Q: When a concrete wall is built on a concrete base slab and both are designed with construction joints that include a waterstop, shouldn't the joints match up? We built a water tank with 25-foot-high walls on a 3-foot-thick base mat that's about 50x50 feet. Plans called for construction joints with a waterstop at 25-foot spacings in the base mat. Plans also showed contraction joints with waterstops in the wall, but the wall joints were offset as much as 4 feet from the base-slab joints.Hairline cracks developed in the wall as shown in the sketch, and water came through the cracks when the tank was leak-tested. We had to epoxy inject the cracks to stop the leakage. I believe this wouldn't have happened if the joints had matched up. Is there an American Concrete Institute (ACI) or Portland Cement Association (PCA) document that says joints in a base slab should match with joints in a wall?

We checked ACI 350R-89, Environmental Engineering Concrete Structures, ACI 301-96, Specifications for Structural Concrete, and PCA's Building Movements and Joints but found no mention of a need to match joint locations. However, a 1981 article on joints in sanitary-engineering structures deals with this subject (Ref. 1). Author Roger Wood says that any joint in a structure should preferably go through the entire structure in one plane. He marks the joints on the first conceptual plans with big, heavy black lines, creating a visual effect that resembles a model of the structure after it's hit with a meat cleaver. Each slice made in the model is a joint location.Wood explains his rationale for keeping the joints in one plane as follows: "Each joint is, to some degree, a discontinuity in the structure. Movement may take place at a joint. I can protect the joint from leakage due to movement by waterstops and sealants. If the joints are not in line and movement occurs in a portion of the joint it will probably tear a crack in the concrete above until the crack intercepts another joint. There is no waterstop or sealant present at cracks to prevent leakage."This discussion seems to describe what happened to the tank you built. And Wood clearly agrees with you that joints in the base slab and walls should match up.

  1. R. H. Wood, "Joints in Sanitary Engineering Structures," Concrete International, April 1981, p. 54.

Reader response:

Concerning the question on whether or not to line up construction joints that include a waterstop (p. 630), you said that after checking several American Concrete Institute (ACI) and Portland Cement Association (PCA) documents, you found no mention of a need to match joint locations. However, ACI 224.3R-95, Joints in Concrete Construction (chapter 3, section 3.3.2, second paragraph), states:

Contraction and expansion joints within a structure should pass through the entire structure in one plane (Wood 1981). If the joints are not aligned, movement at a joint may induce cracking in an unjointed portion of the structure until the crack intercepts another joint.

Although this paragraph is taken from the chapter on joints in buildings, the topic of the referenced paper by Roger Wood is sanitary-engineering structures.Grant T. Halvorsen

Structural Engineering and Concrete Materials

Wheaton, Ill.