On the cement bag, the week number, month and year of manufacturing are mentioned, and this can be checked before use.

Fineness defines the surface area of cement particles present per unit weight, which implies that more fineness means more particles in unit weight. This enhances the reaction rate which in turn will result in faster gain of strength at earlier stages.

Cement which is in the form of a fine powder tends to absorb moisture present in the atmosphere. When it absorbs moisture it hydrates, and when subsequently used does not contribute to the strength development. Jute bags (gunny bags) in which cement is bagged are neither airtight nor damp-proof and do not prevent absorption of moisture. Cement deteriorates in quality on long storage.
Cement bags in woven polythene bags or paper bags are not likely to deteriorate to the extent mentioned above. The loss of strength also depends on the condition of the godown. It is advisable to use cement within three months of its bagging or to test the cement for its strength if stored for longer periods. Hence cement bought first should be used first.

The initial set is when the cement paste loses its plasticity and stiffens considerably. The final set is the point when the paste hardens and can sustain some minor load. Both are arbitrary points, and these are determined by Vicat needle penetration resistance.

Slag cement can be used for all plain and reinforced concrete constructions, mass concrete structures such as dams, reservoirs, swimming pools, river embankments, bridge piers, etc. It is used with advantage where low heat of hydration and resistance to alkali-silica reaction is desired, for structures in aggressive environments where chemical and mildly acidic waters are encountered (where the use of OPC is not recommended), for marine constructions, dykes, wharves, etc where sulphatic water is encountered. In short, PSC can be used wherever OPC is used.

There are many differences as mentioned below.
A. Differences in Composition
OPC means Ordinary Portland cement and PPC means Portland Pozzolana cement. As per IS, PPC will have pozzolanic material in it. In the Western and Southern part of India [SR1] [TK2] PPC is mainly fly ash based. It contains 15% to 35 % of fly ash as per IS 1489.
B. Differences in the Hydration Process
Fly ash contains silica which reacts with Calcium Hydroxide (by-product of primary hydration) and converts it into strength giving compound CSH gel.
C. Differences in Durability
Structures built with PPC are more durable as compared to OPC. Due to silica presence in Fly Ash, in PPC secondary hydration process takes place. Due to this secondary hydration, capillary pores get filled up unlike in OPC and concrete gets denser as time passes.

Supplementary Cementations Materials (SCM) like silica fumes, meta-kaolin, fly ash, and slag are the materials which improve the properties of concrete and enhance its durability, by reducing pore size in concrete through better particle distribution and increasing packing density of the concrete.