PURPOSES : High temperatures induce excessive expansion in pavements, thus causing the closure of contraction joints between expansion joints. This results in the integration of slabs within the expansion joints into a unified slab. Compressive forces are generated owing to the friction that ensues between the unified slab and lower base layer. As the integrated slab expands and exceeds the allowable width of the expansion joint, the end restraint generates an additional compressive force. The escalating force, which reaches a critical threshold, induces buckling, thus compromising stability and causing blow-up incidents, which poses a significant hazard to road users. The unpredictable nature of blow-up incidents render their accurate prediction challenging because the compressive force within the slab must be predicted and the threshold for blow-up occurrence must be determined. METHODS : In this study, a GWNU blow-up model was developed to predict both the compressive force and period of blow-up incidents in jointed concrete pavements. The climate conditions, pavement structure, materials, and expansion joints were considered in this model. In the first stage of the model, the time at which the integrated slab expanded and surpassed the allowable width of the expansion joint was determined, and the compressive force was calculated. Subsequently, the compressive force within the integrated slab, considering both the end restraints and friction, was predicted. A large-scale blow-up test was performed to measure the blow-up force based on changes in the geometric imperfections. The measured blow-up force was adopted as the blow-up occurrence threshold, and the point at which the predicted compressive force within the slab exceeded the blow-up force was identified as the blow-up occurrence time. RESULTS : Using the GWNU blow-up model, the blow-up occurrence on the Seohean Expressway in Korea is predicted in the presence or absence of the alkali-silica reaction (ASR). Analysis is conducted using the expansion joint spacing and width as variables. As the expansion joint spacing increases, blow-up occurs sooner, and as the width increases, only the expansion joint life decreases. When applying an expansion joint spacing of 300 m and a width of 100 mm under an ASR with 99.9% TTPG reliability, the sum of the expansion joint life and blow-up occurrence time is 16 years. CONCLUSIONS : In the case of jointed concrete pavements where ASR occurred, installing an expansion joint spacing of 300 m and a width of 100 mm does not satisfy the design life of 20 years, and the expansion joint width minimally affect the blow-up occurrence time. To prevent blow-up incidents, a spacing of less than 300 m for the expansion joint is recommended. Based on the analysis results, the blow-up occurrence time and location can be predicted from the characteristics of the installed expansion joint, through which blow-up incidents can be prevented via preliminary maintenance.

PURPOSES : The increase in particulate matter due to increased air pollutant emissions has become a significant social issue. According to the Ministry of Environment, air pollutants emitted from large-scale businesses in 2022 increased by 12.2% compared to the previous year, indicating that air pollution is accelerating owing to excessive industrialization. In this study, TiO2, which is used to reduce airborne particulate, was used. The TiO2 coating fixation and dynamic pressure coating-type TiO2 fixation methods were used to solve the material peeling phenomenon caused by gravity, which is a limitation when the TiO2 penetration method is applied to a vertical concrete structure along the road. The long-term durability and performance were analyzed through environmental resistance and NOx removal efficiency evaluation experiments. These analyses were then assessed by comparing the NOx removal efficiency with the dynamic pressure permeationtype TiO2 fixation method used in previous studies. METHODS : To evaluate the long-term durability and performance of the TiO2 coating fixation method and dynamic pressure coating TiO2 fixation method for vertical concrete structures, specimens were manufactured based on roadside vertical concrete structures. Environmental resistance tests such as the surface peeling resistance test (ASTM C 672) and freeze-thaw resistance test (KS F 2456) were conducted to evaluate the long-term durability. To evaluate the long-term performance, the NOx removal efficiency of TiO2 concrete owing to road surface deterioration during the environmental resistance test was evaluated using the NOx removal efficiency evaluation equipment based on the ISO 22197-1 standard. This evaluation was compared and analyzed using the dynamic pressure infiltration TiO2 fixation method. RESULTS : The long-term durability of the TiO2 coating fixation and dynamic pressure coating TiO2 fixation methods were evaluated using environmental resistance tests. During the surface peeling resistance test, the TiO2 material degraded and partially detached from the concrete. However, the NOx removal efficiency was ensured by the non-deteriorated and fixed TiO2 material. The long-term performance was confirmed through a freeze-thaw resistance test to evaluate the NOx removal efficiency after 300 cycles of surface deterioration. The results showed that when the TiO2 coating fixation and dynamic pressure infiltration TiO2 fixation methods were applied to vertical concrete structures, the durability of the structure was not compromised. In comparison to the dynamic pressure infiltration TiO2 fixation method, the NOx removal efficiency observed during the surface peeling resistance test was lower, while the freeze-thaw test exhibited notably higher removal efficiency. CONCLUSIONS : To solve the material peeling phenomenon caused by gravity, the long-term durability and performance were evaluated by applying the TiO2 coating fixation and dynamic pressurized coating TiO2 fixation methods to vertical concrete specimens. Long-term durability was confirmed through environmental resistance tests, and long-term utility was secured by measuring the NOx removal efficiency according to surface degradation. These findings show that implementing the TiO2 coating fixation method and dynamic pressure coating TiO2 fixation methods on-site effectively reduce NOx.

