Mitigation of ASR in the Presence of Pavement Deicing Chemicals

Transcription

1 Mitigation of ASR in the Presence of Pavement Deicing Chemicals IPRF Project 01-G % On-Board Review Meeting (Interim Report) September 8, 2005 Room G212, Civil Engineering Building Purdue University West Lafayette, IN Principal Investigator Prasada Rao Rangaraju, Ph.D., P.E. Assistant Professor of Civil Engineering 208, Lowry Hall, Department of Civil Engineering Clemson University Clemson, SC, Phone: (864) ; Fax: (864)

2 I. INTRODUCTION This report constitutes the 60% review report for IPRF Project 01-G study Mitigation of ASR in the Presence of Pavement Deicing Chemicals. This report is divided into three parts. Part-I covers the scope of the mitigation study, the experimental materials, test methods and the research approach. Part-II covers the evaluation of the ASR mitigation potential of fly ashes and slag in presence of the deicer chemicals. In this part, results of modified ASTM C 1260 tests, changes in dynamic modulus of elasticity of mortar bars, and images from visual and SEM-EDX examination are presented. Part-III presents the results of modified ASTM C 1260 tests conducted to evaluate lithium admixtures for their ASR mitigation potential in presence of potassium acetate deicer solution and 1N NaOH solution. The scope of this research and the research approach in this study were developed based on some important observations made in the IPRF 03-9 study Potential for ASR in the Presence of Pavement Deicing Chemicals. The materials and test methods used in IPRF 04-8 study are from the same sources as those used in the IPRF 03-9 study. The results of unmitigated tests conducted in the IPRF 03-9 study were therefore considered as control results to evaluate the effectiveness of the selected mitigation measures. Only a brief description of the materials and test methods used in this study will be presented in this document. For a more detailed description on the materials used and the test methods employed, the readers are referred to the 20% and 60% review reports for the IPRF 03-9 study [1, 2]. IPRF 04-8 Study 60% Report 2

3 PART 1 INTRODUCTION, SCOPE OF PROJECT, MATERIALS AND TEST METHODS IPRF 04-8 Study 60% Report 3

4 1. SCOPE OF THE IPRF 04-8 STUDY IPRF 04-8 study on mitigation of ASR in presence of deicers was initiated after preliminary findings from IPRF 03-9 study suggested that the airfield pavement deicers indeed caused significant expansions and cracking in mortar bars containing reactive aggregates. The scope of this research project is limited to evaluating the effectiveness of selected mitigation measures against the effects of potassium acetate deicers. Additional tests were also conducted using 1N NaOH soak solution as reference. Other deicers such as sodium acetate, sodium formate and potassium formate are not considered in this study. The mitigation measures studied in this research include: Fly ash o Low-Lime Fly Ash o Intermediate-Lime Fly Ash o High-Lime Fly Ash Slag 30% Lithium Nitrate Solution The scope of this study was limited to conducting a series of modified ASTM C 1260 tests using four different sources of reactive aggregates and two different sources of non-reactive aggregates. In addition, other tests such as dynamic modulus of elasticity of mortar bars, ph of the soak solution, and SEM-EDX investigation are being conducted to understand the mechanisms involved. 2. EXPERIMENTAL PROGRAM 2.1 MATERIALS Deicers and Reagents: In this study, a commercial grade potassium acetate deicer that has a concentration of 50% wt. solution (6.4 molar) was used as a soak solution in the modified ASTM C 1260 tests. The choice of 50% solution as soak solution in the modified ASTM C 1260 test was based on practical and realistic considerations. In routine anti-icing operations, a 50% wt. potassium acetate solution is used over the concrete pavement surface, whereas in deicing operations, solid deicers such as sodium acetate are applied on snow or ice to melt it. Though the melting action of snow and ice will dilute the concentration of the deicers, it is very likely that with repeated applications of the deicers and through repeated cycles of freezing and thawing and wetting and drying, the pore solution within the concrete, particularly in the near-surface region, would go through periodic cycles of dilution and concentration. Therefore, the use of 50% wt. solution of potassium acetate deicer presents a realistic, yet severe exposure condition for investigating the influence of deicers. Also, a reagent grade sodium hydroxide (NaOH) was used in this study to investigate the effectiveness of mitigation measures in presence of 1N sodium hydroxide soak solution in the modified ASTM C 1260 test. IPRF 04-8 Study 60% Report 4

