1 C. Balachandran, J.Olek, P.R. Rangaraju and S. Diamond

The Role of Potassium Acetate Deicer in Accelerating ASR in Concrete 1 Pavements: Relation between Laboratory & Field Studies 2

3 Chandni Balachandran* 4 SES Group & Associates LLC 5 614 Biddle Street, 6 Chesapeake City, MD 21915 7 tel. (202)-493-3057 8 fax. (202)-493-3161 9 email: chandni.balachandran.CTR@dot.gov 10 (former graduate student at Purdue University) 11 12 Jan Olek 13 Professor 14 Purdue University 15 School of Civil Engineering, Room G223 16 550 Stadium Mall Drive 17 West Lafayette, IN, 47907 18 tel. (765) 494-5015 19 fax. (765) 496-1364 20 email: olek@purdue.edu 21 22 Prasad Rangaraju 23 Associate Professor 24 220 Lowry Hall 25 Dept. of Civil Engineering 26 Clemson University 27 Clemson, SC, 29634-0911 28 Ph: (864)-656-1241 29 email: PRANGAR@clemson.edu 30 31 Sidney Diamond 32 Professor Emeritus 33 Purdue University 34 School of Civil Engineering, Room G223 35 550 Stadium Mall Drive 36 West Lafayette, IN, 47907 37 email: diamond@ecn.purdue.edu 38

*Corresponding Author 39 40 Date of submission: 08/01/2010 Word count: 6202 41 Figures (6): 1500 42 Tables (2): 500 43 TOTAL: 8202 44

TRB 2011 Annual Meeting Paper revised from original submittal.

2 C. Balachandran, J.Olek, P.R. Rangaraju and S. Diamond ABSTRACT 1 About fifteen years after the introduction of alkali acetate and alkali formate deicers into the 2 market, premature deterioration was observed on some airfield pavements exposed to them. 3 Based on the characteristic map cracking pattern observed on pavement surfaces, this distress 4 was suspected to be caused by accelerated alkali silica reaction (ASR) induced by repeated 5 applications of these deicers. Laboratory-based research indicated that ASR-reactive aggregates 6 may undergo active deterioration when intimately exposed to such deicers under conditions 7 promoting accelerated reaction. This paper describes investigations conducted on cores collected 8 from an airport whose de-icing operations involved repeated application of potassium acetate 9 (KAc) deicer. Detailed microscopic investigation of these cores indicated that more or less 10 uniform distress existed throughout the depth of the pavement, although in one of them the 11 distress was due to alkali carbonate reaction rather than alkali silica reaction. However, 12 investigations into the depth of penetration of deicer into these pavement cores showed that only 13 very limited incursion had occurred. A companion laboratory study was performed to estimate 14 the extent of deicer penetration under different laboratory exposure conditions. The study 15 revealed that even in a relatively aggressive wetting and drying exposure regime, the ingress of 16 the deicer was very limited. Thus it was concluded that despite the fact that KAc deicer can 17 induce severe ASR under the aggressive laboratory conditions, penetration into field airport 18 pavements may be so limited that, in some cases at least, the KAc deicer does not appear to be 19 the primary source of alkalis for the ASR distress observed in the field. 20 21 Key words: alkali silica reaction (ASR), potassium acetate deicer (KAc), scanning electron 22 microscopy (SEM), deicer penetration, airport pavement, distress, exposure conditions. 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45

TRB 2011 Annual Meeting Paper revised from original submittal.

3 C. Balachandran, J.Olek, P.R. Rangaraju and S. Diamond INTRODUCTION 1 Extensive application of deicers on concrete runways and taxiways is an indispensable part of the 2 winter maintenance of many airports. In the past, urea and glycol-based chemicals were 3 traditionally used as both an aircraft and pavement deicers. However, the environmental 4 concerns associated with these traditional deicers ushered in an era of a new class of deicers 5 (mostly alkali acetates and alkali formates) in the early 1990s. Around fifteen years after the 6 introduction of these deicers, premature deterioration was detected on some airfield pavements 7 that had been repeatedly exposed to them. Based on visual inspection of the pavement surfaces, 8 the cause of the observed distress was alleged to be alkali silica reaction (ASR), which was 9 suspected of being triggered or enhanced by application of these deicers. 10 Alkali silica reaction is a chemical reaction between alkali hydroxides dissolved in the 11 pore solution of affected concrete and certain reactive forms of silica in the aggregate. The result 12 is expansion, cracking, and progressive deterioration of the concrete. 13 Although abundant literature is available on the adverse role of commonly used highway 14 deicers in aggravating ASR (1-5), the traditional airport deicers did not seem to have been 15 causing similar durability problems (6-7). However, with the introduction of the new generation 16 of airport pavement deicers (i. e. alkali-acetate or alkali formate products), the durability 17 concerns have been raised regarding their potential role in triggering or exacerbating the ASR. 18 A preliminary laboratory study was initiated by the Innovative Pavement Research 19 foundation (IPRF) in 2004 to investigate the possible role of alkali acetate deicers in inducing 20 ASR in concrete (8). The published results of this investigation (9-11) indicated that concrete 21 containing reactive aggregates could indeed undergo active ASR distress when small samples 22 were intimately exposed to alkali acetate deicer, especially at higher temperatures. The damage 23 so induced was indicated by obvious expansion, severe cracking, and significant reduction in the 24 dynamic modulus of elasticity. Microstructural investigations yielded strong evidence of the 25 development of ASR gel in such specimens. However, the pore solutions removed from such 26 specimens sometimes indicated hydroxyl ion concentrations lower than the levels normally 27 required to trigger conventional ASR, and the investigators concluded that the mechanism of the 28 ASR distress invoked by exposure of concrete to the alkali-acetate deicers was different from 29 that associated with conventional ASR. 30

