KENYA STANDARD  KS 2932:2021  
ICS ##.### 
1st  Edition  
  
 © KEBS yyyy  
 Precast concrete waffle units    
 
 
 
 
 
 
KS 2932: 2021  
ii © KEBS 2021  – All rights reserved  
 TECHNICAL COMMITTEE REPRESENTATION  
The following organizations were represented on the Technical Committee:  
1. Atkins Consulting Engineers Limited.  
2. Bamburi Cement Lafargeholcims  
3. Bens Electronics Service Ltd  
4. East African Portland Cement Plc  
5. Handisi systems Ltd  
6. Institution of Engineers of Kenya  
7. Institution of Quantity Surveyors of Kenya  
8. Jomo Kenyatta University of Agriculture and Technology  
9. Kenya Builders & Concrete Company Ltd  
10. Kenya Electricity Transmission Company Ltd  
11. Malaba Keya and Partners Consultants  
12. Mate rials Testing and Research Division  
13. Ministry of Transport, Infrastructure, Housing, Urban Development & Public Works  
14. Ministry of water and sanitation  
15. Nairobi Western Bypass project  
16. National Housing Corporation  
17. Orkidstudio_ Design and Build  
18. QuestLinks Engineering Ltd  
19. Questworks Limited  
20. Stroutel Africa Limited  
21. Technical University of Kenya  
22. Surtech  
23. Kenya Bureau of Standards — Secretariat  
REVISION OF KENYA STANDARDS  
In order to keep abreast of progress in industry, Kenya Standards shall be regularly review ed.  Suggestions for 
improvements to published standards, addressed to the Managing Director, Kenya Bureau of Standards, are 
welcome.  
© Kenya Bureau of Standards, 2021  
Copyright. Users are reminded that by virtue of Section 25 of the Copyright Act, Cap. 13 0 of 2001 of  the Laws of Kenya, copyright subsists 
in all Kenya Standards and except as provided under Section 25 of this Act, no Kenya Standard produced by Kenya Bureau of Sta ndards 
may be reproduced, stored in a retrieval system in any form or transmitte d by any means without prior permission in writing from the 
Managing Director.   KENYA STANDARD  KS 2932:2021  
ICS ##.###  
1st  Edition  
 
© KEBS 2021  – All rights reserved  iii 
  Precast concrete waffle units   
 
Kenya Bureau of Standards,  Popo Road, Off Mombasa Road,  
P.O. Box 54974 - 00200,  Nairobi, Kenya  
 +254 020 6948000, + 254 722202137, + 254 734600471  
 info@kebs.org  
 @KEBS_ke  
 kenya bureau of standards (kebs)  
  
KS 2932: 2021  
iv © KEBS 2021  – All rights reserved  
 Foreword  
This Kenya Standard was prepared by the Concrete and Concrete Technical Committee under the guidance of 
the Standards Projects Committee, and it is in accordance with the procedures of the Kenya Bureau of 
Standards  
During the preparation of this standard, reference was made to the following document (s):  
KS 829: Specification for precast concrete channels, edgings and quadrants  
KS 2834: Concrete kerb units 
  Requirement s and test methods  
Acknowledgement is hereby made for the assistance derived from this (these) source (s)  
 KENYA STANDARD  KS 2932 :2021  
 
© KEBS 2021  – All rights reserved  1 
 Precast concrete waffle units    
1. Scope  
 
This Standard defines and specifies requirements and conformity for concrete waffle.  
 
2.  Normative references  
 
The following referenced documents are indispensable for the application 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.  
 
KS 95, Specification for natural aggregates for use in concrete.  
 
KS EAS 18 -1, Cement Part 1: Composition, specifications and conformity criteria for common cements  
 
KS 2846, Mixing water for concrete — Specification for sampling, testing and assessing th e suitability 
of water, including water recovered from processes in the concrete industry, as mixing water for 
concrete  
 
KS 1780 -1, Building lime - Part 1: Definitions, specifications and conformity  
 
KS 2770 -1, Admixtures for concrete, mortar and grout - Part 1: Common requirements.  
 
