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Ultra High Performance Fiber Reinforced Concrete (UHPFRC) is an innovative material with great mechanical and durability performances, high ductility and toughness. Although the mechanical behaviour of UHPFRC has been extensively studied in the last years, the damage mechanisms and permanent strains of this material when subjected to flexural loads need to be further investigated, in order to quantify and to better predict the performance of UHPFRC structural elements.

The use of Textile Reinforced Mortar (TRM) systems represent a valid alternative to traditional strengthening techniques, to improve mechanical strength and seismic performance of masonry buildings. Their effectiveness has been validated by several studies [1-4]. However, the TRM contribution in the mechanical behavior of masonry walls, subjected to simple compression, has not yet been fully investigated. In this study, an experimental campaign with the objective of studying the efficiency of TRM systems, applied to clay brick masonry panels, is presented. Compression tests were conducted on clay brick masonry panels with dimensions of 250x1000x1200 mm3. Glass fiber bidirectional fabrics were applied on both sides of the panels, coupled with lime-based mortar, and connected with stainless steel helical connectors. The total thickness of the reinforcement system is 30 mm. The effect of the TRM reinforcement on the mechanical behavior of the panel is analyzed and experimental results are compared with those of unreinforced panels in terms of ultimate strength and failure modes.

The use of Fabric Reinforced Cementitious Matrix (FRCM) systems to reinforce existing masonry and concrete structures is nowadays a well-established practice. The mechanical characterization of FRCM systems is of fundamental importance to define the correct parameters needed to design a strengthening intervention. However, some aspects regarding FRCM tensile behaviour need to be further investigated. The aim of this paper is to provide a detailed overview on the mechanical behaviour of FRCM specimens subjected to tensile tests. In this context, the effect of fabrics’ overlapping on the global behaviour of the system is extensively analyzed. Different sample’s configurations have been studied: one reinforced with a single layer of bidirectional glass fabric and three others with different fabrics’ overlap lengths, varying between 100 and 200 mm. Digital Image Correlation (DIC) has been also used to measure displacements in experimental testing. A phase-field model, that accounts for brittle fracture of cementitious matrix and fabric reinforcement and possible slippage at the fabric-to-matrix interface, has been developed. The variational formulation has been implemented in a finite element code to simulate the tensile behaviour of FRCM systems and the effects of using different fabrics’ overlap lengths.

This paper is aimed at exploring mechanical, electrical and self-sensing properties of cement-based mortars through the addition of short carbon fibers , at different dosages (2%, 3%, 4% by weight of cement). Compression and bending tests on carbon fiber reinforced mortars (CFRM) were performed. The addition of carbon fibers showed to enhance the mortars’ flexural strength by increasing the fibers content, while no improvement was found in the compressive strength . Electrical resistivity of the CFRM, at different days of curing, was evaluated by AC impedance measurements, using two stainless steel wire meshes as electrodes. The electrical resistivity decreased with time, until reaching a constant value after about 60 days of curing. Carbon fibers were able to drastically reduce the mortar resistivity, up to values below 150 Ω cm. The effect of fibers dosage on the ability of the mortar to change its electrical resistivity when subjected to different stress states was also studied. The specimens were gradually loaded up to 50–60% of the maximum compressive strength, carrying out two loading/unloading cycles, while resistivity was measured using a conductivity meter. Depending on the fibers dosage and stress state within the material, CFRM resistivity changed with significant variations.

Glass fiber reinforced polymer (GFRP) bars are currently used as internal reinforcement of concrete structures, as an alternative to traditional steel rebars, to avoid corrosion problems and durability issues. GFRP bars are usually made of continuous glass filaments embedded within a polyester (for non-structural applications) or vinyl ester resin. These resins have been used for many years in several technological fields and widely employed as matrices for composite materials with structural functions. However, since the matrix plays a fundamental role in protecting the fibers from the external environment, the development of new organic matrices able to withstand aggressive environmental conditions while keeping a low cost of production is certainly of great interest. In this study, the possibility of using a modified acrylic resin (ModAR), never employed for such applications, as matrix for GFRP bars has been investigated. Physical, mechanical and durability tests have been carried out, according to international standards, to evaluate the technical feasibility of using ModAR matrices. Experimental results showed that ModAR GFRP bars are able to offer high thermal resistance while keeping physical and mechanical properties within standard limits.

