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Sustainability and Durability in Concrete

Er Anil Kumar Pillai B.E( Hons), EMBA, MBA,MIE

AGM - Technical Services , Ramco Cements Ltd

Abstract

Concrete and related activities play a major part in reducing green house gas emissions.. When we think about sustainable development it indicates that we must not lose our ability to meet the needs of future generation by overexploitation of resources to meet the present needs. Carbon dioxide emissions are the primary green house gas emissions. Cement & Concrete industry has a vital role to play in the reduction of greenhouse gas emissions. Concrete industry has been one of the largest consumer s of natural resources and energy. Our codes will have to increasingly emphasise on performance based parameters for concrete rather than prescriptive based measures. This will further enhance the scope for usage of blending materials like flyash. This paper therefore will discuss on the need to enhance durability in concrete structures as enhancing life of a concrete structure is also one of the ways to ensure sustainability.

Introduction

One may expect that by the middle of this century about 10 billion people will be placing stresses on the worlds natural resources which will lead to further environmental problems { 1}.Therefore natural resources will have to be either optimised or alternative sources are to be utilised . The construction industry which utilises huge quantities of resources needs to consider conservation of resources as one of the major objective. This problem is particularly acute, since cement production as well as fly ash generation in China and India are expected to increase significantly in the next few decades.{2} A balance between growth and environment friendliness will have to be targeted through political, economic and social initiatives. New technologies can and will lessen damaging environmental impacts if they are employed wisely, guided by the market system under some main pillars, such as better efficiency, better cost-effectiveness, better use of energy resources, better environment, better energy security, and better sustainable development {3}In fact, the valuation of the costs of the impacts of climate change, and hence of the curative value, has been the subject of another extensive and multi-volume study by leading economics specialists {4}.

Green House Gas Emissions due to Concreting

Current average consumption of concrete is about 1 tonne per year per every living human being and due to its large consumption and usage of aggregates; even small reductions of green house gas emissions per ton of manufactured concrete can make a significant global impact {5}.

Aggregate mining and manufacture has considerable land use implications{6} Transport , mixing and insitu placement of concrete leads to carbon dioxide emissions as each of the activity requires energy input

Energy Intensive process of Cement Manufacturing

Cement production is a highly energy-intensive process and the manufacture of Cement consists of three major process steps (Figure 1): raw material preparation, clinker making in the kiln, and cement making. Raw material preparation and cement making are the main electricity-consuming processes, while the clinker kiln uses almost all the fuel in a typical cement plant {7}.

Clinker production is the most energy-intensive production step, responsible for about 70%–80% of the total energy consumed {8}

Cement Manufacturing Process

Source : Carbon dioxide emissions from the global cement Industry ErnstWorrell, Lynn Price, Nathan Martin, Chris Hendriks, and Leticia Ozawa Meida3 Annu. Rev. Energy Environ. 2001. 26:303-29.

Carbon dioxide emissions from the production of concrete stem from two primary sources: the energy used in the production of cement and the chemical process of calcining limestone into cement (CaCO3 -> CaO + CO2). Each is a major contributor {9} Therefore optimising the percentage of clinker will help in conservation of energy and natural resources like limestone.

Green Engineering & Sustainable Development

Ritter (2003) {10} defines green engineering as follows: "Transforming existing engineering disciplines and practices to those that lead to sustainability. Green Engineering incorporates development and implementation of products, processes, and systems that meet technical and cost objectives while protecting human health and welfare and elevating the protection of the biosphere as a criterion in engineering solutions." Kibert (2005) {11} argues that in green construction the term "building demolition" would be replaced by "building deconstruction".

Probably the first person who formulated the term Sustainable development was Hans Carl von Carlowitz (1645 - 1714), a forester in Saxony, Germany{12},who called for sparing use of trees to give the forest a chance to regenerate and sustain itself. {2}.A frequently quoted definition for sustainability is: "…meeting the needs of the present without compromising the ability of future generations to meet their needs" {13}

Increasing Compliance with requirements of sustainability :

Lam et al. (2009){14} suggest five factors which lead to successful implementation of green specifications: 1) Green technology and techniques, 2) Reliability and quality of specification, 3) Leadership and responsibility, 4) Stakeholder involvement and 5) Guide and benchmarking systems. According to Ambec and Lanoie (2008){15} the differentiating channel as second revenue increasing channel is more likely to work when 1) customer is willing to pay more for green, 2) information regarding the green product [process] is credible and available and 3) the process [process] is hard to imitate.

