FINAL TECHNICAL REPORT September 1, 2005, through December 31, 2007

Project Title: EVALUATION OF SULPHATE ATTACK FROM ILLINOIS FLY

ASH ON CONCRETE STRUCTURES ICCI Project Number: 05-1/6.1B-3 Principal Investigator: Sanjeev Kumar, Southern Illinois University Carbondale Project Manager: Dr. Francois Botha, ICCI

ABSTRACT

Several projects have successfully been completed within the last decade where Illinois coal combustion products (CCPs) were used as a part of concrete and other value-added products. However, effects of high soluble sulfate content in Illinois fly ash, when used as environment, e.g. embankment, on the strength and durability of conventional concrete structures buried into this material have not received due attention. Consequently, utilization of Illinois CCPs is still very limited. Illinois Department of Transportation (IDOT) and City of Springfield (COS) are using several hundred thousand cubic yards of Illinois fly ash for construction of embankments for a major interchange in Springfield, Illinois. However, concerns about the high soluble sulfate content in the Illinois fly ash and uncertainty about its effects on the concrete structures, e.g. light pole and traffic light foundations, concrete pipes, and other similar structures, are limiting the possible use of larger quantities of the Illinois fly ash. Utilization of Illinois CCP could increase several folds if the effects of high sulfate content in the Illinois fly ash on the buried concrete structures are known. The objective of this project is to develop data to quantify the effects of high soluble sulfate content of Illinois fly ash on conventional concrete structures buried into this material. The goals of the proposed study have been accomplished by conducting a comprehensive laboratory and field evaluations. The project was intended to establish required data so that the engineering community and contractors can make informed decisions on the possible effects of high sulfate contents in the Illinois fly ash, if any, without the fear of jeopardizing the performance of concrete structures.

EXECUTIVE SUMMARY Fly ash has long been recognized as a construction material used frequently in portland cement and concrete products, structural fills, embankments, and road bases/subbases. Several projects have progressed over the last few years for large volume use of fly ash and bottom ash to make value-added marketable products, e.g., ceramic tiles, fiber-reinforced cement composites, bricks, piles, and other building materials. However, most of the projects completed on the large volume utilization of Illinois CCPs involved their use as a part of concrete or products. Although, it has been recognized that the Illinois CCPs have high soluble sulfate content, its effects when used as environment, e.g., embankment, on the strength and durability of concrete structures buried into this material have not received due attention. Recent tests conducted by Illinois Department of Transportation (IDOT) show soluble sulfates in the Illinois fly ash at a level which may be detrimental to concrete structures embedded into this material. The main objective of the proposed study is to develop required data to quantify the effects of high soluble sulfate content of Illinois fly ash on conventional concrete structures buried into this material. To achieve the intended objective, mortar samples were tested in the laboratory to evaluate the effect of soluble sulfates on the strength, length change, weight change, and relative dynamic modulus of the samples. In addition, tests were performed on concrete samples which were buried into the Illinois fly ash. Sample Preparation Cement mortar samples were prepared in general accordance with ASTM C305 “Standard Method of Mixing of Hydraulic Cement pastes and Mortars of Plastic Consistency”. Prisms of size 1 x 1x 11¼ inches having gage length of 10-inches and 2-inch cubes samples were prepared by tamping the mortars into the molds. Samples were allowed to cure in the molds for 24 hours and then in water for either 7 or 28 days. The samples were then placed in sulfate solution, or Illinois fly ash solution, and water. Samples placed in water were used as control samples to measure the relative effect. Concrete samples were also prepared in accordance with relevant ASTM standards. Prisms of size 2x2x12 inches having a gauge length of 10¾ inches and cylindrical samples of size 4 x 8 in. were prepared and buried into Illinois PCC fly ash. Similar samples were also buried into regular soil to be used as control samples. Testing Procedures Samples placed in the sulfate solution, fly ash solution, and water were removed at regular intervals to test for compressive strength, splitting-tensile strength, length change, weight change, and relative dynamic modulus based on fundamental transverse resonant frequency measurements. The concrete samples buried into the fly ash and regular soil were also removed and tested for compressive strength, splitting tensile strength, length change, weight change, and relative dynamic modulus. When cement mortar or concrete samples are placed in sulfate solution, fly ash solution, and water, the pH of the solution increases. Some studies suggest that during the sulfate

testing, the pH of the solution should be maintained close to 7. Therefore, a test setup shown in Figure 1 was manufactured to automatically control the pH of the sulfate and fly ash solutions to a value between 7 and 7.2. However, samples placed in the sulfate and fly ash solutions, without any control of pH, were also tested.

