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NISTIR 6962

The Virtual Cement and Concrete Testing

Laboratory Consortium

 Annual Report 2002

 Editor: Jeffrey W. Bullard
NISTIR 6962

The Virtual Cement and Concrete

Testing Laboratory Consortium

Annual Report 2002

Editor: Jeffrey W. Bullard

Building and Fire Research Laboratory

January 2003

U.S. DEPARTMENT OF COMMERCE

Donald L. Evans, Secretary

TECHNOLOGY ADMINISTRATION

Phillip J. Bond, Under Secretary of Commerce for Technology

NATIONAL INSTITUTE OF STANDARDS AND TECHNOLOGY

Arden L. Bement, Jr., Director
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Contents

Contents .........................................................................................................iii

Virtual Cement and Concrete Testing Laboratory Consortium...............1

VCCTL Technical Notes and Software Notes.............................................4

VCCTL Publicity..............................................................................................6

VCCTL Consortium Members.......................................................................7

Materials Characterization ............................................................................8

Hydration Research .....................................................................................13

Rheological Properties................................................................................16

Elastic Properties .........................................................................................21

Durability Research......................................................................................24

Case Study I ..................................................................................................28

Case Study II .................................................................................................30

Case Study III ................................................................................................32

NIST/Industry VCCTL Funding ...................................................................34

NIST Equipment and Facilities ...................................................................35

For More Information ...................................................................................39

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Virtual Cement and

Concrete Testing

Laboratory Consortium

Annual Report 2002

Background

The Virtual Cement and Concrete Testing Laboratory (VCCTL) Consortium was formed in

January 2001. Headquartered in the Building and Fire Research Laboratory (BFRL) at the

National Institute of Standards and Technology (NIST), the consortium originally consisted

of three NIST laboratories: BFRL, the Information Technology Laboratory (ITL), and the

Materials Science and Engineering Laboratory (MSEL), and six industrial members: Cemex,

Dyckerhoff AG, Holcim Inc., Master Builders Technologies (MBT), the Portland

Cement Association (PCA), and W.R. Grace & Co.- Conn. The overall goals of the

consortium were—and continue to be—to develop a virtual testing system that will reduce the

amount of physical concrete testing needed and expedite the research and development

process. This will result in substantial time and cost savings to the concrete construction

industry as a whole.

The VCCTL Consortium Oversight Board, consisting of one representative from each

member organization and the VCCTL Consortium Manager from NIST, governs the activities

and direction of the consortium. The oversight board meets twice each year to review

research progress and set the scope and agenda of future research. Within each industrial

participant’s laboratory, one researcher is assigned to participate in the research programs of

the consortium. Once per year, the most recent version of the VCCTL system software is

installed on a Linux-based PC1

 at each participating member’s laboratory.

The ultimate goal of the consortium is to address durability and service life prediction, but the

members recognized that first efforts must be concentrated towards enhancing the current

microstructure models and property calculations. Therefore, the three major initial research

topics of the consortium were: 1) enhancements to the cement hydration and microstructure

development model to consider additional supplementary materials such as slags and

limestones and the prediction of pore solution concentrations, 2) computation of the elastic

properties (elastic modulus, creep, shrinkage) of three-dimensional microstructures,

 1 Commercial equipment, instruments, and materials mentioned in this report are identified to foster

understanding. Such identification does not imply recommendation or endorsement by the National

Institute of Standards and Technology (NIST), nor does it imply that the materials or equipment

identified are necessarily the best available for the purpose.
2

and 3) experimental measurement and computer modeling of the rheological properties

(viscosity, yield stress) of cement-based materials.

This document reports the activities of the VCCTL Consortium in 2002.

Overview of Activities in 2002

The 2002 calendar year represents the second year (hereafter called Year 2) of the initial

three-year consortium term. Year 2 witnessed significant growth in the membership of the

consortium. Sponsored research expanded into new areas, while existing topics of

investigation were further refined in response to major progress in research.

Three new members were welcomed into the VCCTL Consortium in Year 2:

• The International Center for Aggregates Research (ICAR), Austin, Texas, USA

• Verein Deutscher Zementwerke eV (VDZ), Düsseldorf, GERMANY

• Sika Technology AG, Zürich, SWITZERLAND (effective January 2003)

In addition, two other organizations have expressed interest in joining the consortium and are

expected to become members in Year 3:

• Association Technique de l’Industrie des Liants Hydrauliques (ATILH), Paris,

FRANCE

• National Ready Mix Concrete Association (NRMCA), Silver Spring, MD, USA 

With these new and prospective members, the VCCTL Consortium is well represented by

major research and service organizations, by every major constituent of concrete—cement,

aggregate, and chemical admixtures, and by the major manufacturers of concrete.

One of our industry partners, Degussa Construction Chemicals/MBT, underwent major

organizational changes throughout 2002. An unfortunate consequence of these changes was

their decision to discontinue their participation in the VCCTL Consortium for the present. As

a chemical admixture supplier, MBT was one of our more active participants over the past

two years. Their VCCTL representative, Dr. Davide Zampini, was instrumental in modifying

the CEMHYD3D hydration model to allow deactivation of clinker surfaces. The consortium

will miss the contributions of MBT, and of Dr. Zampini in particular, and we sincerely hope

that they would choose to renew their participation in the future.

Year 2 was also marked by major strides in research, which built upon the momentum

established in the first year [1]. Collaborative investigations between NIST researchers and

the industry members led to better understanding and improved computer models in several

areas of research, as summarized in the table on the following page.
3

Materials

Characterization

Calibration of PSD measurements, aggregate shape and size

analysis/database

Hydration Tracking pore solution composition, model for dependence of

hydration kinetics on pH, influence of alkali salts on hydration

Elasticity Elastic moduli at early ages

Rheology Cross-calibration of rheometers, simulation of rheometer flows,

simulation of suspensions with real aggregate shapes

Durability Sulfate attack models and database

Considerable effort was placed on upgrading and enhancing the user interface to the VCCTL

models. The flexibility and portability of a web-based interface was retained while at the

same time adding considerable automation of data entry tasks that previously required tedious

and time-consuming typing. The VCCTL User’s Guide that accompanies the software has

been completely updated, and the web forms in Version 3.0 are now extensively linked to the

User’s Guide to provide context-specific help for virtually every entry of every form. Users

will also notice a new “look and feel” to the interface, some of which will be evident in this

report.

Note that each of the major research sections in this report begin with a quote. Several of

these quotes were taken from Hal Taylor’s famous book, Cement Chemistry [2], to pay tribute

to this great cement scientist who passed away in 2002.

References

[1] “The Virtual Cement and Concrete Testing Laboratory Consortium Annual Report 2001,”

NISTIR 6840, U.S. Department of Commerce. Edited by D.P. Bentz, December 2001.

[2] H.F.W. Taylor, Cement Chemistry. 2nd Edition. Thomas Telford Publishing, London,

1997.
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VCCTL Technical Notes

and Software Notes

Technical Notes

• Technical Note VCCTL-01: Estimation of the Degree of Hydration of Portland Cement

by Determination of the Non-Evaporable Water Content

• Technical Note VCCTL-02: SEM/X-ray Imaging of Cement Powders

• Technical Note VCCTL-03: Quantitative Determination of Calciumsulfate Dihydrate

and Calciumsulfate Hemihydrate in Cement by Means of Thermogravimetric Analysis

(from Dyckerhoff)

• Technical Note VCCTL-04: Estimation of the Degree of Hydration of Cement by

Measurement of Chemical Shrinkage

• Technical Note VCCTL-05: Measuring the Viscosity of Cement Paste and Mortar (due

in 2003)

• Technical Note VCCTL-06: Standard Method for Measuring the Particle Size

Distribution of Cement (due in 2003)

• Technical Note VCCTL-07: Wet/Dry Cycling Method for Determining Resistance to

Sulfate Attack (due in 2003)

Software Notes

• Software Note VCCTL-01: CONCRETEVIEW software

• Software Note VCCTL-02: Software for Hydration/Drying of 2-mm Thick

Microstructures

• Software Note VCCTL-03: Computation of Cement Paste Elastic Properties
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Manuals

• D.P. Bentz and G.P. Forney, “User’s Guide to the NIST Virtual Cement and Concrete

Testing Laboratory. Version 1.0”. NISTIR 6583. U.S. Department of Commerce,

November 2000.

• J.W. Bullard, “User’s Guide to the NIST Virtual Cement and Concrete Testing

Laboratory. Version 3.0” to be published in early 2003.

