CHAPTER ONE

1.0       INTRODUCTION

Concrete has over the year been regarded as the first choice among other materials in the civil engineering construction industry.  This is because concrete has the immense advantage over natural stone or other materials. In that it can be moulded easily while it is still wet to any shape or size.  Moreover its materials are readily available and its production is simple.

These concrete is a construction material made from, cement, water and aggregates (coarse and fine).  The cement and water mixed together form a paste, which binds the other materials in to a composite unit, and the process of bringing these materials together is called mixing.

The legacy of concrete is as enduring as the materials itself.  Its evidence abounds in construction industry and human history.  Concrete have a desirable physical and chemical properties from it production, testing for strength, durability, workability and its flexibility, which allows for easy handling.  However the correct proportion of ingredients, placement, and curing of concrete are still critical for optimization of concrete properties.  Making concrete structures without vibration have been done in the past.  For examples placement of concrete under water is done by the use of termite without vibration.  Mass concrete and shaft concrete can be successfully placed with vibration.  But the above example of concrete are generally of lower strength and difficult to obtain consistent quality.  The modern application of self-compacting concrete (SCC) is focused on high performance, better and more reliable and uniform quality of concrete.

Self-compacting concrete is a concrete mix that can be placed without vibration even in congested placement conditions, Shetty (2007). It has several advantages: (a) faster placing with no mechanical vibration and minimum screening (b) improved surface finish (c) ability to fill restricted spaces and hard to reach places (d) improved pumpability (e) reduction/elimination of vibration noise (f) uniform composition of concrete as placed.

• HISTORICAL BACKGROUND AND PERSPECTIVE OF THE PROJECT

Recognizing the lack of uniformity and complete compaction of concrete by vibration, as lead to the development of self-compacting concrete (SCC), Nigeria has started to developed and used SCC that does not require vibration to achieve full compaction in recent days.  Because for several years the problem of the durability of concrete structures was a major topic of interest in the construction industry.  To make durable concrete structures, sufficient compaction by skilled workers is required.

However, the gradual reduction in the number of skilled workers in construction industry has lead to a similar reduction in the quality of construction work.  One solution for the achievement of durable concrete structures independence on the quality of construction work, the employment of self-compacting concrete which can be compacted into every corner of a formwork, purely by means of its own weighted and without the need for vibrating compaction.

By employing self-compacting concrete (SCC) the cost of vibrating compaction can be saved and the compaction of the concrete in the structure can be assured.  However, the total cost for the construction cannot always be reduced, except in large scale construction.  This is because the convention construction system is strongly based on the necessity of the vibrating compaction of concrete.  Self-compacting concrete can greatly improve construction systems previously based on conventional concrete requiring vibrating compaction. (Indian Concrete Journal, 2009).

 

This sort of compaction which can easily cause segregation has been an obstacle to the rationalization of construction work.

Once this obstacle has been eliminated, concrete construction can be rationalized and a new construction system, including formwork, reinforcement, support and structural design, can be developed.

The development of self-compacting concrete has recently been one of the most important developments in the construction industry.  The purpose of this concrete concept is to decrease the risk due to the human factor, to enable the economic efficiency, more freedom to designers, and construct work. This concrete can flow through and fill gaps of reinforcement and corners of moulds without any need for vibrations and compaction during the pouring process.  Because of that, SCC must have sufficient paste volume and proper paste reology.

Paste volumes are usually higher than for conventionally placed concrete and typically consist of high powder contents and water powder ratio. Sarkar (2007).

In the issue of production of SCC, there is no standard method for SCC mix design and many academic institutions; precast and contracting companies have developed their mixed proportioning methods.  The mix designs often use volume as a key parameter because of the important of the need to over fill the voids between the aggregate particles.  In any case the constituent materials are the same as those used in traditional vibrated concrete.

1.2       STATEMENT OF THE PROBLEM

In the Nigerian construction industry, self-compacting concrete is faces with the problem of mix proportions, high cost of production for the optimum compressive strength.  Another problem concrete producer’s face when producing SCCs is the sensitivity of these concretes to weighing errors.  Most of the construction industry in Nigeria adopt conventional concrete base on these problem.  In this project, the problem being known the indigenous construction industry can take advantage by finding this project in the production and testing of self-compacting concrete, in order to achieve higher compressive strength, workability, durability and compactability in concrete industry.

1.3       AIM OF THE STUDY

This project was carryout to know the production and testing of self-compacting concrete in Nigerian environment.  It is arm at

• Judge whether the concrete is self-compactable or not.
• To evaluate deformability or viscosity for estimating proper mix-proportioning if the concrete does not have sufficient self-compactability
• To study the feasibility of using self-compacting concrete mix develops with different supplementary cementitious materials for field application.
• To evaluate changes in SCC behaviour when the ingredients quantities vary.
• To examine the cost differences of producing superplasticised concrete and the conventional strength concrete of the same mix proportion and at the same water/cement ratio.
• To investigate the effect of change in dosage of superplasticiser on concrete strength and workability and hence determine the right dosage that will optimize the properties of the concrete mix.
• To known the effects of super plasticisers on the compressive strength and workability of concrete and also determine the dosage that will optimize concrete durability.

1.4       SCOPE OF THE STUDY

This study is limited to the following:

• Binding material use: Ordinary Portland cement.
• The aggregate used were coarse aggregate, and fine aggregate sand.
• The size of coarse aggregate was 5- 15mm
• Poretable water was used.
• The high performance superplasticiser was used. (Complast SA 430)
• Concrete cube mould of 150 x 150 x 150mm were used.