Optimization Design On Cementitious Materials For Low Shrinkage Concrete Of Medium Strength

Cracking of concrete is easily caused by concrete shrinkage which would reduce its structural life. Therefore cementitious materials optimization design of the low shrinkage concrete has an important guiding significance which could improve the security of concrete structures. Based on the gray system theory, GM (1, N) model of mortar 28d strength under standard curing conditions and GM (1, N) model of mortar stripping strength under steam curing conditions are established which could quickly predict 28d strength of cementitious material. On this basis, mortar corresponding to similar 28d strength of concrete is prepared and is used to conduct a shrinkage test. GM (1, N) model of mortar shrinkage is established according to the gray system theory. Througth GM (1, N) model of mortar shrinkage,28d shrinkage values of different cementitious material could be predicted and low shrinkage cementitious material could be selected. Finally the low shrinkage concrete could be designed by the selected low shrinkage cementitious material and the corresponding water-binder ratio.Results show that three main influence factors (i.e. water-binder ratio, the volume ratios of C-S-H to unhydrated particles and bulk density) on mortar 28d strength under standard curing conditions and mortar stripping strength under steam curing conditions were obtained by the grey relational analysis. GM (1,4) model of mortar 28d strength was built based on this and had a high accuracy of simulation which the average relative error value of the model was 3.09% and all relative error of strength simulation values were less than 8%. GM (1,4) model of mortar stripping strength was built based on this and had a high accuracy of simulation which the average relative error value of the model was 3.61% and all relative error of strength simulation values were less than 8%.In the mortar shrinkage test three main influence factors (i.e. the volume ratios of C-S-H to unhydrated particles, deformation resistance factor and water-binder ratio) on mortar shrinkage were obtained by the grey relational analysis. Based on this, GM (1,4) model of mortar shrinkage was built and had a high accuracy of simulation and good reliability which the average relative error value of the model was about 8.39% and all relative error of strength simulation values were less than 15%. Cementitious material shrinkage at 28d can be forecasted by testing simple experiments which mortar corresponding to similar 28d strength of concrete is prepared. Low shrinkage cementitious materials can be achieved by this model. It is a simple and applicable method, avoiding tedious shrinkage tests.