Making concrete requires a precise mix of cementitious materials, aggregates of various sizes, water, mineral additives, and specific chemical admixtures. This complex process involves determining the right proportions, mixing, compacting, and molding, finally allowing the concrete to harden into a solid stone-like structure. In actual production and construction, the concrete ratio is crucial. By accurately determining the key parameters, you can ensure the quality of the project while also achieving efficient resource use.
1. Normal concrete with a design ratio
Obtain Engineering Data
In the engineering and construction process, the design ratio of ready-mixed concrete must strictly adhere to the project’s requirements. This ensures that the concrete’s strength meets actual needs while maintaining the safety and durability of the project. Compliance with relevant standards and technical specifications is essential.
Consider Raw Material Quality
In designing the concrete mix ratio, it is essential to assess the quality of raw materials comprehensively. The mix ratio should be adjusted as needed based on the actual condition of these materials.
Consider environmental conditions.
In summer, high temperatures cause faster water evaporation from the concrete surface. Effective measures must be taken to prevent slumping or drying cracks during construction. By adjusting the sand ratio, the moisture content and evaporation rate can be balanced, reducing the risk of drying cracks and collapse.
Establishment of enterprise-quality database
When designing concrete ratios, the first step is to perform design calculations and select parameters based on available information, theoretical systems, and specification experience. Establishing an enterprise-quality database is also essential.
1.2 Selection of key parameters
1.2.1 Basis for Parameter Selection
When determining the water content, adjustments can be made based on the type of sand used. Fine sand may increase water consumption by 5-10 kg/m³ of concrete, while coarse sand may reduce it by 5-10 kg/m³. For more fluid concrete, start by measuring the actual water needed for a 90mm slump as a base parameter, and then gradually increase the water content as the slump increases, typically requiring an additional 5 kg of water for every 20mm increase in slump.
When selecting the sand ratio, it is important to follow specific guidelines: fine sand requires a reduction in the sand rate, coarse sand allows for an increase, and for thin-walled construction, a higher sand rate is recommended.
1.2.2 Sensitive factor analysis
In concrete preparation, if the quality of raw materials changes, it is necessary to analyze the potential impact on concrete performance. Regression analysis can be used to clarify the relationship between parameters and characteristic values. If a clear functional relationship cannot be established, the relationship can be understood through data listings.
1.2.3 Adjustment of parameter selection
Parameter selection adjustments should be informed by experience and refined through the accumulation of extensive data. This process can be viewed as trend adjustment, where the potential impact on concrete performance is accurately calculated based on changes in parameters, thereby mitigating the influence of potential factor variations.
Additionally, these adjustments are subjective and require quantitative analysis of each factor’s effect. The final parameter selection should be verified through trial mix results.
2. Trial Matching
2.1 Selection of actual engineering raw materials
2.1.1 Representative sampling
When sampling from material piles, various factors such as pile size, orientation, and environmental conditions can influence the process. Continuous and balanced sampling methods are necessary to obtain the materials required for trial mixes.
2.1.2 Sample making
During the sample preparation process, it is crucial to ensure that the sample accurately represents the raw material and maintains a high degree of homogeneity. The quadrature method is commonly used as a standard sampling technique.
2.1.3 Data collection
First, collect all raw material inspection reports from daily operations. Next, establish a dedicated database for these reports, and combine the data with statistical test results to analyze the accuracy of reports from various suppliers. If a supplier’s inspection reports prove consistently accurate over a long period, they can be directly used in the concrete mix design.
Additionally, it is important to collect every inspection and test report from raw material suppliers. For cement supplied by a fixed source, accurately understand the actual strength growth pattern and use regression analysis to predict the 28-day strength of the cement.
2.2 Mixing method during trial mixing
Ready-mixed concrete is typically mixed using either the water addition method or the separate feeding method. Since different mixing methods are often used, it is essential to know the specific method employed by your mixing station during the trial mixing process. Based on this knowledge, a suitable mixing method should be developed for the trial mix.
2.3 Concrete performance and strength test
First, after determining the concrete mix ratio, conduct a strict test mix according to the specified parameters. Test the actual slump and workability of the concrete. If the workability and slump do not meet the standards, fix the water-cement ratio and continuously adjust the sand rate and quantity until the requirements are met to establish the benchmark mix ratio.
Typically, more than three different ratios are used for concrete strength testing. One ratio is used as the benchmark, while the other two ratios are adjusted by increasing or decreasing the benchmark ratio by 0.05. The water content of the benchmark ratio is maintained, while the sand rate is increased or decreased by 1%.
If conditions permit, the following is required in selecting the number of strength test mix test block sets:
a. Count the 3-day and 7-day strength growth rates in conjunction with the 28-day strength.
b. Calculate the standard deviation and coefficient of variation of strength for 3-day, 7-day, and 28-day strengths.
cues 3-day strength to derive 28-day strength.
d. Determine the strength of the test mix results.
3. Adjustment of concrete proportion after trial mixing
1. Workability and Slump Check:
Start by assessing the workability and slump of the test-mixed concrete. Adjust the water content based on these results.
2. Setting Time and Admixture Adjustment:
Next, determine the actual setting time and recheck workability. Based on these findings, optimize the amount of admixtures and the sand ratio. If the concrete shows poor water retention or an excessively long setting time, control the addition of admixtures and moderately increase the sand ratio. Conversely, if the concrete has high consistency and significant slump loss, increase the admixture or reduce the sand ratio. Be aware that adjusting admixtures may affect the water reduction, so adjustments to the water-cement ratio and water content may also be necessary.
3. Water-Cement Ratio and Aggregate Calculation:
Determine the concrete water-cement ratio based on strength test results, which will also dictate the amount of cementitious materials needed. If the concrete strength is too high, the water-cement ratio can be increased. In cases of tight schedules, the 3-day or 7-day strength can be used to estimate the 28-day strength, allowing for appropriate adjustments to the water-cement ratio. Finally, calculate the amounts of coarse and fine aggregates based on the measured concrete density and the sand ratio established during the test mix.