TitleHigh-volume natural volcanic pozzolan and limestone powder as partial replacements for portland cement in self-compacting and sustainable concrete a b s t r a c tA laboratory study demonstrates that high volume, 45% by mass replacement of portland cement (OPC) with 30% finely-ground basaltic ash from Saudi Arabia (NP) and 15% limestone powder (LS) produces concrete with good workability, high 28-day compressive strength (39 MPa), excellent one year strength (57 MPa), and very high resistance to chloride penetration. Conventional OPC is produced by intergrinding 95% portland clinker and 5% gypsum, and its clinker factor (CF) thus equals 0.95. With 30% NP and 15% LS portland clinker replacement, the CF of the blended ternary PC equals 0.52 so that 48% CO 2 emissions could be avoided, while enhancing strength development and durability in the resulting self-compacting concrete (SCC). Petrographic and scanning electron microscopy (SEM) investigations of the crushed NP and finely-ground NP in the concretes provide new insights into the heterogeneous fine-scale cementitious hydration products associated with basaltic ash-portland cement reactions.

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The passive films formed on the 9%Cr, 0.1%C, microcomposite steels (ASTM A1035) in highly alkaline environments, such as concrete pore solutions, were studied. In-situ surface-enhanced Raman spectroscopy (SERS) was conducted during cyclic potentiodynamic polarization experiments to characterize the formation and breakdown mechanisms of the passive films formed. A solution of 0.55 M KOH + 0.16 M NaOH, with and without chlorides (0 % and 3.5 % NaCl), was used for the SERS experiments. In addition, the corrosion performance of microcomposite steels as a function of pH (9–13) and ionic strength of the solution (from 10-5 to 10-1 M) was evaluated via polarization resistance (Rp) experiments, and compared to the performance of regular carbon steel. Results show that the passive film formed on the microcomposite steel seems to be characterized mainly by the presence of Cr(OH)3 and minor amounts of Fe species; more specifically Fe3O4 and a Fe(III) phase. The film is considerably more protective than that formed on conventional carbon steel under the same test conditions. Microcomposite steel has not shown a reduction of polarization resistance as a function of pH drop when the ionic strength of the medium was kept constant, in a stark contrast to the behavior verified for the regular carbon steel rebar.