Cement / Concrete
Cement/Concrete is of utmost importance in construction industry. During the construction phase various strength/workability tests are carried out. These tests include:
Cement consistency is determined with the help of Vicat’s apparatus. The purpose of the test is to determine the water content required to produce a cement paste of standard consistency. The mould of the apparatus is filled with fresh cement paste. The plunger of the apparatus is released and allowed to penetrate in the cement paste. The cement paste is said to have standard consistency if the penetration is 5 – 7 mm.
Setting time of cement paste is measured with the help of Vicat’s apparatus. This is helpful in determining the water content to be used depending upon the desired workability. There are two phases in the stiffening of cement paste. Initial setting time is the time when cement starts losing its plasticity and final setting time is the time when cement completely loses its plasticity. The initial set is the time from the addition of water to cement till the time at which plunger penetrates the cement paste by 5 – 7 mm. Whereas, final set is the time from the addition of water to cement till the time at which plunger needle makes an impression on the paste.
Concrete Mix Design
Concrete Mix design is the process of determining required and specifiable characteristics of a concrete mixture, ability to continually meet or exceed specifications (durability and strength) is the primary considerations in concrete mix design. The strength and workability of concrete depends upon the different constituents of that make up the concrete namely cement, water, coarse aggregates, fine aggregates and admixtures. In order to have first-hand knowledge of the behaviour of concrete on the site, various concrete mix having different characteristics are prepared and tested. The most suitable concrete mix according to the site conditions is then used.
Concrete Slump Test
Workability of freshly mixed concrete is determined by concrete slump test. A slump cone is placed on a non-absorbent surface. Cone is filled up with concrete in three layers. Each layer is tamped with tamping rod of standard dimensions. After filling up the cone, the cone is lifted upwards. As a result concrete subsides and there is a fall in height of concrete after the removal of cone which is termed as slump.
Compressive strength is determined by axially loading the sample through a machine and noting down the reading at the point of failure. The compressive strength is calculated from the failure load divided by the cross-sectional area resisting the load and reported in units of pound-force per square inch (psi).