Supplying silica-fume concrete for a major project can be a very good or a very bad experience for you as a concrete producer. Regardless of how uniform your concrete is or how well you meet the project specifications, if your customer, the contractor, isn't experienced with placing and finishing this type of concrete, your concrete will probably be blamed for any problems that come up. Here are some pointers that will help you help your customer make the job go well.
Do your homework
- Determine the best point in the batching sequence to add the silica fume.
- Mix the concrete thoroughly.
- Don't overload your mixers.
- Get your air content correct before the project starts.
- Address the "stickiness" issue head-on.
Tutor your customer Thoroughly discuss the characteristics of silica-fume concrete:
- Silica-fume concretes differ in the rate of slump loss and the rate of concrete setting. These concretes exhibit little or no bleeding.
- Silica-fume concrete doesn't require very much finishing.
- Silica-fume concrete gains strength quickly once it sets and begins to harden. Cracking has occurred on some projects where a contractor has delayed stressing post-tensioning tendons. Just remember that concrete will reach the stressing strength very quickly.
- Silica-fume concrete requires a higher slump than conventional concrete for similar placement conditions.All of these points should be discussed at a pre-pour meeting. A job well done may lead to more projects with silica fume and an opportunity to expand the use of this value-added product. The article also covers the necessity of using fogging and evaporation retarders to prevent plastic shrinkage and the need for continuous curing of silica-fume concrete.
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