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Structural lightweight concrete (SLWC) has superior properties that allow the optimization of super tall structure systems for the process of design. Because of the limited supply of lightweight aggregates in Korea, the development of structural lightweight concrete without lightweight aggregates is needed. The physical and mechanical properties of specimens that were cast using normal coarse aggregates and different mixing ratios of foaming agent to evaluate the possibility of creating structural lightweight concrete were investigated. The results show that the density of SLWC decreases as the dosage of foaming agent increases up to a dosage of 0.6%, as observed by SEM. It was also observed that the foaming agent induced well separated pores, and that the size of the pores ranged from 50 to 100 μm. Based on the porosity of concrete specimens with foaming agent, compressive strength values of structural lightweight foam concrete (SLWFC) were obtained. It was also found that the estimated values from proposed equations for compressive strength and modulus of elasticity of SLWFC, and values obtained by actual measurements were in good agreement. Thus, this study confirms that new structural lightweight concrete using normal coarse aggregates and foaming agent can be developed successfully.

The purpose of this research is to verify the performance of hardening accelerator in cement paste through mechanical performance evaluation and micro structure analysis on hardening accelerator for development of super high early strength concrete. The research results showed that hardening accelerator produced Ca(OH)2 when hydrated with cement, enhancing the degree of saturation of Ca ion by using differential thermal analysis. Moreover, porosity was reduced rapidly as capillary pores were filled by hydration products of C3S. According to the experiment using hydration measurement testing, when 1% and 3% of accelerator were mixed, hydration rate increased toward the second peak point compared to high early strength cement, before the first peak point disappeared. It turned out that adding accelerator accelerated the hydration rate of cement, especially C3S. The shape of C-S-H is shown depending on the amounts of accelerator added and the production and age of Ca(OH)2 by using SEM to observes hydration products. Therefore, it's evident that hardening accelerator used in this research increases amounts of Ca(OH)2 and accelerates C3S, it is effective for the strength development on early age.

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This study investigated the physical properties and electromagnetic pulse (EMP) shielding performance of cement paste containing small-diameter carbon fibers to develop an EMP-shielding cement. Small-diameter carbon fibers were used as a cement admixture because the powders were approximately 100 μm in length and were visually powder-shaped. As a result of the experiment, it was indicated that ordinary Portland cement do not have shielding performance. However, cement paste with 5% carbon fibers showed effectiveness in compressive strength and EMP shielding. However, the shielding performance did not increase when the cement contained more than 5% carbon fibers. Furthermore, a review of the EMP shielding performance relative to the thickness of the specimen showed that the plain cement without small-diameter carbon fibers did not increase the shielding performance with an increase in thickness, but the shielding performance of the specimens with small-diameter carbon fibers increased with an increase in thickness. Therefore, it was more effective to increase the thickness of the cement containing 5% carbon fibers rather than increasing the carbon fiber content.