Aggregates Concrete
Aggregates Concrete - Related Videos
10:10
Aggregates for Concrete and Asphaltic Mixes
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2023
Source: Roberto Leon, Department of Civil and Environmental Engineering, Virginia Tech, Blacksburg, VA Concrete and asphalt are by far the most common construction materials used today. Concrete is a composite material consisting of cement, water, air, coarse aggregate, and fine aggregates. Fine aggregates are typically sands and coarse aggregates are natural or crushed rocks. Chemical admixtures to modify certain specific properties are also commonly used (i.e., superplasticizers to make the...
01:29
Preplaced Aggregate Concrete
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2024
Preplaced aggregate concrete is ideal for construction environments that are not easily accessible. The process begins by properly wetting the gap-graded coarse aggregates to remove the dirt, then placing it in the form and compacting it. Voids are filled with a mortar mix pumped under pressure through slotted pipes. This mortar typically consists of Portland cement, pozzolan, fine aggregates, water, and a fluidizing aid. The pozzolan helps reduce bleeding and segregation while improving the...
11:23
Tests on Fresh Concrete
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2017
Source: Roberto Leon, Department of Civil and Environmental Engineering, Virginia Tech, Blacksburg, VA Concrete consists of two phases, a cement paste phase comprised of cement, water, and air, and an aggregate phase comprised of coarse and fine aggregates. There are two key considerations when designing a concrete mix. First, the concrete must be workable and easy to cast in the forms in its fresh condition, even when the forms are packed with steel reinforcement. In this condition, it is the...
01:26
Alkali Aggregate Reaction in Concrete
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2024
The alkali-aggregate reaction in concrete involves natural siliceous minerals in aggregates reacting with alkaline hydroxides derived from cement alkalis. This reaction forms an alkali-silica gel that absorbs water, swells, and increases in volume, which is confined by the surrounding cement paste, creating internal pressures that crack and disrupt the concrete. The extent of expansion and damage can be partly attributed to the alkali-silica reaction's osmotic hydraulic pressure and the...
10:09
Tests of Hardened Concrete in Tension
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2023
Source: Roberto Leon, Department of Civil and Environmental Engineering, Virginia Tech, Blacksburg, VA In a previous laboratory focused on concrete in compression, we observed that concrete can withstand very large stresses under uniaxial compressive forces. However, the failures observed were not compressive failures but failures along shear planes where maximum tensile forces occur. Thus, it is important to understand the behavior of concrete in tension and particularly its maximum strength...
FAQs
Aggregate grading governs particle packing and the quantity of cement paste needed to fill spaces. A well-considered distribution of sizes can improve fresh-mixture workability while limiting unnecessary paste demand. Because paste content affects the hardened composite, grading decisions also influence permeability, shrinkage, stiffness, and durability. Engineers therefore treat grading as a central mix-proportioning variable, not merely a description of particle sizes.
Particle shape, surface texture, and moisture condition alter how aggregates behave during mixing and hardening. Shape and texture affect packing and workability, while moisture changes the water condition used in the mixture. These variables can change paste requirements and the resulting balance of strength, durability, and economy. Controlling them helps engineers produce more consistent concrete rather than relying on size grading alone.
Cement hydration produces the binding action that converts a packed mixture of aggregate, cement, and water into a hardened composite. The aggregate provides the principal structural framework, while the hydrated cement paste holds particles together. This interaction allows aggregate characteristics to influence the final material's stiffness, strength, permeability, shrinkage, and resistance to abrasion.
Aggregate selection requires balancing technical performance with economic and environmental objectives. Sand, gravel, crushed stone, and recycled particles may be considered as components of the mixture, while engineers evaluate their effects on strength, durability, workability, and cost. Including recycled particles can support more sustainable construction, provided the resulting proportions meet the intended engineering requirements.
Mix design should address grading, particle shape, surface texture, and moisture, then relate those characteristics to the required concrete performance. Engineers proportion the aggregate with cement paste and water to achieve suitable workability and hardened properties. The selected balance can be adjusted for targets such as strength, permeability, stiffness, shrinkage control, durability, and economical material use.
Aggregate testing supplies information needed to judge whether selected particles and proportions are suitable for a concrete mixture. In conjunction with mix design, testing helps engineers account for grading, shape, texture, and moisture effects on packing and workability. The resulting decisions support more reliable control of strength, durability, permeability, cost, and overall construction performance.
Aggregate decisions affect concrete used in pavements, foundations, bridges, and buildings, where performance demands differ by application. Engineers use proportioning and testing to align the mixture with required strength, stiffness, durability, abrasion resistance, permeability, and shrinkage control. These choices also influence construction economy and the potential use of recycled particles for more sustainable projects.