Aesthetic properties of concrete surfaces: An experimental study employing three typical formworks with emphasis on reusability

This study investigated the surface characteristics of three types of formworks (plastic, plywood, and steel) and the corresponding quality of the concrete surface after repeated use. The size and frequency of bugholes, the distribution of grey levels and their standard deviation, as well as surface roughness and contour profile of the concrete surfaces were quantitatively analyzed. The results indicated that the aesthetic quality of the concrete deteriorated with repeated use while the rate of deterioration varied depending on the formwork type employed. When plywood formwork was used 15 times, the concrete surface exhibited a noticeable adhesion phenomenon. The occurrence of both bugholes and color differences in plastic formwork remained consistently minimal throughout the tests compared to the other two types of formworks. In contrast, the steel formwork consistently displayed a higher number of bugholes, with a significant increase after 20 uses; however, no consistent trend in grey level differences was observed. The sequence of concrete surface roughness (Ra) mirrored that of the formwork surface roughness, arranged in the following order: plywood > steel > plastic. The differences in surface roughness among the concrete specimens were not as pronounced as those among the various types of formworks. The repeated use of each formwork type resulted in more pronounced fluctuations in the peaks and valleys of the roughness profile curves, along with an increase in the height differences between them. Formwork types and the number of reuse cycles appeared not to influence the fundamental pattern of the contour curves of the concrete.