Rheological properties of grouts with viscosity modifying agents as diutan gum and welan gum incorporating pulverised fly ash

Abstract

This investigation was undertaken to evaluate the influence of the dosage of the second generation of viscosity modifying agent (diutan gum) on fluidity and rheological parameters of cement-based materials grout compared to welan gum. All grouts were made with 0.40 water-to-binder ratio (W/B). The fresh properties of control grouts made without any viscosity modifying agent (VMA) and with superplasticizer (SP) were compared to those of grouts made with 0.02, 0.04, 0.06 and 0.08% diutan gum by mass of binder. Similar mixes made with welan gum were compared to those containing diutan gums. The effect of admixtures on fluidity and rheological parameters are discussed in this paper. The effect of the replacement of cement by pulverised fly ash (PFA) was also investigated. Grouts with replacements of PFA of 5, 13 and 20% by mass were used with the same W/B. Similar control grouts and mixes incorporated different dosages of PFA made with welan gum were made in order to compare the fluidity and the rheological parameters to the previous grouts made with diutan gum. The results show that the increase of the dosage of diutan gum and welan gum for a given dosage of SP increases significantly the yield value, the apparent and plastic viscosity and reduces the fluidity. With an increase in dosage of SP, the apparent viscosity at low shear rate decreases dramatically than that at high rate of shear rate due to the pseudo-plastic rheology of the grouts containing VMA. Both VMAs exhibited high apparent viscosity values at low shear rates which were attributed to the entanglement and intertwining of VMA polymer chains at low shear rate and association of water between adjacent chains. For a given dosage of VMA, diutan gum showed a high apparent viscosity than welan which could be attributed to the molecular weight and to the long-side chain of diutan gum leading to greater entanglement and intertwining. For any given dosage of SP, the diutan gum exhibited higher yield value and plastic viscosity than welan gum. Diutan gum grouts demonstrate a greater yield value and apparent and plastic viscosity than welan gum for control and PFA grouts. The replacement of cement by PFA resulted in a reduction of yield value and an increase in plastic viscosity.