Factors Affecting Properties of Concrete

Concrete is a composite product obtained artificially by hardening of mixture of cement, sand, gravel and water in pre-determined proportions. When these ingredients are mixed, they form a plastic mass which can be moulded in desired shape. It gets hardened into hard solid mass. Water is one of the important ingredients of concrete. This is required not only for chemical reaction, but also for curing purposes. The chemical reaction of cement and water, in the mix, is relatively slow and requires time and favorable temperature for its completion. Depending on the quality and proportions of the ingredients used in the mix, the properties of concrete has enough strength in compression, but has little strength in tension. Due to this, concrete as such is weak in bending, shear and torsion. Hence the use of plain concrete is limited to applications where great compressive strength is the main requirement and where tensile stresses are either totally absent or are extremely low.

• W/c ratio: Strength, elasticity, durability and impermeability of concrete is increased with decrease in w/c ratio, provided the concrete is workable. Shrinkage is increased with greater w/c ratio.
• Cement content: With increase in cement content, w/c ratio is decreased and consequently, strength, elasticity, durability and permeability is increased. More cement improves workability but it also increases shrinkage which is undesirable.
• Temperature: Rate of setting and hardening of concrete is high at higher temperatures. If temperature of concrete falls below 0°C, free water in concrete turns into ice crystals and since ice has greater volume than the same quantity of water, the concrete is completely disrupted. Such concrete on thawing will have no strength. If the temperature is more than the freezing temperature, cool concreting gives better ultimate strength, durability and less shrinkage.
• Age of concrete: Strength of concrete goes on increasing with age, though the rate of