Investigation of the possibility of estimating concrete strength by porosity measurements

The possibility of estimating concrete or mortar strength by measuring the total water porosity by a very simple method is investigated. Cube strengths of mortar and concrete specimens are correlated with water porosity measured from ‘intact’ pieces taken from the failure cones of the crushed cubes. It is shown that it is not possible to acquire a satisfactory correlation of strength and the measured total water porosity of the mortar or concrete mix. However, a very promising correlation (correlation coefficient R>93%) is obtained if the ‘calculated average paste porosity’ P _p is substituted for the measured total water porosity of the mix P _m . P _p can be determined from the measured porosity P _m of the mix, the porosity of the aggregates and the volumetric proportions of the constituents. For the range of strengths investigated, it can be inferred that the strength class of a cement (OPC 35 or OPC 45) does not significantly influence the correlation, but a slightly different correlation seems to exist for pozzolanic cements.