Crushed or recycled concrete aggregates (CCA/RCA) is an increasingly popular material as a replacement for natural aggregates in concrete due to industry demands for more recycled, lower carbon and responsibly sourced materials. In the UK, the majority of CCA is utilised in non-structural applications such as: a general fill material, road base/subbase or in low-grade concrete. Recycled aggregate producers however, are seeking new ways to incorporate CCA into higher value applications such as structural concrete to increase profits. Opportunities to incorporate CCA into structural concrete may also arise because of project demands for sustainability or in situations where natural aggregates are in short supply. Limited research has been published regarding the effect of coarse CCA on the durability of structural concrete, particularly in respect to water and chloride ion ingress and possibility of corrosion initiation. The aim of this EngD research programme was to investigate the effect of coarse CCA and supplementary cementitious materials (SCMs) on the durability performance of structural concrete, with particular emphasis on the key liquid transport mechanisms within concrete, namely absorption by capillary action, diffusion and migration. This addressed an industry concern regarding the detrimental effect of coarse CCA which has resulted in a limit on replacement levels of coarse natural aggregates in structural concrete, as defined in Eurocodes and local national standards for concrete. In this study, structural concrete was produced with varying levels of coarse CCA replacement (up to 100%), from five different sources and/or structural elements across the UK, with various combinations of SCMs to replace in part the Portland cement. Petrographic analysis was used as an innovative technique to characterise the coarse CCA sources to determine suitability which yielded positive results. The durability performance of the resultant concrete was analysed by exposing the concrete to aggressive chloride environments. The results indicate that the inclusion of coarse CCA, even as low as 20%, had a detrimental effect on the durability performance of structural concrete, in relation to absorption by capillary action, diffusion and migration. This effect however, can be offset through the use of SCMs, which have been shown to outperform control Portland cement concrete with 100% natural aggregates in durability performance tests. The results also suggest that cementitious materials had a greater influence on durability performance than the type and source of coarse aggregates used. It is recommended that the replacement of natural aggregate with coarse CCA be limited to 30% in cases where compliance with the 28 day characteristic strength is of particular importance. If the criterion for compliance at 28 days can be relaxed and the compressive cube strength of concretes with SCMs tested at later ages for conformity (56 or 90 days), then higher quantities of coarse CCA may be incorporated up to 60% to produce a more sustainable structural concrete. It is recommended that Portland cement is partially replaced with 50% ground granulated blast-furnace slag (GGBS) to produce a CEM III/A concrete. This is a significant step towards the potential wider implementation of coarse CCA in structural concrete, provided a suitable quantity of SCM is adopted along with a reliable and consistent source of coarse CCA.

Os resíduos de concreto apresentam grande potencial para serem reciclados quando comparados com outros resíduos, entretanto, o número de estudos realizados no Brasil é muito pequeno dificultando a utilização deste material em dosagens estruturais. Em virtude disso, desenvolveu-se um estudo teórico-experimental visando caracterizar algumas propriedades do agregado e do concreto reciclado; no estudo teórico exploraram-se aspectos relacionados à geração, deposição, processos para recuperação, britagem, casos práticos, pesquisas envolvendo reciclados de concreto e as recomendações normativas existentes. No desenvolvimento experimental, analisou-se a influência do período decorrido entre a moldagem e a reciclagem do concreto nas propriedades dos agregados e concretos. Os resultados indicam que resíduos reciclados logo após sua geração, contribuem positivamente para as propriedades mecânicas do concreto, devido à existência de grande quantidade de partículas não-hidratadas de cimento, tais concretos obtiveram resultados superiores para a resistência à compressão e tração quando comparados aos concretos com agregados naturais. / The concrete residues show a large potential to be recycled when compared with other residues; however, the number of studies in Brazil is very small hindering the use of this material in structural dosage. By virtue of that, it was developed a theoretical-experimental study to characterize some properties of aggregate and recycled concrete; in the theoretical study it was explored aspects related to the generation, deposition, processes for recovery, crushing, practical cases, researches involving recycled of concrete and the existent normative recommendations. In the experimental development, it was analyzed the influence of the period elapsed between the molding and the recycling of the concrete in the properties of the aggregates and concretes. The results indicate that residues recycled soon after generation, these contribute positively to the mechanical properties of the concrete due to the existence of large amount of nonhydrated cement particles, such concretes obtained results superiors for the compression strenght and tensile strenght when compared to the concretes with natural aggregates.

