See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/299129521 Experimental study on flexural behaviour of inorganic polymer concrete beams reinforced with basalt rebar Article in Composites Part B Engineering · March 2016 DOI: 10.1016/j.compositesb.2016.03.021 CITATIONS 4 READS 98 2 authors, including: Mingzhong Zhang University College London 36 PUBLICATIONS 191 CITATIONS SEE PROFILE All in-text references underlined in blue are linked to publications on ResearchGate, letting you access and read them immediately. Available from: Mingzhong Zhang Retrieved on: 14 September 2016
Experimental study on flexural behaviour of inorganic polymerconcrete beams reinforced with basalt rebar
Xiaochun Fan a, Mingzhong Zhang b, *
a School of Civil Engineering and Architecture, Wuhan University of Technology, Wuhan 430070, Chinab Advanced and Innovative Materials (AIM) Group, Department of Civil, Environmental and Geomatic Engineering, University College London, London WC1E6BT, UK
a r t i c l e i n f o
Article history:Received 7 August 2015Received in revised form4 February 2016Accepted 11 March 2016Available online 19 March 2016
Corrosion of reinforcing steel and the severe degradation of mechanical properties with temperature andfire conditions are the weakest points of steel-reinforced concrete structures and fibre reinforcedpolymer (FRP) system, respectively. In this paper, the basalt reinforced inorganic polymer concrete (IPC)beamwhich combines the specific characteristics of IPC and basalt reinforcement such as good corrosionresistance and fire resistance was proposed. The inorganic polymer binder was made of fly ash, groundgranulated blast-furnace slag and alkaline activating solution. The mechanical properties of IPC weremeasured and compared with those of reference ordinary Portland cement (OPC) concrete. The flexuralbehaviour of basalt reinforced IPC beam was investigated and compared to control steel-reinforced OPCconcrete beam. The measured ultimate flexural capacity of basalt reinforced IPC beam was comparedwith the predicted value obtained using the guidelines for FRP-reinforced OPC concrete beam. Resultsindicated that the elastic modulus of IPC was very close to OPC, while the compressive strength andflexural strength of IPC were around 80% of those of OPC. The IPC beam reinforced with basalt rebarexhibited a two-stage load-midspan deflection response that was different from control concrete beamdue to the different mechanical properties of basalt and steel rebars. The crack patterns in basalt rein-forced IPC beam were found to be similar to control beam, however, the maximum crack width of basaltreinforced beam was approximately 2 times that of control beam. The guidelines for FRP-reinforcedconcrete beam were adequate for predicting the flexural strength of basalt reinforced IPC beams.
Concrete is the most widely used man-made material in theworld. The sustainability has become an increasingly importantcharacteristic for concrete infrastructure, as the manufacture ofPortland cement accounts for a significant proportion of raw ma-terial consumption and nearly 7% of global CO2 emissions [1].Inorganic polymers, also called geopolymers, are conventionallyproduced by synthesizing pozzolanic compounds or aluminosili-cate source materials with highly alkaline hydroxide and/or alka-line silicate. Over the last two decades, inorganic polymer concretes(IPC) have emerged as novel engineering materials with the po-tential to become a substantial element in an environmentallysustainable construction and building products industry [2,3].
.hang).
Industrial by-products, such as fly ash (FA) and ground granulatedblast-furnace slag (GGBFS) are commonly used as the source of IPCdue to the low cost and wide availability of these materials. It hasbeen shown that compared to ordinary Portland cement (OPC)concrete, IPC has many attractive properties, such as good fireresistance, good resistance to chloride penetration, acid attack,freeze-thaw cycles, etc. and can help reduce embodied energy andcarbon footprint by up to 80% [4e6].
