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.
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
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These black, heavy cotton t-shirts, that extol the
benefits of concrete say "durable" on the front and "the
one material you trust between you and disaster" on the back
with the Think Harder.Concrete logo. Comes in Large,
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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:
|Water-cement ratio (w/c)—accurate
control of water-cement ratio is a key component to control of strength
properties of the material.
| Aggregate gradation—changes
in aggregate gradation, increased fineness or void content, may increase
water demand, workability, and paste requirements. These changes may
increase the potential for segregation, bleeding, and shrinkage.
|Cement fineness—cement fineness
affects heat of hydration, water demand, strength gain characteristics,
and workability. Changes in fineness can introduce the possibility
of incompatibilities between cement and chemical admixtures, shorten
setting times, and affect setting characteristics complicating timing
for sawing of joints.
For a complete list of issues and test methods that
are recommended for quality control of concrete pavements, click
CP Road Map “Moving Advancements into Practice”
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.
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
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.
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.
of Performance Properties of Ternary Mixtures: Laboratory Studies on Concrete
A new report from the National Concrete Pavement
Technology Center (NCPTC) provides results of research on ternary cementitious
materials mixtures used in concrete. The blending of two or three SCMs provides
one tool to optimize durability, strength, or economy. A goal of this research
was to provide the quantitative information needed to make sound engineering
judgments pertaining to the selection and use of ternary mixtures. This
will lead to more effective utilization of SCMs and blended cements, enhancing
the life-cycle performance of concrete and minimizing the cost of pavements
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
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.
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.
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.
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
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.
listing of industry conferences.
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