Ultra-high performance fiber reinforced concrete (UHPFRC) is considered a promising material for many applications where high compressive and tensile strength, small thickness and high energy absorption capacity are required. However, although these materials were introduced in the mid-1990s, a comprehensive investigation regarding its tensile characterization is still particularly challenging. Different tensile test setups have been used by many researchers, in order to obtain reliable results, but today there are currently no testing standards available that define test conditions, specimen geometry and analytical procedures to fully characterize the tensile properties of UHPFRC.

The possibility of producing high-volume fly ash (HVFA) recycled aggregate concrete represents an important step towards the development of sustainable building materials. In fact, there is a growing need to reduce the use of non-renewable natural resources and, at the same time, to valorize industrial by-products, such as fly ash, that would otherwise be sent to the landfill. The present experimental work investigates the physical and mechanical properties of concrete by replacing natural aggregates and cement with recycled aggregates and fly ash, respectively. First, the mechanical properties of four different mixtures have been analyzed and compared. Then, the effectiveness of recycled aggregate and fly ash on reducing carbonation and chloride penetration depth has been also evaluated. Finally, the corrosion behavior of the different concrete mixtures, reinforced with either bare or galvanized steel plates, has been evaluated. The results obtained show that high-volume fly ash (HVFA) recycled aggregate concrete can be produced without significative reduction in mechanical properties. Furthermore, the addition of high-volume fly ash and the total replacement of natural aggregates with recycled ones did not modify the corrosion behavior of embedded bare and galvanized steel reinforcement.

The use of Fabric-Reinforced Cementitious Matrix (FRCM) systems as externally bonded reinforcement for concrete or masonry structures is, nowadays, a common practice in civil engineering. However, FRCM durability against aggressive environmental conditions is still an open issue. In this paper, the mechanical behavior of a glass FRCM system, after being subjected to saline, alkaline and freeze&ndash, thaw cycles, has been investigated. The experimental campaign includes tensile tests on the fabric yarns, compression and flexural tests on the matrix and tensile tests (according to AC434) on FRCM prismatic coupons. The effects of the different environmental exposures on the mechanical properties of both the constituent materials and the composite system have been investigated and discussed. Ion chromatography analysis has also been performed to better understand the damage mechanisms induced by environmental exposures and to evaluate the ions&rsquo, penetration within the inorganic matrix. Alkaline exposure was shown to be the most detrimental for Alkali-Resistant (AR) glass fiber yarns, causing a reduction in tensile strength of about 25%. However, mechanical properties of the FRCM composite seemed not to be particularly affected by any of the artificial aging environments.

Electromagnetic shielding and propagation in concrete structures are getting more and more interest in radiation hazard problems and wireless communications. The protection of sensitive environment is nowadays carried out by appropriate shielding room made of metallic walls. Their efficacy is counteracted by their heaviness, not adequate for the installation over existing building walls. The using of concrete composites filled by conductive elements represents a valid alternative to metallic shielded room since they can be adopted to directly build up the building walls and/or to easily plaster existing walls. Graphene oxide powder and metallic fibers are being currently investigated as fillers in the manufacturing of electromagnetic shielding cementitious composites. The novelty of the present work is the characterization of a multi-reinforced cement realized by combining such two filler typologies: the synergistic effects of graphene oxide microparticles and short steel fibers result in enhancement of both mechanical properties and EMI effectiveness of the cementitious composites.

