(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 utilized to strengthen concrete by reinforcement.

Cement is a powdery substance that consists of calcium, silicon, aluminum, iron, and other ingredients. It is used as a binding material in the construction industry. When mixed with water, it forms a paste that hardens after some time. On the other hand, concrete is a composite material made up of aggregates (such as sand and gravel), cement, and water. Cement acts as the binder in concrete, holding the aggregates together and giving the material its strength.

1. Tensile Strength: Concrete has high compressive strength (ability to withstand forces pushing on it) but low tensile strength (ability to withstand forces pulling on it). This limitation can cause concrete structures to crack or break under tension, such as when bending or stretching. 2. Shrinkage and Creep: As concrete dries and hardens, it can shrink and develop cracks, reducing its overall strength. Additionally, concrete can slowly deform under long-term sustained loads, a phenomenon known as creep. This can lead to a loss of pre-stress or deflection in the structure, affecting its stability and serviceability. 3. Susceptibility to environmental factors: Concrete structures are vulnerable to damage from environmental factors such as temperature fluctuations, chemical reactions, and moisture. For example, freezing and thawing cycles can cause concrete to crack and weaken, while corrosion of steel reinforcement can lead to structural failure.

1. Steel Reinforcement: Steel bars or mesh can be embedded in the concrete to increase its tensile strength and provide better resistance to cracking and deformation. The steel reinforcement can carry the tensile loads, while the concrete carries the compressive loads, forming a strong and durable composite material. 2. Pre-stressed Concrete: Pre-stressing involves applying tension to steel reinforcement before the concrete is cast. This creates a compressive stress in the concrete, which helps counteract tensile stresses that will be applied to the structure during service. Pre-stressed concrete can better resist tension and has reduced cracking compared to conventional reinforced concrete. 3. Fiber Reinforcement: Adding fibers, such as steel, glass, or synthetic fibers, to the concrete mix can improve its tensile strength, ductility, and impact resistance. The fibers help distribute stresses more evenly within the concrete, reducing the risk of cracking and increasing the material's overall durability.