Neofiber

About Neofiber
Neofiber is based on a swiss patent for producing a polypropylene fiber to be used to eliminate or reduce shrinkage in concrete. It has a tensile strength of more than 400 N/mm2, comparable to that of steel. The polypropylene fiber compared to other plastics such as polymid or polyester has a low strain to rupture of 13 %. As the tension for stretching of plastics is almost proportional, polypropylene corresponds to a high modulus of elasticity (E-Mod.) for plastics of approx. 5000 N/mm2. The Emodulus is a very important factor in the performance of the Neofiber.
At a density of 0,915 polypropylene is processed into a foil and net structure as fine as a film, and twisted into threads by a special process. The threads are processed further into rope-like cords and cut to lengths from 19 - 64 mm. This endproduct behaves neutral when brought into contact with almost all type of chemicals and is in particular unaffected by alkalis and certainly will not rust.

The effect of Neofiber in concrete
Neofiber is a patented admixture for cement and lime bonded materials such as concrete, mortar, cellular lightweight concrete (CLC) and mortar as well as cast and artificial stone and is used to prevent cracks and to improve the overall quality.
Different type of fibers are known to have been used in concrete in the past. Asbestos, steel and glass fibers enhance the tensile strength, their application however require the use of special equipment and the dosage rate is rather high. The costs for those fibers are consequently high and their use is therefore limited to special fields.
Neofiber improves the overall quality of concrete and makes it more resistant to different influences. Adding Neofiber to concrete ensures that it is reinforced three-dimensionally with a well distributed fine skeleton of fibers in the very early stages, making it resistant to inner tensions introduced by shrinkage, drying, temperature variation , slight deformations of formwork and other enviromental factors detrimental to the quality of concrete whatever its cross-section.
Adding Neofiber reduces micro-and macro-cracking arising in all cement-bound materials. In certain spheres, for example the bonding of fixed secondary steel reinforcement in prefab and casting , the avoidance of cracks is of paramount importance. Neofiber replaces much of the steel reinforcement used for the control of cracking caused by shrinkage, drying and temperature variation.

How to use Neofiber
Best distribution and opening of the Neofiber fiber-thread is achieved in adding the fiber to the dry mix of sand, cement and gravel and before adding the water. The fiber-thread unbundles to a fine net and begins to dissipate during mixing. This continuous after adding the water until homogeneously distributed. 1 kg of Neofiber if added to each other would reach a length of 1 km. The mix is then ready for use in the normal way. Its workability is very good. Many years of research and of trials lead to optimum doses and distribution of the fiber in concrete, in particular to overcome the "balling" of the fiber due to electrostatic charge.
The unique net structure of Neofiber overcomes this effect by inducing amutually repelling effect permitting optimum distribution. It has been proven that adding 1 kg of Neofiber to
1 m3 of concrete (0,1 volume addition) produces the best results.

Reaction of Neofiber in concrete
To achieve good workability of a cement mix substantially more water is required - than essential for the chemical reaction of the cement. 20 - 25 % of the weight of the cement used has to be added as water for hydration and is chemically bonded, and to 12 % is retained in the crystal space. The remainder of the water added serves only as a lubricant and sooner or later will evaporate and in doing so will leave cavities behind. This leads to shrinkage deformation the degree of which depends upon different factors. The following diagrams show the main influences on the degree of shrinkage: Air moisture, air-movement and water content in ratio to the cement. The vertical scale shows shrinkage in mm/m and the horizontal one the concrete age by hours. Both diagrams clearly show that the greatest deformations take place within the first five hours after casting.



The effect of the influences described are to be observed clearly on the surface. This diagrammatic presentation features the differential shrinkage across a section of the concrete and the shrinkage points appearing in the matrix.



The following diagram features the development of strength curve aswell as the shrinkage tension forces and shows also clearly the internal shrinkage at the critical points is beyond the ability of the concrete to withstand the forces. In such cases, where the force exceeds the resistance the concrete will tear. The practical effect is evident in concrete too and this phenomena is responsible for the formation of shrinkage cracks, which often are camouflaged initially by the friction on the form work surfaces.



Recent research shows that the concrete is not at all passive during the period when the cement links are formed and that measurable inner movements take place (up to 8m at speeds of up to 0,3 m/min). The consequence is tearing of the half-solid matrix. Not yet solid cement "glue" flows into the cracks ( a self-healing effect) but that a weak zone is remaining where the binding agent previously was.
The larger the early cracks are, the more significant are the weak zones around these. The effect of the weak locations acts together with the weakness contributed by the porosity due to the surplus water and create areas of lowest strength. The dimensions and arrangement in the structure and combinations of one beneath the other are critical in determining the ultimate characteristics of the concrete.
When the formation of the cement bond process begins, the Neofiber already gives a tensile strength to the young concrete. Using Neofiber the curve of the tensile strength of the concrete is above the curve for the internal tensions produced, as shown in the following diagram. Neofiber is to be understood as acting as a fine reinforcement in the specific plane where cracks are likely to be propagated thus distributing the tensions developing locally in the concrete and reducing the weak zones to smaller units.



In this connection the relatively high E-modul of Neofiber is important, because the main effect of Neofiber endures so long until the E-modul of the concrete rising from zero in the course of setting and strength development reaches the one of the - fiber reinforcement.

Neofiber therefore is most effective during the very early age the concrete, enabling the very sensitive phases of the cement bond to become stablished without damage. This is why shrinkage problems can be overcome by using Neofiber and at the same time the overall quality of concrete improves substantially.
Practical tests prove that the concrete quality is improved enormously when adding Neofiber. The danger of damaging edges can be completely eliminated and it is even possible in many cases to remove formwork earlier permitting better utilization of expensive formwork.

Neofiber is produced in different qualities, the main types of which are
N 05: length 19 mm
N 10: length 38 mm
N 15: length 57 mm
N 24: length 64 mm

The selection of individual type of fiber is determined by the maximum size of the aggregate used in the concrete. Coarser aggregate requires a longer fiber to ensure adequate tying length.

Economy of Neofiber
Any additive added to concrete increases cost. At a low dosage of only 1 kg per one cubicmeter of concrete Neofiber adds very little to the cost especially when casting slender walls. Neofiber certainly adds up to the overall quality of concrete.
Considering that conventional steel mesh can be partly or totally replaced by Neofiber in many cases reduces the cost even for reinforcement. Whilst steel mesh is placed in a specific part of the wall, Neofiber is mixed in the concrete and thus acts three-dimensional. Saving conventional steel mesh means also savings in labour in placing the steel mesh into the mold. Concrete can be vibrated easily without reinforcement taking space or possibly getting damaged.
Neofiber-reinforced concrete can be quicker and easier placed by the labour and many
admixture may become obsolete. Surface crack control is more effectively carried out using a non-rusting fiber.
Neofiber is normally supplied in plastic bags of 1 kg each facilitating adding of the fiber to the mixer.