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There is growing interest in applying external reinforcement to existing structures using advanced materials such as composite (fiberglass, basalt, carbon) rebar, which can impart exceptional strength. Worldwide, there are a number of brands of composite rebar recognized by different countries, such as Aslan, DACOT, V-rod, and ComBar. The number of projects using composite rebar increases day by day around the world, in countries ranging from USA, Russia, and South Korea to Germany.
=== Bamboo Reinforced Concrete ===
Bamboo reinforced concrete (BRC) is a natural composite material composed of bamboo strips as an alternative to steel reinforcement used in traditional concrete structural design. With up to 90 genera and 1500 species of bamboo³, the material has the potential to serve as an environmentally friendly, high-strength and low-weight alternative to other types of reinforcement seen in traditional concrete design. Physical in-lab work, technological softwares, and case studies using life cycle assessment were performed in order to understand how bamboo is an ideal candidate for structural applications. In one study, bamboo reinforced concrete, itself, was tested under various conditions (by varying longitudinal reinforcement, treatment, and texture) to compare the varied strengths more narrowly within the material¹. Additionally, through both experimental testing and artificial neural networks (ANN) using the MATLAB interface², plain concrete (PC), steel-reinforced concrete (SRC), and bamboo reinforced concrete (BRC) were compared for a deepened study of its tensile strength and deflections under loading. In a final study, physical applications and LCA environmental analysis of bamboo compared to timber, steel, and plain concrete highlight the strengths as to why bamboo should be highly considered as a promising new alternative for sustainable construction³. However, given the plentiful research already completed, it is evident that further analysis is needed to optimize the design and performance of BRC, and to better understand its long-term durability as a construction material.
==== '''A. Author’s Approach to Testing''' ====
An overall approach to testing the material properties of bamboo reinforced concrete consists of tensile testing, with two point and four point bending tests, to examine flexural strength and an Artificial Neural Network analysis of the material using MATLAB software to analyze the serviceability. LCA Analysis was the primary testing technique used to evaluate the environmental impact of the material.
===== '''i) ''Material Properties''''' =====
Flexural behavior of BRC in beam scenarios is continuously being researched. Current research conveys that under pure bending of a four-point bending test, bamboo reinforced concrete has similar or higher flexural properties than plain cement concrete (PCC) and steel reinforced cement concrete (RCC). Multiple designs of bamboo reinforced concrete have been tested and compared to traditional and steel reinforced concrete. Beams containing 2.8% and 3.8% bamboo reinforcement in respect to the beam’s cross section have been examined¹. Branching from the different percentages of reinforcement, testing conditions were changed to provide a total of eight combinations of different BRC. For each percent of bamboo reinforcement, the bamboo was either treated or untreated then left as its natural outer texture or engraved with a predetermined groove pattern. The bamboo was treated with a BondTite⁴ to create a waterproof surface and to create a bond layer between the concrete and bamboo. The groove pattern used for the grooved specimens, was grooves engraved around the thickness of the bamboo reinforcement with a 10-mm semicircle groove pattern¹. This groove pattern was determined by prior pull out tests of the bamboo used for reinforcement. For the concrete mix design of the beams, M20 grade concrete was used with an aggregate mixture of 70% - 20 mm and 30% - 10 mm aggregate¹. 30 total beams with dimensions of 140 mm x 150 mm x 1100 mm were tested under a 100 kN cavity flexural testing machine¹. The ultimate load, first crack load, average ductility, and maximum shear strength were all determined from the flexural testing performed on such beams and can be found in more detail in Section C.
In a separate study, the strength of the material was not the focus of the tensile testing, but rather the deflection. Nine beams were tested, three plain concrete (PC), three reinforced with steel (RC), and three reinforced with bamboo (BRC)². The samples were between 9 and 12 inches long and the concrete being used was Grade M20 with 28 day curing time. For the steel reinforced beam, Fe 250 grade bars were used. The BRC bars were treated with Sikadur 32 gel⁵ to improve the adhesion of the material. Using a 60-ton universal testing machine, a two point bending test was performed using a gradual loading rate of 1 mm/min². The maximum deflection was taken at midspan for each 75 mm x 150 mm cross section of the nine beams. ANN using MATLAB was used to then further analyze the load-displacement data<sup>2</sup>. As background, ANN is an A.I. software that processes known parameters, called neurons, runs a specified function, in this case Levenberg-Marquardt algorithm and a nonlinear logistic-sigmoid transfer function, and provides an output for testing. The three input parameters for the ANN testing were load applied, tensile strength of reinforcement, and percentage of reinforcement. These values came directly from the experimental data. The desired output from the model was the predicted deflection of the member. Using the ANN analysis, 122 data points were provided, with 80% of the data selected randomly for training and the other 20% left out for testing<sup>2</sup>. Five sample runs were performed in order to obtain the most accurate data. The results from this testing can be found in Section C below.
