1.  Mix Proportion  Tasks  Basic Requirements  Principle  Steps and Methods  Design of Preliminary Mix  Ascertaining the basic mix proportion  Laboratory mix Proportion  Working Mix Proportion §4.6 Mix Proportion Design of Concrete

2.  Design of Preliminary Mix  Ascertaining the basic mix proportion  Laboratory mix Proportion  Working Mix Proportion Steps and Methods

3. Design of Preliminary Mix Laboratory mix Proportion Ascertaining the basic mix proportion Working Mix Proportion

4. Design of Preliminary Mix Determining the produce strength of concrete.  According to Specification for Mix Proportion Design of Ordinary Concrete. (JGJ55-2000)  The produce strength of concrete should be determined by the following formula: f cu ， 0 — the produce strength of concrete, MPa; f cu ， k —designed cubic standard compression strength of concrete; σ — standard deviation of concrete strength.

5. How to get   If no statistical data available,  can be calculated according to the following formula.  If no statistical data available, select  according to the table blow.Concrete strength grade Less than C20 C20 ～ C35 Higher than C35 σ4.05.06.0 Tab.4.6.1 Selection of 

6. Selection of Water-Cement Ratio  According to strength ratio  c =1.13

7. 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

8. Environment condition Structure type Maximum of w/c Minimum of cement, kg Con - cret e Reinf orced concr ete Pre- stress ed concr ete Co n- cret e Reinf orce d concr ete Pre- stress ed concre te Dry environment Normal residences and offices-0.650.60200260300 Da mp envi ro- nme nt Without thawing High humidity room; Outside the house; in the earth and water (non- corrosive) 0.700.60 225280300 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 250280300 Damp environment with thawing and deice Exterior and interior members with thawing and deice 0.50 300

9. Estimating the quantity of mixing water W 0  According to slump, coarse aggregate and maximum particle diameter, mixing water can be estimated from the following table(Tab.4.6.3).

10. Tab.4.6.3 Mixing Water in Stiff Concrete and Plastic Concrete Thickness of concrete composite Maximum size of gravel (mm) Maximum size of crushed stone (mm) ItemsIndexes102040162040 Thickn ess （ S ） 15 ～ 20 10 ～ 15 5 ～ 10 175180185160165170145150155180185190170175180155160165 Slump (mm) 10 ～ 30 30 ～ 50 50 ～ 70 70 ～ 90 190200210215170180190195150160170175200210220230185195205215165175185195

11. Mixed water quantity is constant with the requirement of mobility in the certain range of W/C quantity, when the materials are fixed.Mixed water quantity is constant with the requirement of mobility in the certain range of W/C quantity, when the materials are fixed. The principle means that different W/C will produce different strength concrete with common mobility in the same water quantity.The principle means that different W/C will produce different strength concrete with common mobility in the same water quantity. Principle of fixed water quantity

12. Calculating cement quality in 1m 3 concrete  Cement quality can be calculated from the following equation.  In addition, the calculated C 0 should not less than the value in Tab4.6.2 for durability demands.

13. Selecting proper ratio of sand to gravel, Sp. Calculating Method  Calculating Method  Table Select Sp in the following table (Tab.4.6.4)  Testing Method Select Sp by slump test result

14. W/C W/C Maximum size of crushed stone, (mm) Maximum size of gravel, (mm) 162040102040 0.400.500.600.70 30 ～ 35 33 ～ 38 36 ～ 41 39 ～ 44 29 ～ 34 32 ～ 37 35 ～ 40 38 ～ 43 27 ～ 32 30 ～ 35 33 ～ 38 36 ～ 41 26 ～ 32 30 ～ 35 33 ～ 38 36 ～ 41 25 ～ 31 29 ～ 34 32 ～ 37 35 ～ 40 24 ～ 30 28 ～ 33 31 ～ 36 34 ～ 39 Tab.4.6.4 Selection of Sp(%)

15. two methodsThere are two methods to calculate S 0 and G 0. –absolute volume –assume an apparent density Calculating volume of sand (S 0 ) and gravel (G 0 ).

16. The first methodThe first method is that the volume of concrete composite equals to the whole volume of ingredients. C 0 、 S 0 、 G 0 、 W 0 —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.

17. Calculating volume of sand (S 0 ) and gravel (G 0 ). The other methodThe other method is to assume an apparent density of concrete composite at first. Then,  When C 0, S 0, G 0, W 0 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.

18. Ascertaining the basic mix proportion  The proportion that has been adjusted feasibility is called Basic Proportion. Tab.4.6.5 Adjustment of concrete feasibility SlumpAppearanceAdjustment Highthin; easy to bleed keep Sp ， raise S and G Lowthick; easy to isolatekeep w/c, raise C and W

19. Low slump High slump Increase the cement paste with fixed W/C Increase the use of aggregates with fixed Sp How to Adjust Feasibility

20. 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 –C 拌 ’=C o + △ C S 拌 ’=S o + △ S –G 拌 ’=G o + △ G W 拌 ’=W o + △ W How to Adjust Feasibility

21. 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

22.  There are two selections: select the group that satisfies strength demand with minimum cement the W/C has certain f cu,0 according to linear figure by laboratory test values. C/W C/W C / W Laboratory mix Proportion

24. Obviously, it is not practical to mix 1 m 3 concrete in the laboratory. So, the proportion still needs adjusting apparent density as following. Laboratory mix Proportion

25. –ρ oh r — tested density of concrete composite; –ρ oh c —— calculated density of concrete composite. – ρ oh r — tested density of concrete composite; –ρ oh c —— calculated density of concrete composite.  If  ρ oh r -ρ oh c  ≯ 2%ρ oh c, the proportion after strength adjustment is Laboratory Mix Proportion ；  If  ρ oh r -ρ oh c  >2%ρ oh c, all the ingredients plusδ, the proportion is Laboratory Mix Proportion.

26. 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.