Experimental Analysis of Nano CaCO? and Polyethylene Terephthalate in Cementitious Composites

Abstract

This research investigates the impact of using polyethylene terephthalate (PET) granules in place of fine aggregate and nano calcium carbonate (CaCO?) particles as a partial replacement for cement on the microstructure and mechanical performance of M40 grade concrete. Nano CaCO?, a naturally occurring material, possesses a finer particle size compared to cement, which enhances the particle packing and provides a spacer effect within the mix. Recycled PET waste in granular form contributes to sustainable construction by reducing reliance on natural aggregates. The study evaluates compressive strength, split tensile strength, and flexural strength at 7, 14, and 28 days of curing to assess both early and later-age performance. Results indicate that combining PET and nano CaCO? can lead to the development of lightweight, high-strength, and eco-friendly concrete, aligning with the goals of durable and sustainable infrastructure.

Introduction

The study investigates the mechanical performance and sustainability benefits of concrete modified with nano calcium carbonate (CaCO?) and recycled polyethylene terephthalate (PET). The aim is to enhance concrete’s structural properties while promoting eco-friendly alternatives to natural fine aggregates and minimizing plastic waste.

Background and Motivation:

• Concrete is essential in global construction but faces challenges in sustainability due to excessive resource extraction and high carbon emissions.

• Natural sand, commonly used as a fine aggregate, contributes to environmental degradation.

• PET, derived from plastic waste, and nano CaCO?, a nanomaterial with known filler and nucleating effects, offer sustainable substitutes.

• Plastic waste is a growing global concern, with production doubling from 180 million tons in 2000 to 360 million in 2020.

Materials and Methods:

• Materials Used:

  • Cement: Ordinary Pozzolana Cement (OPC), as per IS:1489–2015.

  • Fine Aggregates: Zone II river sand (IS 383:2016).

  • Coarse Aggregates: 20 mm natural aggregates.

  • Nano CaCO?: 15–40 nm particle size, 98% purity.

  • PET: Granules ≤ 4.75 mm, 10% by volume of fine aggregate.

• Mix Design:

  • Designed for M40 grade concrete (target mean strength: 48.25 N/mm²).

  • Nano CaCO? content varied from 0% to 3%, PET fixed at 10%.

  • Water-cement ratio: 0.37, with added superplasticizer.

  • Concrete was tested for compressive, split tensile, and flexural strength at 7, 14, and 28 days.

Key Findings:

1. Fresh Concrete Density:

• Fresh density decreased with higher nano CaCO? content due to lower bulk density and particle agglomeration.

• Range: 2518 kg/m³ (control) to 2330 kg/m³ (highest replacement level).

2. Compressive Strength:

• Strength peaked at 0% nano CaCO? (51.62 N/mm² at 28 days) and declined progressively with increasing nano CaCO?.

• Reason: Hollow nature and lower shell strength of CaCO? nanoparticles reduce load resistance.

3. Split Tensile Strength:

• Followed a similar downward trend as compressive strength.

• Maximum at 4.14 N/mm² (control) and minimum at 3.46 N/mm² (highest CaCO? content at 28 days).

4. Flexural Strength:

• Also showed a reduction with higher nano CaCO?.

• From 4.51 N/mm² (control) to 3.47 N/mm² at 28 days with 3% nano CaCO?.

Discussion and Implications:

• Nano CaCO? acts as a nucleation agent and can accelerate cement hydration at low doses, but excessive content causes particle agglomeration and reduces strength.

• PET improves sustainability but its inert nature may limit bonding strength.

• Optimal dosage of nano CaCO? is critical; beyond a certain threshold, mechanical properties deteriorate.

• Results emphasize the importance of balancing performance with environmental benefits in sustainable concrete design.

Conclusion

An in-depth evaluation was carried out to study the effect of nano calcium carbonate (CaCO?), used in varying proportions from 0% to 5%, as a partial replacement for fine aggregate in concrete. The compressive strength results varied depending on the percentage of nano CaCO? added, displaying no consistent trend across all mixes. At higher replacement levels, the improvement in mechanical properties was limited. This reduction in performance is likely due to poor dispersion of nano particles caused by agglomeration within the slurry and cement matrix. Previous studies have indicated that nano CaCO? can accelerate the hydration process of cement, thereby enhancing early-age strength. In the current investigation, the mix containing 2% nano CaCO? showed the most favorable results, underlining the potential of nano CaCO? to improve the mechanical characteristics of cementitious materials when optimally used. The key findings from this study are summarized below: 1) The fresh density of the concrete mix with 5% nano CaCO? (NC5) was found to be 34.46% lower compared to the control mix (NC0). The density of the concrete modified with nano CaCO? ranged from 2518 kg/m³ to 2308 kg/m³. Additionally, workability decreased as the nano CaCO? content increased. 2) Although the compressive strength of concrete incorporating nano CaCO? was lower than that of NC0, the mix with 2% nano CaCO? (NC2) still met the target mean strength requirements. 3) The split tensile strength of the nano CaCO? concrete showed a minimum reduction of 2.18% in NC1 compared to NC0. 4) A minimum reduction of 5.2% in flexural strength was observed in NC1 when compared with the control mix. 5) The inclusion of PET granules up to 10% had no significant impact on the workability of the concrete mix. However, increasing PET content beyond this point led to a slight decrease in workability. Similarly, the density of the mix decreased with higher PET content due to the lower specific gravity of PET compared to natural sand.

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Copyright

Copyright © 2025 Nitin Tiwari, Ushendra Kumar. 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.