•Structural concrete with fine and coarse recycled concrete aggregates (RCA) was studied.•RCA of different origins were used: from real waste and produced in laboratory.•The mechanical, durability ...and long-term performance of concrete with RCA was analysed.•Similar performances using different RCA can be achieved.•Total incorporation of RCA in the production of structural concrete is deemed possible.
This investigation intends to analyse the effects of the variation of different types of recycled concrete aggregates (RCA) on structural concrete. For this purpose, two source concrete (SC) mixes, one produced in the laboratory and another in a precasting plant, were considered. The experimental campaign included mechanical, durability and long-term tests: compressive strength in cubes; splitting tensile strength; modulus of elasticity; abrasion resistance; water absorption by immersion and by capillarity; resistance to carbonation; resistance to chloride ion penetration; shrinkage and creep. The recycled aggregate concrete (RAC) mixes were compared with a reference concrete (RC) produced solely with natural aggregates (NA). Concerning the replacement percentages for fine and coarse recycled concrete aggregates (FRCA/CRCA%), the following were considered: 25/25; 50/50; 100/0; 0/100 and 100/100%. The results show that it is possible to achieve similar performances using RCA from different SC but with similar compressive strengths. In fact, RAC mixes achieved results comparable to RC in several properties.
•Recycled Concrete Aggregate (RCA) is a future material towards sustainable development.•Properties of Recycled Aggregate Concrete (RAC) and its performances are comprehensively documented.•Advanced ...mixing approaches and incorporation of mineral additives for improving the properties of RAC.
The ever increasing population and urbanization has led to construction of high rise structures and demolishing existing old low rise ones. This has become not only the cause of natural resources depletion at an alarming rate but also gradually becoming a challenge for sustainability. Concrete industry consumes a majority of natural resources especially in developing countries. In recent years the concrete industry has started using Construction and Demolition (C&D) waste in structural concrete application owing to the availability of waste from demolition of old structures and the reduction in cost of acquiring aggregates. This can allow the concrete industry to reduce its carbon footprint and thus help it to continue to grow without harming the environment. In this backdrop, this paper provides an account of properties of concrete prepared with recycled aggregate, analyses the important findings on Recycled Aggregate Concrete (RAC) in the recent time and discusses the suitability of its usage in construction. The open literature suggests that the durability and mechanical properties of RAC is slightly inferior than that of conventional concrete. However, with the use of admixtures and modified mixing approaches, the desired properties of RAC can be obtained. Collation and analysis of more than 200 research papers in this area on various facts of Recycled Aggregate Concrete, on one hand, may be considered as a step ahead for formation of design methodology and, on the other hand, a valuable stating document for further research.
Proton exchange membrane water electrolyzers (PEMWEs) driven by renewable electricity provide a facile path toward green hydrogen production, which is critical for establishing a sustainable hydrogen ...society. The high working potential and the corrosive environment pose severe challenges for developing highly active and durable electrocatalysts for the oxygen evolution reaction (OER). To date, iridium (Ir)‐based materials, largely metallic Ir and Ir‐based oxides, are the most suitable OER electrocatalysts for PEMWEs due to their balanced activity and durability. Tremendous efforts have been devoted to improving the specific activity of Ir species to reduce the cost; however, advances in enhancing the durability of Ir‐based electrocatalysts are rather limited. In this review, the recent research progress on tackling the stability issues of Ir‐based OER electrocatalysts in acid media is summarized, aiming to provide inspiration for designing highly active and stable Ir‐based electrocatalysts. The OER mechanism and the associated failure modes of active Ir species are summarized. Then, mechanistic studies on the dissolution behavior of Ir species and experimental attempts on enhancing the durability of Ir‐based electrocatalysts are discussed. The personal perspectives for future studies on Ir‐based OER electrocatalysts are also provided.
The durability of iridium (Ir)‐based electrocatalysts is critical to proton exchange membrane water electrolyzers, but current studies are not adequate. Herein, the durability issues of Ir‐based oxygen evolution reaction electrocatalysts in acid media are reviewed with a focus on the dissolution behavior of active Ir species, aiming to provide inspiration for the future development of Ir‐based electrocatalysts.
Research into the extreme feats of endurance that humans and some animals achieve has uncovered a range of metabolic and physiological adaptations along with their evolutionary origins.
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•La0.5Ba0.5CuxFe1−xO3−δ is used as a cathode for H-SOFC on BZCY electrolyte.•Thermal expansion, oxide-ion and proton conductivity varies with the Cu/Fe ratio.•An initial power density ...exceeding 820 mW cm−2 is obtained at 700 °C.•Increase in the ohmic rather than polarization resistance dominates the degradation.
