Extrusion-based additive manufacturing of concrete products. Revolutionizing and remodeling the construction industry

Additive manufacturing is one of the main topics of the fourth industrial revolution; defined as Industry 4.0. This technology offers several advantages related to the construction and architectural sectors; such as economic; environmental; social; and engineering benefits. The usage of concrete in additive technologies allows the development of innovative applications and complexity design in the world of construction such as buildings; housing modules; bridges; and urban and domestic furniture elements. The aim of this review was to show in detail a general panoramic of extrusion-based additive processes in the construction sector; the main advantages of using additive manufacturing with the respect to traditional manufacturing; the fundamental requirements of 3D printable material (fresh and hardened properties), and state-of-the-art aesthetic and architectural projects with functional properties

Influence of Waste Tire Rubber Particles Size on the Microstructural, Mechanical, and Acoustic Insulation Properties of 3D-Printable Cement Mortars

3D printing technologies of construction materials are gaining ground in the building industry. As well documented in the literature, these advanced manufacturing methodologies aim to reduce work-related injuries and materials waste, enhancing architectural flexibility which would enable more sophisticated designs for engineering and aesthetic purposes. In this framework, the development of functional and eco-sustainable printable materials represents an extremely attractive challenge for research, promoting digital fabrication to reach its maximum cost-effective and technological potentials. The use of recycled tire rubber particles in 3D printable Portland-based compounds is an exclusive contribution in this field. This line of research aims to integrate the well-known engineering performances of rubber-cement materials with the advanced peculiarities of additive manufacturing methodologies. As an innovative contribution, the authors propose here a detailed study on the possible relationship between rubber particle size and technological properties of the 3D printable mix. Specifically, two groups of continuous size grading polymer aggregates (0-1 mm rubber powder and 1-3 mm rubber granules as fine and coarse fractions, respectively) were analyzed in terms of impact on rheology, print quality, microstructure, mechanical properties, and acoustic insulation performance. Concerning the print quality, rubber aggregates altered the fluidity of the fresh mix, improving the adhesion between the printed layers and therefore enhancing the mechanical isotropy in the post-hardening sample. A remarkable influence of the rubber gradation on the compounds’ behaviour was found in hardened properties. By comparing the rubberized compounds, the fine polymer fraction shows greater interfacial cohesion with the cement paste. However, more significant mechanical strength loss was found due to a greater reduction in density and increased porosity degree. On the other hand, mortars doped with larger rubber particles tend to have a higher unit weight, finest pore distribution, minor mechanical strength drop, and higher ductility but worse interface binding with the matrix. Regarding the acoustic insulation properties, a proper balance between rubber powder and granules in the mixes allows to obtain comparable/superior performance compared to plain mortar but the effect of the aggregate size is strongly dependent on the sound frequency range investigated. Future findings revolve around applicability studies of these formulations in civil and architectural fields, benefiting from the design flexibility of 3D printing. Doi: 10.28991/cej-2021-03091701 Full Text: PD

Aerogel technology for thermal insulation of cryogenic tanks. Numerical analysis for comparison with traditional insulating materials

The traditional choice of insulation material for liquefied natural gas (LNG) transportation with cryogenic tankers is the back-filled perlite-based system. However, aiming to further cut down the insulation cost, spare additional arrangement space, and provide safety in installation and maintenance, the requirement of looking for alternative materials still exists. Fiber-reinforced aerogel blankets (FRABs) could represent good candidates in designing insulation layers for LNG cryogenic storage because of their ability to ensure adequate thermal performance without the need to create deep vacuum conditions in the annular space of the tank. In this work, a finite element method (FEM) model was developed to study the thermal insulation performance of a commercial FRAB (Cryogel ® Z) for application in cryogenic storage/transport LNG tanks, comparing it with the performance of traditional perlite-based systems. Within the reliability limits of the computational model, the analysis proved that FRAB insulation technology gave encouraging results and might be potentially scalable for transporting cryogenic liquid. In addition to demonstrating superior performance in terms of thermal insulating efficiency and boil-off rate over the perlite-based system, as far as a perspective of cost savings and space gain, FRAB technology allows for higher levels of insulation without vacuum and with lower thickness of the outer shell, which is therefore beneficial for storing more material and lightening the weight of the LNG transportation semitrailer

Zeolite-Clinoptilolite conditioning for improved heavy metals ions removal: a preliminary assessment

