Construction and Demolition Wastes (CDW) serves as an effective filler for highway subgrades, demonstrating commendable performance characteristics. The efficient utilization of CDW not only contributes to environmental sustainability but also yields significant economic benefits. This study employs discrete element simulation to develop a triaxial sample model comprising particles with four distinct levels of sphericity. By varying the combinations of sphericity, brickconcrete ratio, and void ratio, triaxial simulation tests are conducted, and the critical state soil mechanics framework is applied to fit the critical state line (CSL) of the samples. The results indicate that sphericity, brick-concrete ratio, and void ratio substantially influence the macroscopic mechanical properties of CDW. Notably, as sphericity increases, the peak deviatoric stress of the samples decreases, and significant volume deformation occurs. The slope of the CSL in the q-p ' plane diminishes, while the slopes of both forms of the CSL in the e-log p ' plane increase. Furthermore, a decrease in the brick-concrete ratio enhances the anti-deformation and compressive capacities of the samples. As the brick-concrete ratio decreases, both the slopes and intercepts of the CSL in the e-log p ' plane exhibit an upward trend. Conversely, an increase in the void ratio leads to a reduction in the overall strength and anti-deformation capacity of the specimens, an increase in the compressibility of the specimen volume, an elevation of the CSL slope on the q-p ' plane, and a gradual increase in both the slope and intercept of the semilogarithmic form of the CSL on the e-log p ' plane, as well as a gradual increase in the slope of the power-law form of the CSL.

The cement-stabilization technique is employed on natural and recycled granular materials to improve their mechanical properties. The strength of these materials is assessed by the unconfined compressive strength on laboratory compacted specimens, typically after 7 days of curing. Standards and technical specifications specify different values of specimen height and diameter and different loading modes of testing. This makes the comparison between different materials and with the acceptance limits of technical specifications difficult. The research investigates the effect of specimen size and loading mode on the unconfined compressive strength of both natural and recycled cement-stabilized granular materials. The results revealed significant differences in strength due to variations in specimen size and loading mode. As expected, an increase in specimen slenderness resulted in a decrease in compressive strength. A linear regression model was developed to quantify the effect of the experimental variables on the compressive strength of the two cement-stabilized materials.

The use of ordinary Portland cement for the stabilisation of granular materials in road construction undermines the effort on sustainability made by using recycled aggregate in substitution of natural ones. This requires the use of low-impact binders so that the road construction industry complies with the prevailing environmental regulations. This study compares the mechanical and environmental properties of construction and demolition waste (CDW) aggregates stabilised with different binders: (i) a Portland-limestone cement as a reference, (ii) a pozzolanic cement, (iii) an experimental pozzolanic cement containing waste clay from the lightweight aggregate production, and (iv) a binder with alkali-activated CDW fines. In the laboratory experiments, both strength and resilient properties were considered, while the environmental impact was assessed in a cradle-to-gate scenario through a life cycle analysis (LCA). The stabilised mixture with pozzolanic cement achieved comparable strength and stiffness while exhibiting a lower environmental impact than the mixture containing Portland-limestone cement. The addition of waste clay to the pozzolanic cement significantly reduces its environmental impact albeit more binder is required to compensate for the lower mechanical properties. The alkaline activation of the fine particles in the CDW aggregate enabled the creation of a stabilised mixture with high strengths and resilient modulus. However, this alternative stabilisation technique requires further optimisation to mitigate the significant environmental impact. The engineering evaluations of the stabilised granular mixtures studied have considered both mechanical and environmental factors intending to contribute to the scientific debate on how to make roadworks sustainable and conserve natural resources.

Utilising recycled materials, such as construction and demolition waste (C&DW), into soil improvement projects offers a promising solution to reduce the environmental impact of the C&DW industry. This approach helps address issues related to waste generation, resource depletion, and environmental degradation, while enhancing the overall sustainability and resilience of soil stabilisation efforts. This study investigates the effectiveness of incorporating recycled C&DW into cement-treated peat and clayey soils to enhance their strength and stiffness. To achieve this goal, laboratory experiments were conducted on over 296 soil specimens to assess their Unconfined Compressive Strength (UCS), small-strain Young's modulus (E0) and shear modulus (G0). These tests included varying curing times (28, 60, 90, and 120 days), different cement and recycled material content, and water-to-cement ratios. Moreover, laboratory testing methods for determining geotechnical parameters are often time-consuming and prone to challenges. In this context, reliable predictive models, such as artificial neural networks (ANNs), offer an efficient alternative for accurately assessing these parameters. The findings of this research reveal that, along with cement content, the water-to-cement ratio (w/c) and curing time are key factors influencing the strength and stiffness of treated soft soils, underscoring their critical role in soil stabilisation. Additionally, while minimizing cement content and increasing RM yield improvements in both peat and clay, the effect is more pronounced in peat due to the time-dependent nature of pozzolanic reactions. This suggests that achieving optimal performance with increased strength and stiffness requires a carefully balanced RM content. Finally, the study demonstrates that ANN-based models can accurately predict the strength and mechanical properties of soft soils, offering a viable alternative to traditional UCS and FFR tests.

