EARTHQUAKE RESISTANT BUILDINGS WITH HOLLOW INTERLOCKING BLOCKS

Transcription

1 EARTHQUAKE RESISTANT BUILDINGS WITH HOLLOW INTERLOCKING BLOCKS TRAINING MANUAL FOR ARCHITECTS AND ENGINEERS Auroshilpam, Auroville , TN INDIA Tel: +91 (0) / Fax: +91 (0) earth-institute@auroville.org.in Website:

2 EARTHQUAKE RESISTANT BUILDINGS WITH HOLLOW INTERLOCKING BLOCKS TRAINING MANUAL FOR ARCHITECTS AND ENGINEERS Author: Satprem Maïni Auroville August 2001 Revised April pages AUROVILLE EARTH INSTITUTE Ref: TM. 03 Humanity as a whole No rights reserved! All parts of this publication may be reproduced, by any means, without the written permission of the author. Feel free to disseminate this information anywhere!

3 CONTENT FOREWORD PREFATORY NOTE PART ONE EARTHQUAKES AND STRUCTURES 1.1 Earthquakes 1.2 Earthquake effects on a structure 1.3 Principles for earthquake resistance PART TWO SOIL AND STABILISATION 2.1 The raw material 2.2 Principles for soil identification 2.3 Soil stabilisation 2.4 Stabilisation calculation 2.5 Improving and stabilising soils 2.6 Testing soils PART THREE COMPRESSED STABILISED EARTH BLOCKS 3.1 Basic data on CSEB 3.2 Sustainability and environmental friendliness of CSEB 3.3 Hollow interlocking blocks for earthquake resistance 3.4 Blockyard organisation 3.5 Quality control 3.6 Cost analysis 3.7 Economic feasibility study PART FOUR DESIGN AND MASONRY 4.1 Basic design guidelines for CSEB 4.2 Basic design guidelines for earthquake resistance 4.3 Design guidelines for hollow interlocking blocks 4.4 Laying Hollow Interlocking CSEB 4.5 Bonds with the blocks Bonds with the blocks Example of plan with the block Example of plan with the block 295 SELECTED BIBLIOGRAPHY I ii

4 PREFATORY NOTE This manual presents the basics on earthquake mechanisms, the various stages of a manual production line using the AURAM equipment for Hollow Interlocking CSEB. It gives also the guidelines for earthquake resistant buildings, using the technologies developed by the Auroville Earth Institute for earthquake resistance. These technologies are based on stabilised earth for the foundations, plinth and walls. The system used for the load bearing walls is masonry built with hollow interlocking compressed stabilised earth blocks, which are reinforced with reinforced cement concrete (RCC). The technology has government approval: - The Government of Gujarat, India, (GSDMA) as a suitable construction method for the rehabilitation of the zones affected by the 2001 earthquake in Kutch district. It is allowed to build up to 2 floors. - The Government of Iran (Housing Research Centre) as a suitable construction method for the rehabilitation of the zones affected by the 2003 earthquake of Bam. It is allowed to build up to 3 floors (8m high). - The Government of Tamil Nadu, India, (Relief and Rehabilitation) as a suitable construction method for the rehabilitation of the zones affected by the 2004 tsunami of Indonesia. ii

5 PART ONE EARTHQUAKES AND STRUCTURES 1

6 1.1 EARTHQUAKES Origin of earthquakes The earth was a single land about two hundred million years ago. This land split progressively over a long period of time and it gave tectonic plates. Theses tectonic plates are still moving and earthquakes are the result of these movements. Therefore, the continents of the earth are like several pieces of a crust the tectonic plates, which are floating on a viscous mass the magma. The latter is like a thick liquid composed of rocks in fusion. Under various circumstances, these tectonic plates are still moving, very slowly, towards each other or away from each other. These movements generate a lot of friction, which generate tensions and compressions in the earths crust. This friction is like energy, which gets stored in the deepest strata of the ground. Earthquakes happen when the ground cannot accumulate anymore this energy, which is then released with violence on the surface of the globe. The original focus of the earthquake is called the hypocentre. It lies deep into the ground. The geographical point on the surface, which is vertical to the focus, is called the epicentre. TECTONIC PLATES 2

7 Seism types Seisms can be of various natures. The most frequent ones are due to the movement of tectonic plates. Earthquakes can have other natures: volcanic or caving in. - Tectonic earthquakes are the most devastating ones. The energy stored, due to the slow friction during a very long period of time, is tremendous. The earth crust is plastic enough to store this energy for a long time and without elastic failure. When the earth crust cannot store anymore this energy, it is released in the form of a tectonic earthquake. - Volcanic earthquakes are due to the movement of magma under the earth crust. Its causes can be a local push of magma, which breaks the earth crust. A caving in of an underground cavity, which was created by a magma movement, can also be its origin. The other origin of volcanic earthquakes is volcanic explosions and eruptions. Volcanic earthquakes are not much devastating. - Caving in earthquakes are quite exceptional. The caving in of the ceiling of underground cavities creates them. They can happen everywhere on the globe and they are not very powerful and devastating. Seismic waves The seism focus generates spherical pulses, which propagate like concentric waves. They are called body waves. These initial waves have a longitudinal action and they are called primary or P waves. These waves induce second body waves, S waves. When P & S waves reach the surface they create 2 other waves: Love & Rayleigh waves. P Waves Their manifestation creates a change in volume and generates compression and dilatation of the ground. Their velocity is high: 5 to 8 Km/s. S waves They also called shear or transversal waves and they are very destructives. The soil oscillates vertically and perpendicularly to their direction. Their velocity is lower than P waves: 3 to 5 Km/s. L waves (Love waves) They are also transversal ones, like S waves. The soil oscillates horizontally and perpendicularly to their direction. Their velocity is like S waves. R waves (Rayleigh waves) The soil oscillates in an elliptical movement, counter clockwise to their direction. Their velocity is a little lower than S waves. 3

