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This article in SSSAJ

  1. Vol. 56 No. 6, p. 1843-1848
     
    Received: July 11, 1991


    * Corresponding author(s):
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doi:10.2136/sssaj1992.03615995005600060032x

Stability of Synthetic Sand-Clay Aggregates after Wetting and Drying Cycles

  1. M. J. Singer ,
  2. R. J. Southard,
  3. D. N. Warrington and
  4. P. Janitzky
  1. Dep. of Land, Air and Water Resources, Univ. of California, Davis, CA 95616

Abstract

Abstract

We hypothesized that the lack of structure and low aggregate stability characteristic of many California Central Valley soils was due, in part, to infrequent wetting and drying cycles. We created synthetic aggregates by drying a slurry of 0.1- to 0.5-mm-diam. acid-washed quartz sand and varying amounts of Ca-saturated reference smectite, kaolinite, or illite at 40 °C. The resulting dry mixtures were crushed and sieved, and the 0.5- to 1.0- and 1.0- to 2.0-mm-diam. synthetic “aggregates” were subjected to up to 80 wetting and drying cycles. The wet aggregate stability (Yoder method) of 1.0- to 2.0-mm-diam. aggregates with 5% clay decreased, regardless of clay type, after 32 wetting and drying cycles. The smectite and illite 0.5- to 1-mm-diam. aggregate stability did not change significantly after 32 cycles. Following a decrease after eight cycles, wet stability for the 0.5- to 1-mm 5% kaolinite aggregates increased to equal the zero-cycle stability after 32 cycles. Increasing clay content to 25% increased the initial smectite wet aggregate stability, but decreased the kaolinite and illite wet aggregate stability for both aggregate size fractions. Scanning electron micrographs of the smectite-sand aggregates showed that the sand grains became more tightly packed and clay became more uniformly distributed over the grains and formed grain bridges with increasing number of cycles. We attribute variation in response to wetting and drying cycles to different clay-clay and clay-sand interactions caused by inherent structural differences among the clays.

This work was funded in part by a grant from the Kearney Foundation of Soil Science.

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