STRENGTHENING CONCRETE HOLLOW SECTION GIRDER BRIDGE USING POLYURETHANE-CEMENT MATERIAL (PART B)

This paper presents experimental study to retrofitted reinforced concrete Hollow Section Bridge. The study was carried out on the White River Bridge structure (Bai xi da Qiao / China). The effect of retrofitting on stress and strain of beams at the critical section was studied. Evaluating the bridges girder after strengthening using new material called PolyurethaneCement material (PUC) as an external material .This study present the strain and deflection before and after strengthening the bridge girders. The results has shown that the overall state of the bridge structural strengthening is in good condition. The enhancement was significant in stiffness of the bridge structure. Regarding to the results of static load test, the experimental values strain and deflection are less than theoretical values, indicating that the stiffness of the structure, overall deformation and integrity satisfy the designed and standard requirements and the working performance are in good condition, and flexure capacity has a certain surplus.


INTRODUCTION
Strengthening of Bridges have been taken into account since several last decades. Many analytical models have been developed (Ahmed and Gemert, 1999;Jansze, 1997;Raoof and Zhang, 1997;Saadatmanesh and Malek, 1998;Varastehpour and Hamelin, 1997) which can be use different method to predict the load carrying capacity using different material such as FRP ( Fiber Reinforced Polymer) to strengthen the reinforced concrete structures (beams, columns, piers, ….). FRP composites is used as the confining material of the concrete columns, piers, and beams. The results indicate that the FRP wraps could increase the compressive strength, axial strain at ultimate stress, ductility and deformation capacity of the concrete columns significantly (Matthys et al., 2006;Sheikh, 2007).
Recently Polymer composites are considered of wide use as construction material (Van Gemert et al., 2004;Ohama, 2011). These composite can be obtained by partially replacing the cement hydrate binders with polymeric modifiers such as water soluble polymers polymer, powders dispersion, monomers, and liquid resin (Chandra and Ohama, 1994). The obtained composite mixes compared to the conventional cement pastes, cement polymer composites enhances tensile strength, compressive strength, flexural strength, adhesive properties, good workability and increasing the flexibility of composites (Ohama, 1995;Cota, 2012;Razl, 2012).
The aim of the assessment is in particular to establish the safe load carrying capacity of a bridge.
In the last decades, the traffic loads and speeds drastically increased. As a consequence, many existing bridges are now subjected to loads and speeds higher than those for which they have been designed for. Moreover, due to insufficient maintenance, many of them have severely deteriorated over their years of service thus considerably reducing their capacity. The analyzing the increase of the transport capacity and service life of existing bridges must be considerable.
In order to demonstrate new and refined methods developed within this paper, field tests of existing bridges were carried out before and after strengthen the bridges.
In this study using new material polyurethane-cement (PUC), have been developed by Haleem et al. (2013) can be used in construction and maintenance structures. PUC has excellent mechanical properties, bonding and adhesive properties with concrete surface. This material can be made simply preparing method and cast in site without extra technical requirement. Haleem et al. (2013) applied PUC to strengthen reinforced concrete bridge T-beams in full scale and the results was could effectively improve the flexural strength capacity for retrofitted beams. Moreover the PUC material have ability to control the crack propagation. In addition, this material improved the stiffness of the beam where cracks propagation was confined.

Haleem K. Hussain
Furthermore, this material can make the repair or retrofitting of bridge elements more effective, easy to handle and cheaper.

BRIDGE DESCRIPTION
The upper structure of bridge : The bridge consist of 16 span each span had 20 m length, span width of 11.75m, arranged: 0.5m (side-wall) +2.5 m (hard shoulder) +2 The right hand side of bridge exposed to fire accident, resulting spalling in the bottom concrete slab, exposed tendons; and spalling of cap beam concrete.
Through the test program, stress and deflection was measured for the bridge span structure under static load for control section and compare with theoretical calculations, the actual structure of tested stress and deflection of control section meets design specifications (Highway regulation (JTG D60), 2004).
Through the field loading test, the comparative analyses of experimental were carried out on the span-2 and span-3 of the bridge after the fire accident to assess the carrying capacity of the structure, and then determine the extent of damage and according to the results the maintenance recommendations were made (Haleem, 2016). Fig. 1 shows the cross section view of the bridge Kufa Journal of Engineering, Vol. 9, No. 1, 2018 27  This study will considering strengthening the bridge using PUC material to enhance the capacity of damaged span , and making comparison the result before and after strengthen.

