Swell compression testing on Kaolinite Gypsum Systems.pdf

Kelden Andrews, UK CAER
Tom Robl, UK CAER
Tristana Duvallet, UK CAER
Bob Jewell, UK CAER

Description

Swell compression testing on Kaolinite Gypsum Systems Authors Mr. Kelden Andrews - United States - University of Kentucky Center for Applied Energy Research Dr. Thomas Robl - United States - University of Kentucky Center for Applied Energy Research Dr. Tristana Duvallet - United States - University of Kentucky Center for Applied Energy Research Dr. Bob Jewell - United States - University of Kentucky Center for Applied Energy Research Mr. Ewen Floch - France - Polytech Dijon Abstract The understanding of soil swell mechanics and mechanisms is critical to both the treatment of soils for stability as well as site selection for structures in areas where soil swell may be a problem. Soils rich in kaolin clay are of concern for their potential to swell. Its principal mineral, kaolinite (Al2Si2O5(OH)4, is alumina rich and, with the right surrounding environment or because of treatment, may be exposed to calcium, and sulfates, and may become unstable and expansive. To investigate this, kaolinite clay with various doses of gypsum and small amounts of calcium hydroxide (.3 - .7wt%) was placed into a swell compression test (ASTM D4546, Test C) to measure the rate of expansion and how additional loading on the soil would slow or collapse that expansion. Lower doses of Kaolinite (1 and 2.5%wt) had unpredictable swell with an initially high expansion followed by collapse as the loads increased. The collapse began at about 3/4 tsf (US tons per square foot). The higher doses had a gradual swell and significantly enhanced load-bearing capabilities, marking them a greater concern for building. After testing, samples were removed and examined using SEM to see morphological changes to identify ettringite and/or thaumasite crystals. None were found in the examined samples, even in the samples with 20 % wt. gypsum and calcium hydroxide additions. This combined with the relatively low pH of the sample’s expansion solution (about 8) suggests an Alkali sulfate attack was present but other mechanisms were likely at work as well, other options are discussed to try and explain the phenomena.

 
May 14th, 3:30 PM May 14th, 5:00 PM

Swell compression testing on Kaolinite Gypsum Systems.pdf

Grand Rapids, Michigan

Swell compression testing on Kaolinite Gypsum Systems Authors Mr. Kelden Andrews - United States - University of Kentucky Center for Applied Energy Research Dr. Thomas Robl - United States - University of Kentucky Center for Applied Energy Research Dr. Tristana Duvallet - United States - University of Kentucky Center for Applied Energy Research Dr. Bob Jewell - United States - University of Kentucky Center for Applied Energy Research Mr. Ewen Floch - France - Polytech Dijon Abstract The understanding of soil swell mechanics and mechanisms is critical to both the treatment of soils for stability as well as site selection for structures in areas where soil swell may be a problem. Soils rich in kaolin clay are of concern for their potential to swell. Its principal mineral, kaolinite (Al2Si2O5(OH)4, is alumina rich and, with the right surrounding environment or because of treatment, may be exposed to calcium, and sulfates, and may become unstable and expansive. To investigate this, kaolinite clay with various doses of gypsum and small amounts of calcium hydroxide (.3 - .7wt%) was placed into a swell compression test (ASTM D4546, Test C) to measure the rate of expansion and how additional loading on the soil would slow or collapse that expansion. Lower doses of Kaolinite (1 and 2.5%wt) had unpredictable swell with an initially high expansion followed by collapse as the loads increased. The collapse began at about 3/4 tsf (US tons per square foot). The higher doses had a gradual swell and significantly enhanced load-bearing capabilities, marking them a greater concern for building. After testing, samples were removed and examined using SEM to see morphological changes to identify ettringite and/or thaumasite crystals. None were found in the examined samples, even in the samples with 20 % wt. gypsum and calcium hydroxide additions. This combined with the relatively low pH of the sample’s expansion solution (about 8) suggests an Alkali sulfate attack was present but other mechanisms were likely at work as well, other options are discussed to try and explain the phenomena.