Reports

• “The Virtual Cement and Concrete Testing Laboratory Consortium Annual Report

2001”. Edited by D.P. Bentz. NISTIR 6840. U.S. Department of Commerce, December

2001.
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VCCTL Publicity

Presentation to the ACI Strategic Development Council as part of the New Technology

Showcase, Orlando, FL (November 18, 2002). “VCCTL: A Web-Based Virtual Cement

and Concrete Testing Laboratory.”

Special presentation by E.J. Garboczi to the Research Committee of the National ReadyMixed Concrete Association, Arlington, VA (October 6, 2002). “VCCTL: A Web-Based

Virtual Cement and Concrete Testing Laboratory.”

Special 90-minute presentation by J.W. Bullard and E.J. Garboczi at the Portland

Cement Association meeting, Chicago, IL (September 16, 2002). “VCCTL: A WebBased Virtual Cement and Concrete Testing Laboratory.”

Daily Commercial News and Construction Record (September 13, 2002). “Facility

Provides Virtual Testing for Concrete.”

Special symposium organized by G.J. Frohnsdorff and C. Ferraris, presented to ASTM

Committees C-01 and C-09, Salt Lake City, UT (June 26, 2002). “The Virtual Cement

and Concrete Testing Laboratory.”

• Concrete Construction (November, 2001). “Virtual Concrete Laboratory”

• The Concrete Producer (October, 2001). “E-Concrete: Let's Try a Little Left Thinking”

• Government Computer News (August 27, 2001). “NIST Team Sees in Stereo” (available at

http://www.gcn.com/20_25/news/16941-1.html)

• Engineering News Record (June 25, 2001). “Website Aims to Cut Concrete Analysis”

(available at http://www.enr.com/itnews/it62501e.asp )

• Civil Engineering (June, 2001). “Virtual Concrete Lab Saves Time, Reduces Material Cost”

• NIST Technology at a Glance (Spring, 2001). “Co-Op Corner, Virtual Cement Laboratory”

• NIST Update (February 20, 2001). “Virtual Lab Consortium to Test Concrete and Cement

Formulas”

• Concrete Technology Today- PCA (December, 2000). “ The Future of Materials Testing?

Virtual Testing of Concrete Will Save Time and Money”

VCCTL Newsletter. In Year 2, NIST began publishing a quarterly VCCTL Newsletter,

which is distributed to members of the VCCTL Consortium and to users who login to the

public domain site for the VCCTL software (Version 1.0). The newsletter highlights

applications by users of the public domain version and also gives periodic tips for using the

software. The VCCTL Newsletter is intended as a source of useful information as well as a

publicity tool for the consortium.

NEW

2002

NEW

2002

NEW

2002

NEW

2002

NEW

2002
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VCCTL Consortium Members

NIST

Dr. Jeffrey W. Bullard (BFRL)

Dr. Judith Devaney (ITL)

Dr. Chiara F. Ferraris (BFRL)

Dr. Glenn P. Forney (BFRL)

Dr. Edward J. Garboczi (BFRL)

Dr. Vincent A. Hackley (MSEL)

Mr. John Hagedorn (ITL)

Mr. Peter Ketcham (ITL)

Dr. Nicos S. Martys (BFRL)

Mr. Steve Satterfield (ITL)

Mr. Paul Stutzman (BFRL)

Mr. John Winpigler (BFRL)

Holcim, Inc.

Dr. Weiping Ma

Portland Cement Association

Dr. Paul Tennis

W.R. Grace & Co.- Conn.

Dr. Vijay Gupta

Dr. David Myers

Cemex Trademarks

Worldwide, Ltd

Mr. Juan Charquero

Ms. Karen Ornelas

Mr. Javier Vazquez

Dyckerhoff AG

Dr. Claus-Jochen Haecker

Verein Deutscher

Zementwerke eV (VDZ)

Dr. Martin Schneider

Dr. Georg Locher

Dr. Maria Teresa Alonso

Association Technique de l’Industrie des

Liants Hydrauliques (ATILH)

Dr. Alain Capmas

Prof. Denis Damidot (Mines de Douai)

Sika Technology AG

Dr. Robert Flatt

International Center for Aggregates

Research (ICAR)

Prof. David W. Fowler (U. Texas at Austin)
8

Materials Characterization

There is an underlying philosophy [in] the branch of engineering known as

“materials science”: To understand the properties (i.e. observable

characteristics) of engineering materials, it is necessary to understand their

structure on the atomic and/or microscopic scale. [1].

Background

Without meticulous characterization of the starting materials, it is practically impossible to

formulate fundamental microstructure models of the hydration and properties of a cement

paste, mortar, or concrete. One of the signature features and strengths of the CEMHYD3D

hydration model is its incorporation of microstructural information with unprecedented levels

of detail.

Proper characterization of cement-based materials is not a trivial task. The starting powders

typically consist of a wide distribution of particle sizes, each particle of which is composed of

multiple phases with variable chemical compositions. Many products of hydration are

amorphous or poorly crystalline, and these may be finely intermixed. An additional

complication is that some microstructural characteristics have not been rigorously defined. In

some cases it has not been possible even to properly calibrate measurements, like those of

particle size distribution (PSD), because of the absence of an accepted reference material or

standard methodology.

Recognizing the critical importance of materials characterization for predictions of

microstructure development, physical properties, and durability, the consortium has

continually sought to achieve greater accuracy and detail in these types of measurements, and

to supply robust, calibrated measurement techniques where those have been lacking.

Activities in Year 1

Particle Size Distribution. In collaboration with ASTM Subcommittee C01.25, it was

established that there is no standard test for measuring the PSDs of cements. NIST obtained

data generated by an ASTM-sponsored round-robin test in 2000. NIST used these data to

initiate an analysis of the type of techniques that are used most commonly, and to develop a

method for determining a statistically valid mean PSD from the distributions generated by

multiple laboratories. A small VCCTL round-robin test also helped determine a logical

course of action: 1) establish a reference material, and 2) determine which parameters need to

be controlled using the laser diffraction technique (wet or dry).

SEM/X-ray Imaging. NIST has pioneered the use of SEM/X-ray imaging for the

quantitative characterization of cement powders [2]. This analysis produces a 2-D image of

the cement powder in which each pixel is identified as one of the major phases of portland

cement, as shown in Figure 1.
9

Research in Year 2

Particle Size Distribution. At the May 2002 meeting of the VCCTL Consortium, it was

agreed that to improve measurements of cement particle size distribution, it is neccesary to

develop a method for separating the individual PSDs of clinker and gypsum phases in

interground cements. Initial efforts focused on physically separating gypsum from clinker in

interblended or interground cements, by selectively sedimenting the powder in a liquid having

a density between the average densities of gypsum and clinker phases. However, this method

was unsuccessful, probably due to some degree of interphase particle agglomeration.

Common methods to deflocculate a powder suspension, such as the use of a chemical

dispersant and ultrasonic agitation, were investigated but also were unsuccessful. A more

promising method may be to use a laser scattering technique to measure the particle size

distribution of a cement that has been suspended in a liquid, the refractive index of which is

accurately matched to that of the calcium sulfate phase(s). The close matching of refractive

indices could effectively eliminate the gypsum particles as scattering centers, thus allowing

the measurement technique to sample only the clinker particles. Preliminary results of this

method indicate that benzyl alcohol/ethanol mixtures can be designed to closely match the

average refractive index of gypsum.

With the recognition that a standard method for measuring PSD does not exist, the consortium

took the lead in trying to establish such a standard. Working through ASTM Subcommittee

C01.25, Dr. Ferraris (NIST) prepared two reports analyzing two ASTM round-robin tests

[3,4]. The first round-robin was organized by ASTM and included data from 21 participants.

Because no information was gathered during this round-robin about how the measurements

were made (only the generic method was stated ) it was deemed insufficient to establish a

standard method or a reference material. Nevertheless, it helped develop the methodology to

analyze the data. The second round-robin was planned by NIST in collaboration with ASTM

and included laboratory members of the proficiency program from the Cement and Concrete

Reference Laboratory (CCRL) as well as VCCTL members. There were 41 participants in

this round-robin. As data were collected on the parameters used to prepare the specimens and

to analyze them, it was used to define a reference material and some basic understanding of

the standard method. Reference material SRM-114p, distributed by NIST and used for Blaine

calibration, was selected. The PSD established in the second round-robin will be included in

the SRM-114p certificate in early 2003. The reference material would be used to “calibrate”

an instrument or to validate the procedure used in a laboratory. It was also established that

most (93 %) of the cement laboratories use a laser diffraction technique, with either liquid

100 μm

C3S C2S C3A

C4AF Gypsum

AS2

CaO/

CaCO3

Silica

Mg(Ca)O

CAS2 Slag

K2SO4

Figure 1: Processed 2-D image of CCRL Cement 140.
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Figure 2: (Top) Photograph of a

streambed rock (volume = 5x104 mm3).

