Analysis of temperature stresses in concrete breakwater elements

Abstract

In this report, the results of a numerical parameter study on temperature stresses caused by hydration of cement in concrete breakwater elements are shown. Two different geometries were analysed namely hollow cubes and tetrapods. The problem encountered in solid cube breakwaters is the undesirable temperature build up between the core and the outside surface. The main reason for the temperature build up, is the thermal heat, which is generated due to the heat of hydration of cement from the time of casting. This thermal gradient induces eigen-stresses and causes the early age cracking. The choice of a hollow cube is a way to reduce the temperature gradient and thus the eigenstresses. A parameter study is undertaken in order to arrive at an optimum dimension based on the thermal gradient and the eigen-stresses. The variables are the cube dimension (i.e., height H = 2, 3 and 4 m with the inner diameter to the height ratio d,/H = 0.4), the size of the hole (d= 0.9, 1.2 and 1.5 m for the 3 m hollow cube only), the cement content (225 and 325 kg/m3), the initial concrete mix temperature (5, 15 and 25 °C) and the degree of isolation (with and without isolation). For the analyses of the tetrapods, two geometries were chosen. The total height H of the tetrapod was 3.11 and 4.15 m with corresponding diameters D = 1.5 and 2 m. The favourable conditions for the reduction in the temperature gradient and the tensile stress peak for the hollow cubes were: the low mix temperature, the larger hole diameter, the low cement content and the smaller hollow cube. From the range of hollow cube specimens analysed, it appears the 2 m hollow cube is the best choice based on the temperature gradient as well as the tensile stress peak generated.