<P> Very finely ground cements are made from mixtures of cement with sand or with slag or other pozzolan type minerals that are extremely finely ground together . Such cements can have the same physical characteristics as normal cement but with 50% less cement particularly due to their increased surface area for the chemical reaction . Even with intensive grinding they can use up to 50% less energy to fabricate than ordinary Portland cements . </P> <P> Pozzolan - lime cements . Mixtures of ground pozzolan and lime are the cements used by the Romans, and are present in extant Roman structures (e.g. the Pantheon in Rome). They develop strength slowly, but their ultimate strength can be very high . The hydration products that produce strength are essentially the same as those produced by Portland cement . </P> <P> Slag - lime cements . Ground granulated blast - furnace slag is not hydraulic on its own, but is "activated" by addition of alkalis, most economically using lime . They are similar to pozzolan lime cements in their properties . Only granulated slag (i.e. water - quenched, glassy slag) is effective as a cement component . </P> <P> Supersulfated cements contain about 80% ground granulated blast furnace slag, 15% gypsum or anhydrite and a little Portland clinker or lime as an activator . They produce strength by formation of ettringite, with strength growth similar to a slow Portland cement . They exhibit good resistance to aggressive agents, including sulfate . Calcium aluminate cements are hydraulic cements made primarily from limestone and bauxite . The active ingredients are monocalcium aluminate CaAl O (CaO Al O or CA in Cement chemist notation, CCN) and mayenite Ca Al O (12 CaO 7 Al O, or C A in CCN). Strength forms by hydration to calcium aluminate hydrates . They are well - adapted for use in refractory (high - temperature resistant) concretes, e.g. for furnace linings . </P>

Describe the mechanism of strength development of cement