rwanda standard 484: 2021

ICS 91.100.15

Reference number

DRS 484: 2021

© RSB 2021

RWANDA STANDARD

DRS

484: 2021

First edition

2021-mm-dd

Adobe blocks (Rukarakara) — Specification

DRS 484: 2021

©RSB 2021 - All rights reserved ii

In order to match with technological development and to keep continuous progress in industries, standards are subject to periodic review. Users shall ascertain that they are in possession of the latest edition

© RSB 2021

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DRS 484: 2021

iii ©RSB 2021 - All rights reserved

Contents Page

Foreword ................................................................................................................................................... iv

1 Scope ............................................................................................................................................. 1

2 Normative references ................................................................................................................... 1

3 Terms and definitions .................................................................................................................. 1

4 Requirements ................................................................................................................................ 4 4.1 Dimensions and tolerances ......................................................................................................... 4 4.2 Shape and appearance ................................................................................................................ 4

5 Materials and Manufacturing ....................................................................................................... 4 5.1 Materials ........................................................................................................................................ 4 5.1.1 Soil ................................................................................................................................................. 4 5.1.2 Water .............................................................................................................................................. 5 5.1.3 Fibres ............................................................................................................................................. 6 5.1.4 Stabilisers ..................................................................................................................................... 6 5.2 Manufacturing process ................................................................................................................ 6 5.2.1 Mud preparation ........................................................................................................................... 6 5.2.2 Forming block ............................................................................................................................... 7 5.2.3 Curing block .................................................................................................................................. 7

6 Performance criteria..................................................................................................................... 8 6.1 Strength ......................................................................................................................................... 8 6.2 Cracking ........................................................................................................................................ 8 6.3 Resistance to water ...................................................................................................................... 9 6.4 Resistance to abrasion ................................................................................................................ 9

Annex A (normative) Soil tests ............................................................................................................. 10 A.1 General ........................................................................................................................................ 10 A.2 Procedure .................................................................................................................................... 10 A.2.1 Snake Test ................................................................................................................................... 10 A.2.2 Wash Test .................................................................................................................................... 11

Annex B (normative) Drop test ............................................................................................................. 16 B.1 Procedure .................................................................................................................................... 16 B.2 Result ........................................................................................................................................... 16

Annex C (normative) Determination of moisture content .................................................................. 19 C.1 Procedure to determine appropriate moisture content .......................................................... 19

DRS 484: 2021

©RSB 2021 - All rights reserved iv

Foreword

Rwanda Standards are prepared by Technical Committees and approved by Rwanda Standards Board (RSB) Board of Directors in accordance with the procedures of RSB, in compliance with Annex 3 of the WTO/TBT agreement on the preparation, adoption and application of standards.

The main task of technical committees is to prepare national standards. Final Draft Rwanda Standards adopted by technical committees are ratified by members of RSB Board of Directors for publication and gazettment as Rwanda Standards.

DRS 484 was prepared by Technical Committee RSB/TC 009, Civil engineering and building materials.

In the preparation of this standard, reference was made to the following standards:

1) BS EN 772-1, Method of test for masonry units. Determination of compressive strength

2) Rwanda Building Code-Version 2:2019 Official Gazette No. Special od 19/04/2019

The assistance derived from the above source is hereby acknowledged with thanks.

Committee membership

The following organizations were represented on the Technical Committee on Civil engineering and building materials (RSB/TC 009) in the preparation of this standard.

CIMERWA

Enabel

EGC Ltd

GECO Africa

Mass Design Group

Rwanda Housing Authority (RHA)

Rwanda Inspectorate, Competition and Consumer Protection Authority (RICA)

Standard Geotechnical Engineering and Construction Ltd (STAGECO Ltd)

SJEC Ltd

University of Rwanda/College of Science and Technology (UR-CST)

Rwanda Standards Board (RSB) – Secretariat

DRS 484: 2021

1 ©RSB 2021 - All rights reserved

Adobe blocks (Rukarakara) — Specification

1 Scope

This Draft Rwanda Standard provides the requirements, sampling and test methods for adobe blocks, also known as “Rukarakara” for interior and exterior use in masonry walling.

