In recent years, the need for sealants in rigid pavement joints has become debatable, partly beca... more In recent years, the need for sealants in rigid pavement joints has become debatable, partly because of the unpredictable field performance of joint sealants. This inability to predict sealant performance stems from the fact that there is no laboratory evaluation method that accurately simulates field traffic and environmental loading conditions. A laboratory testing method was developed to predict the performance of rigid-pavement joint sealants. A research team at Virginia Tech designed a fixture that allows the evaluation of joint sealants under cyclic shear and static horizontal deflections. Shear deflection simulates vehicular loading, and horizontal deflection simulates expansion and contraction of concrete slabs due to temperature variation. Concrete specimens were prepared at a typical water-to-cement ratio of 0.45. Two aggregate types were used in the concrete mixes to evaluate the effect of aggregate type on sealant performance. Two commercially available sealants were investigated in the study. Sealant performance was evaluated for different joint widths and joint expansion. Specimens were loaded cyclically to failure; a 20 percent cohesive or adhesive debonding was considered a failure. A limited number of specimens were exposed to freezing and thawing cycles. The study showed quantitatively the effects of joint width, joint expansion, concrete aggregate type, and freezing and thawing cycles on sealant performance. Statistical models were developed to predict the number of loading cycles to failure for each sealant.
In June 1994, a secondary road pavement section 150 m long was instrumented in Bedford County, Vi... more In June 1994, a secondary road pavement section 150 m long was instrumented in Bedford County, Virginia. This pavement section was composed of nine individual sections each 15 m long. Sections 1 through 3 had a limestone base course 100 mm thick (VDOT 21-B); Sections 4 through 6 had a base course 150 mm thick; and Sections 7 through 9 had a base course 200 mm thick. Three sections were stabilized with geotextiles, three were stabilized with geogrids at the base course-subgrade interface, and the other three were kept as control sections. One section from each stabilization category was included in each base course thickness group. The outside wheel path of the inner lane was instrumented with strain gauges, pressure cells, piezoelectric sensors, thermocouples, and moisture sensors. A Keithley 500-A data acquisition system was used to collect instrument responses on-site. Some of the data collected by the instruments are discussed. Section performances based on the instrumentation response to controlled and normal vehicular loading indicated that geosynthetic stabilization provided significant improvement, which was found to be in agreement with rut-depth measurements.
A study was conducted to evaluate the effect of the basic properties of Portland cement concrete ... more A study was conducted to evaluate the effect of the basic properties of Portland cement concrete (PCC) and chloride presence (in PCC) on its dielectric properties over the microwave frequency range of 0.1 to 1 GHz. PCC specimens were prepared at three w/c ratios, 0.35, 0.45, and 0.55, using three aggregate types, limestone, quartzite, and active-silica, and two types of cement, type I and high alkali. Other PCC mixes were prepared and contaminated with two methods, addition of sodium chloride (NaCl) to the mixing water and immersion of hardened PCC specimens (prepared at a 0.45 w/c ratio) in 6% (by wt) NaCl solution after 28 days of curing. The dielectric properties were evaluated using a coaxial transmission line designed to allow measurements over the frequency range of 0.1 to 1 GHz. The dielectric properties of PCC specimens were evaluated over curing time. Powdered PCC samples were obtained from chloride contaminated specimens and chloride contents were determined using Virginia Tech Procedure. The results showed significant effects of curing time on the dielectric properties of PCC specimens and insignificant effects of w/c ratio, air entrainment, and cement type. The dielectric properties showed a significant difference between PCC specimens with different aggregate types. The chloride presence (in PCC) did not influence significantly the PCC dielectric properties.
An experimental study was conducted to investigate the feasibility ofusing ultrasonic waves to de... more An experimental study was conducted to investigate the feasibility ofusing ultrasonic waves to detect the basic properties of Portland cement concrete (PCC). The experimental programme was initiated to investigate the effect of watercement ratio (w/c), aggregate type, air entrainment, and curing time on measured ultrasonic wave velocity and signal energy. Three wlc ratios (0.35, 0.45 and 0.55) were evaluated. Two aggregate types (quartzite and limestone) were included in the PCC mixes separately. Mixes were prepared as non-air entrained and with air entrainment. Thus, a total of twelve batches were prepared. Ultrasonic measurements were performed on 7.5 x 10 x 40 em PCC specimens at 1, 3, 7, 14,21, and 28 days of moist curing using direct and indirect measuring methods. Ultrasonic waves were used at two frequencies, 54 and 340 kHz. Collected data was analysed based on ultrasonic wave velocity and signal energy.
An experimental study was conducted to detect chloride contamination in Portland cement concrete ... more An experimental study was conducted to detect chloride contamination in Portland cement concrete (PCC) using signal energy of ultrasonic waves. PCC prisms, 7.5 x 10 x 40 ems, were prepared with wlc ratio of 0.45 as non-air entrained PCc. Chloride contamination of pcc was accomplished using two methods : in the first method, chloride was added to the mixing water while in the second method, PCC specimens were immersed in 6 percent (by weight! chloride solution. Powdered PCC samples were collected to measure the exact chloride content. Least significant difference (LSD) statistical test was used to compare the effect of different chloride concentrations on signal energy. Chloride added to mixing water of pcc was undetected by signal energy. However, PCC specimens immersed in chloride solution showed a reduction in signal energy as the chloride concentration increases.