Figure 1: Testing of mortar samples placed in sulfate solution maintained at pH between 7 and 7.2 is in progress

Test Results Figure 2 shows the change in length of the prisms made from cement-sand mixtures and kept in sulfate solution and fly ash solution compared to those kept in water. The pH of the solution was not controlled. The samples were placed in sulfate and fly ash solutions after 7 days of curing. Results presented in Figure 2 show that the length of the samples increased with the increase in the age, irrespective of whether they were in sulfate solution or fly ash solution or water. It is important to note that the length change caused by the fly ash solution is greater than that caused by water but is less than the change caused by the sulfate solution prepared as per ASTM standards. Figure 3 shows the length change results for samples kept in fly ash solution maintained at pH between 7 and 7.2. Samples made from cement-sand-silica fume mixtures were also tested. The results show that the change in length of cement-sand (CM) samples placed in fly ash solution is higher compared to those which were placed in water. The samples with silica fume show lower length change than that was observed from cement-sand samples.

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Figure 2: Length change from cement mortar prisms submerged in sulfate solution, fly ash solution, and water (7-days curing in water and No pH control)

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Figure 3: Length change from mortar prisms of cement and cement + 5% silica fume submerged in fly ash solution and water (28-days curing in water and

automatic pH control) Figure 4 shows the compressive strength of cement-sand mortar samples submerged in the sulfate solution and fly ash solution compared to those kept in water. The pH of the solution was not controlled. The samples were placed in sulfate and fly ash solutions after 7 days of curing. Tests were performed at various curing ages. Results presented in Figure 4 show that the compressive strength of samples placed in water increased sharply and then the rate of increase in strength decreased. However, it is important to note that the compressive strength of samples placed in water kept increasing with curing age. On the other hand, samples placed in sulfate solution and fly ash solution showed increase in strength similar to that observed from samples placed in water but after about 60 days in sulfate or fly ash solution the strength decreased. The long term strength from samples placed in sulfate solution or fly ash solution was slightly

less than that was observed from samples placed in water. Samples submerged in fly ash solution performed better than those placed in the sulfate solution.

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Figure 4: Compressive strength of cement mortar samples submerged in sulfate

solution, fly ash solution, and water (No pH control) According to Mehta (2000) “the presence of high concentrations of sulfate in soil or water should not lead anyone to conclude that the concrete deterioration must have been caused by chemical sulfate attack”. In general, the results obtained from the tests performed show that the samples placed in the Illinois fly ash solution performed better than those placed in the sodium sulfate solution prepared as per ASTM standards. Negligible salt crystallization was observed in the samples placed in the Illinois fly ash solution whereas significant salt crystallization was observed in the samples placed in sodium sulfate solution. Therefore, it was concluded that the concrete placed in Illinois fly ash is not likely to get damaged due to salt crystallization, the phenomenon which is referred to as physical sulfate attack.

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OBJECTIVES The Illinois Department of Transportation (IDOT) and City of Springfield (COS) are using several hundred thousand cubic yards of Illinois fly ash for construction of embankments for a major interchange in Springfield, Illinois. However, concerns about the high soluble sulfate content in the Illinois fly ash and its effects on the concrete structures, e.g. light pole and traffic light foundations, concrete pipes, and other similar structures, are limiting the possible use of larger quantities of the Illinois fly ash. Therefore, the main objective of the proposed study is to develop required data to quantify the effects of high soluble sulfate content of Illinois fly ash from City Water Light and Power (CWLP) on conventional concrete structures buried into this material.

