Study On The Influence Of Temperature On The Carbonation Performance Of γ-C₂S

γ-C₂S is a high carbonation activity calcium silicate mineral,which has great application prospects in the manufacture of low carbon building products from industrial tail gas carbon mineralization.The effect of temperature on the carbonation performance of calcium silicate minerals has not been systematically studied in current research,and the positive and negative effects of temperature on the carbonation performance ofγ-C₂S at different ambient temperatures.The paper is based on the National Natural Science Foundation of China（NSFC）project"Basic research on carbonation mechanism and regulation ofγ-type dicalcium silicate and its application"（NO.51672200）,which systematically investigates the effect of temperature on the carbonation properties ofγ-C₂S and broadens the development,application potential and prospect ofγ-C₂S in new low-carbon building materials.new ideas for the green and sustainable development of building materials.The main work carried out in the thesis and the main results obtained are as follows:（1）For the first time,the law of positive and negative effects of temperature on carbonation reactivity and carbonation products was proposed.It is found that higher temperature can improve the carbonation reactivity ofγ-C₂S,and higher temperature will lead to higher compressive strength and compressive strength ofγ-C₂S in the early stage.However,with the increase of temperature,the development of long-term compressive strength and carbonation will be inhibited.The 24 h compressive strengths reached 114.11 MPa,105.06 MPa,80.95 MPa,58.22 MPa and 68.58 MPa at 0°C,20°C,40°C,60°C and 80°C,respectively.The increase in temperature enhances the dissolution of Ca²⁺while decreasing the solubility of CO₂ in the aqueous phase.In addition,the accompanying exotherm of the reaction further increases the sample temperature,leading to the gradual depletion of pore water,which is not conducive to the sustainability of the carbonation reaction.Finally,carbonation of the samples at lower temperatures produces calcite,the main polycrystalline form of calcium carbonate,which has a lower specific density than aragonite and thus favors the formation of denser structures.The interaction of these factors explains the differences in compressive strength and carbonation development at different temperatures.（2）More accurate prediction of temperature effects on carbonation properties by surface coverage models.The reaction kinetics of compression molded samples differ from the case of loosely connected particles covered by a water film layer or immersed in a highly dilute suspension,as evidenced by significant deviations from the n-values in the commonly used kinetic functions.The combination of hindered diffusion between CO₂ particles and increased pore water depletion in the closely packed and highly reactiveγ-C₂S samples affects their reaction further.Therefore,an improved kinetic model was used to incorporate the moisture dissipation effect by assuming that the reaction occurs only in the reactive surface region covered by moisture but not by reaction products.The model was able to predict the temperature effect more accurately.（3）The effect of Mg Cl₂-doped solution on the carbonation properties ofγ-C₂S at-10℃was investigated.The carbonatedγ-C₂S doped with Mg Cl₂ solution at-10℃showed excellent reactivity and mechanical properties after carbonation and maintenance:the 24 h compressive strength of 0.2M～1M samples increased from10.32 MPa of 0M sample to 115.68 MPa,157.80 MPa,178.56 MPa,151.04 MPa and 143 MPa,respectively.γ-C₂S products after carbonation at-10℃are dominated by calcite type calcium carbonate with the presence of a small amount of aragonite.The main mechanism of high carbonation reaction activity of Mg Cl₂-dopedγ-C₂S solution at-10℃includes the following two aspects:firstly,Mg Cl₂ can lower the freezing point of the sample pore solution,so that it can still retain part of the unfrozen aqueous solution at-10℃,providing a carbonation environment for the initial reaction;secondly,the exothermic carbonation ofγ-C₂S at the early stage of the reaction increases the temperature of the sample and dissolves part of the frozen water At the same time,it promotes the dissolution of Ca²⁺inγ-C₂S,which further accelerates the carbonation reaction rate.