Durable concrete

This blog has been created by the author, Dr J D Bapat, to inform viewers about the technological advances in durability and the sustainability of concrete.

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Independent Professional: Experienced educator and management consultant for engineering educational institutions, researcher, trainer, technical consultant on sustainable technologies, related to cement manufacturing and characterisation, using industrial and agricultural wastes in cement and concrete, durability of concrete and fuel cell power.

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Sunday, June 30, 2013

Pulverized Fuel Ash (PFA) or Fly Ash (FA) for Durable Concrete


The “pulverized fuel ash” (PFA) or the so-called fly ash (FA), used as a mineral admixture in cement and concrete, is a product of the pulverized coal firing system, through conventional boilers, mostly used in the thermal power plants. While carbon burns in oxidizing surroundings, the inorganic mineral matter gets sintered and liquefied at high temperature. The melt flows down the walls of the furnace and about 25% gets collected as “bottom ash” (BA). It is crushed before disposal. The rest, PFA or FA, gets entrained in the up-flowing hot gas in the form of fine particles, which get trapped in the economizer, air-preheater, mechanical separator, and, finally, battery of electrostatic precipitators (ESP).

As a general practice in many countries, PFA and BA are mixed with water and transported to ash ponds/lagoons. The ash thus deposited in lagoons is called “lagoon ash” (LA) or “pond ash.” It causes problems besides occupying huge stretches of agricultural land. Notwithstanding the greater utilization of PFA (and BA) in recent times in cement and concrete, in bricks, and for land filling, a large quantity of ash still lies unutilized. It is now well established that replacing cement with fly ash improves long term strength and durability. 

As per several estimates, the cement industry contributes about 5% of the global generation of carbon dioxide. The cement industry’s sustainable program developed by the World Business Council for Sustainable Development (WBCSD) prepared an “Agenda for Action” for a 5 year period from 2002 to 2007, endorsed by the leading cement manufacturers of the world. The agenda addressed the issues of (a) climate protection, (b) fuels and raw materials use, and (c) emission reduction besides other issues.

Ref: “Mineral Admixtures in Cement and Concrete”, CRC Press (http://www.crcpress.com/product/isbn/9781439817926). Author: Dr J D Bapat (http://www.drjdbapat.com)
Written for engineers, book focuses on making more workable and durable concrete using mineral admixtures. For each mineral admixture, book looks at manufacturing and processing, physical characteristics, chemical and mineralogical composition, quality control, and reported experiences. It also examines the provisions of national standards.It encourages engineers to more effectively use these and other wastes in cement and concrete to support more sustainable growth of industry. Buy this book online to obtain 20 % discount and free shipping. Download details: http://bit.ly/online_purchase

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Saturday, November 5, 2011

Nano technology in concrete


Eden Energy reports development of concrete reinforcement using carbon nano-fibers (CNF) and carbon nano-tubes (CNT). The new technology increases the flexural strength of concrete.That will reduced concrete beam dimensions and reduced overall building heights due to thinner floor depths. It can also reduce the amount of steel reinforcement necessary to adequately support structural load leading to reduced project material costs substantially.

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Sunday, January 4, 2009

Guidelines to select cement for concrete

GUIDELINES TO SELECT CEMENT FOR CONCRETE


Concrete is used as a material to build varieties of structures under different surrounding conditions. Here are some guidelines to select appropriate cement or binding material for concrete used for different structural applications.

Sl No

Application

Comments

1

Conventional structural

Select cement for economy

2

Concrete in non-aggressive environment

Any cement as per the Standards. Blends of OPC with GGBS or FA or alternatively PPC or PSC, as per the Standards, have been extensively and successfully used in non-aggressive environment

3

Large placements where temperature rise, due to heat of reaction, is to be kept as low as possible

Best results are likely to be achieved with cements with mineral admixtures contents in excess of 50% GGBS or 25% FA.

4

Structural precast

Choice of cement for precast elements will depend mainly on strength requirements at early ages. High early strengths, without steam curing, will be achieved most economically with cements of strength Grade 43 and higher and with low mineral admixture content. Cements with higher mineral admixture content are better suited to steam curing. Where there is no requirement for rapid strength gain, the choice of cement should be based on economy

5

Precast bricks, blocks and pavers

Provided the elements have sufficient strength to allow handling at an early age, typically the day after casting, the choice of cement should be based on economy.

6

High-performance or High-strength concrete

Strength Grade 43 or higher may be used. The inclusion of about 8% silica fume is common practice in this application. Other mineral admixtures may also be used for durability or economic benefits. Superplasticiser is an essential ingredient in high-performance concrete. The compatibility of the cement/binder material and the Superplasticiser is important and needs to be checked.

7

Reinforced concrete in marine environment

Research and long-term field experience shows that best results in marine environment are obtained, using concrete with cement replacement > 50% by GGBS or FA around 30%

8

Concrete with alkali-reactive aggregates

Cement replacement should be > 40% GGBS or > 20% FA, for alkali-reactive aggregates

9

Concrete exposed to sulphate attack

OPC with 5-8% C3A possesses good resistance towards sulphate attack. Using high levels of GGBS as cement replacement (above 50%) improves sulphate resistance