CHEMICAL RESISTANCE BASALT FIBERS FOR CONCRETE REINFORCEMENT

Artificial stone materials (concrete), are characterized by low resistance to tearing and shrinkage cracks during solidification. Eliminate the formation of cracks in several ways, for example, a secondary reinforcement, which is carried out in structural concrete steel reinforcement, and in slabs - or welded wire mesh modifying binder using polypropylene, glass, basalt fibers, metal fibers. The latter method is more progressive. It eliminates the structural problems associated with the use of welded wire reinforcement in the ceiling, and also solves the problem of its location and allows you to save on the purchase of metal. For example, the polypropylene fiber may replace welded wire mesh that prevents the formation of shrinkage cracks in the concrete. In plate comprising fiber bending strength to 2% higher. At a certain dosing fiber replaces the secondary reinforcement and provides the plasticity of concrete, but does not replace structural steel reinforcement. The main properties of the fibers as secondary reinforcement - is to control the subsidence and the formation of plastic shrinkage cracks. In addition the use of concrete with fiber reinforcement inherent properties such as uniform protrusion of water, high resistance to abrasion, chipping and shock effects, low permeability, high durability under conditions of freezing and thawing, chemical inertness and high grip. However, the polypropylene fiber has drawbacks. It deformed even with small tensile loads, it is aging, i.e. lose their properties over time, so as it burns when exposed to open flame.
            These drawbacks are absent in the application of basalt fiber. The structure of concrete with basalt fibers (bazaltotsementa) close to the structure, with the ferrocement reinforcement steel meshes. However bazaltotsement has a higher strength and deformability, as reinforcing its basalt provides a higher degree of dispersion reinforcement basalt stone itself has a higher strength of 1800 - 2500 MPa than steel mesh. Furthermore, bazaltotsement can tolerate large elastic deformations, because basalt fiber tensile plastic strain does not have, and on the elasticity than steel. Hardening cement paste is formed hostile environment that destroys the surface of the fiber, forming a shell. Fiber strength is decreased by 10%, but at the expense of adhesive strength of the formed shells stone and fibers increases so the strength of the product increases. When using thicker fibers (bolee100mkm.) Does not change their strength.
     Made of rock, basalt fiber does not react with the salts or dyes, so concrete solutions with the addition of fiber can also be used in the construction of offshore structures and architectural and decorative concrete. The pavements fiber protects concrete reinforcement from penetration antiice salts and aggressive substances, and increases residual strength and resistance to freeze-thaw cycles, increases the surface roughness. Use of high-quality concrete with special additives including mono fiber reinforcement provides resistance to fall to temperatures protecting against faults, cracks and flaking surfaces eliminates plastic and shrinkage cracks and increases the durability of the surface, edges and a seam, as well as resistance to abrasion and impact, provides early compressive strength, i.e. the strength which conventional concrete acquires only after 28 days from the time of installation.
Bazaltotsementa main features are its high strength in all types of stress states and the ability to carry large deformations in the elastic state. The relative deformation of cement stone without cracking up 0.7 - 0.9%. Such deformation in 35-45 times more than the ultimate elongation reinforced cement stone, a significant increase in the deformability and strength of cement is by eliminating the effect of basalt fiber stress concentrations in areas weakened by structural defects of the cement stone (sinks, cracks and the like).
The most significant effect of basalt fiber reinforced concrete beams found in without transverse reinforcement. Thus, the bearing capacity of the inclined cross-sections of beams without stirrups is increased by 45% with an increase in the percentage of basalt fiber from 10 to 12.5% ​​and 84% compared to the same period beams without particulate reinforcement. In the presence of shear reinforcement influence disperse reinforcement decreases slightly. The bearing capacity of the inclined cross-sections in combination with basalt fiber reinforced beams is increased by 8-10% [1]. At the same time the load-crack formation is increased by 20-30% and the opening width of dipping fractures under loads of 0.5-0,6 breaking decreases by 1.5-2 times. Analysis of the results of the tests showed that the use of rough basalt fibers in the most expedient designs, which set the clamps on the design requirements. This is achieved 100% reduction in consumption of steel that goes to the transverse reinforcement. In designs that include clamps, based on the requirements of crack resistance, the use of particulate reinforcement allows to reduce the opening width of oblique fractures and partly to reduce the consumption of transverse reinforcement [1].
When using basalt fiber in an amount of 40% strength cementitious products from izvestkovoshlakovogo bending is 20 MPa, the compressive-69 MPa. It is found that the phase of the cement stone compound, fiber reinforced, different from the reference. The total content of substances larger in cementitious composites. There is an increased concentration of tumors along the fiber reinforcements. And in reinforced cement stone hydrate phase predominantly formed in the crystalline state and echinated form that confirmed research by other authors [2].
There were conducted tests to determine the strength of continuous basalt fiber. Measure the diameter of the fibers was conducted in accordance with GOST 6943.2-79. Experimental results stay basalt fiber synthetic hardening Portland cement liquid phase under normal conditions are shown in Table 1. In order to increase the accuracy of the experiment fibers are treated with a hot mixture of Ca (OH) 2 (Table. 2). Results of testing samples of basalt fiber reinforced cement are given in Table 3.
The experimental results support the use of continuous basalt fibers as well as coarse fibers as reinforcing admixtures in concrete mixtures for construction. The smaller the diameter of the basalt fiber, the greater the decrease in its strength in the cement environment. This occurs most rapidly over 3-6 months. The process of reducing the strength of a general nature of fading. The highest level of strength loss observed in alyumoborsilikatnih fibers consumed in the concrete reinforcement. [2]
Possible areas of application of basalt fiber: concrete floors, airport runways, high-speed highways, industrial floors in workshops where established heavy equipment, internal reinforcement of tunnels and canals, slope reinforcement, repair and reconstruction of buildings, the coating of metal surfaces of steel structures, concrete water channels, fire-retardant construction, military facilities, and the construction of earthquake-proof homes. The main advantages of reinforced concrete with basalt fibers: reducing the thickness of the concrete layer in half compared to conventional concrete, respectively, the total construction cost, reducing labor costs associated with the installation of wire mesh in the sewers and underground water channels, the thickness of the concrete coating significantly reduced, decreasing the cost of repairs and maintenance thanks to the durability of fiber reinforced concrete. Effect on concrete reinforcement basalt fiber depends on its length and the ratio of length to diameter. Theoretically longer fibers and with large length to diameter ratio better than shorter. However, the long fibers are more difficult to put in the gunning concrete, and they are distributed to the worst concrete. Fibers provide three-dimensional reinforcement of the concrete as compared to traditional valves, which provides a two-dimensional reinforcement. According to years of research NDІBK, durability rough basalt fibers in the environment of a cement stone is at least a hundred years. [1]

