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CLOSE THIS BOOKSmall-Scale Manufacture of Stabilised Soil Blocks (ILO - WEP, 1987, 204 p.)
CHAPTER IV. FORMING
VIEW THE DOCUMENTI. BUILDING STANDARDS AND BLOCKS
VIEW THE DOCUMENTII. COMPRESSIVE STRENGTH: DENSITY AND MOULDING PRESSURE RELATIONSHIPS
VIEW THE DOCUMENTIII. BLOCK FORMING METHODS
VIEW THE DOCUMENTIV. SOIL TESTING PRIOR TO PRODUCTION
VIEW THE DOCUMENTV. BLOCK SIZES
VIEW THE DOCUMENTVI. PROPOSED TECHNICAL STANDARDS FOR COMPRESSED SOIL BLOCKS
VII. SOIL BLOCK MAKING MACHINES
VIEW THE DOCUMENT(introduction...)
VIEW THE DOCUMENTVII.1. The CINVA-Ram press
VIEW THE DOCUMENTVII.2. The CETA-Ram press
VIEW THE DOCUMENTVII.3. Landcrete press/Presse Terstaram
VIEW THE DOCUMENTVII.4. Tek-Block press
VIEW THE DOCUMENTVII.5. Winget block making machine
VIEW THE DOCUMENTVII.6. Ellson Blockmaster Stabilised Soil Block Press
VIEW THE DOCUMENTVII.7. Consolid AG
VIEW THE DOCUMENTVII.8. Supertor block making machine
VIEW THE DOCUMENTVII.9. Maquina block making machine
VIEW THE DOCUMENTVII.10. Brepak block making machine
VIEW THE DOCUMENTVII.11. Zora hydraulic block press
VIEW THE DOCUMENTVII.12. Latorex system
VIEW THE DOCUMENTVII.13. Astram block making machine
VIEW THE DOCUMENTVII.14. Tecmor equipment
VIEW THE DOCUMENTVII.15. Meili 60 manual soil block press
VIEW THE DOCUMENTVII.16. Terrablock Duplex Machine
VIEW THE DOCUMENTVIII. WORLD SURVEY OF SOIL BLOCK MAKING EQUIPMENT

Small-Scale Manufacture of Stabilised Soil Blocks (ILO - WEP, 1987, 204 p.)

CHAPTER IV. FORMING

I. BUILDING STANDARDS AND BLOCKS

Several factors should be considered before starting a stabilised soil block operation. These include: the type of stabiliser to be used; whether the soil is suitable for stabilisation; whether the formed block will meet local building standards and whether stabilised soil blocks will be strong enough to be used as load-bearing elements.

One of the aims of this memorandum is to make the reader aware of the problems associated with the use of soil in the construction industry, especially in developing countries.

In the majority of developing countries, building standards are not yet developed or applied, especially in the field of soil construction. A number of current soil construction techniques are inefficient and wasteful of resources. The quality of the building materials produced can also be improved.

In view of the above inefficiencies, the International Union of Testing and Research Laboratories for Materials and Structures (RILEM), formed in 1983, a technical working committee for ‘laterite-based materials’. The objective of this committee was to produce an international draft building standard covering the use of stabilised soil building blocks. However, it is becoming increasingly clear that it is difficult to propose one set of building standards to meet all requirements throughout the world. For example, a minimum wet strength of about 1.4 MN/m2 has been recommended by a number of building authorities, while the soil brick specification of the state of New Mexico (United States) states that the average compressive strength of rammed earth soil bricks should be 2.04 MN/m2, and that only one out of five blocks may have a compressive strength of not less than 1.63 MN/m2.

There is, in general, a wide variation of acceptable standards which reflect, to some extent, local weather conditions. Blocks with wet compressive strengths of 2.8 MN/m2 or higher (i.e. minimum requirement for fired bricks and concrete blocks - see Chapter I, section III.1) should be suitable for one and two-storey buildings. Furthermore, they would probably not require external protection against the weather. For one-storey buildings, blocks with a compressive strength of 2.04 MN/m2 would probably be strong enough, but where rainfall is high, an external protective coating may be required. Since the wet strength of a stabilised soil wall may be less than two-thirds of its dry strength, all compressive strength tests should be performed on samples which have been soaked in water for a minimum of 24 hours after the appropriate curing period.

The final wet compressive strength of a soil block depends not only on the type of soil but also on the type and quantity of stabiliser that has been used, the forming pressure used to mould the block, and the subsequent curing conditions.

As stated earlier, the wet compressive strength of a stabilised soil building block is determined after the block has been totally immersed in water for a period of 24 hours. If the block is weighed before and after immersion, a moisture absorption figure can be determined.1 If this figure is greater than 20 per cent, the resulting external wall built with this type of block may need an external rendering to improve its long term durability.

1 This figure is equal to the percentage increase of the weight of the dry block after immersion in water for 24 hours (see Chapter V).

II. COMPRESSIVE STRENGTH: DENSITY AND MOULDING PRESSURE RELATIONSHIPS

Before discussing the principles involved in forming a stabilised soil block it is useful to analyse the relationships between the following variables: (i) the compressive strength of a block; (ii) its density and (iii) the moulding pressure used to make a block. These relationships have been investigated in a study on stabilised soil construction published by the United Nations in 19582 The study describes tests performed on two different types of soil from Burma, each stabilised with 5 per cent cement.

2 The study is described in Fitzmaurice, 1958.

The first relationship cited in the study is shown in figure IV.1 where the dry density is plotted against the dry compressive strength of the block.1 It can be seen that the relationship between dry strength and density is almost linear. It may be stated that the strength or durability of a block increases as the dry density increases.

1 The specimen used for the study are soil cylinders with a diameter of 76 mm and a length of 80 mm. The cylinders are crushed dry after a curing period of two months.

The second relationship cited in the study is shown in figure IV. 2 where the dry density is plotted against the compaction or moulding pressure for a series of tests at various moisture contents. This set of results is important because various machines and various methods of compaction will yield different results in terms of compressive strength. The main conclusion derived from the tests is that dry density increases as the compacting or moulding pressure increases. Dry density is also dependent upon the moisture content of a mix. It can be seen that, for a given compaction pressure, the dry density generally increases as the moisture content decreases.

