International Concrete Abstracts Portal

In many countries, structures in reinforced concrete “of historical interest” are covered by preservation legislation. In striving to restore them, scholars make use of knowledge accumulated over time. Less well known is the technological research that was part of the production and use of cements and concrete mixtures for reinforced concretes, whose durability has always been a prime concern. Historic works bear witness to their ability to last over time and to the ways in which structures and materials age and deteriorate, thus providing evidence as to the validity of the expectations of durability which existed when the work was designed. The systematic collation of data relating to such artefacts and the repairs they have undergone would be of great use (e.g. with regard to the components used in the original work and in the repairs). Furthermore, collaboration with manufacturing companies and research laboratories should allow us to make use of recently-developed prepacked mortars and concrete in new repair work, assessing their compatibility with old materials and monitoring their performance over time. The resultant database and experimental results would provide clues useful in moving beyond current rudimentary practices, laying the basis for a shift from “concrete repair to concrete conservation”.

Service life calculations are now treated more in detail in standards and in particular in fib Model Code 2010. The new performance is introduced in addition to probabilistic calculations. In spite of the advances made it is necessary to apply the new approaches with care because any of the existing models have been calibrated in the same concrete more than a couple of decades and then, the predictions may present substantial errors. In addition, the calculation of the propagation period and the limit state of corrosion are aspects not well defined as the MC2010 does not considers any model for the propagation stage. In present paper are analysed some aspects of service life models proposing improvements. A universal statistical distribution of chloride threshold is presented and the consideration of an Initiation Limit State as defined by ISO 13283 is proposed for the depassivation onset. Finally, are illustrated trough examples that the probability of failure for deterioration processes should not be a fixed value but it would depend on the rate of deterioration.

In the present work, a coupled environmental-mechanical damage model for structural analysis of RC elements subjected to aggressive action - originally developed by some of the authors - is presented and further enhanced, introducing some innovative formulations. In particular the effect on structural performance of rebars corrosion, induced both by chloride attack and carbonation, and of freeze-thaw cycles is analyzed. To this aim, the environmental damage parameter is re-formulated and splitted in two contributions in order to better represent the degradation of concrete caused by cracking due to different processes (e.g. development of expansive products during corrosion, pressure induced by internal ice formation). The proposed models are implemented in the finite-element framework OpenSees, developed at Berkeley, University of California and validated by comparison with a number of experimental tests. In the first part of the paper the proposed constitutive models are introduced discussing the most relevant features and characteristics. Then, in the second part of the paper, the validation tests are presented and the obtained results are compared with experimental ones, proving that the model is suitably accurate in reproducing the main aspects observed during experiments: i.e. failure load, ultimate displacement and failure mode.

In this paper, the carbonation resistance of various concrete mixtures incorporating supplementary cementitious materials exposed to atmospheric CO₂ concentration in Austin, Texas, USA, was investigated. The paper provides a detailed description on the creation of an outdoor exposure site to place and monitor concrete specimens under ambient air exposure conditions. Two exposure conditions were investigated, including specimens that were placed outdoors unsheltered and in sheltered environments protected from direct rainfall. The depth of carbonation was measured after 730 days of exposures. Additionally, relative humidity (RH), temperature, and environmental CO₂ concentrations in the air were also monitored at the site to provide a general indication of the conditions at the exposure site. Various factors were investigated including water-cementitious materials ratio, type and dosage of supplementary material, and cement type. The depth of carbonation of mixtures without supplementary material was moderate. The addition of supplementary material significantly increased the carbonation depth, especially when replacement levels exceeded 30% of cement by mass. The results were exacerbated for those concrete specimens that were placed outdoors but sheltered from direct rainfall.

Architectural works by major architects from the twentieth century have often been subject to restoration campaigns intended to redeem them from decay (sometimes from neglect) in order to present them as “monuments” of the twentieth century. In particular, in architecture in which exposed reinforced concrete plays a key role in architectural, figurative, symbolic and cultural terms, the theme of repairing/replacing the concrete cover is a fundamental issue in the restoration project. Analyzing the methods, materials and techniques of intervention used in several campaigns of restoration of buildings built before World War II (the church of Notre-Dame du Raincy by Gustave and Auguste Perret in France and Rudolf Steiner’s Goetheanum at Dornach near Basel in Switzerland) or after the War (Figini and Pollini’s housing built in Milan and the Olivetti Factory in Crema by Zanuso) provides an opportunity to identify best practices, and also critical factors and weaknesses of the different approaches used in the restoration of these buildings from the 1980s to the present.