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Compressive strength test of concrete by cube test

Cube Test: In this test chque a compressive strength of concrete. Take a cube mould which dimentions are 150 mm×150 mm×150 mm (l×b×h) symultenouly. 

Also used a tamping rod of 16mm dia.Before the filling of cube mould apply the oil in the internal surface prolerly by which mould open eayly and surface be come smooth.

On the cube writedown the casting date, grid number, footings, columns, beams, or slab.

 After 12 hours remove from mould and sink in quring pond. Generly we are cast 6 cubes, 3 cubes test after 7 days and 3 cubes test at 28 days. If you can test at 14 days then need to be cast of 9 cubes. In each test take 3 cubes and consider avrage value of all 3rd.After 7 days concrete cubes dry prolerly in the persence of sun. 

Weight the cube one by one and writedown. The each weight of concrete cube not less than 8.1 kg.

How we proove that the weight of concrete cube should not be less than 8.1 kg.

Given dimentions of cube are length =150mm=0.15m, width=150mm=0.15m, depth=150mm=0.15m, so that the volume of cube =length ×width×height =0.15×0.15×0.15=0.3375 m3, as we know that the density of PCC =2400 kg/m3, Now we have volume and density of the concrete cube, so we will find the weight of concrete cube.As we know that Mass/weight =volume ×density =0.3375×2400=8100 grams=8.1 kg, 

hence we find that the weight of concrete cube should not be less than 8.1 kg. Now we fixed the cube one by one in the CTM machine prolerly and apply the load gragualy by hydroulic presser and by dial gauge black and red both pendulom togather gragualy move towards 25,50,75,100,125,150 KN,...... at a time the cube does be come collaps and red pendulom stop at 400 kN, 410kn and 415kn or 400000 N, 410000 N, 415000 N at the 1st,2nd,3rd cube. 

After the colaips of the cube black pendulom return towards 0. We know that area of cube =150×150 =22500 mm2If the grade of concrete is M25, where 25 N/mm2 is the compressive strength of cube after 28 days.

We know that concrete grained strength after 7 days 65% of 25 will be 16.25 N/mm2 ,

 14 days 90% of 25 will be 22.5 N/mm2 , and 28 days 90% of will be 25.75 N/mm2. We will find the one by one Compressive strength of 1st, 2nd and 3rd cobe afte 7 days.Strength of 1st cobe =load/area =400000/22500=17.77 N/mm2 

Strength of 2nd cube =410000/22500=18.22 N/mm2.Strength of 3rd cube =415000/22500 =18.44 N/mm2

Finally we will find the average strength of 1st,2nd,3rd cube which are shall not be less than 16.25 N/mm2.

 Average strength of 1st, 2nd and 3rd cobe =(17.77+18.22+18.44)/3=18.14 N/mm2 which is greater than 16.25 N/mm2. Hence the concrete strength is ok. Similarly we will find the Compressive strength of concrete after 14 days, 28 days and conformed that the strength of concrete is ok or not. 

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