Philip G. Malone

Microstructure, strength, and reaction products of ground granulated blast-furnace slag activated by highly concentrated NaOH solution

Ground granulated blast-furnace slag was reacted in 5 M (pH 14.7) and 1.5 M (pH 14.2) NaOH solutions at a water/slag ratio of ∼0.4, and characterized by unconfined compressive strength testing, scanning electron microscopy, energy dispersive spectroscopy, and x-ray diffraction. The reacted material consisted of a dense layered matrix interspersed with unreacted glass particles and regions of reaction products with higher porosity. CSH(I) and (C, M) 4 AH 13 were identified by x-ray diffraction. The C-S-H (calcium silicate hydrate) phase is proposed to consist mainly of structurally imperfect layers of tobermorite, interleaved with layers of (C, M) 4 AH 13 . Other cations, most significantly Na + , are incorporated into the structure. Use of the highly concentrated solution (5 M) produced a higher degree of reaction and, consequently, higher compressive strength (38 MPa after 28 days for 5 M solution vs 21 MPa for 1.5 M).

Salt related expansion reactions in Portland-cement-based wasteforms

Abstract A small-scale study was conducted to investigate the expansion of a simulated salt-cement wasteform made with a salt mixture containing sodium nitrate, sodium sulfate, and sodium chloride blended with water and Type I Portland cement. The total salt loading was 39.4% by mass of simulated wasteform. Samples cured at 23°C hardened within 90 h and showed strength averaging 11.67 MPa after 23 days. Samples cured at 23°C and 55°C expanded when subjected to temperature cycling from 1 to 25°C. The samples cured at 55°C required only four cycles to disintegrate after showing 14% expansion. Samples cured at 23°C required eight cycles before disintegrating after showing 16% expansion. X-ray diffraction patterns from 1-, 4-, 6-, and 21-day-old samples showed the characteristic patterns of halite, sodium nitrate, darapskite, and unreacted Portland cement. Samples older than 1 day also showed portlandite, sodium sulfate and calcium chloroaluminate hydrate which were not found in the younger sample. The results are consistent with the hypothesis that expansion is due to recrystallization of confined soluble salts. Results suggest thatwasteforms containing such high loadings of soluble salts may disintegrate if subjected to thermal cycling.

Laser-induced fluorescence in contaminated soils

A fiber-optic fluorometer that uses laser excitation has been developed to perform field screening of contaminated soils at hazardous waste sites. The unit uses a nitrogen laser and an optical multichannel analyzer to develop data on contaminate concentrations in soil in place at a site. The unit operates with a soil cone penetrometer and can obtain data down to a maximum depth of approximately 50 meters. Use of this equipment allows rapid mapping of the distribution of leaked or spilled contaminants that contain fluorescing components. The soil fluorometer has been particularly useful in tracking the movement of hydrocarbons, such as diesel fuel or gasoline.

Rapid Soil Stabilization and Strengthening Using Electrokinetic Techniques

Abstract : The Army has a requirement to develop methods of strengthening soil to support rapid runway and roadway construction. A study was undertaken on the use of DC current applied to soil to form cementing phases in the soil. Preliminary work was on the use of zinc. aluminum. and iron in a variety of granular materials. Metal ions primarily form soft metal hydroxide gels that produce no immediate soil strengthening. Passing current through soil mixed with an alkali-reactive silicate produces rapid hardening with strength to 2,000 psi.

Durable roadside protective structures for low-volume roads

Data compilations on accidents nationwide show that 30% of all traffic fatalities and 16% of all injuries occur when a vehicle goes into a ditch or strikes a fixed obstacle on the roadside. Highway traffic barriers and crash cushions are not economical for use on low-volume roads, even though they could be helpful in reducing fatalities and injuries. Sand-filled barrels and metal barriers that undergo controlled deformation are relatively expensive and require significant investments in placement, inspection, maintenance, and repair. A crash cushion design based on scrap tires encased in foamed, fiber-reinforced concrete is being developed and can provide a versatile, low-maintenance safety barrier that is also resistant to vandalism. The composite scrap tire–and–concrete protective barrier uses a skeleton of scrap tires as an attachment point that can serve to lift, place, and anchor a mass of foamed, fiber-reinforced concrete in place on the roadside. The foamed, fiber-reinforced concrete crushes like wood under impact from tools or projectiles, so the modules are difficult to vandalize and can survive scrapes from graders or snow removal equipment. Module array can be developed on the basis of weight distribution in sand-filled barrel arrays. Potential uses for the barrier modules include protection of bridge piers, bridge railings, and obstacles on curves. The durability and economy of these units make them a practical option for use in improving safety on low-volume roads, especially in remote areas.

Performance of Cement-Basedseal Systemcomponents Inawaste Disposal Environment

A grout based on portland cement, Class F fly ash, and bentonite clay was developed as part of the closure system of shallow subsurface structures for disposal of low-activity radioactive wastes. Heat output, volume change, and compressive strength of the sealing grout were monitored with time, at elevated temperature, and in physical models, to determine if this closure grout could maintain adequate volume stability and other required physical properties in the internal environment of the disposal structure. To determine if contact with an alkaline liquid waste would cause chemical deterioration of the sealing grout, cured specimens were immersed in a liquid waste simulant containing high concentrations of sodium and aluminum salts. Over a period of 21 days at 60 °C, specimens increased in mass without significant changes in volume. X-ray diffraction of reacted specimens revealed crystallization of sodium aluminum silicate hydrate. The new phase has an X-ray diffraction pattern similar to that of the commercial syntheticzeolite, Losod. Scanning electron microscopy used with X-ray fluorescence showed that clusters of this phase had formed in grout pores, to increase grout density and decrease its effective porosity. The testing was repeated at 100 °C for 5 days using a simulant containing sodium hydroxide and aluminum nitrate and the results were similar. Physical and chemical tests collectively indicate acceptable performance of this grout as a seal-system component.