| TECHNICAL |
(Below): Sprinkling fine material with a sieve. (Below): Paver silhouettes were visible on the base course after the removal of the pavers.
The first in a series of experiments on how the use of geotextiles affects clogging in permeable interlocking concrete paving (PICP) installations was run by the Civil Engineering Department of the University of Cape Town (UCT) during May/June. Supervised by Prof Neil Armitage and civil engineering Master’s student Motlatsi Monyake, the day-to-day execution of the research work was conducted by fourth-year civil engineering student Josh Blackshaw, with additional input from Monyake. “The primary goal of this and the research to come is to provide South African PICP users and designers with solid recommendations on PICP design based on empirical evidence, rather than what we think the answers are,” said Armitage. Worthwhile experiment “We were feeling our way with this initial experiment and, as could be anticipated, the results were by no means conclusive. Although we didn’t achieve our chief objective, namely to get one or more of the research cells clog completely, the experiment certainly proved worthwhile. If nothing else, it provided a stepping-stone for further research. “But it did more. For example, it revealed that no matter how good the
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PRECAST | ISSUE THREE | 2021
UCT CONDUCTS EXPERIMENT ON GEOTEXTILE CLOGGING IN PICP infiltration properties of geotextiles, they do cause some loss of infiltration capacity. Moreover, the choice of geotextile seems to make very little difference to the rate of clogging.” The laboratory testing involved four cells (A-D) which mimicked live PICP installations. Each cell comprised the following: a 200mm sub-base layer of 1925mm aggregate; a 50mm base course of 9mm aggregate; a 50mm bedding layer of 2-6mm aggregate, and grit stone of 2-3mm for insertion between the pavers. Cell A was devoid of a geotextile layer, while cells B, C and D had different geotextiles installed between the base course and the bedding layer. These were: Fibretex F25 (heatsealed/treated) – cell B; Kaytech Bidim A1 (needle-punched/non-woven geotextile) – cell C, and Kaytech Kaytape S120 (woven geotextile) – cell D.
Careful assessment “We chose the Fibretex F25 because it’s similar to Inbitex, which forms part of the Aquapave standard PICP package. Everyone in SA knows Bidim, so it was an obvious choice. For cell D, we wanted a geotextile with large openings, which was why we opted for Kaytape. “All the cells followed the same drop-off curve and there was no discernible difference in behaviour between the geotextile and nongeotextile cell. By the end of the experiment, inf iltration rates had declined on the following basis: cell A by 83,6% from 12 861 to 2 106mm/hr; cell B by 94,5% from 11 523 to 637mm/hr; cell C by 84,7% from 10 363 to 1 590mm/hr, and cell D by 91,7% from 10 670 to 889mm/hr.” (See Tables 1 and 2.) Using a sieve, loadings of fine material (pollutant) recovered from Blue Route Mall and previous PICP laboratory experiments
