| This research is a part of "Experimental study and design method for thecombined force performance of the recycled concrete structural member and themechanical properties of the recycled concrete structure in the freeze-thawconditions"(Project approval No.51278151) which is funded by National NaturalScience Foundation of China.With the accelerated process of modernization, the construction industry hasentered the era of rapid development. Due to the extensive use of concrete, the wasteof resources, environmental pollution, waste treatment and other issues have been soserious that can not be ignored. Recycled concrete technology, which can solvethese problems and ensure the sustainable development of human society, has beenwidespread concerned.In China, at present, studys about frost resistance of recycled concrete wereless, and the conclusions were not the same. There are many factors that caninfluence the anti-freeze durability of recycled concrete, and this article focused onthe influence of the air content of original concrete on the mechanical properties andfrost resistance of recycled concrete. The article also took the air content of recycledconcrete, replacement rate of recycled coarse aggregate and other factors intoconsideration, aiming to conduct a comprehensive analysis of the mechanism offreeze-thaw damage of the recycled concrete.As known to all, the frost resistance of concrete depends on mortar, andair-entraining agent essentially increases the air content of mortar in concrete. Inorder to exclude the interference of gravels, to analyze the effect of air content ofmortar in original concrete on the frost resistance of recycled concrete obviously,and distinguish the new and old mortar in recycled concrete, in this article, originalmortar was instead of original concrete, which was made by white cement with theair content of2.1%and7%. And the mechanical testings of mortar were carried out.Non air entraining recycled aggregate and air entraining recycled aggregate, asraw materials of two kinds of recycled concrete, were got by crushing and sievingthe original mortar. Changing the air content of recycled concrete, replacement rateof recycled coarse aggregate, pretreatment methods of the recycled coarse aggregate,these two types of recycled concrete were subdivided into10groups, witch wereused to conduct to mechanics performance tests and shrinkage test.These10groups of recycled concrete were also used to conduct the freeze-thawtest, with200freeze-thaw cycles. Comparisons among these groups of recycled concrete on their frost resistance were made by comparing mass lose rate, dynamicelastic modulus loss and strength loss rate in freeze-thaw conditions. Analyzewhether the air content of original concrete would impact the frost resistance ofrecycled concrete, and find out how the air content, the replacement rate of recycledcoarse aggregate and other factors affect the frost resistance of recycled concrete.Microanalysis was designed to study the microstructure of these two kinds ofrecycled concrete. Observe the different appearance and failure modes betweenthese two kinds of recycled concrete under the freeze-thaw environment, and studythe mechanism of fracture of recycled concrete in freeze-thaw condition. |
