NISTIR 7096

The Virtual Cement and Concrete 

Testing Laboratory Consortium 

Annual Report 2003 

Editor: Jeffrey W. Bullard 
NISTIR 7096

The Virtual Cement and 

Concrete Testing Laboratory 

Consortium 

Annual Report 2003 

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
i

Contents 

Contents...........................................................................................................1

Virtual Cement and Concrete Testing Laboratory Consortium...............3

VCCTL Publications .......................................................................................6

VCCTL Publicity..............................................................................................8

VCCTL Consortium Members.....................................................................10

Materials Characterization...........................................................................11

Hydration Research......................................................................................16

Rheological Properties ................................................................................20

Mechanical Properties .................................................................................27

Durability Research......................................................................................31

Case Study I...................................................................................................34

Case Study II..................................................................................................36

Case Study III.................................................................................................39

NIST/Industry VCCTL Funding ...................................................................42

NIST Equipment and Facilities....................................................................42

For More Information ...................................................................................47 
2

DISCLAIMER 

Certain trade names or company products are mentioned in the text to specify 

adequately the experimental procedure and equipment used. In no case does such 

identification imply recommendation or endorsement by the National Institute of 

Standards and Technology, nor does it imply that the equipment is the best 

available for the purpose.
3

Virtual Cement and Concrete 

Testing Laboratory Consortium 

Annual Report 2003 

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 Trademarks 

Worldwide, Ltd., Dyckerhoff AG, Holcim (US) Inc., Master Builders Technologies 

Inc. (MBT), the Portland Cement Association (PCA), and W.R. Grace & Co. 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 each year, the most 

recent version of the VCCTL system software is installed on a desktop computer 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, and 3) 

experimental measurement and computer modeling of the rheological properties 

(viscosity, yield stress) of cement-based materials. 
4

This document reports the activities of the VCCTL Consortium in 2003. 

Overview of Activities in 2003 

The 2003 calendar year represents the third and final year (hereafter called Year 3) 

of the initial three-year consortium term. At the start of Year 3, the consortium was 

comprised of eight industry members: Cemex Trademarks Worldwide, Ltd., 

Dyckerhoff AG, Holcim (US) Inc., the International Center for Aggregates 

Research (ICAR), the Portland Cement Association (PCA), Sika Technology AG, 

Verein Deutscher Zementwerke eV(VDZ), and W.R. Grace & Co.. During Year 3, 

three new members were welcomed into the consortium: 

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

FRANCE 

• National Ready Mixed Concrete Association (NRMCA), Silver Spring, 

Maryland, USA (as of January 2004) 

• Master Builder Technologies (MBT), Cleveland, Ohio, USA (as of January 2004). 

The VCCTL Consortium continues to represent every major constituent of 

concrete—cement, aggregate, and chemical admixtures, the major manufacturers of 

concrete, and major research and service organizations. 

One of our charter industry partners, Dyckerhoff AG, made major changes in its 

research focus and personnel in 2003. One of these changes was to discontinue 

participation in the VCCTL Consortium. Dyckerhoff had been one of the most 

active research participants throughout the first three years of the consortium. Their 

VCCTL representative, Dr. Claus-Jochen Häcker, contributed several key research 

advances, including modifying the dissolution behavior of sulfates in CEMHYD3D 

and the experimental measurement of elastic properties of cement paste phases. 

Dyckerhoff’s participation and perspectives will be missed by the consortium. 

Year 3 witnessed a number of important research advances in each of the VCCTL’s 

major focus areas. These advances are summarized in the following table. 

Materials 

Characterization 

Direct measurement of gypsum PSD in cement powder; 

tomographic analysis of aggregates from 19 sources, 

characterization of cement particle shapes

Hydration Incorporation of real cement particle shapes, integration 

of actual cement PSD into models; calculation of onepixel particle bias; improvements in fly ash reaction 

kinetics 

Elasticity Validation of effective medium theory for mortar and 

concrete elastic moduli predictions; exploration of 

compressive strength predictions from elastic moduli 
5

Rheology A simulation of a parallel plate rheometer was 

developed; and interparticle interaction potentials were 

introduced in the DPD model 

Durability Three models were made available through the NIST 

website; progress was made in development of an 

accelerated test for determining the sulfate resistance of 

a cement. 

As in previous years [1,2], most of this progress was made possible only by 

collaborative efforts between NIST and the industry partners, a fact that 

demonstrates once again how critical the consortium arrangement has been to 

accelerating research. 

Further enhancements also were made in Year 3 to the web-based VCCTL interface, 

augmenting the major changes made in Year 2. Among these are the ability to 

search online for desired files needed as input in the user forms, added flexibility in 

the specification of microstructure parameters in CEMHYD3D, and links to 

common next steps at the bottom of most forms to make navigation of the forms 

easier. 

References 

[1] “The Virtual Cement and Concrete Testing Laboratory Consortium Annual 

Report 2002,” NISTIR 6962, U.S. Department of Commerce. Edited by J.W. Bullard, 

January 2003. 

[2] “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. 
6

VCCTL Publications 

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: Rheological measurement of cement paste/mortar 

using a parallel plate rheometer 

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

Distribution of Hydraulic Cement and Related Compounds by Light Scattering 

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

Resistance to Sulfate Attack (due in 2004) 

• Technical Note VCCTL-08: Pore solution extractor (due in 2004) 

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 

• Software Note VCCTL-04: Software for the Degradation of Hydrated 

Microstructures Due to Magnesium Sulfate Attack 
7

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”. Distributed to consortium members as part of the 

VCCTL Version 3.0 software distribution. 

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

Laboratory. Version 1.1”. NISTIR 6984. U.S. Department of Commerce, March 

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. 

• “The Virtual Cement and Concrete Testing Laboratory Consortium Annual 

Report 2002”. Edited by J.W. Bullard. NISTIR 6962. U.S. Department of 

Commerce, January 2003. 
8

VCCTL Publicity 

NEW 2003 E.J. Garboczi, “The Virtual Cement and Concrete Testing Laboratory—

Progress Report and ASTM Relevance.” Presentation to ASTM Committees 

C01 and C09, Tampa, FL. (December 10, 2003). 

NEW 2003 J.W. Bullard, et al., “Virtual Cement and Concrete”. Chapter 10 in Innovations 

in Portland Cement Manufacture. Edited by J. Bhatty and S. Kosmatka. Portland 

Cement Association, in press.

NEW 2003 R.C. Meininger, “Virtual Aggregates,” Rock Products. October 1, 2003. 

Available online at http://rockproducts.com/ar/rock_virtual_aggregates/

NEW 2003 “NRMCA Participates in Development of Virtual Concrete Testing Lab.” 

