concrete mix design & concrete test cubes

1. CONCRETE MIX
DESIGN
&
CONCRETE TEST
CUBES
Presented By:
Dipika Agarwal
Laxmi Salunkhe
Seema Shah
Suyog Dongare

2. CONTENTS
CONCRETE MIX DESIGN
 Introduction
 Specification of concrete
 Target mean strength of concrete
 Aggregates
 Determination of aggregate to cement ratio (A/C)
 Correction for specific gravity
 Correction for flakiness
 Determination of concrete density
 Cement content in concrete mix
 Concrete mix by Weight
 Total aggregate content
 Determination of W/C
2

3.  INTRODUCTION :
+ + +/- Additives
=Concrete +
CONCRETE MIX DEPENDS ON :
Workability
5 categories:
•Very high
•High
•Medium
•Low
•Very low
Strength
Finished surface
Consistency
Durability = Quality of material, environmental effect
Compactibility
Mobility
Stability or cohesiveness
Water content in concrete mix
Nature of aggregate particles
(shape, surface, porosity)
3

4.  SPECIFICATION OF CONCRETE :
Environmental
effect
Mixing Compacting Batching Transporting Placing Cement
content
Strength Water - cement ratio Aggregate - cement ratio
Fly ash
GGBFS
 TARGET MEAN STRENGTH OF CONCRETE :
New site
• No old track record is available
• Requires at least 30 test strength results of
same grade of concrete
Old site
• Old track records
is available
Methods – determined by following situation
4

5.  Formula to calculate TARGET MEAN STRENGTH (Fm) –
Fm = Fck + t X s
Where,
Fm = target mean strength
Fck = strength of concrete
( Strength achieved in 28 days )
t = constant
( probability of no. Of results fall below Fck )
s = standard deviation
( 30 hourly test results collected & tested daily using all 24hr samples mixed together )
 AGGREGATES
 Types --------------------------Types --------------------------
Coarse Aggregates
Particles greater than
4.75mm.
E.g.- Gravel and
crushed rock
Downgraded Coarse Aggregates
Size may be either 40mm CAN and
20mm CA1 or 30mm CAN and
15mm CA1
Fine Aggregates
Particles passing
through 9.5mm sieve
E.g. - Natural sand
5

6.  Properties ---Properties ---
Physical
• Texture
• Structure
• Composition
Chemical
• Solubility
• Reactivity
• Weathering
resistance
S.
No.
Properties of
Aggregate
Influence on Concrete
property
1. Porosity Strength / absorption
2. Chemical stability Durability
3. Surface texture Bond grip
4. Shape, size Water demand, strength
 Shape of Aggregates ---Shape of Aggregates ---
Rounded gravel Irregular gravel Crushed rock
6

7.  Fineness of Aggregates :Fineness of Aggregates :
Influence the water demand of concrete mix
or strength.
Classified in 4 zones –----Classified in 4 zones –----
Zone 1
Coarse sand
Zone 2
Normal sand
Zone 3
Fine sand
Zone 4
Very Fine sand
The selection of proportion of FA is given
by Department of Environment (DOE), UK
 Maximum size of the AggregatesMaximum size of the Aggregates
(MAS) :(MAS) :
Mostly MAS is 10mm, 20mm or 40mm
is used.
For massive work, MAS is 150mm or
above is used.
Limitation of MAS :
Minimum dimension of concrete section to be cast is < 4 X MAS
7
Zone 1
Zone
2
Zone 3
Zone 4

8. Determination of Aggregate to Cement Ratio (A/C):
A/C ratio can be calculated if following factors are known or determined:
 Shape of the aggregate
 Maximum aggregate size (10mm,20mm,40mm)
 Zone of aggregates (1,2,3,4)
 Degree of workability
 Water-to-cement ratio
If concrete ingredients consist of coarse crushed and natural fine aggregates then A/C is
adjusted as follows :
 Determine A/C for crushed aggregates for the MAS fixed for the Mix (Say Aca)
 Determine A/C for rounded or irregular gravel aggregates for MAS fixed for the Mix
(Say Afa)
 Calculate A/C of the concrete mix (Say A’) as per formula
A’ = Aca (%of CA1+%of CA2) + Afa (%of FA1)
100 100
Where,
Aca = Actual coarse aggregate
Afa = Actual fine aggregate
FA1 = Fine aggregate (zone 1)
CA1 = Coarse aggregate (zone 1)
CA2 = Coarse aggregate (zone 2)
8