The emerging problem of nickel allergy is increasingly widespread due to the increase in nickel content in everyday foods. The physicochemical structure of the zeolites makes it possible to adsorb nickel ions in solution. The properties of molecular sieves, together with those of a size and a chemical composition compatible with the human gastrointestinal tract, are present in a particular zeolite called clinoptilolite. In this work, a type of natural clinoptilolite was characterized before and after being subjected to two different conditioning processes with NaCl to increase its adsorption efficiency and specificity against nickel. The three forms of clinoptilolite, natural, conditioned, and biconditioned, were compared based on analysis of absolute density, X-ray diffraction pattern, granulometry, porosity, chemical composition, and grain morphology. Finally, nickel ion removal tests were performed in an aqueous solution that simulates the conditions of the gastrointestinal tract. The Ni2+ removal efficiency of natural clinoptilolite is 73.2%, while after conditioning it reaches 96.6%. Double conditioning with Na does not generate a considerable increase in removal efficiency which remains at 96.8

Tire recycled rubber for more eco-sustainable advanced cementitious aggregate

This research focused on using ground tire rubber (GTR) with different grain sizes as a replacement for the mineral aggregates used in a cement-based mixture suitable for extrusion-based Additive Manufacturing. The use of two types of GTR particles and the possibility to apply rubberized mixtures in advanced manufacturing technologies are the innovative aspects of this work. At the base of this strategy is the possibility of achieving cementitious aggregates, which would potentially be improved regarding some technological-engineering requirements (lightness, thermal-acoustic insulation, energy dissipation capacity, durability) and environmentally sustainable. The integration of waste tires into cement-based materials is a promising solution for the reuse and recycling of such industrial waste. In addition, this approach may involve a considerable reduction in the use of natural resources (sand, water, coarse mineral aggregates) needed for the building materials production. The purpose of the research was to investigate the effect of sand-GTR replacement on certain chemical-physical properties of mixtures (permeable porosity, surface wetness, and water sorptivity), closely related to material durability. Besides, the role of rubber on the printability properties of the fresh material was evaluated. GTR fillers do not alter the rheological properties of the cement material, which was properly extruded with better print quality than the reference mixture. Concerning chemical-physical characterization, the GTR powder-granules synergy promotes good compaction of the mixture, hinders the cracks propagation in the cement matrix, decreases the permeable porosity, improves the surface hydrophobicity and preserves optimal water permeabilit

Recent advances in Geopolymer technology. A potential eco-friendly solution in the construction materials industry. A review

In the last ten years, the Portland cement industry has received wide criticism due to its related high embodied energy and carbon dioxide footprint. Recently, numerous “clean” strategies and solutions were developed. Among these, geopolymer technology is gaining growing interest as a functional way to design more eco-friendly construction materials and for waste management issues suffered by various industries. Previous research has highlighted the attractive engineering properties of geopolymeric materials, especially in terms of mechanical properties and durability, resulting in even higher performance than ordinary concrete. This review provides a comprehensive analysis of current state-of-the-art and implementations on geopolymer concrete materials, investigating how the key process factors (such as raw materials, synthesis regime, alkali concentration, water dosage, and reinforcement fillers) affect the rheological, microstructural, durability, and mechanical properties. Finally, the paper elucidates some noteworthy aspects for future research development: innovative geopolymer-based formulations (including alkali-activated blends for additive manufacturing and thermo-acoustic insulating cellular compounds), concrete applications successfully scaled in the civil-architectural fields, and the perspective directions of geopolymer technology in terms of commercialization and large-scale diffusion

Multi-physics analysis for Rubber-Cement applications in building and architectural fields. A preliminary analysis

Generally, in most countries, there are no strict regulations regarding tire disposal. Hence, tires end up thrown in seas and lands as well as being burnt, harming the living beings, and are therefore considered a very dangerous pollution source for the environment. Over the past few years, several researchers have worked on incorporating shredded/powdered rubber tires into cement-based material. This strategy shows a dual functionality: Economic–environmental benefits and technological functionalization of the building material. Rubber-modified cement materials show interesting engineering and architectural properties due to the physical-chemical nature of the tire rubber aggregates. However, the abovementioned performances are affected by type, size, and content of polymer particles used in the cement-based mixtures production. Whereas an increase in the rubber content in the cement mix will negatively affect the mechanical properties of the material as a decrease in its compression strength. This aspect is crucial for the use of the material in building applications, where proper structural integrity must be guaranteed. In this context, the development of innovative manufacturing technologies and the use of multi-physics simulation software represent useful approaches for the study of shapes and geometries designed to maximize the technological properties of the material. After an overview on the performances of 3D printable rubber-cement mixtures developed in our research laboratory, a preliminary experimental Finite Element Method (FEM) analysis will be described. The modeling work aims to highlight how the topology optimization allows maximizing of the physical-mechanical performances of a standard rubber-cement component for building-architectural applications

Simple and reliable eco-extraction of bioactive compounds from dark chocolate by Deep Eutectic Solvents. A sustainable study