In a separate laboratory study, a ‘pH jump’ phenomenon was found to occur when highly 31 concentrated alkali acetate solutions of moderate pH levels (ca. pH 11) were mixed with calcium 32 hydroxide. Very high pH levels (in excess of pH 14) were produced, even though comparatively 33 low hydroxyl ion concentrations were found to be present. It appeared that the pH jump so 34 produced might play a pivotal role in promoting ASR attack induced by KAc (8, 11-14). 35 While important at the fundamental level, the observations and conclusions drawn from 36 these laboratory ASR studies do not necessarily provide explanations of the field distress 37 observed at various airports. This is mostly because of the differences between the laboratory 38 and field exposure conditions as well as the fact that the laboratory experiments are typically 39 conducted on relatively small mortar or concrete specimens. Further, the results of about the 40 only study found in the literature (15) that involved a direct comparison between field concrete 41 obtained from an airport pavement deiced with KAc and specimens of the same concrete 42 conditioned in the laboratory with KAc deicer solution indicated that there was no clear 43 correlation between the characteristics of the two. In addition, deicer penetrations into concrete 44 under real or simulated pavement exposure conditions had not previously been measured. In the 45 light of the above shortcomings, a comprehensive investigation was conducted which included a 46

TRB 2011 Annual Meeting Paper revised from original submittal.

4 C. Balachandran, J.Olek, P.R. Rangaraju and S. Diamond detailed laboratory study to address the gaps in the knowledge of the influence of KAc deicer on 1 concrete and also a forensic investigation of cores removed from three airports (A, B and C) 2 which used this deicer on their pavements (16). This paper presents the results of a laboratory-3 based investigation to study deicer penetration and a detailed forensic investigation of cores 4 collected from only one airport (Airport A) experiencing apparent ASR distress. The 5 investigation included microscopic evaluation of the microstructure of concrete and deterination 6 of the depth of penetration depth of KAc deicer into the pavement. Similar investigations are in 7 progress for pavements from several other airports. 8 9 EXPERIMENTAL PROGRAM 10 The experimental program of this study included determination of KAc deicer penetration into 11 series of laboratory concretes subjected to variable exposure conditions and determination of 12 both deicer penetration and microstructural changes in field concrete extracted from taxiways of 13 the airport at which potassium acetate was repeatedly used during de-icing operations. 14 15 Methodology for Laboratory Study of Deicer Penetration 16 This portion of the investigation was designed to measure the extent of penetration of KAc 17 deicer into concrete cylinders over which the deicer solution was ponded, under several different 18 laboratory-controlled exposure regimes. Concretes incorporating reactive as well as non-reactive 19 aggregates were investigated. The depth of penetration was measured by water extraction of 20 potassium and acetate ions from powders obtained from repeated milling (profile grinding) of the 21 concrete to progressive depths. The test matrix (with corresponding specimen labels) is shown 22 in Table 1. The details of sample preparation and the different exposure conditions are 23 elaborated on in the following sections. 24 25 TABLE 1 Test Matrix with Specimen Labels 26

Exposure Condition

Length of Exposure (months)

Specimen Type Non Reactive Concrete

Spratt Concrete

Room Temp (RT). (23°C/73.4°F)

3 NR_RT_3 SP_RT_3 6 NR_RT_6 SP_RT_6

Alternate Wetting & Drying Cycles (WD)

3 NR_WD_3 SP_WD_3 6 NR_WD_6 SP_WD_6

Low Temperature (4.4°C/40°F)

3 NR_40F_3 SP_40F_3 6 NR_40F_6 SP_40F_6

27 Materials 28 29 Deicer: A commercial grade liquid potassium acetate (KAc) deicer was used in this study. The 30 deicer, which is a 50% (by weight) aqueous potassium acetate solution (6.5M) with some 31 proprietary corrosion inhibitors, was used in the same concentration as supplied for field use. 32 33 Aggregates: Non-reactive coarse aggregate used in this investigation was a crushed limestone 34 obtained from a local quarry near West Lafayette, IN. The reactive coarse aggregate used was a 35 highly reactive siliceous limestone aggregate (obtained from the Spratt Quarry in Ontario, 36

TRB 2011 Annual Meeting Paper revised from original submittal.

5 C. Balachandran, J.Olek, P.R. Rangaraju and S. Diamond Canada). The fine aggregate used in this study was the ASTM C 778 standard sand obtained 1 from Ottawa, IL. 2 3 Cement: Ordinary ASTM C 150 Type I high alkali (Na2Oeq= 0.86%) portland cement was used 4 to prepare the concrete specimens. 5 6 Specimen Preparation 7 Four concrete cylinders (4 in. (102 mm) x 8 in. (203 mm)) were prepared from each of two 8 companion mixtures, one with the Spratt reactive aggregate, the other with the non-reactive 9 limestone. In the subsequent sections, concrete with non-reactive aggregate is referred to as NR 10 concrete; that containing Spratt limestone is designated as SP concrete. The aggregate grading 11 of both mixtures conformed to the requirements of ASTM C 1293 (MSA=3/4 in. (19 mm)). The 12 mix proportions for the NR concrete were as follows: 420 kg/m3 (26.2 lbs/ft3) cement, 678 kg/m3 13 (39.2 lbs/ft3) fine aggregate, 1102 kg/m3 (68.8 lbs/ft3) coarse aggregate and w/c of 0.435. The 14 mix proportions for the SP concrete were almost identical, being 420 kg/m3 (26.2 lbs/ft3) cement, 15 669 kg/m3 (41.8 lbs/ft3) fine aggregate, 1088 (67.9 lbs/ft3) kg/m3 coarse aggregate and w/c of 16 0.435. 17

