Question

What are the details of the following things: Sitting time , WATER CONTENT Slump test , Flow teble ,Shear strength ASTM , Consolidation test

Answer 1

SEING TIME:

When water is added to cement, the cement paste starts to loose its plasticity and becomes hard. The time taken by the cement paste to completely loose its plasticity and becomes hard is called Setting time. It is measurd with Vicat apparatus.

Initial setting time: The time period between water added to cement and cement paste starts to loose its plasticity

or

The time period ellapsed between the moment water is added to the cement and the needle of Vicat apparatus fails to penetrate the mould of 5mm when measured from bottom.

Final setting time: The time period between the moment water added to cement and cement paste completely looses its plasticity.

or

The time period between the moment water added to cement and the time which the needle of Vicat apparatus makes an impression on surface of the mould, while the apparatus fails to do so is called Final setting time

Water content and Slump test:

The ratio of water mixed in concrete is very important. If the quantity of water is too less then hydration of cement will not be proper it results into porus and week concrete. If the quantity of waer is too high then concrete will be more workable but does not give sound concrete. Hence proper water cement ratio is must to prepare a concrete mix. For this purpose we generally use Slump Cone test

The cone is a steel one and of 30 cm high, 20 cm diameter at base and 10cm diameter at top and also provided with andles at sides. Concrete is filled in the cone in layers of 7.5 cm at a time each layer tamperd with a steel rod 25 times. Just after slump cone has filled it is lifted with the help of handles. The extent by wich the concrete drops is called Slump and is measured from top of cone to top of concrete after cone has removed. Smaller of slump value indicates a sound concrete.

Flow table:

Flow table test of concrete also meaures the quality of concrete concerning its consistency cohesiveness and its proneness to segregation. It also measures Water cement ratio and workability of concrete.

The test apparatus consists of a metal table having thickness 1.5mm and dimensions 750mm*750mm. A metal cone or mould of hieght 20cm lower diameter of 20 cm and upper diameter of 13 cm.. the middle prtion of table consists of concenriccircle of diameter 200mm to place the cone on it. Pour the freshly prepared concrete in two layers each layer is tamped 25 times. Slowly lift the mould vertically up. The flow table is raised at the height of 12.5mm and dropped. The same is repeated for 15 times in 15 seconds. Measure the spread of concrete in diameter horizontally and vertically with scale. The arthematic mean of two diameters shall be the flow vaue in millimeters. Lesser the flow value more sound will be concrete mix.

Consolidation test:

Settlement that soil undergo as a response of placing loads on to the ground. It is a time dependant process. It is required in designing of foundation.During consolidation pore water in the voids of saturated clay ges squeezed out reducing the volume of clay hence causing settlement.

Measure the inner diameter and height of consolidation ring to calculate its volume. Prepare the soil specimen for test by trimming and pacing soil in ring. Determine mass of ring with soil. Place the specimen and ring and place upper disc. Pace 1.5kg load on first day 3 kg on second day 6kg on third day and 12 kg on 4th day. Determine the height of specimen each day and draw time vs settlement graph.

Height of solids

Determine change in height

Determine final height of specimen

Height of voids

Final void ratio