QSI Methods for Determining the Quality of the Surface Finish of Concrete

The surface finish of a concrete element may become an index of its quality, relating the external and internal porosity with the mechanical and durability properties. Few methods are used to determine the surface quality of concrete elements. Mention must be made the Quality Surface Index (QSI) proposes a simplified method to quantify the surface occupied by the pores in relation with the total surface inspected, analyzing groups of pores by their diameter. The method of the CIB W29 (Commission W29 “Concrete Surface Finishings”) proposes an inspection of the concrete element and its visual comparison with some standard templates. Finally, the digital processing of images allows the zones with surface defects to be delimited and quantified according to premises of quality introduced into the control software. These three methods are employed in this work and are applied in three concrete walls situated three meters from the observer (M-1, M-2 and M-3). Following the conversion of the results of the method with ImageJ and QSI, the results suppose differences that go from 0.1 tenths (2%) for M-3 up to 0.3 tenths (8%) for M-1. All values are within the obtained range with CIB W29 templates. This can validate the QSI and digital processing methods and allows a quick verification of the results. With the digital method, it is obtained that 23.5% of the total pores of M-1 have a diameter of less than 10 mm2 and 44% of less than 100 mm2. For M-2 and M-3 the proportions of pores with a dimension below 10 mm2 is of 43.1% and 27.7%, respectively, and that 77.5% and 60.7% are smaller than 100 mm2. From all the above it can be highlighted that M-1 is the one with the lowest amount of pores, however the proportion of the largest is greater than for M-2 and M-3. In the case of M-3, although it has a lower proportion of larger pores than M-1, its greater amount means it is the worst in terms of surface finish of the three.