ADDITIVES TO CONTROL SLAKING IN COMPACTED SHALES

MARIAPPA SURENDRA, Purdue University

Abstract

Many combinations of durability and strength can be expected when dealing with shales to be used in compacted highway embankments. The classification systems used to group shales into durable and non-durable categories are based on their slaking properties and often do not consider the hardness, degradability or the physico-chemical properties. Hard and durable shales can be placed as a rock fill, while the soft and non-durable shales must be thoroughly degraded and placed in thin lifts as a soil fill. The hard and non-durable shales are difficult to stabilize by mechanical means, such as increased compactive effort. However, due to their non-durable nature, they often develop excessive settlements during the service life of the embankment and even cause slope failures.^ In this study chemical additives were investigated that could either: (a) help break down the shales during placement or (b) reduce the deterioration caused by slaking during the service life of the compacted shale embankment. The Slake Durability Test was used to evaluate the change in durability effected by various chemical additives in the slaking fluid, as well as lime in the compaction water. Chemical composition and pore size distribution of the shales were also investigated to determine their effects on durability. The principal conclusions from this investigation on selected Indiana shales were: (1) Slaking of non-durable shales cannot be attributed solely to the "air-breakage" phenomenon. (2) The slake durability index of the New Providence (a hard and non-durable) shale was increased by using 0.1N solutions of sodium chloride, calcium sulfate, and ferrous sulfate as the slaking fluid. Aluminum sulfate reduced the slake durability index when used at the same concentration. (3) The slake durability of Mansfield (a soft and non-durable) shale was increased by using calcium sulfate, aluminum sulfate, and ferrous sulfate at a concentration level of 0.1N. Ferric chloride decreased the slake durability index. (4) The sodium absorption ratio (SAR) from the saturation extract test can be used to estimate the durability of shales. (5) The parameters (cumulative porosity, median diameter and spread factor) of the pore size distribution of shale aggregates can be used to predict the durability. (6) Lime mixed with the compaction water increased the slake durability index of the compacted New Providence (a hard and non-durable) shale. Sixty days of curing period and 3% lime were found to be sufficient. (7) Lime did not effectively increase the durability of compacted Osgood (a hard and non-durable) shale. (8) Increased durability of compacted shales with lime is accompanied by increases in dry and soaked unconfined compressive strengths. ^

Degree

Ph.D.

Subject Area

Geological Survey|Engineering, Civil

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