ICS 91.100.30 
 
Reference number  
RS nnn-n: yyyy 
© RSB yyyy 
  
 RWANDA 
STANDARD  DRS 
 425-2020  
 
1st edition  
2020-mm-dd 
 
Admixtures  used in concrete   —
Specifications  for Fly Ash  
 
 
 DRS 425: 2020 
©RSB yyyy - All rights reserved                  ii 
 In order to match with technological development and to keep continuous progress in industries, 
standards are subject to periodic rev iew. Users shall ascertain that they are in possession of the latest 
edition  
 
 
 
 
 
 
 
 
© RSB yyyy 
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 mechanica l, 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  
P.O Box 7099 Kigali -Rwanda  
KK 15 Rd, 49  
Tel. +250 788303492  
Toll Free: 325 0 
E-mail: info@rsb.gov.rw  
Website: www.rsb.gov.rw  
ePortal: www.portal.rsb.gov.rw    DRS 425: 2020 
iii                ©RSB yyyy - All rights reserved  
 Contents  Page 
Foreword  ................................ ................................ ................................ ................................ ............................  iv 
1 Scope  ................................ ................................ ................................ ................................ ......................  1 
2 Normative references  ................................ ................................ ................................ ............................  1 
3 Terms and definitions  ................................ ................................ ................................ ...........................  1 
4 Classification and Grading  ................................ ................................ ................................ ...................  2 
4.1 General  ................................ ................................ ................................ .......Error! Bookmark not defined.  
4.2 Class N  ................................ ................................ ................................ ................................ ...................  3 
4.3 Class F  ................................ ................................ ................................ ................................ ....................  3 
4.4 Class C  ................................ ................................ ................................ ................................ ...................  3 
5 Performance requireme nts ................................ ................................ ................................ ...................  3 
6 Methods of Sampling and Testing  ................................ ................................ ................................ ....... 6 
7 Storage and Inspection  ................................ ................................ ................................ .........................  6 
8 Rejection  ................................ ................................ ................................ ....Error! Bookmark not defined.  
9 Packaging and Package Marking  ................................ ................................ ................................ .........  6 
10 Supplier’s Certification  ................................ ................................ ................................ .........................  6 
Annex  A (inforrmative)   Effectiveness of Fly Ash or Natural Pozzolan in Preventing Excessive 
Expansion of Concrete due to Alkali Silica Reaction  ................................ ................................ ........  7 
Annex  B (informative)  Supplier's certi fication report (Example)  ................................ ................................ . 8 
 DRS 425: 2020 
©RSB yyyy - All rights reserved                  iv 
 Foreword   
Rwanda Standard s are prepared  by Technical Committees and approved by R wanda 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 ratified  by me mbers of RSB Board o f Director s for publication and 
gazettment as Rwanda Standards.  
DRS 425 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  (s): 
1) GBT 1596 : Fly Ash Used for Cement and Concrete  
2) ASTM C618 - 19 : Standard Specification for Coal Fly Ash and Raw or Calcined Natural Pozzolan for Use 
in Concrete  
The assistance de rived from the above source is hereby acknowledged with thanks.  
Committee membe rship  
The following organizations were represented on the Technical Committee on Civil Engineering  and Building 
Materials RSB/TC 009) in the preparation of this standard.  
City of Kigali  
Green Effect Engineering  
Integrated Polytechnic Regional Centre –Kigali (IPR C) 
NPD  
REAL Contractors Ltd  
Rwanda Housing Authority (RHA)  
Rwanda Transport Development Agency (RTDA)  
Standard For Sustainability (SFS)  
TEMACO Builders   DRS 425: 2020 
v                ©RSB yyyy - All rights reserved  
 Gasabo 3D  
Masss Design Group - Rwanda  
Institut d’ Enseignement Supérieur ( INES - Ruhengeri ) 
Amajyambere I ndustry Co Ltd  
NPD Ltd  
Rabbit Construction Ltd  
Institution of Engineers Rwanda  
CIMERWA Ltd  
University of Rwanda – College of Science and Technology (UR -CST)  
Rwanda Standards Board (RSB) – Secretariat  DRS 425: 2020 
©RSB yyyy - All rights reserved                  vi 
   
