Dale P. Bentz (
[email protected]) ACI Intermountain Chapter Concrete Spring Symposium April 7, 2016
NIST Background In the Minds of the Founding Fathers “Uniformity in the currency, weights, and measures of the United States is an object of great importance, and will, I am persuaded, be duly attended to.” George Washington, State of the Union Address, 1790
From the U. S. Constitution 3
Early NIST: Established by Congress in 1901
Eight different “authoritative” values for the gallon Nascent electrical industry needed standards
National Archives
American instruments being sent abroad for calibration Consumer products and construction materials uneven in quality and unreliable 4
NIST Today: Mission To promote U.S. innovation and industrial competitiveness by advancing
©Robert Rathe
measurement science, standards, and technology in ways that enhance economic security and improve our quality of life ~3000 employees ~3700 guest researchers
5
Concrete Goals (Bridge Decks and others) • Structural and non-structural members that withstand their physical and environmental loads throughout their intended service life – Strength considerations (design-based) – Durability (concerns are usually moisture related) • Diffusivity, permeability, sorptivity • Freeze-thaw performance, corrosion, sulfate attack, ASR
• Want to assure that HPC stands for “High Performance Concrete” and not “High Probability for Cracking” • Goals have been elevated with the advent and adoption of 75 to 100 year service life requirements
Agenda • Early-Age Cracking (Causes, Measurement, and Mitigation) • Sustainability (Materials Perspective) • Service Life Prediction (Real World Scenarios)
Examples of Importance of Early-Age Cracking of Bridge Decks in the US 2003 FHWA Nationwide HPC Survey Results --- Most Common Concrete Distresses 1) Early-age deck cracking (56.6 % of responses were a 4 or 5=often) 2) Corrosion (42.3 % ---- definitely linked to cracking) 3) Cracking of girders, etc. (31.4 %)
Others (sulfate attack, ASR, F/T, overload, poor construction quality were all below 25 % level) 2005 NRC/Canada report stated that “over 100,000 bridges in the U.S. have developed transverse cracking of their deck shortly after construction”
One Example of Some Problem Bridges NISTIR 7841 Study of Early-Age Bridge Deck Cracking in Nevada and Wyoming
Dale P. Bentz Paul E. Stutzman Aaron R. Sakulich W. Jason Weiss
January 2012
Potential contributors: Autogenous shrinkage (batched at low w/cm) Drying shrinkage
True contributors: Retempering of concrete High air contents Drying shrinkage Environment (drying following rainy season)
Available at http://www.nist.gov/customcf/get_pdf.cfm?pub_id=910303
Cylinder Samples vs. Insitu Concrete 60 MPa = 8700 psi
Strength from drilled cores
High air contents were generally removed during cylinder consolidation and therefore not detected by in-place quality checks, even by fresh air content measurements
Air contents from petrography analysis
25 mm field of view showing high air content of concrete
Simple transverse cracks impact service life substantially! Impact of a small (50 µm wide by 20 mm deep) crack on service life Variable
𝐶𝑟𝑒𝑏𝑎𝑟 𝐶𝑒𝑥𝑡 = 0.1 𝐶𝑟𝑒𝑏𝑎𝑟 𝐶𝑒𝑥𝑡 = 0.3 𝐶𝑟𝑒𝑏𝑎𝑟 𝐶𝑒𝑥𝑡 = 0.5
51 mm cover 76 mm cover 102 mm cover 5% silica fume (51 mm) 7% silica fume (51 mm) Corrosion inhibitor (51 mm) Epoxy-coated rebar (51 mm)
Service life (years)
Change from uncracked case
23 65 126 69 113 67 167
(32 %) (14 %) (8 %) (33 %) (34 %) (22 %) (18 %)
Impact of a large (500 µm wide by 40 mm deep) crack on service life Variable
𝐶𝑟𝑒𝑏𝑎𝑟 𝐶𝑒𝑥𝑡 = 0.1
𝐶𝑟𝑒𝑏𝑎𝑟 𝐶𝑒𝑥𝑡 = 0.3 𝐶𝑟𝑒𝑏𝑎𝑟 𝐶𝑒𝑥𝑡 = 0.5
51 mm cover 76 mm cover 102 mm cover 5% silica fume (51 mm) 7% silica fume (51 mm) Corrosion inhibitor (51 mm) Epoxy-coated rebar (51 mm)
Service life (years)
Change from uncracked case
1 26 83 2 4 4 16
(97 %) (66 %) (39 %) (98 %) (98 %) (95 %) (92 %)
Jones, S., Martys, N., Lu, Y., and Bentz, D., “Simulation Studies of Methods to Delay Corrosion and Increase Service Life for Cracked Concrete Exposed to Chlorides,” Cement and Concrete Composites, 58, 59-69, 2015.
Early-Age Performance of Concrete • Criticality of early-age performance for long term SRA – Slower drying durability • Cracking at early ages – Thermal considerations – Autogenous deformation considerations
– Structural/design considerations
• Measurement technologies – Effects of cement fineness
• Mitigation strategies – Mixture proportions
– Shrinkage-reducing admixtures (SRAs) – Internal curing
Internal curing
Cement Fineness Trends and Cracking
Cement fineness has consistently increased from 1954 to the present day Finer cements: - have an increased early-age heat release - increased semi-adiabatic temperature rise (thermal cracking) - increased autogenous shrinkage due to smaller pore sizes - all of which lead to a greater propensity for early-age cracking
Cracking during Transition • Thermal deformation Heat released during hydration causes temperature rise (50 oC or more) and expansion of young, compliant concrete
Heat generation
- reports of water boiling inside CA concrete
Shrinkage will occur during subsequent cooling of hardened, stiffer concrete If heating/cooling is too rapid and/or concrete is restrained (externally or internally), cracking may occur Semi-adiabatic temperature rise
Temperature (oC)
80
Tmax
70 60 50
dT/dt
40 30 20 0
1000
2000 Time (min)
3000
4000
Cooling
Cracking during Transition • Autogenous deformation Volume occupied by cement hydration reaction products is significantly less (10 % or more) than that of starting materials After setting (in a sealed system), this chemical shrinkage will be directly translated into a measurable autogenous deformation Once again, if concrete is restrained (externally or internally), cracking may occur Analogous to drying shrinkage, but drying is internal
Autogenous shrinkage
Empty pore creates capillary stresses and induces shrinkage of paste
What about high performance concretes (HPCs)? • Thermal cracking – HPCs usually contain more cementitious binder and perhaps silica fume, both of which accelerate and increase heat release rate and may thus exacerbate thermal cracking
• Autogenous deformation cracking – Finer pore structure of HPC and greater self-desiccation both greatly increase autogenous deformation (and potentially cracking)
• What about UHPC? – UHPC is heavily reinforced with fibers (steel and other) so that cracking is distributed as (nearly invisible) micro cracks as opposed to more damaging macro cracks
Measurement Technologies • Early age heat generation and reaction rates – Isothermal calorimetry • Differential Scanning Calorimetry (DSC), TAMAir, Isocal, etc.
