In a world grappling with the mounting challenge of plastic waste, researchers have uncovered a promising avenue for repurposing one of the most ubiquitous forms of plastic pollution: polypropylene bottle caps. A study led by Pattharaphon Chindasiriphan from the Center of Excellence in Innovative Construction Materials at Chulalongkorn University in Bangkok, Thailand, has demonstrated that these often-discarded bottle caps can be transformed into a valuable resource for sustainable pavement construction.
The study, published in the journal *Cleaner Materials* (which translates to “Materials for a Cleaner Environment”), explores the use of plastic aggregate (PA) derived from polypropylene bottle caps in controlled low-strength material (CLSM) for pavement base applications. CLSM, a flowable, self-compacting material, is commonly used as a backfill or base material in construction projects.
Chindasiriphan and his team investigated two types of binders for the CLSM: traditional cement-based binders and innovative alkali-activated material (AAM) binders. The AAM binder, produced from high-calcium fly ash activated with sodium hydroxide, offers a more sustainable alternative to traditional cement, as it does not require heat curing and significantly reduces CO2 emissions.
The researchers replaced natural river sand with PA at varying levels, from 10% to 30% by volume, to assess the impact on the material’s properties. Their evaluations covered a range of factors, including flowability, bleeding, unit weight, unconfined compressive strength (UCS), resilient modulus (MR), and stiffness.
The results were encouraging. While increasing the PA content did reduce the slump flow, density, and mechanical performance of the CLSM, the reductions were manageable. “At 10% PA, cement-based CLSM exhibited a 31.6% reduction in 28-day UCS and a 20% drop in MR,” Chindasiriphan noted. “However, it still met the strength requirements for both base and subbase layers.”
The AAM-based CLSM also showed promising results. “For every 10% PA added, we observed a reduction of 1 MPa in UCS and 4.7% in MR,” Chindasiriphan explained. “Mixtures with up to 10% PA met the subbase criteria, offering a more sustainable alternative with up to 65% lower CO2 emissions compared to conventional mixes.”
The study’s findings have significant implications for the construction and energy sectors. By repurposing plastic waste, the research offers a dual environmental and economic benefit. It provides a sustainable solution to the growing problem of plastic waste while reducing material costs and CO2 emissions in construction projects.
Moreover, the use of AAM binders in CLSM opens new avenues for sustainable construction practices. As Chindasiriphan pointed out, “The AAM-based CLSM not only reduces CO2 emissions but also performs comparably to traditional cement-based materials, making it a viable option for future construction projects.”
This research could shape future developments in the field by promoting the use of recycled materials and sustainable binders in construction. It highlights the potential of innovative solutions to address environmental challenges while meeting engineering performance requirements.
As the world continues to grapple with the impacts of plastic pollution and climate change, studies like this offer hope and practical solutions. By turning waste into a valuable resource, we can move towards a more sustainable and circular economy.