FINAL DRAFT UGANDA 
STANDARD  
  FDUS 849
First Edition
2009-mm-dd
 
 
Reference numbe r
FDUS 849: 2009
 © UNBS 2009y 
  
Specification for stabilized soil blocks  
 FDUS 849: 2009 
ii © UNBS 2009 – All rights reserved
 Compliance with this standard does not, of itself confer immunity from legal obligations 
A Uganda Standard does not purport to include all necessary provisions of a contract. Users are 
responsible for its correct application  
© UNBS 2009  
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilised in any 
form or by any means, electronic or mechanical, in cluding photocopying and microfilm, without prior written 
permission from UNBS. 
Requests for permission to reproduce this document should be addressed to 
The Executive Director 
Uganda National Bureau of Standards 
P.O. Box 6329 
Kampala  
Uganda 
Tel: 256 414 505 995 
Fax: 256 414 286 123 
E-mail: unbs@infocom.co.ugFDUS 849:2009 
© UNBS 2009 – All rights reserved  iii
 Contents Page 
Foreword ............................................................................................................................................................iv  
1 Scope ......................................................................................................................................................1  
2 Normative references ............................................................................................................................1  
3 Terms and definitions ...........................................................................................................................1  
4 Materials .................................................................................................................................................2  
4.1  Cement ...................................................................................................................................................2  
4.2  Lime ........................................................................................................................................................2  
4.3  Soils ........................................................................................................................................................2  
5  Shape, dimensions and tolerances .....................................................................................................2  
5.1 Dimensions ............................................................................................................................................2  
5.2  Tolerances ..............................................................................................................................................2  
6 Physical properties ............................................................................................................................... 7 
6.1 Dry compressive strength ....................................................................................................................7  
6.2 Wet compressive strength ...................................................................................................................7  
6.4 Water absorption ...................................................................................................................................7  
6.5 Density ....................................................................................................................................................7  
6.6 Weathering .............................................................................................................................................7  
6.7 Shrinkage cracks ...................................................................................................................................7  
5.8 Visual Inspection ...................................................................................................................................7  
Annex A (normative)  Measurement of Dimensions .......................................................................................8  
Annex B (normative)  Determination of compressive strength ...................................................................11  
Annex C (normative)  Determination of modulus of rapture ........................................................................14  
Annex D (normative)  Determination of water absorption ...........................................................................16  
Annex E (normative)  Determination of bulk density ....................................................................................18  
Annex F (normative)  Weathering test ............................................................................................................19  
 FDUS 849: 2009 
iv © UNBS 2009 – All rights reserved
 Foreword 
Uganda National Bureau of Standards (UNBS) is a parastatal under the Ministry  of Tourism, Trade and 
Industry established by the Act of Parliament of 198 3, of the Laws of Uganda.  UNBS is mandated to co-
ordinate the elaboration of standards and is  
(a) a member of International Organisation for Standardisation (ISO) and  
(b) a contact point for the WHO/FAO Codex A limentarius Commission on Food Standards, and  
(c) the National Enquiry Point on TBT/SPS Agr eements of the World Trade Organisation (WTO). 
The work of preparing Uganda Standards is carried out through Technical Committees. A Technical 
Committee is established to deliberate on standards in a gi ven field or area and consists of representatives of 
consumers, traders, academician s, manufacturers, governme nt and other stakeholders. 
Draft Uganda Standards adopted by the Technical Committ ee are widely circulated to stakeholders and the 
general public for comments. The committee reviews the comments before recommending the draft standards 
for approval and declaration as Uganda Standards by the National Standards Council.  
Committee membership 
Good Earth Trust  
Makerere University 
Ministry of Energy and Mineral Development, Geological Survey and Mines 
Uganda National Bureau of Standards FDUS 849:2009 
© UNBS 2009 – All rights reserved  v
 Introduction 
Soil is perhaps the oldest and most abundant building materi al available to mankind. However, the use of Soil 
as a conventional building material is limited in this country. With increasing need to house an ever growing 
population, the use of earth must  be re-visited in view of its abundance and versatility.   
 FINAL DRAFT UGANDA STANDARD FDUS 849: 2009
 