PURPOSES : During the summer of 2018, a heat wave (temperatures > 33°C) lasted for more than 30 days, causing blow-ups at eight different locations in South Korea. The blow-up phenomenon occurred when the internal temperature of the concrete slab increased. Simultaneously, as the concrete slab expands excessively, the length of the end of the slab increases, thus resulting in a lateral compressive force; when the slab cannot withstand this force, it rises or breaks. Blow-up is caused by a variety of factors, including increased temperature and humidity, accumulation of incompressible substances inside discontinuous surfaces, alkali–silica reactions, and aging of the concrete pavement. Several researchers have presented models to forecast blow-ups, such as the A. D. Kerr and G. Yang models, which have been applied to explain the blow-up phenomenon. However, this model has some limitations. This paper discusses a method to overcome these limitations. METHODS : Buckling, the most important theory describing the blow-up phenomenon, was reviewed, and the buckling principle was confirmed. Subsequently, the input variables of the Kerr and Yang models and the mechanism for predicting the occurrence of blow-ups were identified. The PGBA program was used to confirm the lifetime of the expansion joint and the blow-up occurrence time based on the expansion joint spacing to review the limitations of the two studied models. RESULTS : The Kerr and Yang models did not consider variables such as the expansion joint spacing or length of the integrated adjacent slab. In other words, it is necessary to reconsider the appropriateness of blow-up time predictions in relation to changes in expansion joint spacing and slab length. The expansion joint lifetime and blow-up occurrence time were predicted using the PGBA program. It was confirmed that as the expansion joint spacing increases, the expansion joint lifetime decreases. However, the blow-up occurrence time was shown to be the same (equal to 59 years), which is a limitation of the Kerr and Yang models used in the PGBA program. This resulted in a limitation in which variables for the expansion joint spacing cannot be used. CONCLUSIONS : Through blow-up simulation experiments and actual field data, an appropriate slab length should be determined, and a blow-up model should be developed based on the slab length. If a blow-up prediction based on concrete slab length and a blow-up model based on are developed, the blow-up prevention technology will be applied to the appropriate blow-up time and location to avoid traffic accidents and reduce human and property damage.

PURPOSES : Advancements in science and technology caused by industrialization have led to an increase in particulate matter emissions and, consequently, severity of air pollution. Nitrogen oxide (NOx), which accounts for 58% of road transport pollutants, adversely affects both human health and the environment. A test-bed was constructed to determine NOx removal efficiency at the roadside. TiO2, a material used to reduce particulate matter, was used to remove NOx. It was applied to a vertical concrete structure using the dynamic pressurized penetration TiO2 fixation method, which can be easily applied to vertical concrete structures. This study was conducted to evaluate the NOx removal efficiency of the dynamic pressurized-penetration TiO2 fixation method in a test-bed under real roadside conditions. METHODS : A test-bed was constructed in order to determine the NOx removal efficiency using the dynamic pressurized penetration TiO2 fixation method on the roadside. The dynamic pressurized-penetration TiO2 fixation method was applied by installing a vertical concrete structure. NOx was injected into the test-bed using an exhaust gas generator. By installing a shading screen, the photocatalytic reaction of TiO2 was suppressed to a maximum concentration of 1000 ppb along the roadside. The removal efficiency was evaluated by measuring NOx concentrations. In addition, illuminance was measured using an illuminance meter. RESULTS : From the results of the analysis of the NOx removal efficiency in the test-bed which the dynamic pressurized type TiO2 fixation method was applied to, an average removal efficiency ranging from 18% to 40% was achieved, depending on the illuminance. Similarly, according to the results of the evaluation of the NO removal efficiency, an average of removal efficiency ranging from 20% to 62% was achieved. Thus, the NOx removal efficiency increased when the illuminance was high. CONCLUSIONS : From the results of the experiment conducted, the efficiency of NOx removal per unit volume was obtained according to the illuminance of TiO2 concrete along an actual road. Field applicability of the dynamic pressurized-penetration-type TiO2 fixation method to vertical concrete structures along roads was confirmed.

