Influence of polycarboxylate superplasticiser and polyacrylamide on the mirror effect of fair-faced concrete.

Fair-faced concrete (FFC) with a mirror effect was successfully prepared. The grey value standard deviation, porosity, crack rate and glossiness of the concrete surface were used to characterise the apparent quality of the FFC. The effect of polycarboxylate superplasticiser (PSP) and polyacrylamide (PAM) viscosity-modifying admixture on the mirror effect of the FFC was investigated. Changes in the hydration products and microstructure of the FFC were monitored by means of X-ray diffraction, thermogravimetric analysis, scanning electron microscopy and mercury intrusion porosity, and the potential mechanism was analysed. The results indicate that PAM reduced the number and size of calcium hydroxide (Ca(OH)2) crystals and changed the morphology of these crystals from a large-size parallel stacking state to a small-size edge eroded structure. PAM also refined the pore size of the concrete; the most probable pore size at the optimum dosage level was 13.73 nm, which was much lower than that at other PAM dosage levels. The use of PSP introduced air, which had an adverse effect on the concrete surface. However, PSP can also improve the flowability of concrete and make it easier for bubbles to discharge. The combined action of PSP and PAM provided a better mirror effect for the FFC. [ABSTRACT FROM AUTHOR]