ARIZONA CONCRETEJohn McCollamGeology 101, Section
12262Randy Porch20 November 1996 ARIZONA CONCRETEAccording
to the Mine Faculty at the University of Arizona, cement is manufactured
primarily from suitable limestone and shale rocks. Arizona had two
dry-process cement plants in 1969, namely the Arizona Portland Cement
Company plant in Pima County, near Tucson, and the American Cement
Corporation plant at Clarkdale, in Yavapai County (52-53).The use of
cementing materials goes back to the ancient Egyptians and Romans, but
the invention of modern portland cement is usually attributed to Joseph
Aspdin, a builder in Leeds, England, who obtained a patent for it in 1824.
Currently, the annual world production of portland cement is around 700
million metric tons (Danbury).Many people use the words concrete and
cement interchangeably, but they=re not. Concrete is to cement as a
cake is to flour. Concrete is a mixture of ingredients that includes cement
but contains other ingredients also (Day 6-7). Portland cement is
produced by pulverizing clinker consisting essentially of hydraulic calcium
silicates along with some calcium aluminates and calcium aluminoferrites
and usually containing one or more forms of calcium sulfate (gypsum) as
an interground addition. Materials used in the manufacture of portland
cement must contain appropriate proportions of calcium oxide, silica,
alumina, and iron oxide components. During manufacture, analyses of all
materials are made frequently to ensure a uniformly high quality
cement.Selected raw materials are crushed, milled, and proportioned in
such a way that the resulting mixture has the desired chemical
composition. The raw materials are generally a mixture of calcareous
(calcium oxide) material, such as limestone, chalk or shells, and an
argillaceous (silica and alumina) material such as clay, shale, or
blast-furnace slag. Either a dry or a wet process is used. In the dry
process, grinding and blending operations are done with dry materials. In
the wet process, the grinding and blending are done with the materials in
slurry form. In other respects, the dry and wet processes are very much
alike.After blending, the ground raw material is fed into the upper end of a
kiln. The raw mix passes through the kiln at a rate controlled by the slope
and rotational speed of the kiln. Burning fuel (powdered coal, oil, or gas)
is forced into the lower end of the kiln where temperatures of 2600°F to
3000°F change the raw material chemically into cement clinker,
grayish-black pellets about the size of 1/2-in diameter marbles.The
clinker is cooled and then pulverized. During this operation a small
amount of gypsum is added to regulate the setting time of the cement.
The clinker is ground so fine that nearly all of it passes through a No. 200
mesh (75 micron) sieve with 40,000 openings per square inch. This
extremely fin gray powder is portland cement (Kosmatka and Panarese
12-15). Dany Seymore of Show Low Ready Mix said that the cement
used by Show Low Ready Mix is trucked in by Apex Freight Company
and comes from the cement plant in Clarkdale, Arizona, now know as
Phoenix Cement. Their aggregate comes from Brimhall Sand and Rock
in Snowflake, Arizona. Show Low Ready Mix uses Fly Ash from the
A.P.S. power plant just out side of Joseph City, Arizona, in their cement.
The mixtures they use are as follows:Silicia Dioxide Cement
21% Ash 62%Aluminum Trioxide Cement 4% Ash
23%Ferric Oxide Cement 3% Ash 6%Calcium Oxide
Cement 64% Ash 3.5%Mag. Oxide
Cement 2.5% Ash 1.2%Sulfur Trioxide Cement 3%
Ash .2%These combine to make: 1. Tricalcium silicate C3S 2.
Dicalcium silicate C2S 3. Tricalcium aluminate C3A 4. Tetracalcium
aluminoferrite C4AF1 and 2 make up 75% of cement. 1 and 2 plus H2O
equal CSH (Calcium Silicate Hydrate) which is the glue. Fly Ash is C3S
plus C2S which equals Calcium hydrazide which is a white stuff and
water soluble. Calcium Hydrazide and Fly Ash equal CSH. The winter
and summer mixtures are different due to the weather conditions. For
winter, Fly Ash is not used because it inhibits the set time of the concrete.