NRMCA E-NEWS. November 24, 2003. 

NEW 2003 “Virtual Cement and Concrete—The Coming Revolution in Concrete 

Technology.” Special symposium held at the ACI Spring 2003 Convention,

Vancouver, Canada. April 1, 2003. 

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

Technology Showcase, Orlando, FL (November 18, 2002). “VCCTL: A WebBased Virtual Cement and Concrete Testing Laboratory.” 

• Special presentation by E.J. Garboczi to the Research Committee of the National 

Ready-Mixed 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 

Web-Based 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” 
9

• 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 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 1.1). 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. 
10

VCCTL Consortium Members 

NIST 

Dr. Jeffrey W. Bullard (BFRL) 

Dr. Judith Devaney (ITL) 

Dr. Chiara F. Ferraris (BFRL) 

Dr. Edward J. Garboczi (BFRL) 

Mr. John Hagedorn (ITL) 

Mr. Peter Ketcham (ITL) 

Dr. Nicos S. Martys (BFRL) 

Mr. Steve Satterfield (ITL) 

Mr. Paul Stutzman (BFRL) 

Holcim (US) Inc. 

Mr. Barry Descheneaux 

Mr. Al Innis 

Portland Cement Association 

Dr. Paul Tennis 

W.R. Grace & Co.- Conn. 

Dr. Vijay Gupta 

Dr. David Myers 

Cemex Trademarks Worldwide, Ltd 

Ms. Karen Ornelas 

Mr. Javier Vazquez 

Dr. Davide Zampini 

Dyckerhoff AG 

Dr. Claus-Jochen Häcker 

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) 
11

Materials Characterization 

The properties of materials depend upon their internal structure. In turn, the 

properties influence the performance of a material, both during manufacture 

and in ultimate service [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 Years 1 and 2 

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

was established that there was no standard test for measuring the PSDs of cements 

and no reference material existed. NIST was instrumental in 1) analyzing the data 

that were already available from a round-robin conducted by ASTM [2] and 2) 

organizing a second, more extensive, round-robin and analyzing the data [3]. The 

main result was to establish that: 1) the most used method by the cement industry is 

the laser diffraction technology; 2) the particle size distribution of the standard 

reference material (SRM), cement SRM 114p, was established and now is included in 

the certificate provided by NIST with the material; 3) the basis of a standard 

procedure was developed. Therefore, now the industry has a reference material that 

can be used to calibrate an instrument or to validate the laser diffraction procedure 

used in a laboratory. 
12

The efficacy of calcium sulfate in Portland cement, for controlling C3A hydration 

and microstructure development, has been demonstrated to depend on its spatial 

distribution and specific surface area [4]. Because both of these factors are expected 

to depend on the PSD of the calcium sulfate component, research was initiated in 

Year 2 to find and validate techniques for measuring the PSD of calcium sulfate 

after it has been blended/interground with clinker. By the end of Year 2, a novel 

approach using the wet laser diffraction technique had been identified. More 

details on the technique and its validation are given in the next section. 

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

quantitative characterization of cement powders [5]. 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. 

Research in Year 3 

Particle Size Distribution. To pursue further the goal of providing industry with a 

method to measure the PSD of cement, two actions were pursued in year 3. The first 

one is related to the SRM 114p cement, whose stocks are fast diminishing. Therefore, 

NIST initiated a procedure to produce the next generation SRM, SRM 114Q. This 

procedure includes the purchase of a large stock of cement, the homogeneisation of the 

material, the production of 100 000 vials in sealed containers, and the characterization of 

the material by a round-robin. This process is expected to be completed in 2004. NIST

developed a standard procedure that was provided to the members as Technical Note 

#6. This standard was presented to ASTM subcommittee C01.25 and to the Task Group 

on PSD but was rejected because the Task Group wants to develop a standard that 

includes all possible methods, i.e., SEM, EZS, sieving, and sedimentation. The Task 

Group wants to use the SRM 114 curves developed for laser diffraction as a reference for 

all other methods. NIST’s opinion is that this is not a valid approach because none of the 

methods measure the PSD directly. They all rely on assumptions (spherical particles, 

perfect dispersion, refractive indexes, etc.) and models to determine the PSD from the 

measured values. Also, from the round-robins conducted and a survey of Cement and 

Concrete Reference Laboratory (CCRL) members, it is clear that no statistical values 

could be obtained as the users of methods other than laser diffraction are few (1-3 at 

most). We will pursue the possibility of convincing ASTM to consider developing a test 

for PSD by laser diffraction. 

PSD of Gypsum in Cement 

The goal was to be able to determine the PSD of gypsum after it has been mixed or 

interground with clinker. This implies finding a method that can either physically 

separate the gypsum from the clinker or optically isolate the gypsum. Several 

unsuccessful tentative attempts were made to physically separate the gypsum using 

the density difference between the clinker particles and the gypsum. The method 

adopted was to use the laser diffraction device instead. The principle of the method 

is to render some particles, the gypsum for instance, “invisible” by matching the 

real refractive index with the medium. 
13

Material Real Refractive 

Index 

Isopropanol (IPA) 1.39 

Benzyl Alcohol (BA) 1.54 

Clinker 1.7 

Gypsum 1.525 

Preliminary results show that the method is valid. A gypsum and a ground clinker 

were blended and measured in IPA and in benzyl alcohol (BA). The various real 

refractive indices of interest are given in Table 1. 

A mixture of gypsum and clinker dispersed and measured in BA will result in only 

the clinker PSD being measured, while in IPA both are measured. By properly 

weighting and subtracting the BA curve from the IPA curve, one can in principal 

obtain the gypsum PSD. The same technique could be used for other components if 

the relevant refractive indices were known. 

Figure 1 shows an example obtained from an interblended clinker and gypsum. 

Inside the small circle in Figure 1, the calculated gypsum distribution is very 

different from the measurement of gypsum alone. This error is probably due to the 

small differences between IPA and BA data. The error is amplified by the 

multiplication to obtain the correct compound relative ratios. It also could be due to 

Table1: Real components refractive indices for dispersants and cement components. Values are 

reasonably consistent over a range of wavelengths. For the solid components, the values reported are 

averages over all phases and crystallographic orientations 

Figure 1: Gypsum PSD in interblended cement. In the circle are the data 

that are suspicious (see text for explanation). 

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

0.1 1 10 100 1000

Size [μm]

Volume %

IPA

BA

only Gyp

Gyp Meas
14

systematic errors in the measurements. NIST is investigating methods to eliminate 

these errors. 

