Control of clogging in permeable concrete pavements

Abstract

This thesis aims to improve the understanding of clogging and the effects this has on permeable concrete, and to develop new permeable concretes that are more durable and resistant to clogging without the need for frequent maintenance. Permeable concrete, also known as pervious concrete, is used to reduce urban flooding as it allows water to flow through normally impermeable infrastructure. It is prone to clogging by particulate matter and predicting the long-term performance of permeable concrete is challenging as there is currently no reliable means of characterising clogging potential. New methods were developed to study clogging and define clogging potential. The tests involved applying flowing water containing sand and/or clay in cycles, and measuring the change in permeability. Three methods were used to define clogging potential based on measuring the initial permeability decay, half-life cycle and number of cycles to full clogging. We show for the first time strong linear correlations between these parameters for a wide range of samples, indicating their use for service-life prediction. The problem which leads to clogging in existing permeable concrete is the pore network that is highly tortuous, with variable cross-section and random interconnectivity. As a result, it is important to develop new permeable concretes that have uniform pore structures with tortuosity of 1. This thesis reports on the development of cementitious materials that can be poured on-site, or provided as pre-cast elements, forming a low tortuosity connected porosity microstructure so that surface water is effectively transferred from one side of the permeable pavement to the other, with minimal risk of clogging. High-strength clogging resistant permeable pavement (CRP) was prepared by introducing direct channels of varying size and number into self-compacting mortar. In all cases, permeability and compressive strength proved to be far higher than conventional permeable concrete. More significantly, not a single sample became clogged despite extensive cyclic exposure to flow containing sand and/or clay. We show for the first time a high strength clogging resistant permeable pavement capable of retaining sufficient porosity and permeability for storm-water infiltration throughout the service life while having a high compressive strength to utilise permeable pavement in heavy loading applications. This innovative system will help alleviate urban flooding and contribute towards a more sustainable urbanisation. In order for the new design to be considered a truly successful innovation it is necessary to examine means by which the work done in a laboratory setting can be utilised in a large-scale commercial setting. Several methods have been investigated. While each of these methods has benefits and limitations, collectively they constitute a valid range of possible approaches for potential in-situ and pre-cast delivery of CRPs on a large scale.