A Contribution from ACI Committee 236
Deicing Salts and Durability of Concrete Pavements and Joints Mitigating calcium oxychloride formation by Prannoy Suraneni, Vahid Jafari Azad, O. Burkan Isgor, and W. Jason Weiss
C
oncrete sidewalks, driveways, and pavements in the northern half of North America are increasingly showing signs of a specific form of damage that forms primarily along the joints.1-3 This damage is troubling, as it can emerge during the first decade of service2 and can be both difficult and costly to repair.4,5 For example, repair of joints in damaged concrete has been estimated to cost in excess of a million dollars a mile.2 Examples of the pattern of damage created in pavement are shown in Fig. 1. Although the actual cause of the damage is complex, it can be attributed to two primary factors: The fluid saturation of the concrete leading to conventional freezing-and-thawing damage; and A reaction (phase change) between the chloride-containing deicing salts and the cementitious matrix.6-8 While the first factor has received extensive study, little has been reported about the second factor. Recent work6,8 has suggested that the reaction between deicing salts and the cementitious matrix in concrete can be the dominating deterioration mechanism over a more classic form of freezing-and-thawing damage, particularly when the deicing salt concentrations are rather high, and this damage can even occur at temperatures above freezing. This article aims to inform concrete designers, specifiers, and inspectors about this lesser known deleterious reaction between cement paste and deicing salts in the hope that steps will be taken to minimize damage.
•• ••
States are typically chloride-based, although formate- and acetate-based formulations also exist. In this article, we focus on chloride-based deicing salts. While chloride-based salts can reduce the amount of ice on the pavement surface, making it safer for pedestrians and cars, saltwater solutions can be absorbed or diffuse into the concrete. As deicing salt solutions are transported into concrete, it is known that a portion of the chlorides in the salt can react with the hydrated aluminate phases of the concrete, forming Friedel’s and Kuzel’s salts.9 In addition, the chlorides in the deicing salt can react with the calcium hydroxide (Ca(OH)2) in the cementitious matrix and form an expansive product called calcium oxychloride.8,10
Deleterious Reaction between Cement Paste and Chloride
Deicing salts are generally used to melt ice that forms on concrete. Deicing salts used in the United
Fig. 1: Pavement showing premature joint cracking and damage2 www.concreteinternational.com | Ci | APRIL 2016
51
Table 1:
Comparison of different tests to quantify calcium oxychloride damage Test
Most typical phase tested
Information provided Quantity of calcium oxychloride that can be developed by a mixture
LT-DSC
Ground hydrated paste/mortar
TGA
Ground hydrated paste/mortar
Temperature at which calcium oxychloride forms for various salt concentrations The total amount of calcium hydroxide in a mixture
Damage in a sample LGCC
Hydrated mortar/ concrete cylinders
The temperature at which phase change and/or damage occurs
Calcium hydroxide is found in all portland cement concretes, and is formed from the hydration reactions of the alite (3CaO•SiO2) and belite (2CaO•SiO2) phases in cement (approximately 75% by mass of a typical Type I cement).11,12 It is this Ca(OH)2 that can potentially react when concrete is exposed to sufficiently high concentrations of deicing salts.10,13 While it is possible that this reaction can occur with sodium chloride (NaCl), little damage can be attributed to the formation of an expansive phase in mortars saturated by NaCl solutions,14 although other forms of damage may occur. However, when other deicing salts, such as calcium chloride (CaCl2)8,15 or magnesium chloride (MgCl2)6,7 are used, the potential for calcium oxychloride formation increases dramatically. The