Using self-consolidating concrete in vertical and overhead applications has become an accepted and proven concrete repair method. Based on the orientation of the repair, pumping self-consolidating concrete can be the required method of placement for this material. However, pumping can also be the preferred method of application, over form-and-pour techniques, as it can save time and money.
KING provides self-consolidating concrete technology in a pre-packaged solution. Our company offers MS-S6 SCC for shallow depth repairs of 25 mm (1 inch) to 75 mm (3 inches) and MS-S10 SCC for full depth repairs of 50 mm (2 inches) or greater. When pumping MS-S6 SCC or MS-S10 SCC in a closed-form vertical or overhead application, the following recommendations should be considered in order to ensure success.
FORMWORK
• Formwork should be designed to be stronger than normal concrete formwork, in order to account for the hydraulic pressure exerted by the self-consolidating concrete and any additional pressure from pumping.
• Formwork should be designed to allow for air to escape from high points in the form and provide points to observe the progression of the pour. If necessary 13 mm (½ inch) plastic tubing can be placed at extremely high points, to ensure that the air is pushed out of the form.
• Minimum hose and valve sizes should be 38 mm (1½ inches) for MS–S6 SCC Concrete and 50 mm (2 inches) for MS-S10 SCC.
• Different types of valves can be used to connect hoses to the formwork, although the most common type is the guillotine valve which can be seen in Figure 1. The guillotine valve can be struck and closed when the self-consolidating concrete reaches or progresses beyond the valve opening.
• Valves should be spaced at a maximum distance of 600 mm (2 ft) in both the horizontal and vertical directions of the formwork.
• Formwork should be sealed as tightly as possible at the joints, as the paste of self-consolidating concrete tends to leak from the form more readily than normal concrete.
PUMPING SEQUENCE
• Pumping should begin at the lowest point in the formwork and move toward the highest point in the formwork, to allow air to escape through the subsequent valves and air vents.
• All of the valves should be open during the pumping procedure until the concrete has progressed to the subsequent valve, at which point the current valve should be closed and the hose should be moved to the subsequent valve for pumping to continue.
• The entire section of self-consolidating concrete should be pumped in one pour, without stopping. This procedure will help the concrete already in the formwork from losing slump flow before the formwork is completely filled.
PRIOR TO PUMPING
• Ensure that the concrete pump intended for use is capable of pumping self-consolidating concrete with either 6 mm (1/4 inch) aggregate (MS-S6 SCC) or 10 mm (3/8 inch) aggregate (MS-S10 SCC), over the required distance. This information should be available from the concrete pump manufacturer, although testing the pump set-up prior to commencing the work is also beneficial in some circumstances.
• Host a pre-pour meeting to outline the pumping procedure and responsibilities of all crew members involved in the pour.
*Note: KING’s technical staff is available for pre-pour meetings or on-site consultations, in order to help contractors achieve a successful concrete repair.
• Ensure that constant communication between the pump operator and the individual responsible for valve and hose placement can be maintained.
• Fill the formwork with water prior to pumping, in order to check for water tightness and to saturate the parent concrete and formwork.
• Ensure that the parent concrete and formwork is in a Saturated Surface-Dry (SSD) condition, and that all excess water is removed from the formwork, prior to pumping MS-S6 SCC or MS-S10 SCC.
SELF-CONSOLIDATING CONCRETE
• For the optimum balance between strength development and slump flow retention, concrete temperatures should be maintained between 10 ºC and 21 ºC (50 ºF and 70 ºF).
• Maintain the concrete slump flow (Figure 2) between 600 mm and 700 mm (24 inches and 28 inches) at the exit of the pump hose, in order to promote proper consolidation. If the slump flow is below 600 mm (24 inches), the self-consolidating concrete may not be fluid enough to navigate highly congested zones of rebar.
DURING AND AFTER PLACE MENT
• Do not vibrate the self-consolidating concrete during placement as this action can cause segregation. If necessary, tap the outside of the formwork to ease placement and indicate the level that the concrete has reached in the formwork.
• The pump operator should be notified to stop pumping as soon as any stress on the formwork or anchorage becomes apparent, when the concrete reaches the highest point of the form, or when the maximum design pressure of the formwork is reached. It is possible to blowout the formwork and cause failure if the pressure in the formwork becomes too high.
• Once pumping has stopped, the last valve should be closed and the concrete should be allowed to set and begin to develop strength. The forms should not be removed until the concrete has achieved 75% of the indicated 28 day compressive strength.
This report is intended for use as a guide only. Please consult the Technical Services Department of King Packaged Materials Company for further information regarding the pumping of self-consolidating concrete for a specific application.