Fiber Reinforced Cementitious Matrix (FRCM) systems have emerged in recent years as an effective tool for strengthening and retrofitting of the existing built heritage. The effectiveness of FRCM systems is strongly related to the bond developed at the interface between inorganic matrix and fabric reinforcement and between the inorganic matrix and the substrate. However, since the major weakness is often located at the matrix-to-fiber interface, the study of stress-transfer mechanisms between fibers and matrix, and a better understanding of the failure processes become of fundamental importance. In this paper, interface bond-slip relations are derived from pull out tests on multifilament carbon yarns embedded in a cementitious matrix. Two different types of yarns are investigated, dry and pre-impregnated with epoxy resin. A variational model able to reproduce the mechanisms of interface debonding and frictional slippage observed in experiments is developed, where the constitutive parameters are calibrated on the base of the experimental data available from pull out tests. The model is implemented in a finite elements code, and pull out and double shear bond tests on masonry substrates are simulated. Finally, numerical results are compared with experimental evidences.

Polymeric coatings are widely used to enhance the load bearing capacity and chemical durability of alkali-resistant glass (AR-glass) textile in cement-based composites. The contact zone between coated yarns and concrete matrix plays a major role to enable the stress transfer and has still to be improved for the full exploitation of the mechanical behavior of the composite. As a new approach, this paper studies how the addition of nanoclay particles in the polymer coating formulation can increase the chemical bond between organic coating and inorganic matrix. This includes the description of the water-based coating preparation by dispersing sodium montmorillonites, whereby the resulting coating nanostructure is characterized by X-ray diffraction and energy dispersive X-ray spectroscopy. Single glass fibers were treated by dip-coating. Atomic force microscopy was used to determine the surface roughness, and the effect on the fiber tensile properties was studied. Moreover, the morphological and chemical characteristics of the coatings were compared with the results obtained from single fiber pull-out (SFPO) tests. It was shown that the incorporation of nanoclays leads to increased interfacial shear strength arising from the ability of nanoclay particles to nucleate hydration products in the fiber-matrix contact zone.

This experimental work aims to evaluate the strengthening effectiveness as well as the mechanical behavior of different Fiber Reinforced Cementitious Matrix (FRCM) systems. The use of mortars with different strength classes coupled with fabrics made of carbon, basalt or PBO fibers has been investigated. In the case of both carbon and basalt fibers a polymer coating was also applied, in order to check the likely improved adhesion with mortars. These composite systems have been characterized by means of tensile and double shear bond tests. Tensile tests have been performed with clevis grips (AC434.13), by changing the contact length of the metal tabs used to grip the ends of the specimen, in order to understand the influence of the latter on the FRCM tensile characterization. Different bond lengths were analysed in double shear bond tests, using clay brick walls as substrate, so as to evaluate the influence of the bond length depending on the reinforcement system used. Carbon and PBO were also coupled with high-performance mortar so as to understand the effect of using high performance cementitious mortar as matrix for composite systems. Finally, FRCM performance and failure modes when reinforced with multiple carbon fabric plies have been investigated.

Carbon nanotube reinforced concrete composites (RCC) were characterized in microwave bands currently employed in wireless telecommunication systems. Dielectric permittivity was retrieved by waveguide method and adopted to compute shielding effectiveness of RCC structures having different thickness/filler content. The shielding was also evaluated by reverberation chamber set up; theoretical calculations and measured values are in close agreement, thus testifying to the procedure reliability. Finally, a frequency selective absorber made of RCC layers was designed with the aid of a numerical optimization tool (particle swarm algorithm); the discussion of results is supported by a finite element method analysis of the layered structure.