8 Measure of seism Two scales measure earthquakes: the Richter scale and the Mercalli scale. - The Richter scale gives a quantitative measure of earthquakes. It defines the magnitude of an earthquake, which is the amount of energy released on the surface. The Richter scale is logarithmic: each whole number increase in magnitude represents a ten-fold increase in the measured amplitude of the seism. This scale has no upper limit, but the largest known shocks have had magnitudes up to 8.8 to 8.9. The earthquake of January 2001 in Gujarat was measured at 6.9 by the Indian seismographs and at 7.8 by the Japanese and American seismographs. - The Mercalli scale assesses the effects of an earthquake. It defines the intensity of the earthquake, which is expressed from 1 to 12. The intensity and thus the effect of the seism are related to the distance from the epicentre. It is based on more subjective effects, like movement of furniture, extents of damages to structures, modification of the landscape, etc. Earthquake effect Earthquakes don t directly kill people. Ground shaking destroys infrastructure and buildings and hence, it is of a material nature. Death of people is occurred by the collapse of buildings in which they live. Therefore, the real cause of life s loss is badly built or un-appropriate constructions, which instantly collapse without warning. Ground motion during an earthquake As we have seen previous page, the hypocentre of an earthquake generates various types of waves. When they reach the surface, the ground shakes everywhere horizontally and vertically especially near the epicentre. The motions are always reversible and this implies that buildings vibrate in all directions and in a very irregular manner due to the inertia of their masses. Seism prediction It is not possible to predict earthquakes. Parameters involved and the absence of sufficient data makes it impossible to foresee, where, when and with which magnitude would strike an earthquake. Earthquake prevention If it is not possible to predict earthquakes, it is possible to prevent major damages and most of life s losses. India is divided in five zones and there are several Indian standards, which defines building codes for earthquake resistance. The design of every engineered or non-engineered building must follow it. Further, the construction must be well built, that means by people who should follow the state of the art in construction, or at least the basics of masonry, and who are conscious of their responsibility in the execution of a building, which must resist an earthquake. The prevention of earthquakes is based on the possibility of buildings to resist earthquakes without sudden collapse. Seismic zones India has been mapped in 5 zones, according to the risk of earthquakes: zone 5 has the greatest risk for earthquakes (See IS 1893: 1984). These zones are mainly based on the Mercalli scale. They are related to: - Intensity and magnitude of past earthquakes - Probability of earthquakes - Nature of the ground and soil-foundation system - Risk occurred because of the density of population and/or buildings 4

9 Seismic zones of India 1.2 EARTHQUAKE EFFECTS ON A STRUCTURE Structural elements, such as walls, columns and beams, are only bearing the weight of the building and the live load under normal conditions: mostly compression forces for the walls and columns, and vertical bending for the beams. Under dynamic load, they also have to withstand horizontal bending and shear forces, and extra vertical compression forces. Failure mechanism of walls GROUND MOTION IN THE WALL PLANE 5 GROUND MOTION PERPENDICULAR TO THE WALL

10 Typical damages in a masonry building 1: Diagonal shear crack of piers 2: Horizontal shear crack of long pier 3: Bending cracks at feet and lintels 4: Bending crack of wall (bad corner bond) 5: Bending crack of spandrel 6: Bending crack of gable 7: Plaster peeling off 8: Crushing of weak masonry under vertical ground motion 9: Damage of corner eaves under vertical ground motion 10: Badly anchored roof, pulled out by vertical ground motion 11: Falling of tiles from the roof eave 12: Damage of tiles roof with shear (roof not braced) Khavda Badly built buildings Near Bhuj Ludiya Adobe buildings, which withstood the earthquake of Gujarat Ludiya 6

11 Bad bonds and no through stones Typical shear crack in a pier Shear crack Shear crack in filler wall Crack due to bending & shear Bending cracks at door Overturning of parapet wall Prag Mahal Bhuj, Built at the XIX th Century Well built = Minor damages 7

12 Failure due to collapse of walls or columns Failure due to collapse of column Failure due to shear & bending Stirrups too weak Steel bars not centred Stirrups too weak No steel angle in the corner Not enough gap between 2 buildings No anchorage in the column 8

13 1.3 PRINCIPLES FOR EARTHQUAKE RESISTANCE Though hi-tech technologies exist in Japan and USA, it is not economically possible to build earthquake proof buildings, especially for low-income groups and small projects. But it is possible to build easily earthquake resistant buildings, without much extra cost, and which would not collapse suddenly without warning. Any new building which is located in the zones 3, 4, 5 must be designed to resist earthquakes. For projects, like houses, this can be satisfied by a well built construction, which follows all basics of masonry guidelines, like bond pattern, mortar quality, brick or stone laying, etc. In the case of the last earthquake of January 2001 in Gujarat, some traditional houses made of adobes or stones withstood very well the seism violence. They were simply well designed and well built. An earthquake resistant building is able to accumulate a lot of energy without major failure. It will swing and sway and it might be damaged. But it would not collapse before giving very visible signs. Therefore, people would be able to leave the building before it would collapse. An earthquake resistant building, which has been damaged, could most of the time be repaired. Terminology - Band or ring beam A reinforced concrete or reinforced brick runner, which ties all the walls together. It imparts the horizontal bending of the walls. - Box system A structure made of a load bearing masonry wall without a space frame. The walls, acting as shear walls, are resisting the horizontal forces. - Brittleness The possibility of a structure to crack and collapse easily. It is arising either from the use of brittle materials or from a wrong design. The opposite of brittleness is ductility. - Centre of gravity The point through which the resultant of the masses of a system acts. It corresponds to the centre of gravity of the plan. - Centre of rigidity The point through which the resultant of the restoring forces of a system acts. It is the rotation point of the structure and it is related to the masses of the vertical parts of a building. - Ductility The ability of a building to bend, sway and deform by a large amount without collapse. The building may crack and get damaged in some parts, but it would not collapse. The opposite of ductility is brittleness. A building built with brittle materials can be made ductile with a proper design and with the incorporation of various reinforcements. - Plasticity The property of a material, and especially a soil, to be submitted to deformation without elastic failure. A humid soil is quite plastic and can absorb a lot of energy before breaking. A dry soil will be less plastic, but will still be able to absorb more energy than stones or fired bricks before failing. - Shear wall A wall, which resists lateral forces in its own plane. Shear walls are structurally linked with other cross walls and with floors and roofs, which acts as diaphragms. Wide piers and buttresses are considered as shear walls. - Vertical tie A RCC reinforced member, which ties the various ring beams, from plinth to roof. Site location The nature and stability of the natural ground will affect the buildings. It is not always or rarely possible to select a site for its characteristics for earthquake resistance. Spontaneous human settlements have another approach to select a place. Very loose sands and sensitive clay should generally be avoided. These two types of soils are liable to be destroyed by the earthquake and they will loose their original structure. Especially, if soils without cohesion get saturated with water they might loose their shear resistance and get liquefied. Design and construction quality Major damages and collapse are, in most the cases, attributed to wrong design and particularly to very poor quality constructions made by bad workmanship. Much less damaged would occur if masons, contractors, engineers and architects were always following the basics of masonry guidelines such as: Simple and appropriate design Proper bonds with appropriate and well laid mortar Etc. Good detailing in general Good overlap of steel bars and good cover with concrete 9

