Experimental study on flexural behaviour of inorganic polymer concrete beams reinforced. with basalt rebar

Transcription

1 Experimental study on lexural behaviour o inorganic polymer concrete beams reinorced with basalt rebar Xiaochun Fan a, Mingzhong Zhang b,* a School o Civil Engineering and Architecture, Wuhan University o Technology, Wuhan , China b Advanced and Innovative Materials (AIM) Group, Department o Civil, Environmental and Geomatic Engineering, University College London, London WC1E 6BT, UK Abstract: Corrosion o reinorcing steel and the severe degradation o mechanical properties with temperature and ire conditions are the weakest points o steel-reinorced concrete structures and ibre reinorced polymer (FRP) system, respectively. In this paper, the basalt reinorced inorganic polymer concrete (IPC) beam which combines the speciic characteristics o IPC and basalt reinorcement such as good corrosion resistance and ire resistance was proposed. The inorganic polymer binder was made o ly ash, ground granulated blast-urnace slag and alkaline activating solution. The mechanical properties o IPC were measured and compared with those o reerence ordinary Portland cement (OPC) concrete. The lexural behaviour o basalt reinorced IPC beam was investigated and compared to control steel-reinorced OPC concrete beam. The measured ultimate lexural capacity o basalt reinorced IPC beam was compared with the predicted value obtained using the guidelines or FRP-reinorced OPC concrete beam. Results indicated that the elastic modulus o IPC was very close to OPC, while the compressive strength and lexural strength o IPC were around 80% o those o OPC. The IPC beam reinorced with basalt rebar exhibited a two-stage load-midspan delection response that was dierent rom control concrete beam due to the dierent mechanical properties o basalt and steel rebars. The crack patterns in basalt reinorced IPC beam were ound to be similar to control beam, however, the maximum crack width o basalt reinorced beam was approximately 2 times that o control beam. The guidelines or FRP-reinorced concrete beam were adequate or predicting the lexural strength o basalt reinorced IPC beams. Keywords: A. Polymer (textile) ibre; B. Mechanical properties; B. Microstructures; B. Strength; Geopolymers 1. Introduction Concrete is the most widely used man-made material in the world. The sustainability has become an increasingly important characteristic or concrete inrastructure, as the manuacture o Portland cement accounts or a signiicant proportion o raw material consumption and nearly 7% o global CO2 emissions [1]. Inorganic polymers, also called geopolymers, are conventionally produced by synthesizing pozzolanic compounds or aluminosilicate source materials with highly alkaline hydroxide and/or alkaline silicate. Over the last two decades, inorganic polymer concretes (IPC) have emerged as novel engineering materials with the potential to become a substantial element in an environmentally sustainable construction and building products industry [2,3]. Industrial by-products, such as ly ash (FA) and ground granulated blast-urnace slag (GGBFS) are commonly used as the source o IPC due to the low cost and wide availability o these materials. It has been shown that compared to ordinary Portland cement (OPC) concrete, IPC has many attractive properties, such as good ire resistance, good resistance to chloride penetration, acid attack, reeze-thaw cycles, etc. and can help reduce embodied energy and carbon ootprint by up to 80% [4-6]. * Corresponding author. Tel: +44 (0) address: mingzhong.zhang@ucl.ac.uk (M. Zhang) 1

