Compressing Experimental Research On Drying Shrinkage Of Recycled Concrete Based On Pretreatment Of Recycled Coarse Aggregate

With the soaring development of construction industry, resources (sand, stone, etc.) which are widely used in concrete are becoming deficient and environment problem is increasingly prominent. To offer a possible sustainable development method for concrete industry, a new building material which is environmental friendly emerges as the times require——recycled concrete. By applying the recycled concrete technology, not only can the environment be protected, but also distinct economic and ecological benefits can be acquired. The drying shrinkage of recycled concrete is obviously different with that of normal concrete because of remarkable difference between recycled coarse aggregates and normal aggregates. Researches on this area is rare at present, this paper mainly investigates the drying shrinkage performance of recycled concrete when pretreatment methods are taken in recycled concrete coarse aggregates, the main tasks and conclusions are summarized as follows:1. Basic performance and pretreatment methods of recycled coarse aggregates were investigated, the results showed that the apparent density and bulk density of recycled coarse aggregates were bigger and that the water absorption rate and crush index of recycled coarse aggregates were higher when compared with that of nor mal coarse aggregates. As a consequence, the basic performance of recycled coarse aggregates was worse than normal coarse aggregates. After three methods (pre-wet, aggregates enveloped with cement, aggregates enveloped with cement and silica fume mixture) were applied to recycled coarse aggregates, it was found that the cube crushing strength of recycled concrete was improved distinctly. The method when aggregates enveloped with cement and silica fume mixture was conducted turned out to be the most efficient approach.2. The influence different recycled coarse aggregates replace rates have on the drying shrinkage characteristic of recycled concrete was investigated and compared with that of normal concrete. The results showed that with the increase of recycled coarse aggregates rates, the drying shrinkage strain of recycled concrete increase apparently, furthermore, the development rate of recycled concrete with 100% replacement rate was bigger than that of 50% replacement rate.3. The influence three methods (pre-wet, aggregates enveloped with cement, aggregates enveloped with cement and silica fume mixture) have on the drying shrinkage of recycled concrete was analyzed and compared with that of normal concrete. The results indicated that the drying shrinkage strain of recycled concrete reduced with a certain degree after three methods were applied, among them, the method when aggregates enveloped with cement and silica fume mixture was taken turned out to be the most efficient way to reduce drying shrinkage strain.4. After analyzing the shrinkage deformation values got from the experiment and comparing it with those calculated from several widely-used drying shrinkage models of concrete, an appropriate GL2000 drying shrinkage model was selected as a reference. By combining the results of drying shrinkage experiment obtained in this paper which took the influence of different recycled coarse aggregates replace rates and different strengthening pretreatment methods into account and taking parameters correction, a suitable model for drying shrinkage prediction can be established, it can improve the accuracy of model prediction.