1. Introduction
Bridges play a critical role in road traffic and are vital to the overall transport system. With socio-economic progress, the transport sector is booming and the volume and load capacity of vehicles has increased remarkably, changing dramatically from what it was in the past. Due to the rapidly increasing vehicle load, acid rain, temperature and other natural factors, a series of diseases occur in the normal service period of the bridge. For example, structural cracks, deterioration of concrete materials, corrosion of steel bars [
1,
2,
3]. Diseases of bridges will have different degrees of impact on their security, suitability and sustainability of the structure, which will reduce the carrying capacity of the bridge and may even threaten the normal functioning of the bridge [
4]. Appropriate bridge strengthening methods can improve the bearing capacity of Bridges and extend the service life of Bridges [
5,
6,
7].
The bonding steel plate reinforcement method can limit the development of cracks and improve the flexural performance of Bridges [
8,
9,
10]. However, steel plates are difficult to accommodate when faced with irregular concrete surfaces and are prone to rusting problems in the natural surroundings. The method of attaching fiber materials is to attach high-strength fiber materials to the surface of the reinforced members with epoxy resin to exert the high strength and good durability of the composite materials [
11,
12,
13]. However, carbon fiber cloth/plates are weaker and not as effective in improving structural stiffness, as well as having a greater material cost.
The prestressed steel wire (PSW) reinforcement method is to anchor the PSW to the reinforced beam body, and spray composite mortar to bond it to the reinforced beam body as a whole [
14,
15,
16]. Compared with the reinforcement method of steel wire mesh and composite mortar [
17,
18], the ability to exploit the maximum tensile strength of the wire, thus dramatically increasing the efficiency of material utilization, and will not fail due to the peel and damage of thin layer of mortar. The PSW reinforcement method is an active reinforcement method, which can significantly improve the stiffness and bearing capacity of the main beam. However, the polymer mortar (PM) sprayed outside the steel wire has low tensile strength, and a large number of cracks appear in the cracks of the original beam before reinforcement, which affects the durability of both the PSW and the steel bars of the original structure.
Polyurethane concrete (PUC) materials are designed to be extremely flexible and lightweight, with excellent bond strength and resistance to acid and caustic attacks [
19,
20,
21]. In this paper, polyurethane concrete-prestressed steel wire (PUC-PSW) is proposed to strengthen reinforced concrete structures. The steel wire is tensional and anchored on the surface of the reinforced beam body, and then the steel wire is embedded in the PUC composite material by pouring PUC composite material, which is a composite reinforcement method combining the active force of the steel wire and the passive force of the PUC. For the experimental study on the flexural reinforcement of PUC-PSW, the reinforcement effect of PUC material was explored with the embedding material, anchoring form of wire, thickness of PUC material, number of wire and loading method as variables.
6. Conclusion
In this paper, PUC material is used as the embedded material of steel wire to form a new method of PUC-PSW reinforcement. Light and high strength PUC materials can not only bond and anchor PSW, but also passively participate in the structural force. The problems of easy cracking, easy falling off and affecting the durability of PSW are solved by using mortar or composite mortar as embedded material. In this paper, the static test of PUC-PSW reinforced beam is studied and analyzed. The test results show that:
(1) Compared to PSW strengthening, PUC-PSW strengthening can improve the yield and ultimate loads of the strengthened beams considerably. The yield load and ultimate load of the PUC-PSW reinforced beam (20mm thick PUC) are increased by 24.1% and 44.6%, respectively, compared with the corresponding PSW reinforced beam. Even if the steel wire in the reinforced layer is removed, the yield load and ultimate load are increased by 2.2% and 19.4%, respectively.
(2) The ability of PUC-PSW reinforced to limit crack development is better than that of PSW reinforced beams, especially after the main beam steel bars yield. The PUC material does not crack during the whole loading process until the final reinforcement layer breaks, combined with the good chemical corrosion resistance of the material, this phenomenon can theoretically increase the durability of the steel wire; The stiffness of PC-PSW reinforced beam is obviously higher than that of PSW reinforced beam.
(3) Strength, stiffness, and crack-limiting capacity of reinforced beams improve with growing thickness of the PUC of the reinforcement layer and decrease with decreasing prestressing of the wires. Compared with the intact reinforced beam, the deflection of the load-reinforced beam is larger than that of the directly reinforced beam, and the structural stiffness and yield load are reduced, but the ultimate bearing capacity is not significantly reduced.
