A discrete transport-mechanical approach for modelling the durability of concrete

T Technology (General)

Fahy, Caroline ; Grassl, Peter

University:University of Glasgow

Department:School of Engineering

关键词: Reinforced concreteCoupled transport-mechanicalComputational modellingCrackingHydraulic fracture;   

Others  :  http://theses.gla.ac.uk/5761/1/2014FahyPhD.pdf

来源: University of Glasgow

【 摘 要 】

Reinforced concrete is one of the most commonly used structural materials in the world andis used for buildings and many different types of civil engineering structures, such as bridges,tunnels and airports. The majority of these structures are required to remain in service forat least 50 years while some are expected to last well over 100 years. Fracture of thesestructures leads to an increase in the permeability of the concrete which in turn can result inincreased ingress of water and other aggressive agents, such as chlorides or carbon dioxide,that accelerate the deterioration of these structures. Likewise, the mechanical properties ofthe concrete can be affected by the transport of moisture into the structure. The increase inmoisture can lead to a reduction of the strength and the stiffness of the material.The costs arising from structural failure are extremely high and in practice repair work tendsto be implemented even when it is not entirely necessary. Therefore reliable approaches thatcan describe the interaction between the transport and mechanical properties of concrete andpredict resulting structural degradation are of great benefit for practising engineers. Numericalmodels, such as the one proposed in this work, could be used for predicting when arepair is really necessary.In this work, a transport-mechanical lattice approach to modelling the durability of concreteis proposed. The discretisation of the specimen domain is based on a dual Delaunay andVoronoi tessellation in which the edges of the Delaunay triangles form the mechanical elementsand the transport elements are placed along the edges of the Voronoi polygons. Themechanical response of the concrete is described using an isotropic damage constitutive law,while the transport of moisture through the specimen is described using constitutive lawsdeveloped for mass transport through porous materials.Both the mechanical and the transport models are assessed individually before the couplingiibetween the two models is implemented. The accuracy of the proposed coupled approachis validated through the analysis of an elastic thick-walled cylinder, in which the numericalresults are compared with an analytical solution derived as part of this work. The proposedcoupled approach is then applied to the case of corrosion-induced cracking of reinforcedconcrete structures. In this approach, the corrosion products are assumed to behave as afluid and therefore values of fluid properties are required. A value of viscosity is determinedbased on the analysis of a concrete specimen containing a single reinforcement bar. Finally,the proposed approach is applied to a concrete specimen containing four reinforcement barsto assess the approach as a predictive model.As expected with the concrete specimen containing a single reinforcement bar, very goodagreement between numerical and experimental results is obtained. In the case of a specimencontaining four reinforcement bars, it is observed that for small attack penetrationdepths the proposed approach is in very good agreement with experimental results. As theanalysis continued, however, the numerical approach under-estimated the crack width whencompared to experimental results.