5 Aggregates: In this study, four types of reactive aggregates and a reference non-reactive aggregate were used. The non-reactive aggregate is a quarried dolomite from Illinois that has an established history of good field performance and has been used a reference non-reactive aggregate in other laboratory studies [3]. The four reactive aggregates include: Spratt Limestone This aggregate is obtained from Spratt quarry in Ontario Province of Canada. It primarily consists of calcite with minor amounts of dolomite and about 10% insoluble residue. The reactive component of the rock is reported to consist of 3% to 4% of microscopic chalcedony and black chert, which is finely dispersed in the matrix [4]. This aggregate has an established history of being alkalisilica reactive in field structures and has been used as a reference aggregate in numerous ASR studies. NM Rhyolite A reactive gravel from Las Placitas Gravel Pit from Bernalillo County in New Mexico. This aggregate primarily consists of rhyolite that has shown very high levels of reactivity [3, 5]. NC Argillite This aggregate is a quarried material from the slate belt of North Carolina from Gold hill Quarry in North Carolina. This aggregate primarily consists of reactive metatuff/argillite. This aggregate has an established history of poor field performance in several bridge structures in North Carolina [6]. SD Quartzite This aggregate is obtained from crushing quarried rock from Sioux Falls quarry, located in the southeastern South Dakota. This aggregate consists of strained quartz grains that are cemented with interstitial secondary quartz cement. In addition, the interstitial matrix also consists of microcrystalline quartz, hematite and kaolinite. This aggregate has an established history of reactivity in concrete pavements in Minnesota and South Dakota [7, 8] Cement: In this study a high-alkali cement (Type I) with a Na 2 O equivalent of 2% and an autoclave expansion of 8% was used. The chemical composition of the cement is provided in Table Supplementary Cementing Materials (SCMs): In this study, three fly ashes with different lime (CaO) contents (low 5.2% CaO; intermediate 15.7% CaO; and high 29.4% CaO) and a ground granulated blast furnace (GGBF) slag (Grade 120) were used. In this initial phase of research, fly ashes and slag were incorporated in the mix by replacing 25% and 40% portland cement by mass, respectively. Additional testing is presently underway to assess the effectiveness of fly ash at 15% and 35% replacement levels and slag at 50% replacement level. The chemical composition of the fly ashes and the slag are provided in Table 1. IPRF 04-8 Study 60% Report 5

6 TABLE 1 - Chemical Composition of Cementitious Materials Used in the Standard and Modified ASTM C 1260 Tests Oxide, % High- Alkali Cement Low- Lime Fly Ash Intermediate Lime High Lime Slag SiO Al2O Fe2O CaO MgO SO Available Alkali LOI Na2O equivalent K2O Insoluble Residue C3A C3S TiO Mn2O Lithium Admixture A commercially marketed lithium admixture (30% lithium nitrate solution) for ASR mitigation was used in this study. This liquid is an odorless white to yellow colored solution with a ph ranging between 7 and 9.5 at 25 C. The specific gravity of this solution is between 1.2 to 1.3 g/cc, at 25 C TEST METHODS Standard ASTM C 1260 Test Procedure [9] The standard ASTM C 1260 test known as Accelerated Mortar Bar Test is a method to assess the reactivity of aggregates. In this test, mortar bars (25 mm x 25 mm x 285 mm) with gage studs at ends are prepared at a water-to-cement ratio of 7. The aggregate-to-cement ratio, by mass, is maintained at After 24 hours of curing in a moist cabinet, the mortar bars are demolded. The mortar bars are then transferred into a storage container with sufficient water to immerse all samples. The sealed container is placed in an oven at 80ºC for 24 hours. After 24 hours, the mortar bars are removed from the oven and a zero reading is taken. The mortar bars are subsequently transferred into a 1 N sodium hydroxide solution, which is preheated to 80ºC. Length change readings are taken thereafter at periodic intervals to determine the percent expansion. In this research, the length-change measurements were taken up to 56 days. Generally, an expansion of 0.1% or less at 14 days of immersion in the sodium hydroxide solution is considered to indicate the innocuous nature of the aggregate. Expansion greater than % at 14 days is considered to indicate the potentially reactive IPRF 04-8 Study 60% Report 6

