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The behavior of lightweight cement-based and alkali-activated mortars after exposure to temperatures of 500, 750, and 1000 °C was compared. In cement-based mortars, cement was partially replaced (40 vol%) by several refractory fillers (coal fly-ash, biomass fly-ash, cocciopesto, metakaolin). In alkali-activated mortars, metakaolin was partially substituted (0, 25, 50 wt%) by coal fly-ash. The substitution of cement by 40% metakaolin and the substitution of metakaolin by 50% fly ash enhances the resistance to high temperatures of cement-based and alkali-activated mortars, respectively. After exposure to 1000 °C, the high residual compressive strength of cement-based mortars with metakaolin is due to the formation of new crystalline species, whereas in alkali-activated mortars is due to their high densification.

The article focuses on the development of innovative and multifunctional mortars with low environmental impact for indoor applications acting as passive systems to moderate extremes of humidity and to lower the concentration of pollutants. Mortars are manufactured by keeping constant the water/binder ratio, using sand as reference aggregate, and by replacing the total volume of sand with zeolite. In some mixes the aggregate, is also at 25vol% by wool natural fibers. Regardless lightness, zeolite thanks to its pozzolanic activity, helps to improve the compressive strength of mortars manufactured with wool fibers. In addition, the combination of zeolite and wool increases the hygro-thermal performance of mortars: water vapor resistance factor (22% lower than the reference), moisture buffering value (100% higher than the reference), and thermal conductivity (66% lower than the reference), respectively. Depolluting properties of zeolite-based mortars, in terms of adsorption capacity, are 65% lower than that of reference mortar.

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.

Common alkali-activated materials (AAMs) are usually manufactured with highly alkaline solutions. However, alkaline solutions are dangerous for workers who must wear gloves, masks, and glasses when handling them. This issue makes common (or two-part) AAMs not user-friendly and problematic for bulk production if no safety procedures are followed. In this paper, the possibility of manufacturing alkali-activated pastes and mortars without alkaline solution is investigated. These innovative one-part AAMs have been prepared with metakaolin as the aluminosilicate precursor, potassium-rich biomass ash as the alkaline activator, and water. AAMs have been prepared by varying the K/Al molar ratio: pastes have been studied in terms of reaction kinetics, through isothermal calorimetry, and mortars have been tested in terms of mechanical compressive strength. Results show that the K/Al molar ratio governs both the reaction kinetics and the mechanical strength of these innovative materials. The highest compressive strength is obtained when the K/Al ratio is equal to 2.5 and the water/solid ratio is equal to 0.49. If biomass ash is heated at 700 &deg, C to decompose the calcium carbonate, its reactivity and the final compressive strength increase.

The corrosion behaviour of bare and galvanized steel reinforcements in geopolymeric and cementitious mortars, at three strength classes, has been investigated throughout the curing period and exposure to wet-dry cycles in 3.5% NaCl solution. During the curing, the high alkalinity of geopolymers prolongs the active state of both bare and galvanized steel. During the chloride exposure, fly ash geopolymers give the highest protection to reinforcements. The higher alkalinity of geopolymers compared to cement mortars seems to decrease the minimum free chloride threshold necessary to induce corrosion for galvanized steel, but it increases that for bare steel.

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.

Carbon-based fillers from industrial wastes and commercial ones were compared to improve the properties of lime-based mixes. As commercial fillers, graphene nanoplatelets and activated carbon were used, whereas as industrial wastes a char obtained by the gasification of biomasses and a used foundry sand were chosen. Carbon-based wastes were found to be a good cost-effective alternative to commercial carbon based fillers to increase the compressive strength (of about 25%) and to reduce water capillary absorption (of about 50%) thanks to the paste refinement; to enhance depollution capacity (of about 25%) and increase both electrical conductivity (up to 65%) and electromagnetic shielding effectiveness (of about 6%) of the hardened compounds thanks to the carbon content.

Alkali-activated and cementitious mortars belonging to R1 ≥ 10 MPa, R2 ≥ 15 MPa and R3 ≥ 25 MPa strength classes were tested and compared in terms of workability, dynamic modulus of elasticity, porosimetry, and water vapor permeability. Capillary water absorption, drying shrinkage, resistance to sulfate attack, and corrosion behavior of embedded bare and galvanized reinforcements were also investigated. In alkali-activated mortars, drying shrinkage is higher than that of cementitious mortars but restrained shrinkage is lower due to lower modulus of elasticity. Pore dimensions affect water vapor permeability, more pronounced in alkali-activated mortars, and capillary water absorption, much lower in fly ash ones. The high alkalinity of fly ash and metakaolin mortars delayed the achievement of the passive state in particular for the galvanized reinforcements but after 1 month of curing they reached the same corrosion rates of those embedded in cementitious mortars.

