UGANDA STANDARD  
  DUS 2033  
First Edition  
2018 -09-10 
 
 
 Reference number  
DUS 2033 : 2018 
© UNBS 2018   
  
Solid concrete block  — Specification  
 DUS 2033 : 2018  
ii © UNBS 2018  – 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 ap plication  
© UNBS yyyy  
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, including 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 41 4 333 2 50/1/2/3  
Fax: +256 41 4 286 123  
E-mail: info@unbs.go.ug  
Web: www.unbs.go.ug  DUS 2033 : 2018  
© UNBS 2018  – All rights reserved  iii 
 Contents  Page 
Foreword  ................................ ................................ ................................ ................................ .............................  v 
1 Scope  ................................ ................................ ................................ ................................ ......................  1 
2 Normative references  ................................ ................................ ................................ ............................  1 
3 Terms and definitions  ................................ ................................ ................................ ...........................  1 
4 Specification, grade, code and mark  ................................ ................................ ................................ ... 2 
4.1 Specification  ................................ ................................ ................................ ................................ ..........  2 
4.2 Density grade  ................................ ................................ ................................ ................................ .........  2 
4.3 Strength grade  ................................ ................................ ................................ ................................ ....... 2 
4.4 Code and Mark  ................................ ................................ ................................ ................................ ....... 2 
5 Raw material  ................................ ................................ ................................ ................................ ..........  3 
5.1 Cement  ................................ ................................ ................................ ................................ ...................  3 
5.2 Fine aggregate  ................................ ................................ ................................ ................................ ....... 3 
5.3 Coarse aggregate  ................................ ................................ ................................ ................................ .. 3 
5.4 Admixture  ................................ ................................ ................................ ................................ ...............  3 
5.5 Additive  ................................ ................................ ................................ ................................ ..................  3 
5.6 Water  ................................ ................................ ................................ ................................ .......................  3 
5.7 Radionuclide Limited Standard  ................................ ................................ ................................ ...........  3 
6 Requirements  ................................ ................................ ................................ ................................ .........  3 
6.1 Dimension deviation  ................................ ................................ ................................ .............................  3 
6.2 Appearance quality  ................................ ................................ ................................ ...............................  3 
6.3 Density grade  ................................ ................................ ................................ ................................ .........  4 
6.4 Strength grade  ................................ ................................ ................................ ................................ ....... 4 
6.5 Maximum water absorption  ................................ ................................ ................................ ..................  5 
6.6 Drying shrinkage and relative moisture content  ................................ ................................ ................  5 
6.7 Frost resistance  ................................ ................................ ................................ ................................ ..... 5 
6.8 Carbonation coefficient and softening coefficient  ................................ ................................ ............  6 
7 Test method  ................................ ................................ ................................ ................................ ...........  6 
7.1 Dimensional deviation and appearance quality  ................................ ................................ .................  6 
7.2 Density grade  ................................ ................................ ................................ ................................ .........  6 
7.3 Strength  ................................ ................................ ................................ ................................ ..................  6 
7.4 Drying shrinkage and relative moisture content  ................................ ................................ ................  6 
7.5 Maximum water absorption  ................................ ................................ ................................ ..................  6 
7.6 Carbonation coefficie nt ................................ ................................ ................................ ........................  6 
7.7 Softening coefficient  ................................ ................................ ................................ .............................  6 
7.8 Frost resistance  ................................ ................................ ................................ ................................ ..... 6 
8 Inspection rules  ................................ ................................ ................................ ................................ ..... 7 
8.1 Inspection classification  ................................ ................................ ................................ .......................  7 
8.1.1  Delivery inspection  ................................ ................................ ................................ ................................  7 
8.1.2  Type inspection  ................................ ................................ ................................ ................................ ..... 7 
8.2 Lot grouping rules  ................................ ................................ ................................ ................................ . 7 
8.3 Sampling  ................................ ................................ ................................ ................................ ................  7 
8.4 Judgment rules  ................................ ................................ ................................ ................................ ...... 8 
8.4.1  Dimensional deviation and appearance quality  ................................ ................................ .................  8 
9 Product qualification certificate, stacking and transportation  ................................ .........................  8 
Annex  A (normative)  Test methods for compressive strength of concrete bricks  ................................ .... 9 
A.1 Instruments and equipment  ................................ ................................ ................................ .................  9 
A.1.1  Material testing machine  ................................ ................................ ................................ ......................  9 DUS 2033 : 2018  
iv © UNBS 2018  – All rights reserved  
 A.1.2  Sample preparation platform  ................................ ................................ ................................ ................ 9 
A.1.3  Leveling instrument  ................................ ................................ ................................ ............................... 9 
A.1.4  Straight steel ruler  ................................ ................................ ................................ ................................ .9 
A.1.5  Glass plate or impervious steel plate  ................................ ................................ ................................ ..9 
A.2 Sample  ................................ ................................ ................................ ................................ .................... 9 
A.3 Sample preparation  ................................ ................................ ................................ ............................... 9 
A.3.1  Preparation of concrete brick samples with height ≥ 40mm and < 90mm.  ................................ ......9 
A.3.2  Preparation of concrete brick samples with height ≥90mm.  ................................ ..........................  10 
A.4 Sample curing  ................................ ................................ ................................ ................................ ..... 10 
A.5 Test steps  ................................ ................................ ................................ ................................ ............  10 
A.6 Result calculation and assessment  ................................ ................................ ................................ .. 11 
Annex  B (normative)  Test method for carbonization coefficient  ................................ ...............................  12 
B.1 Equipment, instrument and reagent  ................................ ................................ ................................ . 12 
B.2 Sample  ................................ ................................ ................................ ................................ .................  12 
B.3 Test procedure  ................................ ................................ ................................ ................................ .... 12 
B.4 Result calculation and assessment  ................................ ................................ ................................ .. 12 
Annex  C (normative)  Test method for softening coefficient  ................................ ................................ ...... 13 
C.1 Apparatus  ................................ ................................ ................................ ................................ ............  13 
C.2 Sample  ................................ ................................ ................................ ................................ .................  13 
C.3 Manufacturing of test pieces  ................................ ................................ ................................ .............  13 
C.4 Test procedure  ................................ ................................ ................................ ................................ .... 13 
C.5 Result calculation and assessme nt ................................ ................................ ................................ .. 13 
Bibliography  ................................ ................................ ................................ ................................ .....................  15 
 DUS 2033 : 2018  
© UNBS 2018  – All rights reserved  v 
 Foreword  
Uganda National Bureau of Standards (UNBS) is a parastatal under the Ministry of Trade , Industry and 
Cooperatives established under Cap 327 , of the Laws of Uganda , as amended .  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 Alimentarius Commission on Food Standards, a nd  
(c) the National Enquiry Point on TBT  Agreement  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 given field or a rea and consists of key stakeholders 
including government, academia, consumer groups, private sector and other interested parties.  
Draft Uganda Standards adopted by the Technical Committee are widely circulated to stakeholders and the 
general public for c omments. The committee reviews the comments before recommending the draft standards 
for approval and declaration as Uganda Standards by the National Standards Council.  
The committee responsible for this document is Technical Committee UNBS /TC ###, [name of  committee] , 
Subcommittee SC ##, [name of subcommittee] . 
This second/third/… edition cancels and replaces the first/second/… edition ( US nnn-n:yyyy), which has been 
technically revised.  
US nnn consists of the following parts, under the general title Introductory element — Main element :  
  Part n: Part title  
  Part [n+1]: Part title  
  Part [n+2]: Part title  
 DUS 2033 : 2018  
vi © UNBS 2018  – All rights reserved  
  
