The portland cement consists of tricalcium silicate $(3 \mathrm{CaO} \cdot \mathrm{SiO}_2)$, dicalcium silicate
$\left(2 \mathrm{CaO} \cdot \mathrm{SiO}_2\right)$, tricalcium aluminate $\left(3 \mathrm{CaO} \cdot \mathrm{Al}_2 \mathrm{O}_3\right)$ and tetra-calcium aluminoferrite
$\left(4 \mathrm{CaO} \cdot \mathrm{Al}_2 \mathrm{O}_3 \cdot \mathrm{Fe}_2 \mathrm{O}_3\right)$. Hence, the major constituent in it is $\mathrm{CaO}$ and $\mathrm{SiO}_2$. The percentage of $\mathrm{CaO} \approx 64 \%$ and $\mathrm{SiO}_2$ is $21 \%$.