INVESTIGATING STRAW BALE AS A WALLING MATERIAL

INVESTIGATING STRAW BALE AS A WALLING MATERIAL

ABSTRACT

This project is the investigation of mechanical properties of straw bale as a walling material in building construction. Straw which is a local material, which is more economical than other conventional walling materials could be used as an elements in building when baled. This study shows the edges that straw bale has over other conventional walling materials (sand crate block), availability, ease of constructions, economical amongst others. The minimum plaster thickness (coating) which when applied to the straw bale wall that can give the optimum strength was found to be from 15mm-20mm this is obtained from compressive strength test.

CHAPTER ONE

1.0 INTRODUCTION
1.1 BACKGROUND OF THE STUDY
In the construction industry today, the need to construct buildings with materials that are viable, affordable, easily harnessed, and sustainable has become a necessity as to the fact that the prices of conventional building materials are sky rocketing by the day and are getting limited in terms of their availability. The construction of building with materials that are workable, low cost, and plentiful has become factors to consider in the construction industry.

Straw bale is one material that has proven to have all the requirements earlier stated. Straw bale buildings have high compressive strength, energy efficient, and could withstand bad weather conditions (Roger, 2002).
Likewise, Chuck Bruner (1970) said “after the earthquake, there wasn’t a single crack in the house.

Straw bale is a renewable resources and it is grown annually and are found in large quantity around the country. The straw from the harvest homes of the United States major grains could be used to construct five million, two thousand square foot house every year (Matts, 1978).

This straw bale is a plant structure between the root crown and the grain head and it is composed of cellulose, hemi-cellulose, and silica, some of the plants that produce straws include wheat, rice, oats, and barley. Straw bale are mostly harvested by farmers and are usually made by them (unskilled labour) which makes building with straw bale easy and workable (King, 1998).

Straw is appealing as a building material for several reasons, first of all in grain production, straw is inexpensive and since straw is a secondary waste material from grain production, most at times used as food for animal bedding while some farmers also burn them in open field producing significant air pollution, releasing much of carbon monoxide into the atmosphere which could lead to the depletion of the ozone layer, In some areas most straws are tilled back into the soil, there is also evidence that too much straw may not be good for soil, and will throw off the balance between soil bacteria and fungi, reducing soil fertility, so if all this straws are put into better use as to be used in the construction industry, problem of soil infertility and ozone layer depletion will be greatly reduced (Butchart, 1994).

The bales are masses of straw compressed into rectangular block shape and bond together with steel wire or propylene twine. The springy tubular stalks of rectangular blocks are bound with steel wire or propylene twine (Harvest Homes, 2004).

With the increased industrialization of farms, other types of the bales are beginning to predominate in many areas, shapes, and sizes:

1. Jumbo bale: Rectangular blocks which consist of two types, the small ‘two-string’ rectangular block which is 18 in (460mm) wide, by either 14 or 16 in (350 to 400mm) high, and 32 to 48 in (0.8 to 1.2m) long. And the three-string “commercial bale” which is 21 in wide, by 16 in high, by 3 to 4ft long. These sizes range from 40 to as much as 100 pounds (18 to 45kg). Even larger “bulk” bales are now becoming common, 3 by 3ft (1 by 1m), or 3 by 4ft (1m by 1.2m) by 6ft (2m) long and bales of 4 by 4 by 8ft (1.2 by 1.2 by 2.4m) long, weighing up to a ton.

2. Circular bales: Disks bound with twine of typical dimension 4 to 5ft (1.2 to 1.5m) in diameter and up to 3ft thick and are machine handled.

3. Super compressed bales: Ordinary bales compressed to roughly twice the original density.(Chris, and Catherine, 2002).

There are two primary ways of building with straw bales.
i. Load bearing or Nebraska style.

ii. Post and beam / In – fill / non- load bearing method
 

In load bearing straw bale construction, bales are stacked and reinforced to provide structural walls that carry the roof load. While in post and beam method, a wood, metal or masonry structural frame supports thero of and bales are stacked to provide non- structural insulating walls.With either alternative, the bale walls are plastered or stuccoed on both the interior and exterior of the wall. The study will be based on the former.

The load bearing straw bale construction employs relatively simple techniques that are forgiving to novice builder and yet have sufficient flexibility to allow the creation of design features such as curved walls(King, 1998).

Moreover, a straw bale demonstrates excellent insulating properties such as thermal, sound and fire resistance. Also the structural capacity of the straw bale construction is surprisingly good (Adedeji, 2007).

It should be added that the technology of straw bale construction is still rapidly evolving .It is highly rated for ‘build ability’ because it can bevery straightforward. And it is important to keep bales during storage and construction and to try and eliminate vermin. During construction, tarpaulins or plastic sheets should be kept ready for covering otherwise vermin’s may destroy unprotected walls. Although it may not be dried, if bales do get wet slightly, they can often be dried out sufficiently to be usable.Lastly, it has been found that straw bale walls are very resilient and in the event of damage they can be repaired. Wet bales can be taken out and replaced (Harvest Homes; 2004).

1.2 AIMS AND OBJECTIVES
i. To evaluate the Compressive Strength of straw bale as a walling material (Plastered straw bale wall and un-plastered straw bale wall).

ii. To assess how available and low cost straw bale material could be in building construction.

iii. To make appropriate recommendation.

1.3 SCOPE
– Determination of the strength of straw bale (load – bearing type) in building construction.
– Evaluating the compressive strength of straw bale as a walling material.
– Comparison of the cost of using straw bale in building construction to sandcrete block.

1.4 LIMITATIONS OF STUDY
This study may be limited in terms of getting unskilled labour in caring out the block production in large quantity and getting adequate information concerning the specified building material as it is not well recognised as a method of construction in the construction industry. Time constraints may also affect the level of detailing required of this study.

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