Mechanical and durability behaviour of growing concrete structures

Purpose – This paper seeks to analyse 3D growing concrete structures taking into account the phenomenon of body accretion, necessary for the simulation of the construction sequence, and carbon dioxide attack. Design/methodology/approach – A typical 3D segmental bridge made of precast concrete is studied through a fully coupled thermo-hygro-mechanical F.E. model. The durability of the bridge is evaluated and carbonation effects are considered. Creep, relaxation and shrinkage effects are included according to the theory developed in the 1970s by Bažant for concretes and geomaterials; the fluid phases are considered as a unique mixture which interacts with a solid phase. The porous material is modelled using n Maxwell elements in parallel (Maxwell-chain model). Findings – First, calibration analyses are developed to check the VISCO3D model capabilities for predicting carbonation phenomena within concrete and the full 3D structure is modelled to further assess the durability of the bridge under severe conditions of CO2 attack. Originality/value – The adopted numerical model accounts for the strong coupling mechanisms of CO2 diffusion in the gas phase, moisture and heat transfer, CaCO3 formation and the availability of Ca(OH)2 in the pore solution due to its transport by water movement. Additionally, the phenomenon of a sequential construction is studied and numerically reproduced by a sequence of “births” for the 3D finite elements discretizing the bridge. The fully coupled model is here extended to 3D problems for accreting bodies (as segmental bridges) in order to gather the effects of multi-dimensional attacks of carbon dioxide for such structures.