Recycling of Concrete by Partial Replacement of Heat Processed Waste Aggregate

Abstract

Concrete is the second highest abandon material on the earth surface after water, it is inorganic in nature therefore it can be a big cause of the construction inorganic unsustainability by accumulating solid waste on the earth surface, in concrete coarse aggregate is the major component of the concrete hence in this research work recycled concrete made with the heat processed used coarse aggregate in first generation concrete, it is qualitative work so it is concentrated on the strength and durability of the concrete made of the partial replacement of the heat processed coarse aggregate, first generation concrete can be further utilize as the second generation by heat and mechanical treatment, mortar starts loosing the bonding between cement and aggregate temperature above 3000C, in this research work recycling of aggregate from waste concrete chunks are heat treated and mechanical rubbing optimum utilization of this recycled aggregate is achieved 15% possible replacement of conventional aggregate with the heat processed aggregate.

Introduction

• Growing urbanization increases concrete demand.

• Conventional concrete uses natural coarse aggregates (from stone mining), leading to:

  • Depletion of natural resources

  • Increase in construction and demolition (C&D) waste

• Recycled Coarse Aggregate (RCA) from demolished concrete is a potential substitute.

• Problem: RCA has a mortar layer adhered to it, reducing strength and altering physical properties (e.g., water absorption, density).

???? 2. Objectives

1. Reduce mortar content on recycled aggregates using heat processing and mechanical abrasion.

2. Compare with other mortar removal techniques (e.g., acid treatment).

3. Evaluate fresh and hardened concrete properties using treated RCA.

???? 3. Literature Review Insights

• Katerusha (2021): HCl treatment removes up to 35% mortar and improves properties like:

  • ↓ Water absorption

  • ↑ Specific gravity

  • ↓ Crushing value

  • ↑ Impact value

• R.S. Selvi (2019): Studied concrete with Barite, Diatomite, Silica Fume, Fly Ash under high temperatures (105°C to 800°C); Barite showed superior thermal performance.

• Alperkurt (2017): Metakaolin improves compressive and flexural strength; optimal replacement at 15%.

• Shafiq et al. (2015): Studied RCA replacement (0%, 30%, 40%, 50%) – strength decreased with higher RCA content.

• Dwivedi (2014): Impurities in RCA (mainly mortar) affect:

  • ↑ Water absorption

  • ↓ Specific gravity & density

  • ↑ Impact & crushing value

• Other Studies: Mineral admixtures (e.g., Fly Ash, Silica Fume) affect workability, hydration, and reactivity. Two types: chemically active vs microfiller.

???? 4. Methodology

?? Mortar Removal Techniques

• Heat Processing at 300–500°C, followed by mechanical abrasion (Los Angeles Machine, no steel balls).

• Acid Treatment (AT-RCA) using HNO? and toothbrush to fully remove mortar — used as baseline for mortar percentage comparison.

???? Aggregate Sampling

???? Concrete Sample Naming

???? Tests Conducted

• Fresh Concrete: Slump cone test (for workability)

• Hardened Concrete:

  • Compressive strength

  • Flexural strength

???? 5. Key Results

???? Material Properties

???? Mortar Removal Efficiency

???? Fresh Concrete (Workability)

• Slump decreased with more RCA content.

• RCA and ashes (like RHA) reduce workability.

• Not suitable for Self-Compacting Concrete (SCC).

• Thixotropic behavior observed during mixing.

????? Hardened Concrete

• Compressive Strength (M25 target): Decreased with higher RCA content.

• Flexural Strength: Also showed reduction compared to control (CR-0).

• Weight Loss: Observed at 14 and 28 days for analyzing cement-water relation.

Conclusion

Used concrete having thick cover of the mortar, thickness of the cover can be reduced by heat treatment and mechanical rubbing. Complete mortar removal is not possible either by heat treatment or acid treatment because some mortar take place in micro cracks. Mechanical properties of aggregate recovered by heat treatment is possible. Maximum utilization of HT-RCA in concrete 15% by weight of the total coarse aggregate. Increasing the percentage of HT-RCA leads decrease in workability continuously, Strength is under the permissible limit up to 15% of replacement. Adhere mortar strength can be varying sample to sample due to its age and grade of the concrete hence HT-RCA having high deviation in effort of recycling.

References

[1] S. Esen, Yuksel. \"Effect of High Temperature in Concrete for Different.\" KSCE Journal of Civil Engineering, 2017: 1-7. [2] Katerusha, Dmytro. \"Barriers to the use of recycled concrete from the perspective of executing companies and possible solution approaches - case study Germany and Switzerland.\" Research Unit International Economics, School of Business and Economics, RWTH Aachen University, Templergraben 64, 52062 Aachen, Germany, 2021. [3] Li, Nan. \"Projection of cement demand and analysis of the impacts of carbon tax on cement industry in China.\" The 7th International Conference on Applied Energy – ICAE2015, 2015: 1766-1771. [4] Marinkovic´, S. \"Comparative environmental assessment of natural and recycled aggregate concrete.\" Waste Management, 2010: 2255-2264. [5] Murali, G. \"EXPERIMENTAL STUDY ON RECYCLED AGGREGATE CONCRETE.\" International Journal of Engineering Research and Applications (IJERA), 2012: 407-410. [6] Roy, D.M. \"A REVIEW OF THE CEMENT-AGGREGATE BOND.\" CEMENT and CONCRETE RESEARCH, 1978: 277-286. Sharma, Alok. \"Recycled Course Aggregate Concrete Application.\" International Journal for Research in Applied Science & Engineering Technology (IJRASET), August 2020: 721-726. [7] V., Val Dimitri. \"Life-cycle cost analysis of reinforced concrete structures in marine environments.\" Structural Safety, 2013: 343-362. Yehia, Sherif. \"Strength and Durability Evaluation of Recycled Aggregate Concrete.\" International Journal of Concrete Structures and Materials, 2015: 219–239.

Copyright

Copyright © 2025 Avichal Srivastava, Shashank Gupta, Rakesh Gupta. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.