Table 1
The strength of basalt fiber after being in a synthetic liquid phase Portland

Treatment time, hour.	The diameter of the basalt fiber, micron
	5		10		20
	Tensile strength, MPa
	MPa	%	MPa	%	MPa	%
0	0,093	100	0,105	100	0,065	100
3	0,081	87,5	0,095	90	0,064	100
24	0,081	87,4	0,092	87	0,062	95
720	0,08	86	0,077	74	0,061	93
2160			0,073	70
4320			72	68

 table 2
The strength of basalt fiber tear when handling hot mixture Са(ОН)₂.

Treatment time, hour.	The diameter of the basalt fiber, micron
	50		70		90
	Tensile strength, MPa
	MPa	%	MPa	%	МПаMPa	%
0	0,044	100	0,029	100	0,030	100
3	0,043	97	0,028	96
6	0,042	95	0,026	89	0,029	96,5

 

Curing condition of samples	Reinforcement ratio by weight,   %	Age sample day
		3	7	28	90
		Tensile strength samples bending, MPa
the normally wet	9-12	23   23   25	26   27   23	46   45   53	68   53   47
The steaming	9-12	24   21   19	25   23   22	32   30   29	33   39   30

The fibers are not amenable to electrochemical corrosion, in contrast to conventional valves which is an electrical conductor and the cathode gives in effect.

  

LITERATURE

1. Куртаев А.С., Сулейменов С.Т., Естемесов З.А. и др. Композиционные материалы на основе вяжущих. Киев,  АН УССР  ИПМ ,1991. С.21.
2. Рабинович Ф.Н., Зуева В.Н., Макеева Л.В. Стойкость базальтовых волокон  в среде гидратирующих цементов.// Стекло и керамика. 2001.№12 С.12-14.