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

George Mason University, Fairfax VA

Investigators

Abstract

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.