Mix ProportionMix ProportionTasksTasks Basic RequirementsBasic RequirementsPrinciplePrincipleSteps and MethodsSteps and Methods
Design of Preliminary MixAscertaining the basic mix proportionLaboratory mix ProportionWorking Mix Proportion
§4.6 Mix Proportion Design of Concrete
Design of Preliminary MixAscertaining the basic mix
proportionLaboratory mix ProportionWorking Mix Proportion
Steps and Methods
Steps and Methods
Design of Preliminary Mix
Laboratory mix Proportion
Ascertaining the basic mix proportion
Working Mix Proportion
Design of Preliminary Mix
Determining the produce strength of concrDetermining the produce strength of concrete.ete.
According to Specification for Mix Proportion According to Specification for Mix Proportion Design of Ordinary Concrete . Design of Ordinary Concrete . (JGJ55-2000)(JGJ55-2000)
The produce strength of concrete should be dThe produce strength of concrete should be determined by the following formula:etermined by the following formula:
• fcu, 0—the produce strength of concrete, MPa;
• fcu, k—designed cubic standard compression strength of concrete;
• σ—standard deviation of concrete strength.
645.1,, kcuocu ff
How to get How to get
If no statistical data available, can be calculated according to the following formula.
11
22,
n
fnfn
icuicu
If no statistical data available, select according to the table blow.
Concrete Concrete strength gradestrength grade
Less than Less than C20C20
C20C20~~C35C35
Higher Higher than C35than C35
σσ 4.04.0 5.05.0 6.06.0
Tab.4.6.1 Selection of
Selection of Water-Cement RatioSelection of Water-Cement RatioAccording to strength ratioAccording to strength ratio
0,cuce
ce
fABf
Af
C
W
bcecce frf
cc=1.13=1.13
)/(0, BWCAff cecu
Selection of Water-Cement Ratio
• According to durabilityAccording to durability To meet the demands of durability, the
calculated w/c should not excess the value in following Tab.4.6.2.
Tab.4.6.2 Maximum of W/C and Minimum of Cement
Environment condition
Structure type
Maximum of w/c Minimum of cement,
kg
Con-
crete
Reinforced concrete
Pre-
stressed
concrete
Con-
crete
Reinforce
d concrete
Pre-
stressed
concrete
Dry environment
Normal residences and offices - 0.65 0.60 200 260 300
Damp enviro-nment
Without thawing
•High humidity room; Outside the house; in the earth and water (non-corrosive)
0.70 0.60 0.60 225 280 300
Thaw
-ing
•Exterior members under thawing; member under thawing in the earth
and water (non-corrosive);•Interior members under thawing in a High humidity
0.55 0.55 0.55 250 280 300
Damp environment with thawing and deice
Exterior and interior members with thawing and deice
0.50 0.50 0.50 300 300 300
Estimating the quantity of mixing water W0
According to slump, coarse aggregate and maximum particle diameter, mixing water can be estimated from the following table(Tab.4.6.3).
Tab.4.6.3 Mixing Water in Stiff Concrete and Plastic Concrete
Thickness of Thickness of concrete concrete
composite composite
Maximum size of Maximum size of gravel (mm) gravel (mm)
Maximum size of Maximum size of crushed stone (mm) crushed stone (mm)
Items Items Indexes Indexes 1010 2020 4040 1616 2020 4040
ThickneThicknessss
(( SS))
1515~~ 20201010~~ 151555~~ 1010
175175180180185185
160160165165170170
145145150150155155
180180185185190190
170170175175180180
155155160160165165
SlumpSlump((mmmm))
1010~~ 30303030~~ 50505050~~ 70707070~~ 9090
190190200200210210215215
170170180180190190195195
150150160160170170175175
200200210210220220230230
185185195195205205215215
165165175175185185195195
• Mixed water quantity is constant with the Mixed water quantity is constant with the requirement of mobility in the certain range requirement of mobility in the certain range of W/C quantity, when the materials are of W/C quantity, when the materials are fixed.fixed.
• The principle means that different W/C will The principle means that different W/C will produce different strength concrete with produce different strength concrete with common mobility in the same water quantity.common mobility in the same water quantity.
Principle of fixed water quantityPrinciple of fixed water quantity
Calculating cement quality in 1m3 concrete
Cement quality can be calculated from the following equation.
In addition, the calculated C0 should not less than the value in Tab4.6.2 for durability demands.
WCWC /00
Selecting proper ratio of sand to Selecting proper ratio of sand to gravel, Sp.gravel, Sp.
