LABORATORY EVALUATION ON PERFORMANCE OF GLASS FIBER REINFORCED PLASTIC MORTAR PIPE CULVERTS

This paper investigated the performance and behaviour of glass fiber reinforced plastic mortar (FRPM) pipes under different loading conditions. FRPM pipes with inner diameter of 1500 mm were prefabricated in factory. Mechanics performance testing (ring and axial compressive strength and elastic modulus), stiffness and fatigue test were carried out in laboratory. Ring stiffness test provided pipe stiffness (PS) which is a function of geometry and material type of pipe through parallel plate loading test (PPLT). The fatigue test and micro-structure measure method were used to evaluate the durability effects of FRPM under repeated compression load. Results indicated that FRPM pipes had better mechanic performances as the road culverts under soils. It may be helpful for the design and construction of FRPM culverts.


INTRODUCTION
Glass fiber reinforced plastic mortar (FRPM) pipe is a kind of new composite material using resin as matrix material, glass fiber and its products as reinforced material, and quartz sand as filling material.According to the production process, it can be divided into three categories named fixed-length winding, centrifugal casting and continuous winding.Due to the excellent corrosion resistance, good bearing capacity, small internal resistance, long service life, easy installation, rapid construction time and lower initial and long-term maintenance costs, FRPM pipes have been widely used in road engineering.
As an important part of highway engineering, culverts make up a significant proportion of all road projects both on the quantity and the project cost.FRPM pipes arising in the 1970s were always used as a flexible composite pipe.FRPM pipeline was made initially from 1979 in Italy, and then spread to China, European and African countries.By 1992, all kinds of FRPM pipelines used as sewage pipe, fire hose, water and waste water pipe had reached 1020 km in Italy, from 200 to 3050 mm in diameter.FRPM pipelines with large diameter accounted for about 40%.The pipes used in Spain, Monaco, Nigeria, the united Arab emirates, Saudi Arabia, Iran and other countries, are about 400 km.In 1979, sand glass fiber reinforced plastic pipeline was made in Italy, successively used in China, European and African countries.Rafiee and Amini (2015) performed the study of failure mechanism of FRPM, developed the continuous failure damage model (SFM), and verified it through the different layer structure of mechanical properties of FRPM test.Ouellette and Beach (1981) studied the design method of FRPM pipeline, suggested that based on the structural feature of FRPM and load requirements, the maximum load, flexural strength, shear strength and the bearing capacity of each layer must be calculated.Sung and Jin (2015) predicted the long-term performance of FRPM pipe under continuous internal pressure.According to the data of the continuous internal pressure test, they found that the linear regression analysis is suitable to predict the failure pressure of FRPM after 50 years.Rafiee and Reshadi (2014) observed the GRP tube under hydrostatic pressure and found that the first fracture (FPF) and the functional failure (FF) pressure increased linearly with the core thickness increasing.Xia, etc. (2001) investigated the mechanical properties of composite pipes under internal pressure.The stress-strain relationship was obtained.At the same time, they pointed out that the axial tensile stiffness of the inner surface of the pipeline was larger than that of the outer surface.
Through investigation of FRPM pipe in service, we found many FRPM pipes with disease, due to the existing design and construction method.The deformation and stress characteristics of culvert structure under loads of filled soil are still not very clear.Therefore enough guidelines for design and construction were not provided.For the former problems of FRP pipes in highway bridge engineering application, both in terms of design standard and mechanics analysis, or in the construction process and quality control on test methods and standards, still need to conduct more in-depth theoretical and applied basic research work, to guide the application of FRP pipes in highway bridge engineering before has good prospects for development.

FRPM Pipes Description
Glass fiber used here is a kind of improved glass without boron and alkali, ECR roving -2400-906, produced by Jiangsu composite materials co.LTD.As shown in Figure 1 (a), it can be used in the production of acid and water resistance glass fiber, and it is one of the new materials designed for underground pipe, tank and so on.The glass fiber surface mat refers to the glass fiber reinforced plastic products which can form resin layer.It is typically implemented with the alkali glass surface mat (Figure 1 (b)).Glass fiber stitched mat (Figure1(c)) is available to sew it into the short cut fiber or long fiber by using stitched knitting machine.1.
The mort used is quartz sands that generally selected to remove dust or other debris in the drying process.The following technical indicators are presented in Table 2.