An experimental program was conducted to study the effect of chloride contamination of portland c... more An experimental program was conducted to study the effect of chloride contamination of portland cement concrete (PCC) on its complex permittivity over low radio frequencies (RF) range (0.1-40.1 MHz). Two types of aggregate (quartzite and limestone) were used to prepare the PCC mixes at a water to cement ratio (w/c) of 0.45. Two methods were used to induce chlorides into PCC: partial immersion in NaCI solution (6% by weight) and the addition of NaCI to the PCC mixing water. For the NaCI addition to the mixing water, three levels of chloride content were used. Dielectric measurements were taken for PCC specimens during the 28-day curing period and continued for six months. Powder PCC samples were collected periodically to estimate the chloride content in the PCC specimens. Results showed that complex permittivity of PCC specimens (immersed in NaCI solution) quantitatively increased as the chloride content increased, until quantitatively 75% of the chloride content estimated theoretical saturation volume. Aggregate type and frequency also show a significant effect on the measured dielectric constant.
Electrical characterization of portland cement concrete (PCC) is necessary for reliable operation... more Electrical characterization of portland cement concrete (PCC) is necessary for reliable operation of many electromagnetic nondestructive evaluation (NDE) techniques.
Determining asphalt cement (AC) content of hot-mix asphalt (HMA) for quality control/quality assu... more Determining asphalt cement (AC) content of hot-mix asphalt (HMA) for quality control/quality assurance using extraction methods is a lengthy, time-consuming, and hazardous process. A demand for a faster and safer method led to the development of different nuclear gauges capable of predicting the AC content of HMA samples. Measuring the AC content of compacted specimens by nuclear gauges is a new technique whose feasibility was evaluated. A total of 216 Marshall compacted specimens were cast and tested in an attempt to develop correction models. The study program investigated the effect of various HMA parameters on the measured AC content, including aggregate gradation and type, air void content, moisture content, AC content, and specimen weight. Specimens were prepared at two different mix design formulas using AC-30 and compacted at two different compaction efforts to investigate the effect of air voids. Specimens (1200 g each) used for calibration were prepared at 3 to 7 percent AC content, whereas specimens prepared for measurements were prepared at 4 to 6 percent. Quartzite and diabase aggregate were used as open and dense graded in prepared mixes. Three levels of moisture content in HMA were evaluated. Different calibration models were developed for different asphaltic mixtures. The evaluated nuclear gauge for measuring AC content for compacted HMA specimens produced satisfactory results when the parameters of tested and calibration parameters were the same. The study found that specimen weight is the most significant factor. Other parameters have different degrees of influence on the measured AC content. Statistical models were developed to correct for the evaluated parameters.
Nine instrumented flexible pavement test sections were constructed in a rural secondary road in s... more Nine instrumented flexible pavement test sections were constructed in a rural secondary road in southwest Virginia. The nine test sections, each 15 m (50 ft) long, were built to examine the effects of geogrid and geotextile stabilization. Three test sections were constructed with a geogrid, three were built with a geotextile, and three were nonstabilized. The test section base course thicknesses ranged from 10.2 cm (4.0 in.) to 20.3 cm (8.0 in.), and the hot-mix asphalt (HMA) thickness averaged 8.9 cm (3.5 in.). Geosynthetic stabilization was placed on top of the subgrade layer. The pavement test sections were heavily instrumented with two types of pressure cells, soil and HMA strain gauges, thermocouples, and soil moisture cells. In addition, strain gauges were installed directly on the geogrid and geotextile. An extensive instrumentation infrastructure was constructed to locate all instrumentation, cabling, and data acquisition facilities underground. Instrument survivability has ranged from 6 percent for the strain gauges mounted on the geotextile to 100 percent for the soil moisture blocks after 8 months of operation. The majority of instrument failures occurred either during construction or the first few weeks of operation. The data acquisition system is triggered by traffic passing over piezoelectric sensors and operates remotely. The corresponding data are transferred via modem to Virginia Polytechnic Institute and State University for processing. It is planned that the performance of the pavement test sections will be monitored for a minimum of 3 years.
As part of ongoing research, a new testing method was developed to evaluate the effect of joint w... more As part of ongoing research, a new testing method was developed to evaluate the effect of joint width and freezing and thawing on the performance of three types of commercially available one-component rigid pavement joint sealants (A, B, and C): A is a low modulus silicone, B is a self-leveling silicone, and C is a polyurethane used with a primer. The effect of joint width on sealant performance was mvestIgated usmg two joint widths (6.5 mm and 19 mm), while the weathering effect of freezing and thawing was evaluated by exposing specimens to 50 cycles of rapid freezing and thawing prior to testing. Sealant performance was affected by joint width. A joint width of 6.5 mm offered higher sealant failure resistance than the 19 mm joint width. Exposure to freezing and thawing cycles reduced the number of loading cycles that caused failure for sealants A and C, and increased it for sealant B. The three sealants experienced a higher rate of stress reduction over the number of loading cycles after freezing and thawing conditioning.