7 nature of aggregate. Expansions in between 0.1% and % require additional confirmation by either conducting petrographic examination (ASTM C 295), concrete prism test (ASTM C 1293), or by evaluating the field performance to ascertain the reactivity of the aggregates Modified ASTM C 1260 Test to Evaluate SCMs Two modifications to the standard ASTM C 1260 test were adopted to evaluate the ASR mitigation potential of fly ashes and slag in the presence of potassium acetate deicer solution. These modifications included (i) using a 50% wt. solution of potassium acetate deicer as a soak solution for mortar bars, instead of a 1N NaOH solution (ii) replacing portion of the portland cement in the mortar mixtures with supplementary cementing material. The procedure to prepare mortar bar specimens and their subsequent storage regime is identical to the procedure described in standard ASTM C 1260 test, with exception of the storage duration. In this research, the mortar bars were stored for 56 days in the soak solution, instead of typical 14 days as required in the standard ASTM C 1260 test procedure. The extended testing was conducted to assess the effectiveness of mitigation measures in suppressing the effects of ASR at later ages (i.e. > 14 days). During the course of 56 days, periodic length-change measurements were taken at 0, 3, 7, 11, 14, 21, 28, 42 and 56 days. The results of all the standard and modified ASTM C 1260 tests discussed in this research study are based on an average of readings obtained from 4 mortar bars Modified ASTM C 1260 Test to Evaluate Lithium Admixtures Potassium Acetate Deicer Soak Solution In case of evaluation of lithium nitrate solution as a potential mitigation measure for ASR induced by deicer solutions, initially a modified ASTM C 1260 test procedure was proposed in which the soak solution would consist of 50% potassium acetate solution with adequate lithium nitrate solution to maintain a range of Li/K molar ratios from 0.5 to However, soon it was realized that it was difficult, if not impossible, to dissolve adequate amounts of lithium nitrate salt, in a 50% solution of potassium acetate to achieve the desired levels of Li/K molar ratio. Based on this finding, the test matrix for evaluating lithium nitrate admixture was altered and expanded to study three different scenarios: (i) (ii) Lithium nitrate admixture in the mortar bar only, with 50% potassium acetate deicer soak solution. The dosage of lithium in the mortar bars was based on the Li/Na molar ratio of the mix, with Na being the alkali content of the cement used. In this study the Li/Na ratios of 5, to 0.50, 0.75 and were used. Lithium nitrate admixture in the soak solution only In this study, the lithium nitrate solution was added only to the potassium acetate deicer soak solution, and not in the mortar bars. Also in this study, the influence of concentration of potassium acetate solution was evaluated at different levels of lithium dosage. Table 2 shows the compositions of soak solutions employed in this study. IPRF 04-8 Study 60% Report 7

8 TABLE 2 Compositions of Potassium Acetate Lithium Nitrate Combined Soak Solutions Evaluated in this Study Li/K Concentration of PA Deicer Solution Molar 1M 2M 3M 6.4M 0.19 X X X X 0.74 X X X None Based on the results from these studies, and if necessary, a third series of tests will be conducted in which lithium nitrate solution will be added to the mortar bars and to the soak solution as discussed below. (iii) Lithium admixture in bar and soak (If Necessary) a. Li/K molar ratios of soak solutions from 5 to for a base concentration of potassium acetate at 3M N NaOH Soak Solution Parallel studies were also conducted with 1N NaOH solution for all the three different scenarios mentioned above, i.e.: (i) Lithium admixture in the bar only at Li/Na molar ratio of 3, 0.74, and 1.25 (ii) Lithium admixture in the soak solution only at Li/Na molar ratio of 3, 0.74, and 1.25 (iii) Lithium admixture in the bar and the soak solution at Li/Na molar ratio of 3, 0.74, and Dynamic Modulus of Elasticity The dynamic modulus of elasticity (DME) of the mortar bars was measured at periodic intervals to quantify the physical distress occurring in the mortar bars subjected to the standard and modified ASTM C 1260 tests. The DME values were determined using the resonant frequency method based on impulse excitation technique based on ASTM E [10]. A GrindoSonic TM instrument was used to determine the resonant frequencies of the mortar bars. In this test, the mass and the resonant frequency of the mortar bar specimens was determined soon after taking the length-change measurements. For the sake of simplicity, the dimensions of the mortar bars were assumed to be constant (i.e., 25mm x 25mm x 285mm) and the effects of the metal gage studs at the ends of the bars were neglected, as it was a common factor for all measurements and would have a relatively small effect on the DME results. DME values of mortar bars were calculated for the same ages at which length-change measurements were made. Changes in DME values were correlated with expansion measurements to understand the progressive deterioration in stiffness of the mortar bars SEM and EDX Analyses SEM in back-scattered mode and EDX analysis were conducted on polished sections of mortar bars from standard and modified ASTM C 1260 tests, using a Hitachi S3500N electron microscope. The instrument was operated at an accelerating voltage of 20KeV, in a IPRF 04-8 Study 60% Report 8

