A study was carried out, using heat flow calorimetry, XRD, FTIR and SEM imaging analysis, of different influences which were exerted by the type of polymer, on the hydration behaviors of cement pastes. It is shown that both styrene-butadiene rubber latex (SBR latex) and hydroxypropylmethyl cellulose (HPMC) can cut down the cement hydration heat evolution rate and total heat between 5 h and 20 h. The former has a weaker influence but can play a positive role in enhancing the latter. XRD and FTIR analysis show that SBR latex and HPMC have played a negative role on the contents of Ca(OH)₂ in cement pastes cured for 24 h, and there is a relationship of mutual promotion between SBR latex and HPMC in terms of inhibiting the formation and growth of Ca(OH)₂, but this inhibiting effect becomes weaker at 72 h. HPMC has the superior inhibiting effect owing to its special OH groups compared to SBR latex.

It was reported that the influence of polymer on the cement hydration depends on interactions between polymer particles with cement grains or cement hydrates [19], [20]. The interactions include physical and chemical effects. For the SBR, SBR particles rapidly dissolve in the solution, then absorb onto the cement grains, and finally form dense polymer film [20]. This film can prevent calcium ions and other ions entering and dissolving from the surface of cement grains. This film effect will inhibit the formation of cement hydrates. Similar to the effect of polymer-film, HPMC can improve the viscosity of pore solution [16]. Sticky solution is bound to weaken the mobility of ions, which must prevent the formation of cement hydrates.

In addition this result of the reduction of the quantity of effective ions, lots of researches have shown that the hydrogen bonding and chemical complexation form between OH-groups of polysaccharides and metal-hydroxylated species exist on the mineral surfaces [21], [22], [23], [24]. Any kind of chemical combination with calcium ions will yield the reduction of its concentration, which leads to the inhibition of some hydration products.

So it can be concluded that mechanism, though, is different for the influence of SBR and HPMC on cement, the interactions between SBR or HPMC particles and cement indirectly reflect in the cement hydration retardation. Because of this, synergistic or accumulative retardation effect exists between SBR and HPMC on cement hydration at early age. However, OH-groups in the molecular structure of HPMC (see from Fig) enables HPMC has stronger effect compared to SBR, which only rely on physical adsorption and film effect.

Molecular structure of HPMC.

Link: https://www.sciencedirect.com/science/article/pii/S2214509516300468