===== '''''ii) Environmental Impact''''' =====
A third study was performed to run a life cycle assessment comparing the environmental impact of bamboo, timber, concrete, and steel. At its core, LCA assesses the environmental effects during the life cycle of a material from the extraction of raw materials to its end of life. The life span, amount of waste produced, and recyclability of the material are all taken into account for the analysis. In this study, the TWIN model was used to holistically capture the estimation of environmental effects for the four materials<sup>3</sup>. The case study of the bamboo pedestrian bridge in the Amsterdam woods, referred to in Section B, was used for the analysis in comparison to other common building materials. In order to quantify the environmental impact, LCA gave scores to each of the materials<sup>3</sup>. For example, the bamboo was environmentally scored based on the amount of boron used in preservation or the distance for transport of the material. A cost breakdown was also performed in this study, but is not being used as part of the comparative analysis for the materials. The results of this LCA analysis can be summarized in Section C.
==== '''B. Case Studies of BRC Application''' ====
Bamboo reinforced concrete is becoming increasingly popular in the construction industry as a sustainable alternative to traditional reinforced concrete. Several case studies of the structural applications of bamboo, alone, have been assessed under LCA analysis and compared to timber, concrete, and steel. Although this analysis did not explicitly run an analysis on BRC, the LCA performed on bamboo itself helps to highlight the environmental benefits of the material alone. The bamboo species ''Guadua angustifolia'' produced in Costa Rica and transported to the Netherlands was used to assess bamboo as a structural material in such case studies across Western Europe<sup>3</sup>. These studies include the bamboo tower at the ''Phenomena'' exposition Zurich and Rotterdam, the pedestrian bridge in the Amsterdam Woods, the ZERI-pavilion, an open theater in Berlin, and the pavilion ''Bamboo summit city'' in Rotterdam<sup>3</sup>. The application of bamboo in the construction of the Amsterdam pedestrian bridge is highlighted as the case that LCA was then performed on. In this example, bamboo had been used for columns, beams, and rails. Several interviews were conducted with people and industry workers involved in the construction process for all five applications of bamboo in order to qualitatively measure the successes and failures of each situation<sup>3</sup>. The environmental impact of bamboo in the construction process can be quantified through the life cycle analysis as described in Section A.ii in combination with such case studies.
==== '''C. Main Results:''' ====
From the four point testing under the first study, it is evident that the flexural behavior of bamboo reinforced concrete is always stronger than plain cement concrete, however, both reinforcement types of bamboo reinforced concrete have weaker flexural behavior than steel reinforced cement concrete. After testing, the best design for all flexural properties was determined to be the bamboo reinforced concrete with the design of 3.8% bamboo reinforcement with treated and grooved bamboo¹. The maximum shear strength and ultimate load of the 3.8% BRC and RCC are comparable to one another and with further research, BRC has the potential to have the same ultimate load and maximum shear strength of RCC. A summary of the flexural behavior findings of the 3.8% bamboo reinforced concrete, steel reinforced cement concrete and plain cement concrete beams can be found in Table 1 below.
''Table 1 - Comparison of Flexural Behavior BRC, RCC and PCC Beams''
{| class="wikitable"
|'''Beam Type'''
|'''First Crack Load (kN)'''
|'''Ultimate Load (kN)'''
|'''Energy Consumption (Joules)'''
|'''Maximum Shear Strength (kN)'''
|-
|3.8% Bamboo Reinforced Concrete (BRC)
|42.0
|65.3
|367.7
|32.67
|-
|Steel Reinforced Cement Concrete
(RCC)
|57.0
|67.3
|431.7
|33.67
|-
|Plain Cement Concrete
(PCC)
|22.0
|23.7
|15.7
|11.83
|}
From the ANN load-deflection testing, it was found that BRC has a higher load carrying capacity compared to both PC and RC. On the same note, the BRC beams could therefore sustain larger deflections from loads compared to the other two beams. Table 2 below summarizes the overall results found from such testing. It is evident that the collapse load for BRC is higher than that of PC and RC.
''Table 2 - Comparison of Collapse Loads and Displacement for PC, RC, and BRC Beams''
{| class="wikitable"
|'''Beam Type'''
|'''Collapse Load [kN]'''
|'''Max Disp. [mm]'''
|-
|PC
|10.13
|0.36
|-
|RC
|12.21
|1.83
|-
|BRC
|13.11
|2.05
|}
As a summary to the ANN testing, BRC has a 30% higher load-carrying capacity compared to PC with 1.5% area of reinforcement. BRC has an 8% higher load-carrying capacity compared to RC with 1.1% area of reinforcement.² The strength and resilience of BRC is evident through this increased load-carrying capacity of the material. Thus, BRC continues to serve as a promising material to be used for sustainable construction and structural design.
