Study On Properties Of Composite Cementitious Materials With Different Lithological Stone Powder

The utilization of manufactured sand powder can not only solve the shortage of common mineral admixture resources such as fly ash and slag powder,but also promote the green application of manufactured sand which has become the focus of current research.In order to determine the effect of different lithological stone powder on the properties of composite cementitious materials and promote the application of stone powder as a new type of mineral admixtures,limestone,granite,tuff and quartzite manufactured sands were used as raw materials in this thesis to obtain corresponding stone powder after grinding.The influence of lithology,content and fineness of stone powder on the properties of composite cementitious materials and the effect mechanism were studied through the combination of micro and macro tests to attain the composition design of composite cementitious materials.The main conclusions are as follows:(1)Particle distribution,mineral composition and microscopic structure of different lithological stone powder were analyzed.When the specific surface areas of different lithological stone powder were similar,45μm sieve residue of stone powder was in order of tuff>granite>limestone>quartz.The angularity of granite and quartz powder was more notable than that of limestone and tuff powder.The mineral composition of stone powder had an obvious impact on Zeta potential and the adsorption of polycarboxylate superplasticizer.Limestone powder had a dense and uniform structure composed of calcite and low adsorption for polycarboxylate superplasticizer.The higher solubility of calcite made powder particle more negative and repulsive force enhanced.Quartz powder was composed of quartz except a small amount of impurities.The surface of quartz powder was smooth and dense.Zeta potential of quartz powder was close to zero and the adsorption of polycarboxylate superplasticizer was slightly higher than cement.Tuff powder was composed of quartz and zeolite,and the negative charge and the adsorption of polycarboxylate superplasticizer both increased obviously with time.Granite powder was composed of quartz,feldspar and mica and Zeta potential was significantly negative.The intercalation effect of mica made the absorption of polycarboxylate superplasticizer by granite powder obviously higher than that by the other lithological stone powder.(2)The effect of lithology,content and fineness of stone powder on properties of composite paste was studied.Limestone powder was beneficial to improve the workability of the composite paste;quartz powder had slight adverse effect on the workability of the composite paste;tuff powder was not conducive to maintaining the fluidity;granite powder had a significant adverse effect on workability.For the initial fluidity,limestone and tuff powder had an improvement especially when the content was30%,and the improvement of limestone powder was better than tuff powder;quartz powder had less effect on the initial fluidity;granite powder significantly reduced the initial fluidity.For the fluidity retention,limestone powder was conducive;both tuff and granite stone powder were not conducive,of which the adverse effect of granite powder and large amount of tuff powder was more significant;quartz powder had negligible effect on the fluidity retention.When the specific surface area of stone powder increased,the fluidity of limestone,quartzite and tuff powder-cement composite pastes decreased significantly,but the fluidity of granite powder-cement composite paste varied slightly.Water requirement of normal consistency of composite cementitious materials was related to MB value and particle distribution of stone powder.The larger MB value and the narrower particle distribution,the higher water requirement of normal consistency.(3)The effect of lithology and fineness of stone powder on the hydration process was illustrated.Limestone and tuff powder shortened the setting time,while granite and quartz powder extended the setting time.The setting time decreased as the fineness of stone powder increased.When the specific surface area of stone powder was about 500or 700 m~2/kg,the setting time of the composite pastes containing granite and quartz powder was equivalent to that of the reference group.When the specific surface area of stone powder was about 370 m~2/kg,the heat release of the composite pastes containing tuff powder was significantly higher than that of the other composite pastes;When the specific surface area of stone powder was about 500m~2/kg,the heat release of composite pastes modified with different lithological stone powder was in order of quartz>limestone>Granite>Tuff;when the specific surface area of stone powder was about700 m~2/kg,the dispersion of cement weakened due to the excessively fine stone powder,so the heat release of quartzite,limestone and granite powder-cement composite pastes reduced,while the heat release of tuff powder-cement composite paste increased due to pozzolanic activity.(4)The effect of lithology and fineness of stone powder on the properties of composite mortars and dry shrinkage was studied.When the specific surface area of stone powder was about 370m~2/kg,the 28d compressive strength of composite mortars was affected by chemical action in order of tuff>limestone>granite>quartz;when the specific surface area of stone powder was about 500m~2/kg,the compressive strength of quartz powder-cement composite mortar had the most significant increase because chemical effect of stone powder weakened and the effect of filling and particle morphology increased;when the specific surface area of stone powder was about700m~2/kg,the compressive strength of limestone,granite and quartz powder-cement composite mortars decreased because the dispersion of cement by stone powder weakened,while the compressive strength of tuff powder-cement mortar increased due to the pozzolanic activity of tuff powder.The fineness of stone powder had the consistent impact on the total heat release at 72h and the compressive strength at 28d.Different lithological stone powder could reduce the dry shrinkage of composite mortars and decrease the risk of cracking.As the fineness increased,the dry shrinkage of the composite mortars increased.The greater the total porosity and the proportion of 10-50nm pore of composite mortar,the greater the dry shrinkage.Considering the grinding cost and the effect of stone powder on the properties of cementitious materials,the best specific surface area of quartzite and granite powder was about 500 m~2/kg,while the best specific surface area of limestone and tuff powder was about 370m~2/kg.(5)In order to reduce the adverse impact of stone powder on the properties of composite cementitious materials,the properties of stone powder-fly ash/slag powder-cement composite cementitious materials were discussed.Both fly ash and slag powder could obviously improve the workability of the stone powder-cement composite pastes,of which the improvement of fly ash was better than slag powder.Both fly ash and slag powder improved the compression strength of stone powder-cement composite mortars.Activity indexes exceeded 70%when stone powder and fly ash/slag powder were mixed at different proportions which met the standard requirements of the composite admixture.The recommended optimal mixing ratio was:granite powder:fly ash/slag powder=1:2,tuff powder:fly ash/slag powder=2:1.