La0.5Ba0.5CuxFe1−xO3−δ (0 ≤ x ≤ 1) perovskite was investigated as a cathode for a protonic solid oxide fuel cell (H-SOFC) using BaZr0.1Ce0.7Y0.2Oδ (BZCY) electrolyte. A maximum electric conductivity (76.84 S cm−1 at 700 °C) was achieved in the air at the composition of La0.5Ba0.5Cu0.4Fe0.6O3−δ. Comparing to La0.5Ba0.5CuO3−δ (LBC), the increase in Fe content increased the Dchem (1.07x10−5 to 1.74x10−5 cm2 S−1) and Kchem (1.12x10−10 to 3.01x10−10 cm2 S−1) at La0.5Ba0.5Cu0.2Fe0.8O3−δ (LBCF28) but decreased the proton conductivity from 7.5 to 4.3 mS cm−1. Either Fe doping in LBC or Cu doping in La0.5Ba0.5FeO3−δ increased the thermal expansion coefficient (TEC), but a low TEC among samples with mixed cations was achieved at La0.5Ba0.5Cu0.5Fe0.5O3−δ (LBCF55) (16.12 ppm K−1). LBC suffered from superficial decomposition in the ambient air, causing an ohmic resistance loss of the full cell on Ni(O)-BZCY support. A high initial cell performance (820 mW cm−2) can be achieved for the cell with LBCF55 and LBCF28 cathode but the latter was unstable under a cathodic bias owing to the increase in ohmic resistance owing to the production of intermediate layer between electrode and electrolyte. With better stability than LBCF28 and higher performance than LBC, LBCF55 was regarded as a viable cathode material for H-SOFC. This work explores systematically the behavior of a perovskite with mixed Cu and Fe cations as a cathode for H-SOFCs.
As luxury fashion brands need to address the environmental impact of their products (both internally and externally), a framework to achieve a common and accessible language becomes paramount to ...avoid confusing claims. Tools, such as Life Cycle Assessment and Eco-Design, help companies assess and reduce the negative effects of their products on the environment; nonetheless, more work is needed. The desire to create durable goods is a direct reaction to the current throw-away culture perpetuated by planned obsolescence during the production phase of many fast-fashion brands. However, without a proper understanding of the term ‘durability’ and its different dimensions, a common language cannot be adopted by the various actors in the value chain (both up- and down-stream). Particularly, the characteristics of terms such as ‘resilience’ are mistakenly confused with those of ‘durability.’ Here, we review the literature from 2011 to date for determining clear definitions for both terms. A self-developed analysis framework was used for the systematic review of the literature, slightly adapting the methodology from an established process. The different levels (A, B, and C) of the framework reveal, in a structured manner, what a ‘durable’ or ‘resilient’ product is (at every stage of its lifecycle). We show that two dimensions should be considered for both concepts: ‘intrinsic’ (also referred to as ‘physical’ in the existing literature) and ‘extrinsic’ (often referred to as ‘emotional’). Most authors fail to acknowledge the existence of both terms or use them inconsistently. Consequently, a thorough assessment of product durability and resilience is lacking, as studies have focused solely on one of the two dimensions or on a single lifecycle stage (most often the design phase) of a product. Thus, beyond its original aim, our model analysis framework can also help evaluate the environmental impact of luxury fashion products at each stage of their lifecycle.
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•The use of an intrinsic and extrinsic dimension is preferred over physical and emotional.•Resilience differs from durability and enables products to bounce back from environmental changes.•All the lifetime stages should be considered to assess a product's durability and resilience.•The analysis framework can serve as a working tool for environmental impact assessment.
•Reviewed the degradation mechanisms for PEM fuel cells.•Summarized the steady-state durability test results and experimental conditions.•Evaluated the in-situ accelerated stress test results and ...protocols.•Scrutinized the ex-situ accelerated stress test results and experimental techniques.
Durability is one of the most significant technical barriers to successful commercialization of polymer electrolyte membrane (PEM) fuel cells for practical vehicular applications. It is determined by the aging (degradation) and malfunction of various components during the long-term operation. Therefore, understanding the mechanisms of degradation modes in different components is crucial to the development of high-performing and long-lasting PEM fuel cells. In this review article, the critical degradation modes in major cell components, including membranes, catalyst layers, gas diffusion layers, and distribution plates, are comprehensively reviewed and analyzed, and the potential causes are described. Advanced experimental techniques to investigate the PEM fuel cell degradation modes reported in literature include steady-state durability tests and accelerated stress tests (ASTs). The steady-state durability test is straightforward but time-consuming and costly; therefore, ASTs are often applied to accelerate durability testing. For comparable results among different research studies, the experimental protocols and conditions have to be consistent, and the details of these experimental techniques are systematically reviewed in this article. The experimental results with a focus on the degradation modes, degradation rate, and test time of the PEM fuel cells have been reported. Finally, in order to understand the root causes of degradation modes and to develop the mitigation strategies, ex-situ ASTs in literature have been reviewed, including the effects of cyclic temperature, humidity, water wet-dry, freeze-thaw, clamping stress, and vibration operations.
The degradation mechanisms of natural fiber in the alkaline and mineral-rich environment of cement matrix are investigated. Cement hydration is presented to be a crucial factor in understanding fiber ...degradation behavior by designing a contrast test to embed sisal fibers in pure and metakaolin modified cement matrices. In addition to durability of sisal fiber-reinforced cement composites determined by means of flexural properties, degradation degree of the embedded fibers is directly evaluated by proposing a novel separation approach. The results indicate that, by reducing alkalinity of pore solution, metakaolin effectively mitigates the deterioration of natural fiber. By combining results of thermogravimetric analysis and microstructure, the alkali degradation process of natural fiber, which consists of hydrolysis of lignin and hemicellulose, stripping of cellulose microfibrils and deterioration of amorphous regions in cellulose chains, is visually presented. Two new concepts of mineralization mechanism, calcium hydroxide (CH)-mineralization and self-mineralization, are also proposed and quantitatively characterized.
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