New development of sprayed concrete with improved waterproofing, durability and sustainability performance

Concrete production accounts for a substantial portion of global CO2 emission. One of possible ways to reduce the carbon footprint of concrete is to optimize the concrete mix design approach. This paper investigates the integration of sustainability, cost and durability performance with concrete mix based on artificial neural network. Carbonation-induced corrosion resistance is used for characterizing the durability performance of concrete mix. A dataset on natural carbonation coefficient, compressive strength and concrete mix design of concretes with various supplementary cementitious materials (SCMs) is established. An artificial neural network is trained, and used in designing a concrete mix with optimized sustainability, cost and durability performances given a target compressive strength. The results show that the artificial intelligence is promising in integrated concrete mix design with favorable sustainability, cost and durability performances.

Low carbon concrete for prefabricated modular construction in circular economy: An integrated approach towards sustainability, durability, cost, and mechanical performances

During the last decades, turbo machine efficiency was considerably increased by using more efficient seals. Brush seals, as a compliant contacting filament seal, have become an attractive alternative to conventional labyrinth seals in the field of aircraft engines as well as in stationary gas and steam turbines. The aim of today's research related to brush seals is to understand the characteristics and their connections, in order to be able to make performance predictions, and to ensure the reliability over a defined operating period. The wear behavior is essentially influenced by frictional contacts at the seal-to-rotor interface during operation. For realistic investigations with representative circumferential velocities, the TU Braunschweig, Germany, operates a specially developed steam test rig which enables endurance investigations under varying operating steam conditions up to 50 bar and 450 °C. Wear measurements and the determination of seal performance characteristics, such as blow down and bristle stiffness, are enabled by an additional test facility, using pressurized cold air up to 8 bar as a working fluid. This work presents the chronological wear development on both rotor and seal sides in a steam test lasting 25 days or 11 days, respectively. Interruptions after stationary and transient intervals were made in order to investigate the degree of wear. Two different seal arrangements, a single tandem seal, and a two-stage single seal arrangement, using different seal elements were considered. Besides a continuous wear development, the results clearly show that the abrasive wear of the brush seal and rotor is mainly caused by transient test operations, particularly by enforced contacts during shaft excursions. Despite the increasing wear to the brushes, all seals have shown a functioning radial-adaptive behavior over the whole test duration with a sustained seal performance. Thereby, it could be shown that the two-stage arrangement displays a load shift during transients, leading to a balanced loading and unloading status for the two single brush seals. From load sharing, and in comparison with the wear data of the tandem seal arrangement, it can be derived that the two-stage seal is less prone to wear. However, the tandem seal arrangement, bearing the higher pressure difference within one configuration, shows a superior sealing performance under constant load, i.e., under stationary conditions.

Manufactured sand (M-sand or MS) conserves natural resources and enhances concrete performance and sustainability. However, a comprehensive and updated review is required to summarize and compare the weak and strong points of MS in concrete compared to natural sand (N-sand). This review synthesizes the current research on MS as an alternative material in concrete production. The review discussed the background and current problems associated with natural river sand in the construction industry, the production of MS, biographic analysis, physical and chemical properties of MS, the impact of MS on concrete strength, durability, microstructure, and sustainability performance. Results indicate that MS has physical and chemical properties comparable to N-sand, and produces concrete with improved strength, durability, microstructure, and sustainability. However, MS negatively impacts the flowability of concrete. Finally, the review recommends proposed research gaps that need to be explored in the future.

Geopolymer concrete has emerged as a promising alternative to traditional Portland cement -based concrete due to its reduced environmental impact, improved mechanical properties, and potential for sustainable construction practices. This paper presents a comprehensive review of recent advancements in geopolymer concrete technology, focusing on key research findings, innovative materials, and novel applications. A systematic analysis of 40 selected research articles is conducted to elucidate the progress made in the field, covering topics such as material composition, mechanical properties, durability, sustainability, and structural performance. The review highlights the diverse range of materials used in geopolymer concrete, including fly ash, metakaolin, recycled aggregates, and various fibers. Furthermore, it examines the influence of different additives, curing methods, and mix design parameters on the properties of geopolymer concrete. The paper also discusses emerging trends such as the incorporation of hybrid fibers, utilization of waste materials, and development of high -performance geopolymer composites. Finally, future research directions and potential challenges in the widespread adoption of geopolymer concrete are outlined, aiming to contribute to the advancement of sustainable construction practices worldwide.

The increasing demand for sustainable construction materials has led to exploring alternative resources, such as mine tailings in ultra-high-performance fiber-reinforced concrete (UHPFRC). Conventional concrete production is associated with significant environmental impact and resource depletion, necessitating the search for sustainable alternatives. This study investigates the effects of incorporating mine tailings powder (MTP) and mine tailings sand (MTS) as substitutions for cement and quartz sand on the mechanical and durability properties of UHPFRC. The current study focuses on evaluating the workability, compressive strength, indirect tensile strength, modulus of rupture, sulfate resistance, autogenous shrinkage, thermal performance, porosity, hydration kinetics, and phase composition of UHPFRC with varying MTP and MTS contents. Results indicate that the optimal mix of 15% MTP and 60% MTS enhances compressive strength by 12.49% (165.2 MPa at 90 days), reduces autogenous shrinkage by 49.28% (1023 microns at 180 days), and significantly improves sulfate resistance, with a residual compressive strength of 115.2 MPa and a mass loss of 25.4%. The workability tests show a decrease in flow spread from 274 mm in the control mix to 221 mm in the mix with 25% MTP and 100% MTS. Indirect tensile strength increased by 23.53% (23.1 MPa at 90 days), and the modulus of rupture improved by 23.04% (23.5 MPa at 90 days) with the optimal mix. Mercury intrusion Porosimetry reveals increased total pore volume, especially in larger pore sizes, with the highest intrusion observed in the mix containing 5% MTP and 20% MTS. The heat of hydration analysis shows a delayed Tmax from 30 h in the control mix to 36 h with 15% MTP and 60% MTS, indicating a slower and more controlled hydration process. X-ray diffraction analysis demonstrates a reduction in peak intensities, marking a transition from crystalline to more amorphous structures with increasing mine tailings content. The improved microstructural characteristics, such as reduced porosity and enhanced hydration stability, contribute to the material’s long-term durability and mechanical performance, making it a viable option for sustainable construction practices.

Thanks to their compliant nature and superior leakage performance over conventional labyrinth seals, brush seals found increasing use in turbomachinery. Utilizing high temperature super-alloy fibers and their compliance capability these seals maintain contact with the rotor for a wide range of operating conditions leaving minimal passage for parasitic leakage flow. Consequently, the contact force/pressure generated at seal rotor interface is of importance for sustained seal performance and longevity of its service life. Although some analytical and numerical models have been developed to estimate bristle tip pressures, they simply rely on linear beam equation calculations and other such assumptions for loading cases. In this paper, previously available analytical and/or numerical models for bristle tip force/pressure have been modified and enhanced. The nonlinear cantilever beam equation has been solved and results are compared to a linear cantilever beam equation solution to establish application boundaries for both methods. The results are also compared to experimental data. With the support of testing, an empirical model has been developed for tip forces under operating conditions.

Rheology, durability, and mechanical performance of sustainable self-compacting concrete with metakaolin and limestone filler