Evaluation of glass fiber reinforced polymer (GFRP) Performance on ...

International Conference on Civil Engineering, Architecture and Urban Cityscape

28 July 2016, Istanbul University, Turkey

Evaluation of glass fiber reinforced polymer (GFRP) Performance on compressive strength of semilightweight perlite concrete Hamid Moharami , Hassan Soheili , Pedram Farnood Ahmadi*

1. Associate professor Hamid Moharami, [email protected] 2. Master of structural engineering Hassan Soheili, [email protected] 3. Master of construction management Pedram Farnood Aamadi, [email protected]

Abstract In this days due to increasing importance of concrete consumption some researches have been done about lightweight or semi-lightweight concrete with perlite, in order to prevent from damages of seismic earthquake loads, execute specific architectural plans or implement some projects with materials which are compatible with environment, so research about the application of lightweight material (like perlite) is necessary. The purpose of this study is to present and discuss the experimental results about the impact of glass fiber (GFRP) on semi-lightweight concrete with crushable aggregate (perlite). In this paper the effect of GFRP jacket on the compressive strength of the cylindrical specimens has been checked. experiments were conducted on the 12 specimens, 3 samples were confined with two layers, 3 samples with a layer and the others with no jacket which contains (three specimens with perlite grains and others without perlite grain), it was found that Volumetric strain of semi-lightweight concrete with perlite particles compared to traditional concrete specimens is noticeable while lateral strain is low, so the impact of confinement with GFRP on compressive strength will not be significant. But with this confinement axial strain reach to plastic range, in this case the stability of the samples will be increased by jackets against the applied loads.

Key words: Concrete, Lightweight Perlite, Compressive Strength, Lateral Strain, GFRP

1. Introduction Perlite is an amorphous siliceous volcanic glass, derivative from the hydration of obsidian. Perlite particles consist about 2–5% water that known as internal water1, internal water of perlite evaporate from porous at the temperature of (870-1100 ºC)., at this temperature perlite particles expand up to about 15-20 times in comparison to its original volume2. this days due to many aspects like low heat conductivity and low unite Wight, lightweight property of concrete has been acceptable3. in some cases in order to diminish seismic loads of earthquake replacement of expanded perlite in Structural and non-structural application may be a solution for reducing damages4.the



price of EPA(expanded perlite aggregate) is lower than pumice, expanded clay and other lightweight materials almost , this is another advantage of perlite in comparison of others5. Many studies have been conducted to present energy saving with new production like bricks from lightweight materials which contain cement, perlite, clay, and another materials like amylum, gypsum, water glass6 or many research have forced on structural aspects of perlite which have explored new methods to know the impact of perlite grains on concrete7. On the other hand fiber-reinforced polymer FRP about the 15 years ago have been used as reinforcements (jackets), in another word engineering knowledge have been introduced this reinforcement technique in structural dimensions. One subdivision of this material is glass fiber reinforced polymer GFRP8. In this study we describe the effectiveness of GFRP on compressive strength of semi-lightweight concrete with perlite particles and was seen that repetition of this confinement with GFRP on strength is not significant, the improvement of compressive strength is about 5-20 percent. Difference between this study with another research which have been conducted before is repetition of confinement with three level specimens which are analyzed with strain and characteristics of perlite aggregate.

2. Methodology and techniques The concrete specimens are cylindrical with radiuses =15 and length of 30cm which have been fabricated according to the standard ASTM C192. Specimens have been cured at water in 14ºC for 28 days with same mix design (mix 1 is for specimens with perlite grains and mix 2 designed for common samples) which are shown in table 1. construction method was same, first aggregate were added according to their density (from low density to high) then aggregates with their water absorption mixed for 2 minutes , after that cement with water that have mixed separately were added to mixer then the admixture were mixed for 5 minutes. It should be mentioned we had 30 second rest time between this 5 minutes almost. Water absorption and unite weight of perlite are 0.23 and 71.14% respectively9. The 12 specimens were made, 3 samples were covered with two layers (Type3), three samples with a coating layer (Type2) and the others with no coating (Type1). The ratio of hardener and resin was 1:3 which was used as epoxy on glass fiber according to manufacturer recommendation, GFRPs composites were under pressure to be prepared for tensile test about 7 day, then the test was conducted on GFRP and was seen what tensile stress is tolerated by GFRP, although the tensile tests of glass fiber composites have been measured according to standard ASTM D303910 .the surface of samples was cleaned before wrapping GFRP on specimens then the wrapped specimens have been allowed to remain at room temperature (24-25ºC) for 7 days to obtain acceptable resistance. Two strain gages were set to measure axial and volumetric strain in order to track displacement and was seen the correlation between strain and compressive strength (Fig. 2) and three gages were set to measure lateral strain with 120º, the average of lateral strains were



calculated. The loading on specimens was continues with constant speed. We grind surfaces due to uniform distribution of pressure force, it should be noted that the load was not interrupted by the first failure, in this case we could able to see maximum strain. In this study fuller curves was used in order to achieve maximum aggregate density, in this case the seeds under sieve (#200) were eliminated. The maximum aggregate size which was used in the concrete is 9.51 mm then after determination of aggregate on each sieve 50% was replaced with perlite by volume. micro silica about 12% by weight of cement was used to reduce CA(OH)2 in cement paste and increase the mechanical properties of concrete, also the consumption of micro silica or all material which have been obtained from plant’s wastes can be in line with sustainable development .Super plasticizer based on polycarboxylate was used which is a new generation of concrete additives, one of advantage of this plasticizer can be increasing concrete flow with reduction of water consumption without any aggregate separation.

