Study of the Effect of Different Type of Clays on the Initial Flowability of Mortars in the Presence of Polycarboxylate Superplasticizers
Paolo Fornoni, Matteo Destefani, Emanuele Moretti, Francesco Surico, Gilberto Artioli, Maria Chiara Dalconi
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Clay bearing sand, polycarboxylate superplasticizers, sustainability, Methylene Blue test
The presence of impurities, particularly clays, in sands and aggregates can severely affect the performances of the superplasticizers, particularly polycarboxylate (PCEs). Due to both the large specific surface and the possibility to intercalate the polyoxyethylene side chains of PCEs, clays can capture a large amount of PCEs and correspondingly decrease their efficiency in dispersing the cement particles. From the analytical point of view, the Methylene Blue value (MBV) is the most well-recognized field test to quantify the clay content in the sands. In this work, the MBV of several clays and sands collected from job sites (technical sands) with different origins and lithology was measured and the loss of the initial flowability of mortars prepared with these sands and clays was evaluated. Results indicated that the loss of initial flowability of the mortars, in which the standard sand was partially replaced only by clays, was directly related to the MBV. For the mortars prepared with the technical sands, this direct relationship was not verified: other parameters like the mineralogical composition of the sands tested, their particle size distribution, surface water absorption, and ultra-fine content < 0.075 mm (0.03 in.) could contribute to determining their flow behavior.