Corrosion of reinforcing steel is the leading cause of deteriora-tion of reinforced concrete (RC) structures. In recent years, anincreasing attention has been paid towards the replacement oftraditional steel bars with fibre reinforced polymer (FRP) as internalconcrete reinforcement to solve the problem of rebar corrosion inRC structures. The most commonly used FRP reinforcing bars forconcrete structures are made from glass (GFRP), carbon (CFRP) andaramid (AFRP). However, the performance of GRRP and AFRPwouldbe significantly affected by the alkaline environment within con-crete [7]. CFRP reinforcing bars are too expensive to be
X. Fan, M. Zhang / Composites Part B 93 (2016) 174e183 175
implemented in normal civil engineering structures [8]. A new typeof reinforcing bars made from basalt fibre (BFRP) has recentlygathered attention as an alternative to other FRPs because of its costeffectiveness, ease of manufacture, high temperature resistance,freeze-thaw performance and good resistance to vibration andimpact loading, corrosion and acids [9e12]. In addition, BFRP hasbetter durability in alkaline conditions compared to GFRP [13].Because of these outstanding characteristics, BFRP fibres have beenused either as internal reinforcement for new concrete structuresor as external strengthening for existing concrete structures [14].
Over the past few years, many efforts have been made toinvestigate the mechanical behaviour of steel- and FRP-reinforcedinorganic polymer (geopolymer) concrete, and BFRP reinforcedconcrete in order to offer a solid theoretical basis for the use ofgeopolymer concrete and BFRP in concrete structures. With respectto the interaction between reinforcement and geopolymer con-crete, Songpiriyakij et al. [15] experimentally studied the bondingstrength between the embedded steel rebar and substrate geo-polymer concrete made of fly ash, rice husk and bark ash and silicafume, and showed that the bond strength of rebar and geopolymerwas slightly higher than that of control OPC concrete (1.05e1.12times). Sarker [16] used the beam-end test method to measure thebond strength of low calcium fly ash-based geopolymer concretewith deformed steel rebars and compared with the equivalent OPCconcrete system. The geopolymer concrete was observed to havehigher bond strength than OPC concrete, which was attributed tothe higher splitting tensile strength of geopolymer concrete relativeto OPC concrete of the same compressive strength. Castel andFoster [17] carried out the standard RILEM pull-out test to inves-tigate the bond between geopolymer and deformed and smoothsteel rebars. The used geopolymer binder was composed of 85.2% oflow calcium fly ash and 14.8% of GGBFS. The 28-day bond strengthand the overall bond stress-slip behaviour of the geopolymerconcrete were found to be similar to those of OPC concrete. Mennaet al. [18] studied the flexural behaviour of reinforced geopolymerconcrete beams strengthened with high strength steel cord andCFRP to evaluate the effectiveness of strengthening. Results indi-cated that geopolymer matrix provided a very good adhesion toconcrete substrate and to reinforcement. With respect to BFRPreinforced concrete, Tomlinson and Fam [19] evaluated the flexuraland shear performances of concrete beams reinforced with BFRPrebar and stirrups, and found that the beams with BFRP hadsignificantly higher strengths than control steel-reinforced coun-terparts with the same reinforcement ratio. Ge et al. [20] carriedout a series of experiments including tensile test, standard pull-outtest of BFRP bars and static flexural test on hybrid concrete beamsreinforced with BFRP bars and steel bars, and observed that thebond strength between BFRP rebar and concrete is similar to that ofsteel rebar and concrete. These previous studies have shown thatthe systems of steel rebar and geopolymer concrete, and BFRP rebarand OPC concrete have a similar bond behaviour and mechanicalperformance to control steel-reinforced OPC concrete, which leadsto the idea in this study of combing BFRP rebar and IPC (geopolymerconcrete) in a composite system to improve the durability andsustainability of concrete structures. According to authors' knowl-edge, the mechanical behaviour of IPC beam reinforced with BFRPreinforcement has not been extensively investigated elsewhere.
In this work, the mechanical properties including compressivestrength, flexural strength and elastic modulus of IPC are studiedand compared to reference OPC concrete. The inorganic polymerbinder is composed of both fly ash and GGBFS. Afterwards, theflexural behaviour of IPC beam reinforced with BFRP rebar in termsof ultimate flexural strength and cracking patterns and develop-ment is investigated in detail and compared with that of controlsteel-reinforced OPC concrete beam to understand the failure
mechanisms of BFRP reinforced IPC beam. A comparison betweenthe theoretical previsions of the flexural behaviour of the testedbeams calculated according to the recommendations for FRP-reinforced OPC concrete beam and experimental data for BFRPreinforced IPC beam was carried out to estimate whether theguidelines for FRP-reinforced concrete system are adequate forpredicting the flexural strength of IPC beams with BFRPreinforcement.
