PSI - Issue 13

Libor Topolář et al. / Procedia Structural Integrity 13 (2018) 1177 – 1182 Author name / Structural Integrity Procedia 00 (2018) 000 – 000

1179

3

2. Materials and experimental setup

For the experimental part, concrete specimens with dimensions of 0.1 × 0.1 × 0.4 m were prepared in the laboratory of the Institute of Technology of Building Materials and Components, Faculty of Civil Engineering, Brno University of Technology. Each mixture was divided into six temperature sets, the reference set was kept at 20 °C and the remaining sets were divided into individual firing temperatures 400, 600, 800, 1000 and 1200 °C. The composition of the mixtures used during the experiments is given in Table 2. All the specimens were kept in a water bath for 28 days. Each test specimen was pre-dried in a laboratory oven at 110 °C for 72 hours. This procedure removed free water from the specimens and consequently spalling of the specimens (Zhao et al. (2014)) at temperatures above 400 °C. During firing, the temperature in the oven was set to at an increase of 5 °C/min and the target temperature was then maintained for one hour. The specimens then cooled freely with access to air in the oven to the laboratory temperature.

Table 2. Mixture design for 1 m 3 Topolář et al. (2017 a) or Topolář et al. (2017b)

Weight (kg)

Compound

Mixture A

Mixture B

Mixture C

Cement CEM I 42.5R (Mokrá)

345

Water

160

173

176

Superplasticizer (Sika Viscocrete 2030)

2.8

2.5

3.1

Sand 0/4 ( Žabčice)

848

896

813

–

–

Gravel aggregate 4/8 (Olbramovice) Gravel aggregate 8/16 (Olbramovice) Gravel aggregate 11/22 (Olbramovice)

1010

– –

980

521 391

–

Fig. 1. The arrangement of acoustic emission sensors on specimen during the three-point bending test.

Three-point bending tests were performed after the specimens were exposed to the prescribed thermal-stress levels. Ten specimens from each set were tested. During the tests, the acoustic emission activity was recorded. Four acoustic emission sensors were attached to the surface by beeswax – see Fig. 1. Acoustic emission signals were recorded by measuring equipment DAKEL XEDO with four acoustic emission sensors IDK-09, including 35 dB preamplifier. To eliminate the mechanical and electrical noi se, a guard sensor was used (Topolář et al. (2017a)). The loading tests were carried out using a Heckert FPZ 100/1 testing machine at a laboratory of the Institute of Building Testing, Faculty of Civil Engineering, Brno University of Technology. The beam specimens with an initial central edge notch were loaded under three-point bending test using the displacement-controlled method, which is more suitable for monitoring the behaviour of specimens after crack initiation and during its propagation. The initial notch was made by a diamond blade saw before testing. The depth of the notches was about 33 mm for all specimens ( Topolář et al. (2017b) ).