• ASTM C1702-15b Standard Test Method for Measurement of Heat of Hydration of Hydraulic Cementitious Materials Using Isothermal Conduction Calorimetry • ASTM C1679-14 Standard Practice for Measuring Hydration Kinetics of Hydraulic Cementitious Mixtures Using Isothermal Calorimetry
– Semi-adiabatic calorimetry • Adiacal, coffee cup, Q-drum, etc. – If you have a thermocouple, you can build your own!!! • ASTM C1753-15 Standard Practice for Evaluating Hydration of Hydraulic Cementitious Mixtures Using Thermal Measurements
– Chemical shrinkage (proportional to heat release) • ASTM C1608-12 Standard Test Method for Chemical Shrinkage of Hydraulic Cement Paste
– Loss on ignition • Difficult at early ages due to hydration continuing during specimen preparation (ethanol quench), resolution issues
Measurement Technologies • Isothermal calorimetry assesses heat production at constant temperature conditions •
Results can be expressed as heat flow or integrated to get total heat release vs. time
•
Previously limited to cement pastes or mortars – But, Isocal and TAMAir units for concrete now exist
•
Experiments at three different temperatures (10, 25, and 40 oC) can be used to estimate activation energy (needed for application of maturity method) Heat Release (J/g cement)
Heat Flow (W/g cement)
0.005 Coarse -1 0.004
Coarse -2 Fine -1
0.003
Fine -2
0.002 0.001 0.000 1
10
100
1000
350 300 250 200 150 100 50
Coarse-1
Coarse-2
Fine-1
Fine-2
Type II limit
Type IV limit
0 0
40
Time (h)
80
120 Time (h)
w/c=0.35 cement pastes
160
200
240
Measurement Technologies • Semi-adiabatic calorimetry assesses temperature rise with controlled (or at least measured) heat loss • Results expressed as temperature vs. time • Can be used on pastes, mortars, or concretes • Can be used in both the field and in the laboratory – Mixture design – Quality control 70
Temprature ( o C)
Coarse 60
Fine Ambient
50
Ambient-2 40 30 20 0
8
16
24
32
40
48
56
64
72
Time (h)
w/c=0.35 cement pastes
Measurement Technologies • Chemical shrinkage assesses the imbibition of external water into a hydrating cement paste due to the fact that the hydration products occupy less volume than the reactants • Standardized in 2005 as ASTM C1608 by subcommittee C01.31 • Burrows has advocated that the 12-h chemical shrinkage be less than or equal to 0.0105 mL/g cement for a crack resistant cement (Burrows, et al., Three Simple Tests for Selecting Low-Crack Cement, Cement and Concrete Composites, 26 (5), 509-519, 2004.) Chemical shrinkage (mL/g cement)
0.06
Coarse
0.05
Fine
0.04 0.03 0.02 0.01 0.00 0
24
48
72
96
Time (h)
120
144
168
Very simple test to conduct!
Example of Chemical Shrinkage (CS) Hydration of tricalcium silicate (major component of OPC) C3S + 5.3 H C1.7SH4 + 1.3 CH
Molar volumes 71.1 + 95.8 107.8 + 43
CS = (150.8 – 166.9) / 166.9 = -0.096 mL/mL or
-0.0704 mL/g cement For each lb (g) of tricalcium silicate that reacts completely, we need to supply 0.07 lb (g) of extra curing water to maintain saturated conditions (In 1935, Powers measured a value of 0.053 for 28 d hydration – 75 %); important for internal curing
Measurement Technologies • Early age deformations and cracking – Corrugated tubes (with digital dilatometers) for mortar and paste autogenous deformation – Concrete cylinder or prism molds for mortar/concrete autogenous deformation – Cracking frames
– Ring tests for restrained shrinkage/expansion and early age cracking – Acoustic emission measurements
Measurement Technologies (Pastes and Mortars) Custom-built digital dilatometers (Developed by Prof. O.M. Jensen – Technical University of Denmark)
Specimens sealed in corrugated polymeric tubes and stored at constant temperature Method approved by ASTM C09.68 in 2009 as ASTM C1698 AutoShrink equipment available from Germann Instruments
Measurement Technologies (Concretes)
Measurement Technologies (Mortars/Concretes) Mortar
Concrete Developed at SIKA (Lootens and Oblak) ASTM test method under development in C09.68 (Volume Change)
1”x1”x10”
3”x3”x10”
Can perform autogenous or autogenous/drying experiments from time of casting onward
Measurement Technologies Restrained ring shrinkage and cracking test (ASTM C 1581-09a test method) Y
ST ROC RIS
ST
ST
RIC ST
h is the height of the ring in the out of plane (z) direction
Any questions: Contact Prof. Jason Weiss at Oregon State Univ. Residual Stress (MPa)
3.0 Fine Cement Coarse Cement
Visible Cracking
2.0
1.0 Tension
0.0 Compression
-1.0 0
12
24
36
48
60 72 Time (h)
84
96
108
120
Dual Ring with Temperature Control
Developed in a Purdue University/NIST collaboration Rings constructed of Invar to minimize thermal (CTE) effects Can measure both expansion and contraction - Important for systems with internal curing Can actively cool sample to induce cracking, if needed
Currently being standardized within AASHTO Schlitter, J.L., Senter, A.H., Bentz, D.P., Nantung, T., and Weiss, W.J., “Development of a Dual Ring Test for Evaluating Residual Stress Development of Restrained Volume Change,” Journal of ASTM International, 7 (9), 13 pp., 2010.
