Application of the Sharp Front Model to capillary absorption in a vuggy limestone

The unusual pore size distribution and in particular the presence of large pores in certain construction materials, results in an anomalous sorptivity and a marked deviation from the standard t1/2 law. In this paper, we report the results of water and ethanol uptake tests carried out in order to investigate the imbibition behaviour of a vuggy limestone. The experimental data confirm that capillary absorption into a natural building stone with bimodal pore size distribution does not obey simple t1/2 kinetics. Sharp Front (SF) analysis is therefore used to model the liquid transport properties of this material as a linear combination of absorption into the coarse pores and into the finer matrix pores. The results of the analysis indicate that the overall capillary absorption into a vuggy limestone may be described reasonably well as the sum of two processes: a capillary absorption into the large pores with the low capillary suction, which does not follow the classical t1/2 behaviour; and a slow capillary absorption into the fine pores which obeys the standard t1/2 law. We also note that water matrix sorptivity is almost 50% lower than expected for a simple complete-wetting capillary scaling. This is an example of a water sorptivity anomaly in natural building stones which is attributed to incomplete wetting.