An experimental study was conducted to evaluate the effects of crumb rubber (CR) on mechanical properties of roller compacted concrete (RCC) for use in pavements. In the experiment, proportions of 0%, 10%, 20% and 30% by volume (vol) CR, were incorporated into RCC as sand replacement material. Mixtures were made at cement contents of 275 kg/m3 (11%) and 201 kg/m3 (8.6%). The water content quantities used to prepare RCC mixtures, were determined from the moisture-dry density relationship obtained based on the soil compaction approach. Various mechanical properties were measured comprising compressive strength, splitting tensile strength, ultrasonic pulse velocity, static and dynamic moduli of elasticity. Also measured were pore-related physical tests consisting of water absorption and volume of permeable pores. It was found that cement content has significant influence on the amount of CR that can be suitably utilized in RCC mixtures. The RCCs prepared at the adequate cement content of 275 kg/m3, exhibited suitable performance for all mixtures containing up to 20% vol CR content. Results showed that the standard relationships between compressive strength, static and elastic moduli as established for normal concretes, are also applicable to RCCs.

Pavement inundation disrupts natural drainage, causing its structural damage and potential failure. This study investigates the impact of moisture fluctuations on pavement failure through four distinct approaches. Firstly, the critical strain at the top of the subgrade layer in unsaturated conditions was predicted using non-linear visco-elastic layer analysis. Secondly, structural number (SN) was established to evaluate the pavement strength under unsaturated conditions. Thirdly, the impact of rising groundwater levels on the structural strength of pavement layers was determined using maximum capillary height from soil suction. Finally, characteristic deflection and static moduli of the lateritic subgrade after a rainfall event were determined from field investigations with Benkelman beam deflectometer (BBD). Simulation in KENLAYER showed that the critical compressive vertical strain above subgrade due to different axle loading for bound and unbound granular layers varied with moisture fluctuation. Calculated SN values showed reduced capacity under saturated conditions compared to optimum moisture under the same traffic. BBD test revealed that the static moduli of the subgrade were lower due to increased moisture content, emphasizing the importance of moisture control and effective drainage for the structural integrity of pavements.

Traditional soil stabilization methods have been used for many years to improve the load-bearing capacity, durability, and erosion resistance of soil; however, they have some potential drawbacks including air and water pollution, and increased energy consumption. The most used stabilizer, cement considered for its performance and cost-effectiveness is responsible for approximately 5-7% of total carbon dioxide (CO2) emissions worldwide. But nowadays, the global trend incorporates sustainability goals while choosing appropriate soil stabilization. In this direction, various sustainable stabilizers, such as enzymes, and pozzolanas have gained significant attention in recent years. This study explores using a calcium-based mineral stabilizer and GGBS, a byproduct of Iron furnace, as a potential alternative to cement in soil stabilization for flexible pavement construction. The main objective of the paper is to evaluate the mechanical properties of the stabilized soils using CBR followed by the designing of pavements and a comparative life cycle assessment of cement-stabilized flexible pavement construction with mineral-stabilized pavement in SimaPro software, with a cradle-to-gate approach, using the ReCiPe 2016 Endpoint (H) method. The scope of the study is to provide insights into the feasibility and environmental impacts of using mineral stabilizers for soil stabilization in pavement construction. The study's findings indicate that the pozzolanic reaction during the stabilization process played a crucial role in enhancing the CBR values. This improvement led to a reduction in pavement thickness, highlighting that mineral-stabilized pavements demonstrate lower energy requirements and reduced greenhouse gas emissions thus serving as a viable and sustainable choice for pavement construction.

The use of geo-synthetics, such as geotextiles, has the potential to enhance the inherent engineering and geotechnical properties of subgrade soils that exhibit poor conditions. The use of geotextiles in pavement construction has many advantages, including enhanced subgrade strength and the ability to construct flexible pavements that are both efficient and cost-effective since it reduces the pavement thickness. In the realm of flexible pavement system development, the significance of subgrade soils and their inherent characteristics, including permeability and strength, is well acknowledged. The study included conducting experiments to investigate the use of geo-polymeric materials like geo-textiles on improving the mechanical properties of the subgrade soils under varying moisture conditions. Geotextiles possess good tensile resistance as it is made up of good polymeric material like polyester, polypropylene and polyethylene. Geotechnical tests including grain size analysis, Atterberg limits, California bearing ratio test, and compaction tests, were conducted. CBR tests and UCS tests were conducted by placing the geotextiles in a singular arrangement at various depths and subjecting them to both soaked and unsoaked conditions to assess the soil's strength. The results demonstrate that the use of geosynthetic reinforcement in the soil effectively enhances the strength of the subgrade across various soil types. The optimal performance of geo-synthetics in relation to their placement inside the CBR mold was found to be at a distance of 1/3 of the mold's height from the top. This placement outperformed the alternative distances of 1/2 and 2/3 of the mold's height.

