To facilitate the long term durability predictions of nuclear waste repositories, acceleration methods enhancing calcium leaching process from cementitious materials are needed, even though mechanisms not necessarily comparable to those predominant in a natural leaching process may be developed. In the previously published acceleration methods the samples are very small, which limits further physical or mechanical tests. In this paper, a new acceleration method based on electro-chemical migration is presented. The method although not driven with the same kinetics as in natural leaching, was designed in such a way that unnecessarily destructive by-effects could be minimized while promoting a higher leaching rate for a sample size suitable for further testing the mechanical and physical properties. It is shown that approximately 1 × 106C of electrical charge per paste specimen of size Ø50 × 75 mm (approximately 230 g) is required to leach out the total amount of Portlandite. The chemical and mineralogical properties of leached samples are characterized by various techniques. It is concluded that aged samples are comparable to those leached in a natural leaching process as both are characterized by a layered system comprising an unaltered core delineated by total dissolution of Portlandite followed by a progressive decalcification of the calcium silicate hydrate gel.

Alkali-activated slag is a widely used low-carbon binder. Incorporation of textile can mitigate the brittle weakness of alkali-activated composites. The bonding between fibers and matrix is critical for the performance of textile reinforced mortar. This paper is focused on the effect of different treatment methods on the bonding properties of carbon fiber in alkali-activated slag. The interfacial shear strength of fiber bundles in matrix was determined by the pull-out test. The flexural strength of the reinforced mortar was evaluated by a repeated bending. A scanning electron microscopy test was performed to characterize the interfacial properties of the fiber bundles. The results show that the interfacial shear strength of carbon fibers in matrix is improved by the electroplating with calcium silica slurry (CSS), impregnation in different solutions, and plasma treatments. An electroplating in CSS has the best improvement in the bonding strength with an increase by 620%. The CSS treatment increases the maximum flexural strength of CFT reinforced mortar with 22.5% and 30% at 7 and 28 d respectively, and it significantly inhibits the crack growth under the cyclic loading. This effect becomes more significant after a longer curing age. The electroplating treatment eliminates the cracks in the interface of fiber yarns. Slag reacts with the plated portlandite to strengthen the bonding between mortar and fiber bundles, so it has a better inhibiting effect on the crack growth after a longer curing. © 2023 The Authors

In the middle of 1990, over 30 different mixes of concretes with eight different binders and water-binder ratios of 0.3 to 0.75 were exposed to a highway environment with a heavy de-icing salt spread for the examination of long-term performance, including chloride penetration, reinforcement corrosion and frost attack. This paper presents the results from this long-term study regarding chloride penetration and reinforcement corrosion. The results show that the chloride penetration in concretes under a de-icing salt road environment is much weaker than that in concretes under marine splash environment in Sweden. The estimated critical chloride content for the corrosion initiation is about 0.3 % by mass of binder for rebars with uncracked concrete cover. Considering the chloride redistribution in the surface zone, ClinConc model has been modified so that it can present a better description of the chloride profiles in the concretes at such an exposure site. © 2022 The Author(s)

This report presents the results from a research project financed by Trafikverket, the Swedish Transport Administration, co-financed by Cementa AB.

In this part of the project work about 35 chloride profiles and ten moisture profiles have been measured from various types of concrete specimens exposed to a de-icing salt highway environment for about 20 years. The non-destructive technique, RapiCor, for corrosion measurement was used to assess the conditions of steel embedded in concrete beams with different types of binder and water-binder ratios. The ClinConc model were used to predict chloride ingress in concrete. Some laboratory test methods and numerical simulations were carried out to study the behaviour of concrete after long-term exposure.

The results show that chloride ingress profiles measured after 2

0 years’ exposure under the de-icing salt highway environment are in general lower than those measured after the similar exposure duration under the marine splash environment.

Non-destructive corrosion measurement by RapiCor instrument is in general in reasonably good agreement with chloride ingress. The corrosion rust observed from the destructive examination verified again that the non-destructive technique RapiCor is a useful tool for detection of ongoing corrosion of steel in concrete.

