Abstract
Numerous studies have indicated that FRP-confined recycled aggregate concrete(RAC)is a particularly effective method to overcome the shortcomings of RAC(e.g.low strength,poor durability).The recycled polyethylene terephthalate(PET)composites are relatively new type of environmentally-friendly fibers with bilinear tensile stress-strain relationship and high energy absorption capacity[1-3].The combination of recycled PET FRP jacket and RAC provides a good solution for the reuse of waste plastics and construction garbage.In this study,the axial compression tests of 24 RAC cylinders(150 mm×300 mm)externally confined by PET FRP were carried out.Dif ferent parameters such as the recycled aggregate(RA)replacement ratio(i.e.0%,33%,67%,100%),the number of FRP layers(i.e.1-ply,2-ply,3-ply)were analyzed.More details about the mix proportions of RAC and the flat coupon tensile test of PET FRP can be obtained from reference[4],[5],respectively.
As shown in Figure 1,three strain gauges,with a gauge length of 20 mm,were uniformly distributed on the nonoverlapping zone to determine the hoop strain of the specimen around the mid height of the column.Four linear variable displacement transducers(LVDTs)were fixed every 90 degree to determine the axial strain of the 150 mm mid-height of the column.
Figure 1 Test setup
Figure 2 displays the typical failure mode of specimens with dif ferent RA replacement ratios.When the peak load is reached,the PET FRP jacket seemed to rupture simultaneously in mid-height portions and the coarse aggregates are cleaved outside the overlapping zone.In general,the failure mode has no correlation to the replacement ratio of RA.Similar observations were obtained in the experiments of conventional FRPs(e.g.CFRP,GFRP)-confined RAC(e.g.reference[4],[5],[6]).
Figure 2 Failure mode
Table 1 presents the key results of the specimens.Where tfrp is the thickness of PET FRP jacket;εh,rup,εcu and
are the average actual hoop rupture strain,compressive strength and ultimate axial strain of the wrapped specimens with identical configuration respectively.The compressive strength of the unconfined specimens with RA replacement ratio of 0%,33%,67%,100% is 31.5 MPa,28.6 MPa,25.6 MPa,24.1 MPa,respectively.This proves that the addition of recycled aggregate reduces the strength of concrete.
Table 1 Ke y test results
Note:RX-PET-XX-XXX,where X=the replacement ratio of RA;XX=the number of PET FRP layers(1 represents the specimen externally jacketed with 1ply PET FRP);XXX=the number to differentiate two specimens with identical configuration.
Figure 3 displays that the compressive strength and ultimate axial strain increase significantly with the increase of FRP layers because of the excellent characteristics of large rupture strain for PET FRP jackets.However,Figure 4 shows that the specimens with the same FRP layers and different RA replacement ratios have similar strength and ultimate axial strain,indicating that RA replacement ratio has a marginal effect on the compressive behavior of RAC strengthened with PET FRP.In other words,the confinement effect of LRS FRP can solve the problem of strength reduction caused by the addition of RA.This observation is consistent with that of conventional FRPs-confined recycled concrete[6-9].
Figure 3 Effect of LRS FRP layer on stressstrain behavior of confined RAC
Figure 4 Effect of RA replacement ratio on the stress-strain behavior
The stress-strain curves of PET FRPconfined RAC specimens depict a triplesection pattern with a long smooth transition zone,analogous to the curves of PET FRP-confined natural aggregate concrete(NAC)[5].The first portion is quite similar to unconfined RAC because the confining effect is negligible due to the insignificant lateral dilation of RAC.A smooth transition zone is observed after the first portion when FRP is activated,followed by a linear segment until the rupture of FRP.The experimental curve is different from the bilinear curves of conventional FRPs-confined RAC.The main reason may be that the bilinear characteristics of PET FRP and the occurrence of RA reduce the expansion property of the specimens.