 DRS 425: 2020 
1                ©RSB yyyy - All rights reserved  
 Admixtures  used in concrete  —Specifications  for Fly  ash 
1 Scope   
This Draft Rwanda  Standard specifies requirements,  inspection methods, sampling and test method s of fly 
ash used for cement and concrete.   
The Standard is applicable to the fly ash used as admixture at time of mixing mortar and concrete, and f ly ash 
used as active addition at time of cement production.  
2 Normative references   
The following documents are referred to in the text in such a way that some or all of  their content constitutes 
requirements of this document.  For dated references, only the  edition  cited applies. For undated references, 
the latest edition of the referenced document (including any amendments) applies.  
ASTM C311/C311M –13, Standard Test Methods for Sampling and Testing Fly Ash or Natural Pozzolans for 
Use in Portland -Cement Con crete  
RS EAS 18 -2, Cement — Part 2: Conformity evaluation  
RS EAS 131 -1, Concrete — Part 1: Specification, performance, production and conformity  
RS EAS 148 -1, Cement — Test methods — Part 1: Determination of strength  
RS EAS 148 -2, Cement — Test methods  — Part 2: Chemical analysis of cement  
RS EAS 148 -3, Cement — Test methods  — Part 3: Determination of setting time and soundness  
RS EAS 148 -5, Cement — Test methods  — Part 5: Pozzolanicity test for Pozzolanic cements  
RS 211-3: 2010  Mortar for masonry - Methods of Test: Part 3: Determination of consistence of fresh mortar 
(by flow table)   
RS EAS 148 -6: 2018 Cements  — Test methods  — Part 6: Determination of fineness   
ASTM C187 – 16, Standard Test Method for Amount of Water Required for Normal Consistency of H ydraulic 
Cement Paste  
ISO 19596: 2017 Admixtures for concrete  
3 Terms and definitions   
For the purposes of this standard, the follow ing terms and definitions apply   
©RSB yyyy - All rights reserved                  2 
 3.1 
fly ash  
powder collected in power plant pulverized coal furnace flue gas.   
Note: the fly ash does not include the followings: (1) When the coal is burnt with urban garbage or other 
wastes; (2) when the industrial or urban garbage is burnt in the incinerator; (3) the powder collected at time of 
combustion of the circulating fluidized bed boiler.  
3.2 
reference cement  
Portland cement or ordinary Portland cement conforming to  provisions of  RS EAS 18 , and satisfying the 
strength grade 42.5 required in relevant requirements in the Standard.  
3.3 
testing sample     
reference cement and fly ash to be ins pected  are mixed in the mass ratio 7:3  
3.4 
reference mortar     
reference cement and normal sand with specified grading are mixed in the mass ratio 1: 3 
3.5 
testing mortar     
reference cement and normal sand with specified grading are mixed in the mass rat io 1:3 
3.6 
strength activity index     
compressive strength ratio between the testing mortar and reference mortar in specified age is expressed in 
percentage  
4 Classification  and grading  
 DRS 425: 2020 
3                ©RSB yyyy - All rights reserved  
 4.1 Classification  
4.1.1  General   
According to the category of coal, the fly ash  shall be classified  into type F, C and N.  According to the 
purpose, fly ash shall be divided  into  fly ash for mi xing mortar and concrete and  fly ash as cement active 
addition.    
4.1.2  Class N  
Class N —Raw or calcined natural pozzolans that comply with the appli cable requirements for the class as 
given herein, such as some diatomaceous earths; opaline cherts and shales; tuffs and volcanic ashes or 
pumicites, calcined or uncalcined; and various materials requiring calcination to induce satisfactory properties, 
such as some clays and shales . 
4.1.3  Class  F 
Class F —Fly ash that meets the applicable requirements for this class as given herein. This class of fly ash 
has pozzolanic properties.  
4.1.4  Class C  
Class C —Fly ash that meets the applicable requirements for this class as giv en herein. This class of fly ash, in 
addition to having pozzolanic properties, also has some cementitious properties.  
NOTE  Class F fly ash is typically produced from burning anthracite or bituminous coal, but may also be produced 
from sub bituminous coal a nd from lignite. Class C fly ash is typically produced from burning lignite or sub bituminous  
4.2 Grading  
The fly ash as cement active addition is not graded.  Fly ash for mixing mortar and concrete is divided into 
three grades: grade I, II and III  as specified  in the technical requirements in Table 1  
5 Performance  requirements  
5.1 Physical and Chemical Property Requirements  
Fly ash and natural pozzolans  for mortar and concrete  and fly ash used  as cement active addition  shall 
conform to the  physical requirements prescribed in Table 1 respectively.  
5.2 Chemical Composition  
Fly ash and natural pozzolans shall conform to the requirements as to chemical composition prescribed in 
Table 1.   
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 NOTE 3:  The chemical component determinations and the limits placed on each do n ot predict the performance of the fly 
ash or natural pozzolan with hydraulic cement in concrete, but collectively help describe composition and uniformity of the 
material.  
  Table 1  - Physical and Chemical Property Requirements of the Fly Ash for Mixing Mo rtar and 
Concrete   
 
