COMPARISON OF LOCALLY EXCAVATED SAND WITH RIVER SAND IN TERMS OF STRENGTH IN SANDCRETE BLOCKS

CHAPTER ONE

INTRODUCTION

1.1  BACKGROUND OF THE STUDY

Sandcrete is a yellow-white building material made from a binder (Portland cement), sand in a ratio of circa 1:8, and water. Sometime other ingredients may be added to reduce the amount of Portland cement such as “pozzolanas and rice husk ash”. Sandcrete is similar but weaker than mortan for which the ratio is 1:5. Sandcrete is usually used as hollow rectangular blocks similar to concrete masonry units, often 45cm (18”) wide, 15cm (5.9”) thick and 30cm (12”) with hollows that run from top to bottom and occupy around one third of the volume of the block.

STRENGTH AND USAGE

The final compressive strength of sandcrete can be as high as 4.6N/mm2 which is much less than concrete’s 40N/mm2. Sandcrete is unsuitable for load-bearing columns, and is mainly used for walling of a house - making a fence - Septic tank and soak away tank’s - Building a generator’s house. In Nigeria, measured strength of commercial available sandcrete blocks was found to be between 0.5 and 1N/mm2, which is well below the 3.5N/mm2 that is legally required. This development may be due to the need of the manufacturers to keep the price low, and since the main cost-factor is the Portland cement, they reduce that, which results in a block that starts behaving more like loose sand.

SANDCRETE BLOCK SIZES

They are many different types of blocks used in modern building, they include:

· 9”  hollow blocks (450mmx225mmx225mm)

· 6” hollow blocks (450mmx150mmx225mm)

· 6” solid blocks (450mmx150mmx225mm)

· 5” solid blocks (450mmx125mmx225mm)

· 9” solid blocks (450mmx225mmx225mm)

CONSTITUENT MATERIALS OF SANDCRETE BLOCKS 

These include cement, fine aggregate (sharp sand) and water.  

CEMENT: This refers to any adhesive and the material used in connection with block and it is referred to as “hydraulic cement” because the setting and hardening depends on the preserve of water. The cement widely used in civil work is called “Ordinary Portland Cement”.

FINE AGGREGATE: The two major types of sand used are white and coloured sand. The sand were not free from materials such as dust, silt, tree roots etc. The sources of sand include pits, rivers and sea.

WATER: Any type of water available can be used to mould sandcrete blocks. This includes water from stream, rivers, boreholes etc.

1.2  STATEMENT OF THE PROBLEM

Apart from bad mixing ratios, which happen even some sandcrete blocksproducers add more yield of blocks, some other things can cause blocks to be in bad condition which can affect the quality of the sandcrete produced.   

USING OF BAD CEMENT

Due to the prevailingadverse economic conditions, some sandcrete block makers tend to go for very cheap cement which may not have the required quality to bind a solid block. These block break soon after they are made. Some cement sellers who had cement keptin stock for so long sell it at give away price to the sandcrete block makers if the notice that the quality of the cement has detoriated. 

RE-BAG CEMENT

Another thing to note with cement is that some cement sellers re-bag cement, removing some  quantity of cement or put low quality cement product in a bag of a high quality and trust cement brand. Theration you thought you are using to produce a given quality has been compromised and it will produce a low quality block that can easily break even before it is being used for the project.

1.3 OBJECTIVES OF THE STUDY

· This project research will help us to understand the different strength of sandcrete blocks produced with locally excavated sand and River sand.

· This will also help to know the properties of Nsude sand after laboratory test has been carried out.

. This will help us in determining the moulding methods and properties of sandcrete blocks. These properties are determined by the ratio of block constituents such as cement, water and sand.

1.4  SCOPE OF THE STUDY

The scope of this project work is limited to obtaining the comparison of locally excavated sand with River sand in terms of strength in sandcrete blocks.(Nsude as case study).

1.5  SIGNIFICANCE OF THE STUDY

To help us understand the strength of sandcrete blocks produced with locally excavated sand and River sand in Nsude. To help us determine the properties of Nsude sand after carrying out laboratory test.