The use of adobe blocks specified in this Draft Rwanda Standard applies to all buildings in category two (2) as provided in the Ministerial Order governing the categorization of buildings.

Construction with adobe blocks is regulated by the Rwanda Building Code and other related regulations.

2 Normative references

The following documents are referred to in the text in such a way that some or all of their content constitutes requirements of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.

RS ISO 14688-1, Geotechnical investigation and testing. Identification and classification of soil. Identification and description.

RS EAS 18-1 , Cements ― Part 1: Composition, specification and conformity criteria for common cements

3 Terms and definitions

For the purposes of this standard, the following terms and definitions apply.

3.1

adobe block/ ”rukarakara”

air dried masonry unit made from puddled earth/soil mixture of clay, sand and silt with or without organic materials. It sometimes contains fibres and/or stabilizers

3.2

block

discrete unit of earth masonry with the following dimensions:

length between 200mm and 300 mm;

width between 200mm and 250 mm; and

height between 100mm and 150 mm.

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©RSB 2021 - All rights reserved 2

3.3

clay

fine grained, natural, earthy material composed primarily of hydrous aluminium silicates with grain diameters less than 0.002 mm

3.4

compressive strength

physical property of a material that indicates its ability to withstand compressive forces, usually expressed in N/mm2.

3.5

curing

the process in which adobe blocks are protected from loss of moisture and kept within a reasonable temperature range to increase strength and minimize cracking

3.6

durable

resistant to wear and decay. Durability has a corresponding meaning.

3.7

earth (for earth building)

natural sub-soil comprised of varying percentages of clay, silt, sand and gravel which is unfired and is free of significant organic matter

3.8

erosion

physical and chemical processes by which earth building material is worn away. It includes the processes of weathering and mechanical wear

3.9

fibres

typically, straw but may also be animal hair, or from sisal, agave or bamboo for instance

3.10

gravel

individual rock or mineral fragments that range in diameter from 2 mm to 63 mm

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3.11

mud

mixture of soil and water

3.12

sand

individual rock or mineral fragments that range in diameter from 0.063 mm to 2.0 mm

3.13

shrinkage

decrease in volume of earth material caused by curing or the evaporation of water

3.14

silt

individual mineral particles in a soil that range in size from the upper limit of clay (0.002 mm) to the lower limit of fine sand (0.063 mm)

3.15

stabilisation

improvement of the performance of earth building material properties by the addition of materials which bind the earth particles. Stabilization may increase the resistance of earth to moisture, reduce volume changes, improve strength or durability. Where this standard refers to stabilization it means chemical stabilization

3.16

chemical stabilization

intermixture of cement, lime, gypsum, asphalt emulsion, or other materials with the soil before emplacement, and curing as appropriate for the stabilizer and chemical reaction

3.17

mechanical stabilization

compacting or compressing a plastic earth mixture, or containing earth in permanent forms such as bags

3.18

stabiliser

material including cement complying with relevant standard requirements which is used for stabilization

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4 Requirements

The design, manufacturing and construction requirements in this standard shall be used in conjunction with the requirements of the relevant sections of the Rwanda Building Code.

4.1 Dimensions and tolerances

4.1.1 Adobe blocks shall have the following dimensions:

a) length between 200 mm and 300 mm;

b) width between 200 mm and 250 mm; and

c) height between 100 mm and 150 mm.

4.2.2 tolerances shall be as follows:

a) length: +1mm, -3 mm;

b) width: +2 mm, -1 mm; and

c) height: +1 mm, -3 mm.

4.2 Shape and appearance

4.2.1 Adobe blocks shall be:

a) solid;

b) of nominally rectangular shape; and

c) true to the appropriate acceptable pattern.

