**5.2 Pozzolanic cement**

Pozzolanic cements are blends of Portland cement with pozzolanic material, which might be natural or synthetic. Natural pozzolanas are mostly volcanic in origin like diatomaceous earth. Fly ash, burnt clays, and shales are examples of materials utilized in synthetic pozzolanic.

Pozzolanas are materials (natural or synthetic) that have no cementitious properties, but they contain reactive silica (and alumina). When divided into fine form, they are capable of combining with lime (calcium hydroxide) in the presence of water to create compounds having cementitious characteristics [2, 32].

This cement is widely utilized because it has a strong resistance to different chemical attacks when compared to regular Portland cement.

#### **5.3 High alumina cement**

High alumina cement is a rapid hardening cement produced by fusing a combination of bauxite (aluminum ore) and limestone in a reverberatory or electric furnace or rotary kiln at 1500–1600°C.

The cement consists of about 30–40% lime, 45–50% alumina, up to 10% iron oxides, and preferably no more than 6% silica. Calcium aluminate (CaO · Al2O3) is the main cementing ingredient.

High alumina cement has a high early strength, as it can reach ultimate strength within 24 hours, a high heat of hydration, and a very high durability against high temperatures, frost, and chemical attacks [2, 33].

## **5.4 Slag cements**

Slag is the glass-like byproduct left over after separating a desired metal from its raw ore, and it is generally generated via a blast furnace–oxygen converter method or electric arc furnace. The primary components of these slags are calcium, iron, silicon, magnesium, and aluminum oxides, with lower quantities of phosphorus, manganese, and others depending on the raw materials utilized [2, 34].

