E.A.M.E. Archeti, N.N.B. Salvador
 
This article is based on a survey, carried out in Franca, São Paulo State, Brazil, of the opportunities for waste minimisation in thirteen tanneries in that city, and the potential benefits for environmental management. Waste minimisation opportunities mean the feasibility of implementing practices or measures of waste reduction, pollution prevention and cleaner production, in relation to this industrial activity. This opportunity was defined in terms of waste minimisation indicators found in a bibliographical survey and in data obtained from field research done in those tanneries. Using this information, an "opportunity matrix" was created in order to identify and evaluate alternatives and possibilities for waste minimisation. Potential benefits for industry and the environment are also evaluated, on the basis of this matrix. A discussion about the development and application of the matrix is also presented.

Prediction of inorganic pollutant release from various cement based materials in disposal/utilisation scenario based on the application of a multi-parameter leaching tool box

A. Imyim, L. Tiruta-Barna, R. Barna, J. Méhu

The aim of this study is to assess the long term release of contaminants from cement based stabilised wastes. According to the methodology proposed by the European standard ENV 12 920, the impact of waste in disposal/utilisation scenarios has to be evaluated before being exposed to the environment. For this objective we propose a combined experimental and modelling procedure. Firstly a "tool box" consisting of some tests as the Pore Water simulation test (PW), the Maximum Leachable Fraction test (MLF), the Acid Neutralisation Capacity test (ANC) and the Monolithic Leaching Test (MLT) is used to characterise the waste containing material. Secondly the results of the tests are the necessary input parameters for the coupled physico-chemical leaching model that provides the long-term leaching behaviour. For applying the tool box and the model validation, Ordinary Portland Cement with additives was used to prepare the samples containing 25% of binder, 1% of Pb, and sand. The release mechanisms are described. The model provides the long-term release amounts of pollutants as well as the expected concentrations of pollutants in surrounding natural water over several centuries in the considered scenario conditions.

Recycling options for gypsum from construction and demolition waste

K.C. Vrancken, B. Laethem

Waste gypsum from the construction materials sector is an important part of the construction and demolition waste (CDW). Although pure gypsum can be recycled infinitely, impure waste gypsum is often disposed of or dispersed in the CDW stream. Source separation is not performed on a large scale and sorting units for CDW often do not perform a gypsum selection. The sulphate content is a major criterion in the valorisation of the CDW as a secondary aggregate for concrete. Therefore, the question arises whether the presence of residual gypsum in CDW masonry aggregates is a burden for effective valorisation.

The actual gypsum content and sulphate leachability was studied for a range of sorted and recycled aggregates. This was compared to the overall environmental quality of the material. Visual analysis of the various products from sorting and recycling gave data on the gypsum content. On this basis a material flow diagram of gypsum is set up. This allows to determine the gypsum recycling potential on the Flemish market. In order to optimise gypsum recycling from CDW, source selection measures need to be taken and a centralised collection and treatment system needs to be set up.

Analysis of literature data from 3,000 cement/waste products

I. Fernández, P. Somarriba, A. Irabien
 
In the last two decades a large amount of references regarding cement/waste systems have been published. The information reported in these references has been focused on two main topics: inertization of wastes using cementitious materials as binders through solidification/stabilization techniques (typically low binder dosages) and reutilization of non hazardous wastes after mixing with cementitious materials (typically low waste dosages).

The information contained in near 3,000 cement/waste products collected in a previous work in an Access database has been evaluated according to the following points: level of identification of composition of products (types of components in product formulation – waste, non-waste materials, and water-, elemental and oxides composition of components and physical properties of components), physical and mechanical properties of products, and leaching tests (types of tests and chemistry of the leachate of waste and products).

Wastes have been classified according to the European Waste Catalogue (EWC). From the studied data a certain lack of information on the formulations of the products (e.g. water content is not given in 28% of products). With respect to engineering properties, unconfined compressive strength is reported in 70% of products; nevertheless, very few data for setting time have been found (3-4% of the products).

The main leaching tests performed to wastes and products are European (DIN 38414-S4) and US (USEPA EP-tox and TCLP) standard tests and the main elements measured in the leachate are As, Ca, Cd, Cr, Cu, Fe, Hg, Mn, Ni, Pb and Zn.

Conclusions related to the difficulties, which have been found in the literature data to get a useful description of cement-waste mixings, mechanical properties and environmental behaviour will be explained.

High-performance concrete for sustainable constructions

G.C. Isaia

The growth of the world’s population and the growing demand for new buildings and infrastructure facilities present us with the prospect of a higher cement consumption, specially in the form of more durable concrete structures. However, the environmental impact caused by the increase in the extraction of natural resources and higher CO₂ emissions has given rise to the search for more efficient, environmentally-friendly constructions. To address these needs, high performance concrete has been employed to increase the durability and economic service life of slender structures, to decrease the specific energy consumption and to reduce the environmental impact of these activities. This material plays a dual role, being both more durable and ecoefficient because of its higher resistance to aggressive agents such as chlorides, carbon dioxide, acid rain and other harsh environmental agents. This resistance is produced by the use of one or more mineral additions such as pozzolans or slags, which are usually polluting by-products in the same environment.