Mechanical properties of FRPM test
In order to obtain the ring and axial compressive strength and elastic modulus through the indoor test, the samples were divided into two types including ring and axial direction specimen, and two mechanical indexes consisting of compressive strength and elastic modulus were measured for each type of samples.Test equipment was computer control electro-hydraulic servo universal testing machine (WAW -1000 system), as shown in Figure 2. Electronic gauge is used to measure the displacement.According to the Equation 1, we can calculate the elastic modulus: where： E c is the Elasticity modulus； △P is the Load increment； △L is the Deformation increment corresponding to △P； L is the Thickness of the sample.
The representative test procedure was shown in Figure 4.

Fig. 4 -Fatigue test procedure
Constant amplitude fatigue test was performed by the MTS loading fatigue testing machine, as shown in Figure 5 and Figure 6.This test was conducted at a room temperature, 23.5℃.A stress-control mode was applied.As shown in Figure 4, this method is characterized as: where, Smax1 = 4.12 kN, Smax2 = 7.1 kN.In the process of fatigue test, respectively in cyclic times to: 10000 times, 500000 times, 1 million times, 1.5 million times, 2 million times Equipment downtime due to a static load test.The static load test was carried out with five times of loading and unloading.

Compressive resistance of FRPM
Compressive resistance results were obtained by compressive test.Figure 7 shows the relationship between the displacement and the force of compression strength test.In Figure 7, it can be observed that, from the beginning of the displacement 2.660mm, the force specimen bearing at all measuring points are continuously increased.However, after reaching the peak force of 127.89kN, the curve of graph decreased significantly.Figure 8 shows the destruction sample after compressive strength test.

Fig. 7 -Typical curve of compressive strength testing Fig. 8 -Ring and axial sample destruction form
After determination of limit bearing capacity of FRPM, elastic modulus experiment was carried out with the maximum load is 50% of the ultimate compressive load.The circular and axial elastic modulus is shown in Table 3 and Table 4. From Table 3 and Table 4, we can conclude that the ring and axial elastic module of FRPM are 4.84GPa and 3.04GPa respectively.

Pipe stiffness (PS) of FRPM
Though parallel plate performance test under external load, the load -deformation data shown in Figure 9 were obtained.According to Equation 3, pipe stiffness (PS) is 2.3 MPa, and stiffness factor (SF) is 2.8kPa•m3.6 reflect deflection increment-load data of GH1 and GH2 after different cycles of fatigue load respectively.If the specimens have not damaged after 2 million times of fatigue loading, downtime for static load, we can obtain the ultimate bearing capacity as shown in Figure 10.Experiencing 2 million fatigue loads, FRPM produce the maximum crack width of 1.85 mm at failure stage, and directly maximum crack width is 3.87 mm did not experience fatigue load, as shown in Figure 11.The fatigue crack width is obviously smaller than the crack width without fatigue loading.Thus, due to the development of internal defects after the fatigue loading of FRPM, stiffness and bearing capacity of FRPM is falling, but due to the internal microstructure changing and restructuring, the failure form of FRPM trends from brittle to plastic (Farshad and Necola.,2004).

Fatigue performance of FRPM
Tab. 5 -Deflection increment-load data of GH1

CONCLUSION
In this paper, the mechanical performances of FRPM were investigated.The basic physical and mechanical properties of glass fiber reinforced plastic mortar pipe are analysed, and the technical requirements for the structural parameters, the basic mechanical indexes and durability characteristics of FRPM pipe are analysed.The following conclusions can be drawn.
Resin and quartz sand composite improve compression resistance of FRPM significantly, and the relationship between compression resistance property and loading is linear.The ring and axial elastic modulus is 4.84 , and 3.04 respectively.The influence of quartz sand on compressive resistance property is more significant than glass fiber and resin.
Though parallel plate performance test under external load, the load -deformation relationship were measured and pipe stiffness (PS) is obtained.
The long term performance of FRPM pipes after 2 million fatigue load is degraded up to 25% of the initial performance.Although the ultimate bearing capacity of glass fiber reinforced plastic sand pipe under fatigue loading decreases, the failure form has the trend from brittle to plasticity.
In summary, the culverts constructed with FRPM have a better mechanics and durability performance than those with the concrete.This experiment and the following research provide a reliable basis for the design of FRPM pipe in the application of highway culvert.A trial section of FRPM should be put into effect in the future in order to determine the applicability for different regions.

Fig. 1 -
Fig. 1 -Glass fiber productionResin is DM -196 unsaturated polyester resin produced with Shandong Texas plains new Dongming resin co.LTD.Its physical, chemical and mechanical properties are listed in Table1.

Fig. 2 -
Fig. 2 -Laboratory test systemAccording to the data of laboratory test, the compressive strength and elastic modulus can be obtained by the following calculation method.Roy and Tsai.( 2012 ) calculated the compressive strength of FRPM pipe by:

Table 5 and
Table