Study On The Performance Of Drying Shrinkage In Composite Cement Pastes

With the rapid development of social economy, buliding industry require for the quality of the cement concrete project more and more higher. At the same, the shortage of mineral resources and the extrusive of the environmental pollution problem in the process of the production and the use of concrete day by day, producing the high-performance cement is the development of cement industy for our country. For this reason, it is taken as one of the important project of state973plan to study on the "efficient preparation and lower energy consumption application of cement", so that, the concrete industry can take to the road of healthy development.All kinds of active residue as a supplementary cementitious material and cement concrete in our country industrial production, not only improve the performance of the concrete and reducing the production costs and the continuous consumption of energy and resources, but also relieve a lot of pollution to the natural environment from industrial residue. But, as more and more mineral admixtures, the more widely used in concrete projects, the high volume of supplementary cementitious material in concrete volume stability, especially the early cracking problem are becoming increasingly widespread concern by the industry. The drying shrinkage of the concrete is one of the main reason and the cracks from the drying shrinking lead to the durability of cement concrete down, and sometimes even lead to the structural damage. Therefore, intensive study the characteristics and mechanism of drying shrinkage in cement-based materials has a great significance to solve the drying shrinkage cracking in concrete.This article in two ways, first, mixed with limestone in the fly ash by high temperature calcinations to active and modifie, corrode the fly ash vitreous surface and generate silicate minerals that have activity, increase the activity of fly ash from improve the contact interface of the fly ash particles and the environment, study the impact on its performance from the modified fly ash by measuring the drying shrinkage、strength and degree of hydration. Second, took cement pastes as the research object, using the complex dope by fly ash and slag, fixed its added quantity and change the water to binder ratio, the use of nitrogen adsorption method to determine porosity、specific surface area and pore size distribution data in the pore structure, then discussed that the drying shrinkage characteristic was influenced from the pore structure in composite cement paste by data analysis. The results are as follows:The surface of modified fly ash generated some calcium aluminum silicate like the gehlenite and then improved the activity of fly ash, modified fly ash can effectively inhibit the drying shrinkage of cement paste and the drying shrinkage increase with the increase of limestone content, decrease with the prolong of the holding time, the factors that influence the drying shrinkage of cement paste in addition to the evaporation of water, also because of the activity and the surface morphology of auxiliary hybrid material; the compressive strength of the modified fly ash composite cement paste in7day and28day was increased with the increase of limestone content and the holding time; with the increase of the modified fly ash, the content of chemical bonding water in the cement pastes and the degree of hydration of cement are gradually increased, the hydration products became more and more, the binding capacity of the internal interface of the cement paste are enhanced and the compressive strength are raised and inhibited the drying shrinkage of cement paste.With the increased water to binder ratio, the drying shrinkage of the cement paste that adding the fly ash and slag are increases; with the increase of the age, the shrinkage trend becomes smooth. The total porosity and specific surface area decreases with the increasing age, the trend of its variable quantity are similar to the trend of the change of drying shrinkage, indicated that the change of total porosity and specific surface area have correlation with the change of drying shrinkage. When the water to binder ratio are same, the porosity of capillary pore that pore size distribution range from lnm to25nm decreases by the increasing age, when the age are same, with the increase of the water to binder ratio, the porosity is also increased, especially the porosity of capillary pore that pore radius at about2nm increased more obvious and affects the drying shrinkage most. The porosity of pore radius from1nm to25nm have an effect on the strength, with the growth of the age, the porosity of pore radius from lnm to25nm decreased and the strength increased.