Factors Affecting Strength of Concrete

 

The strength of concrete depends on many factors such a quality of ingredients, their proportion temperature, workmanship and atmospheric condition. The factors affecting the strength of concrete can be discussed as follows;

1. Quality of Ingredients
2. Water/Cement Ratio
3. Coarse/Fine Aggregate Ratio
4. Aggregate/Cement Ratio
5. Age of Concrete
6. Compaction of Concrete
7. Temperature  
8. Relative Humidity
9. Curing

1. Quality of Ingredients

The main ingredients of concrete are cement, sand, aggregates and water. The quality of all these materials determines the quality of concrete and strength of concrete. If the quality of ingredients is good, the strength will be more and if ingredients are of low quality the strength concrete will be less respectively.

2. Water/Cement Ratio

If water cement ratio is less the strength of concrete will be higher. Considering the good workability and full compaction concrete. If compaction is not well at lower water cement ratio, the strength will be less and there may be a chance of not achieve the full compaction. So, only the good workability and compaction must be idle condition for the comparison between w/c ratio and strength of concrete.

3. Coarse/Fine Aggregate Ratio

If the proportion of fines is increased in comparison to the coarse aggregate the overall aggregates surface area will increase if surface area of aggregate has increased the water demand will also increase. Increases in water demand indicate increasement of water cement ratio, on increasing water cement ratio, the strength of concrete will decrease and vice versa.

4. Aggregate/Cement Ratio

If the volume remains the same and the proportion of cement in relation to that sand is increased the surface area of the solid will increase. If the surface area of the solid is increased the water demand will remain same for the constant workability. Assuming on increasing in cement content at constant water content, the water cement ratio becomes less and strength of concrete will be more.

5. Age of Concrete

The hydration of cement increases with the increasing the age of concrete. In controlled curing, of concrete the maximum strength of concrete will achieve at 28 days and will increase in decreasing rate till two years and final strength will achieve only after one to two years of placement. After that the strength of concrete will decrease very slowly.

6. Compaction of Concrete

If the compaction of concrete is sufficient, the strength will be more and if not sufficient, the pores remaining inside the concrete body will reduces the strength of concrete. If there was 10% trapped air in the concrete, the strength will fall down by 30 to 40%

7. Temperature

The rate of hydration reaction is temperature dependent. If the temperature increases the reaction also increases. This means that, the concrete kept at higher temperature will gain strength more quickly than a similar concrete kept at lower temperature. However, the final strength of concrete at higher temperature will be less.

8. Relative Humidity

If the concrete is allowed to dry, the hydration reaction will stop. The hydration reaction cannot proceed without moisture. At 100% relative humidity, the water loss from the concrete body will be in regular way. So, strength of concrete will be higher at lower relative humidity of strength will also be less.

9. Curing

The proper curing of concrete for the specified periods of duration and by specified method, will increase for strength of concrete and vice versa.