Katalin Kopecskó

Improved fire resistance by using Portland-pozzolana or Portland-fly ash cements

Our study was directed to the analysis of the influence of various types of cements on the behaviour of concrete at high temperatures. In our experiments binary blended and ordinary Portland cements were involved: two Portland cements with different clinker compositions and Portland cements containing pozzolanic additives as replacement of clinkers. In the first part of the study we focused on the influence of cement types where cement paste specimens were investigated. Then, based on the results of cement paste specimens, concretes specimens were prepared with some selected types of cements. Most important observation of our experimental study was that the pozzolanic additives and their increased amount have a favourable effect on the heat resistance (fire resistance) properties of concrete.

Behaviour of tyres in fire

The increasing numbers of used tyres constitute a serious threat to the natural environment. The progress made in recent years in the management of polymer wastes has meant that used tyres are starting to be perceived as a potential source of valuable raw materials. The objective of this research was to study the burning characteristics of various used tyres. Waste tyres of seven producers have been tested. In order to understand thermal properties, three different assessment methods were used to study the behaviour of the material: (1) determination of ash content, (2) flame propagation test and (3) thermal analysis. The ash content test can be used to analyse how many percentage of the tyre leaves in the form of smoke or gas. The flame propagation test gives information on the duration of the combustion and the degree of smoke generation. Results of thermal analysis (TG/DTG/DTA) show the degree and speed of the mass changes of the different tyre types, the enthalpy change and the temperature of the reactions during heating. By combustion tests, it was modelled how the tyres behave when they are burning in incineration plant. In terms of recycling, those tyres are better, which have low decomposition temperature and smaller residual mass. This also means that maximum combustion heat can be recovered. After burning, the samples showed the greatest difference in loss of mass; however, all are different in flammability, afterglow time and their thermal stability.

Fire Resistance of Concretes with Blended Cements

An extensive experimental study has been carried out to analyse the post-heating characteristics of concrete subjected to high temperatures up to 800 °C. Major parameters of our study were the type and amount of supplementary cementitious materials (slag, fly ash, trass, silica fume, metakaolin) in cements and the level of maximum temperature (50, 150, 300, 500 or 800 °C). Present study includes analyses of surface cracking and residual compressive strength.

Concrete with Improved Chloride Binding and Chloride Resistivity by Blended Cements

Durability and service life of concrete structures can be endangered by chloride ions. Two phenomena help to keep control of chloride effects. On one hand cements are able to bind chloride ions by their aluminate clinker phases or by the clinker substituting materials. On the other hand resistivity of concrete against chloride penetration can be improved by careful selection of concrete constituents and production. Detailed results of two series of extensive experimental studies are presented herein. Chloride ion binding capacity of tested cements in decreasing sequence was the following: ( ) CEM III/B 32,5 N-S; ( ) CEM III/A 32,5 N; ( ) CEM II/B 32,5 R; ( ) CEM II/B-M (V-L) 32,5 R; ( ) CEM I 42,5 N. Test results indicated that the increasing substitution of clinkers by GGBS improves the chloride resistivity in concrete made with the same water to cement ratio. The application of air entraining agent increases considerably the values of . Based on the migration coefficients ( ) the following sequence of efficiency was found (from the best): CEM III/B 32,5 N > CEM V/A (S-V) 32,5 N > CEM III/A 32,5 N > CEM II/B-S 42,5 R > CEM II/A-S 42,5 N > CEM I 42,5 N.

Improved Fire Resistance by Using Different Types of Cements

Composition and microstructure of hardened cement paste have important influences on the properties of concrete exposed to high temperatures. An extensive experimental study was carried out to analyse the post-heating characteristics of concretes subjected to temperatures up to 800 °C. Major parameters of our study were the content of supplementary materials (slag, fly ash, trass) of cement (0, 16 or 25 m%) and the value of maximum temperature. Our results indicated that (i) the number and size of surface cracks as well as compressive strength decreased by the increasing content of supplementary materials of cements due to elevated temperature; (ii) the most intensive surface cracking was observed by using Portland cement without addition of supplementary materials. The increasing content of the supplementary material of cement increased the relative post-heating compressive strength. Tendencies of surface cracking and reduction of compressive strength were in agreement, i.e. the more surface cracks, the more strength reduction.