S Y N O P S I SThis is thejrst of three papers presenting the results of an investigation into the eflect of material and environmental factors upon the transient thermal strain behaviour of concrete during thejrst heat cycle under load to 600°C. A literature review of transient thermal creep of concrete is presented. It reveals inadequate understanding of this subject for temperatures above 100°C and a lack of data for conditions pertinent to the analysis of concrete structures duringfirst-time heating. This paper also presents results of preliminary work forming background information for the analysis of the transient thermal strain behaviour of unsealed concrete specimens. The complex temperature, moisture and thermal stress conditions developing during thermal transients in concrete test specimens have, therefore, been investigated experimentally and/or theoretically. The 'structural' effects and modiJication of material behaviour caused by these conditions have consequently been minimized by appropriate design of experiment. Characteristics of the individual aggregate and cement paste constituents have been determined by dilatometry, DTA and TGA tests which showed aggregate thermal stability to be a critical factor. Notation a radius of specimen r radial dimension t time Z axial dimension D thermal diffusivity E modulus of elasticity K maximum thermal stress

Synopsis This is the second of three papers presenting the results of an investigation into the transient thermal strain behaviour of concrete during the first heat cycle to 600°C under load. The results during first heating to 600°C under uniaxial compressive load of eight different unsealed concrete andcement paste mixes are presented. The thermal strains were shown to consistof ‘free’ and ‘load-induced’ components which possessed different and distinct properties. The free thermal strains of the unloaded concretes were dominated by the thermal expansion of the constituent aggregate, whilst the load-induced thermal strains (LITS) were identical for temperatures up to about 450°C, irrespective of type of aggregate used, provided certain criteria were met. A ‘master’ LITS curve therefore existed which represented LITS of Portland-cement-based concretes in general. Also LITS was not significantly influenced by the age of the concrete (1 and 9 years) or the initial moisture condition (moist and air-dry). These findings could considerably simplify the analysis of heated concrete structures, particularly since only two strain components are required. Replicate tests were performed to provide a statistical basis for analysis of the results. The effect of aggregate restraint was determined by comparing results from concrete and cement paste specimens. In addition to ‘material’ factors, the effects upon free and load-induced thermal strain of the following ‘environmental’ parameters were examined: temperature level, initial moisture conditioning, preheating, rate of heating and stress level.

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