Study On Reutilization Of Waste Concrete By Mechanochemistry Activation

Great quantities of consumption and unreasonable utilization of natural resources have resulted in its shortage more and more; so, the mankind is being confronted with the serious resources crisis. It has become the one of direction for industry production to utilize fully various industrial wastes and to save the natural resources as much as possible. As a sort of waste produced by demolishing old buildings, waste concrete will result in serious environment pollution if it is not reutilized. At the same time, this also is vast resource extravagance. Ones have carried out a great of studies on the reutilization of waste concrete, and have obtained many achievements. So far, however, these investigations are focused to the recycling aggregate concrete, which is feasible in technique and economy, i.e. to utilize the coarse aggregate separated from waste concrete as recycling aggregate to produce recycling aggregate concrete. But, it exits a series of questions to utilize the binding matrix component (hardened cement paste—HCP) in waste concrete for recycling aggregate concrete production, and no report on utilizing HCP in cement manufacture has been seen. It is a scientific and reasonable method for saving the natural resources that to utilize the fine waste concrete (FWC)formed from separation, which is composed mainly of HCP, as admixture to produce cement and as raw material to burning clinker. The experimental studies on the methods separating coarse aggregate from HCP, using FWC as admixture and raw material in cement production were carried out in this paper, and the mechanisms of FWC in the clinker burning, cement grinding and cement hydration were analyzed in order to supply the theoretical and practical basis for the reutilization of FWC in cement manufacture.The experimental study is divided to three sections, i.e. to separate coarse aggregate form binding matrix by different methods, to utilize FWC as admixture to prepare cement and raw material to burning clinker.The key to reutilize reasonably waste concrete is to effectively separae the coarse aggregate and FWC. The separation experiments were carried out by combining surface active agents treatment and heat treatment of waste concrete with mechanical pulverization. The experimental results indicate that the separating efficiency of waste concrete increases significantly by adding suitable surface active agents. It is found that the effects of anion typed surface active agents Calcium Lignie Sulphonate (CLS) and Sodium Lauryl sulfate (SLS), and strong polar surface active agent Triethanolamine (TEA) are muchbetter than that of non-polar surface active agent. The reason is that they adsorb orientably on the interface of aggregate and binding matrix so that deduce efficiently the interface energy and the interfacial binding strength. The heat treatment temperature has a significant influence on the separating efficiency. When the temperature lower, the separating efficiency only increases slightly; After treated at 500℃, the separating efficiency increases remarkably, which is because the interfacial strength decreases evidently resulted from heat expansion and dehydration of the hydrates in HCP.The separating efficiency of vibrating mill is different evidently from that of ball mill. It is found from comprehensive evaluation of recovery of FWC that the separating efficiency of vibrating mill is higher than that of ball mill. For the case of adding surface active agents, FWC recovery of the latter is higher than that of the former, but the contents of larger particles and SiO2 in the latter are higher than that in the former. For the case of heat treatment, FWC recovery of the latter is higher than that of the former when treated at lower temperature; Whereas the result is opposite when treated at 500℃. In addition, the content of larger particles for ball milling is higher evidently than that for vibrating milling. The results indicate that, more aggregate particles enter into FWC for the case of ball milling because the volume pulverization makes more...