can anyone explain the crack pattern of cement concrete cube ???

can anyone explain the crack pattern of cement concrete cube ???
Higher coarse aggregate content, the use of very fine and high-angularity sand, poor aggregate gradation, incompatible mineral and chemical admixtures, inadequate curing, delayed finishing, high rate of evaporation from concrete surface, and sudden temperature drop are the major causesof plastic shrinkage cracking.
 

Dnyan Deshmukh

Staff member
failure-patterns-of-cubes-jpg.2900


The above image shows the type of failure which can be seen in cubes after crushing in cube testing machine.
It is most important to do analysis of failure observed in cube to find the root causes and taking action on it.

Failure patterns reflects the problem with either cube or cube testing machine, we should record the failure pattern as satisfactory or Unsatisfactory.
Cube shown in image as 1, 2 and 3 indicates the failure pattern as satisfactory, rest all patterns are Unsatisfactory.


When we do cast cubes, it is important to ensure the correct size and it is a cube. De-moulding and transportation of the cube should be done only after concrete attains sufficient strength, else will lead to damages of the corners and edges which may give unsatisfactory failure pattern and could also affect on strength of the concrete (cubes with broken edges could lead to reduction in load carrying capacity of the cube).
If there is much variation in size of the cube, it will also lead to unsatisfactory failure pattern.

The Problems in the CTM machine which could lead to unsatisfactory failure;
1. The main frame of the machine got bend and its axis of loading shifts from its position.
2. The plattens in contact with cube are bent and not flat.
3. Fixed platten or top platten head does not have adjustment, leads to eccentric loading and generation of tensile cracks in cube when the cube shape is having variation in size.

The Human errors which could lead to unsatisfactory failure pattern;
1. Cube not placed at exact position.
2. Cube placed in machine with finish face in contact to platten (the face from which we pour concrete in cube and do finish, it should be on front face where you can read details of cube, it should never go in contact with plattens, as this face is not fully flat).

After recording of the failure patterns of cubes, we should also inspect failed portion of the cube for understanding the failure's and properties of material.