© UNBS 2009– All rights reserved  1
 Specification for stabilized soil blocks 
1 Scope 
 
This Final Draft Standard specifies the requirements for stab ilized soil blocks using cement and/or lime for use
in general construction.   
2 Normative references 
US 310 – 1 Cement – Part 1: Composition, specific ations and conformity criteria for common cements 
US 156 Standard specification for Building lime (including test methods)  
US 288 Lime for soil stabilization 
3 Terms and definitions 
3.1  
Stabilized soil blocks 
 
Building blocks made by a mixture of soil with a por tion of cement and/or lime as a stabilizer.  
3.2 
Nominal size 
 
The size of a co-ordinating space allocated to a masonry unit including allowances for joints and tolerance. 
3.3 
Work size 
 
The size of a block specified for its manufacture to whic h its actual size should conform within the specified 
permissible deviations. 
 
3.4 
Compressive strength 
The average compressive strength at failure when five blocks have been crushed in a compression test 
machine at a loading rate of 150 kN per minute.   
3.5 
Modulus of rupture 
This is the nominal transverse breaking strength of the blocks. FDUS 849: 2009 
2 © UNBS 2009 – All rights reserved
 4 Materials 
 
4.1 Cement  
The cement used for the manufacture of stabilized soil blocks shall conform to US 310 – 1 Cement – Part 1: 
Composition, specifications and confor mity criteria for common cements. 
4.2 Lime   
The lime used for the manufacture of stabilized soil bloc ks shall conform to US 288 Lime for soil stabilization 
and US 156 Standard specification for building limes.  
4.3 Soils  
The soils used for the manufacture of stabilized soil bl ocks shall be free of deleterious and organic materials.   
5 Shape, dimensions and tolerances 
5.1 Dimensions  
Dimensions of stabilized soil bl ock shall conform to Table 1. 
Table1: Standard formats of stabilized soil blocks 
Length (mm)  Width (mm) Height (mm) 
Nominal size Work size Nominal size Work size Nominal /Work size 
200 190 75 65 55 to 65 
200 190 100  90 75 to 90 
300 290 100  90 80 to 95 
300 290 150 140 100 to 115 
400 390 150 140 105 to 120 
400 390 200 190 125 to 140 
 
5.2 Tolerances 
The maximum dimensional deviations for stabilized soil blocks measured in accordance with Annex A shall be 
as specified in Table 2. 
 
 
 
Table 2: Dimensional tolerances for stabilized soil blocks FDUS
© UNBS 2009– All rights reserved 3
  849: 2009 
Dimension Maximum dimensional deviation 
Length + 1 mm  
 - 3 mm 
Width +2 mm  
 - 1 mm 
Height + 1 mm   
- 3 mm 
Surface smoothness sides + 1 mm  
 - 1 mm 
Compression surface +3 mm  
 - 1 mm 
 
All dimensions are in millimetres  
 
 
 Figure1:  Standard block FDUS 849: 2009 
4 © UNBS 2009 – All rights reserved
 
 
Figure 2: Straight single interlocking block  
                                                                
Figure 3: Straight double interlocking block 
 FDUS
© UNBS 2009– All rights reserved 5
  849: 2009 
 
 
Figure 4: Curved single interlocking block 
 
Figure 5:   Curved double interlocking block FDUS 849: 2009 
6 © UNBS 2009 – All rights reserved
 
 
Figure 6: Wide format interlocking block 
 
 
Figure 7: Chamfered edges dimensions 
 FDUS
© UNBS 2009– All rights reserved 7
  849: 2009 
6 Physical properties 
 
