Concrete Design & Placement

Transcription

1 Fox Blocks forms are designed, tested and approved as formwork for reinforced concrete. Following the specification for a concrete mix design and manufacturers recommendations for consolidation will results in a safe and successful build. CONCRETE MIX DESIGN One of the most important aspects of concrete placement is the proper concrete mix design. Proper concrete mix will save time on labor, facilitate concrete consolidation and ensure a successful Fox Blocks wall pour. Concrete mix can vary from region to region throughout the country because the raw materials differ from region to region. There are many factors that govern the design of the concrete mix: Structural Design Requirements Temperature Water Content Additives Delivery Times Placement Methods (Typically by a Concrete Pump) Therefore, the contractor must work closely with the local concrete supplier and inform the supplier that the concrete mix design will be placed in an ICF wall system. Concrete Placement In most areas, Ready Mix Concrete suppliers are familiar with ICFs and have a specific ICF mix design. Fox Blocks insulate the concrete in cold weather permitting the placement of concrete in winter temperatures with supplemental heating. Refer to Technical Bulletin Cold Weather Concrete. Fox Blocks provides concrete specifications and mix guidelines, and the local ready-mix supplier will provide the specific mix design following these specifications, dependent on the local environmental requirements in your area. Additional admixtures such as fly ash, plasticizers and super plasticizers may be added to increase the workability and concrete flow. The contractors should be experienced and knowledgeable about any additives and how they will impact the placement and curing times. CONCRETE MIX GUIDELINES The following concrete mix guidelines must be conveyed to the concrete supplier: Cutting corners on the concrete mix can add cost and problems when you place the concrete into the Fox walls. Compressive Strength Aggregate Size Slump 1

2 Concrete Compressive Strength The 28-day compressive strength of the concrete must be specified to meet the strength used in the design of the Fox Blocks walls. The minimum strength that should be specified is 2,500 psi (17 MPa). A slightly higher compressive strength of 3,000 to 4,000 psi (20 to 30 MPa) can help the flowability and pumpability of the concrete and provide additional strength to the walls with minimal or no additional costs. Compressive Strength Chart for ICFs The characteristics of ICFs provide a very high early compressive strength to the concrete and continued high strength. Concrete Aggregate It is recommended that the aggregate used in the concrete design for Fox Blocks forms follow these specifications. Fox Blocks 4" 6" 8" 10" & 12" Aggregate Size 3 /8" 3 /8" - ½" ½" - ¾" ¾" Using a larger aggregate size, than specified in the 4" and 6" forms, may cause congestion between the form wall and the reinforcement resulting in voids. When using various size forms on a project ensure the aggregate in the mix design is compatible to the small form size. Slump The proper slump allows the concrete to flow and be pumped at an efficient rate. A normal slump for Fox Blocks forms is 5" to 6" which is higher than a concrete mix for a floor, which may be at a 3" slump. Refer to a Fox Blocks Technical Representative before using a self-consolidating concrete mix design. Additional water, added to mix on-site, will reduce the compressive strength of the concrete and affect the water to cement ratio. 2

3 Lower slumps can create voids and honeycombing in the walls, plus may damage the forms during placement. Higher slumps create more hydrostatic pressure within the wall that may cause damage to the forms. The following table has recommended slumps for various Fox Blocks sizes: Fox Blocks Concrete Slump 4" 6" 8" 10" & 12" 6" - 7" 5½" -6½" 5" - 6" 5" - 6" Slump Test The slump specified must be the slump that arrives in the ready-mix truck at the job site. Water should not be added to the concrete at the job site. The following chart provides a visual check of the slump rate as the concrete is placed. Additional water, added to mix on-site, will reduce the compressive strength of the concrete and affect the water to cement ratio. Height of Lift 5" (125mm) Slump Distance Ahead 6" (150mm) Slump Distance Ahead 1 1/2 Blocks (2' - 0") 2' - 4" 3' - 0" 2 Blocks (2' - 8") 3' - 0" 3' - 8" 2 1/2 Blocks (3' - 4") 3' - 8" 4' - 4" 3 Blocks (4' - 0") 4' - 6" 5' - 6" CONCRETE PLACEMENT RATES The speed of concrete placement has many variables that must be considered prior to initiating placement of the concrete in the cavity of a Fox Blocks wall. These variables may be: Linear Length of Wall Wall Height Concrete Volume Temperature Weather Manpower The one uncontrollable factor is weather and temperature. Temperature influences the flow rate for concrete placement. The American Concrete Institute has developed tables related to concrete placement rates at specific temperatures. Pour rates in the Installation Checklist Pre-plan the placement of concrete and utilize the Fox Blocks concrete checklists - Prior to Placement and Post Concrete Placement from the Installation Checklist

4 following table reflect a 2:1 safety factor, as suggested by ACI. These rates assume normal density concrete (150 pcf (2400 kg/m3 ) or less) combined with air temperature. ACI PLACEMENT RATE TABLE Temperature F ( C) Feet/Hour (mm/hour) 40 ( 4 ) 2.2 ft (670 mm) 50 (10 ) 2.9 ft (890 mm) 60 (15 ) 70 (21 ) 80 (27 ) 90 (32 ) 3.4 ft (1040 mm) 4.0 ft (1220 mm) 4.6 ft (1400 mm) 5.2 ft (1585 mm) Placement Fox Blocks builders have found that using an overhead boom pump is the most efficient way to place the concrete in the ICF walls. When using the overhead boom pump, it is important to slow the velocity of the concrete by reducing the diameter of the hose near the end of the line. Avoid using heavyweight metal devices near the end of the hose. Refer to Technical Bulletin Concrete Placement - Lift and Fall Heights Placement of concrete from the top of the wall is not an issue for aggregate separation. The concrete is placed in 4 foot (1.22 m) lifts to ensure proper consolidation. If more than one pour (i.e. a multi-story project) is required, the walls are typically planned to be placed one story at a time. Placement is recommended to begin in the center of a wall and proceed around the perimeter of the project. Avoid placing concrete directly into corner forms, concrete should flow into the corners. Refer to Technical Bulletin Concrete Placement in Corner s. Concrete should be placed below every window opening through the opening left in the sill of the window buck. Fox Block walls must be checked to ensure walls are plumb, square and straight before, during and after the concrete is placed. In cold weather (freezing or below) always protect the top of walls and/or any exposed concrete areas with temporary insulation or insulated tarps. 4

5 CONCRETE CONSOLIDATION The first step towards ensuring a well consolidated solid concrete wall is having the correct slump for a good flowable concrete mix. To prevent voids and honeycombing and ensuring solid contact is made with the reinforcement bars, it is very important to consolidate the concrete. While ICF professionals often employ various methods to accomplish this, Fox Blocks recommends using an internal vibration method. Consolidation should directly follow the placement of the concrete, continuously around the perimeter of the wall. Internal vibration can be used with a light-duty pencil vibrator. The wand should not be greater than 1" (25.4 mm) in diameter. When vibrating the wall internally, always keep the vibrator moving fast in and slow out. Refer to Technical Bulletin Concrete Consolidation Consolidate concrete during each lift, following the person placing the concrete. Extend the vibrator into the lift below, in order to blend the two lifts and avoid any cold joints. Always vibrate around openings to ensure good consolidation around the reinforcement. Prior to concrete placement ensure vibrator is in working order and can reach every wall. Tools for externally consolidation may be used, but it is recommended to vibrate on both sides of the wall. 5