Innovative Bio-composite Sandwich Wall Panels made of Coconut Bidirectional External Veneers and Balsa Lightweight Core as Alternative for Eco-friendly and Structural Building Applications in High-risk Seismic Regions

The research that constitutes this paper is based on a series of publications that aimed at understanding, from an engineering perspective, the optimised mechanical efficiency of senile coconut palm stem-tissues as foundation for non-traditional building applications. Particularly, this study aims at determining, evaluating and analysing the mechanical properties of lightweight bidirectional sandwich-like structure wall panels made of balsa core material and coconut external veneers. To achieve these objectives, 10 test specimens cut from prototype panel 1 (1200 mm high, 600 mm wide and 124 mm total thick) and 10 test specimens cut from prototype panel 2 (1200 mm high, 600 mm wide and 74 mm total thick) were investigated under mechanical and seismic behaviours in accordance to the current American Society for Testing and Materials (ASTM) building standards. Preliminary results show that the proposed wall panels are up to two and three times more efficient, in terms of mechanical high-performance, than equivalent sections of solid wall bricks and concrete block walls, respectively. Therefore, the innovative panels constitute a feasible alternative to reduce/replace typical construction materials (e.g. steel, concrete and bricks) with a significant positive environmental impact that fully address current engineering requirements. These bio-panels are meant to be used as important non-traditional elements during the rebuilding process of low-rise and mid-rise residential buildings that were dramatically affected during the 2016 Ecuador earthquake. Introduction Building collapse or damage is one of the major causes for earthquake injuries and fatalities. The catastrophic Ecuador earthquake in April, 2016, left approximately 35,300 affected dwellings, out of which about 19,500 resulted totally destroyed or demolished. Tragic result of it, around 670 people died and 6,300 individuals were injured [1, 2]. Despite some advantages (e.g. fire By-Products of Palm Trees and Their Applications Materials Research Forum LLC Materials Research Proceedings 11 (2019) 88-98 doi: https://doi.org/10.21741/9781644900178-5 89 resistance and durability) offered by traditional building structures made of typical materials (e.g. steel, concrete, bricks) [3], their partial failure or total collapse during extreme seismic events can lead to critical consequences as hereinabove mentioned. It has been estimated that during the 2016 Ecuador earthquake, many casualties occurred, not only by the structural framing collapse effect, but greatly by the overbalance masonry effect as shown in Fig. 1. Moreover, typical manufactured structural materials all involve very substantial use of energy during their production process, which in turn involves high generation of CO2 to the atmosphere. Indeed, building with steel or concrete is 20 and 9 times, respectively, more CO2 emissions intensive (i.e. compared on mass basis) than structural timber [4, 5]. Fig. 1. Overbalanced brick masonry recorded during the 2016 Ecuador earthquake occurred on April 16, with a moment magnitude of 7.8 and a maximum VIII severe Mercalli intensity. Adapted from [6] Unfortunately, part of the Ecuadorian area affected by the earthquake is currently being rebuilt using the same traditional building methods and materials. The curious aspect of the rebuilding process is that huge amounts of concrete and steel are daily transported to the construction project sites whereas massive plantations of biomaterials surrounding the zone (e.g. coconut palms and balsa trees) are totally disregarded. These observations were the driven force behind the work in this investigation, which aims at addressing the hereinabove stated problems by proposing innovative bio-composite structural wall panels as alternative for masonry construction that makes the most of both fundamentals: (1) the enhanced performance of engineering wood products, cross laminated timbers, specifically, and (2) the optimal mechanical efficiency [7-9], in terms of mechanical performance (i.e. high strength versus moderate stiffness) per unit mass; the optimal mechanical efficiency that is best represented in biomaterials by either a sandwich-like structure (e.g. coconut stem tissues) or a tubular-like structure (e.g. bamboo culms) [10]. Materials and equipment Two wall panel types were built in this study: prototype panel 1 (1200 mm high, 600 mm wide and 124 mm total thick) and prototype panel 2 (1200 mm high, 600 mm wide and 74 mm total thick). The prototype panels resemble a complex sandwich-like structure (see Fig. 2) that is made of two different biomaterials: (1) Ecuadorian balsa hardwood (Ochroma pyramidale) as core material [11], and (2) Ecuadorian coconut palmwood (Cocos Nucifera L) veneers as external boards. The balsawood core material was used in the form of the BALTEK® SB.100 product due to its high level of stiffness to weight ratio [i.e. Avg. Moduli of Elasticity (MOE) perpendicular to the plane of 2,526 MPa for an equivalent basic density of 148 kg/m at an Avg. Traditional masonry wall collapse or partial damage is one of the major causes for earthquake injuries and fatalities By-Products of Palm Trees and Their Applications Materials Research Forum LLC Materials Research Proceedings 11 (2019) 88-98 doi: https://doi.org/10.21741/9781644900178-5 90 moisture content of 12.6%). BALTEK® core material was acquired from the local supplier 3AComposites. Each external board (i.e. one board per external side of each panel as shown in Fig. 2) comprises three coconut veneers glued each other bidirectionally with acrylic vinyl resin following the same principle of cross laminated timbers (CLT) that are used for wall building purposes [12]. Coconut veneers were obtained by peeling process [13] of the peripheral section (Avg. MOE parallel to the fibers of 8,920 MPa for an equivalent basic density of 900 kg/m at an Avg. moisture content of 12.6%) of three mature coconut palm stems. 2-component Polyurethane adhesive (Pur 2C) was used to glue the external coconut boards with the BALTEK® core material. Once fully assembled and glued, each prototype panel were hotpressed at 400 psi and 100 ̊C for about 30 minutes. Fig. 2. Sandwich-like structure wall panel made of Ecuadorian balsa lightweight core and coconut bidirectional external veneers. Methods The research scope of the whole investigation includes the following tests: compression, bending, shear, tension, cyclic assessment, hardness, fire resistance, acoustic isolation, resistance to pathogens, glue and ply-delamination. Yet, only the first two mechanical modes with the corresponding determination of basic density and moisture content properties are included as part of the present paper. Specifically, this paper presents results from (1) axial stiffness and strength in compression and (2) bending strength in flat-wise four-point loading. The mechanical tests were all carried out in an AGS-X Shimadzu universal testing machine (UTM) 300 kN capacity equipped with a non-contact digital video extensometer to measure deformations. Moreover, the acquired results for each mechanical mode were double-checked by pilot testing on selected samples using 5 mm long single-element strain gauges glued on the longitudinal-radial (L-R) external faces (refer to Fig. 3a) of each sample using adhesive cyanoacrylate ester and coated with instant repair epoxy resin/tertiary amine. The experimental equipment was complemented with Wheatstone bridge circuits to connect the strain gauges, a data logger (National Instruments NIcRIO-9074) and a computer for data processing. Before testing and after sanding, each sample was labelled according to the mechanical mode to be investigated. Experimental tests were performed at room temperature and humidity. Axial stiffness and strength in compression According to the ASTM C364/C364M-16 Standard Test Method for Edgewise Compressive Strength of Sandwich Constructions, a total of 10 compressive tests were carried out on 5 smallBy-Products of Palm Trees and Their Applications Materials Research Forum LLC Materials Research Proceedings 11 (2019) 88-98 doi: https://doi.org/10.21741/9781644900178-5 91 clear panels cut from prototype 1, nominal size of 250 mm × 250 mm × 124 mm, and on 5 smallclear panels cut from prototype 2, nominal size of 150 mm × 150 mm × 74 mm (refer to Fig. 3).