普通混凝土参考配合比设计项目说明英.doc

Mix Design of C15/20
1 Environment and Equipment for Test
1.1 The laboratory，the temperature in the standard curing room and the humidity shall meet the requirements of the testing regulations.
1.2 The specifications，range，accuracy of the test equipment shall adhere to the requirements of the testing regulations with passing the check to be qualified by the Institute of Measurement and Testing of TBS.
2 Design Basis
2.1 Design Regulations for the Mix Ratio of the Ordinary Concrete：JGJ 55-
2.2 Standard Specification for Highway Bridge Construction：JTJ 041-
3 Materials Selection
3.1 Cement：Simba42.5R type of cement will be used with the cement test results table below:
PARMETER
UNIT OF MEASURE
SPECIFICATIONSTZS727-
EN 197-1:)
SIMBA
AVERAGE VALUES
Compressive strength mortar test(days)

Mpa
Not less than 10
16
Compressive strength mortar test(28 days)

Mpa
Between 42.5and62.5
46
Lnitial setting time
Minuted
Not less than 60
100
Cement mortar expansion
Mm
Not less than 10
1
Sulphuric anhydride
%SO3
Not less than 3.5
2.5
Chloride content
%CI
Not less than 0.1
0.02
3.2 Fine Aggregate：Medium sand in the Nyakabindi River will be used with the test results table below:
Description
Origin
Sieve Analysis
Fineness Modulus
Yellow Sand
Nyakabindi River Sand
District II
2.9

GRADING FOR Sand
TOTAL MASS BEFORE WASHING
4716(g)
Sieve(mm)
M.retained(g)
% retained
Cumulative retained %
Cumulative passing%
10.0
NILL
NILL
0
100
6.3
5
0.1
0.1
99.9
4.75
170
3.6
3.7
96.3
2.36
998
21.1
24.8
75.2
1.18
807
17.1
41.9
58.1
0.6
816
17.3
59.2
40.8
0.425
680
14.4
73.6
26.4
0.3
490
10.4
84.0
16.0
0.15
505
10.7
94
5.3
0.075
155
3.3
98
2
PAN
90
2
100
0
FM
2.9

3.3Coarse Aggregate：20mm of quarry stones on Nyakabindi Hill will be used with the test results table below:
Description
TFV(for F=400kN)
Flakiness index（%）
ACV
Particle Grade
Gravel
215
23.3
20.6
20mm

TOTAL MASS BEFORE WASHING
5170(g)
SIEVE(mm)
M.retained(g)
% retained
% passing
28.00
NILL
NILL
100
20.00
638
12.3
87.7
14.00
2760
53.4
34.3
10.00
1560
30.2
41
6.3
204
3.9
0.2
5.00
0
0
0.2
2.00
0
0
0.2
1.18
0
0
0.2
0.6
0
0
0.2
0.425
0
0
0.2
0.3
0
0
0.2
0.15
0
0
0.2
0.075
0
0
0.2
pan
3+5
0.2
0

3.4 Water：the stored water in dams will be used with the test results table below:
Parameter
Units
Results
K53+200RHS
4800m2
K61+100LHS
14400 m2
K35+780RHS
4800 m2
pH

7.21
8.44
8.04
Turbidity
NTU
1434
58
19
Total Suspended Solids(TSS)
Mg/L
864
40
11
Conductivity(EC)
uS/cm
176.7
227
985
Total Dissolved Soilds(TDS)
mg/L
97.18
124.58
54
Choride
mg/L
17.47
8.74
32.99
Sulphate(SO42-)
mg/L
15
0
17
Silicate(SiO3)
mg/L
8.71
10.47
46.6

4 Calculation of Design Strength
4.1 Design Contents：the design strength is C15/20 for the ordinary concrete of the Box Culverts and other simmilar uses concrete .The design slump is 25-60mm.

