Kyung-Mo Koo

Hydration Heat and Autogenous Shrinkage of High-Strength Mass Concrete

Abstract In this study, to evaluate autogenous shrinkage of high-strength mass concrete with specimen size and hydration delay effects, the thermal deformation was calculated using thermal expansion coefficient (TEC) corrected by the maturity method, and was subtracted from measured total deformation. And the properties and relations of hydration heat and autogenous shrinkage at early ages were numerically analyzed. In test and analysis results, hydration temperature is affected by specimen conditions such as size and admixture, and change of hydration temperature could affect autogenous shrinkage; the higher hydration temperature and the greater autogenous shrinkage. There is a close relationship between hydration temperature and autogenous shrinkage at early ages, especially between HHV (hydration heating velocity) and ASV (autogenous shrinking velocity); the higher HHV, the higher ASV and the greater ultimate autogenous shrinkage. The points where hydration temperature and autogenous shrinkage start to increase rapidly are due to the consumption of gypsum in the cement hydration process, and are strongly related to the setting time.

A Fundamental Study on the Correlationship between Hydration Heat and Autogenous Shrinkage of High Strength Concrete at an Early Age

In this study, to analyze the correlation between hydration heat and autogenous shrinkage of high strength concrete at an early age, hydration heating velocity and autogenous shrinking velocity as quantitative coefficients which represent the main properties of hydration heat and autogenous shrinkage were proposed. Two coefficients were calculated by statistical analysis and were equal with the regression coefficient. The complemented semi-adiabatic temperature rise test as test method to evaluate the hydration heat and autogenous shrinkage of concrete were proposed. In results of proposed test and analysis method, it was possible that early age properties of hydration heat and autogenous shrinkage of concrete were expressed numerically, and autogenous shrinkage was represented by equation with coefficients of hydration heat.

The Analysis of Early Age Properties of Hydration Heat and Autogenous Shrinkage according to Specimen Size and Retardation of Hydration

Dept. of Architectural Engineering, College of Engineering, Chungnam National University, Daejeon 305-764, KoreaABSTRACT It has been reported that the magnitude and the development rate of autogenous shrinkage of cement paste, mortarand concrete were affected by history and magnitude of inner temperature at an early age. But it was not enough to explain therelation between hydration heat and autogenous shrinkage at an early age, because there was no certain analysis on histories ofhydration heat and autogenous shrinkage in previous studies. In our prior study, to understand the relationship between hydrationheat and autogenous shrinkage of concrete at an early age, the analysis method for histories of hydration heat and autogenousshrinkage was suggested. Based on this method, early age properties of hydration heat and autogenous shrinkage of high strengthconcrete with different sizes and hydration retardation were investigated in this study. As a result of the study, properties of hydra-tion temperature and autogenous shrinkage were different according to specimen size and hydration retardation. However, therewas a close relationship between hydration temperature and autogenous shrinkage at an early age, especially between HHV andASV as linear slopes of the sections where hydration temperature and autogenous shrinkage increase rapidly; the higher HHV, thehigher ASV and the greater ultimate autogenous shrinkage. And it was found that, among the setting time, bend point and tem-perature increasing point, they were close relationship each other on cement hydration process. Keywords : early age, hydration heat, autogenous shrinkage, specimen size, retardation of hydration

Effect of Crack Width and Waterproof Membrane Coatings on the Chloride Ion Penetration of Mortar Substrate

The purpose of this study was to evaluate the salt damage resistance of waterproofing membrane in order to protect the mortar or concrete substrate. Polyurethane and acrylic coating membrane were used, and the salt water immersion test and the chloride ion concentration test were carried out experimentally. Also, the salt damage in mortar was analyzed by comparing with the permeability of each specimens. Waterproofing membrane have a high salt damage resistance more than only non-coated substrate, and prevented the penetration of chloride ion from non-crack to 0.3mm-crack specimens in 13 weeks-accelerating test. Finally, the membrane thickness for suppressing salt damage was estimated from viewpoint of its permeability.

Properties of Autogenous Shrinkage according to Hydration Heat Velocity of High Strength Concrete Considering Mass Member

In this study, to reduce the hydration heat velocity (HHV) of high-strength mass concrete at early ages, phase change materials (PCM) that could absorb hydration heat were applied, and the changes in autogenous shrinkage were investigated, as well as the relationship between the hydration temperature and autogenous shrinkage. The acceleration of the cement hydration process by the PCM leads to an early setting and a higher development of the compressive strength and elastic modulus of concrete at very early ages. The function of PCM could be worked below the original melting point due to the eutectic effect, while the hydration temperature and HHV of high-strength mass concrete can be decreased through the use of the PCM. A close relationship was found between the hydration temperature and autogenous shrinkage: the higher the HHV, the greater the ultimate autogenous shrinkage.