The performance properties of recycled concrete in road pavement materials

Date
2018-03
Journal Title
Journal ISSN
Volume Title
Publisher
Stellenbosch : Stellenbosch University
Abstract
ENGLISH ABSTRACT: Due to a rise in population and industrialisation, the demand on infrastructure in developing countries have increased significantly. The world has been moving towards a more environmentally friendly and sustainable approach to provide the necessary infrastructure to sustain the economy. High quality natural aggregate is a finite resource with declining supply. It is therefore imperative that materials previously regarded as waste, should be recycled and reused. Large amounts of Concrete Demolition Waste (CDW) is created when old infrastructure is destroyed and this material placed in already constrained landfill sites. There has been a shift in perceptions of this material from being a waste to being a valued road construction material in recent years. Recycled Concrete and Masonry Aggregate are widely used in some developed countries, where good quality natural resources are scarce. However, in developing countries that have an abundance of good quality aggregate, but limited knowledge in the field of recycling, this material is often disregarded. Builders’ rubble that have been recycled, such as Recycled Concrete Aggregate (RCA), has shown to be an effective alternative material in structural pavement layers in other countries. In the South African industry, standards and guidelines towards the use of this material has not yet been developed and implemented. The experimental design developed for this study, incorporated two different types of RCA material, the Unexposed material used from the crushing process, and Exposed material that has been treated with the aim to promote rapid self-cementation. In this study, laboratory triaxial tests, which included monotonic and permanent deformation tests were performed. The self-cementing potential of the material was investigated by using two different types of material. These materials were tested at different curing times to investigate the effect on the durability of the material. It was found that RCA material, both Exposed and Unexposed, had large amounts of variability in terms of behaviour. The Exposed RCA more so than the Unexposed RCA. This can be attributed to the reduction in self-cementation potential and the variable dispersion of the cement particles left in the material after processing of the Exposed material. Both materials had very high shear strength parameter values (cohesion and friction angle). Results revealed that the shear parameters are not an indication of the material’s ability to withstand permanent deformation, as was shown for the Exposed RCA material. The Exposed material exhibited similar shear parameters to the Unexposed material. However, the Deviator Stress Ratio for the Exposed material, where stable behaviour in the permanent deformation tests was observed, was much lower than that of the Unexposed material. This suggests that the material relies not only on the matrix of aggregate interlock, but possibly also on the cementitious bonds for shear strength and resistance to permanent deformation. Using the results obtained from permanent deformation results, the best fit model could be identified. The critical parameters that influence the behaviour of RCA were identified as deviator stress ratio, moisture content and density. This has a direct effect on the magnitude of plastic strain in the material. The results from the permanent deformation tests were used to synthesise a transfer function for the Unexposed RCA material. This transfer function can be used to calculate the pavement life of RCA layers within a pavement structure. Pavement analyses were performed on pavement structures that include RCA as either a base or subbase. These results were compared to three typical South African pavement structures. The transfer function that was developed was used to calculate the life for the pavement layers consisting of RCA materials. Although the DSR at which the material performs at satisfactory levels of permanent deformation is lower than that of standard granular materials used in pavement construction, the analysis yielded favourable results. Results showed that RCA material delivered reliable and achievable results for the use of this material in a pavement layer when compared to these standard pavements.