This paper presents a nondestructive evaluation method to characteri.ze portland cement concrete ... more This paper presents a nondestructive evaluation method to characteri.ze portland cement concrete (PCC) based on its dielectric properties. The work reported is part o~an ongolllg study to d~velop a nondestructive evaluation method for PCC structures using electromagnetic waves. A custom-designed parallel plate setup with an HP 4195A Network/Spectrum Analyzer was u~ed t? form the measurement system. A model was established for the measurement system and a set of calIbratIOn standards was developed for the system calibration. Six different PCC batches were cast and their complex permittivity was measured over,2S days of moist curing, with an average of four specimens per batch.~he selected batches covered a representative variation of water to cement ratio and two aggregate types uSlllg Type I portland cement. The complex permittivity of PCC was evaluated over a frequency range of 0.1-40 MHz. Preliminary measurements show~d significant changes in the real part of the dielectric constant versus the curing tim~. How~ver, t~e change. III the loss tangent was less pronounced. Significant differences were also observed III the dlelectnc properties of PCC specimens due to mix-design parameters' variations and the curing state.
The lack of strain characteristics of rigid pavements and bridge deck overlays and the susceptibi... more The lack of strain characteristics of rigid pavements and bridge deck overlays and the susceptibility of flexible pavements and hot-mix asphalt overlays to abrasion wear. fuel spillage, and stripping suggests the search for a material that possesses the unique properties of both Portland cement concrete and hot-mix asphalt such as asphalt-Portland cement concrete composite (APCCC), APCCC is a hot-mix asphalt with a high air void content (25-30%) filled with resin-modified cement grout. The grout consists of Portland cement, fly ash, sand, water, and Prosalvia admixture. The resulting concrete has the properties of both flexible and rigid concrete. A laboratory study was conducted to evaluate the performance of APCCC under control conditions. The program included the following tests: stability, indirect tensile strength, compressive strength, resilient modulus, water sensitivity, freezing and thawing, and chloride intrusion resistance. The tests were performed at three levels of moist curing: no moist curing, one-day moist curing, and three-day moist curing. APCCC specimens were tested over a period of 28 days. The results were compared to those of hot-mix asphalt and Portland cement concrete control specimens. The study concluded that APCCC strength and durability properties are better than those of hot-mix asphalt. The chloride intrusion into APCCC specimens was found to be less than that into normal Portland cement concrete. The study shows that APCCC is an effective alternative material to be used as a bridge deck overlay.
The optimum drying temperature of concrete prior to monomer impregnation was investigated. Mortar... more The optimum drying temperature of concrete prior to monomer impregnation was investigated. Mortar cubes were cast, dried at different temperatures between room temperature and 316~ (600~ and impregnated with monomer and polymerized in situ. The cubes were then vacuum-saturated and their resistivities were measured. The cubes were cut and dried to 104~ (220~ and the influence of drying temperature on the degree of impregnation was evaluated using a mercury porosimeter and a scanning electron microscope-energy dispersive spectroscope. Companion cubes were subjected to ponding-drying cycles in a sodium chloride solution, and the ingress of chloride was determined from powdered samples. Results were used to optimize the drying temperature of concrete for monomer impregnation. The results demonstrated that monomer impregnation of concrete to a desired depth can be achieved at a lower temperature than previously believed.
Recently, the use of preformed membrane systems has increased as a corrosion preventive technique... more Recently, the use of preformed membrane systems has increased as a corrosion preventive technique in reducing chloride intrusion into reinforced concrete bridge decks. However, there is no nondestructive method to evaluate the integrity of in-place preformed membranes. Also, the effectiveness of preformed membranes was not sufficiently addressed. Three different nondestructive methods are evaluated to investigate the integrity of preformed membranes. Ultrasonic pulse velocity is found to be the most feasible. The effectiveness of preformed membranes is investigated by collecting concrete powder samples from bridge decks protected by preformed membranes at three depths. A field evaluation of the preformed membranes' performance is conducted on fifteen bridge decks in three states: New Hampshire, Maine, and Vermont. The membranes were installed on the decks when new. The bridges' ages are varied from 2 to 32 years old. They are exposed to different average annual daily traffic, salt application rate, snowfall, and so forth. Approximately 45 nondestructive tests were carried out, an average of 14 ground truth cores were obtained, and at least 45 concrete powder samples were analyzed for chloride content per bridge deck. The field evaluation concluded that preformed membranes reduce chloride intrusion if they are installed properly and overlaid with an appropriate layer of hot-mix asphalt, which should be kept in a good sen'ice condition. An average life of 40 years is expected for preformed membranes, and an increase of 25 years in bridge deck life is expected.
The increasing use of deicing salts on bridge decks has accelerated their deterioration due to ch... more The increasing use of deicing salts on bridge decks has accelerated their deterioration due to chloride-induced corrosion of steel reinforcement, which causes cracking and spalling. One method being considered as a possible corrosion abatement measure is the removal of chloridecontaminated concrete followed by chemical treatment of the partially exposed rebar through ponding and/or placement of chemically treated mortar. Several commercial and experimental corrosion inhibitors were evaluated in order to determine the most effective corrosion treatment when applied in conjunction with removal of chloride-contaminated concrete. The performances of the inhibitors were evaluated in an accelerated test program. Based on post-treatment electrochemical measurements, calcium-nitrite-based corrosion inhibitor was most effective when applied as a ponding and when placed in backfilled mortar. Several other inhibitors were also sufficiently effective and were recommended for further evaluation in large-scale and field experimentation. On the other hand, several inhibitors affected the hydration process of portland cement.