The specimens were demolded 24 hours after casting and placed in saturated lime water 18 for a period of 14 days. After 14 days of curing they were removed from the lime water and 19 stored in an environmental chamber maintained at approximately 23°C (73.4°F) and 50 % 20 relative humidity for another 14 days. Following this, one cylinder from each mix was set aside 21 to be used to determine the background alkali concentration. Each of the remaining cylinders 22 was then cut to obtain two shorter cylindrical specimens 4 in. (102 mm) in height. The lateral 23 surfaces of all the specimens were coated with a two-part epoxy. A plastic sleeve (4 in. (102 24 mm) diameter, 4 in. (102 mm) height) was placed as a dam around the saw cut face of the 25 cylinders to enable ponding of the deicer solution on this surface.. Before placing the dam, a thin 26 layer of silicone sealant was applied to its bottom following which it was placed over the 27 cylinder and pushed down until approximately 2 in. (51 mm) of the dam extended beyond the top 28 surface of the cylinder. Finally, an external layer of silicone sealant was then applied along the 29 base of the sleeve to securely affix it to the cylinder. Figure 1a shows a schematic of the deicer 30 ponding specimen while Figure 1b shows an actual specimen with the dam installed and ready 31 for test. 32 33 Experimental Set-up 34 As indicated in Table 1, three different exposure conditions were used in this investigation. The 35 room temperature exposure regime involved maintaining a constant level of deicer in the dams of 36 specimens stored in an environmental chamber maintained at 23°C (73.4°F) and 50 % relative 37 humidity. In the wetting and drying exposure regime, the specimens were ponded with deicer 38 for 4 days at room temperature (23°C (73.4°F)), after which the solutions were removed and the 39 specimens dried under halogen lamps for 3 days (the surface temperature during drying was 40 around 30 °C (86°F). In the reduced temperature exposure regime, specimens with ponded 41 deicer solution were continuously stored in an environmental chamber maintained at 40°F 42 (4.4°C). One specimen from each of the three mixes was exposed in each of these environments 43 for each stipulated exposure period. 44

In each of these testing environments, the specimens were supported on small wooden 45

TRB 2011 Annual Meeting Paper revised from original submittal.

6 C. Balachandran, J.Olek, P.R. Rangaraju and S. Diamond rods, as shown in Figure 1b, to allow exposure of the bottom of the specimen to the atmosphere 1 for accelerated ingress of deicer by vapor transmission. The depth of the ponded solution over 2 the specimens was approximately 6 mm (≈0.2 in.) and the level was maintained constant over the 3 entire exposure period (except during the drying phases). 4

5

6 FIGURE 1(a) Schematic of specimen for deicer ponding experiment and (b) Assembled 7 deicer ponding specimen ready for the test 8

Determination of Deicer Penetration 9 After completion of the prescribed exposure period, the penetration profile of the K+ and 10 CH3COO- ions into the specimens were determined as described below. The deicer solutions 11 ponded above the cylinders were discarded and the plastic dams removed, along with the epoxy 12 and silicone sealant on the lateral surfaces. 13

Profile grinding of the cylinders was conducted at depth intervals of 5 mm (0.197 in.), 14 using a drilling machine with a 2 in. (51 mm) drill bit. The concrete powder thus obtained was 15 sieved to pass a 125 μm sieve. A fixed quantity of powder from each layer (10g) was mixed 16 thoroughly with 20g of deionized water, thus maintaining the solids to solvent ratio of 1:2. The 17 resulting slurry was left in a sealed container for 6 hours at room temperature, after which it was 18 filtered under vacuum. The retrieved clear solution was analyzed for K+ ions using atomic 19 absorption spectroscopy and CH3COO- using ion chromatography. 20 21 Methodology for Investigation of Field Cores 22 Cores for the forensic investigation were obtained from three different taxiways (X, Y and Z) of 23 the commercial airport which will be referred to throughout this paper as Airport “A”. Since 24 1994, all the taxiways of Airport A were treated with KAc deicer in combination with an 25 ethylene glycol-based deicer and urea. However, since 1999, the predominant deicer used was 26 KAc (liquid), along with sodium formate and sodium acetate (solid deicers) in some years. A 27 total of 1,306,704 gallons (4,946,414 l) of KAc deicer, 1,413,163 lbs (641 tons) of sodium 28 formate deicer and 1,011,922 lbs (459 tons) of sodium acetate deicer were used at Airport A in 29 the various deicing seasons from 1999 to 2006. Of the three taxiways, severe damage was 30 observed on taxiway X while the other two exhibited relatively minor degrees of distress. The 31 background information about each of the taxiways that has been made available to the 32 researchers is summarized in Table 2, and the pavement condition for each of the taxiways at the 33 core locations is illustrated in Figure 2. Although a total of five cores were removed from these 34 taxiways (X-1, X-2, Y-1, Y-2 and Z-1), due to space limitations only the results for one core 35 from each taxiway (i.e. X-1, Y-1 and Z-1) are presented in this paper. 36

Plastic Sleeve

≈ 4”

≈ 2”

≈4”

Silicone Sealant

Concrete/Paste cylinder

Bottom

TRB 2011 Annual Meeting Paper revised from original submittal.

7 C. Balachandran, J.Olek, P.R. Rangaraju and S. Diamond

The investigations carried out on these cores included conducting a detailed microscopic 1 evaluation of the distress in the cores, and identifying any variation in the intensity of damage 2 with depth. In addition, the depth of deicer penetration into the taxiway pavements was 3 estimated, using a water extraction technique similar to that used in the investigations of 4 penetration into the laboratory-produced concrete cylinders. 5

6

7 FIGURE 2 Pavement condition of Airport A taxiways (a) Taxiway X, (b) Taxiway Y, (c) 8

Taxiway Z. 9

(a)

(c)

(b)

TRB 2011 Annual Meeting Paper revised from original submittal.

8 C. Balachandran, J.Olek, P.R. Rangaraju and S. Diamond

TABLE 2 Pavement Information for Airport A Taxiways 1

Taxiway X Taxiway Y Taxiway Z Year of construction 1999 2003 2004 Approximate age at which distress was evident*

4 to 5 years 4 to 5 years none observed to date

Condition of pavement at time of core removal (2008)*

Severe map-cracking along joints, moderate to low map-cracking in mid-panels.

Minor Damage No visible damage (when dry) and minor cracking (when wet)

Cement Type Type I Cement; Alkali Content = 0.5% Na2Oeq.

Type I Cement; Alkali Content = 0.57% Na2Oeq.

Type I Cement; Alkali Content = 0.61% Na2Oeq.