6.1 Dry compressive strength 
The dry compressive strength at 28 days when tested in accordance with Annex B shall not be less than 2.5 
N/mm2. 
6.2 Wet compressive strength 
When stabilized soil blocks are tested in accordance  with Annex B, the minimum average wet compressive 
strength at 28 days shall not be less than 1.5 N/mm2. 
6.3 Modulus of rupture 
The rupture strength when determined in accordance  with Annex C shall not be less than 0.5N/mm2. 
6.4 Water absorption 
The water absorption of stabilized soil  blocks when determined as described in Annex D shall not exceed 15 
per cent of the original mass.  
6.5 Density 
The density of blocks when determined in accordan ce with Annex E shall not be less than 1 600kg/m3. 
6.6 Weathering 
When subjected to the weathering test carried out in accordance with Annex F the maximum loss of mass 
shall not exceed 15 per cent. 
6.7 Shrinkage cracks 
Shrinkage cracks shall not be more than 0.5 mm wide an d shall not exceed in length 50 per cent of the block 
dimension to which they are parallel; where they are not parallel, thei r projected length shall be measured. 
6.8 Visual Inspection 
All blocks on visual inspection shall be free of brok en edges; honeycombing and such other defects as would 
interfere with the proper placing of the blocks or impair the strength or permanence of construction. 
 FDUS 849: 2009 
8 © UNBS 2009 – All rights reserved
 Annex A 
(normative) 
 
Measurement of Dimensions 
A.1 Test specimens 
   20 blocks shall be selected at random for test. They shall be used for dimensional checks and other  
   tests as described.   
A.2  Apparatus 
A.2.1 GO/NOT GO gauges 
 GO/NOT GO gauges as shown in Figure 8. The length gauge shall be appropriate to the specified 
 length, width and height of block. 
A.2.2 External Calipers 
A.2.3 A rule graduated to 1 mm, for use with the callipers.  
A.3   Procedure 
A.3.1 Length and height 
  Check the compliance of each block for length at the four corners of the end faces (see Figure 9(a))  
  using a GO/NOT GO gauge.  
  Similarly, check the compliance of each block for height at six points (see Figure 9(b)). The height of 
  a block is the smallest of the three dimensions, i.e. width, length and height. The length and height of   each block shall be reported as the respective average to the nearest mm. 
A.3.2 Width 
  Measure the width of each block to the nearest mm at seven random positions as shown in Figure  
  2(c) using the callipers and rule. Calculate and re port the average of the se ven results to the nearest 
  mm.  
 
 
 
 
 FDUS
© UNBS 2009– All rights reserved 9
  849: 2009 
 
All dimensions are in millimetres 
Figure 8: GO/NOT GO Gauges for checking length and height of blocks 
Notes: 1. x is the specified dime nsion of the block plus 3 mm, and 
      y is  the specified dimension of the block 5 mm. 
  2. Keys are used for keeping fittings at both ends in the same plane. 
 
Figure 9a: Four Positions for checking length of whole blocks 
 
 FDUS 849: 2009 
10 © UNBS 2009 – All rights reserved
  
 
Figure 9 (b): Six Positions for checking height of whole blocks  
 
 
 
Figure 9(c): Checking and measuring dimensions of blocks 
A.4 Reporting 
 Report the average length, height and width of blocks.  
 
 FDUS
© UNBS 2009– All rights reserved 11
  849: 2009 
Annex B  
(normative) 
 