14 Khavda Well built buildings which resisted the earthquake in Gujarat Near Bhuj Box system and reinforced masonry The structure should be done in such a way that the walls are bracing each other to prevent bending moment. Walls should also be designed as shear walls to resist the lateral forces in their plane. This means that openings should be small, rather centred and not too close from corners. Reinforcing the masonry should not be a way to improve a wrong design. It would rather be a means to add more strength to the building. 10

15 PART TWO SOIL AND STABILISATION 11

16 2.1 THE RAW MATERIAL Definition Soil is the result of the transformation of the underlying rock under the influence of a range of physical, chemical and biological processes related to biological and climatic conditions and to animal and plant life. Fundamental properties - Granularity or texture = Grain size distribution of a soil. (Percentage by weight of the different grain size) - Compressibility = Ability to be compressed to a maximum. It is related to the energy of compaction and the moisture content = OMC (OMC = Optimum Moisture Content = percentage by weight of water) - Plasticity = Property of a soil to be submitted to deformation without elastic failure. - Cohesion = Capacity of its grains to remain together. Composition of a soil = It is an earth concrete - Gaseous components - Liquid components - Solid components Cement is the binder for concrete. In a soil, the binder is silt & clay. Thus, it is like a concrete, but silt & clay are not stable under water. Therefore they should be stabilised, to maintain some strength when the blocks get wet. The grain size classification adopted by a large number of laboratories is based on the ASTM-AFNOR standards: Pebbles Gravel Sand Silt Clay 200 to 20 mm 20 to 2 mm 2 to 0.06 mm 0.06 to mm to 0 mm For compressed stabilised earth bocks, pebbles should be removed. Good soil for compressed stabilised earth blocks It is much more sandy than clayey. It has a particular proportion of the four components: gravel, sand, silt and clay (Pebbles are screened). Gravel Sand Silt Clay 15 % 50 % 15 % 20 % Typical soils According to the percentage of the four components, the soil will be classified as: Gravely soil Sandy soil Silty soil Clay soil. A more accurate classification will need some subtleties, i.e.: Silty sand soil = Soil mainly sandy with an influent proportion of silt. Sandy silt soil = Soil mainly silty with an influent proportion of sand. Structure of a soil It is how the grains are assembled. There are 3 structures: - Granular structure = A lot of voids (i.e. gravel) - Fragmented structure = Discontinuous (i.e. gravel and clay only) - Continuous structure = the best (i.e. the proportion of the best soil: see above) 12

17 2.2 PRINCIPLES FOR SOIL IDENTIFICATION Sensitive analysis: They follow the four fundamental properties of the earth. They can be practiced by anybody: - Granularity = - The soil is dry / solid or humid: look and touch it to examine the percentage and size of the four components. - Compressibility = - Add a little water to get a moist soil and compress it by hand to try to make ball. - Plasticity = - Add more water and make a ball. - Try to pull the ball like rubber elastic. - Stick a knife into it and cut it with the knife. - Water absorption in a small print done with the thumb in the ball. - Cohesion = - Add much more water to loose the cohesion and to wash the hands. The humus content must be checked: - Humus Content = - An important test is to check the humus, which may give problems with the stabilization: take a moist soil and smell it. The aim of this sensitive analysis is to find out in which categories goes the soil sample: Gravely, Sandy, Silty, Clayey or combined soil i.e. sandy clay. Then, according to this classification, one must look into the recommendations for stabilization and soil improvement. Laboratory Tests They follow the four fundamental properties of the earth, but they need special equipment: - Granularity = Grain size distribution (sieving + sedimentation). - Compressibility = Proctor for getting the OMC. - Plasticity = Atterbergs limits (LL, PL, IP) (SL, LS, LA, CA.) - Cohesion = = 8 test (mortar < 2 mm) For example: Sand 0 < IP < 10 0 < LL < 30 Silt 5 < IP < < LL < 50 Clay 20 < IP 40 < LL 2.3 SOIL STABILIZATION Definition It aims to stabilise under water the binders, which are the silts and clays, in order to obtain lasting properties and strength when the soil gets wet. Procedures PRINCIPLE Mechanical The soil is compacted. Physical Chemical The texture of the soil is corrected by adding or removing aggregates, which are inert materials. Processed products, which are active materials like chemicals, are added to the soil. ACTIONS - Density and mechanical strength are increased. - The water resistance is increased. - The permeability and porosity are decreased. - The soil is sieved to remove the coarse particles. - Different soils are mixed to get a better texture. - Gravel or sand is added to reinforce the skeleton. - Clay is added to bind better the grains. - They help binding the grains of the earth. 13