Rating systems for sustainable design

The US Green Building Council has developed a rating system, originally for the Federal Government, as a guide for green and sustainable design. This system, called "Leadership in Energy & Environmental Design" (LEEDTM) [12], has become a standard adopted by several governmental agencies in its original form or some modified versions of it. {2,16}

In India CII's Indian green Building Council has been taking lot of initiatives in promoting the concept of green buildings. Green Building defined as per IGBC ( CII) is "A green building is one which uses less water, optimises energy efficiency, conserves natural resources, generates less waste and provides healthier spaces for occupants, as compared to a conventional building."

Change in Business Models for Green Construction

In order to change construction from conventional to green a change in business model is required . Green construction leads to green building vis a vis conventional building through conventional construction. This product process matrix in green perspective is shown in Table 1 has been highlighted by Shahin and Magnus{17} .

Shahin and Magnus{17} further highlights that business model may need changes for firms engaged in green construction due to four reasons .

First resource scarcity leads to increase in resource price which could lead to change of target customer ; Secondly Construction related firms may have to comply with new environmentally friendly contract specifications leading to change in distribution channel ; third this may also lead to change in core competency elements and fourth green products and processes may signal prestige to the customers and there could be a niche segment willing to pay the extra cost of greenness incurred implying change in value propositions

	Construction ( Process)	Building ( Product)
Green	Green construction	Green Building
Non green	Conventional Construction	Conventional Building

Product - Process Matrix for Green Construction

Keast and Hampson {18} assert that the viability of the construction industry relies on the ability to foster and transfer innovative products and practices. For a construction-related company this can imply a change in the operations and the skill set of its R&D department and/or its relation to external resource or knowledge source.

Making Cement Manufacturing Eco Friendly

Energy Efficiency Improvement

Cement Manufacturing process has adopted dry process which is much more energy efficient than wet process. Energy can be saved through affecting the cement composition by replacing part of clinker whose production requires high amount of energy by other products with similar properties which may be used without additional heat treatment and generally these products are industrial by products which have already been heat treated such as flyash or blast furnace slag {19}

Flyash and its effect on quality of concrete

Properties of concrete can be improved and embodied green house gas ( GHG) emissions can be reduced by substituting portland cement with flyash a by-product of coal fired power stations. { 20}

Used as a pozzolan in concrete fly ash can easily substitute for 15-35 percent of the cement content of concrete mixes without a reduction in strength. Some formulations may substitute close to 60 percent of the cement content with the use of fly ash. This can amount to reduction of 50 percent of the embodied energy of the concrete .Flyash has also significantly contributed to structures durability by reducing corrosive effects on the reinforcing steel {21, 22}

Making Concrete Eco Friendly.

Emergence of High Performance Concrete

Neville & Atcin traces the gradual evolution of high performance concrete over the last 15 years following the production of concrete with higher strengths of 120 Mpa and higher. High Performance Concrete is not the same as high strength concrete as the emphasis has moved from high strength to other desirable properties of concrete like high modulus of elasticity , high density , low permeability and resistance to some forms of attack {23}

Development of different types of concrete

Lightweight structural concrete with compressive strength ranging from 20 to 41 Mpa and specific weight between 1440 and 1920 kg/m3 allowed multi-storeyed buildings to be built. High cost of Lightweight concrete is balanced by lower concrete weight, reduction in column sizes and more commercial space available. A 52 storey building, the Shell Plaza Houston, Texas fully built in lightweight concrete in 1971 still remains the highest lightweight building in the world.{24}

Emphasis on Durability of Concrete Structures

Durability means that the given concrete structure will continue to perform its intended functions that are to maintain its required strength and serviceability during the specified or traditionally expected service life {25}. Superplasticers based on PCE ( polycarboxylate ethers) allows reduction of water content workability improvement , enhancement of compressive strength and durability .

