Effect of basalt minibars and steel fibers on the mechanical behavior of concrete.

Abstract

The use of steel reinforcement in the form of rebar has been used for many years to improve the tensile and flexural strength of concrete elements. The research and development within the field of concrete is ever expanding due to concrete being the most readily available and widely used construction material. The use of fibers in concrete is not an entirely new concept however increasing amounts of fiber types and materials are being introduced into the market. The mechanical behavior and properties of each of these fibers can drastically differ from each other and constant research is therefore being performed to better understand how different types of fiber reinforced concrete behave.

In this bachelor thesis tests were performed on two types fiber types, conventional steel hooked end smooth fibers and basalt fiber Minibars. The basalt fiber Minibars are a rather new technology which consist of many small micro-fiber basalt filaments that have been spun together to form large macro-fibers of length between 30-50 mm. These Minibars are supposed to act similar to traditional steel fibers by increasing the concretes flexural capacity through acting as tension bridges and limiting crack prorogation.

Volume fractions of 0.5% and 1% were tested for both fiber types and compared to plain concrete. The steel fibers showed a notable increase in compressive strength mean while the basalt fiber Minibars reduced the compressive strength proving to be insufficient at serving as compressive reinforcement. The steel fibers showed no significant increase or decrease when it came to the ultimate flexural strength of the concrete while the basalt fiber minibars caused a notable reduction in flexural strength. The fibers seemed ineffective at increasing the ultimate flexural strength of the concrete, they did however show exceptional post cracking behavior by increasing the concretes ability to carry loads past failure. Additionally, improved modes of failure were observed due to the significantly increase ductility of the fiber reinforced concrete.