Physical Requirement  
Item  Type of 
Fly ash    
Grade I    
Level II    
Level III  
Fineness  
 (Amount retained when wet -sieved on 45μm  
(No 325) sieve, max, %.  F  ≤12.0  ≤30.0  ≤45.0  
C  ≤ 34 ≤ 34 
 ≤ 34 
 N ≤ 34 ≤ 34 ≤ 34 
 
Water Demand Rati o (%) max, percent of 
control  F  ≤95 ≤105  ≤105  
C  105 105 105 
 N 
 115 115 115 
Strength activity indexA 
With portland cement at 7 days, and  
 
at 28 days, min percentage of control  F 
 > 70 > 70 > 70 
C  > 70 > 70 > 70 
 
N > 70 
 > 70 
 > 70 
 
Moisture co ntent max, %  N, F & C  ≤5.0 
Density (g/cm3) N, F & C  ≤5.0 
Autoclave expansion or contraction, max, %  N, F & C  0.8 
Stability (Le chatelier soundness test)/(mm) 
or  
 N, F & C  ≤ 5.0  
Chemical Requirements  
Item Class of 
Fly ash  Requirements  
  
 
Total mass fraction of silicon dioxide (SiO 2), 
aluminum oxide (A1 2O3) and iron sesquioxide 
(Fe 2O3)/% N  ≥70.0  
Total mass fraction of silicon dioxide (SiO 2), 
aluminum oxide (A1 2O3) and iron sesquioxide 
(Fe 2O3)/% F 
 ≥50.0  
 
 C 
 
 ≥50.0  
   
Free calcium oxide (f -CaO) m ass fraction/%  
 
 N 
 Report only  
F  18.0 max  
 C  >18.0  
 
Sulfur trioxide (SO 3) mass fraction/%  N 4.0 
F 
 5.0 
C 
 5.0 
  
Ignition loss (Loss) max, %  
 
  F  6.0A 
 C  6.0 DRS 425: 2020 
5                ©RSB yyyy - All rights reserved  
  N 10 
AThe strength activity index with portland cement is not to be considered a measure of the compressive strength of concrete containing 
the fly ash or natural pozzolan.  The mass of fly ash or natural pozzolan specified for the test to determine the strength activity index with 
portland cement is not considered to be the proportio n recommended for the concrete to be used in the work. The optimum amount of fly 
ash or natural pozzolan for any specific project is determined by the required properties  of the concrete and other constituents of the 
concrete and is to be established by te sting. Strength activity index with portland cement is a measure of reactivity with a given  cement 
and is subject to variation depending on the source of both the fly ash or natural pozzolan and the cement.  
BMeeting the 7 day or 28 day strength activity in dex will indicate specification compliance.  
C If the fly ash or natural pozzolan will constitute more than 20 % by mass of the cementitious material in the project mixture,  the test 
specimens for autoclave expansion  shall contain that anticipated percentag e. Excessive autoclave expansion is highly significant in cases 
where water to cementitious material ratios are low, for example,  in block or shotcrete mixtures.  
 
