioration.
- Alkali-Aggregate Reactivity (ASR): Deleterious chemical reaction between aggregate constituents and cement alkalies. Avoid alkali-aggregate reaction with appropriate testing and measures.

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Description

Test your knowledge on the properties and reactions of aggregates in construction materials. This quiz covers topics such as water soluble sulfates, alkali-aggregate reactions, and aggregate grading. Assess your understanding of the significance of various aggregate properties and their testing methods.