The ClinConc model in general gives reasonably good prediction of chloride ingress front in the bulk concrete but not in the near surface zone due to the drying-wetting cycles in the highway environment. After a certain modification with the consideration of redistribution of bound chloride in the near surface zone, the model can reasonably well describe the chloride ingress profiles measured from the exposure site.

This paper presents some durability and service life models for reinforced concrete structures with regard to chloride ingress, carbonation and frost attack. In the past years a number of models for durability design of concrete structures have been suggested by relevant organisations or international committees. It is necessary to validate these models against long-term field data for their applicability with respect to exposure climate in order to satisfactorily use the models in the durability design and redesign of concrete structures. In this study, various potential models for concrete resistance to chloride ingress, carbonation and frost attack were briefly reviewed. Three models including the simple ERFC, the DuraCrete and the ClinConc, for prediction of chloride ingress were evaluated using the infield data collected from both the field exposure site after over 20 years exposure and the real road bridges of about 30 years old. A physicochemical model for prediction of carbonation depth was evaluated using the infield data collected from the field exposure site after 11 years exposure and the limited data from the real structures with the age of 7-13 years. For the modelling of frost attack, some problems in measurement of critical saturation degree and actual degree of saturation are discussed. According to the comparison results, the simple ERFC overestimates whilst the DuraCrete model underestimate the chloride ingress in most cases. The ClinConc model on the other hand gives reasonable good prediction for both the short-term (one year) and the long-term (21 years) exposure. The Papadakis model for carbonation also gives fairly good prediction of carbonation depth when compared with the Norwegian infield data classified as exposure class XC3|, but underestimates the carbonation depths when compared with the infield data from Norwegian structures in exposure class XC4.

Due to the corrosion of steel in reinforced concrete structures, the concrete with low water-cement ratio (w/c), high cement content, and large cover thickness is conventionally used for prolonging the passivation period of steel. Obviously, this conventional approach to durable concrete structures is at the sacrifice of more CO2 emission and natural resources through consuming higher amount of cement and more constituent materials, which is against sustainability. By placing an economically affordable conductive mesh made of carbon fiber or conductive polymer fiber in the near surface zone of concrete acting as anode we can build up a cathodic prevention system with intermittent low current density supplied by, e.g., the solar cells. In such a way, the aggressive negative ions such as Cl-, CO3 2-, and SO4 2- can be stopped near the cathodic (steel) zone. Thus the reinforcement steel is prevented from corrosion even in the concrete with relatively high w/c and small cover thickness. This conductive mesh functions not only as electrode, but also as surface reinforcement to prevent concrete surface from cracking. Therefore, this new type of covercrete has hybrid functions. This paper presents the theoretical analysis of feasibility of this approach and discusses the potential durability problems and possible solutions to the potential problems.

Cathodic prevention (CPre) technique is a promising method and has been used for the past two decades to prevent steel from corrosion in concrete structures. However, wide application of this technique has been restricted due to high costs of anode materials. In order to lower the cost and further improve this technique, carbon fiber composite anode has been introduced as an alternative anode material with affordable price and other outstanding properties. This paper presents the study of using carbon fiber mesh as anode material for long-term cathodic prevention system and the effect of accelerated current on macro- And microstructure of cementitious materials. In the study, electrochemically accelerated tests were developed for the purpose of shortening the experimental time into a manageable range. An estimation tool was used to predict the service life as well. Chemical and microstructure analyses were carried out by laser-ablation inductively-coupled-plasma mass-spectroscopy (LA-ICP-MS) and scanning electron microscope (SEM). Results indicate that calcium to silicon (Ca/Si) ratio and ion re-distribution in the current-affected zone around the anode were changed due to migration and electrochemical reactions. The predicted service life was in general longer than 100 years. Based on the results from this work, it can be concluded that carbon fiber mesh is suitable for the application as anode in long-term cathodic prevention system in cementitious materials.