Reproducible mini-slump test procedure for measuring the yield stress of cementitious pastes

The mini-slump test is a fast, inexpensive and widely adopted method for evaluating the workability of fresh cementitious pastes. However, this method lacks a standardised procedure for its experimental implementation, which is crucial to guarantee reproducibility and reliability of the test results. This study investigates and proposes a guideline procedure for mini-slump testing, focusing on the influence of key experimental (mixing and testing) parameters on the statistical performance of the results. The importance of preparation of always testing at the same time after mixing, testing each batch once rather than conducting multiple tests on a single batch of material, is highlighted. A set of alkali-activated fly ash-slag pastes, spanning from 1 to 75 Pa yield stresses, were used to validate the test method, by comparison of calculated yield stresses with the results obtained using a conventional vane viscometer. The proposed experimental procedure for mini-slump testing produces highly reproducible results, and the yield stress calculated from mini-slump values correlate very well with those measured by viscometer, in the case of fresh paste of pure shear flow. Mini-slump testing is a reliable method that can be utilised for the assessment of workability of cements

A Climatology of TC Size and Structure Changes During Extratropical Transition

Dzuy Nguyen; Meteorology; dzuy.d.nguyen‐[email protected]. Faculty mentor: Ben Schenkel; School of Meteorology; [email protected]

Rheology of concentrated bauxite residue suspensions

In the Bayer process where aluminium oxide is extracted from bauxite, a solid residue is generated and accumulated in enormous quantities. A typical alumina refinery may produce 10,000 tonnes per day of dry solid waste, one-third to one-half of which is fine mud, known as red mud, and the remainder is sand-sized materials. The existing disposal method of pumping the residue to settling ponds in the form of a caustic slurry of 20 to 30 percent solids by weight, causes many inherent problems such as high pumping energy consumption, rapid wear in pipelines, inefficient use of available land, and environmental pollution. These problems can be substantially reduced if coarse sands are removed from the residue and the fine red mud is disposed of as a dense slurry at 50 to 60 weight percent solids.Since concentrated mineral suspensions usually exhibit non-Newtonian characteristics, detailed knowledge of the rheology of red mud is essential for design of the pipeline transport system and assessment of energy requirements.<br>[...] <br

Characterising highly active nuclear waste simulants

Reprocessing of spent nuclear fuel produces a highly active liquor (HAL) waste stream, which is typically stored over extended periods of many years in waste tanks equipped with extensive heat exchange capability. Over time, particulates are known to precipitate from the HAL within these tanks. Particle simulants provide a route for understanding the physical behaviour of these HAL solids under different agitation and transfer conditions. Particle and dispersion characterisation techniques are used here to understand the behaviour of two types of simulant HAL solids, viz. caesium phosphomolybdate (CPM) and zirconium molybdate (ZM), in dispersion. Distinct properties are established for CPM and ZM and compared to a common oxide particle material titanium dioxide (TiO). The results of this study highlight the influence of key aspects of the HAL particulates, such as size and shape, on relevant solid-liquid properties such as sedimentation and rheology. The influence of bulk liquid properties such as electrolyte concentration and pH is also investigated. The results indicate various possible behaviours within the tanks which may impact the storage, remobilisation and pipeline transport of this class of nuclear waste