(a) What is the distinction between cement, and concrete? (b) Cite three important limitations that restrict the use of concrete as a structural material. (c) Briefly explain three techniques that, are used to strengthen concrete by reinforcement.

Short Answer

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Answer: The main distinction between cement and concrete is that cement is a component of concrete, while concrete is a finished construction material made up of cement, sand, and aggregate combined with water. Three limitations of concrete as a structural material are its low tensile strength, susceptibility to cracking, and low resistance to chemical attack.

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01

(a) Distinction between Cement and Concrete

Cement is a fine, grey powder made from a mixture of limestone, clay, and other materials susceptible to hydraulic hardening when mixed with water. It is a binding material that can bind different materials together when mixed with water, sand, and aggregate. Concrete, on the other hand, is a composite construction material composed of cement, sand (fine aggregate), coarse aggregate, and water. Concrete is formed when water is added to the mixture of cement and aggregate. This allows the cement to bind together the aggregate and sand, creating a solid structure over time. The primary distinction between cement and concrete is that cement is a component of concrete, while concrete is a finished construction material made up of cement, sand, and aggregate combined with water.
02

(b) Three Limitations of Concrete as a Structural Material

1. Low tensile strength: Concrete has excellent compressive strength but poor tensile strength. This limitation means that it can withstand a considerable amount of pressure from above, but it can easily crack and break under tension or when pulled apart. This property restricts the use of concrete in various structural applications where tension loads are present. 2. Susceptibility to cracking: Concrete can be subject to shrinkage during the curing process and develop cracks over time. These cracks may weaken the structure and, if subject to water penetration, can result in corrosion of steel reinforcement or frost damage. 3. Low resistance to chemical attack: Concrete can be vulnerable to acidic or alkaline substances, which can lead to the breakdown of the material over time. This limitation restricts the use of concrete as a structural material in certain environments where it may come into contact with corrosive chemicals or elements.
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(c) Three Techniques for Strengthening Concrete by Reinforcement

1. Steel reinforcements: The most common method of strengthening concrete is by adding steel reinforcement bars (rebars) to the concrete mix. This method allows concrete to withstand higher tensile forces and flexural stresses, increasing its overall structural capacity and durability. 2. Fiber-reinforced concrete: Fibers made of materials such as steel, glass, or plastic can be added to the concrete mixture to improve its strength and resistance to cracking. These fibers help distribute stress more evenly throughout the concrete, making it more resistant to impact and fatigue. 3. Pre-stressing techniques: Pre-stressing is a method that applies a compressive force to the concrete during construction. This force helps counteract tension forces that the concrete may face during its lifetime. By doing so, it helps to reduce cracking and increase the overall strength and durability of the concrete. Two common pre-stressing techniques are pre-tensioning and post-tensioning.

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Most popular questions from this chapter

(a) List four reasons why glass fibers are most commonly used for reinforcement. (b) Why is the surface perfection of glass fibers so important? (c) What measures are taken to protect the surface of glass fibers?

16.25 (a) What is a hybrid composite? (b) List two important advantages of hybrid composites over normal fiber composites.

\(16.16\) It is desired to produce an aligned carbon fiber-epoxy matrix composite having a longitudinal tensile strength of 750 MPa (109,000 psi). Calculate the volume fraction of fibers necessary if (1) the average fiber diameter and length are \(1.2 \times 10^{-2} \mathrm{~mm}\) (4.7 \(\times 10^{-4}\) in. \()\) and \(1 \mathrm{~mm}(0.04\) in. \()\), respectively; (2) the fiber fracture strength is \(5000 \mathrm{MPa}\) \((725,000 \mathrm{psi}) ;\) (3) the fiber-matrix bond strength is 25 MPa (3625 psi); and (4) the matrix stress at fiber failure is \(10 \mathrm{MPa}\) \((1450 \mathrm{psi})\)

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