http://dx.doi.org/10.14718/RevArq.2018.20.2.2116
From the faculty
Renato Cassandro-Cajiao
Universidad Católica de Colombia, Bogotá (Colombia)
Faculty of Design
MA in Sustainable Design
Architect, Universidad Católica de Colombia, Bogotá (Colombia). MA in Sustainable Design, Universidad Católica de Colombia, Bogotá (Colombia).
Professor at the Program of Architecture, Faculty of Design, Universidad Católica de Colombia, Bogotá (Colombia).
https://orcid.org/0000-0001-8064-4655
rcassandro@ucatolica.edu.co
Received: May 23/2018
Evaluated: July 30/2018
Accepted: August 13/2018
To reference this article / para citar este artículo / para citar este artigo:
Cassandro-Cajiao, R. (20I8). Structural thermal panel wall composed of guadua and cardboard. Experimental model applied to the climate of the Coffee Region. Revista de Arquitectura (Bogotá), 20(2), 90-109 doi: http://dx.doi.org/10.14718/RevArq.2018.20.2.2116
Abstract
This paper proposes a SIP (Structural Insulated Panel) type composite panel prototype, a structural thermal panel, as a building envelope wall made of renewable natural materials, specifically bamboo and recycled cardboard. The panel consists of two external OSB (Oriented Strand Board) boards, oriented chipboard, and an intermediate cardboard insulation. In the study, two experimental SIP models are developed, using different manufacturing processes, which are analyzed and compared with four commercial references worldwide. All the panels are simulated thermally and acoustically in the climatic and meteorological conditions of the city of Pereira (Risaralda), in order to evaluate and compare the results, demonstrating thus the viability and competitiveness of the proposed prototype. In addition, this study aims to serve as a reference point for future research in the search for better sustainable construction materials.
Keywords: Life-cycle analysis, environmental contamination, construction materials, OSB panel, SIP panel, forest resources, environmental sustainability.
Resumen
Se propone un prototipo de panel compuesto, tipo SIP (Structural Insulated Panel), panel térmico estructural, como muro envolvente de vivienda, elaborado con materiales de origen natural renovables, específicamente guadua y cartón reciclados. El panel se compone de dos tableros externos OSB (Oriented Strand Board), tablero de virutas orientadas, y un aislante intermedio de cartón. En el estudio se elaboran dos modelos SIP experimentales con procesos de fabricación diferentes, los cuales son analizados y comparados con cuatro referentes comercializados a nivel mundial. Todos los paneles son simulados térmica y acústicamente en condiciones climáticas y meteorológicas de la ciudad de Pereira (Risaralda), con el fin de evaluar y comparar los resultados, lo que demuestra la viabilidad y competitividad del panel propuesto. Este estudio espera servir, además, como referencia de futuras investigaciones en la búsqueda de mejores materiales sustentables para la construcción.
Palabras clave: análisis de ciclo de vida, contaminación ambiental, materiales de construcción, panel OSB, panel SIF? recursos forestales, sostenibilidad ambiental.
Resumo
Propõe-se um protótipo de painel composto, tipo SIP (Structural Insulated Panel), painel térmico estrutural, como muro envolvente de moradia elaborado com materiais de origem natural renováveis, em específico bambu e papelão reciclado. O painel está composto de duas placas externas OSB (Oriented Strand Board), placas de aparas orientadas e um isolante intermediário de papelão. Neste estudo, foram elaborados dois modelos SIP experimentais com processos de fabricação diferentes, os quais são analisados e comparados com quatro referentes comercializados no mundo inteiro. Todos os painéis são simulados térmica e acusticamente em condições climáticas e meteorológicas da cidade de Pereira (Colômbia), a fim de avaliar e comparar os resultados, o que demonstra a viabilidade e competitividade do proposto. Este estudo espera servir, além disso, como referência para futuras pesquisas na busca de melhores materiais sustentáveis para a construção.
Palavras-chave: análise de ciclo devida, poluição ambiental, materiais de construção, painel OSB, painel SI Ff recursos florestais, sustentabilidade ambiental.