In recent years, the need for sealants in rigid pavement joints has become debatable, partly beca... more In recent years, the need for sealants in rigid pavement joints has become debatable, partly because of the unpredictable field performance of joint sealants. This inability to predict sealant performance stems from the fact that there is no laboratory evaluation method that accurately simulates field traffic and environmental loading conditions. A laboratory testing method was developed to predict the performance of rigid-pavement joint sealants. A research team at Virginia Tech designed a fixture that allows the evaluation of joint sealants under cyclic shear and static horizontal deflections. Shear deflection simulates vehicular loading, and horizontal deflection simulates expansion and contraction of concrete slabs due to temperature variation. Concrete specimens were prepared at a typical water-to-cement ratio of 0.45. Two aggregate types were used in the concrete mixes to evaluate the effect of aggregate type on sealant performance. Two commercially available sealants were investigated in the study. Sealant performance was evaluated for different joint widths and joint expansion. Specimens were loaded cyclically to failure; a 20 percent cohesive or adhesive debonding was considered a failure. A limited number of specimens were exposed to freezing and thawing cycles. The study showed quantitatively the effects of joint width, joint expansion, concrete aggregate type, and freezing and thawing cycles on sealant performance. Statistical models were developed to predict the number of loading cycles to failure for each sealant.
In June 1994, a secondary road pavement section 150 m long was instrumented in Bedford County, Vi... more In June 1994, a secondary road pavement section 150 m long was instrumented in Bedford County, Virginia. This pavement section was composed of nine individual sections each 15 m long. Sections 1 through 3 had a limestone base course 100 mm thick (VDOT 21-B); Sections 4 through 6 had a base course 150 mm thick; and Sections 7 through 9 had a base course 200 mm thick. Three sections were stabilized with geotextiles, three were stabilized with geogrids at the base course-subgrade interface, and the other three were kept as control sections. One section from each stabilization category was included in each base course thickness group. The outside wheel path of the inner lane was instrumented with strain gauges, pressure cells, piezoelectric sensors, thermocouples, and moisture sensors. A Keithley 500-A data acquisition system was used to collect instrument responses on-site. Some of the data collected by the instruments are discussed. Section performances based on the instrumentation response to controlled and normal vehicular loading indicated that geosynthetic stabilization provided significant improvement, which was found to be in agreement with rut-depth measurements.
A study was conducted to evaluate the effect of the basic properties of Portland cement concrete ... more A study was conducted to evaluate the effect of the basic properties of Portland cement concrete (PCC) and chloride presence (in PCC) on its dielectric properties over the microwave frequency range of 0.1 to 1 GHz. PCC specimens were prepared at three w/c ratios, 0.35, 0.45, and 0.55, using three aggregate types, limestone, quartzite, and active-silica, and two types of cement, type I and high alkali. Other PCC mixes were prepared and contaminated with two methods, addition of sodium chloride (NaCl) to the mixing water and immersion of hardened PCC specimens (prepared at a 0.45 w/c ratio) in 6% (by wt) NaCl solution after 28 days of curing. The dielectric properties were evaluated using a coaxial transmission line designed to allow measurements over the frequency range of 0.1 to 1 GHz. The dielectric properties of PCC specimens were evaluated over curing time. Powdered PCC samples were obtained from chloride contaminated specimens and chloride contents were determined using Virginia Tech Procedure. The results showed significant effects of curing time on the dielectric properties of PCC specimens and insignificant effects of w/c ratio, air entrainment, and cement type. The dielectric properties showed a significant difference between PCC specimens with different aggregate types. The chloride presence (in PCC) did not influence significantly the PCC dielectric properties.
An experimental study was conducted to investigate the feasibility ofusing ultrasonic waves to de... more An experimental study was conducted to investigate the feasibility ofusing ultrasonic waves to detect the basic properties of Portland cement concrete (PCC). The experimental programme was initiated to investigate the effect of watercement ratio (w/c), aggregate type, air entrainment, and curing time on measured ultrasonic wave velocity and signal energy. Three wlc ratios (0.35, 0.45 and 0.55) were evaluated. Two aggregate types (quartzite and limestone) were included in the PCC mixes separately. Mixes were prepared as non-air entrained and with air entrainment. Thus, a total of twelve batches were prepared. Ultrasonic measurements were performed on 7.5 x 10 x 40 em PCC specimens at 1, 3, 7, 14,21, and 28 days of moist curing using direct and indirect measuring methods. Ultrasonic waves were used at two frequencies, 54 and 340 kHz. Collected data was analysed based on ultrasonic wave velocity and signal energy.
An experimental study was conducted to detect chloride contamination in Portland cement concrete ... more An experimental study was conducted to detect chloride contamination in Portland cement concrete (PCC) using signal energy of ultrasonic waves. PCC prisms, 7.5 x 10 x 40 ems, were prepared with wlc ratio of 0.45 as non-air entrained PCc. Chloride contamination of pcc was accomplished using two methods : in the first method, chloride was added to the mixing water while in the second method, PCC specimens were immersed in 6 percent (by weight! chloride solution. Powdered PCC samples were collected to measure the exact chloride content. Least significant difference (LSD) statistical test was used to compare the effect of different chloride concentrations on signal energy. Chloride added to mixing water of pcc was undetected by signal energy. However, PCC specimens immersed in chloride solution showed a reduction in signal energy as the chloride concentration increases.
