While the influence of paste properties on concrete performance has been extensively studied and in many cases reduced to quantitative relationships, that between aggregate characteristics and concrete performance has not been investigated in detail. Based on previous research that demonstrated significant strength differences for two similar concrete mixtures, one prepared with limestone aggregates and the other with siliceous gravel, a joint study between the National Institute of Standards and Technology and the Federal Highway Administration was initiated to explore in detail the influence of aggregate characteristics on concrete performance. Eleven aggregates of differing mineralogy were identified and obtained both for bulk characterization and for incorporation into two concrete mixtures. The first concrete mixture was based on a 100 % ordinary Type I/II portland cement (OPC), while the second consisted of a ternary 60:30:10 volumetric blend of this cement with 30 % of a Class C fly ash and 10 % of a fine limestone powder. This latter sustainable mixture had exhibited exemplary performance in a previous study. Aggregates were characterized with respect to mechanical and thermomechanical properties, geometrical characteristics, and surface energies. For the prepared concretes, mechanical, thermomechanical, and electrical properties were measured at ages to 91 d and microstructural examinations were conducted to examine the interfaces between aggregates and cement paste. Concrete performance varied widely amongst the different aggregates, with the range/average value for 28-d compressive strength being 32 % for the OPC concretes and 37 % for those based on the ternary blend binder. With the exceptions of relating concrete modulus to aggregate modulus and concrete coefficient of thermal expansion (CTE) to aggregate CTE, weak correlations were generally obtained between a single aggregate characteristic and concrete performance properties.
Citation: Technical Note (NIST TN) - 1963Report Number:
NIST Pub Series: Technical Note (NIST TN)
Pub Type: NIST Pubs
Aggregate mineralogy, aggregate shape, aggregate texture, bond, coefficient of thermal expansion (CTE), interfacial transition zone (ITZ), modulus, strength.