Calculate the theoretical mixture ratio of C25 concrete according to the known conditions;
Standard deviation of concrete strength C25-C35=5.0
Concrete mixing strength =25+ 1.64* standard deviation 5.0=33.2.
Regression coefficient; A b Look up the table according to the variety of gravel, gravel A = 0.46, and gravel B = 0.07.
1, calculate the water cement ratio according to the strength requirements;
Actual strength of cement =42.5* 1. 1=46.75.
Water cement ratio = 0.46 * 46.75/(33.2+0.46 * 0.07 * 46.75) = 0.62.
2. Check whether the water-cement ratio meets the durability allowable maximum water-cement ratio of 0.65, and calculate that the water-cement ratio of 0.62 is less than the specified value.
3. Determine the water consumption per cubic meter of concrete;
The slump is 35-50mm, the maximum particle size of crushed stone is 3 1.5-40 mm, and the water consumption is 175kg/m3.
4. Calculate the cement dosage per cubic meter of concrete;
Water consumption/water cement ratio = 175/0.62=282kg/m3.
Check whether the cement dosage meets the durability allowable minimum cement dosage of 260kg/m3, and calculate whether the cement dosage of 282kg/m3 exceeds the regulations.
5, choose sand ratio = 36%
6, calculate the dosage of sand and stone per cubic meter of concrete, according to the weight method;
Known water consumption per cubic meter of concrete = 175kg/m3, cement consumption =282kg/m3, sand ratio = 36%, assuming that the concrete mixture is 2400kg/m3.
282+G+S+ 175=2400
S/(G+S)=0.36
g+S = 2400-282- 175 = 1943kg/m3
S =(G+S)* 0.36 = 1943 * 0.36 = 699kg/m3
G =(G+S)-S = 1943-699 = 1244kg/m3
The theoretical mixture ratio calculated by gravimetric method is as follows:
Cement 282kg water 175kg sand 699kg gravel 1244kg.
Mixing ratio; 1:0.62:2.48:4.4 1
7, according to the design mixture ratio, do laboratory mixture ratio experiment adjustment, and get the laboratory mixture ratio;
8, conversion of construction mixture ratio, according to the water content of sand and stone in the construction site, get the final actual construction mixture ratio.