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Construction of Paddy Storage Silo Using Vetiver Grass and Clay

Thammanoon Hengsadeekul and Pichai Nimityongskul School of Civil Engineering, Asian Institute of Technology

Pathum Thani, Thailand

Abstract

The purpose of this research was to utilize vetiver grass and clay to construct a paddy storage silo. Vetiver grass has been used to reinforce clay slurry or adobe. Basically vetiver grass serves as reinforced fiber and clay as matrix. Before determining the physical and mechanical properties of the vetiver-clay composite, the properties of vetiver grass and clay must be separately determined. The vetiver-clay bundle was tested in axial compression, flexural, shearing, tensile, bearing, and density. The construction of a cylindrical silo demonstration having a diameter and height of 3 m and capacity of 10 t at the Royal Chitralada Project was made as a pilot project. Changes in the quality of stored paddy were evaluated in terms of moisture content, bulk density, and milling yield collected from various locations in the bin every two weeks for a period six months. During the storage period, ambient temperature and relative humidity, moisture content of paddy at the top, middle and bottom of the bin were recorded. The experiment showed that the quality of paddy stored in a vetiver-clay silo was unchanged.

Keywords: Vetiver grass, vetiver-clay composite, fiber-reinforced composite,

construction material, low-cost storage silo, thermal conductivity.

Introduction

His Majesty King Bhumibhol Adulyadej of Thailand has long expressed his ideas about vetiver, the wonder grass with proven potential in preventing erosion and conserving soil moisture, and its multifold applications. Through his initiatives and deep interest in vetiver, this research was conducted and aimed at transforming vetiver from simply being an agricultural material into a low-cost construction product; namely, the construction of a low-cost storage silo using vetiver-clay composite.

Rice is one of the most important agricultural crops in Thailand. After every harvest season, with a large number of paddy supplies in the market, the paddy price drops low. Farmers are required to sell their crop as soon as possible due to the lack of proper storage for paddy and financial support. If there are low cost and good quality grain silos that could maintain a large quantity of crop in a good condition for a long period, farmers may keep their paddy for a little longer. Research reveals that the use of rice straw-clay

composite was a possible form of grain storage. Vetiver is another ideal type of storage structure in developing countries, which seems to be very appropriate in Thailand where this grass is abundant. It is of interest to study some factors affecting the strength of vetiver-clay composites, and these factors are to be taken into account in the construction and design of vetiver-clay silos (Hengsadeekul and Nimityongskul 2003).

Research Background Utilization of Vetiver Grass as an Income-Generating Crop

The increase in the number of farmers in the light of limited fertile natural resources pushes farmers to bring in vertically integrating utilization of their farm yields to generate more income. Vetiver application is another alternative to be utilized as an income-generating crop. For some situations, vetiver roots and leaves can be replaced as natural materials or used as a mixing composite, which reduces the deterioration of natural resources.

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Vetiver roots can be industrially extracted for essential oil. Vetiver leaves can be used in handicrafts and for household decorative items. Besides, vetiver-clay composite can be used as building materials in the construction industry. Other uses of the vetiver-based products such as for cosmetic industry and pest controls have also been implemented. Fig. 1. To utilize the root of vetiver grass as an

income-generating crop, they are required to plant in plastic bags

The promotion of vetiver grass as an

income-generating crop and its development from merely being an agricultural waste to economical partial substitutes or raw materials would reduce environmental deterioration and deforestation. It would also reduce the importation of pulping paper, save energy, restore and maintain the fertility of natural resources, and finally bring about a better economy and living standards (Nimityongskul and Hengsadeekul 2002). Bin Construction Materials and Methods

The construction materials of a paddy storage bin that may be considered are wood, synthetics, reinforced concrete, metal, and indigenous materials. Selections of construction material that must be taken into consideration are the condition of use and application, location, and climate. Other influences to be accounted for are the strength of the material, economic aspects, construction techniques, progress rate of the construction work, physical and mechanical properties, such as moisture absorption, heat insulation, proof leaking, chemical affection, climatic conditions, refractory, and maintenance (Boumans 1985).

1. Wood is no longer used as a construction material for bins although in the past, it served well for smaller storage units. Synthetic materials (glass fiber reinforced polyester) have already been used successfully for small units, and it is quite possible they will be used for larger units in the future.

