Study On The Setting Retardant Of Alkali-Activated Slag Concrete

Alkali-activated slag concrete is considered as a possible new green material to replace cement because of its simple preparation process,energy saving and environmental protection,and good mechanical properties and durability.However,due to its fast setting property,the plastic time is too short to meet the requirements of the minimum setting time in practical engineering.Based on the analysis of the retarding technology of alkali-activated cementification materials at home and abroad,this paper aims to improve the rapid setting characteristics of Alkali-activated slag concrete,and draws on the modern pharmaceutical slow release preparation technology.In order to reduce the release rate and reaction rate of the Alkali-activated activator into the matrix,a certain proportion of alkali activator was replaced by encapsulation and mold pressing,and the setting time was delayed.In order to explore the performance of the two retarding methods at different substitution ratios and sizes,and find a test group with better comprehensive performance,this paper is mainly divided into two parts:macro performance test and micro analysis test.The specific research is as follows:The different substitution proportion and size of alkali activator Na₂Si O₃powder were taken as the design parameters,and 11 groups were set.The specific variables were as follows:0%,20%and 40%of the substitution proportion variables;Capsule shell size（according to content）:0.5g,1.0g,1.5g in total,tablet size（according to diameter）:6mm,12mm in total two kinds.In addition,282 prisms（40mm×40mm×160mm）,36 cube specimens（40mm×40mm×40mm）and 33 cylinder specimens（100mm in diameter and 50mm in height）were prepared and poured to carry out macroscopic performance tests.According to the requirements of microcosmic test,2-4mm particles and 200 mesh fine powder samples were prepared.Research shows that:（1）Both of the two retarding methods are effective for delaying the setting time of Alkali-activated slag concrete.Using the two treatment methods,the initial setting time of the material can be controlled from 56-196min and the final setting time from 115-319min.It is found through the test that the larger the proportion of substitution,the longer the initial and final setting time and the longer the interval difference,and the interval difference of 40%group is too long,which does not meet the requirements of use.Through the flow performance measurement,it is found that the fluidity of each group in the test is between 180-215mm,and all have good fluidity.（2）The flexural strength and compressive strength of each test group at different ages were analyzed by linear fitting.It is concluded that the mechanical properties of the materials can be reduced by the two retarding methods,and the reduction is more obvious in the early stage.However,compared with the effect of other existing retarders on the mechanical properties of Alkali-activated excited cementification materials,the material strength of this method can be fully developed in the later stage,and the adverse effect on the mechanical properties of materials is less.（3）Through the durability test（dry shrinkage,carbonation resistance,Cl^-penetration resistance,self-repair performance of the net slurry）,it is found that both methods have a certain internal curing performance,and the diffusion method of the tablet compression determines its better effect;The negative effect of capsule is greater than its self-repair because of its weakened more.The compactness of the internal structure of the specimen directly determines the durability of the specimen,and the changes of each performance are generally similar.（4）Through the microscopic analysis method（ultra-deep field three-dime nsional microscope,SEM,EDS,FTIR）,combined with the macro performanc e test data comparative analysis and research,from the experimental group sa mple morphology,micro-area element content,hydration product changes and other perspectives were analyzed.The results show that the method of tablet c ompression and retarding has the best long-term performance,the matrix is m ore dense and the gel product is more uniform.In this paper,the comprehensive performance of each test group was evaluated comprehensively through macro and micro comparative analysis on the basis of experimental exploration,and the function flow and principle of the physical retarder method were reasonably explained.From the perspective of engineering application,the analysis shows that the large-size tablet pressing group（12mm in diameter,height 3mm）has the best comprehensive performance under the 20%replacement ratio.