Study On The Properties Of Polymer Cement-based Materials And Their Hydration Characteristics

The disadvantages of cementitious materials such as brittleness,poor toughness,low tensile strength and bond strength limit the use of cementitious materials.Polymer modified cementitious materials have better toughness.In this paper,a series of studies were conducted on the effects of waterborne acrylic emulsions and waterborne polyurethane emulsions on the properties and hydration characteristics of cementitious materials.The performance characteristics of different types of waterborne polymer emulsions on cementitious materials were clarified by studying the performance of different types and admixtures of waterborne emulsions on the workability,mechanical properties and volumetric stability of cementitious materials.The hydration process,hydration products and microstructure of cementitious materials by different waterborne polymer emulsions were investigated by microscopic tests,such as electron scanning microscopy,pore structure test methods and infrared spectroscopy,to clarify the hydration characteristics of waterborne acrylic and waterborne polyurethane modified cementitious materials.The main conclusions obtained are as follows:（1）Waterborne acrylic emulsion has certain water reducing effect and slow setting effect,which can improve the flexural strength of cementitious materials.The 28d flexural strength of waterborne acrylic acid modified cementitious sand can reach up to 13.46 MPa and 44.18MPa.waterborne polyurethane emulsion will reduce the flowability of fresh cementitious sand and has a strong retarding effect on cementitious materials.（2）The bond strength of modified mortar increases,then decreases and then increases again with 10%-60%of waterborne acrylic emulsion,and the bond strength can reach up to1.84 MPa.The bond strength of mortar decreases with the increase of waterborne polyurethane.（3）Waterborne polyurethane has an enhancing effect on the anti-cracking performance of cementitious materials,and waterborne acrylic acid has a better effect on the anti-cracking performance of cementitious materials.The net cement paste without waterborne polymer modification showed penetration cracks on the third day of the test,and the net cement paste with 30%waterborne acrylic emulsion did not crack at 124th d under the restrained condition.（4）The shrinkage value of cementitious sand at 76d was 6.250×10^-4for 60%of waterborne acrylic acid,and 6.500×10^-4for 76d for 8%of waterborne polyurethane,and the shrinkage value of modified cementitious sand at the same age was greatest for the same amount of waterborne polymer,but the shrinkage value of modified cementitious sand at the same age was greater when the amount of waterborne polyurethane was 12%and the amount of waterborne acrylic acid was When the amount of water-based polyurethane is 12%and the amount of water-based acrylic acid is 10%,the shrinkage value of 76d is 8.214×10^-4.（5）When water-based acrylic acid reacts with cementitious materials,it will delay the reaction with C₃A to a certain extent,and the complexation of water-based acrylic acid is strengthened after the introduction of silica fume,and the needle-like calcium alumina increases in the cementitious materials mixed with water-based acrylic acid,and a large number of calcium alumina crystals fill in the microcracks and micropores of cementitious materials,which improves the microstructure of cementitious materials and increases the micropores with pore size<10nm..（6）When water-based polyurethane reacts with cementitious materials,it reacts with C₃A,C₄AF,C₂S and C₃S in clinker minerals in cement in turn and suppresses the"volcanic ash effect";when calcium and silica are relatively low,water-based polyurethane is more likely to affect the structure of C-S-H and generate reticular and spherical C-S-H,resulting in a large number of pores and causing strength.This results in a large number of pores and causes loss of strength.