9 variable pressure mode. The samples for the investigation were prepared by slicing the bars in a slow-speed diamond saw followed by polishing them on a series of magnetic grit pads on a lapping wheel. 2.3 SAMPLE IDENTIFICATION A specific notation scheme was adopted for the tests conducted in this experimental program, in order to identify the combinations of aggregate, supplementary cementing material (SCM), SCM replacement level and the soak solution type. Since various combinations of materials were used in this study, specific abbreviations were used for the materials and test conducted. The aggregate sources were identified as: (i) NM - Rhyolite from New Mexico, (ii) SP - Spratt Limestone from Ontario, Canada (iii) NC - Argillite from North Carolina (iv) SD - Quartzite from South Dakota, and (v) IL - Dolomite from Illinois The soak solutions were identified as 1N for 1 Normal NaOH solution and PA for 50% wt. solution of potassium acetate deicer. The cement replacement percent by mass was indicated by either 25 or 40 for fly ashes and slag, respectively. The three fly ashes used were identified based on their source. Low lime fly ash was identified as DO (Dolet Hills Power Plant, LA), intermediate lime fly ash as CC (Coal Creek Power Plant, ND) and high lime fly ash as PN (Port Neal Power Plant, IA). Ground granulated blast furnace slag is identified as SL in the mix notation. For example, a test in which Spratt limestone is tested with 25% high lime fly ash in potassium acetate deicer solution would be identified as SP-25-PN (PA). 2.4 TEST MATRIX In this research study, a total of 140 standard and modified ASTM C 1260 tests were conducted to determine the mitigation effects of selected SCMs and lithium admixtures. Comparator readings were taken at 0, 3, 7, 11, 14, 21, 28, 42 and 56 day test ages to assess the length-change in the mortar bars. At these same test ages, dynamic modulus of elasticity of mortar bars for selected tests was recorded to monitor any significant changes. Also, ph of selected soak solutions was monitored. SEM/EDX examination of selected mortar bars was also conducted to ascertain the effects of the reaction on microstructure and composition of the products. IPRF 04-8 Study 60% Report 9

10 PART- II EVALUATION OF ASR MITIGATION POTENTIAL OF FLY ASHES IN PRESENCE OF DEICERS IPRF 04-8 Study 60% Report 10

11 3. EVALUATION OF ASR MITIGATION POTENTIAL OF FLY ASHES IN PRESENCE OF DEICERS 3.1 RESULTS OF STANDARD AND MODIFIED ASTM C 1260 TESTS Figures 1 through 4 show the expansion data in the standard and modified ASTM C 1260 tests for each of the four reactive aggregates - Spratt limestone, NM rhyolite, NC argillite, and SD quartzite, respectively. Figure 5 shows the expansion behavior of mortar bars containing non-reactive IL dolomite aggregate. Expansion data in these Figures illustrate the ASR mitigation potential of fly ashes in presence of 1 N NaOH and potassium acetate soak solutions Spratt Limestone Figure 1A shows the expansions of mortar bars containing Spratt limestone and combinations of fly ash and cement, soaked in 1 N NaOH solution. Based on the expansion of the control bars (with only portland cement) at 14 days (~0.38%), it is evident that this aggregate is considered highly reactive. Figure 1A also shows the expansion behavior of mortar bars with three different fly ashes. It is evident from the Figure that the effectiveness of fly ashes in mitigating the expansion at 25% replacement level depends on the specific fly ash used, particularly its lime content. The low-lime and intermediate-lime fly ashes have shown significant mitigation ability, while the high-lime ash has been ineffective. Figure 1B shows the expansions of mortar bars containing Spratt limestone and combinations of fly ash and cement, soaked in 50% wt. solution of potassium acetate. Based on the expansion of control bars (plain cement) at 14 days (~0.74%), it is evident that Spratt limestone is highly reactive in presence of potassium acetate deicer solutions. However, mortar bars containing low-lime and intermediate-lime fly ashes, show considerably less expansion compared to control bars. In this regard, the use of high-lime fly ash has not been effective in mitigating expansion induced by either 1 N NaOH solution or potassium acetate solution NM Rhyolite Figure 2A and 2B show the expansion of mortar bars containing New Mexico rhyolite aggregate in 1 N NaOH and potassium acetate deicer soak solutions, respectively. Based on the expansion data of control mortar bars from these Figures it is evident that this aggregate is highly reactive in presence of both 1N NaOH soak solution and the potassium acetate deicer soak solution. However, the rate of expansion of mortar bars in potassium acetate deicer solution is considerably higher than in 1N NaOH solution. Expansion behavior of mortar bars with fly ashes in Figures 2A and 2B suggest that only low-lime fly ash provides considerable mitigation up to 14 days with both 1N NaOH solution and potassium acetate deicer solution. However, beyond 14 days even low-lime fly ash at 25% cement replacement level, does not provide any mitigation for this aggregate. It is not clear at this time, the reason for the sudden increase in expansion of mortar bars containing low-lime fly ash beyond 14 days. Similar behavior was observed in case of intermediate-lime fly ash at 7 days. In case of mortar bars with high-lime fly ash, extremely high expansions were observed at very early ages in both 1 N NaOH and potassium acetate soak solutions. IPRF 04-8 Study 60% Report 11

