Observations of leaching of low concentration contaminants from alternative aggregates in road constructions

A.R. Hill, A.R. Dawson

Many materials resulting from domestic and industrial activity could be used as a replacement for natural aggregates in road construction. Environmental protection organisations have raised concern over the potential for resultant contamination of ground and surface water systems. The leaching properties of a selection of aggregate materials are being examined in a testing programme designed to progressively simulate the real conditions within a road construction. The testing programme is described, illustrative data is presented and initial conclusions are drawn.

The use of MSWI (Municipal Solid Waste Incineration) bottom ash as aggregates in hydraulic concrete

B. Quenee, G. Li, J.M. Siwak, V. Basuyau
The general objective of this study is the innovative use of MSWI bottom ash as aggregates for hydraulic concretes, especially in ready to use concretes and in prefabrication.

As first, a complete physical, chemical and mineralogical characterization of a MSWI bottom ash provided by the company YPREMA, was undertaken, in relation to requirements of the experimental standard XP P18-540 (« Aggregates for hydraulic concretes») and environment aspects (composition and concentration of the potential pollutant by fractions). Following this characterization, the aptitude of the MSWI bottom ash to be used with the hydraulic cements (CEM I and CEM III) was evaluated in mortars. The experience with different additions allowed a meaningful treatment protocol to be defined, especially by addition of silica fume which shows a relatively fast set of the mixture and good mechanical resistance. Concretes were first formulated using a CEM I with silica fume. Concretes with a silico-alumineous fly ash, a pouzzolan cement CEM IV/B and a diatomaceous powder were then studied. Results show the possibility of obtaining plastic B20 and B25 concretes with a partial or total replacement of natural aggregates by MSWI bottom ash.

Life-cycle impacts of the use of industrial by-products in road and earth construction

U.-M. Mroueh, J. Laine-Ylijoki, P. Eskola

A two-stage study "Life cycle analysis of road construction and earthworks" was part of a more extensive Finnish research project "Assessment of the applicability of secondary products in earthworks". In the first stage of this work a life-cycle impact assessment procedure for the comparison and evaluation of alternative road and earth constructions was developed. Additionally, a database containing the environmental burdens of the most significant construction materials and unit operations was constructed. In order to evaluate the applicability of the procedure, the use of coal ash, crushed concrete waste and granulated blast-furnace slag in road construction was evaluated in case studies. The use of these secondary products was also compared with the use of natural materials in corresponding applications.

The aim of the second stage was to transfer the assembled data for utilisation as a practical model by creating an inventory analysis program to calculate and compare the life cycle impacts of the most common road constructions and foundation engineering methods. The data obtained in the first stage was also augmented to the extent necessary for this purpose.

The results of case studies indicate that the production and transport of the materials used in road constructions produce the most significant environmental burdens. Production of the bitumen and cement, crushing of materials and transport of materials are the most energy consuming single life-cycle stages of the construction. A large part of the emissions to atmosphere originates from energy production. In the expert assessment, consumption of natural materials and leaching behaviour were also regarded being of great significance.

Assessment of environmental impacts of foundry waste in utilisation and disposal

J. Laine-Ylijoki, M. Wahlström, J. Orkas

In this work the harmful compounds of most commonly used foundry sands in Finland, i.e. green sand, furan sand, ester hardened phenolic sand and sodium silicate sand together with respective dusts were identified. Their environmental impact was evaluated mainly by comparing the content of harmful compounds against target values given for non-contaminated soil. Additionally, an interlaboratory comparison study was arranged in order to get information on the comparability of the metal and polycyclic aromatic hydrocarbons (PAHs) analysis results.

The total Chromium contents of studied foundry sand and dust types generally exceeded significantly the target values given for the evaluation of contaminated soil. However, the leaching of Chromium was as a whole very low. Additionally, foundry sands contained only small amounts of organic compounds compared to the target values given for the contaminated soils. On the other hand in case of foundry dusts phenol concentrations correlated with PAH-concentrations resulting in significant phenol and PAH-concentrations in some dust types. For detailed environmental evaluation further information on the leaching behaviour of different metals from foundry dusts is required, especially when the waste masses are relative big. Results of the interlaboratory comparison, especially for some metals as aluminium and chromium, varied significantly addressing the need for further discussions on advantages and disadvantages of different test methods.

Leaching of PCBs and Chlorophenols from contaminated soil and waste - Influence of leaching test characteristics

M. Wahlström, J. Laine-Ylijoki, M. Pihlajaniemi, M. Ojala

Organic contaminants are found in soil at sites where chemicals containing organics have been used or handled. Sites contaminated with chlorophenols are a typical problem in Finland due to their large use as wood preserving agents at saw mills. The major compounds identified in the contaminated soils are tetrachlorophenols and pentachlorophenols. PCBs were used in the 1960s and 1970s in polysulphides containing sealing compounds for wall elements. The PCB-contents in these compounds were at least 20 % resulting in PCB contamination in soils near the wall elements. PCB-contaminated soils can also be caused from leackage of PCB- condensers. PCBs and Chlorophenols have been chosen in this study as typical organic contaminants with different chemical properties.

The aim of this study was to assess the effect of leaching test characteristics on test results for Chlorophenols and PCBs. Furthermore, the effects of some relevant environmental factors controlling the leaching behaviour were evaluated. The study was especially focused on practical aspects aiming to test conditions ensuring reproducible test results. In particular, the influence of filters and the needed equilibrium time for the leaching process were studied.

