International Concrete Abstracts Portal

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.

This work is part of a project aiming at investigating a new design approach for sustainable and durable concrete structures, which is based on the use of corrosion-resistant reinforcements in order to allow the use of chloride-contaminated raw materials (especially seawater and recycled concrete aggregate (RCA)). Changes in plain concrete properties, as well as the effects on embedded reinforcement (i.e., black steel and glass fiber reinforced polymer (GFRP)) have been studied. Three types of concrete mixes were produced: the first, a standard one, used as the benchmark; the second where freshwater was substituted with seawater; and, the third where chloride-contaminated RCA and seawater were used. For each mix, features of fresh concrete and mechanical properties of hardened concrete were studied. Further information was obtained by microstructural and chemical analyses. Additionally, durability was studied in terms of concrete and reinforcement resistance to aggressive environments. Results show that concrete is not negatively affected by the introduction of seawater in the mix while RCA plays a more important role in concrete properties. As already well established, the use of corrosive reinforcement, such as black steel, is discouraged in chloride-contaminated concrete because of the high corrosion rates due to pitting phenomena.

Concrete durability-related properties are known to be negatively affected due to expansion and cracking that result from factors such as freezing and thawing actions, alkali-aggregate reactions, sulfate attack, corrosion of the reinforcement, shrinkage, and other similar factors. Durability, and, therefore, sustainability of properly designed and constructed concrete structures depends primarily upon the quality of the materials of construction and other simple, but critical, steps. Concrete construction can last 100 years or more if five simple "steps" are followed: (1) materials selection; (2) structure design; (3) construction; (4) quality management; and, (5) timely evaluation, maintenance, and repairs. This is a holistic approach. Most mistakes are made in not satisfactorily following Steps 4 and 5. Conventional mixture proportioning technique used for production of high-strength concrete does not guarantee long-term durability of concrete. Concrete mixtures must be proportioned to attain desired workability, high-dimensional stability, high-strength, and high-durability related properties; i.e., high-quality concrete (HQC). However, mixture proportioning requirements for HQC must be varied according to the type and expected use of the concrete construction. HQC mixtures must have high-quality constituent materials: durable aggregates, low heat of hydration cement, mineral additives, and chemical admixtures. Furthermore, the mixing water must be minimized (i.e. a low water to cementitious materials ration, W/Cm). A strict quality control is also needed in various aspects of the production of HQC. Research activities conducted at the UWM Center for By-Products Utilization (UWM-CBU), CANMET, and elsewhere, have demonstrated that HQC mixtures can be proportioned to obtain strength in excess of 100 MPa (14,000 psi) and service life of 100 plus years.