Expansion joints and the interface zone of road pavement on bridges and overpasses

1. Introduction

There are problems with expansion joints on road bridges and overpasses in Kazakhstan [1-3]. These problems are related to several factors - increased traffic load, climatic conditions, quality of materials and human factor (violation of jointing technology) [4-8]. As it is known transport load includes two main factors: the first is dynamic load associated with the intensity of urban traffic, the second is static load associated with the congestion of urban roads in certain directions (traffic jams in peak hours) [9, 10]. The dynamics of motor vehicle traffic is not constant and the speed limit varies from 2-5 km/h to the permitted range of 60 km/h. The traffic flow also has significant differences in mass, passenger cars weighing from 900 kg to 3.5 tonnes, buses 12-19 tonnes, trucks 2 axles – 18 tonnes; 3 axles – 25 tonnes; 4 axles – 32 tonnes; 5 axles – 35 tonnes are moving on the roads. [11]. Since the axle spacing is different, the dynamic impact is also very different, so wheel impacts cause pavement failure on road bridges and overpasses [12-15]. Prolonged stopping on road bridges and overpasses also adversely affects and deforms the pavement. The increased dynamic impact is due to the difference in height between the top of the expansion joint and the pavement surface, forming a ‘step’ [16-18]. To avoid asphalt concrete rupture, expansion joints are used on road bridges and overpasses, which are made using different schemes and materials [19-20].

The scientific novelty of the work is to determine the indicators of deformation seams and areas of intersection of the pavement on bridges. These parameters remain one of the key sources of operational problems and costs for the maintenance of the bridge structure. In [5-8], several research areas are identified: classification of types of seams and their design features; behavioral studies and mechanisms of joint failure under cyclic loads and temperature changes; design of seamless systems and asphalt pavements; as well as management and maintenance programs.

2. Methodology

The area where the road surface and the expansion joint meet is the most vulnerable part of the bridge surface. It is assumed that the durability and operational reliability of this unit depend not only on the type of seam, but also on a combination of design solutions, material properties and coating technology [21, 22]. Optimization of these factors will significantly reduce the rate of defect formation and increase the service life between repairs.

The expansion joint with rubber compensator consists of three parts: hot-rolled profiled steel beam (profile), rubber seals and anchors. Its advantages are simplicity of construction, ease of installation, durability and convenience. The main types of profile (edging) are: C-type (Fig. 1), F-type (Fig. 2), E-type (Fig. 3). Edge profile - elements OP-DSH-K2, edging in the deformation gap contours of adjacent structures (roadway on the structure, the end of the span structure, the edge of the head part of the support or the wardrobe wall of the stand) anchored in them and designed to absorb forces from overlapping gap elements and to protect the edged elements of the structure from destruction under the impact of vehicles. The list of applied edging in beam expansion joints of OP-DSH-K2 grade. The flanges of the edge profile serve for attaching the waterproofing membrane of the deck (Fig. 4).

Fig. 1Expansion joint with rubber expansion joint type C80

Fig. 2Expansion joint with rubber compensator type F80

Fig. 3Expansion joint with rubber compensator type E80

Fig. 4Edging for expansion joints OP-DSH-K2

Linearity of the shaped profile used in the DS along the length corresponds to the tolerance of 1.0 mm/1 m, within the whole length – 5 mm/10 m, Screw-shape is not more than 1 mm/1 m. The edge bearing profiles are made of shaped (long) rolled products. The manufacturing plant, which carries out shaping of the steel profile by solid hot rolling or solid hot processing, guarantees the absence of hidden defects along the entire length of the profile. At the request of the project the edge profile of the DS can be made by welding of shaped solid drawn profile and long angle rolled section by continuous welded seam according to GOST 14771, at that 30 % (up to 100 % at the request of the opening) of welded seams are subjected to ultrasonic examination. Welded seams of OS-DS-K2 grades meet the requirements of GOST 5264, GOST 8713 and GOST 14771.

Bearing profiles (edging) are treated with an increased degree of anticorrosion protection. Anticorrosive coating of DSH corresponds to the category of corrosive aggressiveness of the atmosphere not lower than C4 (high) according to GOST 346672. Durability of anticorrosive coating corresponds to category H (more than 15 years) according to GOST 346671.

The main elements of the beam expansion joint of OP-DSH-K2 brand are edge bearing profiles (edging), anchoring elements and sealing compensator (Fig. 5).

Fig. 5Girder expansion joint OP-DSH-K2 (section): a – opening of DS; 1 – anchor plate; 2 – anchor ring; 3 – compensator; 4 – edging

Due to the presence of various configurations of the bearing profile execution, as well as a large variability of the anchor elements execution, the design of DS can be applied at any dimensions of the expansion joint lining areas and any thicknesses of asphalt pavement or other pavement.

