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What we have to know about fibres in UHPC 我们必须了解UHPC中的纤维

关键词: 发布时间:2019年01月14日 | 来源:

What we have to know about fibres in UHPC

我们必须了解UHPC中的纤维


Fibres may be considered the most important ingredient in the recipe for UHPC due economical, ductility and durability reasons. ECONOMICAL. An analysis of the raw materials required to produced UHPC shows that approximately 60-80% of the total price is due to fibres in a common UHPC with 2% in volume of steel fibres. This ratio can be much higher if either stainless steel fibres or larger fibre amount is used. DUCTILITY. It is unsafe to design UHPC structures without fibres since a minimum material ductility is required! Fibres provide that ductility when using properly. DURABILITY. Fibres help control cracking, which also contributes to increase the lifespan of structures. That is why is completely necessary to know some key points about its use.

当考虑到经济、延展性和耐久性因素时,纤维可能被认为是UHPC配方中最重要的成分。经济方面,对UHPC生产所需原材料的分析表明,普通UHPC中纤维中的2%含量的钢纤维的价格就约占了总价格的60-80%。如果使用不锈钢纤维或更大的纤维量,该比例会高得多。延展性方面,没有纤维的UHPC设计,其结构是不安全的,因为材料需要最小的延展性!纤维在正确使用时会提供延展性。耐久性方面,纤维有助于控制裂缝,这也有助于延长结构的使用寿命。这就是为什么我们完全有必要了解纤维使用的一些关键点。


Among all available fibres in the market, steel fibres arise as the most suitable ones for structural applications in UHPC. In those structural applications, specially in buildings, in which a certain degree of fire resistance is required, polypropylene fibres are often used in combination with steel fibres. For architectural applications with either none or very low structural requirements, probably PVA and stainless steel fibres are the most common.

在市场上所有可用的纤维中,钢纤维是UHPC中最适合作为结构应用的纤维。在一些结构应用中,特别是在需要一定程度耐火性的建筑物中,聚丙烯纤维通常与钢纤维结合使用。对于无结构要求或者结构要求非常低的建筑应用,聚乙烯醇纤维和不锈钢纤维是最常见的。


This post is focused on steel fibres, particularly, smooth-straight fibres as they have a better balance between economy and efficiency.

这篇文章主要关注钢纤维,特别是光滑-直的纤维,因为它们在经济和效率之间起到更好的平衡作用。


Specifications and compliance criteria of steel fibres are determined by EN-14889. Fibres tipically used in UHPC are Class I (made of cold-drawn wire). For these type of fibres, parameters that must be declared are: Length - Diameter - Slenderness - Yield strength

钢纤维的规格和合规标准由EN-14889确定。UHPC中常用的纤维是I类(由冷拔钢丝制成)。对于这种类型的纤维,必须声明的参数是:长度 - 直径 - 细长度 - 屈服强度


In case of using a special coating, material and amount used must also be declared as it may have an important influence on the fibre - matrix bond, specially in the long-term. Declaration of other parameters included in EN-14889, such as the influence of fibres on concrete consistency or strength, has no meaning in fibres for UHPC, and probably it has not either for conventional fibre concrete. The influence of fibres on these properties not only depend on the fibre by itself, but on the amount used, mixing or pouring technology, grading curve, compressive strength of concrete, … Ensuring a good workability and strength is a task for the UHPC manufacturer and has nothing to do with fibre producers.

在使用特殊涂层的情况下,还必须声明材料(纤维种类)和(纤维)使用量情况,因为它可能对纤维 - 基质粘合具有很大的影响,尤其是在长期使用情况下。EN-14889中包含的其他参数的声明,例如纤维对混凝土稠度或强度的影响,对于UHPC中的纤维没有任何参考意义,并且这可能不适用于传统的纤维混凝土。纤维对这些性能的影响不仅取决于纤维本身,而且取决于纤维的使用量,混合或浇注技术,分级曲线,混凝土的抗压强度等,因此能否确保UHPC具有良好的可加工性和强度,这与UHPC制造商有关,而与纤维生产商无关。


Fibre length

纤维长度


Fibre length is a parameter that must be defined during the project phase, as this parameter may affect cross-section geometry, reinforcement layout and cover. It is commonly accepted that fibre length must be at least 3 times the maximum aggregate size to ensure a suitable behaviour of fibres inside concrete. As fibre length is larger than maximum aggreagte size, cover and rebar spacing limitations established in design standards with the purupose of avoiding segregation of concrete are referred to the fibre length instead of maximum aggregate size in case of fibre reinforced concretes.