4.2.2 They shall be acceptably free from broken edges, honeycombing and other visible defects that could interfere with the proper laying of the units or impair the strength or the stability (or both) of a construction.

5 Materials and manufacturing

5.1 Materials

5.1.1 Soil

5.1.1.1 Soils for Adobe block are a mixture of a binder (clay), silt, sand, and gravel. These mixtures may be naturally occurring local soils or engineered by mixing different soils.

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5.1.1.2 Soil classification by particle size shall be defined in accordance with RS ISO 14688-1 and the recommended particle size distribution for adobe blocks shall be:

a) gravel and sand 30 %-80 %;

b) silt 10 %-30 %; and

c) clay 10 %-40 %.

5.1.1.3 The suitability of soil shall be determined by the Snake Test and Wash Test in accordance with Annex. A. These tests shall be performed by experienced trained masons who understand the local soil behaviour.

NOTE 1 The tests determine that the soil has enough clay to bind the particles together and enough granular particles

to provide strength and limit cracking.

NOTE 2 Mixing different soils may be required to achieve a suitable soil mix. An appropriate mix of soils may be

determined using local knowledge from experienced trained masons, the tests identified in clause 5.1.1.3, or laboratory

testing to achieve the recommended particle size distribution.

5.1.1.4 Soil shall be free from:

a) uncontrolled organic matter. This can typically be achieved by removing the 500 mm topsoil;

b) organic matter likely to rot, break down or sprout;

c) water - soluble salts likely to impair strength or durability; and:

d) large aggregates that may impair strength or homogeneous performance. The maximum aggregates size shall be 25 mm in any dimension.

5.1.2 Water

5.1.2.1 Water shall be from a clean source such as:

a) rainwater;

b) underground water;

c) natural surface water; and

d) potable water.

5.1.2.2 Water shall not contain matters including:

a) soaps,

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b) detergents,

c) oil; and

d) harmful chemicals or sewage.

5.1.3 Fibres

5.1.3.1 Fibres are generally added to blocks to reduce cracking due to drying shrinkage.

5.1.3.2 The fibre length shall be between 5 cm and 7cm.

5.1.3.3 The quantity of fibres depends on the type of soil and type of fibres being used. The optimum quantity can be determined through trial blocks. However, the quantity of fibres shall not be less than 5kg/m3, or 2kg of fibre per 50 blocks sized 30x20x15 cm as a prototype.

5.1.3.4 The type of fibres shall be determined based on local knowledge from experienced trained masons and they shall not rot, breakdown or sprout in the block.

NOTE Fibres like “ishinge” are proven to work well.

5.1.4 Stabilisers

5.1.4.1 Stabilisers may greatly improve strength and durability.

5.1.4.2 Stabilisers should only be used when there is no other viable strategy for achieving the project requirements because they have a high embodied carbon and permanently alter the soil, reducing its potential future uses.

5.1.4.3 If stabilisers are required, the minimum quantity should be used to achieve the project requirements and they shall comply with relevant standards requirements

NOTE 1 Portland cement and lime are the most used chemical stabilisers.

NOTE 2 Stabilisers may impact curing times and the required curing conditions.

5.2 Manufacturing process

5.2.1 Mud preparation

5.2.1.1 The mud shall be prepared so that it meets the requirements of clause 5.2.1.2. If stabilisers are used, they shall be well mixed with the dry soil.

5.2.1.2 Water shall be added to the soil so that the mud has a consistency that enables it to be worked into the mould. Excessive water will increase shrinkage cracks and too little water will make it difficult to compact the mud in the mould. The optimal moisture content for making adobe blocks shall be determined in accordance with Annex C.

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5.2.1.3 Depending on the soil type and its existing moisture content, the volume of soil shall be between 5 and 7 times the volume of water. (Water/soil ratio shall be between1:5 and 1:7)

5.2.1.4 It is recommended to leave the mud for between 12 h and 24 h to improve water distribution and activate the clays cohesive properties. This should not be done if cement stabilisers are used.

