The construction industry strongly relies on concrete and clay bricks for various applications. The escalating demand for these materials, driven by rapid population growth, has led to resource depletion and increased construction and demolition waste (CDW). Recycling CDW into construction materials, particularly in the form of recycled concrete aggregates (RCAs) and recycled brick aggregates (RBAs), has emerged as a promising solution. This study deals with the structural performance of concrete incorporating RCAs and RBAs. The experimental program encompasses material characterization, concrete mix design, and several tests to assess density, compressive strength, bond behavior, and flexural properties. The results indicate that the replacement of fine natural aggregate (NA) with fine RCAs or RBAs has a negligible impact on density, while the partial replacement of coarse NAs with RAs yields modest reductions in compressive strength. Notably, the bond strength between steel rebar and concrete is influenced by the type and content of RA, with specimens containing RCAs exhibiting a higher bond strength than those with RBAs. Empirical models used to predict bond strength generally align with experimental results, with conservative predictions by some models, such as ACI 318, and overestimation by others, such as models proposed by AS-3600 and CEB-FIB. The flexural tests of beams highlight the variation in stiffness and load-bearing capacity with the proportion of NAs replaced by RAs. While beams with 50% NA replacement demonstrate comparable performance to control beams, those with 100% RA replacement exhibit lower cracking and yielding stiffness. Cracking patterns in beams with RAs differ from control beams, with RA-containing beams showing more cracks and an altered crack distribution. The findings underscore the feasibility of using recycled aggregates in construction, with partial NA replacement offering a balance between sustainable material usage and desired structural properties.

It is imperative to design and operate sustainable solid waste management (SWM) systems in cities based on the results of waste amount and characterization study (WACS). In this work, WACS was conducted, and results were used to design an SWM system for an intermediate city of Pakistan. The study revealed that about 110 tons of solid waste per day is generated with a per capita rate of 0.337 kg/day. Around 51.2 $\mathrm{\%}$ of mixed municipal solid waste (MSW) is organic in nature, and its non-scientific disposal is resulting in higher greenhouse gas (GHG) emissions. It was also found that more than 80 $\mathrm{\%}$ of valuables are taken away by the informal sector during the transfer of MSW from the generation source to the dumping site. Ultimate analyses showed that the moisture content (MC) and carbon to nitrogen (C:N) ratio were 64.23 $\mathrm{\%}$ and 51.14 $\mathrm{\%}$, respectively. Proximate analysis revealed that moisture and calorific value were 57 $\mathrm{\%}$ and 3505 BTU/lb., respectively. Based on these results, a material sorting facility (MSF) was proposed, with an estimated investment cost of US $3.64 million. However, efficiency of the existing collection system is limited to 32 $\mathrm{\%}$ only. In order to improve the collection efficiency (>90 $\mathrm{\%}$), an additional investment of US $1.638 million was estimated with an operations and maintenance (O&M) cost of US $19.25 per ton. Existing non-scientific MSW disposal practices contribute 32079.61 CO ${}^2$e tons/year of GHG emissions. The proposed MSF followed by composting is estimated to reduce GHG emissions by 38 $\mathrm{\%}$ to 19722.38 CO ${}^2$e tons/year.

The research work presented in this manuscript focused on the comparative examination of the influence of the Compression Casting Technique (CCT) and the conventional casting method (i.e., compaction through vibration) on the performance of 100% Recycled Aggregate Concrete (RAC). The minimum target compressive strength of 100% RAC was 15 MPa keeping in view its application in the manufacturing of load-bearing concrete masonry units. A total of 28 concrete compositions were prepared by varying the coarse to fine aggregates ratio (i.e., 70:30 and 60:40), cement content (10% and 15%) by weight of total aggregates, casting technique, and applied pressure for compression casting (i.e., 25, 35, and 45 MPa). The concrete compositions were tested to determine their density, compressive strength, Elastic Modulus (EM), and Ultrasonic Pulse Velocity (UPV). For comparison, samples of Natural Aggregate Concrete (NAC) were also tested for the same properties. The results highlighted the positive impact of CCT on the properties of 100% RAC. The compressive strength and EM of fully RAC was increased by 20–80% and 15–50%, respectively, by changing casting method from vibration to CCT. At casting pressure of 35 MPa and 15% cement, compressed 100% RAC exhibited compressive strength higher than vibrated NAC. The UPV value exhibited by 100% RAC was increased by changing the casting technique. The analytical models were proposed using regression analysis of experimental results to predict compressive strength and EM of compressed 100% RAC and NAC. These proposed models were evaluated using statistical parameters, i.e., average absolute error (AAE) and mean (M) and found to be able to predict the compressive strength and EM of RAC with reasonable accuracy as compared to the analytical models already existing in the literature. This study finally concluded that through CCT, 100% RAC with low cement content could achieve minimum target compressive strength of 15 MPa. The development and use of compressed load-bearing 100% RAC construction units would help to achieve sustainability in construction.

This study focuses on different techniques for dispersing Multi-Walled Carbon Nanotubes (MWCNTs) in cementitious materials. The impact of dispersion is observed through electrical resistivity and mechanical properties of cementitious composites. Two contents (0.5 and 1% by mass of cement) of MWCNTs are investigated and three different techniques were used to disperse CNTs in water by sonication: (i) pristine, P-CNT, (ii) functionalized carbon nanotubes by classical approach (dispersive agent, D-CNT), and (iii) by an innovative approach (annealing, A-CNT). Self-sensing response of the material under cyclic compressive loading is measured with Wheatstone Bridge (WSB) circuit. Results showed a detrimental effect of dispersive agent on the resistivity and mechanical properties of cementitious composites irrespective of the content of CNTs. However, the impact of P-CNT and A-CNT on the reduction of mechanical properties is slight. With the use of 1% content of A-CNTs, a stable resistivity response of the material is observed irrespective of the saturation degree. This indicates that content higher than 1% of A-CNTs is not required for the development of smart cementitious composites for structural health monitoring (SHM). The test results of self sensing measurements indicate a poor repeatability of the electrical response for plain mortar under each loading cycle while, stable response is noticed with specimens incorporating 1% of A-CNTs. The maximum variation in fractional change in voltage (FCV) shown by plain mortar is 6.3% indicating high electrical resistance of plain mortar, while in case of mortar containing 1% A-CNTs, variation in FCV is 35% indicating lower electrical resistance and better sensitivity of the material.