2 Corrosion o reinorcing steel is the leading cause o deterioration o reinorced concrete (RC) structures. In recent years, an increasing attention has been paid towards the replacement o traditional steel bars with ibre reinorced polymer (FRP) as internal concrete reinorcement to solve the problem o rebar corrosion in RC structures. The most commonly used FRP reinorcing bars or concrete structures are made rom glass (GFRP), carbon (CFRP) and aramid (AFRP). However, the perormance o GRRP and AFRP would be signiicantly aected by the alkaline environment within concrete [7]. CFRP reinorcing bars are too expensive to be implemented in normal civil engineering structures [8]. A new type o reinorcing bars made rom basalt ibre (BFRP) has recently gathered attention as an alternative to other FRPs because o its cost eectiveness, ease o manuacture, high temperature resistance, reeze-thaw perormance and good resistance to vibration and impact loading, corrosion and acids [9-12]. In addition, BFRP has better durability in alkaline conditions compared to GFRP [13]. Because o these outstanding characteristics, BFRP ibres have been used either as internal reinorcement or new concrete structures or as external strengthening or existing concrete structures [14]. Over the past ew years, many eorts have been made to investigate the mechanical behaviour o steel- and FRP-reinorced inorganic polymer (geopolymer) concrete, and BFRP reinorced concrete in order to oer a solid theoretical basis or the use o geopolymer concrete and BFRP in concrete structures. With respect to the interaction between reinorcement and geopolymer concrete, Songpiriyakij et al. [15] experimentally studied the bonding strength between the embedded steel rebar and substrate geopolymer concrete made o ly ash, rice husk and bark ash and silica ume, and showed that the bond strength o rebar and geopolymer was slightly higher than that o control OPC concrete ( times). Sarker [16] used the beam-end test method to measure the bond strength o low calcium ly ash-based geopolymer concrete with deormed steel rebars and compared with the equivalent OPC concrete system. The geopolymer concrete was observed to have higher bond strength than OPC concrete, which was attributed to the higher splitting tensile strength o geopolymer concrete relative to OPC concrete o the same compressive strength. Castel and Foster [17] carried out the standard RILEM pull-out test to investigate the bond between geopolymer and deormed and smooth steel rebars. The used geopolymer binder was composed o 85.2% o low calcium ly ash and 14.8% o GGBFS. The 28-day bond strength and the overall bond stress-slip behaviour o the geopolymer concrete were ound to be similar to those o OPC concrete. Menna et al. [18] studied the lexural behaviour o reinorced geopolymer concrete beams strengthened with high strength steel cord and CFRP to evaluate the eectiveness o strengthening. Results indicated that geopolymer matrix provided a very good adhesion to concrete substrate and to reinorcement. With respect to BFRP reinorced concrete, Tomlinson and Fam [19] evaluated the lexural and shear perormances o concrete beams reinorced with BFRP rebar and stirrups, and ound that the beams with BFRP had signiicantly higher strengths than control steel-reinorced counterparts with the same reinorcement ratio. Ge et al. [20] carried out a series o experiments including tensile test, standard pull-out test o BFRP bars and static lexural test on hybrid concrete beams reinorced with BFRP bars and steel bars, and observed that the bond strength between BFRP rebar and concrete is similar to that o steel rebar and concrete. These previous studies have shown that the systems o steel rebar and geopolymer concrete, and BFRP rebar and OPC concrete have a similar bond behaviour and mechanical perormance to control steel-reinorced OPC concrete, which leads to the idea in this study o combing BFRP rebar and IPC (geopolymer concrete) in a composite system to improve the durability and sustainability o concrete structures. According to authors knowledge, the mechanical behaviour o IPC beam reinorced with BFRP reinorcement has not been extensively investigated elsewhere. In this work, the mechanical properties including compressive strength, lexural strength and elastic modulus o IPC are studied and compared to reerence OPC concrete. The inorganic polymer binder is composed o both ly ash and GGBFS. Aterwards, the lexural behaviour o IPC beam reinorced with BFRP rebar in terms o ultimate lexural strength and cracking patterns and development is investigated in detail and compared with that o control steel-reinorced OPC concrete 2

3 beam to understand the ailure mechanisms o BFRP reinorced IPC beam. A comparison between the theoretical previsions o the lexural behaviour o the tested beams calculated according to the recommendations or FRP-reinorced OPC concrete beam and experimental data or BFRP reinorced IPC beam was carried out to estimate whether the guidelines or FRP-reinorced concrete system are adequate or predicting the lexural strength o IPC beams with BFRP reinorcement. 2. Materials and Methods 2.1 Inorganic polymer concrete The inorganic polymer concrete used or experiments was made o a mixture o inorganic polymer binder composed o FA, GGBFS and alkaline activating solution, ine and coarse aggregates. FA and GGBFS used in this study were produced by Qingshan Power Station and Wuhan Iron and Steel Company Limited in Wuhan in Hubei Province o China, respectively. The chemical compositions o FA and GGBFS are given in Table 1. The scanning electron microscope (SEM) images o FA and GGBFS morphology are shown in Fig. 1. The alkaline activating solution was obtained by dissolving solid sodium hydroxide (NaOH) into sodium silicate (Na2SiO3) solution with the Na2SiO3/NaOH ratio o Fiteen series o inorganic polymer binder were prepared and tested in order to determine the optimal composition o the mixture accounting or both early-age properties and durability, which was presented in detail in a previous work [11]. The medium-sized sand with ineness modulus o 2.72 was used as ine aggregate. The coarse aggregate was 13 mm nominal size crushed stone. The particle size distributions o ine and coarse aggregates are presented in Tables 2 and 3, respectively. The mix proportion o raw materials in inorganic polymer concrete is given in Table 4. The ine and coarse aggregates were irstly mixed or 2 min. Aterwards, the inorganic polymer binder was mixed together with ine and coarse aggregates or about 3 min ollowed by a gradual addition o ree water. The inorganic polymer concrete was then placed in the moulds and compacted using a poker vibrator. The concrete specimens were prepared or compressive and lexural tests. Table 1 Chemical compositions o ly ash and GGBFS (wt.%) Table 2 Particle size distribution o ine aggregate in inorganic polymer concrete Table 3 Particle size distribution o coarse aggregate in inorganic polymer concrete Table 4 Mix proportion o raw materials in inorganic polymer concrete (kg/m 3 ) Fig. 1 SEM images: (a) ly ash; (b) ground granulated blast-urnace slag 2.2 Basalt rebar Fig. 2 shows the used BFRP reinorcing bar or inorganic polymer concrete beams. It was supplied by Shenzhen Academy o Aerospace Technology. According to the manuacturer the Young s modulus, yield strength and ultimate tensile strength o BFRP rebar are 50 GPa, 600 MPa and MPa, respectively. In order to study the mechanical behaviour o IPC beams reinorced with basalt rebar, it is necessary to examine the stress-strain relationship o basalt rebar. In this work, the uniaxial tensile tests were perormed on ive basalt rebars using a servo-hydraulic testing machine with a capacity o 600 kn according to GB/T [21]. The experimental setup or uniaxial tensile tests is shown in Fig. 3. Load was applied to the rebar through displacement control at a rate o 0.08 mm/s until ailure. The stress-strain relationship o basalt rebars under uniaxial tension is shown in Fig. 4. For each stress-strain curve, it can be seen that there exists an initial elastic region ollowed by a small hardening region until ultimate ailure, although the yielding point is not obvious. The yield strength o these ive basalt rebars is ound to be 659 MPa, 549 MPa, 660 MPa, 657 MPa and 600 MPa, respectively. The tensile strength o them is 678 MPa, 569 MPa, 681 MPa, 673 MPa and 610 MPa, respectively. 3

