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• Lightweight AAM were developed by replacing sand with recycled PVC and waste glass aggregates. • PVC aggregate incorporation enhances the composites' impact energy absorption and thermal conductivity. • PVC and waste glass aggregates in composites led to reduction of the overall carbon footprint. Polyvinyl chloride plastic (PVC) and glass waste have proven to be significant environmental concerns considering their restricted reuse and complicated recycling procedures. Glass and PVC waste materials form a substantial portion of total solid wastes that negatively influence the environment. This study aims to fully replace natural sand with recycled PVC and waste glass aggregates in alkali-activated materials (AAMs). A comprehensive testing programme was employed to investigate the effect of 100 % aggregate replacement on the composites' mechanical performance, water absorption, impact resistance, thermal conductivity, resistance to harsh environments, and microstructural changes. Results revealed that AAMs containing recycled PVC and glass aggregates outperformed their ordinary Portland cement (OPC)-based composite counterparts in terms of mechanical properties, energy absorption, thermal conductivity, and carbon footprint estimation. Although mixtures containing recycled aggregates cannot be deemed for load-bearing applications, these composites exhibited a promising capacity to be used in insulating applications. AAMs containing 100 vol-% PVC aggregates with flexural and compressive strengths of 9 and 11 MPa, respectively, registered the highest energy absorption of about 6 J, three times higher than the AAM control sample, and the lowest thermal conductivity of about 0.5 W/mK, with about 80 % reduction of thermal conductivity compared to the AAM control sample. With the full replacement of PVC and glass aggregates, the most significant decrease in the carbon footprint is achieved for AAM (−352.25 kg CO2-eq) and OPC (−353.94 kg CO2-eq), respectively. [ABSTRACT FROM AUTHOR]

• Nano-Graphite cement composites are high-performance multifunctional materials. • Smooth workability loss of the fresh admixtures. • Improved density and mechanical strength. • Enhanced damping, electrical and thermal conductivity at the lowest dosage. • Reduced water permeability and chloride penetration. In this study an extensive experimental campaign has been conducted on mortars modified with nano-Graphite (nG) aimed to assess the properties of the resulting nanocomposites in terms of density, microstructure, flexural and compressive strength, damping ratio, thermal and electrical conductivity. Permeability properties were also investigated in terms of initial surface absorption, water contact angle, volume of permeable voids and chloride ion diffusion. Premixed mortars have been modified with different dosages of commercial nG, i.e. 0.01%, 0.1%, or 0.2% by weight of cement. The rheological behavior of the fresh admixtures has been investigated. Specimens were casted in bars and hardened in water for 7, 14 or 28 days. At 28 days all samples showed enhanced density (i.e. up to 16%) and mechanical properties (i.e. up to 30%) combined to remarkable decreased overall permeability. The lowest dosage of nG (i.e. 0.01% by weight of cement) resulted in cement nanocomposites with the highest increase in damping ratio, electrical and thermal conductivity, 68%, 30% and 55%, respectively. [ABSTRACT FROM AUTHOR]

• Development of novel 3D printable geopolymer. • Nano-additives improved the mechanical performance of 3D printed structures. • The microstructural analysis revealed the micro-crack arresting effect of nano additives. • The shape retention and buildability of geopolymer was improved with incorporation of nano additives. • Rheology measurements play a crucial role in the selection of printable feedstock. The weak mechanical properties the 3D printed parts can limit the competence of this technology when compared to conventionally cast-in-mold cementitious composites structures. However, experimental results in this study showed that the incorporation of nano additives could improve the mechanical property of printed structures. Six geopolymeric mixtures were designed and tested for their flow-ability, shape stability, buildability and mechanical performance. Different dosage of nano graphite platelets (NGPs) ranging from 0.1% to 1%, by the weight of geopolymer, were incorporated to the best performing geopolymer. The 3D printed geopolymer with 1% of NGPs increased the flexural strength by 89% and 46% compared to the same 3D printed and casted geopolymer without any NGPs, respectively. The same increase for compressive strength was 28% and 12%. Moreover, the geopolymer mix containing 1% of NGPs demonstrated the best shape retention and buildability. [ABSTRACT FROM AUTHOR]

• Safety, sustainability and costs require low amounts of graphene-based materials. • Minimum amounts of graphene-based materials induce a slight thickening. • Graphene-based premixed hardened mortars show density enhancement. • Mechanical strengthening greatly depends on the chosen nanofiller and its dosage. • Minimum amounts of graphene-based materials give predictable mechanical properties. Graphite nano-platelets (GNPs) and graphene oxide (GO) modify cementitious materials from the nano- to the macroscale, resulting in enhanced mechanical properties, durability and, eventually, physical multi-functionality. A systematic study on EN 998-2 premixed mortars modified with GNPs or GO is reported. Rheological properties of fresh mortars were investigated in terms of shear stress (or apparent viscosity) versus shear rate. Mortars were casted in bars and hardened for 28 or 14 days. Density, microstructure, compressive and flexural strength of hardened samples were evaluated and compared. [ABSTRACT FROM AUTHOR]

Incorporating recycled Unplasticised Polyvinyl Chloride (UPVC) aggregates into Alkali Activated Materials (AAMs) presents a promising approach to alleviate the environmental drawbacks associated with conventional recycling methods for UPVC. The distinctive characteristics of UPVC aggregates, as compared to natural sand, pose a challenge in the pursuit of enhancing the mechanical properties of composites. This research aims to achieve net-zero goals and promote circular economy principles by replacing traditional Portland cement (OPC) with low-carbon AAMs and natural aggregates with recycled unplasticised polyvinyl chloride (UPVC) which, accounts for 12% of global plastic production. Coarse and fine UPVC aggregates, measuring 4–6 mm and 0–2 mm, respectively, were incorporated into AAMs. An extensive array of tests was performed to assess their environmental benefits and overall performance enhancements. The results unveiled notable advantages in terms of thermal resistivity and resistance to chloride penetration in the UPVC-infused AAMs. Notably, mixtures containing 100% fine UPVC aggregates exhibited a remarkable 70% reduction in thermal conductivity (0.465 W/mk) when compared to the control. In mechanical assessments, composites containing fine UPVC aggregates surpassed those with coarse UPVC aggregates, showcasing promise for load-bearing applications. Substituting 30% of both fine and coarse UPVC aggregates with sand yielded impressive 7-day compressive strengths of 41 MPa and 35 MPa, respectively. Moreover, the utilisation of energy-dispersive X-ray spectroscopy confirmed the absence of chloride leaching after three months. The incorporation of UPVC waste aggregates led to a significant reduction in the carbon footprint of the tested AAMs. In conclusion, these composites offer an appealing and sustainable solution for both load-bearing and non-load-bearing structures. • Fine and coarse UPVC aggregates were incorporated in AAM. • Fine UPVC demonstrated better compatibility with the AAM. • The highest compressive and flexural strength with fine UPVC are 41 and 9 MPa, respectively. • Fine UPVC recorded the lowest thermal conductivity of 0.465 W/mk. [ABSTRACT FROM AUTHOR]