Supplementary Cementitious Materials

Class C Fly ash, CaO Content = 17.44%, Avail. Alkali Content = NA; S+A+F**= 62.5%; Fineness = 11.3% Ret on #325, Dosage in Concrete = 14.2% Cement Replacement

Class C Fly ash, CaO Content = 27.22%, Avail. Alkali Content = 1.48%; S+A+F**= 59.99%; Fineness = 18.40% Ret on #325; Dosage in Concrete = 15% Cement Replacement

Slag- Dosage in Concrete=40% Cement Replacement

Coarse Aggregate #57 Crushed Limestone, 14-day Expansion in ASTM C 1260 = 0.09%; Sp. Gr = 2.70; Abs% = 0.53

#57 Crushed Limestone; 14-day Expansion in ASTM C 1260 = 0.25%; Sp. Gr = 2.68; Abs = 0.43%

#57 Crushed Limestone, 14-day Expansion in ASTM C 1260 = N/A; Sp. Gr = 2.68; Abs% = 0.78

Fine Aggregate Source

Natural Sand; 14-day Expansion in ASTM C 1260 = 0.29%, Sp. Gr = 2.63; Abs% = 0.99

Natural sand; 14-day Expansion in ASTM C 1260 = 0.24%, Sp. Gr = 2.61; Abs = 1.24%

Natural Sand; 14-day Expansion in ASTM C 1260 = 0.24%, Sp. Gr = 2.60; Abs% = 1.79

* Information on the approximate age at which distress become visible and condition of pavement at time of coring was provided 2 by airport maintenance personnel 3

** S+A+F= Sum of oxides (SiO2+Al2O3+Fe2O3)4

TRB 2011 Annual Meeting Paper revised from original submittal.

9 C. Balachandran, J.Olek, P.R. Rangaraju and S. Diamond Initial Processing & Sectioning of Cores 1 An inventory containing photographs of different views of the cores and a summary of 2 observations from both visual and stereomicroscopic inspection of the intact cores was prepared. 3 Following this, each core was cut vertically into two parts (A & B) as shown in Figure 3a using 4 an oil-cooled saw. After cutting, each longitudinal section of the core was cleaned thoroughly to 5 remove oil from the cut surfaces. 6 7 SEM-EDX Investigation 8 One of the primary objectives of the investigation of the field cores was to establish the nature of 9 the distress and to characterize any effect of deicer exposure on the microstructure. To 10 accomplish this, small specimens (in the form of 20 mm x 20 mm x 15 mm (≈0.8 in. x 0. 8 in. x 11 0.6 in. blocks)) were removed from the sawn surface of each core using an oil-cooled saw. The 12 specimens were removed from three different depths (L-1, L-2 and L-3) as shown in Figure 3b. 13 The location (depth from the top surface) of the individual specimens was as follows: 14

• Level 1 (L-1) -Very top region of the core (≈0-20 mm (0 to 0.8 in.)) 15 • Level 2 (L-2) - Approximately 40 to 61 mm (1.6 in. to 2.4 in.) below the top surface 16 of the core 17 • Level 3 (L-3) - Location based on observed damage or features of interest. These 18

locations were approximately 127 mm (5 in.), 102 mm (4 in.) and 76 mm (3 in.) below the 19 surface of the X-1, Y-1, and Z-1 cores, respectively. 20 Upon removal the specimens were prepared for examination in the scanning electron microscope 21 (SEM). They were examined in the backscattered electron (BSE) mode, combined with energy 22 dispersive X-ray analysis (EDX). In this investigation, emphasis was given to establishing the 23 composition of any ASR gel encountered, its distribution within the microstructure, and any 24 observable effects of the KAc solution on the composition of C-S-H gel encountered 25 26 Specimen Preparation for the SEM-EDX Investigation 27 The small specimens cut from the cores were dried in an oven at 50ºC for 48 hrs and then 28 vacuum-impregnated with a low-viscosity epoxy. The impregnated specimens were lapped and 29 polished using progressively finer diamond-based polishing paste. Each specimen was prepared 30 in such a way that the original orientation of its polished face was towards the cut surface of Part 31 B. A strip of conductive copper tape was then attached to each polished sample, after which they 32 were sputter coated with a thin layer of palladium. Each of the samples was thoroughly 33 examined using an Aspex®LLC personal Scanning Electron Microscope using an acceleration 34 voltage of 15 kV. 35

36 (a) 37

1”

Diameter=4”

Part BPart A

TRB 2011 Annual Meeting Paper revised from original submittal.

10 C. Balachandran, J.Olek, P.R. Rangaraju and S. Diamond

1 (b) 2

FIGURE 3 (a) Top view of core (b) longitudinal section of core with approximate location 3 of SEM specimens. 4

Determination of Deicer Penetration 5 Information about the depth of penetration of the deicer into the concrete pavement was 6 instrumental in understanding both the nature of the observed distress and the role (if any) of the 7 KAc deicers in causing it. The deicer concentration profile with depth was determined by profile 8 grinding of part Part A of the core and analyzing the suspension prepared from the powdered 9 samples for both potassium and acetate ions. 10

The bottom portion of Part A of each core was removed to leave a core length of ≈ 150 11 mm (6 in.), which was suitable to be held in the drilling machine to be used for profile grinding. 12 Profile grinding of the core from the top surface until a depth of 25 mm (0.98 in.) was conducted 13 in depth intervals specified in ASTM C 1556 (17) (assuming a w/c ratio of 0.5), and was 14 continued until a depth of 50 mm (1.97 in.), with depth intervals of 5 mm (0.197 in.). The 15 concrete powder obtained was sieved to pass a 125 μm sieve and stored in labeled glass vials 16 until further chemical analysis was carried out. 17

Water extraction of the ions from the concrete powders obtained from each layer was 18 performed in a manner similar to that previously described. 10 g of powder was extracted for 19 each of the depth intervals from which sufficient powder was obtained. In the topmost layers the 20 amount of powder obtained was less than 10g. For these layers a suitable weight of powder was 21 chosen and mixed with enough deionized water so as to maintain the 1:2 weight ratio of powder 22 to water. Additionally, the pH of these suspensions was measured before filtration, using a glass 23 combination electrode calibrated with a pH 10 buffer and a saturated calcium hydroxide solution 24 (pH 12.54). 25

K+ and CH3COO- ion concentrations in the suspensions were determined as described 26 previously in the section Determination of Deicer Penetration in laboratory specimens, and the 27 OH- ion concentrations were determined by titration with a standardized hydrochloric acid using 28 a phenolphthalein indicator. 29 30

Part B

Location of SEM specimens

2”

Variable depth-based on the condition of the core

L-2

L-3

L-1

TRB 2011 Annual Meeting Paper revised from original submittal.

