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  • ycZhKey Laboratory of Energy Engineering Safety and Disaster Mechanics, Ministry of Education, Sichuan University, Chengdu 610065, PR ChinacAdvanced Research Institute, Chengdu University, Chengdu 610106, PR ChinadDepartment of Civil Engineering, Monash University, CRC) is alumns wto GRCFST colu teel tube (GRCFST). Two section sizes of square hollow sections lled withreduce greenhouse gas emissions, mostly carbon dioxide (CO2),has become a major target for all the human activities and a keyfeature of the sustainable development. Therefore, in infrastruc-ture construction, besides smart structural styles and intelligenttechnology, the low carbon concept should also be taken into ng in cement pro-de anthropgreat potethe production of green concrete with a lower carbon fo[24]. It has better mechanical and chemical properties thwith high compressive strength, low creep, good bondinreinforced steel, as well as good resistance to acid sulphate and re[59]. The application of recycled aggregate concrete (RAC) hasbeen widely studied and approved, however, geopolymeric recy-cled concrete (GRC) is less study and in the focus of our study.In such material, cement is substituted totally by alkali solutionand y ash, and the natural coarse aggregate (NA) is replaced by Corresponding author at: College of Architecture and Environment, SichuanUniversity, Chengdu 610065, PR China. Tel.: +86 13982287467; fax: +86 2886264996.E-mail address: (X.-S. Shi). Construction and Building Materials 81 (2015) 187197Contents lists availabConstruction and BevOver the past few decades, human awareness has beenstrengthened by the global climate changes resulting from therapid expansion of industry and infrastructure, solid waste dispos-al and greenhouse gas emission, etc. To reuse solid waste and OPC is a highly energy consuming process, resultiduction releasing nearly 10% of the total worldwiCO2 emissions [1].Geopolymer concrete is considered to have a 2015 Elsevier Ltd. All rights reserved. ogenicntial inotprintan OPCg withAvailable online 2 March 2015Keywords:Geopolymer concreteRecycled aggregateSteel tubular columnLoad capacityDuctilityLoad-deformation relationship GRC and recycled aggregate concrete (RAC) respectively, with different recycled aggregate (RA) replace-ment ratios of 0%, 50% and 100%, were used in the experiments. The test results indicated that the ulti-mate strength was reduced when adding more RAs in the columns, while the peak strain increased. Theductility of the columns was improved by increasing the RA replacement ratio. Overall, the inuence ofRA on the strength and ductility of GRCFST columns is greater than that of RAC lled steel tubular(RACFST) columns. The assumed theoretical model for predicting load versus deformation relation ofGRCFST columns under axial loading was examined, and a revised theoretical model proposed. Theresults of the new model show good correlation with the experimental results. 2015 Elsevier Ltd. All rights reserved.1. Introduction account. Customarily, concrete is produced by using Ordinary Port-land Cement (OPC) as the binder. However, the manufacturing ofReceived in revised form 18 January 2015Accepted 18 February 2015 lar columns under axial lproperties of GRC lled sh i g h l i g h t s The geopolymeric recycled concrete (G The structural properties of GRCFST co The inuence of RCA replacement ratio A theoretical simulation model of GRCa r t i c l e i n f oArticle history:Received 1 August 2014 layton, VIC 3800, Australianew constructional material.ere rstly tested and analysed.FST and RACFST columns were discussed.mns under axial loading was proposed.a b s t r a c tGeopolymeric recycled concrete (GRC) is a new construction material which takes environmental sus-tainability into account. In this paper, an experimental study was carried on 12 concrete lled steel tubu-oading, in order to ll a knowledge gap on the engineering and structuralaCollege of Architecture and Environment, Sichuan University, Chengdu 610065, PR ChinabStructural behaviour of geopolymeric rectubular columns under axial loadingXiao-Shuang Shi a,b,, Qing-Yuan Wang b,c, Xiao-Lingjournal homepage: www.els led concrete lled steelao d, Frank G. Collins dle at ScienceDirectuilding Materialsier .com/locate /conbui ldmat

