Products of steel slags: An opportunity to save natural resources

H. Motz, J. Geiseler

In Europe and the most other continents there is a great demand of aggregates mainly from civil engineering industry especially for the field of road and concrete constructions as well as for hydraulic purposes like stabilisation of river banks. But there are also the declared targets of the European Community [].

The last statement of the declared targets holds us responsible to save natural resources by using industrial co-products and to increase their utilisation rate wherever their technical and environmental properties are suitable concerning the relevant application field.

Accelerated ASR testing of recycled concrete

D.L. Gress, R.L. Kozikowski, T.T. Eighmy

The work involves research on investigating techniques and procedures to assess the Alkali Silica Reactivity (ASR) expansion potential for concrete made from recycled concrete aggregate (RCA) which was known to have ASR, or is capable of ASR under conditions of increased alkali. Laboratory testing was done to evaluate various testing procedures designed to accelerate the ASR reaction. This included evaluating prisms with variable surface to volume ratios, increased moisture state, and microwave energy.

Standard 280 mm prisms with 76.2 mm faces cast with four 6.35 mm parallel longitudinal holes were shown to not only accelerate ASR but also to lower the coefficient of variation of the expansion data. Expansion of 76.2 mm concrete cubes was found to be significantly accelerated as compared to that of a standard prism. Sealing prisms in evacuated plastic bags with water was also found to effectively accelerate ASR expansion. Concrete prisms were subjected to ASTM C 1260 and ASTM C 1293 conditions and the results were compared to those from modified versions of the same tests including the use of microwaves.

The use of fly ash as a substitute of cement in microsurfacing

A. Nikolaides, N. Oikonomou

The paper describes the results of the addition of fly ash, a well-known by-product of hydroelectric units, in microsurfacing as a substitute of cement. Microsurfacing is a high quality slurry seal and is extensively used, in some countries, for the provision and restoration of skid resistance of the road surface. Microsurfacing technology requires the addition of filler additive (most often cement) in order to control the breaking time of the emulsion.

This paper examines the breaking time of the emulsion, the cohesion and the abrasion resistance of microsurfacing material with fly ash in comparison to microsurfacing with cement. The results have shown that the fly ash is more active than cement, which is an advantage, especially when microsurfacing is applied at low environmental temperatures. Additionally, due to the higher activity of the fly ash the required amount of additive is less than cement. This has a positive effect on the overall filler content in the case of high filler content in the original aggregate mixture. Therefore, the fly ash by-product, the disposal of which causes a great environmental problem, can be used as an alternative material to cement in microsurfacing. The use of fly ash in microsurfacing also reduces its overall cost.

Composition of organic matter in bottom ash from MSWI

I. Pavasars
A rough estimate of the bulk organic matter composition in bottom ash was made in this study. This estimate is based on the earlier results of characterisation of aqueous and non-aqueous bottom ash leachates by different analytical techniques, such as TOC measurements, gas chromatography-mass spectrometry, size exclusion chromatography, UV-VIS spectrophotometry, fractionation on XAD resins, and also on other data presented in the literature. These results suggest that cellulose and lignin are the major organic constituents of the bottom ash. Also fractions of water-soluble high- and low-molecular-weight substances as well as a fraction of organics, extractable with non-polar organic solvents were defined. In these extractable aqueous and non-aqueous fractions a number of individual organic substances have been identified.

Environmental impact of ferrochrome slag in road construction

B.B. Lind, A.-M.. Fällman, L. B. Larsson

Vargön Alloys in Western Sweden is one of the largest producers of ferrochrome slag in Europe. Ferrochrome slag is a by-product from the production of ferrochrome, an essential component in stainless steel. Extensive tests have been carried out on the physical properties of the ferrochrome slag from Vargön Alloys e.g. brittleness, flakiness, mass wasting, Los Angeles value and capillary properties, and it was found to be highly suitable as road construction material. The current level of production of ferrochrome slag is about 150,000 tonnes per year. In untreated conditions the bulk density of the slag is around 1.5 t/m3 and the volume generated can be up to 100,000 cubic metre per year. The slag is crushed and sold in different fractions between 0-100 mm.

The composition and leaching tests of the ferrochrome slag show that the chromium content is high, 1-3%, although leaching under normal conditions is very low. With the exception of potassium (K), which had a potential leaching capacity (availability test) of around 16 %, the leaching of chromium, nickel, zinc and other elements was just a few per cent. However, all these tests were conducted in the laboratory. What happens out in the field, under the influence of acid rain and biological activity, and how does this compare with the laboratory results?

To answer this question an investigation was carried out to study the environmental impact of ferrochrome slag in roads that were built in 1994. The investigation includes soil sampling (total content) and groundwater analysis (filtered and non-filtered samples). In addition, a new method involving the bio-uptake of chromium and other metals by the roots of the dandelion (Taraxacum officinale) was tested. The results show that there was a low migration of particles from the slag to the underlying soil and that the leaching into the groundwater was also low for all the elements analysed. However, there seemed to be a significant uptake of Cr by plants growing with their roots in the slag. An investigation of plant uptake was an important complement to laboratory leaching tests on alternative materials.

