Study on The Hydration Heat Control of Mass Concrete Using Granular Agent Coated by Thermoplasticity Film

Abstract

As the more number of large concrete structures are constructed world-wide, including Korea, the uses of mass concretes with large member sections are increased. But for large concrete structures, high hydration heat induces cracks due to thermal stress, imposing a bad influence on concrete durability. Because of such practical issues, researchers recently showed increased research interests on measures for preventing cracks and repair of them and on reinforcement methods, but not much research is conducted compared to the developed countries. The thermal stress due to hydration heat in large mass concrete structures is a complex result of a number of factors. Excessively high thermal stress or residual stress induces cracks on structure that cause bad influences on stability, durability, and water resistivity of mass concrete structures. In conventional work fields, such as dams, large-scale facilities are required for suppressing hydration heat. But excluding particular cases due to cost increase, there are general cases of structure construction where the method cannot be applied, and thus a new hydration heat control method is necessary. For more efficient exothermic rate control using hydration control, an internal temperature control that considers time factors is required. Most common methods using retarder elongates the duration of concrete setting time, and this also leads to the extended construction time. Thus in this study, approaching from materials aspect, we proposed a new set retarder that could lower the hydration heat of concretes and shorten the setting time. Using the tablets frequently used in the areas of medicine, powder-type set retarder was manufactured as granular-type in a cylindrical shape. By pan-coating the material, the set retarder surface was coated with paraffin. Paraffin is a type of phase transition material that could absorb or release heat to control hydration heat. In this experiment, we used the material as a temperature control material whose melting points ranges between 45 and 47℃. The properties of powder-type set retarder, granulated set retarder, and paraffin-coated granulated set retarder were compared and examined though setting tests. Based on the result, when the retarders are applied to the concretes, their effects on the hardening characteristics of concretes (slump, amount of air) and feasibility are checked. An experiment is conducted to compare durability of the hardened concretes for different retarders and analyze applicability from the concretes (compressive strength). Moreover, from 300×300×300mm sized mock-up test, hydration heat of high-strength concretes was measured. In this work, granulizing set retarder technology and paraffin coating technologies are emerged to control temperature time difference and reduce hydration heat within the concretes. In addition, to confirm its applicability, basic properties such as setting time, compressive strengths were examined. For the future research, based on the basic data from the experiments, various durability tests should be conducted to further confirm the applicability. The confirmed data will be helpful for practical usages in the construction fields and as well as other areas.