This study evaluated the strength properties of compacted lateritic soils reinforced with polypropylene (PP) waste strips cut from recycled plastic packing with the goal of promoting sustainability through using local materials for engineering work and reusing waste materials as low-cost reinforcements. Waste PP strips with widths of 15 mm and different lengths were uniformly mixed with clayey sand (SC) and clay (CL) soils with the goal of using these materials as low-cost fiber reinforcements. The impact of different PP strip contents (0.25% to 2.0%) and lengths (10, 15, 20, and 30 mm) on the unconfined compressive strength (UCS) of the soils revealed an optimum combination of PP strip content and length. Statistical analysis showed that PP strip content has a greater effect than the PP strip length on the UCS for both soils. Results led to the definition of an empirical equation to estimate the UCS of strip-reinforced soils. The results from direct shear tests indicate that the SC soil showed an increase in both apparent cohesion and friction angle after reinforcement, while the CL soil only showed an increase in friction angle after reinforcement. California bearing ratio (CBR) tests indicate that the SC soil experienced a 70% increase in CBR after reinforcement, while the CBR of the CL soil was not affected by strip inclusion.
Abstract The use of local fine-grained soils in geosynthetic-reinforced structures can significantly reduce costs when granular materials are difficult to access. Another beneficial aspect of these soils is that enhanced mechanical behavior is expected with fine-grained soils under unsaturated conditions. With structures built in unsaturated conditions, stability analyses based on unsaturated soil mechanics would properly characterize and accurately predict the structural behavior with fine-grained soils. Accordingly, the interface shear strength between fine-grained soils and geosynthetics should also be assessed by unsaturated pullout or direct shear testing. In this article, the effect of matric suction on the pullout behavior of a polyester geogrid embedded in a fine-grained soil was evaluated using a small-scale testing apparatus. A miniature tensiometer located in the proximity of the soil-geogrid interface enabled monitoring of the matric suction of soil during pullout to evaluate its effect on the interface shear strength. A design approach for prediction of unsaturated interface strength is also assessed in this study. Three typical values of matric suction were identified during pullout: initial, peak, and residual. In the case of interfaces under water inundation, the pore water pressures developed and increased with the increase of overburden pressures. For drier interfaces, matric suction increases with increases of overburden pressure. Significant reductions (60 %) in peak pullout forces were observed for minor increases in soil moisture contents. Analyses using the moisture reduction factor indicated up to a 70 % loss of soil-geogrid interface shear strength as a result of wetting. The increase in unsaturated soil-geogrid interface strength due to the reduction of moisture content was attributed more to adhesion than to friction for the fine-grained soil used in this research. The analytical approach proposed in this study to predict the pullout strength of unsaturated interfaces has been demonstrated to be quite consistent with the actual strength values assessed from the small-scale pullout tests, primarily for higher values of overburden pressures. Matric suction values obtained from the soil-water retention curve were shown to be reliable parameters for use in the proposed analytical approach for prediction of the pullout strength of unsaturated soil-geosynthetic interfaces.
The civil engineering construction industry is nowadays one of the largest consumers of natural resources. Therefore, the proposal of using alternative materials that seek to reduce waste production or the use of previously generated waste is becoming increasingly necessary. This paper evaluated the effect of recycled polyethylene terephthalate (PET) strips on the mechanical properties of a cement-treated lateritic sandy soil. Unconfined compression strength (UCS) tests were conducted in natural and PET strips mixtures in different strips lengths and contents. In addition to UCS tests, compaction tests were also conducted in order to analyze the effect of these inclusions on the properties of a lateritic sandy soil. Lastly, direct shear tests were conducted on natural soil-strip, soil-cement, and soil-cement-strip composites using optimum UCS results. The addition of strips to the soil-cement composite showed an increase in the soil cohesion parameter. The inclusion of strips also provided a more ductile behavior to the soil, presenting greater deformations with fewer stress peaks. Results showed that the recycled strips’ inclusion in soil-cement can provide a material with high strength, ductility, and a highly sustainable alternative.
The use of construction and demolition wastes (CDW) as alternative material in engineering has proved promising applications, especially in pavement layers. However, the high grain breakage of this material has led to uncertainties regarding its performance. The present study assessed the effect of compaction energy on grain breakage of CDW, comparatively to a local sandy-clay (SC) soil with gravels, and mixtures of soil-CDW. Other geotechnical properties were also evaluated for application in pavements. Results showed the feasibility of using CDW as pavement layer material when compacted using modified energy. The local sandy-clay soil was not appropriate for pavement layers, while soil-CDW mixture improved soil geotechnical characteristics, allowing its use as subbase course. Grain breakage analysis, based on a statistical approach, showed that CDW undergoes greater particle size distribution change, not altered by compaction energy increase. Results confirmed that soil-CDW mixture presented superior performance for pavement layers.
With the increased use of geosynthetic interlayers, including geogrids, paving geocomposites and paving mats in asphalt rehabilitation works, an increase is also expected in projects involving the milling of asphalt layers that incorporate these geosynthetics. Although significant experience exists in milling conventional asphalt layers, such experience is limited when the milled material contains polymeric or fiberglass interlayers. Consequently, better understanding is needed on the differences in the milling process in asphalt layers with and without geosynthetics. In this study, an experimental field track was constructed at Salvador International Airport (Brazil), featuring five different geosynthetic-reinforced asphalt test sections that were milled after their construction. Evaluation of the field campaign results indicates that all geosynthetic interlayers proved to be “millable”. However, the milling operations exhibited varying milling efficiencies and resulted in milling byproducts (or Reclaimed Asphalt Pavement with Geosynthetics, G-RAP) with different physical characteristics. An average reduction of 18% in milling efficiency of reinforced asphalt layers was observed compared to that of unreinforced pavements. The G-RAP byproducts were found to include geosynthetic fragments of different sizes but mantained a particle size distribution similar to that of the control RAP. Furthermore, the collected G-RAP showed beneficial impact on mechanical characteristics of asphalt mixtures with 20% G-RAP, particularly in Marshall stability, flow, and indirect tensile strength, confirming their suitability for reuse in transportation applications.
The stress–dilatancy relationship for fiber-reinforced soils has been the focus of recent studies. This relationship can be used as a foundation for the development of constitutive models for fiber-reinforced soils. The present study aims to investigate the effect of recycled polypropylene fibers on the shear strength–dilation behavior of two lateritic soils using the stress–dilatancy relationship for direct shear tests. Results show that fibers improved the shear strength behavior of the composites, observed by increases in the friction angle. Fibers’ orientation at the sheared interface could be observed. The volumetric change during shearing was altered by the presence of fibers in both soils. Overall, results indicate that the stress–dilatancy relationship is affected by inclusions in the soil mix. Results can be used to implement constitutive modeling for fiber-reinforced soils.
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