4 Fig. 2 Basalt FRP bar used or inorganic polymer concrete beams Fig. 3 Setup or uniaxial tensile test o basalt FRP bar Fig. 4 Stress-strain relationship o basalt FRP bars 2.3 Testing program Uniaxial compressive strength was measured at 3, 7 and 28 days on 150 mm concrete cube based on GB/T [22]. The modulus o elasticity and lexural strength were measured at 28 days on rectangular concrete prism ( mm 3 and mm 3, respectively) according to GB/T [22] and JTGE [23], respectively. To investigate the lexural behaviour o reinorced concrete system, two inorganic polymer concrete beams reinorced with BFRP rebar, reerred to as IPCB1 and IPCB2, with size o 120 mm width 200 mm height 2000 mm length were prepared and cast or 28 days. For the purpose o comparison, two ordinary Portland concrete beams o the same size reinorced with steel rebars with a diameter o 14 mm and nominal yield strength o 360 MPa were cast and considered as control concrete beams, which are hereater named as OPCB1 and OPCB2. The diameter o BFRP rebar used in this work is determined according to the method o equal-strength substitution. As such, steel rebar is replaced with BFRP rebar, while the latter has the same strength, i.e., d 1 2 y,1 = d 2 2 y,2, in which d 1 and d 2 are the diameters o steel and BFRP rebars, and y,1 and y,2 denote their nominal yield strength, respectively. The diameter o BFRP rebar obtained using the method o equal-strength substitution is 10.8 mm. However, the rebar in 10.8 mm diameter is not available in the speciications or rebar. Thereore, the 12 mm diameter BFRP rebar was chosen and used or IPCB1 and IPCB2. It should be noted that this would result in an approximately 18% greater contribution o reinorcement to IPC beams than that to OPC beams. Fig. 5 depicts the geometric and loading details o the beam specimens. All the beams were tested as simply supported members, over a clear span o 1.9 m and loaded up to ailure under a our-point bending coniguration with a constant moment region o 0.6 m across the midspan according to GB/T [24]. The load was applied through a 5000 kn hydraulic actuator. The entire test and measurement was carried out under displacement control. The crosshead displacement rate was 0.5 mm/min. During the tests, three vertical linear displacement gauges were used to measure and determine the average midspan delection o the beam at each loading stage. Thus, the corresponding orcedelection curve can be obtained, which is presented in the ollowing sections. Five horizontal linear strain gauges were placed on one side o the specimen to record displacements across the midspan at dierent depths. Displacements at supports were measured by linear variable dierential transormer (LVDT). One strain gauge was bonded to each rebar at its midspan to record the strain o rebar under loading. An automatic data acquisition system was utilized to monitor loading. The IPCB1 beam specimen beore and ater loading is shown in Fig. 6. Fig. 5 Four-point bending coniguration or basalt reinorced inorganic polymer concrete beams Fig. 6 Basalt reinorced inorganic polymer concrete beam specimen: (a) beore loading; (b) ater loading 3. Experimental results and discussion 3.1 Mechanical characteristics Fig. 7 shows the time evolution o compressive strength o OPC concrete and IPC. Three specimens were used to measure the compressive strength. As expected, the compressive strength goes up with increasing curing age. For both OPC concrete and IPC, the compressive strength at 3 days is 48% o 4