 
 UGANDA STANDARD  DUS 2033 : 2018  
 
© UNBS 2018  – All rights reserved  1 
 Solid concrete brick — Specification  
1 Scope   
The Standard specifies the terms, definitions, specifications, grades and marks, raw materials, t echnical 
requirements, test methods, inspection rules, signs, product certificates, and transport of solid concrete bricks.  
The Standard applies to the solid concrete bricks for buildings and structures.  
2 Normative references   
The following referenced doc uments 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.  
US 310 -1 - 2016, Portland cement - Ordinary Portland cement  
DUS 2107 , Test methods for concrete block and brick  
DUS 2109 , Limits of Radionuclides  
US 1681 , Chemical  Admixture s 
DUS 2108 , Sand for Construction  
DUS 1691; Aggregates f or concrete  
DUS 2110 , Lightweight Aggregates  
DUS 2103 , Terms of Wall Materials  
US EAS 12:2014, Potable water — Specification  
3 Terms and definitions   
For the purposes of this document, the terms and definitions given in DUS 2103  and the following apply.  
ISO and IEC maintain terminological databases for use in standardization at the following addresses:  
— ISO Online browsing platform: available at http://www.iso.org/obp  
3.1  
Solid concrete brick   
The solid concrete brick made of cement, aggregates, and r equired admixtures and additives through mixing 
with water, molding and curing (hereinafter referred to as brick). See Fig. 1 for the positions and names of the 
brick.   
2 © UNBS 2018  – All rights reserved  
 
