Effect of typical formworks and release agents on the aesthetical surface quality of concrete

This work investigated the formwork surface characteristics and concrete surface quality. The results showed, release agent types and formwork materials have a great impact on the wettability of formwork/concrete interface, although all the formwork surfaces with/without release agents are hydrophilic. Remarkably inhomogeneous roughness characteristic is only announced with steel formwork. Plywood and steel formworks have almost the same roughness values, however roughness profile of plywood is sharper than it of steel. Mineral oil always correlates to larger surface voids and higher surface void ratio (SVR) values. Steel formwork increases SVR significantly compared to the other two formworks. When SVR <1‰ and small voids (<500μm) >50%, the concrete surface seems to be bughole-free. Rusty stains left by steel formwork aggravates concrete discoloration degree, especially when water-soluble release agents were applied. To improve concrete surface quality, plywood formwork is more favorable despite release agents and vegetable oil based emulsion is more suitable for plastic formwork. The surface area roughness of concretes is mainly determined by it of formworks. The typical micro-groove feature on formwork surface leaves no trace on the formed concrete surface which might be due to the dimension difference between micro-grooves and cement particles and the presence of release agents.