chemical formula for the most commonly observed form of calcium oxychloride is 3Ca(OH)2•CaCl2•12H2O15 and the most common chemical equation showing its formation10 is presented in Eq. (1) CaCl2 + 3Ca(OH)2 + 12H2O 3Ca(OH)2•CaCl2•12H2O (1) Over the last decade, research into the development of damage due to calcium oxychloride formation has moved from identification of the source of the reaction7,16 to testing the hypothesis that removal of Ca(OH)2 significantly reduces the potential for damage to occur.17 Research has been performed to identify the temperature and salt-calcium hydroxide molar ratio ranges in which calcium oxychloride can form.8 Acoustic emission tests of mortars showed that samples saturated with solutions stronger than approximately 15% (by mass) of MgCl2 or CaCl2 cracked and were damaged at room temperature without freezing and thawing.6,8 Additionally, test methods were developed to quantify the amount of calcium oxychloride15,17,18 that can form, and approaches to mitigate the formation have been identified. 52
APRIL 2016 | Ci | www.concreteinternational.com
Sample preparation and testing procedure
Data interpretation
A hydrated cement paste is ground, mixed with a salt solution, and placed in the instrument to undergo a thermal cycle
The amount of calcium oxychloride is measured by the area under the heat flow curve (for example between about 32 and 37°C [89 and 99°F] for samples with 20% CaCl2)
A hydrated cement paste is ground and placed in the testing device and heated
The amount of calcium hydroxide is measured by the change in mass loss between around 380 and 460°C (716 and 860°F)
A sample is conditioned to have a specific degree of saturation
Phase change is assessed by temperature measurement Damage is assessed using acoustic emission, ultrasonic wave velocity, or electrical resistivity
Unfortunately, however, concrete design, specification, and construction have remained relatively unchanged. The potential reaction between deicing salts and the Ca(OH)2 can be reduced to improve concrete performance through simple steps, as described later in this article.
Tests to Quantify Calcium Oxychloride Damage Test methods have been developed to quantify the amount of oxychloride that can form in a given cementitious matrix for the purpose of designing mixtures that are less prone to damage. These tests are described in the following sections and compared from a practical point of view in Table 1.
Low-temperature differential scanning calorimetry
The first test for quantifying the amount of calcium oxychloride that can form for a given salt and a given binder uses low-temperature differential scanning calorimetry (LT-DSC).15,17 An LT-DSC instrument monitors the heat that is generated in a sample when a reaction or a phase change occurs. In this test, hydrated cement paste is ground and mixed with the desired amount of salt solution in a pan, which is then sealed and subsequently placed in the LT-DSC instrument. The sample is exposed to a specific cooling and heating cycle—for instance, from −90 to 50°C (−130 to 122°F). When the temperature increases to a specific temperature (for 20% CaCl2 concentration by mass this is approximately 30°C [86°F]), the amount of calcium oxychloride that forms can be determined by comparing the heat released from the phase change to the heat released in a pure oxychloride system. It should be noted that because this test is done on a ground powder, a large portion of the Ca(OH)2 is exposed to the salt solution and this may result in a much greater reaction extent than would occur in concretes where limited transport may reduce the reaction extent.
Thermogravimetric analysis
