I. Dumitru, R. Munn, G. Smorchevsky

Historically, the concrete and road pavement industries in Australia rely heavily on the use of prime quality natural aggregates. Abundance of high quality natural fine and coarse aggregates, located close to major cities, prescription specifications and seemingly unlimited waste disposal sites, have contributed to this practice.

Despite the successful introduction of the industrial by-products of Fly Ash and Blast Furnace Slag products to concrete and road construction in the 1960’s, it is only relatively recently that both government and private sectors have accepted the view that better utilisation of resources must be achieved. A more ecologically sustainable and responsible attitude is being adopted with respect to waste minimisation, utilisation of by-products, re-use of construction and demolition waste and improved energy efficiency.

Some of the issues and steps to be implemented in this regard are outlined, covering topics such as: recycled concrete aggregate, (RCA), concrete washouts, reclaimed asphalt pavement (RAP), manufactured sands, tunnelling materials, bottom ash and other similar products.

The research carried out, both in laboratory and in the field, demonstrates the suitability of such products in concrete and road pavement applications. It is concluded that some provisions in the current specifications and new performance based specification are necessary in order to accommodate more construction and demolition materials.

The use of reclaimed asphalt pavement (RAP) aggregates in concrete

K.E. Hassan, J.J. Brooks, M. Erdman

The paper presents a laboratory study on the properties of ordinary Portland cement (OPC) concrete made with reclaimed asphalt pavement (RAP) to substitute natural aggregate. RAP aggregates were incorporated in concrete on the basis of maximum packing of the particles to provide a mixture with minimum voids and thus optimum performance. Concretes were made with various combinations of natural and reclaimed aggregates. The resultant mixtures were:

1. control mixture using natural sand and natural gravel.
2. mixture containing reclaimed coarse aggregate and reclaimed fine aggregate.
3. mixture containing reclaimed coarse aggregate and natural sand.
4. mixture containing reclaimed coarse aggregate and natural sand where 30% of the ordinary Portland cement was substituted with fly ash (FA).

Preliminary laboratory investigation of thermally treated recycled concrete aggregate for general use in concrete

J.A. Larbi, W.M.M. Heijnen, J.P. Brouwer, E. Mulder

This paper deals with a preliminary laboratory study to assess the effectiveness of thermal treatment methods to improve the quality of recycled concrete aggregate. The samples used for the study consister of sieved fractions of crushed concrete that were subjected to various thermal treatments at temperatures of either 650^oC or 800^oC. In each case the treatment lasted for a period of 0.5 or 1 hour. After the thermal treatments the samples were first investigated by means of polarising the fluorescence microscopy followed by strength tests on mortar and concrete specimens prepared with one of the treated samples. The thermal treatments caused considerable reductionn in the amount of cement paste or mortar adhering to both the fine and the coarse aggregate particles. The reduction was more pronounced in the case of the samples treated at a temperature of 800^oC than those treated at 650^oC. The integrity of the aggregate particles was found to a large extent to be preserved. The strength development of mortar and concrete specimens prepared with one of the treated samples, was slower than that of conventional river-dredged aggregate but reasonably good. Although this is a preliminary study, the results indicate that thermal treatment of recycled concrete aggregate at a temperature of about 800^oC can yield good quality aggregates, with properties which are reasonably comparable to conventionally used river-dredged aggregates.

Evaluation of solid-stabilized products made from Cr(VI)-containing ferrochrome bag-filter dust

E.W. Giesekke, J.P. Smit, E.A. Viljoen, A.W. Kruger, S.J. Kruger, C.F. Maine

South Africa produces 43% of the world’s ferrochrome. The greatest risk to health and the environment resulting from these operations lies in the toxic, carcinogenic Cr(VI)-containing bag-filter dust (BFD) and sludge obtained from the gas cleaning systems. It is estimated that 100 kt of BFD and sludge are produced per annum. Water leaching tests of BFD indicate that, apart from Cr(VI), the alkaline leachate contains Na, K, SO₄ and Cl. The immobilization of Cr(VI) and salts in cement blocks and fired clay bricks was investigated in this study.

Cement blocks were prepared by mixing crushed slag from ferrochrome and electric arc furnaces with Portland cement (9%) and BFD (15%). These blocks were then cured for 56 days. Water leaching tests conducted on crushed cured blocks indicated that 98% of the Cr(VI) and 50% of the salts added via BFD were immobilized. Compression strengths exceeding 11 Mpa were measured for these cement blocks. The addition of FeCl₂ (1.25%) improved the Cr(VI) immobilization. Partial immersion of whole blocks in water indicated that nearly all the Cr(VI) and 98% of salt originating from the BFD were retained.

Fired clay bricks containing up to 50% BFD were prepared. A firing temperature of 1200 ^oC for 6 hours was required to immobilize Cr(VI) and salts in excess of 99.5% and 93.6%, respectively, as judged by water leaching tests on the crushed material.

The crushed materials from fired clay bricks and cement blocks were subjected to Acid Rain and the US EPA TCLP leaching procedures. The concentrations of Ba, Pb, V, Cr, and Mn were measured in the leachates and their potential impact on the environment assessed according to the Guidelines issued by the South African Department of Water Affairs and Forestry. Leaching of these toxic elements was lower from the crushed, fired clay bricks than from the crushed, cured cement blocks, indicating that clay bricks are the preferred form of stabilization of the ferrochrome BFD.

