Properties comparison of mortars with welan gum or cellulose ether

Welan gum is a type of microbial polysaccharide by fermentation, that could be used as thickener in cement and concrete because of its performance of thicken and anti-bleeding. At present, the most popular thicker in cement and concrete is cellulose ether, especially hydroxy-propyl-methyl cellulose HPMC. This paper reports the different properties between mortars with welan gum or HPMC, as well as standing bleeding rate, mortar fluidity, compressive and adhesive strengths, microstructure by ESEM, rheological properties and electric properties by zeta potential. It was shown that, both welan gum and HPMC are good thickener; however, welan gum has a clear benefit at higher W/C ratios as much less additive is needed. Both welan gum and HPMC meet adhesion requirements, but welan gum has negligible effect on compressive strength, whereas addition of HPMC results in a very substantial decrease of compressive strength. At high shear rates, mortar with welan gum has better stability than that with HPMC. In water, welan gum forms a three-dimensional threaded network whereas HPMC forms a foil. Under shear conditions, the HPMC foil breaks up beyond recovery, while the welan gum network instead crumples up and unfolds again when shear is removed. In addition, welan gum adsorbs better than HPMC, has greater influence on the zeta potential of cement clinker and changed its electric properties. (C) 2015 Elsevier Ltd. All rights reserved.