Durability performance of concrete incorporating Class F and Class C fly ashes Mucteba Uysal ⇑ , Veysel Akyuncu Sakarya University, Civil Engineering Department, Sakarya, Turkey article info Article history: Received 14 November 2011 Received in revised form 13 January 2012 Accepted 25 February 2012 Available online 29 March 2012 Keywords: Class C fly ash Class F fly ash Compressive strength Sorptivity Freezing–thawing resistance abstract This paper presents an experimental study on the durability properties of concretes containing Turkish Class C and Class F fly ashes. A total of 39 mixtures with different mix designs were prepared. In order to characterize the concrete quality, compressive strength of the specimens were obtained. After that, the mixtures containing Class F and Class C fly ashes which had similar compressive strength values to control mixtures at 28 d for each series were used for durability tests. The durability performance of the concretes was assessed from measurements of rapid chloride ion permeability, sorptivity and freezing–thawing resistance tests. The degree of freezing–thawing resistance was evaluated using change of weight, ultrasonic pulse velocity (UPV) and flexural strength after 300 cycles. The test results indicated that Class C fly ash showed higher compressive strength than Class F fly ash. The addition of fly ash improved the rapid chloride ion permeability and sorptivity of concrete. There was a notable reduction in the UPV after the specimens are subjected to freezing–thawing cycles. The amounts of flexural strength loss have been measured in the range of 5.38–29.83%. The use of Class C and Class F fly ashes positively affected freezing–thawing resistance of concretes. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction Concrete is the most important element of the construction industry. In recent years, since durability is one of the critical is- sues to construct reinforced concrete structures with long service life and develop construction technologies due to some economical and environmental reasons, it is important to produce well- designed concrete as a durable construction material [1]. However, large amounts of cement are used in concrete production. Cement is the most cost- and energy-intensive component of concrete. Three billion tons of raw materials are used in each year for cement production in the world [2] and, cement manufacturing is respon- sible for about 2.5% of total worldwide CO 2 emissions from indus- trial sources [3,4]. The use of additional cementitious materials due to technical, economic and environmental considerations has be- come very common in modern concrete construction. The use of these materials in concrete is increasing because they result in lower cost of construction and improve some physical, mechanical and durability properties of concrete in aggressive environments [5]. Mineral admixtures such as silica fume, ground granulated blast furnace slag and fly ash (FA) generally improve the engineer- ing properties of concrete when they are used as a mineral additive or partial replacement of cement [6,7]. Among these mineral admixtures, FA has been used in concrete production for over 52 years in the world. It was used in mass, conventional and high performance concrete to improve the workability, to reduce the heat of hydration and thermal cracking at early ages, and to im- prove the mechanical and durability properties especially at later ages [8]. The main useful effect of FA in concrete consists of three aspects, often called pozzolanic effect, micro aggregate effect and morphologic effect. The pozzolanic effect is the main effect of FA, which states that the unfixed AI 2 O 3 and SiO 2 in FA can be activated by Ca(OH) 2 product of cement hydration and produce more hy- drated gel. Since the gel produced from pozzolanic action can fill in the capillary in concrete, it effectively conduces to concrete strength. The micro aggregate effect of FA states the microbeads in FA can disperse well in concrete and combine firmly with gel produced in cement hydration, and thus promote concrete density. The morphologic effect states that there are many microbeads in FA working as ‘‘lubricating balls’’ when incorporated in fresh con- crete; hence it benefits the fluidity [9]. Fly ash is widely used in blended cements, and is a by-product of coal-fired electric power plants [10]. Two general classes of fly ash can be defined: low-calcium fly ash (ASTM Class F) produced by burning anthracite or bituminous coal; and high-calcium fly ash (ASTM Class C) produced by burning lignite or sub-bituminous coal [11]. Class F is categorized as a normal pozzolan, a material consisting of silicate glass, modified with aluminum and iron. Class F requires Ca(OH) 2 to form strength-developing products (pozzola- nic reactivity), and therefore is used in combination with Portland cement, which produces Ca(OH) 2 during its hydration. It lowers the heat of hydration and improves the durability when used in con- crete as a cement replacement. It also contributes to concrete 0950-0618/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. doi:10.1016/j.conbuildmat.2012.02.075 ⇑ Corresponding author. Tel.: +90 264 295 57 45; fax: +90 264 346 01 51. E-mail address: mucteba@sakarya.edu.tr (M. Uysal). Construction and Building Materials 34 (2012) 170–178 Contents lists available at SciVerse ScienceDirect Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat