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Concrete strength is the core parameter for determining the resistance of concrete structural components, and its variation over time is the basis for establishing a resistance evolution model during service life.
Generally speaking, the strength of concrete increases with age in the early stages, but the growth rate gradually slows down; After entering the middle and later stages, the strength showed a downward trend due to environmental and material degradation.
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In the concrete industry, “experiment” and “test”, “laboratory” and “laboratory” are a set of high-frequency and easily confused professional terms.
They have similar pronunciations and semantic associations, but carry completely different technical connotations and application scenarios, and their standardized use directly affects the accuracy of technical documents.
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Winter concrete faces multiple environmental challenges such as low temperature, slow hydration, and high risk of frost heave.
As the source link of concrete quality control, mix design directly determines the workability, strength development, and long-term durability of concrete in low-temperature environments.
Different from the normal temperature mix proportion, the winter mix proportion needs to be systematically optimized based on current specifications such as GB50164-2011 “Quality Control Standards for Concrete”, GB50666-2011 “Construction Code for Concrete Structures”, JGJ55-2011 “Design Specification for Ordinary Concrete Mix Proportion”, etc.
, in order to address the inhibitory effect of low temperature on hydration reaction, frost heave damage mechanism, and workability characteristics.
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(1) In addition to cement, water, sand, and stone, various chemical additives and mineral admixtures are also important components of raw materials.
Chemical admixtures and mineral admixtures may be composed of one or more substances, as each cement plant’s cement has different mineral composition, fineness, alkali content, C3A content, gypsum form, and types of admixtures.
Different manufacturers and brands of cement with the same performance will inevitably require different amounts of adhesive and admixtures, which increases the complexity of material selection.
This requires performance matching tests to be conducted on the combination of cement, mineral admixtures, and chemical additives.
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Mineral admixtures play a key role in modern concrete technology, and their rational application directly affects the performance and service life of concrete structures.
Volcanic ash, phosphorus slag powder, and fly ash, as common industrial by-products, exhibit differentiated advantages in improving concrete performance due to their unique physical and chemical properties.
In recent years, with the continuous improvement of concrete material requirements in construction engineering, how to scientifically select admixtures to obtain the best performance combination has become a focus of attention in both academic and engineering circles.
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The evaluation of concrete structures in nuclear power plants under long-term irradiation is crucial to ensure their safe operation during their extended service life of 40-80 years.
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Large volume concrete is prone to temperature cracks due to the concentrated hydration heat of cementitious materials, which affects the safety and durability of engineering structures.
The “Construction Standard for Large Volume Concrete” (GB 50496-2018) implemented in 2018 provides a comprehensive solution for crack prevention throughout the entire process, including raw materials, mix proportions, construction techniques, and temperature monitoring.
Today, we will break down the core points and help construction, supervision, and design units accurately implement compliance requirements, while maintaining the bottom line of quality.
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From the perspective of mix proportion analysis, the assumed volume method is generally used to calculate the concrete density, that is, the sum of the masses of each component material in a 1m3 concrete mixture should be equal to the assumed apparent density, and solved together with the sand ratio expression to obtain the amount of coarse and fine aggregates in each cubic meter of concrete.
The assumed apparent density of concrete mixture is generally between 2350-2450kg/m3 (JGJ 55-2011 “Design Specification for Ordinary Concrete Mix Proportion”).
The water cement ratio of high-strength concrete is small, assuming a bulk density of 2350kg/m3 and a slurry ratio.
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When pouring concrete into the mold, it is not allowed to pour and impact the formwork or steel reinforcement skeleton in a concentrated manner.
When the pouring height is greater than 2 meters, a string tube or chute should be used for feeding.
The free height of the pouring from the discharge pipe mouth to the pouring layer should not exceed 1.
5 meters.
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James M.
Shilstone, Jr.
， Concrete technology expert, Command Alkon, Inc.
， Located in Frisco, Texas.
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