본 논문은 염해 환경에 노출된 CFRP Grid로 보강된 콘크리트 보의 휨 거동에 대한 실험적 연구를 보고한다. 실험을 위해 길 이 2,200 mm, 폭 250 mm, 높이 125 mm의 실험체가 제작되었다. 실험변수로 염화물 수용액의 종류(NaCl: 염화나트륨, CaCl2: 염화칼 슘), 사전 하중 가력의 유무 및 염화물 용액 침지 기간(40일, 120일)이 고려되었다. 제작된 실험체는 침지 후 3점 휨 실험이 수행되었다. 초기 균열 하중은 침지 40일 후 증가하였으나, 120일 이후 다시 감소하였다. 파괴 모드는 사전 하중 가력을 통해 균열이 발생되지 않은 실험체에서는 대부분 콘크리트 압축부가 파쇄되는 휨파괴 양상을 보였으며, 사전 하중 가력을 통해 균열이 발생된 실험체는 모두 Pull-Out 파괴가 발생되었다. 염화칼슘에 침지된 실험체에서는 120일 이후 약 10%의 극한하중의 감소가 나타났으며, 염화나트륨에 침지 된 실험체의 극한하중은 미미하게 증가하였다. 균열이 발생된 실험체에서는 모두 120일 이후 극한하중 및 처짐이 급격하게 감소되었다.

콘크리트 구조물은 시간이 경과함에 따라 Steel Re-bar 부식 등이 원인이 되어 주요 구조부재의 내력이 저하된다. 이 를 방지하기 위해 아연도금, 에폭시 코팅, 피복두께 증가 등의 방법이 사용되지만 근본적인 문제가 해결되지 않는다. 최근 들어 Steel Re-bar를 대체할 복합섬유에 대한 연구가 활발히 수행된다. CFRP Re-bar는 경량이며 고강도이고 내식성이 우수하다. Steel Re-bar의 임계온도는 538℃인 반면 CFRP Re-bar의 임계온도는 250℃로 화재에 취약하다. 따라서 건설현장에 적용하기 위한 내 화피복 방안이 필요하다. 본 연구에서는 콘크리트 피복두께(40, 60, 80mm), SFRM(0, 15, 30mm)두께를 변수로 CFRP Re-bar가 배 근된 표준화재 3시간 노출된 콘크리트 기둥 단면의 온도분포를 확인하고, 온도상승에 따른 소재 강도 감소를 고려하여 P-M상관 도를 도출하였다. 이를 통해 건설현장에 CFRP Re-bar를 사용하기 위한 내화피복 두께를 제안하고자 한다. 1시간 내화성능을 만 족하기 위해 콘크리트 피복두께가 60mm 필요하며, 2시간은 80mm가 필요하다. SFRM 15mm를 도포하면 400×400 단면의 경우 2 시간, 600×600과 800×800 단면의 경우 3시간 내화성능을 만족한다.

PURPOSES : The exposed aggregate concrete pavement (EACP) is adopted to achieve low traffic noise and long-term skid resistance in European countries such as Belgium and Germany. In Korea, it is first introduced at the Myeon Cheon field site in 2010. It reduces 3 dB(A) from tire–pavement noise compared with transverse tining. Recent investigations show that EACP can reduce tire–pavement noise by an additional 5 dB(A) compared with transverse tining. In this study, the tire–pavement interaction noise of EACP is compared with that of conventional pavements such as asphalt pavement, next-generation concrete surfaces (NGCS), and transverse tining. METHODS : EACP is constructed at two field sites on the SOC research center and Yeo-Ju test road to compare the noise level via close proximity noise measurement. In addition, the noise is measured using two vehicle type based on vehicle speeds of 60, 80, and 100 km/h. RESULTS : The results of noise measurement obtained from the SOC research center are as follows: Porous asphalt pavement 92.8 dB(A), HMA 96. dB(A), transverse tining 100.1 dB(A), and 8 mm EACP 97 dB(A) at a driving speed of 80 km/h. For the case of the Yeo-Ju test road. The noise levels at a driving speed of 80 km/h are as follows: 6 mm EACP, 93.6 dB(A); asphalt grooving pavement, 94.72 dB(A); 8 mm EACP, 95.2 dB(A); NGCS, 95.2 dB(A); transverse tining, 104.1 dB(A). CONCLUSIONS : The result of noise measurement of two sites in the SOC research center and test road shows that the noise level of the 6 mm EAC is lower than that of concrete pavement, such as tining and NGCS, and similar to that of asphalt pavement. In addition, the noise level of the 8 mm EAC is similar to that of the NGCS pavement. The noise reduction effect of the EAC is greater when small-sized coarse aggregates with lower flat and elongation ratios are used.

