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PCA Cement and ConcreteTechnology Research
Concrete Technology
Home > PCA Cement and Concrete Technology Research
When questions are raised concerning cement and concrete, chances
are that Portland Cement Association engineers can provide the answers.
In addition to serving as a clearinghouse for technical information
on cement and concrete from sources worldwide, PCA itself has sponsored
research directed at extending the boundaries of technical knowledge
in the field since 1918.
Research Reports (Click on titles to
access reports.)
Effect of
Relative Humidity on Expansion and Microstructure of Heat-Cured
Mortars (RD139)
This research report describes the effect of moisture exposure on
expansion in heat-cured mortars due to delayed ettringite formation
(DEF). Mortar bar samples were cured at 90ºC, and then stored
for more than 4 years in moist air at 75%, 80%, 84%, 90%, 92%, 97%,
and 100% relative humidity (RH). Periodic weight and length measurements
were made along with chemical analyses. The results show that DEF-related
expansion is influenced by the level of moisture exposure. The study
suggests that a threshold level of moisture exposure for expansion
to occur seems to be between 92% and 90% RH.
Sulfate
Resistance of Concrete Using Blended Cements or Supplementary Cementitious
Materials (SN2916a)
This literature review discusses the relationship between sulfate
resistance and the chemical, physical, and mineralogical composition
of SCMs. Models predicting sulfate resistance in fly ash-containing
concretes have been cited and discussed. The report also reviews
sulfate resistance of concrete that contains SCMs interground and
optimized at the cement plant as compared to that mixed at the concrete
batch plant. From the very limited data available on the subject,
use of interground SCMs with clinker has shown improved sulfate
resistance for concrete, primarily attributed to finer and better
particle size distributions that enhances the reactivity and reduces
the permeability in concrete. The report also recommends that the
optimization of sulfate should be based on 3-day strength instead
of 1-day strength as in ASTM C 563. This may require a higher sulfate
addition that can potentially improve sulfate resistance, as the
porosity of the system would be markedly reduced.
Sulfate Resistance
of Concrete: A New Approach and Test (SN2486)
This report presents a new approach for testing cement resistance
to sulfate attack that is three to five times faster than the current
ASTM tests. Development of the procedure was based upon insights
into the degradation process by petrographic examination of sulfate-exposed
specimens over time. Also key to the development was the use of
smaller samples and tighter environmental control.
Air-Void Coalescence in Air-Entrained Concrete Mixes (SN2789
and SN2624)
Air-void coalescence, or air-void clustering, occurs when entrained
air voids gather around coarse aggregates within air-entrained concrete.
In numerous cases, a significant decrease in compressive strength
has been attributed to air-void clustering, and recent work has
provided new insight into the potential cause(s) of this phenomenon.
One of the findings of these projects is that coalescence did not
occur in concrete mixes using vinsol resin-based admixtures. A late
addition of water to concrete mixes containing non-vinsol resin
admixtures often led to air-void clustering and its severity increased
when the retempered concrete was mixed for a longer amount of time.
Download the free reports:
(1) An Investigation
on the Cause and Effect of Air-Void Coalescence in Air-Entrained
Concrete Mixes (SN2624), Mississippi
State University
(2) Factor(s)
Affecting the Origin of Air-Void Clustering (SN2789),
CTLGroup
For a summary of the report:
Air-Void Clustering: A Rare
Problem Explained
Application
of Infrared Imaging to Fresh Concrete: Monitoring Internal Vibration
(SN2806)
Infrared imagery can be effectively used as a
quality control tool. The use of infrared imaging would allow a
concrete inspector to determine the location of the vibrator insertion
points in a section of concrete. The spacing of these insertions
could then be checked against specifications and recommendations
for a given mixture. Previous research has established recommendations
for optimal vibrator insertion spacing under various conditions
and thermal imaging could be a useful tool in ensuring that proper
insertion spacing is performed. More.