The green solvents and eco-extraction methods are gaining increasing interest in chemical analysis for bioactive compounds in food matrices. Deep Eutectic Solvents (DES) developed as a greener and more sustainable alternative to organic solvents, owing to their non-toxic, highly stable, and biodegradation-friendly nature. DES application for polyphenols and antioxidant compounds extraction in dark chocolate samples has been evaluated in an integrated study for sustainability assessment, based on multivariate analysis and Life Cycle Assessment (LCA) methodology. A green extraction method based on DES was proposed testing different HBA:HBD pairs (ChCl:Fru, ChCl:Teg, Bet:Fru, and Bet:Teg). DES Bet:Fru resulted in the highest extraction yield in terms of both total polyphenols (0.34–3.37 g GAE/100 g) and flavonoids (1.13–8.32 g RUT/100 g), P < 0.05. Furthermore, the environmental performances of green and conventional solvents (MeOH:H2O, H2O, and MeOH) were evaluated by applying a comparative LCA (c-LCA). The c-LCA study highlighted that conventional extraction for polyphenols in dark chocolate was 60% more impactful than DES. DES pairs analysed quantitatively lowest impacted than conventional methods, considering the macro-categories Human Health (9.99 × 10–8 ÷ 1.54 × 10–7 DALYs), Ecosystem (2.29 × 10–10 ÷ 3.57 × 10–10 species.yr), and Resources (6.57 × 10–3 ÷ 8.96 × 10–3 USD2013)

Enhanced Compatibility of Secondary Waste Carbon Fibers through Surface Activation via Nanoceramic Coating in Fiber-Reinforced Cement Mortars

The utilization of waste fibers in the production of reinforced concrete materials offers several advantages, including reducing environmental strain and socio-economic impacts associated with composite waste, as well as enhancing material performance. This study focuses on the development of cementitious mortars using secondary waste carbon fibers, which are by-products derived from the industrial conversion of recycled fibers into woven/non-woven fabrics. The research primarily addresses the challenge of achieving adequate dispersion of these recycled fibers within the matrix due to their agglomerate-like structure. To address this issue, a deagglomeration treatment employing nanoclay conditioning was developed. The functionalization with nanoclay aimed to promote a more uniform distribution of the reinforcement and enhance compatibility with the cementitious matrix. Various fiber weight percentages (ranging from 0.5 w/w% to 1 w/w% relative to the cement binder) were incorporated into the fiber-reinforced mix designs, both with and without nanoceramic treatment. The influence of the reinforcing fibers and the compatibility effects of nanoclay were investigated through a comprehensive experimental analysis that included mechanical characterization and microstructural investigation. The effectiveness of the nanoceramic conditioning was confirmed by a significant increase in flexural strength performance for the sample incorporating 0.75 w/w% of waste fibers, surpassing 76% compared to the control material and exceeding 100% compared to the fiber reinforced mortar incorporating unconditioned carbon fibers. Furthermore, the addition of nanoclay-conditioned carbon fibers positively impacted compression strength performance (+13% as the maximum strength increment for the mortar with 0.75 w/w% of secondary waste carbon fibers) and microstructural characteristics of the samples. However, further investigation is required to address challenges related to the engineering properties of these cementitious composites, particularly with respect to impact resistance and durability properties

Carbon-Fiber-Recycling Strategies: A Secondary Waste Stream Used for PA6,6 Thermoplastic Composite Applications

With a view to achieving sustainable development and a circular economy, this work focused on the possibility to valorize a secondary waste stream of recycled carbon fiber (rCF) to produce a 3D printing usable material with a PA6,6 polymer matrix. The reinforcing fibers implemented in the research are the result of a double-recovery action: starting with pyrolysis, long fibers are obtained, which are used to produce non-woven fabrics, and subsequently, fiber agglomerate wastes obtained from this last process are ground in a ball mill. The effect of different amounts of reinforcement at 5% and 10% by weight on the mechanical properties of 3D-printed thermoplastic composites was investigated. Although the recycled fraction was successfully integrated in the production of filaments for 3D printing and therefore in the production of specimens via the fused deposition modeling technique, the results showed that fibers did not improve the mechanical properties as expected, due to an unsuitable average size distribution and the presence of a predominant dusty fraction ascribed to the non-optimized ball milling process. PA6,6 + 10 wt.% rCF composites exhibited a tensile strength of 59.53 MPa and a tensile modulus of 2.24 GPa, which correspond to an improvement in mechanical behavior of 5% and 21% compared to the neat PA6,6 specimens, respectively. The printed composite specimens loaded with the lowest content of rCF provided the greatest improvement in strength (+9% over the neat sample). Next, a prediction of the "optimum" critical length of carbon fibers was proposed that could be used for future optimization of recycled fiber processing