- - AGRICULTURE CORE CURRICULUM - - (CLF2000) Advanced Core Cluster: AGRICULTURE MECHANICS (CLF2500) Unit Title: CONCRETE/MASONRY _____________________________________________________________________________ (CLF2504) Topic: FORM PREPARATION AND Time Year(s) REINFORCEMENT 3 Hours 1 / 2 / 3 / 4 _____________________________________________________________________________ Topic Objectives: Upon completion of this lesson, the student will be able to: Learning Outcome #: (K-3) - Build proper forms. (K-4) - Mix, pour, reinforce, finish, and cure concrete. Special Materials and Equipment: Form and batter boards, builder's twine, stakes, wire mesh, rebars, wire, level, nails, hammers, rakes, 100 ft. tape, shovels 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: Teacher observation of student work and quiz by instructor. TOPIC PRESENTATION: FORM PREPARATION AND REINFORCEMENT A. SITE PREPARATION 1. Selection of Site 2. Lot lines are located and checked! a. This provides protection for the owner. b. The lines must be completed by a registered engineer or licensed surveyor. 3. Clearing and Rough Excavation of Area a. The site should be cleaned of all debris and refuse. b. Where no grading is needed, the site can be laid out and batter boards erected. c. If the site is on a steep slope or rugged terrain, rough grading must be completed before laying out building lines. d. Topsoil should be removed and stock piled where it will not interfere with the construction. Later it will be used for the finished grade. 4. Laying Out Building Lines a. It is best to establish lines using a leveling instrument. b. Lines can, however, be taken off lot markers. 1) It is important that distances be perpendicular to existing lines and that building lines be square. a) To establish a right angle, use the 3-4-5 method based on the Pythagorean theorem. b) Locate corners formed by the intersection of the outside wall surface. c) Drive stakes into the ground and then set tacks in the tops at the exact spot for the corner. c. After lines have been set up, check them carefully. 1) Measure the lengths and widths. 2) Measure the diagonals which should be equal. 3) An out-of-square foundation can cause continuous problems and frustrations throughout construction. 5. Batter Boards a. They are set up around the building layout stakes. b. Their purpose is to preserve the building lines after layout stakes have been removed because of necessary excavation for footings and foundations. c. Locate them about 4 feet beyond the building lines where excavation work will not disturb them. d. To Make Batter Boards: 1) Use 2 x 4's for the stakes and 1 X 6's for the ledger boards. 2) Drive in stakes to desired depth. 3) Nail ledger boards to the stakes, making sure they are level and at a good working height slightly above the top of the foundation. 4) All the batter boards should be level with each other. 5) Ledger boards should be long enough to extend past each corner. e. To Establish New String Lines: 1) Pull the two strings so they pass directly over the layout stakes, then use a plumb bob to line up the strings directly over the tack. 2) Mark the top of the ledger boards where the string lines cross and then make a shallow saw kerf at the mark. 3) Pull the string lines tight and fasten them to nails driven in the back of the ledger boards. 4) Make sure the lines are set in the saw kerf. 6. Final Excavation: a. Remove lines from batter boards when completing excavation work. b. The highest elevation on the perimeter of the excavation is the control point for establishment of the depth of excavation and the height of the foundation. 1) Foundations should extend about 8 inches above the finished grade so the wood finish and framing members will be protected from soil moisture. 2) The finished grade should be sloped so surface water will run away from the foundation. 3) It is important that the foundation be located below the frost line so no damage is incurred when the soil freezes. c. The depth of the excavation may be limited by the overall levelness of the site, slope to the street, curb or existing concrete foundation height, and the elevation of the drainage or sewer lines. B. Preparation of Forms 1. Definitions a. A form is a metal or wooden structure that confines the concrete to the desired shape or form until it sets or hardens enough to stand by itself. b. A footing is a concrete base that provides a solid, level foundation for concrete, brick, or block walls. 1) Because the footer is wider than the wall, it spreads the building weight over a wider area. a) The common practice is to make footing the same height and twice as wide as the thickness of the wall it supports (on good load-bearing soil), ie., a 4" thick wall would have a footing at least 4" high and 8" wide. b) Footing must be placed below the frost line in order to prevent structural damage. c) The footing should be placed on all rock or all soil and not a part of each; this prevents uneven settling. 2. Form and Footing Construction a. Form boards are temporarily nailed to stakes and to each other. 1) Duplex head nails are used to help in form removal. 2) In order to allow nail removal, always nail through the stake into the form board; never nail from the inside. 3) Be sure the stakes do NOT stick up above the top of forms as this will greatly affect the finished work; saw stakes off flush with the form. 4) Coat form boards with old crankcase oil, form oil, or diesel fuel since this prevents sticking to the concrete and allows easy removal. b. Footing Forms: 1) After excavation is complete, replace lines on batter boards and locate corners again with plumb bob. Drive stakes to mark points, making sure they are level with top of footing. 