PURPOSES : Roller-compacted concrete pavement (RCCP) is a superstiff-consistency concrete pavement that exhibits excellent strength development owing to a hydration reaction and interlocking aggregates owing to the roller compaction. A zero-slump concrete mixture is generally used. Hence, it is important to control the consistency of the RCCP mixture to prevent the deterioration of the construction quality (such as material separation during paving). The workability of the RCCP is characterized by its consistency and controlled by the Vebe time, whereas a conventional concrete pavement is controlled based on the slump test. The consistency of the RCCP changes over time after concrete mixing owing to delivery, construction time delays, etc. Thus, it is necessary to use the optimum Vebe time to achieve the best construction quality. Therefore, this study aims to develop a Vebe time prediction model for efficiently controlling the consistency of RCCPs according to random time variations. METHODS : A Vebe time prediction model was developed using a multiple linear regression analysis. A dataset of 131 samples was used to develop the model. The collected data consisted of variables with large potential effects on the consistency of the RCCP, such as the water-cement ratio (W/C), sand/aggregate ratio (S/a), water content (ω), water content per unit volume (W), cement (C), fine aggregate (S), coarse aggregate (G), water reducing admixtrue (PNS), air-entraining admixture (AE), delay time (T), air temperature (TEM), and humidity (HUM). In the multiple linear regression analysis, the mentioned parameters were used as the independent variables, and the Vebe time was the dependent variable. The Vebe time prediction models were evaluated by considering the adjusted R2 and p-values. The selection of the model was based on the largest R2 value and an acceptable p-value (p<0.05). RESULTS : The Vebe time prediction model achieved an adjusted R2 value of 64.14% with a significance level (p-value) of less than 0.05. This shows that the predictive model is adequately described for the dependent variable, and that the model is suitable for Vebe time predictions. Moreover, the significance level of the independent variables is less than 0.05, indicating significant effects on the Vebe time (i.e., the dependent variable). CONCLUSIONS : The Vebe time prediction model developed in this study can be used to estimate Vebe times with an R2 of 63.33% between the measured and predicted values. The proposed Vebe time prediction model is expected to be effectively utilized for the quality control of RCCP mixtures. Moreover, it is expected to contribute to achieving good RCCP construction quality.

PURPOSES : Recently, air pollution caused by particulate matter has been worsening. Among the substances generating particulate matter, NOx is the main precursor of particulate matter and is widely distributed in areas with a high volume of traffic. TiO2 has been used as a material for removing NOx through a chemical reaction as a photocatalyst. In this context, the reduction of NOx through TiO2 concrete is proposed. However, the research on the surface deterioration on the performance of TiO2 concrete is not documented yet. Therefore, the objective of this study was to evaluate the long-term durability and NOx removal efficiency of TiO2 concrete by considering the concrete surface deterioration. METHODS : Freezing–thawing resistance test (KS F 2456) and scaling test (ASTM C 672) were performed to investigate the variation in the TiO2 penetration distribution and NOx removal efficiency of TiO2 concrete corresponding to surface deterioration. The long-term durability of TiO2 concrete was evaluated through an environmental resistance test and changes in TiO2 penetration depth and distribution characteristics. In addition, the NOx removal efficiency of TiO2 concrete was evaluated as surface deterioration occurs. RESULTS : As a result of the freeze–thawing resistance test, a relative dynamic elastic modulus of more than 80 % was detected. In addition, a TiO2 penetration depth of 0.3 mm, NOx removal efficiency of 11.2 %, and a 30 % of TiO2 surface prediction mass ratio were achieved after 300 cycles. As a result of visual observation of the scaling test, “0, no scaling” was secured. After 50 cycles of scaling test, the TiO2 penetration depth, NOx removal efficiency, and TiO2 surface prediction mass ratio were 0.3 mm, 36.3 %, and 63 %, respectively. Through the results of the environmental resistance test, the excellent long-term durability and NOx removal efficiency of TiO2 concrete were confirmed. CONCLUSIONS : As a result of the experiment, long-term durability and NOx removal efficiency of TiO2 concrete were secured. The application of TiO2 concrete can be a good alternative with long-term performance and durability.

