Kenneth J. Reid

Compressive Strength of Municipal Sludge Ash Mortars

Sludge ashes produced by the incineration of municipal sewage wastes are becoming increasingly difficult to dispose of in landfills, and there is a resulting increase of interest in disposal by inorporation in building materials. In the present study, a comprehensive test program was developed to examine the potential for using the ash as a fine aggregate in mortar. The strength characteristics of mortars prepared from sludge ash with addition of fly ashes (both Classes C and F) and varying amounts of cement and lime were cured under standard laboratory conditions for periods of 1, 3, 7, 14, and 28 days before testing for compressive strength. The results indicate that the addition of sludge ash adversely affects the strength behavior of mortars. Although partial substitution of sludge ash with fly ash gave improved results, strengths were always less than those obtained from control mortars using sand. Addition of fly ashes also improves mortar workability. The addition of lime in place of cement reduces strength.

Moderate strength concrete from lightweight sludge ash aggregates

Abstract A range of artificial aggregates has been developed from incinerated municipal sludge ash and tested in concrete. The ash is either pelletised or slabbed, and subsequently fired until it sinters and expands to form lightweight products. From the tests conducted on size, grading, bulk density, absorption and compressive strength, it appears that both the pellets and slabs have potential as lightweight aggregates. Their use in producing moderate strength concrete of up to 2000 psi and unit weight 50 lb/cu ft (800 kg/m3) via steam curing has specifically been investigated. Although concrete prepared from the pellet form of aggregates are somewhat heavier, they exhibit superior strength than those prepared from the slabs and commercial aggregates derived from expanded clays. It is anticipated that because of their spherical shape and uniform size distribution, the pellets could provide better workability and compaction; and their lower moisture absorption may also render them as potentially better thermal insulators.

Lightweight aggregates from incinerated sludge ash

A range of artificial aggregates has been developed from incinerated sewage sludge ash. The ash is either pelletized or slabbed and subsequently fired until it sinters and expands to form lightweight products which are later graded for use as aggregates in concrete. From the standard tests conducted on size grading, bulk density, absorption and fracture strength, it appears that both the pellets and slabs are potentially suitable as lightweight aggregates in concrete. Preliminary studies on concrete incorporating these aggregates support this hypothesis. No studies of potential containment release at high temperature was made during these studies.

Use of thermal analysis in the hydration studies of a type 1 portland cement produced from mineral tailings

Abstract A high-strength Type 1 cement produced from raw taconite and copper-nickel tailings of Minnesota is the subject of hydration studies by using thermal methods such as TGA and DTA. Hydration is measured in terms of hydration product formation and the amount of bound water and free calcium hydroxide incorporated in them. When cured under identical conditions, the Type 1 “tailing” cement, compared to an ordinary Type 1 Portland cement, exhibits better hydration properties. This is attributed to its higher tricalcium silicate content, a component that hydrates faster and also contributes much to the strength development. Correlation between the degree of hydration and strength is suggested and a simple mathematical expression relating these parameters proposed.

PORTLAND CEMENT PRODUCTION USING MINERAL WASTES

A Type I Portland cement has been produced using anorthite from copper-nickel tailings and raw taconite tailings. The cement exhibited better strength properties than ordinary Type I Portland cement and gave a stronger concrete when tested under identical curing conditions. Factors leading to the attainment of these higher strength values are identified and their effects on the ultimate mechanical properties of cement are discussed. It is also anticipated that the compositional variety of tailings may also have other beneficial effects on long-term cement behavior such as resistance to sulfate attack.

Recovering Zn, Pb, Cd and Fe from electric furnace dust

In the operation of a typical mini-mill, about 1 to 2% of each charge to the electric furnace is converted to dust, which is collected as particulate matter in the baghouse system. The dust is considered hazardous because it contains lead and cadmium. However, it also contains large, recoverable quantities of zinc and iron. To make the dust environmentally acceptable and to recover the valuable content, pyrometallurgical processing was studied on a laboratory scale. The experimental results show that successful removal of zinc, lead and cadmium and considerable upgrading of iron from the electric furnace dust have been accomplished, and that a nonhazardous inert slag have been formed by pyrometallurgical processing at two temperatures.

Application of Plasma Technology in Iron and Steelmaking

The potential for the application of plasma technology in metal oxide reduction and in iron and steelmaking is outlined and discussed. Recent evolution and developments in the plasma-based reactors employed in the production of iron, steel, and ferroalloys have been reviewed; the current status is outlined in terms of process control, flexibility in the raw materials consumed, product quality, and energy conservation. The advantages and limitations of thermal plasma-based reactors have been critically outlined and their potential to seriously challenge the blast furnace/basic oxygen furnace steelmaking route is considered.

In-Flight Plasma Reduction of Domestic Chromite

This paper explains the principle of the new sustained shockwave plasma (SSP) reactor, which achieves in-flight reduction of minerals. Initial research is described in which an open 40 kW SSP reactor is used to assess the feasibility of in-flight reduction of a low-grade, domestic chromite concentrate. The effect of feed and operating conditions are discussed and a reduction mechanism based on both conventional theory and conditions thought to exist within the sustained shockwave plasma is postulated. In conclusion, the ongoing research program at the Mineral Resources Research Center (MRRC) and the potential for plasma processing of minerals are outlined.

The derivation of kinetic parameters in analysis of portland cement for portlandite and carbonate by thermogravimetry

The analysis of hydrated portland cement can be facilitated by the use of thermal analysis techniques. This is especially true with regard to the estimation of the portlandite phase (calcium hydroxide [Ca(OH) 2 ]) which isone of the major phases in set portland cements. There are various references in the literature to the use of thermogravimetric analysis (TG) for the estimation of free Ca(OH) 2 . Papers by Midgley and Ramachandran have shown it to be reliable. It has been used by Dollimore et al. to estimate the Ca(OH) 2 in portland cement (OPC), OPC/pulverized fly ash (PFA), and OPC/PFA/polymer pastes. It is also shown here that the method can be adapted to indicate the relative crystallinity of the Ca(OH) 2 present. Taking the investigation into a higher temperature region on the thermal analysis equipment also means that an estimate of the calcium carbonate can also be made. This is important in aged mortars. The method can be extended to cover the quantitative analysis of calcium sulfate if present.

Application of thermodynamic and kinetic principles in the reduction of metal oxides by carbon in a plasma environment

The application of plasma technology to metal oxide reduction is discussed with reference to established thermodynamic and kinetic principles. ΔG°-T diagrams for the corresponding metal oxide, metal carbide, and C-CO reactions are presented and the important role played by thepCO/PCO2 ratio examined. On the basis of these theoretical considerations, supported by some earlier experimental results conducted on the reduction of iron and chromium oxide concentrates in the form of taconite and chromite by carbon within a plasma reactor, the tendency to form either elemental metals or carbides is discussed. It is also suggested that the reduction of taconite by carbon takes place in two stages within the plasma medium. In the first stage, ferric oxide is reduced to wustite by carbon, and in the second stage wustite is reduced to metal. It is also postulated that in the first stage of reduction, ferric oxide may also be reduced to wustite through an exchange reaction between ferric oxide and iron, without CO evolution. The rate controlling step for the first stage of taconite reduction is thought to lie at the gas/slag interface generated within the plasma environment, while the second stage of reduction is controlled by carbon gasification by CO2.