With the rapid growth of shield-discharged soil (SDS), there is an increasing demand for effective recycling and transformation methods. This study aims to develop an alkali-activated controlled low-strength material (CLSM) by utilizing ground granulated blast furnace slag (GGBFS) and fly ash (FA) as precursors, SDS as fine aggregate, and sodium hydroxide (NaOH) solution as an activator. The Box-Behnken design (BBD) within the response surface methodology (RSM) framework was employed, considering liquid-to-solid ratio, alkali equivalent, aggregate-to-binder ratio, and foam agent content (FC) in SDS as key factors. Regression models were constructed to analyze the effects of these factors on flowability, bleeding rate, setting time, compressive strength, elastic modulus, and water absorption. The results confirmed the effectiveness of RSM in determining optimal conditions for material performance. In addition, microscopic analyses were conducted to explore hydration products, microstructural characteristics, and pore distribution. The findings revealed that the fresh density of the CLSM ranged from 1460 to 1740 kg/m(3), classifying it as a low-density material. The 28-day compressive strength varied from 1.837 to 7.884 MPa, while the setting time ranged between 1.2 and 5.6 hours. These properties comply with the ACI 229 standard and are suitable for practical applications. Interestingly, when the aggregate-to-binder (A/B) ratio was between 0.2 and 0.4, increasing the ratio did not lead to a consistent reduction in mechanical properties. Instead, the properties initially decreased and then improved. Moreover, an increase in foam agent content (FC) extended the setting time and reduced mechanical strength. The correlation coefficients of all models exceeded 0.98, with a coefficient of variation below 10 % and a signal-to-noise ratio greater than 4, demonstrating strong reliability and accuracy of the models. Additionally, the average relative error between predicted and experimental values in six scenarios was under 6 %, validating the feasibility of optimizing the design of alkali-activated CLSM using RSM. The formation of Ca(OH)(2) crystals facilitates early strength development, resulting in final cementitious materials reticular, fibrous C-S-H, C-A-H, and other gel-like hydration products. Calcium promotes the formation of gels such as C-S-H, shortening the setting time and enhancing microstructural density. This study provides valuable insights for optimizing the design of alkali-activated CLSM containing SDS, thereby expanding methods for utilizing construction and demolition waste.

This paper aimed to investigate the feasibility of partially or completely replacing natural aggregates with recycled aggregates from construction and demolition wastes for low-carbon-emission use as coarse-grained embankment fill materials. The laboratory specimens were prepared by blending natural and recycled aggregates at varying proportions, and a series of laboratory repeated load triaxial compression tests were carried out to study the effects of material index properties and dynamic stress states on the resilient modulus and permanent strain characteristics. Based on the experimental results and by considering the main influencing parameters of the resilient modulus and permanent deformation, an artificial neural network (ANN) prediction model with optimal architecture was developed and optimized by the particle swarm optimization (PSO) algorithm, and its performance and accuracy were verified by supplementary analyses. A shakedown state classification method was proposed based on the unsupervised clustering algorithm, and a prediction model of critical dynamic stress was established based on the machine learning (ML) method and the shakedown state classification results. The research results indicate that the stress state has a greater influence on the resilient modulus and permanent deformation characteristics than other factors, and the shear stress ratio has a significant effect on the shakedown state. The resilient modulus and critical dynamic stress of such specimens vary linearly with confining pressure. The improved PSO-ANN prediction model exhibits high prediction accuracy and robustness, superior to several other commonly used ML regression prediction algorithms. The resilient modulus and critical dynamic stress prediction methods based on ML algorithms can provide technical guidance and theoretical basis for the design and in-service maintenance of similar unbound granular materials.

This study investigates the performance of two waste materials, steel slag and construction and demolition waste (CDW), as potential backfill materials for reinforced earth (RE) applications under cyclic loading conditions. Consolidated-undrained cyclic triaxial tests were conducted on the materials to investigate the material behavior. The study also assessed the influence of incorporating geogrids on the cyclic performance of the materials. Both the waste materials exhibited cyclic behavior similar to that of conventional sand, with maximum deviator stress observed in slag, followed by CDW. The presence of slightly higher fines content in slag and CDW resulted in increased excess pore pressure compared to sand. The incorporation of geogrid enhanced the cyclic strength of both slag and CDW. In the first cycle, an improvement of 26% and 20% was observed with the inclusion of geogrid in slag and CDW, respectively, at a frequency of 1 Hz. In addition, the use of geogrid resulted in a reduction in excess pore water pressure generation. At a given frequency, the shear modulus of slag and CDW was found to be higher than that of sand. In the initial loading cycle, the shear modulus of slag was 54% higher, and CDW was 26% higher compared to sand. With the inclusion of geogrid, the dynamic shear modulus of sand, slag and CDW in the first cycle improved by 18%, 28%, and 25%, respectively. Sand exhibited a higher damping ratio compared to slag and CDW. However, the influence of geogrid on the damping ratio was found to be negligible. Furthermore, a 2D numerical investigation was conducted to explore the potential implementation of slag and CDW in practical applications, specifically in RE walls under railway loading. Numerical simulations revealed a significant reduction in wall deflection when slag or CDW was used as backfill compared to conventional material. The peak horizontal facing displacement values were found to reduce by 48% and 32% for slag and CDW, respectively, when compared to the use of sand.

