Research On Composite Early Strength-enhanced Grinding Aids

The grinding aids are admixtures which can help grinding in cement grinding withoutcompromising the health of people and the performance of cement and concrete, significantlyimproving the crushing efficiency or reducing energy consumption of product, which are oneof the important technical measures of energy saving for cement companies. In addition toimproving the cement grinding efficiency, new-type grinding aids can improve the cementmortar strength. The effect of alcohol amine type grinding aids is reflected in the dispersion ofcement particles, which is less effect on the growth of cement specific surface area butsharply increased the concentration of particles, which leads to improvement of cement28dmortar strength, while the cement early strength will be less growth, and the waterrequirement of normal consistency rises, and the compatibility between the admixture andcement become worse. Thus, the development of grinding aids, which can improve thematerial grindability and cement specific surface area, but low growth on the concentration ofparticle, plays an important role in reducing the power consumption of cement grinding andimproving the quality of cement; When the clinker are largely replaced by the admixturehaving pozzolanic activity, it vastly decrease cement early （1d,3d） strength, It is sadversely tothe durability of concrete by adding early strength agent to increase the early strength,because it will bring harmful ions. Therefore, the research of early strength-enhanced grindingaids without harmful ions play an important role in reducding the amount of cement clinkerfor the same strength grade cement and the durability of the concrete.We evaluate the grinding effect and strength-enhanced effect of five kinds of grindingaids, and two of the most optimized combination are respectively obtained from theorthogonal test on the three grinding aids having good grinding effect or strength-enhancedeffect, which are Z₁（A0.03%, B0.06%, E0.02%） and Z2（A0.03%, B0.06%, D0.05%）.Compared with the blank sample, the surface area of cement added Z1and Z2respectivelyincrease by41m²/kg and39m²/kg,0.045mm sieve residue respectively decreases by8.4%and7.5%,3d compressive strength increases by6MPa and5.7MPa,28d mortar strengthchanges little. The Z1is better at the grinding effect and3d strength-enhanced effect, so theultimate early strength-enhanced composite grinding aids is Z1.The strength-enhanced mechanism is studied by adding grinding aids in the molding andin the cement grinding.1d、3d mortar strength、bound water and hydration heat of cementadded ginding aids by two ways increase compared with blank samples, while1d、3d mortar strength、bound water and hydration heat of cement added ginding aids by two ways aredifferent. The results show that:（1） grinding aids promote early hydration of cement mineralsand improve cement mortar strength, which is called chemical strength-enhanced effect.（2）The strength-enhanced effect of grinding aids in the grinding on cement mortar strengthmainly include reflect in two aspects, which are chemical strength-enhanced effect andphysical strength-enhanced effect because of the change of cement particle size distribution.（3） Compared with physical strength-enhanced effect, chemical strength-enhanced effect ofgrinding aids has a greater contribution to the early cement mortar strength.Grinding mechanism of grinding aids is studied by X-ray diffraction analysis andinfrared absorption analysis, comparing some diffraction peak and absorption peak of cementadded grinding aids with the black sample. Compared with the black sample, the results showthat the peak instensity of some strong peaks of cement added grinding aids decrease, andintegration area reduce, and some absorption peaks of infrared absorption analysis shift tolower wavenumber side, and peak becomes obtuse, and peak intensity decrease. This indicatethat materials grindability is impoved after adding grinding aids, and the cement addedgrinding aids in the grinding process produce more lattice distortion or lattice defects, and thebond strength decline in the same grinding time.