Application of recycled concrete aggregates (RCA) has increased recently as a sustainable alternative in concrete construction. Although application of RCA has substantially grown over the past decades, issues related to its structural performance and long-term behaviour still prevent its widespread application, especially in structural purposes. In this study, a new mixture proportioning method called the “Equivalent Volume (EV)” method is proposed for RCA concrete, which is developed on the assumption that the RCA mix is based on a companion conventional concrete mix having the same volume of “cement paste and aggregates” as the companion mixture. RCA mixes containing different aggregate types and mechanical properties were designed using the EV method. Chemical, mechanical and non-destructive tests were performed and their performance was investigated. Finally, a quality control protocol for evaluating the suitability of RCA sources for structural applications is proposed. Results show that the EV method seems a promising approach to mix-proportion eco-friendly recycled concrete mixes. Moreover, the RCA type and properties seem to influence in the behaviour of RCA concrete and thus should be accounted in the mix- design.

Ce travail se situe dans le cadre du projet ANR VBD ECOREB qui œuvre avec le projet national PN RECYBETON à la levée des verrous technologiques propres à l’utilisation des granulats recyclés en vue de la formulation des bétons de structure.Pour cette étude six bétons de granulats recyclés correspondant à deux classes de résistance C25/30 et C35/40 et à une classe de consistance S4 sont élaborés. Ces formulations, définies dans le cadre du PN RECYBETON, sont conçues à partir de deux formulations de référence en substituant partiellement ou complètement les granulats naturels par des matériaux issus du recyclage des bétons. Un programme expérimental a été réalisé pour déterminer les propriétés du béton à l’état frais et à l’état durci. Les résultats des essais mécaniques montrent que pour la même classe de résistance à la compression, l’incorporation des granulats recyclés dans le béton induit une diminution de la résistance à la traction et du module d'élasticité .aussi bien qu’une augmentation de la déformation au pic et de la déformation ultime. Sous compression cyclique du type charge-décharge, l’endommagement au pic de contrainte augmente lorsque le taux de substitution est important alors que la vitesse d’endommagement devient plus faible. La campagne d’essais du fluage menée sur des poutres chargées en flexion trois points indique que la cinétique du fluage est influencée par la présence des granulats recyclés et elle est d’autant plus accélérée que le taux de remplacement est important.Les résultats expérimentaux de cette étude ainsi qu’un nombre important des résultats rapportés dans les références bibliographiques ont permis d’évaluer la validité des relations analytiques développées pour prédire les propriétés mécaniques du béton des granulats naturels en vue de leur utilisation pour le béton des granulats recyclés. On montre que ces expressions nécessitent la connaissance de la résistance moyenne à la compression, fcm aussi bien qu’un coefficient qui tient compte de l’effet des granulats recyclés. La comparaison entre les courbes contrainte-déformation obtenues dans le cadre de cette thèse et certains modèles montre, qu’avec les modifications proposées, ils décrivent d’une manière satisfaisante le comportement jusqu’à la rupture. / This work is part of the ANR VBD ECOREB which aims with the project PN RECYBETON to remove the technological locks for the use of recycled aggregates for the formulation of structural concretes.For this study, six concretes of recycled aggregates corresponding to two classes of compressive strength C25 / 30 and C35 / 40 and S4 class of workability are developed. These mixtures, defined in the framework of the PN RECYBETON, are derived from two reference formulations by substituting partially or completely the natural aggregates with materials resulting from the recycling of concretes. An experimental program was carried out to determine the properties of concrete in fresh state and hardened state. The results of mechanical tests show that for the same class of compressive strength, the incorporation of recycled aggregates into the concrete induces a decrease in the tensile strength and the elastic modulus as well as an increase in the peak and ultimate strains. Under loading-unloading compression, the damage at the peak stress increases when the substitution rate is high while the damage rate becomes lower The creep tests carried out on beams loaded under three-point bending indicate that creep kinetics are influenced by the presence of recycled aggregates and is accelerated as the replacement rate is important.The experimental results of the present study together with an extensive number of results reported in the literature have allowed evaluating the current relationships used for predicting mechanical properties of recycled concrete aggregates (RAC). The validity of many analytical expressions of the stress-strain relationship has been also studied and the effect of replacement ratio was taken into account. It was pointed out that design codes relationships dedicated to assess the mechanical properties and the stress-strain compressive curve of natural aggregates concretes (NAC) are not adequate to predict the behavior of recycled aggregates concrete (RAC). It is established that these properties are related to fcm and to a parameter, which takes into account the effect of the recycled aggregates. The comparison between the stress-strain curves obtained in this thesis and some models shows that, with the proposed modifications, these models satisfactorily describe the behavior up to failure.

