Study On The Effect Of Stone Powder On The Properties Of Alkali-activated Slag System

Cement is the most widely used building raw material in the world.The production of cement consumes large amounts of energy and minerals,and meanwhile causes lots of CO₂ emissions.Alkali-activated material is a green cementitious material with hydraulicity generated by the reaction of silicon-aluminum industrial waste with an alkali activator.It has great economic and environmental benefits and may have the potential to displace cement as a new building raw material.Meanwhile,the waste stone powder from the stone industry is randomly stacked,leading to serious environmental pollution.Now,stone powder is used as cement replacement to prepare green building materials,but the application of stone powder in alkali-activated materials is rare.In this paper,the effect of stone powder on the properties of alkali-activated materials was studied.In this paper,quartz powder,limestone powder,dolomite powder,and magnesite powder were mixed with the alkali-activated slag system.Firstly,the physical and chemical properties of the raw material were characterized.The influence of stone powder on the reaction process and products of alkali-activated slag system were studied via isothermal calorimetry,XRD,thermogravimetric analysis and FTIR.Then,the influence of stone powder on the rheological properties of alkali-activated slag paste was studied via rheometer,optical microscope,and Zeta potential.In addition,the interface properties between stone powder and alkali-activated slag paste was investigated using scanning electron microscopy（SEM）.Meanwhile,the effects of stone powder on the pore structure and mechanical properties of alkali-activated slag paste were investigated using a mercury porosimeter and universal testing machine respectively.Finally,the effect of stone powder on drying shrinkage and mass loss of alkali-activated slag paste was studied.Based on the above research,the results are as follows:（1）Limestone powder and dolomite powder have the largest particle size,slag is the smallest,quartz powder and magnesite powder are in the middle.Meanwhile,magnesite powder has the largest specific surface area.The four stone powders have irregular shapes,and there are laminated lamellar structures on the surface of magnesite powder.The sequence of surface zeta potential of raw material particles is as follows: limestone powder > dolomite powder > quartz powder > slag > magnesite powder.（2）The incorporation of stone powder reduces the reaction extent of alkali-activated slag system.Except for the reference group,limestone powder and dolomite powder have slight reactivity,promoting the growth of reaction products.Thus,the heat flow and cumulative heat release of the alkali-activated slag paste are relatively high.The reactivity of quartz powder and magnesite powder is weak.Furthermore,their particle size is small,so the amount of slag replacement per unit volume is large.Therefore,the heat flow and cumulative heat release of the alkali-activated slag paste are relatively low.The incorporation of stone powder does not change the types of reaction products in the alkali-activated slag system.（3）As the stone powder content increases,the rheological properties of alkali-activated slag pastes mixed with limestone powder,dolomite powder,and quartz powder gradually improve,but the rheological properties of alkali-activated slag paste mixed with magnesite powder gradually deteriorate.The potential of limestone powder and dolomite powder is higher than slag,leading to a high electrostatic repulsive force with slag.Moreover,both of them have larger particle sizes.These result in spatial steric hindrance,lubrication,and "ball bearing effect",and thus significantly improve the rheological properties of alkali-activated slag paste.The potential of quartz powder is slightly larger than slag,and its particle size is slightly larger than slag,so there is a certain improvement in the rheological properties of alkali-activated slag paste.The specific surface area of magnesite powder is the largest,which increases water absorption,and its potential is lower than slag,resulting in weak rheological properties of the paste.（4）High stone powder content leads to a dilution effect,and as the stone powder content increases,the compressive strength of the paste gradually decreases.Limestone powder and dolomite powder have slight reactivity,so there is strong adhesion between their surface and alkali-activated slag paste.Moreover,their particle size is big,and a low amount of slag replacement per unit volume leads to a large number of reaction products,which results in a slight increase of capillary pores compared to the reference group.Thus,the compressive strength of alkali-activated slag paste decreases slightly.The reactivity of quartz powder and magnesite powder is weak.The adhesion between their surface and the paste is also weak.Furthermore,they have small particle size,and a large amount of slag replacement per unit volume causes a low number of reaction products,which leads to a significant increase of capillary pores compared to the reference group.Therefore,the compressive strength of alkaliactivated slag paste decreases significantly.（5）As the stone powder content increases,the proportion of capillary pores in the paste increases,and the outflow of free water accelerates,so the mass loss and drying shrinkage of the alkali-activated slag paste gradually increases.Except for the reference group,the expansion of dolomite powder in the alkali-activated slag paste offsets partial drying shrinkage,and thus the drying shrinkage and mass loss of the alkali-activated slag paste with dolomite powder are minimal.The drying shrinkage and mass loss of alkali-activated slag paste mixed with quartz powder and limestone powder are in the middle.However,magnesite powder makes the proportion of capillary pores in the paste increase significantly and thus the drying shrinkage and mass loss of alkali-activated slag paste are maximum.There is a positive correlation between drying shrinkage and mass loss.As the mass loss increases,the drying shrinkage gradually increases.