2. Metal bins are mainly used for smaller storage units and for provisional installations. The advantages of this bin are short construction time, providing a smooth surface and low co-efficiency of friction, easily installed inside an existing building, possible for a complicated design and easily enlarged with simple welding work. The limitations are demand of regular maintenance, chemical affection and corrosion, possible for the implosion caused by the vacuum inside the bins, the risk of condensation in steel counter-acted by heat insulation of wall and roof.

3. Concrete bins serve well for larger, permanent storage units that require a long life span and minimum maintenance. The advantages of concrete bins are the high storage capacities, unlimited in design, easy to construct corner curves, water and fire proof, very low chemical affection, low maintenance needs and easy to clean. The limitations are demand for stronger foundations to support a high dead weight, time consumption in construction, high construction costs, providing a rough surface of interior walls caused by residue, air bubbles, high co-efficiency of friction, loss of volume due to the thickness of walls, and occurrence of condensation.

Factors of Grain Deterioration

Respiration - Sign of Grain Activity: Research reveals that through the use of vetiver-clay composite, it was possible to construct paddy storage. It is of interest to study some factors affecting the strength of vetiver-clay composites, and these factors are to be taken into account in the construction and design of vetiver-clay silos. The major concerning factor is the respiration activity of paddy. See the diagram below: Paddy + O2 (air) CO2 + H2 O + heat

Paddy is a living organism and can develop a respiration mechanism. The process

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would be accelerated when there is a higher heat and moisture content; as a result, the paddy would respire more. The reaction is mostly found in a stored mass of wet paddy where it rapidly results in an increasing temperature. To reduce the process to a minimum, it is necessary to control the main physical factors of deterioration, which is a combined effect of temperature and moisture content and ambient gases. Biological agents such as insects, rodents and birds and technical factors like the length of time of storage, paddy condition, storage structure and packing are all related factors of paddy deterioration (Cruz 1989).

Experimental Investigation Experimental Program

A research on the right age of vetiver grass for harvest and mixture with clay was investigated. The preparation of raw materials and techniques in producing vetiver fiber-clay bundle was also studied. Furthermore, the research established the architectural and structural engineering design of a grain silo and the suitable materials to use to prevent rain-washing the surface. The experimental program is shown as follows:

Fig. 2. Flow Chart of the Experimental Program

Preparation of Materials Vetiver Grass and Clay:

In preparing vetiver grass and clay, only fresh vetiver grass should be used and must be dried for four to five days to reduce the water content to less than ten percent, and to prevent the occurrence of insects and fungi fertilization. Clay used for the fabrication of a vetiver grass-clay bundle must be cohesive and must have high plasticity. It should be fine, smooth and uniform, and free from impurities such as broken tiles, roots, twigs, or organic matter. Clay should be sun-dried (perhaps by crushing into small pieces) for at least four to five days to reduce its water content to less than five percent. Then, the sun-dried clay would be soaked in water at the ratio of 2:1 (clay : water) for twenty-four hours and mixed manually until a uniform slurry is formed.

Fig. 3. (above) Fresh vetiver grass and dried vetiver grass, (below) clay and sun-dried clay

Vetiver-Clay Silo Demonstration: Location: Royal Chitralada Projects Dimension: Diameter 3.00 m., Height 3.00

m., Lift up from the ground 1.20 m. (for outlet)

Capacity: 20 cu.m. (approx. 10 ‘Kwian’*) Structural Work and Additional Equipment:

Foundation: Reinforced concrete Ground Wall and Slab: Cement-block filled

with reinforced concrete Storage Wall: Vetiver-clay bundle and coated

with a mixture of fresh cow-dung, clay and chopped vetiver or rice husk

Roof: Bamboo structure thatched with vetiver bundle overlapping. Comprising of two layers, *Kwian is a Thai unit of volume equals to 2,000 L.

