快速法检测湖南湘江砂、卵石集料碱活性

Identification of Alkali Reactivity of Sands and Gravels from Xiangjiang River in Hunan Province by Accelerating Tests

采用岩相法、快速砂浆棒法和压蒸法综合评价了湘江湘阴段、望城段、湘潭段砂和卵石的碱活性.结果表明:砂均由石英、长石、云母和杂砂岩碎屑等组成,卵石均由质量分数各约50%的硅质石英岩和杂砂岩组成,砂、卵石中的杂砂岩均含有一定量的隐晶石英和微晶石英,三河段砂之间及卵石之间矿物组成无明显差异;三河段砂在快速砂浆棒法中均呈现出碱活性,但在压蒸法中其膨胀率与样品制备方式有关;三河段卵石在快速砂浆棒法和压蒸法中的膨胀率均大于碱活性限值,具有碱活性;三河段砂、卵石碱活性来源于所含杂砂岩中的隐晶石英和微晶石英;制备能代表砂、卵石组成的样品是岩相法和压蒸法准确判定其碱活性的关键.

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 con- stituents 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 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.