A Study on the Exothermic Properties and Reproducibility of Cement Paste Containing Electro-conductive Materials

Abstract

Due to abnormal climate by global warming, disasters caused by heavy snow and freezing are increasing in Korea as well. Current solution towards this disaster is mainly using chloride-based de-icing material, by direct or systemic spraying way. However, there are limitations in terms of current way such as follows; environmental pollution, corrosion of vehicle and facility, deterioration of concrete, time and expense-wasting problem. To solve out this limitation through construction material itself, electro-conductive exothermic concrete was developed. This concrete has a property of largely reduced electric resistance by mixing electro-conductive material. Researches on the utilization of this concrete were proceeded for the purpose of de-icing for road, floor heating, ground resistance reducing, and electromagnetic shielding. However, these researches remarkably decreased due to a problem which is a difficulty of securement of exothermic reproducibility in regards to same composition ratio of electro-conductive materials. The objective of this study is to find an optimized electro-conductive material and usage amount when mixed with cement, and to secure exothermic reproducibility. This electro-conductive material would be utilized as construction material for de-icing. For the purpose of the study, differently from conventional studies, several materials were mixed with cement to perform electrical conductivity. Improved graphite, for example, Flake graphite(FG), Expanded graphite(EG), Conductive graphite(CG) were experimented as test materials. In the conventional studies, natural graphite was mainly used for the study. In addition, as metal powder types, nickel, tin, and lead was tested. Lastly, high-range water reducing air entraining agent(superplasticizer with AE) was tested as well. This material has not been tested at all in developing electro-conductive concrete. With those materials, under low temperature (-3℃) environment, exothermic property, reproducibility, strength, and micro chemical analysis of sample specimen before and after application of voltage was carried out. Heat-generating temperature of specimen was measured. Cement paste specimen was made by adding graphite and electro-conductive materials. Test temperature was –3℃. As a result, specimen which FG and high-range water reducing air entraining agent(superplasticizer with AE) was added only showed heat-generation. When voltage was applied in the order of DC 10V, 30V, and 50V in the interval of 20 minutes, the temperature was increased up to about 80℃ and the specimen showed very high exothermic reproduction possibility. In case of using FG, it showed more excellent flexural and compressive strength than other electro-conductive material. The strength drop was relatively lesser than compressive strength. This result is judged that electro-conductive cement paste is not appropriate for structural material but showed possibility of deicing construction material such as finishing material. As a result of XRD and XRF test, which the specimen was [FG10%+WR2%] that only showed excellent exothermic performance and reproduction possibility under low temperature environment, the peak of graphite largely decreased and the amount of carbon was 2 times increased. This result is judged that polymer or Methacrylic acid (MAA, an unreacted monomer) component of high-range water reducing air entraining agent(superplasticizer with AE) reacted with graphite electrochemically and is synthesized to another organic compound which gave exothermic reproduction performance. Micro crack of concrete, which occurs by shrink and expansion of material caused by thermal change, or expansion coefficient difference between materials, causes variation of resistance and generates critical impact on exothermic reproducibility. Therefore, usage of air permeable synthetic resin which keeps moisture and passes heat, or addition of chemical material such as epoxy and acrylic agent, or chemical admixture, or carbon fiber is judged to be essential for the purpose of controlling crack.