Processor grades calcium carbonate for fly ash substitution, SCC

Huber Carbonates launched a series of ground calcium carbonates earlier this year at The Precast Show in Denver, underscoring the powders’ capacity to replace fly ash; improve concrete mix workability; contribute to self-consolidating mix spread profile; and, maintain consistent white color without impacting fresh or hardened concrete properties.

Raw feed for HuberCrete Prime, Preferred or Extra Fine gradations at Huber Carbonates’ flagship limestone mine and processing mill, Marble Hill, Ga.

HuberCrete calcium carbonate is processed in Prime, Preferred and Extra Fine grades of these respective median particle size and Blaine fineness profiles: 15-24 µm, 300-500 m2/kg; 8-13 µm, 500-700 m2/kg; and 3-5 µm, 700-1,000 m2/kg. Prime is the most cost effective for fly ash replacement and will not cause fluctuations in admixture dosage requirements. HuberCrete Extra Fine helps to improve surface finish characteristics from most concrete mixtures, as the particles impart smoothness and accentuate form reliefs. Preferred calcium carbonate offers a finer particle distribution than fly ash and provides a better early hydration reaction, Huber Carbonates engineers note.

Each HuberCrete gradation, they add, a) enables concrete practitioners to take full advantage of the particle packing effect of companion mix design materials; b) has neutral effect on curing time; and, c) contributes to a project’s LEED rating potential through the lowering of portland cement requirements and finished structures/surfaces’ solar performance characteristics.

While not pozzolanic, HuberCrete powders promote sub-micron level reactivity by providing calcium surface area augmenting formation of hydrated cement compounds. Testing in self consolidating concrete mixes with target 24-in. spread, HuberCrete Extra Fine and Prime specimens attained compressive strengths of 100 percent at 18 hours against portland cement controls. At 28 days, Extra Fine and Prime concrete specimens exhibited respective compressive strengths of 102 percent and 90 percent compared to controls.

HuberCrete and other calcium carbonate products are milled at facilities integrated with Huber Carbonates underground limestone mines in Marble Hill, Ga., Quincy, Ill., and Marble Falls, Texas. The new powder series meets ASTM C1797 Specification for Ground Calcium Carbonate and Aggregated Mineral Fillers for Use in Hydraulic Cement Concrete. — Huber Carbonates LLC, Atlanta,