Also used is accelerators to help the concrete set faster. A material
called Fibermesh is used in the concrete for reinforcement and to control
cracking as the concrete sets. Mr. Seymore also states that heat and
moisture are the main components to make concrete set up.The concrete
is mixed out of the plant into the truck so the materials can be feathered
together and mixed up properly. The PSI ratings are determined by the
mixture of sand, aggregate, cement, water, and chemical additives that
are mixed together. The most common mixtures for residential are 2500
to 3000 PSI.Concrete cannot be delivered any where that is more than 90
minutes away from the batch plant, unless a chemical inhibiter is used to
put the concrete to sleep until it reaches the sight of delivery. Then
another chemical is added to activate the concrete.Show Low Ready Mix
mixes approximately 25,000 to 30,000 cubic yards of concrete in Show
Low per year. That is only 70 to 75 percent of the total concrete poured
in Show Low. There are a few other companies that also handle the
Show Low area.Concrete is basically a mixture of two components:
aggregates and paste. The paste, comprised of Portland cement, (the
term APortland cement@ pertains to a calcareous hydraulic cement
produced by heating the oxides of silicon, calcium, aluminum, and iron.)
Water binds the aggregates (sand and gravel or crushed stone) into a
rocklike mass. The paste hardens because of the chemical reaction of
the cement and water. The paste is composed of Portland cement, water,
and intrapped air or purposely entrained air. Cement paste ordinarily
constitutes about 25% to 40% of the total volume of concrete. Since
aggregates make up about 60% to 75% of the total volume of concrete,
their selection is important. Aggregates should consist of particles with
adequate strength and resistance to exposure conditions and should not
contain materials that will cause deterioration of the concrete. Aggregates
are generally divided into two groups: fine and coarse. Fine aggregates
consist of natural or manufactured sand with particle sizes ranging up to
3/8 inches; coarse aggregates are those with particles retained on the
No.16 sieve and ranging up to 6 inches. The most commonly used
maximum aggregate size is 3/4 inch or 1 inch. A continuous gradation of
particle sizes is desirable for efficient use of the cement and water
paste.For any particular set of materials and conditions of curing, the
quality of hardened concrete is determined by the amount of water used
in relation to the amount of cement . Some advantages of reducing water
content are: increased compressive and flexural strength, lower
absorption, increased resistance to weathering, better bond between
successive layers and between concrete and reinforcement, less volume
change from wetting and drying, and reduced shrinkage cracking
tendencies. The less water used, the better the quality of the concrete,
provided it can be consolidated properly. The freshly mixed (plastic) and
hardened properties of concrete may be changed by adding admixtures
to the concrete, usually in liquid form, during batching. Admixtures are
commonly used to: adjust setting time or hardening, reduce water
demand, increase workability, intentionally entrain air, and adjust other
concrete properties (Kosmatka and Panarese 1-2). After completion of
proper proportioning, batching, mixing, placing, consolidating, finishing,
and curing, hardened concrete becomes a strong, noncombustible,
durable, abrasion-resistant, and practically impermeable building material
that requires little or no maintenance. Concrete is also an excellent
building material, because it can be formed into a wide variety of shapes,
colors, and textures for use in almost unlimited number of applications.
Works CitedACement and concrete.@ The 1996 Grolier Multimedia
Encyclopedia. CD-ROM. Danbury: Grolier, 1996.Day, Richard. The
Home Owner Handbook Of: Concrete and Masonry. New York: Bounty
Books, No Copyright Date. Kosmatka, Steven H., and William C.
Panarese. Design and Control of Concrete Mixtures. Skokie, Ill.:
Portland Cement Association, 1990.Seymore, Dany. President
of Show Low Ready Mix. Personal interview. 11 November
1996.College of Mines Faculty, University of Arizona. Arizona: Its
People and Resources. Tucson, AZ.: The University of Arizona
Press, 1972.
. ARIZONA CONCRETEJohn McCollamGeology 101, Section
12262Randy Porch20 November 1996 ARIZONA CONCRETEAccording
to the Mine Faculty at the University of Arizona, . (Danbury).Many people use the words concrete and
cement interchangeably, but they=re not. Concrete is to cement as a
cake is to flour. Concrete is a mixture of ingredients