 
Fig.1  Solid Concrete Brick  
1 – side face;  
2 – bedding face;  
3 – width (B);  
4 – length (L); 
5 – top surface;  
6 – height (H).  
4 Specification, grade, code and m ark 
4.1 Specification  
Main brick dimension: 240 mm× 115mm× 53mm. The other specifications are to be determined upon 
consultation by the supplier and the buyer.  
4.2 Density grade  
Density g rade includes grade A (≥2,100 kg/m3), grade B (1,681 kg/m3~2,099 kg/m3) and grade C (≤1,680 kg/m3) 
by concrete density.  
4.3 Strength grade  
Compressive strength of the brick includes six grades: C40, C35, C30, C25, C20, and C15. 
4.4 Code and Mark  
4.4.1  The code of solid concrete br ick is SCB. 
4.4.2  Products shall be marked in the following sequence: code, specification, strength grade, density grade, 
and standard No.  
Examples of marks:  
For a conforming concrete brick with specification of 240 mm× 115mm× 53mm, compressive strength of C25, 
and density grade of grade B : 
SCB 240×115×53 C25 B  DUS 2033 : 2018  
© UNBS 2018  – All rights reserved  3 
 5 Raw material  
5.1 Cement  
It shall comply with the provisions of US 310 -1  
5.2 Fine aggregate  
It shall comply with the provisions of DUS 2108  
5.3 Coarse aggregate  
5.3.1  Crushed stone and pebble shall c omply with US1691 , and maximum grain size is better to be not 
more than 15 mm. 
5.3.2  Lightweight aggregate shall comply with DUS 2110  
5.3.3  Granular ore slag shall comply with US 310 -1 
5.4 Admixture  
Coal ash shall comply with US 310-1, and ground granulated  blast furnace slag (GGBS) shall comply with US 
310-1 
5.5 Additive  
It shall comply with the provisions of US 310 -1 
5.6 Water  
Water shall comply with US EAS 12  
5.7 Radionuclide Limited Standard  
All the raw materials adopted shall comply with DUS 2109 . 
6 Requirements  
6.1 Dimension deviation  
Dimension deviation shall comply with Table 1.  
Table 1  Permissible variation in dimension  
Project name  Standard value  (mm)  
Length  -1~+2  
Width  -2~+2  
Height  -1~+2  
6.2 Appearance quality  
Appearance quality shall comply w ith the provisions in Table 2.   
4 © UNBS 2018  – All rights reserved  
 Table 2  Appearance q uality  
Project name  Standard value  (mm)  
Height difference of shaped surface  not more than  2 
Crooked  not more than  2 
Projected dimension in three directions at missing 
edge/corner  Shall not 
simultaneous ly 
be more than  10 
The projected dimension of crack length  not more than  20 
Complete face *  Shall not be less 
than One side face and one top surface  
a Any face with one of the following defects shall not be called as a complete face:  
1) Damage dimensio ns caused by any defect on the side face or top surface are more than 10mmX10mm 
simultaneously;  
2) Crack width on the side face or top surface is more than 1mm and its length exceeds 30mm.  
6.3 Density grade  
Density grade shall meet the provision of Table 3. 
Table 3  Density g rade   
Density grade  Mean value of 3 bloc ks (kg/m3) 
Grade A  ≥2100  
Grade B  1681~2099  
Level C  ≤1680  
6.4 Strength grade  
6.4.1  Strength grade shall meet the provision of table 4.  DUS 2033 : 2018  
© UNBS 2018  – All rights reserved  5 
 Table 4  Compressive s trength   
Strength Grade  Compressive strength:  (MPa) 
Average  Minimum value of a single brick ≥  
C40 40.0 35.0 
C35 35.0 30.0 
C30 30.0 26.0 
C25 25.0 21.0 
C20 20.0 16.0 
C15 15.0 12.0 
6.4.2  Strength grade of bricks with density grade B and C shall be no less than C15 and that of bricks w ith 
density grade A shall be no less than C20. 
6.5 Maximum water absorption  
Water absorption shall meet the provision of table 5 according to density grade of concrete bricks.  
Table 5  Maximum water a bsorption  % 
Maximum w ater absorption of concrete bloc ks with different dens ity grades (mean value of 3 bloc ks) 
≥2100kg/m3(grade A)  (1681〜2099)kg/m3(grade B)  ≤1680kg/m3(grade C)  
≤ 11 ≤ 13 ≤ 17 
6.6 Drying shrinkage and relative moisture content  
Drying shrinkage and relative moisture content shall meet the provision of table 6.  
Table 6  Dry shrinkage and relative m oisture c ontent  ％ 
Drying Shrinkage  Mean value of relative moisture content  
Humidity  Medium  Dry 
≤ 0.050  ≤ 40 ≤ 35 ≤ 30 
Note 1: Relative moisture content is the ratio of moisture content to water absorption of solid concrete bricks;  
Where, w - relative m oisture content of solid concrete bricks, %;  
w1 - moisture content of solid concrete bricks, %;  
w2 - water absorption of solid concrete bricks, %.  
Note 2: Humidity in the region of use   
Humid ity – regions with annual average relative humidity more than 75% ; 
Medium – regions with annual average relative humidity between 50% and 75%;  
Dry – regions with annual average relative humidity less than 50%.  
6.7 Frost resistance  
Frost resistance shall meet the provision of table 7.   
6 © UNBS 2018  – All rights reserved  
 Table 7  Frost r esistance  ％ 
Service conditions:  Frost resistance 
indicators  Mass loss  Strength loss  
Hot-summer and warm -winter zone  F15   
Hot-summer and cold -winter zone  F25 ≤ 5 ≤ 25 
Cold region  F35   
Severe Cold Area  F50   
6.8 Carbonation coefficient and softening coefficient   
Carbonation coefficient shall be no less than 0.80 and softening coefficient shall be no less than 0.80.  
7 Test m ethod   
7.1 Dimensional deviation and appearance quality   
