The global construction sector faces a dual environmental crisis: the cement industry contributes approximately8% of global anthropogenic CO2​ emissions , and the extensive demand for sand depletes natural resources. Concurrently, managing non-biodegradable Low-Density Polyethylene (LDPE) plastic waste from packaging and large volumes of agricultural biomassBiomass is a complex biological organic or non-organic solid product derived from living or recently living organism and available naturally. Various types of wastes such as animal manure, waste paper, sludge and many industrial wastes are also treated as biomass because like natural biomass these More is a critical environmental challenge. A study by Barman et al. in the International Journal of Scientific Research and Technology tackles these issues by investigating the feasibility of producing sustainable cement bricks through the partial replacement of cement with biocharBiochar is a carbon-rich material created from biomass decomposition in low-oxygen conditions. It has important applications in environmental remediation, soil improvement, agriculture, carbon sequestration, energy storage, and sustainable materials, promoting efficiency and reducing waste in various contexts while addressing climate change challenges. More and sand with shredded LDPE plastic waste. The research explored how blending these two waste streams affects the brick’s core engineering properties to establish optimal mix proportions.

The study developed three prototype bricks with increasing levels of waste material substitution. Biochar replaced cement (C). Shredded LDPE plastic replaced fine aggregate/sand (S). The mixes were prepared with a standard cement-to-sand ratio of 1:6 and a water-cement ratio of 0.50. The three key replacement levels tested were: Prototype 1 (10% C with biochar, 5% S with LDPE), Prototype 2 (20% C with biochar, 10% S with LDPE), and Prototype 3 (30% C with biochar, 15% S with LDPE). The performance of these prototypes was evaluated based on comprehensive tests, with compressive strength being the most critical mechanical property. At 28 days of curing, Prototypes 1 and 2 both achieved a compressive strength of 7.0 MPa. This strength is comparable to that of first-class clay bricks and meets the minimum standards for non-load-bearing applications, which typically range from 3.5-7.0 MPa. While the clay brick reference achieved a higher 12.0 MPa , the initial strength reduction caused by the partial cement replacement in Prototype 2 was compensated for by the slower pozzolanic or filler effect of biochar by the 28-day mark. However, Prototype 3 achieved a lower final strength of 6.0 MPa, suggesting that replacing 30% C and 15% S reaches a threshold where the increased waste content negatively affects structural performance.

Water absorption, a key indicator of durability and porosityPorosity of biochar is a key factor in its effectiveness as a soil amendment and its ability to retain water and nutrients. Biochar’s porosity is influenced by feedstock type and pyrolysis temperature, and it plays a crucial role in microbial activity and overall soil health. Biochar More, yielded highly positive results. All three prototypes exhibited lower water absorption rates than the traditional clay brick ( 18.0%). The most successful was Prototype 1, recording the lowest absorption rate of 11.0%. The absorption rates increased slightly with higher waste content (Prototype 3 reached 16.0%), a phenomenon attributed to the micro-voids formed by the hydrophobic LDPE at the aggregate-cement interface and the inherent porosity of biochar.

Regarding other durability and safety aspects, the surface hardness of the bricks showed a decreasing trend as LDPE content increased. Prototype 1 retained a ‘Hard’ rating, comparable to conventional bricks, as the low plastic content did not significantly compromise the cement matrix. Efflorescence was negligible to slight in Prototype 1. A crucial safety finding was the introduction of flammability due to the LDPE content. Prototype 1 (5% LDPE) showed low flammability, with only minor surface melting and no sustained burning, making its fire risk acceptable for some applications. Conversely, Prototypes 2 and 3 (with 10% and 15% LDPE, respectively) exhibited moderate to high flammability, including sustained flaming and significant smoke emission, necessitating their restriction to non-fire-critical applications.

The study concludes that the optimal mix, Prototype 1 (10% C replacement by biochar, 5% S replacement by LDPE), offers the best balance of structural and environmental properties, achieving 7 MPa strength and 11% water absorption. This innovation technically validates a pathway for waste valorization , effectively diverting two problematic waste streams from landfills, conserving virgin resources, and sequestering carbon in the building material. This research actively promotes the principles of a circular economy in the construction sector.

Source: Barman, P. J., Sarkar, S., Borah, A., Dutta, D., Barman, D., Tamuli, D., Das, G., Borsaikia, H., & Saikia, M. (2025). Experimental Study on Cement Brick Using Low-Density Polyethylene (LDPE) Plastics and Biochar. Int. J. Sci. R. Tech., 2(9), 121–129. Sources