Civil Engineering - Building Materials - Discussion

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.

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.

Ordinary Portland Cement (OPC) is graded according to their strength. The grade indicates the compression strength (mpa) of the concrete that will attain after 28 days of setting.

Aluminum has a quick setting quality when mixed as raw material then how high alumina cement has more setting time as compared to opc, Even the aluminum amount is high.

The activated lime pozzolana mixtures are rapid setting, the initial sets being obtained in 1-2 hr and the final within 24 hr.