Name: how cement curing changes porosity
Uploaded: 2024-11-07T14:48:30.000Z
Duration: 1 min 18 s
Channel: JoVE

Quando la pasta di cemento fresca si solidifica, passa da uno stato fluido a una massa solida, intrappolando l'acqua in varie forme, come l'acqua gel, l'acqua capillare e l'acqua combinata.
L'acqua gel, che è intrappolata all'interno dei pori del gel di cemento, costituisce in genere circa il 28% del volume totale del gel di cemento.
Circa il 23% della massa del cemento secco è costituito dall'acqua combinata che è associata ai vari prodotti risultanti dal processo di idratazione.
Quando la pasta cementizia ha più acqua di quella necessaria per l'idratazione, l'acqua in eccesso forma pori capillari, che costituiscono circa il 18,5% del volume originale del cemento e sono spesso riempiti d'acqua.
Il rapporto tra il volume combinato del gel e dei pori capillari e il volume complessivo della pasta cementizia determina la porosità totale della pasta cementizia.
Il rapporto acqua/cemento è un fattore cruciale, poiché l'acqua in eccesso crea pori più capillari, portando a una maggiore porosità e a una pasta cementizia indurita potenzialmente più debole.
Una corretta stagionatura può ridurre la porosità consentendo un'idratazione continua, che riempie i pori capillari con prodotti per l'idratazione.

porosità nel calcestruzzo

Porosity in Cement Paste

La porosità del calcestruzzo è una misura degli spazi vuoti all'interno della sua struttura. Questi spazi influenzano significativamente la sua resistenza e durata. Quando acqua e cemento interagiscono, una reazione chimica chiamata idratazione crea una pasta semisolida. Questa pasta include acqua combinata, che costituisce circa il 23% della massa secca del cemento, e acqua gelificata, che riempie minuscoli vuoti noti come pori di gel, che rappresentano circa il 28% del volume di gel di cemento.


 L'equilibrio tra acqua e cemento nella miscela è fondamentale: influenza l'entità dell'idratazione e, di conseguenza, la porosità e la resistenza del calcestruzzo indurito. In un processo di idratazione ideale, lo spazio extra non occupato da prodotti di idratazione solidi forma pori capillari, che rappresentano circa il 18,5% del volume di cemento originale. Mentre il calcestruzzo indurisce, l'idratazione continua può riempire i pori capillari con prodotti di idratazione, aumentando la densità del materiale.


 Per un'idratazione completa e una resistenza ottimale, il processo di stagionatura deve essere gestito con attenzione. Esso consente un'ulteriore idratazione, riducendo la porosità riempiendo gli spazi capillari con prodotti di idratazione più stabili e, di conseguenza, densificando la pasta. Questo processo meticoloso è fondamentale per ottenere un calcestruzzo durevole e di alta qualità, meno suscettibile al degrado ambientale e meccanico.

Porosità nel calcestruzzo

Quando la pasta di cemento fresca si solidifica, passa da uno stato fluido a una massa solida, intrappolando l'acqua in varie forme, come l'acqua gel, l'acqua capillare e ...

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how cement curing changes porosity

Cement curing changes porosity in the hardened paste. Porosity means the void spaces inside concrete. These spaces affect both strength and durability. When water and cement react, hydration forms a semi-solid paste that traps water in different ways.

Some of that water becomes combined water. It makes up about 23% of the cement's dry mass. Other water stays as gel water, which fills very small voids called gel pores. Gel pores account for about 28% of the cement gel volume.

The water-to-cement ratio is important in the mix. It controls how much hydration can happen. That, in turn, affects the porosity and strength of the cured concrete. In an ideal hydration process, the space not filled by solid hydration products becomes capillary pores, which are about 18.5% of the original cement volume.

As concrete cures, hydration can continue. More hydration products can fill the capillary pores and make the material denser. Careful curing helps complete this process and reduces porosity. The result is durable, high-quality concrete that is less likely to break down under environmental and mechanical stress.

How Cement Curing Changes Porosity

tensile strength considerations of concrete

tensile-strength-considerations-of-concrete

How Cracks Limit Concrete Strength

Concrete tensile strength is limited by tiny cracks inside the material. The cement paste itself can be much stronger in theory than it is in practice. In real concrete, the measured strength can be up to a thousand times lower than the theoretical value. These small cracks help explain that gap. When a load is applied, stress rises at the crack tips. This idea is described by Griffith's theory of brittle fracture. In brittle materials, cracks can grow quickly once the stress at their tips...

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behavior-of-concrete-under-compressive-load

Concrete Failure Patterns Under Compression

Concrete failure patterns under compression show how the material responds to different kinds of direct stress. These patterns help explain concrete’s structural integrity. Under uniaxial compression, where force acts in one direction, cracks often form parallel to the load. These parallel cracks come from local tensile stress, which is pulling stress that appears perpendicular to the compression direction. As uniaxial loading continues, angled cracks may also appear. These cracks are linked...

porosity in cement paste

Cement curing changes porosity in the hardened paste. Porosity means the void spaces inside concrete. These spaces affect both strength and durability. When water and cement react, hydration forms a semi-solid paste that traps water in different ways. Some of that water becomes combined water. It makes up about 23% of the cement's dry mass. Other water stays as gel water, which fills very small voids called gel pores. Gel pores account for about 28% of the cement gel volume. The...

