This project was done at the United States Borax & Chemical Corporation
plant in Boron (Death Valley), California. Concrete containing ten percent
silica fume was used for a slab and a drainage ditch. Both are exposed to
sulfuric acid and borax. The water-cementitious material ratio of the
concrete was approximately 0.40. As might be expected for Death Valley,
conditions during the placement were extremely harsh: the estimated rate of
evaporation from the concrete surface was over 3.9 L/m2/h (0.8 lb/ft2/hr),
which is almost four times the rate at which ACI recommends taking
precautions to prevent plastic shrinkage cracking for concrete without
silica fume. For this project, the concrete was fogged until curing
compound was applied. Wet burlap covered by plastic sheeting was placed
over the curing compound. The concrete also contained polypropylene fibers
to help protect against plastic cracking. The concrete was placed and cured
without cracking. This slide shows preparation for placement of the slab.
The Silica Fume Association
38860 Sierra Lane, Lovettsville, VA 20180
Tel: 540.257.4224 Fax: 540.822.9456
