blended cement

All about cement, types of cement grades and blended cement!

An English brick layer, Joseph Aspdin, in 1824, first discovered cement and called it Portland cement as it resembled a limestone found in Portland. The Portland cement is made up of –:

·         Lime (CaO)                        60 – 70%

·         Silica (SiO2)                      20 – 25%

·         Alumina (Al2O3)                5 – 10%

·          Ferric oxide (Fe2O3)          2 – 3 %

There are many types of cement out there for engineering and construction purposes like Portland Pozzolana Cement (PPC), Sulphate Resisting Portland Cement (SPC) and Ordinary Portland Cement (OPC). Ordinary Portland Cement should be used for house construction. It is very important to keep in mind the environment of the construction site while selecting a type of cement. This is for durability considerations of buildings and structures. Making a prudent choice now, regarding a type of cement, saves the repair and restoration costs later and also, more importantly, avoids the construction of awry and lopsided structures that may prove calamitous in the future.

The Ordinary Portland Cement is available in the following types of cement grades:

1.      33 Grade Ordinary Portland Cement – The fineness of 33 grade OPC should be between 225 and 280. It has low compressive strength and therefore is not normally used where M-20 or higher grade of concrete is required. It is used for general civil construction work, plastering, flooring, etc.

2.      43 Grade Ordinary Portland Cement – It is the most popular general purpose cement in the country today. It is used where a member takes high tensile stress, for grades of concrete between M-20 and M-30. RCC works, precast items, asbestos products such as sheets, pipes, etc are some of the applications of 43 grade OPC.

3.      53 Grade Ordinary Portland Cement – It is used where concrete grade higher than M-30 is required. It is suitable for cold weather concreting. Its applications include PSC works, bridge, roads, multi-storied buildings etc.

BLENDED CEMENT

DictionaryOfConstruction.com defines blended cement as a hydraulic cement consisting of an intimate and uniform blend of (a) granulated blast-furnace slag and hydrated lime, (b) Portland cement and granulated blast-furnace slag, (c) Portland cement and pozzolan, or (d) Portland-blast-furnace slag, cement, and pozzolan. Blended cement is produced by intergrinding Portland cement clinker with the other materials or by a combination of intergrinding and blending.

The advantages of using blended cements are so many that now they are being considered superior to the hitherto deemed best, OPC category of cements.  The technical advantages of using blended cement include –

1.      It uses less water and therefore helps in keeping the water-cement ratio low.

2.      Using blended cement improves durability of structures as it is finer as compared to OPCs and therefore the permeability of concrete is less.

Using blended cement also has lower environmental impact. The environmental advantages of using blended cement include –

1.      Blended cements save energy to the tune of 0.8 to 1.2 MWH/ton of cement.

2.      7% of total pollution that is caused by cement production alone can be proportionately reduced if more blended cement is used.

3.      Conserves natural resources.