Aspects of self-cementation when applied in roads

Rudman, Chantal (2019-04)

Thesis (PhD)--Stellenbosch University, 2019.

Thesis

ENGLISH ABSTRACT: Worldwide, the growing volumes of traffic have led to the increase in an expanding infrastructure that must be continually maintained. Congruent with these developments are undesirable environmental consequences, including depletion of natural resources. Given the fact that the construction industry is responsible for more than 40% of extracted materials [Fadiya et al., 2014], and subsequently generates large amounts of construction waste, it is ominous that the roads industry should be a key player in implementing austerity measures. These actions should include progressing to more efficient construction practices and the reuse of materials to alleviate the strain on already overburdened natural resources. Many initiatives and developments have been implemented towards this goal and conventional road construction materials replaced with alternative options such as construction demolition waste – better known as recycled concrete aggregate (RCA) and recycled crushed masonry (RCM). The Netherlands, for example, has been processing RCA and RCM for use in road layers as common practice since the late 1970s and has developed industry norms towards successful utilisation within the construction industry. These applications have been highly satisfactory. It has been reported that mix compositions of RCA and RCM exhibit self‐cementing characteristics. These characteristics could be beneficial to road design. Unfortunately, they are also associated with unforeseen challenges that become more complex when considering mechanisms such as self‐cementation, which manifests over time and potentially influences the performance of such a material. The long‐term performance of this type of self‐cementing, secondary material is not fully understood and long‐term behaviour is often difficult to predict. The change in response of governing mechanisms brought on by self‐cementing could lead to a change in failure behaviour. Potentially, the material could transform between characteristics of an unbound material, governed by rutting and permanent deformation failure, to that of a bound material, in turn governed by fatigue and subsequent cracking behaviour. These could lead to undesired defects, which may appear randomly in terms of severity and therefore require an assessment of the scope of what the long‐term physical, mechanical and durability performance of these materials could entail. Often these changes and associated risks are minimised through decreasing variability of the material when processed in a formalised industry. In emerging markets, characteristic of many developing countries, risk is increased due to informal practices. The current research investigates the range of variability in which the behavioural response of the materials can manifest. It includes the way in which self‐cementing manifests in the micro‐ and macrostructure and the short‐ and long‐term structural performance associated with self‐cementation of RCA. Additionally, the intrinsic and extrinsic factors associated with durability concerns manifesting as a result of the potential transforming nature of RCA, between characteristics of an unbound to a bound layer, are investigated. The research in this regard includes the consequences of carbonation as well as the modelling of test data and its potential for shrinkage crack patterning as a result of fatigue failure behaviour. The results reveal that some benefit can be derived from exploiting the self‐cementing characteristics of the material, but that caution should be exercised in curtailing risk during application of the material within road layers. Finally, guidelines are proposed that account for the factors that may affect the long‐term performance of this material, so that it can be incorporated into normal practice. These considerations include aspects concerning the structural and durability performance of the material (especially in informal markets where standardised processing of materials is not the norm) and the application in construction practices and design considerations.

AFRIKAANSE OPSOMMING: Groeiende verkeer wêreldwyd het gelei tot uitgebreide infrastruktuur wat konstant onderhou moet word. Tesame met hierdie ontwikkelinge, is die ongewenste omgewingsimpakte en die uitputting van natuurlike hulpbronne. As ‘n mens in ag neem dat die konstruksie industrie verantwoordelik is vir die gebruik van meer as 40% van ontginde materiale [Fadiya et al., 2014], en diensooreenkomstig groot getalle van konstruksie afval genereer, is dit onheilspellend dat die padindustrie die sleutel speler behoort te wees in die implementering van toepaslike maatreëls. Hierdie aksies hoort progresiewe konstruksiepraktyke sowel as die hergebruik van materiale wat druk op ons reeds natuulike hulpbronne sit, te bevorder. Baie initiatiewe en ontwikellinge is reeds geïmplementeer om hierdie doel te bereik. Dit sluit in byvoorbeeld die vervanging van konvensionele padmateriale met alternatiewe opsies soos konstruksie demolisie afval of alternatiewelik genoem; herwinde beton aggregaat (RCA), of herwinde baksteen aggregaat (RCM). In Nederland byvoorbeeld, word RCA en RCM reeds hergebruik vanaf die 1970’s. Hulle het ook industrie norme onwikkel tot suksesvolle verbruik in die konstruksieindustrie. Hierdie toepassings is bewys om hoogs suksesvol te wees. Dit is gerapporteer dat mengsels van RCA en RCM self‐sementering eienskappe weerspieël. Hierdie eienskappe kan voordelig wees vir padontwerp. Ongelukkig kan dit ook met onvoorsiene uitdagings kom waar dit meer kompleks kan raak wanneer meganismes wat oor tyd ontwikkel ook ingesluit word. Hierdie verwikkelinge kan moontlik die potensiële gedrag van die materiaal beinvloed. Die lantermyn gedrag van hieridie tipe self‐sementerende, sekondêre materiaal is nie ten volle verstaan nie en gewoonlik moeilik om te voorspel. Die verandering in gedrag van prominente meganismes as gevolg van self‐sementering kan lei tot verandering in die falingsmeganisme. Moontlik kan die materiaal transformeer vanaf ‘n materiaal met eienskappe eenselwig met ongebonde materiale (permanente deformasie faling) tot ‘n materiaal eenselwig met gebonde eienskappe. Wat dus dan lei tot vermoeiing en manifestering van krake. Hierdie kan lei tot ongewenste gevolge, wat ewekansig verskyn in terme van erns. Dit kort dus ‘n assessering van die omvang van die langtermyn fisiese‐, meganiese‐ en duursaamheidsgedrag wat hierdie materiaal kan reflekteer. Gewoonlik kan hierdie veranderinge en geasosieerde risikos bekamp word deur die materiaal in ‘n geformaliseerde omgewing te prosseseer. In ontluikende markte, karakteristiek van baie onwikkelende lande, word hierdie risiko vergroot as gevolg van informele praktyke. Die huidige navorsing ondersoek die omvang van veranderelikheid in die gedrag van die materiaal. Dit sluit in die manier hoe self‐sementering kan manifesteer in die mikro‐ en makrostruktuur en die kort‐ en langtermyn strukturele gedrag geassosieer met self‐sementering van RCA. Addisioneel, kan die intrinsieke en ektrinsieke faktore geassosieer word met duursaamheidsgedrag as gevolg van die tranformerende gedrag van RCA. Die navorsing in die opsig sluit beide die gevolge van karbonasie sowel as die modellering van toetsdata vir die potensiele krimpingskrake. Die resultate wys dat voordeel wel verkry kan word deur die gebruik van die materiaal, maar dat versigtigheid nagevolg moet word om risko te minimeer. Laastens word riglyne vir normale praktyk voorgestel. Hierdie riglyne sluit beide strukturele en duursaamheidgedrag in, vir beide kort‐ en langtermyngedrag. Die riglyne is gerig op inforrmele markte waar standaard prossesering van materiale nie die norm is nie, asook aanwending in konstruksie praktyke sowel as ontwerp oorwegings.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/105922
This item appears in the following collections: