The Effects of Mix Variables on Concrete Fracture Mechanics Parameters

An extensive testing program using three-point bend specimens has been conducted to ascertain the influence on fracture mechanics parameters of the concrete mix variables: aggregate-matrix bond and strength, cementitious bindings, and gradation of fines. Specifically, the variables were: crushed limestone, crushed and polished limestone, quartzite, river gravel, expanded IC ratio, fly ash and silica shale, normal graded sand, gap graded sand, W These were organized into twenty-four groups of tests involving 352 beams. Testing was conducted using notched beams according to proposals by RILEM -- GF (Hillerborg), Ksc, Ee (Gsc), CTODc (Jenq and Shah) and by 1 1 Karihaloo/Nallathambi. Precracked beams in which dye was inserted to reveal the crack front prior to testing to failure were also used to evaluate same parameters. 111 1 influence of a wide spectrum of mix mCJA•.f"'ll'V:lfl 1l-.C" properties of concrete as defined by the ......... ..,.., ...... ,._, ....... the RILEM (1990) two-parameter ma....-nnr'l ofKarihaloo and Nallathambi 991). were notched and then loaded to failure- formation of a process zone while be reflected the measured load tests were conducted using a closed loop 2 bending in an inverted pos1t10n. cnl•'.H">CJA·ma.in't measurements CMOD and load point (LPD) and due to avoiding measurement of spurious deformations - 991) Kan (1993). The beam dimensions were (254 thickness t = 5 27 mm) and span S = 40 in. tests were organized in groups according to the type of o-o-1·a.o-t-;:::i. used in as shown in Table 1. mixes had a maximum coarse aggregate size between 13 19 mm . ...,..., ........... "..., were cast steel molds along with companion 3 in. x 6 in. (7 5 cylinders. After curing one day, the specimens were demolded a fog room for 84 days. They were then removed and placed •J>•r-n.-.,>n environment for 7 days and tested on the 92nd day. On the test ............... , .