- - AGRICULTURE CORE CURRICULUM - - (CLF2000) Advanced Core Cluster: AGRICULTURE MECHANICS (CLF2500) Unit Title: CONCRETE/MASONRY _____________________________________________________________________________ (CLF2502) Topic: CONCRETE PROPORTIONS Time Year(s) 2 Hours 1 / 2 / 3 / 4 _____________________________________________________________________________ Topic Objectives: Upon completion of this lesson, the student will be able to: Learning Outcome #: (K-1) - List the ingredients and characteristics of concrete. (K-2) - Calculate the amounts and costs of materials required for a particular application. Special Materials and Equipment: Sand and gravel samples, quart jars with thight lids, household lye References: Burke, Stanley R., & Wakeman, T. J. (1990). MODERN AGRICULTURAL MECHANICS (2nd ed.). Danville, IL: Interstate Publishers. Cooper, Elmer L. (1987). AGRICULTURAL MECHANICS: FUNDAMENTALS AND APPLICATIONS. Albany, NY: Delmar Publishers. Editors of Reader's Digest. (1973). COMPLETE DO-IT- YOURSELF MANUAL (7th ed.). Pleasantville, NY: Reader's Digest Association. Phipps, Lloyd J., & Reynolds, Carl L. (1990). MECHANICS IN AGRICULTURE (4th ed.). Danville, IL: Interstate Publishers. Wagner, Willis H. (1979). MODERN CARPENTRY: Building Construction Details in Easy-to-Understand Form (4th ed.). So. Holland, IL: Goodheart-Willcox. Resources: Ahrens, Donald L. (1988). CONCRETE AND CONCRETE MASONRY. Available from: Hobar Publications, 1234 Tiller Lane, St. Paul, MN 55112 Phone: (612) 633-3170 (Catalog available) Evaluation: Quiz by instructor, results from aggregate testing, and completion of worksheet. TOPIC PRESENTATION: CONCRETE PROPORTIONS A. Mixture of Ingredients - Since part of the mixture can greatly affect the strength and durability of the concrete after it hardens, using the correct proportion of each part is critical. 1. Cement Paste a. This is the mixture of cement and water that determines the concrete's strength; it varies according to water-cement ratio. 1) Water-Cement Ratio a) These are usually 5, 6, or 7 gallons of water to 1 sack of cement; the most common ratio is 6:1. b) This amount of water takes into account the water in the sand. 2) Cement comes in 94 pound sacks containing 1 cubic foot. 3) Sand has some water attached to its particles. This moisture needs to be estimated and an allowance made for it. The more moisture there is in the sand the less water needs to be added when mixing. a) Damp sand falls apart when squeezed into a ball. It contains about 1/4 gallon of water per cubic foot. b) Wet sand forms a ball when squeezed but leaves no noticeable moisture on the palm. This is the most usual kind and contains about 1/2 gallon of water per cubic foot. c) Very wet sand forms a ball when squeezed and leaves moisture on the palm. It contains about 3/4 gallon of water per cubic foot. Note: To obtain a more durable concrete to withstand severe weather conditions and/or traffic, add less water. 2. Ratio of Cement:Fine Aggregate (Sand):Coarse Aggregate (Gravel) a. Ratio is expressed as a three digit number called a mix, for example, 1:2:3. 1) A mix means one part cement, two parts sand, and three parts gravel. 2) The mix proportions can be based on either weight or volume. a) A ratio of 1:2:3 can be stated 1 cu. ft. (sack) of cement, 2 cu. ft. of sand, and 3 cu. ft. of gravel. b) It can also be 100 lb. (approximately a sack) of cement, 200 lbs. of sand, and 300 lbs. of gravel (1 cu. ft. of aggregate is approximately 100 lbs.). b. A correct mixture assures that: 1) Each particle of sand and gravel is covered with cement paste. 2) Each particle is bound to others when the cement paste dries and hardens. c. The intended use of the concrete also determines the ratio of the ingredients. Recommended ratios for mixing concrete for different types of uses can be found in charts in any basic books about concrete (consult references and resources listed). 3. Coarse Aggregate Size a. Should not exceed 1/3 the slab thickness. b. Should not exceed 1/5 the wall thickness. c. Maximum size is 1 1/2 inch with the most common being 3/4 inch. 4. Mixture Yield a. Generally, the volume of mixed concrete will be about two-thirds the combined volume of the items used in the mix. b. Examples of how much material should be used to make 1 cubic yard of concrete can be found in charts in any basic book about concrete (consult references and resources listed). 