INTRODUCTION AND BACKGROUND Several million tons of fly ash, bottom ash, and boiler slag are currently produced annually by coal burning power-generating plants. The largest volume of coal combustion products in Illinois consists of fly ash and bottom ash. Typically, most of these ashes are disposed off by dumping in ash ponds or hauling to landfills. Because of the increasing costs associated with coal combustion ash disposal and the environmental regulations in place; the federal, state and local agencies, as well as the private sector have been taking an active part in sponsoring and promoting a growing number of programs and research studies to develop alternate methods for profitable and environmentally safe uses of these products. Fly ash has long been recognized as a construction material used frequently in portland cement and concrete products, structural fills, embankments, and road bases/subbases. Several projects have progressed over the last few years for large volume use of fly ash and bottom ash to make value-added marketable products, e.g., ceramic tiles, fiber-reinforced cement composites, bricks, piles, and other building materials. However, most of the projects completed on the large volume utilization of Illinois CCPs involved their use as a part of concrete or products. Although, it has been recognized that the Illinois CCPs have high soluble sulfate content, its effects when used as environment, e.g., embankment, on the strength and durability of concrete structures buried into this material have not received due attention. Recent tests conducted by Illinois Department of Transportation (IDOT) show soluble sulfates in the Illinois fly ash at a level which may be detrimental to concrete structures embedded into this material. To achieve the intended objective, the execution of the project was divided into three tasks. The purpose of Task I of the project was to study the effects of soluble sulfates on cement mortar samples by using the sulfate solution prepared as per ASTM standard under controlled laboratory conditions. Task II of the project consisted of preparing Illinois fly ash solution (leachate) and studying the effects of sulfates in the Illinois fly ash on cement mortar samples under controlled laboratory conditions. Task III of the project consisted of preparation of conventional concrete specimens and burying them

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into Illinois fly ash and regular soil in the field to evaluate the effects of sulfates on the concrete structures under actual environmental conditions. Based on our discussions with IDOT engineers, the following matrices were prepared and tested in this study.

1. Portland cement-sand mortar mixes 2. Portland cement-sand-silica fume (5%) mortar mixes 3. Portland cement concrete mixes

EXPERIMENTAL PROCEDURES

Mixing Procedure for Preparing Mortar Samples – Tasks I and II The following mixing procedure as outlined in ASTM C305 was adopted for mixing cement-sand and cement-sand-silica fume matrices and preparing mortar samples. Figure 5 shows a picture of the mortar mixing in progress.

(1) The specified quantities of cement, sand, silica fume, and water were weighed using electronic scale.

(2) The dry paddle and the dry bowl were placed in the position in the mixer and all the mixing water was placed in the bowl.

(3) The mixer speed was adjusted to slow speed, i.e., 140 ± 5 rpm and the cement was added slowly into the water while the mixer is running. For matrices with silica fume, the measured quantity of silica fume was added immediately after the cement. The mixing continued for about 30 seconds.

(4) The entire quantity of sand was added slowly over a 30 second period, while mixing at the slow speed.

(5) Mixer was then stopped and the speed was adjusted to the medium speed, i.e., 285± 10 rpm. Mixing was then started again which continued for additional 30 seconds.

(6) Mixer was stopped again for 1.5 minute. During the first 15 second of this interval, the mortar that got collected on the sides of the bowl was quickly scraped down into the batch and the bowl was covered with a lid.

(7) Mixing was started again and continued again for one minute at the medium speed. Any mortar sticking to the sides of the bowl was quickly scraped down into the batch with the scraper.

(8) After completing mixing, flow of the matrices was checked by performing flow test and the samples were prepared.

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Figure 5: Mortar mixing in progress

Mixing Procedure for Preparing Concrete Samples – Task III The following mixing procedure was adopted for mixing conventional concrete and preparing concrete samples:

(1) The specified quantities of cement, fine and coarse aggregate, and water were weighed using electronic scale.

