Civil Engineering - Building Materials - Discussion

The initial setting time of lime-pozzolana is generally two hours (120 minutes).

This is the time it takes for the cement paste to start losing its plasticity when mixed with water.

Type of Cement - Initial Setting Time:

Ordinary Portland Cement (OPC) - 30 minutes (min).
Rapid Hardening Cement (RHC) - 30 minutes (min).
Portland Pozzolana Cement (PPC) - 30 minutes (min).
Portland Slag Cement (PSC) - 30 minutes (min).
Low Heat Cement - 60 minutes (min).
Sulphate Resisting Cement - 30 minutes (min).
Quick Setting Cement - 5 minutes (min)** (sets very fast!)
High Alumina Cement - 30 minutes (min).
Lime-Pozzolana Cement - 90 minutes (min).

The correct answer is 120 minutes.

Lime-Pozzolana (120 minutes): This mixture has a slower chemical reaction compared to standard Portland cement. As per standards like IS 4098, the initial setting time is generally specified as two hours (120 minutes) to allow the slow pozzolanic reaction between lime and silica to begin.

30 minutes: This is the minimum initial setting time for Ordinary Portland Cement (OPC) and Portland Pozzolana Cement (PPC).
60 minutes: This is typically the minimum initial setting time for Low Heat Cement.
90 minutes: While some specific masonry cements or asbestos cement products might have a 90-minute requirement, it is not the standard for general lime-pozzolana mixtures.

Answer: The initial setting time of lime-pozzolana is 120 minutes because the reaction between lime and pozzolanic materials is relatively slow compared to standard cement hydration.