PURPOSES : The exposed aggregate number (EAN) and mean texture depth (MTD) of exposed aggregate concrete pavement (EACP) influence the functional performance of EACP in terms of pavement noise and skid resistance. The selection of the exposure time of EACP is important because the designed EAN and MTD of EACP can be achieved when the exposure process is performed at an appropriate time. On the one hand, too early exposure may cause protrusions and unwanted removal of aggregates and mortar. On the other hand, late exposure may cause difficulty in exposure of the mortar. In this study, a method to determine the optimum exposure time for EACP is suggested using a non-destructive method. METHODS : A set of laboratory tests was performed to investigate the variation in EAN and MTD of EACP according to the elastic modulus obtained by non-destructive equipment. From the results of this investigation, the optimum exposure time using the non-destructive method and the exposure time window (ETW) method was suggested. In addition, the usefulness of ETW suggested by laboratory tests was verified from a field application. RESULTS : From the laboratory tests, it was found that the targets of the surface condition of EACP (EAN: 59 per 25 cm2, MTD: 1.39 mm) can be achieved when the concrete elastic modulus is higher than 20GPa. The proposed guideline using the non-destructive method was applied for the field construction of EACP and achieved similar results. CONCLUSIONS : It was found that the proposed guideline for determining the exposure time window based on non-destructive testing is useful.

PURPOSES : Nitrogen oxides (NOx) are the main precursors to generate fine particulate matter, which significantly contribute to air pollution. NOx gases are transmitted into the atmosphere in large quantities, especially in areas with a high volume of traffic. Titanium dioxide (TiO2), which is a photocatalytic reaction material, is very efficient for removing NOx. The application of TiO2 to concrete road structures is a good alternative to remove NOx. Generally, TiO2 concrete is produced by mixing concrete with TiO2 . However, a significant amount of TiO2 in concrete cannot be exposed to air pollutants or UV. Therefore, an alternative method of penetrating TiO2 into horizontal concrete structures using a surface penetration agent was proposed in a previous study. This method may not only be economical but also applicable to various types of horizontal concrete structures. However, the TiO2 penetration method may not be applied to vertical structures because it has a mechanism for the penetration of TiO2-containing penetration agents via gravity and capillary forces. Therefore, this study aimed to evaluate the applicability of the pressurized TiO2 fixation method for existing vertical road structures. METHODS : For the application of vertical concrete structures — such as retaining walls, side ditches, and barriers — the applicability of a static and dynamic pressurized TiO2 fixation method was evaluated according to the experimental conditions, considering the amount of pressure and time. The penetration depth and distribution of TiO2 particles in the concrete specimen were measured using SEM/EDAX. In addition, the NOx removal efficiencies of TiO2 concrete were evaluated using the NOx analysis system. RESULTS : As a result of measuring the penetration depth and distribution of TiO2 in the concrete, it was found that the surface-predicted mass ratio increased with increasing pressure and time. In the case of the static pressurized fixation method, it was confirmed that a pressure time of at least 10 s at a pressure of 0.2 MPa and 5 s at a pressure higher than 0.3 MPa were required to achieve a NOx removal efficiency higher than 40 %. Conversely, for the dynamic pressurized fixation method applying a hitting energy of 16.95 J, NOx removal efficiencies higher than 50 % were secured in a pressure time of more than 3 s. CONCLUSIONS : The results of this study showed that the static and dynamic pressurized TiO2 fixation method was advantageous in penetrating and distributing TiO2 particles into the concrete surface to effectively remove NOx. It was confirmed that the proposed method to remove NOx was sufficiently applicable to existing vertical concrete road structures.

