Interlocking hollow core blocks in Journal of Architecture

Interlocking hollow core blocks Author: Anil Laul
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INTERLOCKING HOLLOW CORE BLOCKS
An Environment Conscious Sustainable Building Product / Technology

Issues & Basis

Shelter is a basic human requirement affecting the largest number of people worldwide. The building Industry accounts for nearly half of the GNP of most nations. It is interesting to note the following points regarding buildings and building related activity:

The building industry is the largest consumer of resources whether it is materials, capital or energy.
It causes the largest amount of environmental degradation as a result of quarrying, mining process, depletion of natural resources.
It is also one of the largest progenitors of waste output, for example, construction debris, etc.
Building materials produced in industrial processes are responsible for pollution and global warming.

·         Monopolised Industrial processes increase cost of building products resulting in a rubber-stamping effect of products and negating a response to locally available materials and needs.

·         The building industry is second only to agriculture in providing employment for the maximum number of people.

Walling materials constitute approximately 30% of construction and the largest mass and surface area of a building.

·         They account for the maximum capital resource in the structure.

·         They have the largest surface area and account for maximum recurring maintenance costs.

·         Failure of the walls is the single largest factor responsible for the collapse of structures in case of calamities such as earthquakes.

·         Maximum thermal exchange in a building takes place through walls.

Unfortunately, apart from high technology surfacing materials that have emerged over the years, the basic performance criterion required of a walling material remains unexamined. The entire development has revolved around stronger walls to give more resilient surfaces whereas logically the decisions should have been based around   resilient surfaces with lean back up materials for the body of the wall.

The strength requirement of a walling material rated at 150 Kgs/sq cm in itself is a fallacy. The soil bearing capacity is usually 2 to 3 Kg/sq cm and the load on a wall is less than 1 Kg/sq cm per floor. The high compressive strength of a walling block is the direct consequence of its surface requirements. The ideal block would therefore require a resilient non-erodable surface with a lean backup body material. Another important criterion should be the feasibility of manufacture at the site, with minimal capital.

                        Uniformly distributed load on wall is less than 0.5 kg / sq. cm.

                        Soil bearing capacity is less than 3 kg / sq. cm.

Why does the walling material require a strength of 150 kg / sq. cm.?

Crushing strength of any walling material is a direct consequence of impermeable surface requirements.

The hollow core interlocking blocks address all these issues comprehensively. The analytical approach results in a sustainable product that results in reducing environmental impacts, integrates efficient use of resource, resists earthquakes, is locally responsive and promotes greater equity.

The hollow core interlocking blocks have these intrinsic characteristics:

Impermeable non-erodable diaphragm with colour and texture.
Lean back up material for the body of the block with rationalised crushing strength. Appropriate locally available material such as fly ash, burnt rice husk, stablised mud or exfoliated vermiculite may be used.



The system rationalises the building product industry and the procedure in order to

Minimise waste.
Facilitate localized production and material usage.
Suit individual needs and aesthetics.
Promote micro enterprise.

Integrating the Architect, Engineer, Artist, and the Artisan

CONSTRUCTION PROCEDURE

A mould of mild steel of the required shape and size is manufactured as shown below
The male and female profiles are made to interlock. The desired impermeable diaphragm is laid at the bottom of the mould, which could be waste material such as stone, broken tiles or PVC chips (A laterally inverted pattern is sketched on a piece of paper and PVC chips are glued on, forming the exterior non-erodable diaphragm.)

Rich cement slurry is poured over the first impermeable diaphragm. A lean backup material (fly ash, burnt rice husk, mud) is then laid over and compacted. A pipe is then inserted in the mould. The balance mould is filled up leaving enough space to finish the second impermeable diaphragm if so desired.

Marble powder is spread over the finish, which acts as a dewatering agent. This is washed using a soft paintbrush and water. The pipe is removed first by rotating it gently. The block is de-moulded after few minutes of casting and cured for 48 hours before usage.

Every action is Best performed at the lowest level that it can be Best performed

ADDITIONAL BENEFITS

Simple procedure -universally accessible.
Integral permanent finish – lower maintenance costs
Does away with expensive scaffolding for post- construction finishing.
Horizontal bore allows for easy handling by the mason.
Filling the hollow core with waste polyethene can increase thermal insulation.
A technology that cuts across economic barriers.

Using interlocking blocks as a base, several adaptations are possible. Holes on both sides are also possible in order to accommodate additional services if required.

Interlocking blocks with holes in both directions

LEARNING FROM TRADITION

Year after year we have to contend with natural disasters such as earthquakes and cyclones. Today’s walls unfortunately are the most susceptible, owing to their inability to withstand horizontal thrust. Reinforced cement concrete bands do solve the problem to a certain extent but the life span of such solutions is often environmentally questionable. Feasible solutions however to withstand these thrusts, involve prohibitive costs. Yet traditional practices in the Maharashtra region of India, in and around Pompeii, southwards from Naples, Dresden in Germany, and Palestine used very simple variations to counter problems of lateral thrusts during earthquakes and cyclones. Traditional solutions also existed for containing the swelling or contraction of soil in black cotton soil areas. Stone masonry was used diagonally in order to absorb lateral vibrations.

