ICS 91.100.15  
 
Reference number  
DRS  310:2022 
© RSB 2022 
  
 RWANDA 
STANDARD  DRS  
310  
 
First edition  
2022-mm-dd 
 
Burnt clay paving units  — Specification  
   
DRS  310: 2022 
©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 2022 
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized 
in any form or by any means, electronic or mechanical, including photocopying and microfilm, without 
prior written permission from R SB. 
Requests for permission to reproduce this document should be addressed to : 
Rwanda Standards  Board  
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KK 15 Rd, 49  
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Toll Free: 3250  
E-mail: info@rsb.gov.rw  
Website: www.rsb.gov.rw  
ePortal: www.portal.rsb.gov.rw   DRS  310: 2022 
iii                ©RSB 2021  - All rights reserved  
 Contents  Page 
Foreword  ................................ ................................ ................................ ................................ ....................  v 
1 Scope  ................................ ................................ ................................ ................................ .............  1 
2 Normative references  ................................ ................................ ................................ ...................  1 
3 Terms and definitions  ................................ ................................ ................................ ..................  1 
4 Classification  ................................ ................................ ................................ ................................  2 
5 Requirements  ................................ ................................ ................................ ................................  2 
5.1 Appearance  ................................ ................................ ................................ ................................ ... 2 
5.1.1  General  ................................ ................................ ................................ ................................ ..........  2 
5.1.2  Shape  ................................ ................................ ................................ ................................ .............  2 
5.1.3  Surface appearance  ................................ ................................ ................................ .....................  3 
5.2 Dimensions  ................................ ................................ ................................ ................................ ... 3 
5.3 Warpage  ................................ ................................ ................................ ................................ ........  3 
5.4 Modulus of rupture  ................................ ................................ ................................ .......................  4 
5.5 Moisture  expansion  ................................ ................................ ................................ ......................  4 
5.6 Compressive strength ................................ ................................ ................................ ..................  4 
5.7 Water absorption  ................................ ................................ ................................ ..........................  5 
6 Dispatch information  ................................ ................................ ................................ ....................  5 
7 Inspection and test methods  ................................ ................................ ................................ ....... 5 
7.1 Inspection  ................................ ................................ ................................ ................................ ...... 5 
7.2 Method of taking samples  ................................ ................................ ................................ ...........  5 
7.2.1  Sampling during loading and unloading  ................................ ................................ ....................  5 
7.2.2  Sampling from a stack or a vehicle  ................................ ................................ ............................  5 
7.3 Test specimens  ................................ ................................ ................................ .............................  5 
Annex  A (normative)  Measurement of dimensions and plan area  ................................ ......................  6 
A.1 Determination of dimensions  ................................ ................................ ................................ ...... 6 
A.1.1  Apparatus  ................................ ................................ ................................ ................................ ...... 6 
A.1.2  Preparation of test specimens  ................................ ................................ ................................ .... 6 
A.1.3  Procedure  ................................ ................................ ................................ ................................ ...... 6 
A.2 Determination of plan area  ................................ ................................ ................................ ..........  6 
A.2.1  Rectangular paving units  ................................ ................................ ................................ ............  6 
A.2.2  Shapes other than rectangles  ................................ ................................ ................................ ..... 7 
A.2.3  Measurement of plan area  ................................ ................................ ................................ ...........  7 
Annex  B (normative)  Test for warpage  ................................ ................................ ................................ .. 8 
B.1 Apparatus  ................................ ................................ ................................ ................................ ...... 8 
