The suitability of crushed concrete or recycled concrete aggregate (RCA) materials has been evaluated for use as pavement material for unbound basecourses. This paper covers the general engineering properties and response to cyclic loading as determined by repeated load triaxial testing (RLTT). In Australia, pavements commonly consist of granular basecourses and subbases supporting thin bituminous seals (asphalt or spray—chip seal). In this paper, a study is presented of the performances of three South Australian basecourse products, nominally 20 mm. The basecourse products included two RCA materials and a local virgin aggregate (quartzite). The resilient modulus and permanent deformation behaviour of RCA mixtures were investigated at different levels of moisture contents (90, 80, and 60% of optimum moisture content), subjected to a simplified stress regime suited to Australian construction. In terms of both resilient modulus and accumulation of permanent deformation, the RCA material performed be...

During last decade, researchers’ interest in nanotechnology applications, particularly in the field of pavement materials, has been increasing. This research work focused on the investigation of the properties of asphalt binder modified with different percentages of two different nanomaterials. These materials are nanoclay, and nanosilica. The nanosilica was manufactured from two different sources: silica fume and rice husk. Nanomaterials and asphalt binder were first characterized. A mechanical mixer was then used at 1500rpm to mix the nanomaterials with the binder. Required mixing time was determined. Three different nanomaterial percentages were mixed with the binder. The modified binders were tested for rheological properties. Results showed that, nanosilica synthesized from silica fume tends to decrease the penetration value and increase the softening point temperature. The nanoclay on the other hand was found to increase the penetration and decrease the softening point temperature. At temperature of 135°C and up to 150°C, increasing nanosilica percentage was found to increase Brookfield Rotational Viscosity (RV), while nanoclay, at small percentages, increased the RV and then decreased it at higher percentages. At higher temperature, up to 165°C, the RV values did not change significantly using both nanomodifiers. Nanosilica from rice husk showed improvement in the RV results. Finally, the Dynamic Shear Rheometer (DSR) results showed obvious improvement in the performance grade leading to higher resistance to permanent deformation

Natural weak cohesive subgrade soils are considered low quality foundations for pavement structures that may lead to significant pavement distresses. Several solutions can be proposed to enhance pavement behavior under cyclic loads such as stabilizing clays with cement or lime, removing and replacing weak material, or increasing the base thickness to reduce the stresses on subgrade. Despite the effectiveness of using additives like lime and cement for subgrade stabilization, cement and lime are considered environmentally unfriendly owing to the generated emission during their production. Recently, several researchers have shown the potential of using biopolymers as alternative for traditional additives. This study investigates the feasibility of using sodium alginate biopolymer for treating weak cohesive subgrades particularly under repeated traffic loads for pavement construction applications. Two different soils (clay and silt), representing a typical range of cohesive soils in the delta region in Egypt, were investigated. The sodium alginate was added to the cohesive soils in the range of 0% to 6% using two different mixing methods (wet and dry). The experimental program included basic engineering tests, resilient modulus, and unconfined compressive strength tests, along with other chemical tests such as Fourier transform infrared spectroscopy (FTIR) and thermal gravimetric analysis (TGA). In addition, scanning electronic microscope (SEM) images were performed for both untreated and treated soils at different alginate contents. Results showed that the resilient modulus of the treated subgrade soils generally increased with the increase in sodium alginate content up to an optimum value of 2% and 4% for clayey and silty soils, respectively. This significant improvement was reached in the first 4 days of curing with continuous gain of strength up to 28 days. This increase in resilient modulus was found to be dependent on the soil type, alginate concentration, curing time, and treatment method. The microlevel tests, TGA, SEM, and FTIR, confirmed the presence of the cementation polymer due to sodium alginate that increased the bond and cross-linking between particles, and consequently an increase in the soil stiffness and strength occurred.

Stabilized base/subbase materials provide more structural support and durability to both flexible and rigid pavements than conventional base/subbase materials. For the design of stabilized base/subbase layers in flexible pavements, good performance in terms of resilient modulus (M_r) under wet-dry cycle conditions is required. This study focuses on the development of a Particle Swarm Optimization-based Extreme Learning Machine (PSO-ELM) to predict the performance of stabilized aggregate bases subjected to wet-dry cycles. Furthermore, the performance of the developed PSO-ELM model was compared with the Particle Swarm Optimization-based Artificial Neural Network (PSO-ANN) and Kernel ELM (KELM). The results showed that the PSO-ELM model significantly yielded higher prediction accuracy in terms of the Root Mean Square Error (RMSE), the Mean Absolute Error (MAE), and the coefficient of determination (r²) compared with the other two investigated models, PSO-ANN and KELM. The PSO-ELM was unique in that the predicted M_r values generally yielded the same distribution and trend as the observed M_r data.