2. Materials and methods
2.1. Inorganic polymer concrete
The inorganic polymer concrete used for experiments was madeof a mixture of inorganic polymer binder composed of FA, GGBFSand alkaline activating solution, fine and coarse aggregates. FA andGGBFS used in this study were produced by Qingshan Power Sta-tion and Wuhan Iron and Steel Company Limited in Wuhan inHubei Province of China, respectively. The chemical compositionsof FA and GGBFS are given in Table 1. The scanning electron mi-croscope (SEM) images of FA and GGBFS morphology are shown inFig. 1. The alkaline activating solution was obtained by dissolvingsolid sodium hydroxide (NaOH) into sodium silicate (Na2SiO3) so-lution with the Na2SiO3/NaOH ratio of 1.53. Fifteen series of inor-ganic polymer binder were prepared and tested in order todetermine the optimal composition of the mixture accounting forboth early-age properties and durability, which was presented indetail in a previous work [11]. The medium-sized sand with fine-ness modulus of 2.72 was used as fine aggregate. The coarseaggregate was 13 mm nominal size crushed stone. The particle sizedistributions of fine and coarse aggregates are presented in Tables 2and 3, respectively.
The mix proportion of raw materials in inorganic polymerconcrete is given in Table 4. The fine and coarse aggregates werefirstly mixed for 2 min. Afterwards, the inorganic polymer binderwasmixed together with fine and coarse aggregates for about 3minfollowed by a gradual addition of free water. The inorganic polymerconcrete was then placed in the moulds and compacted using apoker vibrator. The concrete specimens were prepared forcompressive and flexural tests.
2.2. Basalt rebar
Fig. 2 shows the used BFRP reinforcing bar for inorganic polymerconcrete beams. It was supplied by Shenzhen Academy of Aero-space Technology. According to the manufacturer the Young'smodulus, yield strength and ultimate tensile strength of BFRP rebarare 50 GPa, 600 MPa and 650e1000 MPa, respectively. In order tostudy the mechanical behaviour of IPC beams reinforced withbasalt rebar, it is necessary to examine the stressestrain
Fig. 2. Basalt FRP bar used for inorganic polymer concrete beams.
X. Fan, M. Zhang / Composites Part B 93 (2016) 174e183176
relationship of basalt rebar. In this work, the uniaxial tensile testswere performed on five basalt rebars using a servo-hydraulictesting machine with a capacity of 600 kN according to GB/T5224-2014 [21]. The experimental setup for uniaxial tensile testsis shown in Fig. 3. Load was applied to the rebar throughdisplacement control at a rate of 0.08 mm/s until failure. Thestressestrain relationship of basalt rebars under uniaxial tension isshown in Fig. 4. For each stressestrain curve, it can be seen thatthere exists an initial elastic region followed by a small hardeningregion until ultimate failure, although the yielding point is notobvious. The yield strength of these five basalt rebars is found to be659 MPa, 549 MPa, 660 MPa, 657 MPa and 600 MPa, respectively.The tensile strength of them is 678 MPa, 569 MPa, 681 MPa,673 MPa and 610 MPa, respectively.
2.3. Testing program
Uniaxial compressive strength was measured at 3, 7 and 28 dayson 150 mm concrete cube based on GB/T 50081-2002 [22]. The
Table 4Mix proportion of raw materials in inorganic polymer concrete (kg/m3).
Specimen Cement Inorganic polymer binder
IPC e 425OPC 340 e
modulus of elasticity and flexural strength were measured at 28days on rectangular concrete prism (100 � 100 � 300 mm3 and100� 100� 400mm3, respectively) according to GB/T 50081-2002[22] and JTGE30-2005 [23], respectively.
