Thesis (MScEng)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: A major challenge for our society is the protection of the environment. Some of the important
issues are the reduction in the consumption of energy and natural raw materials, as well as the
increase in consumption of waste materials. At present these topics are getting considerable
attention as part of sustainable development programs. The use of recycled concrete aggregates
(RCA) from construction and demolition waste (C&DW) in construction, as alternative to virgin
(natural) aggregates, has strong potential. The use of RCA preserves natural resources and
reduces the space required for the disposal of RCA in landfill. It is estimated that 16 thousand
million (billion) tons of concrete (and 25 billion tons of aggregate) were used in 2010. Of the 2-3
billion tons of C&DW which are produced worldwide every year, South Africa contributes 5-8
million tons. This amount is increasing rapidly every year. Significant amounts of demolished
concrete find their way to landfill sites. A solution for excess waste production would be the
utilization of RCA together with an improvement in the final quality of RCA. It might be an
important breakthrough for our society in our attempt towards sustainable development.
Worldwide, infrastructure has developed a great deal since the beginning of the twentieth
century. Much of the core infrastructure, including roads, bridges, water systems, and sewers,
was put in place during the first half of that century. Aggregates used as construction materials,
as for instance in road pavements, or as an ingredient of concrete, are important components of
infrastructure. Urbanization involves reduction of natural aggregate (NA) resources, but
environmental concern and the rising cost of NA is the reason that recycled materials from
different sources (like roads, buildings) are being used more and more with NA in new
construction work.
Environmental awareness is increasing in every country for many reasons and sustainable
development is demanded of all industries, including the building and construction industries. By
nature, construction is not environmentally friendly, and sometimes it also changes the behavior
of nature in many ways. Recycling is one of the most important ways to minimize the waste that
comes from different sources, thereby avoiding repetition of, and additional environmentally
hazardous practices. It may create new wealth by diminished transport and production costs and
sparing of landfill site space and cost. It has the potential to extend the life of natural resources
by adding a source of material, thereby reducing environmental interference and impacting on
nearby construction sites, all of which improve sustainability of our natural resources.
Much research on the uses of RCA has been performed during the last few decades. In fact, most
of them showed that the strength class of recycled aggregate concrete (RAC) is adequate for use
as structural concrete although volume changes in and durability performance of RAC in
comparison with natural aggregate concrete (NAC) are still being debated and researched. Some
researchers found that the durability of concrete produced with RCA is inferior, but others have
found it to be sufficient for use in structural concrete. The fact that an insufficient number of studies have been carried out on the durability aspects, has limited the use of RCA as material for
road construction.
The aim of this study is to determine the suitability of using the RCA in structural concrete based
on its strength, stiffness, dimensional stability and durability. Three types of RCA designated
RCA1, RCA2 and RCA3 in this study, were taken from three different sources. These materials
were tested to establish their mechanical characteristics for use as aggregates in concrete. In the
experimental program RCA was used at replacement percentages of 0%, 30% and 100% to
(partially) replace NA in order to study its suitability as aggregate in concrete, and to what level
of NA replacement its behavior is satisfactory for structural application.
A single compressive strength class was studied, due to the limited time. By performing tests of
compressive strength, Young’s modulus, creep, shrinkage, and durability performance, it has
been found that selected types of RCA show a real possibility for use as aggregate in concrete.
When concrete with a RCA replacement of 100% was compared with NAC100% there was a
small decline in strength, but when concrete with a RCA replacement of 30% was compared with
NAC100% the results showed almost equal strength. A slight reduction in durability
performance was found for RAC30% compared with NAC100%, but similar dimensional
stability performance in terms of specific creep and drying shrinkage was measured for
RAC30% and NAC100%. Based on detailed experimental results obtained from this thesis
project, a number of recommendations have therefore been made for RCA characteristics that
will be used in concrete mixes also taking into account the quality of RCA. Some suggestions are
proposed based on the mechanical properties and durability of the concrete. In the final
conclusions, future studies on RCA properties are suggested, which would help us in increasing
our knowledge in the application of RCA, and which may lead to the optimal production of
structural concrete in a sustainable way. In general the use of RCA in concrete is feasible and
good quality RCA at 30% replacement of NA may be suitable for any kind of structural concrete. / AFRIKAANSE OPSOMMING: ‘n Groot uitdaging vir ons samelewing is die beskerming van die omgewing. Van die belangrike sake is die vermindering in die verbruik van energie en van natuurlike, onverwerkte materiale
asook die groter verbruik van afvalmateriaal. Hierdie onderwerpe kry tans aanienlike aandag as
deel van volhoubare ontwikkelingsprogramme. Die gebruik van betonaggregate, herwin vanaf
konstruksie-en slopingsafval, en gebruik in konstruksie as alternatief vir ongebruikte natuurlike
aggregate, het goeie potensiaal. Die gebruik van herwonne aggregaat beskerm natuurlike
hulpbronne en verminder die oppervlakte en volume wat nodig is vir die weggooi daarvan op
stortingsterreine. Dit is beraam dat 16 duisend miljoen (biljoen) ton beton (en ongeveer 25
biljoen ton aggregaat) gedurende 2010 gebruik is. Van die 2-3 biljoen ton konstruksie-en
slopingsafval wat jaarliks wêreldwyd gegenereer word, dra Suid Afrika 5-8 miljoen ton by.
