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Extractive and mining operations are one of the largest waste producing streams in the world. In general, mining operation is accompanied with the production of stone and slurry wastes. Such wastes occupy large land near the mining area and the fine slurry particles cause bronchial, vision and skin disorders in the nearby inhabitants. Present study examines the suitability of using dimension limestone waste as fine aggregate in concrete. Twenty-six concrete mixes were examined by replacing river sand fine aggregate with crushed sand, slurry and manufactured sand (MS). Test results indicated that MS formulated by blending crushed solid stone waste (85%) and slurry (15%) can be used as fine aggregate in concrete. Concrete cast with MS demonstrated superior strength and reduced bleeding, permeability and void formation within the concrete. The use of MS will contribute to bulk utilisation of waste as it can completely replace river sand in concrete, hence, promoting sustainable development in the region by consuming both types of stone waste in significant quantities. [ABSTRACT FROM AUTHOR]

A study examining air-entrainment in fly ash concretes combined with different Portland cements (PCs) is described. Tests were carried out (using five PCs, ten fly ashes and a standard chemical reagent (to entrain air)) on paste suspensions (foam index), mortar and concrete to quantify the material effects. Preliminary tests indicated that the foam index increased with the fineness (specific surface area (SSA) (by nitrogen adsorption Brunauer-Emmett-Teller (BET) method)) of the PC used (varied by grinding) with fly ash. Reductions in the property were found with increasing alkali content in the paste suspensions (by sodium hydroxide addition), which tended to be slightly greater with higher SSA/lower alkali content fly ash. Tests on the wider range of PCs and fly ashes gave a strong correlation between their combined SSA and foam index, with their combined alkali content having less effect on the latter. The influence of fineness was again apparent in the mortar tests, which also showed that when PC and fly ash were of comparable SSA, a change in either material had a similar effect on air-entrainment. However, fly ash had an increasing influence as the difference in this between materials became greater. The results also suggest that air losses after mixing tend to increase with the SSA of PC + fly ash (and hence admixture dose). Similar effects were generally noted in the tests made on concrete. A possible approach to controlling air-entrainment in fly ash concrete may therefore be to ensure that its SSA is similar to that of the PC with which it is used. A test method to enable this to be evaluated is suggested. [ABSTRACT FROM AUTHOR]

A study examining damaging alkali-aggregate reaction (AAR) in concretes containing recycled aggregate is described. This considered masonry units, concrete, demolition waste, road planings, slate and plasterboard. Alkali release tests indicated that masonry units tended to release more alkali than recycled concrete (with higher levels generally obtained from recently produced materials), with slate and plasterboard giving least. Accelerated mortar expansion (reactivity) test results suggested there was a low risk of AAR for the materials. Concrete tests were then made using BS 812-123 exposure conditions. The concretes were proportioned (i) following the standard mixes (NaO = 7·0 kg/m) with recycled materials replacing fine or coarse aggregate in a low-reactivity aggregate combination and (ii) at high alkali level (NaO = 5·4 kg/m) with the materials as fine aggregate in a normal-reactivity aggregate combination. The tests for (i) gave results for the recycled materials indicating low reactivity, with classifications of non-expansive or probably non-expansive to BRE Digest 330. For (ii), expansions for the materials were mainly similar/slightly higher than those found for (i). However, recycled concrete that previously exhibited damaging AAR had greater expansions. Selected concretes were exposed at an external site for up to 8·5 years, during which observations by microscopy were carried out. These gave general agreement with the laboratory tests. The practical implications of the study are reviewed. [ABSTRACT FROM AUTHOR]

The paper describes a study carried out to investigate how fly ash influences sulfate-heave in lime-stabilised soils. Five different clays having a range of total potential sulfate contents were tested. Quicklime was added at 3·0, 4·5 and 6·0% (by mass of dry soil) and two fly ashes with different characteristics were used at levels of 6, 12, 18 and 24%. A ground granulated blastfurnace slag was also considered for comparative purposes. Swelling tests followed the BS EN 13286-49:2004 accelerated (40°C) volumetric method. Mellowing period, exposure temperature, mineralogical development, unconfined compressive strength and porosity of the test mixes were also considered in studying fly ash effects on the process. Swelling generally increased with overall sulfate content in the lime-stabilised mixes and reduced with increasing fly ash level and coarseness. The mechanisms involved appeared to depend on the characteristics of the fly ash used. In the case of coarse fly ash, this was attributed to a mainly physical phenomenon associated with increased pore space in the system to accommodate expansive sulfate products forming, which contrasted with enhanced fly ash reactivity and increased strength of the lime-stabilised structure for fine material. [ABSTRACT FROM AUTHOR]