Dimensional deviation and appearance quality shall follow DUS 2107 . 
7.2 Density grad e  
Density test shall be conducted according to DUS 2107 . 
7.3 Strength  
Strength test shall be conducted according to Appendix A.   
7.4 Drying shrinkage and relative moisture content   
Test method shall follow DUS 2107 . Measuring gauge length of dry shrinkag e test shall be 150mm.  
7.5 Maximum water absorption   
Test method shall follow DUS 2107 . 
7.6 Carbonation coefficient  
Test method shall follow Appendix B.  
7.7 Softening coefficient   
Test method shall follow Appendix C.  
7.8 Frost resistance   
Test method shall  follow DUS 2107 . Post -freezing strength contrast test shall be conducted along with 
contrast sample according to Appendix A.   DUS 2033 : 2018  
© UNBS 2018  – All rights reserved  7 
 8 Inspection r ules  
8.1 Inspection classification  
Product inspection is divided into delivery inspection and type inspection.  
8.1.1 Delivery inspection   
Delivery inspection involves dimensional deviation, appearance quality, strength grade, density grade, 
maximum water absorption and relative moisture content.   
8.1.2  Type inspection   
Type inspection involves all items in technical requirements of this standard. Type inspection shall be 
conducted in one of the following cases.  
a) Trial production approval inspection of new products;  
b) Raw materials and process etc. have great changes which might influence product performance after 
normal production;  
c) Half a year during normal production;  
d) Production is recovered after production suspension for over three months;  
e) When the results of delivery inspection have relatively large difference with the results of the last type 
inspectio n; 
f) When type inspections are put forward by the General Administration of Quality Supervision, 
Inspection and Quarantine of the People’s Republic of China.  
8.2 Lot grouping rules   
Composition rules and size  of inspection lot shall be followed . 100,000 b ricks produced with the same raw 
material and process and at the same grade level shall be one batch. The number of bricks less than 100,000 
shall be calculated as one batch.  
8.3 Sampling   
8.3.1  Samples of dimensional deviation and appearance quality inspe ction shall be taken with random 
sampling method. 50 bricks shall be selected from product stacking of the inspection lot for inspection.  
8.3.2  With respect to samples of other inspection items, bricks of the following quantity shall be selected 
from sampl es passing appearance quality inspection with random sampling method. If the number of samples 
is insufficient, brick samples (passing appearance quality and dimensional deviation inspection) shall be taken 
from the batch of bricks for item inspection.  
a) Strength  10 bricks   
b) Density  3 bricks   
c) Drying shrinkage and relative moisture content  3 bricks   
d) Maximum water absorption   3 bricks   
e) Frost resistance  10 bricks    
8 © UNBS 2018  – All rights reserved  
 f) Carbonation coefficient  10 bricks   
g) Softening coefficient  10 bricks  
8.4 Judgmen t rules   
8.4.1  Dimensional deviation and appearance quality   
Dimensional deviation and appearance quality shall follow double sampling plan. The number of 
nonconforming products d 1 shall be checked out according to quality indicators specified in tables 1 and 2. 
Judgment shall be made according to the following rules:   
When d 1 ≤ 7, dimensional deviation and appearance quality are qualified;   
When d 1 ≥ 11, dimensional deviation and appearance quality are unqualified;   
When d 1 > 7 and d 1 < 11, 50 bricks shall be selected from the batch again for inspection and the number of 
noncon forming products d 2 shall be checked out. Judgment shall be made according to the following rules:   
When (d 1+ d 2) ≤ 18, dimensional deviation and appearance quality are qualified;   
When (d 1+ d 2) ≥ 19, dimensional deviation and appearance quality are unqual ified;   
8.4.2  When density, strength, drying shrinkage and relative moisture content, frost resistance, carbonation 
coefficient and softening coefficient inspection results meet tables 3, 4, 5, 6 and 7 and indicators of technical 
requirements in 6.8 in cha pter 6 respectively, the corresponding grade of the batch of products shall be 
identified as qualified; when any one item is unqualified, it shall be identified as unqualified.  
9 Product q ualifica tion certificate, stacking and t ransportation  
9.1 Bricks sh ould be packaged appropriately when leaving factory and product qualification certificate shall 
be provided, including:   
a) Factory name and trademark;   
b) Lot number and brick quantity;   
c) Product mark and inspection result;   
d) Number of product qualifi cation certificate;   
e) Production date;   
f) Signature and seal of the inspection department and the inspector.  
9.2 Bricks shall be stacked in batches based on specification and grade and shall not be stacked in a mixed 
form.  
9.3 Rain-proof measures shall be taken for bricks during stacking and transportation.  
9.4 Collision and throwing are prohibited during handling. Bricks shall be stacked up gently. Tilting by skip 
bucket is prohibited.  
9.5 Products with curing and stacking age less than 28d shall not le ave factory  Symbols (and abbreviated 
terms) . DUS 2033 : 2018  
© UNBS 2018  – All rights reserved  9 
 Annex  A 
(normative)  
 