12 3.1.3 NC Argillite Figure 3A and 3B show the expansion of mortar bars containing North Carolina argillite in 1N NaOH and potassium acetate deicer soak solutions, respectively. Based on the expansion behavior of the control bars data, it is evident that this aggregate is highly reactive in both 1N NaOH and potassium acetate deicer soak solutions. However, the rate of expansion of mortar bars in potassium acetate solution is considerably higher than in 1 N NaOH solution. Also, the expansion of mortar bars at 14 days (typically considered in characterizing the aggregate reactivity) is substantially different between the two soak solutions. This indicates that the aggregate reactivity, as characterized by the standard ASTM C 1260 test, may not be very representative in situations where exposure to potassium acetate deicer solutions is to be expected. In terms of the mitigation potential of the fly ashes, it is evident that the high-lime fly ash is highly ineffective in mitigating the expansions in both 1N NaOH and potassium acetate soak solutions. Particularly, in potassium acetate soak solutions, the presence of high-lime fly ash in mortar bars causes even higher levels of expansion than control bars. With NC argillite aggregate, intermediate and low-lime fly ashes appear to be effective in mitigating the expansions in mortar bars in 1N NaOH and potassium acetate soak solutions. In particular, these ashes appear to be more effective in mitigating expansions in potassium acetate solutions than in 1 N NaOH solution SD Quartzite Figure 4A and 4B show the expansions of mortar bars containing SD quartzite in 1N NaOH and potassium acetate deicer soak solutions, respectively. It is evident from the expansion behavior of control bars that, this aggregate is highly reactive in the presence of 1N NaOH and potassium acetate deicer solutions. Similar to the behavior of NC argillite, mortar bars containing SD quartzite show almost twice the expansion with potassium acetate deicer solution, compared to 1N NaOH solution at 14 days. From a mitigation standpoint, the low-lime and the intermediate-lime fly ashes appear to be highly effective in mitigating mortar bars expansions in potassium acetate deicer solutions, compared to 1N NaOH solution. On the contrary, mortar bars with high-lime fly ash showed higher levels of expansion in potassium acetate solution than 1 N NaOH solution. Also, mortar bars containing high-lime fly ash showed more expansion than control bars in both potassium acetate and 1 N NaOH solutions IL Dolomite (Reference Non-Reactive Aggregate) Figure 5A and 5B show the expansion of mortar bars containing IL dolomite in 1N NaOH and potassium acetate deicer soak solutions, respectively. IL dolomite has an established history as a non-reactive aggregate [3]. Modified ASTM C 1260 tests on mortar bars containing low-lime and intermediatelime, fly ashes indicate no significant expansion in either 1 N NaOH solution or potassium acetate deicer solution. Mortar bars containing high-lime fly ash show slightly higher levels of expansion in potassium acetate deicer solution, compared to 1 N NaOH solution. However, the magnitude of these expansions is relatively low compared to other reactive aggregates as seen in Figure 1 through 4. IPRF 04-8 Study 60% Report 12