Mitigation Strategies • Thermal cracking – Use a low heat release cement (ASTM Type IV or invoke optional heat of hydration requirement on ASTM Type II – 290 J/g cement at 7 d) • Difficult to find in U.S. currently (Type IV not produced) • U.S. cement fineness constantly increasing since 1950
Mitigation Strategies • Thermal cracking – Reduce heat release rate by replacing cement with slowly reacting fly ash, slag, or limestone powder • may increase autogenous shrinkage at early and/or intermediate ages
– Reduced paste content (discussed more in sustainability to follow) – Chilled aggregates or ice additions as part of mixing water – Use cooling pipes in large concrete pours ($$$$) – Liquid nitrogen cooling – Use phase change materials (PCMs) that “absorb” hydration heat during their phase change from solid to liquid (melting) Mihashi, H, Nishiyama, N, Kobayashi, T, Hanada, M., “Development of a Smart Material to Mitigate Thermal Stress in Early Age Concrete,” In: Control of Cracking in Early Age Concrete, 2002. pp. 385-392. Paraffin-encapsulated hydration retarder
Mitigation Strategies • Paraffin Wax as an example of a phase change material – Wax melts at around 50 °C – ΔH of about 150 J/g
Temperature ( oC)
80
Control
70
LWA/PCM
60
PCM only
50 40 30 20
• (water/ice is about 333 J/g)
0
1000
2000
3000
4000
Time (min)
– For a typical concrete with 400 kg/m3 of cement • Maximum calculated temperature rise of 85 °C • With an addition of 350 kg/m3 of wax, maximum calculated temperature rise is reduced to 63 °C
• Wax can be added in “powder” form to concrete or can be “embedded” in lightweight aggregates (LWA) –
Sakulich, A.R., and Bentz, D.P., “Incorporation of Phase Change Materials in Cementitious Systems Via Fine Lightweight Aggregate,” Construction and Building Materials, 35, 483-490, 2012.
Mitigation Strategies • Autogenous deformation and cracking – Magnitude of autogenous (and drying) stresses are controlled by the Kelvin-Laplace equation cap
2 ln( RH ) RT rpore Vm
– Two variables that end user can exploit to their advantage are: • Decreasing surface tension (γ) of the pore solution Shrinkage-reducing admixtures (SRA)
• Increasing the size of pores (rpore) being emptied during the self-desiccation that accompanies the ongoing chemical shrinkage (or drying) Internal Curing Increased Cement Particle Spacing
Autogenous Deformation - SRAs • SRAs can reduce surface tension of pore solution by up to 50 % • Autogenous stresses should also be 50 % of level without SRA
• Thus, SRAs can reduce autogenous shrinkage as well as drying shrinkage • SRAs also modify pore solution viscosity, and influence evaporative drying rates and plastic shrinkage cracking, all in a positive manner – Negatives include their generally high cost ($$), tendency to sometimes detrain air, and potentially enhanced susceptibility to freeze/thaw issues
Autogenous Deformation --- SRA w/cm=0.35 mortar, sealed curing, 30 oC 100
2 % SRA No SRA
Microstrain
0
-100
-200
≈ 50 % reduction
-300 0
100
200
300
400
Time (h)
500
600
700
Drying with and without SRAs No SRA – Faster drying
Water wicks from within sample to surface
SRA – Slower drying Marangoni Effect
Boundary layer forms at top surface to slow evaporation
Concrete Solutions (Particle Spacing) • Coarser Cements
70 Fine
– Strength reduction: 25% at 28 d
Blaine fineness: Coarse – 310 m2/kg Fine – 380 m2/kg
Coarse Ambient
50
Ambient-2 40 30 20 0
8
16
24
32
40
48
56
64
72
Time (h)
w/c = 0.35 pastes Deformation (microstrain)
– Reduce autogenous shrinkage due to increased interparticle spacing
Temperature (oC)
– Reduce temperature rise and decrease rate of temperature decrease during semi-adiabatic curing due to reduced reactivity (lower surface area)
60
200
Fine Coarse
100 0 -100 -200 0
7
14
21
Time (d)
w/c = 0.35 mortars
28
Concrete Solutions (Particle Spacing) Semi-adiabatic Calorimetry - Type I/II cement
– Reduces autogenous shrinkage due to increased interparticle spacing – Strength reduction: 7% at 28 d
70
w/c=0.35
60
w/c=0.4
50
Ambient
40 30 20 0
8
16
24 Tim e (h)
Deformation (microstrain)
– Reduces temperature rise and decrease rate of temperature decrease during semi-adiabatic curing due to reduced cement content and increased heat capacity (more water)
Temprature ( o C)
• Increased w/c
32
40
48
Pastes w/c=0.35
100
w/c=0.4
50 0 -50 -100 -150 -200 0
7
14 Time (d)
Mortars
21
28
– Reduce autogenous shrinkage due to increased interparticle spacing (D50 of 50 μm to 100 μm) and carboaluminate formation at early ages – Strength reduction: 7 % at 28 d
Type I/II w/c=0.35
158
60
10 % Limestone w/cm=0.357
140
50
Ambient
122
40
104
30
86
20
68 0
8
16
24
32
40
Time (h)
200
48
56
64
o
70
Temperature ( F)
– Reduce temperature rise and decrease rate of temperature decrease during semiadiabatic curing due to reduced cement content (dilution)
Deformation (microstrain)
• Limestone (coarse) replacements for cement
Temperature (oC)
Concrete Solutions
72
Pastes Type I/II w/c=0.35
150 100
10 % limestone w/cm=0.357
50 0 -50 -100 -150 -200 0
7
Mortars
14 Time (d)
More on fine limestone replacements in sustainability to follow
21
28
Autogenous Deformation - IC • In internal curing (IC), internal reservoirs of extra curing water are supplied within the 3-D concrete microstructure – Pre-wetted lightweight aggregates (LWA) – Superabsorbent polymers (SAP) or polymer-coated sand – Saturated wood fibers – Crushed returned concrete aggregate
• Significantly reduces autogenous shrinkage at early and later ages – Reduces plastic and delays drying shrinkage as well
• May also enhance hydration and strength in the longer term (7 d and beyond)
Curing Concrete from the Inside Out Question: Why do we need IC? Answer: In practice, IC is being used mainly to reduce/delay early-age cracking by maintaining a high relative humidity within the hydrating cement paste! This can be particularly important in lower w/cm (≤ 0.4) concretes when capillary pores depercolate within a few days. If your concrete isn’t cracking at early ages, you may not need internal curing (may help with curling/warping). Capillary pore percolation/depercolation first noted by Powers, Copeland and Mann (PCA-1959).
