IS 7328 : 2008High Alumina Cement

IS 7328:2008 is the specification for High Alumina Cement (HAC) — a calcium-aluminate cement (not a Portland cement) that develops very high strength within ~24 hours and resists high temperature and chemical attack. Its mainstream use is refractory concrete and rapid-repair, *not* general structural RCC — because of a well-known durability hazard, conversion.

It sits in the special-cement family:

• IS 269 — OPC (the structural cement HAC is not a substitute for) · IS 8041 — Rapid-Hardening Portland Cement (the *Portland* fast-strength option)
• IS 456 — concrete (whose assumptions HAC structural use can violate) · IS 10262 — mix design

HAC hydrates very rapidly to high early strength and tolerates heat and many chemicals — but its calcium-aluminate hydrates are metastable:

• Conversion: over time, especially at warm/moist conditions, the initial hydrates convert to a denser stable form, increasing porosity and substantially reducing strength — historically the cause of serious structural failures where HAC was used for structural RCC
• Consequently HAC is not used for structural reinforced concrete in normal building work; its legitimate domain is refractory/heat-resistant concrete, and rapid-strength repair/temporary works where conversion is accounted for or irrelevant
• It also must not be mixed with Portland cement / lime (flash set), and is sensitive to placing temperature

The engineering point: HAC buys extraordinary early strength and refractoriness, but its long-term structural strength cannot be relied upon due to conversion — the single most important fact about this cement. Specify it for refractory and short-term applications, design any strength reliance on the *converted* (lower) strength, and never treat it as a high-early-strength structural OPC.

Scenario A — refractory lining / heat-resistant concrete: HAC (IS 7328) with refractory aggregate is correct — high-temperature resistance is its purpose; design accordingly.

Scenario B — fast structural strength wanted: do not use HAC for structural RCC. Use Rapid-Hardening Portland Cement (a true Portland cement) or accelerated OPC — they don't suffer conversion.

Scenario C — rapid repair / temporary works: HAC may be used where the high early strength is exploited and long-term reliance is not placed on it (or the converted strength governs design).

Always: never blend HAC with Portland cement/lime (flash set); control placing temperature; design any retained-strength requirement on the post-conversion strength.

The decision is fundamentally *which cement family* — HAC's job is refractoriness and speed, not durable structural strength, and confusing it with a fast Portland cement is a historically catastrophic error.

1. Using HAC for structural RCC as a 'fast-strength cement'. Conversion reduces long-term strength — a cause of real structural failures; use RHPC instead.

2. Designing on the high early (unconverted) strength. Any retained-strength reliance must use the converted (lower) strength.

3. Blending with Portland cement or lime. Causes flash set — never mix cement families.

4. Ignoring placing-temperature/moisture conditions. Warm, moist conditions accelerate conversion and worsen the strength loss.

5. **Confusing it with Rapid-Hardening *Portland* Cement.** Different cement families — IS 8041 RHPC is the Portland fast-strength option, not HAC.

• IS 8041 — Rapid-Hardening *Portland* Cement (the fast structural option — not HAC)
• IS 269 — OPC (HAC is not a substitute) · IS 456 — concrete (structural assumptions HAC can violate)
• IS 10262 — mix design · IS 4031 Part 1 — physical tests
• IS 8043 / IS 6909 — other special cements (hydrophobic / super-sulphated)

IS 7328 is current (2008) and the **most safety-critical 'know what it is *not* for' cement in the stack. High alumina cement is superb for refractory and rapid applications, but conversion — the metastable calcium-aluminate hydrates reorganising over time into a more porous, weaker structure, accelerated by warmth and moisture — has caused notorious structural collapses where it was misused as a fast-strength structural cement. The non-negotiable practitioner rules: HAC is not** a structural RCC cement; never rely on its high early strength for long-term capacity (design on converted strength); never blend it with Portland cement/lime; and do not confuse it with Rapid-Hardening *Portland* Cement, which is the correct fast-strength structural choice. Used in its true domain it is excellent; substituted for structural cement it is a historic disaster.