Why is High Alumina Cement not used for general building structures?

Due to the risk of 'conversion' in warm, moist environments, which causes a significant and unpredictable loss of strength and durability. This is detailed in Appendix A.

What is the minimum compressive strength for HAC at 1 day?

The minimum 24-hour compressive strength is 30 MPa, as per Table 2. This rapid strength gain is its key feature.

What are the main chemical requirements for HAC?

The total alumina (Al2O3) content must be at least 32%, and the ratio of Al2O3 to lime (CaO) must be between 0.85 and 1.30, as specified in Table 1.

Is this standard still active?

Yes, IS 6452:1989 has been reaffirmed (most recently in 2021) and is the current standard for HAC in India, though its use in structural applications is limited by other codes like IS 456.

IS 6452

: 1989

High Alumina Cement for Structural Use - Specification

CurrentSpecializedSpecificationMaterials Science · Flooring and Paving

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This standard specifies the manufacturing process, chemical composition, and physical properties for high alumina cement (HAC). It outlines mandatory requirements for strength, setting time, and soundness, along with the necessary testing procedures. The standard includes a crucial appendix warning against the improper use of HAC in structures due to potential strength loss from 'conversion'.

Specifies requirements for high alumina cement used in structural applications, including properties like setting time and strength.

Quick Reference Values

Minimum Alumina (Al2O3) content by mass32%

Ratio of % Alumina (Al2O3) to % Lime (CaO)0.85 to 1.30

Minimum initial setting time30 minutes

Maximum final setting time600 minutes

Minimum 1-day compressive strength30.0 MPa

Minimum 3-day compressive strength35.0 MPa

Maximum expansion in Le Chatelier test5 mm

Practical Notes

The most critical consideration for HAC is the 'conversion' phenomenon, where the cement's hydration products change in warm (>25°C), moist conditions, leading to a significant loss of strength and increased porosity. Its use in load-bearing structures is therefore highly restricted.

HAC must never be mixed with Ordinary Portland Cement (OPC) or lime, as this can cause a 'flash set' and unpredictable long-term behavior.

It is primarily suitable for applications requiring rapid hardening, high-temperature resistance (refractory concrete), or resistance to chemical (sulfate) attack.