9. Correction for Specific Gravity:
The specific gravity (relative density) of an aggregate is the ratio of its weight to the
weight of an equal volume of water displaced by the aggregates
 Ranges between 2.6 to 2.9
Lower or higher specific gravity changes A/C ratio ,hence needs correction:
A”= A’ca (actual specific gravity) + A’fa (actual specific gravity)
2.5 2.6
A”= A”ca + A”fa
Where,
A” = Corrected A/C
A’ca = Actual specific gravity of coarse aggregate
A’fa = Actual specific gravity of fine aggregate
A”ca = Corrected specific gravity of coarse aggregate
A”fa = Corrected specific gravity of fine aggregate
9

10. Correction for Flakiness:
 The aggregate is said to be flaky when its least dimension is less than 3/5th
(or 60%) of
its mean dimension
 Mean dimension, is the average size through which the particles pass, and the sieve
size on which these are retained
e.g., mean size of the particles passing through 25 mm sieve and retained on 20 mm
sieve is (20+25)/2=22.5 mm
If the least dimension is less than 3/5 x (22.5) = 13.5 mm, then the material is classified
as flaky
Flaky or angular aggregates have greater surface area -to-weight ratio therefore, it
is necessary to apply correction factor for flakiness
A/C ratio = A”x 0.95
A” = Specific gravity
 If workability is correct ,A/C ratio is correct
 Workability is more , increase A/C ratio
 Workability is less , reduce A/C ratio
10

11. Density of Concrete (Kg/CuM)
 Concrete density can be worked out by actually weighing the standard concrete cubes
 Volume of standard concrete cube = 3.375 x 103
cum
Concrete Density = Average Weight of the cube (Kg)
Volume of the cube (cum)
Determination of concrete density:
Cement content in concrete mix:
Concrete mix by weight:
Total aggregate content:
CEMENT Content (Kg/CuM) =
1+ A / C + W / C
WATER Content (Kg/CuM) = W / C X Cement Content (Kg/CuM)
AGREEGATE Content (Kg/M) = A / C X Cement Content (Kg/CuM)
11

12. Determination of W/C:
• W/C determine for compressive strength 33 N/mm2 is 0.52.
• Durability condition specifies Max. W/C = 0.55.
• W/C determine for compressive strength 38 N/mm2 is 0.48.
• Durability condition specifies Max. W/C = 0.45 and corresponding A/C = 4.60 .
1.If workability is < targeted, A/C to be reduced and fresh trial taken.
2.If workability is > targeted, A/C can be increased provided durability criteria of Min.
Cement and Maximum W/C are not violated.
3.If cohesiveness is <, proportion of fine aggregates and / or cement can be increased.
CONCLUSIONCONCLUSION
• The Engineer will have to exercise at times, his judgement based on his experience &
skill for finalising the most economic concrete mix.
• The systematic working of concrete mix design improves the quality & performance of
concrete structures.
• It also helps in economic usage a cement as well as gives overall economy.
• From this information Engineers gets help to work out correctly the concrete mix design
instead of using conventional nominal concrete mixes.
12

13. Concrete
blocks
For
sampling

14. Age to strength relation – chemical compositions and fineness
Higher early strength
content of Tricalcium cilicate > Dicalcium cilicate
Finer ground cement > coarse ground cement
CONTENTS
CONCRETE TEST CUBES
Introduction
Parameters affecting compressive strength
Sampling
Equipments
Procedure for filling and compacting
Identification, curing and testing concrete cubes
Requirement of compression testing machine
Acceptance criteria for compressive strength
Modes of failures
Conclusion 14

