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Traditional Portland cement-based composites have a great environmental impact. Alkali-activated binders can offer an alternative, particularly if they can be obtained even partially from waste. Two residuals derived from the finishing steps of the traditional ceramic industry have been used as possible polymerizable sources mixed with metakaolin. Moreover, to contrast the low dimensional stability of alkali-activated materials and their mechanical brittleness, natural fibers derived from the Arundo donax plant have been added to the mortars. The use of renewable natural fibers instead of synthetic ones can contribute a further environmental advantage. The fresh (consistency) and cured (mechanical) properties of composite materials prepared with residuals and metakaolin were analyzed here. For comparison's sake, a reference set of composite materials not loaded with fibers but with an identical binder/sand and liquid/binder ratio was cast. A room-temperature curing condition was selected that, although inadequate to promote the short-time reactivity of the wastes, has a minimal energy requirement and allows on-site applications. A small-scale decrease in the properties in the compression mode tests was observed in the waste-modified mortars, while the Arundo addition improved their flexural strength and dimensional stability. [ABSTRACT FROM AUTHOR]

The internal structures and the hygroscopicity of bio-based boards consisting of giant reed (Arundo donax L.) and hazelnut shells as bio-aggregates, and a sodium silicate solution as the adhesive, were investigated. The aim was to evaluate the influence of each material (the bio-aggregates and adhesive) and their distributions in the boards on the final performance. By carrying out X-ray computed tomography, the internal structures and the porosities of the boards were determined, allowing important considerations of their hygroscopicity. The voids' percentages were between 26% and 36% of the total volume of the composites. Both the materials and the composites demonstrated high hygroscopicity. In particular, the mixtures of the bio-aggregates and the sodium silicate allowed reaching a moisture buffering value of 7.44 g/(m2%RH) for the A. donax-based composite, 3.86 g/(m2%RH) for the hazelnut-shell-based composite, and 4.65 g/(m2%RH) for the mixture-based composite. Besides the identification of the contributions of the materials, a detailed discussion of the assessed properties was carried out to use these bio-based boards in vernacular historic construction. The results show how the aggregate type and the adhesive content affected the final behavior, demonstrating the importance of a conscious material choice. Furthermore, helpful information for the future development of these types of bio-based boards and their possible optimization was provided. [ABSTRACT FROM AUTHOR]

There is an increasing need for the use of materials with low carbon emissions, especially in the construction sector, which is responsible for a large amount of emissions. In this perspective, bamboo can play a crucial role; it grows very fast and is an effective carbon sink, having good mechanical properties. It has been used for millennia in specific contexts and territories, such as scaffolding in Asia. This paper aims to demonstrate how bamboo scaffolding can be a viable option in Europe as well. Two prototypes of scaffolding are calculated for the refurbishment of two- or three-story buildings, a common typology in European urban and extra-urban residential areas. The dimensions of the considered scaffolding are 1.8 m and 1.0 m for bay lengths and 1.5 m and 0.8 m for bay lifts. The bamboo considered in the analysis grows in temperate climates, dimensionally smaller in diameter and thickness than tropical ones. Connections play a crucial role, and this paper proposes simple steel connections that are easily removable and suitable for standardized assembly processes already available on the market. [ABSTRACT FROM AUTHOR]

Natural fibers were used to modify alkali-activated fly-ash mortars. Arundo donax is a common, fast-growing, widespread plant with interesting mechanical properties. Short fibers of different lengths (from 5 to 15 mm) were added at a 3 wt% ratio to the binder amount to the alkali-activated fly-ash matrix. The possible effects on the fresh and cured properties of the mortars deriving from the different lengths of the reinforcing phase were investigated. The flexural strength of the mortars increased by up to 30% at the longest fiber dimensions, while the compressive strength remained almost unchanged in all of the compositions. The dimensional stability was increased slightly upon the addition of the fibers, depending on the fiber length, while the porosity of the mortars was reduced. Moreover, contrary to what was expected, the water permeability was not increased by the fibers' addition, irrespective of their length. The durability of the obtained mortars was tested through freeze–thaw and thermo-hygrometric cycles. The results obtained so far underline a fair resistance to the changes in temperature and moisture and a better resistance to the freeze–thaw stresses of the reinforced mortars. [ABSTRACT FROM AUTHOR]

