Influence of Curing Conditions on

Water Loss and Hydration in Cement

Pastes with and without Fly Ash

Substitution

Dale P. Bentz

NISTIR 6886
iv

NISTIR 6886

 Influence of Curing Conditions on

Water Loss and Hydration in Cement

Pastes with and without Fly Ash

Substitution

Dale P. Bentz

Building and Fire Research Laboratory

July 2002

U.S. Department of Commerce

Donald L. Evans, Secretary

Technology Administration

Phillip J. Bond, Under Secretary for Technology

National Institute of Standards and Technology

Arden L. Bement, Jr., Director
iii

ABSTRACT

The proper curing of concrete is paramount to achieving desired strength and durability

performance in the field. Because blending components often react at different rates

from portland cement, blended cements may require that special attention be paid to

prolonged curing. This report summarizes an exploratory study on the influence of

curing conditions on water loss and hydration in ASTM Type I and blended portland

cement pastes with a water-cementitious materials ratio (w/cm) of 0.40. The blended

cement contains about 20 % by mass fly ash substitution for cement. Water loss/gain

under various curing conditions is monitored both globally by bulk mass (loss)

measurements and locally using the NIST X-ray absorption apparatus. Hydration is

assessed based on the measurement of non-evaporable water content after 31 d of curing.

Curing conditions include no curing (exposed to the environment throughout the curing

period), sealed curing, and saturated curing for 1 d, 3 d, and 6 d. The cement paste with

the fly ash substitution is observed to be more sensitive to curing conditions than the

conventional Type I portland cement paste.

Keywords: Building technology; cement paste; curing; fly ash; evaporation; hydration.
iv

Contents

Abstract ______________________________________________________________iii

List of Figures _________________________________________________________ v

List of Tables __________________________________________________________ vi

1 Introduction _______________________________________________________ 1

2 Experimental_______________________________________________________ 2

3 Results ____________________________________________________________ 5

4 Discussion ________________________________________________________ 13

5 Summary and Conclusions __________________________________________ 13

6 Acknowledgements_________________________________________________ 14
v

List of Figures

Figure 1. SEM/X-ray composite image of the ASTM Type I portland cement. _______ 2

Figure 2. SEM/X-ray composite image of the blended cement containing about 20 % by

mass fly ash. ___________________________________________________________ 3

Figure 3. Relative water loss/gain vs. time for the cement pastes with and without fly ash

exposed to various curing regimens._________________________________________ 5

Figure 4. X-ray profiles (differences in counts) for pastes without and with fly ash,

immediately exposed to the drying environment in the X-ray chamber. _____________ 6

Figure 5. X-ray profiles (differences in counts) for pastes without and with fly ash, sealed

throughout the curing period. ______________________________________________ 7

Figure 6. X-ray profiles (differences in counts) for pastes without and with fly ash,

saturated for 1 d and then exposed to the chamber environment.___________________ 8

Figure 7. X-ray profiles for samples saturated for 3 d (72 h) and then exposed to the

chamber environment.____________________________________________________ 9

Figure 8. X-ray profiles for samples saturated for 6 d (144 h) and then exposed to the

chamber environment.___________________________________________________ 10

Figure 9. Evaporable water loss (g water/g ignited powder) for top and bottom sections of

cement pastes without and with fly ash, exposed to various curing conditions._______ 11

Figure 10. Non-evaporable water loss (g water/g ignited powder) for top and bottom

sections of cement pastes without and with fly ash. ____________________________ 12
vi

List of Tables

Table 1. Area fractions from SEM/X-ray analysis for the two cements. _____________ 3
1

1 Introduction

For many construction projects, concrete is the material of choice. Concrete structures

can be designed to be strong and durable in a variety of aggressive environments. In

practice, proper curing (suitable temperature and moisture availability) is critical to

achieving concrete that lives up to its intended functionality.1 Blended cement concretes

may be particularly sensitive to curing conditions, as blending components such as fly

ashes and slags may not react as rapidly as the base cement. In these cases, prolonged

moist curing may be required to achieve full development of strength and durabilityrelated properties.