Content
Introduction
Context
Composite SIP panel
Methodology
Experimental procedure
Results
Referents
Thermal simulation of referents
Acoustic simulation – referents
Experiment development
Model 1
Model 2
Comparative evaluation of results
Thermal insulation
Acoustic insulation
Current situation of the guadua industry in Colombia
Discussion
Conclusions
References
This article presents the results of the research entitled "Panel wall composed of guadua for housing units," which was completed as a degree work to obtain the title of Master in Sustainable Design at the Universidad Católica de Colombia, within the research line of Design and Technology. The project was carried out between 2015 and 2017, and its main objective was to develop a composite wall panel model using renewable natural materials, as a building envelope or exterior wall for housing units in a warm tropical zone.
The continuous growth of world population and its demand for housing makes the construction of dwellings an ongoing research topic that seeks to optimize materials regarding resistance, durability, functionality, economy, low environmental impact, and energy consumption in their life cycle.
Replacing the conventional materials of housing construction with renewable natural materials such as guadua, in places where there are guadua crops and production, is a tangible alternative for social and economic sustainability, since its industrialization will have benefits such as employment generation and low housing construction costs with interior comfort.
The importance of this tree or gramineae in construction and industry in Colombia is evident and has a promising future. According to the engineer Edgar Giraldo (2003, p. 19) and Mejía et al. (2009), "in Colombia, approximately 100,000 people derive their livelihood from the exploitation, management, and commercialization of guadua." Its benefits start with its planting since it is the best CO2 pollutant collector, including also oxygen generation, rapid growth, and multiplicity of applications (construction, textiles, ornamentation, and medicine).
The Regional Autonomous Corporations (CAR, for its initials in Spanish) are the entities responsible for ensuring the care and use of natural resources, through the Single Regulatory Decree of the Environment and Sustainable Development Sector (Decree 1076 of 2015), as well as the Forest Statute of the region, which regulates the exploitation of this and other species. In this case, the entity regulates the sustainable management of guadua from its planting to the execution of projects that allow its development with economic and social benefits for the region with the greatest number of crops, that is, the Coffee Region, which includes the departments of Caldas, Quindío and Risaralda, Tolima and Valle del Cauca (Mejía & Moreno, 2013).
During a field visit in mid-June 2017 to the factories or companies of "Induguadua" in La Tebaida, and "Armeideas en Guadua" in Calarcá, located in the Coffee Region, it was evident that the resulting waste percentage ranged from 30 to 40%, noting that in most cases these are used as fuel for the drying process of the guadua or for the production of coal, which produces a large amount of CO2 and further pollutes the environment. For this reason, it is a priority to propose alternatives for the use of this waste that do not pollute and take advantage of the excellent physical, mechanical, and aesthetic qualities of guadua for a variety of uses.
The global situation due to climate change, environmental pollution, and population increase requires a permanent search for alternatives and more efficient solutions for sustainability regarding production process, manufacturing, use and recycling, and energy consumption reduction, with a minimum production of CO2 emissions and other polluting gases.
The environmental impact and energy consumption of conventional construction materials, such as cement, concrete, clay, and PVC, are a major global concern, which makes it necessary to rethink building architecture by returning to its origins in the construction sector, using local materials with low energy costs and minimal environmental impact.
In the history of Colombia, in informal population settlements around the main cities, guadua has had—and continues to have—a constant and representative presence, which is one of the reasons why it is called with the derogatory term of "wood of the poor" (Colorado, n. d.).
The generalized idea that guadua does not offer security for complex constructions and that its use should be limited only to popular-type dwellings was so influential that architects and engineers ignored, for years, historical testimonies that spoke of a tradition that had been developed since the end of the 19th century, in which bamboo was precisely the preferred material to build and to counteract earthquakes that shook the coffee region and other areas of similar conditions in the country (par. 32).
Today, it can be confirmed that these antecedents awoke in professionals, technicians, researchers, and farmers a futuristic vision towards the use of this natural, renewable, and sustainable resource, which is urgent to be materialized in specific projects.
