International Concrete Abstracts Portal

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.

Calcium-sulphoaluminate cement (CSA) represents an eco-friendly alternative to ordinary portland cement (OPC), thanks to its lower energy consumption, special production process and raw materials. Life-Cycle Analysis (cradle-to-gate) according to ISO 14040 standard series showed a potential for substantial reduction of the environmental impacts, as well as natural resource use. Nowadays, CSA cement is being used more in construction industry thanks to its high early-age compressive strength and shrinkage-compensating behavior. This paper presents concrete mixtures with pure CSA and with OPC-CSA blends both in terms of environmental impact indicators from Environmental Product Declarations, and in terms of mechanical and rheological performance focusing on workability, compressive and flexural strength development, drying shrinkage and dynamic elastic modulus evolution from very early ages.

The existing assets need maintenance actions (assessment, repairs and prevention) and related construction works share is increasing in Europe; ISO International Organization for Standardization through its competent Technical Committees has then recently carried out an important activity on reliability, durability and maintenance of concrete structures publishing basic, fundamental Standards concerning these subjects. CEN is planning the revision of the Eurocodes with the same objectives. Italy shows risky contexts, synthetically analyzed, which strongly suggest to improve planning, design, construction and maintenance practices for new and existing concrete structures. Designing for durability and maintenance planning are strictly correlated. This paper, focusing on the above subjects, analyzes specific issues: design guidelines, briefing, maintenance procedure and design validation.

Concrete floor on ground represents an important application for concrete use in Italy. Despite their widespread use, a large percentage of concrete floors does not meet the performance requirements in terms of functionality and durability for various reasons; among them, restrained shrinkage cracking and curling represent one of the most important causes of defects. Cracking is mainly due to the drying shrinkage in presence of internal and external restraints, while curling is due to the shrinkage gradient due to the floor thickness. An analytical approach to shrinkage cracking and curling is often overlooked by designers in lieu of the design of contraction joints that allow the cracking of concrete under controlled conditions. Nowadays, the growing needs of concrete floors purchasers in terms of durability and functionality suggests the use of special concretes for flooring. For instance, the use of shrinkage-compensating concretes reduces the number of contraction joints and enhances the concrete slab performances. This study presents the non-linear finite element analysis of a jointless floor made with a shrinkage-compensating concrete obtained with the use of a blend of calcium sulpho-aluminate cement and ordinary Portland cement.