Effect of
Minor Elements on Clinker and Cement Performance: A Laboratory Analysis
(RD130)
This research report reviews the effects of lead, molybdenum, antimony,
copper, cadmium, beryllium, titanium, vanadium, chromium, manganese,
nickel, and zinc in quantities of 0.5% or 0.25% by mass on performance
characteristics of clinker. Properties examined include clinker
hardness (grindability), setting time, and strength development.
The effects of these metals on clinker phase distribution and microstructure
are also examined.
Effects of
Internal Curing Methods on Restrained Shrinkage and Permeability
(SN2620)
Early age properties of concrete are vital to its long-term performance.
The purpose of this thesis was to investigate the ability of internal
curing methods including superabsorbent polymers (SAP) and saturated
lightweight aggregate to mitigate autogenous shrinkage and restrained
shrinkage. This thesis also examines the changes in properties of
concrete and mortar, such as permeability, when SAP, lightweight
aggregate or shrinkage reducing admixtures (SRA) are introduced
to the mix. This research found that mortar containing SAP was able
to minimize the amount of autogenous shrinkage, but reduced the
compressive strength considerably, similar to air-entraining concrete.
SAP was also able to leave voids in the concrete, which simulate
normal entrained air. SRA was most effective at reducing drying
shrinkage. Lightweight aggregate had an interlocking bond with the
paste at the interfacial transition zone; thus increased its tensile
strength properties. Appendices are available upon request.
Effect of
High-Temperature Curing on Concrete Durability SN2869
Two phase research about (1) effect of high-temperature curing (65ºC
to 95ºC ) on concrete durability and (2) the effects of lithium
admixtures, alkali-silica reaction and freeze-thaw microcracks,
and chloride ingress on the potential for DEF.
Volumetric
Measurement in Water Bath – An Inappropriate Method to Measure
Autogenous Strain of Cement Paste (SN2925)
Shrinkage and expansion of hydrating cementitious materials are
important characteristics to understand to control cracking. One
technique for evaluating autogenous strain places fresh cementitious
pastes in an elastic rubber membrane immersed in water. The change
in volume can then be monitored by the amount of water displaced
by the immersed sample, for example by measuring its weight change.
Volumetric and linear measurements of autogenous strain should in
principle give identical results. However, results from the volumetric
method are typically 3 to 5 times the results from the linear technique.
By performing measurements in a paraffin oil bath instead of water,
absorption through the elastic membrane was eliminated, and similar
results between volumetric and linear measurements were obtained.
Chemical
Path of Ettringite Formation in Heat-Cured Mortar and Its Relationship
to Expansion (SN2526)
Delayed Ettringite Formation (DEF) is a deterioration mechanism
that occasionally affects concrete exposed to high curing temperatures.
To provide a better understanding of DEF, research in this doctoral
dissertation investigated mortar and concrete systems made with
various mixing and curing parameters to observe detailed changes
in pore solution chemistry, solid phase development, and changes
in physical properties. This holistic approach revealed that relationships
exist between the physical properties and expansive behavior.
Chemical
Path of Ettringite Formation in Heat Cured Mortar and Its Relationship
to Expansion: A Literature Review (RD136)
The issues related to delayed ettringite formation (DEF) have received
much attention since this particular concrete deterioration process
was first reported. Despite many attempts to develop a fundamental
understanding, the mechanism involved is still unclear and remains
controversial. This literature review aims to present each aspect
of DEF-related issues in a comprehensive manner to help readers
develop an overview.
Expansions
in Mortar Bars Subjected to Accelerated Curing (RD132)
Evaluation of the expansion of mortar bars, cured at various elevated
temperatures. None of the mortar bars expanded when cured at temperatures
of 70 C and below, even after five years of storage.. Thermal analysis
revealed that the majority of the sulfate in the cement was present
as ettringite except for one sample, with high C3A level, that had
not expanded.
