Transcript Examination of Wood-Derived Powders and Fibers for Internal Curing of Cement-Based Materials

Examination of Wood-Derived Powders
and Fibers for Internal Curing of
Cement-Based Materials
Fourth International Seminar on Self-Desiccation and Its
Importance in Concrete Technology
June 20, 2005
Benjamin Mohr
Laura Premenko
Kimberly Kurtis
School of Civil and Environmental Engineering
Georgia Institute of Technology
Atlanta, GA, USA
Hiroki Nanko
Institute of Paper Science and Technology at Georgia Tech
Atlanta, GA, USA
Motivation
•
The use of lightweight aggregate for internal curing can
negatively impact strength and can lead to variability in
performance.
•
Superabsorbent polymers (SAPs) are more controllable but
are relatively expensive compared to lightweight
aggregate.
•
Wood-derived materials may be an alternative to other
internal curing materials, while providing consistency at a
lower cost.
Objectives
1.
To evaluate ability of certain wood-derived materials for
mitigating autogenous shrinkage.
2.
To determine the impact of wood-derived materials on
the relative compressive strength of high-performance
cementitious mixes.
3.
To assess the effects of wood-derived materials on
cement hydration through isothermal calorimetry.
Outline
1.
2.
3.
4.
5.
6.
Examination of Materials
Autogenous Shrinkage
Compressive Strength
Isothermal Calorimetry
Durability Concerns
Ongoing/Future Work
Internal Curing Materials (1)
The following wood-derived materials were investigated
for their potential use as internal curing agents.
TMP fibers
Cellulose powders
Kraft fibers
Wood powder
Internal Curing Materials (2)
• The SAPs had a particle size distribution of 1-100 µm.
• SAP absorption capacity (k = 10) was conservatively estimated based
on previous research.
• The absorption capacity of the wood-derived materials was determined
by image analysis
Kraft fibers
and
cellulose powder
(k = 1)
TMP fibers
and
wood powder
(k = 3.3)
• Wood powder was found to release water at twice the rate of TMP
fibers, due to their shorter fiber length. Thus, wood powder was used
at twice the dosage of TMP fibers to account for this difference.
Autogenous Shrinkage
Methodology
•
Samples were prepared in triplicate with a
base w/cm = 0.30 and 10% cement
replacement with metakaolin by mass.
•
Autogenous shrinkage was measured as
described by Jensen and Hansen1.
w/cme =
0.01
Kraft fibers
1.0%
Cellulose powder
1.0%
TMP fibers
w/cme =
0.025
w/cme =
0.050
w/cme =
0.075
w/cme =
0.10
0.75%
1.5%
2.25%
3.0%
Wood powder
SAPs
1
1.5%
0.25%
0.50%
3.0%
0.75%
1.0%
Jensen, O.M., Hansen, P.F., A dilatometer for measuring autogenous deformation in hardening cement paste.
Materials and Structures 28, 406-409 (1995).
w/cme =
0.15
4.5%
Autogenous Shrinkage Results (1)
Autogenous deformation (microstrain)
400
0
-400
-800
-1200
-1600
0.1
1
10
100
Time (days)
Control
1% kraft fibers
1% Vitacel
1% Arbocel
• Kraft fibers and cellulose powders were ineffective for internal curing
applications.
• Mass fractions capable of mitigating autogenous shrinkage could not
be achieved due to low absorption capacity and poor workability.
Autogenous Shrinkage Results (2)
Autogenous Deformation
(microstrain)
400
0
-400
-800
-1200
-1600
0.1
Control
1
0.25% SAP
Time (days)
0.50% SAP
10
0.75% SAP
100
1.00% SAP
• With 0.50% SAPs by mass, shrinkage was reduced by 43.0%.
• Dosage rates greater than 0.50% (w/cme = 0.05) actually led to slightly
increased shrinkage.
• The use of SAPs were not as effective as anticipated, possibly due to SAP
type and/or particle size.
Autogenous Shrinkage Results (3)
Autogenous Deformation
(microstrain)
400
0
-400
-800
-1200
-1600
0.1
Control
1
0.75% TMP
Time (days)
1.50% TMP
10
2.25% TMP
100
3.00% TMP
• Shrinkage was reduced by 80.4% compared to the control with 2.25%
TMP fibers by mass.
• Dosage rates greater than 2.25% (w/cme = 0.075) did not show further
improvements in shrinkage reduction.
Autogenous Shrinkage Results (4)
Autogenous Deformation
(microstrain)
400
0
-400
-800
-1200
-1600
0.1
1
10
Time (days)
Control
1.50% wood powder
3.00% wood powder
4.50% wood powder
• Shrinkage was reduced by 82.4% compared to the control with
4.5% wood powder by mass (w/cme = 0.15).
100
Autogenous Shrinkage Summary (1)
• Kraft pulp fibers and cellulose powders were ineffective
for internal curing applications. Mass fractions capable
of mitigating autogenous shrinkage could not be
achieved due to low absorption capacity and poor
workability.
• TMP fibers and wood powder reduced autogenous
shrinkage to a greater extent than the superabsorbent
polymers, when comparing equivalent water entrainment
rates (i.e., w/cme).
