Effect Of Curing Regime On The Drying Shrinkage For Cement Paste

With transport project developing more cement was needed. So how to product cement with littler energy and how to use cement more effective has been put on agenda. This introduces high dosage of mineral admixture, which reduces the endurance of concrete. The drying shrinkage of cement is one of Crisis points for concrete endurance ability. High rate of drying shrinkage will create a lot of micro crack which will reduce the ability of endurance. So this paper try to find a way to reduce the drying shrinkage of cement and exploit the mechanism of drying shrinkage in order to direct a way for practical work.According from capillary theory, for a capillary pore with certain radius, if the vapor pressure of its is greater than that of environment, then the capillary water will loss, and the smaller the capillary radius, the smaller the relative vapor pressure, the harder for water loss. Clearly, drying shrinkage is highly relatively with mess lose and pore structure for sample with RH around55%.In this paper slag cement paste was cured with three different methods, standard curing and water curing in temperature of20℃or60℃for different ages then put the sample into standard curing box. The slag/fly-ash blend cement beams were demoulded after24hours, then immerged them for2d,3d,6d and13d, respectively Drying shrinkage, mass loss, pore size distribution, and the mess of combined water for different samples with different ages was tested. The relationship between drying shrinkage and mess loss pore size distribution, hydration process also has been invested, and explored the complex mechanism of drying shrinkage of cement paste.The main thesis achieved by this paper has listed as follow.1, Slag composite cement cured by different methods indicates that the sample cured in standard curing box pronounces smaller drying shrinkage than cured in water. Water curing cement beams under60℃show less drying shrinkage than those under20℃.2, Fly ash/slag composite cement paste, immerged in the water before drying for2ds,3ds,6ds and13ds, donate that the longer curing time the smaller drying shrinkage; The drying shrinkage for early age is more obvious, with the extension of age. growth of drying shrinkage become more smoothly and drying shrinkage rate became stable; For specimen with longer curing time, the time for its drying shrinkage curve get stabilization also become longer. 3, The drying shrinkage curve of different specimen show the same trend, that the greater the mass loss rate, the more water evaporates, the greater the drying shrinkage.4, Mass loss is due to evaporation of capillary water. Measuring the pore size distribution of samples with different curing method and different ages obtain when the content of the pore during3-4nm is higher, the greater the corresponding drying shrinkage.5, The drying shrinkage of cement is highly relate with hydration degree. Measuring the chemical compound water content of sample found that drying shrinkage is highly correlate with hydration process,and when the hydration ratio is high, even if the content of3-4nm pole increase, the drying shrinkage do not increase o This can be explained by this that at high hydration ratio, more hydration products produced which will increase the stability of cement paste system.Drying shrinkage of compound cement paste has the same trend with mass loss indicating that evaporation has introduced the internal paste shrinkage. And pore size distribution measurement combined with calculated through Laplace equation donate that when the content of pore during the range of3-40nm is high,the drying shrinkage also greater. The total amount of hydration products, affecting the internal elastic modulus of cement paste enhancing the resistance for shrinkage. So does the mass loss of composite paste, pore size distribution and hydration processes.Drying shrinkage of cement paste composite has aroused growing concern, This paper has analyzed the inert change of compound cement paste by exploring the relational ship of "drying shrinkage-mass loss-pore size distribution-the hydration process (elastic modulus)," as well as the reason of drying shrinkage in blend cement, hoping offer an approach for research drying shrinkage of blend cement paste.