The second test method that has been used to estimate the potential for calcium oxychloride formation is thermogravimetric analysis (TGA). In this test, the mass of a finely powdered paste sample is monitored as the sample is heated to 1000°C (1832°F) under the flow of an inert gas, typically N2. TGA can be used to accurately estimate the amount of Ca(OH)2 in pastes, with errors of about 1 g/100 g sample (1%) at later ages.11 Preliminary, unpublished results from the authors on a wide range of mixtures show that the amount of calcium oxychloride determined from LT-DSC increases linearly with the amount of Ca(OH)2 determined from the TGA, with the proportionality constant being close to the value predicted from simple chemistry. However, it should be noted that the TGA measures the total Ca(OH)2 while LT-DSC measures only the Ca(OH)2 that has reacted with the deicing salt. As such, differences can occur if a “protective” ring forms around the Ca(OH)2 as in the case of carbonation19 or topical treatments.20
Longitudinal guarded comparative calorimetry
The third test that can be used to quantify the amount of damage that occurs due to calcium oxychloride formation is longitudinal guarded comparative calorimetry (LGCC).6,8,14
Mortar samples saturated with various concentrations of deicing salt (NaCl, CaCl2, or MgCl2) are placed in the LGCC instrument and run through a defined thermal cycle. Damage is quantified using acoustic emission. At lower salt concentrations (below 10% by mass), damage is due to conventional freezing and thawing; however, at higher salt concentrations, damage is observed due to calcium oxychloride formation.6,8
Approaches to Minimize Damage
The aforementioned tests have been used to reveal three strategies to mitigate the formation of calcium oxychloride. The first strategy is to use supplementary cementitious materials (SCMs) to reduce the amount of the calcium hydroxide in concrete. The SCMs work both by dilution— reduction in Ca(OH)2 content because of reduction in cement content, and by pozzolanic reaction—silica and alumina from the SCMs react with Ca(OH)2 to form calcium (alumino) silicate hydrate. LT-DSC experiments have shown that a volume replacement of 20% of the portland cement by fly ash or slag cement (between 15 and 20% mass replacement) reduced the calcium oxychloride formed by approximately 50%, and almost no oxychloride was detected at SCM mass replacements of around 60% (between 50 and 60% mass
1/2 page
www.concreteinternational.com | Ci | APRIL 2016
53
Table 2:
Compositions (% mass) of different cements in the experimental and thermodynamic modeling studies ID
Blaine fineness, m2/g
C3S
C2S
C 3A
C4AF
SO3
Alkalis
C1
377
58.2
12.3
7.0
10.0
3.26
0.72
C2
388
62.0
13.0
6.0
10.0
2.78
0.52
C3
401
54.0
17.0
6.0
10.0
3.30
0.56
C4
399
54.0
17.0
6.0
9.0
2.70
0.57
C5
410
47.0
21.0
8.0
10.0
3.71
1.09
C6
373
56.4
13.1
8.1
8.8
2.80
0.59
C7
388
61.0
8.0
6.0
9.0
3.50
0.55
C8
370
52.0
16.0
8.0
9.0
3.90
0.72
C9
388
49.6
20.2
6.7
8.7
3.23
0.29
C10
383
52.0
18.0
7.0
10.0
3.10
0.56
Table 3:
Compositions (% mass) of different SCMs in the experimental and thermodynamic modeling studies ID
CaO
SiO2
Al2O3
Fe2O3
MgO
Alkalis
SO3
CF1
15.89
54.41
19.31
5.75
3.13
1.57
2.24
CF2
10.99
52.74
21.17
6.53
2.83
0.56
0.57
CF3
12.40
52.63
16.53
6.05
4.14
1.38
0.63
CF4
13.00
47.30
16.50
6.10
5.30
0.88
0.90
SF1
1.01
90.17
0.48
1.49
2.55
0.40
0.13
S1
40.00
35.00
12.00
1.00
8.00
0.60
9.00
Notes: CF1 through CF4—Class F fly ash; SF1—silica fume; S1—slag cement
replacement).15,18 Measurements on numerous cement-SCM blends from across the country are ongoing to build a database of compatible formulations for reducing oxychloride damage. The potential of using SCMs to reduce the formation of calcium oxychloride can also be shown through thermodynamic modeling, which is briefly presented herein (using only limited data for comparison). A thermodynamic modeling platform, GEMS,21 using the thermodynamic properties of portland cement hydrates in the system,22 was employed to simulate the reduction in Ca(OH)2 that occurs when SCMs are used with portland cements. The simulation results were compared with available preliminary experimental data, which provide Ca(OH)2 amounts of several blends of cement and SCM with compositions given in