Effect Of Superabsorbent Polymer Composites And Polypropylene Glycols On The Fresh And Hardened Properties Of Alkali-activated Slag

In recent years,researchers have found the alkali-activated slag（AAS）,which are commonly prepared by reacting potentially active raw materials（ground granulated blast-furnace slag,fly ash,calcined clays,etc.）with an alkaline activator,the use of alkali-activated slag instead of cement can effectively reduce CO₂ emissions.However,its large shrinkage and easy cracking have limited the wide application of alkali-activated concrete in engineering.In order to control the drying shrinkage of AAS concrete,The mechanism and feasibility of applying composite superabsorbent polymer composite（SAP）and polypropylene glycol（PPG）to alkali-activated slag is further explored.The results of this work provide important technical support for the engineering application of SAP composites and polypropylene glycols on alkali-activated concrete systems.The main research works as follows:（1）The novel poly（sodium-acrylate acrylamide）superabsorbent polymer composites modified by micro-Si O₂ and kaolin clay particles as the inorganic filling materials are designed and synthesized.The SAP characterization by using scanning electron microscopy,fourier transform infrared spectrometer analysis,thermal gravimetric analyzer,the gravimetric‘tea bag’method and so on,including the thermal stability,water preserving capability and swelling behavior.Based on the experimental results,the relationship between the microstructure and properties of the novel SAP composites and ordinary SAP is analyzed;（2）Compared with ordinary SAP,the effects of novel SAP composites（the addition of 0.25%and 0.5%）on the fresh and hardened properties of alkali-activated slag pastes are investigated,including workability,setting time,compressive strength,pore structure,drying shrinkage and mass loss.The research focuses on the microstructure of SAP,this opens the opportunities of tailoring the molecular and composition of SAP composites for properties control of alkali-activated concrete systems;（3）The effects of polypropylene glycols（the addition of 0.5%and 1%）with three molecular weights on the fresh and hardened properties of alkali-activated slag pastes are investigated,this is similar to the experimental method of SAP composites.Based on the mechanism of PPG in alkali-activated slag,the influence of different molecular weight on drying shrinkage reducing efficiency is studied,it is proved that relative humidity,surface tension,pore size distribution and miscibility are the key factors affecting the drying shrinkage.