Investigation of Physical and Chemical Clogging Phenomena in Underdrain Stormwater Systems Utilizing Geotextiles

在美国和世界各地，拆除材料和建筑垃圾的产量一直在逐步增加，尽管用于处理的土地越来越有限，而且越来越昂贵。因此，使用回收的未装订材料已变得广泛。近年来，在土木工程应用中，从回收破碎混凝土生产的骨料（称为再生混凝土骨料- RCA）的使用大幅增加，以降低生产成本，施工时间，并从事可持续实践。随着使用量的增加，人们对RCA的物理、机械和环境特性进行了广泛的研究，以支持其在各种岩土工程应用中用作回填或结构填料的适用性。尽管以前的研究，从RCA渗滤液中沉淀钙质物质（特别是方解石的沉积）的潜力尚未得到很好的理解。不了解这种行为可能会导致基于不正确的使用，不适当的设计或不必要的限制的意想不到的后果，特别是在排水雨水系统中。例如，当雨水系统采用天然土壤/集料设计时，它们主要是针对土工布过滤器的物理堵塞进行评估。然而，对于RCA，仅仅评估物理堵塞是不够的，因为这种现象是基于细颗粒的迁移，并不能描述从RCA中析出方解石的潜力。本研究的主要目的是调查和了解在类似于地下排水系统的条件下，RCA土工布介质中导致方解石沉淀和晶体生长的化学现象。这是一项为期一年的探索性实验研究计划，旨在检查现有方解石沉淀率模型的适用性，以及自然水域中方解石晶体生长动力学理论模型。目的是量化和预测方解石降水发生在RCA。将尝试回答以下问题：(1)方解石晶体在土工布上的沉淀；(2)利用机制PWP模型逼近RCA中方解石沉淀动力学；(3)量化物理堵塞现象与化学堵塞现象的区别；(4)根据化学和物理堵塞现象的耦合作用来确定土工布的使用能力下降程度。这项探索性研究的结果也将确定复杂性，可能需要进一步、更长时间和更深入的调查，以进行后续研究计划。这项研究的结果将在以下方面产生革命性的知识：(1)理解化学现象；(2)区分与RCA一起建造的土工布对地下排水系统的物理和化学堵塞。

The production of demolition material and construction waste has been increasing at a gradual pace in the United States and around the world, although the land for disposal is becoming limited and more expensive. Consequently, the use of recycled unbound material has become widespread. In recent years, there has been substantial increase in the use of aggregate produced from recycling crushed concrete (referred as recycled concrete aggregate - RCA) in civil engineering applications to reduce production costs, construction time, and engage in sustainable practices. With increased usage, the physical, mechanical, and environmental properties of RCA have been widely investigated to support its suitability for using it as backfill or structural fill in variety of geotechnical applications. Despite previous research, the potential of precipitating calcareous material (in particular, deposition of calcite) from RCA leachate is not well understood. Not understanding this behavior may lead to unintended consequences based on incorrect use, inappropriate design, or unnecessary limitations especially in underdrain stormwater systems. For example, when stormwater systems are designed with natural soils/aggregates, they are primarily evaluated against the physical clogging of the geotextile filter. However with RCA, evaluating the physical clogging alone is not sufficient as this phenomenon is based on migration of fine particles and does not describe the potential of precipitating calcite from RCA. The main objective of this research is to investigate and understand the chemical phenomena leading to calcite precipitation and crystal growth within geotextile media from RCA under conditions similar to underdrain stormwater systems. This is a one-year exploratory experimental research program to examine the suitability of existing calcite precipitation rate models, and theoretical calcite crystal growth kinetics models in natural waters. The objective is to quantify and predict the calcite precipitation occurrence in RCA. An attempt will be made to answer questions regarding (1) precipitation of calcite crystals over geotextile; (2) approximation of the kinetics of calcite precipitation from RCA using the mechanistic PWP model; (3) quantifying the difference between physical and chemical clogging phenomena; and (4) defining the degree in reduction in serviceability of geotextile based on coupling the effects of both chemical and physical clogging phenomena. The findings from this exploratory research will also identify the complexities that may require further, longer, and more in-depth investigation for a follow-up research program. The outcome of this research will yield transformative knowledge in terms of (1) understanding the chemical phenomenon and (2) differentiating between physical and chemical clogging of underdrain stormwater systems with geotextiles constructed alongside RCA.