(Bottom) Spherical harmonic expansion,

using 300 terms, of a computed

tomography (CT) scan of the same rock.

suspension or aerosol handling of the cement powder. Therefore, NIST agreed to develop a

standard procedure to be submitted to ASTM in Year 3, based on laser diffraction.

Aggregate Shapes. Ed Garboczi (NIST) began a joint project with ICAR to

mathematically represent and analyze aggregate shapes. The project encompasses (1)

developing ways to experimentally capture the

three-dimensional images of aggregate assemblies,

using X-ray computed tomography, (2) using

image analysis to isolate individual aggregate

pieces from the data, and (3) creating and storing a

mathematical description of the aggregate shape

using spherical harmonic expansion [3]. Several

trials were made to validate the general procedure,

and an assessment was made of the convergence of

the spherical harmonic expansion. Figure 2 shows

a comparison of the spherical-harmonic expansion

of the initial data for a single rock particle.

The ultimate objective of this project is to provide

a database of aggregate shapes for accurately

modeling the macrostructure of concrete. A

skeletal database of shapes will be included in

Version 3.0 of the VCCTL software. Ongoing

work is focusing on analyzing different types of

aggregate (e.g. riverbed vs. crushed) for common

characteristics and on enhancing the database.

Case Study II in this report provides additional

detail and validation of the spherical harmonic

analysis of several rock samples by comparing the

predicted volume of each to the true volume

measured by immersion in a liquid.

SEM/X-ray Imaging. Much of the microstructural characteristics of cements are obtained by

segmenting a series of 2-D SEM images into constituent phases, with the aid of X-ray maps

for the relevant elements. Segmentation is accomplished pixel-by-pixel, using an algorithm

that steps through a decision tree based on the intensity of the X-ray signal for each element at

a particular location. In Year 2, the decision tree was expanded to include slag-like material

and a calcium aluminosilicate compound as possible additional phases, as shown in Figure 1.

In addition, the color scheme for representing phases was changed to more closely match the

actual colors of the phases when they are HF-etched and examined by reflected-light

microscopy.

Although it is fairly routine, the segmentation procedure involves a considerable amount of

user intervention and somewhat subjective decisions, especially when thresholding the

intensities of the signals for each element’s X-ray map. Researchers in the Information

Technology Laboratory (ITL) at NIST are actively pursuing applications of machine learning,

which can be a powerful tool for analysis of complicated images. The SEM segmentation

procedure could be made simpler and more automated if a way could be developed to

implement machine learning. With sufficient testing and documentation, such a segmentation

protocol could be distributed to the VCCTL Consortium members as part of the software

within a year.
11

Future

Work in Year 3 will build on the research progress made in 2002, and will include the

following research/development activities:

Particle Size Distribution Analysis

1. Validate refractive index matching to gypsum as a way to isolate the particle size

distribution of clinker in interground/interblended cements.

2. Develop formulations for benzyl alcohol/ethanol mixtures that are index-matched

respectively to gypsum, hemihydrate, and anhydrite forms of calcium sulfate.

3. Create and validate an algorithm for deconvoluting the individual contributions of two

separate particle size distributions from a mixture in which one of the PSDs is known.

4. Complete documentation of reference data for PSD of SRM-114p

5. Develop next-generation SRM 114q as a standard reference material for calibrating

particle size analyzers.

6. Draft a standard cement PSD measurement method as a VCCTL TechNote and for

ASTM.

Aggregate Shape Characterization

1. Refine and optimize procedures of image and mathematical analysis of aggregates (joint

work between NIST and ICAR)

2. Extend the project to characterize shapes of cement particles, and incorporate cement

particle shape in CEMHYD3D hydration model.

3. Search for more generally available 3D imaging techniques, besides X-ray computed

tomography, for use by consortium members.

References 

[1] J.F. Shackelford. p. 11 in Introduction to Materials Science for Engineers. Macmillan

Publishing Company. New York, NY (1985).

[2] D.P. Bentz, P.E. Stutzman, C.J. Haecker, and S. Remond, “SEM/X-ray Imaging of

Cement-Based Materials,” 7th Euroseminar on Microscopy of Building Materials, Delft,

The Netherlands, 457-466 (1999). Available online at

http://ciks.cbt.nist.gov/monograph/eurosem/semcolor.html
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[3] C.F. Ferraris, V.A. Hackley, A.I. Aviles, and C.E. Buchanan, “Analysis of the ASTM

Round-Robin Test on Particle Size Distribution of Portland Cement: Phase I”. NISTIR

6883. U.S. Department of Commerce, May 2002. Available at

http://ciks.cbt.nist.gov/~monograph/nist6883/nistir6883.htm .

[4] C.F. Ferraris, V.A. Hackley, A.I. Aviles, and C.E. Buchanan, “Analysis of the ASTM

Round-Robin Test on Particle Size Distribution of Portland Cement: Phase II”. NISTIR

6931. U.S. Department of Commerce, December 2002. 

 [5] E.J. Garboczi, “Three-Dimensional Mathematical Analysis of Particle Shape Using XRay Tomography and Spherical Harmonics: Application to Aggregates Used in

Concrete,” Cem. Conc. Res. 32 [10], 1621-38 (2002). Available at

http://ciks.cbt.nist.gov/monograph/paper134/mono134.html .
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Particle Size

Distribution

w/c ratio, gypsum,

degree of flocculation

3D Particle

Microstructure

Autocorrelation

functions from

2-D image of

actual cement

3-D cement with

clinker phases, gypsum,

and additives

Curing conditions,

thermal condition,

kinetic coefficients

Reaction/Diffusion

Model

Prediction of hydrated

microstructure plus

various properties

Figure 3: Schematic of CEMHYD3D models.

Hydration Research

Mathematical modelling [of hydration] has the objective of quantifying

knowledge of the hydration process and microstructure of the resulting material

...thus allowing the effects of changes in inputs or assumptions contained in the

model to be examined [1].

Background

Because the physical, chemical, and durability properties of cement and concrete are

ultimately dependent on their hydrated microstructures and phase composition, a

microstructure-based model of hydration serves as the core of the Virtual Cement and

Concrete Testing

Laboratory software [2].

The 3-D model of

hydration

(CEMHYD3D) [3,4] is

currently recognized as

the most extensive,

complete, and robust

cement paste microstructure model in the

world. The general flow

of the model may be

summarized by several

steps, as shown in Fig. 3.

As hydration executes in

the model, a series of

output files is created to

monitor specific

properties—chemical

shrinkage, heat release,

setting, capillary porosity

percolation, pH, and

strength.

Activities in Year 1

During 2001, research

focused on three

subtopics: 1) modeling

and experimental

measurements on systems

containing limestone

fillers, 2) development of
14

a framework for incorporating reactions for slag into CEMHYD3D, 3) modeling of the pH

and ion concentration of the pore solution during hydration, 4) creation of options in

CEMHYD3D for curing under sealed conditions and for specifying the nature of heat transfer

between system and surroundings, and 5) addition of a supplementary model to monitor

hydration/drying in 2 mm-thick slabs [5].

Research in Year 2

Influence of Alkali Species on Hydration. This project was initiated in late 2001 and has

made substantial progress in Year 2, although several outstanding questions remain. The goal

of this project is to link pore solution pH to hydration kinetics and to validate the modeling

with inter-laboratory experiments on different cements with intentional addition of sodium

and potassium salts. Modification of CEMHYD3D was undertaken at NIST to make a

preliminary accounting of the acceleration in hydration with increasing pH, in which the

dissolution probability of all four clinker phases was made to depend in the same way on pH.

