Technical Manual: Conduits through Embankment Dams (FEMA 484)

Conduits through Embankment DamsWaterstopControl jointFigure 73.—Typical control joint used in reinforcedcast-in-place concrete conduit construction.Longitudinal reinforcement is continuous throughthe joint.possible, vertical construction joints should be avoided because of concernswith getting a good bond on a vertical joint surface.The joints previously described are planned joints that allow for good procedures totreat the joint. Sometimes during construction, interruptions occur during theplacement of concrete and require an unplanned joint. This type of joint is referredto as a “cold joint.” Great care should be exercised to avoid cold joints because thistype of joint introduces the possibility for higher porosity, weakened shear andtensile strength, and decreased durability. Typical cold joint treatments include highpressure washing or wet sandblasting to remove mortar coatings, or othercontaminants, followed by a high volume, low pressure washing and vacuuming toremove all excess water and debris. If the surface of the cold joint is not properlycleaned, this will result in a lack of bond between the existing surface and newconcrete. After cleaning, the surface should be maintained in a damp conditionbefore placing the new concrete.Time delays are specified between placement of adjacent sections at joints to allowthe concrete to dissipate heat resulting from the peak hydration temperature. Thelonger the concrete is given to cool, the smaller the stresses at control andconstruction joints and the openings at contraction joints due to the volumetricchange in the adjacent sections. The length of the time delay can be affected by theconcrete mix, the thickness of the sections, the placement temperature of theconcrete, and the ambient temperature surrounding the concrete as it cures.Temperature-measuring instruments can be used as an aid in minimizing the curingtime between adjacent concrete placements while also minimizing the jointseparation between the same placements. These instruments can also be used in104