5. Slump Test: slump is a rough measurement of concrete's consistency and workability. a. Common slumps used for most jobs are 3 - 4 inches. Slump should never exceed 6". b. The slump is determined by a test using a conical cylinder and a portion of the concrete batch to pour. The cylinder has a 4" diameter opening at the top and an 8" diameter opening at the bottom, and is 12" high. The test is performed as follows: 1) Place moistened cone-shaped container on a flat, level surface. 2) Fill the container 1/3 full with sample of concrete. 3) Rod this layer 25 times using jabbing strokes with a 5/8" solid steel rod - jabbing strokes as this helps to settle the concrete. 4) Add a second layer until the container is 2/3 full. 5) Rod this layer an additional 25 times. 6) Finally, fill the cone to the top edge and level it. 7) Rod a final 25 times. Remove any spilled concrete from around the base of the cone. 8) Lift the cone off the rodded batch within five seconds. 9) Without a retaining device the concrete will slump or fall from the original 12" height. 10) The difference in the original height and the final height is known as the slump. ________________________________________________________ ACTIVITY: 1. Using Supplemental Worksheet #1, have students complete an organic matter test and silt/clay test on their sand samples. 2. Determine moisture content of sand samples. Test different samples of different moisture ranges. 3. Using the charts found in basic texts about concrete, solve problems on Supplemental Worksheet #2. More problems can be added if time permits. ________________________________________________________ Supplemental Handout #1 TESTING A SAND SAMPLE FOR SILT AND CLAY Procedure: 1. Fill a one-quart glass jar to a depth of 2 inches with the sand sample to be tested. 2. Add water until the jar is 3/4 full. 3. Screw on the lid and shake vigorously for one minute to mix all particles with water. 4. Shake the jar sideways several times to level the sand. 5. Place the jar where it will not be disturbed for 1 hour for a silt test or 12 hours for a clay and silt test. 6. After 1 hour, measure the thickness of the silt layer on top of the sand. 7. If the layer is more than 1/8 inch thick (more than 3% silt), the sand is not suitable for concrete unless the silt is removed by washing. 8. If the layer is not 1/8 inch thick in 1 hour, let the mixture stand for 12 hours. Then remeasure the layer(s) that have settled on the sand. 9. If the silt plus clay layer exceeds 1/8 inch, wash the sand before using it in concrete. TESTING A SAND SAMPLE FOR ORGANIC MATTER Procedure: 1. Place half a pint of clear drinking water in a clear glass quart-size jar. 2. Dissolve a heaping teaspoonful of regular household lye in the water. 3. Add half a pint of the sand sample to the solution. 4. Place a leakproof lid over the jar and shake it vigorously for a minute or more. (Be careful not to spill any of this solution since it is poisonous and highly injurious to the skin, clothes, and other materials.) 5. Let the sample stand for 24 hours. 6. The color of the liquid indicates whether the sand contains too much organic matter to be used in making concrete. Clear solution - sand is clean and free of organic matter Straw color (color of apple-cider vinegar) - presence of organic matter but can still be used to make concrete Darker colored solution - indicates too much organic matter present to be used in making concreteSupplemental Worksheet #2 NAME: _________________________ DATE: _________________________ CALCULATING PROPORTIONS A concrete driveway is to be poured on a level surface. The slab will be 5 inches thick. 1. Specify the maximum size aggregate that should be used on the 5-inch slab. __________ inch(es) 2. Specify the trial batch ratio which should be used for the driveway. ______ : ______ : ______ 3. How many sacks per cubic yard should be used? __________ sks. 4. How much sand and gravel are needed to make one cubic yard of concrete? __________ cu. ft. and __________ cu. ft. 5. If a total of 10 cubic yards of concrete is needed, how much total cement, sand, and gravel should be mixed? __________ sks. , __________ cu. ft. , and __________ cu. ft. 7/22/91 JD/tf #%&C