Test methods for compressive strength of concrete b ricks  
A.1 Instruments and equipment   
A.1.1  Material testing machine   
Relative error of indicated value of testing machine shall be not more  than ±1%. Its lower compression plate 
shall be spherical hinge bearing. Expected maximum breaking load shall be between 20% and 80% of range.  
A.1.2  Sample preparation platform   
Sample preparation platform must be smooth and level and may be made of metal or other materials.  
A.1.3  Leveling instrument   
Specification 250mm - 300mm.  
A.1.4  Straight steel ruler   
Division value 1mm.  
A.1.5  Glass plate or impervious steel plate   
The plate thickness shall not be less than 6mm.  
A.2 Sample  
Number of samples: 10  
A.3 Sample p reparation   
A.3.1  Preparation of concrete brick samples with height ≥  40mm and <  90mm.  
a) Samples shall be cut off or sawn into two half bricks, the length of which shall not be less than 90mm, 
as shown in figure A.1. If it is less than 90mm, standby s amples shall be taken otherwise for 
complement.  
b) After the bedding face of the two half bricks cut off is wiped with dripless wet cloth, they shall be 
stacked up in the opposite direction of fracture surface on sample preparation platform. Cement paste 
of appropriate consistency made of grade 42.5 ordinary Portland cement not exceeding 3mm thick 
shall be applied in the middle section. Water cement ratio shall be not more than 0.3. Upper and lower 
faces shall be trowelled with the same cement paste not exceed ing 3mm thick. Upper and lower faces 
of test piece made must be parallel to each other and vertical to the side face, as shown in figure A.2.  
  
