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In this contribution, low-reactive circulating fluidized bed combustion (CFBC) fly ashes (CFAs) have firstly been utilized as a source material for geopolymer synthesis. An alkali fusion process was employed to promote the dissolution of Si and Al species from the CFAs, and thus to enhance the reactivity of the ashes. A high-reactive metakaolin (MK) was also used to consume the excess alkali needed for the fusion. Reactivities of the CFAs and MK were examined by a series of dissolution tests in sodium hydroxide solutions. Geopolymer samples were prepared by alkali activation of the source materials using a sodium silicate solution as the activator. The synthesized products were characterized by mechanical testing, scanning electron microscopy (SEM), X-ray diffractography (XRD), as well as Fourier transform infrared spectroscopy (FTIR). The results of this study indicate that, via enhancing the reactivity by alkali fusion and balancing the Na/Al ratio by additional aluminosilicate source, low-reactive CFAs could also be recycled as an alternative source material for geopolymer production.

Abstract A study undertaken at the University of Liverpool has investigated the potential for using construction and demolition waste (C&DW) as aggregate in the manufacture of a range of precast concrete products, i.e. building and paving blocks and pavement flags. Phase II, which is reported here, investigated concrete paving blocks. Recycled demolition aggregate can be used to replace newly quarried limestone aggregate, usually used in coarse (6 mm) and fine (4 mm-to-dust) gradings. The first objective, as was the case with concrete building blocks, was to replicate the process used by industry in fabricating concrete paving blocks in the laboratory. The compaction technique used involved vibration and pressure at the same time, i.e. a vibro-compaction technique. An electric hammer used previously for building blocks was not sufficient for adequate compaction of paving blocks. Adequate compaction could only be achieved by using the electric hammer while the specimens were on a vibrating table. The experimental work involved two main series of tests, i.e. paving blocks made with concrete- and masonry-derived aggregate. Variables that were investigated were level of replacement of (a) coarse aggregate only, (b) fine aggregate only, and (c) both coarse and fine aggregate. Investigation of mechanical properties, i.e. compressive and tensile splitting strength, of paving blocks made with recycled demolition aggregate determined levels of replacement which produced similar mechanical properties to paving blocks made with newly quarried aggregates. This had to be achieved without an increase in the cement content. The results from this research programme indicate that recycled demolition aggregate can be used for this new higher value market and therefore may encourage demolition contractors to develop crushing and screening facilities for this.

An industrial treatment was performed by the Sasil plant of Brusnengo (Biella, Northern Italy), which is part of the Gruppo Minerali S.p.A. (Novara, Northern Italy), to consider the reclamation of bentonite bonded moulding sands obtained from the Teksid Italia S.p.A. cast iron foundry plant in Crescentino (Vercelli, Northern Italy). An evaluation of the fine particles produced by the wet-mechanical regeneration treatment was made with the purpose of proposing their recycling as binding agents in moulding operations in the cast iron foundry and for the production of tiles in the ceramic industry. The pre-mixed product sold by bentonite suppliers (35% coal dust and 65% bentonite, 0.15 [UNKNOWN]/kg) could be made from the recovered fine fraction below 0.025 mm with the addition of active clay and coal dust, thus obtaining a product that will have physico-chemical properties similar to those of calcic bentonite. The improvements due to the addition of the fine particles to the usually employed clay for tile production were also underlined from the results of several baking tests. The recovery and recycling of sands and fine particles obtained from the reclamation of bentonite moulding sands will lead to a saving of raw materials and landfill space, with economic and environmental advantages.

Abstract Rammed earth is a traditional construction technology that has proven to be sustainable. This paper explores further improvement of its multifunctional performance by increasing the strength, reducing moisture permeation and increasing the thermal resistance. Surface application of microbial cementation was found to increase the strength by 25%. The water permeability and erosion of the blocks also reduced by 24% and 62% respectively, due to surface application of microbial cementation. The thermal test showed that addition of crumb rubber resulted in a temperature difference of around 30 °C even after 6 h. However, the addition of crumb rubber also reduced the strength. This research demonstrates that significant improvement of overall performance of rammed earth materials can be achieved through various treatments. However, the overall performance requirements are specific to the engineering application and synergistic and antagonistic interactions must be considered to obtain an optimal performance.

After ordinary Portland cement (OPC) concrete, geopolymer concrete (GPC) is the most advanced form of concrete. GPC has many advantages including improved strength and durability properties. High early age strength and ambient curing of GPC helps to reduce the construction time. Factors such as binder materials, alkali-activated solution, and curing methods control GPC’s strength properties. Moreover, when industrial byproducts such as fly ash and ground granulated blast-furnace slag (GGBS) are added to GPC, this leads to advantages such as reduced carbon dioxide emission, ability to reuse of waste materials, thus saving valuable lands from getting converted into dump yards, cost reduction, and so on. Moreover, the energy required for the extraction of raw materials is also reduced. In this paper, GPC’s strength and durability characteristics, its mix design procedure, its effect of fibers on mechanical properties, and its structural performance are comprehensively reviewed. Moreover, the development of high-strength GPC using fly ash with sodium hydroxide as an alkaline solution under oven curing condition is highlighted. To develop GPC from different binder materials, trial and error methods are proposed. Rangan’s mix design procedure is used for fly ash-based GPC. Moreover, the inclusion of fibers, it was found, improves the ductile nature of GPC. Suggestions and scope for future GPC-related research are also included.