Cement paste Water reservoir
Larger “sacrificial” pores within the reservoirs to minimize stress/strain
Autogenous Deformation Results
Deformation (microstrain)
w/cm=0.35 mortar, sealed curing, 30 oC 50 LWA20 0 SAP
-50 -100
LWA08 -150
Control FSF -200 0
5
10 Time (days)
15
20
Autogenous Deformation Results Control IC-LWAS(2) CCA-3000 LWA-CCA1000 blend
Microstrain
200
IC-LWAS (1) CCA-1000 CCA-5000
100 0 -100 -200 -300 -400 -500 -600 0
7
14
21
28
35
Time (d) Mortars with slag (20 %) blended cement
42
49
56
CCA = crushed (returned) concrete aggregates
IC added via fine LWA/CCA to increase total “w/c” from 0.30 to 0.38 (0.36) Note – chemical shrinkage of slag hydraulic reactions is ~0.18 g water/g slag or about 2.6 times that of cement
Degree of Hydration and Strength 70 FSF 60
LWA20
50
LWA08 SAP
40
70
0.80
56
0.64
42
0.48 IC strength
28
0.32
Control strength IC hydration
14
0.16
Control hydration 0
30 0
10
20
0.00 0
30
1
2
3
4
5
6
7
8
Age (d)
Time (days) 125
w/cm = 0.3 HPM with silica fume blended cement
100 75 Control
50
IC
25 0 0
10
20
30 Time (d)
40
50
60
Degree of hydration
Compressive Strength (MPa)
80
Strength (MPa)
Compressive strength (MPa)
w/cm = 0.35 mortars, sealed curing
Three-Dimensional X-ray Microtomography • X-ray microtomography allows direct observation of the 3-D microstructure of cementbased materials – Example: Visible Cement Data Set http://visiblecement.nist.gov
• In October 2005, experiments were conducted at Pennsylvania State University to monitor threedimensional water movement during internal curing of a high-performance mortar over the course of two days
After mixing
1 d hydration
All images are 13 mm by 13 mm
2 d hydration
Aqua indicates drying Red indicates wetting
Subtraction: 1 d – after mixing
Three-Dimensional X-ray Microtomography
Three-dimensional subtracted image of 1 d hydration – initial microstructure showing water-filled pores that have emptied during internal curing (4.6 mm on a side)
2-D image with water evacuated regions (pores) overlaid on original microstructure (4.6 mm by 4.6 mm)
Three-Dimensional X-ray Microtomography DEMAND==SUPPLY Empty porosity within LWA from analysis of 3-D microtomography data sets scales “exactly” with measured chemical shrinkage of the cement for first 36 h of curing Scaled =0.36 w /c=0.33 w /c=0.3 w /c=0.27 w /c=0.24 w /c=0.21 w /c=0.18
0
10
20
30
40
50
60
70
80
10
20
30
40
50
60
70
80 1400
abs= 5 % abs= 10 %
1200 1000
abs= 25 % abs= 30 %
800
abs= 35 % abs= 40 %
600 400
LWA addition (lb/yd 3)
abs= 15 % abs= 20 %
600
700
800
900
Cement content (lb/yd3)
Water demand (lb/yd 3)
0
500
Starting with the cement content in the graph on the upper right, find the chemical shrinkage of the mixture (a good default value is 0.07). Proceed to the value on the y-axis and starting with this same value in the graph on the upper left, find the line for the mixture’s w/c ratio. (Note that there is a single (thick) line for all w/c ratios greater than or equal to 0.36 as for these w/c ratio values, it is assumed that complete hydration of the cement powder can be achieved.) Proceed to the value on the x-axis and starting with this same value in the graph on the lower left, find the line for the absorption (dry mass of aggregate basis) of the lightweight aggregate. Finally, proceed to the value on the y-axis to obtain the recommended level of lightweight aggregate (dry mass basis) to be added to the concrete mixture. This replacement should then be conducted on a volumetric basis, replacing an equal volume of normal weight aggregates with pre-wetted (SSD) lightweight aggregates.
200 0
Also available in SI units!
Characterizing Properties of LWA for IC • In 2012, ASTM committee C09 published ASTM C1761/C1761M-12 Standard Specification for Lightweight Aggregate for Internal Curing of Concrete – Provides instructions on measuring physical properties and absorption/desorption of LWA for internal curing applications – Updated version -15 now available from ASTM
Question: How far can the water travel from the surfaces of the LWA? Answer: Equation balancing water needed
(hydration) vs. water available (flow) (Menu selection #2) “Reasonable” estimates --early hydration ---- 20 mm
middle hydration --- 5 mm late hydration --- 1 mm or less
“worst case” --- 0.25 mm (250 μm) Early and middle hydration estimates in agreement with x-ray absorption-based observations on mortars during curing
Question: How are the internal reservoirs distributed within the 3-D concrete microstructure? 30 mm by 30 mm
Answer: Simulation using NIST Hard Core/Soft Shell (HCSS) Computer Model (Menu selections #3 and #4) Returns a table of “protected paste fraction” as a function of distance
from LWA surface
Yellow – Pre-wetted LWA Red – Normal weight sand Blues – Pastes within various distances of an LWA
http://concrete.nist.gov/lwagg.html
Where has IC been used in practice? • 2005 – Railway transit yard and CRC paving in Texas (w/cm=0.43 for transit yard) • 2008-present – More than a dozen bridge decks in New York (w/cm=0.33 to 0.40) • 2011-present - Bridge decks in Indiana (w/cm=0.39 to 0.42) • 2012-present - Bridge decks in Utah (w/cm=0.44) – Also bridge decks in Ohio, Georgia, Virginia, Illinois, and North Carolina (constructed or planned)
• 2011-12 - Water tanks (10 million gallons) in Colorado
Internal Curing Applications (TXI & Texas DoT – Villarreal, Crocker, Reeves, Friggle)
• 2005 - RR intermodal facility constructed • 250,000 yd3 of low slump IC material • 6 months: 1 crack, 5.5 years: miniscule drying or plastic shrinkage cracking • CRC Paving for TxDOT
CRC Pavement
Railway Transit Yard
Indiana Field Trials - Conventional and IC mixtures in Sister Bridges
Courtesy of Prof. Jason Weiss, Purdue University
•
Implemented as a change order to existing Monroe County Bridges in 2010
•
Bridges cast using conventional ready mix concrete and conventional procedures
•
Shows that this is a ‘very off the shelf technology’ – replace some FA with FLWA
Monroe County IN (DiBella et al. 2012) • Simple Change in Mixture Proportions
• IN - Plain Slabs Cracked; IC has one crack as of 2015
• IC has improved transport properties
Field comparison (Monroe Co, IN) Plain bridge deck (Monroe Co.) 1 year after casting.
Bridge deck with internal curing (Monroe Co.) “Crack free 18+ mos after casting”
Crack Surveys on Utah Bridge Decks at 8 Months Age
But IC decks have cracked more since then (delay as opposed to elimination)
Sustainability, what’s it all about?
– Definition: 1987 UN conference defined sustainable developments as those that “meet present needs without compromising the ability of future generations to meet their needs” • “Do onto future generations as you would have them do onto you” (Robert Gillman, In Context) • “Leave no trace” --- National Parks motto
– One of the key concerns of the 21st century
How can concrete materials contribute to sustainable construction? • Two significant manners – Reduce carbon dioxide emissions and the consumption of energy • During the fabrication and curing of the cement/concrete
– Increase the service life of the concrete and minimize the required maintenance • Principal concern continues to be corrosion of steel reinforcement – Reduce cracking – Reduce the penetration of chloride ions (and carbonation)
Sustainable Concrete Sustainability push is increasing emphasis on replacing/reducing cement in concrete
How ? (disregarding alternative cements)
How much reduction?
