국내에서는 공용 중인 교량의 덧씌우기식 교면 포장 공사에서 빠른 개통을 위해 초속경 시멘트와 라텍스를 이용한 초속경 LMC 콘 크리트가 주로 적용된다. 고속도로에서는 교통 개방을 위한 콘크리트의 기준 강도를 압축강도 21MPa로 정하고 있다. 본 연구에서는 시공된 콘크리트의 강도 추정을 위한 적절한 비파괴 시험 방법을 선정하기 위해 약간의 손상을 포함하는 Break-off 시험을 적용하였 다. 실내 실험을 통해 수립된 시험 절차에 따라 47개 현장에서 시험을 수행하여 압축강도와 상관관계를 분석하였고, 현장적용성을 확 인하였다.

국내 시멘트 콘크리트계 교면포장의 개방강도는 압축강도를 기준으로 하고 있으나, 현장의 양생 조건과 동일한 콘크리트의 강도를 추정하여야 한다. 약간의 손상을 포함하는 비파괴 시험이 표면에서 측정하는 방법보다 압축강도와 상관관계가 높으므로, 본 연구에서 는 Break-off 시험과 압축강도의 관계를 도출하기 위한 일련의 연구를 수행하였다. 6개의 초속경 LMC 배합에 대해서 Break-off 시험을 수행하였고, 국내 교면포장 현장에 적합한 코어의 크기를 정하였다. 또한 유압펌프와 압력게이지, 가력부로 구성된 자체 시험기를 개 발하였다. Break-off 시험 결과 압축강도와 높은 상관관계를 나타내었고, 국내 시멘트 콘크리트 교면포장의 경계조건을 고려할 경우, 높이 70mm의 코어를 형성하는 것이 합리적이고, 신설포장이나 단면보수의 경우 높이 50mm인 코어를 사용할 수 있도록 제안하였다.

이 연구는 셀룰로오스 또는 실리카를 포함하고 있는 목재, 왕겨 및 축분 바이오차로 시멘트 또는 잔골재를 대체한 콘크리트 의 강도시험을 통하여 역학적 특성을 파악한 것이다. 시험결과에 따르면, 바이오차 종류에 따른 강도는 왕겨 바이오차 혼입 콘크리트가 가장 크고, 다음으로 목재 바이오차였으며, 축분 바이오차가 가장 낮은 것으로 나타났다. 그리고 시멘트 또는 잔골재의 대체율에 따른 콘크리트 강도는 왕겨 바이오차의 대체율이 증가할수록 강도가 감소하였으나, 목재 및 축분 바이오차의 경우에는 대체율에 따라 강도 가 증가 하였다. 또한, 바이오차를 혼입하지 않은 보통 콘크리트와 비교하여 왕겨, 목재 및 축분 바이오차 순으로 최대 강도가 90%에 서 99%까지였으며, 압축강도로 추정하는 휨강도 또는 쪼갬인장강도 또한 보통 콘크리트의 상관 계수와 비슷하였다. 이와 같은 시험결 과를 근거로, 바이오차를 혼합한 콘크리트의 역학적 특성은 대체율에 따른 차이에도 불구하고 보통 콘크리트와 비슷한 강도를 확보할 수 있으므로 바이오차를 콘크리트의 새로운 혼화재료로 사용할 수 있을 것으로 판단된다.

PURPOSES : The purpose of this study is to confirm the thermal expansion characteristics of concrete mixed with 1% waste glass fine aggregates, which is the amount stipulated for recycled aggregates in the current quality standard. METHODS : The coefficient of thermal expansion was measured by applying AASHTOT 336-10 using a LVDT. The results measured were used as physical properties in a finite element analysis to confirm the change in tensile stress and the displacement of the right angle section of the upper slab of a concrete pavement due to admixture substitution. RESULTS : The thermal expansion coefficients of concrete based on the replacement rate of the admixture when the waste glass fine aggregates are replaced are within the range of the thermal expansion coefficients of concrete specified in the Federal Highway Administration report. As the replacement rate of the admixture increases, the thermal expansion coefficient of concrete decreases. As the thermal expansion coefficient decreases, the slab pavement curling displacement and the tensile stress of the center of the upper slab of concrete decrease. CONCLUSIONS : In the short term, the presence or absence of waste glass fine aggregates does not significantly affect the thermal expansion coefficient of concrete. However, in the long term, waste glass fine aggregates are reactive aggregates that causes ASR, which creates an expandable gel around the aggregates and results in concrete expansion. Therefore, the relationship between ASR and the thermal expansion coefficient must be analyzed in future studies.

PURPOSES : Currently, the domestic construction industry is dominated by large-scale projects such as roads, ports, airports, and buildings. Construction on such projects is generally conducted simultaneously, but the process and quality management are led by a small number of responsible managers. In the case of road pavements, owing to rapid industrial development, economic growth, and the expansion of social overhead capital investment in the road construction industry, highways and general national roads have been constructed on a large scale. Therefore, this study aimed to improve and develop domestic concrete production and construction quality management by improving the reliability and transparency of production quality management and simplifying business processes. This was accomplished through the development of an Internet of Things (IoT)-based cement quality management system capable of automated design and build (D/B) construction and real-time monitoring. METHODS : The "IQ" system is a quality management system for enabling real-time monitoring of D/B quality at the time of concrete production and according to the designated age by utilizing quality test equipment developed with an LTE-Bluetooth function. It is possible to immediately identify and respond to quality problems through real-time monitoring, secure a reliable quality D/B because the quality test results cannot be arbitrarily manipulated, and to simplify the work process through the automatic D/B construction. In addition, improved quality control can be achieved through real-time information sharing and feedback system operations between contractors, managers, and personnel involved in construction. The quality control test items for developing the IQ system are the compression and flexural strengths, as these can be used to determine the design standard strength of pre-curing concretes (such as their slump and unit quantity) and the adequacy of the workability and durability, as well as the air volume to predict the durability, and the chloride content in the sections where reinforcement is used. CONCLUSIONS : This study identified difficulties and limitations in quality management according to the operation method in the domestic quality management systems, and in the real-time monitoring between managers and contractors. Thus, it was necessary to establish an improved systematic and reliable quality management system. The IQ system was developed to solve this problem.

PURPOSES : The purpose of this study is to identify the dynamic behavior of a cement concrete paving machine (paver) by measuring its response using accelerometers. This is because the dynamic behavior of pavers affects the quality of data from various applications of IoT sensors, such as laser, ultrasonic, optical sensors and so on. Therefore, it is believed that the understanding of dynamic behaviors can contribute to the effective use of various IoT sensors for the acquisition of real-time quality control data in pavement construction. METHODS : Dynamic signals are obtained using accelerometer sensors to identify the dynamic characteristics of paving machines. The main parameters for acquiring dynamic signals are the status of the machine’s operating or standby conditions, and available locations for attaching various IoT sensors. Time domain data are logged at a particular sampling speed using a low-pass filter, subsequently, they are converted to digital data, which are analyzed on three rectangular axes. In addition frequency analysis is conducted on the measured data for identifying the peak frequencies, via FFT (Fast-Fourier-Transform) using MATLAB. RESULTS : The magnitude of the x-directional vibration is higher than that of any other direction under the paver’s operating or standby condition. However, signals from the smoother beam show that the z-directional vibration is more significant in the operating status. It means that the primary vibration depends on the location. Furthermore, the peak frequencies are quite various depending on the status of a paver and its sensing location. CONCLUSIONS : The magnitude of machine vibration and peak frequencies at each status or location are identified from time- and frequency-domain data. When using IoT sensors for quality control or monitoring pavements in construction, the dynamic characteristics of a paver should be considered to mitigate the interference of signals from the paver body or its elements.

PURPOSES : The objective of this study is to evaluate the mechanical properties of ternary blended cement concrete incorporated with pulverized reject ash (PRA) or pulverized fuel ash (PFA) based on a comparison with those of ordinary Portland cement (OPC) concrete. METHODS : To produce the concretes, the level of OPC replacement is set at 60%, which comprises 30%~45% ground granulate blast furnace slag and 15%~25% of fly ash (FA). The FA can be categorized into PFA, 4PRA (fineness 3,930 cm2/g3), and 8PRA (fineness 7,840 cm2/g3). The compressive strength, surface electric resistivity, initial absorption coefficient, and chloride ion penetrability of OPC and the ternary blended cement concrete are measured at predetermined periods after water curing. RESULTS : It is discovered that the mechanical properties of concrete with 8PRA are better than those of OPC concrete. The performance of 4PRA concrete is worse than that of 8PRA concrete, indicating that the fineness of the PRA can affect the mechanical properties of the ternary blended cement concrete. CONCLUSIONS : The use of PRA is feasible for the production of ternary blended cement concrete, provided that the appropriate mix design and grinding technology are used.

PURPOSES : For high driving performance and service life of cement concrete pavement, construction quality must be secured. The construction quality is to be measured after pavement construction, but in this case, it is difficult to improve construction quality. Therefore, it is necessary to develop a method for measuring and correcting the profile of the pavement and subbase so that the construction quality can be monitored immediately after construction. METHODS : The device that can measure the construction quality of cement concrete pavement has been developed. Through the experiment simulating the field situation, the profile of the pavement and subbase was measured and calibration method was developed. RESULTS : In the measured profile, an outlier by the sensor and noise by the sensor and vibration were measured, and a step-like profile was measured differently from the acture one. To remove outliers, the boxplot outlier removal method was applied by overlapping each data group. The noise were removed by a low pass filtering. And, it was calibrated to a profile similar to the acture one through the sampling interval adjustment and the weighted moving average method. CONCLUSIONS : The method that can measure and calibrate the profile that is almost identical to the actual one has been developed. Accordingly, it is expected that the performance of the pavement can be improved by accurately monitoring the construction quality immediately after construction.