5.2.1.5 If fibres are used then they shall be evenly mixed into the mud.

5.2.1.6 It should be demonstrated through prior experience that fibres will not rot, break down or sprout in the block.

5.2.2 Forming block

5.2.2.1 The size of the block shall be determined based on the design and construction requirements. The influencing factors include:

the size and weight to allow safe and efficient handling;

thickness of the wall to be built since it is common to use a single block width;

corner bonds. Different sized blocks may be required at corners; and

excessive shrinkage may occur in larger blocks. Blocks with dimensions greater than 300mm are not recommended and should be considered carefully.

5.2.2.2 The internal face of the mould shall be cleaned of any stuck mud and soaked before the new mud is added to limit soil adhesion.

5.2.2.3 The blocks shall be manufactured where they are to be cured and close to where they will be stored to avoid damage due to transporting them between locations.

5.2.2.4 Mud shall be added to the mould in at least three layers of approximately equal thickness and compacted into the corners.

5.2.3 Curing block

5.2.3.1 It is recommended that blocks are air dried, not sun-baked. This is to say that they should be shaded from direct strong sunlight, especially in the first 4 days of curing, but still have adequate airflow around the blocks. Excessive exposure to strong sun can accelerate surface drying and cause cracking. If curing in a shaded area is not possible, in the case of strong sunlight the blocks shall be covered with grass or banana leaves or a layer of soil or sand to prevent immediate cracking.

5.2.3.2 Protection from rain and surface water is extremely important throughout the curing period and when in the wall and not covered by a roof. A plastic sheet shall be used to protect the blocks from rain however it should not limit airflow or drying of blocks for long periods of time.

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NOTE Other forms of rain protection such as banana leaves provide limited protection during large rainfall and do not allow the blocks to dry if placed directly against them. Raising the blocks off the ground and providing a bund around the

curing area will help to protect them from surface water during large rainfalls.

5.2.3.3 Following initial drying, the blocks should be turned onto their side when strong enough to do so, and then rotated every 3-4 days. Depending on the size of block and the weather, curing may take between 1 week and 2 months, and blocks shall not be used before they are fully cured. When they are fully cured, the block has the same colour as the dry soil they were made from, and when tapped with a coin they produce a ‘clear ring’.

5.2.3.4 Dry blocks shall be stacked in rows not exceeding 7 number.

5.2.3.5 Blocks stabilised with cement shall be damp cured for at least 1 week before being air dried. During damp curing the blocks are not allowed to dry.

6 Performance criteria

6.1 Strength

6.1.1 Compressive strength shall be performed in accordance with BS EN 772-1:2011+A1:2015.

6.1.2 The minimum compressive strength is 0.5N/mm2.

6.1.3 The Block Drop Test may be used as an indicator of strength.

6.1.4 At least 20 trial blocks should be made using the same materials and techniques expected to be used in the future manufacture of blocks. These trial blocks should be tested using the Block Drop Test and if 80% pass the blocks may be considered to have met the required minimum compressive strength as per Annex B .

6.1.5 If any part of the mixture or manufacturing process changes during construction then the testing described in clause 6.1.4 shall be performed again. Any of the following would require testing to be performed again:

soil from another location is used;

the type of soil in the pit clearly changes, often indicated by changes in colour or particle size; and

fibre type or quantity of fibre is changed.

6.1.6 If still suitable, the broken blocks from the test may be used in the building as half blocks at openings or wall ends.

6.2 Cracking

6.2.1 Cracks occur due to the natural shrinkage of blocks as they cure.

6.2.2 Cracks that do not impair structural integrity or handling of blocks are acceptable.

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6.2.3 Cracks less than 3 mm in width are typically acceptable.

6.2.4 It is recommended that not more than 10 % of blocks in a wall contain cracks wider than 3 mm and longer than 75 mm or, irrespective of the crack length or width, deeper than 10 mm along any part of the crack.

