Basalt fiber reinforced concrete

Along with the widespread use of reinforced concrete special attention, in our opinion, deserve composite materials, in which the role of the matrix performs the cement stone produced based on Portland cement, as well as valves, various mineral and polymer fibers, and metal mesh and chips. Fibers provide three-dimensional reinforcement of the concrete as compared to traditional valves, which provides a two-dimensional reinforcement.
Currently, you can add two directions of creation of composite materials:
- Composites high modulus fibers (steel, asbestos, glass, basalt);
- Composites low modulus fibers (nylon, polyethylene, polypropylene, etc.).
Each composite reinforcing materials have different advantages and disadvantages, but most researchers prefer composites using as a reinforcing material of basalt fibers.

Artificial stone, porous materials (concrete), are characterized by low resistance to tearing and shrinkage cracks during curing. One significant disadvantage of such products is the destruction of the angles produced structures. Avoid the formation of cracks and chips possible in several ways, such as secondary reinforcement wire mesh or rebar, welded wire. But the most effective method of modifying cementitious mixtures basalt, polypropylene and metal fibers. It solves the problems associated with the use of weld fittings in the ceiling, which saves on metal. Thus the polypropylene fiber when replacing a welded wire mesh to prevent the formation of cracks in the structure and increases its bending strength of more than 2%. If a certain percentage of fiber in the mixture, it replaces the secondary reinforcement and provides flexibility, but does not replace structural steel reinforcement. Along with this, the polypropylene fiber has drawbacks: it is deformed at low stress in tension, loses its properties with time and burns when exposed to open flame.

Concrete structure using basalt fibers approaching structure with reinforcement with steel mesh, but basalt concrete has a higher strength, because its reinforcing basalt fiber has a higher degree of dispersion in the rock to be reinforced, the fiber itself has a higher strength than the steel mesh. Basalt concrete structures can withstand a lot of stress deformation, due to the fact that the very fiber tensile plastic deformation has not, as of elasticity than steel. The relative deformation of cement stone without cracks up to 0.9 - 1.1%. Such deformation in 45-55 times higher than the limit elongation of reinforced cement stone. However, the hardening of the cement stone formed an aggressive environment that destroys the fiber surface, forming a shell, and the strength of the fiber decreases slightly to 15%. But due to the strength of coupling shells stone and fiber increases and thus increases the strength of the structure itself. When using the coarse fibers (40 microns), their strength does not substantially decrease. Increasing the strength of cement is due to the effect of basalt fiber on stress concentration in places weakened by structural defects or increased porosity (in the foam materials).
Fibers made from chemically inert rocks do not react with the salts or dyes and because binding fiber admixture with additives can be used during the construction of offshore structures in the manufacture of architectural building designs with complex surfaces, decorative concrete. In the production of pavements using basalt fiber asphalt coating protects it from penetration of anti anti ice salts and aggressive substances, increases surface hardness.

Basalt fiber diameter of 18-60 microns is practically does not change its strength at long-term (up to one month) stays in the environment hardening Portland cement. The strength of the thinner fibers in the same conditions, is gradually reduced. The intensity of the loss of strength increases with decreasing fiber diameter. This situation was also confirmed in the work (12). According to the author, the diameter of the basalt fiber should be in the aisles of 40 - 200 microns, with a length of sections 10 - 20 mm, and its tensile strength up to 1500 MPa.
Stay basalt fiber for 6 hours in an environment of concrete hardening, heated to a temperature of 96 C, and then holding for 45 hours at normal temperature does not lead to significant changes in the strength properties of the fiber. Under the same conditions, glass fiber loses its strength 23-35%. The studies found that the addition to the cement matrix of basalt fibers allows:

To increase the compressive strength of the samples at 30 - 40%;
- To increase the strength of the axial tension in three - four times;
- To increase the toughness of the composite in 3 - 4 times.
The strength of composite articles depends on the degree of embedment of the reinforcing fibers in the cement matrix. In theory, the strength of the composite increases with increasing content in the fibers. However, the reinforcing properties of the concrete matrix with increasing amounts of fibers are reduced. When the volume of the fiber tends to 1, the volume of the cement matrix tends to 0, and the strength of the composite will also be zero. Therefore, there is a certain ratio of the fiber and the matrix in which the matrix can provide the maximum degree of embedment of the fibers. According to some researchers optimum amount of basalt fibers in the composite should be 20% by weight of cement (9, 10, 12).
The length of the sections of continuous basalt fiber on the one hand determined by the terms of a uniform distribution of the fibers in the cement matrix (too long fiber promotes the formation of tangled fibers in the form of "hedgehogs") and short fibers worsen the degree of reinforcement of the cement matrix. In this regard, the optimum length of cut taken in the aisles 10-20mm.