5.3  Alkali Content  
Expressed in Na2O+0.658K 2O calculation value. When there is alkali conten t requirement in the fly ash 
application, it shall be determined through negotiation between the supply and requisitioning parties.  
Table 2 The Physical and chemical property requirements of the fly ash as cement active addition  
 
Item Physical and Chemical  Performance Requirement  
F C N 
Ignition loss (Loss)/%  ≤8.0 
Water content/%  ≤1.0 
Sulfur trioxide (SO 3) mass fraction/%  ≤3.5 
Free calcium oxide (f -CaO) mass fraction/%   ≤1.0 
 ≤4.0 ≤4.0 
Total mass fraction of silicon dioxide (SiO 2), aluminum 
oxide (Al 2O3) and iron sesquioxide (Fe 2O3)/%   
≥70.0  ≥50.0   
≥70.0  
 Density/(g/cm3)  ≤2.6 
Stability (Le chatelier soundness test)/mm  ≤5.0 
 Strength activity index  ≥70.0  
5.4 Calcium Sulfate Hemi hydrate  Content  
For the fly ash discharged by the dry method or semi -dry desulphurization process, the calcium sulfate 
hemihyd rate content is required to be tested (CaSO 3•1/2H 2O), which shall be not more than 3.0%.  
5.5 Uniformity  
Characterized by fineness, the fineness of single sample shall be not more than the maximum deviation of the 
average fineness value of previous 10 sampl es (average value of all aforementioned samples, if the sample 
size is less than 10), the maximum deviation scope shall be determined through negotiation between the 
buyer and seller.   
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 6 Methods of Sampling and Testing  
6.1 Sampling  and test ing of fly ash or n atural pozzolan  shall be done  in accordance with the requirements of 
Test Methods PD ASTM C311/ C311M . 
7 Storage and Inspection  
7.1 The fly ash  shall be packaged in a material that safeguards the quality,  safety and integrity of the product. 
it shall also be stored so as to permit easy access for proper inspection and identification of each shipment  
7.2 The fly ash shall be stored in dry and cool place that allows easy access for inspection and 
identification, and in suitable waterproof building to maintain  quality of the cement. It shall be stored on pallets 
not in contact with the walls / floors and roof.  
8 Packaging , labeling and Marking  
8.1 Packaging  
When the fly ash or natural pozzolan is delivered in packages, the class, name, and brand of the producer, 
and the weight of the material contained therein, shall be plainly marked on each package. Similar information 
shall be provided in the shipping invoices accompanying the shipment of packaged or bulk material.  
8.2 Marking and labelling  
Each bag of fly ash  shall be  legibly and indelibly marked with the following information  in English language : 
a) the manufacturer’s name , address, (fac tory physical address)and/or  trademark;  
b) class  of fly ash ; 
c) net weight in kilograms;  
d) date of packing and/or batch number  
 
9 Supplier’s Certi fication  
9.1 Upon request of the purchaser, in the contract or the order, a supplier’s report shall be furnished stating 
the results of tests made on samples of the material and certifying the product conforms to all applicable 
requirements of this standar d. In addition, the report shall include the percentages of magnesium oxide 
(MgO), sodium oxide (Na2O), potassium oxide (K2O), and calcium oxide (CaO), all determined as described 
in Test Methods C311/C311M. The report shall also include the total alkali c ontent of the material, expressed 
as equivalent percentage of sodium oxide (Na 2Oe). 
 
 DRS 425: 2020 
7                ©RSB yyyy - All rights reserved  
 Annex  A 
(inforrmative)  
 
 Effectiveness of Fly Ash or Natural Pozzolan in Preventing Excessive 
Expansion of Concrete due to Alkali Silica Reaction  
If properly proportioned in co ncrete mixtures, both fly ash and natural pozzolan have been shown to prevent 
excessive expansion due to alkali silica reaction. The quantity of fly ash or natural pozzolan required to 
mitigate alkali silica reaction, measured in terms of portland cement r eplacement, is dependent  on the 
properties of the fly ash or pozzolan, reactivity of  the aggregate and the alk ali loading of the concrete.  
 
 
 
  
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Annex  B 
(informative)  
 
Supplier's certification report (Example)  
To provide uniformity for reporting the results of tests performed on pozzolans under this specification, and 
affirming compliance to the applicable limits of this standard, an example report of analysis is shown in Fig.1 
below.  
 
 
 
 
 
 DRS 425: 2020  
 
Price based on  nnn pages  
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