Browsing by Author "Venter, Cindy"
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- ItemAsphalt permeability and moisture damage(2019-04) Venter, Cindy; Jenkins, Kim Jonathan; Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering.ENGLISH ABSTRACT: For several years the design methods for a pavement surface have evolved. Starting with the very first bituminous road surface which was laid in Paris, France, in the eighteen-fifties. The main purpose of a surfacing layer is to protect the underlying layers from moisture ingress. These supporting layers can absorb the forces imposed by repeated traffic if the layers are kept moisture-free. Thus, the only layer preserving the supporting layers is the bituminous surface mixture. The research covered in this study analyses the permeability of asphalt surfacing specimens. The permeability of an asphalt surface is a measure of the amount of air, water and water vapour that penetrates the layer. Layers with adequately low permeability will promote long term durability of the surface and protect the underlying pavement layers from the ingress of water. This research study is focused on investigating ‘Asphalt Permeability and Moisture Damage’. As part of this research study, extensive laboratory experiments and testing were required to investigate the permeability of asphalt cores and how moisture ingress influences the inter-connected voids. To determine if the inter-connected voids increased after MIST (Moisture Inducing Simulating Test) conditioning, CT-scanning (Computed Tomography) images were used for further analysis. After initiating an extensive literature review and identifying factors which can influence the permeability of asphalt, an experimental research methodology was developed to achieve the primary and secondary objectives. Several asphalt cores were acquired from different sources all over South Africa, which was used for laboratory testing. This research methodology was executed at Stellenbosch University where all the results and conclusions related to this study were reported. The primary objective of this research study is to analyse the permeability of asphalt cores by means of the laboratory Marvil and High Pressure Permeability (HPP) tests; and through this to determine the influence of pressure and moisture on the permeability of asphalt cores. The secondary objectives of this research study are focused on the determination of the volumetric properties of various asphalt cores, and determining if a correlation exists between the: • Marvil and HPP; • Marvil and air void content; and • HPP and air void content. It was also necessary to develop asphalt permeability classification ranges for the Marvil and HPP under laboratory conditions. The primary choice for testing permeability of asphalt surfacing in South Africa is the Marvil permeability test. This test uses no external pressure and is only reliable on the water pressure inside the apparatus at atmospheric pressure, which is minimal. The Marvil apparatus was re-designed for laboratory use, and then used to test the permeability of various asphalt cores for this research study. A second permeability test was used in order to gain more insight into how pressure could affect the asphalt surfacing behaviour. The High Pressure Permeability (HPP) test was designed by Ockert Grobbelaar in 2016 in order to simulate the effect of normal speed traffic and its hydrostatic effect on surfacing layers (Grobbelaar, 2016). The asphalt cores were tested at three realistic pressure intervals based on previous research, namely 100, 150 and 200 kPa (Jenkins & Twagira, 2009). The HPP test was conducted before and after moisture damage was induced by the use of the Moisture Inducing Simulating Test (MIST), to analyse what the effect on the permeability of the asphalt cores would be. After completing the permeability and moisture damage testing, the Indirect Tensile Strength (ITS) test was performed on the cores to determine if MIST conditioning influences the tensile strength of an asphalt core. For these cores, it was concluded that MIST conditioning causes a decrease in tensile strength for an asphalt core. Further results from the CT-scans also indicated that MIST conditioning increases the inter-connected voids in an asphalt core. Results of the secondary objectives indicated that a correlation exists between the permeability results of the Marvil and the HPP for several of the asphalt cores. However, correlation only exists for the HPP at 100 and 150 kPa testing pressure, but at 200 kPa inconsistencies exist - leading to high variability in the results. It is postulated that testing pressures of 200 kPa and above lead to a great risk of leakage and other secondary effects during testing. Finally, asphalt permeability classification ranges were developed for the Marvil and HPP under laboratory conditions which can be used for future research.