Experimental Static and Dynamic Characteristics of Recycled Waste Tire Rubber Particle-Cement-Sand Composite Soil

To investigate the static and dynamic characteristics of rubber-sand composite soil (RS soil) reinforced with cement, a series of triaxial compression tests and resonant column tests was performed by considering the influence of rubber content (10%, 20%, 30%, 40%, and 50%), cement content (0, 1.5, 2.5, 3.5 and 4.0 g/100 mL), and effective consolidation confining pressure (50, 100, and 150 kPa). Compared with the RS soil, the addition of cement significantly improved the shear strength of a cement-rubber-sand composite soil (RCS soil), based on an undrained shear test. The increase in cement content not only makes the elastic modulus and cohesion of the RCS soil increase but also reduces the internal friction angle of the RCS soil. With the increase in rubber content, the failure of the RCS soil samples changes from strain-softening to hardening, and the prediction equation of the initial elastic modulus of the RCS soil is given herein when the recommended cement content is 3.5 g/100 mL. The effects of rubber content, cement content, and effective confining pressure on the dynamic shear modulus and damping ratio of the RCS soil were studied via the resonant column test. The test results show that the increase in rubber content slows down the modulus attenuation of the RCS soil, but increases its damping ratio. The test results also show that the increase in cement content makes the bonding force between particles greater so that the modulus attenuation of the RCS soil becomes slower and the damping ratio is reduced. At the same time, according to the change rule of the maximum dynamic shear modulus of the RCS soil with the rubber content, when the recommended cement content is 3.5 g/100 mL, an empirical formula and recommended value of the shear modulus G_max of the RCS soil are proposed.

Performance Improvement Effect of Asphalt Binder Using Pyrolysis Carbon Black

The generation of waste tires is rapidly increasing. Waste tire pyrolysis is an alternative to waste tire recycling. The main substances extracted in the waste tire pyrolysis method include oil, carbon black, and iron. In this study, carbon black from the pyrolysis of waste tires was used to modify and improve the permanent deformation properties of the asphalt binder, and 0%, 5%, 10%, 15%, and 20% of pyrolysis carbon black by weight were mixed in raw asphalt, which is called AP-3 and AP-5. Laboratory tests, such as the softening point test, flash point test, rotational viscometer test, dynamic shear rheometer test, and bending beam rheometer test, were carried out. The use of pyrolysis carbon black increased the softening point and rotational viscosity at 135 °C. When using 15% PCB for AP-3 and 10% PCB for AP-5, the performance improvement effect of the resistance to permanent deformation was significant. The use of pyrolysis carbon black decreased fatigue at room temperature and improved the resistance of low-temperature cracking up to −12 °C but gave poor results at −18 °C.

Dynamic Shear Modulus and Damping Ratio of Sand-Rubber Mixtures under Large Strain Range

Adding rubber into sands has been found to improve the mechanical behavior of sands, including their dynamic properties. However, ambiguous and even contradictory results have been reported regarding the dynamic behavior of sand–rubber mixtures, particularly in terms of the damping ratio. A series of cyclic triaxial tests were, therefore, performed under a large range of shear strains on sand–rubber mixtures with varying rubber volume contents, rubber particle sizes, and confining pressures. The results indicate the dynamic shear modulus decreases with increasing rubber volume content and with decreasing particle size and confining pressure. The relationship of the damping ratio to the evaluated parameters is complicated and strain-dependent; at shear strains less than a critical value, the damping ratio increases with increasing rubber volume content, whereas the opposite trend is observed at greater shear strains. Furthermore, sand–rubber mixtures with different rubber particle sizes exceed the damping ratio of pure sand at different rubber volume contents. A new empirical model to predict the maximum shear moduli of mixtures with various rubber volume contents, rubber particle sizes, and confining pressures is accordingly proposed. This study provides a reference for the design of sand–rubber mixtures in engineering applications.