• Increase aggregate content 75 %, when possible
• 70 % 75 % can give a 17 % reduction in cement
• Replace cement with SCMs or ternary blend with ground limestone
• ~ 40 % to 60 % reduction with either Class C or Class F fly ash (ternary blends)
• Replace cement (paste) with ground (fine) limestone
• 10 % with no water reduction
– Similar to SCC concretes in The Netherlands and elsewhere
25 % or more with a reduced w/p
Binary and Ternary Binder Blends
Mixture Proportions and Performance of Concretes with 10 % Limestone Powder Replacing Cement Objective: 40 MPa or 5800 psi concrete (564 lb/yd3 cement) Material Cement Limestone Coarse aggregate Fine aggregate Water HRWRA w/p
100 % OPC 335 kg/m3 --1 040 kg/m3 858 kg/m3 134 kg/m3 1 675 mL/m3 0.400
10 % 1.6 µm limestone 302 kg/m3 28 kg/m3 1 040 kg/m3 858 kg/m3 134 kg/m3 1 675 mL/m3 0.406
10 % 16 µm limestone 302 kg/m3 28 kg/m3 1 040 kg/m3 858 kg/m3 134 kg/m3 1 675 mL/m3 0.406
Volume-based replacement, mass-based w/c=0.44 for limestone mixtures
PERFORMANCE EQUIVALENCE? Mixture
Time of Initial Set
Time of Final Set
1-d strength
3-d strength
28-d strength
56-d RCPT
56-d resistivity
OPC
3.73 h
5.20 h
19.8 MPa 2870 psi
28.8 MPa 4180 psi
46.5 MPa 6740 psi
2 470 C
7.0 kΩ∙cm
10 % 1.6 µm limestone
3.17 h
4.63 h
17.9 MPa 2600 psi
29.3 MPa 4250 psi
40.8 MPa (44.5 MPa)
2 390 C
7.8 kΩ∙cm
10 % 16 µm limestone
4.00 h
5.50 h
17.6 MPa 2550 psi
29.1 MPa 4220 psi
39.7 MPa (42.8 MPa)
2 790 C
7.4 kΩ∙cm
(56-d)
Mixture Proportions and Performance of Concretes with ~25 % Cement Reduction (Paste Replacement) OPC
Cement (kg/m3)
343
6.7 µm limestone (broad PSD) -1 254.9
6.7 µm limestone (broad PSD) -2 248.1
Limestone powder
---
127.3
178.2
Water
171.45
152.9
136.5
Fine aggregate (silica sand)
822
822
822
Coarse aggregate (Dolomitic LS)
1082
1082
1082
HRWRA (L/m3)
1.08
2.5
2.5
w/c (w/p)
0.50 (0.50)
0.60 (0.40)
0.55 (0.32)
Cement reduction
---
25.7 %
27.7 %
Slump (cm)
14.6
24.1
17.1
Mixture
Time of Initial Set
Time of Final Set
1-d strength
7-d strength
28-d strength
91-d strength
Ult. drying shrinkage (28 d)
91-d resistivity
OPC
4.2 h
5.6 h
17.9 MPa 2600 psi
34.2 MPa 4960 psi
40.5 MPa 5870 psi
46.9 MPa 6800 psi
470 µstrain 380 µstrain
6.8 kΩ∙cm
1-6.7 µm limestone
3.9 h
5.5 h
16.1 MPa 2340 psi
32.9 MPa 4770 psi
38.2 MPa 5580 psi
43.9 MPa 6370 psi
480 µstrain 400 µstrain
6.2 kΩ∙cm
2-6.7 µm limestone
2.9 h
4.3 h
21.4 MPa 3100 psi
38.9 MPa 5650 psi
43.5 MPa 6310 psi
53.0 MPa 7690 psi
390 µstrain 290 µstrain
7.1 kΩ∙cm
PERFORMANCE EQUIVALENCE?
What about HVFA concretes? • A 3:1 by volume ratio of fly ash to limestone powder has worked well in several laboratory studies at NIST & FHWA – 30:10 FA:limestone to replace 40 % of cement by volume – 45:15 FA:limestone to replace 60 % of cement by volume
• A concurrent reduction in water content may be needed to achieve required strength levels – Switching to a Type III cement is a further option
• High range water reducer requirements may increase or decrease – Lower water content increases need for HRWRA
– Fly ash (and limestone) generally decrease HRWRA required at a fixed water content (less flocculating cement particles)
HVFA Concrete Mixture Proportions: Phase I Constant Water Content fly ash type
Materials
fly ash vol. frac.
limestone vol. frac.
OPC 1
40F 2
30F10L 3
40C 4
30C10L 5
60F 6
45F15L 7
60C 8
45C15L 9
100*
60
60
60
60
40
40
40
40
0
40
30
0
0
60
45
0
0
0
0
0
40
30
0
0
60
45
10
0
10
0
15
0
15
Cement (% volume of total cementitious) Type F fly ash (% volume of total cementitious) Type C fly ash (% volume of total cementitious) Limestone 0.7 µm (% volume of total cementitious) Coarse aggregate, lb/yd3
0
0
1750
1750
1750 1750
1750
1750
1750 1750
1750
Fine aggregate, lb/yd3
1444
1444
1444 1444
1444
1444
1444 1444
1444
Water, lb/yd3
226
226
226
226
226
226
226
226
226
w/cm (by mass)
0.4
0.46
0.45
0.43
0.43
0.5
0.48
0.45
0.45
*OPC mix = 564 lb/yd3 of cement (335 kg/m3) HRWRA – 7.7, 3.8, 3.0 fl oz/cwt (100 lbs. cementitious) for PC, F ash, C ash Low slumps of ≥ 1” (25 mm)
Phase II Concretes: Details • Target was a 1 d strength of 13.8 MPa (2000 psi) • For 40 % replacement mixtures, w/cm was reduced by replacing water with fine aggregate (sand), maintaining a 40 % cement reduction – w/cm = 0.34 and 0.37 for F and C ash, respectively
– HRWRA dosage was also increased as needed • 15.0/4.0WR and 6.0 for F and C ash, respectively (C still less than control)
• For 60 % replacement mixtures, a Type III cement was used and w/cm was also reduced – Updated mixtures achieved an overall ~50 % cement reduction – w/cm =0.31 and 0.33 for F ash; w/cm =0.29 and 0.32 for C ash
– water replaced with the ternary blend of powders • HRWRA of 12.3 and 10.0 for F and C ash, respectively
Results: Strengths and Costs 3A
4-40C
7.4 [1080]
8.5 [1230]
18.6 [2690]
28.8 [4180]
12.9 [1870]
15.4 [2230]
35.5 [5150]
16.3 [2370]
46.5 [6750]
5A
6-60F
7.4 [1080]
9.0 [1310]
16.3 [2370]
27.6 [4010]
16.0 [2320]
18.7 [2720]
18.7 [2720]
32.9 [4780]
19.0 [2760]
25.7 [3730]
31.6 [4580]
42.5 [6160]
70.13
55.81
56.99
53.62
42.67
$1.51
$2.17
1d strength (MPa)[psi] 3d strength (MPa)[psi] 7d strength (MPa)[psi]
19.8 [2870]
28 d strength (MPa)[psi]
Cost/MPa at 28 d $/(m3·MPa)
5 30C10L
2-40F
Projected cost ($/m3) [$/yd3]
3 30F10L
1-OPC
7 45F15L
7A
7B
8-60C
Not meas.
