**4. Conclusions**

*Compressive Strength of Concrete*

**120**

(β-CS) [53].

**Figure 8.**

endothermic reaction which is as follows:

only at temperatures in the region of 900°C.

hydrates less rich in water and donation without it being formed of anhydrous compounds. These are mainly di-calcium silicates (β-C2S) and β-wollastonite

*ATG and ATD powder of concrete HPC at (a) 20°C, (b) 600°C, and (c) 900°C [18].*

The last peak coincides with the temperature of 800°C. It is well defined that in the temperature range from 700–900°C, the limestone decomposes, so this peak indicates the decomposition of calcium carbonates (CaCO3), also known as "calcite," by releasing lime accompanied by a release of CO2 [5] according to the highly

CaCO3 CaO + CO2.

A quasi-linear decrease is observed up to 800°C, and the concrete exhibits a severe decrease in the density above 800°C. This decrease in density is related to two phenomena, i.e., complete dehydration and anhydrous formation, which take place

From the study, one can conclude that, when using HPC specimen, the speed of temperature rising influences the drop in strength between 400 and 600°C.