10 © UNBS 2018  – All rights reserved  
 Unit: mm  
 
Figure A.1  Schematic d iagram for length of half b rick  
Unit: mm  
 
1 – Neat paste layer thickness ≤3mm;  
2 – Neat paste layer thickness ≤5mm.  
Figure A.2  Schematic Diagram for Thickness of Cement Paste Layer  
A.3.2  Preparation of concrete brick samples with height ≥90mm.  
Samples shall be prepared with bed -mortar method. That is, place a glass sheet on sample p reparation 
platform, put a piece of wet packing paper on the plate, apply a layer of cement paste of appropriate 
consistency made of grade 42.5 ordinary Portland cement less than 3mm thick on the paper, wet the bedding 
face of samples with a wet cloth, put  the compression face above cement paste steadily, apply pressure to the 
other compression face slightly and make the whole cement layer and the compression face of bricks mutually 
bonded. The side face of bricks shall be vertical to the glass sheet. After  cement paste is solidified 
appropriately, turn it over along with the glass sheet and put it on another glass sheet with paper and paste, 
then place bed mortar and adjust the level of glass sheet with levelling instrument . 
A.4 Sample c uring   
Plastered sam ples prepared shall be placed in an unventilated room with temperature not lower than 
20°C±5°C for no less than 3d before test.  
A.5 Test s teps  
A.5.1  Measure the length and width of the junction surface or the compression face of each sample for 
twice and take their mean value respectively to the accuracy of 1mm.  DUS 2033 : 2018  
© UNBS 2018  – All rights reserved  11 
 A.5.2  Samples shall be uniform and steady without impact or vibration when they are placed in the middle of 
the compression plate and subject to loading vertical to the compression face. Loading sp eed should be 
4kN/s -6kN/s till sample damage. Maximum breaking load P shall be recorded.  
A.6 Result calculation and a ssessment  
A.6.1  Compressive strength (R P) of each sample shall be calculated according to formula (A.1) to the 
accuracy of 0.01MPa.  
1) .......(A. .......... .......... ..........LBPRp
 
Where:  
RP- compressive strength, MPa;  
P – Maximum breaking load in Newton (N);  
L – length of compression face (junction surface), mm;  
B – width of compression face (junction surface), mm.  
A.6.2  Test result shall be expressed as arithmetic  mean of compressive strength of samples and the 
minimum value of a single brick to the accuracy of 0.1MPa.  
A.7 Cement may be replaced with other plastering materials in the process of preparing compressive 
strength test specimen so as to shorten its curin g period .  
12 © UNBS 2018  – All rights reserved  
 Annex  B 
(normative)  
 
