A good ratio is both “tested” and “waited” for.
Cement, slag, fly ash, water cement ratio, aggregate gradation – with multiple variables, the combination space can explode directly.
By relying on orthogonal experiments to achieve a 28 day strength from mixing to extrusion, a set of ratios has a long cycle, high cost, and consumes both manpower and time.
Traditional empirical formulas find it difficult to fully understand the thick nonlinear relationship between components and strength.
If the prediction is biased, the engineering risk will be amplified accordingly.
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