Determination of compressive strength 
B.1  Test specimens 
  Ten whole blocks shall be selected at random from the sample after carrying out the dimensional  
  checks.  Five blocks shall be used for dry compressive strength and another five for wet compressive   strength. 
B.2  Principle 
B.2.1 Dry compressive strength 
  A unit is placed in a compressive testing machine and subjected to increased compression until it  
  fails. The compression strength is calculated from the maximum load. 
B.2.2 Wet compressive strength 
  A unit is immersed in water for a specified period of time. The unit is then tested using the same  
  principles as clause B.2.1. 
B.3  Apparatus 
B.3.1 Loading machine 
  A compression loading machine either hydraulic or screw type with adequate capacity and capable  
  of applying the loads at rates specified in clause B.4. 
  The machine shall be fitted with two steel platens which shall be self-aligning. 
  The bearing faces of both platens should exceed the test specimen by not less than 15 mm length in   length and breadth and shall not depart from a plane by more than 0.06 mm. Should the bearing  
  faces of the platens be smaller than required, st eel plates of adequate size may be placed centrally  
  between them and the test specimen. Their thickn ess shall be equal to at least one-third of   
  the greater difference in dimension in between the machine platen and the test specimen, when    centrally placed but not less than 25 mm. 
B.3.2 Measuring rule 
  A rule that can be read accurately to 1.0 mm over the dimensions of the units being tested. 
B.3.3 Water bath 
  A water bath of sufficient size to hold the specimens without them touching each other and sufficient 
  depth to ensure that the specimens will be complete ly immersed in water for the full duration of the  
  test. 
B.4  Dry compressive strength 
B.4.1 Procedure 
  The procedure of each specimen shall be as follows: FDUS 849: 2009 
12 © UNBS 2009 – All rights reserved
 (a) Measure and record the following dimensions, to the nearest millimetre: 
(i) The width (B) of each specimen as described in clause A3; 
(ii) The length (L) of each specimen as described in clause A3. 
(b) Clean and wipe the surfaces of the test specimen removing all loose debris. Clean the bearing 
surfaces of the platens on the testing machine,  and any steel plates to be placed between the 
specimen and platen. 
(c) Place the specimen between two pieces of 3 mm thick plywood, the length and width of which shall 
exceed the corresponding dimensions of the sp ecimen by less than 25 mm each plywood shall be 
used only once. The specimen shall be placed in the testing machine such that the centre of the bed 
face coincides with the loading axis of the machine.  
(d) Apply the load without shock and increase it continuou sly at a uniform rate of 150 kN/min until failure 
occurs.  
(e) Observe and record the maximum load (W ) at failure. D
 
B.5  Wet compressive strength 
B.5.1  Procedure 
  The procedure for each specimen shall be as follows: 
(a) Measure and record the following dimensions to the nearest millimetre: 
(i) The width (B) of each specimen as described in clause A3; 
(ii) The length (L) of each specimen as described in clause A3. 
0 0(b) The specimen shall be immersed in water at 15 C to 30 C for 24 h. 
(c) The specimen shall be removed from the water bat h. They shall then be wiped clean with a piece of 
cloth. 
(d) The procedure for the compression testing shall proceed as described in clause B.4.1 to clause B.4.1 
(d).  
(e) Observe and record the maximum load (W ) at failure. W
 
B. 6 Calculation of results 
The compressive strength of each specimen (dry or  wet) shall be calculated from the the following 
expressions: 
AWW
AWD
   =  DC or  =  WC  
 
 FDUS
© UNBS 2009– All rights reserved 13
  849: 2009 
Where, 
 C D = dry compressive strength in N/mm2; 
 C W = wet compressive strength  in N/mm2; 
 W D = total load at which the dry specimen fails, in Newtons; 
 W W = total load at which the wet specimen fails, in Newtons; 
 A = the smaller bed face area, in square millimetres. 
 Length (L) and width (B) taken for whichever of  two bed faces produces the smaller area. 
 
B.7  Reporting 
 Report the average of the compressive strengt h; either dry or wet of the five specimens. 
  
 
 
 
 FDUS 849: 2009 
14 © UNBS 2009 – All rights reserved
 Annex C  
(normative) 
 
Determination of modulus of rapture 
 
C.1  Test specimens 
  Five whole blocks shall be selected at random from the sample after carrying out dimensional   
  checks. 
C. 2  Principle  
  Five blocks are tested by applying a load through tw o bars, with the specimen laid flatwise, until the  
  specimen fails. The maximum bending moment is used to calculate the lateral modulus of rapture. 
C.3  Apparatus 
C.3.1 Loading machine 
  A compression loading machine either hydraulic or screw type with adequate capacity and capable  
  of applying the loads at rates specified in clause C.4.4.  
  The machine shall be fitted with support bars and loading bars which will permit the loading of test  
  specimens as simple beams as shown diagrammatically in Figure 10. The support and loading bars    shall be not less than 25 mm and not more than 40 mm in diameter, parallel and normal to the axis of 
  the specimen. 
C.3.2 Measuring rule 
  A rule that can be read accurately to 1.0 mm over the dimensions of the units being tested. 
C.4   Procedure 
C.4.1  Measure and record the following dimensions, to the nearest millimetre:  
(i) The width (B) of each specimen. 
(ii) The height (depth) (D) of each specimen. 
(iii) The distance ( l) between the supporting bars in the testing machine (see Figure 10). 
 