13 4. EVALUATION OF ASR MITIGATION POTENTIAL OF SLAG IN PRESENCE OF DEICERS 4.1 RESULTS OF MODIFIED ASTM C 1260 TESTS Figures 6A and 6B illustrate the potential of slag to mitigate expansion in mortar bars containing reactive and non-reactive aggregates in the modified ASTM C 1260 test procedure, using 1N NaOH and potassium acetate deicer soak solutions, respectively. It is evident from the data that slag at 40% cement replacement level, is not very effective in mitigating expansions in potassium acetate solution. In particular, mortar bars containing NM rhyolite show very rapid and excessive expansions within a short duration of 7 days. Other aggregates show similar behavior, although in a less pronounced manner. The nonreactive IL dolomite does not show any significant expansion in either of the soak solutions. Based on this data, it appears that slag at 40% replacement of cement, may not be very effective in mitigating expansions in potassium acetate deicer solutions. In case of 1 N NaOH soak solution, mortar bars containing slag show lower expansions, particularly at early age (i.e. < 14 days), however, upon subsequent storage, these bars show significantly higher levels of expansion. 5. RESULTS OF DYNAMIC MODULUS OF ELASTICITY (DME) Figure 7 shows the drop in dynamic modulus of elasticity of mortar bars for each of the four reactive aggregates containing the three fly ashes, in 1 N NaOH and potassium acetate deicer soak solutions. Based on the data presented in this Figure, it is evident that mortar bars containing high-lime fly ash (PN) show a pronounced drop in DME values both in 1 N NaOH and potassium acetate deicer solutions. This change in dynamic modulus is consistent with the expansion data presented in previous Figures. Mortar bars prepared with Spratt limestone, NC argillite and SD quartzite and containing low-lime fly ash (DO) and intermediate-lime fly ash (CC) showed excellent performance in potassium acetate deicer solution, compared to 1 N NaOH solution. This behavior is consistent with the expansion data in the modified ASTM C 1260 test, for the respective aggregate sources. Based on this data, it appears that low-lime and intermediate lime fly ashes are very effective in mitigating ASR induced by potassium acetate deicer. However, high-lime fly ash is not only ineffective in this regard, it is harmful as well. 6. RESULTS OF VISUAL AND SEM-EDX EXAMINATION Figure 8 shows the nature of cracking on the surface of mortar bars containing high-lime fly ash with each of the reactive aggregate soaked in potassium acetate deicer solution. Extensive cracking of the specimens was observed in most cases. Also, in most cases a pronounced arching of the mortar bars was observed, most noticeable in mortar bars prepared with NM rhyolite aggregate (see Fig. 8B). The inner side of the curvature in these mortar bars has always been the hand-finished surface. IPRF 04-8 Study 60% Report 13

14 Figure 9 shows the SEM micrographs and EDX spectra of polished sections of mortar bars prepared with NM rhyolite and each of the three fly ashes. Data for other aggregates is not provided in this paper for sake of brevity. It is evident from the Figure that extensive reaction of the aggregate could be observed in case of mortar bars prepared with high-lime fly ash. In these mortar bars, severe alteration of the microstructure of the cement paste was also noticed. In particular, the reaction product (i.e. ASR gel) did not possess its characteristics features of desiccation cracks and gel-like amorphous mass; rather it appeared to be a poorly crystalline material that is rich in potassium and silica, with minor amounts of calcium and aluminum (see Fig. 9(A2)). Figure 9D shows an EDX spectra from location indicated in Figure 9(A2). In case of mortar bar samples prepared with intermediate-lime fly ash for NM rhyolite aggregate, some reaction rims could be observed around the aggregate particles (see Fig. 9(B2)). These rims are rich in potassium and silica with minor amounts of calcium and aluminum. The level of distress observed in these mortar bars is consistent with the expansion observed in the modified ASTM C 1260 test. Mortar bars containing low-lime fly ash, do not show any significant distress (see Fig. 9C1 & Fig. 9C2). 7. DISCUSSION Based on the results of this study, it appears that low-lime and intermediate-lime fly ashes, at 25% replacement level, are effective in mitigating expansion due to ASR, induced by potassium acetate deicer. However, high-lime fly ash is very ineffective at this dosage. This finding is corroborated by the evidence from length-change measurements and changes in dynamic modulus of elasticity. Visual and SEM-EDX evidence also indicate the extent of the severe reactions that occurred in samples. In this study, ground granulated blast furnace slag at 40% replacement level was not found to be very effective in mitigating expansion due to ASR, induced by potassium acetate deicers. It is suspected that the high lime content of the slag may be interacting with the potassium acetate deicer solution and increasing the ph of the soak solution, thus rendering the conditions necessary for aggregates to react. Similar findings were observed with control mortar bars in an earlier study [1,2]. 8. CONCLUSIONS Based on the results obtained in this study, the following conclusions can be drawn in general: 1. The effectiveness of fly ash in mitigating ASR in presence of potassium acetate deicer depends on its composition, in particular, its lime content. In general, the lower the lime content of the fly ash, the more effective the fly ash is in reducing the expansions. 2. The influence of the lime content of the fly ash in mitigating ASR is more pronounced in case of the mortar bars soaked in potassium acetate deicer solution, compared to those soaked in 1 N sodium hydroxide solution. In particular, the use of high-lime fly ash at in mortar bars exposed to potassium acetate deicer solutions tends to aggravate the situation more, than to act as a mitigation agent. 3. Slag may be ineffective in mitigating expansions due to ASR induced by potassium acetate deicers, at 40% cement replacement level. IPRF 04-8 Study 60% Report 14

