A.PORTLAND CEMENT B.AGGREGATE – (Sand, Gravel, Crushed Rock) C.WATER - (Clean and Pure) D.ADMIXTURES- when necessary
I. Portland Cement 1.Portland cement was named for the Isle of Portland, a peninsula in the English Channel where it was first produced in the 1800’s. 2.Since that time, a number of developments and improvements have been made in the production process and cement properties.
I. Portland Cement Cont. 3.The production process for Portland Cement first involves grinding limestone or chalk and alumina and silica from shale or clay. 4.The raw materials are proportioned, mixed and then burned in a large rotary kiln at approximately 2500 degrees until partially fused into marble-sized masses known as clinkers.
I. Portland Cement Cont. 5.After the clinker cools, gypsum is added, and both materials are ground into a fine powder which is Portland Cement. 6.Portland Cement is then distributed in 94 pound sacks containing 1 cubic foot.
I. Three Types of Portland Cement are used for agricultural applications 1.Type I – Cement is a general purpose and the most common type. Unless an alternative is specified, Type I is usually used. 2.Type II – Cement releases less heat during hardening. It is more suitable for projects involving large masses of concrete- heavy retaining walls, or deadmans for suspension bridges.
I. Three Types Of Portland Cement Cont. 3.Type III – A. Type III cement produces concrete that gains strength very rapidly. B. It is very finely ground and sets rapidly, making it useful for cold weather jobs.
II. WATER 1.Good Water is essential for quality concrete 2.It should be good enough to drink- free of trash, organic matter and excessive chemicals and/or minerals. 3.The strength and other properties of concrete are highly dependent on the amount of water and the water-cement ratio. 4.Water should be kept as low as possible within the mix. 5.5-6 gallons per sack of cement is acceptable.
III. AGGREGATES 1.Aggregates occupy 60 to 80 percent of volume of concrete. 2.Sand, Gravel, crushed stone are the primary aggregates used. 3.All aggregates must be essentially free of silt and /or organic matter. 4. Coarse Aggregates should not exceed 1/3 the slab thickness and 1/5 the wall thickness. 5.Maximum size is 1 ½ inch with the most common being ¾ inch.
III. DETERMININING AGGREGATE SIZE 1.Aggregate size depends on the end use: A.The maximum aggregate size should be no larger than one- third the thickness of the concrete. B.Aggregate size should also be less than three-fourths the clear space between reinforcing bars where rebar is used
IV. ADMIXTURES 1.Admixtures are ingredients other than Portland Cement, Water and Aggregates. 2.Admixtures are added to the concrete mixture immediately before or during mixing.
IV.RETARDING ADMIXTURES A.Are used to slow the rate of concrete hardening. B. They are useful for concrete that is placed during hot weather.
IV.ACELERATING ADMIXTURES A.Such as Calcium Chloride, are used to increase the rate of hardening - usually during cold weather. B.Do not use more than 2 lbs. of calcium chloride per bag of cement. C.Do not use calcium chloride with other additives.
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