| Because of the low price and large store of Limestone powder,it can be used as a concrete mineral admixture to solve the problem of insufficient supply of Supplementary Cementing Materials,which has a good prospect.At present,more and more researchers have studied the durability of limestone-Portland cement composites,but the problem of durability still exists.Therefore,it is still necessary to use suitable supplementary materials and reasonable design methods to improve the durability of limestone powder-cement composites.In this thesis,the influence of limestone powder content and fineness on the porosity,water absorption rate and charge passed of cement-based materials was studied by the method of mixture design.The influence mechanism of metakaolin on the resistance to chlorine penetration of limestone powder-cement composite cementitious materials was also studied by GEMS thermodynamic simulation method,and the improvement measures resist chlorine penetration and sulfate erosion were proposed.The main conclusions are as follows:(1)In the research,the water absorption,porosity and charge passed all gradually increased with the increase of limestone powder content,but the effect of changing fineness was very limited.In addition,the three durability properties of porosity,water absorption and charge passed are closely related.Incorporation of limestone powder resulted in an increase in coarse pores in the specimen,and thus an increase in overall porosity.The pore size of this part of the increased pores belongs to the range of capillary pores.So,the increase of capillary pores will significantly increase the water absorption rate of the solid specimen,which also leads to the improvement of the specimen’s ability to absorb chloride salt liquid,and the free chloride in the pores will also increase.In addition,the incorporation of limestone powder also reduces the content of the phase with the capable of solidifying or combining chlorine,which further reduces the resistance to chlorine permeation,so the measured charge passed is improved.(2)The decrease in water absorption of the specimens after incorporating metakaolin was not due to the refinement of pores.The experimental results show that the incorporation of metakaolin will lead to a phase transition(conversion of Hemicarboaluminate to Monocarboaluminate,etc.),resulting in volume reduction of the solid phase,increase in total pores,which leads to the increase of sample pores and pore size and the decrease of later strength.Although the incorporation of metakaolin weakened the ability to chemically bind chlorides,the increased gel can adsorb chlorides in the gel interlayer and aggregate with calcium through electrostatic interactions,reducing the free chlorides in the pore solution.As a result,the charge passed of the sample is greatly reduced.The addition of metakaolin can improve the durability of the sample such as water absorption and charge passed without significantly affecting the strength and porosity.Therefore,metakaolin is an excellent improvement material.(3)In the sulfate attack,the incorporation of glass powder significantly reduces the expansion of the specimen in the early ages,and the reduction increased with the increase of the glass powder content.The incorporation of glass powder in the subsequent sulfate attack can also inhibit the expansion rate.Due to the low pozzolanic activity of glass powder,it has little effect on the strength of the sample after being corroded by sulfate dry-wet circulation in the early stage.However,after the dry-wet circulation reaches 90 times and later,the glass powder can relieve the loss of strength to a certain extent.33 Figures,14 Tables,90 References... |
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