Influence of the HLB value of polycarboxylate superplasticizers on the flow behavior of mortar and concrete

• PCEs can instigate fast or slow speed of flow to concrete.
• This effect is observed only at w/c ratio < 0.4.
• The speed of flow is dependent on PCE composition.
• Only PCEs exhibiting high HLB value provide fast flow.
• HLB value describes hydrophilic–lipophilic balance in macromolecule.

Applicators of mortars and concretes admixed with polycarboxylate superplasticizers routinely observe that at low water-to-cement (w/c) ratios (e.g. < 0.40), the mortar or concrete can attain a sticky, viscous consistency and honey-like, creeping flow behavior which is highly undesirable for pumping, placement and compaction of such concrete. Only a few special polycarboxylate superplasticizers can provide concretes which flow rapidly (a water-like flow behavior). To investigate the reason behind this rheological behavior, slump cone, flow line and funnel tests were conducted. It was found that the hydrophilic–lipophilic balance (HLB) value of a polycarboxylate copolymer determines whether a PCE will instigate a water-like flow behavior in a concrete. The higher the HLB value, the more hydrophilic is the molecule and the stronger the flow speed enhancing effect. From the PCEs tested, the APEG-types produced the best water-like flow behavior, followed by IPEG- and MPEG-type PCEs.