4.2 Calculation Steps of the Mix Ratio:
     Calculated as follows:
Test with strength:
fcu，0 ≥ fcu，k 1.645σ
σ standard deviation of concrete strength - 5.0
fcu，o ≥ 15 +1.645 × 5 =23.2Mpa
in which：the fcu ,0 ---- Mix Strength of Concrete (MPa)
       the fcu，k ---- Standard Value of Compressive Strength of the Concrete Cube (MPa)
         the σ ---- Standard Deviation of Concrete Strength (MPa)
The Strength Standard Deviation of Concrete shall be calculated and determined in accordance with the comparable statistical of the same type concrete and shall meet the requirements below:
① During the calculation，the number of intensity samples shall not be less than 25 groups.
② When the concrete strength grade is C20 or C25 level and the calculated strength standard deviation value is less than 2.5MPa，the standard deviation used for calculation of the mix strength shall be taken with no less than 2.5MPa；when the concrete strength grade is equal to or greater than C30 level and the calculated strength standard deviation value is less than 3.0MPa，the standard deviation used for calculation of the mix strength shall be taken with no less than 2.5MPa.
5 The Basic Parameters in Concrete Mix Ratio Design
5.1 The determination of water for the plastic concrete
Determination of water per cubic meter of concrete shall meet the following requirements:
① When the water-cement ratio is in the 0.4 - 0.8 range，the water used can be selected from the table below in accordance with the species，size，and consistency of concrete mixture as requested in construction of the coarse aggregate.        

Water for the Plastic Concrete (Kg/m3)

Consistency of Mixture
Max Particles of Gravel（mm）
Max Particles of Aggregate (mm)
Item
Index
10
20
31.5
40
16
20
31.5
40
Slump (mm)
10-30
190
170
160
150
200
185
175
165
35-50
200
180
170
160
210
195
185
175
55-70
210
190
180
170
220
205
195
185
75-90
215
195
185
175
230
215
205
195

Note 1：the water in the above table is taken as per average value when using the medium sand；when using the fine sand，the water can be increased with 5-10Kg for per cubic meter of concrete；and the water can be reduced with 5-10Kg when using coarse sand.
  2：the water shall be adjusted accordingly when mixed with various additives or admixtures.
If the water-cement ratio is less than 0.4，or the concrete using a special molding process is used，the water shall be determined by experiments.

According to Design Regulations for the Mix Ratio of the Ordinary Concrete (JGJ 55-)，the water can be reduced with 5 ~ 10kg when using the course sand.
The medium sand is selected (coarse，FI=2.9) in our laboratory；and so the mWo =190kg/m3.

5.2 Determination of Sand Ratio per cubic meter of concrete
If the slump is 10-60 mm，the sand ratio can be selected from the table below in accordance with the species and size of the coarse aggregate.
Concrete Sand Ratio (%)
Water-cement
ratio（W/C）
Max Particles of Gravel（mm）
Max Particles of Aggregate (mm)
10
20
40
16
20
40
0.4
26-32
25-31
24-30
30-35
29-34
27-32
0.5
30-35
29-34
28-33
33-38
32-37
30-35
0.6
33-38
32-37
31-36
36-41
35-40
33-38
0.7
36-41
35-40
34-39
39-44
38-43
36-41

Note 1：values in this table are selected when using the medium sand；when using the fine or course sand，the sand ratio can be increased or reduced accordingly.
2：the sand ratio shall be increased appropriately when just using a single grain of course aggregate to mix the concrete.
3：for the thin-wall parts，the larger value shall be selected.
4：the sand ratio in the above table refers to the weight ratio of the total sand and aggregate.
5：when the slump is greater than 60mm，the sand ratio of concrete can be determined by the test，but also can be adjusted by 1% of increase with each 20mm slump of increase on the basis of the above table.
6：when the slump is less than 10 mm，the sand ratio shall be determined by the test
According to the menu，here we choose 36% of the sand ratio as our requirment

5.3 Calculation of the Water-cement Ratio：
0.46 of the aa，0.07 of the ab，and the coefficient of cement grade surplus 1.10 shall be taken:
W/C=aa×fce,g×γc ×/(fcu,o +aa×ab×γc× fce,g)
=0.46×42.5×1.1/（23.2＋0.46×0.07×42.5×1.1）
=0.87
 aa、ab ----- Regression Coefficient
       fce ----- The Measured Value of compressive strength of concrete for 28 days
① When there is no measured value of compressive strength for 28 days，the fce value in the formula may be determined as follows:
         fce=γc* fce,g
γc -------- the surplus coefficient of the grade value of cement strength can be determined according to the actual statistical data.
fce，g ------- Grade Value of Concrete Strength (MPa)
② fce value can be calculated through the strength for 28 days which is calculated
The regression coefficients such as aa and ab shall be determined as the following:
(ⅰ) The regression coefficients of aa and ab shall be determined through the relationship of the water-cement ratio and the concrete strength which is set up by the experience of cement aggregate used in the construction.
(ⅱ) The regression coefficients can be selected from the table below when lacking of the statistical data of the above test.
Stone Variety
Coefficient
Aggregate
Gravel
aa
0.46
0.48
ab
0.07
0.33

