Fracture Toughness and Impact Strength of High-Volume Class-F Fly Ash Concrete Reinforced with Natural San Fibres
Results of experimental investigation carried out to study the effects of addition of natural san fibres on the fracture toughness and impact strength of high-volume fly ash concrete are presented in this paper. San fibres belong to the category of ‘Natural Bast Fibres’, also known as ‘Sunn Hemp’. Its scientific (botanical) name is Crotalaria Juncea. It is mostly grown in the Indian Sub-Continent, Brazil, Eastern and Southern Africa, and in some parts of the U.S.A. Initially, a control mixture without fly ash was designed. Then, cement was replaced with three percentages (30, 40 and 50%) of low-calcium (Class F) fly ash. Three percentages of san fibres (0.30, 0.60 and 0.90%), having 25 mm length, were used. Tests were performed for compressive strength, fracture toughness, and impact strength at the ages of 28 and 91 days. The test results indicated that the replacement of cement with fly ash decreased the compressive strength and fracture toughness, and had no significant effect on the impact strength of plain (control) concrete. Addition of san fibres did not affect significantly the compressive strength, increased the fracture toughness and impact strength of high-volume fly ash concrete as the percentage of fibres increased.
Characteristics of concrete reinforced with San fibers
This paper presents the results of an experimental investigation carried out to determine the physical and mechanical properties of natural San (Crotolaria Juncea) fiber, and its effect on compressive strength, splitting tensile strength and flexural strength (modulus of rupture) of concrete. San fiber is a natural fiber, which is widely available in many parts of India, and has good tensile strength. Concrete mixtures were prepared with three volume fractions of San fibers viz. 0.25%, 0.50%, 0.75%, and three fiber lengths viz. 20 mm, 25 mm, 30 mm. Experimental results of the mechanical properties of the San Fiber reinforced concrete have been compared with the theoretical model developed by Pakotiprapha et al. [10]. Comparison of the theoretical and experimental results shows good agreement.
Fly Ash Concrete Mix Design and the Water-Cement Ratio Law
When the water-cement ratio law was proposed by Abrams in 1918, the use of fly ash and silica fume as replacements or substitutes for part of the cement was virtually unknown. Consequently, the effects of fly ash and silica fume were not considered in the development of Abrams' law. Since the early 1960s, concrete mix compositions have changed, and cement is no longer the only cementitious material in concrete mixes. In a high percentage of situations, today's cementitious material content is made up of cement plus fly ash. This study investigates the applicability of Abrams' law to concrete mixes containing fly ash. As initially expected, it was found that Abrams' water-cement ratio law is not directly applicable to mixes with fly ash. An alternative augmented water-cementitious materials ratio law is proposed for designing concrete mixes containing fly ash.