RESEARCH OF STRENGTH AND CONDITION OF CEMENT-CONCRETE PAVEMENT ON BRIDGES BY NON-DESTRUCTIVE METHODS

The article presents the results of determining the strength of non-destructive methods of cement concrete pavement on bridges. According to the results of the research, a differential curve, a reliability curve and the inverse value of the accumulated frequency of compressive strength of cement concrete are constructed. It is established that the cement concrete of the investigated objects corresponds to the strength class according to the normative documents. However, the results of visual, instrumental and thermal imaging inspection of areas on the bridges revealed a number of defects in the cement-concrete pavement and pavement slabs, which can lead to loss of the pavement structure strength. In particular, it was found that the destruction of the inspected reinforced concrete slabs of bridges mainly occurs under the influence of corrosion and loss of the working part volume of the steel reinforcement, unsatisfactory condition of the compensation seams on the supports. It is determined that cracks in reinforced concrete slabs occur due to low resistance of concrete to bending loads, due to which steel reinforcement is exposed to aggressive environments. In turn, it was proved that structural cracks in concrete occurred due to excessive loading, which led to overstrain of the structure, and non-structural cracks - due to internal stresses caused by thermal loads and various linear expansions of materials. Thermal imaging study revealed a significant difference in temperature in the pavement structural elements, which in the future leads to the destruction of cement-concrete pavement. It was found that the peeling of the protective layer of metal reinforcement on the studied bridges is caused by the phenomenon of electro-chemical corrosion. The experience analysis of cement-concrete pavement of the studied objects allows to prepare proposals for the construction of cement-concrete pavement of bridges and overpasses using modern materials, in particular, non-metallic reinforcement. determining strength cement-concrete

Introduction. The modern advanced applications in science field of road repairs and construction opens a real prospect of increasing the transit attractiveness in our country. Significant weight load using transport corridors falls on the road surface and construction of road bridges. Since the main disadvantage of asphalt pavements on bridges is insufficient track resistance and low durability then the necessity arises in replacing them on cementconcrete pavements, taking into account modern engineering solutions. This solve the problem in necessity to impose seasonal restrictions on heavy vehicles passage, and the associated overpayment for passage, which compensates cost of road repairs. Based on analysis of foreign experiences, existing regulations and requirements for cement-concrete pavement on bridges and it is gives possibility to choose an effective technology for installation and maintenance [1][2][3][4][5][6][7][8].
Main part. In Ukraine, pavement structures (PS) are classified into two main types -non-rigid and rigid. At the same time, experience shows that under different climatic conditions, intensity and traffic composition, cement concrete pavement are more durable (18 -50 years) than asphalt (6 -12 years) [9][10][11][12].
At present, the vast majority of roads in Ukraine have asphalt pavements with a carrying capacity of no more than 115 kN (11.5 tons) per axle, and a total elasticity modulus up to 300 MPa. Load from 13 tons an axis demands increase in total elasticity modulus of to 390… 400 MPa, thus tension in a paving layer reaches to 7,0… 7,5 MPa that in 2,5… 3,0 times exceeds limits of durability and shear resistance of usual asphalt concrete. To avoid overstraining the pavement is advisable to use special technical solutions [7,[12][13].
In 2002, for the first time in Ukraine, cement-concrete pavement was laid on bridges as part of the aftermath of a catastrophic flood in the Zakarpattia region on Shopurka river in Velykyi Bychkiv in the Rakhiv district on the H 09 highway. However, cement-concrete pavement performance indicators have been insufficiently studied.
In 2019, the research team of the National Transport University performed instrumental and thermal imaging surveys of bridges with cement-concrete pavements. Also, the strength was determined by non-destructive methods (sclerometer) of bridges cement-concrete pavement H 09 highway (Table 1).
At the points where the strength study of the cement concrete pavement was performed, the following defects were found: -local chipping in area of deformation joints; -exposure of crushed stone of cement-concrete pavement; -shrinkage cracks; -longitudinal and transverse cracks; -oscillations of the bridge during the passage of heavy vehicle; -destruction of bridge slabs due to peeling of the protective layer from metal reinforcement; -corrosion of metal reinforcement due to the opening of cracks; -uneven subsidence of the ground on the approaches; -unsatisfactory condition of expansion joints. It was also found that the cement concrete of the investigated bridge corresponds to the strength class B 40 ( Fig. 1-2).
For in-depth analysis of defects in pavements and structures, a survey was conducted on problem areas of the bridge by thermal imaging (Fig. 3-5). Histogram analysis of the pavement temperature changes on the bridge showed that the temperature difference between cement and asphalt pavement is 7-10 ºС at an air temperature of 29 ºС. Thermal imaging evaluation of study local chipping in deformation joints places ( Fig. 6-8) showed a significant temperature change in the seam structure and pavement. In the area of concrete pavement peeling and potholes near the seam destruction, temperature was 36°C, and the temperature inside the seam was 42°C. To determine the reliability results of study, was performed a similar instrumental and thermal imaging survey on experimental areas of cementconcrete pavement on the bridges M 07 highway Kyiv -Kovel.
The M 07 highway was reconstructed due to the unsatisfactory cement-concrete pavement condition and inconsistency of carriageway geometrical parameters. To ensure the homogeneity of the partially destroyed concrete pavement and the removal of internal stresses, the guillotine was broken into fragments. The results of statistical processing to determine the strength of cement concrete on the inspected bridges on M 07 highway are given in table. 2-3. As a result of the recalculation, it was obtained that the concrete strength of two sections is almost the same and corresponds to the strength class B 40. According to the results of the sections inspection M 07 highway, longitudinal and transverse cracks, chipped corners, protrusions, ruptures and clogging of joint seals, destruction and cracks in expansion joints, peeling and chipping of cement concrete slabs, subsidence and protrusion coverage were found on the bridges (Fig. 9-14). Analysis of research shows that the reinforced concrete slabs of bridges destruction is mainly due to the process of corrosion and loss of volume steel reinforcement working part, unsatisfactory condition of the expansion joints on the supports. On the other side, cracks occur in reinforced concrete slabs due to low resistance of concrete to bending loads, due to which steel reinforcement is exposed to aggressive environments. Structural cracks in concrete occur due to excessive loading, which leads to overstrain of the structure, and nonstructural cracks occur due to internal stresses caused by thermal loads and various linear expansions of materials [3]. To solve the research problems and determine the prospects for further research by author's team, is proposed, to use a number of methods and design solutions, such as treatment of steel reinforcement with anti-corrosion materials, use of nonmetallic reinforcement and high-performance concrete. In particular, new noncorrosive materials have recently been actively sought to reinforce concrete structures, such as fibrous polymer composite (FRP), which is estimated to solve the above problem, especially in harsh environment [7].
Conclusions. According to results of visual, instrumental and thermal imaging inspection, was found that one of the main problems that causes cement concrete pavement destruction on highway road sections and on bridges is the condition of expansion joints. Therefore, at least three expansion joints without pins and gaskets must be installed in front of bridges and overpasses. Seams should be filled with highly compressible material, such as sand treated with bitumen.
On category I-III roads with embankments over 3 m high made of large fragmented soils, with embankments in swamps with partial peat, on overpasses through railways, where is expected uneven subsidence of the ground, is recommended to arrange cement-concrete pavements and reinforced concrete.
And it is established that the peeling of the protective metal reinforcement layer is caused by the phenomenon of electro-chemical corrosion. Therefore, it is advisable to use non-metallic reinforcement for cement-concrete pavement and slabs of bridges carriageway. Гамеляк І.П., Харченко А.М., Дмитриченко А.М., Цибульський В.М., Густєлєв О.О.