In beam expansion joints, sealing expansion joints are used [21, 23], which allow for a displacement of the structure from 40 to 120 mm. For beam expansion joints with an opening of 100 mm and above, which are used on motorways near settlements with a permitted speed of motor vehicles over 90 km/h, as well as on roads in the settlements themselves, it is recommended to use additional noise-reducing structures. Here are two options of design solutions for noise reduction:

1) Application of special noise-reducing plates, such beam DSs are labelled ‘OP-DS-K2-shp’ (Fig. 6).

Fig. 6Expansion joint OP-DSH-K2-shp with noise-reducing plate

2) Application of expansion joint designs with special wave-shaped edge profiles, such beam joints are labelled ‘OP-DSh-K2-v’ (Fig. 7).

Fig. 7Special wave-shaped edge profiles OP-DSH-K2

3. Results

A survey of 28 bridge structures with various types of expansion joints showed that the junction area of the pavement is one of the most vulnerable parts of the bridge bed.

The average frequency of defects during the first 5 years of operation was 18 % for C80 type seams, 12 % for F80 and 9 % for E80.

The most common damages were: the formation of a “bump” (up to 35 % of cases), cracking in asphalt concrete (27 %) and local subsidence (21 %).

For structures older than 10 years, the failure rate increased by more than 2 times.

Tests of samples of asphalt concrete mixtures and sealing materials revealed that

the modulus of elasticity of asphalt concrete in the interface zone decreased by 15-20 % after 200 thousand loading cycles.

The materials used in the F80 and E80 seams demonstrated higher crack resistance (fatigue limit increase by 22-25 % compared to C80).

Elastomeric seals have shown durability higher by 30 % compared to traditional bitumen mastics. The main quantitative results are shown in Table 2.

Let us calculate the total temperature displacement of the free end of the span structure by applying the formula [24]:

where: ${\gamma }_T$ is the reliability coefficient for temperature effects; $\alpha$ is the coefficient of linear thermal expansion, (1∙10^-3); $L$ is the design length of the span structure from which the displacements are determined (2×24 m); ${\mathrm{\Delta }}_T$ – range of change of design temperatures from $T_{min}$ to $T_{max}$ taking into account the increase of this range due to the heating of the structure under the influence of sunlight, including non-uniform heating and non-uniform temperature distribution along the cross-section of the element [25].

Normative air temperatures in warm and cold seasons should be set equal: $t_{n,T}\approx$ + 40 °C; $t_{n,X}\approx$ –40 °C; can be accepted $t_{3,T}=t_{n,T }$ – 15 °C; $t_X=t_{n,X}$ + 15 °C.

The distances between the edges of OP-DSH-K2 expansion joints of types C80, F80 and E80 measured at different temperatures in the range from –30 °С to +30 °С are shown in Fig. 8.

Fig. 8Diagram of dependence of displacement of expansion joints on temperature

4. Discussion

The calculated width determined by the Eq. (1) of one joint from the action of temperature –40 °C is equal to half of this value, that is, if by calculation $\mathrm{\Delta }T$ turned out to be 16 cm, the half will be 8 cm. For a comfortable passage through the deformation joint the value of its opening should not be more than 8 cm [23, 26], otherwise due to the ‘failure’ of car wheels between the edging dynamic coefficient ($1+\mu$) increases, which is an additional unfavourable factor, increasing the impact of traffic load on the bridge spans. The presence of defects in the area of expansion joints significantly increases this coefficient ($1+\mu$) due to the disturbance of the smoothness of the carriageway micro-relief.

Judging from the results of Fig. 10, the presented types of expansion joints fulfil this task perfectly. The best performance at different temperatures in the range from –30 °C to +30 °C, i.e. the smallest displacement between the edge profiles of the OP-DSH-K2 expansion joints of the F80 type at –30 °C outside temperature was 6.8 cm, and at +30 °C the displacement was 5.4 cm.

5. Conclusions

It has been established that after commissioning of bridges and overpasses in a couple of years deformations, displacements, deep cracks and potholes in the zones of expansion joints will be inevitable in the zones of road asphalt concrete pavement with the depth from 3 cm to 10 cm. As a result of the research:

1) It is established that the interface zone of the deformation seam and the pavement is the most vulnerable element of the bridge bed, where dynamic loads from vehicles and thermal deformations of structures are concentrated.

2) Experimental studies have shown that the main causes of premature destruction of the coating near the seam are the accumulation of plastic deformations in asphalt concrete and impaired adhesion between the layers.

3) Quantitative dependences between the parameters of the seam design and the rate of formation of coating defects have been revealed, which makes it possible to predict the timing of the inter-repair period.