Ammad Hassan Khan

Roads and such other light infrastructure founded on expansive clays (EC) frequently develop cracks and emerge as the predominant structural failures. The primary objective of this research is to determine the viability of utilizing waste thermoplastic particles (WTP) in tandem with slake lime (SL) as a novel stabilization strategy to enhance the geotechnical behaviour of EC. For this purpose, valorisation of waste high-density polyethylene (HDPE) and polyvinyl chloride (PVC) was systematically evaluated across a series of experimental investigations, both with and without subsequent SL addition. Mechanical performance was assessed through unconfined compressive strength (UCS), California Bearing Ratio (CBR), and swell potential (Sp) tests, while microstructural and chemical analyses employed X-ray diffraction (XRD) and scanning electron microscopy (SEM) to reveal the stabilization mechanism. Key findings reveal that a combination of optimal dosages—such as 7.5% HDPE and 4% SL or 4% PVC and 4% SL—substantially enhanced shear strength and resistance to swelling that meets standard specification thresholds for road subgrade material (e.g., soaked ≥ 5% CBR and Sp ≤ 0.5%). The synergy between the primary stabilizer SL and secondary reinforcement (HDPE/PVC particles) consistently outperformed single-additive treatments, attributed to improved inter particle bonding, formation of calcium-silicate hydrate (C-S-H), and reduced porosity. Collectively, these findings demonstrate that the waste HDPE and PVC particles, in combination with SL, offer an innovative approach to improving the engineering properties of EC in geotechnical applications for sustainable development and reducing plastic accumulation in terrestrial ecosystems.

There has been an increase in plastic production during the past decades, yet the recycling of plastic remains relatively low. Incorporating plastic in concrete can mitigate environmental pollution. The use of waste polyethylene terephthalate (PET) bottles as an aggregate weakens properties of concrete. An alternative is to use PET bottles as a binder in the mortar. The PET binder mixed with sand results in weak mortar. Marble and iron slag can enhance PET mortar properties by preventing alkali reactions. This study examines the mechanical and durability properties of PET mortar with different mixes. The mixes were prepared as plastic and marble (PM); plastic and iron slag (PI); plastic, sand, and marble (PSM); plastic, iron slag, and marble (PIM); and plastic, sand, and iron slag (PSI). PM with 30–45% plastic content had increased compressive and flexural strength up to 35.73% and 20.21%, respectively. PI with 30–35% plastic content showed strength improvements up to 29.19% and 5.02%, respectively. However, at 45% plastic content, strength decreased by 8.8% and 27.90%. PSM, PIM, and PSI specimens had nearly double the strength of ordinary Portland cement (OPC) mortar. The durability of PET mortar in chemical solutions, mainly 5% HCl and 20% NaOH, indicate that mass decreased after 3, 7, and 28 days. All specimens showed good resistance to HCl and NaCl solutions compared to OPC mortar. However, its resistance to NaOH is low compared to OPC mortar. PET mortar without cement showed higher strength and durability than cement mortar, making it suitable for paver tiles, drainage systems, and roads.

The circular economy encourages the production and consumption of sustainable embankment geomaterials and their blends utilizing recycled waste materials in roads, railway tracks, airfields, and underground structures. Geomaterials comprising high-plastic soft expansive clay pose excessive settlement during cyclic traffic/railway/airfield loading resulting in uneven geometry of overlying layers. This paper demonstrates multiobjective optimized improvement of expansive clay (C) geotechnical characteristics by cost-effective agro-wastes additives at microlevel (by 3 to 12 rice husk ash, i.e., RHA), nanolevel (by 0.6 to 1.5 rice husk derived green nano-SiO₂, i.e., NS), and synergistic micro to nanolevel (NS-RHA). The swell potential, resilient modulus (MR), initial elastic modulus (Es), unconfined compressive strength (UCT), and California bearing ratio (CBR) of C and its blends were determined. The chemical characterization of C and its blends were conducted through Fourier transform infrared spectroscopy (FTIR) and optical microscopic tests. The outcome of this study depicted that the cost ratio for the optimized composite, i.e., (1.2 NS-9 RHA)/(9 RHA) is 1.22 whereas stiffness ratio MR (NS-RHA)/MR(RHA) and Es (NS-RHA)/Es(RHA) and strength ratio UCT(NS-RHA)/UCT(RHA) and CBR(NS-RHA)/CBR(RHA) were found to be 2.0, 1.64, 2.17, and 2.82, respectively. FTIR revealed the chemical compatibility between C, RHA, & NS from durability perspective. Cost-stiffness results of this study can be applied by geotechnical experts to economize the green stabilization of C by use of agro-waste for sustainable development.