Preliminary experiments, also conducted at NIST, revealed several complications, such as the

importance of experimental mixing procedure in establishing a homogeneous distribution of

alkali species, and the possibility of syngenite precipitation in cements with high initial

potassium content. Suitable modifications were made to CEMHYD3D to allow for syngenite

formation, and modifications were also made to experimental mixing procedures to better

homogenize the alkali species. Concurrent experiments for validation were conducted on

three different cements at NIST, Cemex, and Dyckerhoff during Year 2. The three cements

examined were CCRL Cement 140 (at NIST), a white cement (at Cemex), and a Type I

Portland cement (at Dyckerhoff). The model predictions of degree of hydration closely

matched experimental results for CCRL Cement 140, but were considerably poorer for the

other two cements. Specifically, the predicted degree of hydration at later ages (e.g. 28 days)

was much higher than the observed degree of hydration. The discrepancy is likely due to

unrealistic or incomplete model assumptions, but the possibility of systematic differences in

experimental procedure at the three laboratories cannot yet be discounted. Therefore, an

investigation of the discrepancies in Year 3 will involve

1. repeating the experiments on identical equipment at NIST (to ensure minimal

systematic error due to differences in procedure or equipment calibration),

2. repeating at Cemex and Dyckerhoff the experiments using CCRL Cement 140, and

3. making a critical reexamination of CEMHYD3D to better account for other

influences of alkali species other than pH. This will also involve the incorporation of

more realistic algorithms for altering the solubility of anhydrous phases.

Despite the mixed results of these experiments, Version 3.0 of the VCCTL software will

include an option in CEMHYD3D to allow pore solution pH to influence hydration rates. As

CEMHYD3D is improved in this respect, upgrades to the model will be distributed to the

consortium members.

Future

In addition to this continuing work on alkali influences, Year 3 will see an effort to further

refine CEMHYD3D for predicting hydration behavior of blended cements with slag and/or fly

ash additions. Limestone reactions will also be further incorporated and validated. These are

areas in which the expertise and collaboration of several consortium members, including

Cemex, Dyckerhoff, VDZ, and W.R. Grace, will be essential for making rapid progress.
15

Specific Goals

1. Collect fundamental experimental data on solubility curves of clinker compounds as a

function of pore solution composition/pH.

2. Modify CEMHYD3D to allow for possible pH influences on individual cement clinker

phases and hydration product characteristics. Make preliminary tests of modified models

with existing experimental data.

3. Repeat at NIST the alkali-effect experiments conducted by Dyckerhoff and Cemex, to

separate the influences of different material sets from the possible influences of

instrumentation and measurement techniques at these laboratories.

4. Repeat at Cemex and Dyckerhoff the alkali-experiments conducted by NIST on CCRL

Cement 140.

5. Design and perform experiments to test the effects of soluble gypsum forms on the

influence of alkali components.

6. Extend the model to include the dependence of the reactivities of slag and fly ash on pore

solution pH.

References 

[1] H.F.W. Taylor, p. 237 in Cement Chemistry. 2nd Edition. Thomas Telford Publishing,

London, 1997.

[2] D.P. Bentz and G.F. Forney, “User’s Guide to the NIST Virtual Cement and Concrete

Testing Laboratory. Version 1.0,” NISTIR 6583, U.S. Department of Commerce,

November 2000. Available at http://vcctl.cbt.nist.gov/vcctlman .

[3] D.P. Bentz, "Three-Dimensional Computer Simulation of Cement Hydration and

Microstructure Development," J. Amer. Ceram. Soc., 80 (1), 3-21, (1997). Available at

http://ciks.cbt.nist.gov/monograph/AmCeram/ACSmain.htm .

[4] D.P. Bentz, "CEMHYD3D: A Three-Dimensional Cement Hydration and Microstructure

Development Modelling Package. Version 2.0," NISTIR 6485, U.S. Department of

Commerce, April 2000. Available at http://ciks.cbt.nist.gov/~bentz/cemhyd3dv20 .

[5] D.P. Bentz, “The Virtual Cement and Concrete Testing Laboratory Consortium Annual

Report 2001,” NISTIR 6840, U.S. Department of Commerce, December 2001.
16

Rheological Properties

...fresh concrete is no longer considered as a material with a single parameter,

called consistency or workability [1].

Background

At NIST, there is an ongoing program with the goal of predicting the rheological performance

of concrete from its composition. A hierarchical approach, starting with cement paste and

progressing to mortar and concrete, is used by which the rheological properties at one level

are used as input to compute those at the next. This approach consists of the following steps:

1. measuring the rheological properties of the cement paste to determine the influence

of chemical admixtures and supplementary cementitious materials,

2. measuring mortar rheological properties to determine the influence of air and sand

content,

3. predicting rheological properties of concrete via computer simulation [2-4] using

measurements on mortar and/or cement paste and information about the size and

shape distributions of the coarse aggregates

A novel computer simulation approach allows NIST to take the rheological properties

measured on mortar, add the coarse aggregates with their shape and PSD, and predict the

concrete rheological properties. The advantage of this approach is that several tests could be

done by one operator on cement paste or mortar in a day, while concrete testing requires

several operators and much more material. The model is based on the theory of dissipative

particle dynamics (DPD) [5-7], which combines aspects of cellular automata and molecular

dynamics. The method described in Refs. [6,7] was modified by Martys at NIST for

application to the flow of concrete. The model itself requires powerful computers, so NIST

has built a database, included in Version 2.0 of the VCCTL software, that catalogues the

relative viscosity1

 of a concrete with a coarse aggregate defined by its size distribution. The

database at present does not include the effect of aggregate shape.

The goals of the VCCTL Consortium in this area are 1) to establish standard tests for the

influence of air and mix proportioning on the viscosity of mortar, 2) to validate the modeling

approach for a wide range of systems with different supplementary cementitious materials

(SCM) and chemical admixtures, and 3) to extend the VCCTL database to include realistic

shapes and wider size distributions of common aggregates.

 1 The relative viscosity is the ratio between the viscosity of the concrete and that of the mortar with the

same composition as the mortar component in the concrete.
17

Figure 4: Relative viscosity vs. volume concentration of coarse

aggregates in concrete. Comparison of results from various

rheometers. The line is given only to guide the eye and it is not

intended as a reference function.

1

10

100

0 20 40 60

Volume concentration of coarse agg. [%]

relative viscosity

BML #1

BML #2

BML New #3

IBB #1

IBB #2

IBB #3

Activities in Year 1

A methodology to test mortar was developed by modification of the parallel plate rheometer

used previously for cement paste. A database was created to collect aggregate size

distributions and graphs of relative viscosity versus aggregate concentration. A partial

validation of the modeling approach was made possible by rheological measurements on

mortar and concrete, provided by W.R. Grace using a BML rheometer [8,9] and

Degussa/MBT using an IBB rheometer.

The DPD model was modified to include air as a second fluid phase. Air was introduced as

spherical bubbles, which may subsequently deform under shear forces. The two fluid phases

were modeled as being immiscible to prevent dissolution of air into the paste. Validation of

this model was an objective of Year 2 research.

Research in Year 2

Standard Measurement Method. One aspect of the project is to determine experimental

procedures and materials that can be used for cross-calibration of results on different types of

rheometers in different laboratories. Considerable progress has been made in pinning down

the effects of rheometer geometry (the wall, plate gap, and specific effects of plate serration).

A VCCTL TechNote, which describes the methodology developed to measure the rheological

properties of cement paste and/or mortar, will be available in late January 2003. An

interlaboratory experimental study, performed at W.R. Grace and Degussa/MBT, provided

data on concrete and mortar viscosities and their dependence on air content. Plots of relative

viscosity versus volume fraction of coarse aggregate were shown to be in reasonably good

agreement across laboratories

using different rheometer

geometries, as shown in

Figure 4. These results lend

support to the claim that the

influences of geometry and

experimental procedure can

be scaled out of the

measurements to some extent,

yielding truer measurements

of the actual rheological

properties of the material, by

using relative viscosity

instead of plastic viscosity

[10]. The influence of air

content on the flow of

concrete was also

investigated, and Fig. 5

shows the relationship

between air content and

relative viscosity while the

coarse aggregate

concentration in concrete or the sand concentration in mortar is kept constant. It seems that

the relative viscosity increases with air content up to about 10 % and then decreases at higher

values. The model predicts correct trends in the relative viscosity up to 10 % air content.
18

Figure 6: Comparison of DPD model to experimental data on the

dependence of relative viscosity of fresh concrete on the volume fraction of

coarse aggregate. The first three sets of data in the legend are the

simulations, and the remainder are the experimental data as in Fig. 4.

1

10

100

0 20 40 60

Volume concentration of coarse agg. [%]

relative viscosity

Model #1

Model #2

Model #3

BML #1

BML #2

BML #3

IBB #1

IBB #2

IBB #3

Modeling. The DPD model, modified to simulate the flow properties of fresh concrete,

shows good agreement with experimental measurements of relative viscosity as a function of

coarse aggregate volume fraction (see Fig. 6). This model has been used to incorporate

realistic crushed aggregate shapes (see the section on Characterization of Aggregate Shapes

on p. 5). The use of more realistic shapes appears to make qualitative and quantitative

changes in the predictions of viscosity and of flow through rebar compared to that using

spherical aggregate

shapes (see Case

Study III). The

differences are

probably at least

partly due to

differences in the

packing efficiency of

the aggregate. DPD

models can be used to

simulate the influence

of entrained air, as

well as to simulate the

flow of fresh concrete

within different types

of rheometers.

