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Core Construction

Dayton, OH: Cement-Bentonite Vertical Barrier, Englewood Dam Crest Improvements


Geo-Con successfully completed work on dam crest improvements at the Englewood Dam located approximately 15 miles northwest of Dayton, Ohio. The Englewood Dam is a critical part of an ambitious five-dam system managed by the Miami Conservancy District to control floodwaters in the over 5,000 square mile Great Miami River Basin. The crest improvements included installation of a cement-bentonite vertical barrier wall necessary to raise the impermeable core of the dam to minimize seepage through the dam during maximum flood stage. A higher strength backfill material (100 to 400 psi) was required to support highway loads from Federal Route 40 which follows the crest of the dam.

Geo-Con installed the vertical barrier wall 4,471 feet long by 30 feet deep (97,900 sf) employing proven slurry trench techniques. However, in order to meet the strength requirement for the cutoff wall while maintaining a low permeability, Geo-Con developed a unique cement-bentonite slurry mix design containing Type S cement, which is a slag cement, and natural bentonite. This was the first project completed by Geo-Con using slag cement to create a relatively impermeable vertical barrier wall with significant strength.

Slag cement, as the name implies is produced by milling blast furnace slag into a granular form. This material has a long successful track record in Europe in the construction of vertical barriers but it has been only recently that slag-based cements have become readily available in the Untied States. The primary use of slag cements in the United States is to produce specialty lightweight concrete for the construction industry.

Typical cement-bentonite mixes using Type I or Portland cement would barely meet the permeability requirement and fall significantly short of the short term and long-term strengths. Simply increasing the cement content of the mix to increase strength would result in unacceptable permeability results. Although the strength gain develops much slower with slag-cement, unlike Portland Cement, slag-cement is not affected by the introduction of bentonite into the slurry.

Results of Geo-Con's rigorous quality control and laboratory testing program indicated the slurry backfill material developed the required strength of 100 psi within 28 days of cure and permeability was maintained below 1 x 10-6 cm/sec as required. The Miami Conservation District was so pleased with the results of the project, the specifications for future dam rehabilitation projects will include Type S cement as the material of choice for cutoff walls.


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