B.2 Test specimens  ................................ ................................ ................................ .............................  8 
B.3 Procedure  ................................ ................................ ................................ ................................ ...... 8 
Annex  C (normative)  Test for modulus of rupture  ................................ ................................ ................  9 
C.1 Apparatus  ................................ ................................ ................................ ................................ ...... 9 
C.2 Preparation of test specimens  ................................ ................................ ................................ .... 9 
C.3 Procedure  ................................ ................................ ................................ ................................ .... 10 
C.4 Calculation  ................................ ................................ ................................ ................................ .. 10 
Annex  D (normative)  Test for moisture expansion  ................................ ................................ .............  11 
D.1 Apparatus  ................................ ................................ ................................ ................................ .... 11 DRS  310: 2022 
©RSB 2021  - All rights reserved                  iv 
 D.2 Preparation of t est specimens  ................................ ................................ ................................ . 11 
D.3 Procedure for refired units  ................................ ................................ ................................ ....... 11 
D.4 Procedure for units as received  ................................ ................................ ...............................  12 
D.5 Calculations  ................................ ................................ ................................ ................................  12 
Annex  E (normati ve)  Determination of compressive strength  ................................ .........................  13 
E.1 Apparatus  ................................ ................................ ................................ ................................ ... 13 
E.2 Procedure  ................................ ................................ ................................ ................................ ... 13 
E.3 Calculation of compressive strength ................................ ................................ .......................  13 
Annex  F (normative)  Determination water absorption and saturation coefficient  .........................  14 
F.1 Test specimens  ................................ ................................ ................................ ..........................  14 
F.2 Accuracy of weighing  ................................ ................................ ................................ ................  14 
F.3 Procedure for 24 -hour immersion test  ................................ ................................ ....................  14 
F.4 Procedure for 5 -hour boiling test  ................................ ................................ .............................  14 
F.5 Calculation of saturation coefficient ................................ ................................ ........................  15 
 DRS  310: 2022 
v                ©RSB 2021  - All rights reserved  
 Foreword   
Rwanda Standard s 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 S tandards adopted 
by Technical committ ees are ratifie d by me mbers of RSB Board of Director s for publication and gazettment as 
Rwanda Standards.  
DRS  310 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 standard:  
SANS 1575:20 07 Clay paving units  
The assistance de rived from the above source is hereby acknowledged with thanks.  
Committee membership  
The following organizations were represented on the Technical Committee on Building materials and civ il 
engineering  (RSB/TC 009) in the preparation of this standard.  
Advanced Construction Technology Services (ACTS) Ltd  
Afriprecast Ltd  
Bridges to Prosperity  
CIMERWA Ltd  
Integrated Infrastructure Company (IIC) Ltd  
Ruliba Clays Ltd  
Rwanda Housing Authority (R HA) 
Rwanda Inspectorate, Consumer Protection and Competition Authority (RICA)  
Rwanda Transport Development Agency (RTDA)  
SJEC Ltd -Nyamirambo  
Rwanda  Standards Board  (RSB) – Secretariat  DRS  310: 2022 
1                ©RSB 2021  - All rights reserved  
 Burnt clay paving units  — Specification   
1 Scope  
This Committee Draft  Rwanda Standard specifies the requirements , sampling  and test methods for burnt clay paving 
units.  
2 Normative references  
There are no normative references in this document  
3 Terms and definitions   
For the purposes of this standard, the follow ing terms and definitions apply.  
3.1 
burnt clay paving unit 
paving unit manufactured from clay or other material that has similar characteristics, which may be mixed with 
fuel or other additives, and pressed, or extruded and cut, or moulded to the required shape and dried followed by 
firing at a sufficiently high temperature to ensure adequate vitrification of the unit.  
3.2 
chamfer  
sloped arris on the wearing surface of the  unit, extending not more than 7 mm from the nominal edge of the unit  
3.3 
durability  
ability to withstand specified exposure conditions without impairing either the performance or the appearance 
of a paving unit  
3.4 
spacer nibs  
vertical ribs or protrusions on the vertical faces of paving units that do not protrude more than 3 mm from such 
faces   
©RSB 2021  - All rights reserved                  2 
 3.5 
wearing surface  
surface or surfaces of a paving unit that the manufacturer has designed to be laid uppermost and to be subject 
to tra ffic in use  
 
