Research Of Low Heat Portland Cement For Marine Engineering

Cement is the main cementitious material for concrete buildings,and its performance is directly related to the safety and durability of offshore engineering.According to the marine environment and engineering characteristics,marine mass concrete has requirements for early strength,low heat and good corrosion resistance.The existing low-heat Portland cement has the characteristics of low hydration heat and high strength in the late stage,which can solve the problem of concrete cracking caused by cement hydration heat release,but the early strength is low and the seawater erosion resistance should be further improved.Therefore,it is urgent to develop low-heat Portland cement with early strength,low heat and good corrosion resistance for marine engineering requirements.In this paper,XRD,FT-IR,SEM-EDS,DSC-TG,microcalorimeter and other testing methods were used to study the influence of trace element doping on the crystal structure of dicalcium silicate,in order to improve the calcium disilicate and cement.The activity provides a theoretical basis;based on the results of this study,the mineral composition of low-heat portland cement clinker for marine engineering is optimized and matched,and the relationship between strength,hydration heat and erosion resistance and composition of cement is studied;The low-heat portland cement anti-seawater erosion mechanism for engineering provides technical support for the development and development of low-heat portland cement for marine engineering,and draws the following main conclusions:?1?In order to improve the hydration activity of dicalcium silicate,the correlation between the type and amount of doping ions and the crystal structure of dicalcium silicate was studied,and the corresponding optimum dosage was obtained.The results show that the effect of ionic doping is:P₂O₅>SO₃>BaO,the optimum dosage of P₂O₅ and SO₃ is 1.64%,4.75%,BaO dosage should be?11.55%;when ion composite doping,trace SO₃ makes P₂O₅ the optimum amount of BaO is significantly reduced,which proves that the ion composite doping has better stable activation effect.?2?In order to improve the early strength and seawater erosion resistance of low heat portland cement,the influence of clinker mineral composition on the performance of low heat portland cement seawater erosion resistance,chloride ion diffusion coefficient,hydration heat and shrinkage rate was studied.Considering various properties comprehensively,the best clinker mineral composition range of marine low-heat cement is obtained:C₃A content 4%⁸%,C₂S content 40%⁴5%,and comprehensive performance is good.?3?The variation law of low heat portland cement hydration products in marine engineering in seawater and fresh water was studied,and the mechanism of seawater erosion resistance of low heat portland cement used in marine engineering was preliminarily clarified.The results show that in the seawater environment,the cement hydration product Ca?OH?₂ reacts with SO₄^2-and Mg²⁺to form AFt,Mg?OH?₂ and CaSO₄·2H₂O,which causes the hydration product to expand.On the other hand,C-S-H reacts with Mg²⁺to form M-S-H with poor gelation,which leads to deterioration of gelation performance of cement hydration products.In addition,C₃A hydration products can react with Cl^-in seawater to form friedel salt.As C₃A content in clinker increases,friedel salt content increases.It reduces the free Cl^-content in the pores of cement stone,which is beneficial to improve the chloride ion resistance of low heat portland cement used in marine engineering.