Access Type

Open Access Thesis

Date of Award

January 2015

Degree Type

Thesis

Degree Name

M.S.

Department

Geology

First Advisor

Jeffrey L. Howard

Abstract

Many cities worldwide have areas of vacant land produced by building demolition. This open space has attracted great interest as a potential resource for green infrastructure, urban agriculture, and other purposes related to urban renewal. Unfortunately, rock-like artifacts (e.g. brick, mortar, concrete) are often present in great abundance in demolition site soils. These artifacts make the soil difficult to till, create obstacles for root penetration, and limit the soil’s water-holding capacity, infiltration and aeration. As an alternative to physical removal, this study was carried out to test the feasibility of using hygroscopic compounds as soil amendments to accelerate the mechanical disintegration of these artifacts in situ using natural freeze-thaw/wet-dry processes. Bench-scale tests were carried out to simulate 5 to 8 years of freeze-thaw/wet-dry cycling using dilute (3%) solutions of deicing salts (NaCl, CaCl2, salt mixture), fertilizer salts (MgSO4, Al2(SO4)2, (NH4)2SO4), and organic compounds (CH4N2O, C12H22O11, humate), which were added to a commercial topsoil containing clay bricks, concrete and sand-lime brick (simulating mortar). In the absence of visible disintegration, the effectiveness of each treatment was evaluated by uniaxial compression testing, and petrographic analysis of microporosity. Sand-lime brick showed visible disintegration by all treatments except CaCl2. The clay and concrete bricks generally lacked visible signs of deterioration, but showed a consistent decrease in compressive strength with all treatments. The greatest loss in strength (30%) occurred with the use of urea, sugar and the salt-mixture; however humate and all three sulfate compounds produced an average loss in strength of 20% or more. Petrographic analysis of concrete and clay bricks treated with NaCl and sugar showed an increase in microporosity which is inferred to be the cause of strength loss. Microporosity in the concrete was due to dislodging of calcite grains in the limestone aggregate, whereas that in clay bricks resulted from dislodging of silt-sized quartz temper. The treatments had no significant effect on pH, and electrical conductivity measurements showed that the salinities of all soils (except treated with the salt-mixture) were below a level detrimental to plant growth. These results support the hypothesis tested that hygroscopic compounds can be added as amendments to demolition site soils to accelerate and effect the mechanical breakdown of artifacts on a time scale (< 10 years) short enough to be useful in the near future.

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