Effect Of Waste Ceramic On Strength And Shrinkage Properties Of Alkali Activated Slag

Alkali activated slag（AAS）cement shows fast strength development and excellent mechnical properties,while the high risk of large shrinkage and high cost hinder the industrial application of AAS.Applying waste ceramic powder as a raw material for preparing alkali-activated cement,the strength and shrinkage of blended AAS was studied.Combined with the microstructure characterization,the volume stability and strength change of waste ceramic powder-AAS systems were further investigated under dry-wet cycles.To explore the feasibility of using waste ceramic powder as new raw materials,this study investigated the effects of its blending amount on the early reaction,compressive strength of hardened products,shrinkage and microstructure properties.Results show that the incorporation of ceramic powder can delay the setting time of paste due to its lower reactivity than slag.Alkali activated 100%ceramic powder cannot set and harden at room temperature as normal cement does.The compressive strengths of mortars with 10～50%ceramic powder develop slowly before 28 d,but increase progressively and become comparable to alkali activated 100%slag at 90 d.However,strength decreases significantly when more than 50%ceramic powder is used.As expected,blending ceramic powder can effectively reduce autogenous shrinkage but will increase drying shrinkage of AAS,while blending a small amount（less than20%）has little negatively effect on drying shrinkage though.Given the comprehensive properties of the tested pastes and mortars,waste ceramic powder can be regarded as valuable raw materials.In-depth studies on the development characteristics of compressive strength and volume stability of waste ceramic powder-AAS mortars were conductedunder dry-wet cycles(particularly containing SO₄^2-and Cl^-),to provide valuable application guidancein hydraulic and marine environment.This study investigates the influence of tap water and seawater dry-wet cycles on compressive strength,pore structure,capillary water absorption coefficient and phase composition of waste ceramic powder-AAS.The highest compressive strength is found in the AAS with 20%waste ceramic powder and even higher than that of the reference slag mortar,but more than 20%ceramic powder has negative effect.In dry-wet cycles with seawater,The compressive strength of AAS increased and then decreased with the number of cycles.In standard curing and dry-wet cycles with tap water,waste ceramic powder improves the capillary water absorption coefficient of AAS mortar.In dry-wet cycles with seawater,blending with 20%waste ceramic powder reduce the capillary water absorption coefficient of AAS mortars,but more than 20%ceramic powder has negative effect.Results show that introducing a small amount of waste ceramic powder is beneficial to the performance stability of AAS under marine environment.To further improve the stability of AAS at dry-wet cycles,hydrophobic agents with different molecular structures were added to waste ceramic powder-AAS systems,andits modification influence was studied.It is found that the adding of hydrophobic agent lowers the early age-compressive strength of waste ceramic powder-AASand its compressive strengths decrease with the increase of waste ceramic powder content.After adding hydrophobic agent,the pore structure of waste ceramic powder-AAS becomes larger in a specific range,while the waterproof effect is better.Hydrophobic agent does not participate in the hydration reaction of AAS.Under standard curing and dry-wet cycles with tap water,the stearates hydrophobic agent exhibits better resistance to dry-wet cycles.In the seawater dry-wet cycles,however,silane hydrophobic agent shows better effect.