An experimental program was conducted to study the effect of chloride contamination of portland c... more An experimental program was conducted to study the effect of chloride contamination of portland cement concrete (PCC) on its complex permittivity over low radio frequencies (RF) range (0.1-40.1 MHz). Two types of aggregate (quartzite and limestone) were used to prepare the PCC mixes at a water to cement ratio (w/c) of 0.45. Two methods were used to induce chlorides into PCC: partial immersion in NaCI solution (6% by weight) and the addition of NaCI to the PCC mixing water. For the NaCI addition to the mixing water, three levels of chloride content were used. Dielectric measurements were taken for PCC specimens during the 28-day curing period and continued for six months. Powder PCC samples were collected periodically to estimate the chloride content in the PCC specimens. Results showed that complex permittivity of PCC specimens (immersed in NaCI solution) quantitatively increased as the chloride content increased, until quantitatively 75% of the chloride content estimated theoretical saturation volume. Aggregate type and frequency also show a significant effect on the measured dielectric constant.
Electrical characterization of portland cement concrete (PCC) is necessary for reliable operation... more Electrical characterization of portland cement concrete (PCC) is necessary for reliable operation of many electromagnetic nondestructive evaluation (NDE) techniques.
Determining asphalt cement (AC) content of hot-mix asphalt (HMA) for quality control/quality assu... more Determining asphalt cement (AC) content of hot-mix asphalt (HMA) for quality control/quality assurance using extraction methods is a lengthy, time-consuming, and hazardous process. A demand for a faster and safer method led to the development of different nuclear gauges capable of predicting the AC content of HMA samples. Measuring the AC content of compacted specimens by nuclear gauges is a new technique whose feasibility was evaluated. A total of 216 Marshall compacted specimens were cast and tested in an attempt to develop correction models. The study program investigated the effect of various HMA parameters on the measured AC content, including aggregate gradation and type, air void content, moisture content, AC content, and specimen weight. Specimens were prepared at two different mix design formulas using AC-30 and compacted at two different compaction efforts to investigate the effect of air voids. Specimens (1200 g each) used for calibration were prepared at 3 to 7 percent AC content, whereas specimens prepared for measurements were prepared at 4 to 6 percent. Quartzite and diabase aggregate were used as open and dense graded in prepared mixes. Three levels of moisture content in HMA were evaluated. Different calibration models were developed for different asphaltic mixtures. The evaluated nuclear gauge for measuring AC content for compacted HMA specimens produced satisfactory results when the parameters of tested and calibration parameters were the same. The study found that specimen weight is the most significant factor. Other parameters have different degrees of influence on the measured AC content. Statistical models were developed to correct for the evaluated parameters.
Nine instrumented flexible pavement test sections were constructed in a rural secondary road in s... more Nine instrumented flexible pavement test sections were constructed in a rural secondary road in southwest Virginia. The nine test sections, each 15 m (50 ft) long, were built to examine the effects of geogrid and geotextile stabilization. Three test sections were constructed with a geogrid, three were built with a geotextile, and three were nonstabilized. The test section base course thicknesses ranged from 10.2 cm (4.0 in.) to 20.3 cm (8.0 in.), and the hot-mix asphalt (HMA) thickness averaged 8.9 cm (3.5 in.). Geosynthetic stabilization was placed on top of the subgrade layer. The pavement test sections were heavily instrumented with two types of pressure cells, soil and HMA strain gauges, thermocouples, and soil moisture cells. In addition, strain gauges were installed directly on the geogrid and geotextile. An extensive instrumentation infrastructure was constructed to locate all instrumentation, cabling, and data acquisition facilities underground. Instrument survivability has ranged from 6 percent for the strain gauges mounted on the geotextile to 100 percent for the soil moisture blocks after 8 months of operation. The majority of instrument failures occurred either during construction or the first few weeks of operation. The data acquisition system is triggered by traffic passing over piezoelectric sensors and operates remotely. The corresponding data are transferred via modem to Virginia Polytechnic Institute and State University for processing. It is planned that the performance of the pavement test sections will be monitored for a minimum of 3 years.
As part of ongoing research, a new testing method was developed to evaluate the effect of joint w... more As part of ongoing research, a new testing method was developed to evaluate the effect of joint width and freezing and thawing on the performance of three types of commercially available one-component rigid pavement joint sealants (A, B, and C): A is a low modulus silicone, B is a self-leveling silicone, and C is a polyurethane used with a primer. The effect of joint width on sealant performance was mvestIgated usmg two joint widths (6.5 mm and 19 mm), while the weathering effect of freezing and thawing was evaluated by exposing specimens to 50 cycles of rapid freezing and thawing prior to testing. Sealant performance was affected by joint width. A joint width of 6.5 mm offered higher sealant failure resistance than the 19 mm joint width. Exposure to freezing and thawing cycles reduced the number of loading cycles that caused failure for sealants A and C, and increased it for sealant B. The three sealants experienced a higher rate of stress reduction over the number of loading cycles after freezing and thawing conditioning.
This paper presents a nondestructive evaluation method to characteri.ze portland cement concrete ... more This paper presents a nondestructive evaluation method to characteri.ze portland cement concrete (PCC) based on its dielectric properties. The work reported is part o~an ongolllg study to d~velop a nondestructive evaluation method for PCC structures using electromagnetic waves. A custom-designed parallel plate setup with an HP 4195A Network/Spectrum Analyzer was u~ed t? form the measurement system. A model was established for the measurement system and a set of calIbratIOn standards was developed for the system calibration. Six different PCC batches were cast and their complex permittivity was measured over,2S days of moist curing, with an average of four specimens per batch.~he selected batches covered a representative variation of water to cement ratio and two aggregate types uSlllg Type I portland cement. The complex permittivity of PCC was evaluated over a frequency range of 0.1-40 MHz. Preliminary measurements show~d significant changes in the real part of the dielectric constant versus the curing tim~. How~ver, t~e change. III the loss tangent was less pronounced. Significant differences were also observed III the dlelectnc properties of PCC specimens due to mix-design parameters' variations and the curing state.
