Joan Llorens

The degradation of the natural fibers in the hydraulic binder alkaline matrix is widely known. This study investigates the effect of two fiber treatments, namely immersion in sodium hydroxide (NaOH) solution and hornification, in two types of alkaline environmental ordinary Portland cement (OPC) and a mixture of OPC and natural hydraulic lime (NHL). After curing for 28 days, the specimens were subjected to 25 and 50 dry–wet aging cycles to evaluate their degradation behavior. Subsequently, the specimens underwent flexural and compressive strength tests. This study reveals that the specimens with the mixed binder of ordinary Portland cement (OPC) and natural hydraulic lime (NHL), after 50 aging cycles, reached toughness values in the descending branch compared to the total toughness obtained in the flexural–displacement diagram, of 17% and 27% for the treatment with NaOH and hornification fiber, compared to 3% and 10% obtained for the matrix with an OPC binder. Therefore, the inclusion of NHL as a matrix binder provided better softening behavior than those with only the OPC binder, providing better protection of the fibers against environmental alkalinity due to matrix alkalinity. In addition, the hornification treatment better preserved the fibers throughout the aging process.

Dry-stone structures are traditional constructions that are present everywhere around the world, with their stability working mostly by gravity. Contrarily to their in-plane behavior, their out-of-plane response is very brittle and is fully controlled by the geometry, as well as the contact properties, between units (stones). Two main local failure modes of dry-joint contact are identified to lead to the global failure of the structure: (i) sliding and (ii) joint opening. Most of the existing studies investigated full structures to obtain the global response and/or couplet only, with the aim of only characterizing the contact. The present experimental work studies the effect of sliding and joint opening between stones at different scales: couplets, structures made of a few (up to five) blocks, and full walls, as well as varying the way the masonry units are assembled within a single structure. Different stones are employed to quantify potential differences. All the structures are loaded up to the collapse with a tilting table to induce out-of-plane actions. Repeatability tests are also conducted to better understand the effect of contact variability. This study unveils that the heterogeneity of the dry-joint contact, as well as the repartition of the blocks, affects the global response (both in terms of load capacity and failure mode). It also confirms that the most critical local failure mode is produced by the joint opening.

There is growing emphasis on developing green composites as a substitute for oil-based materials. In the pursuit of studying and enhancing the mechanical properties of these composites, tensile tests are predominantly employed, often overlooking the flexural properties. This study focuses on researching the flexural properties of abaca-fiber-reinforced bio-based high-density polyethylene (BioPE) composites. Specifically, composites containing 30 wt% of abaca fiber (AF) were treated with a coupling agent based on polyethylene functionalized with maleic acid (MAPE). The test results indicate that incorporating 8 wt% of the coupling agent significantly improved the flexural strength of the composites. Thereafter, composites with AF content ranging from 20 to 50 wt% were produced and subjected to flexural testing. It was observed that flexural strength was positively correlated with AF content. A micromechanics analysis was conducted to evaluate the contributions of the phases. This analysis involved assessing the mechanical properties of both the reinforcement and matrix to facilitate the modeling of flexural strength. The findings of this study demonstrate the feasibility of replacing oil-based matrices, such as high-density polyethylene (HDPE), with fully bio-based composites that exhibit comparable flexural properties to their oil-based counterparts.

Composite materials containing natural reinforcement fibers, generally called biocomposites, have attracted the interest of both researchers and manufacturers, but the most environmentally advantageous combinations include a bio-based matrix, as well. With this in mind, a poly(lactic acid) (PLA) matrix was reinforced with natural fibers from hemp, both untreated strands (UHSs) and soda-bleached fibers (SBHFs). The preparation of the subsequent fully bio-sourced, discontinuously reinforced composites involved kinetic mixing, intensive single-screw extrusion, milling, and injection molding. Up to a fiber content of 30 wt%, the tensile modulus increased linearly with the volume fraction of the dispersed phase. Differences between SBHFs (up to 7.6 Gpa) and UHSs (up to 6.9 Gpa) were hardly significant (p = 0.1), but SBHF-reinforced composites displayed higher strain at failure. In any case, for the same fiber load (30 wt%), the Young’s modulus of PLA/hemp biocomposites was greater than that of glass fiber (GF)-reinforced polypropylene (5.7 GPa), albeit lower than that of PLA/GF (9.8 GPa). Considering all the measurements, the contribution of each phase was analyzed by applying the Hirsch model and the Tsai-Pagano model. As a concluding remark, although the intrinsic tensile modulus of SBHFs was lower than that of GF, the efficiency of those natural fibers as reinforcement (according to the rule of mixtures) was found to be higher.

