Fracture properties of green mortars with recycled sand

Urbanisation is consuming huge amounts of sand, being the basic element of concrete and glass, two of the most popular construction materials. Unfortunately, sand mining is causing environmental damage and drastically reducing the amount of raw resources. The main topic of this research is to investigate the use of Construction and Demolition waste finer fraction - namely recycled sand - to totally replace the standard one into traditional mortars. From the analysis of the mechanical characterization of specimens, it is possible to state that recycled sand could represent a new resource for green and sustainable mortars

Increase the fracture energy of foamed concrete: Two possible solutions

The aim of the present paper is to investigate the influence of the curing conditions and the addition of an eco-friendly filler, biochar, on the flexural strength and fracture energy of a "green" special concrete characterized by lightness, high thermal and acoustic insulation properties and excellent fire resistance: foamed concrete. The study aims to highlight the properties of this promising material that, depending on its density, can be used for both structural and non-structural purposes. In fact, if the material is designed with a density not exceeding 800 kg/m3, it can be employed in interior partitions or in high energy-efficiency building envelopes; on the other hand, if the material is designed with a density greater than 1400 kg/m3, it can be used for structural purposes. All this makes it legitimate to state that it is a material that can be engineered according to specific needs. In this contribution the possibility to improve the fracture energy through biochar addition in this special concrete is also analyzed and presented. In particular, two different dry density were investigated: 800 kg/m3, and 1600 kg/m3. The first one for non-structural applications, the second for structural purposes. With regard to the biochar, used for 1600 kg/m3density, two different percentages, 2% and 4%, were investigated. Two different curing conditions were analyzed, namely in air at 20°C, wrapped in cellophane at the same room temperature and cured in water at 20 °C. Three-point bending tests in CMOD (crack mouth opening displacement) mode and compressive tests on the two-halves of the broken specimens have shown interesting results. Curing conditions significantly affect the fracture energy and the addition of biochar at 2% concentration seems to be beneficial in improving the fracture behavior of foamed concrete

feasibility and effectiveness of exoskeleton structures for seismic protection

Abstract In this study, a self-supporting structure, namely an exoskeleton, is considered as set outside a main structure and suitably connected to it. From the structural point of view, the exoskeleton is conceived as a "sacrificial" appendage, called to absorb seismic loads in order to increase the performance of the main structure. From the architectural and technological point of view, additional functions may be associated through an integrated design approach, combining seismic with urban and energy retrofitting. Particular and attractive applications can therefore be envisaged for existing buildings. A reduced-order dynamic model is introduced, in which two coupled linear viscoelastic oscillators represent the main structure and the exoskeleton structure, respectively, while either a rigid link or a dissipative viscoelastic connection is considered for the coupling. The equations of motion are set in non-dimensional form and a parametric study is carried out in the frequency domain to confirm that exoskeleton structures can be feasible and effective in reducing earthquake-induced dynamic responses

Considerations over the Italian road bridge infrastructure safety after the Polcevera viaduct collapse: past errors and future perspectives

In the last four years, Italy experienced the collapse of five road bridge: Petrulla viaduct (2014), Annone (2016) and Ancona (2017) overpasses, Fossano viaduct (2017) and Polcevera (2018) bridge. Although for deeply different reasons, the collapses occurred can all been gathered into the same common cause: the (lack of) knowledge of the effective structural condition, a serious problem that affects existing constructions. As it will be shown in the paper, different problems such as missing of the as-built designs, an appropriate construction and movement precautions, a heavy vehicle checking, and a material decay monitoring can nevertheless be addressed as an inadequate knowledge of what is happening to/in the structure. In the first section, the paper will report a short description of the failures for the five bridges, while in the second part a main set of problems involved in bridge safety and maintenance will be discussed. Finally, in the third part, a review on innovative and peculiar investigation and monitoring techniques will be illustrated. The collected results can shed new light on future perspectives for the Civil Engineering sector, sector that has to be ready for facing the challenges of preservation, restoration and/or replacement of the existing infrastructural constructions, worldwide

