Effect Of Carboxymethyl Starch On The Rheological/Solidification Properties Of Slag-based Geopolymer And Its Application

In order to adjust the rheological performance and controllability of the geopolymer slurry,carboxymethyl starch?CMS?was selected as a rheological modifier for geopolymer,the effect of CMS on the rheological properties and the later hardened properties were studied,furthermore,the application of CMS in geopolymer extrusion-molding and geopolymer based coating were also evaluated.The primary experimental conclusions are listed as follow:?1?CMS is compatible with geopolymer,and can effectively improve the thixotropy,yield stress,plastic viscosity and structural-recovery ability of the slurry.The zeta potential results indicate that CMS was presenting in the continuous alkaline liquid phase,which affected the fixed and chemical reaction state of slag particles resulted from steric hindrance effect.DSC results show that the maximum heat flow decreased from 0.068?V/mg to 0.049?V/mg and peak temperature decreased from 83.6?to 70.3?after 1.5 g CMS composition,indicating that CMS retarded geopolymerization.ATR-FTIR results show that when the CMS dosage increased from 0 g to 1.50 g,the Si-O-T?Si or Al?absorption band shifted from 963 cm^-1to 978 cm^-1after 65 minutes reaction,indicating that CMS reduced the gel production of geopolymer slurry.?2?CMS could extend the setting time of geopolymer,decrease the drying shrinkage and improve crack resistance,while CMS did not affect the 28 d mechanical properties.CMS enlarged the pore size distribution of geopolymer and generated more capillary pores.FTIR and XRD results show that CMS did not change the functional groups and amorphous structure of geopolymer,therefore it could be suppose that CMS did not participate in the geopolymerization reaction,but did affect the reaction rate and degree of the geopolymer by the water retention and thickening effect of CMS.?3?CMS could be applied to prepare a geopolymer based plastic coating,when 15.40 wt%CMS was composited,the plastic viscosity,yield stress and thixotropy of the prepared coating could reach 9.075 Pa·s?92.643 Pa and153547 Pa·s^-1respectively,making the coating possessed good construction properties.The compressive strength,flexural strength and bonding strength of geopolymer coating could reach 55.09 MPa,8.06 MPa and 2.11 MPa respectively,which gave the coating with excellent mechanical properties and satisfied with the Chinese Building Coating Standard GB/T9779-2005.SEM shows that the homogenous microstructure was formed in the CMS/geopolymer composition structure,and therefore it improved the stability of volume,the shrinkage was reduced to 605??which imparted the coating with excellent crack resistance ability.In summary,the experiment concluded that CMS could be used as a high-efficiency water-retaining thickener for alkali-activated geopolymer,implying that combining renewable polymer materials with geopolymers showed promising potential in research.