Research On Effect Of Superabsorbent Polymer On Performance Of Cement Mortar

The application of superabsorbent polymer in concrete is to reduce the risk of cracking due to autogenous shrinkage.This study tested the water absorption and release characteristics of different types of SAP in different solutions,focusing on the effects of superabsorbent polymer adding ways,dosage,and types on working performance,mechanical properties and volume stability of mortar.Mercury intrusion porosimetry and scanning electron microscopy were conducted to investigate the relationship between the microstructure and the macroscopic properties of the mortar after the addition of SAP.The results of water absorption test and mortar consistency test show that SAP with large particle size has a slower water absorption rate.Pre-absorbent treatment will reduce water absorption capacity of SAP in cement matrix.Compared with mortar mixed with dry powder SAP,the penetration of fresh mortar mixed with pre-absorbed SAP is larger,but the penetration loss with time is also greater.The mechanical performance test shows that SAP types,dosage,and adding ways all affect the amount of free water in the mortar and the number of defects,and then affect the mechanical properties of the mortar.Increasing the amount of internal water conservation will have a greater impact on the mechanical properties of the mortar.The adverse effect of SAP on the mechanical properties of mortar is mainly reflected in the early stage of hydration,and has little effect on the later strength.The results show that the strength of the later stage of the mortar is mainly affected by the ratio of total water/binder,and the mechanical property of the mortar decreases with the increase of the ratio of total water/binder.In addition,SAP's adverse impact on early flexural strength was greater than its impact on early compressive strength.Contraction test shows that the SAP dosage and the addition method will determine the amount of internal curing water under the condition with extra water and affect its inhibitory effect on autogenous shrinkage of the mortar.Increasing the amount of internal curing water will inhibit autogenous shrinkage.However,increasing the amount of internal curing water will increase the ratio of total water/binder and decrease the strength of mortar.Although the early drying shrinkage slightly decreases,the later period will tend to become larger.Under the condition with no extra water,the SAP can still reduce the autogenous shrinkage,indicating that the inhibitory effect of the internal curing water on autogenous shrinkage is greater than the effect of simply increasing the ratio of water/binder.However,the effect of SAP on the drying shrinkage is rather limited,indicating that it's the ratio of total water/binder affects the dry shrinkage of mortar.The microscopic analysis shows that SAP can significantly reduce the porosity,specific pore volume,critical pore diameter,and the most probable pore diameter of the mortar without extra water.However,these parameters are less variable with the same consistency of mortar.However,whether or not there is extra water,SAP can refine the pore structure of the mortar,reduce large pores between 50 and 1000 nm,increase the number of small pores smaller than 50 nm.What's more,dry powder SAP has more significant refinement of pore structure.The capillary pore refinement is mainly due to the internal curing effect of SAP with extra water.The capillary pore refinement is mainly due to the fact that SAP absorbs water and reduces the ratio of effective water/binder of matrix without extra water.