Reinforcement corrosion initiation and activation times in concrete structures exposed to severe marine environments

The chloride corrosion threshold of steel in concrete depends not only on concrete and steel properties but also on the potential of the steel while it is still in the passive condition. An innovative model to predict corrosion in reinforced concrete structures is presented, incorporating potential dependence and corrosion macrocell effects. The novel approach integrates the initiation and the propagation stages of corrosion in a single predictive model. The model is applied to a generic, partially submerged, reinforced concrete marine pile. The purpose of this paper was to establish and illustrate the concept of a functional approach to implement potential-dependent chloride threshold in corrosion damage projections, plus articulation of the initiation and propagation stages, in one predictive model. The long-term damage projection results are markedly lower contrasted with those of an identical system with a time-invariant chloride threshold. The results show that implementing chloride threshold depende...

Service Life Forecasting for Reinforced Concrete Incorporating Potential-Dependent Chloride Threshold

The critical chloride threshold is a key parameter in the service life design of reinforced concrete structures exposed to chloride-bearing environments. This paper investigates the role of concrete composition, and particularly the effect of supplementary cementing materials, on the chloride threshold. To simulate real exposure conditions, ponding tests were carried out on reinforced concrete specimens with bars in free corrosion conditions and corrosion initiation was detected through corrosion potential and corrosion rate measurements. After two and a half years, the ponding was followed by an ageing period and the initiation of corrosion was further detected with anodic potentiostatic polarisation tests. Results of the tests showed several limitations of the approach based on chloride penetration and monitoring of free corrosion parameters to investigate the chloride threshold. In spite of this, a possible role of natural pozzolan and coal fly ash additions in leading to higher values of the chloride threshold and ground limestone in promoting lower values of the chloride threshold could be observed.

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Investigation on the effect of supplementary cementitious materials on the critical chloride threshold of steel in concrete

A theoretical analysis of mechanical and durability enhancement of circular reinforced concrete columns repaired with UHPC

Review of available systems and materials for splicing prestressed-precast concrete piles

Posttensioned concrete cylinder piles produced using a centrifugally cast, vibrated, roller-compacted process have shown promising corrosion resistance in marine environments. Three bridges in the Florida panhandle with ∼40 years in aggressive marine service and one newly constructed marine bridge utilizing concrete cylinder piles were examined. The older marine bridges showed minimal corrosion distress despite a low design concrete cover over the steel hoop reinforcement (2 cm to 4 cm). Typical concrete distress included minor rust staining (not necessarily indicating corrosion of reinforcement steel) and thin longitudinal cracks (likely caused by mechanical damage from pile driving). Chloride ion diffusivity was low, in the order of 1 × 10−9 cm2/s. Other measured parameters such as concrete resistivity, porosity, and water absorption indicate low permeability. Chloride analysis of cracked and uncracked concrete cores from the older bridges in this study did not show pronounced preferential chlo...

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Corrosion Performance of Concrete Cylinder Piles

The rapid construction of prefabricated components of reinforced concrete structures using 3D printing concrete as a permanent formwork is a promising way to organically combine 3D printing with traditional construction technology. The bonding property of the contact interface between the 3D-printed permanent formwork and internal post-cast concrete is crucial for the 3D-printed structure to maintain the overall mechanical performance. In this study, the roughness of 3D-printed formwork (10 mm, 15 mm, 20 mm) and the age difference between the formwork and post-cast concrete (1 d, 3 d, 7 d, and 14 d) were set as variables to investigate their influence on the interfacial tensile and shearing bonding properties. Additionally, computerised tomography (CT) scanning was used to visualise the meso-structure of the interfacial zones and the pore characteristics were quantified. The microstructure and hydration products of the bonding interface were detected, and the gradient structure of the interface transition zone of the 3D printing formwork was presented. A plastic limit analytical mechanical model of the interfacial shear strength was established. The results show that the tensile and shear properties of the bonding interface were the best when the layer height of the printing formwork was 20 mm, and it is recommended to cast internal concrete materials after 7 d of 3D printing formwork moulding. 

L. Yao

Papers

Corrosion Performance of Concrete Cylinder Piles

Interfacial bonding properties of 3D printed permanent formwork with the post-casted concrete