Recommendations on the Use of Various Chemical Water Reducing Agents with Ultra High Strength Concretes

Ultra-High Strength Concrete (UHSC) is a high-strength concrete formulated to provide compressive
strengths exceeding 130 MPa. UHSC materials typically have a very low water-to-cement (w/c), which
requires the use of a chemical admixture in order to make the material workable for placing, handling
and consolidating. Superplasticizer are commonly used for this purpose. A superplasticizer is a type
of chemical admixture used to alter the workability (viscosity) of fresh concrete. The workability of
fresh concrete is often of particular importance when the w/c is low and a particular workability is
desired. Superplasticizers are developed from different formulations, the most common being
Polynaphthalene Sulfonate (PNS), Polymelamine Sulfonate (PMS) and Polycarboxylate Ether (PCE).
This study investigates the impact of multiple superplasticizers on the compressive strength and
rheological performance of two UHSC mixture. Overall twelve different types of superplasticizers were
used in this study. Six PNS based superplasticizers; three of various compositional strengths (high,
medium, normal range) from a local provider, and three of the same compositional strengths (high,
medium, normal) from a leading manufacturer. Additionally, six different PCE base superplasticizers
of the same compositional strengths, three from a name brand provider, and three from a local
provider were also used. Specific properties assessed were the superplasticizers viscosity, concrete
workability through the mortar-spread test, concrete rheology, and 7, 14, and 28 day UHSC
compressive strengths. Two mixtures were produced with two w/cm (0.20 and 0.15), which would
subsequently increase the amount of superplasticizer needed, from 34.7L/m3 to 44.5L/m3. The results
show that the name brand high range composition PCE based superplasticizer produced the overall
highest spread, lowest viscosity, and a highest compressive strength at all ages tested. There were
mixed results between both the locally provided admixtures as well as the PNS versus PCE at all
other compositional ranges. Additionally, the rheology test also demonstrated that the name brand
high range PNS, and UHSC produced with the name brand PNS high range, had a lower viscosity at
all angular speeds than the others tested.