The discarded mill tailings behind the dam will cause disasters at any time. A solution to this problem may be to utilize those wastes, e.g. mill tailings from magnetite, as the Manufactured Fine Aggregates (MFA) for preparation of concretes. The mill tailings from magnetite can be considered as new resources of sand. However, in production of MFA from mill tailings, the particles smaller than 75 μm were strictly eliminated. The degranulation results in not only lower utilization of the resources but also worse micro grading of MFA. The micro fines, i.e. powdery mill tailings from magnetite, supplements powder content in concrete systems in w/c>0.40 to modify the ratio of water to total powder (w/p). The perfect micro grading for good workability can be reached in the case of optimal w/p ratio. The filling effect owing to perfect micro grading of powdery mill tailings makes concretes more compact and the pozzolanic constituents in micro particles of the tailings contribute to the strength of concretes.
It is in great request to substitute foamed concrete for organic thermal insulating materials that are inflammable and liberate virulent gases on burning. In current study, felsite powder (powdery magnetite mill tailings) was used as filler and Solvay distiller waste (DW) was used as hardening accelerator for foamed concrete. The results showed that the strength and strength-to-density ratio of foamed concrete in cement-felsite powder system is much higher than those in cement-sand system and cement-lime-sand system. The Solvay distiller waste, suspending agent and polypropylene fiber can improve performances of foamed concrete such as cohesion and strength. DW can reduce shrinkage in forming process of foamed concrete.
Development and utilization of recycled aggregate concrete can solve the processing difficulties caused by a lot of waste concrete. Experiments results showed the higher replacement percentage of recycled aggregate concrete, the lower its bulk density. Both drying shrinkage degree and drying shrinkage sustained time of recycled aggregate concrete increase with increasing its replacement percentage. The ultimate bearing capacity of recycled aggregate concrete decreases as its replacement percentage increases. Elastic modulus of recycled aggregate concrete decreases with increasing its replacement percentage. The variation characteristics of deformation modulus and elastics modulus along with their replacement percentage are similar. Both of them decrease with increasing their replacement percentage. Deformation modulus of recycled aggregate concrete is more sensitive to the variation of its replacement percentage.
The demolished concretes have ever been considered as homogeneous materials and simply crushed to produce recycled aggregates which can only be used for low strength concretes. In mechanical processes of intergrinding in combination with pre-crushing, the sieve residue in each size fraction varies with grinding time and residue-grinding time curves of most fractions have their inflection points that can be considered as termination of separation. The original state aggregates (OSA) so recycled are up to standard of grade II original coarse aggregates specified in China’s standard Pebble and Crushed Stone for Building (GB/T 14685-2001) and can be applied in moderate strength concretes with a bit higher strength than that of original concretes from which the OSA derived. In this method, the OSA can be separated furthest from cement pastes and mortars while suffering minimum damage in separation processes and can retain higher strength.
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