Study On Effect Of The Main Cement Characteristic To Compatibility Of Water-reducing Admixture With Cement

Development of modern concrete science depends greatly on the use of chemicaladmixtures,that has extended the application fields of concrete and is believed to be the third breakthrough in progress of concrete technology. However,the compatibility of chemical admixtures with cement still remains a common problem.As one of the most important concrete chemical admixture,water-reducing agent (WRA) has extensively used hi concrete for a long time. Thus the problem of incompatibility of WRA with cement occurs frequently and many researchers attach great importance to it. After adoption of new cement standard in China,the main characteristic of cement materials changed a lot compared with the former ones. As a result,there will certainly be some change in the compatibility of WRA with cement.In this thesis,the effect of cement characteristic,such as clinker composition,particle properties and mineral admixture used in cement,on the compatibility of WRA with cement was studied. The cause of incompatibility of WRA with cement was analyzed hi consideration of fluidity and Zeta-potential of cement paste,as well as amount of WRA adsorbed on cement particle surface. In order to testify the analysis,the test of slump of concrete was carried out.It,is found that the saturation dosage of WRA is increased and the fluidity loss of cement paste is accelerated,as the specific surface area of cement particles is increased. It's also found that the increase roundness of cement particles has little effect on the saturation dosage of WRA,but it improves fluidity of cement paste and reduces the fluidity loss,especially in the case of lower w/c ratio. While the cements having approximate specific surface area,the increase in amount of fine particle smaller than 3 u m improves the initial fluidity of cement paste,but it reduces its ability for remaining the flowing property.Addition of slag in cement takes little effect on saturation dosage of WRA,and so is the change in dosage and fineness of slag in cement. But they have obvious effect on fluidity and fluidity loss of cement paste. Addition of fly ash hi cement decreases the saturation dosage of WRA,but the dosage and fineness of fly ash have little effect on this saturation dosage. Additionally,the ability of WRA for dispersing cement particles could be strengthened when the dosage of slag and fly ash is increased,and so is their specific surface area of slag and fly ash.It is proved hi this research that the initial fluidity of cement paste depends on the amount of WRA adsorbed on the unit surface area of cement particle,the more the adsorption of WRA is,the better the initial fluidity will be. In addition,the fluidity loss of cement paste at a certain time is depends on the concentration of WRA remaining in cement paste at that time. The higher the remained concentration is,the lower the fluidity loss will be.In the final part of this thesis,the mechanism of "water-reducing effect" of mineral admixtures in cement paste was discussed and analyzed. It is shown that the "water-reducing effect" of mineral admixtures is mainly caused by three effects of particles of mineral admixtures,i.e. adsorption effect (mineral admixtures can affect adsorption of WRA on cement particle) ,particle compacting effect (pores of the packing system of cement particles can be partially tilled by finer particles of mineral admixtures) and spherical particle effect (the more sphericized particles of mineral admixtures will reduce hydraulic radius of cement particles,which making solid particles easy to spin and slide in paste system).A new technology getting feasibility of high economic and social benefits of separately grinding cement clinker and mineral admixtures in order to produce high quality cement is proposed by the author.