Roger K. Seals

Stabilization of phosphogypsum using class C fly ash and lime: assessment of the potential for marine applications.

Phosphogypsum (PG, CaSO(4).H(2)O), a solid byproduct of phosphoric acid manufacturing, contains low levels of radium ((266)Ra), resulting in stackpiling as the only currently allowable disposal/storage method. PG can be stabilized with class C fly ash and lime for potential use in marine environments. An augmented simplex centroid design with pseudo-components was used to select 10 PG:class C fly ash:lime compositions. The 43cm(3) blocks were fabricated and subjected to a field submergence test and 28 days saltwater dynamic leaching study. The dynamic leaching study yielded effective calcium diffusion coefficients (D(e)) ranging from 1.15 x 10(-13) to 3.14 x 10(-13)m(2)s(-1) and effective diffusion depths (X(c)) ranging from 14.7 to 4.3mm for 30 years life. The control composites exhibited diametrical expansions ranging from 2.3 to 17.1%, providing evidence of the extent of the rupture development due to ettringite formation. Scanning electron microscopy (SEM), microprobe analysis showed that the formation of a CaCO(3) on the composite surface could not protect the composites from saltwater intrusion because the ruptures developed throughout the composites were too great. When the PG:class C fly ash:lime composites were submerged, saltwater was able to intrude throughout the entire composite and dissolve the PG. The dissolution of the PG increased the concentration of sulfate ions that could react with calcium aluminum oxides in class C fly ash forming additional ettringite that accelerated rupture development. Effective diffusion coefficients and effective diffusion depths alone are not necessarily good indicators of the long-term survivability of PG:class C fly ash:lime composites. Development of the ruptures in the composites must be considered when the composites are used for aquatic applications.

State of the art on stabilization of hazardous organic liquid wastes and sludges

The principal motivation for undertaking this study was to examine stabilization techniques to determine the technical feasilibity of stabilizing/solidifying organic liquid wastes and sludges. The performance of the processes must often be judged on the basis of the manufacturers claims rather than the evaluation of an impartial referee. The study was largely concerned with documenting the state‐of‐the‐art and identifying promising directions for additional research. The most recent available literature, supplemented by telephone contacts with vendors and companies, were the primary information sources. Based on an exhaustive search of the research literature dealing with the solidification and stabilization of hazardous organic wastes, the following observations can be made: (1) Few adequately documented studies have been reported on the performance (physical and chemical stability) of solidified and/or stabilized mixtures containing hazardous organic wastes. (2) Almost no published information exists o...

A preliminary assessment of the use of an amorphous silica residual as a supplementary cementing material

An amorphous silica (AS) by-product was investigated as a possible supplementary cementing material (SCM). Standard ASTM tests for the SCM as well as specific surface area measurement, electron microscopy, Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (SRD), {sup 29}Si nuclear magnetic resonance (NMR) spectroscopy, thermal analysis, and cement paste and mortar cube strength studies were conducted. A 10:90 AS:OPC paste (w/cm of 0.4) and mortar cubes (w/cm = 0.50 to 0.60) were prepared. AS is a white amorphous material ({bar x}=29{+-}9(1{sigma}) nm) with a surface area of 95,000 m{sup 2}/kg, the latter resulting in a high water demand. All of the AS in 10:90 AS:OPC paste reacted by 7 days, consuming more than 50% of the calcium hydroxide. The compressive strength of OPC paste remained unchanged with the addition of AS but that of mortar increased.

STABILIZATION OF SULFATE-CONTAINING SOIL BY CEMENTITIOUS MIXTURES MECHANICAL PROPERTIES

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.

The influence of admixtures on the strength and linear expansion of cement-stabilized phosphogypsum

Abstract The effect of admixture content, dry density and curing condition on linear expansion of cement-stabilized phosphogypsum (CSPG) was studied over a ninety-day period. The phosphogypsum was stabilized using 8% Type I portland cement. Cylindrical CSPG specimens (51mm x 102 mm) were fabricated by static compaction (ASTM D 698) at three density levels: standard Proctor maximum dry density (13.7 kN/m3) and 5% on either side of this density with a moisture content (20%) corresponding to the maximum standard Proctor dry density. CaCl2 (1% and 2 %) and Daraset (0.05% and 0.15%) as a percentage of the amount of cement, were added to CSPG. Curing conditions were (at ambient temperature): open to air, moisture-controlled and soaked. Selected specimens were analyzed by derivative thermogravimetry and scanning electron microscopy. When cured under moisture-controlled environment, CSPG had a short initial period of expansion irrespective of the dry density or admixture content. Increasing dry density led to a period of contraction following expansion. At the same dry density, the additon of CaCl2 led to a period of no length change while the addition of Daraset led to more initial expansion. The length change, over time, of air-cured CSPG specimens was negligible. The correlation between ettringite content and expansion was crude. For soaked specimens, ettringite growth was widespread and unusually high. Compacted at the lowest density (13.0 kN/m3) and cured in moisture-rich environments, CSPG deteriorated significantly.

Phosphogypsum as a Component of Flowable Fill

Phosphogypsum (PG) is a by-product of the production of phosphoric acid, a key ingredient in the manufacture of fertilizers. Large amounts of PG have been stockpiled in Florida, Louisiana, and Texas, as well as other parts of the world. The means of using and disposing of this by-product with minimal environmental impact have been developed in research spanning almost 20 years. A study was conducted to investigate PG as a potential component of flowable fill materials along with Class C fly ash. Both Class F and Class C fly ashes have been used successfully to provide flowability and strength characteristics to flowable fill. A number of mix proportions of PG and fly ash were tested for flowability, time of setting, and unconfined compressive strength in a preliminary test series. Using the results of these preliminary tests, three final design mixtures were developed. These mixtures were then subjected to different physical and engineering property tests, including flowability, time of setting, unconfined compressive strength, flexural strength, dimensional stability, and permeability. Tests were also conducted to evaluate the environmental effects of the individual mixtures. These tests included the toxicity characteristic leaching procedure and radon emission testing. The results of this study indicated that PG can be used successfully as a component of flowable fill.

Calibration of a Dynamic Penetrometer for Compaction Quality Control of Boiler Slag

A dynamic penetrometer was designed for the purpose of evaluating compaction quality in fills constructed with boiler slag. Laboratory and field calibration tests were conducted to study the effect of densification on dynamic penetration resistance. The effects of specimen preparation method (pluviation and impact compaction) and saturation on dynamic penetration resistance were investigated in the laboratory. A 0.91-m (3-ft)-deep test fill with dimensions of 6.1 m (20 ft) by 30.5 m (100 ft) was prepared in the field. Dynamic penetration resistance and in situ densities were recorded in this slag fill after 0, 2, 4, 6, 10, and 16 passes of a smooth drum vibratory roller of 5.6 tons (11.2 kips). The field-resistance values were compared with laboratory values. Charts are provided to aid both in selecting the lift thickness/number of roller passes and also for field assessment of densification in boiler slag using the dynamic penetrometer.