foundation system of burj al arab

Concrete Microcracking Basics

We know that failure of concrete associated with cracking; so understanding the cracks formation, propagation and factors influencing them are very important in concrete technology. Here, we will know about microcracking. We have already discussed about plastic shrinkage cracking, formation of cracking due to alkali-aggregate reaction, plastic settlement cracking in concrete and cracking related to reinforcement corrosion. We have learned about arrival time, causes and location of appearance of cracking elaborately for the convenience of reader. You can visit this post for additional information.

It is observed that even before application of load, concrete remains in cracked form. Are you surprised? Or you are taking it normal as a consequence of bad workmanship or improper mix design. Dear reader even their have no fault in mix proportions and placing process, there have cracks. Cracks exist between interface of cement paste and coarse aggregate, surprisingly before concrete members are left for service. 

Microcracks in white lines; concrete sample under the neutron radiograph
Dear reader we are talking about microcracking, as discussed above, this is due to foreseeable mechanical difference in properties of both two interfacing components. These cracking are also prominent with thermal movement or shrinkage.

Microcracking is found normal strength concrete; but not uncommon in concrete produced with low water to cement ratio specially cured (wet cured). The water/cement ratio may be as low as 0.25. Experiments reveal that microcracking (before loading or preloading) in concrete is responsible for lower tensile strength.

Microcracks are not defined in respect of sizes, but for reference we can provide upper limit of them; this is 0.1 mm which can not detected by naked eyes of human. Neutron radiography is used to measure various aspects of microcracking. In the next post we will discuss about propagation and behavior of microcracking under loading as a percent of ultimate strength. Please stay with us for few post, we will discuss about all aspects of microcracking through them.

1 comment:

  1. What is the reason for the existence of microcracks even before the concrete is subjected to external load?