Key Engineering Materials Vol. 916

Abstract: There has been considerable attention drawn to the application of textile reinforced mortar (TRM) composites for strengthening existing masonry and concrete structures. These composites are made from textile fibers embedded in an inorganic matrix and act as externally bonded reinforcement (EBR). Therefore, a careful observation must be made of the bond of the mortar to the substrate and the bond of the mortar to the textile. Despite numerous studies of the bond behavior of TRM composites conducted in recent years, no constitutive bond behavior law under cyclic loading has been determined. In most available studies, the most common method of testing TRM-to-substrate bonds is the single-lap shear test. Contrary to that, the bond performance of fibers to mortar has received little attention and has been the subject of this study. This paper describes a laboratory study investigating the textile's interfacial bond behavior to the mortar fiber under cyclic loading. It was shown that cycling can cause a loss in strength, which varies with the number of cycles.

Abstract: Despite all the advantages of applying natural fibers in structural composites, their expected short life span constitutes a challenge due to their hydrophilicity and deterioration in alkaline lime or cement matrices. The present paper proposes eco-friendly hydrophobic coatings to protect natural fibers in lime mortars resorting to polymers reinforced with hydrophobic beeswax micro colloids. The physical, mechanical and chemical characterization suggest the potential of the coated fibers for NTRM casting and further investigation of their interface and bond behavior with the mortar.

Abstract: In the last decade, textile-reinforced mortar (TRM) composites have been introduced as a sustainable solution for the strengthening of masonry structures. As an externally bonded reinforcement system, it consists of textile fibers embedded in an inorganic matrix (e.g., lime or cement mortar) applied to the substrate. Even though many studies have been focused on characterizing the mechanical behavior of TRM composites in recent years, there are still some drawbacks, including their tensile performance and few studies about multilayer textiles arrangement. This work aims at clarifying the effect of adding a second textile layer to TRM composites and investigating how textile arrangement affects the tensile behavior of the composite system. For this purpose, AR-glass and steel-based TRM composites were used in single layer and multilayer with different arrangements embedded in a lime-based mortar. The results show that using two plies of textile mesh improves the tensile response of TRM composites. In addition, it is found that the arrangement of different layers in the matrix influences the TRM response in different stress stages. The addition of a thin layer of mortar between two layers seems to improve the stiffness in uncracked condition and slightly decreases the final strength of TRM. Thus, the present study makes a step toward optimizing the arrangement of textiles in multilayer TRM composites.

Abstract: Over the decades, innovative techniques have been introduced and developed in the building heritage which make use of composite materials whose main objectives are bending and shear reinforcement, increasing ductility and limiting cracks. The use of composite materials with steel, carbon, glass and aramid fibers are already codified in the technical standards, now the challenge is the use of more sustainable materials. This paper focuses on a simple and effective bamboo fibers reinforcement of structural and non-structural commercial products such as mortar and plaster with different mechanical characteristics, trying to improve ductility without worsening their strength and mechanical stiffness. In particular, a plaster and a mortar with 2% (by weight) of bamboo fibers of Phyllostachys Iridescens species has been analyzed. A mechanical characterization is carried out evaluating flexural strength, compressive strength and fracture energy. The effectiveness of the reinforcement is shown through the comparison with the unreinforced materials.

Abstract: This paper aims at investigating the matrix-to-textile stress transfer in a fabric reinforced cementitious matrix FRCM system, not bonded to any substrate, under shear loads. To this end, direct shear tests are performed on a basalt FRCM specimen introduced into an innovative properly designed four-hinge frame loaded by a universal testing machine. The role of the single components in the global shear behavior of the FRCM is experimentally analyzed. Digital image correlation (DIC) is adopted for evaluating both the displacement and strain fields as well as for detecting the damage. Furthermore, the shear response of the tested FRCM material is reproduced via an effective numerical approach that considers the nonlinear behavior of the mortar and the possible micro-mechanisms that arise between the textile and the matrix, introducing suitable interfaces joining the FRCM constituent layers, i.e. textile and mortar layers. Experimental outcomes highlighted the non-negligible influence of the matrix in the shear response of the composite, both in strength and stiffness. The proven DIC technique demonstrated to be suitable also for this novel test type, since it allows to obtain shear strains, location and amplitude of cracks with satisfying accuracy, such as to make direct shear tests results a benchmark to be used for numerical simulations. Numerical analyses are performed in order to verify the efficiency of the proposed model in reproducing the mechanical behavior of FRCM composites under shear loads and in describing the damage patterns during the loading process.

Abstract: On 3DPC, the layers are made through a process where the cement mortar is extruded through a nozzle that follows a predetermined circuit. The classic method of formwork generates a uniform element, while 3D printing generates a non-homogeneous element. Such an innovative process offers new horizons to explore. One of these is the cohesion between the two printed layers and all their mechanical properties. The objective of this work is to study the shear action of two printed layers. To understand the mechanisms, the tested specimens were made in four different ways. The first using a formwork made for the occasion. The second way involves the creation of a printed specimen with a continuous printing path. The third has a time interval of about an hour between the second and third layer. The fourth also has an interval of one hour between the same layers with the addition of a special additive mortar used for the casting recovery. The results obtained reflect on the differences between different specimens and regulations. The differences between the specimens that are studied concern the single printed specimens, the formwork specimens and the printed ones. At a regulatory level, the results of the printed specimens are compared with the regulations concerning the same tests carried out on specimens made of masonry and mortar.