3.6 
work size  
size of paving unit, normally expressed in terms of the dimensions of length, width and thickness specified for 
its manufacture, to which the actual size should conform to specified permissible deviations.  
4 Classification  
Burnt cl ay paving units shall be of one of the classes given in Table 1, as required.  
Table 1 — Classification of burnt clay paving unit  
1  2  
Class  Description  
A  Units that are selected or produced for their durability and for a 
high degree of uniformity in size and shape, and that have 
dimensions such that the ratio of work size length to work size  
width is approximately 1:1; 2:1 or 3:1  
B  Units that are selected or produced for their durability and for 
their uniformity in size and shape.  
5 Requirements  
5.1 Appearance  
5.1.1  General  
If required for the purposes of assessing the consistency of colour and the wearing surface texture, a 
sample of 10 units shall be selected and retained as a reference range.  
5.1.2  Shape  
5.1.2.1  Units may be with or without spacer nibs on faces designed to be in contact with the jointing 
medium. The wearing surface of units may be with or without indentations, serrations or similar patterns.  
5.1.2.2  Class A units may have chamfered arises.  DRS  310: 2022 
3                ©RSB 2021  - All rights reserved  
 5.1.2.3  Class B units shall have uniform arises that are not chamfered .  
5.1.3  Surface appearance  
The units shall be well fired and shall be reasonably free from cracks, from damage to edges and corners, 
from pebbles , from expansive particles of lime  and other defects that would adversely affect their general 
appearance or servic eability (or both) .  
5.2 Dimensions  
5.2.1 The work size of a paving unit shall be as required and as stated by the manufacturer or the client  
5.2.2 Class A units shall have dimensions such that the ratio of work size length to work size width is 
approximatel y 1:1, 2:1 or 3:1.  
5.2.3  The nominal thickness of a paving unit shall not be less than 50 mm.  
5.2.4  When determined in accordance with Annex A:  
a) the dimensions of an individual unit shall not differ from the stated work size by more than the 
relevant t olerances given in columns 2 to 4 (inclusive) of Table 2; and  
b) the average dimensions of 32 units shall not differ from the stated work size by more than the 
relevant tolerances given in columns 5 to 7 (inclusive) of Table 2.  
Table 2 — Tolerances on work sizes  
1  2   3  4  5  6  7  
Class   Individual units  
mm  Average dimensions of 32 units mm  
Length   Width  Thickness  Length  Width  Thickness  
A  ± 5   ± 3  ± 3  ± 2.5  ± 1.5  ± 1.2  
B  ± 6   ± 4  ± 4  ± 3  ± 3  ± 2  
5.3 Warpage  
When determined in accordance with Annex B, the warpage of units shall be within the following limits:  
a) class A units: the warpage of any individual unit shall not exceed 3 mm; and  
b) class B units: the warpage of any individual unit shall not exceed 4 mm.   
©RSB 2021  - All rights reserved                  4 
 5.4 Modulus of rupture  
When 10 units are tested in accordance with Annex C, the average modulus of rupture shall be not less than 
the nominal modulus of rupture given in column 2 of Table 3, appropriate to the class of unit. The modulus of 
rupture of individual units shall be not less than the appropriate of the values given in column 3 of Table 3.   
NOTE  This  requirement does not apply to paving units of length less than 80 mm.  
Table 3 — Modulus of rupture  
1  2  3  
Class  Nominal modulus of 
rupture  
MPa  Minimum individual modulus of 
rupture  
MPa  
A  4.0  1.5  
B  3.0  2.0  
5.5 Moisture expansion  
When determined in accordance with Annex D, the Estimated Batch Average (EBA) for the moisture expansion 
of refired units or of units as -received shall not exceed 0.25 %.  
5.6 Compressive strength  
The average compressive strength when tested in accord ance with  Annex E  shall be as in table 4 .  
Table 4 — Compressive strength  
Grade  Nominal thickness, 
mm Compressive strength, 
N/mm2 Applications  
Heavy duty (H)  60mm, 80mm  40 Main roads, heavy 
industrial applications  
Medium duty (M)  60mm  35 Estate roads, domestic 
driveways and parking 
areas  
Light duty (L)  50mm  25 Domestic driveways and 
parkings, sidewalks  
 DRS  310: 2022 
5                ©RSB 2021  - All rights reserved  
 5.7 Water absorption  
The average water absorption by weight after 24 hours immersion in cold water when determined in accordance 
with Annex F  shall be not  more than 10 percent.  
6 Dispatch information  
Each consignment of units shall be accompanied by a dispatch note  on which the following information is given:  
a) manufacturer's name or trade name or trademark;  
b) class of the units; and  
c) work size of the units.  
d) Test report  from competent authority or standardization/quality mark when required by the customer  
7 Inspection and test methods  
7.1 Inspection  
Each unit in the sample shall be inspected for compliance with all the requirements of the standard, for which 
tests to assess compliance are not given in Annex A to D (inclusive).  
7.2 Method of taking samples  
7.2.1  Sampling during loading and unloading  
A total of 32 units shall be taken at approximately evenly spaced intervals throughout the loading o r unloading 
operation.  
7.2.2  Sampling from a stack or a vehicle  
A total of 32 units shall be taken from different positions evenly spaced throughout the stack or load, but 
if this is impracticable, units from the upper courses shall be moved and the units from various positions 
within the stack or load (and if possible, from the sides of the stack or load) shall be taken.  
7.3  Test specimens  
To carry out all the tests, 32 units are required as set out below. After inspecting the required number of units and 
measuring 32 units for dimensions and warpage, allocate sampled units  to the remaining tests as follows:  
a) modulus of rupture: 10;  
b) compressive strength: 8  
c) water absorption: 5 and 
d) b) moisture expansion test: 9.  
  
