Study On Hydration And Carbonate Water Corrosion Resistance Of Metakaolinsugarcane Bagasse Ash-portland Cement Ternary System

The karst landscape in Southwest China is widely distributed,and the groundwater in karst areas often has high concentrations of dissolved CO₂,which poses new challenges to the durability of cementitious materials.From the perspective of green environment and economic benefits,the most concise and efficient way to enhance the durability of cementitious materials is to incorporate supplementary cementitious materials（SCMs）into cementitious materials.Metakaolin（MK）and sugarcane bagasse ash（SCBA）are active and easily available SCMs,which can effectively improve the durability of cement-based materials,but there is little research on their impact on the corrosion resistance of cement materials to carbonic acid water.In this paper,the composition design of metakaolin-sugarcane bagasse ash-silicate cement system was carried out by ternary center of gravity method to study the corrosion process and mechanism of ternary gel system before and after carbonic acid water corrosion.In this paper,the effects of MK and SCBA on the properties of cement paste were investigated by analyzing the compressive and flexural strengths with different mix proportion under standard curing conditions,and the effects of MK and SCBA on the pore structure,chemical composition and physical phase composition in silicate cement paste were analyzed by ¹H NMR,SEM,XRD,TG/DTG,and FTIR tests.The results showed that the compressive strength of the paste was highly linear with the chemically bound water content,and the incorporation of MK and SCBA could effectively improve the mechanical properties and chemically bound water content of the paste after standardization,reduce the Ca（OH）₂ and AFt content in the system,transform more low-density C-（A）-S-H gels with low Ca/Si ratio,and improve the pore structure of the paste.When the cement paste was compounded with 20%MK and 5%SCBA,the cement paste had the optimum compressive strength and the highest percentage of Q^1,2 content after 150 d of standard conditioning,119%and 168%of the control group,respectively,and the Ca（OH）₂ content in the paste was almost zero.In this paper,the physical phase changes of cement paste after carbonate water corrosion were analyzed by XRD-Rietveld,TG/DTG,FTIR and SEM.The results show that the carbonic acid water corrosion causes the carbonization and calcium dissolution of hydration products such as Ca（OH）₂and C-（A）-S-H in the cement paste successively,which affects the mechanical properties of the paste.The appropriate amount of MK and SCBA can reduce the Ca（OH）₂ content of the system and generate more low Ca/Si ratio C-（A）-S-H gels that are difficult to be eroded,which improves the corrosion resistance of the cement paste against carbonic acid water.When MK dosing was 20%and SCBA dosing was 5%,the mortar had the lowest corrosion depth after 90d of corrosion,which was 71%of the control group.Finally,this paper analyzes the mechanical properties of mortar subjected to carbonic acid water corrosion were also initially investigated by analyzing the changes of Vickers microhardness,compressive strength and pore structure of cement paste before and after corrosion.The results show that after the cement paste is eroded by carbonic acid water,a dense carbonized layer is formed at the corrosion front,which has higher mechanical strength than the paste in the non-corrosion area;as the corrosion continues,the carbonized layer forms a gel layer by the effect of calcium dissolution,and the mechanical properties are subjected to lower,meanwhile,with the extension of the corrosion age,the growth rate of the thickness of the carbonized layer is gradually lower than that of the gel layer,which is externally manifested by the deterioration of the pore structure and the overall mechanical properties of the paste mechanical properties decreased.