PSI - Issue 11

Alisson Rodrigues de Oliveira Dias et al. / Procedia Structural Integrity 11 (2018) 84–90 Author name / Structural Integrity Procedia 00 (2018) 000 – 000

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Fig. 5. Comparison of means by the Tukey test.

Finally, Table 4 presents the values of the factors of variation of the VPU in concretes according the types of fck in each temperature.

Table 4 - Factors of variation of UPV according to temperature. Fck (MPa)

Temperature (°C)

REF. 100% 100% 100% 100%

200°

400°

600°

800°

20,0 30,0 40,0 50,0

96,75% 99,23% 99,45% 98,90%

75,92% 85,28% 79,75% 84,21%

39,56% 52,01% 54,67% 43,00%

10,63% 24,29% 18,16% 34,10%

4. Conclusion

Concrete is a material widely used, mainly for its properties and durability. However, when subjected to high temperatures it undergoes deterioration like color change, cracking, loss of mass, displacement and, mainly, decrease of rigidity and mechanical resistance. It was verified through ANOVA that the type of cooling has no influence on the reduction of ultrasonic pulse velocity. As to the fck of the concrete, it is evident that the velocity of ultrasonic propagation in the concrete is affected drastically when subjected to high temperatures, especially from 400 °C. This fact can be proven by the analysis of variance perfomed. In addition, concrete with lower fck has higher values of UPV reduction, which is probably due to a greater amount of porosity and cracks in the concrete when subjected to high temperatures. For example, the 20 MPa concrete between the temperatures of 200 °C and 800 °C has a UPV variation of 4106 m/s to 451 m/s, which shows a drastic reduction. Finally, the knowledge of this behavior of ultrasonic pulses in the concrete allows us to know better the structure exposed at high tempertures, relating the possible loss of resistance to the amount of voids present in its interior after this exposure.

Acknowledgements

The authors are grateful to the Civil Engineering Graduate Program in Structures and Civil Construction of the Federal University of Ceará, CAPES for funding, to the Department of Metallurgical and Materials Engineering and to the technicians and scholarship holders of the Civil Construction Materials Laboratory of the University.