11 C. Balachandran, J.Olek, P.R. Rangaraju and S. Diamond RESULTS 1 2 Results of Investigation of Laboratory Concrete Cylinders 3 The “background” potassium ion concentration was determined to be approximately 0.007M for 4 both SP concrete and NR concretes. Figures 4(a)-4(f) show the K+ and CH3COO- ion 5 concentration profiles measured after 3 months and again after 6 months for the SP concrete and 6 NR concrete in the three different exposure regimes. The data for 15-20 mm (0.6-0.78 in.) 7 interval for the NR concrete sample in the wetting/drying exposure regime was deemed to be 8 erroneous because of a sealing problem, and was omitted from Figure 4b. 9 10 Deicer Penetration in Cyclic Wetting & Drying Exposure (WD) Regime 11 It is evident from Figures 3(a) and 3(b) that the penetration depth of the KAc deicer does not 12 appear to be significantly different between concretes containing the reactive aggregate and the 13 non-reactive aggregates. The penetration of deicer into both types of concrete exposed to the 14 wetting and drying exposure regime was found to be approximately 15 mm (0.6 in.) at 3 months 15 (12 wetting and drying cycles) and between 20 and 25 mm (0.78 to 1 in.) at 6 months (24 wetting 16 and drying cycles). 17

In a similar study conducted by Wang (18) to estimate the ion penetrations from selected 18 deicers, the wetting and drying cycles used were much more frequent, and the technique used to 19 determine the potassium ion concentrations was based on a cation exchange method typically 20 used for soils. The results of Wang’s study indicated the potassium ion penetrations to be about 21 30 mm after 60 wetting and drying cycles. Considering the differences in the exposure regime 22 and method of potassium ion analysis, the ion profiles determined from the two studies appear to 23 be comparable. 24 25 Deicer Penetration in Room Temperature Exposure (RT) Regime 26 As expected, in the constant exposure regime at room temperature, at 3 months the deicer 27 penetration was less than in the wetting/drying exposure regime. After 6 months the penetration 28 depths were more or less similar. From Figures 4c and 4d, it appears that after 3 months, the 29 penetration depth of the deicer is marginally higher for NR concrete than for the SP concrete. 30 However, for all practical purposes, the penetration of deicers into concrete at room conditions 31 (approximately 10-15 mm (0.4 - 0.6 in.)) after 3 months and ca. 20 mm (0.78 in.) after 6 months) 32 can be considered to be independent of the aggregate type. 33 34 Deicer Penetration in Reduced Temperature (4.4 ºC/40ºF) 35 The K+ and CH3COO- ion profiles for SP concrete and NR concrete for constant KAc deicer 36 exposure at 40°F (4.4°C) are shown in Figures 4e and 4f. Similar to what was observed in the 37 other exposure regimes, the deicer penetration was again found to be essentially independent of 38 the aggregate type. In most cases, this exposure regime was observed to result in slightly smaller 39 penetration of deicers than the room (23°C (~73°F)) temperature exposure in most cases. The 40 general depth of penetration observed here was very limited, being approximately 10 mm (0.4 41 in.) after 3 months with no appreciable increase in the next 3 months. 42 43 Comparison of Effect of Different Exposure Regimes on Deicer Penetration 44 As anticipated, the W-D exposure regime proved to be the most severe of the three exposure 45 conditions used and resulted in higher penetration depths of the deicers in the first 3 months. 46

TRB 2011 Annual Meeting Paper revised from original submittal.

12 C. Balachandran, J.Olek, P.R. Rangaraju and S. Diamond However, the 6-months data indicate that the depths of penetration in the wetting-drying 1 exposure were only slightly higher than those obtained at room temperature. Further, for both 2 periods of exposure, the penetration induced by exposure to constant room temperature was more 3 or less identical (although slightly higher) to that observed at 40°F (4.4°C). Extending exposure 4 of the specimens for 3 additional months induced only a slight increase in deicer penetration. 5

For all practical purposes, the ion profiles in each exposure regime were found to be more 6 or less independent of the aggregate type. Presumably any cracking or other effects of ASR in 7 the ASR-reactive aggregate concretes would require a more prolonged period to develop. 8

Even in the aggressive wetting and drying exposure regime, the ingress of the KAc deicer 9 into the concretes was not substantial, and was limited to about 1 in. (25 mm) after 6 months. 10 Equally important, the ionic concentrations found in the 1:2 suspensions prepared from 11 powdered concrete were extremely low (<0.8M) even at the top of the zone penetrated. It should 12 be recalled that the concentration of the KAc solution used was 6.5M. 13 14

15 (a) (b) 16

17 (c) (d) 18

0.00

0.20

0.40

0.60

0.80

0 5 10 15 20 25 30 35 40 45

Ion

Con

cent

ratio

n (M

)

Depth from surface (mm)

K ion profile_3 mths_SP_WD

K ion profile_6 mths_SP_WD

Ac ion profile_3 mths_SP_WD

Ac ion profile_6 mth_SP_WD

0.00

0.20

0.40

0.60

0.80

0 5 10 15 20 25 30 35 40 45

Ion

Con

cent

ratio

n (M

)

Depth from surface (mm)

K ion profile_3 mths_NR_WD

K ion profile_6 mths_NR_WD

Ac ion profile_3 mths_NR_WD

Ac ion profile_6 mth_NR_WD

0.00

0.20

0.40

0.60

0.80

0 5 10 15 20 25 30 35 40 45

Ion

Con

cent

ratio

n (M

)

Depth from surface (mm)

K ion profile_3 mths_SP_RT

K ion profile_6 mths_SP_RT

Ac ion profile_3 mths_SP_RT

Ac ion profile_6 mth_SP_RT

0.00

0.20

0.40

0.60

0.80

0 5 10 15 20 25 30 35 40 45

Ion

Con

cent

ratio

n (M

)

Depth from surface (mm)

K ion profile_3 mths_NR_RT

K ion profile_6 mths_NR_RT

Ac ion profile_3 mths_NR_RT

Ac ion profile_6 mth_NR_RT

TRB 2011 Annual Meeting Paper revised from original submittal.