6.2.5 Cracks may be reduced by modifying the soil mix, limiting the size of the blocks, modifying fibre content, or reducing curing speed.

6.3 Resistance to water

6.3.1 Unstabilised earth can lose much of its structural strength when moist or wet. Rukarakara should not therefore be used for below-grade applications such as foundations or retaining walls. When exposed to weather, Rukarakara is very susceptible to water erosion which may reduce the width of the wall over time. This is a common problem at the base of walls where a horizontal cavity develops due to rain coming down the face of the wall and rain splash from the ground.

6.3.2 There is no minimum requirement for the block itself because durability provisions should be put in place to protect the block from water, and therefore it may never encounter durability issues, even if the block itself is not resistant to water.

6.3.3 Recommended methods of protecting the block from water include:

a) adequate roof overhangs to reduce driven rain - recommended length of roof overhang for full protection is one third of the wall height

b) sacrificial protection layer, typically an earth plaster that is maintained over time; and

c) elevating the blocks, for example on a stone plinth, above any potential ground water or rainwater splash back - recommended elevation 200 mm above external ground level, 50mm above internal ground level

6.3.4 Stabilization can also be used to increase resistance to water.

6.4 Resistance to abrasion

6.4.1 Adobe block is susceptible to erosion from abrasion. Abrasion is particularly common at corners of buildings and doorways, which are areas key to the structural integrity of buildings. Excessive erosion will reduce structural integrity.

6.4.2 There is no minimum requirement for the block itself because the block may be protected from abrasion and therefore never encounter performance issues even if the block itself is not resistant to abrasion.

6.4.3 The recommended method of protecting the block from abrasion is to add a sacrificial protection layer, typically an earth plaster that is maintained over time. Increasing the thickness of this layer at the corners of buildings and either side of doorways will increase protection to areas of the building most susceptible to abrasion.

6.4.4 Stabilization can also be used to increase resistance to abrasion.

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Annex A (normative)

Soil tests

A.1 General

The Snake Test and Wash Test shall be performed to determine if the soil is appropriate for making adobe blocks. The process is as follows:

a) Perform the snake test using the methodology below.

b) If the soil fails the snake test (i.e. the soil cannot be rolled into a 3 mm diameter thread) then the soil is not plastic enough and is not recommended for making adobe blocks.

c) If it passes the snake test (i.e. the soil sample can be rolled into a 3 mm diameter thread), the wash test shall be performed in accordance with the methodology below to work out the percentage of coarse material (sand and gravel) in the soil.

d) If the amount of coarse material in the soil is outside the recommended values in this document, which is 30 to 80 %, the soil is not recommended for adobe blocks.

e) If the amount of coarse material in the soil is within the recommended values in this document then the soil is recommended for adobe blocks and trial blocks shall be made.

A.2 Procedure

A.2.1 Snake Test

A.2.1.1 The purpose of the snake test is to check the plasticity of soils. Being plastic means that they have a noticeable amount of clay. To do that, place a small amount of wet soil free from gravel between palms. Confirm the moisture content is correct according to Annex C. Roll the soil until it forms a long, round thread of about 3 mm diameter. If it fails to be rolled into such a thread, it will not be plastic and not recommended for making adobe blocks. Where this is the case - the soil can be mixed with a finer soil in order to increase plasticity, and this test should be repeated. The typical process is presented below.

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Figure 1: Snake test demonstrating soil has appropriate plasticity levels

A.2.1.2 As a note, it is essential to make sure that the soil is not too dry or too wet. If it is too dry, it may crumble in hands immediately after starting to roll it, and if it is too wet, it may tend to stick to hands resisting to get rolled between palms of hands.

Figure 2: Left - too dry, Right - too wet

A.2.2 Wash Test

A.2.2.1 Materials required:

• Soil, roughly 3kg

• Weighing scale of 0.1kg accuracy

• Large plastic sheet

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• Buckets x 2

• 1L bottle for measuring water

A.2.2.2 Take a representative sample of soil of about 3kg, free from vegetation debris and other organic material. The soil for making adobe blocks should be collected after stripping off the top soil to a depth of at least 0.5 m from the ground surface.

