5.1.4. Thermogravimetry (TG) and Differential Thermal Analysis (DTA)

In order to determine the effect of thermal treatment on the content of calcium hydroxide and calcium carbonate in RCM, the samples were subjected to thermogravimetry and differential thermal analysis. In Figures 8 and 9, the weight losses of material when heated to 1100 ◦C are presented for non-calcined and calcined RCM (at a temperature of 650 ◦C), respectively.

**Figure 8.** Thermal changes of RCM without thermal and mechanical treatment.

**Figure 9.** Thermal changes of RCM after thermal and mechanical treatment at temperature 650 ◦C.

Table 5 presents the content of bound water, portlandite and calcite in RCM specimens calculated on the basis of plots in Figures 8 and 9 and according to [35,36].


**Table 5.** Content of selected components of RCM.

The quite high content of calcium carbonates in both tested specimens is noteworthy. It results from the applied heating temperature equal to 650 ◦C, which does not cause the decomposition of CaCO3. This phenomenon occurs at a temperature above 750 ◦C, as indicated by peaks associated with mass losses in Figures 8 and 9. The higher CaCO3 content in calcined RCM can be explained by the presence of aggregate in the tested specimen. In the RCM specimen after heat treatment, however, there was no peak of portlandite, which confirmed a sufficiently well-selected RCM treatment temperature (Figure 9). Earlier heating of concrete rubble resulted in the disintegration of calcium hydroxide into calcium oxide and water, as evidenced by its lack in the tested RCM specimen in comparison with the untreated specimen. In the presence of water, free calcium oxide has the ability to undergo rehydration, as evidenced by the test results obtained.
