Polyvinyl alcohol fiber, commonly referred to as PVA fiber, is a high-performance synthetic fiber that plays an important role as a reinforcing and toughening material in the field of building materials, especially in cement-based composites. It is a key additive for improving the properties of concrete and mortar due to its unique physicochemical properties.
High strength and high modulus: with high tensile strength and elastic modulus, it matches the modulus of the cement matrix well and can effectively transfer stress.
Hydrophilicity and dispersion: The molecular chain contains a large number of hydroxyl groups and has good hydrophilicity. It can be evenly dispersed in the cement slurry and is not easy to agglomerate, which is a key property superior to many synthetic fibers.
Alkali corrosion resistance: Stable performance in high alkalinity (pH> 12.5) environments resulting from cement hydration, with no corrosion or strength attenuation, and excellent durability. This is in sharp contrast to polypropylene (PP) fibers that are not resistant to alkali.
Bonding to cement matrix: Its surface properties can form good chemical bonding and mechanical engagement with cement hydration products (such as C-S-H gel), and the interfacial bonding strength is high.
Mechanism of toughening and cracking resistance: In the plastic stage and early stage of hardening of concrete/mortar, plastic shrinkage cracks are effectively suppressed; after hardening, it can bridge micro-cracks and delay their expansion, significantly improving the toughness, crack resistance and impact resistance of the material.
Polyvinyl alcohol fibers are mainly used in the preparation of high-performance fiber-reinforced cement-based composites.
Reinforced anti-crack mortar:
For exterior wall plastering anti-cracking mortar, thermal insulation system plastering layer, instead of or in combination with alkali-resistant glass fiber mesh, to provide three-dimensional full-section reinforcement and suppress shrinkage cracks.
High toughness concrete products:
Used to manufacture thin-walled components, prefabricated hanging plates, cable slot covers, etc., to improve the bending toughness and impact resistance of products and reduce damage during transportation and installation.
Engineering structural repair materials:
Mixed into quick repair mortar or concrete to reduce the plastic shrinkage and dry shrinkage of the repair material itself and improve the ability to work with the original base surface.
High Performance Sheet:
It is one of the core reinforcing fibers for the manufacture of asbestos-free fiber cement boards (such as calcium silicate boards, fiber cement pressure boards), giving the boards high strength, light weight, and non-combustible characteristics.
Refractories:
Used in refractory castables, micropores are left after fiber combustion at high temperatures, which can relieve the stress caused by water evaporation and prevent bursting.
| Characteristics | Polyvinyl alcohol (PVA) fiber | Polypropylene (PP) fiber | Steel fiber |
|---|---|---|---|
| Density | medium (1.3 g/cm ³) | Low (0.91 g/cm ³) | Height (7.8 g/cm ³) |
| Tensile strength | High (800-1600 MPa) | Medium (300-700 MPa) | Very high (500-2000 MPa) |
| Modulus of elasticity | High (25-40 GPa) | Low (3.5-5 GPa) | Very high (200 GPa) |
| alkali resistance | Excellent | poor | Good (but may rust) |
| Main Role | Toughened, cracked, enhanced | Mainly inhibits plastic shrinkage cracking | Significantly enhances toughness and impact resistance |
| Cost | higher | low | high |
| Dispersion | Excellent (hydrophilic) | General (hydrophobic, requires treatment) | easy to agglomerate |
Content selection:
Usually 0.5% to 2.0% by volume, depending on the performance requirements. When used for mortar crack resistance, the commonly used content is about 0.9 to 1.2 kg/m ³.
High dosage may affect workability and surface finish.
Fiber Specifications:
Length: Common 6mm, 12mm, 18mm. Short fibers (6-12mm) are mainly used to inhibit plastic shrinkage cracks; medium and long fibers (12-18mm) have a more significant improvement in performance after hardening.
Diameter/fineness: fine denier fibers have good dispersion and high reinforcement efficiency.
Mixing process:
It is recommended to use the post-mixing method: first stir the aggregate, cementitious material and water for about 1 minute, then add PVA fibers, and extend the mixing for 1-2 minutes until the fibers are evenly dispersed.
Use a forced mixer and avoid drum mixers to ensure even dispersion.
Mix ratio adjustment:
The addition of fiber will slightly reduce the fluidity of the mixture. The same slump can be maintained by fine-tuning the amount of water reducer or slightly increasing the mix water, but the total water consumption needs to be strictly controlled.
Construction and Maintenance:
During plastering construction, the surface may be slightly rough due to the bridging effect of fibers, allowing for secondary light collection.
Maintenance is crucial, and early wet maintenance needs to be strengthened to give full play to the role of fibers in inhibiting dry shrinkage cracks.
Specify requirements: Choose the appropriate fiber type, length and content according to the main objectives of the project (whether it is crack prevention, toughening or reinforcement).
Verification of performance: Before use, the dispersion of the fibers in a specific mixing ratio, the effect on workability, and the final mechanical properties such as crack resistance and impact resistance should be verified by trial matching.
Inspection materials: Check product test reports, focusing on key indicators such as tensile strength, elongation at break, elastic modulus, and alkali resistance retention.
Pay attention to compatibility: When sharing with other admixtures such as water reducer and air entraining agent, a compatibility test should be carried out.
Polyvinyl alcohol fiber is a high-quality cement-based composite reinforced fiber with high alkali resistance, high modulus and high adhesion. It can significantly improve the crack resistance, toughness and durability of mortar and concrete through the dual action of physical reinforcement and chemical bonding. It is especially suitable for projects sensitive to cracking, requiring high-toughness thin layers or harsh alkali environments.
When applying, it is necessary to grasp the three cores of "appropriate dosage, uniform dispersion, and standardized maintenance". Although its cost per kilogram is higher than that of polypropylene fiber, its excellent alkali resistance, high modulus, and strengthening effect make it have outstanding technical and economic value in high-quality projects that require long-term performance. It is one of the preferred fiber varieties for the preparation of high-performance, long-life cement-based products.