Aggregate Shape Characterization. In Year 2, we demonstrated how to 

characterize aggregate shape using a combination of x-ray tomography and 

spherical harmonics [6]. In Year 3, we further validated and streamlined this 

approach [7]. At the May 2003 VCCTL meeting, a call was put out for consortium 

companies to send several aggregates to NIST, which was going to pay The 

Pennsylvania State University Center for Quantitative Imaging to collect x-ray 

tomographs of these aggregates (about $25K). After the images were analyzed, the 

shape data would be added to the aggregate database in VCCTL 4.0. Several 

companies sent aggregates (Cemex, Holcim, PCA, ATILH, Sika, ICAR). There was 

a several month delay due to equipment problems at Penn State, which were 

resolved. As of this report, almost all the aggregates have been scanned and 

processed. All this shape information will be put into the VCCTL 4.0 database, 

along with size, elastic moduli, absorption, and maximum packing information (to 

the extent obtainable). 

Figure 2 shows the kind of statistical analysis that can be done after the shape 

information is obtained. The graph was done for an ICAR crushed granite coarse 

aggregate. The solid line is an exact theoretical curve for a sphere, surface area 

S = 4.84 V2/3, where V is the volume of the particle. The dashed line is a curve of the 

same form fit to data for a GR sand, S = 8.1 V0.63. The similarity of the exponents is 

because the GR aggregates are ordinary 3-D particles. The larger coefficent in the 

power law is a measure of the non-sphericity of the particles. 

Figure 2: Surface area of particles as a function of their volume

The ultimate objective of this project is to provide a database of aggregate shapes for 

accurately modeling the macrostructure of concrete. Ongoing work is focusing on 

0

500

1000

1500

2000

2500

3000

0 2000 4000 6000 8000 10000

Spheres

GR

Surface area, mm2

Volume, mm3
15

analyzing different types of aggregate (e.g. riverbed vs. crushed) for common 

characteristics and on enhancing the database. 

Future 

Particle Size Distribution. The SRM 114Q will be developed and further action 

will be taken to convince ASTM that a standard test is paramount for the industry. 

The optical method for isolating the PSD of gypsum in cement will be validated 

further and refined in the coming year. 

Aggregates. The aggregates database will continue to expand and include more 

information (mineralogical composition, water absorption, etc.) for each entry. The 

VCCTL software, especially that dealing with rheological and mechanical properties 

of concrete, will access the database directly to read particle size and shape 

distributions that are required for predicting properties. 

References 

1. L.H. Van Vlack. p. 1 in Elements of Materials Science and Engineering. Fifth 

Edition. Addison-Wesley, Reading, MA, 1985. 

2. 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 . 

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 II”. NISTIR 6931. U.S. Department of Commerce, December 2002. 

4. F.J. Tang and E.M. Gartner, “Influence of Sulphate Source on Portland Cement 

Hydration,” Adv. Cem. Res.1 [2] 67-74 (1988). 

5. 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

6. E.J. Garboczi, “Three-Dimensional Mathematical Analysis of Particle Shape 

Using X-Ray 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 . 

7. S. Erdogan, P.Quiroga, D. Fowler, H. Saleh, R.Livingston, E.J. Garboczi, P. 

Ketcham, and S. Satterfield, “Three-dimensional shape analysis of coarse 

aggregates: Methodology and preliminary results on several different coarse 

aggregates,” in preparation (2004). 
16

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 concrete are ultimately 

dependent on the composition and microstructure of its binder, a microstructurebased model of cement paste hydration is at the core of the Virtual Cement and 

Concrete Testing Laboratory software [2]. For several years, the 3-D model of 

hydration (CEMHYD3D) [3,4] has been recognized as the most extensive, complete, 

and robust cement paste microstructure model in the world. As hydration 

proceeds, a series of output files is created to track specific properties—chemical 

shrinkage, heat release, setting, capillary porosity percolation, pH, and strength. 

Activities in Year 1 

During 2001, research focused on five subtopics: 1) modeling and experimental 

measurements on systems containing limestone fillers, 2) development of 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]. 

Activities in Year 2 

Research in 2002 concentrated primarily on incorporating in CEMHYD3D the 

influence of alkali species on hydration kinetics. The pH was used as the sole link 

between pore solution and hydration kinetics, and the dissolution rates of all clinker 

phases were assumed to change by a prescribed amount that depended only on pH 

and not on the clinker phase itself. This modeling work was performed in parallel 

with considerable experimental efforts at Cemex, Dyckerhoff, and NIST to measure 

the hydration rate of cements intentionally doped with alkali salts. Model 

predictions compared favorably with experiments on one cement, but were 

unsatisfactory for two other cements. Other modeling research included (1) 

extending CEMHYD3D to arbitrary system sizes and (2) automatic tracking of 

nonevaporable water content. 
17

1 10 100 1000

time (h)

0.0

0.2

0.4

0.6

0.8

α

bias = 1.0

bias = 10

bias = 5.0

Research in Year 3 

Alkali effects. CEMHYD3D was modified to allow pH to influence the reaction 

rate of any given phase independently. Further experimental data on the influence 

of alkali species were obtained at W.R. Grace. Much of the apparent disagreement 

between model and experiment was discovered to be likely due to inadequate 

characterization of the dissolution rate of submicron cement particles. For cements 

containing fly ash, effort was placed on more accurately capturing the reaction rate 

of fly ash phases. This was accomplished by introducing a pH-dependence on 

pozzolanic reaction rates to simulate the observed induction period of many fly 

ashes. Fly ash consumption predicted by the model now compares favorably with 

the limited experimental data that are available [6]. 

Dissolution of submicron particles. Since Year 1, a dissolution bias could be 

implemented to simulate accelerated dissolution of one-pixel particles. In Year 3, an 

equation was derived to explicitly calculate the required one-pixel dissolution bias 

based on the particle size distribution in the submicron range. This equation was 

incorporated into CEMHYD3D. This improvement goes a long way toward 

reconciling prior disagreements between predicted and experimental hydration 

rates, especially at early ages. 

Surface deactivation. 

Beginning in Year 2, users 

could choose to render inert 

for a specified time a certain 

fraction of all the surface sites 

in a cement, as a way to 

simulate the action of 

retarders. In Year 3, this 

feature was extended to allow 

deactivation of any fraction of 

any surface type, including 

hydration products such as 

portlandite. 

Real particle shapes. The 

Visible Cement Data Set [7] 

was used to extract and 

reconstruct real shapes of 

cement particles (clinker and 

gypsum). The source of the cement particle images was CCRL cement 133. 