Proper curing is especially critical in achieving a discontinuous pore structure in

concretes with water-cementitious materials ratios (w/cm) of 0.45 and lower. A

discontinuous pore structure is important in producing a durable concrete, as it will limit

both water and ion ingress into the interior of the concrete structure. Based on

measurements of permeability, Powers concluded that capillary discontinuity is a

function of both w/cm and degree of hydration, with higher w/cm requiring longer

hydration times to achieve a discontinuous capillary pore structure.2 He therefore

suggested curing the concrete only until this discontinuity is achieved, as further

“saturated” curing would result in little if any further water flow into the concrete.3

Based on a microstructural model for cement paste hydration, Bentz and Garboczi

suggested a critical capillary porosity threshold value of about 20 % to achieve this

discontinuity.4 For any starting w/cm ratio, if hydration can reduce the initial capillary

porosity to 20 % or so, a discontinuous pore structure will be formed.

In this paper, fundamental studies on water loss and hydration in small cement paste

specimens (w/cm=0.40, with and without fly ash substitution) exposed to various curing

conditions are presented. Water loss is monitored globally using bulk mass loss

measurements and locally using the NIST X-ray absorption apparatus. The examined

curing conditions include immediate exposure to the X-ray chamber environment

(nominally at 23 oC and 55 % RH), sealed curing for 31 d, and saturated curing (with

water on top) for 1 d, 3 d, and 6 d, followed in each case by exposure to the chamber

environment.
2

2 Experimental

Two cements supplied by a U.S. cement manufacturer were employed in this study. The

first was an ASTM Type I portland cement (Blaine fineness of 343 m2/kg) and the second

was an interground mixture of the first cement with a class F fly ash to produce an IP

blended cement (Blaine fineness of about 400 m2/kg). Color-coded SEM/X-ray

composite images of the two cements are provided in Figures 1 and 2. Volumetric phase

fractions determined from the SEM/X-ray composite images are provided in Table 1. As

would be expected, the volumetric composition of the IP cement (in terms of the four

principal clinker compounds: C3S, C2S, C3A, and C4AF) is dominated by that of the Type

I portland cement that was interground with the fly ash to produce the blended product.

Cement pastes with a w/cm of 0.40 were prepared by mixing the cement powder and

water together by hand in sealed plastic bags for two to three minutes. Freshly-mixed

pastes were removed from the plastic bags and cast into small plastic “UV” cuvettes (10

Figure 1. SEM/X-ray composite image of the ASTM Type I portland cement. Red is

tricalcium silicate, aqua is dicalcium silicate, green is tricalcium aluminate, yellow is

tetracalcium aluminoferrite, pale green is calcium sulfate, white is free lime, blue is

potassium sulfate, and magenta is periclase. Image is 256 ìm x 200 ìm.
3

Table 1. Area fractions from SEM/X-ray analysis for the two cements.

Phase Area fraction

Type I cement Type IP cement

C3S 0.6266 0.4271

C2S 0.0910 0.0651

C3A 0.0727 0.0495

C4AF 0.0794 0.0574

Calcium sulfate 0.0759 0.0914

Free lime 0.0076 0.0155

K2SO4 0.0134 0.0051

“Periclase” 0.0080 0.0072

Silica 0.0089 0.0771

Aluminosilicate 0.0060 0.1849

CAS 0.0105 0.0197

Figure 2. SEM/X-ray composite image of the blended cement containing about 20 % by

mass fly ash. Colors are as in Figure 1, but additionally, orange is an aluminosilicate (fly

ash), dark green is silica (fly ash), and dark blue is calcium aluminosilicate (fly ash).

mm by 10 mm by 40 mm), each cuvette being mounted on a “LegoTM”1 block base plate

using a two-component epoxy adhesive. The cuvettes could be conveniently sealed using

small plastic caps to minimize mass loss during sealed curing and then mounted on a

 

