Long-term Durability Of Concrete Structures Research Articles

Development and Verification of an Integrated Physicochemical and Geochemical Modelling Framework for Performance Assessment of Cement-Based Materials

In this study, a multi-scale model called DuCOM (Durability COncrete Model), which is developed by the Concrete Laboratory at the University of Tokyo, is extended by coupling the geochemical code PHREEQC. The coupled numerical framework can address physicochemical and geochemical processes such as the hydration of cement particles, pore structure formation, multispecies transport, activity effect, thermodynamic reaction between aqueous solution and solids, etc. in cementitious materials, and therefore, it can potentially be used to assess the long-term durability of concrete structures. The model prediction for the composition of cement hydrates, pore solution chemistry, calcium profiles for the cement paste exposed in pure water, and calcium and sulphur profiles for the cement paste immersed in the sodium sulphate solution are qualitatively and quantitatively compared with experimental results obtained from literature. Finally, the importance of the strong coupling among various processes and mechanisms in the DuCOM-PHREEQC system is discussed.

Effectiveness of Nondestructive Methods for the Evaluation of Structures Affected by Internal Swelling Reactions: A Review of Electric, Seismic and Acoustic Methods Based on Laboratory and Site Experiences

Internal swelling reactions (ISR) (which mainly comprise alkali-silica reaction, alkali-carbonate reaction, delayed ettringite formation, etc) are damage processes that affect the long-term durability of concrete structures. The reactions are apparently characterized by series of closely spaced, tight map cracks with wide cracks appearing at regular intervals, and excessive tensile stresses in rebars. These phenomena are alarming for affected structure managers as they deal with people safety and structures operation. Moreover, there is no easily implemented way to stop the reactions. Prediction of concrete expansion, structural degradation, and assessment of efficiency and periodicity of repair works are crucial issues. The aim of this work is to explore the applicability of some nondestructive techniques (NDT) of investigations (electric, seismic, and acoustic methods) to differentiate the structure zones affected or not by the ISR for different exposure conditions. The collected experience highlights that the coupling between some of those nondestructive (ND) methods can reduce the measurement uncertainty and eliminates the factors that may influence the characterization of the structure parts affected by ISR. Nevertheless, for a complete structure reassessment, it is also desirable to refer to global geometrical/topographical survey and to destructive analysis methods on some cored samples for chemical analysis, petrography, and residual expansion measurements.

Coupled Mechanical and Chemical Damage in Calcium Leached Cementitious Structures

Long-term durability of concrete structures must be faced both from the point of view of cracking and physical degradations. In this paper, the relevance and the sensitivity of an existing constitutive relation aimed at modeling mechanical and chemical damage is examined. This constitutive relation is based on a scalar continuum damage model. The chemical degradation mechanism is calcium leaching. It is observed that the model predictions, i.e., the lifetime of cement-based beams subjected to leaching, are very sensitive on the tensile strength and fracture energy of the sound material. The existing model predicts the response of bending beams subjected to various states of leaching prior to any mechanical loading. The simulation of the size effect tests shows that the mechanical internal length and the damage threshold of the material cannot be considered to be constant. The internal length ought to decrease and the damage threshold should increase.

Expansive Reactions in Concrete Observed by Soft X-Ray Transmission Microscopy

ABSTRACTAlkali-silica reaction, sulfate attack, and reinforcing steel corrosion can compromise the long-term durability of concrete structures. The anticipated economic impact of an extensive infrastructure repair scheme has produced a renewed interest in the development of advanced characterization methods to assess the degree of deterioration in the concrete experiencing these deleterious reactions. The products of the alkali silica reaction, sulfate attack, and corrosion as well as the cement hydration products are extremely sensitive to humidity. Consequently, characterization techniques that require high vacuum or drying, as many existing techniques do, are not particularly appropriate for the study of these reactions in concrete as artifacts are introduced. A high resolution instrument which allows the examination of these reactions and their products without drying and at normal pressures will promote understanding of the reactions and provide further insight into means of mitigating the damage they cause. Only soft x-ray transmission microscopy provides the required high spatial resolution to observe the reaction process in situ. The alkali-silica reaction can be observed over time, in a wet condition, and at normal pressures, features unavailable with most other high resolution techniques. Soft x-rays also reveal information on the internal structure of the sample. This paper reviews published and ongoing applications of soft x-ray transmission microscopy for the study of expansive reactions that occur in concrete.

Oberflächenschutzsysteme für das Erstellen von hochbeständigen Betonkonstruktionen / Protective Coatings of Concrete Structures for High Durability

Abstract In practice concrete structures are often exposed to various environmental impacts which determine strongly durability of concrete and concrete structures. Costs of restoration of damaged concrete structures may be extremely high, in some cases higher than demolition and rebuilding. Not only real costs and financial investment for repair measures may be exorbitant, but limited use and negative impacts on the environment have to be taken into consideration too. In this paper a concept to reach sufficient durability is being developed in which technical, ecological and economical requirements are implied. For the realisation of this concept cement-based coatings with particular high resistance against chloride penetration and carbonation play a central role. It will be shown in this contribution that this type of coatings can protect the load bearing structure in an efficient way for a predetermined period. In this way long-term durability of concrete structures and reinforced elements exposed to aggressive environment can be achieved in both an economic and ecologic way.