The lack of strain characteristics of rigid pavements and bridge deck overlays and the susceptibi... more The lack of strain characteristics of rigid pavements and bridge deck overlays and the susceptibility of flexible pavements and hot-mix asphalt overlays to abrasion wear. fuel spillage, and stripping suggests the search for a material that possesses the unique properties of both Portland cement concrete and hot-mix asphalt such as asphalt-Portland cement concrete composite (APCCC), APCCC is a hot-mix asphalt with a high air void content (25-30%) filled with resin-modified cement grout. The grout consists of Portland cement, fly ash, sand, water, and Prosalvia admixture. The resulting concrete has the properties of both flexible and rigid concrete. A laboratory study was conducted to evaluate the performance of APCCC under control conditions. The program included the following tests: stability, indirect tensile strength, compressive strength, resilient modulus, water sensitivity, freezing and thawing, and chloride intrusion resistance. The tests were performed at three levels of moist curing: no moist curing, one-day moist curing, and three-day moist curing. APCCC specimens were tested over a period of 28 days. The results were compared to those of hot-mix asphalt and Portland cement concrete control specimens. The study concluded that APCCC strength and durability properties are better than those of hot-mix asphalt. The chloride intrusion into APCCC specimens was found to be less than that into normal Portland cement concrete. The study shows that APCCC is an effective alternative material to be used as a bridge deck overlay.
The optimum drying temperature of concrete prior to monomer impregnation was investigated. Mortar... more The optimum drying temperature of concrete prior to monomer impregnation was investigated. Mortar cubes were cast, dried at different temperatures between room temperature and 316~ (600~ and impregnated with monomer and polymerized in situ. The cubes were then vacuum-saturated and their resistivities were measured. The cubes were cut and dried to 104~ (220~ and the influence of drying temperature on the degree of impregnation was evaluated using a mercury porosimeter and a scanning electron microscope-energy dispersive spectroscope. Companion cubes were subjected to ponding-drying cycles in a sodium chloride solution, and the ingress of chloride was determined from powdered samples. Results were used to optimize the drying temperature of concrete for monomer impregnation. The results demonstrated that monomer impregnation of concrete to a desired depth can be achieved at a lower temperature than previously believed.
Recently, the use of preformed membrane systems has increased as a corrosion preventive technique... more Recently, the use of preformed membrane systems has increased as a corrosion preventive technique in reducing chloride intrusion into reinforced concrete bridge decks. However, there is no nondestructive method to evaluate the integrity of in-place preformed membranes. Also, the effectiveness of preformed membranes was not sufficiently addressed. Three different nondestructive methods are evaluated to investigate the integrity of preformed membranes. Ultrasonic pulse velocity is found to be the most feasible. The effectiveness of preformed membranes is investigated by collecting concrete powder samples from bridge decks protected by preformed membranes at three depths. A field evaluation of the preformed membranes' performance is conducted on fifteen bridge decks in three states: New Hampshire, Maine, and Vermont. The membranes were installed on the decks when new. The bridges' ages are varied from 2 to 32 years old. They are exposed to different average annual daily traffic, salt application rate, snowfall, and so forth. Approximately 45 nondestructive tests were carried out, an average of 14 ground truth cores were obtained, and at least 45 concrete powder samples were analyzed for chloride content per bridge deck. The field evaluation concluded that preformed membranes reduce chloride intrusion if they are installed properly and overlaid with an appropriate layer of hot-mix asphalt, which should be kept in a good sen'ice condition. An average life of 40 years is expected for preformed membranes, and an increase of 25 years in bridge deck life is expected.
The increasing use of deicing salts on bridge decks has accelerated their deterioration due to ch... more The increasing use of deicing salts on bridge decks has accelerated their deterioration due to chloride-induced corrosion of steel reinforcement, which causes cracking and spalling. One method being considered as a possible corrosion abatement measure is the removal of chloridecontaminated concrete followed by chemical treatment of the partially exposed rebar through ponding and/or placement of chemically treated mortar. Several commercial and experimental corrosion inhibitors were evaluated in order to determine the most effective corrosion treatment when applied in conjunction with removal of chloride-contaminated concrete. The performances of the inhibitors were evaluated in an accelerated test program. Based on post-treatment electrochemical measurements, calcium-nitrite-based corrosion inhibitor was most effective when applied as a ponding and when placed in backfilled mortar. Several other inhibitors were also sufficiently effective and were recommended for further evaluation in large-scale and field experimentation. On the other hand, several inhibitors affected the hydration process of portland cement.
To understand the dielectric properties of PCC and better correlate them with type and severity o... more To understand the dielectric properties of PCC and better correlate them with type and severity of PCC internal defects, a study was conducted to evaluate PCC complex permittivity and magnetic permeability over a wideband-of frequencies (100 kHz to 10 GHz) using both time domain and frequency domain techniques. Three measuring devices were designed and fabricated: a parallel plate capacitor, a coaxial transmission line, and transverse electromagnetic (TEM) horn antennae. The TEM horn antenna covers the microwave frequencies (0.5-10 GHz). The measurement technique involves a time domain setup that was verified by a frequency domain measurement. Portland cement concrete slabs, 60x75x14 cm, were cast (intact and with defects); defects include delamination, delamination filled with water, segregation, and chloride contamination. In this paper, measurements using the TEM horn antennae and the feasibility of detecting flaws at microwave frequency are presented. SPIE Vol. 2946 / 29 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 08/02/2013 Terms of Use: http://spiedl.org/terms 12.
