Researchers at RMIT reported a laboratory method for making lightweight concrete in which waste tire rubber replaced all of the conventional coarse aggregate. The key was not simply adding rubber: specially designed steel molds pressed the fresh mix as it set. In the tested mixes, this preloading improved strength compared with normally cast rubberized concrete.
What “100% tire-rubber aggregate” means
The 2022 RMIT study replaced 100% of the conventional coarse aggregate in its tested formulation with waste tire rubber particles. It did not replace cement, sand, or every aggregate fraction in concrete. The paper, “An Innovative Study on Lightweight Concrete for the Complete Replacement of Conventional Coarse Aggregates by Waste Tire Rubber Particles,” was published in Resources, Conservation & Recycling. Read the study.
The distinction matters: this is a result for specific lightweight-concrete mixes, not evidence that any concrete recipe can use tire rubber for all its aggregate or that the material is approved for every structural application.
How the researchers strengthened the rubberized mix
Pressure while the concrete set
Rubberized concrete can lose strength because tire rubber bonds poorly with cement paste. The study describes water entering pores in the rubber during mixing and voids remaining at the rubber–cement interface as the material sets. To address this, the team cast the mixes in purpose-built steel molds that applied pressure while the fresh concrete hardened. The intended effect was to compress rubber particles and pores and improve their interface with the cement matrix.
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The researchers compared this preloaded material with normally cast rubberized concrete. Their results therefore show the effect of preloading within the study; they are not a direct strength comparison with ordinary concrete made using mineral coarse aggregate.
What the tested mixes achieved
The study authors reported that, compared with normally cast rubberized concrete, preloaded mixes achieved increases of up to the following amounts:
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| Measure | Reported increase | Comparison |
|---|---|---|
| Compressive strength | Up to 97% | Preloaded versus normally cast rubberized concrete in the study |
| Flexural strength | Up to 59% | Preloaded versus normally cast rubberized concrete in the study |
| Tensile strength | Up to 20% | Preloaded versus normally cast rubberized concrete in the study |
The paper also reports a maximum compressive strength of 18 MPa at a density of 2,000 kg/m³ for its tested formulation. These are experimental results, not guaranteed specifications for a commercial product or other mix designs. RMIT’s account of the study summarizes the method and findings.
How this result compares with other rubber-concrete studies
Rubber-concrete performance depends on which aggregate fraction is replaced, the replacement amount, the mix, and any processing treatment. The following studies use different materials or methods, so their percentages and strength results should not be treated as direct comparisons with RMIT’s preloading work.
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| Study and material | Replacement tested | Reported finding |
|---|---|---|
| 2023 study: waste-tire fine aggregate replacing river sand | Up to 75% | As replacement increased, slump, density, and mechanical strength declined. The authors said 20% could be used in some structural concrete with relatively low design strength. Study |
| 2022 study: recycled aggregate and crumb rubber | Crumb rubber at 5%, 10%, 15%, and 20% | The tested 5% level was described as usable for structural applications under that study’s conditions. Its 28-day compressive strength was 21.1% below recycled-aggregate concrete and 32.8% below the control concrete. Study |
| 2024 study: high-performance concrete with tire-rubber fine aggregate | 5%, 10%, and 15% | Strength compromise was minimal up to 10% and more noticeable at 15%; rubber increased ductility and damping. Study |
These results reinforce why a high replacement percentage cannot be separated from its material fraction and method: replacing fine aggregate is not the same as replacing coarse aggregate, and RMIT’s pressure-assisted process is a specific intervention.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.What the study does—and does not—establish
The findings establish laboratory performance for the formulations and conditions tested. The reported material is a structural lightweight-concrete formulation under the paper’s criteria, but that does not amount to blanket approval for all buildings or uses. The available reports do not establish routine commercial production, an available preloading system, or validated field-scale performance.
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As study co-author and team leader Prof. Jie Li told New Atlas, replacing typical concrete’s coarse aggregate with used tire rubber could reduce natural-resource consumption while addressing the challenge of disposing of used tires. New Atlas’s 2022 report quotes Li and describes the research.
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