Study On The Relationship Between The Ingredients And Dry Shrinkage Performance Of The Low Alkalinity Sulphoaluminate Cement

The low alkalinity sulphoaluminate cement is one kind of ordinary sulphoaluminate cement series, and mainly used for GRC manufactures. In the GRC, 90% gel material is the low alkalinity sulphoaluminate cement. Therefore, the expansion and dry shrinkage properties of this kind of cement have great effect on the quality of GRC manufactures. To a certain degree, many people have made research on the expansion of the low alkalinity sulphoaluminate cement, but there is little information about the research on the dry shrinkage of this kind of cement. There is no specification for determining dry shrinkage. Thus, the thesis puts forward the dry shrinkage test method of the low alkalinity sulphoaluminate cement and studies the relationship between the ingredients and the dry shrinkage performance of the low alkalinity sulphoaluminate cement.Firstly, the thesis puts forward two test methods that measured dry shrinkage according to JC/T453-2004 < Physical Checking Method of Self-stressing Cement > and JC/T603-2004 < Dry Shrinkage Test Method of Cement Mortar>, and selects the cement of certain factory to perform an experiment by different dry shrinkage test methods. We think the good method should have larger dry shrinkage value and better replication. From the experiment, it can be ascertained that the sample size is 25mm × 25mm × 280mm (available length is 250mm), the operate course is the same as JC/T603-2004 and the humidity should be 30%. After 52-56 days, the sample reaches the balance. The thesis selects the clinkers of three factories and produces twenty-seven different cements with different addition of gypsum and limestone. The fundamental physical performance experiments determine the qualified cements. Then the dry shrinkage experiment is carried out. The results indicate that, as far as the same clinker is concerned, the dry shrinkage of the low alkalinity sulphoaluminate cement mortar sample increases with the rising addition of gypsum within certain limits when the addition of limestone is sure. Such is not the case that the dry shrinkage increases with the rising addition of gypsum. And when the addition of gypsum is sure, the relationship between the dry shrinkage and the addition oflimestone is that only within certain limits of the limestone the dry shrinkage reaches the maximum. As far as different clinkers are concerned, the higher the quantity of C4A3S in the clinker is, the larger the dry shrinkage that hydrating C4A3 S causes under the condition of the same addition of gypsum and limestone. At last, microcosmic analyses of hydration production of partial cements with different curing days have been carried out and the mechanism of dry shrinkage of the low alkalinity sulphoaluminate cement paste has been studied. From XRD and DTA, it can be ascertained that the dry shrinkage of the low alkalinity sulphoaluminate cement paste is mainly caused by calcium aluminate sulphate hydrate under the condition of 30% humidity. From MIP, it can be ascertained that pores less than 50nm have influence on dry shrinkage performance of the low alkalinity sulphoaluminate cement.To sum up, the thesis puts forward the simple and reliable test method that measures dry shrinkage and the relation between ingredients and dry shrinkage performance of the low alkalinity sulphoaluminate cement. And it provides reference for the enterprises to produce the low alkalinity sulphoaluminate cement of better constancy of volume. And it brings forward further relative task needing investigating on dry shrinkage property of cement.