Version 4.0 of the

VCCTL software will

include an expanded

database of aggregate

shape and size

distributions to allow

the user more flexibility in approximating an actual concrete for computation of relative

viscosity. Version 4.0 also should include the air content as a parameter to consider in the

prediction of relative viscosity.

Figure 5: Influence of air on the relative viscosity. Comparison of results from modeling,

mortar measurements and concrete measurements.

0

2

4

6

8

10

12

14

0 5 10 15 20 25

air content in medium [%]

Relative Viscosit

y

Mortar/sand 45%

Mortar/beads 45%

IBB 50%

BML 39%

model 45%
19

Future

VCCTL research into rheological properties is poised for some important breakthroughs in

2003. A large part of the systematic work to establish standard measurement techniques has

been completed. Further modeling work is necessary to determine the flow patterns formed in

different rheometers, and to validate the DPD model with experimental data. A new 128-

processor computer acquired by NIST in 2002 will greatly accelerate this work. With these

foundations in place, future work will exploit the power of combined modeling and

experimental research to reveal important relationships between mix proportioning and the

flow properties of fresh concrete. Specific goals include:

1. Finalize TechNote that describes procedure for measuring viscosity of cement paste

and/or mortar.

2. Gather more measurements on mortars and concrete with different air contents and airentraining agents, in collaboration with W.R. Grace.

3. Develop the model and database to examine real-case scenarios

• Simulate parallel plate rheometer with walls

• Initiate work in collaboration with SIKA to model interactions between particles

• Increase the database to include shape and more distributions of aggregates

• Further validate and develop the model to include the influence of air content on

flow. Modify the database to include the influence of air content.

4. Investigate the usage of the LCPC model to predict the yield stress from the concrete

composition.

References 

[1] F. de Larrard, p. 81 in Concrete Mixture Proportioning: A Scientific Approach. Modern

Concrete Technolgoy Series, Volume 9. Edited by A. Bentur and S. Mindess. E & FN

Spon, London (1999).

[2] C.F. Ferraris, “Measurement of the Rheological Properties of Cement Paste: A New

Approach,” pp. 333-42 in Intl. RILEM Conference The Role of Admixtures in High

Performance Concrete. Edited by J.G. Cabrera and R. Rivera-Villareal, (1999). Available

at http://ciks.cbt.nist.gov/monograph/rilem1999/rilemmain.htm .

[3] C.F. Ferraris and N. Martys, “De la pâte de ciment au béton: modélisation et mesures

expérimentales des propriétés rhéologiques,” pp. 226-30 in Proc. Rhéologie Génie Civil et

Environment, 36 ème Colloque du Groupe Francais de Rhéologie. Marne-la-Vallée,

France, October 10-12, 2001.

[4] C.F. Ferraris, F. de Larrard, and N. Martys, “Fresh Concrete Rheology”, in Materials

Science of Concrete VI. Edited by J.P. Skalny. American Ceramic Society, Westerville,

OH, (2001). Available at

http://ciks.cbt.nist.gov/monograph/materialscience2000/msmain.htm .
20

[5] R.D. Groot and P.B. Warren, “Dissipative Particle Dynamics: Bridging the Gap between

Atomistic and Mesoscopic Simulation,” J. Chem. Phys. 107, 4423-35 (1997).

[6] P.J. Hoogerbrugge and J.M.V.A. Koelman, “Simulating Microscopic Hydrodynamic

Phenomena with Dissipative Particle Dynamics,” Europhys. Lett. 19, 155-60 (1992).

[7] J.M.V.A. Koelman and P.J. Hoogerbrugge, “Dynamic Simulations of Hard-Sphere

Suspensions under Steady Shear,” Europhys. Lett. 21, 363-68 (1993).

[8] “Comparison of Concrete Rheometers: International Tests at LCPC (Nantes, France) in

October 2000,” NISTIR 6819, U.S. Department of Commerce. Edited by C.F. Ferraris

and L. Brower, September 2001.

[9] C.F. Ferraris, “Measurement of the Rheological Properties of High Performance Concrete:

State of the Art Report,” J. NIST Research 104 [5], 461-78 (1999).

[10] C.F. Ferraris and N.S. Martys, “Relating Fresh Concrete Viscosity Measurements from

Different Rheometers”. Submitted for publication to ACI Materials Journal, October

2002.
21

Elastic Properties

Cement paste is extraordinarily complex elastically, with many... different

chemically and elastically distinct phases and a complex microstructure. This

complexity further increases in concrete, as aggregates are added [1].

Background

The elastic behavior of engineering materials, especially those materials intended for

structural applications, is a critical design factor for any project in which they will be used.

For this reason, the elastic properties of metals, ceramics, and structural composites have been

subjects of experimental and theoretical interest for many years. The same cannot be said for

concrete, however. Though one of the most extensively used structural materials in the

history of civilization, concrete has probably had the least attention paid to it by composite

theoreticians and experimentalists. This situation is probably due, in part, to the enormous

structural complexity of the material. Concrete is a random composite material over many

length scales, consisting of phases, e.g. aggregate and capillary porosity, that differ in their

intrinsic elastic moduli by many orders of magnitude. As a result, the effective elastic moduli

of concrete cannot be predicted accurately by most of the analytic theories that are useful for

other classes of materials.

Despite the little progress that has been made in predicting the elastic properties of cement

and concrete, these properties are of great importance to industry. In addition to the

significance of elastic response in the design of structures, there is growing interest in using

the elastic moduli of a mortar or concrete as an estimator of other important mechanical

properties such as its compressive strength. (Prediction of strength from theoretical models is

even more difficult than the prediction of elastic moduli). As a result, a major component of

research within the VCCTL Consortium is directed toward developing robust numerical

procedures that can predict the effective elastic moduli of cement, mortar, and concrete.

Activities in Year 1

A finite element package for computing the elastic moduli of composite materials has been

written at NIST [2] and validated on a diverse range of material classes [3-6], and was

incorporated into Version 2.0 of the VCCTL software package. The finite element program

operates directly on the same digital images that are generated by the other components of the

VCCTL software, such as CEMHYD3D. This enables the true spirit of a “virtual lab” to be

realized, because the user can create, hydrate and compute elastic properties of a

microstructure, all within the same software package. It is important to realize, however, that

the elastic calculations are only as good as the phase elastic moduli input. One ongoing task

of the VCCTL Consortium is to measure the individual phase elastic moduli needed, along

with cement paste elastic moduli as a function of degree of hydration, cement particle size,

and w/c ratio. This work will help develop the easy-to-use elasticity software module into a

tool that is even more accurate.
22

As part of that effort, Dyckerhoff provided experimental measurements of the elastic moduli

of a series of cement pastes, with w/c = 0.25–0.60, and cured under saturated conditions for

various times. Dyckerhoff also provided experimental data on the elastic moduli of

polycrystalline ettringite. NIST researchers gathered published values of the intrinsic elastic

moduli of minerals commonly found in cement/cement paste. Agreement between model and

experiment was quite reasonable (usually within 5 %) for later-age specimens, but more

serious discrepancies were evident for early-age specimens.

Research in Year 2

In Year 2, research focused on refining the predictions of the elastic moduli of cement paste at

early ages (hours to several days after set). The finite element method used in the VCCTL

software, by default, establishes an elastic connection between any two solid pixels that are in

contact across faces, edges, or corners, even when the pixels in question are anhydrous

cement phases belonging to two different particles. A compelling argument can be made for

the elimination of connections between different anhydrous particles on the basis that such

particles experience only weak van der Waals attractions that are easily broken in elastic

measurements. When such connections are eliminated by removing the elastic stiffness from

one of each pair of connecting pixels, remarkable improvements are made in the agreement

between early-age predictions and experimental observations, as shown in Fig. 7.

