Application Of Limestone Powder In Commercial Concrete

Limestone powder is a new low-cost mineral admixture,which is increasingly used in the production of commercial concrete.However,the uncalcined limestone powder with low activity is not clear about the effect of compounding with other mineral admixtures in practical applications.Therefore,in this paper,the workability and strength of concrete was researched by replacing slag powder or fly ash with the actual production of commercial concrete,limestone powder,or limestone powder-coal gangue composite admixtures.In addition,the effect of different activators on the activity of limestone powder and the mechanism of action were also studied.The guidance for the proper application of limestone powder in commercial concrete was provided.The main research results of the paper were as follows:Firstly,the effect of limestone powder replacing the different amounts of fly ash or slag powder on the workability and mechanical properties of concrete was researched.The results showed that limestone powder replaces fly ash or slag powder in the mix ratio of C50,C60 and C70 concrete,and has little effect on the slump and degree of expansion of the concrete mix.However,with the increase of the limestone powder,the blending time of the concrete significantly decreased.Compared with the control group,when limestone powder replaced fly ash or slag powder,it had little effect on the compressive strength of C50 and C60 concrete.However,for C70 concrete,the compressive strength reduced when the substitution amounts of limestone powder waere more than 40%.Secondly,the basic properties of composite admixtures of limestone powder and coal gangue were studied,and the effect of the composite mineral admixtures in place of fly ash on the workability and mechanical properties of concrete was reasearched.The results showed that the fineness of the limestone powder-coal gangue compositeadmixture is comparable to that of the second-grade fly ash,and the 7 d activity index of the composite admixture is 68%,and the 28 d activity index can reach 77%.When the amount of substitution was less than 60%,the slump and degree of expansion of the concrete mixture increased with the increase of the amount of fly ash replaced by limestone powder-comminal coal gangue compound admixture.However,when the amount of substitution was more than 60%,the slump and degree of expansion of the concrete mixture gradually decreased as the amount of substitution increased.Compared with the control group,composite admixtures replacing fly ash had little effect on compressive strength of concrete for 3 d,7 d and 28 d.Finally,the effect of different activators on the activity of limestone powder was studied.The systematic research of the effect of limestone powdered cement slurry on fluidity,strength,hydration heat,and chemically combined water with adipic acid added was focused.The mechanism of action was analyzed by X-ray diffraction and scanning electron microscopy.The results showed that the addition of adipic acid increases the fluidity and the 3 d strength of cement paste with limestone powder,and also improves the early hydration temperature and early hydration combined water volume.The concrete with adipic acid produced more hydration of calcium aluminate at3 days,resulting in a more dense structure of the hydration product.