total voids in concrete

Concrete Voids and Strength

Concrete voids affect both strength and permeability. They include gel water, capillary pores, and entrapped air. In hydrated cement paste, gel water is held within the cement hydration products. Physically entrapped or adsorbed water also supports the hydration process. As cement hydrates, the space needed for the products from a cubic centimeter of cement is estimated to double. Capillary pores are the open spaces left inside the hydrated paste. Their size depends mainly on the...

pore size distribution

Concrete Porosity and Durability

Concrete porosity and durability depend strongly on pore size distribution in hardened cement paste. Capillary pores are much larger than gel pores, and in partially hydrated cement paste they form a connected network that lowers strength and raises permeability. Higher permeability makes concrete more vulnerable to freeze-thaw damage and chemical attack. The risk also depends on the water-to-cement ratio. A higher ratio can leave more space for capillary pores to remain open. As cement...

microcracking in concrete

How Concrete Cracks Before Failure

Concrete can develop tiny cracks before any outside load is applied. These microcracks usually form at the boundary between coarse aggregate and hydrated cement paste. They often result from small volume changes caused by stress-strain differences, heat, and moisture movement. At first, these microcracks stay stable. They usually do not grow much until the concrete reaches about 30 percent of its ultimate strength. As the load rises, the material can begin to change more quickly. When...

water cement ratio

Concrete Strength and Water Balance

Concrete strength depends on the balance between water and cement in the mix. This water-cement ratio is the weight of water compared with the weight of cement. It affects strength, durability, and how well concrete resists environmental stress. Abrams’ law shows that less water usually makes stronger concrete. Water is still needed for hydration, which is the chemical process that binds water and cement. It also helps the mix stay workable and compactable. Some water must be absorbed into the...

aggregate cement ratio

How Mix Ratio Changes Concrete Strength

The aggregate cement ratio changes how concrete performs. It is the weight of aggregate divided by the weight of cement in a concrete mix. This ratio affects strength, workability, and durability, so it is an important part of concrete design. A higher aggregate cement ratio makes the mix leaner. Lean mixes have less cement paste to coat and lubricate the aggregate, so they can be harder to work with. At the same time, they may increase strength because the concrete has less total porosity, or...

transition zone

Concrete Transition Zone and Its Porosity

The concrete transition zone is the thin region where aggregate meets cement paste. It has more pores than the surrounding material, so it is usually weaker at first. The bond around the aggregate comes mainly from Van der Waals forces, which are weak attraction forces between particles. When concrete is compacted, this zone often has a higher water-cement ratio near the aggregate. That extra water can form thin water films around the coarse aggregate. These films increase porosity and help...

relation between tensile strength and compressive strength of concrete

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Concrete Strength Testing: Tension vs. Compression

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fatigue strength of concrete

Concrete Fatigue Under Repeated Loads

Concrete fatigue describes how concrete can weaken or fail when loads are applied again and again, even when each load is below the material’s strength limit. This property matters because it affects the durability and service life of concrete structures. In materials science and engineering, fatigue is a key reason concrete may not last as long as expected under real use. Concrete can fail in two main ways through fatigue. Static fatigue, also called creep rupture, happens under a constant...

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Concrete Impact Resistance in Real Use

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abrasion resistance of concrete

Concrete Wear Tests and Surface Durability

Concrete wear tests show how well a surface can stand up to abrasion and long-term use. Abrasion is the wearing away of a material by rubbing, scraping, or contact with moving solids. This property matters because concrete surfaces can lose material under vehicle traffic or when solids carried in water brush against them. The transcript describes three tests used to measure concrete abrasion resistance. In the revolving disc test, three plates rotate against the concrete, and silicon carbide...

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fiber reinforced concrete

Concrete Strength with Added Fibers

Fiber-reinforced concrete is concrete that includes added fibers to improve strength and durability. It uses hydraulic cement with fine or coarse aggregates, plus separated, non-continuous fibers mixed through the material. These fibers can come from steel, glass, and polymers, as well as natural sources such as sisal and cellulose or manufactured sources such as polypropylene and Kevlar. Steel fibers are often preferred because they are strong and tough. They help concrete resist cracking and...

prestressed concrete

How Concrete Is Preloaded for Strength

Prestressed concrete is a construction method that preloads concrete so it can handle more stress. High-strength steel strands are stretched before or after the concrete is loaded in service. The goal is to put the concrete into compression. That compression helps balance the tension the structure will face later. By reducing tension, prestressing helps limit cracks in the concrete. It can also let a structure carry greater loads or span longer distances than conventional reinforced concrete.

ferrocement

Ferrocement Mesh and Mortar Design

Ferrocement is a construction material made from dense layers of mesh or fine rods covered fully in cement mortar. It is a form of reinforced concrete, but it uses mesh instead of the larger steel bars found in standard reinforced concrete. This structure gives ferrocement its thin, flexible form. The material is built from wire meshes and a mortar made of cement and sand. The mortar is usually mixed in a 1:2 or 1:3 ratio. The water-to-cement ratio is kept between 0.40 and 0.45. This helps the...

non-destructive tests for concrete strength

non-destructive-tests-for-concrete-strength

Concrete Strength Checks Without Breaking It

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key terms and concepts

Learn how hydration, gel water, and capillary pores affect cement paste porosity, strength, and durability as concrete cures.

How Cement Curing Changes Porosity | JoVE K12

JoVE Core Civil Engineering provides a foundational exploration of essential construction materials in civil engineering, focusing on bricks, stones, steel, wood, and concrete through easy-to-understand animated videos. This collection covers the properties, manufacturing processes, and practical applications of these materials. Additionally, the accompanied science-in-action videos demonstrate the research experiments performed in laboratories.

civil engineering

How Cement Curing Changes Porosity

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