Patent Application
20150110555
The invention relates to slab of concrete with fiber for paving roads of low traffic or similar, which presents a smaller thickness and predetermined width and length dimensions.
The present invention further relates to the method of manufacturing fiber slab for paving roads of low traffic, and with the method for paving roads of low traffic.
The unpaved roads are highly polluting, since the movement of vehicles on them, generates large amounts of dust; therefore, it is recommended that they be paved with gravel in order to make them more passable, since it is possible to eliminate the dust production. However, on gravel roads vehicles have less stability and adhesion, and to transit on unpaved roads is recommended that vehicles circulate at moderate speed and have their tires properly inflated, so that the stones do not break the tread.
In addition to this, the cost of maintenance of these roads is very high, especially in those which circulate trucks, since the surface of boulders based on granular materials tends to decompact with the traffic of vehicles, eliminating the good quality material of the surface and producing calamine and pits on the surface.
The problems identified in the unpaved roads generate the need to pave the road with other materials or to perform some treatment to the ripped surface to improve transitability of vehicles. Generally, the solution in these cases is the asphalting of the road. Furthermore, there is the possibility of concrete paving the road but this solution although more durable, can be more expensive than the process of asphalting. In addition to the above described, in both cases it is necessary to remove a portion of the existing road and to replace it with a good quality granular paving, to obtain both the structural capacity and the existing soil erosion; This not only increases the cost of the solutions, but it is also not-sustainable because it requires removing material out of the road.
Additionally, when choosing the most suitable material for paving, in the case of concrete, the dimensions of the slabs used in paving roads must be taken into consideration. Usually, the concrete slabs for paving roads have dimensions which usually have the width of a via, usually 3.500 mm, having a length of 3.000 to 6.000 mm. To bear the burden of heavy trucks that generate the greatest efforts and stresses to which the slabs are subjected, it is necessary to worry about the slab thickness, since the thickness is important to prevent cracking of the slabs. Moreover, some of the slabs designs of the prior art have armor, mesh or ironworks in their structure in order to ensure the durability of the slab, but such an aggregate results in a considerable increase in the cost of slab design. Moreover, in the state of the art concrete with fibers are developed which consist of concrete made from cement containing fine and coarse aggregate, and staple fibers, where the fibers may be natural or artificial and have the function of reinforcing the cement mass, increasing the fatigue resistance and thus slowing the growth of cracks, thereby increasing ductility to transmit the force through the cracked section. Moreover, the reinforcing fibers improve the impact resistance, and allow contraction joints distance by hydraulic shrinkage. The fibers most used for this type of concrete are fibers of steel, glass, polypropylene, carbon and aramide, and in general are called structural fibers.
In fiber concretes, once produced the first crack of the concrete matrix, the tensile stress should be distributed on the fibers present in the cracking zone, and these must hold together the edges of the crack at the lowest possible width. By continuing to increase the tensile stress, the concrete begins to deform, this is why it is very relevant for the behavior of residual fibers.
This effect in conjunction with the support provided by the soil generates a different pattern of cracks in the concrete without fiber, distributing efforts and reducing fatigue in the crack tip, greatly increasing the capacity of load cycles and, therefore, the duration.
For the Determination of the Residual Strength:
The residual strength although is not a real property but an engineering effort, calculated based on the properties of the section, according to the theory of engineering simple bending for linear and nonlinear elastic materials (seamless), in practical terms is a material's ability to continue taking loads once cracked.
The addition of fiber increases the flexural strength of a slab, a fact that is demonstrated in the testing of supported on floor slabs, but is not clearly reflected when testing of beam in the air are performed.
The current pavement designs are directly linked to the flexural strength of concrete (MOR) and do not take into account the residual strength that the fibers provide. Therefore, the beam tests do not reflect the actual contribution of the fibers in the concrete in the pavement design. Consequently, for testing of beam, the design would deliver the same thickness of a concrete pavement with fibers to one without fibers.
By testing, a series of load-deformation points is obtained, as illustrated (ASTM 1609) (
In FIG. 4., P1 represents the strength of the concrete, that is to say, the maximum load that resists the said concrete (MOR); P150.0.75 corresponds to the residual strength, that is to say, the load that the concrete resists to deformation of S/600, where S is the separation between supports (mm); and P150.3.0 corresponds to the residual resistance, that is, a load that the concrete resists to deformation S/150.