Cylinderical samples 1 mm in diameter were made by Dale Bentz and imaged at the 

ESRF facility, Grenoble, France. The imaging was done at a resolution of 0.95 

μm/voxel length, using 10243 voxels. More details and actual data can be found at 

http://visiblecement.nist.gov. Many images were taken at various degrees of 

hydration. Only the earliest age, 3 h, was used for this work. At this point, set had 

just occurred, so that stable imaging could be done, but not enough hydration had 

taken place to significantly disturb the shape of the particles of interest, of diameter 

5 μm and above. Real shapes can now be used to construct 3-D microstructures in 

Figure 3: Influence of one-pixel dissolution bias onhydration 

kinetics of a Dyckerhoff Rumelange cement paste.
18

exactly the same way as spherical particles have been used in the past (see Case 

Study I) 

New phases. Lime (CaO) was added to CEMHYD3D as a possible cement phase. 

Using available thermodynamic data as a guide, CaO was assumed to dissolve 

readily in water to form solid CH. Solubility data for CaO in water was compared 

to that for gypsum and portlandite to assign a value for the relative dissolution 

probability of free lime. However, this value should be examined closely and 

adjusted as more experimental data become available. The orthorhombic 

polymorph of C3A, which is known to be more reactive in water than the cubic 

form, also was added as a new phase. The orthorhombic form of C3A currently is 

set to dissolve 1.5× more readily than the cubic form. 

Centralization of model parameters. As a way to manage the complexity of 

CEMHYD3D more effectively, the adjustable parameters used within the model 

were collected together in a single input file. Also, each parameter was documented 

in a separate file. These parameters, and their documentation, now may be viewed 

and edited through the user interface and then submitted for any given hydration 

simulation, without the need to recompile the code. 

Future 

CEMHYD3D has been shown to be an extremely powerful and useful tool for 

modeling the microstructure development of cement pastes. Nevertheless, the 

model in its current form is limited in its ability to accurately capture the kinetics of 

hydration. The reason for this is two-fold: (1) certain important mechanisms that 

control hydration rates, especially at late ages, are not included in the model, and (2) 

the model has no intrinsic time scale with which to dictate the progression of time. 

The model compensates by using a user-specified time conversion factor and an 

assumed parabolic relation between model cycles and time. A major goal in Phase 

II of the consortium will be to endow the hydration model with more realistic 

kinetics. A second major objective of hydration research is to more accurately link 

pore solution chemistry to cement hydration and to make the model extensible to 

new cement phases or mineral admixtures. 

Reaching these goals in Phase II will require a significant overhaul of the structure 

and algorithms of CEMHYD3D. The program likely must be rewritten in an objectoriented language, which in turn will involve a restructuring of data. Although this 

is a major undertaking with its own risks, it offers several outstanding 

opportunities. Chief among these is that, by making the next-generation model 

more extensible, the code should be easier to understand and modify in the future. 

Furthermore, details of validation will be embedded in the documentation to 

provide a concise, but complete, history of code development. Effort will be placed 

in the near term on correctly modeling ordinary portland cement before moving on 

to incorporate mineral admixtures. 

Major Goals for Phase II 

1. Mechanistic basis for time stepping to replace empirical time conversion 

scheme. 
19

2. Limited diffusion of selected ions through C-S-H and pozzolanic C-S-H gels 

3. “On-the-fly” specification of new cement compounds or mineral admixtures. 

4. More accurate, thermodynamically based tracking of pore solution composition, 

with corresponding links to reaction kinetics. 

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. 

6. X. Feng, et al., “Estimation of the Degree of Hydration of Blended Cement 

Pastes by a Scanning Electron Microscope Point-Counting Procedure Cem. Conc. 

Res., in press. 

7. D.P. Bentz, et al., “The Visible Cement Data Set,” J. Res. Natl. Inst. Stand. Technol.

107, 137-148 (2002). 
20

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 and expanded in Version 4.0 of the VCCTL 

software, that catalogues the relative viscosity, i.e. the ratio of the concrete viscosity 

to that of the mortar, of a concrete with a coarse aggregate defined by its size 

distribution. 

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. 
21

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. 

Activities in Year 2 

From a combination of experimental measurements and simulation, it was 

established that the use of the relative viscosity concept allows the direct 

comparison of results from rheometers with different geometries. In other words, if 

the relative viscosity is considered instead of the plastic viscosity, data obtained 

with mortar using a small modified parallel plate rheometer or with concrete in two 

rheometers such as IBB and BML can be plotted on the same graph and seem to 

follow the same trend. This process is detailed in Ref. [10]. 

It was also shown that increases in the air content leads to a decrease in the relative 

viscosity both in mortar and concrete. This will allow determining the influence on 

concrete rheology of the air content introduced by a selected air-entraining agent 

(AEA) using mortar instead of concrete to perform the test. A first attempt to 

simulate the influence of air was also initiated. 

The simulation was modified to allow for variation of the size distribution and 

shape of the coarse aggregate to determine its influence on the concrete flow. In 

addition, crushed aggregates shapes, based on X-ray tomography images, were 

introduced in the simulation. In agreement with field experience, the viscosity of a 

concrete with crushed aggregate was predicted by the simulation to be higher than 

a concrete with the same volume fraction of round coarse aggregate. 

Research in Year 3 

Experimental 

Standard Measurement Method. One of the goals of this project is the prediction 

of the concrete rheology from the measurements on cement paste or mortar. The 

influence of air content is also one of the concerns. This year, a VCCTL Technical 

Note, which describes the methodology developed to measure the rheological 

properties of cement paste and/or mortar, was prepared. This is the starting point 

to allow other laboratories to measure the plastic viscosity of cement paste or 

mortar. The goal is eventually to standardize this methodology in ASTM. Extensive 

tests linking experimental results and modeling were conducted to better 

understand the critical geometrical parameters of the parallel plate rheometer used 

at NIST. This rheometer was modified to allow mortar measurements. The 

modification involves changing the top and bottom plates and the introduction of 
22

Top plate

Bottom plate

Confinement A

h

e

Top plate

Bottom plate

Confinement A

h

e

0

2

4

6

8

10

0 10 20 30 40 50 60

Volume concentration of agg. [%]

relative viscosity

Model #2

SIKA PP60-M4

SIKA PP60-M8

SIKA PP60-M8

Figure 4: Schematic of the mortar rheometer. The parameters, A, h and e are used to characterize the 

geometry

confinement walls (Figure 4). The use of a lattice Boltzman model of fluid flow 

determined that the three important parameters are A (distance between the wall 

and the top plate), h (gap between the two plates) and e (thickness of the top plate). 

