Carbonation of cement stabilised materials in pavement layers

Beardmore, Ricki-Lee (2018-03)

Thesis (MScEng)--Stellenbosch University, 2018.

Thesis

ENGLISH ABSTRACT: The remarkable increase in global traffic has encouraged innovative pavement designs capable of satisfying environmental, economic and social needs. The construction and demolition industry has had a major influence on the environment in terms of the amount of natural resources used as well as the high volume of waste produced. Landfills are being occupied at a steadfast rate, with an annual estimated 5-8 million tons of Construction Demolition Material (CDM) generated in South Africa, of which, approximately 1 million tons is concrete rubble. In developing countries, where natural resources are uncommon, sophisticated recycling and crushing techniques are implemented to produce high quality Recycled Concrete and Masonry Aggregate. South Africa is a country rich in Natural Aggregate (NA) which has conceivably led to limited exploration into the use of alternative sources aggregate. Recycled Concrete Aggregate (RCA) and Recycled Concrete Masonry (RCM) has been used successfully in the application of pavement materials in other sectors of the world. However the full scope of RCA and RCM as a pavement material in South Africa is limited at this point in time as further knowledge pertaining to the recycling field and understanding of the behaviour and performance of these material is required. In understanding the behaviour and performance of RCA, it must first be determined whether this material would be characterised as a bound or unbound pavement material, or somewhere in between. The scope of this research study aimed at gaining a better understanding of the durability issue most commonly associated with bound materials, known as carbonation. The experimental design incorporates the development of an accelerated lab carbonation procedure and implemented this by carbonating two types of RCA material with and without added cement. The two material types are distinguished by their grading which are continuous grade and gap grade. To better understand the influence of extrinsic and intrinsic properties on the carbonation potential of RCA, the two material types, with and without the addition of cement, were subjected to accelerated carbonation at curing times of 1, 7 and 28 days. Following the carbonation of the RCA material, the study undertook laboratory strength tests which include Unconfined Compressive Strength (UCS) tests as well as Indirect Tensile Strength Tests (ITS) and were performed on both non-carbonated and carbonated RCA material. The self-cementing potential of RCA was investigated by observing the results of the aforementioned tests and together with the outcome of carbonation, the material types were scrutinized in terms of their performance as a bound and/or unbound material as well as potential durability issues incurred as a measure against their extent of carbonation. The carbonation results revealed that RCA material with 0% added cement, readily carbonates regardless of the curing time and grading of the material, which alludes to lightly cemented materials being more susceptible to carbonation. RCA material with 2% added cement indicates greater resistance to carbonation but is inclined to be less resistant to carbonation as curing time is increased. Grading also had an influence on the resistance to carbonation when 2% cement was added to RCA, with continuous grade exhibiting higher resistance to carbonation than gap grade RCA. A methodical analysis of the influence of variables (density, cement, moisture and grading) showed the interdependency and non-linearity of variables and correlation exist between this and UCS as a strength parameter to measure carbonation, but that the governing variable change with the strength development of the material. The most important finding is the potential susceptibility of lightly stabilised materials to carbonation. It is imperative that guidelines are provided to mitigate these risks on the handling of these materials prior and during placement is provided to mitigate these risks.

AFRIKAANSE OPSOMMING: Die merkwaardige verhoging in globale verkeer het aanleiding gegee tot meer innoverende plaveiselontwerpe wat beide meer ekonomiese, omgewings en sosiaal verantwoordelik is. Die konstruksie en demolisie industrie het ‘n groot impak op die omgewing in terme van die hoeveelheid natuurlike bronne wat deur hulle ontgin word, sowel as die hoë volume afval wat geskep word. Stortingsterreine word volgemaak teen ‘n kommerwekkende spoed, met ‘n jaarlikese tempo van tussen 5-8 million ton, vanwaar 1 miljoen ton betondemolisie is. In ontwikkellende lande, waar natuurlike bronne gewoonlik meer skaars is, word gesofistikeerde herwinning en breking tegnieke geimplimenteer om sodoende Herwinde Beton en Baksteen (HBB) te produseer. Suid-Afrika het aansienlik meer natuurlike bronne tot hulle beskikking wat tot minimale gebruik van alternatiewe bronne van aggregaat tot gevolg het. Herwinde Beton (HB) en Herwinde Baksteen (HKB) is al suksesvol gebuik in ander sektore van die wêreld. Nietemin, hier in Suid-Afrika, en spesifiek in plaveislels, is die gebruik van HBB minimal as gevolg van onkunde oor die herwinningsveld en ‘n verstaan van die gedrag van die materiaal. In orde om die gedrag te verstaan, moet dit eers geidentifiseer word of die materiaal as ‘n “gebonde” of “ongebonde” materiaal gekaraktiseer moet word, of dalk iets tussenin. Die omvang van die navorsingsstudie is om beter insigte oor die duursaamheid van die materiaal te verkry. Iets wat tipies gepaard gaan met gebonde materiale is karbonasie. Die eksperimentele ontwerp inkorporeer die ontwikkeling van ‘n versnelde lab karbonasie procedure, sowel as die gebruik van hierdie apparaat deur twee verskillende tipes HB, een sonder en een met sement. Die twee materiaal tipes word onderskei deur dat een ‘n kontinue gradering en die ander ‘n nie-kontinue gradering het. Om beter die eksterne en interne eienskappe wat karbonasie potensiaal op HB kan hê te verstaan, is die twee materiaal tipes, met en sonder sement, onderhewig aan die versnelde laboratorium karbonasie proses gesit vir monsters wat 1,7 en 28 dae gekuur is. Nalope hierdie toetse, was die onbeperkte sterkte (UCS) en die indirekte trektoets (ITS) gedoen op beide nie-gekarboneerde en gekarboneerde HB materiaal. Die self-sementering potensiaal van HB was ook ondersoek deur die resultate te analiseer samehangende met die uitkomstes van karbonasie. Materiaal tipes was ook ondersoek vir hulle gedrag in terme van ‘n gebonde of ongebonde materiaal sowel as die vatbaarheid agv die graad van karbonasie. Die karbonasie resultate het gewys dat HB materiaal met geen addisionele sement, maklik karboneer ongeag van die kuringtyd en gradering van die materiaal en wys dus dat moontlik ligte gesementeerde materiaal meer vatbaar is vir die karboneringproses. HB met 2% was meer bestand teen die karbonasie proses, maar hierdie verminder met kuringtyd. ‘n Kontinue gradering HB wys na ‘n hoër bestandheid teen karbonasie as dit van ‘n nie-kontinue gradering. ‘n Metodiese analise van die verskillende faktore (dightheid, sement, vog, gradering) het uitgewys dat hierdie faktore afhankilik van mekaar is, sowel as dat daar ‘n nie-liniere korelasie tussen hulle en die onbeprekte druk sterkte bestaan. Die mees belangrikste bevinding is dat die potensiaal van vatbaarheid vir ligte gesementeerde materiaal. Dit is noodsaaklik dat riglyne ontwikkel op die hantering van hierdie materiaal voor en met plasing word om risiko te verminder.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/103436
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