Figure 1.
Compressive test diagram of polyurethane concrete material.
Figure 1.
Compressive test diagram of polyurethane concrete material.
Figure 2.
Flexural test diagram of polyurethane concrete material.
Figure 2.
Flexural test diagram of polyurethane concrete material.
Figure 3.
Tensile stress-strain curve of steel wire.
Figure 3.
Tensile stress-strain curve of steel wire.
Figure 4.
Specimen size and reinforcement: (a) Longitudinal section; (b) horizontal section.
Figure 4.
Specimen size and reinforcement: (a) Longitudinal section; (b) horizontal section.
Figure 5.
Profile of the reinforced beam.
Figure 5.
Profile of the reinforced beam.
Figure 6.
Reinforcement steps: (a) anchorage; (b) beam end anchorage; (c) beam surface chisel; (d) main beam erection; (e) anchor head extrusion; (f) beam end anchorage; (g) polyurethane concrete mixing; (h) polyurethane concrete pouring.
Figure 6.
Reinforcement steps: (a) anchorage; (b) beam end anchorage; (c) beam surface chisel; (d) main beam erection; (e) anchor head extrusion; (f) beam end anchorage; (g) polyurethane concrete mixing; (h) polyurethane concrete pouring.
Figure 7.
Static load test diagram.
Figure 7.
Static load test diagram.
Figure 8.
Cross section layout of strain gauge.
Figure 8.
Cross section layout of strain gauge.
Figure 9.
Failure mode diagram of beam: (a) beam CB, (b) beam A1, (c) beam A2, (d) beam A2-1, (e) beam A4, (f) beam A5, (g) beam A6, (h) beam A8, (i) beam A9, (j) beam A9-1.
Figure 9.
Failure mode diagram of beam: (a) beam CB, (b) beam A1, (c) beam A2, (d) beam A2-1, (e) beam A4, (f) beam A5, (g) beam A6, (h) beam A8, (i) beam A9, (j) beam A9-1.
Figure 10.
Load-deflection curves of beams CB, A1, A2 and A5.
Figure 10.
Load-deflection curves of beams CB, A1, A2 and A5.
Figure 11.
Load-deflection curves of beams CB, A2 and A2-1.
Figure 11.
Load-deflection curves of beams CB, A2 and A2-1.
Figure 12.
Load-deflection curves of beams CB, A2, A4 and A5.
Figure 12.
Load-deflection curves of beams CB, A2, A4 and A5.
Figure 13.
Load-deflection curves of beams CB, A2, A3 and A7.
Figure 13.
Load-deflection curves of beams CB, A2, A3 and A7.
Figure 14.
Load-deflection curves of beams A5, A8, A9 and A9-1.
Figure 14.
Load-deflection curves of beams A5, A8, A9 and A9-1.
Figure 15.
Load crack curves of beams CB, A2, A4, A5 and A8.
Figure 15.
Load crack curves of beams CB, A2, A4, A5 and A8.
Figure 16.
Cracks of concrete and corresponding composite mortar.
Figure 16.
Cracks of concrete and corresponding composite mortar.
Figure 17.
Concrete cracks and intact polyurethane concrete.
Figure 17.
Concrete cracks and intact polyurethane concrete.
Figure 18.
Load crack curves of beams A2, A2-1, A9 and A9-1.
Figure 18.
Load crack curves of beams A2, A2-1, A9 and A9-1.
Figure 19.
Load comparison diagram of beams CB, A1, A2 and A2-1.
Figure 19.
Load comparison diagram of beams CB, A1, A2 and A2-1.
Figure 20.
Load comparison diagram of beams CB, A2, A3, A5 and A7.
Figure 20.
Load comparison diagram of beams CB, A2, A3, A5 and A7.
Figure 21.
Load comparison diagram of beam A5, beam A6 and beam A8.
Figure 21.
Load comparison diagram of beam A5, beam A6 and beam A8.
Figure 22.
Load comparison diagram of beams A2-1, A9 and A9-1.
Figure 22.
Load comparison diagram of beams A2-1, A9 and A9-1.
Figure 23.
Load-strain diagram of beam A2 and beam A5 rebar, wire and insert material.
Figure 23.
Load-strain diagram of beam A2 and beam A5 rebar, wire and insert material.
Figure 24.
Load-strain diagram of beams CB, A5 and A6 rebar, steel wire and polyurethane concrete material.
