Effect Of Internal Curing On Properties Of Alkali Activated Mortar

As a basic building material,concrete has greatly promoted the development of the construction industry,and will still be in short supply for a long time in the future.But Portland cement industry energy consumption is high,pollution gas emission is large.Alkali activated slag(AAS)cementitious material has fast setting,high strength,high durability and can reduce about 80%CO2 emissions,which is a promising substitute for Portland cement.But the huge autogenous shrinkage limits its application.In this paper,SAP and saturated water perforated cenospheres were used as internal curing agents,and the main goal was to effectively eliminate the autogenous shrinkage of alkali activated slag mortar.The effects of the two internal curing methods of AAS on setting time,compressive strength,autogenous shrinkage and durability were respectively studied.The results show that:(1)The SAP internal curing significantly inhibited the autogenous shrinkage of AAS mortar.When the SAP content was 0.2%,the autogenous shrinkage was completely eliminated,and micro-expansion appeared when the content continued to increasing.The initial setting time of AAS paste was prolonged with the increase of SAP content.When the content of SAP was ≥ 0.1%,the initial setting time was maintained at 90-95min,which was about 30min more than that of the control group.SAP had no obvious effect on the final setting time.SAP internal curing has a negative impact on mortar strength.The more SAP content,the lower the strength,and the maximum loss of compressive strength was about 60%.SAP curing increases the porosity of mortar and decreases the compactness of mortar,but XRD analysis showed that it promoted hydration to a certain extent.(2)The internal curing of perforated cenospheres can effectively inhibit the development of AAS mortar’s autogenous shrinkage,and can completely eliminate it,which is related to the concentration of activator.In the low concentration of activator stimulated AAS,the setting time was prolonged by perforated cenospheres curing,and the retarding effect of the initial setting time was better than that of the final setting time.When the concentration of activator increased,the retarding effect disappeared.The compressive strength of AAS mortar decreases with the increase of the concentration of the activator.For example,compared with 4%alkali-equivalent mortar,the maximum strength reduction range was 36%for 10%alkali-equivalent mortar.The increase of perforated cenospheres content was not good for the early strength of AAS mortar,but could improve the later strength of AAS mortar.The internal curing of perforated cenospheres introduced micro pores,which has a negative effect on the durability of mortar.(3)SAP internal curing can effectively control the autogenous shrinkage of alkali activated slag mortar,but it has a negative effect on the mechanical properties and durability of AAS mortar.Considering that 0.2%content was the best content,the research results have certain reference value for engineering practical application.The internal curing of perforated cenospheres could effectively control the autogenous shrinkage of mortar,and it was not conducive to the early strength development of mortar,but it has no obvious adverse effect on the mechanical properties of mortar in the later stage.The negative effect on AAS mortar was far less than that of internal curing in SAP.The results showed that the perforated cenospheres was an excellent internal curing carrier,which was helpful to promote the practical application of AAS cementing materials.Figure[20]table[4]reference[79]...