To investigate the flexural behaviour of reinforced concretesystem, two inorganic polymer concrete beams reinforced withBFRP rebar, referred to as IPCB1 and IPCB2, with size of 120 mmwidth� 200mmheight� 2000mm length were prepared and castfor 28 days. For the purpose of comparison, two ordinary Portlandconcrete beams of the same size reinforced with steel rebars with adiameter of 14 mm and nominal yield strength of 360 MPa werecast and considered as control concrete beams, which are hereafternamed as OPCB1 and OPCB2. The diameter of BFRP rebar used inthis work is determined according to the method of equal-strengthsubstitution. As such, steel rebar is replaced with BFRP rebar, whilethe latter has the same strength, i.e., d21ffy;1 ¼ d22ffy;2, inwhich d1 andd2 are the diameters of steel and BFRP rebars, and ffy,1 and ffy,2denote their nominal yield strength, respectively. The diameter ofBFRP rebar obtained using the method of equal-strength substitu-tion is 10.8 mm. However, the rebar in 10.8 mm diameter is notavailable in the specifications for rebar. Therefore, the 12 mmdiameter BFRP rebar was chosen and used for IPCB1 and IPCB2. Itshould be noted that this would result in an approximately 18%greater contribution of reinforcement to IPC beams than that toOPC beams. Fig. 5 depicts the geometric and loading details of the
Water Fine aggregate Coarse aggregate
153 615 1262136 633 1298
Fig. 3. Setup for uniaxial tensile test of basalt FRP bar.
Fig. 4. Stressestrain relationship of basalt FRP bars.
X. Fan, M. Zhang / Composites Part B 93 (2016) 174e183 177
beam specimens. All the beams were tested as simply supportedmembers, over a clear span of 1.9m and loaded up to failure under afour-point bending configurationwith a constantmoment region of0.6 m across the midspan according to GB/T 50152-2012 [24]. Theload was applied through a 5000 kN hydraulic actuator. The entiretest 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 wereused to measure and determine the average midspan deflection ofthe beam at each loading stage. Thus, the corresponding force-edeflection curve can be obtained, which is presented in thefollowing sections. Five horizontal linear strain gauges were placed
on one side of the specimen to record displacements across themidspan at different depths. Displacements at supports weremeasured by linear variable differential transformer (LVDT). Onestrain gauge was bonded to each rebar at its midspan to record thestrain of rebar under loading. An automatic data acquisition systemwas utilized to monitor loading. The IPCB1 beam specimen beforeand after loading is shown in Fig. 6.
3. Experimental results and discussion
3.1. Mechanical characteristics
Fig. 7 shows the time evolution of compressive strength of OPCconcrete and IPC. Three specimens were used to measure thecompressive strength. As expected, the compressive strength goesup with increasing curing age. For both OPC concrete and IPC, thecompressive strength at 3 days is 48% of that at 28 days, and the 7-day compressive strength is around 66% of 28-day compressivestrength. A very similar trend in the increase in compressivestrength can be observed for OPC concrete and IPC, although thecompressive strength of IPC at each curing age is approximately80% of that of OPC concrete.
Table 5 shows the flexural strength and elastic modulus of OPCconcrete and IPC, which were measured using three and six spec-imens, respectively. All measures were performed on specimensafter curing of 28 days. It can be seen that the flexural strength ofIPC is about 80% of that of OPC concrete, while the elastic moduli ofthem are very close.
3.2. Loadedeflection response at midspan
Fig. 8 depicts the measured loadedeflection response at mid-span for the tested beams. Values of loads and midspan deflectionscorresponding to the first cracking, the yielding of reinforcingbasalt/steel rebars and the final bending failure of the beam aresummarized in Table 6. As seen in Fig. 8, two control beams OPCB1and OPCB2 show a very consistent three-stage loadedeflectionresponse. Taking OPCB1 as an example, concrete and internal steelreinforcing bar initially work together to resist deformation andonly a small deflection can be observed. In this stage, the slope ofloadedeflection curve is large, which reflects the high stiffness ofthe system. Once the load reaches around 24 kN at a midspandeflection of 1.5mm, the first cracking of beam appears and a loss ofstiffness occurs due to the tensile failure of concrete within themaximum bending moment region. As a consequence, the slope ofloadedeflection curve starts to decrease and the tensile steelreinforcing bar has to bear the load alone. At a load value of 96 kN,another decrease in the slope of loadedeflection curve starts tohappen, which can be ascribed to the yielding of the tensile steelrebar corresponding to 10.5 mm of midspan deflection. Afterwards,there exists a rapid increase in deflection from 10.5 mm to 22 mm,whereas the load value does not change much, just increasing by8 kN. In the meantime, the flexural cracks in terms of both numberand size show a significant increase with increasing deformationuntil the collapse of the beam as a result of concrete crushing in thecompression zone. The ultimate load and midspan deflection arefound to be 104 kN and 15 mm, respectively. The control beamOPCB2 exhibits a very similar trend in terms of loadedeflectionresponse with OPCB1. The first cracking happens at a load valueof 28 kN followed by a loss of stiffness until the yielding of rein-forcing steel bar occurs at a load of 112 kN, which is a little bithigher than yielding load of OPCB1. After yielding, the stiffness ofthe beam decreases and the slope of forceedeflection curve is thesame as that of OPCB1, whereas the ultimate load is 116 kNoccurring at a midspan deflection of 15.7 mm.
