HOW TO DETERMINE DRYING SHRINKAGE OF HARDENED CONCRETE?

Target

This test method describes the process of determining the drying shrinkage or change in length of a concrete sample due to changes in moisture content.

Device

• A length measuring device consisting of a dial gauge capable of measuring lengths up to 0.005 mm accurately. (see picture shown below)

• 50±1 . drying oven capable of maintaining a temperature of⁰

test sample preparation

1. A test sample consists of samples that conform to the following dimension.

2. Cast the concrete samples as per the required dimensions and store it in moist air for 3 to 7 days.
3. Drill a shallow depression in the center of each end of the specimen so that it can accommodate a 6.5 mm diameter steel ball. These steel balls are fixed in this depression by cementing the balls with clear fast hardening Portland cement.
4. After fixing the steel balls, clean the balls to remove the cement on them, and then apply lubricating grease to prevent rust.
5. The test samples are then kept in a moist condition for at least 24 hours to allow the cement to harden. After 24 hours, test samples should be taken from 24 to 30 . Immerse in water made at a temperature of⁰ C up to 28 days. (remember the number of days is counted from the day the samples are inserted)

Testing Process

1. After removing the samples from the water, clean the grease from the balls and immediately measure the length of the sample with a length measuring instrument to an accuracy of 0.005 mm.
2. Then dry the samples in the oven for at least 44 h. After 44 hours of drying, remove it from the oven and cool it in a desiccator for at least 4 hours. After cooling, measure the length of the sample again using the length comparator. ‘Record this reading as’basic wet measurement,
3. Repeat the process of oven drying, cooling and measuring until a constant length is obtained, that is, when the difference between two constant length measurement readings is less than 0.01 mm for the 15 cm sample and less than 0.01 mm for the larger sample. be proportionately higher. ‘Record as’ the last readingdry measure,
4. After taking the dry measurement, measure the length of the specimen adjacent to the balls to the nearest 0.5 mm and record it as ‘.dry length,

calculation

The initial drying shrinkage or drying shrinkage is calculated as the difference between basic wet measurement And this dry measure expressed as a percentage of dry length,

Initial drying shrinkage = [(original wet measurement – dry measurement)/dry length]*100