Frequently Asked Questions

What mix design parameters are required to produce ultra-high-strength concrete above M80 with Auramix 450?

Ultra-high-strength concrete (UHSC) above M80 requires a comprehensive approach beyond simply specifying Auramix 450. Key mix design parameters include: very low water-to-binder ratio (typically 0.22 to 0.28 by weight); high total binder content (450 to 600 kg per cubic metre including cement plus silica fume); silica fume at 5 to 15% of cement weight as partial cement replacement (provides pozzolanic densification and physical filler effect); fine aggregate with maximum particle size below 10 mm (reduces interfacial transition zone weakness); very careful aggregate grading for maximum packing density; and Auramix 450 at the optimal dosage for the target water-cement ratio and slump. Heat curing (steam or autoclaving) can further increase strength in precast applications. Trial mixes with compressive testing at 1, 3, 7, and 28 days are essential before UHSC production.

Is Auramix 450 suitable for use at high ambient temperatures in Indian summer?

Yes. Auramix 450 is specifically engineered for superior workability retention, which is particularly valuable at high ambient temperatures (above 35 degrees C) that accelerate cement hydration and cause faster slump loss in conventional admixtures. The PCE polymer in Auramix 450 releases plasticising activity slowly over time, maintaining workability for longer than standard PCE admixtures at elevated temperature. However, even with Auramix 450, very high temperatures (above 40 degrees C) reduce workability retention compared to standard conditions. Additional hot weather concrete practices (chilling the mixing water or aggregate, using ice, scheduling pours in the cooler early morning hours) should be considered alongside Auramix 450 for critical high-strength concrete in Indian peak summer conditions.

What is the difference between using Auramix 450 for UHSC versus using it for SCC?

In UHSC above M70, Auramix 450 is used at a moderate-to-high dosage to achieve maximum water reduction at a very low water-cement ratio — the goal is low water-cement ratio and high strength, and the workability is typically in the range of 150 to 200 mm slump. In demanding SCC, Auramix 450 is used at a higher dosage to achieve very high slump flow (600 to 750 mm or above) for self-compaction, at a moderate water-cement ratio (0.30 to 0.40) — the goal is maximum fluidity with segregation resistance, not maximum strength. The mix design for UHSC and SCC are fundamentally different: UHSC uses very low water content and high cementite content; SCC uses higher total powder content and a carefully balanced aggregate grading. Both applications exploit the high plasticising efficiency and workability retention of Auramix 450, but for different purposes.