Cement
The most widely used of the construction cements is Portland cement. The cement type used in this research was Portland cement Type I. Table 1 present the cement components used in this study (Haleem et al., 2013).

Polyurethane
The main components of the PUC is polyurethane (PU), which is an excellent polymer elastic material, mainly based on the chemical compounds of isocyanate and a strong chain of oligomeric polyols.
The hardness range of this material is 10-100 ( Table 2 shows the components materials ratio mixing of polyurethane which has used in the study (Haleem et al., 2013). Kufa Journal of Engineering, Vol. 9, No. 1, 2018 29 While the component mixing ratio of the PUC materials was (polyo l: polyisocyanate: cement) was 1:1:3 by weight. These proportion material are listed in Table 3.  (Haleem et al., 2014). This study considered the density of the PUC material to be around 1650 kg/m 3 , Elastic modulus: 4200 MPa, bonding strength, 3.0 MPa (non slip on interface surface between concrete and PUC will be occurred).

Mixing of PUC
The mould was clean and slight oil of interior faces; the material components of polyurethane put it together then cement was added in clean pan and finally mixed together according to the design ratio. Mix process was done using electrical mixer machine for 2-4 minutes to obtain homogenous mixture and then poured in the mould. Some special additive were added to mixes to enhance the reaction of the material.

Critical span
The Span No. 2 and span No. 3 was tested before strengthening and measuring point was appointed at sections A, B, C, and for deflection and tensile strain as shown in Fig. 2 (Haleem, 2016).

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Haleem K. Hussain No. 2 was decreased to 14% because of the fire action.

Design strengthening Detail
The Fig. 3 showing the dimension of substrate PUC layer to strengthen the critical section. The data of design are listed in Table 4. The substrate surface of critical and damaged area of slab girders were cleaning and removing all the rusty reinforcement beside the loose concrete (spalling concrete) using hand tools as shown in Fig. 4. Initial repairing have been made before strengthening the bottom surface with PUC material.
The bottom concrete surface of girders was prepared by cleaning the bottom contact surface with to PUC materials to provide well bonding between concrete and PUC. The mould have was setup and fix properly at the lower surface of girders which need to strengthen. All the joint of mold was closed properly to avoid any leakage of PUC material during the pouring process, where this material has enough flow ability to be leak from the small holes. The components of polyurethane and cement were mix together according to the mix design proportion). Fig. 5 showing the frame of pouring process. During the strengthen procedures, the joint between girder should be keep clean after completion pouring. The completing pouring process after removing the frame are shown in Fig.6.

TEST LOAD CASES
The According to the requirements of the highway bridge carrying capacity testing assessment procedures q  should meet from 0.8 to 1.05. The four cases of the test load, as shown in Table   5.
In order to adopting the performance loading test of the control members, will consider a classification method of loading and the efficiency coefficient q

Load Test Results and Analysis after Strengthening
Loading case 1 of middle span No. 2 results at maximum bending moment of critical section, the strain and the deflection are listed in Table 6 and Table 7 respectively. The efficiency was measured through the calibration factors (or efficiency factor) and also listed in Table 6 and   Table 7.
The relation between the strain at the middle span section and the girder number are shown in Fig. 9 and Fig. 10 shows the relation between the deflections of mid span section versus the girder number.  The loading case -2 have been applied on the bridge lane to deduct the maximum bending moment and maximum deflection at the control cross-section, Table 8 showing the normal strain and calibration coefficients. Table 9 presents the measured mid-span deflection and calibration coefficients of the control section.
The strain at the middle span section and the girder number are relationship shown in Fig. 11 and Fig. 12 shows the relation between the deflections of mid span section versus the girder number. Furthermore, measured deflection of middle span 2 indicating that after the lateral strengthening the structure has been significantly improved.  For load condition case-1 of girder no. 2 at the middle span, the deflection calibration coefficient were between 0.63-0.85 with an average 0.79. After strengthening of the girder no.
2, the deflection calibration coefficients were 0.63 to 0.76 with an average 0.68, indicating that the overall stiffness of the structure after the strengthening has increased by 16%.
Before strengthening, under loading case-2 of girder no. 2, the deflection calibration coefficients were 0.7 to 0.81 with an average 0.76. After strengthening of the girder no. 2, the deflection calibration coefficients were 0.54 to 0.82 with an average 0.66, indicating that the overall stiffness of the structure after the strengthening has increased by 15%.
The deducted results show that after strengthening bridge girders, the vertical stiffness of the structure has been significantly improved and restored the requirements specified in the original design.