Excavations soils from construction sites, when included as Construction and Demolition Waste (CDW) can double waste amount and represent up to 80 % of waste composition. Limited recycling strategies are available for the material. In this work, soils with higher kaolinite contents were selected by X-ray diffraction (XRD) to produce high activity pozzolan. Twenty soil samples were collected in an inert CDW landfill, and seven samples (one-third of the total) containing higher kaolinite content were composed as a single sample for thermal and mechanical activation as pozzolan. At the temperature of 600 C, low crystallinity kaolinite was transformed into amorphous material (37 % g/g) achieving the highest pozzolanic activity [consumption of 519 mg Ca(OH)2/g of the sample]. The replacement of Portland cement by calcined soil (6, 10 and 18 %) had no significant rheological impact on the water to solid ratio and optimal dispersant content and affected slightly the heat and setting time of the pastes; therefore, workable, and technically applicable. The Portland cement replacement by calcined soil, despite a fixed water to solid ratio of 0.3 led to an increase in the water to cement ratios and in the porosities of the pastes. Due to the pozzolanic reaction, 6 and 10% -replacement of Portland cement by calcined soil did not impair the tensile strength of the pastes when compared to that of Portland cement paste. A 42-MPa 28 -day age blended Portland with calcined soil might be feasible to produce regarding Brazilian cement industry standard.

Interlocking Compressed Earth Blocks (ICEBs) have recently surfaced as a valuable and innovative inclusion among earthen building materials. They offer workable answers to the common problems with burned bricks and cement blocks. Researchers frequently used river sand in their studies to address and reduce the finer content in soil. This study explored recipes to make ICEBs from construction and demolition wastes. Fine recycled concrete aggregate (FRCA) was used as a soil modification within the ICEBs as a part of this investigation to support ecofriendly, low-carbon product development driven by global climate concerns and the need for improved construction waste management to combat pollution. ICEBs, made by mixing construction and demolition trash, regulate environmental impact and address the scarcity of building materials. Due to the inherent diversity of soil and the lack of a standardized mix design for the manufacturing of ICEB, 40 different mix ratios were generated using the proportionated blends of sand and FRCA. Based on the compressive strength results, the best recipes representing conventional river sand and the FRCA were selected. The prepared samples of ICEBs using the optimized mix recipes of river sand and FRCA were further analyzed for mechanical, thermal, and durability performance alongside the required forensic endorsements, and the test results were enhanced for both ICEBs compared to first-class burnt clay bricks. Sand-incorporated ICEBs achieved 13.72 MPa compressive strength, while FRCA-incorporated ICEBs reached 13.38 MPa. Both ICEBs showed a noticeable improvement in compressive strength compared to various studies. The durability of ICEBs, in terms of water absorption, improved around 70% compared to fired bricks commonly used in the construction industry. The test findings reveal that FRCA incorporated ICEBs showed 14.3% lower thermal conductivity than ICEBs with sand incorporation. Therefore, the use of ICEBs specially designed with FRCA provides the most sustainable alternative to conventional fired bricks used by the construction sector in the developing countries.

Waste disposal has become a major challenge due to the increasing production driven by urbanization. Two such wastes generated in substantial quantities are steel slag and construction and demolition waste (CDW). The current study explored the stress-dilatancy and critical-state behaviors of geogrid-reinforced recycled steel slag and CDW for evaluating its suitability in various geotechnical applications. A set of consolidated drained triaxial tests were carried out on test samples, with and without geogrid reinforcement, to achieve this objective. The performance of the steel slag and CDW material was compared with that of commonly used geomaterial, namely, sand. Steel slag exhibited higher strength compared to sand and CDW. At a confining stress of 50 kPa, the strength of steel slag was 1.6 times greater than that of sand, while the strength of CDW was 1.3 times higher than that of sand. The effect of geogrid reinforcement on stress-dilatancy and critical-state behavior was quantified for all the materials. Results revealed that the critical-state line rotates in a clockwise direction in the presence of the geogrid. On the other hand, the stress-dilatancy curve of the materials shifted upward with the inclusion of the geogrid. At a confining pressure of 50 kPa, the peak dilation angles of reinforced sand, slag, and CDW were 0.8, 0.7, and 0.9 times that of the unreinforced specimens, respectively. In addition, the strength properties, energy absorption capacity, and modulus degradation of the materials were also evaluated. A mathematical expression was proposed to relate the energy absorption capacity of the geogrid-reinforced materials with the critical-state stress ratio. Moreover, the Li and Dafalias stress-dilatancy model parameters were proposed to capture the stress-dilatancy behavior of the materials. Overall, encouraging performance of the waste materials was observed for potential geotechnical applications.