This work describes the retrospect on the relationship between energy consumption, environmental impact and economic cost of Portland cement concrete structures and the role of high performance concrete in the production of more efficient and durable constructions. A case study of 12 mix proportions with binary and ternary mixtures of fly ash, rice husk ash and silica fume, with cement substitutions of up to 50% in mass is presented. The mixtures that presented lower cost and energy consumption were those with higher pozzolan content and lower cement consumption. It was found that high performance concrete is an appropriate material for more durable constructions. Therefore, it is more environmentally friendly due to its lower social and economical costs.

Significance in the results of total composition and potential leachability of screened MSWI BA from different plants and sampling periods

A.-M. Fällman
 
The purpose of this study was to determine the environmental properties of sorted and aged bottom ash from municipal solid waste incineration (MSWI BA) and the significant variations in these properties between four plants and four different sampling periods over one year. The non-magnetic 0-50 mm fraction, stored outdoor in 10m³ boxes for six months, was used. Duplicate samples of the materials were tested for total content and potentially-leachable amounts, with and without oxidising conditions. Inorganic components were analysed. The results were evaluated by means of an analysis of variance and factorial design evaluation. The total content of the samples was dominated by Si, Ca, Fe and Al. Significant differences were found between plants and samples with regard to major component content. The minor components were dominated by Zn, Cu and Pb although significant differences between plants or samples were difficult to identify for Cu and Pb. The potentially-leachable amounts were dominated by Ca for the major components and Cu and Zn for the minor components. Precision in potential leachability was lacking, especially for Cu and Pb. Oxidised conditions increased the leachability of Cr significantly and in some cases also Cu. The overall conclusion from the study was that the results from the determination of total composition or potentially-leachable amounts of minor components need to be evaluated statistically and that comparisons with limit or guideline values need to take the significance of the measured values into account. The experimental errors should be evaluated separately for each element. Moreover, the experimental errors were not a direct function of the average total or leached amounts. Differences in weathering products in the aged material that carried the elements studied also seemed to have an impact on the error in the measurements.

Effect of mineral admixtures on some properties of sand-lime bricks

Z. Pytel, J. Ma?olepszy
 
The effect of mineral admixtures used in the production of autoclaved sand-lime brick was investigated. The waste materials and by-products of pozzolanic properties- fly ashes, microsilica, were added to the mixture composed of quartz sand and burnt lime. The hydraulic admixture-granulated blast furnace slag and activators (gypsum, etc) were also taken into account.The phase composition and microstructure of materials were characterised using XRD, SEM + EDS and mercury porosimetry. The standard mechanical properties of sand-lime brick were also determined, including absorbability: leaching was not, however, investigated.

Recycling of partially hydrated concrete

A. Katz
 
Concrete having a 28 days compressive strength of 28 MPa was crushed at 1, 3 and 28 days to serve as a source for aggregates for a new concrete, simulating the situation exists in pre-cast concrete plants. The properties of the recycled aggregate and of the new concrete made from it were tested.

Significant changes were observed when comparing the properties of the aggregates based on the various size groups of the aggregates, but not when comparing the effect of crushing age. The properties of the concrete made with the recycled aggregates were only slightly affected by the crushing age when the cement matrix of the new concrete was relatively weak, but some effects were seen for a stronger cement matrix.

Leaching behaviour of a chromium smelter waste heap

D. Deakin, L.J. West, D.I. Stewart, B.W.D. Yardley

This paper reports the results of geochemical sampling and modelling of leachates from a chromite ore processing residue (C.O.P.R.) pile under rainwater infiltration. The waste pile is located in the north of England and consists of 800 000 m³ of waste. The pH of fresh leachate is similar to that of a solution in equilibrium with portlandite Ca(OH)₂, which is a major constituent of the waste. The in-gassing of CO₂(g) causes the pH of the leachates to drop along the drainage ditch and calcite precipitation to occur. The extent of in-gassing is dependent upon the flow rate within the drainage ditch. The dissolution of solid solutions containing residual chromate is likely to control chromate concentrations within the leachate.

Use of sulphate containing sieve sands in building materials

J.P. Brouwer, E. Mulder, J. Frénay, J. Blaakmeer, C. van Opstal

This paper discusses the results of a research project into the use of the fine fractions of demolition wastes for the production of building materials. Often, these wastes contain high amounts of leachable sulphate, which prevents application in an unbound form due to the criteria of the Dutch Building Materials Decree. In order to reduce sulphate leaching, solidification processes were developed to chemically immobilise the sulphate in the form of ettringite. Two types of building materials were developed: a road base construction material, and a concrete product for use as so-called mega blocks. A number of hydraulic binders have been tested for these purposes. For both types of application, products can be made that fulfil both engineering demands and leaching criteria.