PURPOSES : Pavement growth (PG) is a phenomenon whereby the overall length of a concrete pavement increases. The increase in length induces an axial compressive force in the concrete pavement slab, resulting in blow-up and damage of adjacent structures, such as a bridge. PG is influenced by several interacting factors, including climatic conditions, pavement materials, joint systems, incompressible particles (IP) infiltrating the joints or cracks in the slab, and an expansion caused by reactive aggregates in the concrete. However, it is difficult to predict PG and blow-up due to various complicated factors. Therefore, in this study, the pavement growth and blow-up analysis (PGBA) package program was developed to predict the PG and blow-up potential. The PGBA can consider the pavement configuration, expansion joint (EJ) configuration, climatic conditions, and design reliability. To evaluate the effects of influencing factors — such as climatic data, EJ configuration, pavement structures and materials, and design reliability — on PG and occurrence time of blow-up, a numerical example was demonstrated and a sensitivity analysis was performed. METHODS : To predict the PG, the concrete temperature was calculated using an appropriate analytical model. The trigger temperature for pavement growth(TTPG) was predicted using a statistical equation that considers pavement age, joint spacing, and precipitation. An analytical solution for estimating the concrete slab movement was performed. Through the calculated TTPG and the amount of PG, the service life of the EJ (width of EJ) can be predicted compared to the allowable width. In addition, by using analytical and finite elements, the safe temperature(Tsafe) for preventing blow-up occurrence was calculated. The blow-up occurrence was assumed to occur when the variation between the concrete temperature and TTPG was larger than Tsafe. RESULTS :As a result of the sensitivity analysis of maximum temperature and precipitation, the temperature and precipitation increase and the EJ service life and possibility of blow-up decrease. Sensitivity analysis was performed on the thermal expansion coefficient, pavement thickness, base layer type, concrete elastic modulus, and joint rotational stiffness in the concrete pavement structure and properties. In the PGBA program, the coefficient of thermal expansion and the type of base layer significantly affect the EJ life, as do the possibility of blowup and the elastic modulus. The joint rotational stiffness and pavement thickness had little effect on the EJ life but were found to affect the possible timing of blow-up. As a result of the PGBA sensitivity analysis of the width and spacing, which are the specifications of the EJ, the life of the EJ and the possibility of blow-up increased as the joint width increased; however, the EJ life and blow-up increased as the EJ interval reached a certain value. It was found that the possibility of a blow-up occurrence decreased. The results for the PGBA program in extreme weather conditions, the life span of EJs, and the possibility of blow-up in normal climates were reduced by over 50 %. CONCLUSIONS : As a result of PGBA sensitivity analysis, it was found that the substrate type, thermal expansion coefficient, precipitation, and alkali-silica reaction had the greatest influence on pavement expansion and blow-up.

PURPOSES : NOx is a particle matter precursor that is harmful to humans. Various methods of removing NOx from the air have been developed. TiO2 and activated carbon are particularly useful materials for removing NOx, and the method is known as particulate matter precursor reduction. The removal of NOx using TiO2 requires sunlight for the photocatalytic reaction, whereas activated carbon absorbs NOx particles into its pores after contact with the atmosphere. The purpose of this study is to evaluate the NOx removal efficiency of TiO2 and activated carbon applied to concrete surfaces using the penetration method. METHODS : Surface penetration agents, such as silane-siloxane and silicate, were used. Photocatalyst TiO2 and adsorbent activated carbons were selected as the materials for NOx removal. TiO2 used in this study was formed by crystal structures of anatase and rutile, and plant-type and coal-type materials were used for the activated carbon. Each surface penetration agent was mixed with each particulate matter sealer at a concentration ratio of 8:2, and the mixtures were sprayed onto the surface. The NOx removal efficiency was evaluated using NOx removal efficiency equipment fabricated in compliance with the ISO 22197-1 standard. RESULTS : Anatase TiO2 showed a maximum NOx removal efficiency of 48% when 500 g/m² was applied. However, 500 g/m² of rutile TiO2 showed a NOx removal efficiency of up to 10%. When 700 g/m² of coal-based activated carbon and plant-based activated carbon was used, NOx removal efficiencies of up to 11% and 14%, respectively, were obtained. CONCLUSIONS : Rutile TiO2, a coal-based activated carbon, and plant-based activated carbon have lower NOx removal efficiencies than anatase TiO2. A lower amount of anatase TiO2 (500 g/m²), compared to the other spraying volumes, yielded the most significant NOx removal efficiency under optimal conditions. Therefore, it is recommended that 500 g/m² of anatase TiO2 should be sprayed onto concrete structures to improve the economic and long-term performance of these structures.