El presente trabajo de investigación para optar el título en Ingeniería Civil, con énfasis en la rama de construcción, tuvo como finalidad evaluar y comparar el comportamiento del concreto con diferentes proporciones de sustitución de agregado grueso natural (AN) por agregados de concreto reciclado (ACR) con el fin obtener un diseño de concreto que permita la disminucion y uso de agregados naturales, y asi disminuir la depredacion de canteras. El comportamiento se evaluó mediante el análisis de las propiedades mecánicas y durabilidad de los tipos de mezclas realizados con el objetivo de obtener una proporción de sustitución óptima de AN por ACR para que las propiedades se encuentren dentro de los parámetros que indican las normas. Por otro lado, se realizó un modelo de una estructura aporticada para hacer una Evaluación de Impacto Ambiental mediante el uso de la metodología Life Cycle Assessment (LCA) en el programa Athena y, posteriormente, se comparó los resultados obtenidos en dicho programa. / The present research work to choose the degree in Civil Engineering, with emphasis in the construction branch, had the purpose of evaluating and comparing the behavior of concrete with different proportions of substitution of natural coarse aggregate (AN) by aggregates of recycled concrete (ACR ) in order to obtain a concrete design that allows the reduction and use of natural aggregates, and thus reduce the depredation of quarries. The behavior was evaluated by analyzing the mechanical properties and durability of the types of mixtures made with the objective of obtaining an optimal substitution ratio of AN by ACR so that the properties are within the parameters indicated by the standards. On the other hand, a model of a contributed structure was made to make an Environmental Impact Assessment by using the Life Cycle Assessment (LCA) methodology in the Athena program and, subsequently, the results obtained in said program were compared. / Tesis

En la actualidad las cantidades de residuos han incrementado con el pasar de los años, convirtiéndose en una amenaza grave para el medio ambiente. Esto ha generado que reciba mayor atención por las autoridades e investigadores a nivel global, proponiendo usos respetuosos con el medio ambiente de estos residuos, los cuales han ido desarrollando y mejorando en los últimos años. Este estudio profundiza en el posible uso del residuo de vidrio plano como una solución sostenible, al ser adicionados en el concreto. Para esto, se hicieron diseños de mezcla con diferentes cantidades de vidrio pulverizado y se realizaron comparaciones para identificar el efecto en las propiedades del concreto mediante ensayos de asentamiento, resistencia a la compresión y resistencia a la compresión en condiciones de ataque por sulfatos. Los resultados muestran que, para dichas pruebas, la adición de vidrio pulverizado favorece a las características de sus propiedades, presentando además un ahorro económico. / At present the amounts of waste have increased over the years, turning into a serious threat to the environment. This has generated greater attention by authorities and researchers around the world, proposing environmentally friendly uses of these residues, which have been developing and improving in recent years. This study delves into the possible use of pulverized flat glass waste as a sustainable solution, when added to concrete. For this, mixing designs were made with different amounts of glass powder and comparisons were made to identify the effect on the properties of the concrete by slump tests, compressive strength and compressive strength in sulfate attack conditions. The results show that for these tests, the addition of glass powder favors the characteristics of its properties, while presenting an economic saving. / Tesis