15. Age to strength relation – chemical compositions and fineness
Higher early strength
content of Tricalcium cilicate > Dicalcium cilicate
Finer ground cement > coarse ground cement
Introduction
Concrete strength are generally specified by compressive
strengths and the structural design is worked out on that basis.
Exact information
of compressive strength
of concrete depends
on quality control
Parameters affecting
compressive strength
•Cement (quality and grade)
•Water (water-cement ratio)
•Cement storage and transportation
•Cement packaging
•Aggregates
•Concrete workability
•Concrete placement
•Concrete compaction
•Curing of concrete
15

16. 1.65
Higher early strength
Cement
Early strength of cement
Content of Tricalcium silicate (C3S)Content of Tricalcium silicate (C3S)
Finer textureFiner texture
Content of Dicalcium silicate (C2S)Content of Dicalcium silicate (C2S)
Coarse textureCoarse texture
Variation in compressive strength
Supply from
different units
Supply from
different units
Supply from
different brands
Supply from
different brands
Variation of Compressive strength
from the same unit by each set.
Variation of Compressive strength
from the same unit by each set.
SolutionObtain monthly standard
deviation factor
Obtain monthly standard
deviation factor
Obtain co-efficient of
variation
Obtain co-efficient of
variation
Grade of cementGrade of cement
average
compressive
strength for a month
average
compressive
strength for a month
Standard deviation
for the same month
Standard deviation
for the same month
1.65
Experimenting the results by making sample of
cement cube and apply the following formula
Experimenting the results by making sample of
cement cube and apply the following formula
Parameters affecting compressive
strength
16

17. Water
strength of cement Lower the water to cement ratio higher the strength
and durability
Lower the water to cement ratio higher the strength
and durability
Affects in lower w/c ratio as well as higher grade of cementAffects in lower w/c ratio as well as higher grade of cement
Solution – accurately batch water so that it should not exceed much
Cement storage & transportation
Loss in strength In contact with moisture or waterIn contact with moisture or water
Solution – store carefully in water tight condition
must arrive on site with minimum possible time and less handlings
Cement packing
Maintaining strength
Preserve in longer time under same climatic
exposure
Preserve in longer time under same climatic
exposure
Solution – use porous material for packing bags
17

18. Aggregate
size Larger the size less cement water pasteLarger the size less cement water paste
shape Rounded aggregates, lesser surface area, so less c/w pasteRounded aggregates, lesser surface area, so less c/w paste
grading Lesser finer particles , Coarse finer aggregate mixLesser finer particles , Coarse finer aggregate mix
porosit
y
Porous aggregate may crush after adding load, so be with
solids
Porous aggregate may crush after adding load, so be with
solids
Concrete workability
Don't add excess of water,
it will loose its strength
Don't add excess of water,
it will loose its strength
Concrete transportation
concrete cubes are taken from batching plant.
Should not get segregate as it forms honeycomb like porous cavities.
1% trapped air reduce 6% strength
concrete cubes are taken from batching plant.
Should not get segregate as it forms honeycomb like porous cavities.
1% trapped air reduce 6% strength
Concrete compaction
Entrapped air is driven out
by compaction using
vibration techniques
Entrapped air is driven out
by compaction using
vibration techniques
18

19. Concrete curing
Due to inadequate water for
curing concrete surface cracks
and looses strength
So, its essential to cure concrete
cubes and keep moist up to 28
days.
Change in temperature affects
compressive strength, so cure
with 27 degree +/-
Due to inadequate water for
curing concrete surface cracks
and looses strength
So, its essential to cure concrete
cubes and keep moist up to 28
days.
Change in temperature affects
compressive strength, so cure
with 27 degree +/-
Compressive strength = potential energyCompressive strength = potential energy
This test helps
To determine
This test helps
To determine
Variations in concrete gradeVariations in concrete grade
All proportions of various materials in concrete mixAll proportions of various materials in concrete mix
Quality controlQuality control
Rate of gain of strength & time to removal of formworkRate of gain of strength & time to removal of formwork
Purpose of the test
Note: cube strength does not necessarily match with the final concrete structureNote: cube strength does not necessarily match with the final concrete structure
19

