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Innovation in cement and concrete technology: materials, methods and applications
No full textGlobal cement production is the third largest source of anthropogenic carbon dioxide emissions. Nevertheless, although its production is highly energy consuming and it has a severe impact on the environment, cement is an essential product in our society.
Therefore, there is a growing interest in finding sustainable solutions to replace the use of cement, especially in order to reduce its carbon footprint. Answering to the current crucial demand for high-performance building materials, recent research works have explored the possibility of improving the mechanical properties and the durability of cement-based composites via the addition of natural and synthetic micro- and nano-particles and via the self-healing methods.
Some of the emerging green alternatives rely on technological advances that include energy-efficiency and low carbon production methods, new cement formulations and manufactured nanomaterials which improve vital characteristics of construction materials such as strength, durability and lightness.
This Special Issue aims at publishing research novelty regarding materials, methods and applications in cement and concrete technology, in order to provide a platform for knowledge exchange between scientists and field experts. The main goal is to promote innovation in the cement and concrete sector with the important aim of improving sustainability and lowering the CO2 footprint.
This Special Issue aims at publishing a few papers based on presentations done at ESIS TC09-Concrete and enriched with new original results.
We would like to thank the authors for their important contribution and the reviewers for their patient and accurate work, fundamental for adding value to the papers. We hope that the readers will appreciate this Special Issue.
Our warmest thank you to prof. Luca Susmel, Editor in Chief of Theoretical and Applied Fracture Mechanics, who agreed and supported this Special Issue
The exoskeleton: A solution for seismic retrofitting of existing buildings
Full text linkAn exoskeleton is an external steel self-supporting system rigidly linked to an existing building that need to be safeguarded against seismic actions in order to comply with the current technical standards. Its application can guarantee an innovative seismic adjustment that combines structural and safety goals with sustainable properties. The present study deals with the performances of the developed coupled system under seismic actions when a suitable exoskeleton structure is applied to a real construction. It is designed with an in-plane rigid behaviour at each floor and a non-dissipative rigid link connects the primary building to the external structure. Early descriptions of the inner and the external constructions forerun the dynamic analysis, which allows to understand seismic response of the system especially in terms of frequencies and periods of vibration, floor displacements, stiffness and shear forces. Ensuing outcomes highlight the capability the exoskeleton has in taking base and floor shear forces as well as in reducing displacements and deformations of the primary building, so that it is protected from a potential earthquake collapse
An experimental set-up for cyclic loading of concrete
Full text linkInnovative cementitious composite materials are drawing considerable interest due to their substantially improved mechanical properties as compared to ordinary cement-based materials. Their enhanced ductility is promising and particularly suited to structural applications under severe dynamic loading conditions. Cyclic response is essential to understand the effects of loading and unloading on the material, as well as to understanding how it behaves in the transition from tension to compression. It is also fundamental to identify its properties in terms of energy dissipation and strain-rate sensitivity. This paper presents the first part of an ongoing research project which aims to develop the constitutive relationship in innovative cementitious composites and its numerical implementation. Results from this research will facilitate the investigation of the ductility and durability of existing buildings. In this paper, an experimental set-up for uniaxial cyclic loading is described. It was developed to study reversed cyclic compression/tension loadings of innovative cementitious composites. To set the cyclic loading process, cylindrical specimens of concrete were tested. All the tests were performed on a Zwick testing machine with 50 kN load cell. The machine was customised with accessories specifically designed to meet test requirements, avoiding instability and bending moments during the alternating phases of uniaxial compression and tension. Strain gauges were used to measure lateral deformations. The customized machine has shown good performance so far. In order to test specimens with a higher number of cycles and a higher loading rate, improvements to the machine are currently under development. These tests will allow greater insight into the ductility of innovative cementitious composite materials
Definition of inelastic displacement demand spectra for precast industrial facilities with friction and fixed beam-to-column joints
No full textPortal-frame reinforced concrete precast industrial facilities built in Italy between 1960 and 1990 have shown high vulnerability during recent seismic events interesting Emilia region. Post-earthquake damage observations have shown that most of collapses interested portal-frame structures arranged with dry beam-to-column friction joints because of the loss of support due to sliding of beams with respect to columns. At the same time severe damage to column base cross-sections was recognized even in the case of portal-frame systems with beamcolumn connection devices (fxed joints). The paper investigates the dynamic behaviour of portal-frame precast industrial facilities, especially addressing the inelastic displacement demand as function of the generalized mechanical response of beam-to-column joints. Portal-frames are idealized as 2D inelastic single degree of freedom systems. A framework based on a parametric model developed in OpenSees is defned to build inelastic spectra of maximum relative beam-column displacement demands and maximum column top displacement demands. Inelastic displacement demand spectra are defned for four different sites in Italy (Messina, Mirandola,Naples and Turin), characterized by different seismic hazard. Analytical expressions of spectra approximating numerical results are fnally derived to be used for rapid displacement capacity/demand assessments of portalframe industrial buildings with friction joints or fxed joints. The approach can account vertical component of seismic excitation in a simplifed way and can be also used to assess the effectiveness of retroftting interventions