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 : 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: 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.

PURPOSES : In Korea, asphalt overlay has been used as a typical alternative rehabilitation method for deteriorated pavements. However, asphalt overlay has problems due to poor bonding of the asphalt overlay and the old concrete. Recently, concrete overlays, which have advantages such as long-term durability and high structural capacity to carry heavy traffic, have been considered for rehabilitation construction. However, concrete overlays have limitations such as difficulty in opening to traffic and pavement noise. Recently, an appropriate fine-size exposed aggregate concrete pavement technique was reported to solve these problems. Therefore, this study aims to suggest an optimum mixture design of fine-size exposed aggregate concrete overlay (EACO) that can ensure low noise and early strength. METHODS : The optimum mixture design of fine-size EACO is determined to ensure adequate structural performance for early traffic opening and good functional performances such as low noise. Therefore, the optimum mixture proportion is determined based on the optimum design of aggregate content to produce a low-noise pavement texture by controlling the exposed aggregate number (EAN) and mean texture depth (MTD). RESULTS : The water-cement ratio and unit cement ratio were used to determine the mixture designs to achieve workability and adequate strength for early traffic opening. The texture was determined by selecting the maximum size of coarse aggregate smaller than 10 mm with an S/a ratio of less than 30% for low noise. With these mixture proportions, the EAN and MTD were 50±5 / 25cm2 and 1.0±0.2 mm. Respectively, which meet the criteria for EACO. CONCLUSIONS: In this study, an optimum mixture design of EACO for early traffic opening and low noise is suggested by using earlyhigh strength cement, and the pavement texture is implemented considering EAN and MTD. In addition, a pavement surface texture criterion is suggested for the quality control of EACO.

PURPOSES : Exposed aggregate concrete pavements have been adopted in several countries because of their advantages of pavement texture characteristics, which can produce low tire-pavement noise and higher load-carrying capacities. The magnitude of tire-pavement noise greatly depends on the wavelength of pavement texture. The wavelength of exposed aggregate concrete pavement can be controlled with maximum sizing and by controlling the amount of coarse aggregates in the concrete mixture. In this study, the maximum size and the amount of coarse aggregate in the exposed aggregate concrete pavement are investigated to produce equal levels of wavelength in the asphalt pavement. METHODS: A simple method to measure the average wavelength of pavement texture is introduced. Subsequently, the average wavelength of typical asphalt pavement is investigated. A set of mixture designs of exposed aggregate concrete with three maximum-sized coarse aggregates, and three amounts of coarse aggregate are used. The average wavelengths are measured to find the mixture design needed to produce equal levels of wavelength as typical asphalt pavement. RESULTS : With a cement content of 420 kg/m3 and fine aggregate modulus of 30%, the number of exposed aggregates was 48, and the shortest texture depth provided a wavelength of 4.2 mm. According to the number of exposed aggregates, the exposed aggregate concrete pavement could be rendered low-noise, because its wavelength was similar to that of asphalt pavement ranging from 3.9 to 4.4 mm. CONCLUSIONS : Selection of appropriate maximum sizes and the amount of coarse aggregates for exposed aggregate concrete pavement can produce a wavelength texture closely resembling that of asphalt pavement. Therefore, the noise level of exposed aggregate concrete pavement can be reduced with an appropriate maximum size and the amount of coarse aggregates are employed.

PURPOSES : In Korea, concrete pavements with transverse tining, which have excellent skid resistance, have been mainly constructed to secure road bearing capacity and safety. However, transverse tining has higher noise level of approximately 4-5 dB(A) compared with asphalt pavement. As a method to determine low-noise characteristics of concrete pavements, the fine-size exposed aggregate concrete pavement (EACP) has been studied in Korea and abroad. The surface of EACPs consists of exposed coarse aggregates and 2-3 mm removal surface mortar. EACPs have the advantages of maintaining low-noise and adequate skid-resistance levels during the performance period. Although EACPs have been widely studied to reduce noise, quantitative noise analysis with various paving methods has not been performed owing to differences in mixture proportioning, construction conditions, environmental conditions, and measurement methods. Therefore, the purpose of this study is to investigate the low-noise characteristics of fine-size EACPs by comparing noise with various paving methods, including concrete and asphalt pavements. METHODS: In this study, noise data were collected to quantitatively analyze the low-noise characteristics of EACPs compared with various paving methods such as transverse tining, longitudinal tining, SMA, and HMA. RESULTS: The evaluation of the low-noise characteristics of EACPs compared with transverse tining showed that the relative noise of 13 mm EACP with transverse tining was reduced by approximately 2% at 60 km/h, 4% at 80 km/h, and 5% at 100 km/h. The relative noise of 10 mm EACP with transverse tining was reduced to 3%, 7%, and 8% at 50 km/h, 80 km/h, and 100 km/h, respectively. In addition, it was confirmed that the noise of 10 mm EACP was similar to that of asphalt pavement. CONCLUSIONS : It was confirmed that EACP using 10 mm coarse aggregates generates lower noise than that using 13 mm coarse aggregates. Therefore, the use of coarse aggregates smaller than 10 mm needs to be considered to improve the low-noise effect of EACP.

콘크리트 교면포장의 주행쾌적성 및 주행안정성 향상을 위하여 노출 교면 콘크리트 포장에 고기능성 표면처리 공법(NGCS : Next Generation Concrete Surface)을 적용하였다. 노출 교면 콘크리트 포장 구 간에서 NGCS의 적용 전･후에 따른 소음(차량 내부, 외부), 주행쾌적성, 미끄럼저항성, 평탄성 변화 등 기 능성 변화를 조사하였다. 그림 1은 NGCS를 적용한 노출 교면 콘크리트 포장 표면을 보여준다. NGCS 적 용 구간은 총 2개 교량으로 교량 A는 3경간 330m, 교량 B는 단경간 75m으로 구성되어 있다. NGCS 적 용 전･후에 따른 기능성 분석 결과를 표 1에 나타내었다. NGCS 적용 결과 두 교량 모두 소음, 미끄럼저 항성, 주행쾌적성 및 평탄성이 개선되었으며, 특히 장경간 교량에서 기능성 개선효과가 탁월한 것으로 분 석되었다. 향후 노출 교면 콘크리트 포장의 NGCS 공법 적용을 안정적으로 시행하기 위해서 NGCS 표면 의 표면탈리 등을 예방하고 장기 내구성 확보를 위하여 교면 콘크리트의 압축강도 기준을 30MPa로 이상 으로 설정하는 것을 제안하였다.

PURPOSES: This study investigates the mechanical performance of carbon-capturing concrete that mainly contains blast furnace slag. METHODS: The mixture variables were considered; these included Portland cement content, which was varied from 10% to 40% of the blast furnace slag by weight. The specimens were exposed to different conditions such as high N2 and O2 concentrations, laboratory conditions and high CO2 conditions. Mechanical performances, including compressive and flexural strengths and carbon-capturing depth, were evaluated. RESULTS : The slump, air content and unit weight were not affected significantly by the variation in cement content. The strength development when the specimens were exposed to high purity air was slightly greater than that when exposed to high CO2. As the cement content increased the compressive and flexural strength increased but not considerably. The carbon-capturing capacity decreased as the cement content increased. The specimens exposed in the field for 70 days had flexural strength greater than 3 MPa. CONCLUSIONS : The results indicate that cement content is not an important parameter in the development of compressive and flexural strengths. However, the carbon-capturing depth was higher for less cement content. Even after field exposure for 70 days, neither any significant damage on the surface nor any decrease in strength was observed.