Study On Strengthening And Toughening Mechanism Of Mg O-based Basic Salt Cement And Its Coral Concrete

With the development of marine resources,more and more countries have taken in the tide for the construction of ocean islands and reefs.Under the guidance of the policy for the Belt and the Road,China's development and utilization of marine and reef resources are also progressing steadily.However,the traditional concrete is restricted by the marine environment in some aspects,like material source,production process and performance.As the development of the construction,the embarrassing situation of high investment but low income has begun to appear.MgO-based basic salt cement not only has the great cementitious properties of high strength,early strength and cohesiveness,but also the good adaptability to the marine environment.Moreover,the main row materials of the cement can be used in marine chemical products.Combining with the coral sand and the seawater to produce the coral concrete in MgO-based basic salt cement,which can provide new ideas for the construction of island reef.In this paper,the compressive test and flexural test of magnesium alkali salt cement paste and mortar specimens with different mix ratio and different curing temperature are studied.By analyzing the indexes of compressive strength,flexural strength,compression ratio and softening coefficient,we conclude the physical and mechanical laws of magnesium alkaline salt cement under the difference of mix ratio and curing temperature.Based on the theory,this paper gives the best range of mix proportion and curing temperature.Through the microscopic analysis to explain the macroscopic mechanical properties is an effective way to study the mechanism of cement strengthening and toughening.Using SEM to analyze the microstructure of the paste samples with different mixture ratios and different curing temperatures.By analyzing the whiskers' microscopic indexes of number,microstructure and arrangement,the influence of mix proportion and curing temperature on the microstructure of cement is determined.Based on the microscopic features,the best mix proportion and curing temperature is determined.Poor water resistance is the main reason which limited the large-scale engineering practice of the MgO-based basic salt cement.In this paper,an efficient composite modifier named Si3(PO4)4 is used to study the modification law of cement.Through the analysis of the flexural strength,compressive strength,compression ratio and softening coefficient of the modified mortar specimens,the regularities of the modification are obtained with the different mixing ratio and curing temperature.In order to verify the engineering practice value of the MgO-based basic salt cement,the coral concrete in MgO-based basic salt cement is studied under different curing temperatures.After finishing the work of the mix ratio design and the production process research,this paper analyze the indexes of concrete compression,flexural strength,splitting tensile strength and compression ratio.Based on the study,this paper concludes the strengthening and toughening method of the coral concrete in MgO-based basic salt cement.The strength of concrete is modified from two aspects of aggregate gradation and aggregate enhancement,and suggestions for improving the strength of concrete should be made from the aspects of controlling the maximum particle size of aggregate and enhancing the performance of coarse aggregate.Moreover,the concrete with modification is carried out to verify the effectiveness of modifier on improving the water resistance of concrete.