Tests on Concrete

Some of the essential tests conducted on concrete are following:

1. Slump test.
2. Compaction factor test.
3. Crushing strength test.

1. Slump Test: This test is conducted to find out the workability of concrete. It needed a slump cone for test. Slump cone is a vessel with diameter at bottom 200 mm and 50 mm at top and 300 mm high in the shape of a frustum of a cone. This cone is kept over impervious platform and filled with concrete in four layers. With a 16 mm pointed rod for 25 times each layer is stamped. The cone is gently pulled up after filling completely. In the height of the concrete the decrease is called slump.  If the slump Higher, more workable is the concrete. The desired values of slumps for several works have been shown in table described above (suggested value of workability)

                                    Slump test

2. Compaction Factor Test: This is another test to recognize the workability of concrete. This test is conducted in the laboratory. Test equipment consists of and a cylinder and two hoppers fixed to a stand, the dimensions and the distances between the 3 vessels being standardized. Vessel A and B has hinged bottoms whereas cylinder C have fixed bottom. Top most vessel A is filled with the concrete to be tested. The hinged door is opened as soon as it is filled. In vessel B Concrete is collected. Then in cylinder C, the hinged door of B is opened to collect concrete. In cylinder C the concrete is weighted. Assume it be W1.

Now cylinder is filled again with the sample of concrete in 50 mm, layers, which is compacted by vibrating and ramming. Then the weight of compacted concrete is resolute. Assume this weight be W2.The ratio W1/W2 is called compaction factor. For different works the specified values of compaction factor are already listed in workability table.

            Compaction factor test

3. Crushing Strength Test: for casting concrete cubes Metallic moulds of size 150 mm × 150 mm × 150 mm are used. It is properly oiled on its inner surfaces, before filling mould, so that cubes can be simply separated. In 3 layers Fresh cube is filled with concrete to be tested and kept in the room. Cube is removed from the mould after24 hours and kept under water for curing. Cubes are tested after 28 days of curing in the compression testing machine. Cubes are placed over the smooth surface in this test which is in contact with side plates of mould. The crushing load is noted down and crushing strength is found as load divided by surface area (150 × 150 mm2). For quick assessment of strength of concrete, Code denote the desirable strength of concrete for 3 days and 7 days.