Assessing the Degree of Polish on Hardened Concrete Air Void Parameters

Abstract

This study provides much needed insight regarding how the degree of polish on a concrete sample affects the hardened air void parameters. As required by ASTM C457, each hardened concrete sample assessed by any of its three procedures needs to be polished until light reflects off of the surface. However, there is currently little to no insight as to how various degrees of polish will affect the concrete air void parameters. This research aims to fill the gap in the literature by providing a step-by-step procedure, materials necessary, and most importantly, the effect of the degree of polish on the hardened air void system parameters. Four target air void percentages (control at 2%, low at 3 – 5%, medium at 5 – 7%, and high at >8%) were investigated. Two different polishing mediums (silicon carbide and diamond) were investigated at six different polishing pad grit sizes. The results show that the most economical and preferred polishing method uses diamond polish pads. The results also indicate that the first polishing step is crucial in producing a suitable surface for further analysis, which requires using the coarsest polishing medium. Therefore, the results indicate that any further polishing (at finer degrees of polish) is negligible in obtaining the hardened air void parameters following ASTM C457 procedures. The average percent difference across each polish pad grit size investigates was 3.8%. This value amounted to an average hardened air void difference of only 0.1 across all samples. Comparing the average hardened air void percentage across all polish pad grit sizes to the ASTM C231 fresh air percentage reveals an average difference of 6.7%, which constituded a difference of 0.3. Therefore, the results show non-statistically significant variations between any of the degrees of polish investigated, especially between the coarsest polishing medium and the finest polishing medium, which produces the reflective surface as stipulated in ASTM C457.