Sustainable Cement Utilization
[Enugu, Enugu State Nigeria]

CHAPTER TWO
LITERATURE REVIEW
2.0 INTRODUCTION

 This chapter reviews works done on sustainable cement utilization. There has some publications on this topic but not every part of it has been handled. However, the available related literatures in the area of cement production and utilization are reviewed in this chapter and it is handled under the following divisions:

Definition
Types of cement
Manufacturing of cement
Cement factories in Nigeria
Cement production
Capacity and utilization
Importation
Short falls
Alternative to cement
Environmental impact

2.1 DEFINITION
Cement is got by burning a mixture of limestone and clay to form a clinker, then pulverizing the clinker into powder. (Oxford Dictionary 1995). In the most general sense of the word, cement is a binder, a substance which after mixture with water, sets and hardens independently, and can bind other materials together. The word “cement” traces to the Romans who used the term “opus caementicium” to describe masonry which resembled concrete and was made from crushed rock with burnt lime as binder. The volcanic ash and pulverized brick additives which were added to the burnt lime to obtain a hydraulic binder were later referred to as cementum, cementum, cament and cement.

Cement is also defined as the finely pulverized product resulting from the calination of a natural argillaceous limestone at a temperature below fusion. This temperature should be high enough [from 1,850 to 2,350] degrees Fahrenheit to drive off the carbon dioxide as a gas, decompose the clay and cause the formation of aluminates, ferrites and silicates. The burned stone must be finely ground before it exhibits any hydraulic properties. It can be literally defined as a powered substance made of burned lime and clay, mixed with water and sand to make mortar or with water, sand and gravel to make concrete. The mixture hardens when it dries.

2.2 SUSTAINABILITY AND FACTORY-MADE CEMENTS
Factory-Made Composite Cements
Portland Cement CEM I
Sulphate-Resisting Cements
Rapid Hardening Portland Cements
White Cement
Masonry Cement
Expansive Cements
Environmental Cements
Non-Portland Cements

Sustainability and Factory-Made Cements
Integration of sustainability into all its operations now sets the UK cement industry's agenda. For cements to remain viable, their embodied energy and carbon footprint must be reduced over time without jeopardising product performance (Michael 2004). The increasing availability of cements such as CEM II types for use in concrete, mortar and grout plus the continued production of niche Masonry cements for use only in mortar will help the industry to meet its social and environmental obligations and achieve necessary economic objectives. Until now, Portland cement CEM I, of strength classes 42,5 or 52,5, has been the 'traditional' cement in the UK, although it is the least sustainable type given its high proportion of cement clinker. Greener, more sustainable 'non-CEM I' cement solutions incorporating lower proportions of clinker are now generally available in both bulk supply and packed in bags. Use of these non-CEM I factorymade cements should become more and more widespread as prudent specifiers include a cement's sustainability credentials within their specification criteria.

Factory-Made Composite Cements

Used here, the expression, 'factory-made composite cements' means any cement that comprises Portland cement clinker combined (interground or blended) with one or more additional inorganic constituents plus an optimised amount of set-regulator (gypsum). The additional constituents are selected from materials such as power station fly ash, blast furnace slag and limestone, all already familiar to UK concrete, mortar and grouting practice. Therefore, in terms of the British/European standard for common cements, BS EN 197-1, factory-made composite cements, are collectively, types: CEM II, CEM III, CEM IV and CEM V i.e. any 'non-CEM I' cement specified in the standard. Such a use of the term aligns with the UK concrete sector's traditional understanding but is wider than is implied by the standard itself wherein two particular cements, CEM II/M and CEM V, include the word 'composite' in their names. In general, the appropriate use of factory-made composite cements delivers performance equal to that of concrete containing CEM I cement and under certain conditions, can improve on the durability performance achieved.

Furthermore, in the case of use in masonry mortars within the generality of
exposure conditions, factory-made composite cements can achieve the
same level of performance on a one-to-one basis as a CEM I cement within
the same traditional volume mix proportions.

Portland Cement CEM I
Formerly known as ordinary Portland cement (OPC), CEM I is manufactured to conform to British Standard BS EN 197-1. CEM I is the cement that has been most commonly used throughout the world in civil engineering and building works. Concretes and mortars made using CEM I are versatile, durable and forgiving of poor construction practice. In addition, specific properties can be enhanced by altering either the cementmaking recipe or the size of the particles and so producing different cements. However, CEM I is the least sustainable type and use of alternatives is in the ascendancy.

Sulphate-Resisting Cements
The traditional sulphate-resisting cement used in the UK has been sulphate-resisting Portland cement (SRPC), conforming to BS 4027. SRPC is a special type of CEM I cement manufactured to contain a high content of iron oxide in order to limit the amount of the mineral phase tricalcium aluminate (C3A) and thereby increase its sulphate resistance. Additionally, SRPC is normally low alkali cement which benefits concrete in resisting the alkali silica reaction (ASR). However, it is not the only sulphate-resisting cement available. Various factory-made composite cements are also sulphate-resisting including the generally available CEM II/B-V type of Portland-fly ash cement containing at least 25% of fly ash. Such CEM II/B-V cements are permitted for use in the same wide-range of sulphate exposure conditions as is SRPC and are also low in reactive alkalis. Moreover, SRPC is a type of CEM I cement with a high clinker content, it is no longer manufactured in the UK and is becoming more difficult to source. Consequently, greener sulphate-resisting composite cements will continue to grow in importance.

Rapid Hardening Portland Cements
Rapid hardening versions of CEM I cements are available. The average particle size is smaller in these cements and they gain strength more quickly than do ordinary CEM I types. They generate more heat in the early stages and can be useful in cold weather concreting. However, their principal use is in manufacturing precast concrete units where the high early strength of the concrete permits quick re-uses of moulds and formwork.
Cements described as either rapid-setting or extra rapid hardening may be mixtures of CEM I and a non-Portland cement such as calcium aluminate or calcium sulphur aluminate and will tend to both set and harden (gain strength) very quickly