Assessment of the leaching due to degradation factors of stabilised/solidified waste materials

F. Felix, A.L.A. Fraaij, Ch.F. Hendriks

In the Netherlands, only a few applications of Stabilised/Solidified waste materials (S/S-waste materials) are known due to an uncertain long term behaviour of the S/S-waste material. This paper presents an assessment tool to determine the leaching due to degradation factors of S/S-waste materials. The tool is carried out on two cases: stabilised/solidified industrial purification sludge with cement, indicated with A and melted/crystallised sewage sludge. By means of a life time prediction procedure of CIB/RILEM relevant durability tests for the two cases are selected: wet/dry, erosion and freeze/thaw. If, assuming that leaching of hazardous components can be calculated by multiplication of available components with material loss after the durability test and by means of normalisation with Dutch leaching standards, it is clear that erosion of stabilised/solidified industrial purification sludge with cement has the highest contribution to the leaching, even if it is acknowledged that the material loss after erosion is overestimated by 100%. The contribution of the tool to the decision making process can be more transparency of leaching due to degradation factors, thereby helping the decision makers to chose between different S/S-treatments and to chose the best application of the S/S-waste material.

Reuse of secondary lead smelter slag in the manufacture of concrete blocks

R. Cioffi, M. Lavorgna, L. Santoro

A secondary lead smelter slag has been used in a cement based stabilization/solidification process for the manufacture of concrete blocks. The influence of the lead slag on the hydration chemistry has been studied by means of cementitious mixtures containing up to 65% powdered slag. The results have shown that the hydration chemistry is not negatively influenced from both the qualitative and quantitative points of view, provided that the lead slag content is within 30%. Concrete blocks containing 15% cement have been produced by partial substitution of the whole aggregate and each differently sized aggregate class. The maximum amount of substitution was 22%. Blocks of unconfined compressive strength ranging between 23.0 and 25.6 MPa can be produced in this way. The feasibility of the stabilization process has been tested by means of two dynamic leaching tests making use of a CO2-saturated solution and distilled water. The duration of the tests was extended up to 32 days to get information on the long term behaviour of the stabilized products. In this regard, it has been found that lead is released in cumulative amounts of the order of a few parts per million and that the resistance to lead diffusion is high.

Calcium sulphoaluminate cements made from fluidized bed combustion wastes

G. Bernardo, M. Marroccoli, F. Montagnaro, G.L. Valenti

Wastes generated in a bench-scale atmospheric fluidized bed combustor, using two different coals and a high-lime limestone sorbent, were employed as raw materials for the synthesis of calcium sulphoaluminate (4 CaO× 3 Al2O3× SO3) -based cements, which can be utilized for a wide range of applications. Raw mixes containing the bed material were heated in an electric oven in the temperature range 1000°–1200 °C. The best results in terms of reactants conversion and selectivity towards 4 CaO× 3 Al2O3× SO3 were obtained at 1200 °C with the addition of an external source of alumina which was required to avoid melting phenomena or integrate the Al2O3 content necessary for the 4 CaO× 3 Al2O3× SO3 formation.

Synthetic aggregates from combustion ashes using an innovative rotary kiln

P.J. Wainwright, D.J.F. Cresswell

This paper describes the use of a number of different combustion ashes to manufacture synthetic aggregates using an innovative rotary ‘Trefoil’ kiln. Three types of combustion ash were used, namely:

The fine waste ash fractions listed above were combined with a binder to create a plastic mix that was capable of being formed into ‘green pellets’. These pellets were then fired in a Trefoil kiln to sinter the ashes into hard fused aggregates which were then tested for use as a replacement for the natural coarse aggregate in concrete. Results up to 28 days showed that these synthetic aggregates were capable of producing concretes with compressive strengths raging from 33 to 51 Mpa, equivalent to between 73% and 112% of that of the control concrete made with natural aggregates.

The properties of recycled precast concrete hollow core slabs for use as replacement aggregate in concrete

B.E. Marmash, K.S. Elliott
Waste concrete from prestressed precast hollow cored floor units has been recycled for use as replacement aggregate in concrete (RCA). Waste concrete blocks were crushed to –14 mm using cone, impact and jaw crushers. All produced acceptable physical and mechanical properties, although the impact crusher was best suited in most cases. The water absorption of the RCA was 3 to 4 times greater than natural limestone and river gravel used for control purposes. The fine RCA was at the coarse end of the British Standard limit. Concrete made using zero, 20% and 50% replacement of coarse and fine RCA had increased workability at 20% replacement, but this reduced considerably at 50% replacement. Compressive strength of concrete made with RCA was generally within ± 5 N/mm2 of the control value of 62 N/mm2. RCA from the cone crusher produced the highest strengths. The main conclusion is that concrete made with up to 50% replacement of both coarse and fine RCA appears to be comparable with natural aggregate concrete in terms of workability and compressive strength.

Effects of foundry dusts on the mechanical, microstructural and leaching characteristics of a cementitious system

C. Gervais, S.K. Ouki
The disposal or recycling of industrial wastes has been an important and complex issue for the last 20 years. Hydraulic binders have been widely use to treat and/or reuse waste materials. Synthetic wastes are commonly studied but it does eliminate synergistic waste/binder interference effects that can result from real wastes, which are often composed of complex chemical compounds.

The objective of this research was to investigate the possibility of reusing waste from the foundry industry. For this purpose, 3 wastes from foundry plants have been selected based on their common metal contaminants. Therefore, the objective of this paper is to investigate the effects of the major metal contaminants, Pb, Zn and Mn, on the mechanical (setting time, unconfined compressive strength (UCS)) microstructural (X-ray diffractometry (XRD)) and leaching characteristics (acid neutralisation capacity test) of the solidified waste materials. The results showed that the addition of the wastes induced a retardation of the setting time, which is believed to be due to the presence of Zn, which is a known retardant. It was also revealed that, at equal water/cement ratio and after 28 days, the UCS of most waste products is within +10% of the controls. The mineralogical composition, as depicted by the XRD results, was particularly affected as shown by the clear increase of the non-hydrated products. Finally, the addition of the different wastes was shown to have no effect on the buffering capacity of the solidified products.

Physical properties and acid neutralisation capacity of incinerator bottom ash – Portland cement mixtures

A. Polettini, S. Polettini, R. Pomi, P. Sirini

The amount of bottom ash resulting from solid waste incineration typically ranges from 30 to 35% of burnt waste. Although such a residue stream is not classified as a hazardous waste according to the European waste catalogue, disposal of bottom ash may heavily weigh on the overall incineration costs.

Furthermore, the present tendency for solid waste management in industrialised countries is towards reduction of the amount of wastes to be landfilled. With a view to that, technical approaches aimed at reusing residual streams in industrial applications as secondary materials must be strongly encouraged.

As far as bottom ash is concerned, a promising option is represented by blended cement formulation. Bottom ash is indeed characterised by the presence of oxides and alumino-silicates, which might be responsible for strength development during cement hydration. In some cases, depending both on the composition of the original waste and on the combustion technology adopted, bottom ash may also exhibit pozzolanic activity.

It is well known that the properties of hardened cement mixtures made with impurities-bearing materials are strongly affected by the physical-chemical characteristics of the components, as well as the waste/cement dosage.

This paper presents the results of an experimental investigation on the behaviour of mixtures made with Portland cement and bottom ash coming from an Italian medical waste incinerator. In particular, the influence of waste/binder replacement levels and water/solids ratios on strength development and acid neutralisation capacity was investigated.

Different samples were prepared at low and high waste/binder ratios at various amounts of added water in each mixture. Physical properties consisting of setting time, unconfined compressive strength and evaporable water content were measured at different ages.