18 6 Methods Densification Reinforcement Cementation Linkage Imperviousness Waterproofing DEFINITION EXAMPLES Densification Create a dense medium, blocking pores & capillary - Compaction - Adding components - Mixing different soils Reinforcement Create an anisotropy network limiting movement - Straw - Fur - Synthetic fibres Cementation Create an inert matrix opposing movement - Cement - Fly ash Linkage Create stable chemical bonds between clay and sand - Lime Imperviousness Surround every earth grain with a waterproof film - Bitumen & Resins - Various chemicals Waterproofing Avoid the water absorption and adsorption by the surface - Paints, plaster * - White wash Note: * Avoid bitumen and synthetic paints or plasters for earth walls. Variety of stabilisers Fibres (natural or synthetic), cement, lime, fly ash, natural products (straw, fur, blood, juice of plants, latex, etc.), resins, and synthetic products. Suitability of stabilisers and their percentage for earthquake resistant CSEB SUITABILITY MINIMUM % AVERAGE % MAXIMUM % Cement Mostly for sandy soil 5% 7% No technical maximum Economic maximum: 9-10 % Lime Mostly for clayey soil 5% 8% 10% 2.4 STABILISATION CALCULATION Aim It is to define the percentage of stabiliser and the quantities of the different components. Principle The calculations are always done by weight of dry material. As it is impossible to measure weights on site, they have to be transformed into volumes. Then, the dry density (δ) is needed. Formulas They can be used for all stabilisers, but we give here the example with cement. The aggregates are soil or (soil + sand) or (soil + gravel), etc. The total percentage of different aggregates is always 100 % as the binder is not yet included. 1. Density (δ) 2. Theoretical weight aggregates 3. Theoretical volume aggregates (Do it for each aggregate) 4. Exact % cement * Total weight = Weight per litre = Weight cement wanted x (100 - % cement wanted) % Cement wanted = Theoretical weight aggregates x % particular aggregate Density particular aggregate x 100 = Weight cement wanted x 100 Total weight* = (Approximated volume of each aggregate x its density) + cement weight 14

19 How to do? 1. Define the parameters : - Percentage and weight of cement, which is wanted. (Cement quantity should be calculated for not more than 250 litres of aggregates. It often corresponds to not more than 1/3 of a bag per mix). - Percentage of sand, gravel or else, which might need to be added. - Volume in litres of the containers available (Wheelbarrows, buckets, etc). 2. Density check up : Check the dry densities = weight of 1 litre (Formula 1). 3. Weight of aggregates : Calculate the weight of aggregates, required to get the percentage of cement wanted (Formula 2). 4. Transformation : Transform the weight of aggregates into volume for each aggregate (Formula 3). 5. Approximation : Approximate the volume of aggregates, according to the containers, which are available on site: to get practical and easy measurements for the site. Always keep in mind for this approximation that the transportation should be as easy and as fast as possible. 6. Exact % cement : Calculate the exact percentage of cement, according to the weight of approximated aggregates (Formula 4). 7. Selection : Select the result if it is within a tolerance of 3% maximum from the percentage of cement wanted (i.e to 5.15 instead of 5%). 8. Adaptation : If the result is not satisfactory, redo all the process with another approximation for the volume or with other parameters. Practical grid This grid is valid only for one soil with one stabiliser (cement) so as to get ± 7% cement stabilisation. Soil density (δ) Volume of soil (Litres) Weight of cement (Kg) Exact % of cement = 1/3 bag 16.6 = 1/3 bag 16.6 = 1/3 bag 16.6 = 1/3 bag 16.6 = 1/3 bag 16.6 = 1/3 bag 16.6 = 1/3 bag 16.6 = 1/3 bag 16.6 = 1/3 bag Example 1 1. Parameters: - 7% cement wanted and 1/3 bag (16.67 kg) litres wheelbarrows + 15 litres buckets - 100% soil required (no sand added) - Dry density checked for the soil: δ soil = Weight of aggregates (Formula 2): Soil = x (100 7) = kg 7 3. Volume of aggregates (Formula 3): Volume of soil = x 100 = Lt x Approximation: According to the containers available and to transport easily the soil, we choose for the volume of soil: 1 wheelbarrow (150 Lt.) + 1 bucket (15 Lt.)= 165 Lt. 5. Exact % of cement (Formula 4): % = x 100 = 6.96% (165 x 1.35) Selection: 6.96 is within the 3% tolerance ( ) for the cement percentage and we select it. 7. Adaptation: Redoing all the process is not needed. 15

20 Example 2 1. Parameters: - 8% Cement wanted and 1/3 bag cement (16.67 kg) Lt. wheelbarrows + 15 Lt. buckets - 70 % of soil and 30% of sand required - Dry density checked: δ soil = 1.2 and δ sand = Weight of aggregates (Formula 2): Soil + Sand = x (100 8) = kg Volumes of aggregates (Formula 3): Volume of soil = x 70 = Lt. 1.2 x 100 Volume of sand = x 30 = Lt x Approximation: According to the containers available and to transport easily soil and sand, we choose: Sand = 45 Lt. = 3 buckets of 15 Lt. Soil = 100 Lt. = 1 wheelbarrow of 100 Lt. 5. Exact % of cement (Formula 4): % = x 100 = 8.25% (100 x 1.2) + (45 x 1.45) Selection: 8.25 is only 0.1% above the superior limit of the 3% tolerance ( ) for the cement percentage. As there is only 0.1% more, we can select it. 7. Adaptation: Redoing all the process is not needed. 2.5 IMPROVING AND STABILISING SOILS FOR EARTHQUAKE RESISTANT CSEB According to the original soil quality, adding materials like gravel or sand can improve easily the structure of the soil. Note that adding clay is difficult, as it should be powered and this is quite hard to do on site with only manual means. Improvement can also be done by sieving the soil or by mixing different qualities of soil. Stabilising a soil will of course improve it a lot, but it should be done only after improving its structure. Gravely Soil - Sieving, with mesh size # 8 to 10 mm, is indispensable to remove coarse gravel. - A maximum of 15% to 20% by weight of gravel passing the screen will be allowed. - The maximum size for the gravel passing through the sieve will be 10 mm. - If the soil is too gravely, mix with it another soil, which is more clayey. - The minimum cement stabilisation will be 4% by weight, if the clay content is not less than 15 %. - The average cement stabilisation will be 6% by weight. Sandy Soil - Sieving, with mesh size # 10 to 12 mm, is only required to loosen, aerate the soil and break up lumps. - Do not sieve in a very windy area, especially if the soil is dry, so as not to loose the fine clay. - The minimum cement stabilisation will be 5% by weight. - The average cement stabilisation will be 6-7% by weight, if the clay content is not less than 15%. Silty Soil - A slight crushing might be required and sieving, with mesh size # 6 to 10 mm, is required. - Adding some coarse sand (10 to 20 %) might be needed to give more skeletons to the soil, only if the clay content is not less than 20%. When the silt content is high (more than 25-30%) and the sand very fine (0.06 to 1mm), adding coarse sand and a clayey soil will improve the structure. - The minimum cement stabilisation will be 6% by weight. - The average cement stabilisation will be 7-8% by weight. Clayey Soil - Crushing might often be required and sieving, with mesh size # 6-10 mm, is required. - Adding a lot of sand (30 to 40 % ) is most the time needed to reduce the plasticity and to give some skeletons. - The minimum cement stabilization will be 7% by weight and the average cement stabilisation will be 8%. - Lime stabilisation can be used instead of cement. The minimum will be 8 % and the average will be 9% by weight of lime. Then, the adjunction of sand will be reduced. - A combination of cement-lime stabilisation, can give good results. For example: 3% cement + 5% lime + sand as needed. 16