A.2.2.3 Weigh the soil with a scale and record its (wet) weight (Ww).

A.2.2.4 Air dry the soil sample for at least 48h preferably in the sun. Try to disperse the soil over a large plastic sheet so that soil thickness does not exceed 5 mm.

Figure 3: Dispersing soil over large plastic sheet

A.2.2.5 Touch through it thoroughly every 1 to 2 hours turning it in all directions to allow even drying.

Figure 4: Touch through soil thoroughly

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A.2.2.6 Weigh the soil after the drying process and record its dry weight (Ws).

A.2.2.7 Put the dry soil into a bucket and add water little by little while mixing to break clumped soil. You will need to add about 6 liters of water.

Figure 5: Adding water to dry soil in bucket

A.2.2.8 Once all clumped soil has been broken, agitate vigorously using a hand for about 1min. The mixture should look homogenous, there should be no remaining clumps of soil, and instead it should be possible to feel sand grains and gravel pieces.

Figure 6: Agitate soil to break down all clumps

A.2.2.9 After agitation, leave the mixture to stand for about 1 minute. The coarser material will settle to the bottom of the bucket and the fines will remain in suspension.

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Figure 7: Coarser material settles first

A.2.2.10 Pour out the slurry (i.e. fines in suspension) gently into another bucket and stop when you reach the deposit which looks like a thick slurry at the bottom of the bucket.

Figure 8: Pour out the slurry of fine material, keep the coarse material at the bottom

A.2.2.11 Add water, and repeat the process from step A.2.2.7 to step A.2.2.9.

A.2.2.12 Repeat the process over and over again until you remain with clean coarse material (sand and gravel) as a deposit at the bottom of the bucket. The water should appear clear. Air dry the material on a plastic sheet preferably in the sun for at least 4 hours or until it is visually dry. Weigh the dry amount of coarse material and record its weight (Ds).

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Figure 9: Remaining clean coarse material

A.2.2.13 Work out the percent amount of coarse material (sand and gravel) in the soil as (Ds/Ws) x100.

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Annex B (normative)

Drop test

B.1 Procedure

B.1.1 A block shall be selected that is fully cured

B.1.2 The block shall have a length of between 1 and 2 times its width. The block may be cut so that it has this ratio.

B.1.3 It shall be dropped on its corner as shown in Figure 10 from a height of 900mm onto a hard surface, such as compacted earth.

Figure 10: Orientation of adobe block prior to dropping

B.2 Result

B.2.1 The block shall pass if the following criteria are met:

a) it does not shatter or break into approximately equally sized pieces

b) there shall not be a piece broken off that has a dimension either:

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⎯ greater than the smallest dimension of the block. For instance if the block has dimensions 300x200x100, then the maximum size of the broken piece shall be 100mm.

⎯ greater than 150mm.

Figure 11: Shattered block: FAIL

Figure 12: Block broken in half: FAIL

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Figure 13: Small piece broken off block corner: Measure according to Figure 14

Figure 14: How to measure broken piece - if less than 150mm: PASS

B.2.2 The following are recommendations based on the pass rate of at least 20 blocks.

a) > 80% pass rate: block performs well

b) 60-80% pass rate: block is acceptable but recommend improvements, such as mixing with another soil to improve the properties and testing again

c) < 60% pass rate: strongly recommend not using the soil. Mixing with a significant percentage of another soil may improve the properties. Test again after mixing.

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Annex C (normative)

Determination of moisture content

C.1 Procedure to determine appropriate moisture content

The optimal amount of water in a mud paste is determined by taking a handful of the mixture and squeezing it to see how wet it is in the hand, and how much mud exits through the fingers. More information is provided in the table below.

rwanda standard 484: 2021

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