Vetiver Fiber-Clay Composite

Fresh Vetiver Grass

Sun-Dried

Preparation

Vetiver Fiber Bundle

Natural Clay

Clay SlurryComposite

Vetiver Fiber-Clay CompositeTesting

Part a & bProperties of VF & Clayaaaaaaaaaaaaaaaaaaa

1.1 Properties of VF- Natural Moisture Content- Water Absorption Test- Direct Tensile Strength

1.2 Properties of Clays- Specific Gravity- Moisture Content- Liquid Limit and Plastic Limit- Shrinkage Limit- Particle Size Analysis byHydrometer

Part dConstruction of

Vetiver-Clay SiloDemonstration to

evaluate thePerformance

Part cMechanical and Physical

Properties of VFCC

2.1 Direct Tensile Strength

2.2 Axial CompressiveStrength

2.3 Flexural Strength

2.4 Direct Shear Strength

2.5 Bearing Strength

2.6 Density of VFCC- ASTM D2395-83

Dried Vetiver Fiber Sun-Dried Clay

Parametric Studies

• Ages of Vetiver6, 12 and 18 months

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the lower layer with a vetiver-clay bundle and upper layer with a dried-vetiver bundle.

Heat Ventilation Whirl: Equipment used to ventilate the ambient temperature inside the silo.

Flow-Out Equipment: A framework of steel grating of 35 degree sloping down.

Fig. 4. Section of the vetiver-clay silo demonstration

Construction Process: 1. Foundation, Ground Wall and Slab:

The site’s layout was set up. Excavation to the existing soil level or lower than ground level of at least 0.60 m. was required, as it was the sufficient bearing load level. Compacting the bottom level with concrete or brick rubble and coarse sand. Pouring lean concrete, laying steel bars, installing dowel bar, casting concrete footing, and installing wall rebar were the next process. The lower wall of the paddy silo was constructed by using cement blocks filled with reinforced concrete. There would be an exit door for taking the paddy out.

2. Silo Wall: To do the silo wall, it is needed to do one by one layer. One layer comprises of four vetiver-clay bundles on horizontal and eight vetiver-clay bundles on vertical or about 35-40 cm height. The numbers of the layer depends on the height of the wall.

Fig. 5. Construction of foundation and lower wall

Fig. 6. (Above) vetiver grass, clay slurry and making of vetiver-clay bundle

(Below) laying the layers of vetiver-clay bundle The next layer could be done after complete drying the previous layer for a few days. In the process, clay slurry is used as binder. Strong sunlight accelerates the drying process. Increasing the layer by approximately 10% from the required height at each layer should be done in case of settlement. Moreover,

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during laying the final layer, in order to support the roof structure, the installation of dowel bars at every 30 cm of the silo’s perimeter would be required to join the reinforced concrete roof ring beam whose size is about 12 x 18 cm, or hard wooden roof ring beam whose size should be 5 x 15 cm.

Remarks: Clay used in the project was clay of the Rangsit series, which can be sorted out by Soil Taxonomy 1999 as very fine, mixed, semi-active, iso-hyperthermic sulfaqueptic dystraquerts.

3. Coating Process on Vetiver-Clay Silo Wall: The coating process could be done only when the silo wall is completely dried. The natural coating material should be prepared by using cow-dung mixed with clay, rice husk and water. The coat should be 1.0-1.5 cm thick, in order to prevent the vetiver-clay bundle from the rain. Then, the coating wall should be sun-dried for a few days. Maintenance in case the coating slips off is required to extend the life span.

Fig. 7. Coating process by using cow-dung mix

4. Construction of Roof Structure: Bamboo was the major material used for the paddy silo roofing structure. Bamboo with a diameter of four to five centimeters was used and laid on the roof ring beam and joined with a 5 x 10 cm hard wooden crossbeam. The center of the top of the roof was encircled with a ring and an opening of 40 cm in diameter for installation of a heat ventilation whirl. Then, the vetiver-clay bundle was laid on the lower layer of the roof structure as a ceiling for the prevention of heat and insects. The upper layer of the roof structure was composed of small pieces of bamboo and laid every 30 cm of the roof’s perimeter. The upper layer was covered

Fig. 8. Bamboo roof structure-lower layer with vetiver-clay bundle and upper layer with dried-vetiver bundle

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by bundles of dried vetiver grass as a shield from sunlight and rain. To protect the dried vetiver grass spread out from the wind, they were re-bound with a small piece of bamboo.

