The recycling of demolished masonry rubble as the coarse aggregate in new concrete represents an interesting possibility at a time when the cost of dumping such material is on the increase. With growing concerns over the environmental impact of aggregate extraction and the continued rise in aggregate demand in the UK, it is clear that the market is now there for recycled and secondary aggregates. The present investigation consists of experimental and theoretical studies into the effects of using recycled aggregates to produce concrete instead of virgin aggregates. The aggregates used have been recycled from construction and demolition waste. The recycled aggregates were predominately made up of crushed bricks but the aggregates did contain impurities such as timber and mortar. New bricks were crushed to form an aggregate in order to investigate the properties of brick as a material without impurities. The physical properties of the various aggregates were firstly examined and compared with granite aggregate, an aggregate proven in the production of good quality concrete. Concrete was then produced with the aggregates and all the physical and mechanical properties of the concretes were examined in some detail. The results showed that recycled masonry aggregates can be used successfully to produce· concrete of an acceptable standard. New test methods were presented in this investigation to determine brick porosity and water absorption. This involved the testing of broken brick fragments under vacuum, rather than the testing of whole brick units by 5hrs boiling or 24hrs submersion in cold water. The new test methods proved to be easy to perform and provided accurate results. A new test method for estimating the strength of bricks was presented. This involved point-loading of masonry specimens to obtain strength index values. From the pointload results, equations were presented relating the strength index values of brick fragments to the compressive strength of whole brick units. This involved the development of shape factors for different masonry specimens. The point-load test is easy to perform, presents a cheaper alternative to heavy compression machines and can be used on site to determine the suitability of recycled bricks as the aggregate in new concrete.

The collection of source segregated household food waste is becoming increasingly popular, because of its potential to divert biodegradable materials from landfill, increase recycling rates and provide a contaminant-free feedstock for anaerobic digestion. Various types of kerbside household food waste collection systems are operating in the UK and in Europe; however, studies on the energy consumption of integrating source separated food waste with collection of other waste fractions are very limited. A mechanistic model was developed in this research as a waste collection assessment tool (WasteCAT) for scoping and assessment of collection systems. Data collected from six local authorities in England was applied to verify and validate the modelling tool. Fuel consumption and other parameters such as total distance travelled (a proxy for vehicle lifespan), total time spent (a proxy for staffing costs), number of collection vehicles required (a proxy for capital costs), and arrangement of waste types and compartments were also assessed in this research, as these factors may also influence the selection of kerbside waste collection systems. A typical hypothetical town of 25,000 households was chosen to study the performance of separate, co-collection, kerbside-sorted and partially-sorted collection of household waste by different sizes and types of single and compartmentalised collection vehicles at different collection frequencies. Comparing the performance of the four collection systems, kerbside partially-sorted collection required the least fuel, while co-collection of household waste always had the best performance in terms of total travelling distance, time spent and number of collection vehicles required. The difference between the best and the worst systems was up to 156% for fuel use, 131% for distance travelled, 63% for time spent and 141% for vehicles required. Besides that, inappropriate allocation of compartment and waste type could increase fuel use by up to 1.1 times in co-collection, 2.27 times in kerbside-sorted and 3.08 times in kerbside partially-sorted collection. The research shows WasteCAT could provide a powerful tool for exploring alternative options. Keywords: Waste collection, collection vehicles, fuel consumption, food waste.

Urban waste management poses problems in all cities of the world, but it also provides opportunities for innovative resource use. The Thesis begins by defining the waste management problem of Nairobi in context and then analytically reviews the international status of waste management, contrasting the circumstances in developed economies with those in Tropical Africa. An investigation of household refuse in Nairobi, exploring its embodied energy and its value for composting follows as the focus of the Thesis. Typical households were surveyed in relation to their waste management behaviour and agricultural activities. An attempt was made to analyse the physical and chemical composition of household refuse as well as its energy value. In addition to household surveys, a senior local government official and waste disposal crews were interviewed in order to ascertain current policies and management practices in the handling of waste. Particular attention was paid to the Eastlands area of the City. Ways in which refuse is incorporated into the food and energy cycles were identified. Among the important factors discerned are the role of family structure and the economic position of households. The validity of the research is discussed and recommendations are made for the future of waste management in relation to energy and food production in Nairobi. The findings of the research should have wide application in other African countries.