Agro-biogenic stabilization of expansive subgrade soils is trending to achieve cost-effective and sustainable geotechnical design to resist distress and settlement during the application of heavy traffic loads. This research presents optimized remediation of expansive clay by addition of proportionate quantities of waste renewable wool-banana (WB) fiber composites for the enhancement of elastoplastic strain (Ԑ_EP), peak strength (S_p), resilient modulus (M_R) and California bearing ratio (CBR) of expansive clays. Remolded samples of stabilized and nontreated clay prepared at maximum dry density (γ_dmax) and optimum moisture content (OMC) were subjected to a series of swell potential, unconfined compressive strength (UCS), resilient modulus (M_R) and CBR tests to evaluate swell potential, Ԑ_EP, M_R, and CBR parameters. The outcome of this study clearly demonstrates that the optimal WB fiber dosage (i.e., 0.6% wool and 1.2% banana fibers of dry weight of clay) lowers the free swell up to 58% and presents an enhancement of 3.5, 2.7, 3.0 and 4.5-times of Ԑ_EPT, S_p, M_R and CBR, respectively. Enhancement in Ԑ_EP is vital for the mitigation of excessive cracking in expansive clays for sustainable subgrades. The ratio of strain relating to the peak strength (Ԑ_PS) to the strain relating to the residual strength (Ԑ_RS), i.e., Ԑ_PS/Ԑ_RS = 2.99 which is highest among all fiber-clay blend depicting the highly ductile clay-fiber mixture. Cost-strength analysis reveals the optimized enhancement of Ԑ_EPT, S_p, M_R and CBR in comparison with cost using clay plus 0.6% wool plus 1.2% banana fibers blend which depicts the potential application of this research to economize the stabilization of subgrade clay to achieve green and biogeotechnical engineering goals.

The determination of rock seepage characteristics is a complex phenomenon due to the variability, discontinuities, and formation age of rocks. The available literature on rock mechanics covers empirical relationships and approaches for the estimation of seepage characteristics from the rock mass parameters. In this study, an area comprising of infrastructure such as a water reservoir, embankments, roads, etc., constructed on mix rock mass formations was selected. The field and laboratory tests’ geo-mechanical data for the study area were evaluated. The data obtained from the field geo-mechanical engineering tests like Rock Quality Designation (RQD), Rock Core Recovery, Lugeon, etc., were analyzed. The data retrieved from the geological and geotechnical laboratory tests such as petrography, uniaxial compression, Hoek shear, elastic modulus, etc., were also evaluated. Rock mass was characterized based on petrographic and RQD, and was found in the hybrid formation of igneous, metamorphic, and sedimentary deposits. Seepage analysis in the study area was also carried out based on adit and piezometric data (installed in accordance with the mining technology guidelines), using Seep W Finite Element Method (FEM). The seepage observed in adits were compared with seepage calculated from Seep W. The trend of simulated flux was also presented against K ratio. Seepage quantities for different ranges of K ratio were plotted to evaluate interdependency between seepage and K ratio. Correlations of RQD were developed with hydraulic conductivity “k” for igneous, metamorphic, and sedimentary rocks for quick assessment of seepage characteristics of rock mass by RQD. These correlations and seepage related evaluations will be beneficial for the characterization of rock mass in relation to seepage for sustainable infrastructure development.