Calculating MethodCalculating Method
ogos
osp
pS
'''
''
Table Table
Select Sp in the following table (Tab.4.6.4)
Testing MethodTesting Method
Select Sp by slump test result
W/C W/C Maximum size of crushed Maximum size of crushed
stone, stone, (mm) (mm) Maximum size of gravel, Maximum size of gravel,
(mm) (mm)
16 16 20 20 40 40 10 10 20 20 40 40
0.400.40
0.500.50
0.600.60
0.70 0.70
3030~~ 3535
3333~~ 3838
3636~~ 4141
3939~~ 44 44
2929~~3434
3232~~3737
3535~~4040
3838~~43 43
2727~~ 3232
3030~~ 3535
3333~~ 3838
3636~~ 41 41
2626~~3232
3030~~3535
3333~~3838
3636~~41 41
2525~~ 3131
2929~~ 3434
3232~~ 3737
3535~~ 40 40
2424~~3030
2828~~3333
3131~~3636
3434~~39 39
Tab.4.6.4 Selection of Sp(Tab.4.6.4 Selection of Sp(%)%)
• There are two methodstwo methods to calculate S0 and G0.
– absolute volumeabsolute volume
– assume an apparent densityassume an apparent density
Calculating volume of sand (S0) and gravel (G0).
Calculating volume of sand (S0) and gravel (G0).
• The first methodThe first method is that the volume of concrete composite equals to the whole volume of ingredients.
LaWSGC
wasagC
1000100000
%%10000
0pS
GS
S
C0 、 S0 、 G0 、 W0—quantities of each gradients in one concrete composite;0s, 0g—Apparent density of sand and gravel;—quantity of entrained air; if there is no entrained air agent, =1.
Calculating volume of sand (S0) a
nd gravel (G0). • The other methodThe other method is to assume an apparent density of concrete composite at first. Then,
pSGS
S
00
0
ohWSGC 0000
When C0, S0, G0, W0 are determined in the steps above (We call it Primary Proportion), there are still some work to make the last proportion of concrete. At first, use the Primary Proportion to make the concrete composite, and evaluate its feasibility. Adjust proportion according to the following Table.
Ascertaining the basic mix proportion
The proportion that has been adjusted feasibility is called Basic Proportion.
Tab.4.6.5 Adjustment of concrete feasibility
Slump Appearance Adjustment
High thin; easy to bleed keep Sp , raise S and G
Low thick; easy to isolate keep w/c, raise C and W
Low slumpLow slump High slumpHigh slump
Increase the cement Increase the cement paste with fixed W/Cpaste with fixed W/C
Increase the use of Increase the use of aggregates with fixed Spaggregates with fixed Sp
How to Adjust FeasibilityHow to Adjust Feasibility
• Actual apparent density after modifying the blending can be tested when slump conforms with the requirements . It can be used to ascertain the laboratory mix Proportion.
• Ascertaining the basic mix proportion– CC拌’拌’ =C=Coo+ C S△+ C S△ 拌’拌’ =S=Soo+ S △+ S △– GG拌’拌’ =G=Goo+ G W△+ G W△ 拌’拌’ =W=Woo+ W△+ W△
How to Adjust FeasibilityHow to Adjust Feasibility
Laboratory mix Proportion
• Basic Proportion should be adjusted by strength. Prepare concrete composite of three proportions as following and measure their strength.
Group 1: W/C of Basic Proportion, W, Sp
Group 2: W/C+0.05, W, Sp
Group 3: W/C-0.05, W, Sp
There are two selections:
• select the group that satisfies strength demand with minimum cement
• the W/C has certain fcu,0 according to linear fi
gure by laboratory test values.
C/WC/W C /C / WW
0,cuf
Laboratory mix Proportion
• Obviously, it is not practical to mix 1 m3 concrete in the laboratory. So, the proportion still needs adjusting apparent density as following.
Laboratory mix Proportion
– ρoh r—tested density of concrete composite;
– ρoh c——calculated density of concrete composite.
– ρoh r—tested density of concrete composite;
– ρoh c——calculated density of concrete composite.If ρoh r -ρoh c≯B2%ρoh c, the proportion after stren
gth adjustment is Laboratory Mix Proportion ;If ρoh r -ρoh c≯2%ρoh c, all the ingredients plusδ, the
proportion is Laboratory Mix Proportion.
ohcohr /WGSCohc
Working Mix Ratio • Considering water content in sand and gravel,
Laboratory Proportion should be converted to Working Proportion as following.– C’=C– S’=S ( 1+a% )– G’=G ( 1+b% )– W’=W-S×a%-G×b%
C’, S’, G’, W’—quantity of all ingredients of Working Proportion;
C, S, G, W—quantity of all ingredients of Laboratory Proportion ;
• a, b —water content in sand and gravel.