5 that at 28 days, and the 7-day compressive strength is around 66% o 28-day compressive strength. A very similar trend in the increase in compressive strength can be observed or OPC concrete and IPC, although the compressive strength o IPC at each curing age is approximately 80% o that o OPC concrete. Table 5 shows the lexural strength and elastic modulus o OPC concrete and IPC, which were measured using three and six specimens, respectively. All measures were perormed on specimens ater curing o 28 days. It can be seen that the lexural strength o IPC is about 80% o that o OPC concrete, while the elastic moduli o them are very close. Fig. 7 Time evolution o compressive strength o concrete Table 5 Flexural strength and elastic modulus o concrete 3.2 Load-delection response at midspan Fig. 8 depicts the measured load-delection response at midspan or the tested beams. Values o loads and midspan delections corresponding to the irst cracking, the yielding o reinorcing basalt/steel rebars and the inal bending ailure o the beam are summarized in Table 6. As seen in Fig. 8, two control beams OPCB1 and OPCB2 show a very consistent three-stage load-delection response. Taking OPCB1 as an example, concrete and internal steel reinorcing bar initially work together to resist deormation and only a small delection can be observed. In this stage, the slope o loaddelection curve is large, which relects the high stiness o the system. Once the load reaches around 24 kn at a midspan delection o 1.5 mm, the irst cracking o beam appears and a loss o stiness occurs due to the tensile ailure o concrete within the maximum bending moment region. As a consequence, the slope o load-delection curve starts to decrease and the tensile steel reinorcing bar has to bear the load alone. At a load value o 96 kn, another decrease in the slope o load-delection curve starts to happen, which can be ascribed to the yielding o the tensile steel rebar corresponding to 10.5 mm o midspan delection. Aterwards, there exists a rapid increase in delection rom 10.5 mm to 22 mm, whereas the load value does not change much, just increasing by 8 kn. In the meantime, the lexural cracks in terms o both number and size show a signiicant increase with increasing deormation until the collapse o the beam as a result o concrete crushing in the compression zone. The ultimate load and midspan delection are ound to be 104 kn and 15 mm, respectively. The control beam OPCB2 exhibits a very similar trend in terms o load-delection response with OPCB1. The irst cracking happens at a load value o 28 kn ollowed by a loss o stiness until the yielding o reinorcing steel bar occurs at a load o 112 kn, which is a little bit higher than yielding load o OPCB1. Ater yielding, the stiness o the beam decreases and the slope o orce-delection curve is the same as that o OPCB1, whereas the ultimate load is 116 kn occurring at a midspan delection o 15.7 mm. Unlike the control concrete beams, the load-midspan delection curves o IPC beams only consist o two parts. The irst part is very similar to that observed in control beams and the irst cracking loads are close to those o control beams, ollowed by a signiicant loss o stiness. Compared to control beams, the slopes o load-delection curves o IPC beams in the second part are much lower, which can be associated with the lower elastic modulus o BFRP rebar in IPC beams than steel reinorcing bar in control beams and the lower volume raction o reinorcement in IPC beams than OPC beams, as the elastic modulus o IPC is almost the same as that o OPC concrete. In addition, there does not exist an obvious yielding load prior to inal ailure, which is dierent with that detected in control beams. This can be attributed to the act that the stress-strain curve o BFRP rebar in IPC beams is almost linear elastic, since the yield point is not obvious (as seen in Fig. 4) and the hardening region prior to ultimate ailure is very small. This is dierent with that o steel rebar in OPC concrete beams. As a result, there shows a steady increase in midspan delection until the ultimate deormation is reached. The ultimate loads o IPCB1 and IPCB2 are ound to be a little bit lower in comparison to control OPC beams, which may be mainly due to the lower lexural and compressive strength o 5

