Cement - Lime Powder - Mineral Powder Composite Cementitious Shrinkage Characteristic

To make use of the ground limestone and slag powder scientifically and reasonably,and reach the aim of improving the performance of the cement-based materials,a series of experiments on the composite cementitious system,which consists of cement,ground limestone and slag powder,were conducted in this paper.The main resulsts are as follows:1.The physical and mechanical properties of the cement-ground limestone-slag powder composite cementitious systemThe ground limestone and slag powder can improve the workability of the cement-based materials,and double addition make the workability better. The ground limestone shortened the setting time, and the slag powder prolonged the setting time. Moreover, the shortening effect of the ground limestone stronger than the increasing effect of the slag powder. At early age, the proper amount of ground limestone can decrease the water absorption, but increase the chemically bound water content and strength; the law of the late stage was opposite to the early stage. For the early stage,the slag powder can increase the water absorption, but decreased the chemically bound water content and strength.At the late stage, the slag powder decreased the chemically bound water content and the water aborption, but made the strength increased. The double addition of the ground limestone and slag powder can make both of the physical and mechanical properties produce additive effect, and made the samples of every age had better physical and mechanical properties. The sample containing 10% ground limestone and 10% slag powder had a greater show.2. The study of the autogenous shrinkage property of the cement-ground limestone-slag powder composite cementitious systemThe single addition of the ground limestone or slag powder can inhibit the autogenous shrinkage of the paste for 0-1d, and the double addition can make the inhibitory effect more obvious. For 1-180d, the autogenous shrinkage of the hardened pastes increased first and decreased later with the ground limestone content, and which reached the maximum when the ground limestone content is 10%.The autogenous shrinkage of the hardened pastes decreased with the slag powder content increasing for 1-4d; and the autogenous shrinkage increased with the increase of the slag powder content for 4-180d.For the research scope of this paper, the double addition of ground limestone and slag powder was disadvantageous to the autogenous shrinkage for 1-180d. The self-dessication effect was denoted by the self-dessication volume calculated from the chemically bound water content, and we can know that the self-dessication effect can reflect the autogenous shrinkage to some extent. The self-dessication need to be made an intensive study due to its complexity.3. The study of drying shrinkge of the cement-ground limestone-slag powder composite cementitious systemThe drying shrinkage of the mortars increased first and decreased later with the increase of the ground limestone,and which reached the maximum when the ground limestone content is 10%.Meanwhile, the autogenous shrinkage of the sample containing 15% started to be lower than the pure ones.The autogenous shrinkage of the samples decreased with the increase of the slag powder content, and the autogenous shrinkage of all of the sample containing slag powder were lower than the pure ones. When double addition, the autogensous shrinkage can be inhibited only when the slag powder content exceed a certain value. And it was known from the experiment that the sample containing 10% ground limestone,10% or 20% slag powder can get smaller autogenous shrinkage.4. The study of pore structure of the cement-ground limestone-slag powder composite cementitious systemThe addition of the ground limestone and slag powder had little influence on the original porosity of the composite cementitious system.The proper amount of ground limestone can decrease the early porosity, but increased the micropore porosity and the micropore proportion.At the late stage, the addition of the ground limestone increased the porosity and macropre proportion, and the more the ground limestone content is, the more obvious the effect is.The slag powder increased the early porosity of the sample, but decreased the macropore porosity and macropore proportion.At the late age, the addition of slag powder decreased the porosity, but increased the the porosity and the proportion of the micropore.The double addition of ground limestone and slag powder can decreased the porosity and make the pore structure thinner. With the increase of the total amount of the ground limestone and slag powder, all kinds of porosity are decreased, and the macropore proportion get reduction,the micropore proportion was rised.When the total addition amount remains unchanged, the porosity can be reduced and the micropore proportion can be rised efficiently when the mass ratio of the ground limestone/slag powder is more than 1.0.6 The applicaton of the cement-ground limestone-slag powder composite cementitious system in concreteSome aspects should be considered when the mix proportion design of the concrete is made:(1)Polycarboxylate water reducer had less effect on the shrinkage of the samples.(2)The greater the water-binder ratio is, the smaller the shrinkage of the sample is.(3)The more the aggregate content is, the smaller the shrinkage is.Through the verification test of the concrete, some conclusion can be drawn:the concrete containing 10% ground limestone and 10% slag powder had better work performance, mechanical performance and shrinkage resistance capability, which had the slump of higher than 200mm, the 28d cubic compressive strength of 65.5MPa, the shrinkage of 292×10-6. It shows a good correlation between the shrinkage and the age by logarithmic curve fitting. By comparison of the calculated value and the test value, we can know the test value showed a certain reliability.