Study On Inhibition Mechanisms Of Mineral Admixture On Alkali-Aggregate Reaction

In view of the shortage of commonly used concrete admixtures such as fly ash and slag,and environmental pollution caused by industrial waste such as ceramic polishing powder,etc,the effects of the addition of ceramic polishing powder,fly ash and slag powder on the inhibition of alkali-aggregate reaction expansion and mechanical properties of cement-based specimens were studied.The microstructure of the interfacial transition zone between the aggregate and cementitious material and the distribution of elements such as Ca,Na,K,Si and Al on the interface region were calculated and analyzed by SEM and EDS.The inhibiting mechanism of alkali-aggregate reaction by admixtures was investigated,and the common law of mineral admixture inhibiting alkali-aggregate reaction was explored.This study has theoretical and applied significance for the development of new admixtures.The results show that:?1?The ceramic polishing slag,fly ash and slag have significant inhibitory effects on alkali-aggregate reaction,and the inhibitory effects of polishing slag and fly ash is more obvious.In general,the more the amount of mineral admixture is added,the lower the expansion rate of alkali-aggregate reaction.?2?A certain amount of polishing slag,fly ash and slag powder can improve the compressive strength and flexural strength of the material.However,the early strength of the high admixture decreased obviously.The optimum content of the ceramic polishing powder is 20%³0%and the content of fly ash and slag is about30%to inhibit the expansion of alkali-aggregate reaction effectively and achieve the requirements of strength as well.?3?The addition of mineral admixture can reduce the content of Ca?OH?₂ in the interfacial transition zone of aggregates and cementitious materials,decrease the porosity,reduce the width of the interfacial transition zone,and improve the microstructure of the interface.The width of the interfacial transition zone of the base sample without mineral admixture is about 80?m⁹0?m,the interfacial widths of the samples of ceramic polishing powder,fly ash and slag powder are about 48?m⁵7?m,38?m⁵2?m and 40?m⁶2?m,respectively.?4?The distribution rule of the interfacial transition zone between the aggregate and the cementitious material is as follows:The further away from the aggregate surface,the content of Si decreases,the content of Na and Ca increases,Ca/Si and Na/Si increase,and K and Al accumulate in the near aggregate area.In the interface areas without admixture,the Ca and Na are enriched in the interface area,but the distribution of K and Al is more uniform.?5?The inhibition mechanism of alkali-aggregate reaction by the admixtures:on the one hand,the content of Na⁺in the near-aggregate region is reduced by the introduction of admixtures.The decrease of Ca/Si in the interfacial transition zone reduces the alkalinity of the aggregate surface and reduces the possibility of high Na/Si swelling products in the near-aggregate region;On the other hand,K⁺and Al³⁺are enriched in the near aggregate to form non-expansive shelf-like crystal,which is another reason why the mineral admixture inhibits the expansion of alkali-aggregate reaction.Due to the existence of active Al₂O₃ in the system,the effect of K⁺on alkali-aggregate reaction may be lower than that of Na⁺.