DRYING SHRINKAGE OF CEMENT IS 4031 part 10

DETERMINATION OF DRYING SHRINKAGE OF HYDRUALIC CEMENT

Drying shrinkage is defined as the contracting of a hardened concrete due to the loss of capillary water. Drying shrinkage occurs when water starts evaporating from the exposed surface . Due to this drying shrinkage, cracks are noticed on the surface of cement concrete.

TEST STANDARD: IS 4031-Part X: 1988

APPARATUS:

1. Balance
2. Bar mould of size 25x 25mm and 282mm internal length
3. Length comparator
4. Flow table and its accessories
5. Trowel
6. Planetary mixer paddle with bowl and scraper

TEST PROCEDURE:

1. Temperature and relative humidity of the laboratory shall be maintained at 27±2^oC and 65± 5%.
2. The bar mould shall be thinly covered with mineral oil and reference inserts with knurl heads shall be set to obtain an effective gauge length of 250mm.
3. Test mortar shall be prepared by gauging test sample of cement and standard sand in the ratio of 1:3 by mass.
4. The amount of water required shall be measured using flow table to give a flow of 110 to 115% with 25 drops in 15 seconds when the mortar is mixed mechanically. Immediately after the completion of mixing, bar mould shall be filled with test mortar in two layers, each layer being compacted with thumb or forefinger by pressing the paste into the corners, around the reference inserts and along the surfaces of the mould until a homogeneous specimen is obtained.
5. After the top layer has been compacted excess paste shall be cut off flush with the top of the mould and the surface smoothed with few strokes of trowel. During the process of mixing and moulding.
6. The hand shall be protected by rubber gloves. After the mould has been filled, it shall be immediately placed in the moist room at a temperature of 27±2^oC & relative humidity of not less than 90% for 24± 2hours. Specimens shall be removed from the moulds and immediately immersed in water at 27±2^oC and allow them to remain there for six days.
7. Remove the specimens from the water and measure its length using a length comparator. Protect specimens from loss of moisture prior reading for initial length. The temperature of the specimens at the time of initial measurement shall be 27±2^oC.

The difference in length of the specimens gives the drying shrinkage of the cement:

Drying shrinkage (%) = [(Final length of specimen- Initial length of specimen)/ Effective gauge length (250mm)] x 100

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