Bit shape geometric considerations when sampling by dry drilling for obtaining chloride profiles in concrete

When obtaining dust concrete samples by dry drilling to determine chloride content profiles, the common conical shape of the bit tip induces some prob lems for assigning the analyzed Cl- content of each sample to a fixed depth from surface, (which is necessary for applying Cl- transport models): the amount of concrete removed is not the same throughout the length of a singl e drilling step, and concrete coming from depths lower than the nominal dri lling step is also obtained. It is proposed that each Cl- concentration in the profile should be assigned to the gravity centre of the solid sample re ally removed in each drilling step, instead of assigning it to the centre o f the nominal drilling step. A simple method for calculating the gravity ce ntre of each sample obtained by dry drilling, has been developed. The calcu lated values of Cl- diffusion coefficients from a Cl- content profile may b e appreciably lower ii the centres of gravity of the samples, instead of th e centres of the nominal drilling steps, are used for the calculations.