The third relationship cited in the study is shown in figure IV.3, where the dry compressive strength of a block is plotted against the percentage moisture content of the mix. One set of blocks was made in a hand-operated toggle press which was believed to have a compacting or moulding pressure of about 4 MN/m2; the second set of blocks was made in a hydraulic power-driven press, exerting a compacting pressure of about 7 MN/m2. Results from the tests clearly indicate that the higher the compacting pressure the higher the dry compressive strength. They also show that the optimum moisture content (OMC) decreases with an increase of the compaction pressure (refer to points A and B in figure IV.3).

The importance of the moisture content at the time of testing has been emphasised by a number of authors2. Stabilised soil, in common with other porous building materials, is very sensitive to moisture content. The wet compressive strength is always considerably lower than the dry strength. It would be unwise to assume that a wall or pier will never get wet over the entire life of a building. For example, tests carried out on the Burmese soil (stabilised with 5 per cent cement) show that the wet compressive strength was in the range of 40 to 50 per cent of the air dry compressive strength. Consequently, buildings should always be designed on the basis of the wet compressive strength.

2 See Fiztmaurice, 1958.


Figure IV.1. Dry compressive strength-dry density curve

(Source: Fitzmaurice, 1958)


Figure IV.2. Relation between dry density, compaction pressure and moisture content

(Source: Fitzmaurice, 1958)


Figure IV.3. Relation between dry compressive strength, moisture content and compaction pressure

(Source: Fitzmaurice, 1958)

III. BLOCK FORMING METHODS

There are two basic methods of forming a block:

- at constant pressure; and
- at constant volume.

These two methods are briefly described below.

Constant pressure method

When using the constant pressure method to form or compact a soil mix in a mould, the mix is subjected to a uniform pressure which reduces the air voids in the material by moving the soil particles together. This internal soil particle movement lasts until the soil mix develops an internal pressure equal to that of the externally applied pressure, at which time no further compaction movement takes place.

The fixed external pressure, the moisture content of the soil mix and the initial quantity of material deposited into the mould determine the thickness of a block. The production of uniform blocks therefore requires that both the quantity and moisture content of the soil remain constant at all times.

Constant volume

When using the constant volume method, the external compacting pressure varies so that blocks of uniform thickness are produced even though the quantity of soil may vary. However, variation in the quantity of soil results in a variation in the density of blocks produced. Since density affects durability, a wall constructed with blocks of variable density will, in time, suffer from uneven erosion. Therefore, in both the constant pressure or constant volume methods, the weight or volume of a soil mix fed into a mould, as well as the moisture content of the mix, should be kept uniform. Frequent checks should be made to ensure the production of blocks of uniform thickness and density. A device that operates both at constant pressure and at constant volume produces more uniform blocks and is ideal for the production of stabilised soil blocks.

IV. SOIL TESTING PRIOR TO PRODUCTION

Chapter II described various soil testing procedures for determining whether a soil is suitable for block making and the type and amount of stabiliser which should be added. These tests are performed first, since positive results are a pre-requisite for setting up a production unit. Once production starts, the soil mix must be checked for each batch of blocks to determine its moisture content: the latter should be as close as possible to the optimum moisture content, (OMC). For this purpose, two simple ad-hoc site spot checks can be performed. These are described below.

(i) Pick up a handful of soil mix and squeeze it in the hand; the mix should ‘ball’ together and, when the hand is opened, the fingers should be reasonably dry and clean;

(ii) Drop the ‘balled’ sample onto a hard surface from a height of about one metre:

- if the sample completely shatters on impact, this indicates that it is not sufficiently moist;

- if the sample ‘squashes’ into a flattened ball or disc on impact with the hard surface, this indicates too high a moisture content;

- if the sample breaks into four or five major lumps, this indicates that the moisture content of the soil mix is close to the optimum moisture content (OMC).

The soil mixture can then be used for block making. However, to produce blocks of uniform size and density, special precautions must be taken to fill the mould with the same quantity of mix at each pressing. It is thus recommended to pre-weigh each mix. If this is not practical, a small wooden box or tin may be used to ensure that the same volume of mixed soil is used.

A few experimental pressings must be conducted before the correct amount of mixed soil is determined. It is also essential to consult the block machine manufactuer’s operational manual in order to ensure that the block making machine is properly used.

To facilitate demoulding of the blocks and to ensure good clean surfaces and arrisses, it is advisable to moisten the internal faces of the machine’s mould with a mould release agent (usually a form of oil), which can be applied with either a rag, brush or spray.

For low pressure block making machines (employing up to 2 MN/m2 compaction pressure), a mould release agent can take the form of a liquid mud mix. The latter may be simply made by adding a large amount of water to part of a soil mix. For higher compaction pressure machines (operating up to about 15 MN/m2), waste engine oil has often proved satisfactory. Several other mould release agents can be employed (e.g. diesel, kerosene, coconut oil or even liquid detergent). However, used engine oil should be both cheap and easily available.

Experience has shown that the mould should be oiled about every fourth pressing. Approximately 250 blocks can be produced from one litre of used engine oil. The quantity of mould release agent required will depend on the absorption characteristics of the soil.

The application of a mould release agent to the walls of the mould will ensure easier demoulding and produce stabilised soil blocks which better withstand weathering in the field.

If special blocks are to be made (e.g. hollow, grooved or frogged blocks), simple wooden forms should be used. These forms should be coated with a mould release agent at each pressing.

The mould box should be evenly filled and the corners well packed with a pre-determined quantity of soil mix. To obtain a good density block, it is advisable to compress the soil mix in the mould lightly by hand.

V. BLOCK SIZES

The overall dimensions of a block should suit the appropriate system of modular co-ordination in order to reduce the need for excessive cutting or the provision of special-sized infill blocks. The length and width are usually appreciably greater than those of the standard size brick. There are two main reasons for this larger block size: to increase the productivity of masons in wall construction and to reduce the volume of mortar used to cover joints.

