A review of 3D printing low-carbon concrete with one-part geopolymer: Engineering, environmental and economic feasibility

Data Availability: Data will be made available on request.Copyright The Author(s) © 2022. 3D printing is a developing technology that has the ability to use different materials to produce concrete elements with complex shapes. The utilization of geopolymers or alkali-activated materials (AAMs) in 3D printing is receiving significant interest due to the environmental benefits of replacing ordinary Portland cement (OPC). The use of solid activators to produce a one-part geopolymer can help the broader use of geopolymers at large scales, as the corrosive, viscous, and hazardous liquid activators used in two-part geopolymers do not present a feasible large-scale solution for this technology. This paper reviews the 3D printable one-part geopolymers, their compositions, and the effect of different precursor compositions, activator content, and different admixtures on the fresh and hardened properties of the mixtures. The environmental impact and cost assessment of one-part geopolymers produced by conventional and 3D printing methods are also discussed and compared to OPC and two-part geopolymers. This review concluded that one-part geopolymers are easier to mix and use than two-part geopolymers and have a lower carbon footprint than two-part geopolymers and OPC concrete. However, one-part geopolymers may not be as strong as two-part geopolymers, but they are still better than OPC.Part of the DigiMat project, which has received funding from the European Union's Horizon 2020 research and innovation program under the Marie Skłodowska-Curie grant agreement ID: 101029471

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

Data availability: Data will be made available on request.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.10.3030/101029471 - European Union's Horizon 2020 research and innovation program under the Marie Skłodowska-Curie grant agreement ID: 101029471 (DigiMat project)

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

Data availability: Data will be made available on request.Copyright © The Authors 2023. 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.This work was funded as part of the DigiMat project, which has received funding from the European Union's Horizon 2020 research and innovation program under the Marie Skłodowska-Curie grant agreement ID: 101029471. The research leading to this publication benefitted from EPSRC funding under grant No. EP/W022583/1, EP/R010161/1 and from support from the UKCRIC Coordination Node, EPSRC grant number EP/R017727/1, which funds UKCRIC's ongoing coordination

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

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

Data availability: Data will be made available on request.Copyright © The Authors 2023. 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

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

Data availability: Data will be made available on request.Copyright © The Author(s) 2023. 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

Data availability: Data will be made available on request.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.This work was funded as part of the DigiMat project, which has received funding from the European Union's Horizon 2020 research and innovation program under the Marie Skłodowska-Curie grant agreement ID: 101029471. This research was funded in part by the National Center for Research and Development (NCBR), Poland within Project no. ERA-MIN3/140/Recycl3D/2022 (ERA-NET Cofund ERA-MIN3 (Joint Call 2021)). The funding provided by FCT - the Portuguese Foundation for Science and Technology, is acknowledged: references UIDB/04625/2020 (CERIS research centre) and ERA-MIN3/0001/2021 (ERA-NET Cofund ERA-MIN3)

Height and body-mass index trajectories of school-aged children and adolescents from 1985 to 2019 in 200 countries and territories: a pooled analysis of 2181 population-based studies with 65 million participants

Summary Background Comparable global data on health and nutrition of school-aged children and adolescents are scarce. We aimed to estimate age trajectories and time trends in mean height and mean body-mass index (BMI), which measures weight gain beyond what is expected from height gain, for school-aged children and adolescents. Methods For this pooled analysis, we used a database of cardiometabolic risk factors collated by the Non-Communicable Disease Risk Factor Collaboration. We applied a Bayesian hierarchical model to estimate trends from 1985 to 2019 in mean height and mean BMI in 1-year age groups for ages 5–19 years. The model allowed for non-linear changes over time in mean height and mean BMI and for non-linear changes with age of children and adolescents, including periods of rapid growth during adolescence. Findings We pooled data from 2181 population-based studies, with measurements of height and weight in 65 million participants in 200 countries and territories. In 2019, we estimated a difference of 20 cm or higher in mean height of 19-year-old adolescents between countries with the tallest populations (the Netherlands, Montenegro, Estonia, and Bosnia and Herzegovina for boys; and the Netherlands, Montenegro, Denmark, and Iceland for girls) and those with the shortest populations (Timor-Leste, Laos, Solomon Islands, and Papua New Guinea for boys; and Guatemala, Bangladesh, Nepal, and Timor-Leste for girls). In the same year, the difference between the highest mean BMI (in Pacific island countries, Kuwait, Bahrain, The Bahamas, Chile, the USA, and New Zealand for both boys and girls and in South Africa for girls) and lowest mean BMI (in India, Bangladesh, Timor-Leste, Ethiopia, and Chad for boys and girls; and in Japan and Romania for girls) was approximately 9–10 kg/m2. In some countries, children aged 5 years started with healthier height or BMI than the global median and, in some cases, as healthy as the best performing countries, but they became progressively less healthy compared with their comparators as they grew older by not growing as tall (eg, boys in Austria and Barbados, and girls in Belgium and Puerto Rico) or gaining too much weight for their height (eg, girls and boys in Kuwait, Bahrain, Fiji, Jamaica, and Mexico; and girls in South Africa and New Zealand). In other countries, growing children overtook the height of their comparators (eg, Latvia, Czech Republic, Morocco, and Iran) or curbed their weight gain (eg, Italy, France, and Croatia) in late childhood and adolescence. When changes in both height and BMI were considered, girls in South Korea, Vietnam, Saudi Arabia, Turkey, and some central Asian countries (eg, Armenia and Azerbaijan), and boys in central and western Europe (eg, Portugal, Denmark, Poland, and Montenegro) had the healthiest changes in anthropometric status over the past 3·5 decades because, compared with children and adolescents in other countries, they had a much larger gain in height than they did in BMI. The unhealthiest changes—gaining too little height, too much weight for their height compared with children in other countries, or both—occurred in many countries in sub-Saharan Africa, New Zealand, and the USA for boys and girls; in Malaysia and some Pacific island nations for boys; and in Mexico for girls. Interpretation The height and BMI trajectories over age and time of school-aged children and adolescents are highly variable across countries, which indicates heterogeneous nutritional quality and lifelong health advantages and risks