The use of untreated natural fibers to reinforce cementitious composites improves their environmental friendliness, resulting in a more sustainable material. Moreover, the influence of the untreated natural fibers on the hydration process of Portland cement composites presents some uncertainties. According to the literature, the most usual tests to analyze the degree of hydration of cement composites are the differential thermal and thermogravimetric analyses (TGA/dTGA). Several authors propose to analyze data methods to establish the degree of hydration of cement composites. This paper presents the TGA/dTGA test carried out on mortar samples with and without fibers at age 2, 3, 7, 14, and 28 days. The degree of hydration was calculated according to Bhatty’s method. To characterize the raw materials, the quantitative chemical was determined using scanning electron microscopy and energy dispersive X-ray spectroscopy (SEM–EDX). The main findings of this study were that the presence of untreated natural hemp fibers in the OPC composites increased the hydration degree by 9%. The presence of fibers affected the formation of several components. Thus, their presence increased the formation of monosulphate, reduced portlandite, did not affect ettringite, and increased the formation of calcite, thereby improving the sustainable footprint due to the increased CO₂ fixation.

In this study, experimental analysis on the compressive strength of multi-leaf thin-tile masonry is presented. A compressive strength test was carried out on thin-tile, mortar and 48 specimens with two- and three-leaf thin-tile masonry. The results obtained were compared with literature on brick masonry loaded parallel to a bed joint. Based on the results of this study, the failure mode presented the first crack in the vertical interface; this crack grew until the leaf was detached. From this point until collapse, lateral buckling of the leaves was generally observed. Therefore, the detachment compressive strength value was considered relevant. Up to this point, both masonries exhibit similar stress–strain behavior. The experimental values of the detachment compressive strength were compared with the values calculated from the equation generally used in the literature to evaluate the compressive strength of brick masonry. From the results obtained, the following conclusion can be drawn: This equation is only suitable for tree-leaf thin-tile masonry but with more relevant influence on the compressive strength of the mortar. This study concluded that only three-leaf specimens behave similarly to brick masonry loaded parallel to a bed joint. Finally, whether the failure mode was due to shear or tensile stresses in the vertical thin-tile-mortar interface cannot be identified.

Due to its high biocompatibility, bio-degradability, and low cost, cellulose finds application in disparate areas of research. Here we focus our attention on the potential applications of cellulose nanofiber in cement-based materials for the building sector. We first describe the chemical/morphological composition of cellulose fibers, their process and treatment, the characterization of cement-based composites, and their flexural strength. In recent research in this field, cellulose has been considered in the form of nano-sized particles, i.e., cellulose nanofibers (CNF) or cellulose nanocrystals (CNC). CNF and CNC are used for several reasons, including their mechanical and thermal properties, their extended surface area and low toxicity. This study presents some potential applications of lignocellulosic micro/nanofibers (LCMNF) in cement-based composites in order to improve flexural strength. Samples were made with 0.5-1.0-1.5-2.0 wt% of LCMNF obtained from pine sawdust, CEM I (Portland) and a 1:3 cement-water ratio. The composites were then tested for flexural strength at 7, 14, and 28 days and the evolution of flexural strength was assessed after water immersion during 72 h. Scanning electron microscopy was employed to visualize the bond between LCMNF and the cement matrix. Results showed that LCMNF improved the flexural strength of the composite in all the dosages used.

Brick masonry is a very widely used building method. A specific example of use of this masonry is the thin-tile vault. This is characterised by the format of several layers joined together with mortar and in which the position of the bricks means that they bear the load on edges. The main objective of this study is an assessment, based on experimental results, of clay brick masonry behavior when the load is applied parallel to the face of the bricks instead of perpendicular thereto. This study compares the stress-strain behavior, failure modes, compressive strength, and Young’s modulus of this type of masonry with data obtained from scientific literature.