SYMPOSIA PAPER Published: 01 January 1989
STP22881S

A Physical Testing Program for Stabilized Metal Hydroxide Sludges

Source

A proposed method of closing two Resource Conservation and Recovery Act surface impoundments containing metal hydroxide (F006) sludges involved stabilization and on-site disposal. A sample testing program was developed as part of an evaluation of processes offered by various firms interested in performing the stabilization. For this application, the stabilized material was to have sufficient strength to support construction and cover loads, low permeability, long-term durability, and low settlement under anticipated loads.

The test procedures developed to determine those properties were based on standard soil and soil-cement test methods to the extent possible. The standard test methods proposed for use included the ASTM Test Methods for Unconfined Compressive Strength of Cohesive Soil (D 2166), for One-Dimensional Consolidation Properties of Soils (D 2435), Wetting-and-Drying Tests of Compacted Soil/Cement Mixtures (D 559), and Freezing-and-Thawing Tests of Compacted Soil/Cement Mixtures (D 560). A falling-head test was used to determine the coefficient of permeability. Appropriate molds and specimen preparation procedures were sent to each firm with a sample of the raw sludge in order that the stabilized sludge specimens would be prepared in the same manner.

Modifications to the proposed test procedures were required due to the condition of several sets of samples. The procedures for evaluating the freeze-thaw and wet-dry durability were altered by eliminating the brushing and weighing of samples between cycles. This sample handling was eliminated so that the relative effects of environmental exposure could be more readily compared. A few of the samples suffered significant expansion, shrinkage, cracking or some combination of these to a degree that made them unusable.

In general, the specimen preparation procedures and test methods developed worked well for the stabilized sludge samples. The unconfined compressive strength test results were highly variable and ranged from 0.5 kg/cm2 (100 lb/ft2) to over 35 kg/cm2 (70 000 lb/ft2). The compressibility under a load of 1.5 kg/cm2 (3000 lb/ft2) ranged from 0.5% to 5%. The permeability of the stabilized material was generally low and in the range of 10-6 to 10-7 cm/s. The specimens generally withstood more freeze/thaw cycles than wet/dry cycles; several of the specimens lost much of their strength and integrity upon saturation. No strong correlation between any of the physical properties was observed. However, specimens which included cement as an additive tended to fail at low strain, have higher unconfined compressive strength, and were less compressible.

Author Information

Forslund, BL
NTH Consultants, Exton, PA
Smith, LJS
Wilkins Wheaton Environmental Services, Inc., Kalamazoo, MI
Bergstrom, WR
Wayne Disposal, Inc., Ypsilanti, MI
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Details
Developed by Committee: D34
Pages: 214–226
DOI: 10.1520/STP22881S
ISBN-EB: 978-0-8031-5090-4
ISBN-13: 978-0-8031-1261-2