Abstract
A modified method of interpreting a heat flux differential scanning calorimetry records in pore structure determination is presented. The method consists of determining the true phase transition energy distribution due to the melting of water during a differential scanning calorimetry (DSC) heating run. A set of original apparatus functions was developed to approximate the recorded calorimetric signals to the actual processes of the water phase transition at a given temperature. The validity of the proposed calorimetric curves-based algorithm was demonstrated through tests on a cement mortar sample. The correct analysis required taking into account both the thermal inertia of the calorimeter and the thermal effects that are associated with water transitions over the fairly narrow temperature ranges close to 0 °C. When evaluating energy distribution without taking the shifts of the proposed modified algorithm into account, the volume of the pores with radii bigger than 20 nm was greatly overestimated, while that of the smaller pores (rp < 20 nm) was underestimated, in some cases by approximately 70%.
Highlights
Water phase transition in the mortar pore space has long been in the scope of interest and has been investigated by using numerous methods
Thermoporometry through the use of the differential scanning calorimetry (DSC) has been widely applied to study the influence of curing conditions [1,2,3], admixtures [4], additives [5] and the types of cement [6] that are used on the freezing process in cement-based materials
The theoretical principles of thermoporometry were thoroughly described by Brun et al [7]
Summary
Water phase transition in the mortar pore space has long been in the scope of interest and has been investigated by using numerous methods. Even at a small scanning rate, there is always a certain temperature shift of the recorded signals in relation to the temperatures at which the exo- or endothermic processes occur Another approach to eliminate the influence of thermal inertia on the temperature of recorded effects is the quasi-isothermal mode (QI-MDSC) in differential scanning calorimetry [19], which allows for the assignment of the obtained results to temperatures. This method is able to handle samples of the order of milligrams in which temperature gradients are small. The idea of Kozłowski’s solution was used to construct modified algorithm
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