Recycling of industrial waste materials to manufacture environmentally friendly mortars and concretes is gaining more and more interest, in particular for sustainability, rehabilitation and renovation purposes. In the present study geopolymers, which had been made using fly ash as a precursor and were subsequently subjected to curing at room temperature, were investigated. Geopolymeric and cementitious mortars with the same mechanical strength class were compared in both the fresh and hardened states. Despite the higher free shrinkage and lower adhesive strength on brick substrate, geopolymeric mortars behaved better than cement types in terms of lower dynamic modulus of elasticity, higher water vapour permeability, lower capillary water absorption and higher resistance to salt crystallisation.

In order to decrease energy consumption in buildings, a new way to recycle materials coming from biomasses waste in mortars was studied. For this purpose, mortars with water/cement equal to 0.5 by weight and aggregate/cement equal to 3.5 by volume were considered. Cement was replaced by hydraulic lime and sand was substituted with two different types of spruce sawdust shavings (as it is and roasted), biomass bottom ash and biomass fly ash. The results show that mortar prepared with cement has obviously a better mechanical strength and 60% lower capillary water absorption. All unconventional aggregates increase the total porosity of lime mortars. Moreover, biomass fly ash and both spruce sawdust shavings based mortars can be classified as lightweight mortar. Regardless of porosity and lightness, biomass bottom ash improves up to 150% the mechanical performance of lime-based mortars. Concerning durability, bio-based lime mortars show in general nearly twice higher capillary water absorption with respect to the sand lime mortars whit the exception of spruce sawdust shavings and biomass bottom ash. Mortars can be classified as permeable to water vapour. As it is and roasted spruce sawdust shavings are able to increase three and two times the capacity of the mortar to be a hygroscopic buffer in terms of MBV values.

Structural health monitoring to assess the safety, durability and performance of structures can be performed by non-destructive methods such as the measurement of impedance in self-sensing cement-based elements. Cement-based materials, like mortars and concretes, generally have high electrical resistivity but the addition of carbon-based fillers and fibres decreases their electrical resistivity and thus enhances their self-sensing capabilities. In this study, two waste carbon-based fillers, namely, used foundry sand and gasification char were compared to commercial graphene nanoplatelets and used to produce self-sensing cement mortars, both with and without recycled or virgin carbon fibres. The mortars were tested in terms of their mechanical and electrical properties as well as their propensity to capillary water absorption. The results demonstrate that gasification char alone is the best carbonaceous waste for decreasing the electrical resistivity (&minus, 42%) and water absorption (&minus, 17%) of mortars, while their compressive strength remains unaltered. Moreover, although there is a slight reduction in compressive strength and an increase in water suction when gasification char is coupled with fibres, the combination of fillers and fibres has a synergistic effect in decreasing mortars&rsquo, electrical resistivity, especially when recycled carbon fibres are used (&minus, 80%).

This paper aims at analyzing the state-of-the-art techniques to measure electrical impedance (and, consequently, electrical resistivity) of mortar/concrete elements. Despite the validity of the concept being widely proven in the literature, a clear standard for this measurement is still missing. Different methods are described and discussed, highlighting pros and cons with respect to their performance, reliability, and degree of maturity. Both monitoring and inspection approaches are possible by using electrical resistivity measurements; since electrical resistivity is an important indicator of the health status of mortar/concrete, as it changes whenever phenomena modifying the conductivity of mortar/concrete (e.g., degradation or attacks by external agents) occur, this review aims to serve as a guide for those interested in this type of measurements.

There is an increasing interest towards the development of alternative binders for the manufacture of sustainable mortars and concretes. Ordinary Portland cement (OPC) is the most commonly used material in construction, even if its production process is highly polluting. Both calcium sulfoaluminate (CSA) and alkali-activated cements (AAC) are potential alternative binders to be used in both structural (R3 class, with Rc ≥ 25 MPa) and non-structural applications (R1 and R2 classes, with Rc ≥ 10 MPa and Rc ≥ 15 MPa, respectively) according to UNI EN 1504-3. This paper reports the hydration mechanisms and the evolution of porosity of OPC-, CSA- and AAC-based binders. The properties of fresh and hardened mortars, belonging to the above-mentioned mechanical strength classes, were evaluated and compared with particular emphasis on durability properties in terms of capillary water absorption, drying shrinkage, and resistance to sulfate attack. The results show that CSA-based mortars exhibit the lowest drying shrinkage due to their highest elasticity modulus. AAC mortars are characterized by the highest water vapor permeability and the lowest capillary water absorption for the highest presence of large pores (>3000 nm).