4.1 [590]
25.5 [3690]
19.7 [2860]
30.3 [4390]
5.5 [800]
6.9 [1000]
32.3 [4680]
24.8 [3600]
38.4 [5570]
7.3 [1060]
9.4 [1360]
27.8 [4030]
37.7 [5470]
48.2 [6990]
11.9 [1730]
66.36
56.21
57.09
59.21
43.57
50.74
42.97
43.65
$1.80
$1.56
$2.02
$1.52
9 45C15L
9A
9B
2.2 [320]
4.5 [650]
26.8 [3880]
23.0 [3330]
24.4 [3550]
6.7 [970]
10.6 [1540]
39.3 [5700]
34.5 [5000]
35.3 [5120]
28.0 [4070]
9.2 [1330]
17.2 [2500]
47.6 [6900]
44.1 [6400]
16.9 [2460]
45.2 [6560]
38.2 [5550]
12.9 [1870]
25.1 [3640]
61.0 [8840]
56.1 [8130]
49.76
51.41
63.35
61.14
50.35
51.84
63.31
61.04
45.27
38.04
39.31
48.44
46.75
38.49
39.63
48.41
46.67
$1.23
$4.17
$3.04
$1.40
$1.60
$3.91
$2.07
$1.04
$1.09
• In Phase I concretes, fly ash/fine limestone blends resulted in significant strength increases at all ages to 28 d • All of the Phase II concretes exceeded target strengths of 13.8 MPa at 1 d, and all but one exceeded 90 % of OPC control at other ages
Results: RCPT Measurements • Significant improvements in 56-d RCPT values in the systems with the fly ash/fine limestone blends
Results: Surface Resistivity
• Resistivity is the inverse of charge passed in RCPT, thus unlike RCPT values, higher is better • All resistivity values mimic behavior seen in RCPT testing Consistency between these electrical measurements
Moderate Slump Mixtures • Follow-up study at NIST in summer of 2014 formulated HVFA ternary blend mixtures with slumps of 3.5” to 8.5” (90–220 mm) – 40 % replacement for a Type I/II OPC; 60 % replacement for a Type III OPC
• Overall cement reductions of 44.5 % to 63.1 % were achieved – Part of cement reduction was due to stability of HVFA concretes with 75 % aggregates by volume (OPC concretes only stable to 72.5 %) – w/cm ranged from 0.31 to 0.37 (vs. 0.4 for OPC control) • Similar HRWRA required in HVFA mixtures (2 L/m3 to 3 L/m3)
• Similar performance achieved – 28 d strengths ranged from 39 MPa to 44 MPa (Controls both at 42 MPa) – Resistivities of HVFA mixtures at 28 d were 10 % to over 100 % higher than those of corresponding Vagg=72.5 % OPC (I/II or III) control mixtures – Increased resistivity along with increased chloride binding projects significant service life increases for HVFA concretes vs. their OPC counterparts (more to follow) Bentz, D.P., Jones, S.Z., and Snyder, K.A., “Design and Performance of Ternary Blend High-Volume Fly Ash Concretes of Moderate Slump,” Construction and Building Materials, 84, 409-415, 2015. Jones, S.Z., Bentz, D.P., Snyder, K.A., Martys, N.S., Hussey, D.S., and Jacobson, D.L., “Service Life Modeling of Reinforced High Volume Fly Ash (HVFA) Concrete Structures Containing Cracks,” Proceedings International Concrete Sustainability Conference, Miami, FL, 15 pp., May 2015.
Service Life Prediction • Many new concrete structures are being designed for 75 year or even 100 year service life • Modeling the only way to evaluate a concrete mixture’s future • Various models have been developed – Some are free (LIFE365, for example)
• NIST contribution in this area – Focus on the evaluation of real world scenarios • Surface treatment, scarification and overlay
• Influences of cracks and crack fillers on service life
Evaluating Influence of Treatment Options on Service Life
5.90
8
4.72
6
3.54
4
2.36
2
1.18
0
0.00
-
0
5
10
20 15 Time (yr)
25
Treatment at 1 year Treatment at 2 years Treatment at 4 years Treatment at 6 years Treatment at 8 years Treatment at 10 years Treatment at 12 years Treatment at 14 years
12
7.08
10
5.90
8
4.72
6
3.54
4
2.36
2
1.18
0
0.00
0
5
30
http://concrete.nist.gov/~bentz/millandfill/clpenmillandfill.html Collaboration with group of Prof. Spencer Guthrie at BYU
10
15 Time (yr)
20
25
30
Chloride Concentration (kg Cl -/ m3 Concrete)
10
No Treatment Chloride Concentration (lb Cl -/ yd3 Concrete)
7.08 Chloride Concentration (kg Cl -/m3 concrete)
12
3
Chloride Concentration (lb Cl /yd Concrete)
Chloride at 51 mm (2”) depth vs. time Scarification and overlay Sealing at specified age
Influence of Mixture Proportions on Service Life Service Life with Black Rebar OPC, 70.0 % Agg 73 years OPC, 72.5 % Agg 66 years OPC, 75.0 % Agg 50 years 40 % F ash/LS (75 % Agg) 126 years 40 % C ash/LS (75 % Agg) 234 years Increasing Vagg reduces diffusion coefficient, but also produced decreased binding of Cl-, (more water reducer needed) so that projected service life was reduced Chloride concentration at a cover depth of 51 mm for all concretes modeled in this study. Jones, S.Z., Bentz, D.P., Snyder, K.A., Martys, N.S., Hussey, D.S., and Jacobson, D.L., Service Life Modeling of Reinforced High Volume Fly Ash (HVFA) Concrete Structures Containing Cracks, Proceedings International Concrete Sustainability Conference, Miami, FL, May 2015.