Autogenous Shrinkage Summary (2)
• With the TMP and SAP results, there appears to be a
threshold water entrainment dosage above which the
addition of water does not lead to increased benefits.
• For SAPs, this water entrainment threshold value is 0.05
(0.50% SAP) and for the TMP fiber composites, it is 0.075
(2.25% TMP).
• These differences in threshold values may be related to
their respective water release rates. In addition, the
values may also be a function of material distribution and
spacing.
Compressive Strength
Methodology
• Strength was measured at 3, 7, and 14 days to evaluate the
effect of internal curing materials on self-desiccating
cement pastes.
• Samples were cast in the same polyethylene tubes as the
autogenous shrinkage samples.
• Since compressive strength sample size does not conform
to any standards, only relative changes in strength should
be evaluated.
Compressive Strength Results (1)
Average Compressive Strength (MPa)
80
70
60
50
40
30
20
10
0
3
Control
0.25% SAP
7
Age (days)
0.5% SAP
14
0.75% SAP
1.0% SAP
• Strength was similar to the control at low mass fractions (i.e., less than
0.50% SAP).
• Increasing dosage rates led to decreased strength due to a higher w/cm.
• 0.50% SAP was also the optimal dosage rate for both compressive strength
and autogenous shrinkage.
Compressive Strength Results (2)
Average Compressive Strength (MPa)
80
70
60
50
40
30
20
10
0
3
Control
0.75% TMP
7
Age (days)
1.5% TMP
14
2.25% TMP
3.0% TMP
• At dosage rates less than 1.5% (w/cme = 0.05), strength decreased by 15-20%.
• Though the addition of 2.25% TMP fibers significantly minimized autogenous
shrinkage, a 30.9% decrease in strength at 14 days was observed.
• 1.5% TMP is optimal for strength, whereas 2.25% TMP was for shrinkage.
Compressive Strength Results (3)
Average Compressive Strength (MPa)
80
70
60
50
40
30
20
10
0
3
Control
7
Age (days)
1.5% WP
3.0% WP
14
4.5% WP
• There was no significant difference between the control and 1.5% wood
powder (w/cme = 0.05).
• 4.5% wood powder, which minimized shrinkage, led to a 35.1% decrease
in strength.
Compressive Strength Summary
• The wood-derived materials tended to adversely influence
compressive strength more so than the superabsorbent
polymers at low mass fractions (minimal water
entrainment).
• At higher mass fractions, above the critical entrainment
amount, (w/cm + w/cme ≈ 0.35), all materials showed
decreased compressive strength due to an increased in
the net water-to-cementitious materials ratio.
Isothermal Calorimetry
Isothermal Calorimetry Results (1)
Power Evolved (mW/g cement)
3.0
Control
2.5
Control
3% Wood Powder
3% TMP Fiber
3% Kraft Fiber
2.0
3% Kraft
Fiber
1.5
1.0
3% TMP Fiber
0.5
3% Wood Powder
0.0
0
12
24
Time after water addition (hr)
36
48
Isothermal Calorimetry Results (2)
300
Control
3% Wood Powder
3% TMP Fiber
3% Kraft Fiber
Normalized Cumulative
Heat Evolved (J)
250
200
Control
3% Kraft Fiber
150
3% Wood Powder
100
3% TMP Fiber
50
0
0
12
24
Time after water addition (hr)
36
48
Isothermal Calorimetry Summary
• The incorporation of wood-derived materials in cement
paste slightly lowered the overall heat evolved as
measured by isothermal calorimetry.
• TMP fibers showed little effect on the rate of heat evolution.
• Wood powder showed signs of delaying setting time,
though the overall hydration was similar to the other
materials.
• However, these minimal effects should not prohibit the use
of wood-derived materials for internal curing.
What About Durability?
• Wood-derived fiber-cement composites exhibit losses in flexural
strength and toughness with wet/dry cycling1,2.
0 cycles
25 cycles
• For internal curing applications in concrete, this concern may be
negligible as the fibers provide minimal toughening in the presence
of coarse aggregate.
• In addition, self-desiccation may be mitigated at an early age, prior to
any degradation.
1
Mohr, B.J., Nanko, H., Kurtis, K.E. Durability of kraft pulp fiber-cement composites to wet/dry cycling. Cement and
Concrete Composites 27, 435-448 (2005).
2 Mohr, B.J., Nanko, H., Kurtis, K.E. Durability of thermomechanical pulp fiber-cement composites to wet/dry
cycling. Cement and Concrete Research, in press (2005).
Conclusions / Future Work
• Based solely on autogenous shrinkage performance, the optimum
TMP fiber and wood powder dosage rates were found to be 2.25% and
4.50%, respectively. However, these rates led to a 31-35% reduction
in compressive strength at 14 days.
• It was noted that the water release rate appears to be an important
factor in mitigating autogenous shrinkage.
• Research is ongoing to identify TMP fiber and wood powder
morphologies as well as appropriate fiber coatings for optimal
control of the internal curing water release rate.
• Concrete compressive strength should be further investigated to
determine if transition size flaws overwhelm flaws (microcracks)
introduced by wood-derived materials.
Questions?
We gratefully acknowledge support for this research
from U.S. National Science Foundation grant CMS0122068 and the Institute of Paper Science and
Technology (IPST) All Member Research Consortium
(AMRC).