The bond strength at the yarn to matrix interface is one of the key factor affecting the FRCM mechanical behavior. The interaction between multi-filament yarn and cementitious matrix, governed by complex mechanisms, determines the behavior and failure mode of this composite system. An experimental campaign comprising of 20 pull out tests on multifilament carbon yarns embedded in a cementitious matrix was carried out. Different bond lengths have been analyzed, equal to 20 and 50 mm. Failure modes observed were different depending on the bond length: slippage of the yarn for a bond length of 20 mm and failure of the external filaments when the bond length was increased to 50 mm. The maximum load recorded at fibers breakage was lower than the tensile strength of the yarn, confirming the fact that only the external filaments of the yarn are engaged in the load transfer mechanism and the effective area is only a portion of the total area. This work aims to propose a variational model to reproduce the behavior and possible failure modes of multifilament carbon yarns embedded in a cementitious matrix. Smeared crack terms are incorporated into the energy functional of the model to account for possible fracture in the yarn and in the matrix, and for debonding at the yarn-matrix interface. The evolution problem is formulated as an incremental energy minimization problem, and discretized by finite elements. Numerical simulations are able to accurately describe the composite behaviours and to reproduce experimental results.

In this work, the influence of different kinds of fibres on Fibre-reinforced concrete (FRC) cracking behaviour is examined. Several FRC mixtures are designed, in which cement is partially replaced ...

This work is aimed at studying the possibility of reusing waste glass from crushed containers as aggregate for preparing mortars. At present, this kind of reuse is still not common due to the risk of alkali–silica reaction (ASR) between alkalis of the cement and silica of the waste glass. This expansive reaction can cause great problems of cracking and, consequently, it can be extremely deleterious for the mortar durability. The influence of both size and colour of recycled glass coming from crushed containers on the durability of mortars is studied. The attention is focused on both mechanical behaviour, investigated by means of bending and compression tests, as well as durability, studied by means of accelerated tests for evaluating the tendency to expand under alkaline environment due to ASR. Several mortars are prepared by replacing at different rate the quartz sand with coarse glass cullet of different colours: clear (i.e. uncoloured), green and amber. Then, pulverised clear glass is added to the mort...

The use of new methods to strengthen and rehabilitate existing concrete and masonry structures is one of the challenges that the engineering community is facing in recent years. In this field, composite materials are acquiring more and more success, due to lower invasiveness and ease of application if compared to more traditional systems (e.g. steel plates or reinforced concrete jacketing). This work, based on experimental investigations, aims to propose a comparison between three different methods as possible strengthening solutions for existing concrete elements. Twenty compression tests were conducted on reduced scale concrete columns, realized by using a low performance concrete, in order to reproduce the poor mechanical properties of most existing structures. Two of them were left unconfined, while the other ones were reinforced by using Fiber Reinforced Polymer (FRP), Fiber Reinforced Cementitious Matrix (FRCM) or High Performance Mortar (HPM) systems. The effectiveness of the different strengthening techniques and the main differences in terms of structural response were investigated. Experimental results were then compared with predictions deriving from guidelines and theoretical models from the literature.

Already from the beginning, 50 years ago, the first nucleus of researchers establishing the research group, was convinced that the construction sector was the best option for the valorization of industrial by-products as “secondary raw materials”. In fact, this sector is probably the largest consumer of resources and the largest waste generator, consequently it has huge environmental impact. On the other hand, construction materials affect the performance of buildings with respect to safety, health, environmental performance and energy efficiency. Manufacturing of construction products using alternative raw materials; recycling to manage construction and demolition waste; durability and environmental compatibility of materials: all these were the different and challenging fields of research that the group has faced in a continuous effort of innovation and cooperation at national and international level. The focus of the group was already perfectly in line with what is now called “Circular Economy”, which at present is considered a revolution in the way of human economic development. We are sure the group thus contributed to this revolution even before the term was in current use. We feel ready for the next 50.

