Surface features of frost damaged concrete: A study using multi-point micro displacement laser ranging method

Surface scaling caused by cyclic freezing and thawing (F-T) is one of the major damage patterns of concrete pavements or hydraulic structures in cold regions, and the damage will be more serious when deicing salts combined with F-T. The weight method has been employed almost exclusively to evaluate the surface scaling of concrete since the 1940s. A multi-point micro displacement laser ranging (MMD-LR) method was proposed to characterize the evolution of frost pits and surface roughness of concrete, quantitatively. The vertical displacement of measurement points on the scaling surface of concrete exposed to F-T cycles with 3 wt% NaCl solution was determined after every four F-T cycles using the MMD-LR method. The traditional weight method was also employed as a baseline to measure the mass of scaling substances. Results show that mean vertical displacement (Dn), surface roughness (Rn) and mass of scaling substances per unit area (wn) of concrete increase with increasing F-T cycles and w/c from 0.30 to 0.60. Relations of wn with Dn and Rn are regressed as power function and quadratic function, respectively, showing the removal order of scaling substances from cement pastes to fine aggregates. The frost pit on the test surface of higher w/c concrete tends to develop the depth with increasing F-T cycles, while it tends to expand the edge in lower w/c concrete. It is verified that the proposed MMD-LR method is credible for inspecting the surface damage of frost concrete, and providing a new perspective for studying the mechanism of concrete surface damage induced by F-T cycles.