Precast News From China
Hydraulic structures are subjected to the erosion and wear caused by sand carrying water flow, resulting in continuous loss of concrete surface materials.
The abrasion damage affects the durability and safety of hydraulic structures, and the systematic study of concrete abrasion mechanisms and protective measures is of great significance for the long-term operation of hydraulic structures.
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Concrete is one of the most widely used building materials, and its production consumes a large amount of natural resources such as fresh water and river sand.
According to the statistics of the World Health Organization, the shortage of water resources has affected more than 2 billion people, and the annual mining output of river sand is up to 5 billion tons.
Over exploitation has caused serious damage to the river ecosystem.
At the same time, ultra-high performance concrete (UHPC) has become a representative of the new generation of high-performance building materials due to its ultra-high mechanical properties, low porosity, and excellent durability.
In recent years, the application of seawater and sea sand in the preparation of UHPC has attracted widespread attention, but traditional UHPC does not have self sensing function, making it difficult to meet the intelligent needs of marine structural health monitoring.
This study prepared nCB UHPSSC with excellent mechanical properties and self strain sensing ability by incorporating nCB as a conductive filler into ultra-high performance seawater sand concrete, providing a new approach for self sensing concrete in marine structures.
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Marine engineering structures bear both static and dynamic loads, and the durability of concrete is particularly prominent in sulfate attack environments.
Sulfate ions react with cement hydration products to produce expansion products such as gypsum and ettringite, leading to internal expansion, cracking, and surface peeling.
Geopolymer concrete has good corrosion resistance, and basalt fiber can effectively improve the toughness and crack resistance of cement-based materials.
The combination of the two, basalt fiber reinforced geopolymer concrete, has potential applications in marine engineering.
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Polymer concrete is widely used in the field of construction due to its excellent mechanical properties and durability, but its long-term durability in high temperature and freeze-thaw environments still faces challenges.
The influence of commonly used thermosetting resins on the overall performance of polymer concrete has not been fully elucidated, and there is insufficient research on natural and expanded perlite as fillers, resulting in a lack of systematic guidance for actual engineering material selection.
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The rheological properties of concrete, as a core indicator of the workability of fresh concrete, directly determine the construction pouring efficiency, forming quality, and subsequent mechanical performance development.
Its stability is influenced by multiple factors such as raw material characteristics, mix design, and environmental conditions.
In engineering practice, the temperature, humidity, and diurnal temperature differences caused by seasonal changes are key environmental factors leading to fluctuations in the rheological properties of concrete – high temperatures in summer accelerate cement hydration reactions, which can easily cause rapid loss of slump; The low temperature in winter may suppress the adsorption efficiency of additives, which may induce the risk of slump rebound and segregation; The significant temperature difference between day and night in autumn leads to a dynamic fluctuation of “early strength and late weakness” in concrete; The temperature and humidity in spring are moderate, but there are still issues of rheological instability caused by short-term climate fluctuations.
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C80 grade high-strength concrete, with its excellent mechanical properties, has been widely used in service scenarios with strict requirements such as super high-rise pumping columns and large-span bridge anchorages.
However, due to inherent defects such as high self shrinkage caused by low water cement ratio, increased hydration temperature, and multiple microcracks, its durability under multiple corrosion of chloride salts, freeze-thaw cycles, and sulfates is significantly lower than that of medium and low strength grade concrete.
Fly ash, as a large amount of industrial by-products, can refine the pore structure, reduce temperature rise, and improve the interfacial transition zone during the secondary hydration process.
It is regarded as an economical mineral admixture to enhance the durability of high-strength concrete.
However, current research mostly focuses on the influence of dosage within 30% on the performance of C40-C60.
There is still a lack of systematic data on the durability evolution law and damage mechanism of high-grade concrete in the range of 5% to 20% dosage.
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With the continuous expansion of civil engineering scale and the continuous improvement of technological level, some important high-rise and large-span buildings with special functional requirements continue to emerge, such as skyscrapers, super large span bridges, and giant water conservancy hub projects, which require concrete to have higher strength, better durability, and better stability.
These demands have led to the gradual development of concrete from ordinary to high-performance and even ultra high performance.
The improvement of concrete strength is mainly achieved by reducing the water cement ratio, which also leads to a high viscosity of concrete, causing a series of construction problems such as concrete mixing, transportation, and pumping, greatly limiting the promotion and application of high-strength and ultra high strength concrete.
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Bleeding is caused by the poor water retention performance of freshly mixed concrete, where a portion of the mixing water is secreted from the slurry and accumulates on the surface until the cementitious material slurry is fully solidified.
This affects the quality of the concrete; False setting is an abnormal initial solidification or premature hardening phenomenon of cement, accompanied by heat release, which produces expansion joints and reduces the durability and compactness of concrete.
The causes of false setting and bleeding can be generally divided into internal and external factors.
The internal factors mainly depend on the demand for water during cement hydration, while the external factors depend on the environmental climate and concrete vibration process.
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The production method of commercial concrete is different from other commodities, characterized by production based on sales and strong time constraints.
Once the concrete is produced, it is advisable to start unloading within 90 minutes and finish unloading within half of the initial setting time to ensure the quality of the concrete.
Therefore, the manufacturer and user must coordinate and ensure that the feeding speed is consistent with the material feeding speed, so that the concrete supply on the construction site is neither disconnected nor piled up.
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Supervising party: Director L and Engineer W of * * * * Engineering Technology Supervision Co.
, Ltd;.