1

 Certain commercial equipment is identified in this report to specify the experimental procedure. In no

case does such identification imply endorsement by the National Institute of Standards and Technology, nor

does it indicate that the equipment is necessarily the best available for the purpose.
4

larger Lego base plate within the X-ray absorption chamber. These cuvette specimens

were then exposed to different curing regimens with periodic measurements of the

specimen masses and moisture distributions (via X-ray absorption). X-ray results will be

presented for curing times of 4.5 h (approximately the time of setting), 6.5 h, 20 h, 73 h,

and 433 h. For the current study, X-ray absorption measurements were performed at a

spatial resolution of 1 mm. Each cuvette was filled with cement paste to a height of

approximately 30 mm.

Details of the X-ray absorption apparatus and the monitoring of moisture distributions in

hydrating cement pastes have been provided previously.5,6,7 At each spatial position and

time, each measured spectra was characterized by the sum of the counts for the X-rays

transmitted through the specimen, in all 256 energy-level channels of the spectra. As the

cement paste specimen loses moisture locally at some depth, the X-ray “counts”

transmitted through the specimen at that depth will increase. The counts obtained after

any specific curing time are first proportionally normalized via a specimen of dry cement

powder, to account for any minor variations in the X-ray source intensity between

experimental runs. The normalized counts are then referenced (by differencing) to those

achieved near the setting time (about 4.5 h) to infer the change in moisture distribution

for the specimen.6 The “differences in counts” between a specimen at some later age and

the same specimen at its setting time will be positive when a water loss has occurred

(decrease in density allowing a greater transmission of the X-rays) and negative when

water ingress has occurred. Previously, measurements have indicated that moisture

contents (by mass) of porous materials can be determined with a coefficient of variation

of 6 % using the X-ray absorption technique.5

The following five curing conditions were investigated in this study:

a) exposed to the environment of the X-ray chamber

b) sealed with a plastic cap

c) saturated on top for 1 d then exposed to the chamber environment

d) saturated on top for 3 d then exposed to the chamber environment

e) saturated on top for 6 d then exposed to the chamber environment.

With 5 curing conditions and 2 mixtures (with and without fly ash), 10 cuvette specimens

in total were prepared. After 31 d of hydration, the cuvettes were removed from the

X-ray absorption chamber, the specimens were “extruded” from the cuvettes and the top

10 mm of each cement paste prism specimen was removed by notching the specimen on

two opposite sides using a hacksaw and then using a hammer and chisel to break the

specimen in two. Loss on ignition measurements were used to determine the evaporable

(mass loss on heating to 105 oC) and non-evaporable (subsequent mass loss on heating to

1000 oC) water contents of the top 10 mm and the remaining bottom section (about 20

mm in height) of each of the 10 cement paste specimens. Based on the expected

uncertainty of the mass measurements involved in determining the evaporable and nonevaporable water contents (0.001 g), a typical expanded uncertainty8

 in the calculated

water contents is estimated to be 0.001 g of water/(g of ignited powder), assuming a

coverage factor8 of 2.9
5

3 Results

The relative mass losses/gains in water from the paste specimens based on bulk mass

measurements are provided in Figure 3. The specimens exposed to saturated curing,

followed by drying, first gain mass (a negative water change), losing water only when

exposed to subsequent drying. The initial mass gain is due to water imbibition through

the top saturated surface of the specimen to replace the water “lost” internally due to

chemical shrinkage during cement hydration.9,10 For similar curing regimens, the

specimens with the fly ash substitution for cement are observed to consistently lose more

water than those without, indicating a possible increased sensitivity to curing for the

blended cement.

Relative Water Loss/Gain vs. Time

-4

-2

0

2

4

6

8

10

12

14

16

0 100 200 300 400 500 600 700 800

Time (h)

Water change (%)

No fly ash, open

No fly ash, sealed

No fly ash, sat'd. 1 d

No fly ash, sat'd. 3 d

No fly ash, sat'd. 6 d

Fly ash, open

Fly ash, sealed

Fly ash, sat'd. 1 d

Fly ash, sat'd. 3 d

Fly ash, sat'd. 6 d

Figure 3. Relative water loss/gain vs. time for the cement pastes with and without fly ash

exposed to various curing regimens. Positive values indicate a mass loss and negative

values a mass gain (due to water imbibition).