The research focused on the use of guadua, which grows in specific climatic conditions of the tropical zone, with a warm temperate climate, that make up an important part of the Colombian territory. It is used in construction due to its optimal physical and technical properties, so much so that, from pre-Hispanic times, it was the protagonist (with the native species guadua angustifolia) in the construction of dwellings in small towns and peripheral city areas (Varela & Chaviano, 2013). Guadua, during its transformation process to manufacture poles, canoes, slabs, panels or fibers, produces a large percentage of waste, which are generally used as fuel or transformed into charcoal, which generates greater environmental pollution.
The main function of a building envelope is to maintain constant thermal insulation properties and it includes all the elements that divide or separate the exterior from the interior. Its fundamental purpose is to keep the average internal thermal comfort between 18 and 20 °C.
The specific research objective was to take advantage of the resulting residual material, which means approximately 40% of the guadua culm (Figure 1), and to transform it into strands or flakes for the manufacturing of OSB (Oriented Strand Board) boards, in compliance with international regulations (Garay & Damiani, 2013), in order to form the main external surfaces of a SIP (Structural Insulated Panel) or structural thermal panel (Cardenas et al., 2015) (Figure 2), with an intermediate insulator made of recycled cardboard to be used as a building envelope for housing units in the Coffee Region, replacing thus conventional materials and offering a sustainable alternative.
Figure 1. Elements extracted for construction
Source: Own elaboration, 2017, CC BY.
Figure 2. Lightweight composite panel "Eurolight," from the Egger manufacturer company
Source: Egger Inspiración Eurolight (2016, p. 3).
The industrialization of products based on residual or waste wood has solved many problems of raw-material deficit worldwide, and has opened up the opportunity to increase its applications, exalting qualities such as high resistance coefficient and thermal properties, which is reflected in its increased production from 12 million m3 in 1950, to 125 million m3 at present (Fernández, 1993). One of these products is OSB boards, also known as sterling board.
These boards are a relatively new product. The United Nations Organization for Food and Agriculture (FAO), in its statistical database, has global data on OSB, which show a 7% growth in production and commercialization in 2015 compared to the previous year, due to a growing trend towards eco-sustainable production (FAO, 2016). In spite of this, there is no production of OSB boards in Colombia, and the demand is very low, probably due to a lack of knowledge about OSB boards as a construction alternative, as well as to industrialization processes. Experience in other countries shows that these boards are a real, sustainable, and efficient alternative for light, fast, and resistant construction.
Currently, the materials of a SIP type composite panel (structural insulation panel or thermal structural panels) consist of two external boards made with flakes or strips of pine or fir wood (OSB), pressed and joined using chemical adhesives and oriented in the longitudinal sense, as well as two internal ones, placed in the perpendicular sense (Figure 3). Additionally, they have an internal core that functions as a thermal insulation, usually in polystyrene (Arquigráfico, 2016).
Figure 3. Cross orientation of strips in an OSB board
Source: Arquigráfico (2016).
OSB boards are usually sold in a 244 x 122 cm (8x4 ft) format, with a thickness between 7 and 18 mm. Its main uses in construction are as bases for roofs, beams, joists, floors, stairs, as well as exterior and interior wall panels, among others.
OSB boards, according to their characteristics and specifications, are classified into four groups, recognized by manufacturers worldwide; regarding consumption, it is OSB-3 that has been standardized for the specific use of panel in a building envelope wall; and it is the one used for this research. The uses of the four groups are described below:
OSB-1. Interior use, basically furniture. It is the most basic range and its commercialization is currently very limited.
OSB-2. Load-bearing applications in dry environments.
OSB-3. Load-bearing applications in relatively humid environments; it is the most used type of board, with the best quality-price ratio.
OSB-4. High load-bearing performance in relatively humid environments (Santana, 2015).
The most used internal insulation in SIP panels is EPS (expanded polystyrene) sheets, which consist of 98% air and 2% polystyrene. The thermal insulation capacity of a material is defined by its thermal conductivity; its unit is W/(mK) and depends on the material's density (kg/m3). Therefore, thermal conductivity is higher in low-density sheets; it decreases as density increases and reaches a minimum above 30 kg/m3 (Grupo Isotex, 2015).
Expanded polystyrene has no low temperature limit, while the maximum allowable temperature depends on exposure time (Figure 4). In case of short exposure, it can withstand temperatures higher than 100ºC. However, during longer periods of exposure, it tends to deform and lose its rigidity.
