ABSTRACT

Cement is the third most energy –intensive material to produce, behind steel and aluminum. The production of every tonne of Portland cement contributes about one tonne of carbon dioxide (co2) into the atmosphere. Use of reclaimed and recycled industrial by-products, such as supplementary cementing materials (SCMs) to partially replace Portland cement in concrete, reduces green house gas GHG emission and results in sustainable “green “concrete. Additional benefits include minimization of waste disposal for these industrial by-products and lessened pressure on natural resources (such as limestone and iron ore), importantly, concrete using SCMs will generally exhibit an extended service life over conventional concrete.

      In order to promote the wider use of SCMs in concrete and to enhance consistent application and performance of  the technology such that an increase in GHG emission reduction can be achieved, this project report on the use of SCMs in concrete construction has been developed. The objective of this document is to provide basic knowledge in the use of SCMs in concrete, and the impact of SCM on construction. This project was carried out using coal ash as a partial replacement of cement and some tests were perfomed to examine the effect of this on concrete quality.

     Varying percentage from 50%, 40% and 30% replacement pattern was adopted and test like sieve analysis, compressive strength test, slump test concrete cube test performed. The replacement pattern shown that a 30% replacement of coal ash with cement is more sustainable among  the other replacement patterns.

CHAPTER ONE

1.0 INTRODUCTION

1.1 BACKGROUND OF THE STUDY

Cement is the third most energy-intensive material to produce, behind steel and aluminum. It is a very important building material made by man and possesses certain properties and effects in the process of its making. Cement is one of the constituent of concrete, other major component of concrete includes;

a) Natural Aggregate —   (i) Coarse aggregate e.g. Gravel

                                      (ii) Fine aggregate e.g. Sand

b) Water

c) Admixtures

The goal of a very good civil engineer is how to meet the housing and infrastructural needs of the society, and also to create a conducive environment for living. This has necessitated the search for competent, cheap and environmental friendly materials.

In developing countries, like Nigeria, the use of Portland cement is in high demand and due to monopoly of manufacturers there is always a fluctuation in the price and in most case leading to a price hike. This instability affects the large population of average citizen that aspire to own a building. And since construction accounts for much of the capital formation and is usually second only to agriculture as a source of employment, there should be increased local ownership d development of resources, influence public policies to ensure efficient resource use, and enable nations or regions to improve their economies using cheap indigenous materials that are readily available in large quantities at little or no cost, that can replace or partially replace or supplement the conventional cement used in construction. Coal ash is one of the alternate materials that can be used to partially replace cement in the construction industry.

1.2 PROBLEM STATEMENT

Reducing environmental pollution and alleviating poverty in less developed countries are important goals of sustainable development (Costanza, 1996). The Bruntland Report (World Commission on Environment and Development, 1987) first coined the term sustainable development to mean: “development which meets the needs of the present without compromising the ability of future generations to meet their own needs.” And since construction accounts for much of the capital formation and is usually second only to agriculture as a source of employment and a means of alleviating poverty (see Choucri, 1999).

As for the environment, we posit a technical solution to a global problem with cement production that could reduce environmental degradation. We propose substitute ingredients for making cement, i.e. Coal ash. We might conserve natural capital and create social capital simultaneously when we can reduce both environmental degradation and poverty with lower cost cement (Costanza, 1996). Is there a market for “green” concrete? That can reduce both environmental degradation and also improve the quality of concrete. If so, then will social institutions allow green concrete to be utilized? Such thinking is what this document is designed to put into considerations.

1.3 STUDY JUSTIFICATION

Since government policies set the economic and legislative context in which industries operate, government policies could set an agenda that strives to implement sustainability. If the cement companies were to recover economic losses incurred from producing less Portland cement by creating a Coal ash market, it could benefit local purchasers of construction services. This approach may also thwart price collusion in the cement industry. in furthering capacity building, the subsidizing of a beneficial industry could assist in educating workers in skills necessary for coal ash harvest, preparation and use, thereby creating employment and alleviating poverty an the long run (Berry & Berry, 1999).

“Green” concrete using supplementary cementing materials (SCMs) such as Coal Ash is one good example of less-intensive and more environment friendly materials and technology in concrete construction (United Nations Development Programme, 1994). The production of every tonnes of Portland cement, an essential constituent of concrete, releases about one tonne of carbon dioxide (CO2) into the atmosphere. Partial replacement of cement with Coal ash reduces
greenhouse gas (GHG) emissions proportionately and results in a more “green” concrete, through reduced energy consumption (energy required to produce cement) and avoidance of process emissions (limestone calcinations). Additional benefits include minimization of waste disposal (land-fill these industrial by-products), lessened pressure on natural resources (such as reduction in limestone consumption used for the production of cement) and, when coal ash are judiciously, they improve concrete properties and durability (Gowdy, 1999).

1.4 AIMS AND OBJECTIVES OF THE STUDY

The aim of this report is to encourage the use of locally available, competent, cheap and environmental friendly materials to partially replace cement in the making of concrete.

The specific objectives of this study are;

a. To enumerate the effect of coal ash on specific qualities inherent in concrete.

b To examine other relative properties of concrete with coal ash incorporated.

c. To compare the strength of concrete with coal ash with the conventional concrete.

1.5 Definition of Terms

·         Coal Ash: Coal ash is the finely divided residue that results from the combustion of pulverized coal that is carried from the combustion chamber of a furnace by exhaust gases.

·         Supplementary Cementing Materials (SCMs): SCMs are materials that when used with Portland cement contributes to the properties of the hardened concrete through hydraulic or pozzolanic activity or both. Typical examples are coal ash, Ground, granulated blast-furnace slag (GGBFS)

·         Pozzolan: A siliceous, or siliceous and aluminous, material which in itself possesses little or no cementitious value but will, in finely divided form and in the presence of moisture, chemically react with calcium hydroxide at ordinary temperatures to form compounds possessing cementitious properties.

·         Loss on ignition (LOI): The loss on ignition is reported as part of an elemental or oxide analysis of a mineral. The volatile materials lost usually consist of “combined water” (hydrates and labile hydroxyl-compounds) and carbon dioxide from carbonates. It may be used as a quality test, commonly carried out for minerals such as iron ore. For example, the loss on ignition of a coal ash consists of contaminant like un-burnt fuel.

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