The paper aims to provide a comprehensive study on the compositional optimization of high-conductive multifunctional fiber-reinforced cement mortars (FRCMs). Therefore, the effects of three different fiber types: virgin carbon fibers (VCFs), recycled carbon fibers (RCFs), and brass-plated steel fibers (BSFs), added at a broad range of concentrations, as 0.05%, 0.1%, 0.2%, 0.4%, 0.8%, 1.2%, and 1.6% by volume, on the mechanical, electrical and durability properties of FRCMs have been compared. The results showed that RCFs increase the flexural and tensile splitting strength up to 100%, whereas BSFs improve the compressive strength by 38%. Moreover, the fibers decrease both the capillary water absorption and the drying shrinkage by 39%. Electrical conductivity tests show that RCFs decrease the electrical resistivity of mortars up to one order of magnitude, in addition to a percolation threshold between 0.1 and 0.2 vol%.

The possibility of recycling mixed colour waste glass as it is for manufacturing decorative architectural mortars, has been investigated. In mortars, the 0–33–66–100% of calcareous gravel volume has been replaced with recycled glass cullets, with no other inorganic addition. To mitigate the possible alkali–silica reaction, mixes with a hydrophobic admixture were also compared. The obtained results show that the replacement of calcareous gravel with glass cullets of similar grain size distribution permits to reduce the dosage of the superplasticizer admixture to obtain the same workability of fresh mortar; it does not affect significantly the mechanical performances, the water vapour permeability and the capillary water absorption but it reduces significantly the drying shrinkage deformation. The used recycled glass is classified as no reactive in terms of alkali–silica reaction neither in water nor in NaOH solution following the parameters of the current normative, even in the absence of the hydrophobic admixture. The hydrophobic admixture further delays the expansion trigger but not the speed of its propagation.

The total substitution by volume of natural coarse calcareous aggregate by coarse recycled brick aggregate (RBA) and coarse recycled concrete aggregate (RCA) has been investigated to produce more sustainable and environment-friendly mortars. Aggregates were also partially substituted by their fines at 12.5% by volume. Mortars have been tested in terms of mechanical, microstructural, and durability properties. Results show that it is feasible to replace a natural calcareous aggregate entirely by recycled aggregates. In particular, the obtained mortars, even if more porous and more prone to the water capillary absorption than that manufactured with natural aggregates, result in less stiffness and thus are less subjected to crack formation, more permeable to water vapour, and less susceptible to sulphate attack.

In Europe, the total amount of Glass Reinforced Plastic (GRP) waste is increasing. In order to valorise GRP dust (GRPd) waste and to reduce the consumption of nonrenewable resources in building materials, GRPd has been already investigated in cementitious materials where it gives even an improvement in some performances of the final products. Valorisation of GRPd waste in the production of bricks can be considered as a further alternative. In this paper, GRPd waste was substituted to the clay volume at 5% and 10% for the manufacturing of fired clay bricks. All specimens were subjected to a firing temperature of 850°C for 6 hours, then tested and compared in terms of porosity, compressive and flexural strengths, density, and water absorption. Despite a decrease in compressive strength up to 46% with 10% of GRPd substitution and an increase of water absorption from 14% to 29% with 5% and 10% of GRPd substitution, respectively, an increase in terms of lightness (about 10%), maximum flexural strength (up to 31%), and deflections at the maximum load (up to 130%) has been registered by specimens with 10% of GRPd substitution.

This paper deals with the study of calcium sulfoaluminate (CSA) and geopolymeric (GEO) binders as alternatives to ordinary Portland cement (OPC) for the production of more environmentally-friendly construction materials. For this reason, three types of mortar with the same mechanical strength class (R3 ≥ 25 MPa, according to EN 1504-3) were tested and compared; they were based on CSA cement, an alkaline activated coal fly ash, and OPC. Firstly, binder pastes were prepared and their hydration was studied by means of X-ray diffraction (XRD) and differential thermal-thermogravimetric (DT-TG) analyses. Afterwards, mortars were compared in terms of workability, dynamic modulus of elasticity, adhesion to red clay bricks, free and restrained drying shrinkage, water vapor permeability, capillary water absorption, and resistance to sulfate attack. DT-TG and XRD analyses evidenced the main reactive phases of the investigated binders involved in the hydration reactions. Moreover, the sulfoaluminate mortar showed the smallest free shrinkage and the highest restrained shrinkage, mainly due to its high dynamic modulus of elasticity. The pore size distribution of geopolymeric mortar was responsible for the lowest capillary water absorption at short times and for the highest permeability to water vapor and the greatest resistance to sulfate attack.