This paper presents ongoing research to measure the in-situ runway flexible pavement response to ... more This paper presents ongoing research to measure the in-situ runway flexible pavement response to airplane traffic during its service life at the Airport of Cagliari-Elmas in Italy. Understanding how pavement materials respond to traffic and environmental loading is fundamental when designing pavements and assessing their performance. The pavement material behavior is affected by many factors (i.e., load magnitude, material properties, and environmental conditions). The influence of these factors can be simultaneously taken into account by measuring in-situ stresses and strains using embedded instruments. The pavement layers of the Cagliari-Elmas runway were instrumented with a total of 149 instruments: 36 Linear Variable Differential Transformers (LVDTs), 36 pressure cells, four Time Domain Reflectometers (TDRs), 28 T-thermocouples, and 45 HMA strain gauges. The instrumented area, 55m 2 , allows measuring the responses during three main loading maneuvers: taking off, landing, and taxiing. The preliminary data acquired during and after the runway's construction and prior to its opening to airplane traffic and its analysis show that the instrumentation process was a success. The instrument response testing includes FWD, truck, and airplane loading. The loading includes various loading types, magnitudes, and speed. The collected data was successfully compared to preliminary numerical simulations. Further data collection and research will be performed, particularly airplane traffic data analysis. The data analysis will include the effect of the environmental data (i.e. moisture and temperature) and airplane configuration and speed. The collected data will be used to validate advanced pavement modeling and predict pavement runway performance. In addition, data resulting from this research has the potential to support and improve runway pavement design as well as to improve the evaluation process for new and existing runway pavements in terms of their performance and damage prediction.
Transportation Research Board 90th Annual MeetingTransportation Research Board, 2011
This paper discusses how the method of compaction (laboratory, gyratory or field) affects the mea... more This paper discusses how the method of compaction (laboratory, gyratory or field) affects the measured resilient modulus of hot-mix asphalt. The specific research presented was conducted on the asphaltic mixtures placed on the Virginia Smart Road. Three types of laboratory compacted asphaltic mixture specimen, representing different mix production methods, were compared to field compacted asphaltic mixture specimen obtained from coring. In general, irrespective of the mix production method, the resilient modulus values of laboratory-compacted specimens were 50% higher than the resilient modulus values of field-compacted specimens. A model relating asphaltic mixture resilient modulus to its volumetrics was developed using laboratory-compacted specimens’ data. The statistical approach considers both fitting and predicting measures. The model was then used to predict resilient modulus values of field-compacted specimens from their volumetric properties. The calculated resilient modulus values, using the developed model, were 15% higher than the measured resilient modulus values for field-compacted specimens. For the considered mixes, 70% of the difference between laboratory-compacted and field-compacted specimens’ resilient modulus values is attributed to a difference in volumetrics (mainly air voids), while the remaining 30% (or 15% difference) is due to the compaction method (field vs. laboratory).
Laboratory fatigue testing was performed on six Superpave HMA mixtures in use at the Virginia Sma... more Laboratory fatigue testing was performed on six Superpave HMA mixtures in use at the Virginia Smart Road. Evaluation of the applied strain and resulting fatigue life was performed to fit regressions to predict the fatigue performance of each mixture. Differences in fatigue performance due to field and laboratory production and compaction methods were investigated. Also, in-situ mixtures were compared to mixtures produced accurately from the job mix formula to determine if changes occurring between the laboratory and batch plant significantly affected fatigue life. Results from the fatigue evaluation allowed verification of several hypotheses related to mixture production and compaction and fatigue performance. It was determined that location within the pavement surface, such as inner or outer wheelpath or center-of-lane, did not significantly affect laboratory fatigue test results, although the location will have significant effects on in-situ fatigue life. Also the orientation of samples cut from an in-situ pavement (parallel or perpendicular to the direction of traffic) had only a minor effect on the laboratory fatigue life, because the variability inherent in the pavement due to material variability is greater than the variability induced by compaction. Fatigue life of laboratory-compacted samples was found to be greater than fatigue life of field-compacted samples; additionally, the variability of the laboratory compacted mixture was found to be less than that of the field-compacted samples. However, it was also found that batch-plant production significantly reduces specimen variability as compared to smallbatch laboratory production when the same laboratory compaction is used on both specimen sets. Finally, for Smart Road mixtures produced according to the job mix formula, the use of polymer-modified binder or stone matrix asphalt was shown to increase the expected fatigue life. However, results for all mixes indicated that fatigue resistance rankings might change depending on the applied strain level. This study contributes to the understanding of the factors involved in fatigue performance of asphalt mixtures. Considering that approximately 95% of Virginia's interstate and primary roadways incorporate asphalt surface mixtures, and that fatigue is a leading cause of deterioration, gains in the understanding of fatigue processes and prevention have great potential payoff by improving both the mixture and pavement design practices. 17 Key Words 18. Distribution Statement Fatigue life characterization, vibratory compaction, third point bending fatigue, pavement performance No restrictions. This document is available to the public through NTIS, Springfield, VA 22161. 19. Security Classif. (of this report) 20. Security Classif.
