Polyvinyl Alcohol Fiber: An Anti-Crack Reinforcement Component for Cement-Based Materials

In cement-based materials, crack control has always been a matter of concern. Cement mortar and concrete become quite brittle after hardening and are prone to cracking under shrinkage, temperature changes, or loading. Adding fiber is one common approach to improving this situation, and polyvinyl alcohol fiber (PVA fiber) is one of the more widely used synthetic fibers in this field.

What Is PVA Fiber?

Polyvinyl alcohol fiber, abbreviated as PVA fiber, is a synthetic fiber produced by spinning polyvinyl alcohol resin.

PVA fiber has several notable characteristics:

• Good hydrophilicity: The hydroxyl groups in the PVA molecular structure provide good affinity with cement-based materials, allowing the fiber to disperse evenly in mortar

• Moderate elastic modulus: Positioned between polypropylene fiber and steel fiber, it provides reinforcement during the hardening stage without being overly rigid

• Alkali resistance: It remains stable in the alkaline environment of cement-based materials and does not degrade easily

• Non-toxic and odorless: It is considered an environmentally friendly material

What Role Does It Play in Cement-Based Materials?

The role of PVA fiber in mortar or concrete can be summarized in three aspects:

First, it prevents plastic shrinkage cracks.

In the early stages of hardening, moisture evaporates quickly from the surface of cement-based materials. When volumetric shrinkage is constrained, plastic shrinkage cracks tend to form. PVA fibers distributed evenly throughout the material can bear the tensile stress caused by shrinkage, preventing crack formation and propagation. This effect is particularly noticeable in plastering mortars and floor leveling compounds.

Second, it improves crack resistance and toughness.

Hardened cement-based materials are quite brittle and tend to fracture suddenly under impact or bending loads. PVA fibers act as a "bridging" mechanism within the matrix. When a crack develops, the fibers span across the crack surfaces, transferring stress to the surrounding matrix and delaying crack propagation, thereby enhancing the fracture toughness of the material.

Research indicates that the improvement in crack resistance of cement-based materials with PVA fiber ranges from 50% to 70%, depending on fiber length, dosage, and mix proportions.

Third, it reduces early-age shrinkage cracking.

Cement-based materials undergo autogenous shrinkage and drying shrinkage during hardening. PVA fibers restrict the free shrinkage of the matrix, reducing the concentration of shrinkage stresses and thereby lowering the risk of early-age cracking.

Comparison with Other Fibers

Compared with polypropylene fiber, PVA fiber has better hydrophilicity, disperses more evenly in cement-based materials, and is less prone to fiber bundling. Compared with glass fiber, PVA fiber is more stable in alkaline environments and has a longer service life. Compared with steel fiber, PVA fiber has lower density, does not corrode, and causes less wear on processing equipment.

Typical Application Scenarios

First, plastering mortar and interior wall leveling.
Plastering mortar is applied in thin layers over large areas, making it prone to cracking. Adding an appropriate amount of PVA fiber to plastering mortar can effectively reduce surface crazing and cracking due to hollowing.

Second, self-leveling mortar and flooring.
Flooring materials require good flatness and durability. PVA fiber improves the crack resistance and impact resistance of flooring, reducing cracks caused by temperature changes and loads during service.

Third, waterproofing mortar and repair mortar.
Waterproofing and repair mortars are commonly used in areas such as kitchens, bathrooms, and basements, where crack resistance and impermeability are important. PVA fiber reduces drying shrinkage cracks and works together with other waterproofing components.

Fourth, precast components and thin-walled products.
For some thin-walled cement products (such as lightweight wall panels and cement tiles), PVA fiber provides reinforcement, reducing breakage during transportation and installation.

Fifth, shotcrete.
In shotcrete applications such as tunnel linings and slope stabilization, PVA fiber can replace some of the wire mesh, improving the toughness and crack resistance of the applied layer while reducing rebound.

Dosage and Selection

The typical dosage of PVA fiber in mortar or concrete ranges from 0.5 kg to 2.0 kg per cubic meter, depending on project requirements. Plastering mortars generally use 0.6-1.0 kg/m³, while flooring and shotcrete applications may use higher amounts.

When selecting PVA fiber, three parameters are worth considering:

• Fiber length: 6-12 mm is common for plastering mortar; 12-20 mm for flooring and precast components

• Tensile strength: The single-filament tensile strength of PVA fiber typically ranges from 1000 to 1600 MPa

• Modulus: Elastic modulus is commonly in the range of 20-40 GPa

It should be noted that the dispersion of PVA fiber in mortar is related to the mixing process. It is recommended to add the fiber during the dry mixing stage and ensure sufficient mixing time for thorough dispersion to avoid fiber bundling.

Summary

Polyvinyl alcohol fiber is a synthetic fiber that provides both crack control and reinforcement functions in cement-based materials. With its good hydrophilicity and compatibility with cement systems, it is widely used in applications such as plastering mortar, flooring, waterproofing mortar, and precast components.

For projects requiring crack control and improved material toughness, PVA fiber is an option worth considering. Specific dosage and fiber specifications should be determined through testing based on project requirements and material proportions.