Abstract: Water with dissolved contaminations is a frequent problem faced in porous building materials such as masonry, or cement-based composites. It regards both contemporary constructions, and those belonging to the cultural heritage. Among soluble salts, sodium sulfate is recognized as one of the most dangerous one. Since crystals of Na₂SO₄ can occur in the variety of forms, its crystallization in pores of a building material is a challenging and not fully recognized issue. The main object of the presented research is to identify the consecutive phase transitions occurring within red clay brick containing sodium sulphate solution during cooling. The first stage of an experimental investigation was performed by means of mercury intrusion porosimetry to verify whether cyclic crystallization has a damaging effect on material microstructure. In the second step of experimental analysis differential scanning calorimetry was applied. The technique was used to monitor the crystallization of sodium sulphate confined in samples during repeating cooling-heating cycles covering temperature range from -20°C to 40°C. It was observed that during primary crystallization, sodium sulfate heptahydrate is the first precipitating phase and the transition begins far below its equilibrium temperature. Subsequently, the heptahydrate transforms into mirabilite, which probably induced rapid ice crystallization. Nevertheless, if decahydrate nuclei are provided in pore solution, sodium sulphate precipitates directly as mirabilite with no heptahydrate formation. Such a pattern is observed for both analysed solution concentration, i.e. 25% and 30%.

Abstract: In various countries, a variety of waste by-products are disposed-off to the local environment, mostly due to lack of innovative initiatives for their utilisation. With human population growing strongly in most developing countries such as in Africa etc., lack of housing has become an endemic concern exacerbated by poverty and unaffordability of conventional construction products. Geopolymer technology provides new insights and possibilities into potential utilisation of a variety of mining and industrial waste by-products, currently being dumped in landfills leading to environmental pollution. This paper focusses on mining and industrial waste products that are currently not being utilised. In South Africa, mine tailings and bottom ash, also colloquially referred to “ash dumps”, exist in enormous quantities. Moreover, some of these waste products are presently an environmental menace responsible for discharge of acid mine drainage found in different geographical locations. The present study reviewed the potential utilization of mine tailings for brick making based on geopolymer technology. Also discussed are risks, hinderances and challenges to waste utilization including lack of public confidence attributed to radioactivity of some tailings-based brick products. While drawing from literatures worldwide, emphasis is placed on environmental and economic benefits of utilising these otherwise disregarded waste materials, to meet local societal needs of poor communities.

Abstract: Geopolymers are known to be environmentally – friendly construction materials that can be used in different applications including concretes and mortars, fire – resistant coating materials, road pavements and masonry units. Despite the economic and environmental – related benefits of utilizing geopolymer products, the production of these materials is also associated with some challenges and difficulties that need to be resolved for the technology to gain recognition and acceptability in the construction industry. In this paper, publications were reviewed to provide some understanding of the problems and challenges of geopolymer brick production. Composition of alkali activator along with curing temperature, are major factors that significantly influence the production cost of geopolymer bricks. Also, incorporation of calcium - rich co - binders into geopolymer mixtures, may lead to reduction in durability resistance of the brick product.

Abstract: Experimental tests proved that the external confinement of masonry columns through Fiber-Reinforced Polymers (FRP) induces increment of axial strength and ductility. Contrary to FRP-confined concrete, for which reliable unified theoretical stress-strain models are available in literature or included in the codes, to develop easy-to-use constitutive models valid for whatever type masonry represents a difficult challenge. In fact, several parameters influence the axial stress-strain response of confined masonry, such as the relative mortar-to-stones strength, masonry texture, deformation capacity of materials, type of reinforcement ad its arrangement. In this paper, a design-oriented stress-strain model devoted to describe the compressive behavior of FRP-confined clay-brick masonry columns is presented. The main scope of the research consists of providing an easy-to-use predictive model, applicable both in the research field and design practice. The stress-strain response of the confined masonry has been idealized in a parabola-rectangular behavior described by Lam and Teng’s equations - originally developed for FRP-confined concrete - adapted to masonry elements. The equations are ruled by the mechanical properties of confined and unconfined masonry, those of composite material and by a parameter that takes into account the dispersion of the experimental data (i.e., variability of materials properties, different stone arrangements and masonry textures). The entire stress-strain behavior has been calibrated by means of the least-squares optimization criterion, based on a sufficient number of experimental results available in the literature. Comparisons between experimental and theoretical stress-strain curves show good accordance of the results. The design-oriented model is able to capture the experimental response of the confined masonry, in terms of initial elastic stiffness, ductility ad maximum confinement pressure.