Semnan University Press Journal of Transportation Infrastructure Engineering 2423-5350 11 4 2026 02 20 Experimental Investigation of the Effect of Cement and Recycled HDPE Granules on the Strength, Durability and Microstructure of Sandy Soil Experimental Investigation of the Effect of Cement and Recycled HDPE Granules on the Strength, Durability and Microstructure of Sandy Soil 107 140 10546 10.22075/jtie.2026.39971.1750 FA Ashkan Gholipoor Noroozi Department of Civil Engineering, Imam Khomeini International University, Qazvin, Iran , Alireza Ardakani Department of civil engineering, Imam Khomeini International University, Qazvin, Iran Journal Article 2025 12 06 ABSTRACT<br /><br />Increasing environmental threats from cement manufacturing and disposal of plastic and polymer waste necessitated the implementation of sustainable alternatives in soil stabilization. This study focuses on the effects of application of cement and recycled high-density polyethylene (HDPE) granules on the strength, and microstructure of sandy soil. The mixtures were prepared with different amounts of cement (5%, 8%, and 11% of dry weight) and recycled HDPE granules (2%, 4%, 6%, and 8% of dry weight) and were subjected to UCS and ITS testing. The microstructural study was also done using scanning electron microscopy (SEM). Tests showed that increasing cement content from 5 to 11% produced compressive strength increases of 340% and a 261% increase in tensile strength over the control sample, which made it more brittle in terms of mechanical response; however, incorporating recycled HDPE granules at the optimal amounts (4-6%) made the mixture more ductile and better overall mechanically. Moreover, the results indicated that incorporating HDPE granules within the range of 4–6%, in conjunction with the optimum cement content, can effectively enhance the durability and strength retention of the stabilized soil under wetting–drying cycles, whereas higher contents lead to a reduction in performance. SEM observations showed that HDPE granules were compatible with the cementitious matrix at these optimum levels. The findings suggest that recycled HDPE granules are able to be used in optimal amounts to improve the mechanical performance of cement-stabilized soils, whereas the sustainable management of polymer waste in geotechnical engineering is served better. Unlike earlier studies that mostly employed virgin or non-recycled polyethylene on clayey soils, This study for the first time employs recycled HDPE granules to enhance the mechanical behavior of sandy soils and thus brings novel insights into the mechanisms by which their strength is improved. ABSTRACT<br /><br />Increasing environmental threats from cement manufacturing and disposal of plastic and polymer waste necessitated the implementation of sustainable alternatives in soil stabilization. This study focuses on the effects of application of cement and recycled high-density polyethylene (HDPE) granules on the strength, and microstructure of sandy soil. The mixtures were prepared with different amounts of cement (5%, 8%, and 11% of dry weight) and recycled HDPE granules (2%, 4%, 6%, and 8% of dry weight) and were subjected to UCS and ITS testing. The microstructural study was also done using scanning electron microscopy (SEM). Tests showed that increasing cement content from 5 to 11% produced compressive strength increases of 340% and a 261% increase in tensile strength over the control sample, which made it more brittle in terms of mechanical response; however, incorporating recycled HDPE granules at the optimal amounts (4-6%) made the mixture more ductile and better overall mechanically. Moreover, the results indicated that incorporating HDPE granules within the range of 4–6%, in conjunction with the optimum cement content, can effectively enhance the durability and strength retention of the stabilized soil under wetting–drying cycles, whereas higher contents lead to a reduction in performance. SEM observations showed that HDPE granules were compatible with the cementitious matrix at these optimum levels. The findings suggest that recycled HDPE granules are able to be used in optimal amounts to improve the mechanical performance of cement-stabilized soils, whereas the sustainable management of polymer waste in geotechnical engineering is served better. Unlike earlier studies that mostly employed virgin or non-recycled polyethylene on clayey soils, This study for the first time employs recycled HDPE granules to enhance the mechanical behavior of sandy soils and thus brings novel insights into the mechanisms by which their strength is improved. https://jtie.semnan.ac.ir/article_10546_0382968ac9bdaa14667fae45e085a416.pdf