Experimental evaluation of adobe mixtures reinforced with jute fibers

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Highlights

  • Varying dosages/lengths of Jute fibers (JFs) are incorporated in adobe mixtures (AMs).

  • Negatively, high JF dosages increase the capillary water absorption of AMs.

  • JFs do not affect the compressive and flexural strength of AMs.

  • JFs improve the thermal/cracking control/toughness/water erosion performance of AMs.

  • The combination of 2.0 wt%-15 mm JFs presents the best performance among AMs.

Abstract

Due to their sustainability as well as physical and mechanical performance, different natural fibers, both vegetal and animal fibers, have been successfully used in adobe mixtures (AMs) to enhance properties such as cracking control, flexural toughness and water erosion resistance, among others. However, the use of jute fibers (JFs), one of the most largely produced vegetal fiber worldwide, has not been extensively studied on AMs. Consequently, this study evaluates the effects of the incorporation of varying dosages (0.5 and 2.0 wt%) and lengths (7, 15, and 30 mm) of JFs on the physical/thermal/mechanical/fracture and durability performance of AMs, a specific type of earth-based construction material widely used globally. Experimental results showed that the incorporation of 2.0 wt% dosages of JFs increased the capillary water absorption of AMs, which might affect AM durability. The latter result could be explained by the additional porosity generated by the spaces left between the JFs and the matrix of adobe, as well as the inherent water absorption of the JFs. The incorporation of JFs significantly improved the behavior of AMs in terms of thermal conductivity, drying shrinkage cracking control, flexural toughness and water erosion performance, without affecting their compressive and flexural strength. For example, flexural toughness indices were increased by 297% and crack density ratio as well as water erosion depth values were reduced by 93% and 62%, respectively, when 2.0 wt%-15 mm length JFs were incorporated into AM. Since the latter combination of JF dosage and length provided the overall best results among AMs, it is recommended by this study as JF-reinforcement scheme for AMs for construction applications such as adobe masonry and earth plasters.

Introduction

Numerous civilizations have used earth-based construction materials (EBCMs) for centuries to obtain reliable and comfortable housing solutions due to their availability, low cost and sustainability, among other advantages [1]. Still nowadays, almost 30% of the global population lives in EBCM houses, and raising up to a 50% in developing countries [2]. Considering that the current world population is approximately 7.8 billons, with a projection of 8.5 billion by 2030 [3], and predictions estimating that most of the population growth will be in developing countries in the following decades [4], the world will continue facing a housing deficit challenge. Specifically in developing countries, the lack of economic resources, fast-growing rate of carbon emissions, and the necessity to import construction materials like steel and cement, pressure governments to find alternative solutions to the aforementioned housing deficit problem [4]. In terms of construction materials, the steel and cement industries produce approximately 12% of global CO2 anthropogenic emissions, which is the largest percentage among construction materials [5], and the need for more sustainable construction materials has been pointed out by many studies [6], [7], [8], [9]. Thus, the use of EBCMs could help mitigating part of the aforementioned challenges, including both housing deficit as well as environmental impacts derived from the production of construction materials [10], [11].

The performance of adobe, a specific type of EBCM, has been subjected to study during the past decades in terms of its durability, mechanical performance, and thermal behavior, among other properties. The use of natural and synthetic micro-fibers (i.e. fibers with lengths and diameters less 20 mm and 0.025 mm, respectively [12]) as reinforcement of adobe has been investigated as a solution to improve the properties of adobe mentioned before. As for natural fibers, the use of jute fibers (JFs) to reinforce adobes is of special interest since jute is one of the cheapest and most produced vegetable fiber worldwide [13]. The use of JFs as reinforcement of earth has been mostly related to the stabilization of soils [14], [15], [16], [17]. Yet, there are limited results about the use of jute as reinforcement of EBCMs like adobe that raise the interest of researchers in late years. Islam and Iwashita [18] studied the compressive strength and toughness performance of plain adobe and adobe reinforced with JFs (1.0 cm long and dosages of fibers from 0.5% up to 4% by weight of soil). The latter study showed that dosages up to 1% of JF did not reduce the compressive strength and slightly increased the compressive toughness when compared to plain adobes. The authors showed that while dosages from 2 to 4% of JFs increased the compressive toughness of reinforced adobe, they also reduced its compressive strength compared to plain adobes. Ahmed and Lucas [19] assessed the effect of JFs (0.1% to 0.5% of JFs by weight of the adobe mix) on the bulk density and compressive strength of adobes. The authors found that there was small reduction on the bulk density of reinforced adobes with the largest JF dosage, whereas there was not impact on the compressive strength of JF-reinforced adobes, with respect of plain adobe. Concha-Riedel et al. [20] assessed the effect of adding different lengths (7, 15 and 30 mm) and dosages (0.5 and 2% by weight of soil) of JFs on the flexural and impact strength as well as the distributed cracking density of adobe mixtures (AMs). They found increments in both flexural strength and impact resistance of adobe mixtures with 2% of JFs as well as a reduction of the distributed cracks, even for low dosages of JFs. Although there are additional studies also assessing the influence of JFs on the compressive performance of EBCMs [21], [22], there are still important properties in terms of durability, mechanical and thermal performance of JF-reinforced AMs that have not been studied yet.

First, durability can be associated with different responses of AMs, one of them is delaying macroscopic cracks formation, which can be achieved incorporating fibers into the mixture. Millogo et al. [23] suggested that the incorporation of short hibiscus cannabinus fibers could delay the propagation of cracks in reinforced adobe. The use of animal fibers in AMs [24] was also reported to be effective controlling restrained drying shrinkage cracking, increasing impact resistance, and fracture toughness without changes on the average compressive and flexural strength compared to plain AMs. Overall, depending on factors such as fiber aspect ratio, mechanical properties, and morphology there are additional studies indicating that natural as well as synthetic fibers can improve fracture properties of AMs [20], [25], [26]. Water erosion of EBCMs is also a variable affecting the durability of AMs. For instance, EBCM walls could show signs of erosion on the top and the bottom part if there is not adequate protection against water exposure [27]. For the latter reason, researchers have developed different ways to test water erosion [27], one that is particularly effective and not too aggressive for adobe is exposing its surface to a constant drip for a certain period of time [28]. EBCMs are also susceptible to water absorption coming from groundwater, condensation, and wind-driven rainfall [29]. As the overall absorption of EBCMs could be increased by the incorporation of natural fibers (due to cluster formation and fiber water absorption [30]), consequently, another important feature that affects the durability of EBCMs is capillary water absorption. Second, the mechanical performance of fiber-reinforced EBCMs depends widely on the mechanical and morphological characteristics of the fibers. As such, Binici et al. [31] showed that the use of plastic fibers could increase the average compressive strength of reinforced adobe over the use of straw and polystyrene fibers. Ghavami et al. [32] showed that EBCMs reinforced with sisal and coconut fibers did not change their average compressive strength. Araya-Letelier et al. [24] reported the effect on average compressive strength of AMs reinforced by varying dosages and lengths of pig hair. The latter study shows that on most of the AMs tested there were no significant effect on their compressive strength caused by the addition of fibers; except for the AM with the highest dosage (i.e.; 2% of fiber by weight soil) and the largest length of fiber (30 mm) that presented a reduction of average compressive strength of 40% with respect to the plain AM caused mainly by fiber clustering. Other studies [25], [33] have also showed that the use of micro fibers, while well mixed and in dosages and lengths that do not generate fiber clusters, do not affect the mechanical strength of EBCMs, yet fiber-reinforcement might increase toughness of EBCMs. Third, current research has proven that the addition of natural fibers has a positive influence on the thermal performance of EBCMs. Particularly, morphological aspects of natural fibers such as the diameter and length, as well as their content, play an important role in the thermal conductivity of the AMs [34]. For instance, Olacia et al. [35] evaluated the thermal conductivity on AMs with straw and seagrass fibers. The main results showed a general reduction in the thermal conductivity; up to 24% and 19% for AMs with the highest concentration of long straw and seagrass fibers, respectively. Additionally, Millogo et al. [23] proved that adobes with high contents and long lengths of Hibiscus cannabinus fibers reduced the thermal conductivity up to 20% compared to a reference sample, without fibers. Taallah et al. [36] concluded that the addition of high contents of palm fibers in compressed earth blocks reduced the thermal conductivity up to 11.4% compared to a sample without fiber addition. These studies also proved that the results of the thermal conductivity were strongly influenced by the physical and hygroscopic properties of the composite earth material, such as density, porosity, and moisture content.

