Study On The Carbonation Performance Of Alkali-activated Slag

Alkali-activated slag（AAS）,as one of an alternative materials for OPC binder,has been found to have lower hydration heat,quicker development of mechanical properties and better compact structure than OPC.After several decades of development and many applications,alkali activated cementitious materials have achieved certain results.But the alkali activated slag itself has some shortcomings,such as large drying shrinkage,poor carbonization resistance and so on.At the same time,the research process is lack of unified standard,so a large amount of research is still needed.In this paper,aiming at the serious carbonization problem of alkali activated slag material,the research mainly focuses on the influence of pretreatment temperature on the carbonization property of alkali activated slag material,on the effects of alkali on AAS carbonation propertiesthe alkali and on the measures to improve AAS carbonization performance.The effect of alkali activator type and alkali content on the carbonization performance of alkali activated slag was studied.The results show that NaOH as the alkali activator on the carbonization depth of alkali activated is greater than that of alkali activated by sodium silicate.The higher the alkali content,the smaller the carbonization depth of alkali activated slag.To improve the carbonization performance of alkali activated slag,Ca（OH）₂powder was added to improve the solid alkaline content.Sodium silicate as activator on the carbonation resistance effect of alkali activated slag containing Ca（OH）₂ powder is better than that of NaOH as activator.The experiment shows that its compressive strength and flexural strength are high,and the carbonization depth is small.Alkali activated slag mortar mixed with 20%Ca（OH）₂ powder activated by sodium silicate has the lowest carbonation depth when carbonized 28d,and 10%Ca（OH）₂ powder alkali activated slag mortar take second place.The compressive and flexural strength of slag mortar after carbonization with Ca（OH）₂ powder by sodium silicate was greater than that of NaOH as activator.However,the compressive strength of alkali activated slag mortar mixed with 10%Ca（OH）₂ powder is greater than that of alkali activated slag mortar mixed with 20%Ca OH)₂ powder.Therefore,alkali activated slag cement with10%Ca（OH）₂ powder activated by sodium silicate possess better mechanical properties and carbonization resistance.The study of the pretreatment temperature on the carbonization performance of alkali activated slag shows that the higher the pretreatment temperature,the faster the drying rate of the alkali activated slag material,the longer the duration of the drying stage,and the shorter the duration of the drying stage.The flexural and compressive strength of the alkali activated slag specimen increases with the increase of the pretreated temperature.With carbonization,the compressive and flexural strength decrease and fluctuate,and the carbonated tends to be stable at 28d.The flexural strength of the pretreatment temperature at 40℃and 60℃,respectively,decreased first and then increased,and the carbonization age of the wave valleys was different,which were carbonated 14d and 7d,respectively.The increase of pretreatment temperature accelerated the deterioration of alkali activated slag mortar’s flexural strength.The carbonization depth of alkali activated slag increases with the increase of pretreatment temperature,and the alkali activated slag material with pre treatment temperature at40℃begins to accelerate degradation after carbonization at 28d,and the alkali activated slag material with the pretreatment temperature of 60℃has accelerated deterioration when carbonized at 14d.In order to reduce the influence of pretreatment temperature on the carbonation depth,a lower pretreatment temperature should be used to study the carbonization of the slag.