13 C. Balachandran, J.Olek, P.R. Rangaraju and S. Diamond

1 (e) (f) 2

FIGURE 4 Ion profiles from concrete cylinders in deicer penetration tests: (a) SP concrete 3 subjected to wetting/drying exposure (b) NR concrete subjected to wetting/drying exposure 4 (c) SP concrete subjected to room temperature exposure (d) NR concrete subjected to room 5 temperature exposure (e) SP concrete subjected to reduced temperature exposure 6 (4.4ºC/40ºF) (f) NR concrete subjected to reduced temperature exposure (4.4ºC/40ºF). 7

8 Results of Investigation of Field Cores 9 10 Results of SEM-EDX Investigation 11 Figure 4 shows representative micrographs collected during the SEM-EDX investigation of the 12 specimens removed from the three levels of the airfield pavement cores X-1, Y-1 and Z-1. The 13 field survey had indicated that Taxiway X was severely damaged while the Taxiways Y and Z 14 exhibited only minor or negligible distress. 15 The SEM-EDX investigation for the Taxiway X core clearly indicated a significant 16 degree of damage attributable to ASR. The examination revealed severe cracking, as shown in 17 Figure 5a. A similar severe degree of cracking was seen at all three levels of the core. The 18 presence of ASR gel was detected within cracks in the aggregates, in the matrix and also along 19 aggregate-paste interfaces, especially at depth L-2 (Figure 5b) and L-3 (Figure 5c). It is 20 important to reiterate that the presence of ASR gel and associated distress was observed in all 21 three levels of the core, despite the fact that, as seen later, only limited KAc penetration appeared 22 to have taken place. Furthermore, abundant ettringite deposits were observed both within voids, 23 but also as thin layers along the walls of cracks in the matrix and along aggregate interfaces. 24 When the EDX analyses revealed that in cases when cracks carrying ASR gel passed through 25 ettringite deposits, a significant content of sulfate ions was incorporated into the ASR gel. 26

The SEM-EDX observations made for Y-1 core indicated only limited degree of matrix 27 cracking and debonding of the aggregates, compared to that observed in the X-1 core. These 28 features were detected in specimens from all three levels, as displayed in Figures 5d, 5e and 5f. 29 Also, some of the air voids were found to be either partially or fully filled with ettringite deposits 30 (Figure 5d) and occasionally also with portlandite. However, almost no evidence of ASR was 31 detected in any of the three specimens. 32

The SEM-EDX investigation of Z-1 core revealed de-dolomitized dolomite aggregate 33 particles (Figures 5h and 5i) and brucite deposits in the matrix (Figure 5g) at all three levels. 34 These findings strongly indicate the occurrence of the alkali carbonate reaction (ACR) at this 35 particular location. Cracking in the matrix and debonding of the aggregates were detected in 36

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TRB 2011 Annual Meeting Paper revised from original submittal.

14 C. Balachandran, J.Olek, P.R. Rangaraju and S. Diamond

1 2

3 4

5 FIGURE 5 SEM-EDX Micrographs for Airport A taxiway cores: a) (Core X-1, L-1 6 specimen) Extensive debonding of siliceous aggregate with cracks propagating from 7 aggregate into matrix but no cracks within aggregate. Cracks around aggregate are devoid 8 of gel b) (Core X-1, L-2 specimen) Crack inside siliceous aggregate lined with Si-Na-Ca gel. 9 Ribbon of gel passing through adjacent matrix. c) (Core X-1, L-3 specimen) Ribbon of gel 10 within siliceous limestone aggregate with traces of K and Na. d) (Core Y-1, L-1 specimen) 11 Empty cracks propagating through matrix, air voids partially filled with ettringite. e) 12 (Core Y-1, L-2 specimen) Empty crack propagating through matrix. f) (Core Y-1, L-3 13 specimen) Crack propagating through matrix with empty air voids in the vicinity 14 (Magnification X100). g) (Core Z-1, L-1 specimen) Brucite deposit in cracked matrix 15 adjacent to the dolomite aggregate undergoing ACR. h) (Core Z-1, L-2 specimen) Dolomite 16 aggregate undergoing de-dolomitization, lighter grey mass surrounding rhombic dolomite 17 particles is calcite. i) (Core Z-1, L-3 specimen) cracks in matrix originating from dolomite 18 aggregate undergoing ACR (indicated by arrow) (Magnification X250). 19

(a) (b) (c)

(d) (e) (f)

(g) (h) (i)

TRB 2011 Annual Meeting Paper revised from original submittal.

15 C. Balachandran, J.Olek, P.R. Rangaraju and S. Diamond SEM specimens from all three levels (Figure 5i). The cracks in the matrix were found to 1 originate from the dolomite aggregates undergoing apparent ACR (Figure 5i). The intensity of 2 damage in the core was less than that observed in Taxiway X core, but slightly more than in 3 Taxiway Y. 4

Altogether, the SEM-EDX investigation provided no evidence that the application of the 5 KAc deicer had instigated or further aggravated ASR. The damage observed in the cores in each 6 case was found to be similar at all the three levels of depth examined. In particular, evidence of 7 ASR, observed only in the Taxiway X core, was detected even in L-3 specimens about 5 in. (127 8 mm) from the surface, far below the depth of KAc penetration shown in the subsequent section. 9 Furthermore, the alkali present in the ASR gel was found to consist of small contents of sodium 10 and little or no potassium. 11 12 Results of Deicer Penetration into Airport Pavements 13 The K+ and CH3COO- ion profiles for the cores examined are summarized in Figure 5. Data for 14 the 0-1mm and the 3-5mm depth intervals are missing due to the insufficient quantity of concrete 15 powder obtained at these levels. 16

