Experiment Study On Preperties Of Air-entrained Natural Pumice Lightweight Aggregate Concrete

In cold areas, researching frost resistance of concrete material is an important aspect which solves the problem of the durability of concrete. As a main measure to improve the frost resistance of concrete,air-entrained concrete has been applied to many kinds of engineering and has got very clear financial and social effects. In this paper, two types strengthen level (LC25,LC30)of pumice lightweight aggregate concrete were designed which adopts natural pumice as coarse aggregate, mainly study the effect of air entraining agent on workability, physical and mechanical performance, frost resistance durability, microstructure of concrete. Discuss predicting model for frost resistance of pumice lightweight aggregate concrete.Firstly, this paper expounds the research on the workability,physical and mechanical performance. The results show that slump of lightweight aggregate concrete increases with the increase of air content, Oven dry density and compressive strength of lightweight aggregate concrete decreases with the increase of air content. The rate of compressive strength of lightweight aggregate concrete decreases is faster than ordinary concrete. To split tensile strength and flexural strength, with the increase of air content, strength increase firstly and then decrease. It is also discovered in experiments that failure form of lightweight aggregate concrete are different from common concrete. Those cracks run through the coarse aggregate instead of being blocked, causing the breaking abruptly and it shows a stronger brittleness characteristic. But the addition of air entraining agent changes the failure form of pumice lightweight aggregate concrete and could reduce its brittleness and improve its toughness effectively, the toughness of air-entrain lightweight aggregate concrete get better than ordinary lightweight aggregate concrete.Secondly, through the freeze-thaw test to lightweight aggregate concrete of different strengthen level and different air content,the project tested the dynamic elasticity modulus and mass loss at the corresponding freeze-thaw cycle times, judging it's frost resistance and observing failure form. To concrete of LC25, the results show that the non-air-entrained pumice lightweight aggregate concrete has high air content, but the frost resistance is small. Therefore it is inevitable to entrain air to improve its frost resistance. In addition, the experiment of air-entrained ones indicated that increasing rate of mass loss and decreasing rate of dynamic elasticity modulus become more slowly with the increase of air content, and the frost resistance of pumice lightweight aggregate concrete gradually becomes strong. To concrete of LC30, the results show that frost resistance durability of pumice lightweight aggregate concrete decrease firstly and then increase with the increase of air content, frost resistance durability not only was related to air content, but also was related to strength. Therefore it is inevitable to add enough air entraining agent to improve its frost resistance durability for pumice lightweight aggregate concrete of LC30 in this experiment. In this way, frost resistance durability can be increased when strength decrease. In addition, on the basis of the frost resistance durability experimental results, combining with finished predicting model, a predicting model for frost resistance of pumice lightweight aggregate concrete was established.Finally, based on cubic compressive strength experiment of pumice lightweight aggregate concrete, hydration products of pumice lightweight aggregate concrete, interfacial transition zone and the distribution of certain element of interfacial transition zone were investigated by SEM and EDXA. The results show that under the action of internal curing of water inside pumice lightweight aggregate, hydration reaction of cement become higher, the part of hydration products filled in the micro defects and cracks of lightweight aggregate, therefore mechanical properties of lightweight aggregate concrete are eventually improved. The failure of pumice lightweight aggregate concrete happen to more in cement paste and interior of lightweight aggregate, than in its interfacial transition zone, strength of interfacial transition zone of pumice-cement paste become stronger.