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.
Performance of high volume fly ash concrete incorporating additives: A systematic literature review
Abstract Fly ash is commonly used as a partial cement replacement material, but this is limited to replacement levels of 30% or less, with significant quantities of fly ash still not utilized globally. There has been significant recent research into High Volume Fly Ash (HVFA) concrete to enable the utilization of fly ash and to reduce CO2 emission by reducing cement demand. This comprehensive review summarizes up to date literature on HVFA concrete with more than 50% of cement replacement using ASTM Class F low calcium fly ash. Firstly, the available HVFA literature in which only fly has been used to replace cement, is categorized based on the replacement level and the mechanical and durability property results are summarized. Secondly, the remaining literature is categorized based on the different material additions to modify the HVFA concrete and the results are compared. The summarized results are discussed to elucidate the mechanisms underlying the reported results. The effect of each material addition on the HVFA concrete properties are also discussed to identify potentially more suitable additives for future development. Overall, this paper will provide an understanding of the current state of HVFA concrete research and the gaps in research for the development HVFA concrete containing higher replacement levels and achieving the required performance. Hence, summarised knowledge would significantly be beneficial to design prospective research towards a sustainable cement-free concrete using industrial waste.
Mechanical Properties, Creep, and Resistance to Diffusion of Chloride Ions of Concretes Incorporating High Volumes of ASTM Class F Fly Ashes from Seven Different Sources
This is a report of an investigation into the performance of 7 low-calcium (ASTM Class F) fly ashes in the high-volume fly ash concrete system. Concrete specimens were tested for compressive strength, Young's modulus of elasticity, creep strain, and resistance to chloride ion diffusion at various ages up to 1 year. The paper describes the study and discusses the results.