HOW DO YOU KNOW WHICH FIBER IS THE BEST FOR EACH CONCRETE SLAB?

When designing a pavement, we must first calculate the stresses that will be created in that pavement due to loads and other circumstances. To do this, we will use Westergaard’s stress calculations. FIBRATEC has developed an online stress calculation that already incorporates the reinforcement information that our V12-AM microfiber is able to provide. Thus, anyone can calculate these stresses in just 15 seconds and determine whether the slab to be constructed can be made using only V12-AM (AR glass microfibers) or not. If the resulting stress exceeds the limit of reinforcement that microfibers can provide, we should opt for synthetic macrofibers and, eventually, for some additional microfibers to avoid microcracking.

The Westergaard stress calculation shows us whether the loads applied will cause “structural cracks” in the bottom of a slab.

Traditionally, when the stresses resulting from the design were small compared to the bending stress that the concrete can withstand (in the case of a 25MPa concrete (C25) around 3.3 MPa – 3.4 MPa), a steel mesh was placed in the upper third of the slab. This mesh does not serve to increase the flexural strength of the slab as is commonly believed. Its task is to absorb the stresses of the plastic shrinkage of the concrete, ensuring that the unavoidable micro-cracks in the concrete remain as micro-cracks and do not become larger (it immobilizes the concrete of the top layer of the slab).

Our 13mm FIBRATEC V12-AM microfiber made in Japan with the highest zirconia content in the world does that job much better, providing a number of benefits as described above that a steel mesh cannot. (See detailed information of V12-AM)

If, on the contrary, the stresses that will be exerted on the slab of our project are higher than those that the concrete can withstand in bending, we will know in advance that cracks will form at the base of our slab due to overloading. Traditionally, this would lead us to place a double steel mesh (double electro-welded mesh). The lower mesh, placed at a distance between 3 and 5 cm from the base, would be in charge of holding the cracks that appear at the base of the slab due to overloading. This mesh placed in the lower third would prevent the propagation of these cracks towards the surface.

We recommend the addition of synthetic macro fibers in order to replace the steel mesh placed in the lower third of the concrete slab. (in a double steel mesh). In particular, the Japanese bi-component macro synthetic fiber BARCHIP MQ58, which unlike others, will not leave any trace on the surface of the slab as long as it will have a quartz polished finish. Using V12-AM and MQ58 simultaneously is equivalent to placing a double steel mesh in a concrete slab.

By the way, our online calculation, besides indicating the feasibility of building a concrete slab using only V12-AM microfiber, it tells us how much point load the slab can withstand depending on the dosage of the fiber, the condition of the base, the type of concrete, the thickness of the slab and the type of loads (racks, forklifts, car, truck …) .

AFTER HAVING USED OUR ONLINE CALCULATION, YOU MAY ENCOUNTER ONE OF TWO POSSIBLE SITUATIONS:

• SITUATION A: The concrete slab is viable using only V12-AM micro fiber
• SITUATION B: The concrete slab requires structural reinforcement with BARCHIP macro fibers in order to “provide residual resistance to stop the propagation of cracks up towards the surface and collapse.

SITUATION A (Your slab can support loads only with the use of V12-AM in dosages ranging from 1 to 3 kg / m³:

You compare the loads that your slab will have to withstand with the loads that our online calculation shows. If the online calculation indicates that the slab with V12-AM micro fibers can withstand higher loads than the slab you need to build requires, than the use of only V12-AM micro fibers is feasible.

Once you have checked the feasibility of the slab using our V12-AM micro fibers manufactured in Japan, you can request a detailed calculation from our technical department for free. This calculation includes factors such as rotational static loads, daily repetition and speed of dynamic loads, stresses produced by the concrete curing process, stress created from the concrete’s own weight, stress due to distances of cut joints, stress relief from the placement of a polyethylene sheet on the ground and other potential factors that may influence the stresses that the concrete will have to withstand. We include safety factors and deliver you a report that justifies the proposed fiber dosage for that given slab.