The experimental data provided by Dyckerhoff were obtained by dynamic acoustic resonance

techniques. The accuracy of the model predictions were shown to improve from nearly 200%

error, for the original model, to no greater than 5% error for the corrected model at low w/c

ratios. For higher w/c ratios (≈0.6) the agreement is poorer, and current research effort is

being placed on determining the source of the error and ways to improve those predictions. E (Gpa)

α

Figure 7: Comparison of measured and predicted values of the elastic modulus of a cement paste as a

function of degree of hydration, α. The symbols represent measured values, the solid lines are model

predictions when uncorrected for artificial connections between particles, and the dashed lines

represent model predictions that are corrected by elminating such artificial connections. The upper set

are for a paste with w/c = 0.3, and the lower set are for a paste with w/c = 0.6.
23

Future

In Year 3, further validation is expected of the finite element code for elastic properties of

cement. Additionally, research activity will broaden to begin to investigate reliable and

accurate ways to address the elasticity of concrete. The following items will be undertaken in

Year 3.

1. Establish validity of corrected elasticity calculations for other cement systems

2. Test the validity of the corrected elasticity calculations at increased system resolution

3. Investigate sources of error in the early-age calculations at higher w/c ratios, and modify

calculation method as necessary

4. Document a procedure for making dynamic measurements of elastic moduli so that interlaboratory comparisons can begin to be made.

5. Investigate applicability of effective medium theory to model the elastic properties of

concrete.

References

[1] p. 8 in “The Virtual Cement and Concrete Testing Laboratory Consortium Annual Report

2001,” NISTIR 6840, U.S. Department of Commerce. Edited by D.P. Bentz, December

2001.

[2] E.J. Garboczi, “Finite Element and Finite Difference Programs for Computing the Linear

Electric and Elastic Properties of Digital Images of Random Materials,” NISTIR 6269,

U.S. Department of Commerce, 1998. Available at

http://ciks.cbt.nist.gov/monograph/manual/man.html .

[3] A.P. Roberts and E.J. Garboczi, “Elastic Properties of Model Porous Ceramics,” J. Amer.

Ceram. Soc. 83, 3041-48 (2000). Available at

http://ciks.cbt.nist.gov/monograph/Tonycer/Tonycer.html . 

[4] A.P. Roberts and E.J. Garboczi, “Elastic Properties of a Tungsten-Silver Composite by

Reconstruction and Computation,” J. Mech. and Phys. of Solids 47, 2029-55 (1999).

Available at http://ciks.cbt.nist.gov/monograph/paper108/tungag.html .

[5] A.P. Roberts and E.J. Garboczi, “Elastic properties of model random three-dimensional

open-cell solids,” J. Mech. Phys. Solids 50, 33-55 (2002). Available at

http://ciks.cbt.nist.gov/monograph/opencell/oc02a.html .

[6] A.P. Roberts and E.J. Garboczi, “Computation of the linear elastic properties of random

porous materials with a wide variety of microstructure,” Proc. Roy. Soc. London A MAT

458, 1033-54 (2002). Available at http://ciks.cbt.nist.gov/monograph/paper127/b06.html .
24

Durability Research

To design a concrete for a specified minimum life, it is necessary to understand

the processes that cause deterioration, including the rates at which these will

occur under the conditions to which it will be subjected [1].

Background

One of the ultimate goals of the VCCTL Consortium is the prediction of service life of

concrete based on fundamental knowledge of the starting materials, mixture proportioning,

curing conditions, and environmental factors. A moment’s reflection will reveal how

complex an exercise it is to make accurate predictions. The field durability of concrete

depends on a myriad of phenomena that interact and compound, beginning with its initial

placement. One must have a reasonably complete understanding of microstructure

development during curing, and of the mechanisms by which the microstructure deteriorates

due to environmental exposure.

The VCCTL models have progressed to offer a comprehensive treatment of microstructure

development and properties of cement pastes, and have begun to expand to include aspects of

aggregate. Although our understanding of the mechanisms of microstructure development is

by no means complete, the framework is in place to enable some preliminary modeling of

durability. For example, Versions 1.0 and 2.0 of the VCCTL software include modules for

simulating the leaching by water of portlandite and other phases from a hydrated cement paste

microstructure. And beginning in Year 2, VCCTL research on durability expanded to include

attack by sulfate salt solutions. These efforts are clearly at an early stage of development, and

research in Year 3 is expected to continue at an increasing rate.

Research in Year 2

VCCTL research in durability has focused in Year 2 on the resistance of cement pastes to

degradation by sulfate attack, and this work has proceeded along two complementary paths.

Sulfate Resistance Database. Researchers at NIST are developing a searchable database

that documents experimental observations of the resistance of different cements to sulfate

attack. For each cement, the database will include microstructural observations as well as

data on the time dependence of expansion, elastic modulus, and other macroscopic properties

as a function of exposure conditions. The database will continue to be developed and

maintained at NIST, and in Year 3 it will be directly linked with the VCCTL software

(Version 4.0). The development of the sulfate resistance database is supported by ongoing

experimental investigations at NIST. This work involves monitoring deterioration of

specimens prepared with various blended cements.

Extensive evidence from microstructure characterization indicates sharp fronts of reaction

products (consumption of monosulfate, decalcification, and gypsum formation, for example),

as shown in Fig. 8. The microscopic observations also reveal a potentially misleading artifact

of the measurement technique: excessive reaction around the pins of the specimen can make
25

Figure 8: Mortar immersed in a solution of

Na2SO4 for varying times. Yellow regions

indicate replacement of CH by gypsum.

6 d 106 d

226 d 264 d

the linear expansion appear higher than it actually is. This artifact has not been recognized

previously, and earlier data should be revisited to determine their validity. It is possible that

much smaller specimens will provide all the information necessary, thus accelerating the test

greatly. This possibility is being explored currently.

In the field, it is often reported that changes in

temperature and/or wet-dry cycles accelerate the

deterioration of concrete. A new test method was

developed at NIST to investigate the validity of

this observation and to determine the material

parameter(s) that influence the deterioration rate.

This study aims at elucidating the influences of

thermodynamic phase stability, pore-size

distribution, and crystallization pressure. VDZ

helped characterize some of the specimens that

are under investigation at NIST.

All of these observations are being used to

formulate and implement improved experimental

procedures for testing cement and concrete

resistance to sulfate solutions. It should be noted

that this experimental program is an excellent

example of the ways that resources are leveraged

at NIST to provide enhanced productivity to the VCCTL Consortium effort. The

development of the sulfate resistance database and the associated experimental program were

sponsored by a separate three-year project through the Portland Cement Association (PCA

Project 99-07).

Modeling Sulfate Attack. A microstructure model, developed jointly by Dale Bentz

(NIST) and Erik Pram Nielsen (Aalborg Portland A/S) to simulate attack of cement paste by

MgSO4 solutions was created in Year 2. The model operates according to principles similar

to CEMHYD3D (agent-based reaction/diffusion events). Along with changes in the

microstructure (see Figure 9), the model also tracks quantities like the volume of each phase

that has reacted and the effective strain as a function of depth, which results from insufficient

reaction space. This model is still in the development/validation stage of research, but will be

included in Version 3.0 of the VCCTL software to encourage its testing by the consortium. 

At larger length scales, a continuum model of ionic transport in cement pore solutions, called

4SIGHT, has been developed and validated over the past seven years [2]. More recently, the

potential of modifying that program to include the types of reactions that occur during sulfate

attack has been demonstrated persuasively [3]. With further work, 4SIGHT has the potential

to accurately predict the velocity and nature of the reaction front during attack by sulfate

solutions (MgSO4 or Na2SO4). Another example of leveraging within NIST, this model was

developed with support from the Nuclear Regulatory Commission, but may be used in Year

3 to supplement the VCCTL effort in this area. A powerful idea is to couple 4SIGHT with the

microstructure model described in the previous paragraph. The result would be a multi-scale

model of sulfate attack, combining the advantages of the well-established thermodynamic and

kinetic principles of 4SIGHT with the ability to model changes in formation factor that

accompany microstructure changes. ATILH, a new member in Year 3, is sponsoring that

kind of research and will help with this part of the VCCTL research.
26

Future

As the foregoing description indicates, research methods into durability, although not new, are

being systematized in a way that enables proper comparison/validation of results. A portion

of the VCCTL activities in this area, therefore, will concentrate on developing standard test

methods for assessing resistance to sulfate attack. Other research will include ongoing work

to develop and validate multiscale models of sulfate attack. Specific goals include:

1. Continue validation of 4SIGHT and VCCTL models of sulfate attack, possibly coupling

these two methods together.

2. SEM/XRD analysis of all specimens currently under test at NIST

3. Publish a TechNote on how to determine the sulfate resistance of a hydraulic cement

using a combination of measurements and modeling.

