Abstract
A new testing method and estimation of the fracture toughness in Mode III (antiplane shear) of concretes containing: 0, 20 and 30% volume content of the class F fly ash (FA) was proposed. Fracture toughness tests were performed on axial torsional machine MTS 809 Axial/Torsional Test System using special device. The Device for the fracture toughness test at the Mode III fracture consisted of the cylindrical specimen with the formed initial crack, steel plates, and screws with washers securing the specimen in the press holders. The specimens applied for experiments were cylinders with dimensions of 150/300 mm, having an initial circumferential notch made in the half-height of cylinders. The specimens were subjected to pure torsion. The studies examined effect of FA additive on the parameter KIIIc. 20% FA additive causes a small increase of the KIIIc in comparison to the concrete without the FA, while 30% FA additive causes a significant decrease in fracture toughness. The fracture surfaces of the specimens analysed macroscopically were planar. Scanning microscopic observations (SEM) indicate that in the fracture surfaces multilevel cracks occur in the shape of semicircles.
Highlights
Introduction and literature reviewAcquisition of natural raw materials and fuels for the economy in Poland and in the world is becoming an increasing problem
That 10% siliceous fly ash (FA) additive slightly affects the value of the parameter KIIc causing its increase by only 1%, whereas 20% and 30% FA additives significantly change the fracture toughness of concrete. 20% siliceous FA additive affects the increase of fracture toughness of concrete by a few percent, while replacement of the cement in the concrete mix with larger quantity of the FA decreases the KIIc more than 10% (Golewski, Sadowski 2014)
Based on the obtained results, it can be concluded that the 20% additive causes an increase fcm after 28 days of curing by 3.1 percent, while the 30% FA additive causes a drop of this parameter by 5.1 percent
Summary
Acquisition of natural raw materials and fuels for the economy in Poland and in the world is becoming an increasing problem. Different types of waste are used as additives to concrete in order to improve its durability, strength and fracture toughness (Meyer 2009; JóźwiakNiedźwiedzka et al 2012; Stehlík 2013; Konkol, Prokopski 2014; Grinys et al 2013, 2015) One of these materials is siliceous fly ash (FA) which is a by-product obtained in the process of hard coal combustion performed in electric power stations and in thermal-electric power stations (Ahmaruzzaman 2010). The cement industry is one of the major areas of the economy, which on a large scale is able to utilize emerging, in the hard coal combustion processes, combustion by-products which are FA Treatments of this type are beneficial for ecological reasons due to reducing the deposit areas of troublesome industrial wastes as well as the economic reasons because of the possibility to replace part of the cement binder in the concrete with FA treated as pozzolanically active microfillers. These waste materials are useful in environment protection, e.g.: as the adsorbents of harmful compounds, or as components of cement binders used for the immobilization of heavy metals (Giergiczny, Król 2008)
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