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Dependence to determine reduction of the strength of concrete and sectional area of armature in time
Saatova Nodira Ziyayevna, Tashkent Automobile and Road Institute, Senior scientific researcher E-mail: [email protected]
Dependence to determine reduction of the strength of concrete and sectional area of armature in time
Abstract: The main purpose of calculation of the degree of salt corrosion of concrete and reinforcement is to assess their effect on the load capacity and life span. As a result of the work developed the method of estimation of influence of salt corrosion of the concrete work and fittings. Depending on the definition proposed for reducing the strength of the concrete reinforcement, and the cross sectional area over time during operation.
Keywords: Corrosion, concrete, reinforcement, salt corrosion, strength, main beam, Plate external console.
There are numerous studies [1; 2; 3], where developed various proposals to determine the depth of corrosion by the chemical composition of hazardous reagents composition of the concrete salts, and other factors. In [1; 2; 3] is considered as the basis ensuring of the thickness of the protective layer of concrete is sufficient for reliable corrosion protection of concrete and reinforcement.
It should be noted that the results of these works are difficult to take into account in practical calculations of the effect of salt corrosion work of superstructures.
This fact requires the development of methods of calculation of resource of superstructures based on the analysis of long-term experimental data available measuring factors directly taken into account in the calculations.
One of such possible areas is to evaluate the effect of salt corrosion through the strength of the concrete and reduce the cross-sectional area of reinforcement. For this purpose, treated during many years of experimental data and obtained in recent years as a result of examination and testing of existing reinforced concrete superstructures [4; 5; 6; 7; 8]. Totally processed results of 32 measurements of the strength of concrete and corrosion of reinforcement in the span of highway overpass in the city of Tashkent.
From Table 1 shows that the strength of concrete slabs external console subject to influence salt corrosion with increasing age decreases substantially. After 43 years of the actual operation of the concrete strength of 20 MPa., which is 50 % below the designed 40 MPa. salt penetration was achieved while almost the entire plate thickness. Table 1. - The results of the test concrete superstructures
The location of the beams Place strength measurements Time from start of operation, years
20 26 32 43
extreme Plate external console 35 30 24 20
The edge of the main beam 38 35 35 32
average Slab 38 40 36 36
The edge of the main beam 40 40 39 36
extreme Plateexternalconsole 34 28 22 21
The edge of the main beam 40 40 36 36
average Slab 35 33 22 22
The edge of the main beam 40 40 38 36
Figure 1 shows the variation in time on the strength of the concrete test results. Also given data to evaluate the effect of salt corrosion of concrete to reduce its strength.
Reducing of the strength of the concrete in the rib of the main beam is much lower than in the slab of the carriageway. To
describe in time reduce of the strength of concrete process proposed by the dependence of the exponential type:
(1)
Ru„ = Rube ~aT, bT b
where: R — design strength; b, a — parameters characterizing the rate of decline in strength over time; T — time from the start of operation, respectively.
In (1) parameters b and a are determined on the basis of the known dependencies of processing of experimental data:
a - —
b0 = e-ar ; JT - T )(lnR- ln Rt )
T N (T-T )
- £
R = ^ '
R
N
T = ^ '
[Ji
N
- I
nR = '=
nR
N
(2)
(3)
(4)
(5)
(6)
where T — the average value of the time; R — the average value of strength.
According to available data the results obtained:
(7)
Fig. 1. Reducing of strength of concrete in salt corrosion As can be seen from Fig. 1 dependence (7) correctly describes the change in the strength of concrete in time.
To determine the degree of influence of salt corrosion on the reinforcement of the slab in the area of the largest opening surface cracks were removed corroded reinforcement (fig. 2). Actual measurements of the diameter of the valve after cleaning the surface of the reinforcement from corrosion products. At the same time we measured the diameter of a corroded valve after opening of the protective layer of concrete without extracting them.
Section 9. Technical sciences
Fig. 2. Corrosion of reinforcement, extracted from the carriageway slab in various years
Fig. 3. Reducing armature's cross-sectional area as a fraction of the original: AS0 — initial area of reinforcement (armature); A — sectional area of the armature after corrosion
Table 2. - The results of measuring the diameters of the valve during the operation superstructures in the conditions of salt corrosion are stored
Measuring number Change of rebar diameter, mm. Notes
1986 y. 1996 y. 2000 y. 2008 y.
1 11.8 9.6 6.7 6.2 Measurements without removing the reinforcement (armature)
2 - 8.5 - 5.9 Measurements with removing the reinforcement (armature)
As shown in Table 2 under the actual diameter of salt corrosion of reinforcement after 43 years of operation decreased almost 2-times. Fig. 3 shows a graph of cross-sectional area reduction valve during salt corrosion
Reducing the cross-sectional area of reinforcement in time dependence can be described by:
(8)
AT=A e 0-015 T,
sT SO '
where ASg — initial area of reinforcement; T — time in years from the start of operation.
As a result of the work developed the method of estimation of influence of salt corrosion of the concrete work and fittings. Depending on the definition proposed for reducing the strength of the concrete reinforcement, and the cross sectional area over time during operation.
References:
1. 2.
3.
4.
5.
6. 7.
Alekseev S. N. Corrosion and protection of reinforcement in concrete. - M. Stroyizdat, 1968. - P. 231. Artamonov V. S., Molgina G. M. Corrosion protection of transport facilities., - M.: Transport, 1976 - P. 192. Moskvina V. M. Corrosion of concrete and reinforced concrete, methods of protection. - M.: Stroyizdat, 1980. - P. 536. Mamajanov R. K. The results of the survey and testing of concrete bridges, operating in conditions of Central Asia//The reliability of man-made structures. - M., 1988. - P. 36-41.
Nizamutdinova R. Z. Resource of concrete bridge spans of the railway lines on industrial/Tashiit. Thesis for the degree, Ph. D. 05.23.15. - Tashkent, 1994.
Kildeeva O. I. Resource of concrete bridge spans the corrosion of reinforcement//Istedod. - 1998. - № 7(7). - P. 100-108. Inspection and testing of road overpass over railroad tracks on the street.Bobur in Tashkent (stage III, congresses construction number 1 and 2, rack crossbars, beams)//Report. Book 3. Center of scientific research and experimental design. - Tashkent, 2006. - P. 110. Ganiev I., Saatova N. Z., Erboev Sh. Condition of concrete bridges in hot climates of the Republic of Uzbekistan. Bridges and tunnels: Theory, Research, Practice. Abstracts ofthe International scientific-practical conference. 11-12 October, 2007. - Dnepropetrovsk, 2007. - P. 14-15.
Tukhtakuziev Abdusalim, leader of the laboratory
Imomkulov Kutbiddin Bokijonovich, senior scientific employee, The Research Scientific Institute of mechanizations and electrifications of agriculture, Republic of Uzbekistan E-mail: [email protected]
Energy-efficient chizel-cultivator
Abstract: In article are brought the results of the studies on development of the technological scheme of the work and schemes of the accommodation worker organ energy-efficient chisel-cultivator.
Keywords: chisel-cultivator, worker organs, blocked cutting, hemi blocked cutting, unlocked cutting, rip perish paw, double-sided reversible ogival paw, unilateral ogival paw, tractional resistance, consumption fuel.