The data shown in Figure 6a indicate that the KAc derived K+ ions penetrated only few 17 millimeters below the surface and that their concentration was negligibly low (< 0.03M). As 18 shown in Figure 6b, the penetration of the CH3COO- ions was also limited to a depth of 19 approximately 20 mm (0.78 in.) and also only in extremely low concentrations. The maximum 20 concentration of acetate ions in the powder suspension was only 0.03M, as observed in 1-3 mm 21 (0.04-0.12 in.) depth interval for core Z-1. The hydroxyl ion concentrations found in the powder 22 suspensions did not appear to follow any trend with depth and hence have not been included 23 here. The same was generally true of the measured pH values. An exception was that the pH of 24 the extreme top layer was found to be a little lower (0.2 to 0.4 pH units) than the remaining 25 layers, presumably due to carbonation; the remaining layers had more or less similar values (in 26 the range of 13 to 12.5). These observations suggest that there was no elevated pH created in the 27 concrete pore solution owing to deicer ingress. In other words, the ‘pH jump’ phenomenon, 28 suspected to be the reaction mechanism accelerating ASR in the presence of KAc deicer (11-14), 29 did not appear to occur here, presumably because the deicer penetration was insignificant in 30 terms of both depth and concentration attained. 31

On the whole, it appears that in these taxiways, the penetration of the deicer as applied 32 routinely during airfield operations was only about 20 mm (0.78 in.) into the pavement, and the 33 concentrations of the K+ and CH3COO- ions found even in this first 12mm (0.5 in.) of pavement 34 were found to be so low (< 0.04M in all cases) that penetration of the deicer can be essentially 35 considered to be insignificant. 36

37

TRB 2011 Annual Meeting Paper revised from original submittal.

16 C. Balachandran, J.Olek, P.R. Rangaraju and S. Diamond

1 (a) (b) 2

FIGURE 6 Ion profiles for Airport A cores: a) K+ ion profile b) CH3COO- ion profile. 3

DISCUSSION 4 Laboratory-based studies were conducted to gage the penetration of deicers into the concrete 5 under several different exposure regimes. The results indicate that the ingress of ponded KAc 6 deicer solution over a 6-month period, even in relatively aggressive exposure regime, was not 7 significant and the concentrations detected within the concrete were very low. 8

Investigations conducted on several cores retrieved from the taxiways of an airport with 9 known history of extensive usage of the KAc deicer also yielded no evidence to suggest that the 10 application of KAc deicer had a direct impact on the damage observed. Severe ASR-induced 11 distress was in one of the cores (X-1), but the intensity of damage (in terms of cracking and 12 presence of gel) was found to be more or less uniform throughout the depth of the pavement. In 13 a core retrieved from a different taxiway of the same airport (Z-1) alkali carbonate reaction was 14 found, but again more or less uniformly with depth. Little or no distress was found in the core 15 extracted from the remaining taxiway of this airport (Y-1). 16

Based on the experimental evidence collected during this study it cannot be univocally 17 concluded that the deterioration due to ASR exhibited in these cores would have been any less 18 severe in the absence of the KAc deicer application, since the investigation indicated that the 19 maximum depth of KAc penetration was minimal (approximately 20 mm (0.78 in.) from the 20 surface) and the KAc was found only in negligible amounts within this limited penetration depth. 21 The fact that clear evidences of ASR were detected 77-127 mm (3-5 in.) below the pavement 22 surface indicates quite conclusively that the ASR distress in this case is not associated with the 23 presence of KAc deicer. 24

Since the study presented here pertains to only one airport, the results may not be 25 generally characteristic of the effects of KAc application to airport pavements. In particular, it 26 appears that limited penetration of the deicer into more or less intact pavement surfaces may 27 have inhibited any potential effect of the chemical. For that reason it cannot be ruled out that 28 penetration may be much more extensive in pavements that had undergone cracking from other 29 causes prior to the application of the KAc deicer. Since the potential of deicing chemicals to 30 cause aggressive ASR damage in concrete specimens has been proven in laboratory studies (8-31 11), the lack of conclusive evidence of KAc deicer induced ASR damage in field concrete 32 specimens should not be interpreted as the lack of potential for such reaction to take place under 33 right set of conditions (e.g extensive cracking due to shrinkage or freezing thawing, high number 34 of wetting and drying cycles or high application rates of deicers). Considering the low tolerance 35 of airfield pavements to any level of cracking, and the associated hazards to aircrafts and 36

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TRB 2011 Annual Meeting Paper revised from original submittal.

17 C. Balachandran, J.Olek, P.R. Rangaraju and S. Diamond personnel on ground, the issue of apparent discrepancies between the field and the laboratory 1 results should be further investigated so (in case the accelerating effect of the KAc on the ASR is 2 confirmed) an effective aggregate screening and ASR mitigation measures could be adopted. 3 Such studies are currently underway and include both forensic investigations of cores retrieved 4 from a number of other airports that used KAc deicer in their winter maintenance operations as 5 well aggregate screening protocols aimed at identifing their susceptibility to the ASR reactions. 6 7 CONCLUSIONS 8 Prior research has been instrumental in evaluating the potential of KAc deicer to induce or 9 accelerate ASR distress in concrete under laboratory conditions involving ready access of the 10 small specimens to KAc solutions (8-10). However, a concerted effort to assess the extent of 11 distress induced by repeated applications of KAc de-icers under field conditions had not 12 previously been attempted. One of the principal objectives of the current study was to 13 investigate the degree to which the reaction mechanisms previously demonstrated to occur under 14 accelerated laboratory conditions are relevant to the distress observed in the field. The findings 15 presented here for cores extracted from one airport suggest that while KAc deicer can indeed 16 induce severe ASR in the aggressive laboratory-based conditions, it does not appear to play a 17 vital role in field distress here, at least in part due to the only very limited penetration that takes 18 place into the concrete. Though only a portion of the data from one of the airports was 19 incorporated in this paper, the findings from the examination of cores from other airports, 20 reported elsewhere (16), corroborate the conclusions presented here. 21

