Soo Won Cha

Nonlinear Analysis of Temperature and Moisture Distributions in Early-Age Concrete Structures Based on Degree of Hydration

In this paper, adequate modeling of early-age concrete is used to realistically analyze the actual concrete structures at early ages. The models are incorporated into a 3-D finite element procedure. Mathematical formulation of the degree of hydration is based on the combination of 3 rate functions of reaction that represent effects of moisture condition as well as temperature. In moisture transfer, moisture transport coefficient, capacity, and sink are strongly dependent on the degree of hydration as well as the water-cement (w/c) ratio. The realistic models and finite element program developed in this work provide fairly good results on the temperature and moisture distribution for early-age concrete and correlate very well with actual test data.

Development of high-performance concrete having high resistance to chloride penetration

The resistance to chloride penetration is one of the simplest measures to determine the durability of concrete, e.g. resistance to freezing and thawing, corrosion of steel in concrete and other chemical attacks. Thus, high-performance concrete may be defined as the concrete having high resistance to chloride penetration as well as high strength. The purpose of this paper is to investigate the resistance to chloride penetration of different types of concrete and to develop high-performance concrete that has very high resistance to chloride penetration, and thus, can guarantee high durability. A large number of concrete specimens have been tested by the rapid chloride permeability test method as designated in AASHTO T 277 and ASTM C 1202. The major test variables include water-to-binder ratios, type of cement, type and amount of mineral admixtures (silica fume, fly ash and blast-furnace slag), maximum size of aggregates and air-entrainment. Test results show that concrete containing optimal amount of silica fume shows very high resistance to chloride penetration, and high-performance concrete developed in this study can be efficiently employed to enhance the durability of concrete structures in severe environments such as nuclear power plants, water-retaining structures and other offshore structures.