Examination
of ASTM C 265 Method of Measurement of CaSO4 in Portland Cement
Mortar (SN2677)
The American Society for Testing and Materials (ASTM)
Test Method C 265 (“Method of Measurement of Calcium Sulfate
in Portland Cement Mortar”) has been studied to determine
the precision of the test method and search for means to improve
it. In a first phase of the project, the particle size fraction
for extraction, the method of crushing, and the time allowed for
processing the sample were studied. A second phase studied extraction
time, water/solid ratio for extraction, curing temperature, and
cement sulfate content. Findings show that none of the studied variables
affected the precision of the test method result.
Performance
of Concrete in Sulfate Environments (RD129)
Concrete technologists interested in durability in sulfate
environments will find this report invaluable. It documents a 16-year
research project carried out to evaluate the performance of concrete
in field and laboratory exposures to sulfate solutions. Variables
studied included cement composition, water to cement ratio, cementitious
materials, and surface treatments. The work affirmed the importance
of controlling the water to cement ratio and permeability of concrete
in maximizing concrete durability. Traditional mechanisms for sulfate
attack are questioned and alternative mechanisms involving salt
crystallization are suggested.
For a summary of the report:
"A New Mechanism for Sulfate Attack
"
Freeze-Thaw Durability
of High-Strength Concrete (RD122)
High-strength concrete has low permeability. So how much entrained air is needed to make it freeze-thaw resistant? That is the question PCA research addressed in a recently released 75-page report, Frost and Scaling Resistance of High-Strength Concrete. The results of the research suggest that, to obtain frost resistance as defined by both ASTM
C 666 and C 672, the ACI 318 requirements for total air content are conservative. Other results showed that air entrainment is not necessary for mixtures with water to cement ratio of 0.25. When scaling resistance is not required, air entrainment may not be necessary for mixtures with water to cement ratio less than 0.35.
For a summary of the report:
"Freeze-Thaw Durability
of High-Strength Concrete"
Long-Term Performance
of Concrete in Seawater (RD119)
Construction officials in coastal areas have long been faced with the challenge of building and maintaining durable concrete structures in a saltwater environment. A recently concluded investigation carried out under PCA's Long Time Study of Cement Performance in Concrete (LTS) program provides key insights into the performance of concrete in seawater. The results of the 37-year study revealed that seawater had no damaging effect on submerged concrete specimens, regardless of their cementitious composition. On reinforced concrete, the program produced some predictable results-namely, that a low-water cement ratio and high concrete cover reduce rebar corrosion. But the program also produced a more interesting result: Concrete positioned above high tide suffered more corrosion damage than concrete placed at mean tide levels.
For a summary of the report:
"Where Concrete Meets the
Sea"
Other Research Resources: (Click on
title for more information or to order)
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Concrete
Research Library
2008 Edition (DVD021)
The Concrete Research Library is a searchable compendium
of over 1,100 PCA concrete research reports dating from 1916
to 2008. Of historical importance is the Development Department
Bulletins DX001 through DX147, the Lewis Institute Bulletins
LS001-LS017, and the full collection of Research Department
Bulletins RX001-RX229. Research & Development Bulletins
(RD001-RD136) discuss pavement cracking, ICF walls, high strength
concrete columns, effect of fly ash on the durability of concrete,
freeze-thaw durability, fire resistance of reinforced concrete
columns, cement kiln dust, ASR, DEF, sulfate environments and
all aspects of concrete properties. Also, there is access to
over 550 Serial No.(SN) reports on topics such as; masonry,
RCC, structural design, durability, concrete technology, soil
cement, paving, architectural concrete, residential, bridges,
and sustainability. |
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Cement
Research Library, 2008 Edition (DVD025)
The Cement Research Library is a compilation of nearly
2000 technical papers and research reports issued from 1916
to May 2008 on the chemistry, technology, properties, and manufacture
of portland and other cements. A user-friendly interface allows
easy searching by author, title, keyword, or a combination. |
PCA Research Reports
Summary
This document provides a list of PCA research reports from the last
three years. The reports are categorized by research projects with
respect to their market or technical area. Categories include Engineered
Structures, Residential, Public Works, Product Standards and Technology,
Energy and Environment, and Manufacturing Technology. Click
here.
For more information on PCA's Research and Development program,
click here.
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