An experimental set-up for cyclic loading of concrete

Abstract Innovative 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

Biochar addition for 3DCP: a preliminary study

This contribution presents the first results of an ongoing research aimed at highlighting the possible reduction in the environmental impact of concrete through the synergy between two interconnected strategies: the exploitation of by-products, in this case biochar, for the realization of 3D printable cementitious conglomerates. Thanks to the use of biochar, the mixes presented are characterized by an excellent dimensional stability in the fresh state, evaluated through the extrusion test. Regarding the hardened state properties, the contribution highlights the effects of biochar-to-cement ratio, water-to-cement ratio (in combination with biochar content) and sand-to-cement ratio on the flexural and compressive strength of the mixes. The evaluation of CO2 emissions shows that a proper mix design could result in a significant reduction in CO2 emissions (up to 43%) while maintaining good mechanical performance (compressive strength of at least 60 MPa)

The use of Biochar to reduce the carbon footprint of cement-based materials

Abstract The 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

influence of pyrolysis parameters on the efficiency of the biochar as nanoparticles into cement based composites

Abstract In 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

new self healing techniques for cement based materials

Abstract: In recent years, researches concerning cement-based materials has been focused not only on the strength and the toughness but also on the durability. In fact, the interest on concrete's self-healing process is increasing, due to the rapidly deterioration of that material which tends to crack and thus quickly deteriorate. In this paper, a new self-healing technology for cement-based materials is proposed. This technology is based on the encapsulation method of repairing agent inserted in randomly distributed shell inside the material during its preparation. Two different kind of shells were used: glass spheres and pharmaceutical capsules. The material the shells are made of has to be endowed with a series of fundamental characteristics. That material has to be inert with respect to the repair agent so that it doesn't react with it, resisting to the severe stress condition that the shells undergo during the mixing, and at the same time being capable of breaking down when the crack intercept them, having a good compatibility with the cement mixture. The results demonstrate that it is possible to use this kind of shell to encapsulate the repairing agent: the crack breaks them and they release the healing agent, which allows patching up the crack

Cyclic uniaxial testing and constitutive modelling of cementitious composite materials

Innovative cementitious composite materials are drawing considerable interest due to their substantially improved mechanical properties, as compared to ordinary cement-based materials: among the others, higher tensile strength, tensile strain hardening, flexural strength, fracture toughness [1] and resistance to fatigue. Their enhanced ductility appears to be promising and particularly suited to structural applications under severe dynamic loading conditions (earthquake, impact, blast) [2]. Accurate constitutive models to simulate the dynamic behaviour of cementitious composites are hence needed, as well as corresponding appropriate testing protocols for their experimental characterisation [3]. In this study, the response of cementitious composites to cyclic uniaxial loadings has been investigated. Cyclic response is essential to understand the effects of unloading and reloading on the material, to examine how it behaves in the transition from tension to compression and to characterise its properties in terms of energy dissipation and strain-rate sensitivity. Different loading schemes have been considered, including reversed cyclic tension/compression loadings, in order to identify the complete stress-strain curve and the transition behaviour, which can occur, for instance, under seismic, fatigue and wind loads. Monotonic quasi-static tension and compression tests have been also performed, to provide a benchmark for the evaluation of the envelope curve of cyclic response. The experimental campaign was carried out on cylindrical specimens, a standard geometry in compression testing of cement-based materials. Several series of homothetic specimens (height to diameter ratio fixed as 2) with different dimensions were tested, to evaluate the influence of scale effects. Variability and reproducibility of the testing results have been taking into account by employing a minimum number of three specimens per loading condition. All the tests were performed, under deformation-controlled regime, on an MTS servo-hydraulic testing machine with 250 kN load cell. The testing machine was customised with accessories designed to meet specific test requirements, avoiding instability and bending moments during the alternating phases of uniaxial compression and tension. Linear variable displacement transducers (LVDT) and strain gauges were used to measure vertical displacements and lateral deformations, respectively. The results obtained experimentally represent a reliable basis for the development of constitutive models suited to numerical simulation. References [1] Restuccia, L., Reggio, A., Ferro, G.A., Kamranirad, R., “Fractal analysis of crack paths into innovative carbon-based cementitious composites”, Theoretical and Applied Fracture Mechanics, 90, 133-141, 2017. [2] Yoo, D. Y., Banthia N. “Mechanical properties of ultra-high-performance fiber-reinforced concrete: A review”, Cement and Concrete Composites, 73, 267-280, 2016. [3] Kesner, K.E., Billington, S.L., Douglas K.S. “Cyclic response of highly ductile fiber-reinforced cement-based composites”, ACI Materials Journal, 100(5), 381-390, 2003