The use of reclaimed asphalt pavement (RAP) is necessary for sustainable and cost-effective road infrastructure construction. This research investigates the effect of the area of weak zones (WZ) on the resilient modulus (M_RT) of mixtures of fresh asphalt with 20% RAP. Experimentation on fresh asphalt–RAP mixtures comprising Superpave (SP-A, SP-B) and Asphalt Institute (MS-2) gradations with 20/30, 40/50, 60/70 and 80/100 penetration grade binders was carried out. WZ were determined based on the analysis of magnified digital images of asphalt specimens obtained using optical microscopy. This study demonstrates that the 20/30 grade binder caused an increase in the M_RT at 25 °C up to 1.8, 2.9 and 9.2 times for a 0.1 s load duration, and 2.4, 3.0 and 9.7 times for a 0.3 s load duration. In contrast, improvement at 40 °C was observed to be up to 1.9, 3.1 and 9.7 times for a 0.1 s load duration, and 1.9, 3.0 and 12.4 times for a 0.3 s load duration in comparison with 40/50, 60/70 and 80/100 grade binders, respectively. Experimental data were validated by factorial analysis. Power trendline equations were also developed between M_RT and WZ to explain the effect of gravel particle orientation on the sustainable resilience of surface course mixtures.

The sustainable design and construction of highways is indispensable for the economic growth and progress of any region. Highway pavements are one of the core transportation infrastructures that require energy efficient materials with durability and an optimized lifecycle. Recent research has proven that warm-mix asphalt pavements prepared with renewable bio-binders are less susceptible to distresses. This study aims to investigate the resilience characteristics (load time, deformation time) of soybean oil modified and unmodified warm-mix asphalts. Aggregates, asphalt binders and asphalt mixes were characterized in accordance with the Superpave Mix Design Criteria. The resilient modulus tests were performed as per ASTM D7369. The test results indicated that the soybean-modified warm asphalt mix samples showed a 20% to 32% reduction in load-carrying capacity than unmodified warm asphalt mixes. The values of the horizontal and vertical recoverable deformations observed in the soybean-modified mixes were found to be 3% to 7% more than in the unmodified mixes. A slight variability (up to 7%) was also observed in the time-response spectra, i.e., peak load, unload and rest periods, in the soybean-modified mixes compared with the unmodified mixes. The Pearson correlation coefficient showed a significant trend between the resilient modulus test parameters for the soybean-modified warm asphalt mixes, i.e., load deformation, load time and deformation time. Soybean oil showed sustainable behavior as a bio-binder, particularly in the deformation-time response for the warm asphalt mixes. However, the effect of soybean in terms of the reduction of the load-carrying capacity from a sustainability perspective needs to be investigated.

Exponential development of post-yield strain (Ԑ_post) is a pivotal indicator of failure in embankments constructed on soft saturated clays. This paper characterizes saturated clay stratum comprising very soft to very stiff stratigraphy, with plasticity index (PI) ranging from 19% to 31%, by performing widely used geotechnical engineering tests, i.e., the prebored pressuremeter (PMT) test, the triaxial (TXL) test, and constant-rate-of-strain (CRS) consolidation. PMT, TXL, and CRS tests were performed at a strain rate range of 0.18%/min to 0.21%/min to explore the yield stress (σ′_y), the pre-yield strain (Ԑ_pre), and the post-yield strain (Ԑ_post). Results indicate that Ԑ_post/Ԑ_pre for PMT, TXL, and CRS stress–strain curves range from 2.7 to 19 in the loading phase and 2 to 21 in the unloading phase. An exponential increase in Ԑ_post/Ԑ_pre is observed in the range of 10 to 21 for very soft to soft clay which is congruent with the realistic sustainable range of 4 to 30 for embankment failure on soft clays worldwide. The evaluated Ԑ_post/Ԑ_pre can be applied for sustainable prediction of post-failure evolution of strains in embankments on soft clays. Simplistic correlations are developed for approximation and prediction of Ԑ_post as a function of σ′_y, Ԑ_pre and maximum applied pressure (P_max) for loading and unloading phases with reasonable accuracy. The intuitive zone of critical ℇ_post is quantified for impending failure in embankments for maximum applied pressure (P_max), ranging from 36 kPa to 100 kPa for very soft to soft clay for use in sustainable embankment design and construction. Variation in predicted versus measured results of an individual site is observed to be within ±10% of line of equality.