Currently, there is an increasing need to incorporate recycled materials, such as rubber, in building materials in order to meet sustainability issues. The use of waste rubber in cement-based materials such as mortar and concrete avoids landfilling and decreases virgin raw materials’ consumption. Waste rubber can be used as a partial replacement of fine aggregate, coarse aggregate or both aggregate fractions. This chapter presents an overview of the research carried out on the use of waste rubber as partial (or full) virgin sand replacement in conventional cement-based mixes, in which the binder is ordinary Portland cement. The effects of rubber waste addition on fresh properties (i.e., workability, setting time, bleeding and segregation, density) as well as on hardened properties (mainly mechanical strength, toughness, ductility, shrinkage, freeze/thaw resistance, fire resistance, thermal insulation, corrosion resistance, resistance to aggressive environmental and sound absorption) of rubberised cement-based materials were reviewed.

Ultra-High Performance Fiber-Reinforced Concrete (UHPFRC) is considered a promising material for many structural applications where high strength and high energy absorption capacity are required. The purpose of this work is to study the uniaxial tensile behavior of soft cast (flowable at casting time) UHPFRC by varying the amount of hooked steel fibers (30-mm long) from 0% up to 2.55% by volume. Direct tensile tests have been performed on dog-bone shaped specimens and Digital Image Correlation (DIC) has been used to measure displacements and deformations and to monitor the evolution of cracks. Then, a phase-field model has been implemented in a FE code and numerical simulations have been performed to better understand the effects of different fiber dosages on the mechanical behavior of UHPFRC composites and on their post-elastic evolution. Concrete matrix and fiber reinforcement have been modeled as brittle and elasto-plastic phases of a mixture, whose internal energies are enriched by non-local damage and plasticity contributions. The different failure mechanisms observed in experiments have been reproduced, including the ductile failure experienced by specimens with sufficiently high fiber dosage, which distinguishes for a strain-hardening phase of matrix multi- micro-cracking that anticipates material failure.

The paper presents the results of an experimental campaign aimed at investigating the in-plane and out-of-plane behavior of tuff and fired clay brick masonry panels reinforced by a commercial, not yet tested, Textile Reinforced Mortar (TRM) system. The TRM, consisting of hydraulic lime mortar coupled with a bidirectional glass fabric (total thickness of 30 mm), was applied on both sides of the panels and connected through stainless-steel helical bars. First, a mechanical characterization of the TRM system was carried out, according to recent guidelines (AC434 and CNR-DT215) by means of tensile tests and single-shear bond tests on the two different substrates. Then, the effectiveness of the reinforcement was investigated through uniaxial compression, diagonal compression and three-point bending tests on masonry panels. After that, experimental results were compared to the predictions of recent guidelines and analytical models available in the literature, by using the mechanical parameters obtained from the TRM mechanical characterization. TRM showed to be very effective in increasing the in-plane shear strength of tuff panels, of about 170%, whereas in the case of fired clay brick ones the increase was limited to 33%. Besides, the diagonal compression strength of reinforced specimens seemed to be strongly influenced by the mortar matrix, instead of by the fabric reinforcement, as it usually happens i.e. for Fabric Reinforced Cementitious Matrix (FRCM) systems. Thus, novel simplified analytical formulations to predict the shear strength of reinforced panels by only considering the contribution of the TRM matrix were provided, discussed and compared to current analytical approaches for FRCM systems. As regards the out-of-plane behavior, the TRM system significantly increased the out-of-plane bending strength and ductility of both tuff and fired clay brick panels. The applicability of current analytical approaches, as well as possible amendments, was also investigated. Finally, the compressive behavior of the walls was not substantially modified by the reinforcement, reasonably due to the low axial stiffness of the connectors and, to a minor extent, because they were dry inserted within the masonry and simply folded over the glass fabric.

