Beyond RCA: Advancing Concrete Performance and Sustainability with Alternative Aggregates from Recycled and Byproduct Materials
Presented By: Kevin Shepherd
Affiliation: Belter Tech
Description: The concrete industry is increasingly challenged to reduce embodied carbon, conserve natural resources, and improve material performance while meeting growing infrastructure demands. While recycled concrete aggregate (RCA) has played an important role in advancing sustainability, it alone cannot address the full scope of environmental and performance challenges facing modern concrete construction. This presentation focuses on alternative aggregates produced from recycled and industrial byproduct materials, highlighting solutions that extend beyond RCA and enable scalable, circular-economy pathways for concrete. The presentation will examine a range of engineered and synthetic aggregates derived from industrial byproducts, post-industrial waste, and recycled materials, emphasizing how controlled processing and material design can produce aggregates with consistent physical properties and predictable performance. Key topics include particle morphology, density, absorption, gradation control, and interfacial transition zone behavior, and how these characteristics influence fresh and hardened concrete properties such as workability, strength development, durability, and thermal performance. Life cycle considerations will be integrated throughout, with discussion of embodied carbon reduction, landfill diversion, regional material sourcing, and alignment with Environmental Product Declarations (EPDs) and emerging low-carbon procurement policies. Case studies from ready-mix, precast, and specialty concrete applications will demonstrate how alternative aggregates can be successfully incorporated into real-world projects while meeting engineering and quality expectations. The presentation will conclude with a discussion of standardization and specification pathways, including quality control frameworks, performance-based acceptance strategies, and opportunities for broader adoption within ACI and ASTM guidance. Attendees will leave with practical insights into evaluating,
Concrete with Muck and Recycled Steel Fibers
Presented By: Alessandro Fantilli
Affiliation: Polytechnic University of Turin
Description: The excavation of new tunnels generally produces a huge amount of crushed rock, so-called muck. Among the possible reuses of this waste material, aggregate of structural concrete is the most attractive, especially from an environmental point of view. Indeed, it permits general contractors to avoid the landfilling of high-quality excavated materials, and concrete industry to reduce the depletion of natural resources. As muck does not always show the same quality during the excavation, ADVANTEX research project was developed with the aim of finding solutions capable of compensating for the performance deficiencies when concrete aggregate changes. Compression and flexural tests were performed on concretes made with muck in place of coarse natural aggregate, with and without the addition of recycled steel fibers from end-of-life tires. As a result, fibers can increase not only the toughness of concretes, but also compressive and flexural strength, regardless of the type of aggregate. As fibers can also substitute steel reinforcing bars in structural elements, the sustainability of concrete made with muck is further increased.
Circular Utilization of Reclaimed Fly Ash and Industrial Wastes for Sustainable Geopolymer Concrete
Presented By: Aamar Danish
Affiliation: Texas State University San Marcos
Description: The declining availability of high-quality fly ash (FA) and the accumulation of industrial and post-consumer wastes present major challenges for sustainable construction and waste management. At the same time, large quantities of FA remain landfilled, while wastes such as end-of-life tire crumb rubber (WCR), waste spent garnet (WSG), and waste foundry sand (WFS) are often disposed of in landfills or stored onsite, occupying valuable land and posing environmental risks. This research investigates the potential of geopolymer technology to upcycle reclaimed fly ash (RFA) together with multiple waste streams to develop sustainable construction materials. RFA and ground granulated blast furnace slag (GGBFS) were used as binders, with river sand (RS), WCR, WSG, and WFS incorporated as fine aggregate replacements. RFA replaced 40–60 % of GGBFS, while RS was replaced by 30–50 % of WCR, WSG, or WFS. The performance of these geopolymers was evaluated under different curing regimes, including ambient-temperature curing (ATC), ambient-temperature water curing (AWC), high-temperature curing (HTC), and high-temperature water curing (HWC). Fresh and hardened properties were assessed through flow diameter, mechanical performance, transport properties, durability indicators, and microstructural characteristics. The results showed that geopolymers containing up to 60 % RFA achieved comparable or improved durability performance compared with mixtures with higher GGBFS content, particularly in resistance to acid attack, drying shrinkage, and high-temperature exposure. Incorporating 30 % WCR provided adequate fluidity and mechanical performance for several construction applications, although higher rubber contents reduced strength. Similarly, at least 30 % of WSG and WFS can replace RS without significant performance loss, while 50 % replacement is feasible with moderate reductions in carbonation resistance. Among the curing regimes, AWC generally produced superior overall performance,
Valorization of Decommissioned Wind Turbine Blades as Aggregates in Concrete
Presented By: Mohamed Ahmed
Affiliation: Universite de Sherbrooke
Description: The increasing volume of decommissioned wind turbine blades (WTBs) presents a critical environmental challenge due to their non-biodegradable fiber-reinforced polymer (FRP) composition. This study investigates the feasibility of repurposing glass fiber-reinforced polymer (GFRP) waste from WTBs as aggregate material in concrete production, with emphasis on mechanical performance and practical implementation. Wind turbine blade aggregates (WTBA) were produced through controlled cutting into the favorable sized particles and incorporated into concrete at 25%, 33 %,66% and 100 % volumetric replacement ratios of natural coarse aggregates. Two aggregate types were evaluated: (a) WTB aggregates without wood and (b) WTB aggregates combined with wood. Both aggregate types underwent surface treatment using an adhesive coating followed by silica fume and fly ash application to improve the interfacial transition zone (ITZ) between aggregates and cement paste. Results show that untreated WTBA and treated with fly ash led to a reduction in compressive strength due to weak bonding and smooth aggregate surfaces. In contrast, surface-treated WTBA by silica fume significantly improved mechanical performance, achieving compressive strength comparable to conventional concrete and enhanced tensile strength due to improved load transfer across the interface. Overall, the results demonstrate that WTBA can be effectively used as an alternative to natural aggregates when appropriate surface treatment is applied. This approach provides a practical solution for recycling composite waste while maintaining structural performance in concrete.
Use of Recycled Tire Rubber Particles in Concrete for Pavement and Structural Construction
Presented By: Qingli Dai
Affiliation: Michigan Technological University
Description: The increasing accumulation of waste tire rubber has created significant environmental challenges and has motivated its use in concrete as a sustainable alternative to natural aggregates. Recycled rubber particles used as partial replacements for fine aggregates can help reduce scrap tire disposal while also lowering the consumption of virgin aggregates in pavement and structural construction. This study investigates the effects of rubber particle size and replacement level on the mechanical properties and durability performance of concrete for practical infrastructure applications. Two rubber particle size ranges were used as partial fine aggregate replacements: larger particles ranging from 1.18 to 4.75 mm and finer particles passing the 0.3 mm sieve. Experimental evaluations included workability, compressive strength, splitting tensile strength, ultrasonic pulse velocity, drying shrinkage, and freeze–thaw resistance. The results indicate that the incorporation of rubber generally reduces concrete strength because rubber has lower stiffness than mineral aggregates and forms a relatively weak interfacial transition zone with the cement matrix. However, the extent of performance reduction strongly depends on particle size. Mixtures containing fine rubber particles showed better strength retention and durability performance than mixtures containing larger rubber particles. The finer particles were more uniformly distributed in the matrix, which improved particle packing, reduced internal voids, and promoted more uniform stress transfer. Field applications have also been evaluated through rigid pavement construction and monitoring in Muskegon, Michigan. Overall, the findings suggest that smaller rubber particle sizes are more suitable for practical pavement and structural concrete applications, providing a better balance between sustainability benefits and engineering performance while supporting beneficial reuse of waste tire rubber in infrastructure construction.