Results and Discussion Properties of Vetiver Grass

The physical and mechanical properties of vetiver grass were determined as shown in Table 1. It can be seen that the tensile strength at the bottom part of vetiver grass is higher than that of other parts. The weakest part of the vetiver grass is the node because there was a failure in the test at that point. As a natural organic fiber, it is rather difficult to obtain the exact value of the ultimate tensile strength of vetiver grass because of variations in the cross section, moisture content, the age of the vetiver grass, and some defects existing in the fiber.

Table 1. Properties of Vetiver Grass Item Description Average

Moisture Content - Dried Condition, %

18.58

Physical Properties

Water Absorption, % 197.52 Direct Tensile Strength ♦ Bottom Part, ksc. 233.79 ♦ Middle Part, ksc. 231.63

Mechanical Properties

♦ Top Part, ksc. 144.91

Properties of Clay

The physical properties of the clay determined by the Geotechnical Engineering Laboratory, School of Civil Engineering, Asian Institute of Technology was classified to be an inorganic clay which had clay properties of more than sixty-five percent as per the weight details as shown in Table 2. This clay is suitably used as a matrix in vetiver-clay composite and stickiness. After dried, the cohesive- ness of the clay is good and helps to bind vetiver grass together in wet and dry conditions.

Properties of Vetiver-Clay Bundle

Axial Compressive Strength: The average axial compressive stress of

all vetiver-clay composite was 25.80 ksc while

Table 2. Properties of clay

Item Description Average Moisture content - dried condition, %

4.8

Specific gravity 2.8 Liquid limit, % 63.5 Plastic limit, % 29.6

Physical properties

Shrinkage limit, % 13.4 the failure of specimens occurred due to the bucking of vetiver grass and separation between the vetiver grass and clay. Vetiver grass also serves as a fiber that contributes axial compressive strength to the composite bundle. The compressive strength of vetiver-clay composite would be increased if the bonding between vetiver grass and clay could be improved.

Fig. 9. Specimens under Axial Compressive

Strength Test and Flexural Strength Test

Flexural Strength:

The individuality of clay or vetiver grass has a little flexural strength while the combination between vetiver grass and clay inductively improves its flexural strength. The average flexural stress of vetiver-clay composite was 23.48 ksc and the average moment was 103.43 kg-cm. The average weight fraction was found to be 11.45%.

Shearing Strength:

The average shearing stress of the bundle was found to be 45.8 ksc, which was approximately 2.5 times higher than that of the straw-clay bundle. The vetiver grass culm/leaf contributed to improve the shearing strength of the vetiver-clay composite.

Tensile Strength: The individual clay is a low ductile

material; however, it increased when vetiver

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grass and clay are combined together. The average stress of a vetiver-clay bundle was 45.18 ksc. The failure of the specimens shows that tensile strength of the vetiver-clay bundle depends mainly on the tensile strength of vetiver grass.

Bearing Strength: In this test, the specimens were loaded

until the vetiver grass and clay separated. The bearing stress was reported at the first crack about 1.94 ksc. The weight fraction of the vetiver-clay bundle was found to be 11.16%.

Density: The specimens were tested in wet and

sun-dried conditions. The result of the density of the dried vetiver-clay composite was found to be 0.98 g/cm3 and the density of the wet condition was 1.39 g/cm3.

Fig. 10. Specimens for properties test Table 3. Properties of vetiver-clay bundle

Item Description Average

Moisture content - Wet condition, %

53.8

- Dried condition, % 8.4

Physical Properties

Density, kg/m3. 980 Axial compressive Strength, ksc.

25.8

Flexural strength, ksc. 23.5 Shearing strength, ksc. 88.6 Tensile strength, ksc. 45.2

Mechanical Properties

Bearing strength, ksc. 1.9

Results of the Vetiver-Clay Silo Demonstration

Temperature and Relative Humidity Inside and Outside Silo:

Fig. 11 shows that the difference of the temperature and relative humidity inside the silo was about 2°C (highest 33.5°C, lowest 31.5°C) and 10% (highest 70%, lowest 60%), respectively, while the difference of the temperature and relative humidity outside of the silo was about 7°C (highest 36.5°C, lowest 29.5°C) and 30% (highest 80%, lowest 50%). Hence, the temperature and relative humidity inside and outside the silo differed 3°C and 15%, respectively. Fig. 11. Graph of the temperature and relative

humidity inside and outside the silo

Test of Moisture Content and Quality of Paddy:

