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※The Main Index Contrast In High Modulus PVA vs Low Modulus PP Fiber                   

※高模量纤维（PVA）与低模量纤维（PP）的性质差异和机理分析

※Property Difference and Mechanism Analysis of High Modulus Fiber (PVA) and Low Modulus Fiber (PP)

对于纤维混凝土复合材料，纤维作为混凝土的增强体，其提高混凝土的极限拉伸值凭借的是高弹性模量与界面粘结强度。

As to fiber concrete composites, fiber is the reinforcement in concrete which can improve the ultimate tensile value of concrete by its high elasticity modulus and interfacial cohesive strength.

PVA纤维与聚丙烯纤维（即PP纤维）的性质对比

Property Comparison between PVA Fiber and Polypropylene Fiber (PP Fiber)

1、物理作用——PVA纤维表面粗糙

PVA纤维的表面粗糙，不同于聚丙烯纤维等其他纤维，能增强纤维与水泥材料间的物理锚固力。

1.    Physical Effect——Rough Surface of PVA Fiber

Rough surface of PVA fiber, which is different from PP fiber and other fibers, can improve the physical anchoring force between fibers and cement materials.

2、化学作用——PVA纤维存在氢键

PVA纤维与PP纤维等的化学成分不同，PVA纤维分子式为 ，同PP纤维 完全不同，化学分子式中羟基能有效与水、水泥基材料结合，形成氢键，PVA纤维表面与水泥基材料之间没有对混凝土抗冻有害的空隙，同时也能有效的增强纤维与水泥基材料的界面粘结力，这是聚丙烯纤维无法具备的，如图3所示；同时化学分子式决定了PVA纤维是亲水性纤维，而PP纤维是憎水性纤维，亲水性纤维比憎水性纤维更能保水，增强纤维混凝土保水性。

2.    Chemical Effect——Hydrogen Bond for PVA Fiber

PVA fiber has different chemical compositions from that of PP fiber. Its molecular formula is while PP fiber is . The hydroxyl can combine with water and cement-based materials effectively to form into hydrogen bond. Between surface of PVA fiber and cement-based materials, there are no interspaces which are harm to frost resistance for concrete; moreover, the PVA fiber can improve interfacial cohesive strength between fibers and cement-based materials, which is not applied in PP fiber (as shown in Fig. 3). Meanwhile, PVA fiber is the hydrophilic fiber and PP fiber is the hydrophobic fiber which is decided by the molecular formula. Hydrophilic fiber, which can improve the water retention capacity of fiber concrete, has more water retention capacity than the hydrophobic fiber.

PVA纤维与水泥净浆界面情况：

Condition of PVA Fiber on the Cement Paste Section:

PP纤维与水泥净浆界面情况：

Condition of PP Fiber on the Cement Paste Section:

3、纤维混凝土断面观察

容易看到PP纤维是从水泥基体中被拔出，而PVA纤维绝大部分是被拔断的，这就会导致，PP纤维的抗拉强度与延伸率无法在混凝土中发挥自己的作用，而PVA纤维则能发挥它的优势。如下图所示。

3.    Section Observation of Fiber Concrete

We can easily see that the PP fiber is pulled out from cement base while most of PVA fiber is pulled out to break, which shows that the PP fiber cannot give full play of its tensile strength and elongation in concrete, while the PVA fiber can fully play its advantages. It is shown as follows.

两种纤维在水泥净浆断面上的情况  Conditions of two fibers on the cement paste section

4、吸收更大能量

PVA纤维的弹性模量是PP纤维弹性模量的10倍，这使得PVA纤维在混凝土受力断裂时，能吸收很大的能量，也就是说PVA纤维混凝土也能承受更大能量的破坏荷载，从而增强了混凝土的韧性。

PVA纤维与其他纤维根本的不同在于弹性模量高、抗拉强度高等特点。纤维的高弹性模量对提高混凝土极限拉伸值之所以有意义，是因为混凝土刚浇筑后不具备强度，这时候混凝土受力可能导致塑性开裂，而高强高模PVA纤维因其弹性模量高于混凝土，可先受力而阻止混凝土开裂。同理在混凝土弹性模量与强度逐渐上升的过程中（即低强度时期），PVA纤维的弹性模量仍然高于混凝土，可以防止大坝混凝土在施工期由于受温度应力或其他大于混凝土抗拉强度的应力对混凝土产生的开裂作用，从而有效的防止了早期裂缝。

4.    Greater Power Absorption

The elasticity modulus of PVA fiber is 10 times of that of PP fiber, which makes that the PVA fiber can absorb great power when the concrete is broken under force, that is, the PVA fiber concrete can bear failure load with greater power and improve the ductility of concrete.

The fundamental difference between PVA fiber and other fibers is that it has high modulus of elasticity, tensile strength and other characteristics. High modulus of elasticity is so meaningful in improving the ultimate tensile value for concrete because the concrete has no strength just after casting, and the concrete under force may cause plastic cracking at this time. However, PVA fiber with high strength and high modulus has higher modulus of elasticity than that of the concrete, and it can under force firstly to prevent concrete from cracking. Similarly, during gradually increasing of the modulus of elasticity and strength for concrete (low strength period), the modulus of elasticity for PVA fiber is still higher than that of the concrete, which can prevent the dam concrete from cracking caused by temperature stress and other stresses greater than concrete’s tensile strength during the construction period, thus it can prevent it from early cracking effectively.