- - AGRICULTURE CORE CURRICULUM - - (CLF2000) Advanced Core Cluster: AGRICULTURE MECHANICS (CLF2500) Unit Title: CONCRETE/MASONRY ____________________________________________________________________________ (CLF2503) Topic: ESTIMATING CONCRETE Time Year(s) MATERIALS 3 Hours 1 / 2 / 3 / 4 ___________________________________________________________________________ Topic Objectives: Upon completion of this lesson, the student will be able to: Learning Outcome #: (K-2) - Calculate the amounts and costs of materials required for a particular application. Special Materials and Equipment: Calculators, volume container examples 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, completion of quantity worksheet. TOPIC PRESENTATION: ESTIMATING CONCRETE MATERIALS A. Volume Estimation - The ability to estimate accurately is a very important skill, since an inaccurate estimate will cause the job to cost more than necessary and ingredients may be wasted. If insufficient material is ordered, the job must be stopped and then restarted with considerable increase in cost and time. 1. Area Calculation a. Calculate the surface area in square feet that the structure will cover. 1) To get square footage of rectangular areas: Area = Length X Width 2) To find the area of a circle: 2 Area = 3.1416 (pi) X R 3) To find the area of a triangle: Area = 1/2 X Base X Perpendicular Height 2. Volume Calculation a. Multiply the calculated surface area by the thickness in feet of the planned structure: Volume = Area X Thickness (Depth) b. When calculating the volume of a long, narrow structure (for example, a building footing): 1) First find the cross-sectional area of the structure: Area = Width X Depth 2) Then multiply the cross-sectional area by the length of the structure. c. The total volume of concrete required is expressed in cubic feet. 3. Unit Conversion a. Concrete is calculated and sold by the cubic yard or the fractional quantities in quarters of a cubic yard. b. To convert cubic feet to cubic yards: Volume (cubic yards) = Volume (cubic feet) divided by 27 4. Dry Bulk Materials a. If purchasing separate ingredients, use a chart found in basic texts about concrete (consult references and resources) to calculate the amounts of each item. 1) Figure out the cubic yards needed for the project. 2) Determine the recommended mixture for the project. 3) Determine the amount of each ingredient by multiplying the value off the chart by the cubic yards needed for the structure. For example, the amount of cement is calculated: Chart Value X Project Size = Cement Needed (sacks/cu.yd.) (cu.yd.) (sacks) b. Cement is bought in whole sacks but separate ingredients can be purchased in increments of a 1/4 cubic yard. B. Mix Ordering - Once the amount of concrete that is needed for a job has been calculated, a decision must be made about the on a method of mixing it. The deciding factors here are the amount of concrete needed, the time required to complete the job, economy, and convenience. 1. Site Mixed (mix-it-yourself): a. This method is for jobs that require less than a cubic yard. b. A 10% waste allowance should be added to the calculated amount of concrete needed. c. A clean storage area is needed for each ingredient: gravel, sand, and cement (must be kept dry). d. This is a very good method when pouring fence posts or small projects such as stepping-stones or walkways. e. This is the cheapest way to mix concrete. f. There are two methods for site mixing: 1) By Hand a) This method is used for very small jobs that require only a few cubic feet. b) Mixing is completed on a watertight, flat surface. c) Measure accurately and mix cement and sand thoroughly. d) Add and mix gravel. e) Add measured quantity of water and mix until every particle has been covered with cement paste. f) Additional water might need to be added to obtain correct workability. 2) By Mixer a) This method is used when more than a few cubic feet of concrete is needed. b) Mixers can be rented from most rental agencies or possibly borrowed. c) The mixture is more uniformly and rapidly completed when done in a mixer d) Mixers are rated by batch size; do not exceed this amount. e) First load the mixer with all the aggregate and half the water; this is pre-measured for the batch size of the mixer. f) Start the mixer, add the sand, cement, and the remainder of the water. g) Allow the batch to continue mixing for at least three minutes, or until all the materials are thoroughly mixed. 