These results are supported by the X-ray counts difference profiles shown in Figures 4

through 8, for each of the five different curing conditions. For the specimens

immediately exposed to the chamber environment (Figure 4), a significantly greater water

loss (higher difference in counts) and a deeper penetration of the drying front (28 mm vs.

20 mm) is observed after 18 d of drying for the specimen containing fly ash. The drying

front penetration depth for each specimen is visually estimated as the depth where there is

a discontinuous change in the “differences in counts” profile.

For the sealed conditions, as indicated in Figure 3, a small mass loss occurred for both

specimens (2 % to 4 % after 700 h of curing). Here, the X-ray profiles shown in Figure 5

indicate a small and relatively uniform moisture loss throughout the specimen thickness

for both the pastes without and with fly ash. But, once again, a greater water loss is

indicated for the system containing the fly ash substitution (higher differences in counts).
6

The benefits of saturated curing can be observed in Figures 6 to 8, where in each case,

water loss from the small specimens is basically prevented as long as the saturated

conditions are maintained. In fact, during this saturated “curing time”, water imbibition

No fly ash paste, exposed, w/c=0.40

-3000

-2000

-1000

0

1000

2000

3000

4000

5000

0 4 8 12 16 20 24 28 32

Position from top (mm)

Differences in counts

6.5-4.5

20-4.5

73-4.5

433-4.5

Fly Ash paste, exposed, w/cm=0.40

-3000

-2000

-1000

0

1000

2000

3000

4000

5000

0 4 8 12 16 20 24 28 32

Position from top (mm)

Differences in counts

6.5-4.5

20-4.5

73-4.5

433-4.5

Figure 4. X-ray profiles (differences in counts) for pastes without and with fly ash,

immediately exposed to the drying environment in the X-ray chamber. All differences

(6.5 h, 20 h, 73 h, and 433 h) are relative to counts obtained for the 4.5 h specimens as

indicated in the legend box. Positive values indicate a local water loss and negative

values indicate a local water gain. The top (exposed surface) of the specimen is at

position 0 and the bottom at position 32.
7

into the specimens is indicated both by the bulk mass measurements in Figure 3 and by

the slight negative differences in counts commonly observed for the earliest ages in

Figures 6 to 8. For the specimens saturated for their first day of curing (Figure 6), the

depth of the drying front after 17 d of drying is about 12 mm for the paste without fly ash

and 20 mm for the paste with fly ash. For the specimens saturated for their first three

days of curing (Figure 7), the depth of the drying front after 15 d of drying is only a few

No fly ash paste, sealed, w/c=0.40

-2000

-1000

0

1000

2000

3000

0 4 8 12 16 20 24 28 32

Position from top (mm)

Differences in counts

6.5-4.5

20-4.5

73-4.5

433-4.5

Fly Ash paste, sealed, w/cm=0.40

-2000

-1000

0

1000

2000

3000

0 4 8 12 16 20 24 28 32

Position from top (mm)

Differences in counts

6.5-4.5

20-4.5

73-4.5

433-4.5

Figure 5. X-ray profiles (differences in counts) for pastes without and with fly ash,

sealed throughout the curing period. All differences are relative to counts obtained for

the 4.5 h specimens.
8

mm for the paste without fly ash and about 10 mm for the paste with fly ash. For the 6 d

specimens (Figure 8), this depth is nearly non-existent for the paste without fly ash and

about 5 mm for the paste with fly ash. In each case, the paste specimens with fly ash

substitution for cement are indeed observed to be more sensitive to curing, both in terms

of an increase in water mass loss and in terms of the greater depth of the “drying front.”

