研究接触时间对再生混凝土骨料浸出液化学性质的影响。
Assessing the impact of contact time on leachate chemistry from recycled concrete aggregates
- 通过改进的批量实验法，监测24小时内浸出液pH、碱度和钙离子变化。
- 初始接触时pH >10，随时间下降；钙离子浓度先快后缓上升，最终趋于饱和。
- 发现碱度在初期剧增后稳定在50-65 mg CaCO3/L，为环境风险评估提供依据。
再生混凝土骨料（RCA）被视为一种可再生利用、力学性能足够的建筑与拆除废弃物，可作为道路基层中天然骨料的替代品。但其应用需关注文献报道的高碱性、高pH浸出液及重金属渗漏风险。现有研究未解决现场与实验室测量结果间的差异，也缺乏对老化RCA浸出液成分随时间变化的研究。本研究采用改进的批量测试方法，分析明尼苏达州公路研究项目现场回收的RCA基层样品，监测24小时内的浸出液pH、碱度及钙离子（Ca2+）浓度，以了解初始接触阶段的浸出液化学特性。结果显示，初始接触时浸出液pH >10，随时间逐渐降低，因与大气二氧化碳反应；钙离子浓度在初始阶段迅速上升，随后缓慢增长直至钙饱和；碱度在初期显著增加后趋于稳定，维持在50–65 mg CaCO3/L之间。
原文摘要 · Abstract (English)
Recycled concrete aggregate (RCA) is recognized as a readily available, mechanically sufficient construction and demolition waste product that is suitable as a base course substitute for natural, virgin aggregate in pavement construction. Environmentally responsible applications of RCA must consider the high alkalinity, high pH leachate, and heavy metal leaching risks reported in the literature. The existing body of literature does not address discrepancies between field and laboratory measurements of RCA leachate pH, nor are there any existing studies of aged RCA leachate composition as a function of time. To consider the influence of contact time on RCA leachate, the present study evaluates recovered RCA base course samples from the Minnesota Road Research highway construction study site using modified batch test methodology. Leachate pH, alkalinity, and calcium ion (Ca2+) concentration were monitored for 24 hours to understand RCA leachate chemistry during the initial contact period. Leachate pH is high upon initial contact with water (pH > 10) and decreases over time as it reacts with atmospheric carbon dioxide. Calcium ion concentration increases rapidly in the initial contact period, then more gradually as calcium saturation is reached. Alkalinity stabilizes (50-65 mg CaCO3/L) after a dramatic increase during the initial contact period.
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