X. Fan, M. Zhang / Composites Part B 93 (2016) 174e183178
Unlike the control concrete beams, the load-midspan deflectioncurves of IPC beams only consist of two parts. The first part is verysimilar to that observed in control beams and the first crackingloads are close to those of control beams, followed by a significantloss of stiffness. Compared to control beams, the slopes ofloadedeflection curves of IPC beams in the second part are muchlower, which can be associated with the lower elastic modulus ofBFRP rebar in IPC beams than steel reinforcing bar in control beamsand the lower volume fraction of reinforcement in IPC beams thanOPC beams, as the elastic modulus of IPC is almost the same as thatof OPC concrete. In addition, there does not exist an obvious
yielding load prior to final failure, which is different with thatdetected in control beams. This can be attributed to the fact that thestressestrain curve of BFRP rebar in IPC beams is almost linearelastic, since the yield point is not obvious (as seen in Fig. 4) and thehardening region prior to ultimate failure is very small. This isdifferent with that of steel rebar in OPC concrete beams. As a result,there shows a steady increase in midspan deflection until the ul-timate deformation is reached. The ultimate loads of IPCB1 andIPCB2 are found to be a little bit lower in comparison to control OPCbeams, which may be mainly due to the lower flexural andcompressive strength of IPC as compared to OPC concrete, as
Fig. 8. Loadedeflection response at midspan for concrete beams.
X. Fan, M. Zhang / Composites Part B 93 (2016) 174e183 179
presented above. However, the ultimate deflections of IPC beamsare about 2.5 times of those of control beams.
3.3. Loadestrain response of concrete
As the strain at different positions along the depth play a crucialrole in the determination of load capacity of reinforced concretebeams under flexure, it is essential tomeasure these strains. Herein,the strains in the constant moment region of beams were obtainedby using five horizontal linear strain gauges at depths of d ¼ 20, 40,100, 160 and 180 mm from the bottom surface at midspan, asshown in Fig. 5. The measured concrete strains of the test beamsunder loads of 20, 40, 60 and 80 kN are shown in Fig. 9. It can beseen that for each beam, the strains at different depths undervarious loading values follow a similar trend that the upper part ofthe beam is in compressionwhile the lower part is in tension. Thereexists a layer above the centre of beam that is subjected to neithertensile nor compressive train, i.e., the so-called neutral layer. Asexpected, the strains along the depth from the top to the bottomseem to be linear regardless of the level of loading, which impliesthat the beam cross sections remain plane during bending and thebond between concrete and reinforcing bar is perfect. All theseindicate that concrete and reinforcing bar are able to work togetherverywell to bear loads and thus the plane cross-section assumptioncan be used to estimate the load capacity of the beams subjected tobending in this study.
3.4. Loadestrain response of rebar
Figs. 10 and 11 show the loadestrain response of reinforcingbars in IPC beam and control beam, respectively. The strains weremeasured at five different locations: the midspan and four pointswhich are 10 cm and 20 cm far from the supporting points, asshown in Fig. 5.
Table 6Load and midspan deflection of concrete beams.