2) Drive a set of grade stakes along the footing line; use a builder's level to keep all the stakes level with the top of the footing. 3) Construct outside forms first, making their tops level with the grade stakes. a) After the outside boards are in place it is relatively easy to set the inside sections. b) Use 3/4 inch plywood or 1 inch lumber for form boards, held in place with metal or 2 X 4 wood stakes every 2 to 3 feet. 4) Use spreader boards to maintain the correct width for the footing; usually 1 X 2's are satisfactory. 5) The top of the footing must be level! c. Wall Forms: 1) Use 3/4 inch tongue and groove lumber or plywood for side forms nailed to 2 X 4 studs every 2 feet. 2) Forms must be strong and well braced to withstand the side pressure created by the heavy, wet concrete. a) This pressure increases as the height of the wall is increased. b) Wall ties (tie rods) are used to prevent the sides from spreading outward or warping inward. - These combine the features of old wood spreaders and wire ties. - Many different manufactured devices are available. d. Slab-On-Ground Forms: 1) Concrete is laid directly on ground such as a driveway, sidewalk, or slab floor. a) Soil must be firm and compact, disturbed as little as possible. b) On poorly drained soils, lay a 4"-6" subbase of gravel or crushed rock and compact it. c) A vapor barrier is essential under every section of a slab floor. - This prevents the movement of water from ground into the slab and vice-versa - Common materials used to a create a vapor barrier are 4-mil polyethylene film, 55 lb. roll roofing, or asphalt-impregnated kraft paper. 2) Forms are constructed out of 2" thick wood material. a) 2 X 4's are used for walks. b) 2 X 6's are used for drives and floors. c) Support the forms by using metal or 2 X 4 wood stakes every 3 feet. d) Use soft, clean, straight lumber. e) 1" thick wood material can be substituted for small pours; however, it needs to be supported every 2 feet. f) A slope should be included for all slab construction in order to carry off surface water. A slope between 1/8 to 1/4 inch per foot of width is adequate. C. Concrete Reinforcement 1. What is reinforced concrete? a. It is concrete which has either steel reinforcing rods or wire mesh embedded into it when it is poured. 1) Reinforcement bars (rebars) are used in thicker pours such as foundation footings and building columns. a) They are made of steel and have a rough surface to prevent slipping when embedded. b) Bars are classified by a number system corresponding to the diameter in eighths of an inch, i.e., # 4 rebars are 4/8" (which reduces to 1/2"). - They are available in diameters from 1/4" to 1" and over. NOTE: The rebars used in Diablo Canyon Nuclear Power Plant were #28 and 6 layers thick! c) Rebars are purchased in 20, 40, and 60 ft. lengths. d) Bars can be joined by lapping over ends and wiring together or by welding. - The general practice is to lap bars by 24 times the diameter, i.e., 1/2" rebars should be lapped 24 X 1/2 = 12 inches. e) For most applications, the bars should be placed 1 1/2" from all surfaces; however, 3/4" is allowed at times. - Rods must be kept off the surface of the base material as this will cause rusting. f) Bars are run vertically in walls and horizontally in footings. In thick slabs, they can be placed in a cross- sectional pattern. 2) Concrete slabs are generally reinforced using wire mesh. a) The mesh is steel wire welded to form a cross-sectional pattern. - The sizes are 6, 8, and 10 gauge wire. - Generally a 6-by-6 inch mesh pattern is used. b) Mesh should be rolled out and flattened, then placed inside the forms. c) It can be purchased in different widths and then wired together to form longer or wider pieces. - Different pieces should be overlapped by at least one and a half squares and wired securely. d) It should be located from 1 - 1 1/2 inch below the top surface, approximately in the center of the slab. - Mesh MUST be kept off the base material so some support might be needed. This is to prevent the wire rusting inside the concrete. - As the concrete is being poured, a steel hook is used to pull the mesh up to the desired height. 2. Why reinforce concrete? a. Reinforcement increases the strength of the concrete without adding extra thickness which would add greatly to the cost of the job. b. Reinforcement prevents cracking under stress of floors or driveways where heavy equipment and machinery are used. c. All concrete columns and structures must be reinforced with steel in order to withstand normal stresses. d. On large complicated jobs, consult local construction engineers or concrete contractors regarding the size and amount of steel to use and how it should be placed. ________________________________________________________________ ACTIVITY: 1. Go on a short field trip to a construction site (commercial or residential) and can observe how sites are prepared, forms are constructed, and reinforcement is used. Quiz students on what they observed. 2. Plan a concrete project at the school and have students complete the necessary steps to prepare the site, construct forms, and include the necessary reinforcement. This activity could be worked on throughout this lesson. Coordinate this activity with the next lesson, Placing, Finishing, and Curing concrete. 3. Go out to the athletic fields and practice laying out corner stakes using the 3-4-5 method and the diagonal method. Set up teams of 3-4 students each. ______________________________________________________________ 7/23/91 JD/tf #%&C