Study On The Preparation Of Modified Super Absorbent Polymer And Its Effect On Mortar Performance

Shrinkage cracking in concrete with low water-binder ratio seriously affects the strength and durability of concrete.The use of internal curing methods can significantly reduce the early shrinkage of concrete,suppress the generation of cracks in concrete,and improve the performance of concrete.The current research on internal curing agents in cement-based materials mainly includes the application of inorganic materials internal curing agents(light aggregates;porous ultra-fine powders)and organic materials internal curing agents(superabsorbent polymer,SAP).The effects of the two internal curing agents on the early shrinkage,strength and durability of cement-based materials have advantages and disadvantages.This article designed and synthesized an inorganic/organic composite modified internal curing agent,carried out research on the composition,structure and performance of the modified internal curing agent,and further explored its influence on the self-shrinkage,drying shrinkage,mechanical properties and microscopic properties of the mortar.The main contents are as follows:Inverse suspension polymerization method was used to graft inorganic kaolin into poly(acrylic-co-acrylamide)organic network.The chemical composition,microstructure structure and liquid absorption performance of the modified SAP were studied by FTIR,SEM,laser particle size,tea bag method,etc.In addition,in order to ensure the application of the modified SAP in cement-based materials engineering,the temperature stability and sensitivity to the relative humidity gradient of the modified superabsorbent resin were tested.The modified SAP is round microbeads with uniform particles,and evenly expands into a spherical shape after absorbing water or alkali liquid.In deionized water,the modified SAP with acrylamide has a fast water absorption rate but a low saturated water absorption rate.As the kaolin content increases within a certain range,the modified SAP increases the water absorption rate,but when the kaolin content is too high,the crosslinking degree is further increased,the saturated water absorption rate of modified SAP is reduced.In saturated calcium hydroxide solution and cement slurry supernatant,the composite modified SAP significantly improves the liquid absorption ratio when it is in equilibrium in the alkaline solution.Modified SAP significantly improved the self-shrinkage and drying shrinkage of mortar.As the content of kaolin increases,the rigidity of the modified SAP network increases,and the internal pores increase.As the content of acrylamide increases,the alkali resistance and Ca2+resistance of the modified SAP increase.Both improve the internal maintenance performance of the modified SAP and significantly relieve the mortar.Self-shrinking and drying shrinkage.Due to the pores produced in the cement-based material after SAP water release and drying,the flexural strength and compressive strength of the mortar are reduced to varying degrees after adding the modified SAP.As the content of kaolin increases,the rigidity of the modified SAP network increases,the internal pores increase,and hydration of the mortar is promoted.As the content of acrylamide increases,the alkali resistance and Ca2+resistance of the modified SAP increase,and the liquid absorption rate increases,resulting in internal maintenance optimized,and the loss of flexural strength and compressive strength of the mortar is reduced.SEM,TGA,and MIP were used to study the effects of modified SAP on morphology,degree of hydration,and pore structure in mortar.After the modified SAP releases water in the mortar and dries,it still has a close contact with the cement-based slurry,indicating that the modified SAP has a strong force between the cement and the stone.It basically maintains the original shape during the water release process and is easy to pass through the capillary pores.The effect releases water and the hydration degree of the mortar is higher,but the modified SAP increases the porosity of the mortar and changes the pore size distribution,resulting in a reduction in the strength of the mortar.