(2) An electronically driven counter-clock revolving pan mixer was used for batch

preparation. The pan was cleaned and dried prior to placement of the raw materials. Mixing was started by placing the coarse aggregate into the rotating pan and allowing it to blend with 1/3rd

of the mixing water for a period of 3 minutes. Subsequently, fine aggregate was slowly added and blended with another one third of the measured mixing water, and mixing continued for another 3 minutes. Next, the measured cement and the remaining mixing water were gradually added to the mixer. The mixing process continued for an additional 3 minutes to ensure proper blending.

(3) After mixing was completed, the slump test was performed as described by ASTM C 143 “Standard Test Method for Slump of Hydraulic Cement Concrete.” Each batch of concrete was tested for slump to ensure consistency of mixtures throughout the investigation.

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(4) The matrix was then used to prepare specimens for further testing. Testing Procedure for Mortar Samples – Tasks I and II The following three types of samples were prepared using the mortar mixes:

1. Prisms of size 1 x 1x 11¼ inches having gage length of 10-inches to perform length change, weight change, and relative dynamic modulus based on fundamental transverse resonant frequency tests.

2. Cubes of size 2-inch to perform compressive strength tests. 3. Cylindrical samples of size 2 x 4 inch to perform splitting-tensile strength tests.

All samples were allowed to cure in the molds for 24 hours and then in water for either 7 days or 28 days. After 7 days or 28 days of curing in water, the samples were placed in either sulfate solution, or Illinois fly ash solution, or left in water. Samples left in water were used as control samples to measure the relative effect. Samples placed in the sulfate solution, fly ash solution, and water were removed at regular intervals to test for compressive strength, splitting-tensile strength, length change, weight change, and relative dynamic modulus based on fundamental transverse resonant frequency measurements. When cement mortar or concrete samples are placed in sulfate solution, fly ash solution, or water, the pH of the solution increases. Some studies suggest that during the sulfate testing, the pH of the solution should be maintained close to 7. Therefore, a test setup shown in Figure 1 was manufactured to automatically control the pH of the sulfate and fly ash solutions to a value between 7 and 7.2. However, samples placed in the sulfate and fly ash solutions, without any control of pH, were also tested.

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Figure 1: Testing of mortar samples placed in sulfate solution maintained at pH between 7 and 7.2 is in progress (The same as presented in Executive Summary)

Figure 6 shows a picture of the RDM test on prism samples in progress. Figure 7 shows a picture of the compressive strength test on a cube sample in progress and Figure 8 shows a picture of the splitting-tensile strength on a cylindrical sample in progress.

Figure 6: RDM test on a prism sample in progress

Figure 7: Compression strength test on a cube sample in progress

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Figure 8: Splitting-tensile strength test on a cylindrical sample in progress Testing Procedure for Concrete Samples – Task III The following two types of samples were prepared using the mortar mixes:

1. Prisms of size 2 x 2 x 12 inches having gage length of 10¾-inches to perform length change, weight change, and relative dynamic modulus based on fundamental transverse resonant frequency tests.

2. Cylindrical samples of size 4 x 8 inch to perform compressive strength and splitting-tensile strength tests.

Samples from two types of concrete matrices, regular concrete and concrete with 5% silica fume, were prepared and tested. Regular concrete samples were buried into the Illinois fly ash and regular soil to evaluate the effect of high sulfate content in the Illinois fly ash under field conditions. The concrete samples with silica fume were only buried into Illinois fly ash. Samples buried in soil were used as control samples. Figure 9 shows a picture of the samples being placed into the Illinois fly ash.

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Figure 9: Placement of samples in Illinois fly ash in progress The concrete samples buried into the fly ash and regular soil were also removed and tested for compressive strength, splitting tensile strength, length change, weight change, and relative dynamic modulus. Ultrasonic Tests Ultrasonic tests were conducted on 2-inch cube samples to determine if this testing procedure could be used to detect changes in the samples caused by the sulfate attack. The samples were placed in the sulfate solution and fly ash solution such that only ½-inch of each sample was submerged in the solution. The level of the sulfate and fly ash solutions was maintained by designing and manufacturing the equipment shown in Figure 10.

