The Local Cement plant in Clarkdale (Salt River Materials Group) recently donated about 500 bags of cement to the Cosanti Foundation. We recently had a chance to go to the plant and see how the cement we use in construction is manufactured.
On Friday we (10 of us including most of the workshop and construction staff and also Darina Trendafilova our archives volunteer who documented the trip for the Arcosanti website/blog) had a chance to explore the local cement plant that we get our cement from. We barely made it back to enjoy the Harvest Dinner put together by the Garden/Agriculture dept that had some of the food grown in the garden as part of the meal. The tour began with an introduction by Margie Beach who is Communications Director at Phoenix Cement which is owned by the Salt River Pima tribe through a company called Salt River Materials Group (SRMG).
The plant started in 1959 to help provide cement to construct the Glen Canyon Dam in Page. It came into being just at the right time because it was when Clarkdale was really hurting from some mine closings. At the time, several boardmembers of the American Cement company were cynical, however it proved to be a very austute investment to keep the plant open after the dam was completed taking advantage of the rapid growth in Arizona.
In 1987 facing a challenge to either modernize or close down due to increasing costs, it was bought by SRMG. Modernization of the plant cost 150 millions dollars doubling production and reducing plant emissions (doubled plant production from 700,000 tons to 1.1 million tons, while energy consumption remains at the same level.). The plant has had several upgrades and modernizations that include the recent replacement of the 150 foot long kiln. in 2007 additional upgrades to the plant increased consistency of the cement, reduced emissions and increased productivity.
Recent modernizations had made the plant very efficient both in production and also in terms of energy earning it one of the EPA’s highest Energy Star ratings. It is now about 10 times more efficient by doing things like using heat from the cooling down of clinker to preheat the aggregates going into the kiln. However these kind of improvements really do little to reduce the total net amount of the Concrete industry’s CO2 emissions which amount to around 5-7% of total global CO2 emissions.
One of the most intriguing aspects of the tour was the handout she gave us from the Mineral Information Institute showing a little baby and what the typical American consumer consumers over their lifetime on average. I have to say I was surprised with the level of materials we consume.
A part of the quarry is first cored to analyze them to ensure they are right material for the cement manufacturing plant. Then carefully calibrated explosives charges precisely remove desired limestone deposits. The material is then loaded with giant track hoes onto Big Tonka looking trucks then move 100 tons at a time with wheels that wear out in a year and cost 33k a peice to replace. Then the materials are put into piles and then crushed and added to the Surge Piles. Later they are crushed again while ensuring the right mix using a gamma ray analyzer. The mix then enters the Vertical Raw Roller Mill which then takes the materials and puts them into blending silos where they are stored before going into the Preheater/Calcifier.
The kiln is the heart of the plant basically melting the component ingredients into cement in about an hour long process running at about 2700 degrees. Coal is burned in the amount of around 300 tons a day with total cement production at 3500 tons a day. The flame from the coal dust injected into the kiln goes up to 3000 degree, which makes the concrete klinker that is further processed into concrete by grinding it down and then adding gypsum (which is added to prevent the concrete from setting too fast).
The plant is surprisingly one of only two Portland cement plants in the state. 10 percent of what they produce is bagged and the other 90% is loaded into big semi-trucks and then shipped out to batch plants around the state.
It turns out that in making cement the major ingredients are all produced onsite in the quarry which includes over 3500 acres including the production facility, offices, rail yard, aggregate piles, and open space. There’s enough materials for another 150 years of production at current rates. Ingrediants are limestone 59%, Silicia Clay 22%, volcanic ash 15% (from a mine in NM), Dolomite 3% and Mill scale 1% (they reuse waste byproducts from steel mills).
Working with the major power provider in AZ Arizona Public Service (APS), they also produce/bag fly ash to make effective use of that byproduct of coal production in the concrete industry. Its a way to reduce the landfilling of flyash and also reduce the CO2 emissions of concrete by reducing the amount of cement used. Flyash which is a Pozzolan can take the place of around 17-30 percent the cement in the mixing of concrete. After one month of curing, the flyash is stronger and more flexible than traditional concrete.
Today SRMG is one the largest company’s in the Verde Valley and Northern AZ with 160 people contributing 16.5 million to the local economy through wages, taxes and benefits. Also SRMG provides about 8 million in business to local support businesses such as the CTI trucking company and concrete batch plants located nearby.
They are optimistic about the future despite the current downturn in the economy which has reduced production around 35% and are planning a major 250 million dollar expansion of the plant to double production capacity.