Indian Journal of Engineering & Materials Sciences Vol. 15, February 2008, pp. 14-22 Determination of fracture parameters of concrete based on water-cement ratio Ragip Ince* & Kürşat Esat Alyamaç Firat University, Engineering Faculty, Civil Engineering Department, Elazig, Turkey Received 2 March 2007; accepted 5 February 2008 The aim of this study is to predict formulas based on the Abrams’ Law between fracture parameters of concrete and w/c. Therefore, a series of three-point bend test on specimens were performed. The beams were made from mixes with water/cement ratios varying in the range of 0.34-0.85. The fracture parameters for each mix were calculated according to a popular fracture mechanics approach — two-parameter model. The present experimental data indicate that the fracture parameters of two-parameter model are inversely proportional to w/c ratios. In conclusion, the present test results are in agreement with the Abrams’ Law. Applications of Linear Elastic Fracture Mechanics (LEFM) to concrete were initiated by Kaplan 1 in 1961. In 1970s, experimental investigations on fracture mechanics of cementitious materials have indicated that LEFM was no longer valid for quasi- brittle materials such as concrete 2 . This inapplicability of LEFM is stemming from the existence of a relatively large inelastic zone in front of and around the tip of the main cracks in concrete. This so-called fracture process zone is ignored by LEFM. Consequently, several investigators have developed non-linear fracture-mechanics approaches to describe fracture-dominated failure of concrete structures 3-9 . These approaches primarily involve the fictitious crack model 3 , the crack band model 4 , the two- parameter model 5 (TPM), the effective crack model 6 , the size effect model 7 , the peak load method 8 and the variable-notch one-size test method 9 . Contrary to LEFM, in which a single fracture parameter is used such as the critical stress intensity factor, these models need at least two experimentally determined fracture parameters to characterize failure of concrete structures. Accordingly, they require either a lot of tests (at least three) 7-9 or a closed-loop testing system 3,5 . Analysis of any existing structure is impossible according to fracture mechanics for many approaches stated above, even if possible, specimens cored from structures must be tested after processed to a specific geometry 5,8,9 . In addition, several regression formulas 4,10-12 have been proposed to predict fracture parameters of concrete. Nevertheless, they give a little information about concrete mix proportion in order to design a concrete structure according to fracture mechanics principles. There are many methods for concrete mix design according to compressive strength. The well-known Abrams’ Law 13 , which is an equation correlating the relationship between the strength and water/cement ratio, is a very important tool for determining a concrete mix proportion. In this study, fifteen series of three-point bend tests on specimens were performed to predict formulas based on the Abrams’ Law between fracture parameters of concrete and water-to-cement ratios. The beams were made from mixes with water/cement ratios ranging from 0.34 to 0.85. The fracture parameters for each batch were calculated according to TPM by using the peak load method. Finally, it has been concluded that there were quite strong relations between the fracture parameters of concrete and the water-cement ratio based on Abrams’ Law. Fracture Mechanics of Concrete To analyze a concrete structure according to fracture mechanics, fracture parameters of the cementitious material must be determined at first. The studies on determining the fracture parameters of concrete were initiated by Kaplan 1 . He used the principles of classical linear elastic fracture mechanics (LEFM), which proposes a unique parameter (the critical stress intensity factor K Ic or the critical strain energy release rate G Ic ) for concrete fracture. However, the subsequent experiments revealed that LEFM is not valid for concrete since K Ic __________ * For correspondence (E-mail: rince@firat.edu.tr)