Despite the need of more sustainable EBCMs, to the best of the authors’ knowledge, there have not been studies addressing the influence of JFs on capillary water absorption, thermal conductivity, concentrated drying shrinkage cracking, a detailed flexural toughness evaluation (including digital image correlation, DIC, techniques) and water erosion of AMs. Consequently, the study of those properties represents the novelty of this work, whose goal is to evaluate the effect of different dosages and lengths of JFs on the: (i) physical (i.e.; capillary water absorption, and thermal conductivity); (ii) mechanical (i.e.; compressive and flexural strength); (iii) damage (i.e.; concentrated restrained drying shrinkage cracking, and flexural toughness); and durability (i.e.; water erosion) performance of AMs. Additionally, scanning electron microscopy (SEM) pictures of JFs and the matrix of adobe and energy-dispersive X-ray spectroscopy (EDS) analyses are obtained to make correlations between the microstructure and chemical composition of reinforced AMs with their macroscopic response.

Section snippets

Materials: Soil and JFs

The particle size distribution of the soil used for this work was obtained by a hydrometer analysis, following the standard ASTM D7928-17 [37] for the fraction of soil finer than 75 µm and larger than 0.2 µm, and a sieve analysis, following the standard ASTM D6913/D6913M-17 [38], to determine the particle size distribution for the fraction of soil above 75 µm. The resulting gradation curve is shown in Fig. 1.

To further characterize the clayey soil used in this study, liquid and plastic

Capillary water absorption

Fig. 6 shows the water absorption raise due to capillarity of representative AM specimens at 1 day. Results show that AM J-0.5-7 mixture had no significant differences when compared to AM J-0, whereas AMs J-0.5-15 and J-0.5-30 showed slightly larger values of water raise than AM J-0. On the other hand, all AMs with 2.0% of JFs (i.e.; J-2.0-7, J-2.0-15 and J-2.0-30) presented larger water raise values when compared to AM J-0 and also exhibited a minor trend where water raise increased

Final comments and conclusions

This research evaluated the effectiveness of jute fibers (JFs) as fiber reinforcement of adobes mixtures (AMs) intended for earth-based construction. In particular, six different JF-reinforced AMs were confectioned combining two JF dosages (0.5 and 2.0% of JFs by weight of clayey soil) and three JF lengths (7, 15, and 30 mm) and these JF-reinforced AMs were compared to a seventh plain AM used as control. In detail, the experimental program carried out evaluated the effect of different dosages

CRediT authorship contribution statement

G. Araya-Letelier: Conceptualization, Resources, Funding acquisition, Methodology, Validation, Investigation, Writing - original draft, Writing - review & editing. F.C. Antico: Conceptualization, Methodology, Writing - review & editing. C. Burbano-Garcia: Investigation, Visualization, Writing - original draft. J. Concha-Riedel: Methodology, Writing - review & editing. J. Norambuena-Contreras: Conceptualization, Methodology, Validation, Investigation, Visualization, Writing - original draft. J.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

This research was partially funded by grant PIA-3581-050/Pontificia Universidad Católica de Chile and this support is greatly acknowledged. Also, the authors would like to thank Matias Gutierrez, René Santelices and the technical staff at the laboratory of teaching and research of the School of Civil Construction where most of this research was conducted. FCA thanks Wladimir Vergara for his support with sample preparation at the laboratory of Civil Engineering of Universiad Adolfo Ibáñ.

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