5.4 The Amount of Cement Selected for per cubic meter of concrete：

mCo=mWo/(W/C)= 185/0.87=212kg/m3
mCo --------- the amount of cement for (Kg)
mWo --------- the water for the per cubic meter of concrete with base mix ratio (Kg)
5.5 The determination of the amount of coarse aggregate and sand

The determination of the amount of coarse aggregate and sand shall meet the following requirements
The following formula shall be used When using the gravimetric method:
mCo+mgo+mso+mwo=mcp
βs =mso/mgo+mso*100%
mCo ----- the amount of cement for per cubic meter of concrete
mgo ----- the amount of course aggregate for per cubic meter of concrete
mso ------ the amount of fine aggregate for per cubic meter of concrete
mwo ------ the water for per cubic meter of concrete
βs ---- Sand Ratio (%)
mcp ------- the presumed weight of the per cubic meter of concrete mix (kg)，its value can be taken as 2350-2450 Kg
the amount of fine aggregate mSo =（presumed weight - mWo- mCo）×βs
=（2350-212-185）×0.38
= 742kg/m3
the amount of fine aggregate mGo = presumed weight - mWo- mCo- mSo
=2350-185-212-742
=1211kg/m3
③ The primary mix ratio can be get if calculated by mass method：
mCo ：mSo ：mGo ： mWo=212:742:1211:185
= 1:3.5:5.7:0.87
6 Adjust the workability and propose the base mix ratio
6.1Trial of base mix ratio
0.025m3 of the concrete mixture is mixed by calculation of the primary base mix ratio with a variety of materials as follows：
          Cement：212 × 0.025 = 5.3 kg
          Gravel：1211× 0.025 =30.3kg
            Sand:742 × 0.025 = 18.55kg
            Water：185 × 0.025 =4.6kg
When the concrete mixture is mixed even by calculating the amount of the materials，the slump test shall be done.

6.2 Adjust of base mix ratio
The base mix ratio shall be adjust by the slump test result.
If the test slump is higher than the degsin ，normally we add Aggregate and sand with same sand ratio to achieve the design slump . If it is lower than the design ,we add water and cement with the same water-cement Ratio.
Record how much of the adding materail，than calculate the alternatived base mix ratio
No
Water-cement ratio
Water
(KG)
Cement
(KG)
Aggregate
(KG)
Sand
(KG)
Sand ratio
1
0. 82
185
225
1222
718
37
After adjust
0.82

2
0.87
185
212
1211
742
38
After adjust
0.87

3
0.92
185
201
1198
766
39
After adjust
0.92

Note：for the smaller Water-cement ratio one，the sand ratio shall reduce 1%.for the larger Water-cement ratio one，the sand ratio shall increase 1%. Water per m3 don’t change.
6.3 Make the concrete cubes
For the mix design，we need make 3 lots of testing cubes to test 28days strength according to the base mix ratio/alternatived base mix ratio..
There are different water-cement ratio of minus and add 0.05 with the base mix ratio
No
Water-cement ratio
Water
(KG)
Cement
(KG)
Aggregate
(KG)
Sand
(KG)
Sand ratio
1
0.82

2
0.87

3
0.92

After make the cubes ,measure the weight of cube and calculate the bulk density instead of the assumed density.
No
Assumed density
(KG/m3)
Real bulk density
(KG/m3)
Ratio
Water
(KG)
Cement
(KG)
Aggregate
(KG)
Sand
(KG)
1

2

3

6.4 Test the strength of cubes
No
Water-cement ratio
Water
(KG)
Cement
(KG)
Aggregate
(KG)
Sand
(KG)
28day strengh
1
0.82

2
0.87

3
0.92

7 Finalize the mix desgin
Draw the relationship Water-cement and 28day strengh.find the correpond water-cement ratio of desgin strength 33.2Mp is the final water-cement ratio.
No
Water-cement ratio
Water
(KG)
Cement
(KG)
Aggregate
(KG)
Sand
(KG)
Sand ratio(%)
1