The effect of thermal properties and climatic factors on the response of concrete elements

Abstract

Concrete structures are subjected to complex and highly variable climatic conditions including temperature, wind speed, rainfall, and solar radiation. The thermal behaviour of concrete structures has become an important research area due to the increasing physical size of concrete structures and, more recently, the advent of integral construction methods which have gained popularity for reducing long-term maintenance requirements. While the demand for sustainable materials and construction methods has increased as measures are taken to adapt to and mitigate the effects of climate change, the human economy has grown. The energy required for these activities is released thermally into the atmosphere and is climate forcing. In this dissertation the effect of variations in climatic conditions on the thermal response of simple concrete structures is investigated. After discussing previous studies relevant to this field, an experimental program is described, in which the effects of surface colour (albedo, solar absorptivity and emissivity), member geometry, material properties, and daily and seasonal climatic variations on the temperature distributions of three reference structures constructed in Pretoria, South Africa is studied. A two-dimensional finite element heat transfer model is developed to simulate the effect of these parameters. It is found that high conductivity materials with high albedo surfaces, and minimal cross-sectional depth exhibit uniform thermal gradients. Thus, they are less prone to high stresses that could result in thermal cracking. Such combinations of geometry, materials and surfacing could be implemented as climate adaption and mitigation measures as they simultaneously reduce the urban heat island effect and carbon dioxide emissions as the need for electrical heating and cooling in buildings is reduced.