With the above described data we can calculate the maximum voltage for any value of P with the following equation:
where:
F=Tension (MPa)
P=Load (N)
L=Separation between supports (mm)
b=average width of test tube in the crack (mm)
d=average height of test tube in the crack (mm)
Following the procedure of ASTM 1609 standard, if the fracture occurs in the middle third, the equivalent ratio of bending R3e, is obtained as follows:
As a result, some proposed designs have changed the entry variable of bending strength (MOR) in the current design of pavements. This seeks to include the residual strength that fibers provide when beam tests to concrete pavements are performed.
Other studies have demonstrated (Altoubat. Et al. 2004) that the increase in the bending strength of slabs, due to the use of fibers, is directly related to the residual strength R3,e.
With this, the proposed method for pavement design to incorporate the effect of the incorporation of fibers is given by the following calibration factor:
where:
C2*=Calibration factor of resistance in Equation of fatigue
R3,e=Equivalent ratio of residual strength of 3 mm of deflection in air beam test.
According to the above equation, one fiber concrete that reaches a ratio of residual strength of 20% will increase by 20% the bending strength in a pavement. With this increase the thickness of the slab can decrease or have a longer lifetime for a same thickness.
Based on the highest tensile stress in each loading position, the allowed steps for each condition (Nijk) are calculated based on the equation of fatigue:
where the variables are defined as follows:
Nijkl=Passes permitted for the axle in position k,ç; warp i (temperature), load level j, and critical stress on the top and bottom.
σijkl=Principal stresses calculated using ISLAB2000 for axle in position k,ç; warp i (temperature), load level j, and critical stress on the top and bottom.
MOR=Flexural strength of concrete after 90 days.
C1=Correction factor for the slab geometry and thickness.
C2=Structural correction factor of fiber.
C3=Load correction factor at the edge.
Using Miner's hypothesis, the fatigue damage for each position is determined at the top and bottom of the slab on the basis of the following formula:
where:
FD=Fatigue damage for a given position of the axle k.
nijk=Number of passes for the local stress I for condition i, j, k.
Nijk=Number of allowed passes for the local stress I for condition i, j, k.
In the document JP2004224633, a pretensioned concrete slab is described, which is easily manufactured and reduces losses due to pre-stress. Pretensioned concrete slab consists of a cured body, which composition includes 100 parts of mass of cement, 10-40 parts of particles of fine mass, 15-55 parts of particles of inorganic mass, an agent which reduces the water, and water. The composition may further contain fine aggregates of particles of less than or equal to 2 mm in diameter and one or more types of fibers selected from the group consisting of metal fibers, organic fibers and carbon fibers.
The document CN101823860 describes concrete slabs with powdered fibers, comprising the following components in proportions by weight: 35-40% of quartz powder, 30-35% cement, 6% fiber and 24 to 29% of reaction assistants, wherein the fibers are vegetable fibers and/or glass fibers resistant to alkalis, and the reaction comprises a 23 to 28% of mineral assistant and 1% of chemical assistant. With the mixture slab of concrete with powdered, active and high toughness fibers is obtained, which has the advantage of being lightweight.
On the other hand, the document CN101294430 describes autoclave-aerated concrete slab containing carbon fibers.
The document WO0212630 describes a system and method for constructing large and continuous concrete slabs, without using conventional control joints for contraction. The base of the system is formed by a network of inducing cracks, on which the concrete is poured in such a way that the network is covered by the concrete. The inductors will allow cracking at the slab once the concrete slab is being used.
The national register CL 44.820 describes a method for constructing slab of concrete and the concrete slab formed comprising the construction of slab of concrete whose maximum length is 3 meters and its maximum width is equal to half the width of the track. The formed concrete slab has a size such that one single wheel, or a single set of gear wheels of a vehicle, will be always touching and resting on the slab.
Among the documents of the state of the art, there are documents describing concrete slabs with different types of fibers, but said slabs are not intended for use in pavements of low traffic roads. Therefore, it would be desirable to have a slab of concrete to be used in low traffic roads on existing ground, which is easy to manufacture, with installation and craftsmanship and durability lower costs.
Therefore, an object of the present invention is to provide a slab of concrete with structural fiber, to be installed on low-traffic roads. Another objective is to provide a method of manufacturing a concrete slab in situ on low traffic roads and a method for paving roads of low traffic, with a concrete mixture, which in this case carries structural fiber.
