Design and performance of ternary blend high-volume fly ash concretes of moderate slump

• HVFA concretes of similar performance to moderate slump OPC concretes were produced.
• Fine limestone powder as a ternary addition improved performance of HVFA mixtures.
• With moist curing, surface and uniaxial resistivities provided comparable results.
• Beyond 1 d, there was no correlation between resistivity and strength.
• Increasing aggregate volume fraction can also increase concrete sustainability.

One approach to increasing the sustainability of concrete construction is to replace a significant portion of the ordinary portland cement (OPC) with a supplementary cementitious material, such as fly ash. This paper presents mixture proportions and measured properties for a series of six high-volume fly ash (HVFA) concretes, five containing a ternary component of a fine limestone powder, with cement replacement levels of 40% or 60% by volume, targeting moderate slump (150 mm) applications. Special emphasis is given to electrical resistivity measurements, comparing measurements conducted in a uniaxial vs. a surface configuration, and assessing the capability of measurements of the bulk resistance of the fresh concrete to anticipate setting times in these HVFA mixtures. The degree to which relationships exist between compressive strength and either cumulative heat release or uniaxial resistivity are presented. In general, ternary blend HVFA concretes can be formulated to provide acceptable strengths at both early ages and over the longer term, with an increased resistivity that implies an enhanced durability and increased service life. However, to achieve moderate slumps at the requisite lower water-to-cementitious material ratios, high dosages of high-range water-reducing admixtures (HWRA) will likely be required, which can negatively impact early-age properties (e.g., setting time and 1 d strengths). Thus, optimum mixture proportioning will require the careful selection and evaluation of the available HRWRA products, both individually and in potential combinations. Finally, another viable route to reducing cement content is to increase the aggregate volume fraction, as demonstrated by the OPC control concretes investigated in this study where aggregate volume fraction was increased from 70% to 72.5%, concurrently achieving a 10% reduction in cement content. In the ternary blend HVFA mixtures, further increases to 75% aggregates were possible, resulting in overall cement reductions (per unit volume of concrete) of between 45% and 63%.