Figure 4 shows that if the distance A is not correctly selected, the value of the 

viscosity might not be properly measured. In Figure 5, the data marked SIKA PP60-

M8 are two sets of data using A = 8 mm while the data marked SIKA PP60-M4 is for 

A=4 mm. It is clear that due to the type of aggregates used the value of 8 mm for A 

yields data that are comparable to the concrete data while the smaller A results in a 

viscosity that is too high. A systematic study using standard oils was conducted to 

. 

Figure 5: Influence of mortar rheometer geometry.
23

validate the importance of the various parameters. This study is still in progress to 

measure oils with particles to further calibrate the modified rheometer. This work is 

being done in collaboration with Dr. Mette Geiker (DTU). 

Air Content Influence: The second area of interest was the influence of air content 

on the rheology of mortar and concrete. W.R. Grace provided concrete data and 

NIST produced the mortar data. Figure 6 shows that the mortar measurements 

follow the same trend as the concrete data. It should be noted that, to compare 

concrete and mortar on the same graph in a consistent fashion, all plastic viscosity 

data are reported as relative viscosity. In this case, the relative viscosity is defined as 

the ratio of the viscosity measured in concrete/mortar with air to the same 

concrete/mortar with no air (or better with no AEA implying minimum air). 

Therefore, it can be shown, as previously found, that measurements on mortar 

mimic the concrete behavior. 

Figure 6: Comparison of measurements of concrete and mortar. The curve is not a modelbut is provided 

instead to guide the reader. 

The next step is to model this behavior so as to predict the influence of air content 

on concrete flow. The first thing that should be noted is that one of the reasons for 

the viscosity to decrease with the increase in air content is that the particle 

concentration actually decreases with increasing air content. This can be visualized 

easily by the following equations: 

• sand+coarse aggregate conc. = (sand+coarse aggregates vol.)/Total Vol. 

• Total Vol.= Σ(vol. of air, sand+coarse aggregates, cement, water) 

Therefore, as the total volume is increased by the volume of the air, the sand+coarse 

aggregate concentration is reduced. If the new volume concentration is input and 

the semi-empirical Douglas equation for predicting relative viscosity is used, a 

reduction in the viscosity is observed as shown in Figure 7. This first approximation 

0

0.2

0.4

0.6

0.8

1

1.2

0 5 10 15

Air [%]

Relative viscosity (no air)

Mortar WRG

NIST Mortar

Concrete 32%

Concrete 39%
24

does not account for the total decrease seen in the experimental data. A further 

correction of the Douglas equation should be introduced to account for the changes 

in the paste due to air content (equivalent to an increase in w/c). Further tests are 

planned to systematically prove this methodology. 

Modeling

In Year 3, significant progress was made in our modeling efforts. The rheology code 

was validated for many flow situations and it was also extended to account for 

interparticle interactions and flow in other geometries not unlike that used in some 

concrete rheometers. 

Inclusion of Lubrication Forces The rheology code was extended to include 

lubrication forces for spherical particles. Lubrication forces can help produce a 

shear thickening effect at high solid fractions and shear rates so it was important to 

include this effect. Further, for the purposes of validating the rheology code, it was 

important to include this effect, because there are considerable experimental data 

using charge-neutralized colloidal systems with which to compare. 

Reasonable agreement was found between well characterized experimental data 

and our simulation results. Also, reasonable agreement was found with other, well 

established, but more numerically intensive simulation approaches. 

Examination of the Role of Particle Size Distribution In collaboration with 

Robert Flatt (Sika), we studied the role of particle size distribution on the 

rheological properties of sphere suspensions (see Case Study III). Several empirical 

theories for fitting data were investigated. We found that the Douglas equation 

provided very good fits for a fairly wide range of aggregate size distributions not 

unlike that used in concrete. 

0.00

0.20

0.40

0.60

0.80

1.00

1.20

0 5 10 15

Air content [%]

Relative viscosity (no air)

Mortar #49

Douglas model

Douglas + paste

Figure 7: Comparison of mortar with Douglas equation
25

Introduction of Interparticle Interactions Also in collaboration with Robert Flatt, 

an interaction potential was included in the simulations to account for 

agglomeration of particles. These preliminary investigations were encouraging, in 

that we were able to obtain a Bingham-like behavior in our colloidal system. As 

work on this project continues, we plan to introduce more refined models of 

interparticle interactions to account for the effect of steric hindrance from the use of 

high-range water-reducing admixtures (HRWRA). 

Future 

The simulation and measurement of rheological parameters of concrete need more 

study in two major areas: 

1. Predict the influence of concrete composition (air content, aggregates shape, 

aggregate gradation and content, cement paste rheological) on the plastic 

viscosity by using a combination of measurements and simulation. 

2. Predict the influence of concrete composition (air content, aggregates shape, 

aggregate gradation and content, cement paste rheological) on the concrete 

yield stress. 

Ultimately, these two objectives will help select a mix design for its flow properties 

desired for a specific application while minimizing the trial mixes needed. This will 

be achieved by establishing a methodology to relate flow of a non-newtonian fluid 

in pre-selected geometries with its composition. 

Major goals for Phase II 

1. Validate the concept of multi-scale by determining whether the prediction of 

flow of concrete can be inferred from the mortar measurements and the mortar 

flow from the cement paste measurement. 

2. Determine the influence of air on the rheological properties of concrete. Using a 

combination of theoretical and experimental means, establish a methodology to 

determine the influence of AEA on the rheological response of mortar and 

concrete. 

3. Use simulations of concrete flow to determine the correlation between 

measurements obtained with concrete rheometers and the “real” plastic 

viscosity. 

4. Development of a methodology to measure the yield stress in cement paste or 

mortar. This methodology will be a combination of measurements and 

simulation. The influence of the chemical admixtures, air content and SCM will 

be considered. 

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 
26

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 . 

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 HardSphere 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, N. S. Martys, “Relating Fresh Concrete Viscosity Measurements 

from Different Rheometers”, J. Res. Natl. Inst. Stand. Technol. 108 (2003) 
27

Mechanical 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. Concrete is a random composite material over many length scales, 

consisting of phases, e.g. aggregate, C-S-H, and capillary porosity, which differ 

widely in their intrinsic elastic moduli. 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 

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

6] 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 

As part of the validation effort, Dyckerhoff provided experimental measurements 

of the elastic moduli of a series of cement pastes, with w/c = 0.25 to 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 
28

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

more serious discrepancies were evident for early-age specimens. 

Activities 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), which resulted in much 

better agreement with experimental data in that time regime. Experimental data 

provided by Dyckerhoff were compared to the model predictions, and the error 

was shown to improve from nearly 200 %, 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. 