   
 
 
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© UNBS 2009– All rights reserved 15
  849: 2009 
 
Figure 10: Arrangement of modulus of rupture 
C. 4. 2 Support the test specimen flatwise on a span app roximately 25 mm less than the basic unit length. 
C.4.3 Bring the loading bar which shall be at mid span of the specimen ti bear on the upper surface   
  of the specimen. 
C.4.4 Apply the test load, without shock, at a unif orm rate of 3 kN/min until failure occurs. 
C.4.5 Observe the maximum load (W) carried by the specimen. 
C.5  Calculation of results 
  The modulus of rupture of each specimen sha ll be calculated from the following      
  expressions : 
  Modulus of rupture,  
BDSWl
22=
    
Where, 
 S = stress in specimen at midspan, in N/mm2, 
 W = maximum load at failure, in Newtons, 
  l = distance between the supports, in mm, 
 B = width, face to face, of the specimen, in mm, and  
 D = depth, bed face to bed face, in mm. 
C.6 Reporting 
 Report the average of the modulus of rupture of the five specimens. 
 FDUS 849: 2009 
16 © UNBS 2009 – All rights reserved
 Annex D  
(normative) 
 
Determination of water absorption 
D. 1  Test specimens 
  Five whole blocks shall be selected at random from the sample after carrying out dimensional   
  checks. 
D. 2  Principle  
  A block is saturated by immersion in water for a specified period of time. The specimen is then dried 
  and the amount of water absorbed is then deter mined and used to calculate the percentage water  
  absorption. 
D.3.1 Balance 
  A balance sensitive to within 1 g. 
D.3.2 Drying oven 
  A thermostatically – controlled drying oven capable of maintaining temperature of 105 0C.  
D.3.3 Water bath 
  A water bath of sufficient size to hold the specim ens without them touching each other sufficient  
  depth to ensure that the specimens will be complete ly immersed in water for the full duration of the  
  test. 
D.4  Procedure 
  (a) The specimens shall be immersed in water at 15 0C to 30 0C for 24 h. 
  (c) The specimen shall be removed from the water.  They shall then be wiped with a piece of cloth  
   and within 3 minutes after removing from the water the mass of saturated specimen shall be  
   determined by weighing to the nearest gramme. Record the saturated mass as M 2. 
  (d) The saturated specimens shall be dried in a ventilated oven at 105 ± 5 0C for not less than 24 h 
   and until two successive weighings, at interval s of 2 h show an increment of loss not greater  
   than 0.2 per cent of the last previously determined weight of sp ecimen. Record the mass of the  
   oven dry specimen as M 1. 
D.5  Calculation of results 
D.5.1 Water absorption 
  The water absorption (per cent) for each specimen shall be calculated from the following    
  expressions: 
 FDUS
© UNBS 2009– All rights reserved 17
  849: 2009 
100
11 2xMM MAW−=
 
 
 Where, 
  A  = percentage water absorption, w
  M 1 = mass of oven dry specimen, in grammes, and, 
  M 2 = mass of saturated specimen after immersion in water, in grammes. 
D. 6  Reporting 
  Report all results separately for eac h unit and as average for the five units. 
 FDUS 849: 2009 
18 © UNBS 2009 – All rights reserved
 Annex E 
(normative) 
 
Determination of block density 
E.1  Test specimens 
  Select at random three blocks from the sample for testing. Carry out the dimensional measurements 
  as described in Annex A, noting the av erage length, height and width of each block. 
E.2  Apparatus 
E.2.1 Drying oven 
0  Thermostatically – controlled drying oven ca pable of maintaining temperature at 105 ± 5 C. 
E.2.2 Calculating of volume 
3  Calculate the gross volume of the blocks to the nearest 250 mm  by multiplying the average   
  thickness by the average le ngth and height of the block. 
E.3  Procedure 
0  Dry the three specimen blocks for at least 24 h in a ventilated oven at 105 ± 5 C. 
  Cool the blocks to ambient temperature and weigh.  Repeat these steps until the mass lost in one  
  cycle does not exceed 0.05 kg. 
E.4  Calculation of density 
VM
bC=
 
  w h e r e ,   
3  C  = block density (in kg/m ), b
  M  = oven dry mass (in kg), and 
  V    =  gross volume in blocks (in m3). 
E.5  Reporting 
3  Report the density to the nearest 10 kg/m . 
 FDUS
© UNBS 2009– All rights reserved 19
  849: 2009 
Annex F 
(normative) 
 