Adobe (non-stabilised soil blocks) are normally square in shape and vary in size between 300 × 300 mm and 400 × 400 mm. These dimensions are usually required in view of the relatively low density and strength of these blocks. The relatively large block area results in a lower compressive stress to carry the vertical and lateral loads imposed by the total building weight.

Most countries currently use concrete blocks 400 mm long and 200 mm high, with varying thicknesses up to a maximum of 200 mm. These dimensions are not feasible for stabilised soil blocks because the production of good-quality blocks of this size requires relatively high compacting forces. It is therefore necessary to adopt smaller overall dimensions. It is traditional to lay concrete blocks with 10 mm thick mortar joints. If this is acceptable practice for wall construction, a stabilised soil building block 290 mm long, 140 mm thick and 90 to 100 mm high would be acceptable. With this suggested block size, the following standards should be met:

- with a mortar joint of 10 mm, a module size of 300 mm could be used;

- a double skin wall thickness of 290 mm would be possible;

- if a minimum wet compressive strength of 2.8 MN/m2 is achieved, a single skin wall thickness of 140 mm would be sufficient to carry the vertical and lateral loads in a single storey building (and probably two-storey buildings), provided the foundations are sufficient;

- good durable features should be achieved without the need for costly external protective renderings to resist weathering problems;

- with a density of about 2,000 kg/m3, an individual block will have a dry weight of about 7 kg which is easy for the mason to handle; and

- a wall thickness of 140 mm with a density of 2,000 kg/m3 should provide adequate thermal insulation even when external wall temperatures fluctuate widely. Furthermore, high thermal capacity will be obtained which should help reduce temperature variations inside a building.

VI. PROPOSED TECHNICAL STANDARDS FOR COMPRESSED SOIL BLOCKS

CRATERRE1, the international centre for research and the application of earth construction, recently proposed technical standards for lime stabilised compressed soil blocks. These standards are derived from a study of soil block making machines. They are reproduced in this section with minor alterations suggested by the authors of this memorandum.

1 The acronym CRATERRE stands for ‘Centre de recherche et d’application-terre’ (see Appendix II).

Block dimensions

The study related to blocks which were parallelepipeds with the following maximum dimensions:

Length: 400 mm (exceptionally 500 mm);
Width: 200 mm (exceptionally 300 mm);
Height: 200 mm.

A height of more than 200 mm would make an individual block too heavy for a mason to handle efficiently.

Currently manufactured block types have the following nominal dimensions:

Length: 295 mm
Width: 140 mm
Height: 88 mm

Dimensional tolerances:

Length: +1 mm; - 3 mm
Width: + 1 mm; - 2 mm
Height: + 2 mm; - 1 mm
Surface smoothness sides: + 1 mm; - 1 mm
Compression surfaces: + 3 mm; - 1 mm

Edge smoothness

The maximum sweep for edge smoothness is 2 mm. A roughness is tolerated as long as it is due to demoulding and manipulation. It may be noted that roughness of upper and lower block faces improve mortar joint adhesion as well as the shear resistance of a wall.

Caverns, holes, alveoles

Caverns, holes and alveoles are tolerated on the same terms as smoothness. The following standards are suggested: defects covering less than 1 per cent of exposed surface and less than 15 per cent of non-exposed surface.

Specific density

The suggested specific densities of blocks are shown below:

dry blocks:

- Minimum: 1,700 kg/m3


- Recommended: 2,000 kg/m3

wet (freshly moulded)

blocks

- Minimum: 1,870 kg/m3


- Recommended: 2,200 kg/m3

nominal volume of blocks: 3.634 litres.

Skewness of surfaces

A standard skewness of surfaces is recommended by the study. The exterior faces may be slightly oblique if prescriptions of dimensions, tolerances and forms are respected. The interior surfaces of hollow blocks should preferably be oblique. This is most desirable because it allows for easy demoulding immediately after compaction. The interior spaces of hollow or alveolar blocks may not have sharp corners.

Rugosity of exterior faces

The exterior face of blocks to be coated with mortar or renderings should preferably be rugous, while those which do not receive a coating must be smooth.

Clefts - scaling

These are not tolerated on any surface.

Gaps, cracks, crevices

Micro-cracks are tolerated on all surfaces; macro-cracks are tolerated only on non-exposed surfaces. The width and depth of these cracks may not exceed 1 mm whilst the length may not exceed 10 mm. The total number of cracks may not exceed the average value of one per 100 mm rib length.

Chipped edges

The width and depth of chipped edges may not exceed 10 mm.

Wall thickness of alveolar or hollow blocks

For all faces, the minimum thickness of solid material surrounding the alveoles or hollow blocks should be as follows:

- 35 mm for low pressure blocks (20 da N/cm2 or 2 MN/m2); and
- 20 mm for high pressure blocks (100 da N/cm2 or 10 MN/m2).

Minimal proportion of the load-bearing surface to the nominal surface of hollow blocks

The minimal proportion of the load-bearing surface to the nominal surface of hollow blocks varies with the compaction pressure used for manufacturing the blocks. It is superior or equal to 0.6 for low pressure blocks and superior or equal to 0.4 for high pressure blocks.

Scratches The following standards are suggested for scratches:

- maximum depth: 10 mm;
- maximum width: 15 mm;
- maximum area of scratches on surface: 100 mm2; and
- minimal distance between the edge and a deep scratch: 35 mm. Special blocks

Special blocks may be produced for specific purposes. Some of these are briefly described below.

Blocks with differential stabilisation: these have one or more surfaces or parts which contain more stabiliser than the rest of the block.

Blocks with built-in facing tile: these blocks have one or more surfaces decorated with a special facing tile.

Blocks with treated surface: these blocks have one or more surfaces especially covered with graphic elements or decorative elements treated with a chemical.

Resistance (compressive strength)

The following compressive strengths of stabilised soil blocks are adopted by a large number of countries:

- the dry compressive resistance after 28 days must be equal or superior to 2.1 MN/m2;

- the wet compressive resistance after 28 days (saturated humidification) must be equal or superior to 1 MN/m2.

