Porosity of UHPFRC exposed to high temperatures determined by different techniques

• Main Authors: Korecký, Tomáš, Pokorný, Jaroslav, Fořt, Jan, Čítek, David, Pavlík, Zbyšek
• Format: Conference Proceeding
• Language: English
• Subjects: Building materials; Construction materials; Digital cameras; Digital imaging; Fiber reinforced concretes; Helium; High temperature; Image analysis; Intrusion; Microcavities; Optical fibers; Particle size distribution; Pore size; Pore size distribution; Porosimeters; Porosity; Pycnometry; Reinforced concrete; Service life; Structural members; Workability
• ISSN: 0094-243X; 1551-7616
• DOI: 10.1063/1.4955245

The pore system characterization of an Ultra High Performance Fibre Reinforced Concrete (UHPFRC) exposed to the elevated temperatures is presented in the paper. The porosity and pore size distribution of building materials are of the particular importance because of their clear effect on durability and service life of structural elements and buildings. Material characteristics as mechanical, thermal and hygric properties are strongly dependent on pore system. For porosity measurement, several techniques having specific advantages or disadvantages with respect to the pore size are available. In building materials research, usage of Mercury Intrusion Porosimetry (MIP) with range of the detected pores up to 100 µm is the most common. Nevertheless, in practical measurements, the differences between the porosity values determined by helium pycnometry and MIP are usually observed. It can be attributed to the presence of pores bigger than 100 µm. Based on the literature analysis it is evident that the porosity increases with the amount of fibres used since fibres application reduces workability of fresh mixture and thus cause heterogeneities and microcavities in material microstructure and interfacial transition zone between fibres, aggregates and cement paste. Therefore, the Optical Porosimetry (OP) based on an image analysis is presented in the paper as a suitable supplemental method for classification number, size and shape of bigger pores. At first, porosity is investigated on samples without temperature loading. Then, on samples which are exposed to the temperatures of 400, 800, and 1000 °C respectively. Pores size distribution is studied using mercury intrusion porosimeters Pascal 140 and 440. Images are captured by an optical microscope with an attached digital camera. The obtained results show necessity to apply the combined technique for the assessment of the porosity value.