One of the main concerns in using natural materials in construction, such as bamboo, regards their durability. Ultra violet (UV)irradiation is claimed as a damaging agent; therefore, it is important to study its effect. Several studies have shown that bamboo components such as lignin are subjected to photochemical degradation, but it is not well understood how this affects the mechanical properties of bamboo. The aim of this paper is to explore the correlation between photodegradation and bamboo mechanical performance. Bamboo samples were exposed to accelerated UV ageing for different times (from 6 to 360 h) and then subjected to a four-point bending test. Since one of the ways to stabilize bamboo is to thermally treat it, the tests were conducted on natural untreated bamboo and treated bamboo with a traditional flame treatment. Modifications of the chemical features of the material were analyzed with Fourier Trasform Infra Red (FTIR) spectroscopy, while modifications of the morphological features were analyzed byEnvironmental Scanning Electron Microscopy ESEM and optical microscopy observations. The results show that the bending behavior of bamboo is not compromised by UV exposure up to 360 h. In fact, although a progressive degradation of lignin is reported and cracks in the fiber walls are highlighted from micrographs, no effects were found on the fiber length. [ABSTRACT FROM AUTHOR]

Featured Application: Geopolymers formulated with different types of natural fibers with improved mechanical proper-ties can be obtained and used in civil engineering applications. The performance of different natural fibers (hemp, kenaf and bamboo) used to formulate composites with an alkali-activated matrix based on metakaolin is evaluated. Short fibers were randomly dispersed up to about 3% of the binder weight, and the fresh and cured properties of the derived composites were determined. Up to the investigated fraction, it is still possible to obtain adequate workability without the supply of additional water or additives. Upon modification with fibers, the mechanical behavior changes from completely brittle to pseudoplastic with increased toughness. The flexural strength increases by up to 80% at the highest bamboo amount and up to 20% for kenaf. Hemp fibers have a negligible effect on flexural strength but strongly improve the materials' toughness. Moreover, the addition of fibers does not change the manner in which the material interacts with moisture. Indeed, the water uptake of the modified samples was comparable to that of the unmodified samples, and the composites showed a decreased rate of water diffusion as the amount of fiber increased. [ABSTRACT FROM AUTHOR]

The drying of porous media is of major importance for civil engineering, geophysics, petrophysics, and the conservation of stone artworks and buildings. More often than not, stones contain salts that can be mobilized by water (e.g., rain) and crystallize during drying. The drying speed is strongly influenced by the crystallization of the salts, but its dynamics remains incompletely understood. Here, we report that the mechanisms of salt precipitation, specifically the primary or secondary nucleation, and the crystal growth are the key factors that determine the drying behaviour of salt contaminated porous materials and the physical weathering generated by salt crystallization. When the same amount of water is used to dissolve the salt present in a stone, depending on whether this is done by a rapid saturation with liquid water or by a slow saturation using water vapor, different evaporation kinetics and salt weathering due to different crystallization pathways are observed. [ABSTRACT FROM AUTHOR]

We develop a phase-field model for the liquid-vapor phase transition. The model aims to describe in a thermodynamically consistent way the phase change phenomenon coupled with the macroscopic motion of the fluid. The phase field describes the liquid fraction at any point and the overall water density is a function of the phase field and the pressure. An extra gaseous substance (e.g. air) is allowed in the system and contributes to the mechanical pressure. The phase transition is described by a Ginzburg-Landau equation. The parameter that drives the transition is the partial vapor pressure, which is the relevant quantity for condensation and evaporation phenomena. Moreover, a velocity-dependent term contributes to the phase change in the transition layers where a vapor pressure gradient exists. [ABSTRACT FROM AUTHOR]