No fly ash paste, sat'd. 1 d, w/c=0.40

-3000

-2000

-1000

0

1000

2000

3000

4000

5000

0 4 8 12 16 20 24 28 32

Position from top (mm)

Differences in counts

6.5-4.5

20-4.5

73-4.5

433-4.5

Fly Ash paste, sat'd. 1 d, w/cm=0.40

-3000

-2000

-1000

0

1000

2000

3000

4000

5000

0 4 8 12 16 20 24 28 32

Position from top (mm)

Differences in counts

6.5-4.5

20-4.5

73-4.5

433-4.5

Figure 6. X-ray profiles (differences in counts) for pastes without and with fly ash,

saturated for 1 d and then exposed to the chamber environment. All differences are

relative to counts obtained for the 4.5 h specimens.
9

Further insight into the early hydration behavior and moisture content of the specimens

exposed to the various curing conditions is provided by measurement of the evaporable

and non-evaporable water contents after a total of 31 d of curing. Measured values for

the evaporable and non-evaporable water contents (per gram of ignited cement or

“blended cement” powder) are provided in Figures 9 and 10, respectively. For both

cement pastes without and with fly ash, Figure 9 indicates that all of the other

No fly ash paste, sat'd. 3 d, w/c=0.40

-3000

-2000

-1000

0

1000

2000

3000

4000

5000

0 4 8 12 16 20 24 28 32

Position from top (mm)

Differences in counts

6.5-4.5

20-4.5

73-4.5

433-4.5

Fly Ash paste, sat'd. 3 d, w/cm=0.40

-3000

-2000

-1000

0

1000

2000

3000

4000

5000

0 4 8 12 16 20 24 28 32

Position from top (mm)

Differences in counts

6.5-4.5

20-4.5

73-4.5

433-4.5

Figure 7. X-ray profiles for samples saturated for 3 d (72 h) and then exposed to the

chamber environment. All differences are relative to counts obtained for the 4.5 h

specimens.
10

investigated curing regimens are inferior to the 31 d of sealed curing, in terms of

maintaining a high evaporable water content within the cement paste specimens, which is

in direct agreement with the mass loss measurements provided in Figure 3. On a per

gram of ignited powder (cement + fly ash) basis, the specimens with fly ash are

consistently observed to have a lower evaporable water content, once again in agreement

with the mass loss results in Figure 3. Consistent with the measured penetration depths

No fly ash paste, sat'd. 6 d, w/c=0.40

-3000

-2000

-1000

0

1000

2000

3000

4000

5000

0 4 8 12 16 20 24 28 32

Position from top (mm)

Differences in counts

6.5-4.5

20-4.5

73-4.5

433-4.5

Fly Ash paste, sat'd. 6 d, w/cm=0.40

-3000

-2000

-1000

0

1000

2000

3000

4000

5000

0 4 8 12 16 20 24 28 32

Position from top (mm)

Differences in counts

6.5-4.5

20-4.5

73-4.5

433-4.5

Figure 8. X-ray profiles for samples saturated for 6 d (144 h) and then exposed to the

chamber environment. All differences are relative to counts obtained for the 4.5 h

specimens.
11

of the drying fronts, the top 10 mm section of each specimen is observed to have a

significantly lower evaporable water content than the remaining bottom section.

Unfortunately, for blended cements with pozzolans, the non-evaporable water content is

not a direct measure of cement hydration (or fly ash reactivity), due to water

consumption/ release during the pozzolanic reaction between fly ash and cement. This

effect has been well documented for the case of the similar pozzolanic reaction that

occurs when silica fume is added to cement.11,12 While this, along with differences in the

Blaine finenesses of the two cements, eliminates a direct comparison between the results

Paste without fly ash

0

0.05

0.1

0.15

0.2

0.25

opentop 10

mm

openbottomsealedtop 10

mm

sealedbottomsat'd. 

1 d- top

10 mm

sat'd. 

1 dbottom

sat'd. 

3 d- top

10 mm

sat'd. 

3 dbottom

sat'd. 

6 d- top

10 mm

sat'd. 