20. Sampling
Randomly taken, no extra dry or extra wet concreteRandomly taken, no extra dry or extra wet concrete
Fix for each
day
Fix for each
day
Numbers of concrete mixtures on siteNumbers of concrete mixtures on site
After specific deliveries of materialsAfter specific deliveries of materials
Specifications of different materialsSpecifications of different materials
Quantum of concreteQuantum of concrete
Concrete is being discharged from conventional or transit mixtureConcrete is being discharged from conventional or transit mixture
Min. Frequency of each grade of concreteMin. Frequency of each grade of concrete
Concrete is Poured in four equal incrementsConcrete is Poured in four equal increments
Some by buckets or some by sampling scoop & thoroughly mixedSome by buckets or some by sampling scoop & thoroughly mixed
Quantity per cube – 3kg. (for 100mm cube) & 10kg. (for 150mm cube)Quantity per cube – 3kg. (for 100mm cube) & 10kg. (for 150mm cube)
If concrete is taken from truck or dumper, its necessary to take samples from six
possible locations.
If concrete is taken from truck or dumper, its necessary to take samples from six
possible locations.
After remixing cube mould should be filled up immediatelyAfter remixing cube mould should be filled up immediately
20

21. Equipments
Cube mouldsCube moulds
 Only steel or cast iron
 Made up of three parts
1.two side flanges
2.base plate
3.nut bolts
 Inside faced must be planed and machine
finished
 All internal angles has to be accurate
 Edges and joints must be cleaned
 Surfaces should be coated by mould oil
 Prevent mould from rusting
 All parts should be bolted and then stored
in close room
Tamping rodTamping rod
 Steel bar of 16mm dia.
 600 mm length
 Bullet head
spannersspanners
Mould oilMould oil
scrappersscrappers
Big size scoopBig size scoop
Small size scoopSmall size scoop
A levelling floatA levelling float
Wheel barrowWheel barrow
Cleaning ragsCleaning rags
Non absorbent trayNon absorbent tray
Sharp marking scrapperSharp marking scrapper
Curing tankCuring tank
Polythene sheetingPolythene sheeting
21

22. Process for filling & compacting cube
mould
 must be done into three layers
each app. 50mm
 Must be placed using scoop
 each layer is compacted using tamping rod
 needs 35 stroke for 150mm &
25 stroke for 100mm
 surface level should be planed
 No air gaps in between or
scratches on surface
22

23. Process for identification , curing &
testing
 On the surface level some
identification mark, number and
date has to be scratched and
same noted on paper
 after removal from mould it should
immediately covered with damp jute
Transfer to a room having
humidity90% and temperature 27^
Keep the cube in curing pond of
clean water for 28 days
 automatic compression
machine is better than manual
load application
Machine has a control on rate of
loading, we can apply various
loading while testing its strength
23

24. Precautions need to be taken while
testing
 allow skilled workers only
Fresh water within 7 days only used for curing pond
Cubes has to be deep completely
Storage space has to be without any vibrations
Temperature control from 22 to 30 ^c.
There should not be loss in moisture while travelling from site to testing lab.
A float should be used to push the excess concrete after pouring third layer.
If the mix is too wet, allow water to drained out from mould.
24

25. Requirement of compression testing
machine must be accurate
Well calibrated, well certified
Having capacity to crush cube
TOP PLATEN :
Harden and smooth faces
Fitted on cylinder concentric
with central point
BOTTOM PLATEN :
Plain finished
Rigidly fixed on bearing block
Size more than cube size
Load applying rod
Concrete cube placing space
Selection of machine depends
on size of cube and load
application
25

26. Acceptance criteria for compressive
strength
Note the reading by applying
different loads from machine till the
cube crashes
Compressive strength should not be
less than the characteristic value
26

27. Modes of failures
USUAL FAILURES:
Equal cracking on all four sides
No damage to top and bottom faces
Cracks are vertical zigzag pattern
vertical faces breaks away leaving one
pyramid between
UNUSUAL FAILURES:
Crushed only at one side
Tensile or horizontal cracks only at one side
This indicates lower compressive strength
Reasons
Defects in machine
Faulty manual operation
Faulty casting of cube
Improper curing 27

28. Thank You...