Pressure is mounting in the concrete industry to adopt eco-efficient methods to reduce CO₂ emissions. Portland cement (PC), an essential concrete ingredient, is responsible for over two-thirds of the embodied energy of the concrete, generating about 8% of global greenhouse gas emissions. Extraction and transportation of aggregates and raw materials that comprise concrete mixes are also directly linked to their embodied energy; thus, recycled concrete aggregates (RCA) have been proposed as a promising alternative to increase sustainability in new construction. In this context, many studies have been conducted over the past decades on the properties of RCA concrete. Recent studies have shown that suitable fresh (i.e., flowability) and short-term hardened (i.e., compressive strength) properties might be achieved when the unique microstructural features of RCA are accounted for in the mix-design process of the recycled concrete. However, manufacturing RCA from construction demolition waste (CDW) or returned concrete (RC) presents its unique challenges. Amongst others, the variation in the source of RCA and the presence of damage due to several deterioration mechanisms causes major concern. Due to the presence of reactive aggregates in many quarries in Canada, alkali-silica reaction (ASR) is one of the most common deterioration mechanisms. The durability and long-term performance of RCA concrete are not fully understood and should be further investigated, especially in regards to a) the potential of further (secondary) deterioration of recycled concrete bearing coarse and fine alkali-silica reactive aggregates b) the impact of the severity of the initial reaction on mechanical properties and kinetics of expansion in recycled concrete and c) the impact of using sound and alkali-silica reaction (ASR) affected RCA on the chloride diffusivity (and thus corrosion initiation) of concrete. This work aims to appraise the durability performance of RCA concrete made of 100% coarse RCA, particularly two families of RCA selected (i.e., returned concrete RCA, demolished concrete RCA) to represent waste currently being generated. Furthermore, two types of reactive aggregates are selected to investigate the impact of the source of the reaction (i.e. reactive coarse aggregate as original virgin aggregate - OVA and reactive sand within the residual mortar - RM) within the RCA. ASR is the distress mechanism used to introduce damage to the manufactured RCA. A new mix design technique was used to produce recycled concrete mixtures to increase eco-efficiency, improve fresh-state properties, and reduce cement use in RCA concrete. In conclusion, the initial reaction's location and severity significantly impact the compressive strength, SDT parameters, chloride diffusion rate, and shear strength of concrete specimens. Specifically, the location of the initial reaction can influence the distribution and extension of damage within the various parts of recycled concrete, while the severity of the initial reaction can affect the overall integrity of the aggregates as well as the availability of silica and alkalis for secondary reaction. These results demonstrate the importance of assessing the severity of the initial reaction and its source in order to ensure the durability and long-term performance of recycled concrete made with reactive RCA.

Recycled concrete aggregate (RCA) is often used as a replacement of virgin aggregate in road foundations (base course), embankments, hot-mix asphalt, and Portland cement concrete. However, the use of RCA in exfiltration drainage systems, such as French drains, is currently prohibited in many states of the U.S. The French drain system collects water runoff from the road pavement and transfers to slotted pipes underground and then filters through coarse aggregate and geotextile. The primary concerns with using RCA as a drainage media are the fines content and the precipitation of calcium carbonate to cause a reducing in filter fabric permittivity. Additional concerns include the potential for rehydration of RCA fines. The performance of RCA as drainage material has not been evaluated by many researchers and the limited information limits its use. A literature review has been conducted on the available information related to RCA as drainage material. A survey was issued to the Departments of Transportation across the nation in regards to using RCA particularly in French drains. Some state highway agencies have reported the use of RCA as base course; however, no state reports the use of RCA in exfiltration drainage systems. This thesis describes the investigations on the performance of RCA as backfill material in French drains. RCA was tested for its physical properties including, specific gravity, unit weight, percent voids, absorption, and abrasion resistance. RCA cleaning/washing methods were also applied to evaluate the fines removal processes. The potential for RCA rehydration was iv evaluated by means of heat of hydration, pH, compressive strength, and setting time. The permeability of RCA was tested using the No. 4 gradation. Long term permeability testing was conducted to evaluate the tendency for geotextile clogging from RCA fines. Calcium carbonate precipitation was also evaluated and a procedure to accelerate the precipitation process was developed. The results show that RCA has a high abrasion value, that is, it is very susceptible to break down from abrasion during aggregate handling such as transportation, stockpiling, or placing. The most effective cleaning method was found to be pressure washing with agitation. RCA has not demonstrated the tendency to rehydrate and harden when mixed with water. The permeability test results show that the No. 4 gradation does not restrict the flow of water; the flow rate is highly dependent on the hydraulic system itself, however excessive fines can cause large reductions in permeability over time. It has been determined that No. 4 gradation of RCA can provide a suitable drainage media providing the RCA is properly treated before its use.