The wet compressive resistance quoted above may be suitable for a dry arid zone but an external rendering coat of material would certainly be needed for weather protection. If it is possible to manufacture stabilised soil building blocks with a wet compessive strenght of 2.8 MN/m2, an external rendering application is not required.

When properly conducted tests have shown that wet compressive strengths approaching 2.8 MN/m2 can be obtained, it is appropriate to design higher building stresses and therefore accept the value of 2.8 MN/m2 as standard.

VII. SOIL BLOCK MAKING MACHINES

Although soil has been used as a building material for a very long time, variable climatic conditions have prevented a general adoption of this material, especially in temperate climates.

The production of acceptable quality stabilised soil blocks requires that soil mixes be compacted in order to reduce the air voids within the material and thus improve the strength of the block.

There are two basic methods of moulding a soil block:

- use of soil block presses; or
- casting a mud mix in forms or moulds by hand, using a tamping method.

The adobe block is usually produced with the second method, whereby water and a sandy clay soil are mixed into a mud consistency and formed into blocks. Chopped straw is often added to the mix to reinforce and minimise the drying out shrinkage cracks which will otherwise occur. Adobe block manufacture is illustrated in figure IV.4. The mix is thrown into a simple, open-topped wooden or steel mould form and tamped or pressed by hand to fill the mould space completely. The form is then removed and the operation repeated. After demoulding, the formed block is allowed to dry in the sun.

Sophisticated concrete block making machines exerting compacting pressures of up to 16 MN/m2 have been developed. They produce either a single or several blocks in a single operation. In the latter case, they are called egg-laying machines. These machines, usually expensive, use both direct pressure and vibration and are not suitable for the production of stabilised soil blocks: concrete mixes have a moisture content of about 40 per cent, while stabilised soil mixes have a moisture content of about 15 per cent. Different machines have therefore been developed for the production of stabilised soil blocks. Some of them are described below.


Figure IV.4. Adobe block manufacture

VII.1. The CINVA-Ram press

In the early 1950s, an engineer employed by the Inter-American Housing and Planning Centre (CINVA) in Bogota, Colombia, developed a constant volume soil block making machine which has since been known as CINVA-Ram. This machine is illustrated in figure IV.5.

1 Paul Ramirez from Chile.


Figure IV.5. The CINVA-Ram block making machine

The CINVA-Ram block press consists of a mould box in which a slightly moist soil mix is compressed by a hand-operated toggle lever and piston system. This machine has a tare weight of about 60 kg and employs a maximum compacting pressure of about 2 MN/m2. It could thus be classified as a portable tool for a ‘do-it-yourself’ builder for constructing small houses, walls and farm buildings. The all-steel machine produces blocks 290 mm long, 140 mm wide and 90 mm thick.

This machine has been used extensively in developing countries for the production of stabilised soil building blocks, with mainly cement used as a stabiliser. The following points are worth bearing in mind regarding the use of the machine:

- the initial amount of soil put into the mould box should be closely controlled; and
- the press will not have a long life if it is mishandled on a building site.

The VITA publication, Making building blocks with the CINVA-Ram press1 indicates the following advantages of this block making machine:

- stabilised soil blocks are easier to make than concrete blocks: they can be removed immediately from the press and stacked for curing without a pallet;

- the cost of building materials is greatly reduced, since most of the raw material is locally available;

- transport costs are reduced, since the machine is portable and the blocks are produced near to the construction site;

- if the quality of materials used is good, CINVA-Ram blocks can be superior to adobe and rammed earth;

- blocks are easily handled;

- blocks need no baking, since the curing process is completely natural; and

- the press makes variations of the blocks for the various phases of construction.

1 See VITA, 1977.

VII.2. The CETA-Ram press

The CETA-Ram press was developed by engineers from the Engineering Faculty of the San Carlos University (Guatemala) and researchers from the Centre of Appropriate Technical Experimentation (CETA-Guatemala). It is a modified CINVA-Ram press which allows the production of stabilised soil blocks with vertical holes. These blocks may then be used with vertical steel reinforcements in walls designed to better withstand earthquakes.1

1 The CETA-Ram press was developed in 1976, soon after the earthquake which struck Guatemala. The technological innovation was therefore in response to a real and pressing need to build houses which can better withstand the devastating effects of earthquakes.

A CINVA-Ram press was modified to manufacture stabilised soil blocks 320 mm long, 152 mm wide and 110 mm thick, with two 60 mm diameter holes passing through the thickness of the blocks. This machine, named the CETA press, is illustrated in figure IV.6. It is composed of three main parts:

- a main frame with the upper part forming the walls of a mould; the latter is fitted with a cover that swivels through 90°;

- a movable mould base plate which acts as a piston within the mould body; and

- the toggle mechanism and hand-operating lever.

Prototype CETA-Ram presses have been used extensively on an experimental basis in the building of rural housing. Results from these experiments show that the use of stabilised soil hollow blocks in the building of walls which must be reinforced with steel bars has two main advantages: it speeds up the work and reduces the cost.

In Guatemala, the CETA-Ram press was used for the production of blocks made from one part of cement and eight parts of volcanic material of the pumice type available in large quantities in the country. Produced blocks had compressive strengths ranging from 2.89 MN/m2 to 6.8 MN/m2. It is not specified whether these strengths apply to wet or dry blocks.


Figure IV.6. The CETA-Ram press

VII.3. Landcrete press/Presse Terstaram

The Landcrete block making machine was originally developed by Landsborough-Findlay Ltd. in the early 1950s. Two main models were introduced; a hand-operated toggle mechanism machine and a power-driven version. Both models are sturdy in construction and, according to the manufacturers, simple to operate. However, all references to this type of press are to be found in old literature. Several of the original Landcrete machines have been seen by the authors: in each case the machines were broken and were not operational.