Research in Year 3 

The research in mechanical properties this year focused on (1) validating the 

effective medium theory for mortar and concrete elastic moduli predictions, and (2) 

exploring ways to predict the compressive strength from elastic moduli. 

An effective medium theory was developed several years ago [7] to be applicable to 

mortar and concrete by directly taking into account the interfacial transition zone 

(ITZ). Essentially, the interfacial transition zone is averaged into each aggregate 

particle, making each particle slightly larger and with elastic properties averaged 

over a combination of aggregate and ITZ properties. The ITZ is treated as a uniform 

thickness, uniform property layer around each aggregate particle, which is of course 

an approximation. The sieve analysis of the aggregate is directly taken into account. 

An additional input parameter is the matrix elastic properties.Three sets of data 

were found in the literature upon which to validate this theory. These three sets all 

gave the matrix elastic moduli, the volume fraction and sieve analysis of the 

aggregate, and the elastic properties of the aggregates. All three data sets were for 

mortars. A data set for concrete that was complete enough to use to test the 

effective medium theory was not found. However, since the effect of the ITZ is less 

for concrete than for mortar, it is thought that mortar data supplies a more rigorous 

test for the theory than concrete data. There was good agreement between theory 

and experiment for all three mortars. The details of comparison, along with 

appropriate graphs, are given in Case Study II later in this report. 

Additional work on the elastic properties of mortars was undertaken with 

Dyckerhoff, and with Prof. S.P. Shah at ACBM (Northwestern University). These 

data were not completely analyzed at the time of writing, and will be reported on 

next year. The equations incorporated into VCCTL 4.0 will allow the user to specify: 

matrix moduli, volume fraction of aggregate, elastic moduli of aggregate, size of the 

ITZ, elastic properties of the ITZ, and sieve analysis of the aggregates. A suggested 

use is to compute the cement paste elastic moduli using the desired cement, and 

then to input these values into the mortar/concrete option as matrix moduli so as to 

be able to compute the mortar/concrete moduli. 

There are various empirical equations relating compressive strength and Young’s 

modulus in the concrete literature (ACI, etc.). The purpose of these equations is 
29

really to derive the Young’s modulus, useful in structural calculations, from the 

measured compressive strength. For VCCTL, since elastic moduli can be predicted, 

the use of equations like this is to predict the compressive strength, a useful number 

for quality control and performance, from the predicted elastic moduli. It turns out, 

via conversations with Prof. Franz-Josef Ulm (MIT), that the standard empirical 

equations, which relate the square root of strength to Young’s modulus, do have 

some basis in strength of materials theory. A project has been initiated with Prof. 

Ulm to develop more precise versions of such equations that take into account the 

multi-scale nature of concrete, from the nano level (C-S-H) to the milli-level 

(concrete). This approach is based on nano-indentation of cement paste phases, and 

already has been successful in other, similar materials. An MIT M.S. student, 

funded by VCCTL, will spend 9 months at NIST starting in December, 2003, to 

implement this project. VCCTL 4.0 includes existing ACI empirical equations, 

empirically predicting compressive strength based on computations and predictions 

of elastic moduli. The next version, 5.0, hopefully will contain improved strength 

equations based on the work to be done in the 4th year of the consortium. 

Future 

1. Establish and validate more accurate correlations between concrete elastic 

moduli and compressive strength. 

2. Implement improved predictions of compressive strength within VCCTL 

software. 

3. Improve early-age mechanical property predictions. 

References 

1. D.P. Bentz (editor) “The Virtual Cement and Concrete Testing Laboratory Consortium 

Annual Report 2001,” NISTIR 6840, U.S. Department of Commerce, 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 . 
30

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 . 

7. E.J. Garboczi and J.G. Berryman, "Elastic moduli of a material containing composite 

inclusions: Effective medium theory and finite element computations," Mech. Mater. 33, 

455-470, (2001). 
31

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. 

Activities 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: development of a sulfate-resistance database and 

computational modeling of sulfate attack on cement paste. 

Research in Year 3 

The methodology adopted at NIST to determine the sulfate resistance of concrete 

under sulfate attack is based two major mechanisms: 1) penetration of sulfate ions 

into concrete; 2) chemical reaction of sulfate with the cement hydration products. 

The latter will trigger expansion and deterioration of the specimen. Under the 

sponsorship of FHWA and PCA, some parts of this approach are ready and can be 

made available to VCCTL. This approach is illustrated in Figure 8. 

Modeling 

• CONCLIFE is a model that assumes that once sulfates penetrate into the 

concrete, chemical reaction is initiated and deterioration occurs. This model 

is based on the measurement of the sorption coefficient (ASTM standard 

approved; to be issued in 2004). CONCLIFE-FHWA is available from the 

NIST website (http://ciks.cbt.nist.gov/~bentz/phpct/cmml.html) 

• SULFATE2: a model predicting the expansion of concrete from its 

composition and from the geometry of the specimen was developed by Dr. 
32

Barzin Mobasher (Arizona State University). As per agreement with 

Mobasher, SULFATE2 is now available on the NIST website 

• A semi-empirical model based upon cement phase composition and particle 

size distribution. Once validated, this model could predict the expansion of 

a mortar from mineralogical and the particle size distribution of the cement. 

This model is under development in collaboration with the NIST Statistical 

Engineering Division 

• 4SIGHT; a model that allows the calculation of the formation factor of a 

concrete, is also available from the NIST website 

(http://ciks.cbt.nist.gov/~bentz/phpct/cmml.html) 

Progress was made in designing an accelerated test to determine the expansion of a 

mortar under sulfate attack. Specimen size was reduced from the standard ASTM 

C 1012 mortar bar, with a reduction in test time by a factor of four. This revised 

procedure is in the process of being correlated with C 1012 data. 

Ultimately, with exposure conditions and mix design held constant, the 

performance of cement is based upon the phase composition and fineness. 

Applying accurate means to measure these properties allows exploration of the 

sulfate performance relative to mineralogy and fineness, and identification of the 

significant variables in sulfate-resistant cements. Quantitative X-ray powder 

Figure 8: Schema of the sulfate resistance prediction. The check marks indicated areas that are completed or almost 

operational. The dots indicated areas where progress was made but further work is necessary

Mixture design Select mixture design Select cement

Saturation level complete Partial

Sorption

Diffusion

Models:

• NIST-CONCLIFE

• 4SIGHT

• Mobasher-Tixier

Determine concrete 

susceptibility to 

sulfate ingress

Model 

applicable

Analysis of cement:

XRD/PSD/other

Prepare small specimens

Expose them to sulfate

Models:

• Sulfattack3d

• Statistical model

Determine cement 

resistance to sulfate 

attack

Predict service life of structure

YES NO

Cycles:

Crystallization

pressure

Expansion 

measurement

a a a

a

a

n

n a
33

diffraction analysis of cement mineralogy and SEM imaging of cement 

microstructure are being applied to explore performance – composition property 

relationships. Statistical analyses of the data are being used to identify the most 

significant combination of variables to predict C 1012 performance. Current results 

indicate both a phase composition and fineness component as significant and 

development of non-linear, multi-component models are expected to improve 

predictive capability. 