PURPOSES : Concrete pavement is excellent in structural performance and durability. However, its functionality – such as noise and skid resistance – is a shortcoming. Functionality such as noise reduction and skid resistance of concrete pavement is affected by the texture surface, and the texture surface is classified according to the length of the wavelength. In recent years, Fine-size exposed aggregate concrete pavement has been applied, which has excellent structural performance and durability, and secures functionalities such as noise reduction and long-term skid resistance by randomly forming texture surface. Fine-size exposed aggregate concrete pavements are constructed by removing the surface cement binder to randomly expose coarse aggregate and their functionality is mainly governed by the surface texture. However, deteriorated concrete by tire-pavement friction and deicing agent may cause abrasion and aggregate loss on the surface texture; thus reducing their functional performances. Abrasion is created by the thin cutoff of aggregate texture under repeated tire-pavement friction. In addition, aggregate loss is defined by the detachment of aggregates from cement binder. This study aims to evaluate the abrasion and aggregate loss of Fine-size exposed aggregate concrete pavement surface texture under tire-pavement friction and scaling tests. METHODS : In the study, abrasion and aggregate loss of tining and exposed aggregate concrete surface treatments were evaluated. Deterioration of each surface treatment was replicated by scaling test under ASTM C 672 test method. Afterward, abrasion test was conducted by ASTM C779 to simulate the tire-pavement friction under traffic. Consequently, abrasion and aggregate loss were measured. RESULTS : Abrasion depth of non-scaling tining, 10-mm EACP, and 8-mm EACP was 1.76, 1.12, and 1.01mm, respectively. Compared to scaling surface treatments, the difference of abrasion depth in tining texture was the largest with value of 0.4mm. For both textures of finesize exposed aggregate concrete, abrasion depth difference was about 0.1mm. Moreover, The 10-mm EACP exhibited a 2.6% of aggregate loss rate caused by tire-pavement friction before conducting concrete deterioration test. After 40-cycle scaling test, aggregate loss increased up to 12.2%. For 8-mm EACP, aggregate loss rate was 1.7% on non-scaling concrete. Further, this rate was magnified up to 7.3% for the 40-cycle scaling concrete. CONCLUSIONS : Under non-scaling or scaling tests, fine-size exposed aggregate concrete pavement showed better abrasion resistance than tining texture since tining was formed by aggregates and cement binder. Additionally, rate of aggregate loss was significant when EACP experienced the deicing agent under numerous cycles of freeze-thaw action.