6 IPC as compared to OPC concrete, as presented above. However, the ultimate delections o IPC beams are about 2.5 times o those o control beams. Fig. 8 Load-delection response at midspan or concrete beams Table 6 Load and midspan delection o concrete beams 3.3 Load-strain response o concrete As the strain at dierent positions along the depth play a crucial role in the determination o load capacity o reinorced concrete beams under lexure, it is essential to measure these strains. Herein, the strains in the constant moment region o beams were obtained by using ive horizontal linear strain gauges at depths o d = 20, 40, 100, 160 and 180 mm rom the bottom surace at midspan, as shown in Fig. 5. The measured concrete strains o the test beams under loads o 20, 40, 60 and 80 kn are shown in Fig. 9. It can be seen that or each beam, the strains at dierent depths under various loading values ollow a similar trend that the upper part o the beam is in compression while the lower part is in tension. There exists a layer above the centre o beam that is subjected to neither tensile nor compressive train, i.e., the so-called neutral layer. As expected, the strains along the depth rom the top to the bottom seem to be linear regardless o the level o loading, which implies that the beam cross sections remain plane during bending and the bond between concrete and reinorcing bar is perect. All these indicate that concrete and reinorcing bar are able to work together very well to bear loads and thus the plane cross-section assumption can be used to estimate the load capacity o the beams subjected to bending in this study. Fig. 9 Strains o concrete at dierent positions along the height o beams under various loads: (a) OPCB1; (b) OPCB2; (c) IPCB1 and (d) IPCB2 3.4 Load-strain response o rebar Figs. 10 and 11 show the load-strain response o reinorcing bars in IPC beam and control beam, respectively. The strains were measured at ive dierent locations: the midspan and our points which are 10 cm and 20 cm ar rom the supporting points, as shown in Fig. 5. It can be seen rom Fig. 8 that the change in strain o BFRP rebar against load at midspan ollows a two-stage process: a short linear rise and a gradual increase. In the irst stage, no cracking occurs in the beam and BFRP rebar and IPC work together to bear the tensile orces. As a result, the strain o BFRP rebar goes up linearly with the load. In the beams, the cross-sectional area o IPC in the tensile region is much larger than that o BFRP rebar, while their elastic moduli are o the same order o magnitude (the elastic moduli o IPC and BFRP rebar are 32.1 GPa and 50 GPa, respectively), which results in a much sharper increase in the strain o BFRP rebar compared to that o IPC, as seen rom the slopes o the curves in Figs. 8 and 10. Taking IPCB1 as an example, there is an increase in the strain o BFRP rebar at midspan rom 0 to 648 mm when the lexural loading is increased rom 0 to 20 kn, while the corresponding strain o IPC at midspan only increases rom 0 to 206 mm. As the load increases, the stress o concrete in the tensile region goes up and subsequently reaches the tensile strength o concrete, which gradually leads to cracking at the edge o the tensile region and stress redistribution in this region. In the second stage, the concrete cracking in the tensile region grows urther and the reinorcing bars start to bear the tensile orces alone, which results in a gradual linear increase in the strain o reinorcing bars, in particular or the BFRP rebar whose elastic modulus is around 1/4 o steel rebar exhibiting a much larger deormation compared to steel rebar. The strain o BFRP rebar in IPCB is observed to be approximately our times that o steel rebar in OPCB due to the relatively lower elastic modulus, as seen in Figs. 10 and 11 that the slope o load-strain curve or IPCB is smaller than that or OPCB. This implies that at the same loading level the delection o IPCB is larger than that o OPCB and the corresponding crack width is larger relative to OPCB leading to an even more obvious stress redistribution in the beam. In addition, at midspan the steel 6

7 rebar behaves dierently rom BFRP rebar that the load-strain curve tends to be relatively horizontal beore reaching the ultimate load, which is attributed to the dierence in mechanical properties o steel and BFRP rebars. As shown in Figs. 10 and 11 the load-strain curves or reinorcing bars at endpoints with distances o 10 and 20 cm rom the supporting points consists o three stages, which is similar to the case o midspan point. The end o the irst linear stage corresponds to the occurrence o concrete cracking and the initiation o stress distribution in concrete beams. The stress redistribution o reinorcing bars at endpoints occurs at load values o around 60 kn. This is much later than the midspan point, where the stress redistribution happens at a load o approximately 20 kn. Additionally, the strain o reinorcing bars at endpoints is lower than that at midspan point till the inal ailure o concrete beams, which indicates that prior to inal ailure there exists a strong bond between reinorcing bars and concrete and thus they work well together to bear the orces. Fig. 10 Load-strain curve o basalt reinorcement in IPCB1 Fig. 11 Load-strain curve o steel reinorcement in OPCB1 3.5 Crack patterns Fig. 12 shows the inal crack patterns o reinorced concrete beams, IPCB1 and OPCB1, under lexural loading. The development o cracking in inorganic polymer concrete beam and control concrete beam during loading is depicted in detail in Figs. 13 and 14. The numbers in igures denote the corresponding load values to crack growth. For control concrete beams, the irst cracking occurs within the constant moment zone at load values o 24 kn and 28 kn, respectively. As load increases, more and more cracks orm and spread outward rom midspan into the shear spans. At a load o around 70 kn, the inclined shear cracks occur. With urther increase in load, these cracks propagate towards the compression zone o the beam near the loading point. When the imposed load on the beams approaches the ultimate load capacity, cracks spread very rapidly leading to a smaller concrete compression zone due to an upward shit o the neutral axis, which results in the crush o concrete and inal ailure o concrete beams in compression. The basalt reinorced inorganic polymer concrete beams behave similarly to control concrete beams. The irst cracks are noticed in the constant moment regions on IPCB1 and IPCB2 when the applied load reaches about 22 kn and 24 kn, respectively. As the load increases, the existing cracks develop and some new lexural cracks are ormed in the region between load and support. Upon urther increasing the applied load, the majority o the lexural cracks develops vertically and ater that inclined lexure-shear cracks begin to appear at a load o around 60 kn, which is consistent with the results o load-strain response o basalt rebar in IPC beams as shown in Fig. 10. As the load increases urther, the inclined cracks progress in terms o length and width both upward toward the applied load point and horizontally along the longitudinal BFRP rebar towards the support. As a result, the eective area o concrete section in the compressive region is reduced. Ater additional application o load, the beams eventually ail in compression. Although the cracking loads o control concrete beams are higher than those o basalt reinorced IPC beams, however, the average delection at the irst crack ormation or control beams is ound to be 1.9 mm that is much lower than 3.9 mm or IPC beams. In addition, the number o cracks at ailure or IPC beams seems to be larger than that or control beams. All these indicate that the basalt reinorced IPC beams have higher resistance to racture than control concrete beams. Fig. 12 Crack patterns o concrete beams under lexural loading: (a) IPCB1 and (b) OPCB1 Fig. 13 Crack development in OPCB2 under lexural loading 7

