Procedures

This testing was intended to explore two factors in the application of bentonite composite sheets: lap width and the degree of confinement. A total of three types of bentonite composite sheets were generously provided for testing by several manufacturers. The materials are designated A, B, and C.

The test apparatus consists of a clear plastic box that is 600 mm (23.6 in.) deep, by 400 mm (15.7 in.), by 400 mm (15.7 in.). There is a 1.6 mm (1/16 in.) hole in the center of the bottom of the box. For testing, the box was filled with water to a depth of 500 mm (19.7 in.) and the amount of water flowing out of the hole was measured/

Test specimens of the bentonite materials were prepared by cutting out circular pieces with diameters of 25 mm (1 in.), 51 mm (2 in.), 102 mm (4 in.), and 152 mm (6 in.). The specimens were placed in the bottom of the box, directly over the 1.6 mm (1/16 in.) hole.

Metal shims were placed in the bottom of the box, to support concrete pavers described below. The base shim was equal to the thickness of the dry bentonite specimen; each material was a different thick­ness. This condition is somewhat analogous to the installation of bentonite in a wall application: confining surfaces are present on both sides of the bentonite but spaced apart by the thickness of the bentonite sheet. This initial test condition is referred to as Plus 0.

To simulate the effect of unintentional but possible gaps or irregularities in confinement, three test conditions in addition to Plus 0 were created by adding shims. In separate tests additional shims were stacked on top of the base shim before installation of the concrete pavers. These test conditions have the following designations, Plus 1/16 (shims equal to the thickness of the bentonite sheet plus 1.6 mm (1/16 in.)), Plus 1/8 (shims equal to the thickness of the bentonite plus 3.2 mm (1/8 in.)), and Plus 3/16 (shims equal to the thickness of the bentonite plus 4.8 mm (3/16 in.)).

To resist the expansive pressure of the bentonite in our test apparatus, five concrete patio pavers, each 51 mm (2 in.) by 305 mm (12 in.) by 305 mm (12 in.), were stacked on shims over the specimen.

This test method is not meant to duplicate any actual construction condition; however, it is analogous to a lap in a bentonite waterproofing system. For example, in a test with a 152 mm (6 in.) diameter 5With the test box tilled with water to 500 mm 09.7 in.) and no barrier over the hole in the bottom of the box, water flowed out at a rate of 1407 mL/min {47 o/7min).

FIG. 1—Plus 0 confinement.

specimen, water must pass between the plastic box bottom and a 76 mm (3 in.) width (half the diameter of the specimen) of the overlying bentonite composite to reach the hole and cause a simulated leak. In the roughly analogous condition in actual construction, water must pass between the plastic facer of the lower composite sheet and a 76 mm (3 in.) width of the overlying bentonite composite panel to reach the wall and potentially cause a leak.

Specimens were designated by the material type and the diameter, in inches. For example, a specimen of material type B, with a diameter of 51 mm (2 in.), is designated B2. In this exploratory study one fresh unhydrated specimen was used in each combination of test conditions.

Water flowing out of the hole in the bottom of the test box was captured in a container placed below the test box at the start of a measurement interval. There were three measurement intervals, each approxi­mately ten minutes in length. The test results are expressed as mL/min for approximately the first ten minutes after filling the test box with water, the next approximate ten minute interval, and the third approximate ten minute interval. In most test conditions, this period of approximately 30 minutes was not long enough for leakage to stop. It was, however, a long enough period to create results that distinguished between test conditions and materials.