PURPOSES : Pavement growth (PG) of concrete pavement has been recognized as a major concern to highway and airport engineers as well as to road users for many years. PG is caused by the pressure generation in the concrete pavement as a result of a rise of the concrete temperature and moisture. PG could result in concrete pavement blowup and damage the adjacent or the nearby structures such as bridge structures. The amount of the PG is affected by the complicated interactions of numerous factors such as climatic condition, amounts of incompressible particles (IP) infiltration into the joints, pavement structure, and materials. Trigger temperature for pavement growth (TTPG) is defined as the concrete temperature when all transverse cracks or joints within the expansion joints completely close and generating a pressure in the pavement section. It is one of the most critical parameters to evaluate the potential of PG occurring in the pavement. Unfortunately, there are no available methods or guidelines for estimating TTPG. Therefore, this study aims to provide a methodology to predict TTPG of a concrete pavement section. METHODS : In this study, a method to evaluate the TTPG and its influencing factors using the field measured data of concrete pavement expansions is proposed. The data of the concrete pavement expansions obtained from the long-term monitoring of three concrete pavement sections, which are I-70, I-70N, and Md.458, in Maryland of United Stated, were used. The AASHTO equation to estimate the joint movement in concrete pavement was used and modified for the back-calculation of the TTPG value. A series of the analytical and numerical solutions presented in the literatures were utilized to predict the friction coefficient between the concrete slab-base and to estimate the maximum concrete temperature of these three pavement sections. RESULTS : The estimated maximum concrete temperature of these three pavement sections yearly exhibited relatively constant values, which range from 40 to 45 °C. The results of the back-calculation revealed that the TTPG of the I-70 and Md.58 sections decreased with time. However, the TTPG of the I-70N section tended to be relatively constant from the first year of the pavement age. CONCLUSIONS : The estimation of the TTPG for the three concrete pavement sections showed that the values of the TTPG gradually decreased although the yearly maximum concrete pavement temperature did not change significantly.

PURPOSES: Nitrogen oxide (NOx) is a particulate matter precursor, which is a harmful gas contributing to air pollution and causes acid rain. The approaching methods for NOx removal from the air are the focus of numerous researchers worldwide. Titanium dioxide (TiO2) and activated carbon are particularly useful materials for NOx removal. The mechanism of NOx elimination by using TiO2 requires sunlight for a photocatalytic reaction, while activated carbon absorbs the NOx particle into the pore itself after contact with the atmosphere. The mixing method of these two materials with concrete, coating, and penetration methods on the surface is an alternative method for NOx removal. However, this mixing method is not as efficient as the coating and penetration methods because the TiO2 and the activated carbon inside the concrete cannot come in contact with sunlight and air, respectively. Hence, the coating and penetration methods may be effective solutions for directly exposing these materials to the environment. However, the coating method requires surface pretreatment, such as milling, prior to securing contact, and this may not satisfy economic considerations. Therefore, this study aims to apply TiO2 and activated carbon on the concrete surface by using the penetration method. METHODS : Surface penetrants, namely silane siloxane and silicate, were used in this study. Photocatalyst TiO2 and adsorbent activated carbons were selected. TiO2 was formed by the crystal structures of anatase and rutile, while the activated carbons were plant- and coal-type materials. Each penetrant was mixed with each particulate matter reductant. The mixtures were sprayed on the concrete surface using concentration ratios of 8:2 and 9:1. A scanning electron microscopy with energy dispersive X-ray equipment was employed to measure the penetration depth of each specimen. The optimum concentration ratio was selected based on the penetration depth. RESULTS: TiO2 and activated carbon were penetrated within 1 mm from the concrete surface. This TiO2 distribution was acceptable because TiO2 and activated carbon locate to where they can directly come in contact with sunlight and air pollutant, respectively. Infiltration to the concrete surface was easily achieved because the concrete voids were bigger than the nanosized TiO2 and microsized activated carbon. The amount of penetration for each particulate matter reductant was measured from the concrete surface to a certain depth. CONCLUSIONS : The mass ratio on the surface can be predicted from the mass ratio of the particulate matter reductant measurement distributed through the penetration depth. The optimum mass ratio was also presented. Moreover, the mixtures of TiO2 with silane siloxane and activated carbon with silicate were recommended with an 8:2 concentration ratio.