Figure 4. SIP system, components
Source: Klasspanel (s. f.).
The research considered, in the first instance, antecedents and similar products that exist on the market today, using an experimental-descriptive method to examine the specific characteristics of panels employed in a specific place and climate, which are virtually simulated by means of thermal and acoustic softwares to describe their performance. Additionally, laboratory tests were carried out that complemented the proposed models, regarding resistance to horizontal and vertical load, and acoustic absorption.
It is important to clarify that the scope of this research is limited to the realization of laboratory test models that allow evaluating thermal and acoustic behavior, weight, and horizontal and vertical resistance, to be compared with the values indicated by each manufacturer on the technical sheets, according to the regulations of their respective country of origin (Apa's Corporate, 2015). This, without taking into account all the characteristics of the final product, which would require more time and economic resources.
Figure 5, which corresponds to the conceptual map of the development of this research, shows the parallel processes that were carried out between referents and proposals to address the adjustments or drawbacks of each proposal.
Figure 5. Conceptual map of the development of this research
Source: Own elaboration, 2017. CC BY.
1. Selection of four referents shown in Table 1. These were defined according to several aspects: their similarity in terms of dimensions regarding total thickness (approximately 100 mm), materials of the boards (agglomerated wood), as well as the specific use of panels as an exterior wall or building envelope (objective of the proposed model). In addition, they should be among those with the largest commercial representation internationally.
Table1. Characteristics of the reference SIP panels
Source: Own elaboration, 2017.
2. Realization of thermal and acoustic simulations for each referent (Table 2), by means of the THERM 7.5 and dBKAisla 3.01 softwares, taking as climatic data those of the city of Pereira (Risaralda), which was selected due to being one of the biggest growers and consumers of guadua for construction in the Colombian Coffee Region, with technological, social, and environmental advances in the region. As for the thermal characteristics of the product, data were collected from technical sheets, which in turn correspond to internationally authorized and standardized tables regarding the thermal properties of construction materials (Arquimaster, n. d.).
Table 2. Results of heat transfer through two-dimensional conduction according to panel components
Source: Own elaboration, 2017.
3. Development of two experimental models with the support of the companies Muiskay SAS in Bogotá and Primadera SAS in Cachancipá (Cundinamarca) for the production of OSB boards with guadua strips, following the general characteristics of the referents in terms of dimensions and thickness, and using the proposed basic materials of guadua strips and recycled cardboard.
4. Thermal and acoustic simulations for the experimental models using the THERM 7.5 and dBKAisla 3.01 softwares, with climatic data from the city of Pereira (Risaralda).
5. Laboratory tests of compression and acoustic resistance for the two proposed models.
6. Preparation of comparative tables, with the results obtained in the simulations of referents and experimental models.
7. Results and discussion. Comparative analysis of thermal and acoustic behavior.
8. Conclusions.
The starting point for this study is a theoretical framework built on documentation and bibliographic sources on SIP panels (composed of OSB boards and intermediate insulation), as well as their historical antecedents, materials, technical characteristics, and classification according to international specifications.
The four most representative referents on the international market are selected (Table 1), taking into account only those characteristics (thickness, dimensions, materials, weight, resistance, and thermal transmission) and uses that are similar to the ones proposed in this research. Data for each SIP panel, necessary for the simulation, were obtained from the specifications and technical sheets of each manufacturer, which usually reports the U-value (thermal transmission) and R=1/U (thermal resistance), through global knowledge and application tables (Arquimaster, n. d.; Vagge & Czajkowski, 2012), indicating total thickness and composition as well.
The total thermal transfer of the SIP panel is the sum of the values of its components: exterior OSB board + insulation + interior OSB board.
This table collects main thermal data for each SIP panel, necessary for the simulation, which were obtained from the specifications and technical sheets of each manufacturer, showing as a generalized characteristics the use of a polystyrene insulator and two OSB boards, made of pine or fir strips.
