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.
Compressive stress-strain curves of natural fibre reinforced concrete
The effectsof addition of various percentages and lengths of natural san (Crotoralia J uncea) fibre on the compressive stress-strain curves of concrete are determined. From the compressive stress-strain curves, modulus of elasticityof fibre reinforced concrete are obtained. Three volume percentages of fibres, viz.,0.25, 0.50 and 0.75% and three different lengths, viz., 20, 25 and 30mm are used. Presence of fibres increases the ductility of concrete and does not significantly affect the modulus of elasticity of concrete. The values of modulus of elasticity are compared with a theoretical model based on the law of mixtures. Literature survey reveals that the ductility of cement based materials increases with the addition of uniformly distributed short steel fibres1,2. The reported increase depend upon various factors such as length and volume fraction of fibres present in the mix, type and strength of plain matrix, and orientation of fibres relative of the load. However, the data available on the compressive stress-strain curves of natural fibre reinforced concrete are very scarce. In this paper, an effort has been made to determine the compressive stress-strain curves of san fibre reinforced concrete and from those curves modulus of elasticity of fibre reinforced concrete is determined. Values of modulus of elasticity have been compared with a theoretical model based on law of mixture3. San is a natural bast fibre. It is extracted from a san plant which is grown in many parts of the Indian Sub-Continent. It has good physical and mechanical properties suitable for use in concrete. Table I gives some of the physical properties of san fibre. Experimental Programme In this investigation, the modulus of elasticity which is also called secant modulus, is taken ~s the slope of the chord from the origin to some arbitrary point on the stress-strain curve. The secant modulus
Chromatographic analysis of elastomer antidegradants and accelerators
Summary The use of various chromatographic methods in the analysis of all classes of elastomer antidegradants and accelerators is reviewed. The review of extraction methods is also included.