Q.: Three different strengths of concrete were specified for one of our jobs in the Midwest: 3000 psi for foundations, 4000 psi for flatwork and 5000 psi for structural members above grade. Specifications give the same maximum water-cement ratio for all three concretes 0.44. Working with our concrete supplier, we submitted proposed foundation mix proportions for the engineer's approval. Under pressure to maintain the schedule, we placed the foundations, though the engineer hadn't yet responded. About 30 days later he returned the submittal marked "not approved" because the water-cement ratio calculated out to 0.48.
Are we in trouble, and if so, how bad? Why is the same water-cement ratio limit specified for three different kinds of concrete?
A.: We don't know why the same water-cement ratio is specified for foundations, flatwork and structural members above grade. When both strength and water-cement ratio are specified, it's usually because the water-cement ratio needed for durability is higher than that needed for strength. But a water-cement ratio as low as 0.44 is seldom needed for foundation concrete. ACI 318-95, Building Code Requirements for Structural Concrete, requires a maximum water-cementitious materials ratio of 0.45 for concrete exposed to freezing and thawing in a moist condition, deicing chemicals or high sulfate levels. It requires a 0.40 maximum for corrosion protection of reinforcement in concrete exposed to chlorides from deicing chemicals, salt, salt water, brackish water, seawater or spray from these sources. Since you're in the Midwest, foundation-concrete exposure to sulfates, salts or freezing and thawing is unlikely.
How much trouble are you in? If the owner tries to require you to remove and replace the foundation concrete, your cost would be high. However, you could argue that this extreme measure constitutes economic waste. In 1992, a U.S. Court of Appeals ruled that when a contractor substantially but not strictly complies with a contract's specifications, the owner may not require replacement of the work if replacement would amount to economic waste. The owner may only take a credit (see the article Concrete Law: Ripping Out Work Ruled Economic Waste in Concrete Construction, May 1994, p. 441).
You could argue that as long as strength is adequate, the owner hasn't been damaged by the slightly higher water-cement ratio. The owner would have to prove damage, and it would be very hard to produce data showing that foundation concrete with a 0.48 water-cement ratio is less durable than concrete with a 0.44 ratio, especially when exposure to sulfates, chlorides or freezing and thawing is unlikely. On that basis, you could ask for a use-as-is disposition of this specification nonconformance. Under the economic-waste rule, restoration of any damage to the owner would be limited to reimbursement of the cost of the cementitious material needed to produce a 0.44 water-cement ratio instead of the 0.48 ratio used. As with any legal question, consult with your lawyer before planning your strategy.