Transient thermal strain of concrete: literature review, conditions within specimen and behaviour of individual constituents

Abstract

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

The effect of concrete composition on laser scabbling

“…[14]. 'e' Endothermic peak, Calcium hydroxide (portlandite) dehydroxylation mass loss [12,15,16,17,18]. 'f' Endothermic peak,…”

Specimen size effect on the residual properties of engineered cementitious composites subjected to high temperatures

“…The significant and unique increase of pore volume of macropores for the ECC specimens exposed to 800°C found in this study strongly suggests that pores of this size may be responsible for the significant deterioration in compressive strength, as discussed in next section. The degradation of hydrates (C-S-H gels), which is inevitable [6,7,21] when the exposure temperature is raised to 600°C and above, is the main reason for severe pore structure coarsening.…”

“…However, after exposure to 600°C, the main causes of deterioration in compressive strength might be attributed both to the physical transformation of the matrix and chemical transformation of hydration products. When the temperature was raised to 600°C, decomposition of the major hydrate, known as tobermorite (gel), was inevitable [21], causing severe increase in the microstructure of its matrix and the loss of binder property [6,7]. Moreover, decomposition of fine silica sand at 800°C was also demonstrated by scanning electron microscopy [7].…”

“…Between 400°C and 600°C, average loss in compressive strength is significantly higher compared to the range of 23-400°C and reach to 50%. Beyond 600°C, in the last range, ECC specimens showed severe deterioration, most probably, due to the decomposition of hydration gels [21,28]. The average residual strength was dropped to about 35%, regardless of specimen size.…”

An Overview of Modeling Cement Based Materials at Elevated Temperatures with Mechanics of Multi-Phase Porous Media

“…An Overview of Modeling Cement Based Materialsstructure of porosity and changes of sample dimensions (irreversible in part), [44,45]. The concrete strains during first heating, called load-free thermal strains (LFTS) are usually treated as superposition of thermal and shrinkage components, and often are considered as almost inseparable.…”