For the analysis and simulations, the maximum and minimum temperatures with annual averages were taken into account, as well as precipitation and relative humidity, data extracted from Ideam and Meteonorm for the city of Pereira. It is worth noting that a unique physical-spatial wall condition is sought, with a relationship between the interior and the exterior (inside-outside), without considering any specific space or environment, since it would have variables of all kinds such as: type of terrain, roof, fenestration level, etc., and the objective here is to examine the specific individual contribution of the panel.
An average annual relative humidity of 76.5% and an average rainfall of 228 days/year are factors that directly affect the values of resistance to humidity for the panel (Weather Atlas, 2016). Due to this, reference panels are categorized as OSB-3 boards (according to the European Standard UNE-EN 300), designed to work in humid places, which basically refers to the adhesive with waterproofing action used in the manufacturing of facade panels or building envelopes. Data about the resistance, thickness, and weight per square meter of the referents were also taken into account, in order to compare them with the experimental models.
Thermal simulation of referents
The results obtained in four referents—without considering thermal bridges since the panel is intended to be adapted to existing or particular structures of different characteristics—present minimal variables due to their similar constitution. Their internal temperature difference in response to external conditions indicates comfort
values with average differences that range from 2.1 to 2.8 °C at low or minimum temperatures, and an average decrease of 3.2 to 4.0 °C at high or maximum temperatures (Table 2).
Acoustic simulation - referents
Noises are generally composed of pressure variations of different frequencies. The human auditory system is capable of hearing sounds of frequencies in the range of 20-20,000 Hz. Insulation, in all cases, is an ascending constant that presents less noise absorption when frequency increases (Table 3). Its variations are minimal since the absorption level is directly related to the density of materials and their thicknesses, which in this case are very similar and are p resented as a reference range for the product.
Table 3. Acoustic simulation of referents. Software dBKAISLA
Source: Own elaboration, 2017.
Materials
a) Guadua fiber flakes (Figure 6), made with the waste of the manufacturing process of panels, canoes, slivers and other cuts that are sold for crafts and construction. In this case, they were obtained through the company Induguadua S.A, located at Kilometer 15 via Armenia-La Tebaida.
Figure 6. Recycled guadua fiber and recycled cardboard tubes
Source: Own elaboration, 2017, CC BY-ND.
b) Adhesive for the formation of boards. Pegatex, Carpincol 2500: high-concentration water-based PVA (polyvinyl acetate) synthetic adhesive.
c) Recycled cardboard toilet paper tubes. These were collected for approximately two months, in the homes of family and friends (Figure 6).
d) Adhesivo PVA - 60 adhesive glue to unite the three layers.
e) Exterior waterproofing varnish for permanent contact with humidity.
Manufacturing
The procedure carried out for its manufacturing is not standardized (in the countries where it is produced) with respect to the adhesive used or the type of pressing. What is intended here is to look for an alternative of non-toxic adhesives and lower energy consumption during the pressing.
All the flakes were immersed in Pegatex Carpincol 2500 adhesive, and oriented according to the specifications given for OSB boards, then cold pressed under a pressure or load of 30 MPa (1 MPa = 10.2041 kg-f/cm2) for 3 hours and 40 minutes. They were extracted then in order to apply another layer of PVA adhesive and pressed again for 6 hours and 35 minutes.
• Drying: natural ventilation for 48 hours.
• Application of Deva-TARIMEX waterproofing varnish.
• Assembly of insulation with double cardboard tubes, recycled toilet paper, glued to the external panels with Carpincol 2500.
• Total assembly of the composite panel and final drying (Figure 7
).Figure 7. Manufacturing process of the OSB board, Muiskay company
Source: Own elaboration, 2017, CC BY-ND.
• Deva-TARIMEX waterproof varnish application.
Characteristics
Table 4 shows the main characteristics of the Model 1 composite panel.
Table 4. Model 1: Proposed composite panel
Source: Own elaboration, 2017.
Thermal simulation
An average internal temperature of 17.6 °C is observed with respect to external mínimums of 15.8 °C, resulting in an increase of 1.91 °C. With respect to average maximum external temperatures of 26.3 °C, it decreases to 23.2 ºC with an interior/exterior difference of 2.86 ºC, which is basically due to the vacuum generated by the recycled cardboard tubes of toilet paper rolls, disposed in a double way to give greater resistance, located as insulation inside the panel (Table 5).
