This part of IS 4031 outlines the testing method for determining the soundness of hydraulic cement using an autoclave. The test evaluates the potential delayed expansion of cement paste caused by the hydration of uncombined magnesia (MgO) and free lime under high-pressure and high-temperature steam.
Describes the procedure for determining the soundness of hydraulic cement by the autoclave expansion method.
Quick Reference Values
Specimen dimensions25 x 25 x 282 mm
Autoclave steam pressure2.1 MPa
Temperature corresponding to 2.1 MPa215.7 °C
Time to reach 2.1 MPa45 to 75 minutes
Duration maintained at 2.1 MPa3 hours
Time to reduce pressure to zero after 3 hours1 to 1.5 hours
Key Formulas
Soundness Expansion (%) = ((L2 - L1) / Effective Gauge Length) x 100
Practical Notes
Safety first: Always ensure the autoclave's pressure gauge and safety relief valve are accurately calibrated to prevent over-pressurization.
Thermal shock prevention: Allow the autoclave pressure to naturally fall to zero, open the vent, and then cool the specimens gradually in 90°C water, lowering to 27°C over 15 minutes.
The paste must be mixed at standard consistency, which is determined beforehand using IS 4031 (Part 4).