Composite Bamboo and its Application as Reinforcement in Structural Concrete

Abstract

The fast pace of development in many developing countries has led to an increased demand for building and construction materials for housing and infrastructure projects. Reinforced concrete is one of the most widely used building materials around the world. Unfortunately the majority of developing countries lack the resources to produce their own steel. Steel is not without alternatives. There is a material substitute that grows in the tropical zone of planet, an area that coincides closely with the developing world: bamboo. Research that has been conducted so far in the area of bamboo-reinforced structural concrete has demonstrated two things. First, replacing steel with bamboo as a reinforcement system is technically feasible. Second, up to now, no solution has been found for problems involving swelling, shrinking, chemical and biological decomposition and thermal expansion of raw bamboo in concrete. The primary aim of this pioneering research is to evaluate the suitability of a newly developed bamboo-composite material for use as reinforcement for structural-concrete elements. This thesis also focuses on novel methods to fabricate a bamboo-composite material in an innovative way so that most of the inherent tensile capacity of the fibers is retained. Furthermore, durability aspects such as water absorption, swelling, shrinking, chemical resistance as well as challenges related to thermal expansion are studied and evaluated experimentally through an extensive series of tests. Bamboo Dendrocalamus asper from Indonesia has mechanical properties that are suitable for composite fabrication. New relationships are proposed for estimation of mechanical properties of bamboo Dendrocalamus asper through measuring only the culm diameter and wall thickness after evaluating a total of 4,500 raw bamboo samples. These relationships are useful tools for on-site estimation of the properties of bamboo culms without the need for laboratory facilities. Of the two processing methods investigated in this research, the Bamboo Veneer Composite (BVC) fabrication technique which offers higher mechanical properties compared with the Bamboo Strand Composite (BSC) fabrication technique was chosen after evaluating the mechanical properties of nearly 5,000 bamboo composite samples. The ultimate tensile strength of longitudinal BVC reinforcement is found to be comparable to ASTM A615 grade 60 with a minimum tensile strength of 420MPa, while the BVC stirrup shows an average tensile strength comparable to ASTM A615 grade 40 reinforcing bar with a minimum tensile strength of 280MPa. These values are obtained after investigating tensile properties of close to 1,500 longitudinal and transverse BVC reinforcement samples. vi Water-based epoxy coating and sand particles employed on the surface of around 500 BVC reinforcements proved to be useful firstly, by protecting the BVC reinforcement against potential chemical degradation in the alkaline environment of concrete and secondly, by maintaining the bonding strength with the concrete matrix that is necessary for stress transfer between the concrete matrix and the reinforcement. The longitudinal Coefficient of Thermal Expansion (CTE) of BVC reinforcement and concrete are similar and thus no significant longitudinal residual thermal stresses are developed within concrete beams during hardening. The differential transverse thermal expansion of BVC reinforcement in concrete has been mitigated by firstly providing a concrete cover of two times the thickness of BVC reinforcement and secondly, by ensuring a good bond between the BVC reinforcement and concrete. The transverse residual stresses developed at the interface of the concrete and reinforcement caused by transverse expansion and retraction of the BVC reinforcement during hardening do not result in observable tensile radial cracking around the reinforcement. Therefore, the variation of transverse CTE values has no significant effect on the bonding mechanism. Furthermore, exposures of nearly 500 BVC reinforcements to water and alkaline environments do not show a significant change in physical and mechanical properties. A total of 110 concrete beams are reinforced with BVC material as longitudinal and transverse reinforcement. The BVC-reinforced concrete beams show ultimate failure loads that are comparable to that of reinforced concrete beams with ASTM graded steel-reinforcement bars. It is concluded that the newly developed BVC reinforcement system has much potential for low-cost and low-rise concrete infrastructure where loading and environmental conditions similar to those studied in this thesis are found.