Fly ash dramatically reduced diffusion coefficients, with similar binding, so that service life was markedly increased
Influence of transverse cracks on service life Impact of a small (50 µm wide by 20 mm deep) crack on service life Variable
𝐶𝑟𝑒𝑏𝑎𝑟 𝐶𝑒𝑥𝑡 = 0.1 𝐶𝑟𝑒𝑏𝑎𝑟 𝐶𝑒𝑥𝑡 = 0.3 𝐶𝑟𝑒𝑏𝑎𝑟 𝐶𝑒𝑥𝑡 = 0.5
51 mm cover (34 yrs) 76 mm cover (76 yrs) 102 mm cover (137 yrs) 5% silica fume (51 mm;103 y) 7% silica fume (51 mm;172 y) Corrosion inhibitor (51mm;86) Epoxy-coated rebar (51;203)
Service life (years)
Change from uncracked case
23 65 126 69 113 67 167
(32 %) (14 %) (8 %) (33 %) (34 %) (22 %) (18 %)
Impact of a large (500 µm wide by 40 mm deep) crack on service life Variable
𝐶𝑟𝑒𝑏𝑎𝑟 𝐶𝑒𝑥𝑡 = 0.1
𝐶𝑟𝑒𝑏𝑎𝑟 𝐶𝑒𝑥𝑡 = 0.3 𝐶𝑟𝑒𝑏𝑎𝑟 𝐶𝑒𝑥𝑡 = 0.5
51 mm cover 76 mm cover 102 mm cover 5% silica fume (51 mm) 7% silica fume (51 mm) Corrosion inhibitor (51 mm) Epoxy-coated rebar (51 mm)
Service life (years)
Change from uncracked case
1 26 83 2 4 4 16
(97 %) (66 %) (39 %) (98 %) (98 %) (95 %) (92 %)
Jones, S., Martys, N., Lu, Y., and Bentz, D., “Simulation Studies of Methods to Delay Corrosion and Increase Service Life for Cracked Concrete Exposed to Chlorides,” Cement and Concrete Composites, 58, 59-69, 2015.
Influence of Crack Fillers on Service Life 2-D Cl- maps
Crack fillers can restore service life to be equal to that of uncracked concrete
(a)
(b)
Cl- Threshold
Saturated
Methacrylate/Epoxy
Black rebar
4
73/73
Inhibitor
9
127/128
Epoxy-coated rebar
14
161/162
Jones, S.Z., Bentz, D.P., Snyder, K.A., Martys, N.S., Hussey, D.S., and Jacobson, D.L., Service Life Modeling of Reinforced High Volume Fly Ash (HVFA) Concrete Structures Containing Cracks, Proceedings International Concrete Sustainability Conference, Miami, FL, May 2015.
(c) Chloride concentration in OPC, 70 % aggregate, concrete with (a) crack saturated with 𝐶𝑙 − , (b) crack filled with methacrylate, and (c) crack filled with epoxy at 75 years of chloride exposure.
Caveat: Some epoxies contain Cl themselves
Summary • Designer/contractor toolbox growing rapidly with new tools for measurement of early-age properties, mitigation of early-age problems, and service life predictions • In practice, early-age cracking still seems to be quite difficult to avoid • Best plan forward may be to try to minimize cracking (shrinkage limits, SRAs, and internal curing) but to be prepared to fill the cracks with a non-chloride containing polymer (epoxy, PMMA) • Sustainability appears to be a sustainable topic that is here to stay, and once again there are a plethora of mixture proportion options for producing more sustainable concretes • Exciting future lies ahead for bridge deck engineers
Primary Collaborators NBS/NIST
Non-NIST
Clarissa Ferraris
Ahmad Ardani (FHWA)
Edward Garboczi
Jeffrey Davis (PNDetector)
Scott Jones
Spencer Guthrie (BYU)
Nicos Martys
Claus-Jochen Haecker (SE Tylose)
Max Peltz
Haejin Kim (NRMCA/FHWA)
Kenneth Snyder
Yang Lu (Boise State)
Paul Stutzman
Aaron Sakulich (WPI) Jussara Tanesi (FHWA) Jason Weiss (Purdue/Oregon State)
and many others
Some SRA References • 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 (7), 1075-1085 2001.
• Bentz, D.P., “Curing with Shrinkage-Reducing Admixtures: Beyond Drying Shrinkage Reduction,” Concrete International, 27 (10), 55-60, 2005. • Bentz, D.P., “Influence of Shrinkage-Reducing Admixtures on EarlyAge Properties of Cement Pastes,” Journal of Advanced Concrete Technology, 4 (3), 423-429, 2006. • Lura, P., Pease, B. Mazzotta, G. Rajabipour, F., and Weiss, J. “Influence of Shrinkage-Reducing Admixtures on the Development of Plastic Shrinkage Cracks,” ACI Materials Journal, 104 (2), 187-194, 2007. • Sant, G., Eberhardt, A., Bentz, D., and Weiss, J., ”Influence of Shrinkage-Reducing Admixtures on Moisture Absorption in Cementitious Materials at Early Ages,” ASCE Journal of Materials in Civil Engineering, 22 (2), 277-286, 2010.
Some Cement Fineness References • Bentz, D.P., and Haecker, C.J., “An Argument for Using Coarse Cements in High Performance Concretes,” Cement and Concrete Research, 29, 615-618, 1999. • Bentz, D.P., Garboczi, E.J., Haecker, C.J., Jensen, O.M., “Effects of Cement Particle Size Distribution on Performance Properties of Cement-Based Materials,” Cement and Concrete Research, 29, 16631671, 1999. • Bentz, D.P., Jensen, O.M., Hansen, K.K., Oleson, J.F., Stang, H., and Haecker, C.J., “Influence of Cement Particle Size Distribution on Early Age Autogenous Strains and Stresses in Cement-Based Materials,” Journal of the American Ceramic Society, 84 (1), 129-135, 2001. • Bentz, D.P., Sant, G., and Weiss, W.J., “Early-Age Properties of Cement-Based Materials: I. Influence of Cement Fineness,” ASCE Journal of Materials in Civil Engineering, 20 (7), 502-508, 2008. • Bentz, D.P., and Peltz, M.A., “Reducing Thermal and Autogenous Shrinkage Contributions to Early-Age Cracking,” ACI Materials Journal, 105 (4), 414-420, 2008. • Bentz, D.P., “Blending Different Fineness Cements to Engineer the Properties of Cement-Based Materials,” Magazine of Concrete Research, 62 (5), 327-338, 2010.
Some Internal Curing References •
Bentz, D.P., Lura, P., and Roberts, J., “Mixture Proportioning for Internal Curing,” Concrete International, 27 (2), 35-40, 2005.
•
Bentz, D.P., Halleck, P., Grader, A., and Roberts, J.W., “Water Movement during Internal Curing: Direct Observation Using X-ray Microtomography,” Concrete International, 28 (10), 39-45, 2006.
