Frequently Asked Questions

Where does Auracast 270M fit in the Fosroc Auracast range and when should it be preferred over Auracast 100 or Auracast 450?

The Fosroc Auracast range covers a spectrum of PCE admixtures designed for precast and high-performance concrete, differentiated by their water reduction level, workability target, and early strength development characteristics. Auracast 50 and Auracast 100 are early-strength-oriented products where the primary goal is fast compressive strength development for rapid demoulding in precast factories. Auracast 270M is positioned in the mid-range where the emphasis is on consistent, controlled workability in the S3 to S4 slump class, appropriate for production of a broad range of precast products where a good balance of water reduction, workability, and 28-day strength is more important than maximum early strength. Auracast 450 is the top-of-range product for the highest water reduction and ultra-high-strength or SCC concrete. For a precast manufacturer producing general building components (beams, columns, slabs, stairs) without a critical need for maximum early strength or ultra-high-strength concrete, Auracast 270M provides a versatile and consistent-performing PCE admixture that covers most production requirements.

How is the Auracast 270M dosage determined for a specific concrete mix and target workability?

The appropriate dosage of Auracast 270M is determined by trial mix at the production facility using the actual cement brand and grade, aggregate grading, mix proportions, and ambient temperature representative of production conditions. A series of trial mixes at dosages spanning the recommended range (typically 0.3 to 0.9 litres per 100 kg of cementitious content) at the target water-cement ratio establishes the dose-response relationship for the specific materials. The dosage giving the target slump (or flow for SCC) is then selected, with confirmation testing of compressive strength at 1 day, 7 days, and 28 days. Production dosage adjustments within the range established by trial are normal as cement deliveries, temperatures, and aggregate moisture content change through the production year. Contact Space Arc Engineering for guidance on trial mix methodology and dosage optimisation for Auracast 270M.

Can Auracast 270M be used with fly ash or GGBS cement replacement in precast concrete?

Yes. Auracast 270M is compatible with concrete mixes incorporating fly ash (FA) as partial cement replacement (typically 20 to 30 per cent by weight of total cementitious content for precast) and with GGBS (ground granulated blast furnace slag) as cement replacement. The inclusion of fly ash or GGBS generally reduces the early strength of concrete compared to a 100 per cent OPC mix, which can extend the time to demoulding in precast factories. However, fly ash and GGBS improve the long-term strength, workability, and durability of the concrete. For precast producers using fly ash or GGBS, Auracast 270M provides good compatibility and consistent workability. Where maximum early strength is critical and fly ash is used, Auracast 50 or Auracast 100 with a reduced fly ash replacement level is more appropriate.