The Landcrete press was partly redesigned and is now available from Belgian manufacturers under the name of ‘Presse Terstaram’. It uses a compacting pressure of about 4 MN/m2 and can produce various sizes of stabilised soil blocks from a 295 × 140 mm mould. It weighs about 350 kg. Figure IV. 7 illustrates the Terstaram block-making machine. It shows two operators applying the main compacting force (of 20 tonnes) via a lever arrangement to compact a soil mix. The compacting pressure developed in the machine shown in figure IV. 7 is 2.25 MN/m2, a marginally greater pressure than that applied by the CINVA-Ram press.

VII.4. Tek-Block press

The Tek-Block press was developed by the University of Science and Technology of Kumasi (Ghana). This hand-operated press is illustrated in figure IV.8. It was supposed to replace the previously used Landcrete machine considered unsuitable for Ghanaian conditions.

The Tek-Block press was supposed to overcome the following deficiencies of the CINVA-Ram press:

- some of the materials used on the CINVA-Ram press were too thin in section and tended to deform after relatively short periods of use;

- the adjustable piston guides did not perform well and were poorly adjusted by the workers in the field;

- the top plate locking arrangement of the mould was too weak and could be automated; and

- the mould size (290 × 140 × 100 mm thickness) was rather small considering the labour involved. It could be made larger.


Figure IV.7. Presse Terstaram block making machine


Figure IV.8. The Tek-Block press

Consequently, the Tek-Block machine is made almost entirely of 12 mm steel plate. It cannot be adjusted on site and makes a block size 290 mm long, 215 mm wide and 140 mm thick. It uses the same toggle mechanism as that of the CINVA-Ram press but the main operating lever arm is 2.4 metres long and is made from timber. Thus, if the mould is overfilled, the timber lever arm would break before any damaging stresses would be incurred by the machine. The compacting pressure of the Tek-Block press is about 1.5 MN/m2.

An additional major innovation concerns the covering lid of the mould; it is mounted on the upper handle socket assembly, and may thus be moved away from the mould with a movement of the main operating lever. The Tek-Block machine weighs about 90 kg. The first units of the Tek-Block machine tended to crack and some welds failed. These failures could be avoided with careful manufacturing.

Early site observations showed that a crew of five men and one Tek-Block machine could produce 150 to 175 blocks per day, if given proper incentives, whereas the manufacturers handbook claims a daily output of 200 to 400 blocks.

A powered version of the Tek-block press was developed in the late 1970s. It proved too expensive and the project was terminated.

VII.5. Winget block making machine

The first Winget, shuttle mould, hydraulic block making machine was developed in 1948 and tested in the United Republic of Tanzania where good-quality, stabilised soil blocks 305 mm long, 150 mm wide and 100 mm thick were produced. The compaction pressure was 9.45 MN/m2. The blocks produced had a satisfactory dry crushing strength of about 5.8 MN/m2 after a period of 21 days. A medium-range, clay-content soil was used with a 2.5 per cent addition of cement. Despite these excellent results, it became obvious that profitable production necessitated an increase in the machine output and re-design of some of its parts. This resulted in the development of the Rotary Hydraulic Block Press machine (illustrated in figure IV.9) which is claimed to have a consistently high output rate of 140 blocks per hour. This machine has a tare weight of about 1,150 kg and uses a compaction pressure of 9.5 MN/m2.


Figure IV.9. Winget rotary table mould machine

About 350 of these machines have been sold to some thirty developing countries. Owing to the high compaction pressure, the quality of blocks produced is very good and the production rate is three to four times greater than for a hand-operated machine. One disadvantage of this machine is the need to exert relatively high pressures which could damage the machine if it is not handled by skilled operators. In view of the high initial cost of this machine, demand decreased to such a level that it was decided to discontinue production in the early 1970s.

VII.6. Ellson Blockmaster Stabilised Soil Block Press

The Ellson soil block press was originally developed by Ellson Pty. Since 1978, it has been manufactured under license by Joshi Industries, Rajkot, Gujarat State, India. The latter firm renamed the machine the ‘Ellson Blockmaster Stabilised Soil Block Press’ (illustrated in figure IV.10).

The Ellson Blockmaster machine is an all-steel welded assembly, manually operated, which can produce block sizes of either 290 × 190 × 90 mm thickness or 290 × 140 × 90 mm thickness. It has a tare weight of about 210 kg.

The lever is usually operated by two men who stand on the projecting inclined leg ready for the pull down stroke; these men must apply considerable effort in order to achieved a maximum compaction pressure of about 7 MN/m2, although a leverage ratio of 500 to 1 is used. One significant feature of this machine is the height of the mould from the ground (about 850 cm). This height helps to reduce operator back-ache from bending down too low to remove freshly made soil blocks from the machine.

The manufacturer claims that a labour force of ten men is necessary to produce 750 blocks (290 mm × 190 mm × 90 mm) per day. This includes winning the soil; spreading it out for drying; sieving; mixing; filling the mould; pressing; and carrying away newly pressed blocks for stacking. Two of these machines have been seen in operation by one of the authors. In both cases, the daily output was in the range of 250 to 300 blocks. Each machine had to be rewelded at the lower end of the main operating lever on several occasions. This was due to the high stresses generated during the compaction stroke.

Depending on the nature of the soil and the stabiliser used, the manufacturer claims that well-stabilised dense blocks can be produced, and that the dry crushing strengths of these blocks vary between 4 and 12 MN/m2. Moisture absorption is much lower than that of ordinary burnt clay stock bricks.


Figure IV.10. Blockmaster Stabilised Soil Block Press

VII.7. Consolid AG

During the late 1970s, Consolid AG of Switzerland developed a new process of chemical soil stabilisation for use with cohesive soils on road construction projects. This process involves the use of three stabilising agents: Consolid 444, Conservex and Solidry. Consolid 444 is a silicone-copolymer resin solution which is first mixed with a quantity of water appropriate to the moisture content of the soil being used. Conservex is a type of bituminous emulsion used to enhance the waterproofing properties of Consolid 444. Solidry is a powdered polymer compound, with water resistant properties.

