The strength of concrete is affected by many factors including the quality of raw materials, water/cement ratio, the quantity of aggregate, the age of concrete, temperature etc. In order to produce desired properties of hardened concrete, one must know which factors affect its properties. By controlling those factors the most durable concrete and be formed.
Water-Cement ratio is defined as the weight of water divided by the weight of cement in the concrete mix. Generally, the water-cement ratio is 0.45 and if the ratio is more than 0.45 the extra water will create pores in concrete. The strength of these pores filled with air is essentially zero. As a result, it reduces the strength and durability of concrete.
Type and amount of cement
The major factor that affects concrete compressive strength is the amount of cement. Higher cement content forms shrinkage cracks while concrete is hardening. The type of cement you are using also have an impact on the properties of hardened concrete.
Type and amount of aggregate
Aggregate is one of the most important elements that defines the strength of concrete. The coarse aggregates act like a bone in concrete. Using poor quality aggregate will greatly affect the hardened concrete’s properties. Adding more aggregate decreases the strength of the cement. The strength of concrete can also be affected by the type of aggregate. Angular and rough surface concrete improve the concrete strength because the rough surface of aggregates makes a strong bond between cement paste and aggregates.
On the other hand, round and a smooth surface aggregate decrease the concrete strength. Bigger size aggregate with lower water requirement can produce strong concrete. But, using larger size aggregate without decreasing water content decreases the strength of concrete.
Increased water temperature, either at mixing stage or during curing, increase the speed of strength gain of concrete. In colder climates, outer concrete is exposed to freeze-thaw cycles which are damaging. Freeze-thaw deterioration is a serious threat to concrete durability. All materials expand and shrink with changes in temperature and moisture content. Excessive contraction can cause concrete to crack. The cracks in concrete then allow moisture to penetrate and the cruel cycle of deterioration starts.