白鹤滩水电站地下洞室混凝土浇筑方量巨大,骨料采用玄武岩细骨料+玄武岩粗骨料的组合方案。为保证白鹤滩水电站地下洞室混凝土的耐久性,2017年11月至2021年8月的白鹤滩水电站主体工程施工期间,按季度连续对玄武岩骨料进行取样、跟踪分析,采用多种试验方法综合评价了其潜在碱活性。试验结果表明:白鹤滩水电站施工期玄武岩骨料中含有杏仁玄武岩、角砾熔岩等多种岩石,部分岩石中存有少量微晶-隐晶石英等活性矿物成分;SEM及EDS微观分析表明,含活性成分玄武岩骨料仅在高温和高碱的条件下才会产生危害性膨胀的碱-骨料反应;使用碱含量<0.60%的低热42.5硅酸盐水泥且掺入≥20%粉煤灰作掺合料的条件下,玄武岩骨料用于地下洞室混凝土工程不会产生危害性的碱-骨料反应。

The underground cavern of Baihetan Hydropower Station requires a significant amount of concrete, with a combination of basalt artificial sand and basalt coarse aggregate being adopted for the concrete aggregates. To ensure the durability of the concrete in the underground cavern, the alkali reactivity of the basalt aggregate was monitored quarterly from November 2017 to August 2021 during the construction of the Baihetan Hydropower Station. Various test methods, including the petrographic method, mortar bar rapid method, and concrete prism method, were employed to evaluate the potential alkali reactivity. The experimental findings revealed the presence of other minerals such as amygdaloidal basalt and breccia lava in the basalt aggregates. Additionally, a small amount of active minerals like microcrystalline and cryptocrystalline quartz was identified. SEM and EDS results indicated that these active minerals would only induce harmful alkali aggregate reactions under high temperature and high alkali conditions. Utilizing low-heat Portland cement with an alkali content of less than 0.60% and incorporating a minimum of 20% fly ash in the concrete mixture effectively mitigated the risk of harmful alkali aggregate reactions associated with basalt aggregate.