In a lengthy opinion, the Court of Federal Claims granted in part claims asserted by sureties that assumed responsibility to complete performance of a lock and dam construction contract because defective specifications, delays in government responses, and government directives resulted in compensable delays and changes. The partial denial of the sureties' cost claims was primarily the result of their failure to establish a critical path for the entire project and prove costs and causation for alleged productivity losses. Of the granted claims, the largest award of $6.6 million was for costs and delays attributable to workability issues with the concrete mix. Contract specifications allocated responsibility for the concrete mix between the contractor and the government. The contractor was responsible for selecting samples of mixture components, but the government was responsible for testing samples, performing mixture proportioning studies, and proportioning mixtures.