The present invention relates to a method for paving roads with low traffic, with a slab of concrete, optimized with fiber, to the concrete slab with obtained fiber, and the method for obtaining the concrete with fiber slab.
The present invention will be described below with reference to the drawings, which are included to provide a further understanding of the invention.
The present invention relates to a method for manufacturing a fiber concrete slab for paving low traffic roads or paths, wherein a low traffic road comprises a circulation of no more than 50 trucks per day.
This invention greatly reduces the cost of low traffic roads, making it competitive with the cheapest existing solutions, even with low traffic asphalt pavements. Furthermore, with respect to the latter, the duration will be higher, because the concrete has no significant damage due to environmental agents and fiber. In the case of cracking, it will extend its lifespan even further, making it not only an economic pavement in its initial cost, but also in the design stage.
A table comparing the initial costs of possible concrete structures is described below:
Where “H° Trad” refers to concrete designed by traditional methods, “TCP” refers to concrete protected in the record CL 44,820, and “UTCP” represents the fiber concrete of the present invention.
Furthermore, the present invention relates to fiber concrete slab having a predetermined width and length, depending on the mechanical stresses generated by a standard haulage truck that has a free distance between the front wheels and a track width of a train rear wheels and a length of free distance between the front axle and the rear axle of the train wheels, and about of 5 to 15 cm thick. The present invention used as a reference medium, the support points of a standard haulage truck, generated by the four points of support of its wheels, bearing in mind that a standard haulage truck is typically equipped with two front wheels and two pairs of rear wheels (rear wheels train). For purposes of describing the dimensions of width and length of the fiber concrete slab, the variables D1, D2 and L (
The concrete slab comprises a dose of between 1 kg/m3 (kg of fiber per cubic meter of concrete) and 6 kg/m3 for plastic fibers and between 15 kg/m3 (kg of fiber per cubic meter of concrete) and 40 kg/m 3 of structural metallic fiber. These doses, of such fibers or other to be used should be such that should generate a residual strength of 10% to 50% of the maximum strength of the concrete. The possible fibers to be added to the mixture are fibers of steel, glass, polypropylene or carbon or some other type of structural fiber for concrete and these fibers can be added independently or based on mixtures of the same. The thickness of the slab is approximately between 5 to 15 cm. The minimum dimensions of the width and length of the slab must be higher than 50 cm and the maximum dimensions of width and length of the slab should be less than 2.5 meters. The dimensions of width and length of the slab always allow one wheel, or one wheel train of said standard haulage truck, to be supported and resting on the slab.
In order to ensure that always only one wheel or one set of wheels of the standard haulage truck is touching and resting on the slab, the slab must have a maximum width (Dx) that is minor than the lesser value of free distance between D1 and D2, and a maximum length (Lx) that is minor than the free distance L. Thus, the fiber concrete slab will have a maximum width Dx and a maximum length Lx, thus ensuring that only one wheel or one set of wheels, rests on the slab when the truck passes by the road or highway.
However, in a practical form, paving sections can be further enlarged than the dimensions Dx and Lx, and once manufactured they can be cut according to the dimensions Dx and Lx, allowing natural cracking by retraction of the concrete in addition with loads traffic, they produce these dimensions by cracking of the slab, or inducing the cracking with mechanical devices. This, in such a way to make the cuts or cracking of the pavement slabs to distances that will generate slab dimensions that change the effect of the load of the axles of the trucks or vehicles used as a design reference. In a preferred embodiment of the present invention, the cuts are made of less than 2.5 m in the longitudinal direction and a longitudinal section that decreases the slab width at least to a dimension equivalent to the half of the track width. In the case of Chile, the slabs would be ideally of 1.75 meters long and 1.75 meters wide. These dimensions are not the only possible, but generate a sample that becomes the system more understandable. Currently, this cutting is typically made at distances between 3 to 6 meters in the transverse direction, leaving slabs of these lengths in the longitudinal direction, and the width of the normal track width of 3.5 meters.
The concrete slab will be placed directly on the natural terrain and except in the case of not being suitable or not be uniform, a replacement should be generated, as punctual improvement of the subgrade. Nevertheless, this improvement does not involve adding any additional surface. As an example of this improvement, an excerpt of the Manual of Highways of Chile, is shown.
