Studies of the efficiency of granulated blast furnace slag and limestone filler in mortars - long term strength and cloride penetration

This report is the first part of the project Use of industrial by-products and filler in concrete - long term properties/durability. The aim is to improve the knowledge of long term properties/durability of cement and concrete produced using industrial by-products/fillers in order to promote an efficient, safe, reliable and increased use of such types of materials. The results presented in the report concentrate mainly on determination of material properties of mineral additions/fillers. The next step of the project will be to study the mechanisms governing the influence of mineral additions/fillers on the long-term properties/durability

Chloride transport and chloride thresholdvalues-Studies on concretes and mortars with Portland cement and limestone blended cement

Reinforced concrete is one of the most widely used building materials and if it is properly designed and produced, it is an extremely durable material with a service life up to 100 years. However, under certain environmental conditions the service life of reinforced concrete structures is more limited. Deterioration of concrete structure is in most cases caused by the penetration of aggressive media from the surrounding environment. Chloride initiated reinforcement corrosion is one of the major causes of deterioration of concrete structures. One conflicting issue is how replacing Portland cement with mineral additions influences chloride initiated reinforcement corrosion. This issue is of immediate interest, as there is a steady growth in the use of cement blended with mineral additions, such as blast-furnace slag, fly ash and limestone filler. This is done by the cement and concrete industry to reduce the CO2 emissions linked to Portland cement manufacturing, by limiting the use of clinker in the cement. The main objective of this work has been to further clarify the role of limestone filler as partial substitute to Portland cement on the two main decisive parameters for chloride induced reinforcement corrosion: chloride ingress rate and chloride threshold values. In the first part of this work the chloride ingress was studied both with accelerated laboratory methods and also after field exposure. The initial focus for the second part of the study was to determine the chloride threshold values for the binders investigated in the first part, so a comprehensive view of the effect of limestone addition on chloride initiated corrosion could be presented. However,during the work the need for the development of a practice-related method for determining the chloride threshold values was identified and the focus of the research was redirected to meet that need. The efficiency of limestone filler concerning chloride ingress showed to be dependent on replacement ratio, time (age) and on the test method. It was not possible to draw any rigid conclusion of the limestone filler’s efficiency regarding chloride ingress. But part of the inconsistency in the results was identified to be that limestone filler has two opposite effects on chloride ingress, on one hand contribute to a refinement of microstructure and on the other hand diminishing the chloride binding. The steel surface condition was shown to have a strong effect on the corrosion initiation, and can likely be one of the most decisive parameters attributing to the variability in the reported chloride threshold values obtained in laboratory experiments. The chloride threshold value for the sulphate resistant Portland cement from the laboratory experiments was estimated to be about 1% by weight of binder. For the concrete with limestone blended cement (CEM II/A-LL 42.5R) tested in this work the chloride threshold value was at the same level as for the sulphate resistant Portland cement. From the field study but with a somewhat different definition of chloride threshold value, a chloride threshold value of about 1% by weight of binder was also estimated for ordinary Portland cement and sulphate resistance Portland with 5% silica fume exposed to marine environment

Long-term performance of reinforced concrete under a de-icing road environment

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

Durability and service life prediction of reinforced concrete structures

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. For the frost attack, it is premature to apply the models to the service life prediction so far

An approach for measurement of chloride threshold

Chloride induced corrosion is one of the major causes for degradation of reinforced concrete structures. One of the most important factors in this process is the critical chloride content (chloride threshold value) in the vicinity of the reinforcement that causes initiation of corrosion. In this work the development of a practice-related approach that includes specimen shape, preconditioning, corrosion measurement techniques, and calculation concepts, for determining the critical chloride content are presented. The results in this study showed that the presented approach for determining chloride threshold values functioned fairly well, and suggestions for further improvement are proposed

An approach for measurement of chloride threshold values

Chloride induced corrosion is one of the major causes for degradation of reinforced concrete structures. One of the most important factors in this process is the critical chloride content (chloride threshold value) in the vicinity of the reinforcement that causes initiation of corrosion. In this work the development of a practice-related approach that includes specimen shape, preconditioning, corrosion measurement techniques, and calculation concepts, for determining the critical chloride content are presented. The results in this study showed that the presented approach for determining chloride threshold values functioned fairly well, and suggestions for further improvement are proposed

The influence of reinforcement steel surface condition on initiation of chloride induced corrosion

This paper describes a part of the work in the development of a "standard" test method for determining chloride threshold values required to initiate corrosion on reinforcement in concrete. The prerequisites of the test set-up are that the test conditions should be reasonably comparable to those in service and the test method should be fairly reproducible and as rapid as possible concerning the slow diffusion nature of the investigated phenomenon. This paper presents the results from a study on the influence of steel bar surface condition on chloride induced corrosion. Various electrochemical techniques were employed in the study to monitor the corrosion behaviour of the embedded bars with three different surface conditions. It is shown that the steel surface condition has a strong effect on the corrosion initiation of reinforcement in concrete, and can likely be the most decisive parameter attributing to the variability in the reported chloride threshold values