含碱集料对碱–硅酸反应的影响

EFFECT OF ALKALI-BEARING AGGREGATES ON ALKALI-SILICA REACTION

采用80℃蒸汽养护快速实验方法,研究了2种不同类型含碱集料——霞石正长岩和白岗岩对碱–硅酸反应的影响,并通过在150℃不同的碱溶液中压蒸集料的方法,对含碱集料的析碱机理进行了分析。结果表明:霞石正长岩和白岗岩对碱–硅酸反应膨胀的影响与使用水泥的碱含量有关。在使用低碱水泥时,霞石正长岩和白岗岩使碱–硅酸反应膨胀显著增大,而在使用高碱水泥时,霞石正长岩和白岗岩对碱–硅酸反应膨胀促进作用均减弱;在饱和Ca(OH)2溶液中的霞石矿物能稳定存在,随着碱含量的增加,霞石矿物发生分解,而长石矿物均能稳定存在,与碱溶液的反应仅在长石矿物表面区域进行。长石矿物与混凝土孔溶液中Ca2+之间的离子交换反应是混凝土中长石矿物析碱的主要原因。

The effect of two kinds of alkali-bearing aggregates, nepheline syenite and alaskite on alkali-silica reaction（ASR） were studied using a new accelated test method, by which specimens were cured in steam at 80 ℃. Additionally, through curing specimens in different alkalion solutions at 150 ℃, the mechanism of alkali releasing from alkali-bearing aggregate was analyzed. The results show that the effect of nepheline syenite on ASR is remarkably influenced by the change of alkali content in cement, ASR expansion can be enhanced by nepheline syenite and alaskite in mortar using low alkali cement, while it is reduced in mortar using high alkali cement due to the decrease of alkali release of nepheline syenite and alaskite; Nepheline mineral is stable in saturation Ca（OH）2 solution, but decomposes with the alkali content increasing in saturation Ca（OH）2 solution. Feldspar minerals are stable in alkaline solution, only little dissolution can be found in the crystal interface. It is concluded that alkali releases from feldspar minerals in concrete mainly depend on ion change between surface layer of minerals and Ca^2＋ ion in solution.