<p dir="ltr">The construction industry is one of the largest contributors to carbon emissions, abiotic depletion of natural resources, and waste generation due to the vast quantity of concrete produced. Concrete’s main components have a significant environmental impact. The manufacturing of cement is responsible for 8% of global carbon emissions. In 2019, over 45 billion tons of aggregates were produced. Furthermore, the production of concrete generated over 600,000 tons of concrete waste in 2018.</p><p dir="ltr">Conversely, vegetation consumes 30% of the global carbon dioxide emissions. Recent studies indicated that cryptogamic species, and in particular moss, present a CO₂ uptake of 6.43 billion metric tons more than bare soil. Cryptogamic covers, such as moss and other CO₂ sequestering organisms, are key for the global cycles of carbon and nitrogen. By promoting the growth of living cryptogamic organisms in concrete building facades and roofs, the carbon footprint of concrete can greatly decrease, potentially achieving sub-zero carbon footprint. To attain this solution, cementitious composites must be designed to have an improved bio-receptivity, defined as a material's ability to be colonized by living organisms, or as a substrate to grow living organisms.</p><p dir="ltr">Previous studies show that the bio-receptivity of cementitious composites depends on a material’s acidity and ability to capture and retain water. Yet, the inter-relationship between these properties and bio-receptivity is currently not well understood. Additionally, existing methods to achieve enhanced bio-receptivity in cementitious composites in terms of are often either expensive or counterproductive in terms of sustainability.</p><p dir="ltr">This thesis aims to investigate and develop new methods to create ultra-sustainable composites with enhanced bio-receptivity and low abiotic depletion of natural resources. Additionally, this thesis aims to understand the importance, inter-relationship, and influence of the acidity and water storage properties of cementitious composites on their bio-receptivity.</p><p dir="ltr">The first portion of this thesis is focused on proposing a new method to enhance bio-receptivity of precast cementitious composites elements through accelerated CO₂ exposure treatment and elucidating the function of recycled concrete aggregate use to create ultra-sustainable composites with enhanced bio-receptivity and low abiotic depletion of natural resources. Thus, this study simultaneously tackles the reduction of waste generation and abiotic depletion of natural resources, as well as the promotion of bio-receptivity while reducing the net carbon footprint of the cementitious composites. Results suggested that the proposed accelerated CO₂ exposure treatment enhanced the bio-receptivity of mortars, especially in mortars with RCFA. The combined effect of the RCFA’s high porosity plus the effect of accelerated CO₂ exposures decrease on pH drastically enhanced the ability of promoting moss growth on mortars, enabling the production of low carbon bio-receptive cementitious material with a sub-zero abiotic depletion of natural resources.</p><p dir="ltr">The purpose of the second portion of this thesis was focused on understanding of the inter-related role of the mortar’s porosity, water absorption, and surface pH on the bio-receptivity of cementitious composites. This portion of this thesis also focused on creating a predictive model of bio-receptivity of mortars as a function of water storage properties and surface pH. By conducting this study, the extent of importance of the water storage properties and surface pH on bio-receptivity can be determined. Results suggested that w/c ratio heavily influences the bio-receptivity of mortar, in which a higher w/c ratio increases bulk porosity, water absorption, and decreases the average surface pH. The use of accelerated CO₂ exposure improved bio-receptivity due to and decrease in average surface pH. Additionally, the combined effects of high w/c ratio and accelerated exposure CO₂ exhibited even greater improvements in bio-receptivity. Furthermore, the increase in w/c ratio resulted in the mitigation of accelerated CO₂ exposure adverse effects on bulk porosity and absorption. The developed bio-receptive predictive model successfully predicts the bio-receptivity of mortars as a function of the average surface pH and water absorption. This bio-receptivity prediction model provides us with an instrument to assist in engineering concretes with a target bio-receptivity. The results of this study also show that, while previous literature indicated a maximum pH of 5.0-5.5 to produce a bio-receptive cementitious composite, the pH threshold to obtain a bio-receptive cementitious composite depends on other factors such as porosity of the material, and it is possible to create bio-receptive concretes with a surface pH of 6.2-8.3.</p><p dir="ltr">This research will contribute to creating target-by-design living-engineered concrete facades that can capture CO₂ while reducing the consumption of natural resources.</p>

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.