Influence of polycarboxylate superplasticizer and polyacrylamide on mirror effect of fair-faced concrete

This work successfully prepared fair-faced concrete with mirror effect. The gray value standard deviation, porosity, crack rate and glossiness of the concrete surface were used to characterize the apparent quality of fair-faced concrete. The effect of polycarboxylate superplasticizer and polyacrylamide viscosity-modifying admixture on mirror effect of fair-faced concrete was investigated. The changes of hydration products and microstructure of fair-faced concrete were monitored by the measurements of X-ray diffraction (XRD), thermogravimetric analysis (TG), scanning electron microscopy (SEM) and mercury intrusion porosity (MIP), and the potential mechanism was analyzed. The results indicate that the polyacrylamide reduces the number and size of Ca(OH)2 and change the morphology of Ca(OH)2 crystals from large-size parallel stacking state to small-size edge corrosion structure. The polyacrylamide can refine the pore size of concrete, the most probable pore size at the optimum dosage is 13.73 nm, which is much lower than that at other dosages. The usage of the polycarboxylate superplasticizer will introduce air, which has adverse effect on the concrete surface. But polycarboxylate superplasticizer can also improve the flowability of concrete and make bubbles easy to discharge. The combined action of polycarboxylate superplasticizer and polyacrylamide contributes the fair-faced concrete for better mirror effect.