Tables 2 and 3, respectively. The modeling parameters were selected to be similar to the parameters used in the experiments. Water-binder ratio (w/b) and curing temperature were assumed to be 0.36 and 50°C (122°F), respectively. Because the degree of hydration values of the portland cement in the actual experiments were not known, they were assumed to be equal to 72.9% using the Parrot and Killoh model.23,24 The results of the simulations and their comparisons with available experimental data are provided in Fig. 2(a), (b), and (c), which show the amount of calcium hydroxide that is present in blended systems with Class F fly ash, slag cement, 54
APRIL 2016 | Ci | www.concreteinternational.com
and silica fume replacements, respectively. The red zone in the plots represents the modeling results, assuming different degrees of reaction for the SCMs (25, 50, 75, and 100% reaction shown). The topmost line shows the scenario where SCM has not reacted and the decrease in the Ca(OH)2 is only due to dilution, while the bottom line shows the scenario where SCM has fully reacted and the decrease in Ca(OH)2 is due to both dilution and pozzolanic reaction. In all cases, it is clear from Fig. 2 that SCM addition reduces the amount of Ca(OH)2 in the system, therefore decreasing the available amounts for the formation of calcium oxychloride. Because the amount of decrease in Ca(OH)2 depends on the SCM type, the replacement percentage, the water available for reaction, and the degree of reaction, additional research is necessary to optimize blended cement systems so that calcium oxychloride formation can be avoided. In addition, different types of SCMs can have different confounding effects on concrete; therefore, SCM-specific research is needed. For example, it is reported that slag cement replacements might increase scaling issues in concrete25; therefore, the slag cement replacement levels need to be optimized with the desired reduction in Ca(OH)2 amounts. Furthermore, high levels of SCM replacements are associated with reduction of pH in the concrete matrix; hence, additional optimization studies are required when SCMs are used for mitigating oxychloride
formation in reinforced concrete pavements to minimize the risk of steel corrosion. Supplementary research toward optimization is currently under way. The second strategy is to use carbonation19 to reduce the amount of calcium hydroxide available for reaction. Experiments using LT-DSC showed that no calcium oxychloride was formed after the sample was exposed to accelerated carbonation for about 120 hours, even though the sample still had about 50% of its initial Ca(OH)2 present. This suggests that, in addition to directly reducing the Ca(OH)2 amount, carbonation is also likely forming a protective layer of calcium carbonate around the Ca(OH)2 that prevents it from reacting. Carbonation may likely be very important in practice and may, under favorable conditions, reduce the possible calcium oxychloride damage without active human controls. However, it is also possible to envision a strategy where precast elements or pavement sections are preferentially carbonated to improve their performance, although additional studies must be performed to ensure that other aspects of durability (for example, potential corrosion of steel for reinforced concrete) are also considered when using carbonation as a mitigation strategy. The final strategy that may be used to reduce damage is the application of a topical treatment2,15,18 that provides a physical barrier between the salt solution and the Ca(OH)2. Preliminary LT-DSC tests conducted on cored paste samples indicate that application of a soy-based topical treatment results in significant reductions in calcium oxychloride content. These treatments have been applied in pavement joints, demonstrating the ability to do this in both new and existing pavements.2,20 In light of these promising results, further work on different topical treatments is needed.
