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.

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.

<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>

Many highway and hydraulic structures in North America have been reported to be affected by alkali aggregate reaction (ASR). It is anticipated that most of these structures will be demolished as they approach the end of their service lives. Recycling demolished concrete as aggregates in new concrete is an option that not only reduces the amount of construction demolition waste (CDW) disposed in landfills but also lessens the consumption of non-renewable resources such as natural aggregates. However, the use of recycled concrete aggregate (RCA) in new concrete requires detailed research to make sure that the durability of the recycled material is not compromised, especially if the RCA had been previously affected by ASR. In this research project, coarse recycled concrete aggregate (RCA) is reclaimed and processed from distinct members (i.e. foundation blocks, bridge deck and columns) of an ASR-affected overpass after nearly 50 years of service. RCA concrete mixtures incorporating 50 and 100% replacement are manufactured and stored in conditions enabling further ASR development. Mechanical (i.e. Stiffness Damage Test - SDT) and microscopic (Damage Rating Index - DRI) analyses are performed at a fixed “secondary” induced expansion of 0.12%. Results show that the overall performance of the ASR-affected recycled mixtures depends upon the “past” condition of the RCA particles. Moreover, the DRI was able to capture the “past” and “secondary” induced expansion and damage of affected RCA while the SDT only detected the “secondary” distress development. Lastly, an adapted version of the DRI was proposed to further evaluate the overall damage of recycled concrete along with properly displaying “past” and “secondary” induced distress.

Recycled concrete is among the rising eco-friendly construction materials which helps to reduce waste and the need for new natural resources. However, such concrete may present previous deterioration due to, for instance, alkali-silica reaction (ASR), which is an ongoing distress mechanism that may keep being developed in the recycled material. This work aims to evaluate the potential of further distress and crack development (i.e. initiation and propagation) of AAR-affected RCA concrete in recycled mixtures displaying distinct past damage degrees and reactive aggregate types. Therefore, concrete specimens incorporating two highly reactive aggregates (Springhill coarse aggregate and Texas sand) were manufactured in the laboratory and stored in conditions enabling ASR development. The specimens were continuously monitored over time and once they reached marginal (0.05%) and very high (0.30%) expansion levels, they were crushed into RCA particles and re-used to fabricate RCA concrete. The RCA specimens were then placed in the same previous conditions and the “secondary” ASR-induced development monitored over time. Results show that the overall damage in ASR-affected RCA concrete is quite different from affected conventional concrete, especially with regards to the severely damaged RCA particles, where ASR is induced by a reactive coarse aggregate, as the RCA particle itself may present several levels of damage simultaneously caused by past/ongoing ASR and newly formed ASR. Moreover, the influence of the original damage extent in such RCA concrete was captured by the slightly damaged RCA mixture eventually reaching the same damage level as the severely damaged mixture. Furthermore, the original extent of deterioration influence the “secondary” induced expansion and damage of RCA concrete since the higher the original damage level, the higher the cracks numbers and lengths observed in the RCA concrete for the same expansion level whereas wider cracks are generated by RCA having previously been subjected to slight damage thus indicating the difference in the distress mechanism as a function of original extent of damage. In addition, it has been found that distress on RCA containing a reactive sand generates and propagates from the residual mortar (RM) into the new mortar (NM) as opposed to RCA containing a reactive coarse aggregate, being generated and propagated from the original coarse aggregate (i.e. original virgin aggregate – OVA) into the NM. Likewise, RCA containing a reactive sand caused longer and higher number of cracks for the same “secondary” induced expansion than the RCA made of reactive coarse aggregate. Finally, novel qualitative and descriptive models are proposed in this research to explain ASR-induced distress generation and propagation on RCA mixtures made of reactive fine and coarse aggregates.