Hierdie hoeveelheid word elke jaar vinnig meer. Beduidende hoeveelhede gesloopte beton
beland elke jaar op stortingsterreine. ‘n Oplossing vir die probleem van te veel atval generering
sou wees die gebruik daarvan as herwonne beton-aggregaat, sou saamval met ‘n verbetering in
die uiteindelike kwaliteit van herwonne aggregaat beton. Dit kan dalk ‘n belangrike deurbraak
wees vir ons samelewing in ons strewe na volhoubare ontwikkeling.
Infrastruktuur het wêreldwyd baie ontwikkel sedert die begin van die twintigste eeu. Baie van die
kerninfrastruktuur insluitende paaie, brue, waterstelsels en riole is gebou tydens die eerste helfte
van daardie eeu. Aggregaat gebruik as konstruksiemateriaal, byvoorbeeld in padplaveisels of
as’n bestanddeel van beton, is ‘n belangrike deel van infrastruktuur. Verstedeliking veroorsaak
vermindering van natuurlike aggregaat hulpbronne maar besorgdheid oor die omgewing en die
stygende koste van nataurlike aggregaat veroorsaak dat herwonne materiale vanaf verskillende
bronne (soos paaie en geboue) meer en meer aanvullend tot natuurlike aggregaat in nuwe
konstruksiewerke gebruik word.
Omgewingsbewustheid is om baie redes aan die toeneem in elke land en volhoubare
ontwikkeling word vereis van alle industrieë. Herwinning is een van die hoofmaniere om afval
vanaf verskillende bronne tot ‘n minimum te beperk. Dit skep nuwe rykdom, verminder vervoeren
vervaardigingskoste en benut afval wat anders op stortingsterreine verlore sou gegaan het. Dit
het die potensiaal om die lewensduur van natuurlike hulpbronne te verleng deur ‘n materiaalbron
by te voeg, deur inmenging in die omgewing te verminder, wat almal bevorderlik is om
volhoubare benutting van ons hulpbronne te verbeter.
Baie navorsing is gedurende die laaste paar dekades gedoen aangaande die gebruik van
herwonne aggregaat. Die meeste van die navorsing het inderdaad getoon dat die sterkte van
beton met herwonne aggregaat genoegsaam is vir gebruik as struktuurbeton alhoewel daar wel
debatte gevoer word oor die volumeveranderings en duursaamheid prestasie van herwonne
aggregaat beton vergeleke met dié van natuurlike aggregaat beton. Sommige navorsers het
bevind dat die duursaamheid van beton wat met herwonne aggregaat gemaak is, minderwaardig is maar andere het bevind dat dit voldoen aan die vereistes van struktuurbeton. Slegs die feit dat
daar onvoldoende toetse rakende duursaamheid gedoen is, het die gebruik van herwonne beton
aggregaat beperk tot padboumateriaal.
Die doel van hierdie navorsing is om te bepaal wat die geskiktheid van herwonne betonaggregaat
is vir gebruik in struktuurbeton, gegrond op sterkte en duursaamheid. Drie soorte herwonne
betonaggregaat wat in hierdie studie as RCA1, RCA2 and RCA3 aangedui word, is elk vanaf ‘n
ander bron geneem. Hierdie materiale is getoets om hulle meganiese kenmerke vas te stel vir
gebruik as aggregaat in beton. In die eksperimentele program is 0%, 30% en 100% herwonne
betonaggregaat gebruik om natuurlike aggregaat gedeeltelik be vervang om sodoende die
geskiktheid as betonaggregaat te bestudeer.
Deur toetse uit te voer op ‘n beperkte sterkte-klas beton, soos toetse vir die bepaling van
druksterkte, Young’s modulus, kruip, krimp en duursaamheid, is daar bevind dat sekere soorte
herwonne betonaggregaat heel moontlik gebruik kan word in struktuurbeton. Toe beton met
100% herwonne betonaggregaat vergelyk is met beton met 100% natuurlike aggregaat, is bevind
dat daar ‘n klein vermindering in sterkte was, maar waar beton met 30% herwonne
betonaggregaat vergelyk is met beton met 100% natuurlike aggregaat, het die resultate byna
dieselfde sterkte getoon. Dus op grond van gedetaileerde eksperimentele resultate is ‘n aantal
aanbevelings gemaak vir kenmerke van herwonne betonaggregaat wat in betonmengsels gebruik
sal word met inagneming van die gehalte van herwonne betonaggregaat. Die resultate vir beton
met 30% en 100% herwonne betonaggregaat word vergelyk met beton wat slegs natuurlike
aggregaat bevat. Sekere voorstelle gegrond op meganiese eienskappe en duursaamheid van die
beton word gemaak, asook aanbevelings vir toekomstige studies van herwonne betonaggregaat
wat ons sal help om ons kennis vir die toepassing van herwonne betonaggregaat uit te brei.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/17962 |
| Date | 12 1900 |
| Creators | Chandra Paul, Suvash |
| Contributors | Van Zijl, G. P. A. G., Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Format | 157 p. : ill. |
| Rights | Stellenbosch University |
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