Beam Cracking Yielding
Load (kN) Disp. (mm) Load (kN)
OPCB1 24 1.5 96OPCB2 28 1.8 112IPCB1 22 5.3 e
IPCB2 24 4.9 e
It can be seen from Fig. 8 that the change in strain of BFRP rebaragainst load at midspan follows a two-stage process: a short linearrise and a gradual increase. In the first stage, no cracking occurs inthe beam and BFRP rebar and IPC work together to bear the tensileforces. As a result, the strain of BFRP rebar goes up linearly with theload. In the beams, the cross-sectional area of IPC in the tensileregion is much larger than that of BFRP rebar, while their elasticmoduli are of the same order of magnitude (the elastic moduli ofIPC and BFRP rebar are 32.1 GPa and 50 GPa, respectively), whichresults in a much sharper increase in the strain of BFRP rebarcompared to that of IPC, as seen from the slopes of the curves inFigs. 8 and 10. Taking IPCB1 as an example, there is an increase inthe strain of BFRP rebar at midspan from 0 to 648 mm when theflexural loading is increased from 0 to 20 kN, while the corre-sponding strain of IPC at midspan only increases from 0 to 206mm.As the load increases, the stress of concrete in the tensile regiongoes up and subsequently reaches the tensile strength of concrete,which gradually leads to cracking at the edge of the tensile regionand stress redistribution in this region. In the second stage, theconcrete cracking in the tensile region grows further and thereinforcing bars start to bear the tensile forces alone, which resultsin a gradual linear increase in the strain of reinforcing bars, inparticular for the BFRP rebar whose elastic modulus is around 1/4 ofsteel rebar exhibiting a much larger deformation compared to steelrebar. The strain of BFRP rebar in IPCB is observed to be approxi-mately four times that of steel rebar in OPCB due to the relativelylower elastic modulus, as seen in Figs. 10 and 11 that the slope ofloadestrain curve for IPCB is smaller than that for OPCB. This im-plies that at the same loading level the deflection of IPCB is largerthan that of OPCB and the corresponding crack width is largerrelative to OPCB leading to an even more obvious stress redistri-bution in the beam. In addition, at midspan the steel rebar behavesdifferently from BFRP rebar that the loadestrain curve tends to berelatively horizontal before reaching the ultimate load, which isattributed to the difference in mechanical properties of steel andBFRP rebars.
As shown in Figs.10 and 11 the loadestrain curves for reinforcingbars at endpoints with distances of 10 and 20 cm from the sup-porting points consists of three stages, which is similar to the case ofmidspan point. The end of the first linear stage corresponds to theoccurrence of concrete cracking and the initiation of stress distri-bution in concrete beams. The stress redistribution of reinforcingbars at endpoints occurs at load values of around 60 kN. This ismuchlater than the midspan point, where the stress redistribution hap-pens at a load of approximately 20 kN. Additionally, the strain ofreinforcing bars at endpoints is lower than that at midspan point tillthefinal failure of concrete beams,which indicates that prior tofinalfailure there exists a strong bond between reinforcing bars andconcrete and thus they work well together to bear the forces.
3.5. Crack patterns
Fig. 12 shows the final crack patterns of reinforced concretebeams, IPCB1 and OPCB1, under flexural loading. The development
Failure
Disp. (mm) Load (kN) Disp. (mm)
10.5 10412.3 116 15.7e 92 40e 96 39
Fig. 9. Strains of concrete at different positions along the height of beams under various loads: (a) OPCB1; (b) OPCB2; (c) IPCB1 and (d) IPCB2.
Fig. 10. Loadestrain curve of basalt reinforcement in IPCB1. Fig. 11. Loadestrain curve of steel reinforcement in OPCB1.
X. Fan, M. Zhang / Composites Part B 93 (2016) 174e183180
of cracking in inorganic polymer concrete beam and control con-crete beam during loading is depicted in detail in Figs. 13 and 14.The numbers in figures denote the corresponding load values tocrack growth.
For control concrete beams, the first cracking occurs within theconstant moment zone at load values of 24 kN and 28 kN, respec-tively. As load increases, more and more cracks form and spreadoutward from midspan into the shear spans. At a load of around70 kN, the inclined shear cracks occur. With further increase inload, these cracks propagate towards the compression zone of thebeam near the loading point. When the imposed load on the beamsapproaches the ultimate load capacity, cracks spread very rapidlyleading to a smaller concrete compression zone due to an upwardshift of the neutral axis, which results in the crush of concrete andfinal failure of concrete beams in compression.
The basalt reinforced inorganic polymer concrete beams behavesimilarly to control concrete beams. The first cracks are noticed inthe constantmoment regions on IPCB1 and IPCB2when the appliedload reaches about 22 kN and 24 kN, respectively. As the load in-creases, the existing cracks develop and some new flexural cracksare formed in the region between load and support. Upon furtherincreasing the applied load, the majority of the flexural cracks de-velops vertically and after that inclined flexure-shear cracks beginto appear at a load of around 60 kN, which is consistent with theresults of loadestrain response of basalt rebar in IPC beams asshown in Fig. 10. As the load increases further, the inclined cracksprogress in terms of length and width both upward toward theapplied load point and horizontally along the longitudinal BFRPrebar towards the support. As a result, the effective area of concretesection in the compressive region is reduced. After additionalapplication of load, the beams eventually fail in compression.