21 2.6 TESTING SOILS Sensitive analysis and comments of four typical soils (gravely, sandy, silty, clayey), and a good soil - Look and touch. - Add water to get a humid soil and smell it. - Try to compress the moist soil. - Add water and make a plastic ball. - Try to pull the ball like rubber elastic. - Stick a knife into it. - Cut the ball in two pieces with a knife. - Absorption: do a print with the thumb in the plastic ball & fill it with water. - Wash your hands with water. Comments on the soil to be used Sensitive analysis and comments of various soil qualities Dry density check Measure it for the dry soil to be used. - Take 1.5 litre of loose humid soil. - Dry this sample. - Weight 1 litre of dry soil. - Redo 3 times this check. - Take the average for the dry density. Testing typical soils with a press - Sensitive analysis on various soils. - Experimentation with the four typical soils and good soil with a press: Making 3 blocks of each soil quality. - The detailed results of the experimentation are given next page. Behaviour of typical soil with a press - The moisture is above the OMC (+ +) - A little water is needed for mixing (- -) - A little soil is needed to mould (- -) - A low compression ratio is required (- -) - Little influence of the moisture content on the penetrometre (-) Note: This last result is paradoxical but is due to the granular structure of the soil. - The moisture is above the OMC (+) - A little water is needed for mixing (-) - A little soil is needed to mould (-) - A low compression ratio is required (-) - Big influence of the moisture content on the penetrometre (+ +) - The moisture is below the OMC (-) - A lot of water is needed for mixing (+) - A lot of soil is needed to mould (+) - A high compression ratio is required (+) - Little influence of the moisture content on the penetrometre (-) - The moisture is below the OMC (- -) - A lot of water needed for mixing (+ +) - A lot of soil needed in the mould (+ +) - A high compression ratio is required (+ +) - Very little influence of the moisture content on the penetrometre (- -) 17

22 GRAVELY SOIL SANDY SOIL SILTY SOIL CLAYEY SOIL M I X I N G - Easy (+ +) - Difficult to get the OMC (-) - Little water is required (- -) - Easy (+) - Difficult to get the OMC (-) - Little water is required (-) - Difficult (-) - Easy to get the OMC (+) - A lot of water is required (+) - Very lumpy (+) - Little sticky (+) - Very difficult (- -) - Easy to get the OMC (+) - A lot of water is required (+ +) - Very lumpy (+ +) - Hard to crush (+ +) - Very sticky (+ +) M O U L D I N G - Very difficult (- -) - Less soil is required in the mould (- -) - Very good result with the penetrometre (+ +) - Difficult (-) - Less soil is required in the mould (-) - Not very good result with the penetrometre (-) - Easy (+) - A lot of soil is required in the mould (+) - Not good result with the penetrometre (- -) - Very easy (+ +) - A lot of soil is required in the mould (+ +) - Not very good result with the penetrometre (-) E J E C T I O N - Very easy (+ +) - Not sticking (-) - Easy (+) - Not sticking (-) - Difficult (-) - Sticks a lot in the corners (+) - Very difficult (- -) - High adhesion (+ +) - Sticky in the corners and on the plates (+ +) H A N D L I N G - Difficult (- -) - Edges are very fragile (+ +) - Difficult (- -) - Edges are very fragile (+ +) - Easy (+) - Edges are fragile (+) - Very easy (+ +) - Edges are very cohesive (+ +) H U M I D A S P E C T - Very rough surface (+ +) - Not homogeneous (- -) - Honey comb structure - Rough surface (+) - Homogeneous (+) - Porous structure - Smooth surface (+) - Homogeneous (+ +) - Matt finish - Very smooth surface (+ +) - Very homogeneous (+ +) - Shiny finish D R Y A S P E C T - Easy to break (+ +) - Crumbly (+ +) - No cracks (-) - Easy to break (+) - Crumbly (+) - No cracks (-) - Easy to break (+ +) - Crumbly (+) - Little cracks (-) - Very hard to break (+ +) - Very cohesive (+ +) - Big cracks (+ +) 18

