*4.1.7 Loss on ignition of the cement*

Loss on ignition is a test used in inorganic analytical chemistry, especially for mineral analysis. It entails strong heating (igniting) of a sample of the material to a specific temperature while letting volatile chemicals escape until the mass of the sample reaches a constant value. In most cement types, water is lost around 100–105°C, organic material is burned at around 550°C, and most carbonates are lost between 800°C and 1000°C, as mentioned in ASTM [24].

### **4.2 Chemical properties**

As mentioned previously, the main raw materials that make up cement are limestone and clay (silica, alumina, and iron oxide), as well as many other components including shells, chalk, and blast furnace slag. Chemical examination of cement raw materials reveals important information about cement's chemical properties [25].

**Tricalcium silicate (C3S), (3CaO · SiO2):** This is an important compound that provides early strength of cement paste during hydration (initial sitting).

**Dicalcium silicate (C2S), (2CaO · SiO2):** In contrast to tricalcium silicate, this compound enhances strength acquired after one week.

**Tricalcium aluminate (C3A), (3CaO · Al2O3):** This compound is characteristic for its fast reacting with water, which causes an immediate stiffness of the cement paste. In addition, small amounts of C3A make cement resistant to sulfate.

**Magnesia (MgO)**: A large amount of magnesia in cement can make it unsound and expand, but a small amount can make it stronger. CO2 emissions are also minimized while MgO-based cement is produced. The MgO percentage of all cement is capped at 6% [26].

**Tetracalcium aluminoferrite (C4AF), (4CaO · Al2O3Fe2O3):** Ferrite is a fluxing agent that lowers the raw material melting temperature in a kiln from around 1650–1420°C. Even though it hydrates quickly, it does not make a significant contribution to the hydration process [27].

**Sulfur trioxide and free lime:** Just like magnesia, excessive amounts can cause expansion and the cement to become unsound.

**Alkalis:** The alkali content of cement is determined by the quantities of potassium oxide (K2O) and sodium oxide (Na2O). Too much alkali in cement might make it difficult to control the cement's setting time. When used with calcium chloride in concrete, low-alkali cement can induce discoloration [28].

**Alumina:** Because alumina is chemical-resistant, cement with a high alumina content may tolerate frigid temperatures. It also speeds up the setting time but weakens the cement [29].

**Silica fume:** This is used to increase a range of qualities in cement, including compressive strength, abrasion resistance, and bond strength. Although the use of silica fume extends setting time, it can provide extremely high strength. As a result, cement with a silica fume content of 5–20% is typically used in high-strength cement projects [30].