Table 5.Thermal simulation Model 1
Source: Own elaboration, 2017.
Acoustic simulation
The acoustic simulation shows constant ascending insulation levels in the panel, without variations at 40 acceptable decibels, according to noise, and frequencies between 50 and 250 Hz, the permitted levels being between 55 and 65 decibels. The insulation reaches frequencies up to 1,750 Hz within the acceptable limit, but it does not represent values different from those shown by the referents, only a greater absorption constant in decibels, an average auditory tolerance. The structure of external OSB boards that generates spaces between strips allows a number of sound waves to penetrate through them (Table 6).
Table 6. Acoustic simulation Model 1
Source: Own elaboration, 2017.
Laboratory tests
Acoustics. Acoustic absorption was measured in the laboratory of the Universidad Católica de Colombia, simulating a closed interior space with a cardboard box of one cubic meter volume, placing on one of its sides the experimental model. For internal measurement, a sound level meter was used that recorded decibels according to the applied external noise, at lower frequencies through a noise generator amplifier that indicates frequency as database (Figures 8 and 9).
Figure 8. Procedure of acoustic simulation in laboratory
Source: Own elaboration, 201 7, CC BY.
Figure 9. Equipment used for the Acoustics Laboratory of the proposed panels.
Source: Own elaboration, 201 7, CC BY.
Table 7 shows the results obtained, which reflect external frequency, external and internal noise, and difference, in order to find average acoustic insulation (Figure 10), which showed a difference of 11.88 dB as a result of an absorption percentage that ranges from 18 to 20%, which is representative considering that in a housing unit there are additional elements that make up spaces such as ceilings, roofs, windows, floors, etc.
Table 7. External noise level versus internal level and absorption percentage
Source: Own elaboration, 2017.
Figure 10. Internal insulation results with regard to exterior values
Source: Own elaboration, 2017.
Tests of resistance to compression. A universal single-column tension and compression testing machine (Figure 11) was used to subject the model panel to compression, which showed resistance to the limit of deformation without breaking.
Figure 11. Equipment (hydraulic press) used to test horizontal and vertical load resistance
Source: Own elaboration, 2017, CC BY.
The values obtained, both in vertical and horizontal load testing, are in the range indicated by the selected referents from the global construction market. The panel functions as a non-structural element and its resistance to stress is linked to its function as an envelope (Table 8).
Table 8. Horizontal and vertical resistance test
Source: Own elaboration, 2017.
Materials
a) Guadua fiber strips or shatters as a residue from the manufacturing of panels, canoes, slivers and other cuts that are commercialized as building elements, obtained through the company Induguadua, Armenia-La Tebaida.
b) Adhesive for the formation of boards: urea-formaldehyde.
c) Insulation: triple honeycomb cardboard sheet or Honeycomb board (Table 9) T = 31 mm each; Manufacturer Perlad SAS.
Table 9. Model 2, panels. Technical sheet
Source: Own elaboration, 2017.
d) Adhesive Carpincol 2500-Pegatex to unite the three layers.
e) Varnish (transparent solvent-based urethane) for wood exteriors..
Manufacturing
This model was developed following the main guidelines currently used by manufacturers (Apa's Corporate, 2015), with the only difference of changing pine and fir strips for guadua strips (Figure 12):
Figure 12. Manufacturing process of test samples and board
Source: Primadera SAS, 2017.
• Selection of guadua raw material in flakes or strips (T = 0.6/1.2 mm) with dimensions of 10 to 20 mm wide and 15 to 30 mm long, suitable for manufacturing OSB boards, with a humidity up to 5% through convection oven.
• Cluing the particles with urea-formaldehyde resin with the following specifications: 1,270 kg/m3 density; 65% solids, forming the layers of the board, which is put into a mono-floor press at a temperature of 210 °C, with a specific pressure of 42 kg/cm2 and a pressing time of 4 min. Finally, physical-mechanical tests are carried out in a universal machine, to measure the properties of internal bonding and the modulus of elasticity and rupture.
Due to the technology used in this case, the resulting board is closer to an agglomerated wood board than an OSB board. Therefore, the results presented high physical-mechanical properties, as experienced in agglomerated wood boards.