PURPOSES : This study investigates the abrasion characteristics of coarse aggregate using the Los Angeles (L.A.) abrasion test and the accelerated polishing machine (APM) test. The coarse aggregates are randomly exposed on the surface of asphalt concrete pavements and on exposed aggregate concrete pavements. The exposed aggregates play a very important role in providing skid resistance. Therefore, the adequate abrasion resistance of coarse aggregate must be ensured to maintain the skid resistance during service life. In Korea, the LA abrasion test is conducted according to the KS F 2508 standard for the evaluation of the abrasion resistance of coarse aggregate. However, the road surface abrasion is caused by the friction between the tire and the road surface structure; hence, whether the LA abrasion test, which evaluates the abrasion caused by the impact of coarse aggregates and steel balls, can evaluate the road surface abrasion is questionable. A comparison and an analysis between the APM and LA abrasion tests were conducted herein to evaluate the road abrasion. An analysis was also performed to analyze whether the abrasion characteristics appeared depending on the type of coarse aggregate. METHODS: The results of the APM and LA abrasion tests for various aggregate types were obtained through a series of experiments and literature reviews. The correlation between the LA abrasion loss and the PV data was derived. In addition, the influence of the aggregate type on the abrasion resistance was investigated. RESULTS : An abrasion resistance database was established, and the relationship between the rock types and the abrasion resistance was statistically determined. The results showed that the PV was increased to 0.54 along with a 1% increasing rate of the LA abrasion loss with a 0.67 coefficient of determination. The abrasion resistance was also influenced by the aggregate type, which was found to be statistically significant. CONCLUSIONS: A good relationship between the PV and the LA abrasion loss was obtained, allowing the use of the LA abrasion test (KS F 2508) alone, to reasonably evaluate the abrasion resistance of the exposed aggregate texture. The aggregate types were also found to have an impact on the abrasion resistance.

PURPOSES: The noise problem in concrete pavements has an adverse effect to the road user or nearby residents and is generated by the contact between a tire and the pavement surface. Exposed aggregate concrete pavements have been adopted to solve the tire-pavement noise problem in the United States and Europe. However, the efficiency of the coagulation retarder and exposure equipment used for this kind of pavement has not yet been investigated. Therefore, this study aims to evaluate the ability of the coagulation retarder and exposure equipment in producing the optimum exposed aggregate texture to achieve low pavement noise. A method for the exposure time selection has also been introduced here. METHODS: Sodium gluconate retarders were selected for use in this study. The retarder-water ratios of 1:1, 1:2, and 1:3 were investigated. The retarder was sprayed on a fresh concrete surface with rates of 200 g/m2, 300 g/m2, and 400 g/m2. The aggregates were then exposed to the surface using a steel brush and a water jet. The efficiencies for the low-noise texture, workability, and environmental impact produced by the two exposure devices were estimated. The EAN and the MTD were investigated according to the exposure time. RESULTS : The aggregates were exposed after the retarder was sprayed on the fresh concrete surface; the exposure lasted for 18 h to 26 h each time. The retarder-water ratio of 1:2 and the spraying rate of 300 g/m2 produced an optimum surface texture for low noise. Additionally, the steel brush performed more effectively in exposing aggregate to the surface compared to the water jet. The selected exposure time window (ETW) was 28 h to 35 h. CONCLUSIONS : The optimum retarder was the sodium gluconate retarder with a retarder-water ratio of 1:2 and a spraying rate of 300 g/m2. The steel brush showed a good performance in exposing the aggregates and showing the efficiency of the coagulation retarder in the given environment so as to produce the quality control condition. The ETW was influenced by the construction, mixture design, and construction environment; however, the selected ETW in this study was 26 h~35 h.

PURPOSES : In many European countries, the fine-size exposed aggregate concrete pavement (EACP) technique has been adopted for a quiet pavement. However, different noise reduction levels were reported based on the mixture design and texture conditions. This study aims to suggest a quality control condition for achieving low-noise texture and a mixture design procedure for exposed aggregate concrete overlay (EACO), which will provide the optimum mixture of the surface texture that can reduce the tire-pavement noise. METHODS : The tire-pavement noise is highly influenced by the pavement surface texture. The surface texture of the EACP can be quantified by the mean texture depth (MTD) and the exposed aggregate number (EAN). The optimum condition for the low-noise texture of the EACP was investigated herein based on the analysis of the review of the texture conditions and noise measurement in many EACP sites. RESULTS : The MTD and EAN criteria can be derived according to the investigated relationship between noise and texture condition. The optimum mixture design to satisfy these criteria can be achieved by controlling the maximum size of the coarse aggregate and the S/a. CONCLUSIONS: This study aimed to suggest a quality control condition for achieving low-noise texture and an optimum mixture design for EACO. As a result, we found that the early traffic opening of EACO can be achieved by using high early-strength cement.