KENYA STANDARD                 KS 2932: 2020 
                
   
 
 
 
 
 
 
 
  
 
 
 
 
 
 
 
 
 Precast  concrete waffle  units 
 
 
 
 
 
 
 
 
 
 
©KEBS 2020                         First Edition  2020 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 KS 2932 :2020          
 
ii                     © KEBS 20 20 — All rights reserved  TECHNICAL COMMITEE REPRESENTATION  
 
The following organizations were represented on the Technical Committee:  
 
1. Atkins Consultin g Engineers Limited.  
2. Bamburi Cement Lafargeholcims  
3. Bens Electronics Service  Ltd 
4. East African Portland Cement Plc  
5. Handisi systems L td 
6. Institution  of Engineers of Kenya  
7. Institution  of Quantity Surveyors of Kenya  
8. Jomo Kenyatta University of Agriculture and Te chnology  
9. Kenya Builders & Concrete Co mpany  Ltd 
10. Kenya Electricity Transmission Co mpany  Ltd 
11. Malaba Keya and Partners Consultants  
12. Materials Testing and Research Division  
13. Ministry of Transport, Infrastructure, Housing, Urban Development & Public Works  
14. Ministr y 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 reviewed. Suggestions 
for improvements to published standards, addressed to the Managing Director, Kenya Bureau of Standard s, 
are welcome.  
 
 
 
 
 
 
 
© Kenya Bureau of Standards, 20 20 
  
Copyright. Users are reminded that by virtue of Section 25 of the Copyright Act, Cap. 12 of 2001 of  the Laws of Kenya, copyright 
subsists in all Kenya Standards and except as provided under Section  26 of this Act, no Kenya Standard produced by Kenya Bureau of 
Standards may be reproduced, stored in a retrieval system in any form or transmitted by any means without prior permission in  writing 
from the Managing Director . 
 
 
 
 
 KENYA STANDARD                                 KS 2932  : 2020 
                
 © KEBS 20 20 — All rights reserved            iii  
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Precast concrete waffle  units 
 
 
 
 
 
 
 
KENYA BUREAU OF STANDARDS (KEBS)  
 
Head Office:  P.O. Box 54974, Nairobi -00200, Tel.: (+ 254 020 ) 605490, 602350, Fax: (+254 020 ) 604031  
E-Mail: info@kebs.org,  Web:http://www.kebs.org   
 
Coast Region     Lake Region          Rift Valley Region  
P.O. Box 99376, Mombasa -80100   P.O. Box 2949, Kisumu -40100        P.O. Box 2138, Nakuru -20100  
Tel.: (+254  041) 229563, 230939/40  Tel.: (+254 057) 23549, 22396        Tel.: (+254 051) 210553, 210555  
Fax: (+254  041) 229448    Fax: (+254  057) 21814         
 
 
 
 
 
 
 
 KS 2932 :2020          
 
iv                     © KEBS 20 20 — All rights reserved   
 
Foreword  
 
This Kenya Standard was developed by the 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.  
There is an  increase of construction  of floor slabs using precast waffles  units  in this country.  Though waffle 
slabs are deeper than flat slabs, the reduction in concrete and steel quantities is considerable and where 
exposed, they are aesthetically appealing.  
 
. 
 
               
© KEBS 2017 — All rights reserved                      1 KENYA  STANDARD                       KS 2932 :2020 
 
 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 fo r 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 con crete.  
 
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 the 
suitability of water , including water recovered from pro cesses 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 c oncrete, 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, Eurocode 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 reinforce ment 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 a nd 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 : 2020 
            
                              © KEBS 20 20— All rights reserved  2  
Precast Concrete waffle  units shall meet the p erformance 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 s hall comply to  KS 95.  
  
4.2.3.  Water  
 
The mixing water shall compl y 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 manufactur ing o f 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 unit s shall  be in accordance with KS EN 1992 -1-1 and KS EN 
1994 -1-1 
 
4.3. Dimensions and toleranc es 
 
4.3.1.  Dimensions  
 
Dimensions of preferred sizes of precast concrete waffle s 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: 2020  
 
 
© KEBS 20 20 — 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 speci fied 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 ov er 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 Inspection  
 
 All precast concrete waffle  units  shall be sound and free of defects that s hall 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 t o products made in accordance with this standard 
shall be clearly  stated on the  delivery note, invoice, manufacturer’s or suppliers certificate, or brochure 
relating to a consignment of products:  
 
 
 
 
 
 
 
 
 
 
 
 KS 2932 : 2020 
            
                              © KEBS 20 20— All rights reserved  4 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 a nd the overall height at the face and back of the product.  Calculate the 
average height and width to the nearest 1 mm.   
 
 
 
 
Figure 1 - Waffle plan, section x -x and section y -y 
                          KS 2932: 2020  
 
 
© KEBS 20 20 — All rights reserved          
     5 
 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 capable of applying 
the loads continually and vertically.  It shall be provided with two steel supporting r ollers 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 beare rs 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 10 40 
900 x 900  
600 x 900  
600 x  600 
450 x 900  
300 x  900 
 
450 x450  450 mm  
 
 
 
 
 
  
 
375 mm  
  
 
In eit her 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 loadi ng 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 rollers 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.  Rec ord individual failing loads.  
 
B4. Calculation and  expression of results  
 
The flexural strength Fcf  of (in N/mm2) is given by the equation:  
 KS 2932 : 2020 
            
                              © KEBS 20 20— All rights reserved  6   F cf = 
bd 2l 3p2  
   
   p = the individual failing load (in N);  
   I  = the distance between the sup porting 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 fracture (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 five specimens to the nearest 0.1 N/mm2. 
 
All Dimensions in mm  
 
 
 
 
 Side elevation  
End elevation (BB)  
End elevation (CC)                           KS 2932: 2020  
 
 
© KEBS 20 20 — All rights reserved          
     7 
  
 
Figure 2 — Arrange ment 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. Appara tus 
 
C2.1  Balance — The balance used shall be accurate to within 0.5 per cent of the weight of the smallest 
specimen tested.  
 
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 te st pieces from diagonally opposite corners of each of the three concrete waffle s, 
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).  KS 2932 : 2020 
            
                              © KEBS 20 20— All rights reserved  8  
 
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 ea ch other.  Dry the six specimens in the oven for not less than 24 h and until 
two successive weighings at intervals of 2 h show an increment of loss not greater than 0.2 per cent of the 
last previously determined weight of the specimen.  
 
C4.2  On removal fr om the oven, cool each specimen for 24 ± 0.5 h in the dry airtight vessel.  Weigh each 
specimen and record the mass M 1. Immediately, completely immerse the specimen in water at  
20 ± 5 o C with its longitudinal axis horizontal.  
 
C4.3  Leave the specimen imm ersed 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  
 
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 afte r 24 ± 0.5 h in water (g).  
 
                         KS 2932: 2020  
 
 
© KEBS 20 20 — All rights reserved          
     9 
 Express the results as the mean water absorption of the two specimens for each of the three  precast 
concrete waffle unit s to the nearest 0.1 per cent.  
 
C6. Report  
 
Report the average value of the three means as the water absorpt ion of the concrete waffle s.