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This work reports the potential of using Brick Dust Waste (BDW) as a partial substitute for clay in the development of unfired clay building materials (brick, block and mortar). BDW is a waste material from the cutting of fired clay bricks. There are various reasons necessitating the cutting of bricks — corner bricks, construction of chimneys, and other uses needing bricks of various shapes and sizes. This results in the disposal of BDW as an environmental problem of concern. In order to investigate the clay replacement potential of BDW, four types of mixes were designed at varying BDW replacement levels — 5%, 10%, 15% and 20%. Ground Granulated Blastfurnace Slag, an industrial by-product from steel manufacture was activated using quick lime and the mixture was used to stabilise Mercia mudstone clay for unfired clay production. The 56 day compressive results using cylinder test specimens showed a significant strength gain (up to 2.1 N/mm 2 ). Overall, the results suggest that it is possible to develop unfired clay building material using up to 20% BDW as partial substitutes for primary clay. [ABSTRACT FROM AUTHOR]

Abstract: Wastepaper Sludge Ash (WSA) contains reactive components such as free lime (CaO), and less reactive and inert mineral species. When water is added to WSA some constituents hydrate faster than others, lime being the fastest giving high alkalinity to the solution. If the WSA is combined with Ground Granulated Blastfurnace Slag (GGBS) then the latter, activated by the raised pH, produces new minerals which will contribute further to the strength development of the paste. The kinetics of the hydration reactions and the possible ways of making lime a more effective contributor in activating other phases in the WSA–GGBS system are discussed. [Copyright &y& Elsevier]

Abstract: Wastepaper sludge ash (WSA) requires relatively higher proportions of water than Portland cement (PC) when used as a single binder. This high water demand may be reduced by the addition of secondary binders such as ground granulated blastfurnace slag (GGBS), which improves the hydration properties of the mixes. Based on the already determined physico-chemical properties of WSA a new method of paste preparation is introduced which also enhances the cementitious properties of WSA. The method utilises a wet-grinding stage prior to mixing. Pre-treatment of WSA prior to the addition of GGBS enhances effectively the strength development of the blended binder. Higher compressive strengths are obtained for the paste cube samples made using the new method of paste preparation than those achieved by conventional dry mixing methods. [Copyright &y& Elsevier]

Compressive strength and hydration characteristics of wastepaper sludge ash–ground granulated blastfurnace slag (WSA–GGBS) blended pastes were investigated at a water to binder (w/b) ratio of 0.5. The strength results are compared to those of normal Portland cement (PC) paste and relative strengths are reported. Early relative strengths (1 day) of WSA–GGBS pastes were very low but a marked gain in relative strength occurred between 1 and 7 days and this increased further after 28 and 90 days. For the 50% WSA–50% GGBS blended paste, the strength achieved at 90 days was nearly 50% of that of the PC control paste. Transmission electron microscopy (TEM), X-ray diffraction (XRD) and thermogravimetric (TG) analysis were carried out to identify the mineral components in the WSA and the hydration products of WSA and WSA–GGBS pastes. The principal crystalline components in the WSA are gehlenite, calcium oxide, bredigite and α′-C2S (stabilised with Al and Mg) together with small amounts of anorthite and calcium carbonate and traces of calcium hydroxide and quartz. The α′-C2S and bredigite, which phase separate from liquid phase that forms a glass on cooling, are difficult to distinguish by XRD. The hydration products identified in WSA paste are CH, C4AH13, C3A.0.5CC¯.0.5CH.H11.5 and C-S-H gel plus possible evidence of small amounts of C2ASH8 and C3A.3CS¯.H32. Based upon the findings, a hydration mechanism is presented, and a model is proposed to explain the observed strength development. [Copyright &y& Elsevier]