There must have been good reason for the use of diagonal stone bonding in areas with black cotton soil and in earthquake prone areas. The principles were sound and the contemporary adaptation could very easily bring a turn about in the construction industry, which is consuming vast quantities of natural resources with every problem encountered.

So that the walls may withstand tension, within the engineering practice we add steel – an expensive resource. One has often only to look back and examine the wisdom of the past and dovetail it with the developments of today to arrive at appropriate solutions. Using the plasticity of concrete the simple moulding process delivers an interlocking block with tremendous resilience against horizontal thrusts and the resultant tension.

Examples of diagonal bonding in Pompeii (left above), Naples (left below) and Guatemala (right)

TYPE OF BONDS

Diagonal interlocking to resist lateral thrusts and better load distribution in unpredictable soils.

The diagonal bond has been developed to resist lateral thrusts during an earthquake. These thrusts are transferred diagonally to the foundation.

The diagonal bonding also allows better load distribution while building on unpredictable soils such as black cotton soil, which have a tendency to swell and shrink.

In case of differential settlement of soil the corbelled arch action prevents cracks and in case of swelling, this bond works in reverse and helps in a more even distribution of the loads, thus avoiding collapse.

Mother and Child Centre at New Dudhai, Gujarat

Interlocking Blocks were primarily designed for the earthquake-affected region of Gujarat, India. The entire state, measuring some 10,000 sq. kms, was affected on January 26th 2001. It has been used in the “Mother and Child Centre” and Primary School in the village of New Dudhai, Gujarat, India. Several earth tremors measuring 4.5-5.8 on the Ritcher scale shook Gujarat after the ‘Mother & Child Centre’ was built. The severest of these, 5.8 on the Richter scale, was recorded on 20th January 2002 where most people in Ahmedabad and other metros slept outdoors. Our photographs reveal that buildings using conventional earthquake resistant technology have developed faults while the ‘Mother and Child Care Centre’ has not even developed a single hairline crack. The same principle is also being used for retaining walls for flyovers in Delhi, India, which are designed for earthquake resistance and in addition, to withstand heavy dynamic loads.

Model of ‘Primary School’ being built at New Dudhai, Gujarat



With the recent earth tremors of just under 6 on the Richter scale most of the newly built structures have developed defects

Design Sense Awards, London, selected interlocking Hollow Core Blocks among the six best products for 2001 competing against the likes of Motorola, Philips and Honda in the finals.

Appropriate technology is equally adaptable and applicable to the high-income group as it is to the low-income group. In fact, sustainability of a system will only prove its worth if it percolates from the high-income group to the low-income group. It is the high-income group, which is unsustainable and is setting a wrong example for the low-income group to emulate and aspire for. It is also the high-income group that is hardest hit by inappropriate technologies since the Indian political system supports the low-income group with subsidies in order to garner votes while the high-income group, and more so the middle income group, is finding it difficult to make affordable housing owing to the fact that they are the prime tax payers. The home they build is a gargantuan effort, eating as it does, into a life time savings, not to mention the taxes that go alongside.



Embossed tile is integrated during the manufacture of block

VENTURING BEYOND

Appropriate technologies cannot be restricted to developing nations alone. The developed nations also need to re-examine construction systems so as to conserve resources and put them to better productive use instead of dead investments in buildings. Industrialised nations often use metallic finishes with cavities for condensation and vapour barriers backed with thermally insulating materials. These finishes are fixed over extensive grids of galvanised Iron runners. The main walls are of R.C.C. or brick as the case may be. In order to minimise heating expenses this interlocking block with condensation / vapour barrier thermally insulated with single sheet of aluminium cladding meets the performance criteria required at a much lower cost.

If one were to calculate the actual labour input within the present system of the building of an R.C.C. wall, manufacture and installation of galvanised iron runners and aluminium cladding, the interlocking block with all this integrated would prove not only cost-effective but also act as a labour saving device.

Interlocking Block with Aluminium Cladding

PRE-TENSIONED WALL

Very often, R.C.C. walls are a contradiction in themselves. Steel, which is good in tension, is used in conjunction with concrete, which is good in compression. These are two diametrically opposite characteristics of building materials being forced to behave in unison with one another. Our ancient Indian text, ‘Vastu Vidya’, propagates the use of materials for their inherent value. A very basic statement made by ‘Vastu Vidya’ suggests the use of not more than two materials for roofing. If seen in as correct perspective the ideology is towards the use of materials simply supported over each other rather than in unison. This in itself may contradict the very use of R.C.C. as continuous beams, for their so-called economic considerations and suggests that simply supported structures may perform better. One feels that problems with R.C.C. structures during the recent earthquake in Gujarat have much to be learnt from. The combination of the P and S wave gives rise to a ripple in the R.C.C. structures and reveals massive stresses, resulting in failure.