The use of composite materials for repair and retrofit of structures has become a common use among the engineering community. Fabric Reinforced Cementitious Matrix (FRCM) is a composite material specifically designed for masonry and concrete rehabilitation and is becoming a viable alternative to FRP, whenever the project conditions do not allow the use of organic polymer based composites. FRCM is usually constituted by one or multiple plies of dry fabrics (carbon, glass, aramid, basalt or PBO fibers) embedded into an inorganic matrix. If a polymer is used to either cover or bond the fabric strands, such polymer does not fully penetrate and impregnate the fibers as it would for FRP. The purpose of this research work is to study how different types and amounts of organic coatings applied to a carbon fabric could affect the bond behavior between fabric and mortar. The effectiveness of coating treatments was studied by means of direct tensile, pull-off and shear-bond double-lap tests. Experimentation was carried out on different combinations of fabrics and mortars, by varying the levels of pre-impregnation of the fabric during its manufacturing. In addition, the use of a quartz sand layer applied to the fabric after impregnation was investigated. Experimental evidence shows a promising enhancement of the bond between fabric and matrix and, therefore, of the entire system even with the use of low percentages of resin, depending on the type of mortar used.

In this project several fiber reinforced cement-based composites (FRCCs) were studied, in which a CaO-based expansive agent was added in order to help in reducing the cracking induced by drying shrinkage. Two different kinds of fibers were tested: brass-coated hooked steel fibers and flat and flexible amorphous metallic fibers. All the mixtures were characterized for fresh and hardened state, by measuring the consistency of fresh mixtures, compressive and flexural strength, as well as length changes under drying shrinkage test condition for the hardened state. Their microstructures were also investigated by mercury intrusion porosimeter and SEM observations. The effect on mechanical performance of thermal pre-treatment at 80 °C was also evaluated. Results obtained confirmed the effectiveness of CaO addition (even at a low-dosage) on the stability of mixtures under drying shrinkage. It also proved to be effective in terms of flexural strength improvement when used with brass-coated fibers. The reason of this synergy probably lies in the formation of calcium hydroxyzincate (CHZ) crystals at the interface between the fibers and surrounding cement paste. These CHZ crystals, as observed by SEM, are likely able to noticeably improve the quality of the interface of the fiber-matrix by increasing adhesion.

The shielding effectiveness of cementitious composites is analyzed by means of the nested reverberation chamber method. This feature is evaluated as function of time in order to estimate the aging effects. Different cementitious mixtures are considered and carbon/metallic fibers are put within the mortar in order to improve the shielding effectiveness considering the frequency band from 0.8 GHz up to 8.4 GHz.

Composite systems consisting of fibers in the form of open fabrics embedded within inorganic matrices (Fabric Reinforced Cementitious Matrix, FRCM) have become a well-established technique for strengthening interventions on masonry and concrete structures. In particular, the use of fabrics made of glass fibers coupled with inorganic matrices showed to be very promising, thanks to the high mechanical properties of the fibers, low cost of the raw materials and good compatibility with the substrate, especially in the case of masonry structures. However, the durability of FRCM systems, such as the resistance to salt attack, alkaline environments or moisture, is an issue that hasn't be thoroughly investigated yet. In this study, the effect of saline and 100% Relative Humidity (RH) environments on the mechanical behavior of FRCM systems reinforced with glass fabrics has been investigated. The glass FRCM systems have been studied and characterized considering both the constituent materials (hydraulic mortar and glass fabric) and the substrate (fired clay brick) on which they were applied. Mechanical characterization tests on mortars and fabrics have been performed before and after exposure to different aging conditioning protocols. The same protocols have been adopted for specimens constituted by FRCM strips applied on clay brick substrates, to study the effect of different environments on the shear bond behavior of the composite system.

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.

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.