AFRIKAANSE OPSOMMING: As gevolg van ‘n toename in die bevolking en industrialisering, het die aanvraag na infrastruktuur eksponensieël gegroei. Veral in ontwikkelende lande is hierdie aanvraag noemenswaarding groot. Terselftertyd beweeg die wêreld na ‘n meer omgewingsbewus en volhoubare aanslag om sodoende die nodige infrastruktuur te voorsien. Hoë kwaliteit aggregaat is ‘n beperkte hulpbron met afnemende voorraad. Vir hierdie rede is dit van uiterse belang om materiaal wat van tevore beskou is as rommel, te herwin en hergebruik. Groot hoeveelhede Betonslopingsafval (CDW) word gegenereer met die afbreking van ou infrastruktuur. Tans word meeste van hierdie materiaal in stortingsterreine met reeds beperkte kapasiteit geplaas. In onlangse jare het die persepsie oor die materiaal geskuif van ‘n materiaal wat gemors is tot ‘n materiaal wat as ‘n waardevolle padkonstruksiemateriaal gebruik kan word. In ontwikkelde lande waar hoë kwaliteit natuurlike aggregate ‘n skaars hulpbron is, word materiaal soos Herwinde Betonaggregaat (RCA) en Herwinde Messelwerkaggregaat (RCM) reeds gebruik. Alhoewel, in ontwikkelende lande, waar daar baie keer ‘n oorvloed van goeie kwaliteit materiaal is, maar ‘n tekort aan kennis oor herwinning, word die materiaal dikwels oorsien. Die gebruik van slopingsmateriaal soos RCA is bewys as ‘n goeie alternatief vir beide die kroon- en stutlaag in ander ontwikkelde lande. In Suid-Afrika is standaarde vir die gebruik van die materiaal nog nie ontwikkel en geimplementeer nie. Die eksperimentele ontwerp het twee tipes RCA materiaal ingesluit, naamlik die Onblootgestelde materiaal, wat direk na die opbreekproses gebruik word, en die Blootgestelde materiaal wat behandel word om die self-sementerings proses bevorder. In hierdie was triaksiale toetse, wat monotoniese en permanente vervormingstoetse insluit, uitgevoer. Die self-sementeringspotensiaal van die materiaal was ondersoek deur na verskillende kuurtydperke te kyk, omrede dit ‘n direkte impak op die duursaamheid van die materiaal sal hê. Dit was gevind dat beide die Blootgestelde en Onblootgestelde materiaal groot hoeveelhede variasie toon in terme van gedrag. Die Blootgestelde RCA het groter variasie getoon as die Onblootgestelde materiaal. Dit kan toegeskryf word aan die self-sementering en die veranderlike verspreiding van sement partikels in die materiaal. Albei die materiale het baie hoë skuifsterkte parameters opgelewer. Die resultate het ook gewys dat die skuifsterkte parameters nie gebruik word as ‘n indikasie van die materiaal se weerstand tot permanente vervorming nie, en dit was spesifiek die geval met die Blootgestelde RCA. Die materiaal skuifsterkte parameters van die Onblootgestelde materiaal was vergelykbaar is met die van Blootgestelde materiaal. Tog is die hoeveelheid uitwykspanningsverhouding (DSR) waarby die Blootgestelde materiaal stabiele gedrag onderhewig aan permanente deformasie toetse getoon het baie laer as die van die Onblootgestelde materiaal. Dit wysdat die materiaal moontlik nie slegs op die matriksvergrendeling staat maak nie, maar ook op die sementverbindings om weerstand te bied teen vervorming. Deur gebruik te maak van die bevindinge uit die eksperimentele ontwerp, kan die beste pasmodel wat die langtermyn permanente vervormimgsgedrag van die materiaal voorspel, gevind word. Die kritiese parameters wat die gedrag van die materiaal beïnvloed is geïdentifiseer as die die DSR, voginhoud en die digtheid. Hierdie faktore het ‘n direkte impak op die hoeveelheid plastiese vervorming wat in die materiaal ontstaan. Die resultate van die vervormingstoetse was gebruik om ‘n ontwerpsfunksie te ontwikkel vir RCA materiaal. Die ontwerpsfunksie kan gebruik word om die plaveisellewe van RCA lae binne ‘n plaveiselstruktuur te vind. Plaveiselanalises was uitgevoer op plaveiselstrukture wat RCA materiaal as kroon- of stutlaag bevat. Die gedrag was dan vergelyk met drie tipiese plasveiselstrukture van Suid Afrika. Alhoewel die DSR waarby RCA materiaal voldoende funksioneer minder is as die van ʼn granulêre materiaal, het die analises steeds gunstige resultate gelewer en die RCA materiaal betroubare en haalbare resultate toon.
Description
Thesis (MEng)--Stellenbosch Uniersity, 2018.
Keywords
Recycled Concrete Aggregate, Construction and demolition debris, Pavements -- Material, UCTD
Citation