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Figure 10: Test assembly for submerging samples for ultrasonic testing The ultrasonic test was performed by using two 75 KHz ultrasonic transducers in the transmit-receive mode. The ultrasonic signals were transmitted from a single point on one side of each sample but received at five points on the other side. Figure 11 shows the transmitting and receiving points on samples. After developing some amplification and some signal processing circuitry, tests were done by placing the two transducers on opposite sides. Figure 12 shows the ultrasonic test in progress.

Figure 11: Points used for transmitting and receiving ultrasonic signals

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Figure 12: Ultrasonic testing in progress

RESULTS AND DISCUSSION Tasks I and II Tests on Prism Samples Tasks I and II of the project consisted of studying the effects of soluble sulfates in the Illinois fly ash and standard sulfate solution on the cement mortar samples under controlled laboratory conditions. As discussed previously, two types of cement mortar mixes (cement-sand and cement-sand-silica fume), three types of solutions (sulfate solution prepared as per ASTM standard, Illinois fly ash solution, and water), and two types of pH control (automatic pH control and no pH control) were used as a part of Tasks I and II. In addition, tests were performed on two sets of samples, i.e., placing in sulfate and fly ash solutions after 7 days of curing in water and placing in sulfate and fly ash solutions after 28 days of curing in water. Figure 2 (the same figure as used in Executive Summary) shows the change in length of the prisms made from cement-sand mixtures and kept in sulfate solution and fly ash solution compared to those kept in water. The samples were placed in sulfate and fly ash solutions after 7 days of curing. The pH of the solution was not controlled. Results presented in Figure 2 show that the length of the samples increased with the increase in the age, irrespective of whether they were in sulfate solution or fly ash solution or water. It is important to note that the length change caused by the fly ash solution is greater than that caused by water but is less than the change caused by the sulfate solution prepared as per ASTM standards.

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Figure 2: Length change from cement mortar prisms submerged in sulfate solution, fly ash solution, and water (7-days curing in water and No pH control) -

The same as presented in Executive Summary Figure 3 (the same figure as used in Executive Summary) shows the length change results for samples kept in fly ash solution maintained at pH between 7 and 7.2. Samples made from cement-sand mixtures and cement-sand-silica fume mixtures were tested. The results show that the change in length of cement-sand (CM) samples placed in fly ash solution is higher compared to those which were placed in water. The samples with silica fume show lower length change than that was observed from cement-sand samples.

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Figure 3: Length change from mortar prisms of cement and cement + 5% silica fume submerged in fly ash solution and water (28-days curing in water and

automatic pH control) - The same as presented in Executive Summary Figure 13 shows the weight gain in the prisms made from cement-sand mixtures and kept in sulfate solution and fly ash solution compared to those kept in water. The samples

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were placed in sulfate and fly ash solutions after 7 days of curing. The pH of the solution was not controlled. Results presented in Figure 13 show that the weight of the samples increased with the increase in the age, irrespective of whether they were in sulfate solution or fly ash solution or water. It is important to note that the weight gain in samples placed in the fly ash solution is slightly lower than that gained by samples placed in water but is higher than that gained by samples placed in the sulfate solution prepared as per ASTM standards. Figure 14 also shows the weight gain results similar to those shown in Figure 13 except that the samples were cured in water for 28 days before placing them in sulfate and fly ash solutions. Figure 14 shows that the weight gain in the samples placed in sulfate and fly ash solutions was almost the same as that was observed in samples placed in water.

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Figure 13: Weight gain from cement mortar prisms submerged in sulfate solution, fly ash solution, and water (7-days curing in water and No pH control)

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Figure 14: Weight gain from cement mortar prisms submerged in sulfate solution, fly ash solution, and water (28-days curing in water and No pH control)

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Figure 15 shows the relative dynamic modulus (RDM) of prisms made from cement-sand mixtures and kept in sulfate solution and fly ash solution compared to those kept in water. The samples were placed in sulfate and fly ash solutions after 28 days of curing. The pH of the solution was not controlled. Results presented in Figure 15 show that the RDM of samples placed in sulfate and fly ash solutions was slightly lower than that of samples placed in water.

