| Portland cement is one of the most common building materials. Concrete materials hasbeen widely used due to its high compressive strength, strong adaptability, low price and manyother advantages. However, many disadvantages of cement materials limit its application field,such as its brittleness, not high corrosion resistance and big drying shrinkage deformation.Curing process is an important step after the forming of cement concrete. Concrete willcontinue its hydration process while keeping its water-saturated state of concrete. Curinghumidity decreases, internal water will migrate, thus affecting the hydration process andstructure of cement. Studies have shown that the bigger curing humidity is, the more fully thehydration process is, the higher strength of the concrete is. It is a basic properties of cementbased materials that the volume shrinkage deformation due to the pore water evaporation ormigration. The water in the cement is easy to loss in the dry environment, that causes stress andcrack in cement structure, reduces durability and service life of the cement. Therefore, it is veryimportant to study how to improve the water holding capacity of cement material.Super absorbent polymer (SAP) is a new kind of polymer material, which is insoluble inwater and organic solvents, which is able to absorb hundreds or thousands times of water of itsown weight. It is also superb in the water absorbing speed and water retention properties, evenif it is under high pressure, known as the "molecular reservoir". Water absorbent resin is used asa new curing admixture in cement based materials in the study. SAP is added in the mixingprocess of cement, thus obtaining better strength of the cement without external artificialmaintenance, keeping its water, reducing the shrinkage cracking and achieving the purpose ofself-curing.Our previous studies have proved that the mixing of acrylate can not only improve the porestructure and corrosion resistance of the cement, but also strengthen the cement matrix,improve mechanical properties. In this experiment, self synthesized calcium acrylatemicrosphere is used as a main material to study its effect on the cement. First, the effect ofvarious conditions in the synthesis of calcium acrylate microsphere (stirring speed, monomerconcentration, neutralization degree, the dosage of initiator, crosslinker and dispersant) on the properties of microsphere (particle size and size distribution, water absorbency, waterabsorption rate, water retention rate) is discussed, to determine the optimum process conditionsand dosage in the synthesis of microsphere. The effect on the properties of cement will bestudied after microsphere is obtained. In this experiment, the effect of microsphere onmechanical properties of cement is studied, and also the mechanism of modified cementhydration using the methods of XRD, SEM and pore structure analysis.The ratio of the optimum microsphere is:7.5%monomer concentration,75%neutralization degree,3%the dosage of initiator,0.03%the dosage of crosslinker and5%thedosage of dispersant. The best stirring speed is900r/min-950r/min. The diameter ofmicrosphere is500nm, the water absorption ratio is43g/g.The mixing of calcium acrylate microsphere has little effect on early strength, is beneficialto improve the later strength. The optimum dosage of calcium acrylate microsphere is1.5%，the28d strength of modified sample increases about25%than the blank sample in dry curingconditions.According to the XRD spectra and SEM images, calcium acrylate microsphere promotesthe later hydration process. The microsphere plays a role in water retention and promoteshydration of cement in dry conditions.Through the analysis of pore structure, calcium acrylate microsphere refines the porestructure of28d cement paste effectively, increases the ratio of harmless pore and reduces theratio of harmful pore and reduces the total porosity.In a word, the microsphere improves thepore structure of cement paste. |
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