Preparation of fiber cement mixture on the basis of basalt fiber - the most important operation in the technology of fiber dispersion-reinforced cement mixtures, as the most important factor in ensuring the stability of their properties, a uniform distribution of basalt fibers by volume of the mixture. The most suitable method is vibro extrusion, using which provides uniform incorporation of the fibers into the concrete matrix.
The paper (12) on the basis of generalization of domestic and foreign experience directions formulated effective use of basalt fiber as a reinforcing material:
- For the perception of the main tensile and shear stresses instead the core of shear reinforcement;
- To reduce the length of the working valves of the possibility of failure in the continuation of its area decreasing the bending moment due to the increased strength of adhesion with the valve stem to reduce a length of the fiber-reinforced concrete anchoring;
- To reduce the flow distribution valve and a thin-walled concrete elements, in which a large part is assigned to the reinforcement of the design considerations and concrete cover thickness is a significant part of the element.
Also given the application of composite materials based on basalt fiber:
- In the designs, which are increased requirements for stiffness and crack;
- In buildings experiencing the impact of shock and alternating loads;
- In thin-walled design and construction of complex geometric shapes;
- When itinerant reinforcing the most stressed parts of structures;
- In designs, transverse reinforcement which is intended mainly for the perception of installation and transport of loads;
- In the designs, which are increased requirements for frost resistance, water resistance, abrasion and thermal shock resistance.

In NIISK Construction Committee of Ukraine, Kiev, developed specific technology for preparation of concrete, reinforced with basalt fibers (bazaltofibrobeton). Proposed manufacturing technology with traditional technological schemes and equipment, special feed lines basalt fiber into the mixer with the required sealing of the mix on the shaking table without deep vibration. Scope of the new composite material: flat and thin-walled products, bulk items, rings, tubes, plates facing channels and silage trenches, road and paving slabs, elements of permanent formwork, wall panels, building foundations, and others. At the same time saving the metal fittings on certain types product is 80 to 100%.
  Despite such clear advantages of the composite material, its production did not come out of the stage of development work, due to the absence of large-scale production technology sections of continuous basalt fiber as raw material for the production of concrete products.
This technology developed by JSC "Mineral 7" Yavoriv, Lviv region. In making the fiber instead of the traditional platinum-rhodium bushing installation on the applied bushing alloy, which ensures a low temperature gradient of the area of fiber. Previously used reels of the "NAS" are replaced with the original design of the device with a semi-automatic threading. Which will increase the hourly production of the fiber due to the number of bushing.

 

                                                                                       

 

The chemical composition of the rocks processed.

Oxides	Basalt, Ivanovo-Dolinskoe	Andesite-basalt, Podgornenskoe deposit
SiO2	48,9	52,84
TiO2	2,7	0,50
Al2 O3	15	17,28
Fe2O3	8,8	8,97
FeO	6,4	1,66
MnO	0,2	-
MgO	5,1	6,30
CaO	8,4	7,10
Na2O	2,3	2,20
K2O	0,7	1,60
S	-	-
P2O5	0,3	-
H2O	0,75	-
П.п.п.	2,0	1,77
Сумма	99,7	100,23
Мк	4,9	5,23
Мв	1,97	2,6

 

deposit	Diameter, mkm	Strength limit Tensile, MPa	The dynamic modulus of elasticity, kg / mm2
Basalt, Ivanovo-Dolinskoe	15,3	1700	9*1010
	30	1000	7*107
Andesite-basalt, Podgornenskoe deposit	17,0	1500	8,5*1010

Aggressive environment indicators	Basalt, Ivanovo-Dolinskoe  dр=15,р=15,3 мкм	Andesite-basalt, Podgornenskoe deposit dt cр=17,р=17,0 мкм
Н2О Resistant, %	96,2	99,0
0,5 N NаОH Resistant, %	96,7	84,4
2N NаОН Resistant, %	81,3	77,3
2N  HCI Resistant, %	76,1	82,5

 

The test results of application segments of fiber diameter 30-60 microns and a length of 5 to 15 mm. The fiber content of 0.2% in the concrete.

1. The distribution in the concrete mix - even without the additional time;
2. Compressive strength after 10 days higher than 10% compared with samples without the fibers;
3. The bending strength after 10 days higher than 80% compared with samples without fiber. 

 

Literature

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8. Петросян С.Т. Технология изготовления строительных изделий с использованием штапельного базальтового волокна. Диссертация на соискание ученой степени кандидата технических наук. Ереван, 1988.

9. Ма9. Махова М. Ф., Гребенюк Н. П.  Дисперсное армирование портландцемента базальтовыми волокнами  «Цемент», № 2 1980.

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