纤维长度是必须在制定方案阶段时定义的参数,因为此参数可能会影响横截面积、钢筋布局和覆盖层。通常认为纤维长度必须至少是最大骨料尺寸的3倍,以确保纤维在混凝土内的和易性。由于纤维长度大于最大聚集体尺寸,因此在设计标准中建立的纤维长度而不是纤维增强混凝土的最大骨料尺寸来限制覆盖层和钢筋间距,以避免混凝土的偏析。


Note that UHPC designs tend to minimise cross-sections to achieve maximum efficiency of UHPC and competitiveness. That is why is completely necessary to minimise cover and rebar spacing in design. As these parameters increase according to fibre length, recipes for UHPC keep fibre length as short as possible.

请注意,UHPC设计倾向于最小化横截面积,以实现UHPC的最大效率和竞争力。这就是为什么完全有必要尽量减少设计中的覆盖层和钢筋间距。随着这些参数根据纤维长度增加,UHPC配方中应使纤维长度尽可能短。


Diameter and slenderness

直径和细长


Once fibre length has been defined, the desired slenderness must be chosen. Even though this is not a structural project parameter, it has a strong influence on the matrix - fibre bond, therefore, in the tensile strength and ductility of UHPC. As slenderness is defined as fibre length to diameter ratio, defining the slenderness is the same thing as defining the fibre diameter once its length has been established.

一旦定义了纤维长度,就必须选择所需的细长度。尽管这不是结构工程参数,但它对基质 - 纤维粘合具有很大的影响,因此对UHPC的拉伸强度和延展性也有很大的影响。细长度定义为纤维长度与直径之比,一旦确定了长度,定义出的细长度与定义的纤维直径要统一。


The broad range of fibres available in market makes having the specific fibre type needed to optimise a UHPC design possible!! Choose wisely!!

因为市场上有广泛类型的纤维,所以找到具有优化UHPC设计所需的特定纤维类型成为可能!这需要明智的选择 !!


Look at the following picutre. You can see different steel short-smooth fibres for UHPC available in the market. Common definition is used. First number corresponds to fibre length and second one to the fibre diameter.

看下面的图片。您可以在市场上看到UHPC的不同程度的短-光滑的钢纤维。按照通用定义。第一个数字对应于纤维长度,第二个数字对应于纤维直径。



Yield strength

屈服强度


Another important parameter of fibres is the yield strength of the wire used to manufacture them. Even though maximum stress reached by fibres inside a UHPC is not higher than 1000 MPa, yield strength of wires used to produce them is commonly above 2000 MPa. Why? Is that a waste of money? It may be an attempt to avoid the formation of fibre balls during mixing. High slenderness ratio together with a small yield strength makes fibres easy to bend during mixing without an elastic recovering of deformation, favouring the formation of fibre balls during mixing and leading to lower tensile strength in the hardened state.

纤维的另一个重要参数是用于制造它们的线材的屈服强度。即使UHPC内部的纤维达到的最大应力不高于1000MPa,但用于生产它们的线材的屈服强度通常高于2000MPa。这是为什么?这是浪费钱吗?可能是在混合期间避免形成纤维球的尝试。高细长比和小的屈服强度使得纤维在混合期间易于弯曲而没有弹性的变形恢复,有利于在混合期间形成纤维球并且导致在硬化状态下较低的拉伸强度。


Fibre selection is a key point in the optimum design of UHPC as it has a strong influence on its strength, ductility and price

纤维选择是UHPC优化设计的关键,因为它对UHPC的强度、延展性和价格有很大影响


Tolerances and quality control

公差和质量控制


According to EN-14889 these are the minimum tolerances in a fibre manufacturing process

根据EN-14889,这些是光纤制造过程中的最小公差:



Look at the following fibre diameter measurement. It was supposed to be 0.20 mm!!

看下面的纤维直径测量。它应该是0.20毫米!!



This result leads to following question: how reliable are some of available fibres in market? In the following table the length and diameter measurements of 5 samples taken from 5 different types of fibres are shown, together with their declared properties. In red, nonconformities are highlighted!!

这一结果导致了以下问题:如何保证市场上一些可用纤维的可靠性?在下表中,显示了取自5种不同类型纤维的5个样品的长度和直径测量值,以及它们声明的性质。突出显示红色的为不合格的!



Always demand the standard and declaration of performance to your fibre provider to avoid unpleasant surprises!! The quality of your UHPC depends on it!!

因此您需要始终要求纤维供应商提供标志和性能声明,以避免产生不愉快!您的UHPC的质量取决于纤维!

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