South Rift Civil Chapter

Interlocking Soil Block Technology in Kenya’s Construction Industry 

Housing perspective

Many Kenyans are unable to own houses due to the high cost of building materials. The value of new private building built with block and mortar has been reported to increase by 10.2 per cent from 2016 to 2017. It is estimated that in urban areas, housing needs stand at 150,000 units per year. Yet only 20,000-30,000 units are constructed within the same period, giving a shortfall of over 120,000 units per annum. This shortfall has been met through proliferation of squatter and informal settlements and overcrowding.

To meet the need for adequate housing of Kenya’s population, sustainable investments and continued innovations have been proposed. This has led to development of alternative building materials and technologies.

Masonry construction

Masonry can be regarded as an assemblage of structural units in a particular pattern either bounded by mortar or dry stacked. Besides load bearing, masonry walls are used to partition spaces. Fig. 1 indicates that masonry walls can be constructed by bounding them with mortar or staking them together.

Fig. 1: Masonry construction techniques

Interlocking stabilized soil block (ISSB) technology

This is a technology in which masonry walls are constructed by stacking blocks together. Mortar layers are eliminated and instead the block units are interconnected through interlocking system of the blocks. The blocks are made plumb by help of a wooden or rubber hammer to knock them gently into place. When laying the first course, care must be taken that the blocks are perfectly horizontal and in a straight line, or at right angles at corners. The walls are finished at top below the roof with a ring beam.

ISSB technology has been found suitable in constructing bungalows and maisonettes (47%), with least application to storey structures (3%) (Fig. 2). Material selection by developers is mostly influenced by strength and durability of masonry units. This however, need to be guided by the use of the structure as compared to the kind of the materials being utilized.

The use of a structure greatly determines the type of material to be used. Besides meeting the requirements of the client, the material should ensure sustainability of its use. Therefore, as depicted in Fig. 2, the guiding aspects of utilizing ISSB technology is expected load to be carried, use of structure and importance of structure.

Fig. 2: Preferred walling structures for ISSB technology construction

Performance of interlocking stabilized soil block walls

The three most preferred qualities of ISSB are non-use of joining mortar, ease of construction and natural aesthetic (Fig. 3). However, durability remains to be the main challenge. This can be averted by additives that increase the blocks resistance to abrasion and water absorption.

Fig. 3: Performance rating of the ISSB technology

Factors affecting adoption of ISSB technology

The ISSB have been found to meet the minimum requirements of Kenyan design standards while the walls performance is equally satisfactory compared to mortar bonded masonry. However, there are many factors that affect the adoption of ISSB technology. Fig. 4 indicate that lack of information (56%) hinders the most. Therefore, deliberate campaign awareness should be carried out supported by construction of demonstration projects. Besides documentation of the ISSB technology advantages, there is need to develop a framework for its use on different construction sites so that home owners can be able to experience its performance.

Fig. 4: ISSB technology adoption index

In Kenya, there has been advocacy of conventional materials with aim of using stronger and prestigious material. This has been compounded by the pressure from modernization leading to development of attitude to construction materials. Since the blocks are made of soil, some developers have a feeling that ISSB is reversing the progression of such trend.

The training of construction designers in Kenya has majorly been towards use of conventional materials. The lack of trained personnel coupled with unclear code of standard for the ISSB technology has led to its little specification by the designers for consideration by the clients. This has made earthen construction to be regulated as unapproved and un-regulated material. The present adoption has therefore been left to the premise of the current procedure based on experience, previous use and knowledge gained on site.

Conclusion

Interlocking soil block technology has been used constructing different masonry structures. Its performance on load bearing has been found satisfactory as compared to mortar bounded block masonry. The adoption rate however, is low. Realization of affordable and decent housing as envisage in the Big Four Agenda blue print can be accelerated though adoption of alternative building materials. This will be realized through an elaborate framework for inclusion of alternative building materials in the construction industry.  Deliberate campaigns through demonstration projects and training of skilled persons will increase the technology use. Finally, for the designers to specify use of the interlocking soil block technology, clear and elaborate design standards need to be developed.

What is your experience with interlocking bricks? Do you have any modifications that you have made in the application interlocking bricks? 

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Author Profile 
Sanewu I. Fundi, PhD
Graduate Engineer