You can request this report sending an email to: tecnico@fibratec.eu

SITUACTION B (Your slab cannot work with only AR micro glass fibers):

After having compared your slab’s load requirements to the loads that our micro fibers can deliver in that given thickness using our online calculator, you might find that you need a bigger reinforcement. This means that, if you don’t use macro fibers, you are going to have cracks at the bottom of the slab due to “excess of point loads”. At this point, one of your options would be to increase the thickness of the slab. If you do not have the possibility of increasing the thickness of the slab, you already know that YOUR SLAB WILL CRACK AT THE BOTTOM.

Don’t panic because there is a solution. In this case you will have to use our macro synthetic Barchip fibers.  These fibers will act once the crack occurs at the bottom of the slab stopping their propagation. This type of reinforcement is called STRUCTURAL REINFORCEMENT. The calculation method to determine the dosage for structural reinforcement is TR34.

Although most macro fiber manufacturers prefer describing “long fibers”  as “structural fibers”, we prefer to just say MACRO FIBERS because in order to deliver “structural reinforcement”, you need to add certain minimum quantities of fiber. Otherwise you won’t reinforce structurally the concrete slab and the fiber will not perform as “structural fiber function”.

In order to state that a certain fiber has been able to reinforce structurally a concrete slab, it has to accomplish some conditions when testes in a beam test that is described in our web page. This is very important since you than understand that adding 5 kg of macro glass fibers (36mm long) to structurally reinforce a slab is not possible. According to the norms, in order to accomplish the “structural reinforcement” requirements you would need to add minimum 10kg/m3 of macro glass fiber to the concrete (C25). Adding 5 kg of macro glass fiber would literally mean throwing money down the drain.

The following frequently used statement is totally incorrect: “Instead of placing 2 kg of micro glass fiber, it is better to place 2 kg of macro glass fiber (long) because it is structural”. This statement is misleading since 2 kg of micro glass fiber does an exceptional job of preventing micro cracking as explained at the beginning of this article. However, in order to do this job, hundreds of millions small fibers are needed. Even the addition of 15kg of long (macro) glass fibers would not be able to provide the equivalent benefits of 2kg of 13mm long V12-AM micro glass fibers.

Going back to the example in the previous paragraph, if we were to add 2 kg of macro glass fiber or macro steel fiber, WE WOULD NOT BE DELIVERING ANY BENEFIT TO OUR CONCRETE SLAB because they would not provide “crack prevention” improvements nor would they provide post-cracking “structural reinforcement” due to VERY FEW FIBERS.

LET’S REMEMBER:

MACRO FIBERS (whether glass, steel or synthetic) ACT ESSENTIALLY AFTER THE CRACK HAS OCCURRED. THEIR JOB IS “STOPPING EXISTING CRACKS AT THE BOTTOM OF THE CONCRETE SLAB”. (V12-AM microfibers act throughout the life of the slab to prevent micro cracks).
MACRO FIBERS DO NOT PREVENT MICRO-CRACKING UNLESS THEY ARE DOSED IN HUGE QUANTITIES, WHICH WOULD BE ECONOMICALLY UNFEASIBLE. (V12-AM micro fibers are perfect for this job).
MACRO FIBERS HAVE ALMOST NO INFLUENCE ON THE FIRST CRACKING IN BENDING TEST. (V12-AM micro fibers increase the first breaking strength of concrete because micro fibers improve concrete’s quality eliminating micro cracks).
Calculate yourself the load that a slab can support with our 13mm long V12-AM micro AR glass fiber using our online calculation and if you need a detailed calculation for approval of project management, don’t hesitate to request it sending an email to: tecnico@fibratec.eu

If the load requirements of your slab cannot be satisfied with 2 or 3 kg of V12-AM micro fibers according to our online calculation, send us an email indicating the loads your slab will have to resist, the type of those loads, the thickness of the slab, the type of concrete to be used and provide as many details as possible so we can perform a TR34 calculation for you to deliver a structural reinforcement for your concrete slab.