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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]

The development of new environmental friendly concretes such as rubberized concrete is being promoted due to the environmental problems created by the waste tire rubber. Every year millions of tires are discarded, thrown away or buried all over the world, representing a very serious threat to the ecology. In this study, we analyse the potential of waste tire rubber particles as a partial substitute for fine aggregates in normal strength and high strength cement concrete and the resistance to abrasion has been measured. Statistical Analysis was carried out to strengthen the results obtained from experiments. The results show that the use of tire rubber particles can improve the abrasion resistance of concrete, and this can ensure its applications in pavements, floors and concrete highways, or in places where there are abrasive forces between surfaces and moving objects. [ABSTRACT FROM AUTHOR]