Characteristics (Table 9)
Thermal simulation
Average internal temperatures similar to Model 1 are observed; with regard to external minimums of 15.8 ºC, there is an increase of 1.92 ºC, while in maximum temperatures, an average decrease of 2.85 ºC is observed, which is basically due to good thermal insulation produced by the vacuum between the honeycomb cells in recycled cardboard. This represents important values of internal temperature control, as a fundamental part in the housing comfort of a building (Table 10).
Table 10. Thermal simulation Panel 2
Source: Own elaboration, 2017.
Acoustic simulation
Acoustic simulation values (Table 11) show constant ascending insulation levels in the panel, without variations at 40 acceptable decibels, according to noise, and frequencies between 50 and 250 Hz. Within the permitted levels between 55 and 65 dB, insulation reaches frequencies up to 1,750 Hz within the acceptable limit, but these values are not different from those shown by the referents, only a greater absorption constant in decibels of average auditory tolerance.
Table 11. Acoustic simulation Panel 2
Source: Own elaboration, 2017.
Laboratory tests
Acoustics. Table 12 shows an average absorption of 13.14 dB and an average acoustic insulation of 15 to 20%, a representative percentage that is basically due to the density and compaction of OSB boards, which increases their insulation quality.
Table 12. External noise level compared to the interior of the panel and its absorption percentage
Source: Own elaboration, 2017.
Resistance to compression. When subjecting it to compression, the model panel presented resistance to the limit of deformation without breaking. The values obtained, both with a vertical load of 518 kg and a horizontal load of 1,970 kg, are within the acceptable values in the studied referents (Table 13). The boards presented greater strength and less deformation, but the internal insulation system in cardboard collapsed, which resulted in crushing with horizontal load and a greater resistance with vertical load.
Table 13. Horizontal and vertical resistance test for Model 2
Source: Own elaboration, 2017.
Comparative evaluation of results
Results were evaluated comparing thermal and acoustic simulations, both for referents and the manufactured experimental models, indicating their efficiency in comfort level and allowing an objective and conclusive measurement.
With regard to thermal insulation, the values obtained (Table 14) indicate that both referents and experimental models maintain a relative homogeneity in internal comfort levels. Those with a minimum temperature between 17.71 and 21.9 °C stand out as the best (Model 2), and those with a temperature between 17.38 and 22.38 °C as the most unfavorable (LP SIP, Chile).
Table 14. Thermal simulation results
Source: Own elaboration, 2017.
Insulation levels, according to the norm of acceptable decibels, indicate that Model 2 maintains the same conditions as referent 1 according to what is presented in Table 14, although some of the referents have insulations with higher frequencies, product of denser insulators, but made with petroleum derivatives. Similarly, among the experimental models (Table 15), better levels are observed in Model 2, due to cardboard density and the hermetic nature of the hexagonal composition of the Honeycomb cardboard.
Table 15. Results of acoustic simulations
Source: Own elaboration, 201 7.
Current situation of the guadua industry in Colombia
The protagonist in the current environment for the industrialization of guadua is the following legal framework: Law 99 of 1993, "By which the Ministry of Environment is created, the Public Sector in charge of the management and conservation of the environment and renewable natural resources is reordered, the National Environmental System, SINA, is organized, and other dispositions are dictated;" Resolution 1740 of 2016, "By which general guidelines are established for the management, use, and establishment of guadua and bamboo farms, and other provisions are dictated;" Icontec Standards NTC 6100 (2014), "type I environmental labels. Colombian environmental stamp. Environmental criteria for products of first and second degree transformation of guadua angustifolia Kunth," and the forest self-certification given by the Forest Stewardship Council (FSC); entities and standards that guarantee the quality and future of the project.
On the other hand, the private organizations of guadua farmers have allowed certain integration in search of technification and better socioeconomic and environmental conditions (Figure 13). The manufacturing of the product is projected, in the first instance, for consumption by the inhabitants of the Coffee Region and for a future expansion of its market, with the alternative of using not only residual, but also recycled materials.
Figure 13. Conceptual framework applied to the transformation of guadua
Source: Own elaboration, 2017, CC BY.
