Predicting long term durability of upper red formation sandstones against freeze - thaw and salt weathering action using decay function model

Rocks subjected to cyclic weathering processes such as freeze – thaw and salt crystallization may lose their integrity and be deteriorated during time. By increasing in cycle numbers and their intensity, the rate of deterioration will be increased; however, this rate is not the same for different rocks. In this study long term durability of upper red formation sandstones against freeze – thaw and salt crystallization were evaluated using decay function model. By using this model it is possible to obtain some meaningful parameters and determine deterioration characteristics of rocks. For this purpose, 9 specimens of sandstones (specified by A, B, C, CG, S, S1, Tr, Min and Sh) were collected from different parts of the studied area, then their physical and mechanical characteristics including unit weight, effective porosity, water absorption, P-wave velocity, Brazilian tensile strength and point load strength were determined. In order to assess the effect of freeze – thaw and salt crystallization on physical and mechanical characteristics of sandstones, 60 cycles of freeze-thaw test and 20 cycles of salt crystallization test were performed. Then their effects on tensile strength and point load strength were recorded in different cycles. Also, decay constant and half – life of these parameters were calculated. In addition, slake durability index test was performed in three different cases such as standard (wet state), freeze – thaw (performing test on samples subjected to freeze – thaw action) and salt crystallization (performing test on samples subjected to salt crystallization action). Obtained slake durability index from different cases were used to estimate decay constant and half-life parameters. Bye using these parameters (tensile strength, point load strength and slake durability index test) and applying decay function model, long term durability of sandstones against freeze – thaw and salt crystallization were evaluated. Results show that decay constant and half – life can be used in engineering practice for determining long term durability without consuming more cost and time. Also this model indicates that the disintegration rate of sandstones is different and the half-lives obtained from three parameters are different for each sandstone.