Weathering test 
F.1  Test specimens 
  Two whole blocks shall be selected from the sample  of blocks obtained as described under Annex A, 
  after carrying out the test for dimensional confor mity. The blocks shall be designnated “specimen A”  
  and  “specimen B”, respectively. 
F.2  Apparatus 
F.2.1 Balance 
  A balance or scale of 20 kg capacity, sensitive to 50 g. 
F.2.2 Drying ovens 
  Two thermostatically – controlled drying ovens, on e capable of maintaining temperature at 105 ± 5 
  0C and the other  capable of maintaining temperature at 70 ± 5 0C. 
F.2.3 Water bath 
  A suitable tank  for submerging specimens in water at room temperature. 
F.2.4 Wire scratch brush 
  A brush made of 50 mm x 1.6 mm flat with 0.4 mm wire bristles assembled in 50 longitudinal rows  
  and 10 transverse rows of bristles on 200 mm x 60 mm hardwood block. 
F.3  Procedure 
  Oven dry specimen A at 105 ± 5 0C for at least 12 h or to a constant mass. From this weight,   
  calculate the oven – dry weight (W 1) of specimen A. Carry out further operations on specimen B only 
F.3.2 Submerge specimen B in water at room temperature for 6 h. Remove and immediately place it in an 
  oven at 70 0C for 42 h and remove. Brush all areas of the specimen twice with the wire scratch      
  brush. Hold the brush with the long axis of the br ush parallel to the longitudinal axis of the specimen 
  or parallel to the ends as required to cover all ar eas of the specimen.  Apply these strokes to the  
  height and width of the specimen with a firm st roke corresponding to approximately 1.5 kg force (see 
  note). Eighteen to twenty vertical brush strokes are required to cover the sides of the specimen twice 
  and four strokes are required on each end. 
  NOTE: Measure the pressure as follows: 
    Clamp a specimen in a vertical position on t he edge of a platform scale and set the scale to 
    zero. Apply vertical brushing strokes to the specimen and note the force necessary to   
    register approximately 1.5 kg. 
F.3.3  The procedures described in clause F.3.2 constitu tes one cycle (48 h) of weathering test. Continue  
  the procedure for 12 cycles. After 12 cycles of te st, dry the specimen to constant weight at 105 ± 5 
  0C and determine the final oven – dry weight (W f) of the specimen. The data collected permits   
  calculations of the soil – cement loss of t he specimen after the prescribed test of 12 cycles. FDUS 849: 2009 
20 © UNBS 2009 – All rights reserved
 F.4 Calculation and report 
F.4.1 Calculate the soil – cement loss of the specimen as a percentage of the originally calculated   
  oven – dry weight (W ) of the specimen as follows:   i
100xWW W
if i−
  Soil – cement loss, per cent =   
 
  w h e r e   
 = Oven dry weight   W i
  W f = Final oven-dry weight  
 FDUS
 
© UNBS 2009– All rights reserved  21
  849: 2009 
Certification marking 
Products that conform to Uganda standards may be  marked with Uganda National Bureau of Standards 
(UNBS) Certification Mark shown in the figure below.  
The use of the UNBS Certification Mark is gove rned by the Standards Act, and the Regulations made 
thereunder. This mark can be used only by those licens ed under the certification mark scheme operated by 
the Uganda National Bureau of Standards and in co njunction with the relevant Uganda Standard. The 
presence of this mark on a product or in relation to a product is an assurance that the goods comply with the 
requirements of that standard under a system of supervision, control and  testing in accordance with the 
certification mark scheme of the Uganda National  Bureau of Standards. UNBS marked products are 
continually checked by UNBS for conformity to that standard.  
Further particulars of the terms and conditions of  licensing may be obtained from the Director, Uganda 
National Bureau of Standards.  
 
 FDUS
 
ICS  849: 2009 
 
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