Figure 1: Materials Testing Machine for compressive test

Figure 2: Cylindrical Sample after Failure



Figure 3: The rupture of (GFRP) composites

Table 1: Mix Design Mix

Cement (Kg/m3)

Micro silica (Kg/m3)

Super plasticizer (Kg/m3)

W/C

limestone powder (Kg/m3)

Fine Corse Perlite Aggregate Aggregate (Kg/m3) (Kg/m3) (Kg/m3)

1

619.3

74

8.3

0.3

233.3

525.6

167.0

53.5

2

619.3

74

8.3

0.3

233.3

1083.5

199.5

---

Physical and chemical properties of cement which have been used are shown in table 2. Table 2: Cement Properties

Chemical Properties 27.5 SiO2 (%) 4.4 Fe2O3 (%) 6.7 Al2O3 (%) 49.6 CaO (%) 2.9 MgO (%) 2.5 SO3 (%) 0.6 K2O (%) 0.6 Na2O (%) 4.2 L.O.I (%)

Physical Properties Specific gravity (gr/cm3) 3.15 Specific Surface (cm2/gr) 3200 Setting time, initial (min) 185 Setting time, final (min) 305 Compressive Strength (Mpa) 2 days 17.4 3 days 24.5 7 days 33.2 28 days 45.8

3. Observation and discussion The observation of tests were carried out from the stress-strain test depend on stress-strain curves. Overall plastic strain of the specimens increased with using of GFRP jackets, which depends on tensile strength and efficiency of GFRP. First traditional specimens were tested and lateral-axial strain were recorded, after that the lateral- axial strains of concrete with perlite grains were measured. Strength with increasing cracks on specimens with perlite fell



down after maximum strength with severity. It was expected this undesirable behavior can be improved by creating confinement.After testing samples with jackets, as expected no significant change of compressive strength was seen but according to stress-strain curves more strain was endured after maximum stress, so the toughness of samples increased. 3-1- Mechanical behavior of the jackets (GFRP) GFRP composites were under pressure to achieve the desire tensile strength for 7 days. Forasmuch as this jackets have been used as confining layers, experimental measurement from GFRP was acceptable according to manufacturer recommendation are shown in table 3. Table3: Fiber Properties

Primary fiber direction Tensile Strength Tensile E-modulus Elongation Density Areal Weight Thickness

0⁰ Unidirectional 2300 Mpa 90 Gpa 3.9 % 2.54 gr/cm3 400 gr/m2 0.2 mm

3-2- The compressive strength test The compressive loading has been conducted with hydraulic press (SANTAM STM-1000) that the samples are located between two plates (Fig. 1). According to the test have been done on semi-lightweight cylindrical perlite concrete lateral strain is less than traditional samples (Fig. 4). While axial and volumetric strain is more 11, this is due to crushable perlite grains, with this figure we can consider that jacket in traditional concrete samples with mix design (1) can have good performance because of lateral strain which is more than lateral strain of semi-lightweight perlite concrete .Should be mentioned there is positive correlation between strain-confinement stress and compressive strength.

Figure 4: stress-lateral strain curve



The average stress-axial strain curves of three type specimens are shown in (Fig. 5). Axial strain and compressive strength are shown on the horizontal and vertical axis respectively. As can be seen compressive strength of specimens with a layer of GFRP confinement have been increased about 5% in comparison of type1 samples, while with two layer of GFRP confinement strength have been upgraded to 12% compared to a layer jacket, it can be noted confinement specimens compared to traditional samples is note affordable economically due to this observation, but strain increasing is noticeable, which represent the boost in plastic behavior.

Figure 5: stress-axial strain curves

Changes of lateral-axial strain are shown in (Fig. 6). As can be seen, with increasing of axial strain about 3000 µs, lateral strain have been begun to change. Confinement stress depended on strains on three-dimensional space according to HOOKs law, this means that almost no tension from lateral strain have been imposed on GFRP jackets up to 3000 µs. Note that near the failure lateral strain of sample with perlite grains increase with steep slope.

Figure 6: lateral-axial strain



One of the noticeable observation is the rupture of GFRP composites in semi-lightweight concrete with perlite particles that occurred from Top and bottom of samples due to stress concentration which caused by crushable perlite grains (Fig. 3) because of quick split of perlite grains in the tope-bottom of samples.

4. Conclusion In this research we focused on effectiveness of glass fiber reinforced polymer GFRP on semilight weight perlite concrete in three types, type1 were covered with two layers, type2 samples with a layer and the others with no jacket of GFRP. From the data obtained we can draw the following results: 1) Volumetric-axial strain of semi-lightweight perlite concrete is more than traditional concrete, while lateral strain is less than traditional concrete that were obtained from experiment. Should be noted that lateral strain have been measured from the middle of samples. 2) GFRP by creating confinement on traditional concrete is more effective than concrete which perlite grains are used in its components. This is due to fewer lateral strain of semilightweight perlite concrete compared to traditional concrete that caused by severe crush of perlite grains. It is remarkable that perlite grains are crushed by compaction before fracture of cement paste, due to this matter compressive strength is not improved by GFRP jackets significantly. 3) From the experimental observations the rupture of GFRP composites in this kind of concrete occurred from Top and bottom of samples due to stress concentration caused by nonuniform distribution of stress applied to GFRP in order to crushable perlite grains. 4) Almost no tension from lateral strain have been imposed on GFRP jackets up to 3000µs because of quick split of perlite grains in the tope-bottom of samples. 5) With using layer of GFRP as a confinement, strain increasing is noticeable which represent the boost in plastic behavior in another word the toughness of samples increased.

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