Winn Rock (CaSO4) gravel from a quarry in Winn Parish in north Louisiana was used extensively as a surface course for local parish roads. Stabilization of these roads with Type I portland cement followed by an overlay of asphaltic concrete resulted in heaving. A study was undertaken to investigate the cause or causes of the expansion as well as to identify an alternate means of stabilization. Specimens of representative soil from the affected area were stabilized in the laboratory using various cementitious materials and were cured using a variety of methods. The mix contained 5% to 20% cementitious material. The cementitious materials were Type I portland cement, lime, and supplementary cementing materials such as granulated blast furnace slag (BFS), Class C fly ash (CFA), silica fume, and an amorphous silica (AS). The unconfined compressive strength of the stabilized soil was determined. The effect of size fractions other than the gravel on the expansion was assessed, and the expansion of the specimens over time was monitored. The cement and BFS mixtures almost doubled the compressive strength of the specimens compared with portland cement alone. The finer size fractions were responsible for expansion. The magnitude of expansion was directly proportional to the amount of Type I portland cement, the amount of available moisture, and the curing temperature. Replacement of a part of the portland cement by BFS significantly reduced the amount of expansion even at the highest moisture content. No expansion was detected when CFA and AS partially replaced the cement.

Stabilization of a kaolinite bed by the electrochemical injection of aluminium and phosphate ions has been investigated. Electrical gradients of 2 V/cm or less constituted the predominant driving force for ion transport under a 433 µA/cm2 constant direct current density. The changes in the kaolinite properties and pore fluid characteristics due to electrokinetic treatment were analysed. Average increases in undrained shear strength of 500–600% were observed for phosphoric acid and aluminium sulfate/phosphoric acid treatments of the kaolinite. Electrokinetic processing caused an average increase of 30% in the Atterberg limits. It is hypothesized that injection of phosphate and aluminium ions into the kaolinite specimens modified the pore fluid, leading to an increase in shear strength by ion exchange and precipitation mechanisms. However, the strength increase observed was not homogeneous throughout the specimen.

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Polarized optical microscopy, scanning electron microscopy, and X-ray microprobe analysis were used to investigate the effect of seawater on phosphogypsum (PG):cement composites. Thin surface sections were taken from 85%: 15% PG:cement composites that had been submerged under natural seawater conditions for 1 month and 70%:30% PGicement composites that had been submerged under natural seawater conditions for 1 year. The optical microscopy results revealed a crystalline layer of carbonates on the surface of the 70%:30% composites, which was absent on the 85%: 15% composites. Microprobe analyses indicated that the carbonates, in the form of CaCOj, were formed from Ca2+ and C032contained in the seawater, not from the composites. This CaCOa coating may act as a physical barrier to seawater intrusion into the composites, preventing block degradation. The polarized optical and scanning electron microscopy images of the 85%: 15% composites showed surface disruption, which is hypothesized to be caused by the interaction of seawater and the phosphogypsum. Ruptures and ettringite crystals, formed through the interaction of dissolved sulfate ions and Ca.^Al oxides, were also found throughout the composites. The absence of a CaCO^o uter layer and the subsequent dissolution of PG and the formation of ettringite are potentially responsible for the degradation of the 85%: 15% PG:cement composites. The identification of the CaC03 layer on the 70%:30% PG:cement composites may lead to the development of techniques to increase the integrity of PG:cement composites used for seawater applications.