Influencing Factors And Theoretical Analysis On Anti-cracking Capability Of High Strength And High Performance Concrete

The extensive application of high strength and high performance concrete has already obtained great technique, economy and social benefit, but its early cracking is serious, which is the important problem that the social concerned. The thesis firstly discussed the difference on the reason and the mechanism of cracking between high strength and high performance concrete and normal concrete. Ring test and flat test were adopted for research on the major influencing factors of cracking. From the point of view of optimizing material mix-proportion, the measures were advanced to improve the anti-cracking capability of high strength and high performance concrete. Secondly, distribution of thermal and moisture within young concrete with age and the shrinkage deformation due to their changes were analyzed. Based on theoretical analysis and computational model, a three-dimension numerical simulation software 3C3D(Concrete Cracking Control 3D) was finished in which finite element and finite difference method were both hired. Compared with the known data, good agreement proved it reliable and practicable. Finally, by means of the software, with variant of environmental temperature and relative humidity and different curing conditions, the variety regulation of temperature and humidity and the stress due to them within concrete were analyzed. It provided the reference to improve the anti-cracking capability of high strength and high performance concrete from the point of view of constructional technology and curing requirement.The result shows that the more the binder material or sand rate, the more serious the shrinkage cracking. In the concrete with a low water-to-binder ratio, a bit of difference in the dosage of water will result in big difference on the strength and the anti-cracking capability. The occurrence of cracking is mainly at early age (before 1 day). If the surface is plastered again after 2 hours of casting, the anti-cracking capability will nicely improved. The temperature of surface concrete varies with environmental temperature, but the conductibility of inner concrete is very poor. As a result, a quick decrease of environmental temperature will lead to large temperature gradient and then tensile stressdevelop soon in the thick direction, which will probably occur on the entire cross-section. The change of moisture distribution is concentrated on the surface layer concrete, which is very thin. However, the change inside the concrete is very slight. This unbalanced development of moisture distribution causes large shrinkage stress in the layer concrete and then leads to crack. If the surface is covered or watered after casting of concrete, the influence resulted from change of environmental temperature and relative humidity on concrete will decrease to some extent. Then the shrinkage stress will also decrease and the probability of cracking will be reduced as well.