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.
A brief on high-volume Class F fly ash as cement replacement – A guide for Civil Engineer
Abstract Disposal of fly ash (FA) resulting from the combustion of coal-fired electric power stations is one of the major environmental challenges. This challenge continues to increase with increasing the amount of FA and decreasing the capacity of landfill space. Therefore, studies have been carried out to re-use high-volumes of fly ash (HVFA) as cement replacement in building materials. This paper presents an overview of the previous studies carried out on the use of high volume Class F FA as a partial replacement of cement in traditional paste/mortar/concrete mixtures based on Portland cement (PC). Fresh properties, mechanical properties, abrasion resistance, thermal properties, drying shrinkage, porosity, water absorption, sorptivity, chemical resistance, carbonation resistance and electrical resistivity of paste/mortar/concrete mixtures containing HVFA (⩾45%) as cement replacement have been reviewed. Furthermore, additives used to improve some properties of HVFA system have been reviewed.
EFFECT OF SAND REPLACEMENT ON THE EARLY AGE STRENGTH GAIN AND LONG TERM CORROSION RESISTING CHARACTERISTICS OF FLY ASH CONCRETE
This is a report of the results of experiments carried out to evaluate compressive-strength development and corrosion-resisting characteristics of concrete mixtures in which fly ash was used as an admixture (an equal quantity of sand was replaced). Data were developed for fly ash additions of 0, 20, and 30 % and water-cement ratios of 0.35, 0.40, 0.45, and 0.50. The compressive strength was determined at 3, 7, 14, 28, 56, and 90 days. Concrete samples were partially immersed in a 5 % sodium chloride solution for a period of about 4 years, and corrosion-resisting characteristics of concrete were evaluated by monitoring the half-cell potential and measuring the corrosion rate of embedded steel bars using electrochemical techniques. Results show that addition of fly ash as an admixture increases the early-age compressive strength and long-term corrosion-resisting characteristics of concrete. The superior performance of these mixtures compared to plain concrete mixtures is attributable to the densification of the paste structure due to pozzolanic action between the fly ash and the calcium hydroxide liberated as a result of hydration of cement.