Conference Agenda

The paper presents the experimental campaign on the problem of post-fire rehydration of carbonate aggregates, resulting in expansion and fall of the treated layer at high temperature. In the experimental campaign, three types of aggregates (2-8 and 8-16 mm grain size) are used for the production of concrete specimens: (1) the thermally stable representative of igneous rocks - basalt and two representatives of sedimentary carbonate rocks: (2) dolomite (with 1% calcium carbonate and 25% calcium-magnesium carbonate) and (3) limestone (with 98% calcium carbonate). The 150 mm cubic samples were heated in an electric furnace at 1 °C/min to the set temperature (200 °C, 600 °C, 1000 °C). After heating, the following measurements were compared: mass and density (directly after cooling), compressive strength (after 14 days), and crack development and height of the samples were monitored for 6 days, followed by heating (144 hours). As a result of heating to a temperature of 1000°C, a sharp decrease in concrete mass and an increase in the cross-sectional height of the specimen are observed in concrete with carbonate aggregate. This results in a large reduction in bulk density and compressive strength and in the disintegration of samples containing carbonate aggregate in the days following heating. This peculiarity of carbonate aggregate has already been studied in the literature. Carbonate aggregates have a convincing property as an aggregate used daily in construction. However, these properties deteriorate significantly in the event of fire and more effort needs to be made to disseminate this knowledge.

When repaired RC structures are exposed to fire, there is a risk of fire spalling, as in the case of concrete. Our group previously investigated the fire spalling behavior of cement materials using ring-restrained heating tests and developed heat-resistant repair materials (HRM) that can be used within an application range of 300℃ lower. However, we have not yet examined whether the HRM materials can be applied at temperatures above 300 ℃. In this study, we evaluated the fire spalling behavior of HRM using a ring-restrained heating test, and a small cylindrical electric furnace was used. In addition, the effect of jute fibers on the fire spalling prevention of repair mortar was examined. In a results, the maximum fire spalling depth of the Control specimen was 12 mm, and the fire spalling suppression effect on HRM was confirmed by mixing more than 0.1 vol% of Jute fiber. We discussed the relationship between the restrained stress, vapor pressure, and internal temperature at 5 mm from each specimen. Vapor pressure increased to 8 MPa at 140℃ for the control specimen, and fire spalling occurred. The restrained stress was 4 MPa at 140 ℃. For the jute specimens, the maximum restrained stress ranged from 2 to 3 MPa, and the restrained stress of the jute specimen was lower than that of the control specimen. The maximum vapor pressure in the jute specimens was approximately 11 MPa. Although the maximum vapor pressure of the jute specimen was higher than that of the control specimen, no fire spalling occurred.

The strain components needed to correctly predict the deformation behavior of concrete at elevated temperature are extremely complex given the interdependence of these strain components and hence the difficulties in uniquely defining each of these strain components independently. The Load Induced Transient Strain “LITS” is known to be the most complex and important component for concrete exposed to elevated temperature. This component has been considered in a simplified way in the current design provision by implicitly including it in the uniaxial stress-strain law. This simplification simplifies the complexities for the designer. However, it leads to certain limitations which have already been highlighted in literature based on structural level simulations of reinforced concrete. But its suitability for predicting the deformation and fracture behavior of concrete at elevated temperature remains unanswered. The paper presents results of a numerical investigation aimed at investigating the suitability of the Eurocode 2 stress-strain model for predicting the macroscopic response of concrete under compression at a geometric scale corresponding to material testing level. Different tests from literature on cylinders with varying loading histories and exposed to elevated temperatures are simulated. Based on the simulation results, the paper comments on the macroscopic response at material level which can/cannot be captured using the Eurocode 2 model.

Concrete has been the most widely used construction material in recent decades, while the use of macro-polymer fibres has gained increasing attention due to their significant advantages. Despite the commendable structural performance of concrete, it is crucial to recognize that fiber-reinforced concrete faces a substantial risk when exposed to certain conditions, such as elevated temperatures. Although there is extensive scientific literature on this subject, much of it does not capture the material’s behaviour at the precise moment it is subjected to high temperatures. To address this gap, the present research focuses on analysing the flexural response of fiber-reinforced concrete at 20°C, 165°C, 185°C, and 200°C. For this study, it was essential to carefully isolate the specimens to minimize temperature loss during testing. Upon completion of the tests and thorough fracture surface analysis, the results indicated that polyolefin fibers reduce the risk of spalling; as temperature increases, the residual load-bearing capacity of the material diminishes, approaching that of plain concrete at the highest temperature studied.

The structural integrity and load-bearing capacity of burning buildings can be significantly reduced due to high thermal load. This causes a problem for e. g. rescue workers, as they have to ensure the rescue of people in a burning building even if there is an increased risk of collapse. Predicting safe routes in and out of a burning building is a difficult task that takes resources and expertise. Alternatively, escape routes can be identified using simulations, which require a multidisciplinary and multiscale approach. These simulations may either run in real-time or need to be coupled with artificial neural networks in order to train them such that these neural networks suggest safe escape routes in real-time in case of a fire incident. Computational-fluid-dynamic simulations of the fire provide information about both the temperature and the smoke distribution in the single rooms of a building. Micro-scale simulations describe local material behaviour such as spalling and cracks. Structural-scale analysis provides information about the global structural behaviour of the building including a possible progressive collapse. Nevertheless, a coupling of these multi-physical simulations is needed to identify safe escape routes in a burning building. However, it is not only necessary to couple across scales but also across software platforms, as there is – to the best knowledge of the authors – no simulation framework available that can calculate the stated effects on multiple scales with good accuracy. Consequently, studying these fire-structure interactions necessitates an accurate computational simulation framework that integrates the effects of different physical phenomena. The objective of this contribution is to provide a computational framework for fire-structure simulations to elucidate the interplay between damage of concrete and progressive collapse. In the proposed computational setup, two software packages are used to simulate material damage and the resulting collapse of an exemplary structure under fire. A micro-scale model uses a FEniCs-based solver for the concrete material and a structural-scale model uses ABAQUS for the (progressive) collapse simulation. These solvers exchange information on temperature, stress, and changes in geometry across scales and software through an open-source coupling library, preCICE. The proposed model is illustrated by a numerical experiment that forecasts the damage leading to progressive collapse.