The effect of compacted nylon particles and silica fume on mechanical properties and water absorption of lightweight concrete: experimental and theoretical study

Abstract In the last decade, the global demand for nylon and plastic products has surged markedly. Due to their slow decomposition, recycling and industrial application of these materials is vital. This process not only reduces the amount of plastic waste but also helps mitigate its environmental impact. In construction, these recycled materials offer a sustainable alternative to traditional aggregates in concrete. Moreover, the need to decrease building weight has gained increasing importance. One effective strategy to achieve this is the use of lightweight concrete, which reduces the dead load and, thereby, minimizes the seismic forces acting on a structure. This study explores the incorporation of compacted nylon particles in lightweight concrete. Different proportions of compacted nylon particles, from 0 to 9%, were integrated into the concrete mix as a percentage of the fine aggregates. To further improve the concrete’s properties, varying percentages of silica fume (from 0 to 10% of the cement weight) were added. The properties evaluated included compressive capacity, tensile capacity, elasticity modulus, and water absorption. Additionally, the failure behavior of the specimens was analyzed. The findings revealed that substituting sand with compacted nylon particles generally led to a reduction in mechanical properties, with compressive strength decreasing by 11–39% depending on nylon content and silica fume addition, and tensile strength showing a slight increase at 3% nylon but decreasing at higher contents. The elasticity modulus decreased up to 25% for nylon contents above 6%. Water absorption decreased with increasing nylon content, and the incorporation of silica fume, particularly up to 5% of the cement weight, further reduced water absorption by 4–37% while improving compressive and tensile performance. From the experimental findings, predictive models were developed using regression and sensitivity analyses to estimate the properties of lightweight concrete including different proportions of compacted nylon particles and silica fume. These models are valid within the tested ranges.