Experimental Research On Influencing Factors Of Tensile Creep Of Recycle Aggregate Concrete

Currently, environment and resources issues caused by waste concrete are becoming increasingly prominent. An effective method to tackle these problems is to reuse the recycle aggregates obtained by processing waste concrete, which has profound effect on protecting environment and saving resources, thereby promoting a sustainable development society. Few researches about tensile creep properties of recycle aggregate concrete were reported before and the possibility is very high that the tensile creep behavior between recycle aggregate concrete and normal concrete is very different due to the difference between recycle coarse aggregates and virginal ones. Therefore, the influence recycle coarse aggregates replacement, fly ash addition and mixed addition of fly ash and slag have on the behavior of tensile creep of recycle aggregate concrete was investigated, which hopefully would deepen the understanding of factors that influence tensile creep of recycle aggregate concrete, therefore, the use of recycle aggregate concrete could be promoted. The main efforts accomplished in the thesis are listed as follows:1. Physical and mechanical properties test of recycle coarse aggregates showed that the old mortar which attached to the surface of recycle coarse aggregates led to the fact that recycle coarse aggregates had lower density, higher voidage, higher water absorption and crush index when compared with virginal ones.2. Basic mechanical properties test of recycle aggregate concrete showed that replacing 70% virginal coarse aggregates with recycle ones could cause the decrease of basic mechanical performance of recycle aggregate concrete with varying degrees; although the addition of fly ash enhanced the workability of recycle aggregate concrete, it led to the decrease of basic mechanical performance of recycle aggregate concrete, and it was found the more addition of fly ash, the more decrease it could have; mixed addition of fly ash and slag not only guaranteed the workability of recycle concrete, but also effectively alleviate the decrease extent of basic mechanic performance caused by the addition of fly ash, and it was revealed that the more addition of the mix, the more decrease it showed, while the reduction was lower than the addition of fly ash with the same total amount.3. Uniaxial tensile creep experiment indicated that replacing 70% virginal coarse aggregates with recycle ones increased the tensile creep of recycle aggregate concrete; the addition of fly ash led to the increase of tensile creep of recycle aggregate concrete, and the more addition of fly ash, the more increase it showed; mixed addition of fly ash and slag could apparently narrow down the increase extent of tensile creep caused by the addition of fly ash, moreover, the more addition of it resulted in the increase of tensile creep, but the augment was obviously lower than the addition of fly ash with the same total amount.4. The result from tensile creep test of recycle aggregate concrete was compared with some current concrete tensile creep predicting models and it was found that models that are frequently used were not suitable for predicting tensile total creep of recycle aggregate concrete, while M-Burgers Model with its parameters confirmed by fitting could have better predictions on some test groups in terms of tensile basic creep. M-Burgers Model was chosen afterwards, and some parameters were added to the model to take the effect of recycle coarse aggregates and mineral admixtures into consideration. Finally, a proper predicting model for tensile basic creep of recycle aggregate concrete was built.