©RSB 2021  - All rights reserved                  6 
 Annex  A 
(normative)  
 
Measurement  of dimensions  and plan area  
A.1 Determination of dimensions  
A.1.1  Apparatus  
A.1.1 Steel rule, graduated in increments of 1 mm.  
A.1.2 End stop, having a vertical plane face.  
A.1.2  Preparation of test specimens  
Knock off any blisters and remove loose particles from the faces of each unit.  
A.1.3  Procedure  
Measure, to the nearest 1 mm, the overall dimensions of each unit along the appropriate cen tre-line of each 
face (see figure A1), in each case by placing the appropriate face of the unit against the end stop and measuring 
the distance from the end stop to the opposite face of the unit. Record the mean of each pair of measurements 
as the dimensio ns of the unit and then calculate the average dimensions of the 32 units.  
 
Figure A.1 — Measuring positions  
A.2 Determination of plan area  
A.2.1  Rectangular paving units  
Calculate the plan area by multiplying the length by width, or by using the method described i n A.2.2  
DRS  310: 2022 
7                ©RSB 2021  - All rights reserved  
 A.2.2  Shapes other than rectangles  
A.2.2.1  Apparatus  
A.2.2.1.1  Balance , capable of weighing 100 g to an accuracy of 0.01 g.  
A.2.2.1.2  Sheets of thin cardboard, of uni form thickness.  
A.2.2.1.3  Sharp scissors  
A.2.2.1.4  Steel rule , marked in graduation of 0.5 mm. 
A.2.3  Measurement of plan area  
Place the block, wearing surface uppermost, on the cardboard ( A.2.2.1.2)  and trace around its perimeter with a 
pencil. Cut out the shape accurately and weigh it to the nearest 0.01 g, using the balance ( A.2.2.1.1 ). 
Weigh a rectangle measuring 200 mm x 100 mm, cut accurately from the same cardboard, to the  nearest 0.01 
g. 
Calculate the plan area of the paving unit A, in mm2 using the equation:  
𝐴𝑆 = 20 000  𝑚𝑠
𝑚𝑟 
where  
𝑚𝑟, is the mass of the 200 mm x 100 mm cardboard rec tangle (in g).  
Calculate the plan area to the nearest 10 mm2. 
𝑚𝑠, is the mass of the cardboard shape matching the block (in g).  
 
