Aspects of self-cementation when applied in roads

[摘要] ENGLISH ABSTRACT: Worldwide, the growing volumes of traffic have led to the increase in an expanding infrastructure thatmust be continually maintained. Congruent with these developments are undesirable environmentalconsequences, including depletion of natural resources. Given the fact that the construction industry isresponsible for more than 40% of extracted materials [Fadiya et al., 2014], and subsequently generateslarge amounts of construction waste, it is ominous that the roads industry should be a key player inimplementing austerity measures. These actions should include progressing to more efficient constructionpractices 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 roadconstruction materials replaced with alternative options such as construction demolition waste – betterknown 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 commonpractice since the late 1970s and has developed industry norms towards successful utilisation within theconstruction industry. These applications have been highly satisfactory.It has been reported that mix compositions of RCA and RCM exhibit self‐cementing characteristics. Thesecharacteristics could be beneficial to road design. Unfortunately, they are also associated with unforeseenchallenges that become more complex when considering mechanisms such as self‐cementation, whichmanifests 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 andlong‐term behaviour is often difficult to predict. The change in response of governing mechanisms broughton by self‐cementing could lead to a change in failure behaviour. Potentially, the material could transformbetween 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 thereforerequire an assessment of the scope of what the long‐term physical, mechanical and durability performanceof these materials could entail.Often these changes and associated risks are minimised through decreasing variability of the materialwhen processed in a formalised industry. In emerging markets, characteristic of many developingcountries, risk is increased due to informal practices.The current research investigates the range of variability in which the behavioural response of thematerials can manifest. It includes the way in which self‐cementing manifests in the micro‐ and macrostructureand 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 resultof the potential transforming nature of RCA, between characteristics of an unbound to a bound layer, areinvestigated. The research in this regard includes the consequences of carbonation as well as the modellingof 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 ofthe material, but that caution should be exercised in curtailing risk during application of the material withinroad layers.Finally, guidelines are proposed that account for the factors that may affect the long‐term performance ofthis 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 theapplication in construction practices and design considerations.

[发布机构] Stellenbosch University