4. Complete the sulfate attack database containing all data collected at NIST; provide

search tools and uniform structure

5. Sponsor sorptivity test through ASTM

6. Finalize wet/dry cycling method and sponsor it through ASTM, and prepare a TechNote

describing the method

As Hydrated

Attacked

C3S C2S C3A

C4AF Gypsum

AS2

Hemihydrate

Anhydrite Inert CaCO3

Silica Aggregate Mg/Ca Oxide

CAS2 Slag

CH C-S-H Slag C-S-H

Pozz C-S-H Ettringite AFm

Stratlingite CaCl2 Friedel Salt

FH3 Brucite MS

Other Hydration Products

Saturated Porosity Dried/Empty Porosity

Figure 9: Microstructure changes predicted by sulfate attack model after 100K cycles. The

as-hydrated cement is a CCRL 140 cement with w/c = 0.4, hydrated for 28 d before

commencing sulfate attack.
27

References

[1] H.F.W. Taylor, p. 356 in Cement Chemistry. 2nd Edition. Thomas Telford Publishing,

London, 1997.

[2] K.A. Snyder and J.R. Clifton, “4SIGHT Manual: A Computer Program for Modeling

Degradation of Underground Low Level Waste Concrete Vaults”. NISTIR 5612. U.S.

Department of Commerce, June 1995.

[3] K. Snyder, personal communication, November 2002.
28

Case Study I

Later-Age Elastic Properties of a Type I

Portland Cement

This case study is a good example of the value of consortium collaboration. Version 2.0 of the

VCCTL software included an initial version of the elastic code for directly computing the

elastic properties of cement paste for any degree of hydration. The code was thought to be

accurate for later ages, past 50 % to 60 % degree of hydration, although it had only been

tested for one kind of cement, a cement from Dyckerhoff. Part of this year’s work was to use

another cement, from another company, to further validate the elastic model.

For this process, Holcim supplied the cement, a Type I portland cement, to Dyckerhoff and

also provided particle size distribution analysis. Dyckerhoff made samples from the cement

and measured elastic properties, non-evaporable water contents, and an analysis of the forms

of gypsum present. Dyckerhoff sent samples of the cement to NIST, which did SEM and Xray microprobe analysis to provide the basic information needed for the VCCTL models.

This detailed chemical/particle analysis was then used to translate the non-evaporable water

contents into degrees of hydration. Version 3.0 was used to hydrate the cement, and the elastic

code in version 2.0 was used to compute elastic properties for models that matched the w/c

ratios and degree of hydration used by Dyckerhoff in the experimental samples.

The agreement between experiment and model prediction is excellent; differences between

measured and predicted values are on the order of only 5 %, as can be seen in Figures 10 (14

day old samples) and 11 (56 day old samples) below. The model predictions at w/c = 0.55 and

0.60 have been slightly modified to allow for the bleeding that was seen experimentally.

Essentially, a small decrease in the effective w/c ratio was made to allow for this bleeding. In

the NIST X-ray microprobe analysis, about 8 % of the cement was determined to be nonhydratable material, so this material in the model was treated as inert filler with the

approximate elastic properties of gypsum (dihydrate).
29

0

5

10

15

20

25

30

35

0.2 0.3 0.4 0.5 0.6 0.7

14 d Holcim (modified)

E(exp)

E(mod)

G(exp)

G(mod)

E,G (GPa)

w/c

Figure 10: Comparison of calculated and measured elastic moduli for Holcim cement at 14 days.

0

5

10

15

20

25

30

35

40

0.2 0.3 0.4 0.5 0.6 0.7

56 d Holcim cement - modified

E(exp)

E(mod)

G(exp)

G(mod)

E,G (GPa)

w/c

Figure 11: Comparison of calculated and measured elastic moduli for Holcim cement at 56 days.
30

Case Study II

Quantitative Test of X-Ray Computed

Tomography and Spherical Harmonic Shape

Analysis

Taking a 3-D X-ray computed tomography (CT) picture of a concrete cylinder, and then

extracting and analyzing the gravel shapes with spherical harmonic techniques, will always

produce a particle image of some sort. Deciding whether or not it is correct is a harder

question. There are some obvious indirect checks, of course. If two particles were artificially

connected together in the CT image, a very odd spherical harmonic shape will be produced.

Visually checking can eliminate such gross errors, using the VRML (Virtual Reality

Modeling Language) images in the aggregate database (VCCTL v.3.0). However, the best

check of accuracy is a direct, “head-to-head” check – real rock vs. spherical harmonic image.

That is impossible to do, however, when the source of particle images is a concrete cylinder.

The particles cannot be seen inside the opaque cylinder, and are not easily available by

breaking open the cylinder, as how does one find a given particle, especially when one is not

sure of the shape one is looking for, since that is the very quantity to be checked!

To overcome this problem, a single rock, approximately 80 mm × 60 mm × 40 mm, was

packed in a cylindrical container using cement powder and placed in the X-ray tomography

unit at the Federal Highway Administration Turner-Fairbanks lab*

. The same rock, after

imaging was done, was removed, cleaned, and measured at NIST. Its linear dimensions were

carefully measured and its volume was measured via water displacement, to be about (5.0 +

0.5) ·104 mm3. The spherical harmonic mathematical analysis was performed. Once the

spherical harmonic coefficients are known, almost any shape quantity of the rock can be

computed – volume, surface area, average curvature, etc. The volume of the rock was

computed to be 5.4 ·104

 mm3, well within experimental error. Figure 12 on the next page

shows four different views of the rock, comparing a real digital camera image to the

equivalent view of the VRML image. VRML images are completely rotatable, so that an

equivalent view could be found to the actual views of the real rock. The visual comparison is

excellent, and along with the good quantitative agreement between the measured and

computed volumes, implies that this method of image acquisition and analysis is accurate. An

even more rigorous comparison, utilizing additional shapes, will be published in 2003 (S.

Erdogan, E.J. Garboczi, H.S. Saleh, D. Fowler, and R. Livingston, unpublished).

 *

The actual imaging and image processing was done by Dr. Habeeb Saleh, under the leadership of Dr.

Richard Livingston, at FHWA, and Mr. Sinan Erdogan, from ICAR at the University of Texas, who is a

graduate student under the supervision of Prof. David Fowler.
31

Figure 12: Four comparison views of a digital camera image of the real rock vs. the

equivalent view of the VRML image of the rock produced from the spherical harmonic

expansion.
32

Case Study III

Effect of Coarse Aggregate Shape on Concrete

Plastic Viscosity

This case study shows three applications where the DPD simulation was used to directly

compute the effect of real coarse aggregate shape on the plastic viscosity of a model concrete.

This modeling study shows the potential for the virtual testing concept in concrete rheology. 

Two model specimens were prepared, both with four different size particles, ranging over

approximately a factor of two in volume. One concrete model used crushed aggregate shapes,

based on X-ray computed tomography (see Aggregate Characterization section for details)

of a concrete cylinder. The other model used spherical particles having identical volumes to

the four real-shaped particles. A 3-D view of both models is shown in Figure 13.

Figure 13: 3-D views of the two model concretes used in this case study: (a) four different

real crushed aggregate shapes, and (b) equivalent spherical particles. The aggregate volume

fraction in both cases is 45 %.

Rheological differences were found between the two models. For example, at a volume

fraction of 45 %, the same as that shown in Figure 13, the relative viscosity (viscosity of the

concrete compared to the viscosity of the mortar matrix) of the spherical particles was about

8. In contrast, the relative viscosity of the crushed aggregates was about 15, almost twice as

high. This simple example shows the large effect that real particle shape can have.

By varying the number of aggregates in the simulation, the solid volume fraction can be

controlled. Figure 14 illustrates a further comparison of the two concrete models, showing the

difference in relative viscosity over several different coarse aggregate volume fractions.

Clearly, the effect of the different shapes only becomes apparent for volume fractions greater

than about 30 %, which is well below the practical range, anyway. At practical volume

fractions, above 35 %, the particle shape plays an important role as the relative viscosity

(a) (b)
33

increases, for the crushed aggregates, at a much greater rate in comparison with the spherical

aggregate concrete model.

More than just computing viscosity under simple shear flow, the DPD simulation can also be

used to study and bring physical understanding to complex geometries, like those considered

as candidates for standard tests for self-consolidating concrete. Figure 15 shows the same two

concrete models in a simple simulation of this kind of test, at a coarse aggregate volume

fraction of 45 %. In this test, which is generically similar to real tests used in the industry

(unstandardized at present), concrete flows under a gravity-induced stress downward through

a cage of reinforcing steel bars. There are four such rebars in the figure, oriented

perpendicularly into the page. DPD simulation found that the flow rate in (a) was about one

half that found in (b), a result consistent with the difference in the relative viscosity found for

the two models. This last example illustrates the potential of the VCCTL DPD simulation as a

design tool for self-consolidating and other kinds of concrete, and its ability to directly

simulate test apparatus, giving basic physical understanding of empirical test results that are

too complex for analytical interpretation.