2. Ready-Mix: a. This is the best method to use if the job calls for a cubic yard or more, or if time and convenience are important considerations. b. Additionally, this method is usually more economical when doing a large job. c. A 5% waste allowance should be added to the calculated volume of concrete needed. d. Usually the buyer must specify the maximum size of aggregate, minumum cement content, maximum slump, and load bearing capacity. e. Three Methods for Ordering Ready-Mix 1) Transit Mix a) This is the easiest and cheapest method to use when pouring three yards or more of concrete; less can be ordered but the cost increases. b) The mix is delivered by truck to the exact location. c) It is consistent, well-mixed and prepared to specifications before delivery. d) The user needs no mixing equipment, no storage. e) Since trucks are so big and heavy, planning is needed to insure that the truck can reach the pour site. f) There are additional charges if the truck is not poured out in the 45 minute standby time. 2) Porta Mix (U-Cart, Trailer Mix) - a) This is handled by most concrete batch plants and by some rental companies. b) It can be ordered in 1/4, 1/2, 3/4, and 1 cubic yard amounts. c) It is a very convenient method to pour small jobs around the home. d) The user needs no mixing equipment, no storage. e) It is consistent, well-mixed concrete; however, no specifications can be made. f) It is more expensive than other methods. g) The user needs a sturdy truck to pull the trailer. 3) Sack Mix (Sackrete) a) This comes in 90-pound sacks containing the right amounts of cement, sand, and gravel. b) The user just adds water and mixes; one sack makes around 2/3 of a cubic foot. c) This method is ideal for small jobs, for example, fence posts; the user needs to have a mixer or must hand mix. d) It is quite expensive, approximately four times as much as other methods. _________________________________________________________ ACTIVITY: 1. Locate different concrete structures around the school. Measure the dimensions of the structures and use these measurements to calculate the volume of concrete that was needed to build the structure. 2. Assign each student a company which deals with either transit mix, cart mix, bulk materials, or sack mix to call and find out current prices. 3. Have students complete supplemental worksheet #3. Add some problems of your own. _________________________________________________________ Supplemental Worksheet #3 Name______________________ Date______________________ Estimating Concrete Quantities I. A concrete slab for a steel building is to be poured on a level surface. The dimensions of the slab are: length 40 feet, width 30 feet, and thickness 6 inches. The concrete is to be ordered from a batch (ready- mix) plant. Remember to allow for uneven surface of the dirt base. SHOW ALL WORK! 1. How many cubic feet of concrete are needed? ________ 2. How many cubic yards of concrete are needed? ________ 3. How much concrete should be ordered from the plant? ________ (Remember to round off answer to nearest 1/4 cubic yard.) 4. What is the total cost to complete the job? ________ Make sure to add tax! II. A concrete walkway is needed along the side of a home. The dimensions of the walk are: width 2 feet, length 20 feet, and thickness 3 inches. The concrete will be site-mixed using a borrowed mixer. The walk will be poured in 4 foot long sections for ease of repair in case of uprooting by the neighbor's tree. Remember to allow for an uneven leveling job done by your assistant. SHOW ALL WORK! 1. Calculate the total cubic feet of the walkway. ________ 2. How many cubic yards does the walkway measure? ________ Remember to take into account the uneven soil surface. 3. The recommended mix is 1 : 2 : 2 1/4 using 3/4 inch maximum aggregate. a. How many sacks (cubic feet) of cement are ________ needed to complete the job? (Round off answer to whole sacks.) How much would this amount of cement cost? ________ (Remember to include sales tax.) b. How many cubic feet of sand are needed? ________ How many pounds of sand? ________ c. How many cubic feet of gravel are needed? ________ How much does this amount of gravel weigh? ________ Note: Current prices of materials are needed to make this worksheet complete and accurate. 7/23/91 JD/tf #%&C