Clinker compounds strength-time graph

The four clinker compounds contribute to strength at different rates:

• C3S (tricalcium silicate): hydrates fast and is responsible for early strength (up to 7 days); it keeps contributing up to 28 days.
• C2S (dicalcium silicate): hydrates slowly, contributes little in the first weeks and is mainly responsible for later strength (from 28 days to a year and beyond).
• C3A: reacts rapidly and gives a little strength in the first 1-3 days only.
• C4AF: contributes very little to strength.

 Strength
   ^
   |                          ______________ C3S
   |                  ___---''
   |             _--''                ______ C2S
   |          _-'               ___--'
   |        /             ___--'
   |       /        ___--'
   |      /   ___--'
   |     / _-'
   |    /_' ____________________________ C3A
   |  _/.-'_____________________________ C4AF
   +-----+-----+-------+--------+-------> Age
        3d    7d      28d      90d     1 yr

Hence the early strength of cement depends on C3S and C3A, and the long-term strength on C2S (together with C3S).