Effects of Test Duration and Specimen Length on Diffusion Testing of Unconfined Specimens

Abstract

Abstract Effective diffusion coefficients, D*, of chloride and zinc diffusing in saturated, unconfined specimens of a compacted sandclay mixture are measured for three specimen lengths, L (2.91, 5.83, and 11.60 cm) and three test durations (7, 14, and 21 days). For a specimen length of 2.91 cm, both the chloride and zinc D* values tend to decrease with increasing test duration, possibly due to the measurement of concentration-dependent D* values. For a 14-day test duration, no consistent trend in D* with specimen length is observed, but the overall effect of specimen length on D* is minor relative to the range of measured D* values. A 21-day test duration provides the best correlation between the D* values based on reservoir concentrations, D*Res, and the D* values based on soil concentrations, D*Soil, for chloride for a given test regardless of the specimen length. The effect of test duration on the correlation between D*Res and D*Soil for zinc is minor based on the relatively narrow range of measured zinc D* values. The observed effects of specimen length on the correlation between D*Res and D*Soil for a given test are consistent with the more uniform final porosity distributions in the shorter specimens and the contrasting effects of the non-linear distributions in porosity and dry density that become less significant as the specimen length increases.