This thesis examines the practical engineering problems associated with high-activity radioactive waste disposal. It includes a critical review of all the available disposal options, but focuses on concepts involving deep underground burial in purpose-built repositories. The construction and waste containment properties of crystalline, argillaceous and saliferous host rocks are examined and some inherent uncertainties in predicting their performance as natural barriers to radionuclide migration are described. It is shown that repository construction can introduce anomalous migration paths via peripheral zones of disturbance, rock/backfill separation planes and structural linings unless special preventative measures are taken. For jointed rock masses, it is shown that repository excavations may short-circuit natural flow paths. Repository design proposals from the major nuclear power-producing countries are reviewed, with particular emphasis on crystalline rock repository systems. It is shown that although the international proposals demonstrate the broad feasibility of repository construction, they generally fail to achieve optimum solutions in terms of waste containment. For jointed rocks, an optimisation study is described which demonstrates how adjustment of pre-disposal strategies for conditioning high-level wastes, altering the construction sequence, and manipulating the emplacement configuration can effect reductions in repository size to mitigate against the adverse effects of discontinuities. It is shown that applying the minimum repository size philosophy to other host rocks can also produce benefits in terms of waste containment and construction costs, and some radical design alternatives are proposed incorporating relevant principles. The role of engineered barriers, in the form of high-integrity backfills and waste unit claddings, is examined. Potentially suitable backfills are identified by reference to geochemical stability and radionuclide containment properties, and cost implications are evaluated. Parametric sensitivity studies are performed to demonstrate the influence of waste unit and backfill properties on radionuclide containment, and some new practical design concepts and emplacement techniques are suggested.

Vitrification is a well-established waste treatment method that has been used for silicate based wastes to achieve waste volume reduction and improve chemical stability before further use. However, the poor mechanical strength of the vitrified products has led to a low commercial value and thus an unjustifiable use of energy-intensive thermal technology over the cheaper, although environmentally unsatisfactory, land disposal option. To overcome this issue, the emphasis of this work lies in demonstrating the feasibility of fabricating dense glass-ceramics from several types of waste and combination of wastes, which are generally superior to their parent glasses in their mechanical performance, as well as highly porous glassceramics to be used in building industries as an alternative to conventional waste disposal. The first part of the research work demonstrated the ease of production of an array of relatively dense glass-ceramic material from coal ash from thermal power plants using powder sintering technology. These products had robust physical and mechanical properties suitable to compete against commercially available building materials such as granite and marble for the floor and wall covering applications. A fully-dense, fine-grained, high-strength glass-ceramic was also fabricated from Feslag using an economically viable single-stage melt heat-treatment route. The ironslag derived glass-ceramic material had a unique composition, with an associated microstructure containing a high content of titanium-rich compounds, and has the potential for non-critical load-bearing applications. Finally, the thesis provides the results of an experimental study concerning with the production of highly porous glass-ceramic foams from a mixture of coal ash and waste glass with the addition of an inorganic foaming agent. The correlations between physical, thermal, and mechanical properties were carried out based on results from practical experiments, physical model studies and numerical simulations using X-ray microtomography and finite element analysis. It was concluded that, these waste-derived materials have the potential to be used in building applications where there can be a large demand to meet the large volumes of wastes available.

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Energy from Waste (EfW) technologies are beneficial for both energy generation and as a waste management option. However they face significant challenges due to the heterogeneous nature of municipal solid waste. The overall aim of the research reported in this thesis was therefore to explore some of the problems which hinder the development of commercial scale EfW technologies. A laboratory scale pyrolysis reaction rig has been developed to investigate the effect of temperature, residence time and fuel type on the pyrolysis products. Investigations were also undertaken to establish the composition of gas produced from the pyrolysis of typical waste feedstocks in two commercial scale pyrolysis rigs. An empirical model has been developed to predict the pyrolysis behaviours on a larger scale and comparisons have been made with data from the commercial scale rigs. The research findings showed that the majority of the reduction of mass during pyrolysis occurred within the first 5-10 minutes with a loss of up to 70 % at 550 °C and up to 77 % at 700 °C for paper, newspaper and cardboard. Paper, newspaper and cardboard behaved similarly with solid, liquid and gaseous fractions of approximately 33 %, 53 % and 13 % respectively. Products from the plastics components varied significantly; PET produced the highest gaseous products (42 %) and HDPE produced the highest solid products (45 %). An increase in pyrolysis temperature increased the gaseous products from paper to 34 % to the detriment of liquid and solid yields. The main gases produced from the pyrolysis were found to be CO2, CO and H2, except for the pyrolysis of PVC where the main gases produced, from the high content of hydrochloride, were not identified in this study. An increase in pyrolysis temperature was found to increase the production of CO and H2. The gas produced from commercial rig 1 mostly consisted of CO2 due to the low temperature and the addition of air to the pyrolysis chamber. The gas produced from commercial rig 2 consisted of high volumes of CO and H2 suggesting the rig was operating at a temperature above 550 °C. An empirical model was developed based on laboratory data to allow prediction the effect of a change in MSW composition on the pyrolysis gas. It was found that the addition of newspaper to a waste mix led to a higher production of CO and therefore a higher HHV. In general, the results of this study suggest that the laboratory scale pyrolysis rig used in this study and the empirical models developed, can be employed to predict the behaviour of larger scale commercial pyrolysis systems. However, further experimental investigation on the pyrolysis behaviours of mixed waste samples, especially plastic fractions, is hereby proposed.

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No description available.

No description available.