Concrete is a building material, and the quality of concrete often determines the service life and quality of the building. How to control the quality of concrete? Concrete mix ratio is an important factor to control the quality of concrete, and concrete mix ratio refers to the proportional relationship of the constituent materials (water, cement, sand and stone) in concrete. This article Xianji Net editor will introduce the concrete mix ratio for you Let’s take a look at the design specifications and the calculation method of concrete mix ratio.
Concrete mix design code
The concrete mix ratio is not just a few simple numerical ratios. The concrete mix ratio must not only meet the necessary strength of the building, but also make the concrete mixture have good workability, no segregation, no bleeding, etc., and the economy of the mix ratio Sex.
The design code for concrete mix ratio shall meet the following requirements:
1. Meet the strength grade of concrete design;
2. Concrete and workability that meet the construction requirements;
3. The durability to meet the requirements of concrete use;
4. Save cement and reduce concrete cost under the above conditions.
The concrete mix ratio design process is generally divided into four stages, namely, preliminary mix ratio calculation, reference mix ratio determination, experimental mix ratio determination and construction mix ratio determination. Through this series of work, the optimal mixing ratio of each component of concrete is selected.
Concrete mix design requirements:
Strength requirements
Meeting the structural design strength requirements is the primary task of concrete mix design. Any building will propose "strength design" for different structural parts
Claim. In order to ensure that the mix design meets this requirement, it is necessary to master the relevant standards and specifications of the mix design, combine the quality fluctuations of the materials used, the production level, the construction level and other factors to correctly grasp the "mixing strength" higher than the design strength level. After all, the compounding strength is the concrete strength determined under laboratory conditions. There are many factors that affect the strength in the actual production process. Therefore, it is also necessary to do a timely statistical analysis based on the actual production retained sample inspection data, and perform appropriate Adjust to ensure that the actual production strength meets the requirements of the "Concrete Strength Inspection and Evaluation Standard" (GBJ107). This is the true meaning of the mix design should meet the structural design strength requirements.
Meet the requirements of construction and workability
Determine the slump of the concrete mixture according to the engineering structure position, the amount of steel reinforcement, the construction method and other requirements to ensure that the concrete mixture has good homogeneity, segregation and bleeding will not occur, and it is easy to pour and wipe the surface .
Meet durability requirements
The design of the concrete mix ratio must not only meet the durability requirements such as impermeability and frost resistance proposed by the structural design, but also consider other durability requirements that are not clear in the structural design, such as roads and bridges in severe cold areas, where the water level rises and falls. The structure of the scope, and the structure of the environment exposed to chlorine pollution. In order to ensure that these concrete structures have good durability, it is not only necessary to optimize the design of the concrete mix, but the same important work is to optimize the raw materials used for the concrete before the design of the concrete mix. The selection of good raw materials is to ensure that the designed concrete has The basic premise of good durability.
Meet economic requirements
The production and development of an enterprise cannot do without good economic benefits. Therefore, under the premise of meeting the above technical requirements, the cost of concrete should be reduced as much as possible to achieve the principle of economic and reasonableness. In order to achieve this requirement, mix design should not only rationally design the mix itself, but also optimize the quality of raw materials. Choosing high-quality raw materials with reasonable prices is also a problem that should be paid attention to in the process of concrete mix design, which is not only beneficial to guarantee The quality of concrete is also an effective way to improve the economic benefits of concrete enterprises.
Concrete mix ratio calculation method
The calculation of concrete mix ratio is based on "General Concrete Mix Ratio Design Regulations" (JGJ55-2000) (J64-2000) and "Building Construction Calculation Manual".
1. Calculation of concrete mixing strength
The mixing strength of concrete should be calculated as follows:
fcu, 0≥fcu, k+1.645σ
Among them: σ——standard deviation of concrete strength (N/mm2). Take σ=5.00 (N/mm2);
fcu, 0-concrete compounding strength (N/mm2);
fcu,k——standard value of compressive strength of concrete cube (N/mm2), take fcu, k=20(N/mm2);
After calculation, fcu, 0=20+1.645×5.00=28.23 (N/mm2).