Fig. 14 shows that the moisture content in the paddy after being stored in the silo was slightly lower than that stored before in the silo (moisture content in the paddy on the date loading in silo was 13.50%). The paddy in the top and bottom layers of the silo had moisture content lower than that in the middle layer and the results of the moisture content for a period of six months was 13.10, 13.00, and 12.85%, respectively. The result of this difference was due to the higher temperatures from the roof and

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Fig. 12. Sampling boxes for paddy collection and

loaded paddy silo

better ventilation and moisture migration at the bottom of the silo, which was raised up from the ground. Meanwhile, the quality of brown rice and white rice remained unchanged. The result of the test showed that the total weight of brown rice was 74% (brown rice 49% and broken brown 25%) and the total weight of the white rice was 64% (white rice 28%, and broken white 36%).

Performance Evaluation: Vetiver-Clay Composite: Like unburned

clay brick, vetiver grass is used to reinforce clay slurry or adobe and serves as a reinforced fiber and clay as a matrix. The purpose of this application is to utilize and transform abundant indigenous materials into construction materials, which have good insulation. The advantage of this application is that it requires only exposure to sunlight to dry this product, while the limitations are that it is not waterproof and requires more durable coating material.

Fig. 13. Paddy test instruments (moisture content,

quality test of brown and white rice)

Fig. 14. Moisture content at various layers in the demonstration silo

Structure and construction work: The most

important feature to be accounted for is its structural strength, especially the strength of the vetiver-clay composite wall. In construction work, only wet vetiver-clay bundles need to be formed into a circle then dried before the next encirclement. Therefore, the suitable shape of a silo should be cylindrical with physical and mechanical advantages. Visual inspection of the demonstration silo after loading the paddy, showed no cracks on any part of the silo, but some blisters were found on the coating materials.

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Additional Equipment: Heat Ventilation Whirl (See Fig. 15.) -

Cool air running up from the bottom opening through the grating pipe would add ventilation to the inside of the silo, and the heat ventilation whirl on the roof would ventilate the outside of the silo. It is found that this equipment is very useful and necessary.

Conveyor Equipment - Vertical conveyors and screw conveyors are used for conveying paddy in and out of the silo. This is not necessary for a small silo.

Flow-Out Equipment - A framework of a cone metal grate of 35o downward slope would assist the flow-out of the paddy. By lifting up from the ground floor, the paddy would not have any contact with the floor.

Blowing/Ventilation Equipment - A ventilation motor/blower would accelerate ventilation inside, in case the paddy has a high moisture content. To be suitable with various degrees of moisture content in the paddy, the blowing speed, temperature, timeframe and expenses occurred need to be studied.

Fig. 15. Heat ventilation diagram

Conclusion

The following conclusions were reached after the completion of the research:

Vetiver-clay composite plays a vital role in being a good insulation material that can reduce the effects of temperature and relative humidity outside of the silos. This extends the storage period and maintains the quality of paddy.

Vetiver-clay silos having cylindrical features have proven suitable for structural integrity and construction work on load bearing wall system.

An opening at the bottom allows fresh air to move in and ventilate the heat and moisture up through the top of silo by using the heat ventilation whirl.

References

Boumans, G. 1985. Developments in

Agricultural Engineering, Series 4: Paddy Handling and Storage. Elsevier, Amsterdam, the Netherlands.

Cruz, J.F., 1989. Agricultural Engineering in Development: Warehouse Technique. FAO Agricultural Services Bulletin, No. 74.

Hengsadeekul, T.; and Nimityongskul, P. 2003. Utilization of vetiver grass as construction material for paddy storage. In: Thailand’s Technical Papers for the Presentation at ICV-3, pp. 70-82, ORDPB, Bangkok, Thailand.

Nimityongskul, P.; and Hengsadeekul, T., 2002. The Construction of Vetiver-Clay Composite Storage Bin. In: Summary Report of the Royal Project Foundation for 2002 on Research and Development Project on Vetiver Grass, pp.31-39. The Royal Project Foundation, Chiang Mai (in Thai).