1 Use the ACI 209 expressions for creep and shrinkage lectur

1 Use the ACI 209 expressions for creep and shrinkage (lecture on properties of hardening concrete) and predict the creep and shrinkage for one of your laboratory strength mixtures assuming a concrete slab of 8 inch thickness and: Loading age: at day one Relative humidity: 80% Thickness: 8 inches Concrete composition: as per your mixture designs 2. List five factors that affect the ultimate shrinkage strain a given mixture of concrete will attain.

Solution

2.

The shrinkage of concrete depends on several factors which are listed below.

1. WATER-CEMENT RATIO:

Shrinkage is mostly influenced by the water cement ratio of concrete. It increases with the increases in the water-cement ratio.

2. ENVIRONMENTAL CONDITION:

It is one of the major factors that affect the total volume of shrinkage. Shrinkage is mostly occurred due to the drying condition of the atmosphere. It increases with the decrease in the humidity.

3. TIME:

The rate of shrinkage rapidly decreases with time. It is found that 14-34% of the 20 years shrinkage occurs in two weeks, 40-80% shrinkage occurs in three months and the rest 66-85% shrinkage occurs in one year

4. TYPE OF AGGREGATE:

Aggregates with moisture movement and low elastic modulus cause large shrinkage. The rate of shrinkage generally decreases with the increase of the size of aggregates. It is found that concrete made from sandstone shrinks twice than the concrete of limestone.

5. ADMIXTURES:

The shrinkage increases with the addition of accelerating admixtures due to the presence of calcium chloride (CaCl2) in it and it can be reduced by lime replacement