23 PART THREE COMPRESSED STABILISED EARTH BLOCKS (CSEB) 19

24 3.1 BASIC DATA ON CSEB (For 5 % cement stabilised blocks) Dry compressive strength σ c (After 28 days curing) : 3 to 6 MPa Wet compressive strength σ c (After 28 days curing) : 1.5 to 3 MPa (Test done after 3 days immersion) Dry bending strength σ b (After 28 days curing) : 0.5 to 1 MPa Dry shear strength (After 28 days curing) : 0.4 to 0.6 MPa Water absorption by weight (After 28 days curing) : 8 to 12 % (Test done after 3 days immersion) Apparent bulk density (dry) : 1700 to 2000 kg/m 3 Energy consumption : 110 MJ / m 2 Compare this value with Kiln Fired Bricks, Country Fired Bricks and Plain Concrete Blocks (See below) Pollution emission (CO 2 ) : 16 Kg / m 2 Compare this value with Kiln Fired Bricks, Country Fired Bricks and Plain Concrete Blocks (See below) Notes: - 1 MPa = ± 10 kg/cm 2 - Kiln Fired Bricks are also called Kiln Burnt Bricks or Wire Cut Bricks - CSEB consume per m 2, 5 or 15 times less energy than fired bricks and 2.1 times less energy than plain concrete blocks. - CSEB pollute per m 2, 2.4 or 7.8 times less than fired bricks and 1.6 times less than concrete blocks. 3.2 SUSTAINABILITY AND ENVIRONMENTAL FRIENDLINESS Earth is a local material. Earth construction is a labour-intensive technology and is an adaptable and transferable technology. It is a cost and energy effective material. It is much less energy consuming than fired bricks (5 or 15 times less). It is much less polluting than fired bricks (2.4 or 7.8 times less). A study from Development Alternatives (New Delhi ) gives per m 2 of finished wall: ENERGY CONSUMPTION POLLUTION EMISSION (CO 2 ) CSEB wall = 110 MJ / m 2 CSEB wall = 16 Kg / m 2 Kiln Fired Brick (KFB) = 539 MJ / m 2 Kiln Fired Brick (KFB) = 39 Kg / m 2 Country Fired Brick (CFB) = 1657 MJ / m 2 Country Fired Brick (CFB) = 126 Kg / m 2 Plain Concrete Blocks (PCB) = 235 MJ / m 2 Plain Concrete Blocks (PCB) = 26 Kg / m 2 Note: Kiln fired bricks are often called wire cut bricks. Be aware of the management of resources: It is a crucial issue! If well managed, the production of CSEB will allow new and harmonious developments. On the other hand, if there is no comprehensive management, it can lead to ecological disasters! Always respect our Mother Earth! 3.3 HOLLOW INTERLOCKING BLOCKS FOR EARTHQUAKE RESISTANCE A technology using reinforced hollow concrete block has been developed all over the world since a while. Its principle is to reinforce the masonry by grouting a concrete into the holes of the blocks where stands a steel rod at the critical locations (Corners, ends, near openings, etc,). Horizontal reinforcements are also cast in blocks with a U shape. The technology using Hollow Interlocking Compressed Stabilised Earth Blocks (HI CSEB) is based on the same principle: to reinforce horizontally and vertically the masonry with Reinforced Cement Concrete (RCC) members. The advantage of hollow interlocking CSEB, compared to hollow concrete blocks, is that they offer keys, which interlock in the other blocks. Thus these walls offer more resistance to shear and buildings would be even stronger. They would better resist earthquakes and without major damages. Compressed stabilised earth blocks have another advantage: they are in most cases cheaper and they are always more eco-friendly than concrete blocks. 20

25 Particular requirements for hollow interlocking blocks Interlocking blocks can resist disasters (Cyclones, earthquakes and floods), provided that they are hollow, so as to be reinforced with Reinforced Cement Concrete (RCC), at regular intervals. A hollow interlocking CSEB for earthquake resistance must satisfy these requirements: - Extreme consistency in height (1 mm difference maximum is allowed). - Self-aligning to reduce time-wasting adjustments. - Blocks should be hollow and the vertical holes and U shaped blocks should allow casting RCC, according to requirements: To reinforce regularly the masonry vertically and horizontally. - The interlocking keys must interlock transversally and longitudinally to the wall. They should interlock especially well in the length of the wall, which is subject to the shear stress of the earthquake. - Every course must interlock with each other as well as the header of every block in length: to increase the shear strength of the masonry. - Good seating of the blocks on top of each other for properly transmitting the load bearing: All the block area, including the key, must transmit the load. - A binder must bind them: they must not be dry stacked, as the aim is to get a homogenous masonry. - The binder should be a cement-sand mortar of 5 mm thick. It should be quite fluid in order to be workable. - The mould must allow manufacturing of full size blocks but also 3/4 and 1/2 sizes. The blocks must not be cut to match the bond pattern, which will be detrimental to the accuracy, strength and quality of the masonry. Compressed stabilised earth blocks have a poor bending strength (See table page 20) but this is not so critical because the block itself will not bend but the masonry will do. CSEB have very poor shear strength, which is critical in the case of earthquakes. Interlocking blocks will not have a stronger shear strength compared to ordinary CSEB. But the key effect will increase the shear strength of the masonry if the cohesiveness of the material is high enough to keep the link between the key and the body of the block. (Especially shocks and vibrations of an earthquake) The Auram hollow interlocking blocks The accuracy of the Auram press allows a very regular block height: only 0.5 mm difference in height. This allows the block to get the ideal mortar thickness of 5 mm. Therefore, the block modules are: - 30 x 15 x 10 cm for the rectangular block 295 (29.5 x 14.5 x 9.5 cm) x 25 x 10 cm for the square block 245 (24.5 x 24.5 x 9.5 cm). The hollow interlocking 295 is only meant for single storey buildings. The hollow interlocking block 245 can safely be used up to two storey buildings only. The holes have been maximized (regarding the size of the block and the press design) at 5 cm diameter to allow a proper concrete cover for the steel. The area of the key has been maximized at 9 cm diameter to ensure the maximum adhesiveness of the key on to the block body, so as to resist the shear effect. The height of the key has been determined by having the maximum friction area between blocks to resist the shear and by having the minimum friction on the mould while de-moulding the block from the press. The chamfer angle of the key seeks to be optimum. Variety of blocks 245 Variety of blocks

