Correlation graphs for N24 block and N28 block are slightly different. This shows that
correlation is necessary to improve cover measurement accuracy and correlation should be
carried out for rebars with different sizes.
Cover measurement is often influenced by neighbouring bars (i.e. parallel bars that are close
to the one being measured). In this study, the bar spacing was 100mm. Since cover
measurement accuracy will increase if bar spacing increases, this study does not include other
bigger bar spacing (i.e. 150mm or 200mm).
Bar spacing also affects the maximum measurable cover depth. The maximum measurable
cover depth decreases when the bar spacing decreases. In this study, the bar spacing was
100mm with bar diameters of either 24mm or 28mm, the maximum measurable cover depth
was about 85 ~ 90mm which is deeper than the data provided by the manufacturer in the
owner’s manual
[3]
.
Bar spacing and bar diameter could affect the correlation graphs. Covermeters from different
manufactures could also cause certain variation. Correlation for particular project (particular
bar spacing and bar diameters) and the covermeter to be used can greatly improve cover
measurement accuracy. Correlation is recommended if greater cover measurement accuracy
is required, i.e. a structure subject to aggressive environment and concrete durability is the
major concern.