Recycled concrete aggregates (RCA), derived from demolishing concrete buildings and pavements, have been treated with significant value as a recycled resource. Using RCA instead of virgin aggregates for pavement construction became a feasible approach to conserve construction trash resources since approximately 140 million tons per year were produced in the United States. This research conducted a life cycle cost analysis of stabilized clay subgrade soils in Kansas, USA, combining with RCA from pavements damaged by freeze-thawcycles and theD-cracks process. Class C fly ash and type II Portland cement were stabilizers for subgrade mixture designs. The performance of the mixtures was evaluated through Standard Proctor, unconfined compression strength (UCS), and California Bearing Ratio (CBR) tests. The full-depth flexible pavements incorporating these stabilized subgrades were designed using the AASHTOW are Pavement ME Design (PME) software. Results indicated that a 1:1 mix of Class C fly ash and type II Portland cement was the most effective stabilizer, decreasing the required thickness of the hot-mix asphalt (HMA) layer. The life cycle cost analysis demonstrated that the RCA-stabilized subgrades are economically viable when the chemical stabilizers are used in equal proportions.

The majority of the Australian road network consists of unbound granular pavements with a thin bituminous surfacing. In Queensland, regional and remote areas, economic and environmental considerations encourage the use of locally available materials for the provision of granular pavements resulting in lower use of finite resources and a reduction in material transportation costs and associated emissions. These materials, known as non-standard or marginal materials, typically do not meet all the Queensland standard specification requirements but provide satisfactory performance when properly managed. At present, a universally accepted testing procedure for assessing the performance of non-standard materials is lacking. This paper reports on the first completed stages of a study aiming to investigate the physical and mechanical properties of non-standard materials using a range of laboratory testing: wheel tracking, modified Texas triaxial, California bearing ratio tests, and physical characterisation testing such as particle size distribution, Atterberg limits, compaction test, and apparent particle density measurement. This paper assessed 10 different non-standard materials together with one standard material using the selected laboratory tests. Later stages of the ongoing project, conducted for the National Asset Centre of Excellence (NACoE), will expand this testing and aims to develop a performance-based non-standard material screening tool to assist in material selection and assessments for road pavement construction and maintenance in low-traffic and low rainfall areas.

Principal stress rotation (PSR) significantly affects the cyclic behaviour of subgrade soil. Previous studies on PSR have been generally limited to saturated and isothermal conditions despite subgrade soil experiencing daily and seasonal variations in temperature and suction. This study incorporated temperature- and suction-controlled units into existing hollow cylinder apparatus to conduct cyclic shear tests, both with and without PSR, while maintaining identical cyclic deviatoric stress. The study considered different temperatures (5 degrees C, 20 degrees C, and 40 degrees C) and suctions (0, 10, and 30 kPa). The permanent strain increases and resilient modulus decreases as temperature rises and suction decreases. Furthermore, the incorporation of PSR results in increased permanent strain and decreased resilient modulus, with these changes being influenced by temperature and suction. At zero suction, the permanent strain increases by 130% and 230% at 5 degrees C and 40 degrees C when PSR is incorporated. As suction increases to 10 kPa, these values are 50% and 80%. These coupled effects are likely due to the decrease in the overconsolidation ratio (OCR) with increasing temperature and decreasing suction, with PSR effects being more pronounced at lower OCRs. Furthermore, a new semi-empirical equation was proposed to model these coupled effects on resilient modulus, a critical parameter in pavement design.

