Main Objective
Assess partially replacing coarse aggregate with crumb rubber for lightweight concrete.
COMPLETED RESEARCH
EVALUATE THE EFFECT OF PARTIAL REPLACEMENT OF COARSE AGGREGATES WITH CRUMB RUBBER FOR LIGHT WEIGHT CONCRETE
Using recycled tire crumb rubber as a partial coarse-aggregate replacement to create lower-density concrete and give waste tires a useful second life.
Kampala, Uganda Construction Materials 2026
Project Overview
This research studied Grade 15 concrete in which recycled crumb rubber replaced 0%, 7.5%, 15% and 20% of conventional coarse aggregate by weight. It assessed workability, density, compressive strength and water absorption to identify a practical balance between reduced self-weight and construction performance.
RESEARCH PROBLEM
Waste tires are persistent; aggregates are resource-intensive.
Used vehicle tires are non-biodegradable and difficult to dispose of, while conventional concrete relies on heavy natural aggregates. Crumb rubber can lower concrete weight and recycle tires, but it can also change strength, porosity and workability. This study identifies the mix levels with the best trade-offs.
OBJECTIVES
Research Objectives
Workability
Determine the effect of crumb rubber on fresh concrete slump.
Compressive Strength
Evaluate strength development at each rubber-replacement level.
Optimum Mix
Identify a replacement level with an acceptable balance of strength and reduced density.
MATERIALS
Materials Used
Portland Cement
Binder used in the 1:2:4 Grade 15 concrete mix.
Crumb Rubber
Recycled vehicle-tire particles used in place of coarse aggregate.
Natural Aggregates
Fine aggregate and crushed stone for control and comparison mixes.
Clean Water
Mixing water used in the nominal 1:2:4 concrete mix.
METHODOLOGY
Research Methodology
Concrete was prepared and evaluated across increasing crumb-rubber replacement levels under controlled laboratory conditions.
Material Characterisation
Specific gravity, water absorption and grading were measured for crumb rubber.
Mix Proportions
Four mixes contained 0%, 7.5%, 15% and 20% crumb rubber by coarse-aggregate weight.
Specimen Casting
Grade 15 concrete specimens were cast using a 1:2:4 mix ratio.
Curing
Samples were cured and evaluated at 7, 14 and 28 days.
Performance Tests
Slump, density, strength and absorption were assessed for every mix.
Mix Comparison
Strength and density were compared to identify the most practical replacement level.
KEY FINDINGS
Research Results
Crumb rubber successfully reduced concrete density, but higher volumes reduced compressive strength substantially.
15%
Best balance of weight reduction and 28-day strength
10.35 MPa
28-day strength at the 15% replacement level
2188 kg/m³
Density at the 15% replacement level
16.85 MPa
28-day control strength
1.310
Specific gravity of crumb rubber
2023 kg/m³
Lowest density measured at higher replacement
CONCLUSIONS
Major Findings
Tire-Waste Recovery
Crumb rubber offers a productive destination for recycled vehicle tires.
Reduced Concrete Weight
The lower-density rubber aggregate enabled lightweight concrete behaviour.
15% Was Most Balanced
The 15% mix combined lower density with the strongest modified-concrete result.
RECOMMENDATIONS
Next Steps
Use 15% crumb rubber for lightweight, non-structural applications.
Pre-treat rubber with an alkaline solution or cement slurry to improve bonding.
Use rubberised concrete for pavements, walkways, partition elements and garden slabs.
Study durability and long-term structural performance further.