8 Fig. 14 Crack development in IPCB2 under lexural loading 3.6 Comparison with theoretical previsions Herein, a theoretical prevision o the mechanical behaviour o the tested basalt reinorced IPC beams is computed and compared with the experimental results in terms o predicted lexural capacity and ailure mode. Since the perormance o BFRP rebar is dierent rom reinorcing steel bar, the guidelines or steel reinorced concrete beam may not be applicable to basalt reinorced IPC beam. In this work, the lexural capacity o IPC beams is calculated according to the recommendations o the ACI 440.1R-15 [25] guidelines or the FRP-reinorced concrete beam in conjunction with the ollowing considerations and assumptions: (1) The beam cross sections remain plane during the whole lexural loading process. (2) The strength development o inorganic polymer concrete is similar with ordinary Portland cement concrete, which is described as the ollowing equation. The elastic moduli o these two types o concrete are close to each other, as seen in Table 5. n c c c 1 1 c 0 0 (1) c c 0 c cu with ( 50) 10 0 cu, k cu ( 50) 10 cu, k 5 1 n 2 ( cu, k 50) 60 where σ c and ε c denote the concrete stress and strain, respectively, ε 0 and ε cu represent the concrete strain corresponding to the concrete stress values o c and cu,k, respectively. (3) As seen in Fig. 4, the stress-strain curve o basalt rebar is almost linear elastic. For simplicity sake, it can be expressed by E (2) where σ, E and ε stand or the stress, elastic modulus and strain o basalt rebar, respectively. (4) As the tensile strength o inorganic polymer concrete is much smaller than that o basalt rebar, thereore, this tensile strength can be ignored and the basalt reinorcement is assumed to resist the tensile stress alone. (5) There exists a good bonding between reinorcing basalt and inorganic polymer concrete and the debonding ailure o the reinorcing system would not occur prior to the ultimate lexural load. In act, this assumption can be veriied using the measured load-strain response o basalt rebar at midspan, as shown in Fig. 10. For a basalt reinorced IPC beam, the balanced ailure occurs when the compressive and tensile zones reach yielding at the same imposed load on the beam, and hence the concrete will crush and tensile basalt reinorcement will yield at the same time. In such case, the height o equivalent rectangular stress over the height o the beam is deined as the balanced relative compressive height, ξ y. A schematic diagram o the stress distribution over the beam s cross section or balanced ailure condition is given in Fig. 15. Based on the balance and compatibility conditions, the parameters in Fig. 15 can be obtained as ollows: 1 cu x 1xc h0 (3) cu y bx A bh (4) 1 c y b 0 y 8

9 b 1 y 1 E cu (5) where x is the balanced compression height, x c is the real balanced compressive height, α 1 and β 1 are the coeicients o equivalent rectangular stress and height o concrete, ε cu denotes the ultimate compressive strain ( ε cu = ), y and ε y stand or the nominal yield strength and corresponding yield strain o BFRP rebar, b and h 0 are the width and eective height o beam s cross-section, and ρ b represents the balanced reinorcement ratio o BFRP rebar, which can be expressed as c cu b 11 (6) y cu y The real tensile stress ( ) o the basalt reinorcement when the crushing o inorganic polymer concrete happens can be calculated according to the ollowing balance equations: 1 cbx A x (7) M cbx( h0 ) 2 h0 xc E cu (8) xc Combining Eqs. (7) and (8), we can get 2 E cu 11E c cu 0.5E cu u 4 (9) where ρ is the reinorcement ratio o BFRP rebar in the beam, which is equal to the ratio between the cross-sectional area o BFRP rebar and the cross-sectional area o beam, i.e., A /(bh 0 ). The ultimate lexural capacity o the basalt reinorced IPC beam, M u, can be obtained as: x Mu A ( h0 ) (10) 2 with A x 1 b (11) c According to Eq. (6), the theoretical value o balanced reinorcement ratio or basalt reinorced IPC beam is 0.48%. While the applied reinorcement ratio in this work is 0.95%, which is about 2 times the balanced reinorcement ratio. This implies that the tested basalt reinorced IPC beams would ail in compression, which is consistent with the experimental indings in terms o stress-strain curve and crack patterns. In addition, the applied reinorcement ratio is less than 3 times the balanced reinorcement ratio, which indicates that the tested basalt reinorced IPC beams can be considered as balanced-reinorced beams, as a reinorced concrete beam with a reinorcement ratio varying rom 1.5 times to 3 times the balanced reinorcement ratio is generally deined as a balanced-reinorced beam. Furthermore, the theoretical ultimate lexural capacity o basalt reinorced IPC beam calculated using Eq. (10) is 87 kn, which is very close to the mean value o measured lexural capacity o the tested beams, i.e. 94 kn. The good agreement between the theoretical prediction and experimental data conirms that the design codes or FRP-reinorced concrete beam are applicable to inorganic polymer concrete beam reinorced with basalt rebar. Fig. 15 Stress distribution over the beam s cross-section or balanced ailure condition 9