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Figure 15: Relative Dynamic Modulus (RDM) from cement mortar prisms submerged in sulfate solution, fly ash solution, and water (28-days curing

in water and No pH control) Figure 16 shows the RDM results for samples kept in fly ash solution maintained at pH between 7 and 7.2. The results show that the RDM of samples prepared with 5% silica fume and placed in fly ash solution is almost the same as that of cement-sand samples placed in water. However, RDM of cement-sand samples placed in fly ash solution is slightly lower than those from similar samples placed in water.

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Figure 16: Relative Dynamic Modulus (RDM) from mortar prisms of cement and cement + 5% silica fume submerged in fly ash solution and water (28-days curing in

water and automatic pH control)

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Tests on Cube Samples Figure 4 (the same figure as used in Executive Summary) shows the compressive strength of cement-sand mortar samples submerged in the sulfate solution and fly ash solution compared to those kept in water. The pH of the solution was not controlled. The samples were placed in sulfate and fly ash solutions after 7 days of curing. Tests were performed at various curing ages. Results presented in Figure 4 show that the compressive strength of samples placed in water increased sharply and then the rate of increase in strength decreased. However, it is important to note that the compressive strength of samples placed in water kept increasing with curing age. On the other hand, samples placed in sulfate solution and fly ash solution showed increase in strength similar to that observed from samples placed in water but after about 60 days in sulfate or fly ash solution the strength decreased. The long term strength from samples placed in sulfate solution or fly ash solution was slightly less than that was observed from samples placed in water. Samples submerged in fly ash solution performed better than those placed in the sulfate solution.

Figure 4: Compressive strength of cement mortar samples submerged in sulfate solution, fly ash solution, and water (7-days curing in water and No pH

control) Figure 17 shows the compressive strength of cement-sand mixtures (CM) and cement-sand-silica fume mixtures (CM + 5% SF) after they were placed in fly ash solution and the pH was automatically controlled. The samples were placed in the fly ash solution after 28 days of curing in water. Similar to the results presented in Figure 4, Figure 17 shows that the strength of samples placed in water continued to increase, although at a

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very slow rate, but the strength of samples placed in fly ash solution decreased after about 60 days in fly ash solution.

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Figure 17: Compressive strength of cement mortar samples submerged in fly ash solution (28-days curing in water and automatic pH control)

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Tests on Cylindrical Samples Figure 18 shows the splitting-tensile strength of cement-sand mixtures after they were placed in sulfate solution, fly ash solution and water. The pH of the solutions was not controlled. The samples were placed in sulfate and fly ash solutions after 28 days of curing in water. Similar to the compressive strength results presented earlier, Figure 18 shows that the splitting-tensile strength of samples placed in water continued to increase but the strength of samples placed in sulfate and fly ash solutions decreased after about 60 days in fly ash solution.

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Figure 18: Splitting-tensile strength of cement mortar samples submerged in sulfate solution, fly ash solution, and water (28-days curing in water and no pH

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Task III As discussed earlier, samples from two types of concrete matrices, regular concrete and concrete with 5% silica fume, were prepared and tested under this task. Regular concrete samples were buried into the Illinois fly ash and regular soil to evaluate the effect of high sulfate content in the Illinois fly ash under field conditions. The concrete samples with silica fume were only buried into Illinois fly ash. For the results presented under this task, the symbol ‘CS’ refers to regular concrete samples buried in soil; ‘CF’ refers to regular concrete samples buried in Illinois fly ash; and ‘SFF’ refers to concrete with silica fume samples buried in Illinois fly ash. All samples were placed into soil or fly ash after 28 days of curing in water. Since the attack from chemicals in Illinois fly ash is expected to be very slow under actual field conditions, it was decided to conduct tests on these samples for a long period. Therefore, only one data point, i.e., 90 days after placing the samples in soil or fly ash, is available at this time.

