Research On Meso-scale Simulation Of Concrete Cracking Induced By Helical Strand Corrosion

The prestressed concrete structure plays an important role in the field of civil engineering.With the increase of service time,chlorine ions and other aggressive ions erode the internal strand.The expansion of the corroded strand causes the concrete cracking,which endangering the safety of the structure.It is of great engineering significance to study the corrosion-induced cracking of strand with the help of finite element software to evaluate the durability of structure.In this paper,the crack of concrete cover caused by strand corrosion is investigated by means of numerical simulation.The corresponding meso-scale models of corrosion-induced cracking were established in two-dimensional and three-dimensional respectively to explore the concrete cracking caused by strand corrosion.The influence of correlative parameters on corrosioninduced cracking is discussed.The main work and achievements of this paper are as follows:(1)A plane corrosion expansion model that considering the non-uniform distribution of the corrosion products of strand is proposed.The distribution of corrosion products of the strand is regarded as a semi-ellipse distribution,and a planar corrosion-induced cracking meso-scale cohesive model is established.The proposed model can effectively reflect the influence of nonuniform distribution of corrosion products on corrosion-induced cracks.In the model,the initiation,extending and propagation of micro corrosion-induced crack can be simulated by the deformation and damage of cohesive element.The phenomenon of the corrosion-induced cracks in concrete developing through the weak interface of concrete was found in the simulation.(2)A three-dimensional meso-scale numerical model of strand corrosion-induced concrete cracking is presented.In order to fully consider the influence of the helix structure of the strand on corrosion-induced cracking of concrete structure,the three-dimensional model of the strand is established.Concrete is regarded as three-phase composite material consists of aggregate,mortar matrix and the interfacial transition zones(ITZ)between the two to consider the heterogeneity of concrete.The three-dimensional numerical simulation of corrosion-induced cracking was carried out,and the effectiveness of the proposed model was verified.The prediction precision of corrosion-induced cracking can be highly improved by taking the helix structure of strand into account.And the strand with helix structure leads to more serious corrosion-induced cracking than the reinforcement bar,which needs to pay more attention to in the real structure.(3)The effects of the parameters such as the aggregate volume and the lay length of strand on corrosion-induced cracking are analyzed.The helix structure of the strand leas to its expansion pressure distribution is different from reinforcement bar.The critical corrosion loss of concrete surface cracking increases with the increase in the strand lay length,while the crack width decreases as the strand lay length increase.The smaller the concrete cover is,the smaller the critical corrosion loss of the surface cracks is,and the greater the corrosion-induced crack width is.The distribution of aggregate in heterogeneous concrete has influence on the quantity,initiation location and extension direction of corrosion-induced cracks.The lower the volume of aggregate in concrete,the easier the corrosion-induced cracking occurs,and the wider the width of corrosion-induced crack.