Future 

The development of an accelerated test for determining the resistance to sulfate 

attack of cement includes the use of smaller samples than the ones described in 

ASTM C 1202. This method will reduce the duration of the test by a factor of 3 to 5. 

More validation tests should be conducted in VCCTL Phase II. 

References 

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

Publishing, London, 1997. 

2. P. Stutzman, “Scanning Electron Microscopy Imaging of Hydraulic Cement 

Microstructure”, to be published in Special issue of Cement and Concrete 

Composites on Microstructure, 2004

3. P. Stutzman, “Development of an ASTM Standard Test Method on X-Ray 

Powder Diffraction Analysis of Hydraulic Cements”, Proceedings of the Denver 

of the X-Ray Conference, Denver 2003 
34

Case Study I 

Influence of Cement Particle Shape on 

Hydration Behavior 

New in VCCTL Version 4.0 is the ability to incorporate real-shape cement particles 

when creating a 3-D cement paste microstructure. Other than the qualitative 

differences in the appearance of the initial microstructure, it is an open question 

whether real particle shapes influence quantitatively the hydration kinetics of a 

cement paste. 

Figure 9: CCRL cement 116 

microstructures created with 

spherical particles (top) and 

real-shape particles (bottom) at 

w/c = 0.4 and hydrated for 90 d 

at 25 °C under saturated 

conditions. 

Figure 9 shows slices from 

beginning and 90 d 

microstructures predicted 

by CEMHYD3D for CCRL 

cement 116 with w/c=0.4 

and cured isothermally at 

25 °C under saturated 

conditions. The top row 

shows a microstructure 

created with spherical particles and the bottom row shows a microstructure created 

with real-shape particles. The real shapes were obtained from CCRL cement 133 

using the Visible Cement Data Set [1]. The same PSD was used to create both 

microstructures, and the cement phase proportions are the same to within ±0.00002 

for the volume fraction of any given phase. Therefore, these two microstructures 

can be used to isolate the influence of particle shape on hydration behavior. 

Although the two microstructures initially differ in appearance, there is very little 

qualitative difference in the 90 d microstructures in Fig. 9. Much of the particle 

shape information is lost as hydration proceeds. Based on this, one might expect 

that any differences in hydration behavior will be greatest at early ages. 

Figure 10 shows both the degree of hydration and the fraction of connected solids—

an indication of setting time—as a function of age. The circles are experimental 

measurements of the degree of hydration based on nonevaporable water content. . 
35

10 100 1000

0.0

0.2

0.4

0.6

0.8

Degree of Hydration

Spheres

Real

0 1 10 100

time (h)

0.0

0.5

1.0

Connected Solids

Spheres

Real

Both curves in the first plot intentionally have been fit, by adjusting their β

parameters, to match the experimentally measured degree of hydration at 8 h. 

Negligible differences in the degree of hydration are observed at all ages. 

One significant early-age property that does seem to be slightly affected by particle 

shape is the onset of setting, as shown in Fig. 10. The system with spherical 

particles forms a tenuously connected solid network at 6 h, while the system with 

real-shape particles begins to percolate at 3 h. As the first plot in Fig. 10 shows, this 

difference is not due solely to differences in hydration kinetics, but instead must be 

attributed, at least partially, to a particle shape effect. Spheres are isometric and 

have an aspect ratio of unity, and any departure from sphericity using particles with 

higer aspect ratio, is well known to decrease the percolation threshold of hydration 

products. Nevertheless, the effect produced is quite minor, and the curves for both 

microstructures converge such that by eight hours they are virtually identical. 

Figure 10: Degree of hydration and fraction of connected solids as a function of age for CCRL cement 

116 microstructures shown in previous figure
36

Case Study II 

Validation of effective medium theory for 

prediction of mortar and concrete elastic 

moduli based on knowledge of individual 

component moduli

The following three sets of data were used to validate the effective medium theory 

calculations of mortar elastic moduli: 

 [1] A. Boumiz, “Etude comparèe des evolutions mechaniques et chimiques des 

pates de ciment et mortiers à très jeune age”, French Ph.D. thesis, 1995.

 [2] Zimmerman, King, and Monteiro, “The elastic moduli of mortar as a porousgranular material,” Cem. Conc. Res. 16, 239-245 (1986). 

 [3] O. Ishai, “Influence on sand concentration on deformations of mortar beams 

under low stresses,” J. of ACI 58, 611-622 (1961).

Boumiz data 

This mortar had small sand (quartz) particles, only 8 μm to 300 μm in diameter. For 

this size sand particles, the ITZ is not well-defined for most particles, since the 

aggregate size is on the same order as the cement size. Therefore, no ITZ was used 

in the effective medium theory (EMT). The air content was reported for each 

amount of sand, and was incorporated in the EMT. The effect of air can be 

substantial – it can lower the elastic moduli by a percentage amount equal to 

roughly three times the volume percentage of air. The mortar had w/c = 0.5, and was 

hydrated for 28 d. 

Zimmerman and Monteiro data 

The amount of air was not measured, hence was not included in the calculation. The 

mortar was said to be “well-hydrated,” with w/c = 0.35. The aggregate was quartz 

aggregate, with K = 37 GPa, and G = 44 GPa. The effective ITZ was assumed to be 

0.01 mm in thickness. The Young’s modulus of the ITZ was taken to be half that of 

the bulk matrix paste (EITZ = 0.5 Epaste), and the Poisson’s ratio of bulk and ITZ paste 

taken to be the same. The measured wave speeds were read off a graph, and 

converted to elastic moduli (GPa) using the measured densities.
37

0

10

20

30

40

50

0 0.1 0.2 0.3 0.4 0.5 0.6

Boumiz mortar data

E(exp)

E(emt)

G(exp)

Elastic moduli (GPa)

Sand volume fraction

E

G

G(emt)

10

20

30

40

50

60

0 0.1 0.2 0.3 0.4 0.5 0.6

Monteiro data

E(exp)

E(emt)

G(exp)

G(emt)

Elastic moduli (GPa)

Sand volume fraction

Figure 11: Boumiz mortar data 

Figure 12: Monteiro data 

Ishai data 

Data were listed in terms of fitted straight lines, so the experimental data appears as 

straight lines in the graph below. No amount of air was reported, so no amount of 

air was allowed in the EMT calculation. The value of w/c = 0.32 was used, with 28 d 

sealed curing reported. A “Standard Leighton Buzzard sand” was used. This is 

quartz sand. The sieve analysis was assumed to be the same as ASTM graded 

standard sand (between 0.15 mm and 0.6 mm). The effective ITZ thickness was 

taken to be 0.01 mm, with EITZ = 0.5 Epaste, and the Poisson’s ratio of bulk and ITZ 

paste taken to be the same. 

