Study On Shrinkage Compensating Of Crushed Stone Mortar

The crushed stone is a good kind of materials which can be used to take place of sand. Compared with the ordinary mortar, the mortar that used the crushed stone as the aggregate has better workability and mechanical performance. However, the long-term shrinkage of crushed stone mortar is bigger than the ordinary mortar. This defect can be the important factor which restricts the generalization of the techniques that sand replace by crushed stone. In this article, shrinkage compensating experimental investigation on the crushed stone mortar has been performed by compound expansion agent technique. Major work done is as follows:Firstly, by the analysis about shrinkage mechanism of cement stone and the expansion mechanism of expansion agent, defined the feasibility of research scheme.Secondly, influence of UEA gentle MgO and air-entraining admixture on the shrinkage performance of crushed stone mortar has been studied. Orthogonality Experiment selected compound expansion agent; furthermore, Influence effect of each component's content and curing conditions on the shrinkage compensating has been studied. Results show that the final expanding quantity of shrinkage compensating crushed stone mortar in the water increased with the increase of UEA or gentle MgO; The addition of air-entraining admixture has a significant influence on the shrinkage performance and sensible add amount is around 0.01%; The compound expansion agent selected can compensate the long-term shrinkage preferably, moreover, it has finer economic performance because of low adding amount. It is significant for shrinkage-compensating effect to improve early-age curing condition.Thirdly, by contrast, experimental research has been carried on many performances of shrinkage-compensating crushed stone mortar. Results indicated that the compound expansion agent almost hasn't effect both on setting and frost resistance of crushed stone mortar, but can enhance its permeability resistance ability.At last, microcosmic mechanism has been studied on shrinkage-compensating crushed stone mortar by BET, XRD and SEM methods. Conjuncted with the experiment results, the expansion discipline of Ettringite and Brucite was studied by using the theory of fractal geometry and viscoelastic mechanism model. Results show that mixed with compound expansion agent, the pore ratio of crushed stone mortar decreased and the structure of matrix become denser, however, the strength and elastic modulus at early age decreased because of the inconsistence between the creating speed of Ettringite and the strength development. Not all the crystallization energy comes from the Ettringite and Brucite does to the expansion work, one part of which was consumed in the deformation process, the second part was stored in the paste, the other part was used to densitify the structure of harden cement paste.