  • recycled coarse aggregate (RA) partially or totally. Therefore, due toeliminating cement as well as the CO2 absorbing effect of RCA [10],the CO2 emission problem would be further improved.Concrete lled steel tubular (CFT) columns are well recognisedand widely applied for intelligent composite action, with theadvantages of both steel tube and in-lled materials. In the pastfew decades, many types of materials were encased in the steeltubes, considering environmentally friendly materials in order tominimize pollution and energy consumption, For example, steeltubes lled with RAC [1115] involving the reuse of waste con-crete, self-consolidating concrete without vibration benets forconstruction and energy saving [16,17], and polymers or poly-188 X.-S. Shi et al. / Construction and Buildmer-based materials as positively considered to enhance the struc-tural behaviour of columns with higher tensile and adhesioncapacity, lower weight and shrinkage, as well as high ductility[1820]. So far, research shows that some mechanical propertiesand structural behaviour of RAC lled steel tubular (RACFST) col-umns can be improved with better ductility compare with OPClled steel tubes [11,12,2123]. A few studies on the theory ofRACFST under axial loading have been undertaken [12,24], but lit-tle theoretical research on geopolymer concrete lled steel tubularcolumns has been reported.In our previous study [25] on the microstructure of GRC, it wasshown that, the mechanical properties of GRC is stronger overalldue to the different formation processes that result in much denserand stronger reaction products compared with OPC or RAC. In thispresent study, axial compression experiments were carried out on12 concrete lled steel tubular columns, including 6 RACFST col-umns and 6 GRC lled steel tubular (GRCFST) columns with differ-ent recycled aggregate replacement ratios of 0%, 50% and 100%. Theload capacity, structural behaviour and failure mode were testedand analysed. The theoretical analysis method based on existingmodels to simulate the load versus deformation relation of GRCFSTis discussed and compared with experimental results. Further-more, an improved model is proposed according to the experimen-tal results and the GRC characteristics.2. Experimental program2.1. Material properties2.1.1. Properties of steelCold-formed square hollow sections (SHS) of size 200 mm 6 mm and150 mm 5 mm manufactured to AS 1163 [26] were used in the test program.The mechanical properties of steel were obtained by tensile coupon tests accordingto Australian Standard AS1391 [27]. The coupons were cut from the at face of theSHS along the longitudinal direction of the section. The yield stress and ultimatetensile strength are listed in Table AggregatesThe nominal size of the RA and NA were 20 mm and 14 mm, respectively. Thetest results shown in Table 2 indicate that the RA are lower than those of NA byabout 15%, 18% and 9% for the apparent density, dry density and SSD density,Table 1Mechanical properties of steel.B t (mm) Elastic modulus/std E (GPa) Yield stress/std fy (MPa) Ultimate tensilestrength/std fu (MPa)150 150 5 197/1.53 486/2.83 558/2.83200 200 6 199/1.50 467/4.55 544/5.56Table 2Physical properties of NA and RA.Aggregatetype Apparentdensity/std (kg/m3) Dry density/std (kg/m3) SSD density/std (kg/m3) Waterabsorption/std (%)NA 2850/5.66 2819/5.37 2908/6.44 1.08/0.01RA 2433/2.77 2304/2.58 2645/6.87 5.60/0.11 respectively. However, the water absorption of RA is about as 5 times as that ofNA. This is due to the existence of porous and less dense residual mortar lumpsadhering to the RA, as well as much more micro-cracks being produced duringthe crushing process in RA production.2.1.3. Fly ashFly ash (ASTM Class F) with 2.8% of CaO was used as the main aluminium andsilicate source for synthesizing the geopolymeric binder, mainly consisting of glasswith some crystalline inclusions of mullite, hematite and quartz.2.1.4. Alkali solutionSodium silicate solution (Na2SiO3) with specic gravity of 1.53 and sodiumhydroxide (NaOH) akes of 98% purity were supplied by PQ Australia. Sodiumhydroxide was dissolved using distilled water to provide 8 molarity alkaline solu-tions. Na2SiO3 and NaOH solutions were prepared one day prior to usage.2.2. Specimen preparation2.2.1. Mixture designDue to the high water absorption of RA, the water determined according to theeffective absorption of RA was used to pre-soak the RAs before mixing, and theaggregates were introduced to the mixture in a saturated surface dry (SSD) condi-tion. In order to compare the inuence of the RA content on the concrete lled col-umns, six mixtures were designed with different RA replacement ratios for the RACand GRC concrete. The concrete mixture proportions are summarized in Table 3.The numbers 0, 50 and 100 after the concrete name refer to the RA replace-ment ratio of 0%, 50% and 100%, respectively. W/G is the ratio of total water togeopolymeric binder solids, including y ash and solids in the alkali solution. Themixing of the concrete was undertaken in a mechanical mixer according to the pro-cedure in AS 1012.2 [28].2.2.2. Manufacturing processThe steel tubes were cut into 750 mm lengths. A 20 mm thick steel plate waswelded on one end of the tubes to ensure the atness of the base, as well as actingas the mould for the concrete. Following concrete placement in the tubes, the con-crete was compacted by an electric poker vibrator. The columns were covered withpolyethylene sheets for curing. The mixture was then poured into the steel cylindermoulds of 100 mm diameter 200 mm length for compr