In order to reach climate goals, there is a need to reduce the embodied emissions of concrete. Utilizing recycled materials, such construction and demolition waste, plastics, and MSWI ashes, can help achieve this while promoting a circular economy. However, there are challenges due to the inherent variabilities and/or potential presence of heavy metals and undesirable chemicals in many recycled materials. Academic and industry researchers, practitioners and students should attend this session to learn about the challenges of and potential solutions for the use of recycled materials in concrete.
Learning Objectives:
(1) Review characterization techniques for recycled materials;
(2) Discuss emerging methods to treat recycled materials to facilitate their use;
(3) Discuss impact of treated recycled materials on cement properties;
(4) Discuss potential of implementing emerging treatment processes and resultant recycled materials in practice.
This session has been approved by AIA and ICC for 2 PDHs (0.2 CEUs). Please note: You must attend the live session for the entire duration to receive credit. On-demand sessions do not qualify for PDH/CEU credit.
Utilizing Convex Hull Algorithms to Advance Modeling of Systems with Recycled Concrete Aggregates
Presented By: Matthew Adams
Affiliation: New Jersey Institute of Technology
Description: A computational modeling procedure for generating a random aggregate structure (RAS) for recycled concrete aggregate (RCA) materials is presented in this work. The two-dimensional aggregate generation was based on a convex hull algorithm to randomize arbitrary planar shapes of RCA particles. During the generation of RAS, randomizations of the maximum aggregate size and spatial distribution of RCA particles were considered. Finite-element models for RCA systems were generated based on an extensive image analysis procedure. Numerical analyses were performed for 12 different RCA systems including crushed-shape and rounded-shape aggregates by varying the morphological parameters of the RCA particles. The mechanical performance of RCA systems with different particle shapes, maximum aggregate sizes, adhered mortar content levels, and aggregate ratios were used as factors to evaluate.
Closing the Material and Carbon Loops in Sustainable Concrete Recycling
Presented By: Jialai Wang
Affiliation: University of Alabama
Description: Concrete with ordinary Portland cement (OPC) as the primary binder is the most widely used
construction material globally. However, the production of OPC-based concrete significantly contributes to three major societal challenges: carbon emissions, resource depletion, and solid waste generation. Construction and demolition (C&D) waste has already become one of the largest waste streams worldwide. In line with circular economy principles, this study proposes a pathway to fully recycle end-of-life concrete into new aggregates and highly reactive pozzolanic materials, while also capturing and recycling CO2 emitted during cement and concrete manufacturing. Notably, this process generates no new waste.
Upcycling Demolished Concrete Paste for Use as Alternative Fillers/SCMs via 2-Step Carbonation
Presented By: Shiho Kawashima
Affiliation: Columbia University
Description: To meet climate goals, there is a need to lower the embodied carbon of concrete. A potential pathway is to implement carbon mineralization schemes to convert industrial wastes (e.g. construction and demolition waste) into fillers and supplementary cementitious materials (SCMs). This can simultaneously upcycle waste and provide a permanent form of CO2 storage. Further, by tuning the parameters of the mineralization process, it is possible to tailor the properties of the derived fillers and SCMs with the aim to introduce beneficial properties to the final cement-based system. This talk will present a summary of an investigation where a two-step pH swing approach was implemented on hydrated cement paste (simulating demolished concrete) to produce two products, high-purity calcium carbonate (CaCO3) fillers and Si-rich SCMs.
Investigating Waste Plastic as a Cement Additive
Presented By: Rachel Cook
Affiliation: The University of Alabama
Description: Managing plastic waste is an ever-growing problem. In the next 10 years alone, global plastic production is projected to increase by 40%, and experts expect that the oceans will contain more plastic than fish by weight by 2050. To mitigate this Plastic Tide, this preliminary study investigates the feasibility of plastic waste as a cement additive. A post-consumer semi-crystalline polyethylene terephthalate (PET) was ground using low temperature milling to achieve micrometer and sub-micrometer sized plastic particulates. PET particulates were then incorporated into Portland cement mixtures at = 20 mass % replacements using a liquid-to-solid ratio of 0.50 to form cement-plastic composite matrices. Cement-plastic matrices were evaluated via isothermal calorimetry, micro-computed tomography, and mechanical (i.e., compression) testing. Results provide a positive indication of the feasibility of post-consumer PET as a partial cement replacement material. Overall, the outcomes of this study will help provide an indication on the viability of waste PET as a cement additive.
Surface Modification of Tire Rubber: Treatment Characterization and Impact on the Properties of Cement-Rubber Composites
Presented By: Raissa Ferron
Affiliation: University of Texas at Austin
Description: Surface modification of scrap tire rubber is a potential solution to improve compressive strength of rubberized concrete by altering the surface properties of rubber to enhance cement-rubber bonding. This presentation investigates the surface characteristics of rubber pretreated with a two-step chemical process and evaluates the effectiveness of this treatment process on the fresh and hardened state properties the resultant cement-rubber mortar composite.
The Materials Effects of Municipal Solid Waste Bottom Ash for Use in Portland Cement Concrete
Presented By: Christopher Ferraro
Affiliation: University of Florida
Description: Municipal solid waste incineration (MSWI) offers a sustainable waste management solution, effectively reducing landfill volume while enabling energy recovery. The residual byproducts of incineration, namely bottom ash BA, is often disposed in landfills. This research investigates the potential of utilizing BA as a raw material in concrete production, specifically exploring the role of metallic aluminum in MSWI residues as a natural air-entraining agent. This research focuses on the material aspects of the hydrogen gas generation which takes place in portland cement systems at early ages.
Mechanism of Chlorellestadite Carbonation in WTE Ashes
Presented By: Nishant Garg
Affiliation: University of Illinois at Urbana-Champaign
Description: Chlorellestadite (Ca10 (SiO4)3(SO4)3Cl2) is a commonly occurring phase in thermally treated waste-to energy ashes and eco-cements. CO2 exposure is known to enhance the strength of chlorellestadite-enriched cementitious systems. However, the mechanism through which chlorellestadite develops strength upon CO2 exposure is not well understood. Here, we address this gap by investigating the carbonation behavior of high-purity, synthetic chlorellestadite. Our findings suggest that chlorellestadite carbonation involves three parallel reactions (R1-R3). The first reaction (R1) includes the carbonation of chlorellestadite to form CaCO 3 polymorphs, gypsum, amorphous SiO2 , and calcium chlorosilicate. In R2, the calcium chlorosilicate formed in R1 reacts with CO2 and forms CaCO3 polymorphs, sinjarite, and amorphous SiO2. Finally, in R3, the sinjarite formed in R2 also reacts with CO2 to form CaCO3 polymorphs. Stoichiometric calculations based on reactions R1-R3 indicate that chlorellestadite can theoretically sequester 29.7% of CO2. The observed CO2 reactivity of chlorellestadite can be harnessed to develop chlorellestadite containing cementitious composites where strength development comes from CO2 exposure. These findings indicate that CO2 exposure can facilitate upcycling chloride-rich industrial waste by-products, such as thermally treated waste-to-energy ashes, in cementitious systems.