Asphalt permeability and moisture damage

Venter, Cindy (2019-04)

Thesis (MEng)--Stellenbosch University, 2019.

Thesis

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.

AFRIKAANSE OPSOMMING: Gedurende die afgelope dekades het die ontwerpmetodes van padoppervlaktes heelwat verander. Dit het begin met die heel eerste bitumen oppervlak wat in die agtien-vyftigs op ‘n pad in Parys, Frankryk, neergelê is. Die hoofdoelwit van ‘n oppervlaklaag is om te verseker dat vog nie die kroon- en stutlaag binnedring nie. Hierdie lae kan net die kragte wat deur die verkeersdruk uitgeoefen word absorbeer indien dit vog-vry is. Die oppervlaklaag is die enigste laag wat die stutlae kan beskerm. Hierdie navorsingsprojek handel oor die ontleding van verskillende asfaltkerns en die deurlaatbaarheid daarvan. Die deurlaatbaarheid van so ‘n kern word beskryf as die hoeveelheid vog, water en lug wat deur ‘n asfaltkern dring. Oppervlaklae wat lae deurlaatbaarheid eienskappe besit, sal verseker dat die stutlae langer beskerm sal word teen die indringing van vog. Hierdie navorsingsprojek ondersoek hoofsaaklik ‘Asfalt deurlaatbaarheid en vog skade’. Uitgebreide laboratoruimeksperimente en toetse was uitgevoer om ondersoek in te stel van presies hoe die vog ‘n asfaltkern binnedring, asook die hoeveelheid lugruimtes in ‘n kern. Deur middel van rekenaar tomografie skandering (CT-skandering) was daar ondersoek ingestel om vas te stel of verbinde lugruimtes vermeerder het na die ‘MIST’ kondisionering. Verskeie asfaltkerns was ingesamel van regoor Suid-Afrika en na die laboratorium gebring by Stellenbosch Universiteit. Dit is ook by hierdie instansie waar al die toetse afgelê is en die resultate verkry was. Nadat ‘n uitgebreide literatuurstudie saamgestel was, kon daar vasgestel word dat sekere faktore wel ‘n invloed sal hê op die deurlaatbaarheid van die asfaltkern. ‘n Eksperimentnavorsingsprosedure was saamgestel om te verseker dat die primêre- en sekondêre doelwitte bereik kan word. Die primêre doelwit van hierdie navorsingsprojek is om die deurlaatbaarheid van asfaltkerns te toets deur middel van die Marvil en hoëdrukdeurlaatbaarheidstoets (HPP), en ondersoek in te stel oor wat die invloed van druk en vog op die deurlaatbaarheid van ‘n asfaltkern is. Die sekondêre doelwitte was om die volumetriese eienskappe te ondersoek en vas te stel of daar enige verwantskap bestaan tussen die: • Marvil en die hoëdrukdeurlaatbaarheids (HPP) toets; • Marvil en die lugruimte inhoud; en • Hoëdrukdeurlaatbaarheidstoets (HPP) en die lugruimte inhoud. Dit was ook noodsaaklik om graderings te ontwikkel vir die Marvil en HPP toetse onder laboratoriumtoestande. Die primêre keuse vir die deurlaatbaarheidstoetse van asfalt oppervlaklae is die Marvil toets. Hierdie toets gebruik geen bygevoegde druk op die kern nie en maak slegs staat op die druk wat die water uitoefen tesame met atmosferiesedruk – wat weglaatbaar klein is. Die Marvil apparaat was aangepas om in die laboratorium gebruik te word en sodoende verskillende asfaltkerns te kan toets. ‘n Tweede deurlaatbaarheidstoets was gebruik om te ondersoek hoe die byvoeging van druk die asfaltkerns sou beïnvloed. Die hoëdrukdeurlaatbaarheidstoets (HPP) was ontwerp deur Ockert Grobbelaar in 2016 (Grobbelaar, 2016). Hierdie apparaat was gebruik om die hidrostatiese kragte te ondersoek wat veroorsaak word deur normale verkeerssnelheid op ‘n asfaltoppervlak. Die verskeie asfaltkerns was onder 100, 150 en 200 kPa druk geplaas (Jenkins & Twagira, 2009). Die hoëdrukdeurlaatbaarheidstoets was voor en na ‘MIST’ kondisionering afgelê om sodoende die invloed van die hidrostatiese kragte op die lugruimtes te kon ondersoek. Na die afloop van die deurlaatbaarheids- en vog skade toetse was elke kern se indirektetrekspanning (ITS) getoets. Dit sou meer duidelikheid bied oor die invloed wat die bogenoemde toetse op die monster se sterkte het. Dit het te lig gekom dat die kerns wat onderwerp was aan ‘MIST’ kondisionering wel swakker trekspanningskragte ervaar het. Deur middel van rekenaar tomografie skandering (CT-skandering) was daar ook gesien dat ‘MIST’ kondisionering die lugruimtes binne die kerns vergroot en ook ‘n groter verbinding gevorm het as voor die toetse. Die resultate vir die sekondêre doelwitte het genoegsame bewyse opgelewer om te toon dat daar wel ‘n verwantskap bestaan tussen die deurlaatbaarheidsresultate van die Marvil en die HPP. Hierdie verwantskap bestaan wel net tussen die twee toetse indien die HPP by 100 en 150 kPa getoets word. Sodra die druk verhoog word na 200 kPa verdwyn hierdie verwantskap. Die oorhoofse rede vir hierdie gevolgtrekking is hoofsaaklik dat die apparaat nie akkuraat kan toets teen ‘n hoë druk van 200 kPa nie. Daar was uitdagings ondervind om die apparaat waterdig te hou en te verseker dat die seël nie lek nie. Laastens was daar deurlaatbaarheidsgraderings ontwikkel vir die Marvil asook die HPP onder laboratoriumtoestande wat gebruik kan word vir toekomstige deurlaatbaarheidsstudies.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/105967
This item appears in the following collections: