# Development of a Novel Concrete Curing Method Using Induction Heating System
## 1 Introduction  
It is well established that the low temperature of concrete curing in cold weather significantly impedes the rate of strength development. Specifically, [PERSON] and [PERSON] [1] indicated that no strength gain occurs when the concrete is frozen and is maintained frozen below \(-10\)\({}^{\circ}\)C, because of negligible cement hydration. Therefore, they strongly emphasized that fresh concrete must be protected at an early age to prevent damage from freezing until the adequate strength, 3.5 MPa recommended in accordance with ACI 306R [2], is gained. ACI committee 306 [2] recommends that \"cold-weather correcting practice\" is required to provide sufficient strength and durability to concrete placed in cold weather for it to satisfy the intended service requirements. According to ACI 306R [2], the temperatures of newly placed concretes with cross-sectional sizes of 1800 mm-300 mm should be maintained close to 5-13\({}^{\circ}\)C, respectively, using protection systems. The specific protection system required to maintain the recommended temperatures depends on several factors and it is known that only covering the concrete with insulating materials to use the natural heat of hydration is sufficient in certain cases. However, it may be necessary to construct enclosures and use heating units to maintain the desired temperatures in more extreme cases. Meanwhile, it is well established that high early strength can facilitate concrete production by reducing the construction time, labor, formwork, energy, and environmental impact. Early strength development is strongly influenced by several factors, including the water-cementitious material ratio, cement type and content, age of the paste, and curing method [3]. Although cement can react with water under conditions of room temperature and pressure, such cement would require more time to attain an adequate strength for industrial uses [3; 4]. Consequently, various heat-curing methods for concrete have been recommended and are being used to prevent damage by early freezing; ensure adequate strength in cold weather; and accelerate strength development at an early age for industrial use, particularly in precast concrete plants. For example, a combustion heater or electric heater is commonly used for curing of concrete in construction fields, particularly in cold weather, considering economy. However, the heating and energy efficiency is relatively low and the heater should be vented to prevent the reaction of carbon dioxide (CO\({}_{2}\)) in the exhaust gases with the exposed surfaces of newly placed concrete, to ensure the finish quality of a concrete floor and safety [2]. Certain combustion heaters can cause carbon monoxide poisoning to workers and fire, emphasizing the need for the availability of adequate fire-fighting equipment at the job site at all times. The use of fossil fuels in this curing method has a negative environmental effect because of the considerable CO\({}_{2}\) emission and energy consumption. Curing with steam at atmospheric pressure (live steam curing) or at a high pressure in an autoclave (high-pressure steam curing) is popular for precast concrete production since it provides an ideal curing environment and significant strength development at a very early age [2; 3]. However, non-uniform temperature distributions and simultaneous non-homogenous curing can occur with the application of steam curing [3]. Furthermore, steam curing can cause icing problems around the perimeter of the enclosure and the overheating or drying of the concrete surface [2]. In addition, steam curing uses fossil fuels and has a negative impact on the environment. Internal electric heating using embedded coiled and insulated electrical resistors can also be used to heat concrete [2]. With this system, the internal concrete temperature may be increased to any required level by selecting the appropriate coil spacing or pitch.