   
©RSB 2021  - All rights reserved                  8 
 Annex  B 
(normative)  
 
Test for warpage  
B.1 Apparatus  
B.1.1  Steel rule, graduated in increments of 1 mm.  
B.1.2  Steel straight -edge, of length at least 450 mm.   
B.1.3  Four steel measuring wedges, graduated in increments (indicating increments of thickness) of 1 mm, 
and each of length 60 mm, of width 10 mm and of a thickness that tapers uniformly from 10 mm at one end to 
zero at the other end.  
B.1.4 Flat surface of steel or glass, of size at least 450 mm × 450 mm, and plane to within 0.15 mm.   
B.2 Test specimens  
Use the units previously used in the test for dimensions (see Annex A).  
B.3 Procedure  
B.3.1  Lay each unit on one o f its bed faces on the flat surface. Determine by preliminary trial which of the 
three methods of measurement given in B.3.1, B.3.2 and B.3.3 will give the greatest warpage reading and 
then, using that method, accurately measure the warpage to the nearest 1 mm.  
B.3.2  If the warpage is concave, place the straight -edge lengthways or diagonally along the surface to be 
measured and determine the location that gives the greatest departure from straightness. Measure (using 
either the steel rule or a measuring w edge) the maximum distance between the surface of the unit and the 
lower edge of the straight -edge, and record this value as the warpage.  
B.3.3  If the warpage is convex, so lay the convex surface in contact with the flat surface that the ends of 
the unit  are approximately equidistant from the surface and, using one wedge under each corner, measure the 
distance between each corner and the surface. Record the arithmetic mean of the four measurements as the 
warpage.  
B.3.4  If the unit can be rocked about a diagonal, insert a wedge under each of the other two corners and 
record the mean of the two readings as the warpage.  
 
 
 DRS  310: 2022 
9                ©RSB 2021  - All rights reserved  
 Annex  C 
(normative)  
 
Test for modulus of rupture  
C.1 Apparatus  
C.1.1 Bending device (see Figure C.1), that has an accuracy of 2 % or better, and that consists essentially of 
the following:  
a) two cylindrical supports, each of diameter 20 mm and of length at least equal to the width of the specimen, 
and so spaced that the dist ance between centres is 30 mm less than the length of the specimen, but does 
not exceed 280 mm. One of the supports can pivot slightly, while the other is free to rotate slightly about 
its longitudinal axis;  
b) a cylinder of diameter 20 mm and of length at l east equal to the width of the specimen, that can pivot slightly 
and is centred between the supports;  
c) a mechanism capable of applying a force uniformly along the cylinder (see C.1.1b)) and of increasing the 
stress at a rate of 1 MPa ± 0.2 MPa per second; and  
d) a mechanism that indicates the force applied and records the force of rupture.  C.1.2 Suitable instrument 
for measuring the thickness of the paving unit.  
 
Figure C.1 — Modulus of rupture test  
C.2 Preparation of test specimens  
Immerse each of the specim ens (see 6.3) in water at 22° C to 25° C for 24 h before testing.  
 
©RSB 2021  - All rights reserved                  10 
 C.3 Procedure  
C.3.1 Measure the width of each specimen in accordance with Annex A.   
C.3.2 Measure, to the nearest 1.0 mm, the distance between the centres of the supports.  
C.3.3 So place th e specimen (wearing surface uppermost) on the supports of the bending device that it rests 
symmetrically upon the supports and spans in the longitudinal direction.  
C.3.4 Apply a force to the test specimen at the required rate of increase (see C.1.1c)) unt il failure occurs. 
Record the force at failure.  
C.3.5 Measure the minimum thickness of the specimen along the broken edge.   
C.3.6 Repeat the procedure on each of the remaining specimens.  
C.4 Calculation  
C.4.1 Calculate the individual modulus of rupture MR, in megapascals, of each specimen as follows:  
𝑀𝑅 =3𝐹𝐿
2𝑏𝑑2 
Where,  
F  is the force applied at rupture, in newtons;  
 L  is the span between the supports, in millimetres;  
 b  is the width of the specimen,  in millimetres; and  
d  is the minimum thickness of the specimen, in millimetres, measured along the broken edge.  
C.4.2  Calculate the average modulus of rupture for the sample.  
 