26 3.4 BLOCKYARD ORGANIZATION 6 Stages 2 to 4 persons - Preparation (Digging + Sieving) transport 1 person - Measuring transport 2 persons - Mixing (dry + wet) transport 3 persons - Pressing transport 1 person - Initial curing and first stacking transport 2 persons - Final curing and stacking transport 11 to 13 persons Note: - These numbers are valid for one AURAM press 3000, which can produce 1000 blocks 240 per day, 600 blocks 245 or 295 per day. - The number of persons for the digging & sieving will vary with the type of soil. - The number of persons for the final curing & stacking will depend of the transportation distance. Quality control Do it at every stage of the production line. Key words - Reduce the distance of transportation. - Optimise the ratio output / number of workers, to get the best efficiency. - Organize the block-yard as close as possible from the site. - It is preferable to have a linear organization but a circular one can also be suitable. Typical linear organization 3.5 QUALITY CONTROL Golden rules - To create a joyful atmosphere where every body is conscious of the quality required and check the blocks. - Check the production at every stage (see the production cycle). - Check the quality of the compression with the pocket penetrometre, always for the first block of every mix. - Check the height with the block height gauge, always for the first block of every mix. - Follow daily the production. Record the output, the dates... - Check weekly or monthly, the production with the field block tester (after 28 days). 22

27 During the production STAGE WHAT TO CONTROL MEANS Soil supply Sieving Measuring Dry mixing Wet mix Pressing Initial curing And First stacking Final curing And Stacking The topsoil must be removed. Check the regularity of the supply. Check the depth of veins. If the supply is with lorries, check before unloading. Check the root contents. Adapt the mix if there are some changes in soil supply. Angle of the sieve. Size of the lumps. Percentage of waste. Check that containers are filled according to the requirements. Check that 1 bag of cement is poured in buckets at once. Move 2 times minimum the piles (the best is 3 times). Check the uniformity and homogeneity of the mix. (Especially the colour) Check if there are big lumps and crush them. Move 2 times minimum the piles (the best is 3 times). Check the uniformity and homogeneity of the mix. (Especially the colour) Check the lumps and crush them, if any. Check the moisture content. Check the strength with the pocket penetrometre. Check the height with the block height gauge. See the texture (loose or dense). Have an external look. (Edges, corners, difference in colours, etc.) If the stacking is according to requirement. If the ground is cleaned regularly. The blocks are properly covered with plastic sheets. The quality of the edges after stacking. Check the spaces left in between blocks. Care for the transport. Care for stacking. If the stacking is according to the requirement. Good protection of the piles top with coconut leaves straw or any material for the sunshade. Water during 4 weeks, minimum twice daily (according to the weather). The blocks must not dry during 4 weeks! Drying for 4 weeks before use. Sensitive analysis. Look. Look. Look. Look. Sensitive analysis Block height gauge. Penetrometre Look. Look. Look. 23

28 After the production - Record the data - Number of workers & number of hours worked - Number of bags and number of blocks produced - Calculate the Number of blocks per mix and per bag of cement (not more than ± 2 blocks difference according to average production). - Obviously an entrepreneur will need also to record his stock, salaries, and so on, to manage properly his unit. - Field bending test = Bending test σ b = 3 x F x L 2 x W x H 2 F = load applied on the block, in kg. L = distance of the supports, in cm W = Width of the block, in cm H = height of the block, in cm σ c = ± 5 σ b (This coefficient 5 varies from soil to soil) - Laboratory tests Bending + compression + shear crushing + water absorption. Practical grid for the bending strength test When testing the blocks by bending, not a single block should break below the following load (load applied on the plate). Then, they will resist to a minimum of 5 kg/cm 2 of bending strength, which is within the limits of 5 to 10 kg/cm 2 by dry bending crushing strength. Height Block 290 (29 x 14 cm) Block 240-4/4 (24 x 24 cm) Block 240 1/2 (24 x 11.5 cm) (cm) Load on the plate (kg) Load on the plate (kg) Load the on plate (kg) Note: - The load is the weight applied on the plate of the field block tester. - The weight of the plate from the Auram field block tester is 6.5 kg. - The space between the angle of the field block tester is L = 18 cm. - The calculation takes in account the leverage (5 times) of the AURAM field block tester. 24

