To study the porous structure of the C-S-H formed in cement pastes in the presence of MSWI fly ash, Differential Scanning Calorimetry (DSC) tests were carried out on different cement pastes. Two cement pastes were made: a pure paste Class P-C1 (W/C = 0.4) and a paste containing MSWI fly ash Class P-FA (W/C = 0.4 and 20 % MSWI fly ash in place of cement). The components were blended manually in plastic bags then cured in sealed PVC bottles.
The DSC tests were carried out after (1, 3, 8, 14, 28 and 60) d of hydration. These tests involved measuring the heat flux released by a sample subjected to temperature variation. The heat flow peaks enabled us to identify the temperatures at which changes in state took place within the material. In our tests, the cement pastes underwent a fall in temperature from + 5 ºC to − 60 ºC at a rate of − 0.5 ºC/min. The heat flow peaks allowed us to identify the temperatures at which water solidification takes place within the material. These temperatures are influenced essentially by two parameters: the size of the material's pores and the concentration of the interstitial solution. To differentiate between the influence of these two parameters, the interstitial solutions of the two cement pastes P-C1 and P-FA were replaced by distilled water. The two cement pastes were immersed successively in ethanol for 3 d, in ethylene glycol for 3 d and finally in distilled water for 4 d. The cement pastes were then subjected to a temperature drop from + 5 ºC to − 70 ºC at a rate of − 0.5 ºC/min.