Biochar provides a sustainable carbon sequestration technology, an effective fertilizer in agriculture, a step forward for the profitable and safe disposal of bio-wastes, reduced carbon dioxide emissions and global warming, and a renewable energy source. Using biochar as a bitumen modifier in asphalt pavement construction is under active research. It can prove a sustainable and environmentally friendly alternative, provided it meets the efficiency, strength, and economy challenge. This review focused on the available literature on utilizing biochar as a bitumen modifier for the construction of asphaltic roads. The studies show that biochar's physical and chemical nature has helped project it as a promising bitumen modifier. The biochar, being porous and fibrous, provides a strong, stiff frame in the asphaltic mast and results in the enhancement of both stiffening point and viscosity. This, in turn, leads to a reduction in penetration or increased deformation resistance. This is perhaps the reason for the high performance of biochar-modified asphalt at high temperatures. The increase in viscosity of asphaltic masts was also observed due to biochar amendment, making asphalt more sensitive to temperature. The two important factors, the complex modulus and the rutting factor of the asphalt, were noticed to increase with the addition of 10% biochar. The biochar amendments of up to 20% increased fatigue resistance temperature by 4.6 degrees C. The improvement in the resistance to deformation at high temperatures, probably due to a reduction of phase angle due to adding biochar, is also seen as a significant function of biochar. However, biochar applicability in the field is mainly related to its cost efficiency and performance as a bitumen modifier for asphaltic pavements. So far as the cost economy is concerned, the mean price for biochar (as per available literature) was very high, from $2.65 to $0.09/kg for blended biochar. The price was as high as $3.29/kg in the Philippines to $0.08/kg in India and in the US to $13.48/kg, implying that the market price of biochar is variable worldwide and dependent mainly on the biochar feedstock, cost of labor/living of the area and land costs. On the other hand, its efficiency has not yet been satisfactory at low temperatures. The other noticeable limitations that need to be explored in further research are long-term effects on strength, rutting resistance, and ageing. Also, field studies to support the research and, more importantly, cost economy viz-a-viz other available modifiers need exploration.

The resilient modulus (MR) of different pavement materials is one of the most important input parameters for the mechanistic-empirical pavement design approach. The dynamic triaxial test is the most often used method for evaluating the MR, although it is expensive, time-consuming, and requires specialized lab facilities. The purpose of this study is to establish a new model based on Long Short-Term Memory (LSTM) networks for predicting the MR of stabilized base materials with various additives during wet-dry cycles (WDC). A laboratory dataset of 704 records has been used using input parameters, including WDC, ratio of calcium oxide to silica, alumina, and ferric oxide compound, Maximum dry density to the optimal moisture content ratio (DMR), deviator stress (sigma d), and confining stress (sigma 3). The results demonstrate that the LSTM technique is very accurate, with coefficients of determination of 0.995 and 0.980 for the training and testing datasets, respectively. The LSTM model outperforms other developed models, such as support vector regression and least squares approaches, in the literature. A sensitivity analysis study has determined that the DMR parameter is the most significant factor, while the sigma d parameter is the least significant factor in predicting the MR of the stabilized base material under WDC. Furthermore, the SHapley Additive exPlanations approach is employed to elucidate the optimal model and examine the impact of its features on the final result.

Rutting is a major distress mode in flexible pavements, results from the repetitive loading caused by traffic movement. Pavement deformation consists of both recoverable (elastic) and unrecoverable (plastic) components. The continuous movement of vehicles contributes to the overall deformation in the flexible pavement system, involving all pavement components. In regions with hot climates or in the hot summer season, rutting tends to be more prominent due to the substantial reduction in the viscosity of the asphalt binder. This decrease in viscosity, which is inversely linked to rutting, occurs as temperatures rise, leading to a heightened susceptibility of the Hot Mix Asphalt (HMA) blend to rut formation. However, according to studies, a significant amount of permanent deformation takes place in the unbound layers beneath the asphalt course, it is therefore essential to prioritize attention on these layers. Temperature exerts besides viscosity a substantial impact on asphalt stiffness, leading to the transfer of higher vertical deviatoric stresses to the unbound layers beneath the asphalt course (base, subbase, subgrade). This research presents a study integrating the High Cycle Accumulation (HCA) model into a laminar model to determine permanent deformations in the unbound granular layer of flexible pavements and taking into account the temperature dependent stiffness of asphalt. Rutting depths at the end of the design lifetime were computed, accounting for seasonal stiffness variations. It was shown that the softer asphalt behavior significantly increases the development of ruts in the underlaying soil layers. The findings were compared with results obtained from mean annual temperature and the typical equivalent asphalt stiffness utilized in fatigue tests. Additionally, an analysis was conducted to assess whether the timing of road implementation influences settlements throughout the design lifetime. The results suggest that the sequence of seasons is most relevant during the first year of service, showing a distinct effect at that time. However, with a higher number of axle passes, the initial differences fade away, and the curves start to merge.