| Alkali activated slag(AAS)is an inorganic cementitious material obtained by activating blast furnace slag with alkali metal compounds.It can prepare early-strength,high-strength concrete,and has excellent chemical resistance and high frost resistance.Alkali slag concrete mixture has the characteristics of high viscosity and difficult plastering in engineering application,and the water reducing agent suitable for cement concrete is difficult to effectively plasticize in this system,which restricts the application of alkali activated slag concrete.Therefore,the development and research of efficient plasticization technology of the alkali slag system can provide theoretical support for solving the above problems.In this paper,two different second liquid phases(one-component K,two-component emulsion KN)are used to modify the surface of slag powder,and the state of the slag-activator interface changes to achieve the purpose of system plasticization.This article mainly studies the changes of slag surface state after surface modification of slag by the second liquid phase,the second liquid,the water reducing agent and the synergistic effect of the two on the plasticization performance of AAS,the influence of the second liquid relative to the hydration of AAS.The main result revealed by the study include:The contact angle between the modified composite slag particles and water increases;the pre-wetting of the second liquid phase makes the slag dispersed in the water glass solution,reducing the coating of free water and reducing the specific surface area of the particles;after modification,the adsorption capacity of naphthalene(NF),melamine(F10)and polycarboxylic(P)increases;surface modification will make the zeta potential of the slag in the water glass turn from negative to positive,and the zeta potential after adding water reducer is negative and the absolute value is large.The two second liquid phases can slightly increase the fluidity of AAS slurry and significantly reduce the viscosity and yield stress.The preferred content of K and KN,is1% and 0.4% respectively;the three kinds of water reducing agents increase AAS slurry fluidity: naphthalene(NF)> melamine(F10)> polycarboxylate(P).Both NF and P can effectively reduce the viscosity and yield stress of AAS,but F10 even has a negative effect on the rheology of the system;the synergistic effect of naphthalene and the second liquid can obtain large AAS slurry fluidity and high water reduction rate.The synergistic effect of polycarboxylate and the second liquid can significantly reduce the viscosity and yield stress of the system;the second liquid phase and YP-3 have a good synergy effect.Both K and KN have a slight retarding on AAS,and the coagulation time of the system is increased after compounding with NF;The 7d compressive strength of the hardened body after surface modification is reduced,but it has little effect on the 28 d compressive strength,and has almost no effect on the 180 d compressive/flexural strength of the mortar;the second liquid phase has no effect on the hydration process of AAS slurry(the effect on hydration is related to age),and the incorporation of polycarboxylic acid delayed the second exothermic peak.The delayed effect of the second exothermic peak decreased when the second liquid phase cooperated with P.Compared with the control group,the 3d hydration exothermic heat release of plasticized AAS slurry increased.The loose hydrated calcium silicate gel(C-S-H)is observed in the hydration products of K-AAS.KN had no significant effect on the microstructure of AAS hardened body.After P compound doping,the AAS system appeared ’ lamellar ’ and ’ honeycomb mesh ’ C-S-H. |
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