(a)
(b)
Summary and Recommendations
Increasing damage has been observed in concrete pavements and flatwork when deicing salts are used. While a portion of this damage can be attributed to freezing and thawing of concrete with a high degree of saturation (for example, concrete in sustained contact with water), this article highlights a reaction that can occur between chloride-based deicing salts and phases of the hydrated cement matrix (specifically, calcium hydroxide). The following topics are discussed: The reaction that occurs between the salt and cement matrix to form calcium oxychloride (an expansive phase that causes damage)—for relatively high salt concentrations and temperatures above freezing; The use of three tests to quantify the potential for damage— LT-DSC to quantify the potential calcium oxychloride formation for a given cementitious matrix, TGA to quantify the amount of Ca(OH)2; and LGCC to quantify damage due to freezing and calcium oxychloride formation; Three approaches that could be implemented to minimize damage and further ongoing work—using SCMs to reduce Ca(OH)2 content through dilution and pozzolanic reaction,
•• ••
••
(c) Fig. 2: Preliminary experimental data and thermodynamic modeling results of calcium hydroxide decrease in blended cements with SCM reaction varying from 0 to 100%: (a) Class F fly ash; (b) slag cement; and (c) silica fume. The cement hydration degree was assumed to be 72.9%. The cement and SCM compositions were obtained using averages from Tables 2 and 3, respectively. The experimental results were obtained using mixtures with w/b = 0.36, cured for 25 days at 50°C (122°F) www.concreteinternational.com | Ci | APRIL 2016
55
using carbonation to reduce the availability of Ca(OH)2, and using topical treatments to provide a physical separation between applied deicing salts and Ca(OH)2 in the matrix; and The use of a thermodynamic model, based on first principles, to estimate the chemical reaction associated with calcium hydroxide formation and the resulting calcium oxychloride formation. The authors believe that this line of research can aid in understanding how concrete mixtures can be made more resistant to deicer damage. The test methods described in this article can be used in the development of performance-based mixture proportions or specifications (for example, specifying a calcium oxychloride limit to be verified using the LT-DSC test). Although only around 80 mixtures have currently been tested, it is apparent that prescriptive specifications limiting the volume of SCMs in concrete exposed to deicing salts should be revisited. Such specifications can hinder the development of sustainable mixtures as well as reduce options for increasing a mixture’s resistance to calcium oxychloride formation. While some studies have indicated increased scaling potential in high slump mixtures with high SCM replacement levels, these observations should be balanced
••
Do you have a story to tell? The staff of Concrete International can help you publish an article about your latest project collaboration… ■■ Or how you solved a constructibility issue… ■■ Or any topic related to design and construction.
To get started, contact Rex C. Donahey Editor-in-Chief
[email protected]
56
APRIL 2016 | Ci | www.concreteinternational.com
against the potential for extending service life in systems constructed using lower slump mixtures (less prone to demonstrate scaling), where higher volumes of SCMs can reduce the potential for salt damage. Of course, the amount of SCM replacement must also be optimized for reinforced concrete systems, as the associated reductions in the pH of the concrete matrix might also affect corrosion initiation and propagation. Further research is needed to find optimal solutions.
