Practical application of the torrent permeability test method with the South African durability index approach

Alfred, Sean

Practical application of the torrent permeability test method with the South African durability index approach

Thesis / Dissertation

2025

Publisher

University of Cape Town

Department

Department of Civil Engineering

Faculty

Faculty of Engineering and the Built Environment

Abstract

Tests that assess the potential durability of concrete offer robust evaluation approaches for predicting its performance. The South African Durability Index Approach (SADIA) and the Torrent method are used in South Africa and Switzerland, respectively, to assess the potential concrete durability of the cover layer. Specifically, the Oxygen Permeability Index (OPI) test and the Torrent Permeability Test (TPT) are widely recognized as reliable techniques for evaluating the gas permeability of concrete. Studies have demonstrated the sensitivity of these methods to various factors that affect the properties of hardened concrete. Recent research has shown a strong correlation between the OPI and TPT methods in simulated environmental conditions. A combined approach using both methods has been suggested to improve existing practices for assessing concrete durability. However, the correlation has not been confirmed for site concrete elements, and practical guidelines have not yet been established. This research aimed to develop practical guidelines for an integrated durability assessment strategy involving the OPI and the TPT methods on in-situ concrete elements. Five mixes consisting of two water-to-cement (w/c) ratios (0.5 and 0.6), two concrete grades (30 MPa and 40 MPa), and three binder types (100% CEM I 52.5N, CEM II/A-L 52.5N, and 70/30 CEM I + fly ash) were used to manufacture precast freeway median barriers and representative test panels. The concrete elements' early-age (28 – 56 days) gas permeability characteristics were tested under various environmental exposure conditions (summer and winter) in Cape Town, South Africa. The OPI and TPT methods generally showed good sensitivity to the test variables (w/c ratio, binder type, age, and environmental exposure). There was a strong correlation between the two methods in the summer data but a weak association in the winter data. This difference was attributed to the pore-blocking effect of moisture on the Torrent test, emphasizing how surface moisture may affect the measured results even within permissible moisture levels. Nonetheless, the site correlation in the summer confirmed findings from previous studies. Given this study's findings, it was determined that a combined approach using the Torrent and OPI methods can be implemented based on site-specific conditions. The initial assessment of the structure can be conducted using the Torrent test and, if required, substantiated by the OPI test in moist conditions. It is recommended that moisture correction methods be used to adjust the measured Torrent results in very dry conditions using reference surface moisture values. However, to consolidate the proposed combined practical approach, the results of this research need to be validated through a more extensive study using larger sample sizes, a more comprehensive range of concretes, and varying environmental conditions.