15 9. REFERENCES 1. Rangaraju, P.R., and Olek, J. Potential for Acceleration of ASR in Presence of Pavement Deicing Chemicals 20% Review Report, IPRF, Nov. 2004, p Rangaraju, P.R., and Olek, J. Potential for Acceleration of ASR in Presence of Pavement Deicing Chemicals 60% Review Report, IPRF, Sept. 2005, p Touma E. T., Fowler, D.W., Carasquillo R.L. Alkali-Silica Reaction in Portland Cement Concrete: Testing Methods and Mitigation Alternatives, Technical Report ICAR 301-1F, International Center for Aggregate Research, University of Texas, Austin, p. 520, Rogers, C. Multi-Laboratory Study of Accelerated Mortar Bar Test (ASTM C 1260) for Alkali-Silica Reaction, Cement, Concrete and Aggregates, CCAGDP, 21(2), 1999, p Barringer, W.L. Application of Accelerated Mortar Bar Tests to New Mexico Aggregates, Proceedings of 11 th International Conference on Alkali-Aggregate Reactions in Concrete, Quebec City, Quebec, Canada, June 2000., pp Leming, M. L. Mitchell, J.F., and Ahmad, S. H., Investigation of Alkali-Silica Reactivity in North Carolina Highway Structures, Center for Transportation Engineering Studies/ NCDOT Report , 1996, p Rangaraju, P.R. A Lab Study on Alkali-Silica Reactivity of Quartzites Used in Concrete Pavements of Minnesota. Proceedings of 11 th International Conference on Alkali-Aggregate Reactions in Concrete, Quebec City, Quebec, Canada, June 2000, pp Johnston, D.P., Surdahl, R., and Stokes, D.B. A Case Study of a Lithium-Based Treatment on an ASR-Affected Pavement. Proceedings of 11 th International Conference on Alkali-Aggregate Reactions in Concrete, Quebec City, Quebec, Canada, June 2000., pp ASTM C , Standard Test Method for Potential Alkali Reactivity of Aggregates (Mortar Bar Method), 100 Barr Harbor Drive, ASTM Book of Standard Volumes 04.02, West Conshohocken, PA, 19428, 2004, pp ASTM E , Standard Test Method for Dynamic Young s Modulus, Shear Modulus, and Poisson s Ratio by Impulse Excitation of Vibration, 100 Barr Harbor Drive, ASTM Book of Standard Volumes 03.01, West Conshohocken, PA, IPRF 04-8 Study 60% Report 15

16 n Age Age in (Days) (a) 1N NaOH Age Age in (Days) (b) 50% Potassium Acetate FIGURE 1(A) & 1(B) Expansion of Mortar Bars Containing Spratt Limestone Aggregate in Standard and Modified ASTM C1260 Tests with Fly ashes n n Age Age in (Days) n Fly Fly Ash-CC Ash-DO Age Age in (Days) (a) 1 N NaOH (b) 50% Potassium Acetate FIGURE 2(A) & 2(B) Expansion of Mortar Bars Containing New Mexico Rhyolite Aggregate in Standard and Modified ASTM C 1260 Tests with Fly ashes IPRF 04-8 Study 60% Report 16

