Study On Effect And Mechamism Of New Concrete Earlt Strength Agent

Concrete early strength agent is an admixture that can improve the early strength of concrete remarkably.In the process of construction,it can accelerate the construction progress and improve the production efficiency.However,with the deepening of the research on traditional early strength agents,the problems of traditional early strength agents are gradually exposed:chloride ions in chloride salt early strength agents can accelerate the corrosion of steel reinforcement;Sulfate early strength agent may cause alkali aggregate reaction damage or excessive sulfate erosion damage.However,the study of new early strength agents without chlorine and low chlorine lags behind.Especially with the development of building industrialization and prefabricated building,the use of early strength agent to shorten or replace steam curing is of great significance for the production of precast concrete components.Therefore,it is of great significance to study the new early strength agent in depth.In this project,the embryos,calcium formate,methacrylic acid,iron sulfate and urea were taken as new early-strength agents to be added separately and then combined into cement mortar to explore their influence on the development of cement strength.At the same time,considering the influence of curing temperature and water-cement ratio on the performance of early-strength agents,the mechanism of each early-strength agent was analyzed by microscopic test method.Firstly,this paper studies the influence of the type and content of new composite early-strength components on the development of cement strength.According to the hydration process of cement,early strength components can be determined:embryos that can theoretically reduce the activation energy of products,high-priced cationic Fe³⁺that can accelerate the condensation of c-s-h,and calcium formate that can promote the hydration of C₃S.Under the condition of water-cement ratio of 0.45,the early-strength agents mentioned above were added into cement mortar to study their influence on the properties of cement mortar.The test results showed that different early-strength agents had different influences on mortar,among which the crystal embryo with a content of1.25%,calcium formate with a content of 1.0%and methacrylic acid with a content of0.5%had obvious effects.The initial and final setting time was shortened by 1h on average,the strength was increased by 60%at 12h,the strength was increased by 40%to 60%at 1d,significantly increasing the early strength of cement mortar.Secondly,according to the separate effects of several early-strength components,calcium formate and embryos were added in different amounts to form five composite early-strength agents,namely JS1?1:1?,JS2?3:2?,JS3?4:5?,JS4?6:5?and JS5?1:1?.Methacrylic acid and embryos were mixed with different amounts to form five composite early-strength agents JJ1?1:2?,JJ2?3:4?,JJ3?2:5?,JJ4?3:5?and JJ5?2:3?.The composite early-strength agent was added to the mortar with a water-cement ratio of 0.45.The test results showed that the addition of the composite early-strength agent had no significant effect on the fluidity of the fresh mortar.At the same time,according to the strength data of each age,it can be seen that the early strength effect of JS1,JS2,JJ1 and JJ3 is significant,among which,the strength of JS1 increases 91%at 12h,74.04%at 1d,100%at 1d and 74%at 3d.Then,the effects of water-cement ratio and curing temperature on the properties of early strength components were studied.According to the above test results,according to the varieties of cement,sand fineness,water reducing agent,the dosage of water reducing rate and determine the test water cement ratio of 0.4,0.45,0.5,according to the practical engineering in the different time determines the curing temperature is10?,20?and 40?three temperature.Cross test method was adopted to combine water-cement ratio and curing temperature to explore the influence of water-cement ratio and curing temperature on the performance of JS1,JS2,JJ1 and JJ2.The experimental results show that,as the water-cement ratio increases,the early-strength effect of JS early-strength agent decreases,and the early-strength effect of JS at a higher curing temperature is significant.JJ early strength agent has the best water-cement ratio of 0.45,and its early strength component has the effect of air induction,therefore,the higher curing temperature reduces its early strength effect.Finally,SEM,TG,FTIR,mercury injection and other microscopic methods were used to analyze cement samples with different early-strength components.By studying physical properties of hydration products such as morphology and composition,the early-strength mechanism of different early-strength components was explored.