Innovative and multifunctional mortars for renders and panels were manufactured using white photocatalytic and non-photocatalytic cement as binder. Unconventional aggregates, based on lightweight materials with high specific surface and adsorbent properties, were adopted in order to investigate the possible ability to passively improve indoor air quality. The reference mortar was manufactured with traditional calcareous sand. Results show that even if the mechanical properties of mortars with unconventional aggregates generally decrease, they remain acceptable for application as render. The innovative mortars were able to passively improve indoor air quality in terms of transpirability (70% higher), moisture buffering ability (65% higher) and depolluting capacity (up to 75% higher) compared to traditional ones under the current test conditions.

In the current paper, the effect on Indoor Air Quality (IAQ) of two commercial acrylic-based paints were compared: one (Paint A) for indoor applications, the other (Paint B) for indoor/outdoor applications. Both were applied on an inert and on a real mortar substrate. The possibility of Paint B to passively improve IAQ was also investigated when adding highly porous adsorbent fillers, both as addition or as total replacement of a conventional siliceous one. The obtained results show that all paints have high capacity to inhibit biological growth. Paint A is more breathable and it has a higher moisture buffering capacity. Paint B negatively modifies the beneficial properties of the mortar substrate for IAQ. However, the use of unconventional fillers, especially as addition to the formulation, allows the recovery of the same properties of the substrate or even the enhancement of about 20% of the ability to adsorb volatile organic compounds (VOCs) under the current test conditions.

This paper presents the resistivity and piezoresistivity behavior of cement-based mortars manufactured with graphene nanoplatelet filler (GNP), virgin carbon fibers (VCF) and recycled carbon fibers (RCF). GNP was added at 4% of the cement weight, whereas two percentages of carbon fibers were chosen, namely 0.05% and 0.2% of the total volume. The combined effect of both filler and fibers was also investigated. Mortars were studied in terms of their mechanical properties (under flexure and compression) and electrical resistivity. Mortars with the lowest electrical resistivity values were also subjected to cyclic uniaxial compression to evaluate the variations in electrical resistivity as a function of strain. The results obtained show that mortars have piezoresistive behavior only if they are subjected to a prior drying process. In addition, dry specimens exhibit a high piezoresistivity only when loaded with 0.2 vol.% of VCF and 0.4 wt.% of GNP plus 0.2 vol.% RCF, with a quite reversible relation between their fractional change in resistivity (FCR) and compressive strain.

The effect of fly ash on the corrosion behaviour of galvanised steel rebars in cracked concrete specimens exposed to wet-dry cycles in a chloride solution has been investigated. The obtained results show that the use of fly ash, replacing either cement or aggregate, always improves the corrosion behaviour of galvanised steel reinforcements. In particular, the addition of fly ash, even in the presence of concrete cracks, decreases the corrosion rate monitored in very porous concretes, as those with w/c = 0.80, to values comparable with those obtained in good quality concretes, as those with w/c = 0.45. Therefore, fly ash cancels the negative effect, at least from the corrosion point of view, of a great porosity of the cement matrix.

Performances of structural, moderate and heat insulating lightweight mortars manufactured by replacing sand volume with virgin or recycled expanded polystyrene (EPS) are compared. At the same dosage, replacing virgin EPS with recycled one improves the mechanical performance of mortars without a significant variation in capillary water absorption and water vapour permeability. Recycled EPS mortars have lower thermal insulation properties than those manufactured with a virgin one, but this can be counteracted by increasing the percentage of EPS. To obtain mortars with a certain thermal insulating capacity, an economical saving over than 25% can be reached by using recycled EPS.

This paper discusses the electrical impedance behaviour, measured according to the Wenner’s method, of three different concrete mixes during accelerated degradation tests. Being a first attempt to move from laboratory to in-field applications targeted to long-term monitoring, the same electrode array configuration and set-up (AC current at 10 kHz) is used. Results show that electrical impedance decreases down to 24% in capillary water absorption tests, 77% and 86% in salt-spray chamber and wet/dry cycles with 3.5% NaCl solution, respectively. The two new low-clinker cements adopted seem to improve the measurement sensitivity towards contaminants ingress with respect to the commercial one (reference).

The project, VERAM "Vision and Roadmap for European Raw Materials", aims to deliver a mapping of on-going initiatives on non-food, non-energy raw materials (including metals, industrial minerals, aggregates and wood) at European, Member State, and regional levels both from the Research and Innovation (R&I), industry, and policy perspectives. Moreover, based on a comprehensive gap analysis, VERAM will propose a common long term 2050 Vision and Roadmap in coordination and cooperation with all stakeholders across the value chain. For the first time, two European Technology Platforms (ETPs) together with their corresponding European Research Area Networks (ERA-NETs) are joining forces to develop a common roadmap.