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Tests on Prism Samples Figure 19 shows the relative dynamic modulus (RDM) of prism samples tested under this task. The zero on the x-axis refers to the day samples were placed in the fly ash or soil, i.e., after 28 days of curing. Results presented in Figure 19 show that RDM of all samples increased slightly. The samples placed in Illinois fly ash show a slightly higher increase in the RDM compared to samples placed in soil. The data available at this time are very limited. Therefore, only RDM data are presented herein and no conclusions have been drawn from these results at this time.

Figure 19: RDM of samples buried in soil and Illinois fly ash

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Tests on Cylindrical Samples Figure 20 shows the compressive strength of samples tested under this task. The zero on the x-axis refers to the compressive strength after 28 days of curing in water. Results presented in Figure 20 show that compressive strength of all samples increased slightly. Although, the compressive strength of concrete samples with silica fume is higher, the rate of increase in strength is almost the same for all samples, irrespective of whether they were buried in soil or fly ash. The data from cylindrical samples available at this time are also very limited. Therefore, only compression strength data are presented herein and no conclusions have been drawn from these results at this time.

Figure 20: Compressive strength of samples buried in soil and Illinois fly ash

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Ultrasonic Tests As discussed earlier, the purpose of performing this testing was to evaluate if ultrasonic testing could be used to detect changes in the samples due to sulfate attack. Each sample was taken out of the sulfate solution 4 times over a period of 265 days. Figure 21 shows the time of flight (TOF) measurements from one sample taken at the bottom most point after 40, 85 and 265 days in the sulfate solution. The first plot is the baseline data obtained before placing the sample in the sulfate solution. The arrows show the second peak. Data for the third plot is questionable. Figure 21 shows that the TOF through the sample at Point 1 (bottom most point) decreased with time in the sulfate solution, i.e., the speed of sound through the sample increased with time in the sulfate solution. Speed of sound is correlated to the material properties including density and the porosity of samples. Therefore, the data show that higher sulfate attack resulted in the increase in the speed of sound and a certain change in the material properties.

Figure 21: Ultrasonic signals through a sample after various periods in sulfate solution

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Figure 22 shows the ultrasonic signals at Points 1 through 4 on a sample after 265 days in the sulfate solution. Point 1 is the bottom most point (topmost plot in the figure). Data at Point 5 were bad and therefore, are not shown in the figure. The results presented in Figure 22 show that the TOFs increased with distance from the bottom of the sample, i.e., the speed of sound decreased with distance away from the bottom of the sample. As discussed earlier, it shows that the sulfate attack was higher at the bottom most point. A more detailed analysis would be required to investigate the quantitative changes and de-correlate them with respect to the various factors such as density, porosity, etc. and correlate it to the actual sulfate attack phenomenon.

Figure 22: Ultrasonic signals through a sample at various points after 265 days in sulfate solution

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Environmental Scanning Electron Microscope (ESEM) Test The scanning electron microscope (SEM) is a useful tool for the study of microstructural changes in materials with high spatial resolution. The advent of so called “low pressure”, “wet”, “natural state” or “environmental” scanning electron microscopy has allowed in-situ studies to be carried out on hydrating pastes. This has two-fold benefit in that it eliminates some of the artifacts of damaging specimen preparation and allows real-time in-situ studies to be performed in an environment that maintains the original state of the material. Figure 23 shows the ESEM images of samples placed in water and sulfate solution for 30 weeks. ESEM image of a sample placed in sulfate solution clearly shows formation of fibrous material, possibly ettringite, whereas no such fibers were observed in the sample placed in water.

