MICROSTRUCTURAL CHANGES OF HIGH DENSITY CONCRETES EXPOSED TO HIGH TEMPERATURES

Reinforced concrete structures, when exposed to fire or to high temperatures, might suffer important microstructures changes, which in turn affect their macroproperties, such as compressive strength and porosity. These changes are both chemical and physical in nature, involving the loss of water, thermal expansion and contraction and the modification of the crystalline arrangements of some of its constituents. Their combined action might significantly reduce the resistance of the structural member, inclusive to the point of collapse. Researches in the field of concrete fire resistance are usually focused on the monitoring of the external signs of degradation that are visually noticeable, such as the micro-cracks, expansions and spalling. The chemical and physical changes in the microstructure are less examined, although they are the primary reasons behind the degradation. The research discussed in this paper was designed to look into the determination of the residual properties of mortar and cement pastes after heating exposure at up to 800°C. The changes in the microstructure were monitored with XRD, DTA and dilatometry tests. The results obtained confirmed that high density concretes are vulnerable to spalling and that the degree of deterioration can be correlated to changes in the x-ray difratogram.

• INTRODUCTION

• EXPERIMENTAL INVESTIGATION

• DATA ANALYSIS

• DISCUSSION

• CONCLUSIONS

• REFERENCES