 
 DRS  310: 2022 
11                ©RSB 2021  - All rights reserved  
 Annex  D 
(normative)  
 
Test for moisture expansion  
D.1 Apparatus  
D.1.1 Strain gauge, capable of measuring accurately a dimensional change of 0.002 mm.  
D.1.2 Forced -draught drying oven, capable of maintaining a temperature of at least 105 °C.  
D.1.3 Kiln, capable of being maintained at a temperature of 800 °C ± 10 °C and of reaching such a temperature 
at a rate of 80 °C to 100 °C per hour.  
D.1.4 Steam cabinet, of suitable size, provided with:   
a) a grid that is clear of the water and so fitted that it ensures free circulation of steam between units 
placed on the grid; and  
b) an outlet to prevent the steam pressure from rising above atmospheric pressure.   
D.1.5 Stainless -steel locating discs, of suita ble size.  
D.2 Preparation of test specimens  
Mark each of the units (see 7.3) with an identification mark.  
D.3 Procedure for refired units  
D.3.1 Dry the units in the oven at a temperature of at least 105 °C for a period of at least 15 h and then transfer 
them t o the kiln. Raise the temperature of the kiln to 800 °C at a rate of 80 °C to 100 °C per hour. Keep the 
units in the kiln at a temperature of 800 °C ± 10 °C for 5 h and then allow them to cool, but while they are still 
warm to the touch, place the units in  a desiccator over blue silica gel.  
D.3.2 Ensure that the room temperature does not vary by more than 3 °C for the remainder of the test.  
D.3.3 When the units have cooled to room temperature, remove them from the desiccator and, using a suitable 
epoxy resin, so fix a set of two suitable stainless steel locating discs into both the wearing surface and the bed -
face of each of the units (i.e. one disc at each end of the wearing surface and of the bed -face) that they are a 
press -fit and as near to the  ends of the unit as is practicable. Ensure that the discs are flush with the face and 
firmly in contact with the unit. Allow 24 h for the epoxy resin to set, with the units sealed from moisture, either 
in polyethylene bags of nominal thickness 225 μm or i n a desiccator containing blue silica gel.   
©RSB 2021  - All rights reserved                  12 
 D.3.4 Remove the units from the bags or desiccator and, using the strain gauge, take the measurements  
(original gauge length) between each set of discs. Before each set of measurements is taken, calibrate the 
strain gauge with an appropriate Invar steel bar, and check the gauge calibration at regular intervals during the 
test.  
D.3.5 Place the units in the steam cabinet and subject them, for four consecutive periods of 24 h each, to the 
action of saturated steam  at atmospheric pressure. After each period, allow the units to cool to room 
temperature and keep them at room temperature for at least 24 h before determining the change in distance 
between the set of discs in each unit.  
D.4 Procedure for units as received  
Test the units in the way described in D.3.2 to D.3.5, but do not use a desiccator.  
D.5 Calculations  
D.5.1 Express the increase in length of each of the units, measured after each period of exposure to steam and 
cooling, as a percentage of the original gauge  length. Record, to the nearest 0.01 %, the average x and standard 
deviation σ of expansions after 24 h and 96 h, and the estimated batch average after 96 h of steaming. Record 
also the steam temperature.  
𝐸𝐵=𝑋̅=+[1.86 𝜎
3] 
Where,  
 
𝑋̅ is the average expan sion of units (after 96 h); and   
 σ  is the standard deviation (after 96 h).   
 
 
 
 
 
 
 DRS  310: 2022 
13                ©RSB 2021  - All rights reserved  
 Annex  E 
(normative)  
 
