Name: concrete durability and water penetration
Uploaded: 2024-11-07T14:48:45.000Z
Duration: 1 min 25 s
Channel: JoVE

Permeability refers to how readily liquids or gases can move through concrete. This characteristic is relevant for ensuring the impermeability of structures that retain liquid and resist chemical degradation.
Concrete permeability is assessed with a basic lab test, wherein all sides except the top of a concrete sample are sealed. Pressurized water is then applied to the top surface.
Upon reaching a steady state, which may take around ten days, the volume of water that has permeated through a set thickness of the concrete over a specific duration is recorded.
For concrete, which consists of standard normal-weight aggregates, permeability is determined by the porosity of the cement paste.
The permeability of hydrated cement paste is not only determined by the small pore size within the gel but is influenced by the presence of larger capillary pores.
As hydration progresses, the permeability of the cement paste declines because some of the spaces originally filled with water are closed off.
At lower water-to-cement ratios, typically below 0.6, permeability decreases because the capillaries become segmented or broken up, impeding fluid flow.

permeability of concrete

Permeability of Concrete

Permeability in the context of concrete refers to how easily liquids or gases can pass through the material. This quality is crucial for assessing the water-tightness and durability of concrete structures and their resistance to chemical attacks. Concrete permeability can be determined through comparative laboratory tests. These tests typically involve sealing a concrete specimen from the sides, applying water pressure to the top surface with pressure, and measuring the amount of water passing through, often around ten days, until a steady state is achieved.
The permeability of concrete is not only influenced by the water/cement ratio and the degree of hydration but also by the porosity of the cement paste, which varies with pore size distribution. Capillary porosity plays a significant role, as segmented capillaries reduce permeability compared to interconnected ones. As the cement paste continues to hydrate, its permeability decreases due to the closure of voids initially occupied by water. For durable concrete, it&#39;s advantageous to have a lower water/cement ratio, which helps achieve lower permeability sooner.
It&#39;s also noted that the concrete mix should be dense and use well-graded aggregate for reduced permeability. Additionally, factors like curing methods and aggregate size can affect permeability, with steam-cured concrete usually having higher permeability than moist-cured, unless subjected to specific curing conditions like fog curing to reach desired low permeability levels.

Permeability refers to how readily liquids or gases can move through concrete. This characteristic is relevant for ensuring the impermeability of ...

Education

JoVE Core

Civil Engineering

Unit 1

KEY TERMS AND CONCEPTS

concrete durability and water penetration

Concrete durability depends partly on how easily water and gases can move through it. This property, called permeability, is important for judging water-tightness and resistance to chemical attack in concrete structures.

Permeability is measured with comparative lab tests. In a typical test, the sides of a concrete specimen are sealed, water pressure is applied to the top surface, and the amount of water that passes through is measured. The test is often run for about ten days until a steady state is reached.

Several features of the concrete mix affect permeability. The water/cement ratio and the degree of hydration both matter. The porosity of the cement paste also plays a major role. Pore size distribution is important, and capillary porosity can change how easily water moves through the material.

Interconnected capillaries allow more flow than segmented capillaries, which reduce permeability. As cement paste hydrates, its permeability drops because voids that once held water are gradually closed. For more durable concrete, a lower water/cement ratio helps the mix reach low permeability sooner. A dense mix with well-graded aggregate also helps reduce permeability. Curing and aggregate size matter too. Steam-cured concrete usually has higher permeability than moist-cured concrete, although fog curing can be used in some cases to reach low permeability levels.

Concrete Durability and Water Penetration

concrete-durability-and-water-penetration

Concrete durability depends partly on how easily water and gases can move through it. This property, called permeability, is important for judging water-tightness and resistance to chemical attack in concrete structures. Permeability is measured with comparative lab tests. In a typical test, the sides of a concrete specimen are sealed, water pressure is applied to the top surface, and the amount of water that passes through is measured. The test is often run for about ten days until a steady...

sulfate attack on concrete

Concrete Damage from Sulfate Exposure

Concrete damage from sulfate exposure starts with a whitish discoloration, often first seen at the edges and corners. As the attack continues, the concrete can crack and spall. This deterioration happens when sulfates react with hardened concrete and create new compounds that take up more space than the materials they replace. Sulfates may enter concrete from soil, groundwater, or industrial effluents. Inside the concrete, they can form calcium sulfate and calcium sulfoaluminate. The reaction...

effect of sea water on concrete

Seawater Damage and Concrete Durability

Seawater can damage concrete by changing its chemistry, increasing porosity, and lowering strength. In marine settings, concrete is exposed to dissolved salts and repeated wetting, so its durability depends on how much water can enter the material. One major form of damage is the breakdown of ettringite and gypsum, two concrete minerals that can dissolve in seawater. As these materials are lost, the concrete becomes more porous. Salt can also crystallize inside pores, especially above the...

acid attack on concrete

Concrete Damage from Low pH Water

Concrete damage from low pH water happens when acids react with the hydrated cement paste. This reaction dissolves the paste, so the concrete becomes softer and weaker. The problem is often seen in chimneys, sewers, and industrial settings. The amount of damage depends on how acidic the water is. When pH falls below 6.5, the attack becomes more severe. A pH below 4.5 can cause major concrete damage. The rate of damage also depends on how fast hydrogen ions move through the cement gel. This...

alkali aggregate reaction in concrete

How Moisture Cracks Alkali-Reactive Concrete

Alkali-aggregate reaction in concrete can weaken a structure when siliceous minerals in the aggregate react with alkaline hydroxides from cement. The reaction makes an alkali-silica gel, which pulls in water and swells. As the gel expands inside the rigid cement paste, it creates pressure that can crack and disrupt the concrete. The damage comes from both osmotic hydraulic pressure and the swelling of the solid reaction products. Particle size also matters. Fine siliceous particles can cause...

corrosion of reinforcement

Why Concrete Can Fail Around Rebar

Steel reinforcement in concrete can corrode when its protective environment changes. Fresh concrete is highly alkaline because of calcium hydroxide, with a pH of about 13. That high pH helps form a passive iron oxide layer on the steel surface, which slows corrosion. Over time, carbonation, chloride ingress, and cracking can weaken this protection. Concrete contains hydrated cement paste with salts, and it acts as an electrolyte. Different areas of the steel then behave as anodic and cathodic...

key terms and concepts

Learn how water moves through concrete, how permeability is tested in the lab, and why mix design and curing affect durability and water-tightness.

Concrete Durability and Water Penetration | JoVE K12

JoVE Core Civil Engineering offers a foundational exploration of essential construction materials such as bricks, stones, steel, wood, and concrete, along with fluid mechanics topics like flow over immersed bodies, open channel flow, and dimensional modeling. It also covers key surveying concepts, including leveling, traverse adjustments, curve design, topographic mapping, and geospatial technologies (GPS & GIS). Science-in-action videos showcase laboratory research on materials, fluids, and surveying practices in real-world engineering systems.

civil engineering

Concrete Durability and Water Penetration

Description

Transcript

Tags