References 1. Shi, X.; Akin, M.; Pan, T.; Fay, L.; Liu, Y.; and Yang, Z., “Deicer Impacts on Pavement Materials: Introduction and Recent Developments,” Open Civil Engineering Journal, V. 3, Jan. 2009, pp. 16-27. 2. Jones, W.; Farnam, Y.; Imbrock, P.; Spiro, J.; Villani, C.; Golias, M.; Olek, J.; and Weiss, W.J., “An Overview of Joint Deterioration in Concrete Pavement: Mechanisms, Solution Properties and Sealers,” Purdue University, West Lafayette, IN, 2013, doi: 10.5703/1288284315339. 3. Taylor, P.; Sutter, L.; and Weiss, J., “Investigation of Deterioration of Joints in Concrete Pavements,” Report No. DTFH61-06-H-00011 Work Plan 26, National Concrete Pavement Technology Center, Iowa State University, Ames, IA, 2012, 208 pp. 4. “Highway Deicing: Comparing Salt and Calcium Magnesium Acetate,” Special Report 235, Transportation Research Board, Washington, DC, 1991, http://onlinepubs.trb.org/onlinepubs/sr/sr235.html. 5. Shi, X.; Liu, Y.; Mooney, M.; Berry, M.; Hubbard, B.; Fay, L.; and Leonard, A.B., “Effect of Chloride-based Deicers on Reinforced Concrete Structures,” WA-RD 741.1, Washington State Department of Transportation, 2010, 174 pp., www.wsdot.wa.gov/research/reports/ fullreports/741.1.pdf. 6. Farnam, Y.; Wiese, A.; Bentz, D.; Davis, J.; and Weiss, J., “Damage Development in Cementitious Materials Exposed to Magnesium Chloride Deicing Salt,” Construction and Building Materials, V. 93, Sept. 2015, pp. 384-392. 7. Sutter, L.; Peterson, K.; Touton, S.; Van Dam, T.; and Johnston, D., “Petrographic Evidence of Calcium Oxychloride Formation in Mortars Exposed to Magnesium Chloride Solution,” Cement and Concrete Research, V. 36, No. 8, Aug. 2006, pp. 1533-1541. 8. Farnam, Y.; Dick, S.; Wiese, A.; Davis, J.; Bentz, D.; and Weiss, J., “The Influence of Calcium Chloride Deicing Salt on Phase Changes and Damage Development in Cementitious Materials,” Cement and Concrete Composites, V. 64, Nov. 2015, pp. 1-15. 9. Balonis, M.; Lothenbach, B.; Le Saout, G.; and Glasser, F.P., “Impact of Chloride on the Mineralogy of Hydrated Portland Cement Systems,” Cement and Concrete Research, V. 40, No.7, July 2010, pp. 1009-1022. 10. Galan, I.; Perron, L.; and Glasser, F.P., “Impact of Chloride-Rich Environments on Cement Paste Mineralogy,” Cement and Concrete Research, V. 68, Feb. 2015, pp. 174-183. 11. Scrivener, K.L.; Füllmann, T.; Gallucci, E.; Walenta, G.; and Bermejo, E., “Quantitative Study of Portland Cement Hydration by X-ray Diffraction/Rietveld Analysis and Independent Methods,” Cement and Concrete Research, V. 34, No. 9, Sept. 2004, pp. 1541-1547. 12. Goñi Elizalde, S.; Puertas, F.; Hernández, M.S.; Palacios, M.; Guerrero Bustos, A.M.; Dolado, J.S.; Zanga, B.; and Braoni, F., “Quantitative Study of Hydration of C3S and C2S by Thermal Analysis: Evolution and Composition of C-S-H Gels Formed,” Journal of Thermal
Analysis and Calorimetry, V. 102, No. 3, 2010, pp. 965-973. 13. Birnin-Yauri, U.A.; Garba, S.; and Okeniyi, S.O., “Effect of Mechanism of Chloride Ion Attack on Portland Cement Concrete and the Structure Steel Reinforcement,” Research Journal of Applied Sciences, V. 2, No. 1, 2007, pp. 5-8. 14. Farnam, Y.; Bentz, D.; Hampton, A.; and Weiss, W.J., “Acoustic Emission and Low-Temperature Calorimetry Study of Freeze and Thaw Behavior in Cementitious Materials Exposed to Sodium Chloride Salt,” Transportation Research Record: Journal of the Transportation Research Board, V. 2441, 2014, pp. 81-90. 15. Monical, J.; Villani, C.; Farnam, Y.; Unal, E.; and Weiss, W.J., “Using Low Temperature Differential Scanning Calorimetry to Quantify Calcium Oxychloride Formation for Cementitious Materials in the Presence of CaCl2,” Advances in Civil Engineering Materials, 2016. (in press) 16. Peterson, K.; Julio-Betancourt, G.; Sutter, L.; Hooton, R.D.; and Johnston, D., “Observations of Chloride Ingress and Calcium Oxychloride Formation in Laboratory Concrete and Mortar at 5°C,” Cement and Concrete Research, V. 45, Mar. 2013, pp. 79-90. 17. Villani, C.; Farnam, Y.; Washington, T.; Jain, J.; and Weiss, W.J., “Performance of Conventional Portland Cement and Calcium Silicate Based Carbonated Cementitious Systems during Freezing and Thawing in the Presence of Calcium Chloride Deicing Salts,” Transportation Research Board 94th Annual Meeting, 2015. 