Textural and microstructural influences on the durability of Waikato Coal Measures mudrocks

Abstract

Data on durability, petrography and microstructure are presented for 27 specimens of Waikato Coal Measures mudrocks: fine-grained, carbonaceous rocks, which are dominated by kaolinite clays, and have low durabilities. The poor durability is not caused by swelling clays. Rather, slaking is believed to result from the release of residual stresses within the rock following weakening by water adsorption on to clay surfaces and a consequent loss in cohesiveness. This mechanism favours fragmentation into small, water-stable fragments, rather than dispersion of clays into the water. The amount of day-sized material in the rocks provides the most direct control on the durability, but mierostructural features are also recognized as important: specimens with a discontinuous matrix have a slightly lower durability than those with a continuous matrix.

Assessing the Behavior of Clay-Bearing Rocks Using Static and Dynamic Slaking Indices

“…Previous studies by Moon and Beattie (1995), Erguler (2007), and Erguler and Ulusay (2009) also showed that rock materials break into fragments of varying sizes during the second cycle of the dynamic slake durability test, and that the fragments are much larger than the mesh of the drum. The large fragments that are retained in the drum are therefore classified as durable materials.…”

“…Although many rock types disintegrate following two cycles, they can still have high slake durability index values. Slaking behavior of various types of clay-bearing rocks under wettingdrying processes was studied by several researchers using the dynamic slake durability test (Moon and Beattie 1995;Gokceoglu 1997;Koncagul and Santi 1999;Gokceoglu et al 2000;Sadisun et al 2005;Fuenkajorn 2011;Sebastian Brysona et al 2012). …”

“…Although the dynamic slake durability test, recommended by ASTM and ISRM, indicates the susceptibility of a clay-bearing rock to slake and disintegrate, this test do not provide a reliable quantitative measure. Several studies have increased the number of slaking cycles (Taylor 1988; Moon and Beattie 1995;Gokceoglu ). An important limitation of the test is that the mesh is the same size (2 mm) in all of the drums used to evaluate the disintegration behavior.…”

Durability Assessment of Clay-Bearing Soft Rocks By Using New Decay Index

“…Moon and Beattie [7], Erguler [24], and Erguler and Ulusay [13] also showed that rock materials break into fragments of varying sizes during the second cycle of the slake durability test, and that the fragments are much larger than the mesh of the drum (2 mm). The large fragments that are retained in the drum are therefore classified as durable materials.…”

“…A major focus was on determining the applicability of the slake durability test. The slake durability test is used widely for evaluation of slaking behavior of rocks as a result of wettingdrying processes [7][8][9][10][11][12][13]. However, due to mechanical breaks occurring during the test, immersion of samples in water for only 10 min and the assumption that fragments larger than 2 mm are durable, the slake durability test has some limitations [14].…”