The chapter delves into the deterioration factors affecting highway bridges in Japan, such as salt damage, water exposure, and seismic activity. It highlights practical applications of polymer materials in repairing concrete slabs, preventing water damage, and enhancing seismic resistance. The text also discusses the transition from corrective to preventive maintenance and the importance of regular inspections for longevity. Notably, it presents unique case studies and successful countermeasures implemented in Japan, making it a valuable resource for professionals in the field.
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Abstract
Recently, the deterioration and renovation of the aged bridges are urgent issue. Approximately 30% of more than 700,000 highway and road bridges in Japan have been in service for more than 50 years. The performance and function of them are required equal to be better than those at the beginning of construction and extend the service life. In addition to above, Japan is also a highly seismic country and there have been frequent damages of the bridges due to earthquakes. Therefore, securing the resilience of the bridges corresponding to robustness, redundancy, resourcefulness and rapidity is strongly demanded. In this study, the current status and practical countermeasures for the bridges to ensure the required performance and function, and to enhance the resilience using concrete polymer materials were investigated and discussed. Concrete polymer materials, which have high strength, high early strength development and high durability, are effective for repair and strengthening to sustain the current performance of structures. The main construction contents are as follows;
It is a construction to replace the damaged reinforced concrete floor slab with a more durable floor slab. Treatment of joints of precast prestressed concrete slab is included.
It is a construction to install high-performance floor slab waterproofing on the waterproof layer.
In order to improve the durability of the bridge, it is a construction to attach reinforcing members to the girder.
Seismic retrofit of concrete piers such as steel jacketing is one of main reinforcement technologies.
1 Introduction
More than 700,000 highway and road bridges have been constructed and serviced in Japan. About 9000 km of expressways has been built since 1962. The most advanced technologies of the time for the highway infrastructures were applied. However, deterioration of the structures over time is unavoidable and materials degradation such as neutralization, salt damage and alkali-silica reaction has been exposed during service. Furthermore, those structures were severely damaged by the unexpected external forces such as earthquake and tsunami. Maintenance, which is essential for appropriate service of structures, is changing from corrective maintenance initially to preventive maintenance recently.
In this paper, causes and characteristics of degradative damage of bridges were firstly investigated. Then, practical application of polymer materials, which are indispensable for maintenance of structures, was studied. Those were a repair of deterioration of concrete slab, measures against degradation of water exposure and seismic reinforcement. Finally, efforts to extend service life of bridges were discussed.
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2 Salt Damage and Countermeasures
The main factors of deterioration damage are shown in Table 1 [1]. Salt damage due to de-icing agent, use of sea sand and airborne salt and transient loads are significant. There are many combined deterioration such as damages due to deicing agent and heavy loads, and deicing agent and ASR. Studded tires posed health hazards and its use was prohibited in 1990. After that, the amount of de-icing agent used, increased rapidly and spurred the salt damage. Measures against salt damage are epoxy coating on the concrete structures to suppress salt penetration, use of epoxy-coated rebar and polyethylene-coated strand. Recently the use of stainless steel has increased by assuming long-term service over 125 years. Furthermore, polymer cement mortar mixed with acrylic resin mortar is also used as cross section repair material to improve the adhesion to the concrete members and to control crack occurrence due to shrinkage.
Table 1.
The factors of deterioration damage of highway bridge
Degradation damage factor
Percentage of deteriorated bridges
Note
De-icing agent
51.6%
In some cases, there are overlaps, such as 6.6% due to de-icing agent and vehicle traffic volume, and 3.4% due to de-icing agent and alkali silica reaction
Vehicle traffic volume
31.6%
Sea sand
8.8%
Alkali silica reaction
4.5%
Airborne salt
3.5%
3 Structural Corrosive Environment Subjected to Water
There are unavoidable structural gaps such as both ends of girder and arch bridges, arch bridge from the view point of thermal movement, and the limitations of structural calculation ability as shown in Fig. 1.
Fig. 1.
Unavoidable structural gaps
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Steel and rubber expansion joints which are normally water proofing are installed at those gaps. The damage of the end of girder, bearing and the top of abutment due to leakage of water from expansion joints [2] are often observed as shown in Fig. 2. Especially in snow and cold regions, leaking water contains chloride ion from pavement, which causes severe corrosion. The degradation due to water of exposure around drainage basin is also severe. Measures against degradation of water exposure, are installation of rubber water sealing at the opening of expansion joint, and bearing sealing used by transparent silicone resin of high flexibility and deformability as shown in Fig. 3.
Fig. 2.
Leakage from expansion joint
Fig. 3.
Bearing sealing used by transparent silicone resin
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4 Deterioration of Concrete Slab and Its Countermeasures
Deterioration of concrete slab is diverse. Fatigue damages due to vehicle load and excessive loading are remarkable in addition to salt damage. Those typical pattern are axial and longitudinal cracks and sinking of concrete floor slab. Furthermore, waterproofing of concrete slab was normally not installed before 1987 and most old slabs up to that time caused the segmentation of slabs as shown in Fig. 4. As slab fatigue was accelerated by rain water, blocks of coarse aggregates due to outflowing of cement from the upper surface of slab by polishing action between coarse aggregates and cement mortar are observed.
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As some repair methods for slabs, epoxy resin crack injection, three axial vinylon fiber mesh lining with epoxy resin for prevention of concrete pieces falling [3], and sectional restoration with polymer cement mortar have been applied over 40 years [4].
Typical reinforcement measures of slabs are thickening upper or lower surface of slab by polymer cement mortar, and steel plate and carbon fiber sheet are bonded by epoxy resin as shown in Fig. 5.