Mineralogical, hydraulic and mechanical characterisation of solidified and stabilised MSWI Fly Ash. Contribution of blast furnace slag

S. B. Morel, P. Clastres, A. Pellequer

Ashes produced from the Incineration of Municipal Solid Wastes (MSWI fly ashes) require to be treated before being landfilled in a waste disposal site. One treatment method commonly used prior to landfilling is the solidification/stabilisation process using a hydraulic binder. In this study, ground granulated blast furnace slag was used. This binder is well adapted to the solidification and stabilisation of heavy metals. It also offers good durability with regards to chlorides. MSWI ash studied in this paper are derived from an incineration plant which uses dry flue gas treatment.

First, these MSWI ashes are characterised (unhydrated material, reactivity and mechanical properties of hydrated material). Then, «ash-slag-water» mixtures have been studied to model the properties of fresh and hardened materials. It has been shown that blast furnace slag participated in the solidification/stabilisation of MSWI ashes by : performing the mechanical strength, the durability and the stabilisation of the material.

Then it is shown that an addition of pozzolanic or hydraulic materials performs the solidification and stabilisation properties.

Lead, zinc and chromium (III) and (VI) speciation in hydrated cement phases

I. Moulin, J. Rose, W. Stone, J.-Y. Bottero, F. Mosnier, C. Haehnel
Cement contains trace amounts of hevy metals of various origins. The main source is due to heavy metals naturally present in some of the raw materials used for clinker manufacture. The use of industrial waste as substitutes for fossil fuels may be another source of heavy metals in cement. During the hydration of cement, anhydrous phases dissolve and species in solution react to form hydrated products. Therefore the true fixation of the heavy metals is the one inside the precipitated hydrates after the dissolution of anhydrous phases. This work attempts to characterize lead, zinc and chromium (III) and (VI) speciation in hydrated cement phases.

Thermal treatment of iron oxide stabilized APC residues from waste incineration and the effect on heavy metal binding

M.A. Sørensen, M. Stackpoole, C. Bender-Koch, R. Bordia, M. M. Benjamin,

T. H. Christensen

Iron oxide stabilized APC residues from MSWI were heat treated at 600ºC and 900ºC. The thermal treatments resulted in a change in product stability by forcing a transformation in the mineralogical structures of the products. The treatments, moreover, simulated somewhat the natural aging processes that would take place in a stabilized residue. Consequent changes in crystalline structure and heavy metal binding were examined.

On-site treatment and landfilling of MSWI air pollution control residues

K. Lundtorp, D.L. Jensen, M.A. Sørensen, T.H. Christensen

APC-residues from MSWI are difficult to landfill due to substantial leaching of trace metals. An on-site pre-treatment prior to landfilling of APC-residues is suggested. The treatment involves mixing of APC-residues with a ferrous sulphate solution and subsequent oxidation of the suspension. Bench-scale experiments were carried out with both a semidry APC-residue and a fly ash. After mixing and oxidation the suspension was transferred to model landfills to simulate on-site treatment and landfilling. The waste water from the process, which ran off through the drainage system, contained large concentrations of salts (Cl: 14-30 g/l, Na: 4-9 g/l, K: 5-11 g/l and Ca: 2-12 g/l) but low concentrations of Pb (14-100 m g/l) and Cd (<2-7 m g/l). The treated residues which were left in the model landfills were leached. The leachate contained low concentrations of trace metals (Pb: < 120 m g/l, Cd: < 1.7 m g/l and Cr < 485 m g/l). Colloids larger than 0.4 m m were not important as a transport medium for Pb, Cd, and Cr in this experiment. Substantial reductions were observed compared to a similar leaching of untreated APC-residues. Particularly, the initial release which was reduced by up to 4 orders of magnitude.

Stabilization of waste incinerator APC-residues with FeSO4

T.H. Christensen, K. Lundtorp, D.L. Jensen, M.A. Sørensen, E.P.B. Mogensen

This paper describes a new treatment process to reduce leaching of trace elements (Pb, Cd a.o.) and salts from waste incinerator air pollution control (APC) residues. The process involves mixing of the APC residues with a ferrous sulphate solution and subsequent oxidation of the suspension. The treated product has a significantly reduced content of salts and the heavy metals are bound by the iron oxides formed. The process has been tested on a semidry gas-cleaning residue and a fly ash. The treated products were characterized by leaching tests including pH-static tests. The generated wastewater contained relatively low concentrations of trace elements (e.g. Pb: 29-162 m g/l and Cd: 3.3-7.5 m g/l), but high concentrations of salts (e.g. Cl, Na, K, and Ca). The treatment process reduces the leaching of Pb from the residues by more than two orders of magnitude at fixed pH. Likewise, the Cd leaching was significantly reduced. Similar results were observed for Zn and Cu. The effect on elements that form oxyanions is more uncertain and in the current process there is no reduction in the release of Hg.