OPC, PPC and PSC are variants of Portland cement. Portland cement is formed when clinker is finely ground. When you add gypsum to this Portland cement, it results in Ordinary Portland Cement (OPC). If you add fly ash to Portland cement, it produces Portland Pozzolana Cement (PPC). Similarly, when you add slag to Portland cement, you get Portland Slag Cement (PSC). Essentially, PPC and PSC are blended variants of Portland cement.

The main difference between grey and white cement is the concentration of iron oxide and manganese oxide. Grey cement is called as such due to relatively higher levels of these compounds. On the other hand, white cement has relatively lower levels of iron oxide and manganese oxide. Additionally, white cement has a finer texture and a higher refractive index than grey cement. The fuel used to form grey cement comprises coal, petroleum coke and natural gas. Burning such fuel results in coal ash. Coal ash can contaminate white cement, hence white cement is formed using oil. In construction, grey cement is synonymous with simply cement.

Normally, the concrete must be cured for at least 7 to 12 days. Ensure that the vertical components like columns or wall are cured after they’ve been wrapped in hessian cloth for better results.

Not necessarily. Note that cement is a hygroscopic material, i.e., it has the tendency to absorb moisture quickly. If kept in dry conditions, cement can last longer. If it has been a long time, make sure you test the cement before use.