Consolid AG developed a mobile, stabilised block making plant ‘CLU 3000’. Powered by a 13 hp diesel engine (see figure IV.11), it has a tare weight of about 1,600 kg.

This trailer plant comprises a diesel engine, paddle mixer and feed unit, four cavity rotary table press, soil mixer and the necessary hydraulic components used for pressing. The pressing of a brick is manually initiated by the operator: the mould table rotates and the soil mix is compacted with a compaction force of 15,000 kg corresponding to a pressure of 4.8 MN/m2. The manufacturer claims that the dry compressive strength of such treated bricks is between 3.9 and 9.7 MN/m2. If higher strength bricks are needed, an addition of 1 to 3 per cent cement to the treated soil would result in compressive strengths greater than 10 MN/m2. It is also claimed that a crew of 4 to 5 workers can produce 3,000 to 4,000 bricks per day from one plant.

The authors have no direct experience of this type of machine but have received favourable comments from Ghana and Malaysia. In Ghana, for example, the Ministry of Works and Housing Test Laboratory tested, in 1977 blocks made on the CLU 3000 brick plant and obtained the following average results for stabilised soil blocks:

Dry compressive strength: 3.46 MN/m2;
Wet compressive strength: 1.99 MN/m2.


Figure IV.11. CLU 3000 stabilised soil block making plant

It should be noted that these results are below the figures claimed by the manufacturer.

VII.8. Supertor block making machine

Torsa Maquinas y Equipamentos Ltd. of Sao Paulo, Brazil developed the Supertor block making machine during the 1960s. This company manufactures a range of hydraulically assisted soil-cement block presses. Each machine weighs approximately 1,000 kg and is powered by a 5 hp electric motor. The machines are capable of producing about 20,000 blocks per 8-hour day. One particular model has a mould which can be subdivided to produce 4 blocks in one single pressing, each block measuring 230 mm × 110 mm × 50 mm or 200 mm × 100 mm × 50 mm.

VII.9. Maquina block making machine

This machine was developed during the early 1970s in Bogota, Colombia, and is now widely used in South America. It is a truly local, medium to low-cost machine.1 It operates on the principle of a pull-down lever, similar to that of the Ellson blockmaster machine. It can exert a compacting pressure of approximately 1.8 MN/m2.

1 Detailed description of the machine is provided in Roland Stulz, 1981.

VII.10. Brepak block making machine

Extensive research was conducted at the Building Research Establishment (BRE) in the United Kingdom during the late 1970s on the production of stabilised soil building blocks. It involved a field study of block-making machines available on the market and extensive laboratory studies on the process of soil stabilisation. One important conclusion derived from the studies is that stabilised soil can be an extremely useful building material for developing countries, provided that an adequate programme of testing is carried out on the raw material. Experimental research carried out in BRE indicates that compacting pressures in the range of 8 to 16 MN/m2 could give satisfactory and economical results for the production of good quality stabilised soil building blocks2.

2 See M.G. Lunt, 1980

In the early 1980s, the Oveseas Division of BRE developed a prototype block making machine, referred to as the Brepak machine (see figure IV.12). This machine weighs about 150 kg and produces stabilised soil blocks 290 mm × 140 mm × 100 mm.

Field trials in various parts of the world indicate that about 300 blocks can be produced, on average, during an 8-hour day. A compacting force of about 40 tonnes, equivalent to a compacting - pressure of 10 MN/m2, is exerted by a hand-operated lever hydraulically assisted to produce this pressure. Figure IV.13 illustrates the good-quality blocks that can be produced with this machine.

A joint Anglo-Kenyan research project indicates that large numbers of high-quality blocks may be produced with a Brepak machine. These blocks have the appearance of fired clay bricks and do not need any external rendering to resist the weather.1

1 For further details on this research project, see D.J.T. Webb, 1983.

The Brepak machine is now being used in about 25 countries and is commercially available from Multibloc Ltd., Bristol, United Kingdom (see Appendix IV).

VII.11. Zora hydraulic block press

A simple hydraulic press developed by Zora International Co., Ltd. (United Kingdom) in the early 1980s produces a wide range of stabilised soil blocks. The all-steel press has a mould which can produce building blocks 280 mm long, 125 mm wide and 100 mm thick. The manufacturer claims that this type of press can be operated by unskilled workers and is sturdily built to withstand rigorous outdoor operating conditions with little maintenance. There are three versions, each equipped with hydraulic power supplied from one of the following power sources: a 1 hp electric motor; a 5 hp petrol engine; and manual power. Each model weighs about 800 kg and is fitted with the same basic mould components mounted on an identical two-wheel chassis for easy movement on site.


Figure IV.12. The Brepak machine


Figure IV.13. Stabilised soil building blocks produced by the Brepak machine

An outstanding feature common to all three models is the high compacting pressure of 19 MN/m2 available at the mould head, resulting in a highly compacted, durable product with hardly any wastage during manufacture due to breakage or malformation.

This type of machine is undergoing site trials but no site production rates are yet available. The foregoing information has been taken from existing literature.

VII.12. Latorex system

A Danish firm, Drostholm Products, has developed a plant system for the high speed production of lime-stabilised laterite soil blocks. This plant can use only laterite soils for stabilisation. When compacted mixtures of laterite soil and lime are moist-cured at temperatures between 60 and 97°C over various periods of time, a good quality, durable building material can be produced. Curing at temperatures above 80°C and nearer to 100°C for 24 hours should further improve quality1.

1 For more details, see T.C. Hansen and T. Ringsholt, 1978.

The electrical powered plant developed by Drostholm Products comprises a soil drier, pulveriser, mixing machine and presses with an in-built steam oven for curing the manufactured blocks. A normal size plant has a capacity of about 12,000 blocks per 8-hour day, with an individual block size of 230 mm × 110 mm × 55 mm. It is claimed that steam cured blocks will have compressive strengths varying between 15 MN/m2 and 40 MN/m2.