The research supports the manufacturing process of SIP panels using unconventional materials such as guadua waste strips and recycled cardboard; the results of resistance to compression and thermal and acoustic insulation demonstrate that they are a viable and competitive product compared to those that are now on the market, as well as a sustainable alternative under passive energy principles.
Manufactured SIP panels have two major unfavorable and unsustainable aspects: the use of polystyrene (derived from petroleum) as an internal insulator and phenol-formaldehyde (synthetic resin) as an adhesive applied in high percentages.
Guadua strips as main raw material must reach a dryness between 4 and 5% humidity to guarantee adhesion between strands through pressing. In addition, for its transformation into flakes of specific dimensions and diameters, it requires the prior selection of residual or recycled materials.
In Model 1, the OSB board has a good aesthetic texture and clearly shows the cross-arrangement of strips or flakes (Figure 14), but lower hardness as well, with a horizontal resistance of 1,040 kg/m2, and a vertical resistance of 418 kg/m2, similar to the values indicated by the referents. The adhesive (polyvinyl acetate, PVA) requires greater fixation over the strips since they are very rigid and resistant fibers that leave spaces or cavities among them. However, in the assembly of the SIP panel, its thermal insulation results of +2.90 °C at high temperatures, and -1.9 °C at low temperatures, present very similar values, and also show that recycled cardboard tubes used in the study are a good alternative as thermal and acoustic insulation.
Figure 14. Composition of the reference OSB boards and proposals 1 and 2
Source: Own elaboration, 2017, CC BY.
Model 2 had a greater compaction of guadua strips in the elaboration of the OSB board; for this, it was necessary to mix the strips with other very fine sawdust-like guadua particles to fill up the free spaces between crossed flakes, using phenol-formaldehyde in smaller percentages, in order to avoid its toxicity.
Results evidenced greater horizontal (1,970 kg/m2) and vertical resistance (518 kg/m2), but with irregular texture and lower percentage of flakes in its exterior finish (Figure 14), which is a typical characteristics of OSB boards. In the conformation of the SIP panel, the intermediate insulation of Honeycomb cardboard produced lower values in terms of acoustic absorption.
Similarly, with a weight of approximately 19 kg per square meter, the prototypes are within the average weight of the referents, allowing thus their easy handling for transportation and assembly.
For a sustainable construction, it is necessary to implement different strategies in the selection of materials, manufacturing, assembly, and operation that demonstrate a significant decrease in the C02 emission of the construction product, in this case, during its life cycle from the collection and classification of waste, its transformation, manufacturing, use, and further recycling.
It should be noted that in Colombia regulations are aimed at the manufacturing of agglomerated boards with wood particles, but not at manufacturing with OSB-type strips, which is absent in the country and, consequently, SIP panels of this type are not produced either. Consequently, the results of thermal, acoustic, and resistance factors are compared and validated with the values of experimental laboratory test samples, according to the information provided on the technical data sheets of the referents.
Based on these premises, this research aims to present an alternative that serves as a model in the use of local renewable natural resources that are transformed, manufactured, and used with low environmental impact. In this case, society in the specific place of the study is linked to agricultural economy represented by coffee production, where guadua appears as a protagonist of socio-cultural heritage in the construction of housing units, recognized in turn as part of the identity of the social fabric and its collective memory.
The composite panel wall completes its entire life cycle in the same place for local people, from the recycling of waste material to its transformation, industrialization, commercialization, construction, use and further recycling, in such a way that, for obvious reasons, its energy consumption decreases given that it does not require large amounts of energy for its manufacture and transportation throughout its life cycle.
Finally, data obtained from the experimental models showed that, for the region in question (tropical, warm, wet), thermal envelope becomes a system of heat conservation (night) and cooling (day), maintaining temperature and acoustic insulation, while it is also a passive energy contribution of air conditioning for comfort.
In addition, it is possible to think about further adjustments in the manufacturing and adaptability of existing structures and models to be built, which will have to be considered as the next stage in the development of this research. In this sense, the initial objective was to propose assembly products with renewable natural materials for architectural integration, always within the philosophy of sustainable construction in favor of the quality of life.
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