10 4. Conclusions The lexural behaviour o inorganic polymer concrete (IPC) beams reinorced with basalt rebar was tested and compared with control steel-reinorced ordinary Portland concrete (OPC) beams in this study. A comparison o the experimental results with theoretical prevision o the mechanical behaviour o the tested beams according to the recommendations or the FRP-reinorced concrete beam was carried out. The ollowing main conclusions can be drawn rom the present study: The compressive strength o IPC with the proposed mix design at various curing age was a little bit lower than control OPC. The basalt reinorced IPC beam behaved dierently rom control steel-reinorced concrete beam in terms o load-delection response due to the dierence in mechanical behaviour between IPC and OPC, and basalt and steel reinorcement. For control beam, there existed an obvious yielding stage, while the load-delection curve o IPC beam reinorced with basalt bar did not exhibit such stage. At the same applied load, the delection o basalt reinorced IPC beam was around 4 times that o control beam. The development o cracking and crack patterns in basalt reinorced IPC beam under lexural loading was similar to control steel-reinorced OPC beam, while the maximum crack width o basalt reinorced beam was approximately 2 times that o control beam. Additionally, although the cracking load o control beam was larger than that o basalt reinorced beam, however, the corresponding crack delection o basalt reinorced beam was around one time larger than that o control beam. The theoretical ultimate lexural capacity o basalt reinorced IPC beams calculated using the recommendations or the FRP-reinorced concrete beam was close to the measured ultimate lexural strength o the tested beams, which indicates that such recommendations are adequate or predicting the lexural strength o IPC beams reinorced with basalt reinorcement. In addition, the tested basalt reinorced IPC beams can be regarded as balanced-reinorcement beams. Acknowledgements The authors grateully acknowledge the inancial support rom Wuhan University o Technology through grant number The authors are grateul to all reviewers or their constructive comments and suggestions. Reerences [1] Juenger MCG, Siddique R. Recent advances in understanding the role o supplementary cementitious materials in concrete. Cem Concr Res 2015;78: [2] Duxson P, Fernández-Jiménez A, Provis JL, Lukey GC, Palomo A, Van Deventer JSJ. Geopolymer technology: the current state o the art. J Mater Sci 2007;42(9): [3] Provis JL, Van Deventer JSJ. Geopolymers: structures, processing, properties, and industrial applications, Woodhead Publishing Limited, Cambridge; [4] Bakharev T. Resistance o geopolymer materials to acid attack. Cem Concr Res 2005;35(4): [5] Hu SG, Wang HX, Zhang GZ, Ding QJ. Bonding and abrasion resistance o geopolymeric repair material made with steel slag. Cem Concr Comp 2008;30(3): [6] Soi M, van Deventer JSJ, Mendis PA. Engineering properties o inorganic polymer concretes (IPCs). Cem Concr Res 2007;37: [7] Sim K, Park C, Moon DY. Characteristics o basalt iber as a strengthening material or concrete structures. Compos Part B 2005;36(6-7): [8] Herwig A, Motavalli M. Axial behavior o square reinorced concrete columns strengthened with lightweight concrete elements and unbonded GFRP wrapping. J Compos Constr 2012;16(6):