KS 2770 -2, Admixtures for concrete, mortar and grout - Requirements Part 2: Concrete admixtures  
 
KS EN 1992 -1-1, Eurocode 2: Design of concrete structures Part 1 -1: General rules and rules for 
buildings  
 
KS EN 1994 -1-1, Euro code 4: Design of composite steel and concrete structures Part -1-1: General              
rules and rules for buildings  
 
KS EAS 412 -1, Steel for the reinforcement of concrete - Part 1: Plain bars  
 
KS EAS 412 -2, Steel for the reinforcement of concrete - Part 2: Ribbed bars  
 
KS EAS 412 -3, Steel for the reinforcement of concrete - Part 3: Welded fabric  
 
KS 22, Hot -rolled mild steel bars for reinforcement of concrete - Specification  
 
KS 2168, General concrete works — Code of practice  
 
3. Terms and definitions  
 
For the purposes of this Standard, the following terms and definitions shall apply  
 
3.1.  
concrete waffle unit  
precast concrete unit mainly of rectangular, square or triangular shape that is used in construction of floor 
slabs  
 
4.       Requirements  
 
4.1.  General requirements  
 KS 2932: 2021  
2 © KEBS: 2021 : – All rights reserved  
 Precast Concrete waffle units shall meet the performance criteria stated in this standard.  
 
4.2. Requirement for materials  
 
4.2.1.  Cement  
 
The cement manufacturing the precast concrete waffle units shall comply to KS EAS 18.  
 
4.2.2.  Aggregate  
 
The aggregate shall comply to KS 95.  
  
4.2.3.  Water  
 
The mixing water shall comply to KS 2846.  
 
4.2.4.  Admixtures  
 
The admixture used to manufacture the precast concrete waffle units shall comply to KS 2770.  
 
4.2.5.  Reinforcement  
 
All the reinforcement steel shall comply to KS EAS 412.  
 
4.2.6.  Requirement for production  
 
The production of the concrete and manufacturing of the precast concrete waffle units shall be in 
accordance with KS 2183  
 
4.2.7.  Design of concrete waffle unit  
 
The design of the precast concrete waffle units shall be in ac cordance with KS EN 1992 -1-1 and KS EN 
1994 -1-1 
 
4.3. Dimensions and tolerances  
 
4.3.1.  Dimensions  
 
Dimensions of preferred sizes of precast concrete waffles shall conform to Table 1 below.  
 
Table 1. Sizes of precast concrete waffle unit  
 
Waffle type  Nominal size  
(mm)  Thickness  
(mm)  Depth  
(mm)  
 1200 x 1200   
 
 
 
25 
 
 
 300,450,600  
 1040 × 1040  175,200,250,500  
 900 × 900  150,200,300,450  
 600 × 900  100,150,200,250,300  
 600 × 600  100,150,200,250,300  
 450 ×450  75,100,150,200,250  
 450 × 900  75,100,150,200,250  
 300  ×  900  75,100,150,200,250  
 
Other types of precast waffle units having shapes and sizes other than those given in Table 1, shall be such 
that they conform to the requirements of this standard.  
 
 KS 2932 :2021  
© KEBS 2021  – All rights reserved  3 
  
4.3.2.  Tolerances  
 
The maximum dimensional tolerances for concrete waffle unit when measured in accordance with Annex A shall 
be as specified in Table 2.  
Table 2.  Dimensional tolerances  
 
Dimension  Maximum dimensional deviation  
Length  
Width  
Thickness    2 mm  
  2 mm  
  3 mm  
Squareness of plan 
(difference between 
diagonals)   6mm  
Flatness, straightness  
 
 
Bowing and  
Twisting   Measured over 550 mm to  
 850 mm    2 mm  
 
 Measured over  
 250 mm to 400 mm   1 mm  
 
 
4.4. Flexural strength  
 
When tested as described in Annex B, the mean flexural strength at 28 days shall be not less than 6 N/mm2.  
No individual precast concrete waffle unit shall have a flexural strength of less than 5 N/mm2.  
 