VII.13. Astram block making machine

The Centre for Application of Science and Technology for Rural Areas (ASTRA) in India developed a hand-operated soil block making machine in the mid 1970s. This machine, referred to as the Astram block making machine, consists essentially of a mould in which a block is formed, a toggle lever mechanism mounted underneath the mould body and a frame to support the mould and toggle lever mechanism (see figure IV.14). The mould is interchangeable. There exist currently two sizes of mould for the production of the following block sizes: 300 mm × 145 mm × 100 mm, or 300 mm × 230 mm × 100 mm.


Figure IV.14. The Astram block making machine

From a design point of view, the Astram machine looks like a CINVA-Ram press which would be equipped with the toggle mechanism from the Ellson blockmaster without the projecting inclined legs. It can exert a compaction pressure of about 5 MN/m2. It is stated by the manufacturer that the Astram machine is superior to both the CINVA-Ram and the Ellson blockmaster machine.

VII.14. Tecmor equipment

The manually-operated Tecmor soil cement brick-making machine (model MRC-1)1 is claimed to produce up to 2,000 bricks per day in two sizes: 230 mm × 110 mm × 50 mm, or 210 mm × 100 mm × 50 mm.

1 This machine is manufactured by Equipamentos Meccanicos Ltda. of Brazil (see Appendix III).

The Tecmor machine looks like the CINVA-Ram machine but has improved vertical guiding to facilitate the compacting load application by the main lever arm. The compaction pressure of 2.5 MN/m2 is slightly higher than that of the CINVA-Ram machine. This is due entirely to a longer operating lever. The tare weight of this machine is about 85 kg.

Two other types of hydraulic machine are available under the Tecmor trade name: models HRC-1 and HRC-2. They are both powered by 7.5 hp electric motors. Each factory-installed machine has a production rate of 1,500 units per hour. Model HRC-1 is used for the production of two sizes of common bricks: 230 mm × 110 mm × 50 mm, or 210 mm × 100 mm × 50 mm.

Model HRC-2 is used for the production of two sizes of common hollow bricks (230 mm × 110 mm and 210 mm × 100 mm) and one size of solid bricks (510 mm × 230 mm). The above bricks can be produced in various thicknesses varying from 20 mm to 90 mm.

With the factory-installed machines, the company supplies a rotating sieve and a horizontal pan-type mixer which can mix a batch of 200 kg every three minutes. The above equipment can produce soil cement blocks with one part of cement to fifteen parts of soil. The manufacturer claims that, with about 10 to 15 per cent of water, this is the most economical mix for the production of stabilised soil blocks. However, the manufacturer recommends that tests should be conducted before deciding on a final mix.

VII.15. Meili 60 manual soil block press

The Meili Engineering Company (Switzerland) has developed an improved version of the CINVA-Ram machine, the Meili 60 manual soil block press. This particular machine, which operates on the principle of the off-centre press, is ruggedly built and achieves a compacting force of 20 tonnes, which equates to a compacting pressure of about 5 MN/m2 when producing 250 mm × 125 mm × 80 mm soil blocks1. The manufacturer claims that between 60 and 120 blocks per hour can be produced depending on the size of the labour force employed.

1 For further details on this machine, see SKAT, 1984.

As a result of the successful operation of the Meili 60 soil block making machine in field tests in Guinea, Nigeria and India, the firm developed a power-driven machine, the Meili Mechanpress. It is an automatic soil brick and block making machine based on the original turntable principle used for the Winget rotary table press machine. It is mounted onto a three-wheeled trailer complete with a built-in diesel engine developing 18.5 hp at 2,700 rpm, a horizontal pan type mixer of 150 litres capacity, various moulds and a rotary table press.

The moulds vary from a standard size of 250 mm × 125 mm to a maximum size of 300 mm × 150 mm. The machine can produce one block every 4 seconds. This machine is thus capable of producing about 1,000 high-quality soil blocks per hour. The tare weight of the machine is 1,700 kg.

The authors have no first-hand experience of the above two presses. However, the description in the manufacturer’s catalogue tends to indicate that they include a number of improvements over other similar machines.

VII.16. Terrablock Duplex Machine

The Terrablock Duplex trailer-mounted machine, powered by a 43 hp diesel engine, can produce 300 mm × 250 mm × 100 mm adobe soil blocks at a maximum rate of 10 blocks per minute. This process uses wet soil from the ground and a built-in computer controls the fully automatic operation of block manufacturing.

The main hopper holds enough soil for 10 minutes of continuous operation. A heavy duty, built-in sieve filters out debris and oversize particles, while a vibrating device to the hopper head ensures a consistent flow of soil into the block moulds located at the lower end of the hopper.

A horizontally-mounted, double-acting hydraulic ram is employed to compact the soil within a mould. After compaction, the block is automatically ejected from the mould onto a simple conveyor belt.

The manufacturer claims that the operation of the machine is a simple one-man task. As long as the hopper remains loaded with soil, the machine will automatically produce three to five blocks per minute from each of the two moulds. Enough blocks may thus be produced in one hour to construct a 9 m2 wall 250 mm thick.

The soil used in this process is not stabilised, and the resulting blocks would therefore be called adobe blocks. It is thus essential to treat a Terrablock wall with a fast drying chemical sealant before applying a finish coat of external rendering to prevent erosion.

The Terrablock adobe block making machine is illustrated in figure IV.15.

VIII. WORLD SURVEY OF SOIL BLOCK MAKING EQUIPMENT

The purpose of this chapter is to draw attention to the various types of forming devices available on the market for the production of stabilised soil building blocks.

The presses described in the previous section and others listed in table IV. 1 are obviously not the only ones available on the market. Many other presses produced in both developing and developed countries are currently marketed, but the authors could not obtain information on these presses when this memorandum was being prepared. Additional names of manufacturers and/or suppliers of stabilised soil block making machines are given in Appendix IV, including a very brief description of some of the machines. It must be emphasised, in this context, that the mention of equipment suppliers or manufacturers in this publication does not imply a special endorsement of these by the ILO. The names listed are only provided for illustrative purposes and potential producers of stabilised soil blocks should try to obtain information from as many suppliers as feasible.


