International Concrete Abstracts Portal

After actual fires with plastic materials involved concrete surfaces are often infested with high chloride concentrations, causing a serious risk of corrosion of the reinforcement. Absorption techniques with lime paste have been recommended to remove chlorides from concrete surfaces. To study this reaction concrete beams with different chloride contents, added as sodium chloride, were cast. The chloride distribution in the concrete before and after lime paste treatment and the chloride content of the used lime were determined analytically. The results show that the lime does not absorb chlorides, and within the concrete, the chlorides are redistributed. Further tests were made to study the rate of chloride absorption from aqueous solutions by lime, acti-vated carbon and ion exchange resins. The amount of absorbed chloride was very low. Corresponding the absorption of chlorides by fresh pastes of different cements and completely hydrated cements was studied. An effect of absorption but much more of chemical bond was shown.

Generalised response curves for the transient thermal strain behaviour of concrete have been developed from a series of tests employing a wide range of materials and a lower than normal heating , rate. The latter allowed detailed assessment of underlying "material" behaviour to be made which was not complicated by "structural" effects that develop at a fast heating rate. The temperature, stress and moisture conditions within a cylindrical test specimen have been investigated and a study of the behaviour of individual constituents has confirmed that aggregate thermal stability is a critical factor. Thermal strains during virgin heating were separated into "Free" and "Load Induced" components possessing different and distinct properties allowing successful prediction of residual strains. A master with te m first h analysis the mast While t effect 0 clearly sensitiv thermal curve connecting Load Induced perature up to 450°C was found eating for different concretes of heated concrete structures er curve signified onset of c ransient creep did not occur duringf cracking caused bv thermal inc evident. Strain measurements, the indicators cycle. of damage taking Thermal Strain to exist during thus simplifying Departure from concrete damage. ing cooling, the ompatibility was harefore, proved place during the

A study was carried out to assess the residual strength of reinforced concrete columns after exposure to a standard fire for various lengths of time, and cooling. The use of a mathematical model, an ultrasonic pulse test method and a load test method are investigated. Calculated temperatures and residual strengths of test columns were compared with those measured. Comparisons were also made between calculated and measured pulse velocities. The results indicated that using the calculation procedure and the method of measuring pulse velocity described in the study, the residual strength of concrete columns can be assessed with an accuracy sufficient for practical purposes.

The paper describes a new technique developed by the author for heating concrete rapidly by application of microwave power. Using an appropriate thermal insulation it is found to be possible to heat dry concrete specimens 10°C per minute and 20°C per minute avoiding the development of thermal stresses within the specimens. A series of 90 specimens has been heated 10°C per minute to various maximum temperature levels. The residual compressive strength was measured, and the results are compared to the similar results of the same concrete heated slowly. Applications for the technique are outlined, and a possible future development; is presented.

The present paper is intended to give an overall information on temperatures which may have occured in concrete cross-sections affected by a fire Firstly the paper contains a catalogue of circumstances and vestiges which can be found when the affected building is visited and which allow conclusions concerning the intensity of the fire and the resulting value of damages to the structural elements. For this purpose, residual contents of the building (fire load), the state of building materials, and the evident condition of the concrete structure itself are used. In the second part of the paper, general informations are given on the development of natural fires and on the parameters which in-fluence it. On the basis of two series of experiments - Metz and Lehrte - which gave temperature-time developments in compartments where wood cribs or furniture were burnt, temperature fields are presented for square concrete cross-sections affected from all sides, and for T-shaped sections affected from three sides. It is stated that the presented figures can only be rough approaches for practical work. Short, only introductory informations on residual changes of material properties due to temperature influences are added to facili-tate judgements and decisions. It stands to reason that, if findings won by this guide lead to the conclusion that the structure may be worthy to be kept, more intense and detailed investigations have to be done.