4.5. Water absorption  
 
 When tested as described in Annex C, the water absorption shall not exceed 10 per cent by mass.  
 
4.6. Visual I nspection  
 
 All precast concrete waffle units shall be sound and free of defects that shall interfere with the proper 
placing of the precast concrete waffle unit or impair the strength or permanence of the construction.  
 
5. Sampling  
 
For the purpose of testing compliance with the requirements specified, samples for testing shall be selected 
at random at the site of manufacture, or from a delivered consignment.  
 
6.  Marking and labelling  
  
The name, trade mark or other means of identification of the manufacturing plant shall be marked on the 
precast concrete waffle unit. Other particulars relating to products made in accordance with this standard shall 
be clearly stated on the delivery note, invoice, manufacturer’s or suppliers certificate, or brochur e relating to a 
consignment of products:  
 
 
 
 
 
 
 
 
 
 
 KS 2932: 2021  
4 © KEBS: 2021 : – All rights reserved  
  
Annex A  
Measurement of dimensions  
 
A1. General  
 
Note:    It is recommended that all measurements be made using a suitable steel rule conforming to BS 4372 or BS 4484 or an equivalent  
Kenya Standard.  
  
A1.1  Length  
 
Measure the length of each product to the nearest 1 mm on the face, within 25 mm of the four extreme corners 
of the profile.  Calculate the average length to the nearest 1 mm.  
    
A1.2  Width and height  
 
 Measure the width and height of each product to the nearest 1 mm at both ends.  Measure the width at the top 
and bottom of parallel faces and the overall height at the face and back of the product.  Calculate the average 
height and width to the nearest 1 mm.  
 
 
 
KS 2932 :2021  
© KEBS 2021  – All rights reserved  5 
  
Figure 1 - Waffle plan, section x -x and section y -y 
 
A2. Determination of squareness    
 
Place the stock of an engineer’s square in contact with the moulded faces of the product.  Bring the blade into 
contact with the side of the product.  Using a feeler gauge conforming to BS 957 : Part 2, check that the clearance 
between the square and the side of the product at points not less than 30 mm from the top and the bottom does 
not exceed the appropriate tolerance.  
 
 
Annex   B  
Determination of flexural strength  
 
B1. Test specimens   
 
Five precast concrete waffle units for each type and thickness shall be taken from each production batch after 
carrying out dimensional checks.  
 
B2. Testing machine  
 
The test shall be carried out using flexural strength testing machine of sufficient capacity c apable of applying 
the loads continually and vertically.  It shall be provided with two steel supporting rollers each 38 ± 3 mm in 
diameter or two steel bearers, each 6 mm minimum width on the supporting surface (see Figure 3).  The spacing 
of the rollers or bearers shall be as given in Table 4.  
  
                          Table 4.  Spacing of rollers or bearers for flexural strength test  
   
Waffle  type  minimum spacing centre to centre 
of rollers or minimum clear distance 
between bearers in mm  
 
1200 x 1200  
1040 x 1040  
900 x 900  
600 x 900  
600 x 600  
450 x 900  
300 x 900  
 
450 x450  450 mm  
 
 
 
 
 
  
 
375 mm  
  
 
In either case, one support shall be horizontal and the other so mounted to enable loads to be applied without 
inducing any torsional restraint in the specimen, e.g. by pivoting about an axis parallel to the length of the 
specimen.  The upper member of the loading frame shall be provided with a spherical seating to ensure that the 
load is applied axially without inducing any torsion in the specimen, and a steel platen at least 50 mm wide and 
of length not less than the width of the widest specimen to be tested.  
 
B3. Procedure   
 
Place the specimen symmetrically on the bearers of the testing machine and with its shorter sides parallel to 
the supporting roll ers or bearers.  Position a hardwood fillet 50 mm wide on the upper surface of the specimen 
at the midpoint of the span extending the whole width of the specimen parallel to the supporting rollers or bearer 
(see Figure 3). Apply the load without shock and increase it at a rate not exceeding 1 kN/min for each 100 mm 
of width as tested, until the specimen fails.  Record individual failing loads.  
 