Figure 23: ESEM Images of samples placed water and sulfate solution for 30 weeks

Sample in Water Sample in Sulfate Solution

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CONCLUSIONS AND RECOMMENDATIONS According to Mehta (2000) the presence of high concentrations of sulfate in soil or water should not lead anyone to conclude that the concrete deterioration must have been caused by chemical sulfate attack. Published literature indicates that deterioration to concrete in sulfate rich soils could results from a physical attack or chemical attack. The physical attack is caused by pressures resulting from salt crystallization in the pores of concrete which cause cracking, flaking, and spalling in concrete. The chemical attack involves loss of strength and adhesion associated with formation of gypsum and ettringite resulting from decomposition of cement paste by the penetrating sulfate ions. Figure 24 shows two sets of samples. Two samples on the right were partially submerged in Illinois fly ash solution and two samples on the left were partially submerged in sodium sulfate solution. Notice the salt crystallization on the samples submerged in sodium sulfate solution after only a few weeks in the solution whereas no salt crystallization was observed on samples placed in Illinois fly ash solution. Salt crystallization can generate pressures large enough to cause cracking in the concrete. In poor quality concrete, the progressive loss of mass from the surface can be substantial (Mehta 2000).

Figure 24: Comparison of salt crystallization on samples placed in sulfate solution and fly ash solution

Figure 25 shows a picture of samples after they were partially submerged in sulfate solution (three samples on the right hand side) and Illinois fly ash solution (three samples on the left hand side) for a period of over 300 days. As evident from the figure, samples placed in standard sulfate solution showed some cracking, flaking and spalling at the surface. However, negligible salt crystallization, but no flaking, spalling, or cracking, was observed on the samples placed in the Illinois fly ash solution. This shows that physical attack from concrete embedded in Illinois fly ash due to crystallization of salts in the pores is unlikely.

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Figure 25: Picture of samples after they were partially submerged in fly ash solution

and sulfate solution for a period of over 300 days Mehta (1992) reported that permeability of concrete rather than cement chemistry appears to be the most important factor in sulfate attack. Sulfate attack is seldom found to be the sole phenomenon responsible for the deterioration of concrete structures. Although, formation of ettringite and expansion of concrete due to formation of ettringite is considered as the consequence of chemical sulfate attack, there is no direct correlation between volume of ettringite formed and expansion. The results presented earlier show that (1) the length change of samples placed in sulfate solution and fly ash solution was slightly greater than that from the samples placed in water, (2) the weight gain in samples placed in sulfate solution and fly ash solution was slightly lower than that from the samples placed in water, and (3) the relative dynamic modulus of samples placed in sulfate solution and fly ash solution was slightly lower than that from the samples placed in water. In addition, the compressive and splitting tensile strengths from samples placed in sulfate solution and Illinois fly ash solutions was almost the same as that from the samples placed in water until about 60 days. However, after about 60 days in sulfate solution or fly ash solution, the strengths were observed to be slightly less than those from samples placed in water. Although, the sulfate solution and Illinois fly ash solution caused slightly higher length change, slightly lower weight gain, slightly lower RDM, and slightly lower long-term strength, no visible signs of any distress, cracking, spalling were observed on any sample completely submerged in these solutions (see Figure 26). Therefore, it is the authors’

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opinion that the level of soluble sulfate observed in Illinois fly ash may cause slight reduction strength and durability but are not likely to result in significant deterioration or failure in concrete. However, additional tests to better quantify the magnitude of sulfate attack from Illinois fly ash and its consequences are needed.

Figure 26: Picture of samples after 50 weeks in water, fly ash solution and sulfate solution

REFERENCES Mehta, P.K. (1992). “Sulfate Attack on Concrete – A Critical Review,” Material Science of Concrete III, J. Skalny, ed., American Ceramic Society, pp 105-130. Mehta, P.K. (2000). “Sulfate Attack on Concrete: Separating Myths from Reality”, Concrete International, Vol. 22(08), pp 57-61.

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DISCLAIMER STATEMENT This report was prepared by Sanjeev Kumar, Southern Illinois University Carbondale, with support, in part by grants made possible by the Illinois Department of Commerce and Economic Opportunity through the Office of Coal Development and the Illinois Clean Coal Institute. Neither Sanjeev Kumar, Southern Illinois University Carbondale, nor any of its subcontractors nor the Illinois Department of Commerce and Economic Opportunity, Office of Coal Development, the Illinois Clean Coal Institute, nor any person acting on behalf of either: (A) Makes any warranty of representation, express or implied, with respect to the

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