Figure 24.
Load-strain diagram of beams CB, A5 and A6 rebar, steel wire and polyurethane concrete material.
Figure 25.
Load-strain diagram of beam A5 and beam A8 rebar, steel wire and polyurethane concrete material.
Figure 25.
Load-strain diagram of beam A5 and beam A8 rebar, steel wire and polyurethane concrete material.
Figure 26.
Load-strain diagrams of beams A2-1 and A9 rebar, steel wire, composite mortar and polyurethane concrete materials.
Figure 26.
Load-strain diagrams of beams A2-1 and A9 rebar, steel wire, composite mortar and polyurethane concrete materials.
Figure 27.
Load-strain diagram of beams A5 and A9 steel bars, steel wires and polyurethane concrete materials.
Figure 27.
Load-strain diagram of beams A5 and A9 steel bars, steel wires and polyurethane concrete materials.
Figure 28.
Load-strain diagram of beams A9 and A9-1 Rebar, steel wires and polyurethane concrete material.
Figure 28.
Load-strain diagram of beams A9 and A9-1 Rebar, steel wires and polyurethane concrete material.
Table 1.
Composition of polyurethane concrete.
Table 1.
Composition of polyurethane concrete.
Chemical Composition |
Percent(%) |
Polyether |
25 |
Isocyanate |
25 |
Portland cement |
45 |
Molecular sieve |
5 |
Table 2.
Parameters of beam reinforcement.
Table 2.
Parameters of beam reinforcement.
Group |
Beam number |
The number of steel wire |
Prestress (MPa) |
Embedded material |
Material thickness (mm) |
Anchorage form |
Preload |
Reinforcement under load |
Control beam |
CB |
- |
- |
- |
- |
- |
- |
- |
PSW |
A1 |
5 |
700 |
- |
- |
Anchor gear |
- |
- |
A2 |
5 |
700 |
Mortar |
20 |
Anchor gear + Mortar |
- |
- |
A2-1 |
7 |
700 |
Mortar |
20 |
Anchor gear + Mortar |
- |
- |
A3 |
5 |
700 |
Mortar |
20 |
Anchor gear + Mortar |
Preload |
- |
PUC-PSW |
A4 |
0 |
700 |
PUC |
20 |
- |
- |
- |
A5 |
5 |
700 |
PUC |
20 |
Anchor gear +PUC |
- |
- |
A6 |
5 |
700 |
PUC |
20 |
PUC |
- |
- |
A7 |
5 |
700 |
PUC |
20 |
Anchor gear +PUC |
Preload |
- |
A8 |
5 |
700 |
PUC |
30 |
Anchor gear +PUC |
- |
- |
A9 |
2 |
700 |
PUC |
20 |
Anchor gear +PUC |
- |
- |
A9-1 |
2 |
700 |
PUC |
25 |
Anchor gear +PUC |
- |
- |
Table 3.
Cross-sectional diagram of reinforced beams I-I.
Table 4.
Cracking load, yield load and ultimate load.
Table 4.
Cracking load, yield load and ultimate load.
Group Number |
Beam Number |
Cracking Load (kN) |
Increase Ratio (%) |
Yield Load (kN) |
Increase Ratio (%) |
Ultimate Load (kN) |
Increase Ratio (%) |
Control beam |
CB |
20 |
- |
74.3 |
- |
101.0 |
- |
Steel wire |
A1 |
40 |
100 |
91.4 |
23.0 |
143.1 |
41.7 |
A2 |
40 |
100 |
96.7 |
30.1 |
141.3 |
39.9 |
A2-1 |
50 |
150 |
103.2 |
38.9 |
161.8 |
60.2 |
A3 |
- |
- |
94.1 |
26.6 |
144.5 |
43.1 |
PUC-PSW |
A4 |
25 |
25 |
98.8 |
33.0 |
168.7 |
67.0 |
A5 |
45 |
125 |
120.0 |
61.5 |
204.3 |
102.3 |
A6 |
50 |
150 |
112.0 |
50.7 |
133.1 |
31.8 |
A7 |
- |
- |
118.6 |
59.6 |
192.2 |
90.3 |
A8 |
55 |
175 |
137.0 |
84.4 |
228.5 |
126.2 |
A9 |
30 |
50 |
110.3 |
48.5 |
179.0 |
77.2 |
A9-1 |
35 |
75 |
130.2 |
75.2 |
207.8 |
105.7 |