Figure IV.15. The Terrablock adobe block making machine

Table IV.1. Survey of soil block making machines
IV.1 A: Block making machines described in Chapter IV

Name

Country of origin

Approx. year introduced

Manual (M) or power (P) operation

Gross weight
(kg)

Compacting pressure
(MN/m2)

Max. daily production rate

No of workers

Approx. price
(US$, 1985)

Maximum block size(mm)

Astram

India

Mid 1970s

M

110

5.0

n.a

3-4

375

300 × 230 × 100

Brepak

United Kingdom

1979

M

140

10.0

300

3

1,300

290 × 140

Ceta-Ram

Guatemala

Mid 1970s

M

80

2.4

250

3

450

290 × 140 × 90

Cinva-Ram

Colombia

Early 1950s

M

60

2.0

350

3

300

290 × 140 × 90

Consolid AG

Switzerland

Late 1970s

P

1,600

.8

3,500

62

20,000

250 × 120 × 75

Ellson Block-master

India

Early 1970s

M

210

7.0

750

102

- -

290 × 190 × 90

Landcrete/ Terstaram

Belgium

About 1950

M

320

4.0

1,000

72

1,000

295 × 140 × 90




and P

2,100

2,000


18,000


Latorex system1

Denmark

Mid 1970s

Factory

- -

5.0

12,000

- -

- -

230 × 110 × 55 × 60

Maquina

Colombia

Early 1970s

M

170

1.8

180

4

- -

200 × 150 × 40

Meili

Switzerland

Late 1970s

M

120

5.0

500

- -

700

250 × 125 × 80




and P

1,700

7,000


Supertor

Brazil

Mid 1960s

P

1,000

6.0

20,000

- -

230 × 110 × 50

Tecmor

Brazil

Late 1970s

M

85

2.5

2,000

6

- -

230 × 110




and P

2,500





x 50

Tek-Block

Ghana

Early 1950s

M

90

2.0

250

3

240

290 × 215 × 140

Terrablock

USA

1985

P

5,350

- -

4,800

- -

80,000

300 × 250 × 100

Winget

United Kingdom

1948

P

1,100

9.5

1,150

5

- -

300 × 150 × 100

Zora

United Kingdom

1982

M

230

19.0

- -

- -

3,000

280 × 125



and P

850





× 100

- - = Not available.

IV.1 B: Block making machines not described in the text3

Name

Country of origin

Approx. year introduced

Manual (M) or power (P) operation

Gross weight
(kg)

Compacting pressure
(MN/m2)

Max. daily production rate

No of workers

Approx. price
(US$, 1985)

Maximum block size(mm)

La Palafitte

France

1975

M

- - -

1.4-2.0

240-320

3

- - -

290 × 140 × 90

CENEEMA Earth and Loam Block Press

Cameroon

1979

M

- - -

- - -

320-480

3

- - -

300 × 140 × 110

AVM Block Press

F.R. Germany

1984

M

- - -

- - -

320-480

3

- - -

- - -

SISD Dirt-Cement Brick Press

Thailand

- - -

M

- - -

- - -

320-480

3

- - -

- - -

MARO Block Press

Switzerland

- - -

M

- - -

- - -

320-480

3

- - -

- - -

CTBI Block Press

France

- - -

M

85

- - -

400-720

3

- - -

290 × 145 × 110

UNATA Press

Belgium

- - -

M

80

- - -

320-480

3

- - -

290 × 140 × 90

A.B.I. Block Press

Cte d’Ivoire

- - -

M

- - -

- - -

320-480

3

- - -

-

CTA Block Press

Paraguay

- - -

M

- - -

- - -

600-700

4

- - -

- -

GEO 50

France

- - -

M

100

- - -

160-400

2

- - -

290 × 140 × 90

SATURNIA

Switzerland

1983

M

200

- - -

800-1,200

3

600-1,000

- -

RIFFON Block Press

Belgium

- - -

M

150

- - -

800-960

3

- - -

220 × 105 × 60

CRATERRE PEROU
Block Press

Peru

1982

M

230-280

1.5-2.0

800-960

5

- - -

280 × 280 × 80;
280 × 128 × 80

CERAMAN
Manual Press

Belgium

- - -

M

330

2.1

1,600-2,400

4

- - -

220 × 107 × 70

SEMI-
TERSTAMATIC

Belgium

1953

M and P

765-925

- - -

2,500-5,000

- -

- - -

220 × 105 × 60;
295 × 140 × 90

CERAMATIC
Automatic
Brick Press

Belgium

1953

P

1,650

6.3

12,000-

2

- - -

220 × 107 × 70

LESCHA SBM

F.R. Germany

1976/84

P

- - -

8

5,600

4

- - -

250 × 130 × 75

ECOBRICK 1000

Switzerland

1984

P

600

3-10

800

2

- - -

250 × 120 × 75

TERRE 2000
Presse TMR6750-40

France

1984

P

1,800

9

2,400

- -

- - -

300 × 150 × 150

GEO 500 Semi-Bloc

France

- - -

P

- - -

- - -

1,350

2

- - -

295 × 140 × 90

ULTRABLOC
IMPACT 1 and 2

USA

- - -

P

1,000-1,200

- - -

1,700-2,400

- -

- - -

305 × 140 × 90

TERRA BLOCK
Duplex

USA

- - -

P

3,700-

5-8

2,800-4,800

4

- - -

305 × 140 × 90

Lorev

Italy

- - -

M

150

3.0

- - -

- - -

- - -

300 × 150 × 60

PPB Saret (Teroc)

France

- - -

P

- - -

- - -

800

- - -

- - -

- -

Raffin

France

- - -

M

- - -

2.5

300

4

- - -

260 × 130 × 80

1 The Latorex blocks are steam-cured whilst all the others are atmospherically cured.

2 Estimates include labour for soil preparation and mixing.

3 The information contained in Table IV.1.B is provided for illustrative purposes only. The productivity and other data shown in this Cable have not been checked for accuracy by the ILO. The reader is therefore urged to obtain additional information from the manufacturers listed in Appendix III.

- - = not available.

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