Concrete David P. Shelton, Extension Agricultural Engineer James M. Harper, P.E., Field Engineer, Portland Cement Association For more materials contact the Portland Cement Association
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David P. Shelton, Extension Agricultural Engineer
James M. Harper, P.E., Field Engineer, Portland Cement Association
For more materials contact the Portland Cement Association
Please write or fax the Portland Cement Association on the letterhead from your educational institution, and ask for your educational package on portland cement. They will send you a full-color poster featuring original art created for PCA, as well as an instructional video.
Portland Cement Association
5420 Old Orchard Road
FAX: 847 966 8389
Adapted to Powerpoint by Bill Pannell
Click here to go to teaching ideas
is a mixture of portland cement, water, aggregates, and in some cases, admixtures.
The cement and water form a paste that hardens and bonds the aggregates together.
Concrete is often looked upon as “man made rock”.
It can be placed or molded into virtually any shape and reproduce any surface texture.
In the United States almost twice as much concrete is used as all other construction materials combined.
the Erie Canal
Grand Coulee Dam, which used nearly 10 million cubic yards of concrete, making it one of the largest portland cement concrete projects in history
The ready-mix concrete producer has made concrete an appropriate construction material for many agricultural applications.
Concrete can be finished to produce surfaces ranging from glass-smooth to coarsely textured, and it can be colored with pigments or painted.
Most structural uses, such as beams, slats, and manure tank lids, involve reinforced concrete, which depends on concrete's strength in compression and steel's strength in tension.
Compressive strengths of concrete generally range from 2000 to 5000 pounds per square inch (psi), but concrete can be made to withstand over 10,000 psi for special jobs.
Aggregate - sand, gravel, crushed rock
Admixtures - when necessary
Portland cement was named for the Isle of Portland, a peninsula in the English Channel where it was first produced in the 1800's.
Since that time, a number of developments and improvements have been made in the production process and cement properties.
After the clinker cools, gypsum is added, and both materials are ground into a fine powder which is portland cement.
It is very finely ground and sets rapidly, making it useful for cold weather jobs.Type III
Good water is essential for quality concrete.
It should be good enough to drink--free of trash, organic matter and excessive chemicals and/or minerals.
The strength and other properties of concrete are highly dependent on the amount of water and the water-cement ratio.
Aggregates occupy 60 to 80 percent of the volume of concrete.
Sand, gravel and crushed stone are the primary aggregates used.
All aggregates must be essentially free of silt and/or organic matter.
Admixtures are ingredients other than portland cement, water, and aggregates.
Admixtures are added to the concrete mixture immediately before or during mixing.
produce microscopic air bubbles throughout the concrete.
Entrained air bubbles:
improve the durability of concrete exposed to moisture and freeze/thaw action.
Improve resistance to scaling from deicers and corrosive agents such as manure or silage.Air Entraining agents:
are used to slow the rate of concrete hardening.
They are useful for concrete that is placed during hot weather.
such as calcium chloride, are used to increase the rate of hardening--usually during cold weather.
To produce a concrete that will meet requirements under specific conditions of use.Goals:
With an understanding of these goals, the customer can communicate better with the ready-mix supplier, and obtain concrete that is suited to the project at hand.
Workability of freshly mixed concrete.
Durability, strength, and uniform appearance of hardened concrete.
Workability is difficult to measure but redi-mix companies usually have experience in determining the proper mix.
Therefore, it is important to accurately describe what the concrete is to be used for, and how it will be placed.Workability
A mixture with a sufficiently low ratio of water to cement plus entrained air, if specified, is the most desirable.Durability
Quality depends on the amount of cement and the water-cement ratio.
Hold the water content to a minimum to reduce the cement requirement.Economy
A bag of cement weighs 94 lbs. Typical concrete mixtures include between 5 and 6.5 bags per cubic yard of concrete.
A minimum cement content assures desirable concrete properties, such as workability, durability, and finishability.
Curing is usually the last step in a concrete project and, unfortunately, is often neglected even by professionals.Curing
A seven-day (or longer) curing time is recommended.
Keep water on the concrete during the curing period.
ponding or immersion,
spraying or fogging, and
saturated wet coverings.
Such methods provide some cooling through evaporation, which is beneficial in hot weather.
Can be done by:
covering the concrete with impervious paper or plastic sheets,
applying membrane-forming curing compounds.
application equipment required,
Size and shape of the concrete surface.
This is usually within one to two hours after placement and finishing.
Concrete is a highly versatile construction material, well suited for many agricultural applications.
It is a mixture of portland cement, water, aggregates, and in some cases, admixtures.
Strength, durability, and many other factors depend on the relative amounts and properties of the individual components.
1. Amount of concrete required,
2. use of the concrete,
3. type of cement,
5. maximum water-cement ratio
6. any special admixtures,
7. amount of air entrainment,
8. desired compressive strength,
9. amount of slump, and
10. any special considerations or restrictions
To introduce this lesson get cement, sand, crushed rock and water in jars for the students to look at.
Show powerpoint presentation and video if you acquire it.
Find questions in a textbook and have students look up answers from book. Test or quiz if desired.
Arrange tour of a redi-mix plant and a site which is being poured.
Allow student to mix, place, form and cure concrete in the shop making patio blocks. Forms for round blocks can be made by cutting 3” sections from a 5 gallon plastic bucket with a bandsaw.
Acceptable concrete can be produced by purchasing bags of ready to mix concrete or by mixing from individual components.
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