Abbaspour Aiyoub, Tanyu Burak F, Cetin Bora
Department of Civil, Environmental and Infrastructure Engineering, George Mason University, Fairfax, VA, 22030, USA.
Department of Civil, Construction and Environmental Engineering, Iowa State University, Ames, IA, 50011, USA.
Environ Sci Pollut Res Int. 2016 Oct;23(20):20835-20852. doi: 10.1007/s11356-016-7217-9. Epub 2016 Aug 1.
The focus of this study was to evaluate the effects of stockpiling (aging) on leaching of elements in recycled concrete aggregate (RCA) that may contribute to tufaceous constituent formation. Speciation and leaching controlling mechanisms of these elements were identified via geochemical modeling. The effects of stockpiling were simulated by comparing freshly produced RCA with RCA aged as part of this study for 1 year both in the laboratory and in the field. Leachate samples were generated following batch water leach test (WLT) and US Geological Survey leach test (USGSLT) methods. USGSLTs were conducted both on the laboratory and field samples while WLT was only conducted on laboratory samples. During the laboratory aging, it is observed that the carbonate content of RCA, measured as calcite equivalent, increased 20 % (i.e., from ∼100 to 120 mg/g) within a year time frame. The leachate extracted from RCA showed minor changes in pH and more significant decreases in electrical conductivity (i.e., ∼300 to 100 μS/cm). A comparison between laboratory and field samples revealed that the RCA aged much slower in the field than in the laboratory within a year. Comparisons between two leach extraction methods on the laboratory conditions showed that the total leached concentrations (TLCs) of most of the constituents from USGSLT were appreciably lower than the ones measured via WLT method. The results of geochemical modeling analyses showed that Al, Si, Fe, Ca, Mg, and Cu exist in their oxidized forms as Al, Fe, Si, Ca, Mg, and Cu and results revealed that these elements are primarily controlled by the solubility of gibbsite, hematite, silica gel, calcite, magnesite, and tenorite solid phases, respectively. One of the significant findings of the study was to identify the changes in leaching behavior of Ca, Si, Mg, Al, Fe, and Cu due to carbonation.
本研究的重点是评估储存（老化）对再生混凝土骨料（RCA）中元素浸出的影响，这些元素可能有助于凝灰质成分的形成。通过地球化学建模确定了这些元素的形态和浸出控制机制。通过比较新生产的RCA与本研究中在实验室和现场老化1年的RCA来模拟储存的影响。按照批量水浸试验（WLT）和美国地质调查局浸出试验（USGSLT）方法采集浸出液样本。对实验室和现场样本都进行了USGSLT试验，而WLT仅在实验室样本上进行。在实验室老化过程中，观察到以方解石当量计的RCA碳酸盐含量在一年时间内增加了20%（即从约100毫克/克增加到120毫克/克）。从RCA中提取的浸出液pH值变化较小，电导率显著降低（即从约300微西门子/厘米降至100微西门子/厘米）。实验室样本与现场样本的比较表明，一年内RCA在现场的老化速度比在实验室慢得多。在实验室条件下对两种浸出提取方法的比较表明，USGSLT中大多数成分的总浸出浓度（TLCs）明显低于通过WLT方法测得的浓度。地球化学建模分析结果表明，铝、硅、铁、钙、镁和铜以其氧化形式存在，分别为Al、Fe、Si、Ca、Mg和Cu，结果表明这些元素分别主要受水铝石、赤铁矿、硅胶、方解石、菱镁矿和黑铜矿固相溶解度的控制。该研究的一项重要发现是确定了由于碳酸化导致的钙、硅、镁、铝、铁和铜浸出行为的变化。