The work was a part of the EU-project "Development of standard leaching tests for organic pollutants in soils, sediments and granular waste materials" co-ordinated by ECN (contract SMT4-CT97-2160). The results will give background data for development of standardised leaching test methods for some organic contaminants.

Forecasting the long-term behaviour of municipal solid waste incineration bottom ash: rapid combined tests

F. Bodénan, M. Azaroual, P. Piantone

Municipal solid waste incineration bottom ash is a highly reactive material, especially toward atmospheric CO2, which is why we decided to carry out rapid and simple tests combining accelerated ageing and batch leaching to forecast the long-term behaviour of bottom-ash samples of various origins. By speeding up one of the major reactions, i.e. the carbonation that occurs during the natural maturation of bottom ash, it was possible to determine the maximum pollutant release of the elements (metals, sulphates) most detrimental to upgrading. The final products present higher calcite contents and are characterized by a reduction in leachate metals and an increase in leachate sulphates. The laboratory results are in agreement with a full-scale field study carried out elsewhere. Thermodynamic calculations were also undertaken to determine the cause of the high exothermicity evidenced during the tests because, even though the oxidation of metals (Fe, Al) is mainly invoked to explain the general increase of bottom-ash temperature during maturation, the contribution of the carbonation reactions (with portlandite, wairakite, larnite anorthite) cannot be ignored.

Developments in electroremediation and phytoremediation for the treatment of metal contaminated soils

M.M. Page, C.L. Page

This paper examines certain areas of progress in developing new methods of treatment for metal contaminated soils. Electroremediation, which involves the passage of low intensity direct current between suitably distributed electrodes, may be used either singly or in combination with other approaches for transporting and removing metal ions from soils of low permeability that are difficult to treat by conventional methods. Effective phytoremediation involving the use of metal accumulating plants depends on the selection of mutant types with specific genetic characteristics. A novel approach for the rapid isolation of appropriate strains of members of the genus Brassica is currently under investigation and is outlined in this paper.

Studies on crystalline rice husk ashes and the activation of their pozzolanic properties

J. Payá, J. Monzó, M.V. Borrachero, E. Peris-Mora, L.M. Ordóñez

Characterization, pozzolanic activity determination and pozzolanic activation of rice husk ashes (RHA) containing a high percentage of crystalline silica have been carried out. Two RHA samples from incineration plant and another RHA sample from energy-recovery combustion plant have been compared. Several techniques such as X-ray diffractometry, solubility in boiling KOH solution, conductivity and thermogravimetric monitoring of RHA/lime systems and strength development of RHA/cement mortars have been used for evaluating pozzolanic activity or RHA. Additionally, mechanical treatment of RHA by grinding and increase of curing temperature of RHA containing mixtures became appropriate procedures for activating pozzolanic activity of highly crystalline RHA. The effectiveness of chemical activators such as NaOH solution and powdered Ca(OH)2 also was studied.

Assessment of the ecocompatibility of waste disposal or waste use scenarios: towards the elaboration and implementation of a comprehensive methodology

Y. Perrodin, L. Grelier-Volatier, R. Barna, A. Gobbey

The French concept of "Ecocompatibility" is defined as the situation where the pollutant flux from waste either disposed of or used in specified conditions (physical, hydrogeological, physico-chemical and biological conditions) is compatible with the environmental acceptance of the concerned receptor cells. The chief feature of this definition is to integrate the evaluation of the three following terms : pollutants emission from the waste (source term), transport of the pollutants from the waste to the receptor cells (transport term) and the environmental acceptance of receptor cells (impact term).

The specific objectives of our paper are the introduction of a methodology for the assessment of the Ecocompatibility of waste disposal or waste reuse scenarios and to develop the experimental part of this methodology : laboratory measurements and tests.

First, we introduce the various terms of the methodology. We briefly present a literature survey carried out by 9 research teams consisting of a state of the art on the knowledge and the tools available for the study of each determined term. This work particularly resulted in the identification of influence factors and characteristic parameters to be considered for a relevant assessment of waste ecocompatibility. An experimental programme (field and laboratory scale) followed the literature survey. It aimed to apply the methodology on 3 theoretical scenarios in view of the final methodology elaboration. Finally, we introduce the various steps of the defined methodology and conclude with its application limits.

Research & development methodology for recycling residues as building materials – A proposal

V.M. John, S.E. Zordan

This article presents a proposal of methodology for conducting such research and development. The data/statistics waste collection statistics phase must cover geographical distribution, seasonal variations on production rates, waste management practices, current applications and their related costs and revenues. Waste characterisation must be comprehensive with physical, environmental and chemical aspects, including waste variability and waste contamination from shipping, handling and storage activities. Based on the previous results a broad forecast of potential applications must be developed based on very simple rules like minimisation of transportation distances and energy consumption, etc. Marketing evaluation is a very important step, frequently neglected when choosing the best applications for a particular waste. Other steps are product development and performance evaluation. Environmental evaluation of the new technology is very important because not all recycling is environmentally sound. This evaluation must be based on the life cycle assessment (LCA) and has to consider the environmental benefit of avoiding landfill disposal of the waste and could include leaching or other specific tests or simulations. Also, the technological transference phase must be carefully planned and developed.

Each proposed step is discussed, examples are given and needs for further research emphasised.