The ‘pH jump’ phenomenon, which takes place when the highly concentrated KAc deicer 22 comes in contact with calcium hydroxide (11-14), does not appear to be relevant to the field 23 conditions, also presumably due to the fact that, despite heavy surface application, the deicer 24 apparently does not penetrate significantly into the pavement. Only limited penetration was 25 found even when KAc deicers were ponded over concrete cylinders for periods of up to 6 months 26 under accelerated laboratory-based exposure conditions. In the airport pavement cores 27 examined, even in the extreme top layers of the pavement, where the deicer has permeated to 28 some extent, the concentrations detected were far below the range in which the pH jump reaction 29 mechanism would be applicable. 30 31 ACKNOWLEDGEMENTS 32 The authors gratefully acknowledge the support of the Innovative Pavement Research 33 Foundation (IPRF) for funding this research. The assistance of Tae Hwan Kim in determination 34 of the deicer penetration in laboratory concretes after 6 months is greatly appreciated. The 35 authors would also like to thank Janet Lovell for her help in the experimental part of the 36 research. 37 38 REFERENCES 39 1. Berube, M. A., and J. Frenette. Testing Concrete for AAR in NaOH and NaCl Solutions at 40

38ºC and 80ºC. Cement and Concrete Composites, Vol. 16, No. 3, 1994, pp. 189–198. 41 2. Kawamura, M. and M. Ichise. Characteristics of Alkali-Silica Reaction in the Presence of 42

Sodium and Calcium Chloride. Cement and Concrete Research, Vol. 20, No. 5, 1990, pp. 757-43 766. 44

3. Chatterji, S., N. Thaulow, A. D. Jensen, P. Christensen. Studies of Alkali-Silica Reaction. Part 45 3. Mechanisms by which NaCl and Ca(OH)2 Affect the Reaction. Cement and Concrete 46

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Research, Vol 16, 1986, pp. 246-254. 1 4. Chatterji, S., N. Thaulow and A. D. Jensen. Studies of Alkali-Silica Reaction. Part 4. Effect of 2

Different Salt Solutions on Expansion. Cement and Concrete Research, Vol 17, 1987, pp. 3 777-783. 4

5. Berube, M.A., J. F. Dorion, J. Duchesne, B. Fournier and D. Vezina. Laboratory and Field 5 Investigations of the Influence of Sodium Chloride on Alkali-Silica Reactivity. Cement and 6 Concrete Research, Vol. 33, 2003, pp. 77-84. 7

6. Van Dam, T. J. Design and Construction of Concrete Pavement for Aircraft Deicing 8 Facilities. Research Report IPRF-01-G-002-03-3. Innovative Pavement Research Foundation, 9 Skokie, Ill., 2006, p. 89. 10

7. Wijoyo, I. J. The Durability of Airfield Concrete Exposed to Aircraft Deicers. M.S. Thesis, 11 University of Waterloo, Ontario, Canada, 2007, p. 105. 12

8. Rangaraju, P. R. and J. Olek. Potential for ASR in Concrete in Presence of Airfield Deicing 13 Chemicals. Research Report IPRF-01-G-002-03-9. Innovative Pavement Research 14 Foundation, Skokie, Ill., 2007, p. 127. 15

9. Rangaraju, P. R., K. R. Sompura and J. Olek. Investigation into Potential of Alkali-Acetate 16 Deicers to cause Alkali-Silica Reaction in Concrete. In Transportation Research Record: 17 Journal of the Transportation Research Board, No. 1979, Transportation Research Board of 18 the National Academies, Washington, D.C., 2006, pp. 69-78. 19

10. Rangaraju, P. R., K. R. Sompura and J. Olek. Modified ASTM C 1293 Test Method to 20 Investigate Potential of Potassium-Acetate Deicer Solution to Cause Alkali Silica Reaction. 21 In Transportation Research Record: Journal of the Transportation Research Board, No. 22 2020, Transportation Research Board of the National Academies, Washington, D.C., 2007, 23 pp. 50-60. 24

11. Diamond, S., L. Kotwica, J. Olek, P. Rangaraju, and J. Lovell. Chemical Aspects of Severe 25 ASR Induced by Potassium Acetate Airfield Pavement Deicer Solution. Proceedings of the 26 8th CANMET International Conference on Advances in Concrete Technology, Canada Center 27 for Minerals and Energy Technology, Montreal, Que., Canada, 2006, pp. 261–278. 28

12. Stark, J. and C. Giebson. Influence of Acetate and Formate Based Deicers on ASR in 29 Airfield Concrete Pavements. Proceedings of the 13th International Conference on Alkali-30 Aggregate Reaction in Concrete (ICAAR), Trondheim, Norway, 2008, pp. 686–695. 31

13. Giebson, C., K. Seyfarth and J. Stark. Influence of Acetate and Formate-Based Deicers on 32 ASR in Airfield Concrete Pavements. Cement and Concrete Research, Vol. 40, 2010, pp. 33 537–545. 34

14. Struble, L. and L. Ai. pH of Potassium Acetate Deicing Solution. Technical Note No. 36. 35 Center for Excellence of Airport Technology, Urbana, Ill., 2008, p. 12. 36 http://www.ceat.uiuc.edu/PUBLICATIONS/technotes/TN36_struble_feb2008.pdf. Accessed 37 Oct. 30, 2009. 38

15. Bates, T. J., T. J. Van Dam, D. Gress, K. Peterson and L. Sutter. Comparison of Field and 39 Laboratory Concrete Exposed to Potassium Acetate Runway Deicer. Proceedings of the 40 First International Conference on Recent Advances in Concrete Technology, Washington 41 DC, USA, 2007. 42

16. Balachandran, C. Potential for Inducing and Accelerating Alkali Silica Reaction in Concretes 43 Exposed to Potassium Acetate Deicer: Laboratory and Field Studies. M.S. Thesis, Purdue 44 University, West Lafayette, IN., 2009, p. 409 45

17. ASTM C 1556-04. Standard Test Method for Determining the Apparent Chloride Diffusion 46

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Coefficient of Cementitious Mixtures by Bulk Diffusion. ASTM Volume 04.02 Concrete and 1 Aggregates, West Conshohocken, PA, 2004. 2

18. Wang, K., D. E. Nelsen and W. A. Nixon. Damaging Effects of Deicing Chemicals on 3 Concrete Materials. Cement and Concrete Composites, Vol. 28, 2006, pp 173-188. 4

TRB 2011 Annual Meeting Paper revised from original submittal.