Issue 42

J. Klon et alii, Frattura ed Integrità Strutturale, 42 (2017) 161-169; DOI: 10.3221/IGF-ESIS.42.17 165 M ATERIAL pecimens were prepared from a fine grained cement-based composite, see [14]. A design of mixture composition is based on the standard ČSN EN 196-1 [15]. The fresh composite was made with quartzite sand with the maximum nominal grain size of 2 mm standardized according to ČSN EN 196-1 [15], Portland cement type 42.5 R and water in the ratio of 3:1:0.35 (S:C:W) with addition of a super-plasticizer SVC 4035 in the amount of 1 % by cement mass. This composite was chosen with respect to the previously verified appropriate response of the specimen for static loading (quasi- brittle fracture of the specimen). An idea of preparing the specimens can be formed from Fig. 4. After one day of aging in constant relative humidity provided by foil coated molds, the test specimens were unmolded and stored in a water bath at laboratory temperature. After seven days, the specimens were removed from water, then exposed to free drying and an initiation notch was made with a diamond blade saw. After short drying steel platens were attached to the specimens using epoxy resins Sikadur-31 CF Rapid. The glue thickness was between 2–3 mm as recommended by the manufacturer. The test specimen and the method of sticking steel platens are shown in the pictures in Fig. 5. E XPERIMENTAL PROCEDURE MCT fracture test ilot experiments of the MCT tests were performed on the LabTest 6.1000 testing machine (load range of 0 up to 1000 kN), which is located in the AdMaS Center, the Faculty of Civil Engineering, Brno University of Technology in Brno. The test was controlled by the prescribed displacement of the cross beam at a rate of 0.02 mm/min. Loading force P vs. crack mouth opening displacement ( CMOD ) was monitored and the prescribed cross beam deflection was verified. These values were monitored for all three test configurations (A, B and C). The set-up and detail of the fixture are shown in Fig.6. X-ray tomography Measurement XL-sized specimens broken during the MCT test with modified configurations A and B were cropped into the shape of an irregular block with the approximate dimensions of 105 × 20 × 30 mm. Samples were tomographically measured with one S Figure 4 : Specimens preparation in silicone molds installed in frames made of waterproof plywood. Figure 5 : Specimen after its removal from the silicon mold and gluing of the steel platens to the notched specimen. P