Construction> Pumping the Concrete The Pre-Pour Consultation It is critical that you establish excellent communications with both the concrete delivery company and the pumper truck company. As more and more of these companies become familiar with ICF construction, and Grid-WALL in particular, mis-communication will become less and less a problem. But the importance of having the correct mixture is so vital to the outcome of the project, we want to emphasize that the pre-pour consultation with both of these companies should be thorough and specific.   Last Minute Inspection After all the blocks have been stacked, and all the walls and buckings have been braced, you will want to begin the final cleanout. Loose debris will have fallen inside the walls during the stacking process and needs to be washed out before the pour in order to create a good bond between the wall and foundation. Cut a few small holes in the bottom row of blocks to allow the debris to escape, then from the top of the walls, run water down the voids to wash as much of the debris as  possible out the holes. Cut small holes in the side at the foundation (Save the plugs! Temporarily attach them to the block near the holes from which they were removed). Hose out all loose debris. Glue the plugs back in place. Placing the Concrete Order The composition of your concrete is CRITICAL, so pay close attention to the details in this section.   AMOUNT: You will need to order 1.1 cubic yard of concrete to fill each 100 square feet of Grid-WALL.   PSI: Minimum 3000psi.  In most documents, this designation will appear similar to the following: CONCRETE WALL FILL= ______________ PSI Generally, 3000 PSI Tested Compressive Strength is adequate, but this may vary for a multi story structure or for special loads. As a precaution, on 2 stories and above, take concrete samples for strength testing during placement. SLUMP: 7" SLUMP.   The slump is critical for the mix to flow correctly into the voids of the wall! DO NOT ATTEMPT TO POUR A THICK MIXTURE! AGGREGATE: #3 PEA GRAVEL ONLY!!  DO NOT USE CRUSHED ROCK OR LARGE AGGREGATE! The reason why crushed rock will not work in this application is that the jagged edges will get caught on the rough surfaces as it tries to flow through the forms. Pea gravel is naturally smoother and it is this difference that makes the formula work.  DO NOT SUBSTITUTE!   A Note About Plasticizers: Adding plasticizers increases the strength of the concrete by reducing the amount of water necessary to produce a particular slump. It is especially helpful in hot weather conditions. Ask your cement contractor or engineer for specific details for your application. Ordering the Pumper Truck It is best to use the boom with the least amount of elevation that will do the job. The flow of concrete from a greater height makes the delivered pressure slightly higher. Sometimes trees and other obstacles will not allow for a choice of booms, but, if possible, ask for the boom that will do the job with the least amount of elevation.  The higher the apex of the boom, the greater the delievery pressure at the nozzle. You should request these specialty items to be brought with the concrete delivery: S Pipe 3 inch Reducer Fabric End The 'S' slows the fall of concrete as it is pumped, making it easier to place the flow correctly into the wall.   The reducer slows the flow of the concrete. With no reducer, the concrete will blast from the pump with too much force, putting an unneccessarily high load on the forms. The fabric end allows easier control of the flow—just squeezing the fabric can slow or stop the concrete flow.     Weather Conditions In hot climates, you will find that wetting the walls down first will facilitate the bond between the blocks and the grout, and may make the grout more easily slide through the voids. Adding water to the mix may lower the viscosity of the mix, but it will also prolong the setting of the concrete, and increase shrinkage within the form. Using plasticizers can reduce the water needed to achieve the correct slump and create greater early strength, without the negative effects of excess water. If the weather is near freezing, pouring may still be done. Be aware that at 45 degrees and lower, slump may be affected, and the cure time greatly extended. Grid-WALL™ is an insulating concrete forming system. Most of the heat generated by the curing process will be kept within the form, protecting the concrete from freezing prior to curing. Any concrete not protected by the form should be protected from freezing. A note: Some concrete companies will not pour when temperatures dip below 40 degrees due to liability issues.   The Pumping Process Start pumping at one corner, and slowly fill into the wall. When you see, or people at ground level hear, that the concrete is about 4-6 feet up the wall, move the flow over a few voids. Aim at the "saddle" of the block's nodes, and let the grout slide into the voids on either side. Or aim the side of the void, the goal is to keep the grout from freefalling to the bottom of the wall. Continue in this way, pumping and moving around the wall. While our blocks average 2 1/2 times higher psi strength than styrofoam alone, if you try to place more than 4-6 feet of concrete in one spot (especially if you let it freefall), there is risk of over-stressing the bottom blocks because the grout doesn't have time to run horizontally and relieve the pressure from above. There is normally no need to use a vibrator. “Wobble” the vertical rebar to remove trapped air bubbles, or carefully use a bar to settle the concrete—do not poke through a block! It is more difficult for the concrete to flow through voids that have been partially filled with conduit or plumbing, so go slowly around those areas, and check them carefully with an ice pick or thin bladed screw driver. Once the wall is completely filled, smooth the concrete and place any desired bolts or attachments into the wet concrete.   Access Holes Under Window Buckings This photo shows access holes cut in the bottom the the window bucking. Fill the voids below them completely. Replace the plugs. These holes allow the air to escape when the forms are being filled. They also ensure that the concrete is distributed properly under the windows. They are especially important under wider windows since the concrete has further to flow.   Multi Stories The concrete may be pumped in 4-6 foot lifts, filling a typical wall in two passes. If building more than one story, leave about ½ of the top blocks unfilled to make a contoured bond with the second level pouring. This photo shows rebar sticking out of the poured wall to tie with the rebar for the next floor.   Avoiding problems Wet concrete is heavy! If the pressure inside the forms becomes excessive, the block can break, spilling concrete, and wasting time while the problem is repaired and cleaned up.IF YOU PUMP 4-6 FEET OF CONCRETE PER PASS, THERE SHOULD BE NO REASON TO FEAR A FAILURE. The concrete must fill the forms uniformly and not too quickly. Fill the voids along the sides of doorways and windows that continue all the way to the foundation before filling the short ones over the bucking. Consider carefully, prior to the pour, any restrictions within the voids and how best to fill around them. IMPORTANT: Before pouring, brace the outside of corner forms in both directions to prevent the cement from trying to push them away from the other walls. Brace all walls to the stringline before the pour, and brace any other places you suspect would concentrate force or weight. The idea is to let the concrete fill the forms from the bottom up, as evenly as possible. As the concrete begins to set, the wall becomes stronger, so by the time a second pass is made, the first-pass walls will already be strong enough to take the load of the next pour.   Good Results What you want from the preparation and pour is to see the voids completely filled.  If your plans call for the buckings to be removed, you will see first hand just how well the flow went. This photo shows window buckings removed and the voids completely filled with concrete. A job well done.