Early-Age Behaviour of Fiber Reinforced High Performance Concretes

The aim of this experimental activity was to study the early-age behavior of several Fiber-Reinforced Concretes (FRCs) containing expansive agent. The investigation concerned the evaluation of the influence of different amounts of fibers (dosages of 2.0%, 1.75% and 1.5% by volume of FRCC) on the mechanical performance of FRCs. In particular, hooked brass-coated fibers were used and dead-burnt calcium oxide based expansive agent was employed at a dosage of 40 kg/m3. The attention was focused on the strength development at early ages. Mechanical tests were carried out at 0.25 (i.e. 6 hours, that is time of demolding), 1, 2, 7 up to 28 days of curing. The properties of FRCs were characterized at the fresh state, by measuring flow ability and consistency as well as at hardened state by measuring compressive and flexural strength up to 28 days. Flexural strength was measured on prismatic specimens according to the procedure described in EN 12390-5. The different dosage of fibers did not influence the values of compressive strength, while there is a significant difference in terms of 28-day flexural strength between the several mixtures depending on the different amount of fibers. In all cases at least 20 MPa of 28-day peak flexural strength were achieved

Studio di materiali avanzati a matrice cementizia per l’additive manufacturing

L’additive manufacturing è uno dei temi principali della quarta rivoluzione industriale; definita come Industry 4.0. L'uso del calcestruzzo nelle tecnologie additive è molto promettente e consente lo sviluppo di applicazioni innovative nel settore delle costruzioni; per l’architettura; nel campo del design ed in quello industriale. Le tecniche di additive manufacturing of concrete offrono numerosi vantaggi: riduzione dei tempi e dei costi di produzione, maggiore personalizzazione e libertà nella progettazione, minore spreco di materiale e minori emissioni inquinanti, maggiore sicurezza sul lavoro. Nel presente lavoro è stata effettuata una revisione delle tecniche esistenti e dei vantaggi legati a questo tipo di produzione e sono state descritte le caratteristiche richieste al calcestruzzo affinché possa risultare estrudibile con lo scopo di sviluppare materiali innovativi a base cementizia estrudibili con proprietà funzionali avanzate. Sono state ottimizzate delle miscele a base cementizia stampabili con ottime proprietà meccaniche, contenenti aggregati di riciclo e resistenti alle alte temperature. Il processo di stampa del calcestruzzo utilizza una tecnica di produzione additiva, basata su strati per costruire forme geometriche complesse senza cassaforma e presenta quindi un vantaggio unico rispetto ai convenzionali metodi di costruzione. Le proprietà indurite delle formulazioni e gli effetti del processo di stratificazione su densità, resistenze meccaniche e ritiro igrometrico sono presentati insieme alle implicazioni relative alle proporzioni della miscela. Il lavoro sperimentale dimostrerà il potenziale della stampa del calcestruzzo come nuovo processo produttivo praticabile che può introdurre una maggiore libertà geometrica nel processo di progettazione, oltre a offrire un nuovo mezzo di produzione che potrebbe evitare la necessità di produrre in serie elementi identici in calcestruzzo con un numero limitato di varianti.Additive manufacturing is one of the main topics of the fourth industrial revolution; defined as Industry 4.0. Usage of concrete in additive technologies allows the development of innovative applications in the construction sector; for architecture; in the design field and in the industrial one. Additive manufacturing of concrete techniques offer several advantages: reduction of production time and costs; greater customization and design freedom; less material waste and less polluting emissions, higher level of job security. In the present work, a rewiew of existing techniques, of vantages related to this kind of production has been done and the characteristics required to concrete to be extruded are described in order to develop innovative extrudable cement-based materials with advanced functional properties. Cement-based printing mixtures with outstanding mechanical properties, containing recycled aggregates and resistant to high temperatures have been developed. The concrete printing process uses an additive, layer-based, manufacturing technique to build complex geometrical shapes without formwork and thus has a unique advantage over conventional construction methods. The hardened properties of the formulations and the effects of the layering process on density, mechanical strengths and drying shrinkage are presented together with the implication for mix proportions. The experimental work will demonstrate the potential of concrete printing as a viable new production process that can introduce greater geometric freedom into the design process as well as offering a novel means of manufacture that could avoid the need to mass produce identical concrete parts with limited numbers of variants

Green cement-based materials for 3D printing: preliminary tests and characterization

Introduction Additive manufacturing of cement-based materials is a new challenge for the construction business. Compared to traditional manufacturing, this technology offers important advantages: design freedom, reduction of production costs and times, low pollution and safety. Printable mixture must meet certain requirements in order to guarantee good extrudability, durability and suitable mechanical properties of the final product. University of Marche patented a material that combines remarkable printing characteristics and excellent mechanical performances. The purpose of this work is to study the possibility of modifying the printing mix by adding recycled rubber tires to replace the sand and coarse aggregate of the mixture. This strategy aims to improve some physical-mechanical properties of the material (lightness, toughness, acoustic and thermal insulation) and promote the additive manufacturing to reach its maximum cost-effective and environmental-friendly potentials. Material and Methods Materials used for the experimental work are: a) cement-based printable mixture b) rubber grain/powder from tire recycling processes: powder (0 – 0,8 mm) and granulated (2 – 3 mm). Several rubber-concrete formulations were tested: reference, sand-powder mix and powder-granulated mix. Deposition tests were performed for each mixture in order to monitor the printing properties. From printed artifacts, normed size specimens were extracted for mechanical characterization. Microscopic analysis was performed in order to investigate the fillers distribution in the cement matrix. Results The replacement of the aggregates with rubber grain/powder provided a material with good printability. The type of filler affect the mix composition: in the richest formulations of granulated, it was necessary to increase the mix fluidity. Increased hydration promoted a lower shape stability of the filaments during deposition. Experimental characterizations, performed on rubber-concrete mixtures, show interesting results. Discussion The use of tire rubber as aggregate in cement mix shows promising results in producing an innovative building material with improved performance in terms of lightness, energy absorption and ductility. The choice of the optimal replacement ratio of rubber fillers is related to the achievement of the best compromise between mechanical strength and toughness based on field of application. Future research will concern the effect of rubber on the thermal and acoustic insulation properties of cementitious material

Binders alternative to Portland cement and waste management for sustainable construction – Part 2

The paper represents the “state of the art” on sustainability in construction materials. In Part 1 of the paper, issues related to production, microstructures, chemical nature, engineering properties, and durability of mixtures based on binders alternative to Portland cement were presented. This second part of the paper concerns the use of traditional and innovative Portland-free lime-based mortars in the conservation of cultural heritage, and the recycling and management of wastes to reduce consumption of natural resources in the production of construction materials. The latter is one of the main concerns in terms of sustainability since nowadays more than 75% of wastes are disposed of in landfills

Binders alternative to Portland cement and waste management for sustainable construction—part 1

This review presents “a state of the art” report on sustainability in construction materials. The authors propose different solutions to make the concrete industry more environmentally friendly in order to reduce greenhouse gases emissions and consumption of non-renewable resources. Part 1—the present paper—focuses on the use of binders alternative to Portland cement, including sulfoaluminate cements, alkali-activated materials, and geopolymers. Part 2 will be dedicated to traditional Portland-free binders and waste management and recycling in mortar and concrete production