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With the increasing accumulation of rubber waste, the potential reuse of rubber fillers offers a promising solution to enhance the engineering properties of low-plasticity soils while promoting environmental sustainability. In this study, the effect of rubber waste powders (RWPs) on the consolidation and deformation properties of low-plasticity clay soil (CS) was investigated using a fully automated consolidation testing procedure for clay–rubber mixtures. The study involved adding 2% up to 30% RWPs to Tehran clay, and various parameters were evaluated through consolidation, compaction, and uniaxial strength tests. The results revealed that the consolidation volume of the mixture differed from that of the CS due to the elastic nature of the rubber wastes (RWs). To achieve higher precision, a new equation was proposed to determine the void ratio, along with modified e-log p’ curves for the clay–rubber mixture. Furthermore, the addition of RWPs to the CS resulted in moderated free swelling of the soil while enhancing ductility, compression index (Cc), swelling index (Cs), and recompression index (Cr). However, it was observed that the strength and modulus of elasticity of the mixture decreased with the increase in rubber content. Considering the variations in geotechnical parameters with different rubber contents, the appropriate rubber content can be selected based on specific applications in soil and rubber mixtures, considering the required geotechnical parameters. This study highlights the potential applications of RWPs as a material in civil and geotechnical engineering projects, providing valuable insights for sustainable and eco-friendly engineering practices.

The annual increase in production of industrial wastes, including scrap tire, has created several challenges for societies. Incorporating the wastes as raw materials has been proposed in different industries, using waste tire as physical additives and investigating the geotechnical properties of this mixture can reduce the environmental pollution, as well as offering economic and technical benefits. Clay soils are abundant in southern regions of Tehran where scrap tire is also produced in large quantities every year. Therefore, provided the chance, incorporating these wastes into the soil mix is significant as regards both geotechnical properties and environmental considerations. As a fundamental means of investigation in construction activities, in particular road construction, the compaction test is useful in determining the maximum density and the optimum moisture content of the soil. In this study, considering that this research has not yet been investigated for Tehran clay and has environmental benefits while having engineering application, the optimum moisture content and maximum dry density of the clay mixed with two types of additives (waste tire powder and granules) at various mass fractions (2, 4, 6, 8, 10, 20, and 30 wt%) using standard compaction tests were investigated. The results suggested that the variations of the optimum moisture content and the maximum dry density in both clay mixes demonstrate a certain and predictable trend as the waste content increases. In other words, by increasing the percentage of waste in the mixture, the optimum moisture content is increased, and this increase in the mixture of the tire powder and clay is more than granule and clay. In addition, by increasing the percentage of waste, the maximum dry weight of the mixture was reduced, and this reduction in the mixture of tire powder and clay is almost higher than that of tire granule and clay. Furthermore, relations were presented to estimate the maximum density and the optimum moisture content of the mix to be applied in practice.

With respect to the increasing production of tire wastes, the use of these wastes as an additive in civil engineering has always gained attentions of researchers due to their positive effects on material properties and reduction of environmental problems. Clay soils, as problematic soils, have always caused geotechnical problems including high Atterberg limits and consequently low workability. Tire powder, as one of the products of tire wastes, lacks clay cohesion and it can be effective in altering the plasticity of clay soils. As no comprehensive study has been conducted in this regard specifically on Tehran clay soil yet, this research studies experimentally the effect of adding different percentages of tire powder to clay soil at the Atterberg limits of clay soils with two different types of plasticity. More over according to previous studies, the effect of tire powder on other geotechnical properties of clay soils and the advantages and disadvantages of using tire powder in clay soils are discussed. The results indicate that addition of tire powder to clay soils has positive effects on reducing the Atterberg limits, increasing efficiency, and improving resistance, permeability, swelling reduction, and settlement properties, and reducing soil density and it can be used as an additive in improving clay soils.