Alkali-Aggregate Reactivity

Aggregates containing certain constituents can react with alkali hydroxides in concrete. The reactivity is potentially harmful only when it produces significant expansion. Alkali-aggregate reactivity (AAR) has two forms – alkali-silica reaction (ASR) and alkali-carbonate reaction (ACR). ASR is of greater concern than ACR because the occurrence of aggregates containing reactive silica minerals is more widespread.

Alkali-silica reactivity has been recognized as a potential source of distress in concrete since the late 1930s. The reduction of ASR potential requires understanding the ASR mechanism; properly using tests to identify potentially reactive aggregates; and, if needed, taking steps to minimize the potential for expansion and related cracking.

Read an excerpt from Chapter 11, "Durability," of Design and Control of Concrete Mixtures, 15th edition.

Design and Control of Concrete Mixtures, 15th Edition
The guide to applications, methods, and materials

The industry’s primary reference on concrete technology, this fully revised 15th edition is a concise, current reference on concrete that reflects the latest information on standards, specifications, test methods and guides of ASTM International (ASTM), the American Association of State Highway and Transportation Officials (AASHTO), the American Concrete Institute (ACI), and the National Ready Mixed Concrete Association (NRMCA).

Design and Control of Concrete Mixtures presents the properties of concrete as needed in concrete construction, including strength and durability. This book is a “must have” for anyone involved with concrete. More information and purchase.

Evaluation of Alkali-Silica Reactivity (ASR) Mortar Bar Testing (ASTM C1260 and C1567) at 14 days.
Concrete technologists looking to evaluate the potential for alkali silica reaction (ASR), a chemical reaction between certain reactive minerals in some aggregate and alkalies in the pore solution of concrete, often use accelerated tests. Standard accelerated tests use expansion of mortar bars after 14-days in an aggressive exposure environment to evaluate ASR potential. Download report.

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More Think Harder gear.

Quality Control of Pavements; Issues and Test Methods

The final quality of concrete pavement may be affected by many parameters including the following:

For a complete list of issues and test methods that are recommended for quality control of concrete pavements, click here.

CP Road Map “Moving Advancements into Practice” Briefs

The National Concrete Pavement Technology Center at Iowa State University developed the CP Road Map as the national strategic plan for concrete pavement research. They identified 12 tracks for research and disseminate innovative research for each of these tracks through their “Moving Advancements into Practice” briefs. The most recent MAP Brief is Intelligent Compaction for Concrete Pavement Bases and Subbases. This four-page brief discusses the use of sensors, on-board computers, and GPS to provide continuous monitoring of compaction efforts and feedback for optimization. Read this and other MAP Briefs.

Read the latest issue of their e-newlstter.

MIT Concrete Sustainability Hub Research Briefs

Three new briefs from the Massachusetts Institute of Technology’s Concrete Sustainability Hub (CSH) Concrete Science Platform have been released. These one-page articles summarize exciting results of on-going research activities.

What’s in Your Concrete? (Part 1)
It is well understood that cement chemistry is a complex topic, with dozens of reactions by and between multiple cement phases. These in turn are affected by “impurities” that exist naturally in the raw materials used to make cements. This brief summarizes one of the experimental and analytical tools being developed at the CSH to characterize cement phases and then to validate both chemical models and prototype cements that may be used to lower the environmental impact of concrete.

Clinker: When Impurities Matter
As noted above, clinker crystals are far from chemically pure and “guest ions” (impurities) are known to affect the clinker reactivity, with different types of atoms potentially accelerating or retarding the reactions. A fundamental understanding of the effect of various impurities may permit tailoring of clinker characteristics. In turn, this may translate into improved properties such as higher strength development or enhanced durability.

Designing for Sustainable Pavements
A significant effort of the MIT Concrete Sustainability Hub is focused on determining the economic and environmental impacts of concrete construction using life-cycle assessment (LCA) and life-cycle cost analysis (LCCA) principles. Overdesign can cause excess materials to be used during pavement construction, leading to higher economic costs and environmental impacts. Recently CSH researchers have evaluated conventional pavement designs and designs based on the NCHRP Mechanistic-Empirical Pavement Design Guide (MEPDG). Examples based on low-, medium-, and high-volume highways were evaluated. Results of this work provide conservative estimates that the MEPDG-optimized designs reduce net present cost of highways by roughly 40 to 50 percent and CO₂ emissions by roughly 30 percent. (Factors such as shorter construction times and reduced transportation are not considered in these studies but will increase these benefits.) More information on the MEPDG approach.

Read the most recent news briefs from the CSH.

More information on the MIT Concrete Sustainability Hub Concrete Science program.

The new, combined PCA Professors’ Workshop, is being offered August 1-5, 2011 at the PCA headquarters in Skokie, Ill. This year introduces a new format which includes tracks covering Engineering and economics of concrete buildings; Design and construction of concrete bridges by the AASHTO LRFD; Concrete materials properties; and Design, construction and performance of concrete pavements. The Professors’ Workshop is designed to provide faculty in engineering, architecture, and construction management programs the tools to teach the latest developments in concrete design, construction, and materials. The week-long session includes networking opportunities to exchange ideas with professors from many universities.

Development and Standardization of the NIST Rapid Sulphate Resistance Test
ASTM C1012 is a mortar test method commonly used to determine sulfate resistance of cementitious materials. However, the test requires six months or one year to achieve results. Researchers at the National Institute of Standards and Technology (NIST) have developed a preliminary alternate for this test (see PCA Report SN2486 ) that uses small paste prisms to reduce the duration of testing.

This thesis from the University of Toronto evaluates parameters in the new test with the goal of optimizing the protocol, establishing appropriate expansion limits, and assessing limitations of the procedure. The range of variables evaluated includes details of specimen design, curing regime, water-to-cementitious materials ratio, and prism length.

The 13th International Congress on the Chemistry of Cement will be held on July 3-8, 2011 at the Palacio de Congresos de Madrid in Madrid, Spain. Topics of interest include sustainable production, concrete durability, standardization, and many more.

A workshop on Expansive Reactions in Cement-Based Materials will be held on July 27-29, 2011 at the Oregon State University in Corvallis, Oregon.

The 2011 IEEE-IAS/PCA 53rd Cement Industry Technical Conference will be held at the America’s Center in St. Louis, Missouri on May 22-26, 2011. The conference will include discussions on technical issues in the cement industry and potential solutions and will include tours to two new local cement plants.

The 3rd International Symposium on Ultra-High Performance Concrete and Nanotechnology for High Performance Construction Materials will be held on March 7-9, 2012 in Kassel, Germany. The deadline for abstract submission is April 30, 2011.

The 11th North American Masonry Conference will be held on June 5-8, 2011 at the University of Minnesota in Minneapolis, Minnesota. The themes of the conference include masonry in seismic regions and green technology.

The June ASTM Committee Week will be held in Anaheim, California, June 12 - 17, 2011. Committees C01 on Cement, C09 on Concrete and Concrete Aggregates, C07 on Lime, C12 on Mortars and Grouts for Unit Masonry, C15 on Manufactured Masonry Units, and D04 on Road and Paving Materials will all meet. A special feature of this meeting will be a Workshop on Implications of ASTM E60 Standards on Sustainability for Cement and Concrete to be held Tuesday, June 14, from 7:00 to 10:00 p.m.

The 2nd Advances in Cement-based Materials: Characterization, Processing, Modeling and Sensing conference will be held at Vanderbilt University in Nashville, Tennessee on July 24-26, 2011. Presentation topics include cement chemistry and nano/microstructure, advances in material characterization, and concrete durability.

Complete listing of industry conferences.