Properties Of Delay Released Welan Gum And Its Influence On Hydration Behaviour Of Cement Clinker Phases

Welan gum is one kind of microbial exopolysaccharide with well rheology and efficient anti-bleeding and thickening properties.But the competitive adsorption between welan gum and other superplasticizers like polycarboxylate superplasticizer（PCE）happened remarkably while adding at the same time due to its long side-chain existence and powerful charge density in molecular structure.A new kind of welan gum product named delay released welan gum（DRWG）invented by the research team has better compatible with PCE compared with welan gum,but its effect mechanism on cement hydration process hasn’t been clear yet.This paper is focused on the effect of DRWG on cement hydration products deformation like ettringite,Ca（OH）₂,C-S-H gel.They are investigated by ion concentration changes,zeta potential and admixtures adsorption measurement in three system that C₃A-CaSO₄system,C₃S-H₂O system and C₂S-H₂O system with DRWG or both DRWG and PCE adding.The results show that DRWG improves cement slurry performance and promotes mortar mechanical property due to its better rheological behavior.Besides,delay-releasing working mechanism of DRWG improved above competitive adsorption problem effectively.From the research results of DRWG or both DRWG and PCE in C₃A-CaSO₄system,membrane material of DRWG is dissolved first,and the delay released welan gum is excluded by preferential adsorption of PCE on the surface of C₃A,so the competitive adsorption between welan gum and PCE is improved.In the terms of acceleration C₃A hydration,on the one hand the DRWG has a certain crystal nucleus,on the other hand the gel-like etrringite is dispersed by PCE,and welan gum existing in cement pore solution dissolve and develop net-like structure permitting like SO₄^2-pass and react persistently,so the amout of ettringite is increasing.Due to preferential dissolution of coating membrane and effect of crystal nucleus of DRWG,the preferential adsorption of PCE lead to Ca（OH）₂ and C-S-H better dispersing,thus prompting C₃S or C₂S dissolution rate and C-S-H amount increasing.Besides,the ions of Ca²⁺and OH^-easily pass the net-like space structure induced by welan gum,thus Ca（OH）₂ obtains better growth and uniform distribution.