The reduction of energy consumption in construction, the production of thermally insulating materials, as well as the solution of environmental problems by recycling industrial and municipal waste are key challenges for the next future. For this reason several plasters have been studied, in which virgin raw materials such as natural sand and limestone filler were replaced up to 100% by waste polyethylene terephthalate (PET) particles and pulverized Glass Fibre Reinforced Plastic (GFRP) waste, respectively. Moreover, an attempt was made to combine PET waste particles and wood waste (WW) particles in order to improve functional properties of plasters. As supplementary cementitious material silica fume was employed, which is a further industrial by-product obtained from silicon wafer sawing during the production process of solar panels. Finally, in some mixtures even cement was fully replaced by a combination of lime and hydraulic lime in order to further improve the carbon footprint of these plasters. At the end of the optimisation process, environmentally-friendly plasters have been obtained with 100% waste particles replacing virgin materials, which proved to be energy efficient thanks to the low thermal conductivity values achieved, as well as for their remarkable lightness.

In this work several fibre reinforced cement-based composites (FRCCs) as well as ultra high performance concretes (UHPCs) were studied, in which CaO-based expansive agent was added in order to help in reducing the risk of cracking induced by drying shrinkage. Three different kinds of metallic reinforcing fibres were tested: flat (and flexible) steel-alloy fibres, and brass-coated either hooked or straight steel fibres. All the mixtures were characterised at both fresh and hardened state, by measuring fresh consistency, compressive and flexural strength, as well as length changes under drying shrinkage test. Moreover, FRCC microstructure was investigated by means of Mercury Intrusion Porosimetry (MIP) and Scanning Electron Microscope (SEM) observations. The effect on mechanical performance of a thermal pre-treatment at 80 °C for the first 24 h of curing after casting was also evaluated. Results obtained confirmed the effectiveness of CaO addition on material stability under drying shrinkage; moreover, it seems to produce a beneficial effect on flexural strength if used with brass-coated fibres. The reason of this synergy probably lies in the formation of calcium-hydroxy-zincate crystals at the interface between fibres and surrounding cement paste (phenomenon promoted by dezincification of brass in alkaline environment), able to significantly improve the quality of the interface fibre–matrix by increasing adhesion.

The use of externally applied composite systems to upgrade, strengthen or rehabilitate masonry or concrete structures is well established. However, structural strengthening with organic type composites, such as fiber-reinforced polymer (FRP) systems, may be impractical when the element is exposed to high-temperature service conditions, due to significant degradation of the organic resin. Instead, the use of an inorganic matrix, as in the case of fabric-reinforced cementitious matrix (FRCM) composites, may overcome this problem. The purpose of this study is to evaluate the mechanical behavior under high-temperature conditions of FRCM systems. Different FRCM composites are evaluated and include carbon fabrics ranging from dry to highly-impregnated with an organic resin. The experimental spectrum is comprised of uniaxial tensile and double-shear bond tests performed under temperatures ranging from 20 to 120 °C to determine the influence of temperature over the FRCM mechanical properties. Furthermore, SEM analysis was used to study the damage processes at the fiber-matrix interface post tensile testing. Experimental results show variations in the FRCM mechanical properties if tested at high temperature conditions (caused by the deterioration of the resin coating at the interface fiber-matrix) while residual performance after exposure to elevated temperatures remains unchanged. FRCM reinforced with dry fabrics has proven not to be affected by temperatures up to 120 °C. A numerical model using a fracture variational approach, based on incremental energy minimization, was also developed to simulate the FRCM behavior in double shear tests under different temperatures exposition.

The use of composites with cement matrix seems to acquire an increasing interest in applications to masonry structures, due to their low impact, and a deeper understanding of the mechanical interaction between support and reinforcement is certainly necessary. The effectiveness of these interventions strongly depends on the bond between strengthening material and masonry, on the fibers/matrix interface, as well as on the mechanical properties of the masonry substrate [1]. In this work the attention was focused on the possible improvement of the bond between FRCM and masonry by means of an inorganic primer, which can be spread on the ceramic support before the application of FRCM reinforcement. Two different kinds of brick were tested, in order to simulate more or less porous masonry supports. Results obtained showed that, independently on the kind of brick used (more or less porous) the presence of an inorganic primer always improves bond between masonry support and the cementitiuos matrix of FRCM. In fact, the cementitous matrix of FRCM has been studied and optimized in order to guarantee the best fibers/matrix interface, while it is not necessarily the best option for improving the adhesion with the masonry support. In particular, very effective seems to be the use of very fine inorganic particles (at nanometric scale), which proved to be able to assure the best results in terms of bond strength. Also the fresh consistence of the primer seemed to influence the final result.