6 dbottom

Specimen ID

Evaporable water loss (g/g)

Paste with fly ash

0

0.05

0.1

0.15

0.2

0.25

opentop 10

mm

openbottomsealedtop 10

mm

sealedbottomsat'd. 

1 d- top

10 mm

sat'd. 

1 dbottom

sat'd. 

3 d- top

10 mm

sat'd. 

3 dbottom

sat'd. 

6 d- top

10 mm

sat'd. 

6 dbottom

Specimen ID

Evaporable water loss (g/g)

Figure 9. Evaporable water loss (g water/g ignited powder) for top and bottom sections

of cement pastes without and with fly ash, exposed to various curing conditions.
12

in Figure 10 for pastes without and with fly ash, one can still independently examine their

individual curing sensitivity. For example, the non-evaporable water contents of the

bottom sections of the pastes without fly ash indicate that both 3 d and 6 d of saturated

curing (followed by drying) is slightly superior to sealed curing. For the specimens with

fly ash substitution, 3 d or 6 d of saturated curing provides results that are equivalent to

those achieved by sealed curing, again indicating the increased sensitivity to curing of

this fly ash blended cement.

Pastes without fly ash

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0.18

0.2

opentop 10

mm

openbottomsealedtop 10

mm

sealedbottomsat'd. 

1 d- top

10 mm

sat'd. 

1 dbottom

sat'd. 

3 d- top

10 mm

sat'd. 

3 dbottom

sat'd. 

6 d- top

10 mm

sat'd. 

6 dbottom

non-evaporable water loss (g/g cement)

Pastes with fly ash

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0.18

0.2

opentop 10

mm

openbottomsealedtop 10

mm

sealedbottomsat'd. 

1 d- top

10 mm

sat'd. 

1 dbottom

sat'd. 

3 d- top

10 mm

sat'd. 

3 dbottom

sat'd. 

6 d- top

10 mm

sat'd. 

6 dbottom

non-evaporable water loss (g/g cement)

Figure 10. Non-evaporable water loss (g water/g ignited powder) for top and bottom

sections of cement pastes without and with fly ash, exposed to various curing conditions.
13

4 Discussion

The above results are preliminary in nature and many additional complexities must be

considered before extrapolating them to field performance. While this study was

conducted under isothermal conditions, nearly all field concrete experiences a range (and

diurnal cycle) of curing temperatures. For many field conditions, elevated early-age

temperatures are produced by the heat of hydration of the cementitious materials.

Because the activation energy of fly ash reactions can be about double13 that of cement

hydration (40 kJ/mol being typical for an ASTM Type I portland cement)14, curing

temperatures can have an extremely significant influence on fly ash reactivity and its

pozzolanic reaction with calcium hydroxide during the first days of hydration. The water

loss/gain properties of mortars and concretes may also be different than those of the

cement paste specimens explored in this study due to the presence of the aggregates and

their surrounding interfacial transition zones.

This preliminary study has been conducted at only a single w/cm of 0.40. For lower

w/cm ratios, it would be expected that the capillary pores will close off (depercolate)

early in the hydration process,2,4 minimizing the ingress of needed curing water from the

external environment. In these systems, due to its lower initial reactivity, the fly ash may

end up acting more as an inert reinforcing filler, as the more reactive cement may

consume all of the locally available curing water, with little or none remaining for the

later age fly ash reactions. One possible solution to this problem for low w/cm concretes

is the application of so-called “internal curing”, via the addition of saturated low-density

fine aggregates or superabsorbent (water-absorbing) polymer particles.15

5 Summary and Conclusions

Preliminary studies were conducted to examine the sensitivity of portland and blended

cement pastes, prepared with a w/cm=0.40, to curing conditions. Small specimens of the

two pastes were cast into cuvettes and exposed to five different curing conditions.

Sensitivity to curing was characterized by bulk mass (water loss) measurements, local

water loss inferred from X-ray absorption measurements, and quantification of the

evaporable and non-evaporable water contents achieved following 31 d of total curing.