“The removal of land unsuitable material is necessary when this does not have minimum support capabilities provided in 5.201.3 MC-V5. In summary, materials considered improper will be those meeting at least one of the following conditions:
The minimum value of the width Dx is higher than 50 cm, and alternatively, the maximum dimension of the width is equivalent to half of the normal track. Similarly, the minimum value of the length Lx is higher than 50 cm and the maximum length may correspond to 3.0 meters, depending on the distance between axles of the truck in reference.
The manufacturing method of the fiber concrete slab comprises:
a) determining the width of the slab (Dx) in a free distance Dx, which is smaller than the lowest value between D1 and D2;
b) determining the length of the slab in a free distance Lx, smaller than the value of the length L of free distance between the front axle and the first rear axle of the wheels train of the standard haulage truck;
c) establishing the slab thickness, according to the amount of traffic, traffic loads, the bearing capacity of the natural ground, the concrete strength, the residual strength of concrete and climate; such that the thickness is within the range of 5 to 15 cm;
d) determining the amount of fiber required for a required design residual strength of between 10% and 50% of the maximum strength of the concrete; and preparing the mixture of concrete, adding the fiber dose of between 1kg/m3 and 6kg/m3 for fibers of plastic, and of between 15 kg/m3 and 40 kg/m3 of metal fiber, wherein the fiber is selected from fibers of steel, glass, polypropylene or carbon; and
e) pouring the concrete mixture with fiber directly on the road or path to be paved.
Meanwhile, the method for paving low traffic roads comprises:
a) providing for paving a road or path which have neither asphalt or concrete paving;
b) evening out and leveling the road or path to be paved;
c) determining the width of the slab (Dx) in a free distance Dx, which is smaller than the lowest value between D1 and D2;
d) determining the length of the slab in a free distance Lx, smaller than the value of the length L of free distance between the front axle and the first rear axle of the train wheels of the standard haulage truck;
e) establishing the slab thickness, according to the amount of traffic, traffic loads, the bearing capacity of the natural ground, the concrete strength, the residual strength of concrete, and climate; such that the thickness is within the range of 5 to 15 cm;
f) determining the amount of fiber required for a required design residual strength of between 10% and 50% of the maximum strength of the concrete; and preparing the mixture of concrete by adding the fiber in dose of between 1 kg/m3 and 6 kg/m3, for plastic fibers and between 15 kg/m3 and 40 kg/m3 of metallic fibers, where the fiber is selected from fibers of steel, glass, polypropylene or carbon; and
g) pouring the concrete mixture with fiber directly on the road or path to be paved of the step a), in a size of a paving section greater to the measures identified in c) and d), and dimensioning the paved section to the measures determined in steps c) and d); or
h) pouring the concrete mixture with fiber directly on the road or path to be paved of the step a) in a paving section which has the measures determined in steps c) and d).
The slab of the present invention is only to pave roads that do not have asphalt or concrete paving roads or paths and does not include the renovations of old pavements with concrete bonded overlays. Furthermore, the slabs of the present invention can be placed on any terrain artificially stabilized.
The evening out and leveling of the road to be paved comprises the removal of not suitable material that might be on the same.
In addition, the slabs of the present invention can be manufactured in larger sizes than the measures Lx Dx, and could not be cut to size established by the Dx and Lx measures, such that the road can be paved with slabs of larger sizes than Dx and Lx measures. In this case, when driving vehicles on the road, due to the weight of vehicles, cracks will be produced, leaving by this way, slabs which sizes are such that whenever a single wheel or single wheel train of the standard haulage truck is always supported by the paving slab, touching same.
The slabs of the invention have the particular feature of not requiring any armor, mesh, load transfer bars, tie bars, pins or lateral structural basis in its construction.
The slabs of the present invention, by having structural fiber present an increased resistance to fatigue, increased load transfer and slabs tie to prevent separation or to control soil erosion.
In the X axis of the graph, the value of CBR (California Bearing Ratio) or relative support value of ground is shown, which states in a direct form, a measure of cracking strength.
As an example the following profiles type are shown:
| Number | Date | Country | Kind |
|---|---|---|---|
| 288-2012 | Feb 2012 | CL | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/CL2013/000006 | 2/1/2013 | WO | 00 |
