Identification of alkali reactivity of sands and gravels from Xiangjiang river in Hunan province by accelerating tests

Petrography analysis, accelerating mortar-bar test(AMBT) and autoclave method were used for examining the alkali reactivity of sands and gravels from three regions along Xiangjiang river, that is, Xiangyin, Wangcheng and Xiangtan. Results show that: there are no obvious differences in mineral constituents among the sand samples as well as among the gravel samples. The sands are composed of quartz, feldspar, mica particles and greywacke fragments. The gravels are composed of about 50% (by mass) of both quartzite and greywacke. A fair amount of cryptocrystalline and microcrystalline quartz are noticed in the greywacke in both sands and gravels. The gravels are alkali reactive shown in both AMBT and autoclave method. The sands are reactive in AMBT, while in autoclave method the expansion is linked with the way of sampling methods. The alkali reactivity of both sand and gravel is attributed to the cryptocrystalline and microcrystalline quartz in greywacke in them. Preparation of representative samples of sands and gravels is the key for both petrography analysis and autoclave tests for reliable identification of alkali reactivity.