Ageing behaviour of polyacrylamide-based excavation fluids

Abstract

2Solutions of synthetic polymers based on the chemistry of partially hydrolysed polyacrylamides (PHPAs) are increasingly being used as a replacement for the more conventional bentonite slurries in the construction of bored piles and diaphragm walls. On a construction site, these fluids may be in use for weeks to months and therefore their ageing behaviour is important. However, rather little has been published on the subject and the literature that is available is contradictory. To develop the understanding of ageing behaviour, a series of tests were undertaken on clean solutions of a commercial PHPA designed for civil engineering works. The tests showed that the PHPA fluids showed a gradual reduction in viscosity over the first days after mixing and that the rate of reduction was slightly dependent on the quality of the mix water. These findings are contrary to the rapid initial reduction in viscosity reported in some studies. An extended ageing test showed that the reduction in viscosity had effectively ceased at about 60 d from mixing with a significant proportion of the initial viscosity retained. These test results will allow foundation contractors to be more confident about the use of PHPA support fluids over extended times.

Design and Evaluation of a Polymer Support Fluid in a Soil–Rock Mixture

“…After the same aging for 30 days, the apparent viscosity of the polymer fluid decreased by 26.2% (1.05%/d) at three r/min, by 22.9% (0.92%/d) at six r/min, and by 15.6% (0.62%/d) at 100 r/min. These results showed that a higher spindle speed did not lead to extra shear degradation, consistent with the finding reported by Lam and Jefferis [ 27 ]. The gradual reduction in the apparent viscosity is presumably due to chain disentanglement caused by a conformational change in the polymer molecules [ 28 ].…”

“…The inconsistency between our results and others [ 15 , 18 , 19 , 20 ] may be due to the differences in sample preparation procedures, test methods, and material properties. After a prolonged aging time of up to 30 days, the remaining active viscosity of the polymer was at least 70%, consistent with the study carried out by Lam and Jefferis [ 27 ], who reported that 75% of the original viscosity remained after aging. This finding will promote the confidence of on-site construction workers to use polymer fluids.…”

“…The difference in material properties and clay content plays an essential role in affecting our results and theirs. One finding is that the effect of adding silty clay on the polymer fluid was a reduction in the apparent viscosity, which can be efficiently eliminated by strictly controlling the content of silty clay and replenishing new slurry in time [ 27 ].…”

Editorial

“…The last paper investigates the ageing behaviour of synthetic polymers, such as polyacrylamide-based polymers, as excavation fluids (Lam and Jefferis, 2016). These are increasingly being used as a replacement for the more conventional bentonite slurries in the construction of bored piles and diaphragm walls.…”