29 3.6 COST ANALYSIS Hollow interlocking block 245 produced on site Block size: 24.5 x 24.5 x 9.5 cm, with 5% cement Value: Auroville, April 2005, 1 US $ = ±43.5 Rs. MAIN DATA Press lifespan (600 strokes per day over ± 5.5 years = 10 Lakhs of blocks) (Blocks) 1,000,000 Daily production (Blocks) 600 Annual production = Daily prod. x 26 days x 11 months (1 month = maintenance +heaviest rains) 171,600 Equipment cost (Rs.) 125,000 Buildings [storeroom 15 m 2, simple production shed 75 m 2 ] and infrastructure (Rs.) 40,000 Maintenance for the lifespan of the press (Rs.) 25,000 VARIABLE COSTS Rs./Unit Units Cost / Block % Labour (Man) % Soil (± 80 % = 7.69 m 3 per 1000 blocks) % Sand (± 20 % = 1.92 m 3 per 1000 blocks) % Cement (5 % = bags per 1000 blocks) % Maintenance per block % TOTAL Variable costs (Rs.) % FIXED COSTS % Total Rs. Cost / Block % Investment Cost (Interest) 5.0 % 165, % Equipment Depreciation (= press lifespan) 16.8 % 125, % Building Depreciation (= site duration) 50.0 % 40, % Overheads / Miscellaneous 5.0 % % TOTAL Fixed costs (Rs.) % TOTAL cost per block (Rs.) % NOTES - The production is done on a construction site, which has the minimum set up (simple storeroom, light production shed). The latter would be wasted at the end of the site. - The equipment includes 1 Auram press mould, 1 wheelbarrow 200 Litres, 1 wheelbarrow 350 Kg, 1 soil sieve # 10 mm, 1 sand sieve # 4 mm, plastic sheets, barrel and small tools. - The soil is extracted from the site and its cost includes sieving in the quarry. - The sand cost includes delivery by lorry and sieving on site. - The water cost is included in the overheads / miscellaneous. - The labour cost includes the yearly bonus and the Employee Providence Fund. Comments - The depreciation cost of the equipment, the maintenance of the equipment and the investment cost is only 3.41 % when the cement is % and the labour % (for block-making and soil digging). This implies that one should find a way to reduce the cost of the stabiliser but not the manpower with unskilled labour or the equipment with cheap presses. - The soil dug on site, costs 70 Rs./m 3 that mean Rs./block. If it has to be delivered by lorry, its cost per block would become Rs Thus the cost price of the block would be Rs instead of If the blockyard is organised with a moveable shed, the cost price of a block will be slightly cheaper than for the site production (Rs. 4.91) because the building depreciation is less than for the site production. Cost comparison with Country Fired Bricks (CFB) This comparison includes the difference for the volume & breakage: - Plain CSEB 240 = 24 x 24 x 9 cm with 5% waste at a cost of 4.47 Rs./Block comes to 4.69 Rs. /Block. - Hollow interlocking CSEB=24.5 x 24.5 x 9.5cm+5% waste at a cost of 4.99 Rs./Block comes to 5.24 Rs./Block. - Country fired brick = 22.0 x 10.5 x 6.5 cm with 12% waste at a cost of Rs./Brick comes to 1.60 Rs. /Brick. - As CSEB and CFB have a different size, the cost by volume (including the wastage) is now: Plain CSEB 240 Hollow CSEB 245 Country fired brick (CFB) = 906 Rs./m 3 = 920 Rs./m 3 = 1063 Rs./m 3 Therefore, per m 3 of raw material, CSEB 240 is 17.3 % cheaper than CFB, and HI CSEB 245 is 15.5 % cheaper than CFB. But the cost per m 3 of masonry is quite different (see next page) 25

30 Cost analysis of CSEB masonry with hollow interlocking blocks, produced on site DATA HI CSEB 245 (24.5 cm thick) HI CSEB 295 (14.5 cm thick) Item Rs. Data Rs. Data Rs. Blocks % waste Full blocks per m 2 x Block % waste Full blocks per m 2 x Mortar CSM 1: Litres per m 2 of wall Litres per m 2 of wall 16.1 PCC 1: 1.5: 3 Chips (m 3 ) Litres/m 2 for all the holes Litres/m 2 for all the holes 22.6 PCC 1: 1.5: 3 Gravel(m 3 ) Litres/m of ring beam Litres/m of ring beam 9.0 Steel Φ10TS, Φ6MS (Kg) Kg per m 2 of wall Kg per m 2 of wall Mason m 2 of wall laid per day m 2 of wall laid per day Helpers 75 4 m 2 of wall laid per day m 2 of wall laid per day /2 Labour male m 2 of wall laid per day m 2 of wall laid per day 9.3 1/2 Labour female 60 4 m 2 of wall laid per day m 2 of wall laid per day 5.6 SUB TOTAL PER M Miscellaneous 5 % TOTAL PER M TOTAL PER M 3 1,823 2,167 Reinforcement detail ( 10 TS): 1 vertical tie per running metre + 2 bars per ring beam + PCC in all the holes and 1 ring beam Cost comparison of masonry - Data (Materials delivered on site) - Mason = 150 Rs./day Helper = 75 Rs./day Labour male = 100 Rs./day Labour female = 60 Rs./day - KCP 43 grades = 150 Rs./bag Sieved soil = 70 Rs./m 3 Sieved sand = 360 Rs./m 3 - Plain CSEB 240 = Rs Hollow Interlocking CSEB 245 = Rs CFB = Rs WCB = Rs (WCB are Wire Cut Bricks, also called kiln-fired bricks) - Cost price of walls: - CSEB wall 24 cm thick (Block 240 without plaster) - HI CSEB wall 24.5 cm thick (Block 245 without plaster) - CFB wall 21.5 cm thick (without plaster) - WCB wall 23 cm thick (without plaster) = 320 Rs./ m 2 = 447 Rs./ m 2 = 398 Rs./ m 2 = 599 Rs./ m 2 = 1334 Rs./m 3 = 1823 Rs./m 3 = 1810 Rs./m 3 = 2724 Rs./m 3 Per m 3 of finished wall, CSEB 240 are 26.3 % cheaper than CFB and 51.0 % cheaper than WCB. Per m 3 of finished wall, HI CSEB 245, with reinforcements, are 36.6 % costlier than CSEB 240, and nearly the same cost as CFB (0.7 % costlier) and 33.0 % cheaper than WCB. 3.7 ECONOMIC FEASIBILITY STUDY Today, many small entrepreneurs would like to manufacture blocks to sell them. Indeed, it can be an interesting business, if it is well managed and properly organized. This study is done for Auroville context in March 2005, for the hollow block 245 (24.5 x 24.5 x 9.5 cm). The example studied is for village scale production with manual equipment for 2000 Blocks output per day (2 Auram presses 3000). It shows that the project starts to be viable when two machines are working. The reason is that the fixed costs (overheads: manager, storekeeping. Etc.) are nearly the same if the unit has one or several presses. Notes for the feasibility study - Equipment includes: 2 Auram press mould 245, 2 wheelbarrow 200 Litres, 2 wheelbarrow 350 Kg, 2 soil sieve #10 mm, 2 sand sieve # 4 mm, plastic sheets, 2 barrels and small tools. - Buildings are moveable: office 10m 2, storeroom 20m 2 and a production shed 75 m 2. They are re-used later on. - The management and labour cost includes the yearly bonus and the Employee Providence Fund. - The yearly production is only on 11 months (For maintenance of equipment and heaviest rains) - The loan for the working capital is a demand loan (Short term): Thus, it is not shown in the Inflow / outflow. - The sand cost includes delivery by lorry and sieving on site. - The soil cost includes digging and sieving on site. - Value: Auroville, April 2005, 1 US $ = ±43.5 Rs 26