Potential for recycled concrete aggregate stabilisation with bitumen emulsion and foamed bitumen

Mazibuko, Nokuthula Mandy Antonia (2020-03)

Thesis (MEng)--Stellenbosch University, 2020.

Thesis

ENGLISH ABSTRACT: Bitumen stabilisation is a technology used to improve the strength properties of any aggregate, which is also environmentally friendly. The method of stabilisation requires less energy in comparison to hot asphalt mixes and it causes less pollution when compared to cement stabilisation. The sustainability benefit of BSMs can be improved when recycled materials from construction demolition waste such as recycled concrete is used. The existing TG2 outlines the process to determine whether an aggregate is suitable to be stabilised with foamed bitumen or bitumen emulsion. This research aims to use the same process to determine whether RCA is a suitable aggregate for stabilisation with bitumen emulsion or foamed bitumen. In addition, the BSM classification of the resultant BSM with RCA is determined along with the performance properties of the mix design. The indirect tensile strength (ITS) was used to determine the suitable active filler for RCA stabilised with bitumen emulsion and foamed bitumen. Active fillers considered included 1% lime and 1% cement. Furthermore, the optimum bitumen content for the aggregate was determined and found to be 2.2% for both bitumen emulsion and foamed bitumen. The shear strength parameters and resilient moduli of the optimum mix designs made from foamed bitumen and bitumen emulsion were tested with the monotonic and dynamic triaxial test. The preliminary results indicate that RCA is a suitable aggregate for stabilisation with low viscosity bitumen. Moreover, the ITS results suggest that no active filler is required and a potential BSM 1 layer can be produced with 2.2% bitumen content. This indicates the potential of using this material considering economical relevance. Furthermore, the shear parameters obtained for both binders (bitumen emulsion and foamed bitumen) also indicates that the mix designs can be classified as a BSM 1. Additionally, a high resistance to moisture damage was achieved as shown by the retained cohesion ranging from 88.2 to 90%. Moreover, the resilient modulus analysis indicates a stress dependent behaviour, which can be modelled by existing models used for unbound granular materials. However, care should be taken when stabilisation is done with bitumen emulsion due to the high absorptivity of the mortar, which causes early breaking of the emulsion. Pre-soaking of the aggregate was required to manage this challenge. The pavement life analysis shows that, if the layer is used in the base layer with a G5 subbase a pavement life suitable for a Category B road is obtained. Therefore, the addition of bitumen improves the behaviour and performance of RCA and the results indicate that it can be successfully used in a base layer. Therefore, there is potential for the stabilisation of RCA with either foamed bitumen or bitumen emulsion.

AFRIKAANSE OPSOMMING: Stabilisasie van bitumen is 'n manier om die sterkte-eienskappe van enige aggregaat, wat ook omgewingsvriendelik is, te verbeter. Die metode van stabilisering benodig minder energie in vergelyking met warm asfaltmengsels en dit veroorsaak minder besoedeling in vergelyking met sementstabilisering. Die volhoubaarheidsvoordeel van bitumen gestabiliseerde material (BSMs) kan verder verbeter word wanneer herwinde materiale van konstruksie-afvalafval, soos herwinde beton (RCA), gebruik word. Die bestaande TG2 beskryf die proses hoe om te bepaal of 'n aggregaat geskik is om met bitumen-skuim of bitumen-emulsie gestabiliseer te word. Die doel van hierdie navorsing is om dieselfde proses te gebruik om te bepaal of RCA 'n geskikte aggregaat is vir stabilisering met bitumenemulsie of bitumenskuim. Gevolglik kan 'n mens ook die BSM-klassifikasie verkry wanneer RCA gebruik word. Verder was die gedrageienskappe van die materiaal ook in hierdie navorsing ondersoek. Die indirekte treksterkte (ITS) is gebruik om die geskikte aktiewe vulstof vir RCA te bepaal, gestabiliseer met bitumenemulsie en bitumenskuim. Beide kalk en sement was oorweeg as aktiewe vullers Verder is bepaal dat die optimale bitumeninhoud vir die aggregaat 2,2% was vir beide emulsie en skuimbitumen. Die skuifsterkte-eienskappe en veerkragmodulus modulus van die optimale mengsels gemaak van bitumenskuim en bitumenemulsie is deur monotoniese en triaksiale toetse ondersoek. Die voorlopige resultate dui daarop dat RCA, behandel met 'n lae viskositeit bitumen vir stabilisering, wel geskik is. Volgens die ITS-resultate is geen aktiewe vulstof nodig nie en kan 'n moontlike BSM 1-laag met 2,2% bitumeninhoud geproduseer word. Die skuifparameters wat vir beide binders verkry word, dui ook op 'n moontlike BSM 1-laag wat bestand is teen vogskade, soos aangetoon deur die behoue kohesie wat wissel van 88,2 tot 90%. Daarbenewens dui die veerkragmodulus-analise op spanningsafhanklike gedrag wat deur bestaande ongebonde granulere materiaalmodelle gemodelleer kan word. Daar moet egter voorsorg geneem word wanneer met bitumenemulsie gestabiliseer word as gevolg van die hoe absorptiewe eienskappe van RCA. Om hierdie aspek te bestuur is dit noodsaaklik om die materiaal vogtig te maak voor die finale meng. 'n Ontleding van die falingseienskappe van die materiaal dui op aanvaarbare padlewe (as Kategorie B geanaliseer) wanneer dit as kroonlaag samehangende 'n redelike stutlaag soos 'n G5 toegepas word. Die gevolgtrekking is dat RCA, met die toevoeging van bitumen, die gedrag van RCA kan verbeter. Daar is dus potensiaal vir verdere gebruik van RCA met skuim- of bitumen-emulsie in padlae en moet dus verder ondersoek word.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/107910
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