18. Monical, J.; Unal, E.; Barrett, T.; Farnam, Y.; and Weiss, W.J., “Reducing Joint Damage in Concrete Pavements: Quantifying Calcium Oxychloride Formation for Concrete Made Using Portland Cement, Portland Limestone Cement, Supplementary Cementitious Materials, and Sealers,” Transportation Research Record: Journal of the Transportation Research Board, 2016. (in press) 19. Ghantous, R.M.; Unal, E.; Farnam, Y.; and Weiss, W.J., “The Influence of Carbonation on the Formation of Calcium Oxychloride,” submitted to Cement and Concrete Composites, 2016. 20. Wiese, A.S., “Assessing the Performance of Sustainable and Luminescent Concrete Sealers,” MS thesis, Purdue University, 2015. 21. Kulik, D.A.; Wagner, T.; Dmytrieva, S.V.; Kosakowski, G.; Hingerl, F.F.; Chudnenko, K.V.; and Berner, U.R., “GEM-Selektor Geochemical Modeling Package: Revised Algorithm and GEMS3K Numerical Kernel for Coupled Simulation Codes,” Computational Geosciences, V. 17, No. 1, 2013, pp. 1-24. 22. Matschei, T.; Lothenbach, B.; and Glasser, F.P., “Thermodynamic Properties of Portland Cement Hydrates in the System CaO–Al2O3–SiO2– CaSO4–CaCO3–H2O,” Cement and Concrete Research, V. 37, No. 10, 2007, pp. 1379-1410. 23. Lothenbach, B., and Winnefeld, F., “Thermodynamic Modeling of the Hydration of Portland Cement,” Cement and Concrete Research, V. 36, No. 2, Feb. 2006, pp. 209-226. 24. Parrot, L.J.; and Killoh, D.C., “Prediction of Cement Hydration,” British Ceramics Proceedings, V. 35, 1984, pp. 41-53. 25. Bleszynski, R.; Hooton, R.D.; Thomas, M.D.A.; and Rogers, C.A., “Durability of Ternary Blend Concrete with Silica Fume and Blast-Furnace Slag: Laboratory and Outdoor Exposure Site Studies,” ACI Materials Journal, V. 99, No. 5, Sept.-Oct. 2002, pp. 499-508.
Prannoy Suraneni is a Postdoctoral Researcher in the School of Civil and Construction Engineering at Oregon State University, Corvallis, OR. He received his B.Tech from the Indian Institute of Technology Madras, Chennai, India, in 2008; his MS in civil engineering from the University of Illinois at Urbana-Champaign, Champaign, IL, in 2011; and his PhD in civil engineering from ETH Zurich, Zurich, Switzerland, in 2015. His research interests include cement hydration, supplementary cementitious materials, durability, nondestructive testing, and the use of advanced microscopic techniques to study the early dissolution and hydration of cementitious materials. Vahid Jafari Azad is a Postdoctoral Researcher in the School of Civil and Construction Engineering at Oregon State University. He received his BSc in civil engineering in 2001 and his MSc and PhD in structural engineering from the University of Tehran, Tehran, Iran, in 2003 and 2009, respectively. His research interests include numerical modeling of material degradation, chloride ingress, and corrosion in reinforced concrete. His engineering experience has included designing industrial structures for the petrochemical industry. ACI member O. Burkan Isgor is an Associate Professor of civil and construction engineering at Oregon State University. He received his BS in civil engineering from Bogazici University, Istanbul, Turkey, in 1995, and his MS and PhD in civil engineering from Carleton University, Ottawa, ON, Canada, in 1997 and 2001, respectively. His research interests include materials science of cement and concrete, computational materials science, and nondestructive model-assisted testing of materials and structures. Isgor is a licensed professional engineer in the Province of Ontario. He is a member of ACI Committees 222, Corrosion of Metals in Concrete; 236, Material Science of Concrete; and 365, Service Life Prediction. W. Jason Weiss, FACI, is the Head of the School of Civil and Construction Engineering at Oregon State University. He is Chair of ACI Committee 236, Material Science of Concrete, and a member of ACI Committee 231, Properties of Concrete at Early Ages; and ACI Subcommittee 318-A, General, Concrete, and Construction. He received his BS in architectural engineering from Penn State University, University Park, PA, and his MS and PhD in civil engineering from Northwestern University, Evanston, IL.
Received and reviewed under Institute publication policies. www.concreteinternational.com | Ci | APRIL 2016
57
