The effect of environmental loading on concrete structures

Abstract

This study investigates the thermal and mechanical behaviour of concrete elements under environmental loading, with a focus on South African aggregates - dolerite and dolomite. As South Africa transitions to adopting EN1992-1-1: Design of Concrete Structures (2004), understanding the applicability of international standards to local materials and climatic conditions is critical. The concrete structures in the region are exposed to significant thermal variations, solar radiation, and drying conditions, inducing temperature gradients, shrinkage, and thermal stresses. An experimental programme was conducted, featuring concrete elements of three shapes, cube, flange, and L-section, cast with dolerite and dolomite aggregates. Thermocouples and vibrating wire strain gauges were used to monitor temperature and strain over a three-month winter period, while material characterisation tests determined key thermal and mechanical properties. Finite element models developed in ABAQUS/CAE (2023) were calibrated using experimental data to refine thermal conductivity and solar absorptivity values. Sensitivity analyses evaluated the effects of thermal properties on effective temperatures, temperature gradients, and thermal strains. The results show that aggregate type had a limited influence on thermal and shrinkage responses. Dolomite mixes, with higher thermal conductivity and solar absorptivity, experienced slightly greater temperature variations, while Dolerite mixes showed steeper gradients but lower stress development due to reduced thermal expansion, modulus of elasticity, and conductivity. Geometry also affected strain and stress distributions, with L-sections exhibiting higher residual stresses under environmental loading. These findings highlight the need to calibrate EN1992-1-1 assumptions for local materials and conditions. The study recommends developing standardised thermal property tests for South African aggregates and incorporating calibrated material properties into structural design models.