Study On Freeze-Thaw Failure Performance And Characteristics Of Superabsorbent Polymer Cement Mortar

When concrete is exposed to severe cold environment for a long time,it will be subjected to freezing and thawing,which will cause micro-cracks in its interior and gradually develop until the structure is macroscopically damaged.At present,the main method to improve the freeze-thaw resistance of concrete is to introduce pores: Super Absorbent Ployers(SAP)can play an internal curing effect in cement-based materials,and can also release water after hardening to create a pore system to improve Its frost resistance;Air Entraining Agent(AEA)can also introduce pores in concrete.This paper studies the frost resistance,mechanical properties and microstructure of SAP cement mortar and AEA cement mortar with different particle sizes and different mixing methods,as well as the pore structure evolution and crack initiation during the freeze-thaw cycle.The main research contents and results are as follows:(1)Using slow freezing and thawing test and hardened cement paste porosity analysis test,the porosity structure analysis and freezing resistance test of SAP cement mortar and AEA cement mortar with different particle sizes and mixing methods were carried out.Studies have shown that the dry mixing of SAP will make the cement mortar obtain better frost resistance;the larger the particle size,the better the frost resistance of cement mortar;the dry mixing of SAP produces a pore system that is more ideal than preabsorbent SAP and is more ideal than AEA.Compared with SAP,the hole-making is mainly concentrated in hundred-micron-sized large holes.(2)The pore structure,hydration degree and mechanical properties of cement mortar,hydration degree and mechanical properties of SAP and AEA for cement mortar were compared and studied by means of compressive and flexural strength test,mercury intrusion,thermogravimetry,heat of hydration,and scanning electron microscope.The mechanical properties of cement mortar are significantly better than that of AEA cement mortar,and the compressive strength is even better than that of the blank control group;the incorporation of SAP will make the cement mortar obtain a denser pore structure;the impact of SAP water release on the surrounding cement matrix is divided into " Three stages: rapid water release,"water release weakening",and "slow continuous water release";different SAP mixing methods will affect the water absorption and release process and affect the pore structure and hydration degree;pre-absorbed water mixed with SAP,Dry mixing SAP and AEA have different pore formation forms.(3)Using mercury intrusion test and X-ray CT test to study the changes in the microscopic pore structure of SAP cement mortar and AEA cement mortar during freezethaw failure and the initiation process of cracks.The research shows that: the pores obtained from the mercury intrusion test Fractal dimension can be used as a parameter to describe the pore structure changes of SAP and AEA cement mortar during freeze-thaw process;SAP cement mortar and AEA cement mortar freeze-thaw failure process is different,the crack initiation of the former occurs in the interfacial transition zone around the SAP hole,while the latter occurs in the interface transition zone of the area with less pore distribution.