History of cement
Cement materials have been used since ancient times.
Egyptians used burnt gypsum as a cement while the Romans and Greeks used lime made by heating limestone and adding sand to make a mortar or bigger stones to produce a concrete.
Modern-day cement manufacturing has its roots in work by Joseph Aspdin who took out a patent in 1824 for "Portland Cement," so called because the concrete he made from it looked like Portland stone.
Some 20 years later, Isaac Johnson made the first modern Portland Cement by firing a mixture of chalk and clay at much higher temperatures, similar to those used today. At these temperatures (1400C-1500C), clinkering occurs and minerals form which are very reactive and more strongly cementitious.
Johnson broadly used the same materials to make Portland cement as are used today but there have been three important developments in the manufacturing process:
- Introduction of rotary kilns
- Addition of gypsum to control setting
- Use of ball mills to grind clinker and raw materials
Today, advanced technology makes the whole manufacturing process more efficient while the use of waste materials as alternative raw materials and fuels saves precious natural resources.