Determination of compressive strength  
E.1 Apparatus  
E.1.1  Compression testing machine  
E.1.2  Cypress, pine or softwood plywood packing  4 mm thick and larger than the specimen by a margin 
of at least 5 mm at 11 points.  
E.2 Procedure  
E.2.1  Measure the dimensions of each block before storing it in water and calculate the plan area, as 
described in Annex A. Test a sample of bricks taken as descr ibed in Clause 11 after storing them for 24 ± 4 h 
in water maintained at a temperature of 20 ± 5oC. 
E.2.2  Wipe clean the platens of the testing machine. Remove any loose grit or other material from the contact 
faces of the block. Place timber packing betwe en the upper and lower faces of the block and the machine 
platens. Use fresh packing for each block tested.  
E.2.3  Place the block in the machine with the wearing surface in a horizontal plane and in such a way that 
the aces of the block are aligned with th ose of the machine platens.  
E.2.4  Apply the load without shock and increase it continuously at a rate of 15 ± 3 N/(mm2 min) until no 
greater load can be sustained by the paving block or delamination occurs. Record the maximum load applied 
to the brick.  
E.3 Calculation of compressive strength  
Calculate the crushing strength of each block to the nearest 0.1 N/mm2 by dividing the maximum load by the 
plan area and multiplying by the appropriate factor from table 1. Calculate the compressive strength, expressing 
the value to the nearest 1 N/mm2. 
Table 1 — Thickness and chamfer correction factors for compressive stren gth 
Nominal size thickness (mm)  Correction factors  
Plain block  Chamfered block  
50, 60  
80 1.00 
1.12 1.06 
1.18 
 
  
©RSB 2021  - All rights reserved                  14 
 Annex  F 
(normative)  
 
Determination water absorption and saturation coefficient  
F.1 Test specimens  
Five bricks taken at random from the test sample selected in accordance with Clause 7.3  shall be used for 
determining water absorption and saturation coefficient.  
F.2  Accuracy of weighing  
Specimens shall be weighed to an accuracy of 0.1 % of the mass of the s pecimen using a suitable balance.  
F.3  Procedure for 24 -hour immersion test  
F.3.1  The specimens shall be dried to constant weight (usually in about 48 h to 72 h) in a drying oven at 
110 °C to 115 °C. On removal from the oven, they shall be cooled to room temp erature (20 °C to 25 °C) by 
placing them separately and unstacked on a bench or floor with a strong current of air passing over them 
continuously from an electric fun. When cool, each specimen shall be weighed in a balance sensitive to within 
0.1 % of the weight of the specimen.  
F.3.2 The dry specimen shall be completely immersed, without preliminary partial immersion, in clean (soft, 
distilled or rain) water in a tank of suitable size at 200 °C to 250 °C for 24 h. Each specimen shall be removed, 
the surfac e water wiped off with a damp cloth, and the specimen then weighed. Weighing of any one specimen 
shall be completed within 3 min after removing it from the water.  
F.3.3  Calculation of moisture absorption 24 -hour test ; the water absorption (%) after 24 h' immersion in 
cold water shall be calculated from the expression:  
(𝑊2−𝑊1)
𝑊1×100 
where,  
𝑊1 is dry weight of the specimen, and  
𝑊2 is saturated weight of the specimen after 24 h' immersion in cold water.  
F.4  Procedure for 5 -hour boiling test  
F.4.1  Immediately  after weighing, the specimens shall be returned to the tank, and placed on a grid inserted 
therein as to ensure free circulation of the water between the specimens and the bottom of the tank, and on all 
sides of the specimens themselves. The water shall b e heated to boiling in approximately 1 h boiled continuously 
for 5 h, and then allowed to cool to 20 °C to 25 °C by natural loss of heat for not less than 16 h nor more than DRS  310: 2022 
15                ©RSB 2021  - All rights reserved  
 24 h. Each specimen shall then be removed, the surface water wiped off with a damp  cloth and the specimen 
then weighed. Weighing of any one specimen shall be completed within 3 min after removing it from the water.  
F.4.2  Calculation of moisture absorption 5 -hour test; t he water absorption (per cent) after 5 h' immersion in 
boiling water  shall be calculated from the  
expression:  
Absorption percentage =  (𝑊3−𝑊1)
𝑊1×100    
where,  
𝑊1 is dry weight of the specimen, and  
𝑊3 is saturated weight of the specimen after 5 h immersion in boiling water.  
F.5  Calculation of saturation coefficient  
The saturation coefficient shall be calculated from the following expression:  
Saturation Coefficient = 𝑊2
𝑊3−𝑊1
𝑊3 
Where the symbols have the same significance as in F.3.2 and F.4.2. 
 
 
 
 
 
 
 
 
 
 
 DRS  310: 2021  
 
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