Fig. 12. Crack patterns of concrete beams under flexural loading: (a) IPCB1 and (b) OPCB1.
Fig. 13. Crack development in OPCB2 under flexural loading.
Fig. 14. Crack development in IPCB2 under flexural loading.
X. Fan, M. Zhang / Composites Part B 93 (2016) 174e183 181
Although the cracking loads of control concrete beams are higherthan those of basalt reinforced IPC beams, however, the averagedeflection at the first crack formation for control beams is found tobe 1.9 mm that is much lower than 3.9 mm for IPC beams. Inaddition, the number of cracks at failure for IPC beams seems to belarger than that for control beams. All these indicate that the basaltreinforced IPC beams have higher resistance to fracture than con-trol concrete beams.
3.6. Comparison with theoretical previsions
Herein, a theoretical prevision of the mechanical behaviour ofthe tested basalt reinforced IPC beams is computed and compared
with the experimental results in terms of predicted flexural ca-pacity and failure mode. Since the performance of BFRP rebar isdifferent from reinforcing steel bar, the guidelines for steel rein-forced concrete beammay not be applicable to basalt reinforced IPCbeam. In this work, the flexural capacity of IPC beams is calculatedaccording to the recommendations of the ACI 440.1R-15 [25]guidelines for the FRP-reinforced concrete beam in conjunctionwith the following considerations and assumptions:
(1) The beam cross sections remain plane during the wholeflexural loading process.
(2) The strength development of inorganic polymer concrete issimilar with ordinary Portland cement concrete, which is
X. Fan, M. Zhang / Composites Part B 93 (2016) 174e183182
described as the following equation. The elastic moduli ofthese two types of concrete are close to each other, as seen inTable 5.
8><>:
sc ¼ fc
�1�
�1� εc
ε0
�n�εc � ε0
sc ¼ fc ε0 < εc � εcu
(1)
with
ε0 ¼ 0:002þ 0:5�fcu;k � 50
�� 10�5
εcu ¼ 0:0033��fcu;k � 50
�� 10�5
n ¼ 2� 160
�fcu;k � 50
�
where sc and εc denote the concrete stress and strain, respectively,ε0 and εcu represent the concrete strain corresponding to the con-crete stress values of fc and fcu,k, respectively.
(3) As seen in Fig. 4, the stressestrain curve of basalt rebar isalmost linear elastic. For simplicity sake, it can be expressedby
sf ¼ Ef εf (2)
where sf, Ef and εf stand for the stress, elastic modulus and strain ofbasalt rebar, respectively.
(4) As the tensile strength of inorganic polymer concrete is muchsmaller than that of basalt rebar, therefore, this tensilestrength can be ignored and the basalt reinforcement isassumed to resist the tensile stress alone.
(5) There exists a good bonding between reinforcing basalt andinorganic polymer concrete and the debonding failure of thereinforcing system would not occur prior to the ultimateflexural load. In fact, this assumption can be verified usingthe measured loadestrain response of basalt rebar at mid-span, as shown in Fig. 10.
For a basalt reinforced IPC beam, the balanced failure occurswhen the compressive and tensile zones reach yielding at the sameimposed load on the beam, and hence the concrete will crush andtensile basalt reinforcement will yield at the same time. In suchcase, the height of equivalent rectangular stress over the height ofthe beam is defined as the balanced relative compressive height, xfy.A schematic diagram of the stress distribution over the beam'scross section for balanced failure condition is given in Fig. 15. Basedon the balance and compatibility conditions, the parameters inFig. 15 can be obtained as follows:
x ¼ b1xc ¼b1εcu
εcu þ εfyh0 (3)
a1fcbx ¼ Af ffy ¼ rfbbh0ffy (4)
xbf ¼b1
1þ ffyεcuEf
(5)
where x is the balanced compression height, xc is the real balancedcompressive height, a1 and b1 are the coefficients of equivalentrectangular stress and height of concrete, εcu denotes the ultimatecompressive strain (εcu ¼ 0.0033), ffy and εfy stand for the nominal
yield strength and corresponding yield strain of BFRP rebar, b andh0 are the width and effective height of beam's cross-section, andrfb represents the balanced reinforcement ratio of BFRP rebar,which can be expressed as
rfb ¼ a1b1fcffy
εcu
εcu þ εfy(6)
The real tensile stress (ff) of the basalt reinforcement when thecrushing of inorganic polymer concrete happens can be calculatedaccording to the following balance equations:
where rf is the reinforcement ratio of BFRP rebar in the beam,which is equal to the ratio between the cross-sectional area of BFRPrebar and the cross-sectional area of beam, i.e., Af/(bh0).
