Concrete International May 2015 No. 5 Complete Issue
Click on the cover image for the flip book version.
Protection & Durability
Nomogram for Maximum Temperature of Mass Concrete
Understanding and predicting the thermal behavior of mass concrete can help designers and contractors reduce the probability of crack formation, thus helping to ensure concrete durability. However, reliable simulation models are rather impractical to implement for preliminary investigations, which demand quick calculations. From a practical perspective, rough estimates of mass concrete temperature could be used to guide preliminary mixture design while avoiding complicated calculations. The nomogram developed by the authors allows predicting a preliminary estimate of the maximum temperature achieved in mass concrete structures by taking into account mixture composition and ambient conditions. It is also available as a mobile app in both SI and U.S. customary units.
Back to the Future
For many years, the North American cement industry was well served by the so-called Type I/II cements. This type of cement had C3A contents below 6.5%. While concrete produced with this cement did not exhibit high early strength, it did exhibit good durability. The cement industry is now producing clinkers with higher C3A contents, and these clinkers are also being ground finer to provide high early strength. These changes make it much more difficult to control the rheology of low water-cement ratio mixtures produced with modern admixtures. The authors recommend that the industry produces an alternative cement with a C3A content of about 6% and a coarser grind than currently available.
Electrical Resistivity of Concrete
Electrical resistivity measurement can be used for performance-based evaluation of concrete as an alternative to other tests methods that provide an indication of the concrete’s ability to resist chloride ion penetration. Several techniques have been developed and studied for measuring the electrical resistivity of concrete, including the bulk electrical resistivity and surface electrical resistivity. The adoption of these techniques into standards and guidelines however, has been rather slow. This article discusses the different approaches to measuring the electrical resistivity of concrete and reviews the correlations between the resistivity measurements and certain durability characteristics of concrete.
ACI Officers for 2015-2016
Wood, Awad, and four new Directors elected
ACI’s Award-Winning Papers and Articles
Authors recognized with honors at The Concrete Convention
2014 Concrete Society Awards
More than 450 people attended The Concrete Society
Awards Dinner held at the Grosvenor House Hotel,
Park Lane, London, UK, on October 29, 2014.
Q. My company is the general contractor on a midrise reinforced concrete building. The owner’s inspector is requiring us to remove concrete splatters on the column and wall dowels before we can install the forms for the next level. I have been in this business for more than four decades, and this is the first inspector that has required this action. We have to use wire brushes and grinders to remove the splatter. The splatter also roughens the bar surface, so I don’t understand how it could negatively affect bond. The inspector has cited ACI 301-101 as justification, specifically quoting Section 3.3.