Concrete Cohesiveness
Concrete Cohesiveness - Related Videos
01:07
Cohesion
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2019
Cohesion is the attraction between molecules of the same type, such as water molecules. Water molecules have an overall neutral charge but are polar molecule. An oxygen atom in one water molecule has a partial negative charge that can bind to a hydrogen atom with a partial positive charge in a second water molecule, forming a hydrogen bond. Each water molecule can form up to four hydrogen bonds with other water molecules. Hydrogen bonds are responsible for water's cohesive nature. On a surface,...
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...
12:49
Measurement of Aggregate Cohesion by Tissue Surface Tensiometry
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Cited by 10 •
2011
We describe a method of measuring binding energy, expressible as tissue surface tension, between cells within 3D tissue-like aggregates. Differences in tissue surface tension have been demonstrated to correlate with invasiveness of lung, muscle, and brain tumors, and are fundamental determinants of establishing spatial relationships between different cell types.
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...
08:08
Compression Tests on Hardened Concrete
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2023
Source: Roberto Leon, Department of Civil and Environmental Engineering, Virginia Tech, Blacksburg, VA There are two distinct stages in a construction project involving concrete. The first stage involves batching, transporting, and casting fresh concrete. At this stage, the material is viscous, and the workability and finishability are the key performance criteria. The second stage occurs when the hydration process begins shortly after the concrete is placed in the form, and the concrete will...
FAQs
Paste viscosity helps keep cement paste, water, and aggregate interconnected as fresh concrete moves and is placed. If the paste does not provide sufficient resistance to internal movement, aggregate distribution can become uneven and bleeding or segregation may occur. If viscosity becomes too high, however, the mixture may resist flow and require greater effort during consolidation and finishing.
Aggregate grading affects how particles occupy space within the mixture and how much cement paste is needed to maintain continuity between them. A suitable grading supports uniform distribution and workable flow, while an unfavorable balance can contribute to segregation, bleeding, or difficult placement. This makes grading an important variable when adjusting concrete for pumping, consolidation, and finishing.
Water content influences both the mobility of the fresh mixture and its resistance to particle separation. When the balance is appropriate, concrete can flow while retaining cement paste and aggregate together. An unsuitable water level can weaken cohesion, promote bleeding or segregation, or make the mixture excessively resistant to placement and finishing, affecting later uniformity and strength development.
Chemical and mineral admixtures can modify the interaction between cement paste, water, and aggregate, allowing engineers to adjust cohesion while maintaining workable flow. Their use is relevant when the mixture must pass through pumping, placement, consolidation, or finishing without losing uniformity. The desired result is a balance that limits separation without making the concrete unnecessarily difficult to handle.
Engineers must consider cohesiveness across the entire fresh-concrete workflow rather than only at mixing. The mixture should remain uniform while being transported, placed, consolidated, and finished. Attention to paste viscosity, aggregate grading, water content, and admixture selection supports this continuity. Maintaining that balance helps reduce honeycombing, laitance, uneven aggregate distribution, and related durability concerns.
Adequate cohesion supports reliable movement through pumping and helps concrete remain sufficiently uniform during consolidation. This contributes to consistent aggregate distribution and reduces defects associated with separation, including honeycombing and laitance. In engineering applications, the target is not maximum cohesion: excessive cohesion can restrict flow and increase the effort needed to consolidate and finish the placed concrete.