Reuse of construction waste: performance under repeated loading

The use of recycled aggregates has increased greatly over the last decade owing to enhanced environmental sensitivities. The level of performance required by such materials is dependent upon the applications for which they are used. Many recycled construction wastes have adequate shear strength in relation to various geotechnical applications. However, a possible drawback of these materials is the risk of crushing during repeated loading. The work reported in this paper examined two waste materials: crushed concrete and building debris, both regarded as construction wastes. Tests were also performed on traditionally used crushed rock, in this case basalt. The materials were subjected to repeated loading in a large direct shear apparatus. The amount of crushing was quantified by performing particle size analysis of the tested material. The results have shown that both recycled construction wastes were susceptible to particle crushing. The amount of crushing was influenced by both the vertical pressure and the number of loading cycles. This leads to a marked decrease in peak friction angle

Activation of waste MDF sawdust charcoal and its reactive dye adsorption characteristics

This paper reports an experimental investigation of converting waste medium density fibreboard (MDF) sawdust into chars and activated carbon using chemical activation and thermal carbonisation processes. The MDF sawdust generated during the production of architectural mouldings was characterised and found to have unique properties in terms of fine particle size and high particle density. It also has a high content of urea formaldehyde resin used as a binder in the manufacturing of MDF board. Direct thermal carbonisation and chemical activation of the sawdust by metal impregnation and acid (phosphoric acid) treatment prior to pyrolysis treatment were carried out. The surface morphology of the raw dust, its chars and activated carbon were examined using scanning electron microscopy (SEM). Adsorptive properties and total pore volume of the materials were also analysed using the BET nitrogen adsorption method. Liquid adsorption of a reactive dye (Levafix Brilliant red E-4BA) by the derived sawdust carbon was investigated in batch isothermal adsorption process and the results compared to adsorption on to a commercial activated carbon (Filtrasorb F400). The MDF sawdust carbon exhibited in general a very low adsorption capacity towards the reactive dye, and physical characterisation of the carbon revealed that the conventional chemical activation and thermal carbonisation process were ineffective in developing a microporous structure in the dust particles. The small size of the powdery dust, the high particle density, and the presence of the urea formaldehyde resin all contributed to the difficulty of developing a proper porous structure during the thermal and chemical activation process. Finally, activation of the dust material in a consolidated form (cylindrical pellet) only achieved very limited improvement in the dye adsorption capacity. This original study, reporting some unexpected outcomes, may serve as a stepping-stone for future investigations of recycle and reuse of the waste MDF sawdust which is becoming an increasing environmental and cost liability. (C) 2004 Elsevier Ltd. All rights reserved.