The following conclusions can be drawn from this preliminary study:

1) Cement pastes with fly ash additions are more sensitive to curing than those without,

most likely due to a decrease in initial reaction rates.

2) X-ray absorption drying profile measurements are consistent with bulk measurements

of water mass loss and provide detailed information on the depth of penetration of the

drying front. This is of practical significance for field concrete, where this depth will

correspond to a layer of concrete whose properties may be partially compromised by

improper curing conditions.
14

6 Acknowledgements

The author would like to thank Dr. Xiuping Feng and Mr. Paul Stutzman of NIST/BFRL

for assistance in obtaining the SEM/X-ray composite images provided in Figures 1 and 2.

Funding for this preliminary study was provided by the NIST HYPERCON-Partnership

for High-Performance Concrete Technology (PHPCT) program.
15

References

1) Meeks, K.W., and Carino, N.J., “Curing of High-Performance Concrete: Report of

the State-of-the-Art,” NISTIR 6295, U.S. Department of Commerce, March 1999.

2) Powers. T.C., “Capillary Continuity or Discontinuity in Cement Pastes,” PCA

Bulletin, No. 10, 2-12, 1959.

3) Powers, T.C., “A Discussion of Cement Hydration in Relation to the Curing of

Concrete,” Proc. of the Highway Research Board, 27, 178-188, 1947.

4) Bentz, D.P., and Garboczi, E.J., “Percolation of Phases in a Three-Dimensional

Cement Paste Microstructural Model,” Cement and Concrete Research, 21, 324-344,

1991.

5) Hansen, K.K., Jensen, S.K., Gerward, L., and Singh, K., “Dual-energy X-ray

Absorptiometry for the Simultaneous Determination of Density and Moisture Content

in Porous Structural Materials,” in: Proc. of the 5th Symposium on Building Physics

in the Nordic Countries, Gothenburg, Sweden, Vol. 1, 281-288, 1999.

6) Bentz, D.P., and Hansen, K.K., “Preliminary Observations of Water Movement in

Cement Pastes During Curing Using X-ray Absorption,” Cement and Concrete

Research, 30, 1157-1168, 2000.

7) Bentz, D.P., Geiker, M.R., and Hansen, K.K., “Shrinkage-reducing Admixtures and

Early-age Desiccation in Cement Pastes and Mortars,” Cement and Concrete

Research, 31, 1075-1085, 2001.

8) Taylor, B.N., and Kuyatt, C.E., “Guidelines for Evaluating and Expressing the

Uncertainty of NIST Measurement Results,” NIST Technical Note No. 1297, U.S.

Department of Commerce, September 1994.

9) Bentz, D.P., “Three-Dimensional Computer Simulation of Portland Cement

Hydration and Microstructure Development,” Journal of the American Ceramic

Society, 80 (1), 3-21, 1997.

10) Taylor, H.F.W., Cement Chemistry (Thomas Telford, London, 1997).

11) Yogendran, V., Langan, B.W., and Ward, M.A., “Hydration of Cement and Silica

Fume Paste,” Cement and Concrete Research, 21 (5), 691-708, 1991.

12) Zhang, M.-H., and Gjorv, O.E., “Effect of Silica Fume on Cement Hydration in Low

Porosity Cement Pastes,” Cement and Concrete Research, 21 (5), 800-808, 1991.

13)Bentz, D.P., and Remond, S. “Incorporation of Fly Ash into a 3-D Cement Hydration

Microstructure Model,” NISTIR 6050, U.S. Department of Commerce, August 1997.

14) ASTM C 1074, ASTM Annual Book of Standards, Vol. 04.02 Concrete and

Aggregates, 2000.

15)Bentz, D.P., Geiker, M.R., and Jensen, O.M., “On the Mitigation of Early Age

Cracking,” in Proceedings of Self-Desiccation and Its Importance in Concrete

Technology III, Eds. B. Persson and G. Fagerlund, Lund, Sweden, June 2002.