Temperaturberäkningar i härdande betongkonstruktioner med indata från isoterm kalorimetri

Detta är en Uppsats för yrkesexamina på avancerad nivå från Lunds universitet/Avdelningen för Byggnadsmaterial

Sammanfattning: Because of the significant release of carbon dioxide from the production of cement, the industry has developed several new types of cement. These new cements contain different types of supplementary cementitious materials that give different characteristics. To fully understand the charactaristics of these cements and products made from them, more reserch is needed. An example of such a characteristic is heat development, which is important to be able to predict, especially in massive structures, because of the risk of cracking. The method used today to calculate temperatures in concrete structures has input parameters measured with semi-adiabatic calorimetry. The use of this method is limited by the need to make many tests to evaluate the compressive strength as a function of temperature. In this report a calculation program that use input parameters measured with isothermal calorimetry is evaluated to investigate if it can complete with or replace some of the traditional measures. A concrete structure with temperature sensors was casted to evaluate if the calculation programs could describe the temperature development during the hydration of a real structure. The calculation program with semi-adiabatic parameters could be adapted to the real process with realistic assumptions, but not the calculation program with isothermal parameters. The result from the ''isothermal version'' of the program was different depending on the conditions. In the temperature range of 20-40 °C the results were almost the same as with the semi-adiabatic calculation, but when the concrete temperature exceeded about 45 °C the calculated temperatures were exaggerated. These differences can partly be explained if the cement reactions have a history dependence that means that different reaction products are formed depending on the previous temperatures during the hydration. Generally the temperature curve calculated with isothermal parameters was offset in time. This can however be the result of the method used when preparing the isothermal curves for the calculation program. If this is the case a method probably could be developed to adjust for this problem.

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