•
Bentz, D.P., “Internal Curing of High Performance Blended Cement Mortars: Autogenous Deformation and Compressive Strength Development,” ACI Materials Journal, 104 (4), 408-414, 2007.
•
Kim, H., Bentz, D.P., "Internal Curing with Crushed Returned Concrete Aggregates," NRMCA Technology Forum: Focus on Sustainable Development, 2008.
•
Henkensiefken, R., Castro, J., Kim, H., Bentz, D., and Weiss, J., “Internal Curing Improves Concrete Performance throughout Its Life,” Concrete Infocus, 8 (5), 2230, Sept.-Oct. 2009.
•
Henkensiefken, R., Briatka, P., Bentz, D., Nantung, T., and Weiss, J., “Plastic Shrinkage Cracking in Internally Cured Mixtures Made with Pre-wetted Lightweight Aggregate,” Concrete International, 32 (2), 49-54, 2010.
•
Bentz, D.P., Weiss, W.J., “Internal Curing: A 2010 State-of-the-Art Review,” NISTIR 7765, U.S. Department of Commerce, February 2011.
Some HVFA (and Ternary Blend) References •
Jones, S.Z., Bentz, D.P., Snyder, K.A., Martys, N.S., Hussey, D.S., and Jacobson, D.L., ”Service Life Modeling of Reinforced High Volume Fly Ash (HVFA) Concrete Structures Containing Cracks,” Proceedings International Concrete Sustainability Conference, Miami, FL, 15 pp., May 2015.
•
Bentz, D.P., Jones, S.Z., and Snyder, K.A., ”Design and Performance of Ternary Blend High-Volume Fly Ash Concretes of Moderate Slump,” Construction and Building Materials, 84, 409-415, 2015.
•
Bentz, D.P., ”Activation Energies of High-Volume Fly Ash Ternary Blends: Hydration and Setting,” Cement and Concrete Composites, 53, 214-223, 2014,
•
Bentz, D.P., Ferraris, C.F., and Snyder, K.A., ”Best Practices Guide for High-Volume Fly Ash Concretes: Assuring Properties and Performance,” NIST Technical Note1812, U.S. Department of Commerce, September 2013.
•
Bentz, D.P., Tanesi, J., and Ardani, A., “Ternary Blends for Controlling Cost and Carbon Content: High-volume Fly Ash Mixtures Can be Enhanced with Additions of Limestone Powder,” Concrete International, August 2013.
•
De la Varga, I., Castro, J., Bentz, D., and Weiss, W.J., “Application of Internal Curing for Mixtures Containing High Volumes of Fly Ash,” Cem Concr Comp, 34 (9), 1001-108, 2012.
•
Gurney, L., Bentz, D.P., Sato, T., and Weiss, W.J., “Using Limestone to Reduce Set Retardation in High Volume Fly Ash Mixtures: Improving Constructability for Sustainability,” Transportation Research Record, Journal of the Transportation Research Board, No. 2290, Concrete Materials 2012, 139-146, 2012.
•
Bentz, D.P., Sato, T., de la Varga, I., and Weiss, W.J., “Fine Limestone Additions to Regulate Setting in High Volume Fly Ash Mixtures,” Cem Concr Comp, 34 (1), 11-17, 2012.
•
Bentz, D.P., Ferraris, C.F., Filliben, J.J., “Optimization of Particle Sizes in High Volume Fly Ash Blended Cements,” NISTIR 7763, U.S. Department of Commerce, February 2011.
•
Bentz, D.P., Ferraris, C.F., Galler, M.A., Hansen, A.S., and Guynn, J.M., “Influence of Particle Size Distributions on Yield Stress and Viscosity of Cement-Fly Ash Pastes,” Cem Concr Res, 42 (2), 404-409,2012.
•
Bentz, D.P., Ferraris, C.F., De la Varga, I., Peltz, M.A., and Winpigler, J., “Mixture Proportioning Options for Improving High Volume Fly Ash Concretes,” International Journal of Pavement Research and Technology, 3 (5), 234-240, 2010.
•
Bentz, D.P., “Calorimetric Studies of Powder Additions to Mitigate Excessive Retardation in High Volume Fly Ash Mixtures,” ACI Materials Journal, 107 (5), 508-514, 2010.
Some Limestone (non HVFA) References • Bentz, D.P., Jones, S.Z., and Lootens, D., “Minimizing Paste Content in Concrete Using Limestone Powders - Demonstration Mixtures,” NIST Technical Note 1906, U.S. Department of Commerce, January, 2016. available at: http://dx.doi.org/10.6028/NIST.TN.1906. • Bentz, D.P., Ardani, A., Barrett, T., Jones, S.Z., Lootens, D., Peltz, M.A., Sato, T., Stutzman, P.E., Tanesi, J., and Weiss, W.J., “Multi-Scale Investigation of the Performance of Limestone in Concrete,” Construction and Building Materials, 75, 1-10, 2015.
Some Service Life References •
Jones, S., Martys, N., Lu, Y., and Bentz, D., ”Simulation Studies of Methods to Delay Corrosion and Increase Service Life for Cracked Concrete Exposed to Chlorides,” Cement and Concrete Composites, 58, 59-69, 2015.
•
Bentz, D.P., Guthrie, W.S., Jones, S.Z., and Martys, N.S., “Predicting Service Life of Steel-Reinforced Concrete Exposed to Chlorides: A Discussion of Real-World Considerations for Effective Modeling,” Concrete International, 36 (9), 55-64, 2014.
•
Bentz, D.P., Garboczi, E.J., Lu, Y., Martys, N., Sakulich, A.R., and Weiss, W.J., ”Modeling of the Influence of Transverse Cracking on Chloride Penetration into Concrete,” Cement and Concrete Composites, 38, 65-74, 2013.
•
Guthrie, W.S., Nolan, C.D., and Bentz, D.P., ”Effect of Initial Timing of Scarification and Overlay Treatment on Chloride Concentrations in Concrete Bridge Decks,” Transportation Research Record, Journal of the Transportation Research Board, No. 2220, Maintenance and Preservation of Structures and Equipment, 66-74, 2011.
•
Birdsall, A.W., Guthrie, W.S., and Bentz, D.P., “Effects of Initial Surface Treatment Timing on Chloride Concentrations in Concrete Bridge Decks,” Transportation Research Record: Journal of the Transportation Research Board, No. 2028, Design of Structures 2007, Transportation Research Board, National Research Council, Washington, D.C., 103-110, 2007.
•
Bentz, D.P., Snyder, K.A., and Peltz, M.A., “Doubling the Service Life of Concrete Structures. II: Performance of Nanoscale Viscosity Modifiers in Mortars,” Cement and Concrete Composites, Vol. 32 (3), 187-193, 2010.