Durability study of a sewage sludge-cement-sand system and its environmental impact

S. Valls, E. Vázquez

One of the main objectives of the work is to present an effective alternative for the final destination of urban wastewater sewage sludge, by means of its inclusion in mortar or concrete. To this end, a durability study was performed on the system. The study consisted in subjecting the mortar samples to a process of accelerated carbonation and subsequently assessing the products of the carbonation by ²⁹Si RNM-MA nuclear magnetic resonance of solids and its environmental impact by the NEN-7345 monolithic leaching test. Carbonation at very high concentrations of CO₂ favours the polymerization of the C-S-H and the breakdown of the ettringite, which affects the leaching processes and the concentration of heavy metals and other pollutants in the leachates obtained from the NEN 7345 leaching test.

Quality control and certification of waste materials in Rotterdam

J. van Leeuwen, F. ten Vaarwerk

In this paper the experiences of quality control of secondary materials in Rotterdam are being discussed. Also the experiences of the implementation of quality control within the framework of the Dutch Building Materials Decree (‘Bouwstoffenbesluit’) of both raw (‘primary’) and waste (‘secondary’) materials will be presented.

Influence of the cement type on the stabilisation of fly ashes from municipal solid waste incineration

E. Fernández, A. Macias, A. Guerrero, M.P. Lorenzo, S. Goñi

Municipal Solid Waste Incineration Residues (MSWIR) and specially fly ashes (MSWFA) from gas cleaning devices contain dangerous salts and toxic ions, which may be released to the environment. Therefore, fly ashes must be stabilised before their landfill. In this paper the influence of cement type on the stabilisation of MSWFA from gas-cleaning devices is presented. The cements used were, Fondu calcium aluminate cement (CAC), ordinary Portland cement (OPC) and OPC with 80% replacement by ground granulated blast furnace slag addition (OPC/BFS).

Hydrothermal treatment of fly ash from municipal solid waste incineration

A. Guerrero, E. Fernández, A. Macías, S. Goñi

The effect produced by hydrothermal treatment of fly ashes from municipal solid waste incineration (MSWFA) is discussed in this work. The more interesting results showed that practically 100% of chloride and metal Al from the fly ash are dissolved. CSH gel and katoite (C₃ASH₄) are the main cemented hydrated phases formed after 1 hour of hydrothermal treatment.
 
PVC and PET plastics taken from solid urban waste in bituminous concrete

M. Bocci, S. Colagrande, A. Montepara

In recent years a shortage of natural resources for building transportation infrastructures urged the development of innovative technologies in the field of waste materials deriving from industrial manufactures or domestic use. This study attempts to give a contribution to the recycling of plastics deriving from solid urban wastes (Refuse Derived Plastics - RDP) in bituminous concrete. In particular, this research refers to the use of low degradable plastics, hard and non-mixable with bitumens (PVC and PET), as a possible replacement of a portion of the stone aggregate mixture. The aim was to find a way of reusing waste plastics in order to reduce their volumes in refuse disposal sites and at the same time to reduce the amount of inerts drawn from quarries, which often lead to environmental problems. In the first phase of the research, already carried out by the authors, the limits of this application were defined, as well as the best conditions of use of the above mentioned plastics by means of the traditional mechanical and rheological characterization tests of bituminous concrete (Marshall Test, Indirect Tensile Test, Static Creep Test).

This paper treats the dynamic characterization of mechanical properties of bituminous concrete mixtures added with plastics. Dynamic tests were carried out, which allowed to draw Master Curves as the percentage of plastic material used in the mixtures varied and for different test conditions. Moreover, the fatigue behaviour of the different mixtures of bituminous concrete was analyzed. The results obtained confirmed that it is possible to use RDP to manufacture bituminous concrete, in particular hard plastics non-mixable with bitumens, on the condition that PVC and PET are thin milled, of a small size and used in limited quantities.

Leaching standard for quality control of aggregates

R.. Bialucha

There are quite different attempts to investigate the environmental compatibility of materials which are regarded as wastes and which have to be disposed of on one hand and materials which are considered to be products on the other hand. For the assessment of the environmental compatibility of waste materials which are usually heterogeneous materials with variable composition and unknown origin extensive investigations (consisting of long term characterization, compliance and on site verification tests) are necessary.

For materials which are well known and have been used successfully for many years in building and civil engineering works - like aggregates - such extensive investigations concerning the environmental compatibility are not necessary. These materials have generally been submitted to detailed suitability tests in the laboratory and under practical conditions before putting them into use. Long-term experience has shown that these materials perform in an environmentally sound way.

To ensure that these materials comply with their certified or declared characteristics, production control is used. The production control system is based on continuous testing through factory production control and additionally by regular third party control. Since the production, processing and sale of aggregates is a continuous process, the tests used for production control should be simple and quick to produce results as promptly as possible. Furthermore the tests should produce results which have good reproducibility. Only in this way it is possible to reach quick and reliable pass/fail decisions.

A tank leaching test that was developed in Germany fulfils all these requirements and is therefore suitable for production control of aggregates. Since then this test has been adopted by CEN/TC 154 "Aggregates" in the European draft Standard.