Walls using interlocking blocks attempt to respect this present day contradiction within R.C.C., the continuous holes are used for inserting high tension bars which are pre-stressed from the ends, through the surrounding frame, thus locking the blocks into position. The cavities are then filled with fine river sand. Thus the tension in the walls that may be caused by a horizontal thrust will be taken by the steel and the compression by the concrete both acting independently for their individual characteristics rather than being bonded as in the case of R.C.C. to give rise to contradictory behaviour.

This system also conserves steel. In the case of a pre-fabricated R.C.C. beam, a doubly reinforced mesh of steel with bars at approximately 4” c/c are usually provided in order to take the reversal of stresses during hoisting of the wall panel into position by a crane. The interlocking block is made on site, assembled on the ground, locked into place and pre-stressed with very simple methodologies and the entire wall can be lifted into opposition in the same manner as a pre-fabricated R.C.C. wall.

Model of Pre-tensioned wall

SOCIAL

The blocks are best produced by the use of hand moulds thereby opening up the possibility of permanent resilient finishes for the front face of the block – be it broken stone waste, an aggregate finish or a complete stone integrated during the manufacture of the block.

Permanent finishes are the aspirations of any man who wishes to make a statement of his home

In using simple hand moulding operations, the largest beneficiary is the mason rather than the bank manager who funds expensive machines at phenomenal rates of interest. The construction industry is the largest balanced instrument for the distribution of wealth.

As a result of immense interest generated in our building techniques we are also training 24 women in Gujarat, to take up the manufacture of blocks, which is estimated to increase their earning capacity from Rs.40/day to Rs.200/day.

WATER
The blocks are made at site and cured for only four days at which point of time they are liftable having achieved approximately 30% of their strength. Since transportation distance is not involved these blocks are laid in the wall and the balance curing is done as an integral part of the structure. This process saves up to 50% of the water consumption normally consumed in curing.

ENERGY

The finishes used are in their basic natural form and with a fine non-erodable diaphragm. The body of the block can be a lean mix using minimal cement – a high energy consuming material.

The horizontal bore not only makes it easy to work with, especially for the mason but is an ideal area for the use of waste polythene bags (the current environmental hazard). Since the product is consumed at site there is tremendous amount of saving in transportation energy.

ENERGY CONSUMPTION- BRICK WALL & INTERLOCKING BLOCK WALL

(COMPARISON IS LISTED FOR I CU.M. OF BRICK WALL (230 MM THK.) AND1 CU.M. OF INTERLOCKING BLOCK WALL (200 MM THK.)

S.NO.

DESCRIPTION

QUANTITY

ENERGY KwH/KG OR CU.M.

ENERY CONSUMED

A

BRICK WALL

1

BRICK

500 BRICKS

0.88 /BRICK

440

2

CEMENT

60 KG (1.2 BAGS)

2.25 /KG.

135

3

CEMENT PLASTER

12 MM 1:4

4.7 SQ.M.

20.65 / SQ.M.

97.24

4

CEMENT PLASTER

19 MM 1:4

4.7 SQ.M.

32.69 / SQ.M.

153.64

TOTAL

825.88

B

INTERLOCKING CONCRETE BLOCK WALL

1

CEMENT

168 KG. (3.36 BAGS)

2.25 /KG.

378

2

FINE AGGREGATE

525 KG (0.23 CU.M.)

0.06 /KG.

31.5

3

CEMENT PLASTER

6 MM 1:4

6.25 SQ.M.

10.325 / SQ.M.

64.53

4

CEMENT (POINTING)

21.8 KG.(0.43 BAG)

2.25 /KG.

49.2

TOTAL

523.23

All information is available free on our website – www.anangpur.com

We do not intend to patent any of the technologies, ensuring accessibility to all

OUR ASPIRATION

ASHRA

Academy for Sustainable Habitat Research and Action

The ASHRA is envisaged as a programme to train future professionals in the areas of appropriate building technologies and sustainable planning strategies and develop a corps of sustainable habitat advocates, within the mainstream. The primary target group is architectural and engineering students who are the future decision makers.

The main focus will be to take sustainable practices from lab to land through a network of students with the Anangpur building Centre as the catalyst. A website and over 11 films have been made and the site has been selected as the best educational site by Study Web. These will be used for lectures and online education. Students will be enrolled as members to the website and from this group, the most motivated 30 students will be selected for hands-on training on live pilot projects at the ASHRA’s base at Anangpur Building Centre. After a year of training these students will go back to their colleges to complete their education and influence students and teachers.

The objective of ASHRA is to facilitate the absorption and diffusion of sustainable planning and design practices and technologies into the mainstream and its propagation at a mass level. Through its partners in diverse countries having similar problems it will foster exchange of knowledge and experiences. It will specifically look at the relevance of traditional wisdom in several areas of the world and dovetail it into development practices of today. It will create links between agencies in sustainable development work and educational institutions in a cyclic self-sustaining manner. Typically it takes a few decades for fresh approach and thinking to become part of the conventional education curriculum but through the ASHRA process, hopefully the time taken for this is will be shortened.

The author Mr.Anil Laul is a practising Architect in New Delhi ,India and has been associated with many prestegious pojects both in india and abroad.

Rreferance: http://www.anangpur.asom