Self-leveling lightweight mortars were developed to attain good workability, sufficient compressive strength (at least 5 MPa after 28 days of wet curing), and low specific weight (less than 1100 kg/m3), as well as low thermal conductivity (lower than 0.3 W/m∙K). The attention was also focused on the sustainability of this construction material, which was improved by using in the mixture both glass reinforced plastic (GRP) industrial by-product as filler replacing limestone powder, and recycled aggregates replacing natural sand. GRP is a composite material made of glass fibres dispersed in a resin, usually polyester, widely used in several fields from building to furniture factory to boatyard. The recycled aggregates used were alternatively either wooden waste or polyurethane waste particles. Concerning wooden waste, they are produced by cutting, drilling and milling operations, where wood is removed from a finished product; they are sawdust and offcuts often collected in filter bags or dust collectors. On the other hand, the polyurethane waste particles were obtained as a rejection of a factory producing rubber soles for the footwear industry. The influence of GRP filler and waste particles on fresh mortar workability, compressive and flexural strength of hardened mortar, as well as on its thermal conductivity was examined. An optimization of the mortar mixture proportions was carried out by suitably varying the dosage of the ingredients. The experimental investigation showed that both the material unit weight and its thermal conductivity resulted strongly reduced, thus indicating a high and promising potential for future developments.

In the last decades, the need for upgrading, strengthening and retrofitting of existing concrete structures is rapidly growing. Composite materials showed to be an optimal solution to face this problem, combining high efficacy with low invasiveness. The use of Fiber Reinforced Polymers (FRP) to wrap concrete columns has been widely investigated and became a very successful method to improve their structural performances. However, it has been recognized that FRPs, due to the presence of an organic resin, have a few drawbacks, such as poor mechanical behavior at high temperatures, lack of vapor permeability and impossibility to be installed on wet surfaces. This experimental work aims to propose a comparison between three different innovative methods as possible strengthening solutions for existing concrete columns. The structural behavior of 20 reduced scale concrete columns, realized by using a low performance concrete, in order to reproduce the poor mechanical properties of existing structures, was investigated. Two unreinforced column were tested in compression as reference. Six of them where reinforced by applying an external layer of FRP, with different types of fabric reinforcement (made of carbon or PBO fibers). Six columns were reinforced by using the same fabrics coupled with an inorganic matrix (FRCM) instead of epoxy. Six other columns were reinforced by using a layer of High Performance Fiber Reinforced Concrete (HPFRC) of 3 cm thick. Experimental results have been analyzed and performance of the three reinforcement systems have been compared.

A key concept of sustainability is the preservation of resources, thus adding life to existing concrete structures by means of durable strengthening and rehabilitation methods is a key objective. Composite materials, such as FRCM (Fabric-reinforced Cementitious Matrix), have proven to be a viable option for increasing durability of existing building stock. Experimental works show that the main failure mode of FRCM, applied to masonry or concrete substrates, is by debonding at the fabric/matrix interface. Mere, the idea is to use an epoxy coating and a layer of quartz sand in order to increase the adhesion of the fabric with the matrix. The effectiveness of coating treatments was studied by means of tensile tests, as indicated in AC434 Annex A. Tests were carried out on seven different types of fabric, with different levels of pre-impregnation and with or without quartz sand applied to the fabric surface. Experimental evidence shows a promising enhancement of the bond between fabric and matrix and, therefore, of the entire strengthening system even with the use of low percentages of resin, depending on the type of mortar.