17 n Age (Days) Age in (a) 1N NaOH Age Age in (Days) (b) 50% Potassium Acetate FIGURE 3(A) & 3(B) Expansion of Mortar Bars Containing North Carolina Argillite Aggregate in Standard and Modified ASTM C 1260 Tests with Fly Ashes n %Expansio n Age Age in (Days) (a) 1N NaOH (b) 50% Potassium Acetate FIGURE 4(A) & 4(B) Expansion of Mortar Bars Containing South Dakota Quartzite Aggregate in Standard and Modified ASTM C 1260 Tests with Fly Ashes n Age Age in (Days) IPRF 04-8 Study 60% Report 17

18 n Age (Days) (a) 1N NaOH n Age Age in (Days) (b) 50% Potassium Acetate FIGURE 5(A) & 5(B) Expansion of Mortar Bars Containing Illinois Dolomite Aggregate in Standard and Modified ASTM C 1260 Tests with Fly ashes n NM SP NC SD IL North Carolina Argilite Spratt Limestone South Dakota Quartzite New Mexico Rhyolite Illinois Dolomite n (a) 1N NaOH (b) 50% Potassium Acetate North Carolina Argilite Spratt Limestone South Dakota Quartzite New Mexico Rhyolite Illinois Dolomite NM SP NC SD IL FIGURE 6(A) & 6(B) Expansion of Mortar Bars Containing Slag in Modified ASTM C 1260 Test IPRF 04-8 Study 60% Report 18

19 5.0 (A1) Spratt Limestone, 1N NaOH (A1) Spratt Limestone, (1 N NaOH) (B1) (B1) Spratt Limestone, (50% Potassium Pot. Acetate) Acetate 5.0 Elastic Modulu DME (psi x 10^6 x 10 6 ) Elastic Modulu DME (psi x 10^6 x 10 6 ) Ash-CC Ash-PN (A2) (A2) New Mexico Rhyolite, (1 1N N NaOH) 5.0 Ash-PN Fly (A3) (A3) North Carolina Argilite Argillite, (1 N NaOH) 1N NaOH 5.0 Elastic Modulu DME (psi x 10^6 x 10 6 ) Elastic Modulu DME (psi x 10^6 x 10 6 ) Ash-DO Age in in Days (B2) (B2) New New Mexico Mexico Rhyolite,(50% Potassium Pot. Acetate) Acetate Fly Ash-PN Fly (B3) North (B3) North Carolina Carolina Argilite Argillite, (50% Pot. Pot. Acetate) Acetate Elastic Modulu DME (psi x 10^6 6 ) 3.0 Fly Fly Ash-CC Ash-CC Fly Ash-DO Age in in Days (A4) (A3) South Dakota Quartzite, (1 1N N NaOH) Elastic Modulu DME (psi x x 10^ ) Fly Ash-PN Fly South Dakota Quartzite (50% Pot. Acetate) (B4) (B4) South Dakota Quartzite, Pot. Acetate Elastic Modulus DME (psi x 10^6 x 10 6 ) Fly Fly Ash-DO DME (psi x 10 6 ) Elastic Modulu psi x 10^ IPRF 04-8 Study 60% Report 19

20 FIGURE 7 Drop in Dynamic Modulus of Elasticity of Mortar bars exposed to 1 N and potassium acetate soak solutions. Figure 8(A). Spratt Limestone in Potassium Acetate at 14 day with High Lime Fly Ash Figure 8(B). New Mexico in Potassium acetate at 14day with High-Lime Fly Ash Figure 8(C). North Carolina Argillite in Potassium Acetate at 14 day with High-Lime Fly Ash Figure 8(D). South Dakota Quartzite in Potassium Acetate at 14 day with High-Lime Fly Ash FIGURE 8 Visual images of mortar bars exposed to modified ASTM C 1260 at 14 day test age IPRF 04-8 Study 60% Report 20

21 PN CC DO Figure 9(A1) Figure 9(B1) Figure 9(C1) PN CC DO X Figure 9(A2) Figure 9(B2) Figure 9(C2) FIGURE 9(A,B,C) SEM micrographs and EDX Spectra from mortar bars with NM Rhyolite containing High-Lime (PN), Intermediate-Lime(CC) and Low Lime(DO) Fly Ash, soaked in Potassium Acetate for 56 days. C FIGURE 9(D) EDX Spectra at Location X in Fig. 9A2 IPRF 04-8 Study 60% Report 21