Design,Preparation And Hydration Properties Of Polymer Cement Based Materials At Low Temperature Rise

National strategies such as "Maritime Power" and "One Belt One Road" have set off a new upsurge in the construction of major infrastructure projects.Mass concrete is the main body of infrastructure construction such as island reef construction,sea-crossing bridges,tunnel bridges,etc.The rapid heat release during its setting and hardening process will cause the concrete matrix to crack.In the face of unavoidable extreme harsh environments such as waves,high salt,high alkali,and high cold,the deterioration rate of engineering structures has increased exponentially.Once the concrete cracks,it will inevitably cause irreparable safety accidents and major economic and property losses.The rapid deterioration of the engineering structure caused by the temperature rise of mass concrete is a difficult problem that has plagued the engineering community for a long time and has not been effectively solved.In this study,a low temperature rise polymer（CAMC for short）was designed and prepared,which can effectively control the hydration rate of cementitious materials and provide a new reference for effectively controlling temperature-induced cracking of mass concrete.In this study,combined with experiments and simulations,CAMC was designed and fabricated,and the effect mechanism of CAMC on cement hydration and its influence on macroscopic properties were discussed.Numerical simulation research on concrete damage,discusses the damage law of mass concrete under different working conditions,the main research results are as follows:（1）The carboxyl group was introduced into the chitosan structure through acylation reaction,and an environment-friendly CAMC hydration regulating material was designed and prepared.The optimum preparation conditions were determined:the mass ratio of citric acid（CA）to chitosan（CTS）was 3:1,the reaction temperature was 105℃,and the reaction time was 4 h.The carboxyl group is introduced into the chitosan structure through acylation reaction.CAMC destroys the original intermolecular hydrogen bond structure,reduces its crystallinity and compactness,and forms a surface structure characterized by debris and defects.The water solubility of CAMC is significantly enhanced.CAMC realizes the control of cement hydration heat release process on the basis of effectively controlling the setting time of cement paste.（2）CAMC significantly reduced and delayed the hydration heat release rate and accumulated hydration heat of cement,and the formation of AFt was significantly slowed down and the formation amount increased;The increase in the concentration of Ca²⁺and SO₄^2-in the pore fluid is the main reason for the increase in the amount of AFt;According to the ²⁹Si spectrum analysis,the content of long-chain C-S-H decreased,and the ²⁷Al spectrum showed that the delayed dissolution of aluminum phase in cement clinker minerals delayed the formation of AFt and delayed the transformation from AFt to AFm;CAMC significantly reduced the reaction constants of crystallization nucleation and crystal growth（NG）,phase boundary reaction（I）and diffusion（D）;The thermodynamic model confirms that CH and AFt phases are in supersaturated state,and the time of gypsum from supersaturated state to unsaturated state is also delayed,which confirms the delay of CAMC on gypsum consumption.（3）CAMC can promote the agglomeration of cement particles,and the electrostatic attraction between the adsorption group and cement particles is the main reason for the adsorption of CAMC polymer and cement particles.In the pore solution of cement hydration,the formation of C-S-H is controlled by"non-classical nucleation theory".The retarding mechanism mainly inhibits the formation of hydration products rather than slows the dissolution of cement.In addition,molecular dynamics simulation shows that the polymer mainly adsorbs Ca²⁺in aqueous solution,but has little binding with C₃S.Its inhibition of the formation of hydration products is not caused by the destruction of nucleation,the precipitation of calcium complex on the hydration products and the inclusion of metastable silicate balls,but mainly by the reduction of free Ca²⁺participating in the formation of hydration products.（4）Taking the degree of hydration of cementitious materials as the basic state variable,a concrete damage assessment model under the coupling of multiple factors of"hydration temperature humidity constraint"was studied and established.It was found by comparison that CAMC affected the temperature development process of mass concrete,reduced and delayed the temperature peak value and time of mass concrete,effectively reduced the temperature by more than 10℃,and the maximum damage value of mass concrete in the experimental group was reduced from 0.7 to 0.43compared with the control group,and it is delayed to 2.5d,which greatly reduces the damage probability of concrete and the development of cracks.