Experimental investigation of waste LDPE and quarry dust as a cement replacement for paving blocks

Every day, the world produces a mountain of plastic waste that refuses to disappear, clogging landfills and waterways while conventional construction continues to consume vast amounts of natural resources to make the materials that pave our streets. This creates a difficult puzzle: how to manage the plastic that accumulates without relying on the heavy mining and cement production required for standard paving blocks. The answer might lie in a simple swap, where the cement that usually binds stones together is replaced entirely by melted plastic, and the sand is swapped for the fine dust left over from quarrying rocks. This approach does not just try to hide the waste; it attempts to turn two separate environmental problems into a single, functional building material.

In a study conducted at Takoradi Technical University, researchers set out to test this idea by making paving blocks without a single grain of cement. Instead of the usual mixture of cement, sand, and stone, they used shredded waste plastic known as low-density polyethylene, which is the soft, flexible type found in many grocery bags and bottles, combined with quarry dust, a fine mineral powder. They created several different versions of these blocks, changing the balance between the plastic and the dust to see which mix held together best. One group served as a standard reference, made with traditional cement and sand, while the others were made by melting the plastic and mixing it with the dust in ratios of fifty-fifty, sixty-forty, and eighty-twenty by weight. The goal was to see if these plastic-heavy blocks could stand up to the same tests as the concrete ones, specifically looking at how well they resisted breaking apart, how much water they soaked up, and how they reacted to heat.

The results showed that the plastic blocks were not just a theoretical possibility but a material with distinct and measurable strengths. When the researchers tested how much force it took to split the blocks apart, the best-performing plastic mix, which contained sixty parts plastic to forty parts dust, achieved a strength very close to the traditional cement block. While the cement block reached a specific strength level at twenty-eight days, the best plastic mix reached nearly that same level, proving that the material could hold together under tension. However, the plastic blocks shined brightest when it came to water. The traditional cement block absorbed a significant amount of water after sitting in a bath for three days, but the plastic versions absorbed almost none. The mix with the most plastic absorbed the least water of all, soaking up barely any moisture compared to the heavy uptake of the cement version. This suggests that the plastic creates a barrier that water simply cannot penetrate, a trait that could be very useful in wet environments.

There was, however, a clear trade-off when it came to heat. While the plastic blocks were excellent at repelling water, they were much more sensitive to high temperatures than the cement ones. The researchers heated the specimens until they began to show visible signs of damage, and the results varied depending on the mix. The block with the most plastic started to deteriorate at a much lower temperature than the one with more dust, indicating that too much plastic makes the block vulnerable to heat. The mix that performed best overall for strength was the sixty-forty blend, which offered a strong balance between holding together and resisting water, even though it still had a lower heat tolerance than the cement control.

The study concludes that these cement-free blocks are a viable option, but they are not a one-size-fits-all solution for every road or driveway. Because they are sensitive to high heat and have slightly lower strength than the best cement blocks, they are best suited for areas with light foot traffic, such as walkways, garden paths, or the grounds around buildings, rather than for heavy vehicles or high-heat industrial zones. The research demonstrates that waste plastic and quarry dust can be fused into a durable, water-resistant paving material, offering a practical way to reduce plastic waste while saving natural resources, provided the blocks are used in the right places where their specific strengths can be utilized and their weaknesses avoided.