0

2

4

6

8

10

12

14

16

0 10 20 30 40 50

Volume fraction [%]

Relative viscosity

crushed

Spherical

Figure 14: Plot of relative viscosity for the two concrete models as a function of the volume

fraction of coarse aggregate.

(a) (b)

Figure 15: The two different concrete models being analyzed in a simple “selfconsolidating concrete” type test, where the concrete flows under gravity through a

cage of reinforcing bars. Rebars extend orthogonally into the page, and are shown

at the corners in blue in (a) and in dark red in (b).
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NIST/Industry VCCTL Funding

The following approximate financial figures are based on the 2002 calendar year, consisting

of nine months of fiscal year (FY) 02 (Jan-Sep) and three months of FY 03(Oct-Dec).

Internal funding of Inorganic

Materials Group by NIST $1.25M

External funding generated by group1

_____________________________

$0.50M

_______

Total operating cost of the Inorganic

Materials Group at NIST (includes

salaries, equipment, travel, etc.) $1.75M

VCCTL Finances2

External funding of VCCTL (from

consortium members outside NIST)3 $0.36M (6 × $40K + 2 ×$60K)

Internal NIST funding of VCCTL

research activities

$0.875M (BFRL) + $0.1M (MSEL) + $0.48M (ITL)

= $1.455M

NIST equipment funding BFRL – 128 processor computer - $250K

BFRL – PSD analyzer - $90K

Total = $0.34M

Total NIST funding of VCCTL project

(labor + equipment)

$1.795M

Percentage shares of total VCCTL project

funding

NIST – 83 %

Industry – 17 %

Total cost/industrial share ≈ 5.9:1

Note: Almost all research sponsored by externally funded sources other than VCCTL have the potential

to be included in new versions of the VCCTL software. For example, the new sulfate attack simulation

work being built into Version 4.0 is based on three years of funding by PCA on research into sulfate

attack mechanisms (total of $225K). The Nuclear Regulatory Commission has provided long-term

support of the development of 4SIGHT (see Durability Research section of this report for details).

 1 The Inorganic Materials Group always seeks outside research funding to complement internal projects,

building on expertise to solve problems of interest to industry and other U.S. government agencies. 2 The total amount of VCCTL support in our group, both internal and external, supports the majority of time

of the main researchers, E.J. Garboczi, N.S. Martys, J.W. Bullard, and C.F. Ferraris. VCCTL funds are also

used for some secretarial support and other research that is needed for the VCCTL project, like some of P.A.

Stutzman’s time characterizing cements for the VCCTL cement database.

3 Of this amount, $60K was directed to ITL for support of visualization and parallelization services, and $60K

was directed to MSEL for services in particle size distribution analysis and for research on the effect of

chemical admixtures on cement/water suspensions.
35

NIST Equipment and

Facilities

Materials and Construction Research Division

Microscopy

• Scanning electron microscope equipped with solid-state backscattered electron detector.

Digital image capture, processing and analysis capabilities. X-ray microanalysis

capabilities for qualitative and quantitative spot analyses as well as imaging element

spatial distribution. 

• Automated X-ray powder diffractometer with nine-position sample changer,

adjustable optics, diffracted beam monochromator 

• Light Microscopy Facilities:

• Stereo microscope utilizing apochromatic objectives and single optic axis

• Polarized light petrographic microscope

• Reflected/transmitted light microscope 

• Atomic force microscope utilizing an environmental chamber

• Confocal microscope

• Specimen preparation facilities for SEM, optical microscopy, XRD and XRF. 

• Image Processing: including digital and optical camera. Semi-automated image analysis

is available 

Mechanical Properties

• Compressive testing machines

• Nano-indenter

• Stress measurements of a confined specimen for ASR or sulfate attack studies

Transport Properties

• Gas permeability equipment
36

• X-ray absorption unit for monitoring water movement in materials Gas permeability

equipment

• Electrical conductivity measurement equipment

• Ionic diffusivity measurement equipment

Systems Characterization

• Malvern particle size analyzer, wet and dry capability (new in 2002)

• Particle classifier (new in 2003)

• Atomic absorption

• Infrared spectrometer

• Ion chromatograph

• Thermogravimetric analysis

• Differential scanning calorimeter (DSC)

• Differential thermal analysis (DTA)

• Automated high-temperature furnace to 1600 C

• Dunouy Tensiometer for measurement of the surface tension of solutions.

• Heiden Sorption Analyzer for measurement of absorption/desorption isotherms.

Rheology

• Parallel plate fluid rheometer: stress or strain controlled

• Controlled temperature and speed mixer: This mixer is designed according to the

specifications developed by PCA/CTL and can be used for paste and/or mortar

• Standard tools for flow measurement in cement paste or mortar, like Marsh cone, flow

cone, mini slump

• Slump and modified slump test.

Sample Preparation Laboratory

• Attritor mill (new in 2002)

• Fully equipped laboratory to prepare and cure mortar or cement paste specimens

including Hobart mixers, flow table, vibrating table

• Environmental chambers:

− three cabinets (temperature and RH controlled) (one new in 2002)

− one walk-in (temperature controlled)

− curing cabinet (temperature controlled and RH higher than 98 %) (new in 2002)

• Water baths: 4 table top and one floor unit

• pH controlled units

• Length measurement devices
37

Computational Facilities (Building Materials Division)

• Windows and LINUX-based PCs

• Linux-based cluster with 32 processors

• 128-processor cluster (in procurement process, expected April 2003)

Dispersion & Fine Particle Labs, Ceramics Division (MSEL)

• Matec Applied Science ESA-9800 (electroacoustic analyzer particle mobility)

• Colloidal Dynamics Acoustosizer (electroacoustic spectrometer for particle size and zeta

potential)

• Dispersion Technology DT-1200 (acoustic spectrometer with CVI for particle size and

zeta potential)

• Malvern Zetasizer 3000HS (microelectrophoresis and QELS particle sizer)

• Rheometrics 2000 (controlled stress dynamic rheometer)

• Brookfield DV-II+ Viscometer

• Coulter LS230 (laser diffraction particle sizer)

• Quantachrome AUTOSORB-1 (multi-point surface analysis system for BET surface area

and porosity)

• Quantachrome AUTOSCAN 60 (mercury porosimeter)

• Rosemount Dohrmann DC-80 Total Organic Carbon Analyzer

• AMRAY 1830 Scanning Electron Microscope

• Beckman J2-series High Speed Centrifuge

• Brookhaven X-RAY Centrifuge Particle Size Analyzer

Information Technology Laboratory Central Hardware Facilities (ITL)

Computational Resources

• Four SGI Origin 2000 machines:

- 8 196 Mhz R10000 CPUs, 8 GB of memory, 120 GB of disk space

- 32 250 Mhz R10000 CPUs, 32 GB of memory, 96 GB of disk space

- 32 300 Mhz R12000 CPUs, 32 GB of memory, 193 GB of disk space

- 32 300 Mhz R12000 CPUs, 32 GB of memory, 193 GB of disk space

• One SGI Cluster

- five dual processor R10000 CPUs, with 4 GB of memory

• Three Linux Clusters 

- sixteen 400MHz Pentium IIs connected by a Fast Ethernet network.

- Each CPU has 256MB of RAM and 6GB of local disk storage.

- forty-eight 500Mhz Pentium IIIs connected by a Fast Ethernet network.

- Each CPU has at least 256MB of RAM and 6GB of local disk storage.

- 128 Pentium IIIs connect by a Fast Ethernet network 

- Each CPU has 1GB of RAM and 6GB of local disk storage
38

Visualization Resources

• One SGI Onyx3000

- Four Infinite Reality4 Graphics 

- Sixteen R14000 CPUs (500 MHz)

- 16 GB memory 

• One RAVE two-wall immersive environment with Crystal Eyes software/hardware with head

tracking
39

For More Information

1. Examine Version 1.0 of the VCCTL software package, available at:

http://vcctl.cbt.nist.gov .

2. Visit the VCCTL Consortium information web site at:

http://www.bfrl.nist.gov/862/vcctl

3. Contact the VCCTL Consortium Manager at:

Dr. Jeffrey W. Bullard

National Institute of Standards and Technology

100 Bureau Drive Stop 8615

Gaithersburg, MD 20899-8615 USA

Phone: 301.975.5725

Fax: 301.990.6891

bullard@nist.gov
40