The Role of Polycarboxylic Acid Superplasticizer in Concrete

During the last few decades, researchers have been trying to broaden sources of polycarboxylic acid superplasticizers and enhance their dispersing capability. These admixtures are not only effective in the reduction of water consumption but also have good retarding effects on cement hydration and are excellent candidates for high-performance concrete applications.

In this study, the rheological properties of Fubelite sulfoaluminate cement mixed with different functional admixtures were studied using Viskomat XL rheometer (Schleibinger). The results showed that the addition of polycarboxylic acid superplasticizers significantly improved the rheology of the concrete; compared to the blank sample, sample 2 containing early-strength functional polycarboxylic acid high-performance water-reducing agent Z shows much higher fluidity and lower plastic viscosity. Furthermore, the shear stress of the samples gradually decreases with increasing the dosage of water-reducing admixture, which reflects the effective retarding effect of this admixture on the cement hydration reaction.

The retarding impact of the polycarboxylic acid water-reducing agent is due to its molecular structure, which consists of ether and carboxyl groups that adsorb on the surface of the cement particles. These functions prevent the hydration of water molecules by shielding the cement molecules, and thus the hydration process is substantially delayed2.

The steric hindrance of the polycarboxylic acid high-performance adducts can also play an important role in this case, since the long side chains of these admixtures protrude into the pore solution and produce a strong steric hindrance effect. In comparison, naphthalene-based water-reducing agents only contain sulfonic acid groups with shorter side chains and weaker steric hindrance effect, which cannot retard the hydration of water as well.