Study On The Control Of Shrinkage And Efflorescence Of Alkali Activated Slag Cementitious Material And Its Mechanism

The alkali activated slag cementitious material is a new kind of green cementitious material,which has the advantages of fast hardening,early strength and chemical corrosion resistance.However,the engineering application of alkali activated slag cementitious material is greatly limited due to high drying shrinkage,vulnerable cracking.and efflorescence.In this study,a variety of measures are used to control the shrinkage and efflorescence of the water glass activated slag cementitious material.For the shrinkage of alkali activated slag cementing material,the influence of aggregate to binder ratio,supplementary cementitious material,admixture,super absorbent polymers and fiber on shrinkage and cracking was studied.The results show:?1?With the increase of aggregate to binder ratio from 0 to 2,the linear shrinkage of alkali activated slag mortar decreased obviously,and the cracking degree of the specimen was significantly improved.The mortar strength decreased when the ratio of aggregate to binder exceeded 1,so the appropriate ratio was 1:1.?2?Portland clinker,aluminate cement and sulphoaluminate cement are used as supplementary cementitious materials,and replaced the slag by 2%,4%,6%and 8%,results showed that adding Portland cement clinker to alkali activated slag mortar has obvious effect to shrinkage,and less shrinkage emerged as content increased while aluminate cement and sulphoaluminate cement had no positive but negative effect on shrinkage of alkali activated slag.?3?The plastic expansive agent and super absorbent polymer used as admixture reduced the linear shrinkage ratio of alkali activated slag mortar and reduce the number of surface cracks.And the former had no obvious effect on strength while the latter reduced compressive strength.?4?The addition of fiber can not only improved the crack resistance of the mortar,but also reduced the linear shrinkage,in which the improvement effect of basalt fiber and PVA fiber were better,and carbon fiber is ineffective.The addition of fiber has a positive effect on the improvement of bending strength.For the efflorescence of alkali activated slag,the inhibition effect of aluminate cement and redispersible rubber powder is explored.The results show:?1?Three types of aluminate cement substitute slag powder,respectively,when the CA-50 content is8%,CA-70 content is 6%,CA-80 content is 4%,the mortar showed the best effect of reducing efflorescence,and the chemical composition of the binder is Ca/Si=1.05¹.1,Si/Al=3.0³.15;?2?Three kinds of redispersible powder is blended,respectively,the redispersible powder 5044N is 1%,and the redispersible powder cellulose?30011C?content is 0.05%,redispersible rubber powder?8034H?in the content is 2%when the alkali-activated slag cementing material shows the slightest efflorescence.?3?The components of the effflorescence are mainly Na₂CO₃ and a small amount of CaCO₃.