Abstract
Rheological properties of self-compacting concrete mixes containing a viscosity modifying agent (VMA) in their composition were studied. After preliminary studies self-compacting concrete mixes and, particularly, a fluid concrete mix prone to segregation of its ingredients were chosen. VMA was added in various amounts to that concrete mix to check how it performed in fresh and hardened concrete. Main studies focused on the influence of VMA on the following properties of concrete mixes: the slump flow, the flow time into the diameter of 500 mm and the resistance to segregation in the vertical direction. Moreover, the air content of concrete mixes and the 28-day compressive strength of concrete were measured. Test results showed that VMA significantly influenced the rheological properties of concrete mix, stabilised it and reduced the segregation. It was proved, that the concrete mix modified by VMA used in the optimal amount, featured the smallest scatter of concrete strength results. Besides, the Tukey's test showed that a reduction of the concrete compressive strength is possible to be statistically insignificant when compared to the reference level.
Highlights
Self-compacting concrete (SCC) is one of the newest achievements in concrete technology
The progress is very significant in Japan, USA, Canada and the majority of European countries, including Poland. It concerns studies of rheological properties of SCC mixes (e.g., Szwabowski, Gołaszewski 2010) but their microstructure (ŁaźniewskaPiekarczyk, Szwabowski 2010), the pore structure (Gorzelańczyk, Hoła 2011) and the influence of moisture content on the compressive destruction process in SCC subjected to a multiply changing load (Gorzelańczyk 2011)
The European document prepared by European Federation Suppliers of Specialist Construction Chemicals specifying standards corresponding to SCC is The European Guidelines for Self-Compacting Concrete (EFNARC 2005)
Summary
Self-compacting concrete (SCC) is one of the newest achievements in concrete technology. The segregation negatively influences many properties of hardened concrete, including physical parameters (water absorption, frost resistance) as well as the uniformity of compressive strength (Woyciechowski 2006) in extreme cases. Viscosity modifying agents are used in the form of water soluble polymers increasing the viscosity of concrete mix (cellulose ethers, starch, polyvinyl alcohols), water soluble flocculants increasing attractive forces between cement grains by adsorption (natural resins, styrene and carboxyl polymers), organic emulsions (e.g. acrylics) introducing additional small particles to the mix (Khayat, Ghezal 2003), extra fine inorganic materials featuring high binding, e.g. bentonite, silica fume and some types of fly ash (Lachemi et al 2004a; Leemann, Winnefeld 2007; Rols et al 1999; Woyciechowski 2006). The testing methods of the rheological properties according to EFNARC (2005) were used These include the Abrams cone in the inverted version, the method to test concrete mix segregation modified by MC Bauchemie and European standard measurements of air content and compressive strength. Chemical compounds (%) SO3 Cl– Al2O3 Na2Oeq Insoluble residue (%) Ignition loss (%) Potential compounds (%) C3S C2S C4AF C3A Blaine’s specific surface (m2/kg) Initial setting time (min) Final setting time (min) Volume stability (mm) Compressive strength (MPa) 2 days 28 days
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