Abstract The rapid industrial development and global population growth of the past century have resulted in an exponential increase of resource consumption and thus caused elevated CO2 emissions that, in turn, are held responsible for global warming and associated environmental problems that require urgent solutions. Specifically, increase of cement production causes CO2 pollution and generates a significant amount of concrete waste. Waste concrete, the major component of construction waste, can be efficiently recycled and is mainly used as a roadbed or backfill material. However, as no further resource recycling is expected for waste concrete, more efficient and productive recycling systems are sought after. Herein, waste concrete powder is used to produce added-value inorganic building materials, namely recycled cement and solidification. The characteristics of recycled cement (manufactured through calcination) are evaluated in terms of free lime content, mineral composition, density, color, flow test and strength, and the performance of recycled cement is found to be identical to that of ordinary Portland cement. X-ray diffraction and compressive strength analyses of the solidification manufactured through hydrothermal synthesis show that blocks of the desired strengths can be produced by adjusting the degree of consolidation and curing conditions. Based on these results, this study proposes a concrete waste recycling system to reduce the amount of construction waste and prevent resource depletion.

Abstract The Portland cement manufacturing process is a major contributor to greenhouse gas emissions and depletion of natural resources. The partial substitution of cement by industrial waste such as fly ash, silica fume, slag, stone waste etc. not only contributes to sustainable development, but also enhances the durability of concrete. Among the different wastes investigated in the past, the effect of marble slurry on durability of concrete has not been studied. Cutting, grinding and polishing manoeuvres in marble processing plants generate a large amount of slurry, which adversely affects the environment and humans. The present study examines the feasibility of using marble slurry in concrete production, as partial replacement of Portland cement. Six concrete mixes, containing marble slurry (up to 25%) in place of Portland cement were prepared and evaluated for strength, permeability, porosity, morphology, resistance to chloride migration, carbonation and corrosion. Optimal replacement level of Portland cement by marble slurry was found at 10%.

The paper proposes a novel decision analysis framework and corresponding probabilistic systems representations allowing for the consistent and integral quantification of systems resilience and sustainability. This facilitates–to the knowledge of the authors, for the first time–that decisions relating to the governance of socio-ecologic-technical systems may be optimized with due consideration of their impacts at both local and short-term time scales as well as on global and long-term time scales. The resilience performance of the interlinked system is modeled through the formulation of resilience failure events which occur if one or more of the capacities of the interlinked system are exhausted. Sustainability failure is analogously introduced as the event that one or more of the Planetary Boundaries are exceeded. A principal example shows there is a trade-off between resilience, generation of benefits, consumption of materials, and emissions to the environment. Resilience provides benefits to society but at the same time imposes material consumption and emissions to the environment. Systems can, however, be designed such that resource consumption and associated environmental impacts are reduced and the resilience performance is increased simultaneously. The example further illustrates that social governance system failure may follow from inadequate design and governance of infrastructure.

Abstract Approximately 5%–7% of global Carbon Dioxide (CO2) emissions can be attributed to Ordinary Portland Cement (OPC), which has traditionally been used as the primary binder in concrete. Geopolymer concrete has been widely claimed to have lower global warming potential than OPC concrete, and this claim has formed the basis of many studies examining mix designs and mechanical properties of geopolymer concretes. A major limitation with the vast majority of existing studies is a lack of the direct quantification of the global warming potential of the materials developed. That is, the underlying assumption in the majority of these studies is that geopolymer concrete is more sustainable than OPC based concretes. The aim of this paper is to quantify the CO2 equivalent (CO2-eq) emissions associated with production of a large number of previously developed mix designs (1404 mix designs from 110 studies) including the impacts of curing, allocation and transportation and allowing for variation in energy grid source and the production of the activator solution. When considering the impact of transportation, a case study based on five major capital cities in Australia is presented and the critical transport distances at which the manufacture of geopolymers becomes more emissions intensive than conventional concrete is identified. The results show that the relative CO2-eq emissions of geopolymer and OPC based concretes of the same strength, are highly dependent on the system boundary for analysis, the type of allocation scenario and material transportation distances and mode, and further, that depending on these factors geopolymer concretes can either have significantly lower, or significantly higher CO2-eq emissions than OPC concretes of the same strength. It is expected that the findings of this work can aid in specifying the optimal concrete types for reducing CO2-eq emissions considering the intended use of the concrete.