Alkali activated materials with recycled unplasticised polyvinyl chloride aggregates for sand replacement

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

The impact of waste brick and geo-cement aggregates as sand replacement on the mechanical and durability properties of alkali–activated mortar composites

This study explores the potential of waste brick and geo-cement aggregates as substitutes for natural sand in alkali-activated materials (AAMs) for mortar production. With a focus on achieving net-zero construction and mitigating environmental impact, the study replaces Portland Cement (OPC) and virgin aggregates with waste materials and by-products. The investigation evaluates the substitution of sand (up to 100 % by weight) in AAMs with waste brick aggregates (WBA) and waste geo-cement aggregates (WGA) obtained from demolished construction and research lab waste, respectively. The research methodology involves assessing mechanical, durability, and microstructure properties to assess the performance of the developed AAMs with waste aggregates. Notably, AAM composites containing waste brick and geo-cement aggregates surpass natural aggregate composites in terms of mechanical strength, water absorption, freeze-thaw resistance, acid ingress, and chloride attack. The 7-day 50 % waste brick mixture achieved a maximum compressive strength of 61 MPa, while a 70 % waste geo-cement mortar mixture attained a maximum flexural strength of 12 MPa. Combinations, whether comprising waste brick or geo-cement mortar aggregates, demonstrate compressive strengths well over 40 MPa, rendering them suitable for heavy load-bearing structures. The 50 % waste geo-cement mortar mixture stands out with the lowest water absorption rate of 6 % and the least compressive strength loss of 13 % after the freeze-thaw test, with reductions of 6 % and 18 %, respectively, compared to the control. Additionally, 100 % waste brick AAMs exhibit the lowest compressive strength loss after chloride and acid attack tests, with reductions of 13 % and 2.5 %, respectively. When compared to all other mixtures, the 50 % waste brick aggregates mortar mixture obtained the best overall performance. The composites developed in this study affirm their suitability for use in heavy-load structural components, showcasing favourable mechanical and durable properties. These findings underscore the need for additional exploration in this direction to advance sustainable construction practices

Upcycling end-of-life bricks in high-performance one-part alkali-activated materials

One-part alkali-activated materials (AAMs) can preserve natural resources and lower embodied carbon of the built environment by accommodating various wastes, industrial by-products, and end-of-life materials in their composition. This study investigates the feasibility of using end-of-life bricks in two physical states, powder and aggregate, to partially replace fly ash precursor and natural aggregate in AAMs, respectively. The mechanical characteristics, microstructure, water absorption, freeze-thaw and fire resistance of the modified AAMs were evaluated. The effect of adding different ratios of nano graphite platelets was also investigated. Results showed that brick-based one-part AAMs can achieve mechanical properties, pore structure, water absorption and freeze-thaw resistance comparable to fly ash-based AAM while having 65% better fire resistivity. Incorporating bricks as aggregate resulted in a maximum improvement of 17% and 27% in the AAMs' compressive and flexural strength levels, respectively, and a general enhancement in the freeze-thaw resistance with showing no reduction in compressive strength after exposure to elevated temperature. Incorporating 0.1 wt% nano-graphite further enhanced flexural strength by 30%, decreased water absorption by 18% and improved freeze-thaw resistance compared to the mix without nano-graphite. Moreover, adding up to 0.5% nano-graphite enhanced the fire resistivity of the composite, allowing it to exhibit 19% better strength performance than before exposure

3D printing of limestone-calcined clay cement: A review of its potential implementation in the construction industry

The rapid development in 3D printing applications requires exploring a sustainable printable mixture to decrease the environmental impact induced by the existing Ordinary Portland Cement (OPC) mixtures and enable 3D printing technology to reach its peak efficiency. The high-volume substitution of OPC with supplementary cementitious materials (SCMs) is of significant interest as a promising solution for developing low-carbon feedstock for 3D printing. Yet, those materials share the problem of limited availability. The combination of limestone and calcined clay could be a promising alternative, offering various benefits, including replacing OPC in high ratios. This paper reviews 3D printable limestone calcined clay cement (LC3) mixtures, compositions, and chemical behaviour. The effect of different sand-to-binder ratios, additives content, OPC replacement levels, clay grade and calcination, and admixtures on the fresh, hardened and printing properties of the 3D printed mixtures are critically discussed. The environmental impact and production cost of the LC3 system compared to OPC and other systems are also critically evaluated along with the applications, future directions and research gaps in this field. The findings of this review show that 3D printed LC3 has a similar hardened performance and better microstructure than OPC system. Moreover, cast LC3 system has 30–50% lower environmental impacts depending on the replacement level and better economic feasibility than OPC. Therefore, making it a suitable feedstock for the innovative manufacturing technology of 3D printing

Recycled brick aggregates in one-part alkali-activated materials:Impact on 3D printing performance and material properties

This study investigates the printability of one-part brick powder-based alkali-activated materials (AAMs) containing end-of-life brick particles as aggregate. The novel formulation showcases promise for 3D printing of small to medium-sized building blocks, reminiscent of a Lego-type system, capitalising on the rapid setting time inherent to one-part AAMs. The effect of replacing up to 50% by weight of natural aggregate with brick aggregate on the fresh properties of brick powder-based alkali-activated materials, including slump measurements, flowability, setting time, open time and green strength were investigated. In addition, the flexural and compressive strength of the 3D printed mixtures were determined and compared to those of cast specimens. The buildability and microstructure were also examined. The results showed that incorporating high porous and rough brick aggregate to replace natural aggregate is beneficial in improving the mixtures’ slump, which is essential for retaining the shape of the printed layers. However, it decreased the flowability, setting time and open time when incorporating up to 50% brick aggregate. The green, flexural and compressive strengths were increased with increasing brick aggregate content up to 50% due to enhancing interlock between the binder and brick aggregate, and the better compaction because of the absorption properties of brick aggregate. The mechanical results revealed the better performance of 3D printed specimens than the cast specimens. Moreover, the incorporation of brick aggregate enhanced the buildability of the mixtures showcasing their potential in advancing 3D printing capabilities