A phase-field–based model has been employed for numerical tests on the mechanical response of a shape memory alloy. The model consists of a time-dependent Ginzburg–Landau equation for a scalar order parameter describing the local phase of the material (austenite or martensite), coupled with the balance of linear momentum and the heat equations; the mechanical effect of the martensitic phase transition is described in terms of a uniaxial deformation strain along a fixed direction, making the model suited for predictions over monodimensional specimens. A number of numerical simulations under stress-controlled conditions have been performed to investigate the mechanical behaviour of the model; the results obtained are analysed in relation to the experimental evidences available in the literature and previous investigations under strain-controlled conditions. [ABSTRACT FROM AUTHOR]

The building heritage of many seismic regions worldwide is largely substandard and seismically deficient and would require seismic retrofitting interventions. The use of natural materials with low embedded emissions could lead to a low carbon footprint of the retrofitting intervention. In this perspective, an innovative structural sustainable retrofitting system is proposed consisting of a hybrid steel–bamboo reticular bracing system. Through a preliminary two-dimensional analysis, the capabilities of the system are assessed by varying the size and the number of the culms and inserting engineered bamboo and steel rods. Considering the constraints posed by the openings, a structure that uses steel in the first inter-storey and bamboo in the others is proposed to obtain a significative improvement of mechanical performances. The spatial behaviour of this structure is studied through a three-dimensional numerical model. The seismic analyses show that the exoskeleton structure when conveniently anchored allows to achieve an effective displacement and deformation control on the primary structure, as well as a reduction of its internal forces. The results of the presented work may provide useful preliminary insights. Further research effort is needed to generalize the results to different seismic zones. The proposed seismic retrofitting system could be easily integrated with a thermal coat to also enhance energy saving. [ABSTRACT FROM AUTHOR]

Permeable pavement provides sustainable solutions for urban stormwater management. In this research, the potential of rice bran mixed porous clay bricks were evaluated for permeable pavements. Physical, mechanical and hydrological properties along with stormwater treatment capabilities of the brick samples were assessed. The study found that ratio of rice bran and clay soil has significant impacts on the properties of the produced bricks. Water adsorption and porosity increased with increasing rice bran ratio. Compressive strength of brick samples decreased from 29.6 MPa to 6.9 MPa when the ratio of rice bran was increased from 0% to 20%. The permeability coefficient increased from 4 × 10−4 to 1.39 × 10−2 mm/s with the increase in rice bran from 0% to 30%. The preamble clay bricks were efficient to remove turbidity, total suspended solids (TSS), five days' biochemical oxygen demand (BOD5), and heavy metals (Mn, Cu, and Zn) from stormwater to meet the World Health Organization (WHO) standard for wastewater reuse application. The bricks with ≤10% of rice bran achieved the American Society for Testing and Materials (ASTM) standard of the desire compressive strength and permeability coefficient for pedestrian and light traffic pavements. The porous bricks prepared in this study can be used to construct permeable pavements and would be a sustainable low impact developments technique for stormwater management in urban areas. [ABSTRACT FROM AUTHOR]

One of the main concerns in using natural materials in construction, such as bamboo, regards their durability. Ultra violet (UV)irradiation is claimed as a damaging agent; therefore, it is important to study its effect. Several studies have shown that bamboo components such as lignin are subjected to photochemical degradation, but it is not well understood how this affects the mechanical properties of bamboo. The aim of this paper is to explore the correlation between photodegradation and bamboo mechanical performance. Bamboo samples were exposed to accelerated UV ageing for different times (from 6 to 360 h) and then subjected to a four-point bending test. Since one of the ways to stabilize bamboo is to thermally treat it, the tests were conducted on natural untreated bamboo and treated bamboo with a traditional flame treatment. Modifications of the chemical features of the material were analyzed with Fourier Trasform Infra Red (FTIR) spectroscopy, while modifications of the morphological features were analyzed byEnvironmental Scanning Electron Microscopy ESEM and optical microscopy observations. The results show that the bending behavior of bamboo is not compromised by UV exposure up to 360 h. In fact, although a progressive degradation of lignin is reported and cracks in the fiber walls are highlighted from micrographs, no effects were found on the fiber length.