In order to better understand reflected ground-penetrating radar (GPR) signals from sound concret... more In order to better understand reflected ground-penetrating radar (GPR) signals from sound concrete and delaminated concrete structures, 5 bare concrete slabs and 9 slabs with simulated delaminations were built. Five concrete mixtures were used; all were cast at 1.5 x 1.5 x 0.127 m. Delamination was simulated by placing polystyrene plastic pieces inside slabs during casting. A method was developed to determine the complex dielectric constant of the 5 concrete mixtures. The effect of delamination was studied by comparing signals obtained from the bare concrete slabs with those obtained from slabs with embedded polystyrene pieces. It was found that modeling the reflected signals using an average complex dielectric constant over the entire radar frequency range results in waveforms comparable to the measured ones. It was also found that reflections from air voids located at 50 mm from the surface overlap with the surface reflection. The distorted shape of the reflected signal, however, serves as an indication of the void pressure.
This paper presents the description, calibration procedures, installation, and performance of the... more This paper presents the description, calibration procedures, installation, and performance of the instrumentation used at the Virginia Smart Road to measure flexible pavement response to loading. Also presented are the measured horizontal transverse and longitudinal ...
Ninth International Conference on Asphalt PavementsInternational Society for Asphalt Pavements, Aug 1, 2002
One of the 12 instrumented sections of the Virginia Smart Road was used to evaluate the effect of... more One of the 12 instrumented sections of the Virginia Smart Road was used to evaluate the effect of several loading parameters on the measured stresses at different layers and the measured horizontal transversal strain in the bottom of the hot-mix asphalt (HMA) layer. It was found that speed does not affect the measured vertical compressive stress in all layers, but does significantly affect the measured horizontal transversal strain under the HMA layer. Strain was found to decrease by a factor of 2.7 when the speed increases from 8km/h to 72.4km/h at 25 deg C. Variation in tire inflation from 551.6kPa to 724kPa was found not to affect the measured vertical compressive stress in all the layers and the measured horizontal transversal strain in the bottom of the HMA layer. Vertical stresses under the HMA layer were found to vary linearly with the applied tires' load at 25 deg C.
... Imad L. Al-Qadi Charles A. Via Jr. ... Environmental Engineering Virginia Polytechnic Institu... more ... Imad L. Al-Qadi Charles A. Via Jr. ... Environmental Engineering Virginia Polytechnic Institute and State University, 200 Patton Hall, Blacksburg, VA 24061-0105 voice (540) 231 5262, fax (540) 231 7532, email: alqadi@vt.edu ... Seattle, WA: American Society for Testing and Materials ...
ABSTRACTPortland cement concrete (PCC) structures deteriorate with age and need to be maintained ... more ABSTRACTPortland cement concrete (PCC) structures deteriorate with age and need to be maintained or replaced. Early detection of deterioration in PCC (e.g., alkali-silica reaction, freeze/thaw damage, or chloride presence) can lead to significant reductions in maintenance costs. However, it is often too late to perform low-cost preventative maintenance by the time deterioration becomes evident. By developing techniques that would enable civil engineers to evaluate PCC structures and detect deterioration at early stages (without causing further damage), optimization of life-cycle costs of the constructed facility and minimization of disturbance to the facility users can be achieved.Nondestructive evaluation (NDE) methods are potentially one of the most useful techniques ever developed for assessing constructed facilities. They are noninvasive and can be performed rapidly. Portland cement concrete can be nondestructively evaluated by electrically characterizing its complex dielectric constant. The real part of the dielectric constant depicts the velocity of electromagnetic waves in PCC. The imaginary part, termed the “loss factor,” describes the conductivity of PCC and the attenuation of electromagnetic waves.Dielectric properties of PCC have been investigated in a laboratory setting using a parallel plate capacitor operating in the frequency range of 0.1 to 40.1MIHz. This capacitor set-up consists of two horizontal-parallel plates with an adjustable separation for insertion of a dielectric specimen (PCC). While useful in research, this approach is not practical for field implementation. A new capacitor probe has been developed which consists of two plates, located within the same horizontal plane, for placement upon the specimen to be tested. Preliminary results show that this technique is feasible and results are promising; further testing and evaluation is currently underway.
The use of general descriptive names, registered names, trademarks, service marks, etc. in this p... more The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use.
Civil Engineering Studies, Illinois Center for Transportation Series, 2016
A series of five experimental projects were constructed to better determine the life-cycle cost a... more A series of five experimental projects were constructed to better determine the life-cycle cost and performance of pavement overlays using various types and combinations of recycled materials—namely, reclaimed asphalt pavement (RAP), recycled asphalt shingles (RAS) and crushed concrete. The asphalt binder replacement (ABR) varied from 15% to 48% in the experimental sections. The study of these projects prior to construction, during construction, and for a short monitoring period after construction is intended to determine the impact of various pavement conditions, pavement cross-sections, mix designs, and material properties on the ultimate performance of the hot-mix asphalt (HMA) overlay. This interim report documents the construction and testing to date on two of the five projects in the study—Crawford Avenue/Pulaski Road and US 52 (IL 52 to Laraway Road)—that were constructed in 2014. Distress and profile surveys were conducted before and after construction. Samples were obtained...
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Journal Papers by Imad L . Al-Qadi