B4. Calculation and expression of results  KS 2932: 2021  
6 © KEBS: 2021 : – All rights reserved  
  
The flexural strength Fcf  of (in N/mm2) is given by the equation:  
 
  F cf = 
bd 2l 3p2  
   
   p = the individual failing load (in N);  
   I  = the distance between the supporting rollers or bearers (in mm);  
   B = the average width of specimen at the point of fracture (in mm);  
   d  = the average thickness of specimen at the point of fr acture (in mm).  
 
Express the flexural strength to the nearest 0.1 N/mm2. 
 
 
B5. Report  
 
The following shall be reported:  
 
(i) The individual flexural strength of each waffle unit to the nearest 0.1 N/mm 2; and  
 
(ii) The average flexural strength of the fiv e specimens to the nearest 0.1 N/mm2. 
 
All Dimensions in mm  
 KS 2932 :2021  
© KEBS 2021  – All rights reserved  7 
  
 
 
 
 
 
Figure 2 — Arrangement of loading for flexural strength test  
 
 
Annex   C  
Determination of water absorption  
 
C1. Test specimens  
 
Three precast concrete waffle units for each type and thickness shall be taken from the sample after carrying 
out dimensional checks.  
 
C2. Apparatus  
 
C2.1  Balance — The balance used shall be accurate to within 0.5 per cent of the weight of the smallest 
specimen tested.  
 
Side elevation  
End elevation (BB)  
End elevation (CC)  KS 2932: 2021  
8 © KEBS: 2021 : – All rights reserved  
 C2.2  Suitable concrete sawing machine   
 
C2.3  Ventilated Oven  — The temperature of which shall be maintained at 105 ± 5 oC. 
 
C2.4  Tank  — Deep enough to immerse specimens, containing clean water maintained at a temperature of 
20 ± 5 oC. 
   
C2.5  Dry airtight vessel, e.g. desiccator of sufficient size to contain the specimen to be tested.  
 
C3. Preparation of specimens   
 
Saw two square test pieces from diagonally opposite corners of each of the three concrete waffles, 
approximately 100  mm x 100 mm.  Saw from the full thickness of the waffle unit such that each specimen has 
two sawn and two moulded edges ( see Figure 4).  
 
 
All dimensions are in mm  
 
 
 
 
 
 
 
Figure 3 — preparation of specimens for water absorption test  
 
 
C4. Procedure  
 
C4.1  Place the six specimens in the ventilated drying oven so that each one is not less than 25 mm from 
any heating surface and from each other.  Dry the six specimens in the oven for not less than 24 h and until two 
successive weighings at intervals of 2 h sho w an increment of loss not greater than 0.2 per cent of the last 
previously determined weight of the specimen.  
 
C4.2  On removal from the oven, cool each specimen for 24 ± 0.5 h in the dry airtight vessel.  Weigh each 
specimen and record the mass M 1. Immedi ately, completely immerse the specimen in water at  
20 ± 5 o C with its longitudinal axis horizontal.  
 
C4.3  Leave the specimen immersed in the water for 24 ± 0.5 h. Remove each specimen, shake it to remove 
the bulk of the water and dry it with a cloth as rapidly as possible until all free water is removed from the surface.  
Weigh each specimen and record the mass M 2. 
 
C5. Calculation and expression of results  
 
KS 2932 :2021  
© KEBS 2021  – All rights reserved  9 
 Water absorption of each specimen shall be calculated from the following expression:  
 
Water absorption, per cent = 
100x 
11 2
MM M ) (  
 
where,   
M1   = the mass of specimen oven dry (g); and  
  M2  = the mass of specimen after 24 ± 0.5 h in water (g).  
 
Express the results as the mean water absorption of the two specimens for each of the three precast concrete  
waffle units to the nearest 0.1 per cent.  
 
C6. Report  
 
Report the average value of the three means as the water absorption of the concrete waffles.  KS xxxx: yyyy    
 
© KEBS yyyy– All rights reserved   
  