The life cycle assessment provides valuable information regarding the environmental impact of bamboo compared to traditional construction materials. The data obtained from LCA conveys that bamboo is the most sustainable material in comparison to steel, two types of timber, and concrete. The environmental costs for the transversal beam, column, rail, and longitudinal beam are the lowest for bamboo. One of the greatest environmental benefits of bamboo is its lightweight nature composed of hollow tubular fibers. This inherently leads to less material mass, easier transportation, management, and constructability. Likewise, the production process of bamboo from initial sawing to drying and installation exists on an extremely short timeline compared to other materials. From the case study of the pedestrian bridge in Amsterdam, it was found that a bamboo culm is 20 times more favorable than its alternatives of timber, concrete, and steel.³
==== '''D. Strengths and Weakness of BRC''' ====
From the numerous studies conducted and research already performed, it is evident that bamboo reinforced concrete has more benefits than weaknesses as a construction material. Compared to plain concrete, BRC has a greater tensile strength and larger load-carrying capacity in deflection. Compared to steel reinforced concrete, bamboo reinforced concrete has less tensile strength but also a larger load-carrying capacity. Not only does the strength and capacity of BRC have serious benefits, but bamboo reinforced concrete is also lightweight due to its hollow internal fibers and is strong in the same ways a steel W-shape is. The tubular fibers of bamboo act to resist load in the same way an I-cross section does³. The failure mechanism of bamboo as reinforcement is slow-growing and extremely ductile. Likewise, bamboo itself is fast growing, taking only around 3 to 5 years to fully grow, compared to the 30 year lifespan of wood³. This short timeline in combination with the lightweight nature of the material makes it highly constructible, easy to transport and manage. In terms of fire resistance, bamboo is extremely flame resistant because of the silicate acid that it is composed of. On the environmental side, the production of steel and other conventional reinforcement materials is energy-intensive and generates large amounts of greenhouse gasses. In contrast, bamboo is a carbon-neutral material that sequesters carbon during its growth, and its production process requires much less energy and emits fewer greenhouse gasses. Bamboo is also sustainable in that it helps to mitigate soil erosion and removal of crops due to its strong and resistant roots.
With so many strengths of the material, one of the biggest challenges in using this material in future construction applications is the lack of design codes and specifications associated with BRC. ACI does not yet provide specific guidance for the use of bamboo as a reinforcement material which would make architects and engineers apprehensive about incorporating it into their design. Similarly, steel as reinforcement has been used for decades, such that the historical past of the material ensures safety and serviceability such that owners and contractors like to build with reliable materials that have been known to work in the past. A final large challenge of using bamboo as reinforcement is the lack of homogeneity of the material such that it is very variable in size, shape, and density from one sample to the next. This would also be a challenge in the development of future industry standards.
==== '''E. Citations for BRC Summary''' ====
[1] Mali , P. R., & Datta, D. (2020). Experimental Evaluation of Bamboo Reinforced Concrete Beams. ''Journal of Building Engineering'', ''28''. <nowiki>https://www.sciencedirect.com/science/article/pii/S235271021930347X?casa_token=3Em92k8NEosAAAAA:1saVfvVJXwaer7KkR-1bRVmmwfnlS1-Pb1g2quym_J58Gq6Zr6EYyYhASPc5IHrSTJPYF-baGQ</nowiki>
[2] Mishra, M., Agarwal, A. & Maity, D. Neural-network-based approach to predict the deflection of plain, steel-reinforced, and bamboo-reinforced concrete beams from experimental data. SN Appl. Sci. 1, 584 (2019). <nowiki>https://doi.org/10.1007/s42452-019-0622-1</nowiki>
[3] P. van der Lugt, A.A.J.F. van den Dobbelsteen, J.J.A. Janssen,An environmental, economic and practical assessment of bamboo as a building material for supporting structures, Construction and Building Materials, Volume 20, Issue 9, (2006)
<nowiki>https://reader.elsevier.com/reader/sd/pii/S0950061805001157</nowiki>?
[4] Bondtite Epoxy Adhesives, ASTRAL Adhesives <nowiki>https://www.astraladhesives.com/v/maintenance/epoxy-adhesives/bondtite-epoxy-adhesives/bondtite-fast-clear-57</nowiki>
[5] Sikadur-32 Hi-Mod, USA.sika <nowiki>https://usa.sika.com/en/construction/repair-protection/multi-purpose-epoxies/adhesives/sikadur-32-hi-mod.html</nowiki>
==See also==
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