Even in the most severe environments, extensive literature has shown that it is not the disintegration of the concrete itself but rather electrochemical corrosion of embedded steel which poses the greatest threat to the durability and long-term performance of concrete structures in severe environments {26} . Poor durability and premature service life therefore presents problem for the ecology and is not sustainable.

Increasing use of Pre-cast

Increasing use of Pre-cast elements has increased the speed of building construction. Since precast elements are manufactured in a controlled condition similar to factory there is a lot of optimisation in the usage of resources.

Concrete testing Procedure for evaluating durability of Concrete

RCPT( Rapid Chloride Penetration tests) is the test that evaluates the durability of concrete .Based on the amount of charge ( in coloumbs) as per ASTM C 1202 chloride ion penetrability could be evaluated which indicates the durability of concrete .

Figure 2 Schematic of Chloride Penetration Test (According to ASTM C 1202 Standard) { 27}

Chloride Ion Penetrability based on Charge Passed(ASTM C 1202)
Charge passed (Coulombs)	Chloride ion penetrability
> 4000	High
2000-4000	Moderate
1000-2000	Low
100-1000	Very low
<100	Negligible

It has been observed that concrete using blending materials like flyash and alag leads to low to negligible chloride ion penetrability.

Eco friendly Initiatives taken by the Company

Ramco Cements Ltd ( FormerlyMadras Cements Ltd ) , the flagship company of the RAMCO group has interests in cement, cotton yarn, software systems, fibre cement products and wind energy. The Company has taken initiatives in introducing the latest technology in cement plants and also has initiated number of environmental friendly measures at its Plants . The company also has wind energy capacity of 159.19 MW. The Ramco wind farm has a total of 229 wind energy generators and is the biggest in Asia. The Alathiyur plant of the Company has also been recognized as the "greenest cement plant" in the country by the Delhi based Centre for Science and Environment (CSE), which has awarded it "4 LEAVES" as part of its Green Rating Project. Ramco Cements Ltd is the first and the only cement company to get such a rating in India. Ramco Cements is the first company to bring more than half a dozen new technologies and they include: surface mining technology for limestone mining, vertical mills for cement grinding, fuzzy logic software system for process controls, pre-calciner technology, most modern programmable logic controllers (PLC), advanced x-ray technology for quality control, highly effective ESPs and bag filters for dust control as well as enterprise mobile computing for business processes. The adoption of the state-of the-art technologies has enabled Ramco Cements to be an energy efficient company.

Making Construction Professionals aware of the benefits of using Portland Pozzolona Cement

Ramco Cements Ltd is assisting the Project customers through Concrete Mix design for various structures. The Research Centre is equipped with RCPT ( Rapid Chloride Penetration test ) which is being used by the construction professionals to evaluate durability of concrete .

The Research Centre in coordination with Technical Services Department assists the customers to make good concrete which is durable. An indicative proportion for the most commonly used concrete grades is shown in Table 1.

Concrete grades using OPC and PPC are casted and differences in durability is highlighted through the RCPT . Therefore it is suggested that Projects should also make RCPT mandatory in addition to the evaluation of compressive strengths.

Con- crete Grade	Cement (PPC)	River Sand	12 mm	20 mm	Water		A d m i x t u r e	Free w/c	Slump after 30 minutes	1 d	3 d	7 d	28 d
M20	310	620	500	780		176	-	0.55	82mm	1 0	1 6	2 0	2 8
M25	340	600	500	770		180		0.5	102MM	1 1	1 7	2 5	3 5

Table 1: Mix proportions ( in kg) using PPC: Indicative and to be changed based on site conditions and materials

Conclusions:

Mechanisation of construction and increasing usage of blending materials like Flyash could help in fulfilling the objectives of durability and sustainability .

REFERENCES

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{27} Jun Phil Hwang, Hyun Bo Shim, Sooyoung Lim, and Ki Yong AnnEnhancing the Durability Properties of Concrete Containing Recycled Aggregate by the Use of Pozzolanic Materials KSCE Journal of Civil Engineering (2013) 17(1):155 - 163

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