Also, the acid neutralisation capacity of the hardened material was evaluated in order to investigate the leaching behaviour under different pH conditions. In order to quantify to what extent do the above parameters affect the properties of the solidified products,

Synthesis of solidification experience for synthetic wastes

J.A. Stegemann, N.R. Buenfeld

The NNAPICS project is being conducted to try to predict the effects of impurities in wastes on the final properties of cement/waste products using data mining techniques, such as neural network analysis, applied to data collected from the literature. The data collected by the project includes information for more than 500 solidified products prepared using synthetic wastes. As synthetic wastes are less complex than real wastes, interactions with contaminants should be easier to characterise in products prepared with synthetic wastes. Neural network models were constructed for portland cement systems containing barium, cadmium, chromium, copper, lead, nickel or zinc, as oxides, hydroxides, nitrates, or chlorides, from 8 literature sources. The models were able to predict unconfined compressive strength and pH with excellent correlation between measured and predicted values. The effect of the heavy metals on the Portland cement was more evident for pH, than for unconfined compressive strength.

Re-use of abandoned coal mining waste deposits for the production of construction materials: a case of innovative tendering

D. Smink, J.J.M. Heynen

The Dutch Ministry of Transport, Public Works and Water Management, the Dutch Ministry of Agriculture, Environmental Preservation and Fisheries and the Dutch Province of Limburg all work together in the "Maaswerken" project. In this project several measures (river widening, deepening etc.) are being developed to enhance the discharge capacity of the river Maas (Meuse). Flood risk reduction and navigation improvement are the main targets of the "Maaswerken" project. "Grensmaas" is a particular part of this project and is aimed at (1) flood risk reduction, (2) gravel production and (3) nature development. The location for part of this project is between Maastricht and Roosteren in the Netherlands.

A survey of the area has revealed two large coal mining waste deposits: a 50,000 m3 fly-ash deposit and a 210,000 m3 mining (coal-washery) sludge deposit. The deposits are about 40 years old and both are remains of the former coal mining industry in the region. To fit in with the basic variant of the redesign plans for the bed of the river Maas, these deposits would have to be removed. Several options have been considered with regard to the removal and re-use of these coal mining waste deposits.

On the basis of their physical and chemical characteristics, the materials in both deposits seemed to be suitable for the production of construction materials. This use was considered to be the most sustainable as well as the economically best option for using this material. Firms were invited to tender for the excavation and re-use of the mining wastes. The tender was based on a so-called "design & construct"-contract. The tender will be awarded on the basis of pre-defined criteria, as described in this paper. The sustainability of the end-use of the excavated materials will be a particularly important factor in the awarding of the tender. A final decision has not yet been taken. One of the aims is to provide some insight into how public tenders for a project can stimulate sustainable re-use.

At the conference the latest news will be given about working methods that have been chosen and about the use that is to be made of the materials. If all preparations, tendering and contract-forming negotiations ron smoothly, the work may already have started by the time this conference begins.

Construction waste characterisation for production of recycled aggregate – Salvador/Brazil

A.P. Carneiro, J.C. Cassa, I.A. de Brum, A.M. Vieira, A.D.B. Costa, T.S. Sampaio,

E.P.V. Alberte
The continuous growth of municipal solid waste generation, especially from construction activities, has been responsible for the appearance of many and efficient municipal solid waste management policies from public authorities. An efficient waste management program can avoid inappropriate waste disposal, which can cause damage to both environmental and public health. Additionally, it may even lead to the development of recycling programmes.

Giving special attention to solid waste from civil construction enterprises, it is important to develop environmentally active practices among construction companies with a view to reduce waste generation, increase reuse and recycling. In order to develop alternatives for construction wastes recycling, it is important to provide efficient solid waste characterization studies.

An experimental study has been carried out in the city of Salvador, Brazil. Currently 1,450 tons daily of construction and demolition (C&D) wastes have been generated in Salvador. Solid waste has variable physical characteristics that depend on the construction sector involved, the techniques employed, the construction phase and the social-economic characteristics present in the urban area in question.

This paper presents the results of an intensive study of construction and demolition wastes from Salvador with the intention of creating alternative methods of increasing environmental protection and generation of low price raw materials by recycling solid waste. The principal procedure used involves the characterisation of solid waste according to its physical characteristics and social-economic aspects.

The results of this characterisation identified priority research lines that will help to maximise recycling of C & D waste produced in Salvador and help develop a local construction material market.