| Due to the limitations of the traditional curing methods in the process of low watercement ratio cementitious materials curing,resulting in more serious autogenousshrinkage phenomenon,affecting the durability of cementitious materials products.For such problems,the incorporation of SAP as an internal curing material into the cementitious material is an effective method to suppress autogenous-shrinkage.In this paper,0.25 was used as the reference water-cement ratio,and a total of three additional water-cement ratios of 0.035,0.045,and 0.055 were calculated and adjusted according to the POWERS hydration model,and the effects of the two ways of SAP incorporation with dry powder and pre-absorbed water on the internal curing of net cement paste were analyzed.Based on the phenomenon that SAP is easily affected by the ionic concentration of fresh cement paste due to the preabsorption of tap water,resulting in the loss of internal curing water,five solutions with different relative saturation concentrations were set up using the ratio of tap water to saturated lime water per unit volume to reduce the ionic concentration difference between SAP and cement paste when SAP preabsorbs the solution with high relative saturation concentration.The main results of the paper are as follows:(1)The addition of additional water can significantly improve the poor performance of the blank group,but the test group with two additional water-cement ratios of 0.045 and 0.055 calculated according to the POWERS hydration model has a negative impact on the mechanical properties,but the test group with SAP blended with dry powder and additional water-cement ratio of 0.035 can improve the total water-cement ratio and at the same time can obtain higher The compressive strength of the test group was higher while increasing the total water-cement ratio.In addition,all three additional water-cement ratios were able to reduce the autogenous-shrinkage,but the most obvious one was the test group with additional water-cement ratio of 0.055.(2)All the test groups under the three additional water-cement ratios showed a decrease in flow,shortening of setting time,increase in compressive strength,and decrease in autogenous-shrinkage with the increase of the additional saturation concentration of SAP preabsorption,indicating that SAP achieved a slow-release effect.Using NMR to test the 48 h continuous hydration time of SAP preabsorption with 100%additional saturated water at an additional water-cement ratio of 0.055,it can be seen that the net cement slurry can have a long relaxation time water signal around 8h of age,which proves that SAP can slow release at an early stage and replenish water within a few hours,and summarizes the water release process of SAP preabsorption with high additional saturated water concentration as "fast release first".The process of SAP water release with high relative saturation concentration is summarized as "fast release first,then slow release".(3)With the same total water-cement ratio,additional water-cement ratio and additional water consumption(additional water consumption relative to saturation concentration of 0%),SAP in dry form has smaller flow,faster setting time,better mechanical properties and lower autogenous-shrinkage than SAP in pre-absorption form.By testing the 48 h continuous hydration time and the exothermic rate of hydration of the test group with the additional water-cement ratio of 0.055,it can be seen that SAP in the form of dry powder will rapidly absorb water in the fresh slurry and form water-filled pores,reducing the actual water-cement ratio of the slurry,and the water will gradually diffuse into the cement slurry after the induction period,delaying the appearance of the exothermic peak of hydration;the NMR test results also show that between The NMR test results also showed that the secondary peaks of the test group with SAP mixed with dry powder between 1h and 2h had a migration signal toward the long relaxation direction;while SAP mixed with pre-absorbed water would release a large amount of water at the early stage,and according to the NMR data,there was no relaxation signal of the internal conservation water used for water replenishment. |