The ultimate flexural capacity of the basalt reinforced IPC beam,Mu, can be obtained as:
Mu ¼ Af ff�h0 �
x2
�(10)
with
x ¼ Af ffa1fcb
(11)
According to Eq. (6), the theoretical value of balanced rein-forcement ratio for basalt reinforced IPC beam is 0.48%. While theapplied reinforcement ratio in this work is 0.95%, which is about 2times the balanced reinforcement ratio. This implies that the testedbasalt reinforced IPC beams would fail in compression, which isconsistent with the experimental findings in terms of stressestraincurve and crack patterns. In addition, the applied reinforcementratio is less than 3 times the balanced reinforcement ratio, whichindicates that the tested basalt reinforced IPC beams can beconsidered as balanced-reinforced beams, as a reinforced concretebeam with a reinforcement ratio varying from 1.5 times to 3 timesthe balanced reinforcement ratio is generally defined as a balanced-reinforced beam. Furthermore, the theoretical ultimate flexuralcapacity of basalt reinforced IPC beam calculated using Eq. (10) is87 kN, which is very close to the mean value of measured flexuralcapacity of the tested beams, i.e. 94 kN. The good agreement be-tween the theoretical prediction and experimental data confirmsthat the design codes for FRP-reinforced concrete beam are appli-cable to inorganic polymer concrete beam reinforced with basaltrebar.
4. Conclusions
The flexural behaviour of inorganic polymer concrete (IPC)beams reinforced with basalt rebar was tested and compared withcontrol steel-reinforced ordinary Portland concrete (OPC) beams in
Fig. 15. Stress distribution over the beam's cross-section for balanced failure condition.
X. Fan, M. Zhang / Composites Part B 93 (2016) 174e183 183
this study. A comparison of the experimental results with theo-retical prevision of the mechanical behaviour of the tested beamsaccording to the recommendations for the FRP-reinforced concretebeam was carried out. The following main conclusions can bedrawn from the present study:
� The compressive strength of IPC with the proposed mix designat various curing age was a little bit lower than control OPC.
� The basalt reinforced IPC beam behaved differently from controlsteel-reinforced concrete beam in terms of loadedeflectionresponse due to the difference in mechanical behaviour be-tween IPC and OPC, and basalt and steel reinforcement. Forcontrol beam, there existed an obvious yielding stage, while theloadedeflection curve of IPC beam reinforcedwith basalt bar didnot exhibit such stage. At the same applied load, the deflectionof basalt reinforced IPC beamwas around 4 times that of controlbeam.
� The development of cracking and crack patterns in basalt rein-forced IPC beam under flexural loading was similar to controlsteel-reinforced OPC beam, while the maximum crack width ofbasalt reinforced beam was approximately 2 times that of con-trol beam. Additionally, although the cracking load of controlbeam was larger than that of basalt reinforced beam, however,the corresponding crack deflection of basalt reinforced beamwas around one time larger than that of control beam.
� The theoretical ultimate flexural capacity of basalt reinforcedIPC beams calculated using the recommendations for the FRP-reinforced concrete beam was close to the measured ultimateflexural strength of the tested beams, which indicates that suchrecommendations are adequate for predicting the flexuralstrength of IPC beams reinforced with basalt reinforcement. Inaddition, the tested basalt reinforced IPC beams can be regardedas balanced-reinforcement beams.
Acknowledgements
The authors gratefully acknowledge the financial support fromWuhan University of Technology through grant number631200321. The authors are grateful to all reviewers for theirconstructive comments and suggestions.
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