In all three cases, there was good agreement between theory and experiment. This 

EMT will become part of VCCTL 4.0. 
38

0

10

20

30

40

50

0 0.1 0.2 0.3 0.4 0.5 0.6

Ishai data

E(exp)

E(emt)

G(exp)

G(emt)

Elastic moduli (GPa)

sand volume fraction

Figure 13: Ishai data. 
39

Case Study III 

Effect of Aggregate Size Distribution on 

Concrete Plastic Viscosity 

The role of size distribution of spherical shaped aggregates on relative viscosity was 

investigated in collaboration with Dr. Robert Flatt (Sika). This work will form the 

basis for an optimization of aggregate gradation for flow performance. 

In this study, the particle size distributions were characterized by σ as defined by 

the following equation: 

N

r r

r

i

2 1 Σ( − < >)

< >

σ =

where 

N

r

r

Σ i < >= ; ri = particle radius; N = number of particles, so that < r > is the 

number-weighted average particle radius. The parameter σ is a measure of the 

width of the size distribution. 

In this definition, the particle size distribution is normalized by its average size. By 

this approach, the results can be applied to a broader range of aggregates. For this 

study, we considered σ varying from 0 to 1. A value of σ equal to zero indicates 

that the spheres are mono-size. A value of σ equal to 1 means that the sphere radii 

varied by a factor of 30. Figure 14 shows pictures of a realization of two different 

particle size distributions (PSD), characterized by two different values of σ. 

As a case study, we selected several lognormal particle distributions. Figure 15 

shows the distribution selected. In Figure 15, a standard silica sand (ASTM C778) 

was also included. Note that, when the sand data is properly normalized, the sand 

has a value of σ = 0.6. These simulations involved the inclusion of thousands of 

particles, which up to now would have been nearly impossible by conventional 

methods. Indeed, to the best of our knowledge there are no previous simulations of 

poly-disperse suspensions. Therefore, this work represents a real advance in the 

study of the rheology of suspensions. 

To determine the influence of aggregate size distribution on the relative viscosity, 

the suspensions were sheared using a constant strain rate. The stresses in the 

system were then calculated and used to determine the viscosity of the suspension. 

Figure 16 shows the relative viscosity as a function of solid fraction for the different 

values of σ shown in Figure 15. Note that at low solid fractions there is not much 

difference in the data for different σ. However, as the solid fraction increases, the 
40

relative viscosity clearly decreases with increasing σ. This can largely be 

understood as resulting from the maximum packing of the sphere system increasing 

as the PSD become wider. The solid lines in Figure 16 are fits to the data, based on 

the following semi-empirical equation constructed by Jack Douglas, 















 



 



  +



 



  ⋅ −  



 = − η

η −2 2

0

c

C

C 0 34

C

C 1 0 4

C

C 1 * * * . .

where C is the aggregate concentration, C*

 is the maximum aggregate packing, and 

ηc/η0 is the relative viscosity. The only free parameter in this equation is the 

maximum packing fraction, C*

. This equation provided fits somewhat better than 

the commonly used Krieger-Dougherty equation. 

These results have been included in the newest version of the VCCTL software. In 

the future, we plan to extend this study to included non-spherical particles based on 

the VCCTL database of real shaped aggregates that were derived from X-ray 

tomography measurements. 

Figure 14: Various particle size distributions. See text for a definition of σ. 

 σ = 0.2 σ = 1.0 
41

Increasing σ

0 to 1 

0

10

20

30

40

50

60

70

80

90

100

0.01 0.1 1 10 100

Diameter []

Cumulative [%]

0.2

0.3

0.6

0.8

1

Silica Sand

Silica sand Scaled 0.3

Figure 15: Distribution of aggregates with varying σ used in this case study. 

Figure 16: Aggregate concentration and distribution influence on relative viscosity 
42

NIST/Industry VCCTL Funding 

External funding of VCCTL (from consortium members outside NIST) 

$0.40M (7  $40K + 2 $60K) 

Internal NIST funding of VCCTL research activities 

$0.85M (BFRL) + $0.55M (ITL) = $1.4M 

NIST equipment funding 

BFRL – New scanning electron microscope - $250K 

BFRL – X-ray tomography at Penn State - $25K 

ITL – New floor to RAVE, three new projectors - $215K 

Total = $0.49M 

Total NIST funding of VCCTL project (labor + equipment) 

$1.89M 

Total VCCTL project funding

$2.29M 

Percentage shares of total VCCTL project funding 

NIST – 82 % 

Industry – 18 % 

Total cost/industrial share  5.6:1 
43

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. (New machine in 2003) 

• 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 
44

• X-ray absorption unit for monitoring water movement in materials (to be 

upgraded in 2004) 

• Electrical conductivity measurement equipment 

• Ionic diffusivity measurement equipment 

Systems Characterization 

• Malvern particle size analyzer, wet and dry capability 

• Particle classifier (new in 2003) 

• Quantachrome AUTOSORB-1, a multi-point surface analysis system for BET 

surface area and porosity (acquired in 2003) 

• Quantachrome AUTOSCAN 60 for mercury porosimetry (acquired 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 

Sample Preparation Laboratory 

• Attritor mill 
45

• 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 walk-in (temperature controlled) 

• curing cabinet (temperature controlled and RH higher than 98 %) 

• Water baths: 4 table top and one floor unit 

• pH controlled units 

Computational Facilities (Materials and Construction Research Division) 

• Windows and LINUX-based PCs 

• 32-processor Linux cluster 

• 128-processor Linux cluster (new in 2003) 

• 64-processor Linux cluster (new in 2003)

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. 
46

• 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 

Visualization Resources 

• One SGI Onyx3000 

• Four Infinite Reality4 Graphics 

• 24 R14000 CPUs (500 MHz) 

• 24 GB memory 

• One RAVE two-wall immersive environment with Crystal Eyes 

software/hardware with head tracking 
47

For More Information 

• Examine Version 1.1 of the VCCTL software package, available at: 

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

• Visit the VCCTL Consortium information web site at: 

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

• 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