BOUND WATER CONTENT, PERMEABILITY AND RESIDUAL COMPRESSIVE STRENGTH OF CONCRETE AT HIGH TEMPERATURES

Concrete damage by high temperatures includes weight loss, strength and modulus reductions and the formation of cracks and large pores. Thermal treatment reduces the amount of chemically bound water in the hydrate phase. A rise in temperature affects the pore structure by reducing the specific surface of hydration products. Cement paste becomes more heterogeneous in microstructure and coarser in pore structure. This reveals in higher pore median radius, total porosity and volume of large pores in a weight unit of hydrated cement paste of concrete. Compressive strength is not only significant parameter showing structural integrity of concrete; permeability influences concrete durability as well. To demonstrate this, permeability coefficients at various high temperatures are presented. The key quantitative insight into the hydrate phase decomposition is based on thermal analysis results. Thermo gravimetric (TG) mass losses are related to the hydrate phase changes. The tests employing TG mass losses answer the question if the hydrate phase is present at individual high-temperature levels and what its quantitative state is. Strength estimations and methods of pore intrusion porosimetry with calculated permeability coefficients and thermal analysis are suitable for the interpretation of concrete behaviour when subjected to high-temperature attack. Conclusions are drawn about residual properties of concrete specimens from Temelin (Czech Republic), Mochovce (Slovakia) and Penly (France) nuclear power plant (NPP); when subjected to temperatures up to 800°C. Relations among compressive strength, permeability, pore median radius and bound water content in concretes are discussed and concrete resistance with various mixture compositions is compared.

• INTRODUCTION

• EXPERIMENTAL DETAILS

• RESULTS AND DISCUSSION

• CONCLUSIONS

• REFERENCES