Civil Engineering - Building Materials - Discussion

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.

Lime pozzolana mixture has three types.

LP40 initial setting time is 2 hrs (120 mins) and final setting time is 24 hrs (M4 Grade).

LP20 initial setting time is 2 hrs (120 mins) and final setting time is 36 hrs (M2 Grade).

LP7 initial setting time is 2 hrs (120 mins) and final setting time is 48 hrs (M07 Grade).

This mixture used for masonry mortar, foundation concrete, leveling coarse under floors, road and airfield bases, precast building blocks.

Refer for more details IS:4098-1967.

STANDARD SPECIFICATION:

Type/Name Of Cement, Referenced Indian Standard, Initial Setting Time, mints (min), Final Setting Time, mints (max).

OPC(33), IS:269, 30, 600.

OPC(43), IS:8112, 30, 600.

OPC(53), IS:12269, 30, 600.

SRC, IS:12330, 30, 600.

PPC, IS:1489, P1, 30, 600.

RHPC, IS:8041, 30, 600.

PSC, IS:455, 30, 600.

High alumina, IS:6452, 30, 600.

Super sulphated, IS:6909, 30, 600.

Low heat, IS:12600, 60, 600.

Masonry cement, IS:3466, 90, 1440.

IRS-T-40, Railway, 60, 600.

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).

Pozzolana material particles size is less than 90micron, it does not have any cementing property but shows when it contact with water due to overgrinding (i.e less than 90micron) its rate of hydration increases but less heat of hydration so it shows large initial setting time but in question lime-pozzolana (it means it is a gauged cement) lime also show setting property also some time addition of water.

The calcium hydroxide reacts with the carbon dioxide in the atmosphere to give calcium carbonate that gains cementing properties (Carbonation) as their is low CO2 in air thats why it takes Longer time to Set than OPC which uses water for Setting ! And probably that is why Lime Cement is not used in Under water Structures due to Absence of C02.

A pozzolan is an siliceous or siliceous and aluminous material which, in itself, possesses little or no cementitious value but which will, in finely divided form and in the presence of water, react chemically with calcium hydroxide at ordinary temperature to form compounds possessing cementitious properties.

Initial setting time of OPC 30minutes final 10 hours.
Initial setting time of quick setting cement minutes.
Final setting time of quick setting cement is 30 minutes.
Initial setting time of high alumina cement is 3.5 hours.
Final setting time of high alumina cement is 5 hours.

Pozzolana take that much time because as it contain silicate it react with lime to form c-s-h gell. But it a slow reaction process. While on the other hand cement react with h2O to form a solid structure.

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.