March 5, 2007

Building Codes

Don't water that ready-mixed batch

The old slump test measurement for concrete has been replaced by water-cement ratio rquirements

Jean Sorensen

correspondent

VANCOUVER

Contractors who run a water hose into a truckload of ready-mixed concrete to make it easier to work with run the risk of violating the new B.C. Building Code revisions, contractors were told at the Buildex show held recently.

The new B.C. building codes sets revised strengths standards for concrete and those standards need to be kept in tact when batches are delivered to sites, Murray Frank of Constructive Home Solutions Inc. told contractors, architects, and others in the construction industry attending the session on code revisions.

The session, sponsored by the B.C. Homeowners Protection Office, said the changes apply to which strength of concrete is used in specific applications and how it is tested in the field.

The new Canadian Standards Association (CSA) standard for ready-mixed concrete for residential construction is referenced in Part 9 of the B.C. code. This changes the strength requirement for concrete to 20 Mpa (megapascals) in floor slabs and 32 Mpa for garage floors and exterior stairs. Exterior stairs also require five to eight per cent air entrainment.

The old slump test measurement for concrete has been replaced by water-cement ratio requirements. Frank said because the water-cement ratio is now an issue and a batch plant certificate is prepared, contractors can no longer water cement to make it more workable.

“You are affecting the water-cement ratio,” he says, adding that if the contractor alters the load by adding water, the driver will note the change on his batch certificate and require the contractor to sign-off that he has altered the water-cement ratios. “And, he will no longer assure it,” he says. “You are going on your own.”

This will eventually impact on the building as inspectors will want to see the batch certificates to make sure that the concrete used in floor slabs and walls meets the code requirements.

If some difficulty arises on site, says Frank, it is cheaper in the long run to redirect that load “back home and do that driveway you wanted done and order another load.” In the end, that is cheaper than attempting to water the load and not pass building inspections and having to redo work.

Frank advised that if contractors anticipate there may be a long haul or delay in getting the material on site, then they should ask the batch plant to add in chemical retardant which will delay the setting.

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