Elsevier Editorial System(tm) for Acta Biomaterialia Manuscript Draft Manuscript Number: Title: Microstructural and Mechanical Characteristics of Pressed Adobe Blocks reinforced with Hibiscus cannabinus Fibres Article Type: Full Length Article Keywords: Hibiscus cannabinus fibers; Pressed Adobe Blocks; Microstructural characteristics; Physical and Mechanical Characteristics, Sustainable building material Corresponding Author: Dr Jean-Claude Morel, Corresponding Author's Institution: ENTPE First Author: Younoussa Millogo Order of Authors: Younoussa Millogo; Jean-Claude Morel; Jean-Emmanuel Aubert; Khosrow Ghavami Abstract: This paper presents the results of an investigation on pressed adobe blocks (PABs) reinforced with 0.2 to 0.8 wt.% of 3 and 6 cm lengths of Hibiscus cannabinus fibers from Burkina Faso. The physical and mechanical properties of the PAB composites were established in the laboratory. The microstructural characteristics of the PAB composites were investigated using X-ray diffraction (XRD), thermal gravimetric analyses (TGA), scanning electronic microscopy (SEM) and video microscopy. The results show that the addition of 3 cm long fibers contributed to the reduction of the pore sizes of the PABs and the improvement of the physical and mechanical properties in contrast to the case with the addition of 0.8 wt.% of 6 cm fibers, which had negative effects on the compressive strength. The presence of fibers in PABs improved the behavior of the composite subjected to bending. The improved PAB, except PABs with 0.8 wt.% fibers 6 cm in length, are appropriate for building materials for hygrothermal comfort, according to the standards.
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Microstructural and Mechanical Characteristics of Pressed Adobe Blocks Reinforced With Hibiscus cannabinus Fibers Younoussa Millogoa,b, Jean-Claude Morelb*, Jean-Emmanuel Aubertc, Khosrow Ghavami d a
Institut des Sciences de la Nature et de la Vie (ISNV), Université Polytechnique de Bobo-Dioulasso, 01 BP 1091 Bobo 01, Burkina Faso. b Département Génie Civil et Bâtiment, FRE 3237 CNRS, Ecole Nationale des Travaux Publics de l'Etat, Université de Lyon, Rue Maurice Audin, 69518 Vaulx en Velin cedex, France c Université de Toulouse, LMDC (Laboratoire Matériaux et Durabilité des Constructions), 135, avenue de Rangueil,31 077 Toulouse, France d Pontificia Universidade Catolica (PUC-Rio), Rua Marques de Sao Vicente 225, 22451-041 Rio de Janeiro, Brasil
Abstract
This paper presents the results of an investigation on pressed adobe blocks (PABs) reinforced with 0.2 to 0.8 wt.% of 3 and 6 cm lengths of Hibiscus cannabinus fibers from Burkina Faso. The physical and mechanical properties of the PAB composites were established in the laboratory. The microstructural characteristics of the PAB composites were investigated using X-ray diffraction (XRD), thermal gravimetric analyses (TGA), scanning electronic microscopy (SEM) and video microscopy. The results show that the addition of 3 cm long fibers contributed to the reduction of the pore sizes of the PABs and the improvement of the physical and mechanical properties in contrast to the case with the addition of 0.8 wt.% of 6 cm fibers, which had negative effects on the compressive strength. The presence of fibers in PABs improved the behavior of the composite subjected to bending. The improved PAB, except PABs with 0.8 wt.% fibers 6 cm in length, are appropriate for building materials for hygrothermal comfort, according to the standards. Keywords:
Hibiscus
cannabinus
fibers;
Pressed
Adobe
Blocks;
Microstructural
characteristics; Physical and Mechanical Characteristics, Sustainable building material. 1. Introduction
*
Corresponding author E-mail address :
[email protected] (J.C. MOREL)
1
Formatted: French (France) Formatted: French (France)
During the past three decades, there has been increasing interest in the research and development of nonconventional materials and technologies (NOCMATs), such as local soil, bamboo and vegetable fibers, as ecofriendly materials in a wide range of applications in engineering and in civil construction. Soil has been used in the construction of shelters and houses for thousands of years. At present, approximately 30% of the world’s population still lives in earthen structures [1, 2]. In most developing countries, houses are essentially constructed using locally produced adobe. The binder of this material is composed mainly by the clayey fraction of the soil. Although the traditional application of adobe by local builders goes back thousands of years, their know-how has not been registered systematically for transfer to future generations. As an example of an important aspect of using adobe, at present, it has low mechanical strength in the humid state. Therefore, problems can arise during the rainy period of the year. In Burkina Faso in West Africa, before the introduction of industrial materials, such as steel and concrete, adobe was traditionally stabilized by locally available vegetable fibers. This empirical practice improved the mechanical characteristics of the adobe in different weather conditions. At universities around the world, the emphasis of research and development programs in the past has been directed only to the study of industrialized materials, and thus, the local traditional materials have not been investigated. To improve the mechanical strength and the durability of locally produced adobe, in general, small amounts of quicklime or natural fibers are added to the raw soil material [2-18]. The use of local natural fibers, especially in developing countries, is more beneficial for the population because fibers are locally available in abundance and are cheap. In the available literature, several investigations established the effects of the addition of vegetable fibers such as sisal, coconut, wheat straws, oil palm empty fruit bunches, and lechuguilla on the physical and mechanical properties of soil blocks [2, 4, 6, 7, 10-13, 15-18].
2
In addition to these references, which are mainly about experiments, the literature on soils randomly reinforced by synthetic fibers was reviewed [19-22]. This literature contains some modeling of the reinforcement, which was used previously [23]. According to the analysis of these references, the parameters that determine the relevance of this type of building can be reduced to four: the fiber tensile strength and stability of this characteristic with time (durability), the fiber length and the fiber quantity. The fiber tensile strength directly determines the crack resistance of fiber-reinforced soil. The long-term stability of this feature is not studied in this article, but existing buildings where this type of fiber does not rot in the mix with soil validate it. In addition, PABs are never submerged because of the presence of clay, which means that the building design guarantees that despite the possible drying of the material, the moisture remains sufficiently low not to cause rotting of the fibers. The fiber length determines the pullout resistance of the embedded fiber in the soil matrix and therefore directly determines the reinforcement force, which is less than or equal to the fiber tensile strength. Finally, the amount of fiber determines the intensity of the reinforcement: for small amounts (
