Reinforcing Concrete with Plastic and CDW for Durability

By Nidhi DhullReviewed by Susha Cheriyedath, M.Sc.Nov 18 2024

A recent article published in Scientific Reports examined the mechanical and durability properties of concrete incorporated with waste plastic fibers and treated construction and demolition waste (CDW). The hand-shredded plastic fibers as concrete reinforcements were sourced from polyethylene (PE) bags and polyethylene terephthalate (PET) bottles.

Background

Concrete, the most prevalent construction material, is ideal for various building projects with different load-bearing and environmental conditions due to its strength, long-lasting nature, and adaptability. However, concrete production consumes extensive natural resources, while demolishing concrete structures adds to the growing construction waste management crisis.

Incorporating CDW in concrete can conserve natural resources and reduce landfill waste, promoting a more sustainable construction industry. However, adhered mortar in recycled concrete aggregates increases water absorption, reduces density, and weakens bond strength, negatively impacting concrete’s overall strength and durability.

Various materials and methods have been explored to improve the properties of adhered mortar in recycled concrete aggregates. Notably, plastic waste can enhance the strength and durability of concrete. Therefore, this study investigated the characteristics of concrete comprising treated CDW instead of coarse aggregates and plastic waste fibers from PE bags and PET bottles.

Methods

This study utilized recycled CDW sourced from a solid waste recycling facility. To enhance the surface texture and pore structure of the CDW, it was treated with polyethyleneimine (PEI). The treated CDW was then integrated into concrete at varying proportions to evaluate its performance.

Plastic fibers, derived from discarded single-use PET bottles and PE bags, were manually shredded into uniform sizes of approximately 1.10 mm². These fibers were incorporated into the concrete mixes in weight ratios ranging from 0 % to 1 %, resulting in plastic-fiber reinforced concrete (PFRC).

To assess the mechanical properties, various concrete mixes were tested for compressive, split tensile, and flexural strengths after a 28-day curing period, adhering to international standards. Durability tests were conducted by immersing the concrete specimens in a 10 % concentrated sulfuric acid solution for three months to simulate aggressive environmental conditions.

High-temperature exposure tests were also performed on cubic concrete specimens. These samples were subjected to a six-hour heat treatment at 350 °C in an oven. Changes in the properties of the plastic fibers before and after exposure to high temperatures were analyzed using a scanning electron microscope (SEM), and their elemental composition was further examined through energy-dispersive spectroscopy (EDS).

Additionally, the carbon content within the concrete blocks containing recycled plastic waste was evaluated. The energy consumed during different stages of production was also analyzed to estimate the embodied carbon, providing insights into the environmental impact of the final product.

This comprehensive approach aimed to assess both the performance and sustainability of concrete incorporating recycled CDW and plastic fibers.

Results and Discussion

The M7 concrete mix, incorporating 0.25 % and 0.5 % plastic fibers along with 100 % treated CDW, displayed compressive strength comparable to that of the control concrete. Notably, all mixes containing 0.25 % PET fibers maintained strength on par with the control sample. However, the mix with 0.25 % PET and 1 % PE fibers exhibited the greatest strength reduction (23 %).

At optimal fiber content, the compressive strength increased by 11 % compared to the mix with 100 % untreated CDW. This improvement was attributed to the pretreatment of CDW with PEI, which effectively minimized the material's pore structure. The resulting reduced porosity enhanced the CDW's strength, leading to better overall compressive performance in the concrete.

In terms of split tensile and flexural strength, the M7 mix outperformed the control mix by 11.7 % and 18.2 %, respectively. This improvement was primarily due to the ductile nature of the plastic fibers, which enhanced the mix's ductility and mitigated stress concentrations in areas prone to cracking.

The thermal stability of the concrete mixes was also noted. The control and PFRC specimens showed only slight pale discoloration after sustained exposure to 350 °C, with no visible structural damage. The minimal thermal deformation observed was linked to expansion and contraction processes within the concrete matrix during heat exposure, indicating good resistance to high-temperature conditions.

When subjected to sulfuric acid exposure, both the control and M7 specimens experienced significant erosion, with damage severity increasing over time. However, the M7 mix showed greater resistance to acid-induced deterioration compared to the control, which was attributed to the robust properties of the plastic fibers, providing additional durability under corrosive conditions.

From an economic and environmental perspective, treated CDW emerged as a cost-effective and sustainable alternative to traditional coarse aggregates. The use of treated CDW reduced raw material and transportation costs while contributing to long-term sustainability in construction practices. Additionally, the M7 mix demonstrated 1.3 times lower energy demand and 1.2 times less embedded carbon compared to the control mix, highlighting its potential for reducing the environmental footprint of concrete production.

Conclusion

Overall, the study successfully demonstrated the advantages of incorporating plastic waste and CDW into concrete, providing an effective solution for waste disposal while enhancing the concrete’s mechanical properties.

The waste-incorporating concrete mixes showed compressive strength comparable to conventional concrete, with significant improvements in flexural strength (11.41 %) and tensile strength (17.72 %) at optimal fiber dosages and 100 % replacement of natural aggregate with treated CDW. SEM and EDS analyses confirmed minimal damage to the fibers from acid and high-temperature exposure.

Additionally, the environmental and economic benefits of incorporating plastic waste fibers and treated CDW in concrete were notable. Such sustainable construction practices reduce resource consumption and minimize the environmental impact of concrete structures.

Journal Reference

Duraiswamy, S., Neelamegam, P., VishnuPriyan, M., & Alaneme, G. U. (2024). Impact of plastic waste fiber and treated construction demolition waste on the durability and sustainability of concrete. Scientific Reports, 14(1). DOI: 10.1038/s41598-024-78107-w, https://www.nature.com/articles/s41598-024-78107-w

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