2. Calculation of water-cement ratio
The water-cement ratio of concrete is calculated as follows:
among them:
σa, σb——regression coefficients. Since the coarse aggregate is crushed stone, σa=0.46 and σb=0.07 according to the check-up table of the regulations;
fce——measured value of 28d compressive strength of cement, taken as 48.00 (N/mm2);
After calculation, W/C=0.46×48.00/(28.23+0.46×0.07×48.00)=0.74.
3. Calculation of water consumption
The determination of the water consumption per cubic meter of concrete shall meet the following requirements:
1. Determination of water consumption for dry and hard concrete
1) When the water-cement ratio is in the range of 0.40～0.80, according to the type of coarse aggregate, the particle size and the consistency of the concrete mixture required by the construction, the water consumption is selected according to the following two tables:
2) The water consumption of concrete with water-cement ratio less than 0.40 and concrete with special molding technology should be determined through experiments.
2. The water consumption of fluidity and high fluidity concrete should be calculated according to the following steps:
1) Based on the water consumption with a slump of 90mm in the above table, add 5kg for every 20mm increase in slump, and calculate the water consumption of concrete without admixtures;
2) The water consumption of concrete when admixtures are added can be calculated as follows:
Among them: mwa-water consumption per cubic meter of concrete mixed with admixtures (kg);
mw0-water consumption of concrete without admixture (kg);
β——The water reduction rate of the admixture, and β=500%.
3) The water reduction rate of the admixture should be determined by experiment.
The calculated value of concrete water-cement ratio mwa=0.57×(1-500)=0.703
Since the calculated value of concrete water-cement ratio=0.57, the water consumption is taken as the median value of the table=195kg.
4. Calculation of cement consumption
The amount of cement per cubic meter of concrete can be calculated as follows:
After calculation, mco=185.25/0.703=263.51kg.
5. Calculation of the amount of coarse aggregate and fine aggregate
The reasonable sand rate is determined by the following table:
According to the water-cement ratio of 0.703, the type of coarse aggregate is: crushed stone, coarse aggregate particle size: 20 (mm), check the above table, and take the reasonable sand ratio βs=34.5%;
The amount of coarse aggregate and fine aggregate is determined by the volume method. The calculation formula is as follows:
Among them: mgo——the amount of benchmark coarse aggregate per cubic meter of concrete (kg);
mso——the benchmark amount of fine aggregate per cubic meter of concrete (kg);
ρc——Cement density (kg/m3), take 3100.00 (kg/m3);
ρg——the apparent density of coarse aggregate (kg/m3), taking 2700.00 (kg/m3);
ρs——the apparent density of fine aggregate (kg/m3), taking 2700.00 (kg/m3);
ρw——water density (kg/m3), take 1000 (kg/m3);
α——The percentage of air content of concrete, taking α=1.00;
Combining the above two formulas, the solution is mgo=1290.38 (kg) and mso=679.67 (kg).
The standard mix ratio of concrete is: cement: sand: gravel: water = 264: 680: 1290: 185
Or the weight ratio is: cement: sand: gravel: water=1.00:2.58:4.9:0.7.
Several packs of cement for one side
First of all, the ratio is different, and the specifications of various materials used are also different. The data of the concrete mix ratio (the amount of various materials in each square of concrete) varies with many factors such as the number of concrete, whether the concrete is delivered, the slump size requirements, the type of cement number, the particle size and quality of the stone, and the sand The specifications, quality and water content of the product, whether there is fly ash or other materials, whether there are additives, whether there are impermeability and other special requirements, etc.
Example: How many packs of cement do I need for the C30 concrete?
1. The conventional theoretical weight of each square of concrete is 2400 kg, but in practice the weight of each square of C30 concrete is generally between 2320 and 2490 kg;
2. General C30 non-pumping concrete (only 4 materials: stone 5-40, sand in sand, cement PO42.5, water) reference mix ratio is:
Cement: Sand: Stone: Water=1:1.34:3.07:0.44, the amount of cube is 410Kg+550Kg+1260Kg+180Kg=2400Kg
One side c30 concrete requires 410kg of cement, and the weight of a single package of cement is divided into several types, such as: 30kg per package, 40kg per package, etc., the number of packages of cement required for different single package weights is not determined.
The concrete mix ratio design specification and concrete mix ratio calculation method introduced above are for you. One side of the concrete requires several packages of cement. I hope to provide you with reference and help.