Test method for carbonization coefficient   
B.1 Equipment, instrument and reagent  
Carbonization test box: Box volume shall at least accommodate a group of specimens; ambient environment 
in the box: CO2 concentration (volume fr action): 20%±3%, relative humidity: 70%±5%, temperature: 20° C±5°C. 
1% phenolphthalein ethanol solution: prepared by the ethanol with concentration (mass concentration) of 70%.  
B.2 Sample  
Specimen quantity shall be 10 bricks in 2 groups. A group of 5 bricks  shall be taken as reference test pieces, 
and the other group of 5 bricks shall be taken as carbonization test pieces.  
B.3 Test p rocedure  
B.3.1  Put 7 carbonization test pieces into carbonization box, with specimen spacing of not less than 20mm; 
and put 5 r eference test pieces in the labo ratory with temperature of 15°C -25°C for curing.  
B.3.2  Put 5 test pieces which have been fully carbonized or still not fully carbonized upon carbonization for 
28d into compressive strength test as specified together with 5 r eference test pieces.  
B.4 Result calculation and assessment  
Carbonization coefficient of bricks shall be calculated by formula ( B.1), and shall be accurate to 0.01.  
 
Where:  
Kc - carbonization coefficient of bricks;  
Rc - average compressive strength of 5 c arbonized test pieces, unit: MPa; 
R - average compressive strength of 5 reference test pieces, unit: MPa DUS 2033 : 2018  
© UNBS 2018  – All rights reserved  13 
 Annex  C 
(normative)  
 
Test method for softening coefficient  
C.1 Apparatus  
C.1.1   Testing machine and other instruments shall comply with A.1.  
C.1.2  Wate r pool or water tank.  
C.2 Sample  
C.2.1  Specimen quantity shall be 10 test pieces in two groups.  
C.2.2  The age of test brick shall be more than 28d.  
C.3 Manufacturing of test pieces  
C.3.1  Immerse a group of 5 bricks for the test into water pool or water tan k to reach saturated state. Keep 
water temperature at 15°C~25°C, and water surface more than 20cm above brick specimen.  
C.3.2  Perform fabrication and curing of brick specimen for compressive strength test as per A.3 and A.4 
respectively for a group of  5 bricks not immersed in water and dried by air and a group of 5 bricks saturated 
with water and with dry surface. It is not allowed to substitute cement with other plastering materials.  
C.3.3  The cement for specimen fabrication shall be early -strength ce ment with strength grade of 42.5 or 
higher.  
C.4 Test p rocedure  
C.4.1  Immerse the group of test pieces which have been immersed into water into water pool or water tank 
again to reach saturated state. Keep immersion duration of not more than 4h, and then ta ke out and put the 
specimens on iron wire grid for dripping for 1min.  
C.4.2  Wipe the test pieces with dry cloth. Perform compressive strength test by A.4 respectively for both the 
groups of test pieces, and record maximum failure load of each specimen.  
C.5 Result calculation and assessment  
C.5.1  Compressive strength of each specimen shall be calculated by A.6.1; average compressive strength 
of the specimen group not immersed in water R, and that of the test pieces saturated with water and with dry 
surface R f shall be taken by arithmetic mean of five test pieces, and shall be accurate to 0.1MPa.  
C.5.2  Softening coefficient of concrete brick shall be calculated by formula (C.1), and shall be accurate to 
0.01.  
   
14 © UNBS 2018  – All rights reserved  
 Where:  
Kf softening coefficient of concrete bri ck; 
Rf average compressive strength of 5 brick test pieces saturated with water and with dry surface, 
unit: MPa;  
R average compressive strength of 5 reference brick test pieces dried by air, unit: MPa.  
C.5.3  During the test, in case single -piece compressiv e strength of any brick specimen saturated with water 
and with dry surface is not more than 0.5R, this batch of bricks shall be directly judged as nonconforming 
softening coefficient.  DUS 2033 : 2018  
© UNBS 2018  – All rights reserved  15 
 Bibliography  
[1] GB/T 21144 -2007 , Solid concrete brick   
 
 US nnnn -n: yyyy  
© UNBS 2018  – All rights reserved  17 
 Certificatio n 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 governed by the Standards Act, and the Regulations ma de 
thereunder. This mark can be used only by those licensed under the certification mark scheme operated by 
the Uganda National Bureau of Standards and in conjunction 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 a re 
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.  
 
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ICS nn.nnn.nn  
Price based on nn pages  
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