Influence of surface roughness on concrete nanoindentation

While the application of nanoindentation technology has made great progress in cemented materials, the nanoindentation data show great discreteness. This study proposes an efficient procedure for concrete with coarse aggregate grinding and polishing to provide low surface roughness through a lot of polishing experiments. An integrated investigation, using SEM-EDS and nanoindentation, is performed to study the causes of the discrete nanoindentation data. Thousands of nanoindentation experiments show that surface roughness should be tested before indentation, and the indentation matrix should be within the tested area due to the significant variability of surface roughness. Both surface roughness and micropores in concrete cause indentation data discretisation. The influence of surface roughness which is carried out through quantitative study is the main cause. The mean of the maximum indentation depth of aggregates and cement paste both decrease with the surface roughness and tend to be stable. The influence of surface roughness can be negligible if the root-mean-squared (RMS) roughness of indentation area is less than 120 nm. The corresponding irregular load-depth curves in indentation results should be abandoned.