| Abstract:Stone powder are inevitable in the production process of aggregates such as sand and gravel, it will not only occupy a lot of valuable farmland, but also pullute the environment if we don’t make good use of these stone powder.This paper is based on the National Natural Science Foundation Project "Research on the theoretical basis and practical application of the rock mineral admixture system"(Project number51278497), mainly to study the physical and mechanical properties and durability of the cementrock mineral admixtures cementitious system. The effect of mineral admixtures made of calcareous rock and silicious rock respectively on the setting time of cement, the fluidity and strength of cement mortar and the corrosion resistivity was studied. The main contents and results are as follows:1. The effect of mineral admixtures made of rock on the setting time of cement and the fluidity of cement mortars was studied.(1) The initial and final setting time of cement mortar with ground limestone and ground marble were shortened gradually with the increasing of limestone and marble content. The fluidity of cement mortar was improved with the addition of ground limestone and ground marble, and the value of the fluidity of cement mortar increased gradually with the increase content of ground limestone and ground marble. Whereas the initial and final setting time of cement mortar with ground dolomite was prolonged with the growing of its content. The fluidity of cement mortar was significantly increased when the content of ground dolomite was low, the fluidity of cement mortar decreased gradually with the increase of ground dolomite.(2) The effect of ground granite and ground quartz on the initial and final setting time of cement mortar were the same. The initial and final setting time of cement mortar with ground granite and ground quartz were shortened gradually with the increasing their content. The initial and final setting time of cement mortar with ground basalt was shorter compared with the reference group, and became more and more shorter with the increasing their content. The effect of ground granite and ground quartz and ground basalt on the fluidity of cement mortar were the same. The fluidity of cement mortar was increased when the content of these powders was low, the fluidity of cement mortar decreased gradually when the content increase.2. The effect of mineral admixtures made of rock on the strength of cement mortars was studied.(1) The early-age strength of cement mortars with ground limestone and ground marble and ground dolomite were increased compared with reference group, the bending strength of the specimen increased first and decreased then with the increase of the powder content, the bending strength of cement mortar reached the maximum when the content was5%. However, the later strength of cement mortar decresed with the increase of the content of the mineral admixture, and lower than the reference group. When the content of mineral admixture made of calcareous rock remains the same, the strength of cement mortar increased first and then decreased then with the increase of the fineness of mineral admixture.(2) The strength of cement mortars with ground granite and ground basalt and ground quartz were lower than the reference group for every age, and the larger the content was, the lower the strength were. When the ground granite and ground quartz replace cement of equal quantity, the bending strength of cement mortar decreased with the increased of their content, the early-age compressive strength of the cement mortar increased first and decreased then with the increase of the powder content; the bending and compressive strength of cement mortar with ground basalt increased first and decreased then with the increase of its content, the strength reached the maxmum when the content of ground basalt is10%.3. The effect of the mineral admixture made of rock on the pore structure of cement mortars was studied.The absorption of water and average pore diameter for the early-age of the cement mortar with mineral admixture made of rock was decreased when then content of admixture was low, the absorption of water and average pore diameter was higher than the reference group after14days, and increased gradually with the increase of their content. With the addition of mineral admixture made of silicious rock, the porosity of the cement mortar increased gradually and higher than the reference group.4. The effect of the mineral admixture made of rock on the property of resistance to chloride of the concrete was studied.The addition of mineral admixture made of calcareous rock and silicious rock were harmful to the property of resistance to chloride of the concrete, the electric flux of the concrete increased with the increase of the admixtures and higher than the reference group.5. The failure and mechanism of the cement pastes with ground limestone exposed in sulfate erosion solutions under low temperature was studied.The cement paste specimen with ground limestone suffered Thaumasite type sulfate attack when exposed in Na2SO4solution of different concentrations and5%MgSO4solution of lower temperature(5℃), the degree of damage of the surfaces of the pastes deepened with the erosion time and the increase of the concentration of Na2SO4solution. This is because SO42-in the solution penetrate into the inside of the cement through the pores, CaSO4·2H2O was formed by the reaction of SO42-and Ca(OH)2or C-S-H gel, thaumasite was formed by the reaction of C-S-H gel and CaSO4·2H2O and ground and H2O under lower temperature. The specimen exposed in MgSO4solution suffered even more serious erosion than that exposed in Na2SO4solution when the concentration were5%. This is because not only thaumasite was formed caused by the penetration of SO42-,but also Mg(OH)2was formed, therefore, C-S-H gel was decomposed, which promoted the formation reaction of thaumasite. |
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