Fig. 4.
Segmentation of slabs due to fatigue damage
Fig. 5.
Crack injection, and fiber mesh lining with epoxy resin for prevention of concrete pieces falling
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Recently reinforced concrete slabs which are severely deteriorated or in service over 30 years, are sequentially updated. Prestressed concrete slab units are prefabricated and jointed. Many joint methods for precast PC slabs have been proposed. One of the excellent construction methods is solved by use of polymer cement mortar or epoxy resin mortar having strong adhesion. Injection of these polymer materials into narrow width of 25 mm to achieve continuity is enable to eliminate the weakness of joints of units as shown in Fig. 6 [5].
In addition to conventional rubber and asphalt-based waterproofing materials, the fast curing and sprayable urethane resin [6] is proposed and achieved as shown in Fig. 7.
Fig. 6.
Injection of polymer materials into joint parts between PC slab units
Fig. 7.
The fast curing and sprayable urethane resin
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5 Earthquake Damage and Seismic Reinforcement
Japan is an earthquake-prone country and damages caused by repeated large earthquakes such as Kobe in 1995, Great East Japan Earthquake in 2011 and Kumamoto in 2016. New modes of bridge damages one after another have been observed; those damages are shearing failure of piers, unseating of bridges, and collapse of the piers with multiple rocking columns as shown in Fig. 8.
Fig. 8.
Collapse and unseating of bridges
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In order to prevent these bridge damage, seismic retrofit of existing concrete piers has been executed.
The steel jacketing method used by steel plate and epoxy resin is adopted to increase the strength and rigidity as shown in Fig. 9. The application of carbon/aramid fiber sheet is also adopted when the clearance and weight increase were limited, and the sheets in longitudinal and transverse are effective to increase the flexural strength and shear strength, respectively. Furthermore, the hinges at the top and bottom of rocking piers were fixed by polymer cement mortar to resist the seismic forces in the transverse direction to the bridge axes. In some cases, the multiple rocking piers were improved to the wall type piers by use of reinforced concrete.
A great variety of devices are installed to prevent bridge falling due to earthquake. Those devices are connecting superstructure and substructure by use of shock absorbing chains, steel, steel bracket and concrete block as protuberance. In order to install these devices, steel bolts are anchored in existing concrete pier/abutment by use of epoxy resin. Rubber is regularly used as buffer to moderate the impact of earthquake, and thermosetting polyester elastomer is also used.
The excellent performance of the above seismic reinforcement was confirmed by the earthquakes occurred after countermeasures.
Fig. 9.
Typical jacketing methods and connecting super- and sub-structure by shock absorbing chain
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6 Initial Defects and Subsequent Troubles
The reinforced concrete slab was designed and constructed from the view point of rationality. The minimum thickness of the slabs was 16cm since 1964 to 1968. Damages due to extreme thinness of slabs continued. Currently the thickness of slabs is specified to more than 25cm from the reflection of the original inappropriate design. Sometimes poor construction such as insufficient reinforcing bar cover and honeycomb of concrete causes the defects in concrete structures.
In construction of post tension system prestressed concrete, occurrence of poor filling as non-filling of grouting into cable sheath becomes serious problems. That is a cause of corrosion and fracture of prestressing steel due to entering water to sheath.
The concrete ceiling panels suspended from the top of the concrete tunnels fell on the cars in 2012. The upper part of the bulkhead plate was connected by the adhesive anchor to the top of tunnel as shown in Fig. 10 (a) and two ceiling plates were installed on the lower part of bulkhead plate. The detail of bolt connection to the concrete through roof hanger plate and CT steel are shown in Fig. 10(b).
Several undesirable factors should be mentioned; creep and deformation of adhesives, use of short bolt length of 110mm, and upward construction. Currently this type structures are not adopted.
Fig.10.
(a) Installation of concrete ceiling panel (b) Adhesive Anchor
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After this tunnel accident, all highway bridge and tunnel undergo regular inspections and diagnosis every five years. Seismic reinforcement and preventing concrete pieces falling have promoted by the preventive maintenance.
The deterioration such as salt damage and fatigue of concrete slab in above occurs independently.
Furthermore, combined deterioration due to multiple factors of salt, ASR and loads is concerned actually and individual measures in the application of polymer materials are required.
Even if repair and reinforcement are accomplished, re-deterioration with time and unexpected external forces will act, and regular and proper maintenance are essential for longevity of structures.
7 Conclusions
Practical application of concrete-polymer composites for repair and reinforcement of highway bridges in Japan was overviewed and investigated. The main results obtained are summarized in the following:
In Japan, the highway bridges had been constructed and in serviced under breakdown maintenance for about 50 years since 1962. Main deterioration is seen in reinforced concrete slab due to salt damage, fatigue due to cyclic loading and excessive loading.
Degradation of water exposure such as leakage of water from the expansion joint to girder ends, bearing, and abutment, and water around drainage to slabs is remarkable, and polymer materials have been applied to properly countermeasures.
The typical performance due to application of polymer materials was crack repair, sectional restoration and surface coating. However, slabs of the serious and combined deterioration such as segmentation of bridge deck and fatigue damage must be demolished and renewed.
After great earthquake damage and tunnel crest collapse accident, preventive maintenance such as seismic reinforcement and preventing delamination based on the deterioration diagnosis by periodic inspection has been adopted since 2012.
Deterioration will progress normally due to environment, material degradation and unexpected external force, even if the repair and reinforcement are executed, and so appropriate regular maintenance is essential to ensuring a long-term service life.
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