11 [9] Pavlovski D, Mislavsky B, Antonov A. CNG cylinder manuacturers test basalt ibre. Rein Plast 2007;51(4):36-7, 39. [10] Shi J, Zhu H, Wu Z, Wu G. Durability o BFRP and hybrid FRP sheets under reeze-thaw cycling. Adv Mater Res 2011; : [11] Liu H, Lu Z, Peng Z. Test research on prestressed beam o inorganic polymer concrete. Mater Struct 2015;48: [12] Li W, Xu J. Mechanical properties o basalt iber reinorced geopolymeric concrete under impact loading. Mater Sci Eng A 2009;505: [13] Lee JJ, Song J, Kim H. (2014) Chemical stability o basalt iber in alkaline solution. Fibres Polym 2014;15(11): [14] Wei B, Cao H, Song S. Environmental resistance and mechanical perormance o basalt and glass ibers. Mater Sci Eng A 2010;527(18-19): [15] Songpiriyakij S, Pulngern T, Pungpremtrakul P, Jaturapitakkul C. Anchorage o steel bars in concrete by geopolymer paste. Mater Des 2011;32(5): [16] Sarker PK. Bond strength o reinorcing steel embedded in ly ash-based geopolymer concrete, Mater Struct 2001;44(5): [17] Castel A, Foster SJ. Bond strength between blended slag and Class F ly ash geopolymer concrete with steel reinorcement. Cem Concr Res 2015;72: [18] Menna G, Asprone D, Ferone C, Colangelo F, Balsamo A, Prota A, Cioi R, Manredi G. Use o geopolymers or composite external reinorcement o RC members. Compos Part B 2013;45: [19] Tomlinson D, Fam A. Perormance o concrete beams reinorced with basalt FRP or lexure and shear. J Compos Constr 2015;19(2): [20] Ge W, Zhang J, Cao D, Tu Y. Flexural behaviors o hybrid concrete beams reinorced with BFRP bars and steel bars. Constr Build Mater 2015;87: [21] Standardization Administration o China. Steel strand or prestressed concrete - GB/T Beijing, China; [22] Ministry o Construction o the People s Republic o China. Standard or test method o mechanical properties on ordinary concrete - GB/T Beijing, China; [23] Ministry o Transport o the People s Republic o China. Test methods o cement and concrete or highway engineering - JTGE Beijing, China; [24] Ministry o Housing and Urban-Rural Development o the People s Republic o China. Standard or test method o concrete structures - GB/T Beijing, China; [25] American Concrete Institute (ACI) Committee 440. Guide or the design and construction o structural concrete reinorced with iber-reinorced polymer (FRP) bars - ACI 440.1R-15. Farmington Hills, MI. ACI;

12 Figures (a) (b) Fig. 1 SEM images: (a) ly ash; (b) ground granulated blast-urnace slag Fig. 2 Basalt FRP bar used or inorganic polymer concrete beams 12

13 Fig. 3 Setup or uniaxial tensile test o basalt FRP bar Fig. 4 Stress-strain relationship o basalt FRP bars 13

14 Fig. 5 Four-point bending coniguration or basalt reinorced inorganic polymer concrete beams (a) (b) Fig. 6 Basalt reinorced inorganic polymer concrete beam specimen: (a) beore loading; (b) ater loading 14

15 Fig. 7 Time evolution o compressive strength o concrete Fig. 8 Load-delection response at midspan or concrete beams 15

16 (a) (b) (c) 16

17 (d) Fig. 9 Strains o concrete at dierent positions along the height o beams under various loads: (a) OPCB1; (b) OPCB2; (c) IPCB1 and (d) IPCB2 Fig. 10 Load-strain curve o basalt reinorcement in IPCB1 17

18 Fig. 11 Load-strain curve o steel reinorcement in OPCB1 (a) (b) Fig. 12 Crack patterns o concrete beams under lexural loading: (a) IPCB1 and (b) OPCB1 Fig. 13 Crack development in OPCB2 under lexural loading 18

19 Fig. 14 Crack development in IPCB2 under lexural loading Fig. 15 Stress distribution over the beam s cross-section or balanced ailure condition 19

20 Tables Table 1 Chemical compositions o ly ash and GGBFS (wt.%) Oxide FA GGBFS Silicon dioxide, SiO Aluminium oxide, Al2O Iron oxide, Fe2O Calcium oxide, CaO Potassium oxide, K2O Sulphur trioxide, SO Magnesium oxide, MgO Sodium oxide, Na2O Barium oxide, BaO Others Loss o ignition (LOI) Table 2 Particle size distribution o ine aggregates in inorganic polymer concrete Sieve size (mm) Total percentage retained (%) Total percentage passing (%) Table 3 Particle size distribution o coarse aggregates in inorganic polymer concrete Sieve size (mm) Total percentage retained (%) Total percentage passing (%) Specimen Table 4 Mix proportion o raw materials in inorganic polymer concrete (kg/m 3 ) Cement Inorganic polymer binder Water Fine aggregate Coarse aggregate IPC

21 OPC Table 5 Flexural strength and elastic modulus o concrete Specimen Flexural strength (MPa) Elastic modulus (MPa) OPC IPC Table 6 Load and midspan delection o concrete beams Beam Cracking Yielding Failure Load (kn) Disp. (mm) Load (kn) Disp. (mm) Load (kn) Disp. (mm) OPCB OPCB IPCB IPCB