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The Spring 2020 newsletter of the National Concrete Consortium has the following items:
• Moving Advancements into Practice (MAP) - Brief on Extended-Life Concrete Bridge Decks Utilizing Internal Curing to Reduce Cracking – Results from Ohio DOT Field Trial
• FHWA Concrete Clips - Maturity and Strength Gain, and Admixtures
• Reducing Cracks in Concrete Bridge Decks Using Shrinkage Reducing Admixture - Restrained shrinkage cracking of concrete bridge decks creates a significant durability problem. Major admixture suppliers in the United States have introduced a new category of chemical admixtures called shrinkage reducing admixtures (SRAs). SRAs work by reducing the surface tension of pore water and thereby decreasing the capillary stress and shrinkage induced by drying. Several studies have reported that using SRAs in concrete mixtures is one of the most effective ways of reducing shrinkage cracking. The purpose of this study was to investigate the effectiveness of SRAs in reducing drying shrinkage in Virginia Department of Transportation (VDOT) concrete mixtures and thus reducing cracks in bridge decks.
• Bridge Decks: Mitigation of Cracking and Increased Durability - The application of pre-soaked lightweight aggregates (LWA) as an internal curing agent in concrete to reduce the cracking due to drying shrinkage is thoroughly studied in this report. It is determined that although LWA can significantly reduce autogenous shrinkage, its effect on drying shrinkage is minimal and, in some cases, can even increase the drying shrinkage. Moreover, the combined effects of LWA and expansive cement (Type K), as well as LWA and shrinkage-reducing admixtures (SRAs), on drying shrinkage is also studied. It is shown that the addition of Type K cement or SRA to mixtures containing LWA can significantly reduce drying shrinkage and make the mixture more volumetrically stable.
• Performance-Related Specifications for Pavement Preservation Treatments - This report (1) presents guidelines for preparing performance-related specifications (PRS) for pavement preservation treatments and, if desired, determining pay adjustment factors and (2) illustrates the applicability of these guidelines for selected preservation treatments for flexible and rigid pavements. The guidelines follow a systematic process that considers acceptance quality characteristics and performance measures for preservation treatments. The information contained in the report will be of immediate interest to state materials and maintenance engineers and others involved with the specification and quality aspects of pavement preservation treatments.
• High-Early-Strength High-Performance Concrete for Rapid Pavement Repair - In the construction industry, High-Early-Age-Strength (HES) concrete has traditionally been regarded as a concrete that achieves loading strength in mere days rather than weeks. However, in the last 10 to 15 years, this time has reduced down to just hours. Required minimum compressive strength is determined case by case. For structures and dwellings, the minimum allowed by the International Building Code is 2,500 psi. In road and bridge construction, the minimum is typically 3,000 psi. For airport construction, it is typically 4,000 psi. Due to the accelerated strength gain of HES provided by chemical admixtures, minimum opening strengths are often reduced since the concrete is expected to continue gaining strength after traffic load is introduced. This investigation targets high-early-age-strength concrete for the purposes of road and bridge deck repairs.
Click here to access the newsletter and individual links to the above reports.