Structural foamed concrete: preliminary studies for applications in seismic areas
Full text linkThe experimental research presented in this contribution highlights the possibility of producing foamed concretes with target dry
densities of 1550±50 kg/m3 and 1750±50 kg/m3 for the use in structural applications, thanks to compressive strengths greater than
25 MPa. The lower structural weight compared with ordinary concrete suggests the idea of using this material in seismic areas to
exploit its advantages in relation to inertial forces. However, the reduced elastic modulus compared with ordinary concrete of equal
compressive strength must be considered. In addition to demonstrating the beneficial effect of reducing the maximum diameter of
the fine sand used to produce the foamed concrete, this contribution also shows how the behavior of a reinforced concrete frame
changes (increase in the main vibration mode and decrease of the maximum shear at the base of the frame) if the foamed concrete
presented in this study is used instead of ordinary concrete of equal compressive strength
Influence of pyrolysis parameters on the efficiency of the biochar as nanoparticles into cement-based composites
Full text linkIn this research, a particular kind of biochar provided by UK Biochar Centre has been added as nanoparticles into cementitious composites. Its principle characteristic lies in the standardization of its process production, that makes it suitable to been used as filler in cement-matrix composites, ensuring the reproducibility of the cement mix (I. Cosentino "The use of Bio-char for sustainable and durable concrete", 2017). The pyrolysis parameters and the content of carbon in the standardized biochar influenced its efficiency to enhance the mechanical properties of the cement composites: the results, in terms of flexural strength and fracture energy, have been worse than those obtained in previous studies (L. Restuccia "Re-think, Re-use: agro-food and C&D waste for high-performance sustainable cementitious composites", 2016), in which particles have been produced with higher temperature. However, also with standardized biochar a general enhancement of mechanical properties has been recorded, a sign that they can be used to create new green building materials. (C) 2018 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the ECF22 organizers
Strategies to increase the compressive strength of ultra-lightweight foamed concrete
Full text linkFoamed concrete is a special lightweight concrete characterized by the presence of a stable preformed foam in the mix proportion that give rise to the development of a system of air voids in the material. Its physical and mechanical properties are strongly influenced by microstructural properties, in turn linked to various parameters such as the amount of foam, the presence of mineral additions or chemical additives, the characteristics of the mixing process and so on. Since ultra-lightweight foamed concrete is characterized by excellent functional properties (thermal insulation, sound absorption, fire resistance) but very poor mechanical properties (compressive strength), in this contribution three different ways to improve the compressive strength of this material without worsening its lightness are discussed. More specifically, the three different strategies (improve the consistency of the fresh lightweight cementitious paste through the addition of a viscosity enhancing agent, add silica fume and increase the rotational speed of the vertical mixer) lead to appreciable improvement in the compressive strength of the produced foamed concrete. The most significant increases in compressive strength are associated with the addition of silica fume in the mix, in proportion to 10% of the cement weight
The use of Biochar to reduce the carbon footprint of cement-based
Full text linkThe organic waste management is a most current topic, because its processing and degradation it is responsible for emissions of methane and other greenhouse gases, leading to serious environmental problems. Limited oxygen thermochemical processes, such as pyrolysis or gasification, have demonstrated the energy recovery potential of the treated biomass and its environmental benefits. However, the solid part of the process -Biochar- it is considered as a waste, as only its coarse ash can be used as soil improvers. Nevertheless, several researchers have explored its potential application as green filler in order to reduce the carbon footprint both of cement production and cement-based construction materials. In this work, Biochar microparticles were used both as a filler inside the cement paste and mortar composites and as a substitute for the cement powder inside the mixes. Based on previous work, this investigation has a twofold objective: To understand the full influence of the use of an optimized percentage of Biochar (2% with respect to the weight of the cement) either as a filler in the mixture or as a substitute for cement, while guaranteeing an improvement in the strength without losing ductility. The results showed that 2 wt% of Biochar's particles are sufficient to increase the strength and toughness of the cement and mortar composites and, in place of the cement in the mixture, can maintain the mechanical properties equal to those of the reference samples
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