Concrete Cracks

2017-11-25

Concrete is a heterogeneous, brittle material that is a mixture of gravel aggregates, cement, water and other additional materials.  As a result of concrete construction and deformation, constraints and a series of questions, There are a large number of micro-pores,  cavitation and micro-cracks in the hardened concrete,  Microfissure is usually a harmless crack, which does not endanger the load-bearing, seepage-proofing and other functions of the concrete. However, after the load, temperature difference and other effects of concrete, the micro-cracks will continue to expand and connect, and finally form our  macroscopic cracks, which is in concrete engineering often said cracks .

Concrete cracks caused by several factors. There are many reasons for concrete cracks, shrinkage of concrete cracks are mainly plastic shrinkage, self-shrinkage, dry shrinkage and carbonation shrinkage. Let me explain these definitions briefly:

1, plastic shrinkage

Plastic shrinkage refers to the concrete before condensation, the surface shrinkage due to faster water loss. Plastic shrinkage cracks generally occur in dry heat or windy weather, cracks are mostly wide in the middle, both ends of the fine and the length of different, non-coherent state. The main factors that influence the plastic shrinkage and cracking of concrete are water-cement ratio, concrete setting time, ambient temperature, wind speed, relative humidity and so on.

 2, dry shrinkage
 The main reason for dry shrinkage is the moisture that evaporates over a longer period of time after the concrete has hardened.  As the aggregate shrinkage is very small, so the concrete drying shrinkage is mainly caused by dry shrinkage of cement.

 3, carbonation contraction
Carbonation shrinkage is caused by, in the presence of water,  the action of cement hydration products on the formation of CaCO3, silica gel, aluminum glue and free water  with the contraction of CO in the atmosphere .

 As mentioned above, shrinkage is an inherent property of concrete. Cracking of concrete structures is generally caused by concrete shrinkage, except for factors such as uneven settlement of foundations, premature demolding or overloading. With the widespread use of commercial concrete, the slump of concrete is generally greater than that of on-site mixing. In particular, the large number of pumping concrete used,  worsened the shrinkage of concrete, the possibility of cracks appear more. However, it is only a possibility, not necessarily.