Raw materials are taken from quarries in the form of limestone, shale, iron ore and laterite clay. They provide the elements necessary to form cement, primarily calcium, silica, iron and alumna. The raw material is crushed into a fine powder. The powder is collected, tested and blended for consistency. Once it meets specific chemical requirements, it goes to the next step.

The crushed raw material is conveyed to the top of a 245' high preheating, precalcining tower. It then drops down through a series of vertical cyclone chambers. In about 20-seconds, it is heated from 100 degrees Fahrenheit to 1600 degrees.

This very hot material is then fed into a rotating kiln. It travels through the kiln where it is further heated to between 2700 and 3000 degrees. The heating process only takes about 20 minutes, but crucial chemical reactions take place converting the raw materials into a new substance called clinker. The red-hot clinker is cooled and stored in preparation for grinding.

Cement clinker, along with a small amount of gypsum, is ground into a fine powder in a finish mill or ball mill. Finish mills are large rotating cylinders containing steel balls for grinding. These mills grind the cement so that it is finer than face powder; individual particles are as small as 1/25,000 of an inch. Cement is so fine that it can easily pass through a sieve that’s fine enough to hold water. The cement is then ready to be shipped or stored.

History of Cement Making at RMC Lonestar’s Davenport Plant Site

Cement has been manufactured at the Davenport Plant site in Santa Cruz County, California since 1906. The plant was originally built to supply construction of the Panama Canal and satisfy the demand created by the U.S. Navy’s construction of Pearl Harbor. On April 14, just six months into construction of the plant, the Great Earthquake of 1906 leveled San Francisco.

Responding to the crisis, the plant was completed in 12 months, half the estimated time. Streets, sidewalks and buildings throughout San Francisco were rebuilt with “Santa Cruz Cement”.

Cement from the Santa Cruz Plant has been used to build such landmarks as the Golden Gate Bridge, the San Francisco-Oakland Bay Bridge, the TransAmerica Pyramid Building and the Bay Area Rapid Transit System (BART).

RMC Lonestar
6601 Koll Center Pkwy.
Pleasanton, CA 94566
(925) 426-2148