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.