Experimental and damage modeling research on compression‐shear behavior of carbon fiber recycled aggregate concrete

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To investigate the mechanical properties of polypropylene fiber recycled aggregate concrete (PPFRAC) under compression‐shear, 69 recycled aggregate concrete (RAC) specimens were tested with the parameters of polypropylene (PP) fiber volume content (0, 0.6, 0.9, and 1.2 kg/m3), recycled coarse aggregate (RCA) replacement rate (0%, 30%, 50%, 70%, and 100%), and normal stress (0, 3, and 6 MPa). In the tests, the failure pattern of the specimens was observed, and the effects of the polypropylene fiber content on the direct shear stress, compression‐shear stress, initial shear stiffness, and shear ductility coefficient of the PPFRAC were thoroughly investigated. The results show that as the polypropylene fiber content increases, the direct shear stress of concrete (Natural aggregate concrete and 100% recycled coarse aggregate concrete [100%RCA]) first increases and then decreases gradually. Meanwhile, the best PP fiber content is 0.9 kg/m3 in this study. Furthermore, the compression‐shear stress‐displacement curves of specimens were obtained. The compression‐shear strength under normal stress at 6 MPa is approximately 230% greater than at 0 MPa. However, the peak shear stress of concrete is almost not affected by the replacement rate of RCA. Finally, based on the Mohr circle theory, the compression‐shear calculation model of PPFRAC is verified, and the optimal calculation formula is given.

Section: Shear Load Systemmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Experimental study on mechanical properties of recycled aggregate concrete with polypropylene fiber under combined compression‐shear loading

Liu,

Chen,

Shen

et al. 2023

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“…Although all RA is sourced from the crushing of unused concrete components, 14,15 a distinction is usually drawn between the behavior of the coarse and the fine fractions: The coarse fraction is composed of particles >4 mm that consist of NA and adhered mortar 16,17 . Compared to coarse NA, the presence of adhered mortar in coarse RA lowers its density, raises its water absorption levels, and lessens its adherence within the new cementitious concrete matrix when used as an aggregate 18,19 . All these aspects decrease concrete workability, strength, and elastic stiffness 20 .…”

Section: Introductionmentioning

confidence: 99%

Scaled concrete beams containing maximum levels of coarse recycled aggregate: Structural verifications for precast‐concrete building applications

Fiol

Revilla‐Cuesta

Skaf

et al. 2023

The use of Recycled aggregate (RA) enhances concrete sustainability. If used on an industrial‐scale, structural verification, and testing will be required to confirm that RA concrete can meet relevant industrial standards and the requirements of manufacturers, especially in the precast‐concrete industry. In this paper, an experimental campaign with the participation of a precast‐concrete manufacturer is reported. The objective is to test a self‐compacting concrete (SCC) mix, designed for structural applications, that contains maximum amounts of 100% coarse RA, in order to establish its compliance with the habitual requirements of precast‐concrete manufacturers. Thus, scaled beams (12 × 24 × 180 and 24 × 24 × 130 cm) were subjected to bending, shear‐bending, shear, and long‐term‐deflection tests. In addition, the performance of that SCC mix in the bending and shear‐bending tests was compared with the performance of an SCC mix of similar compressive strength containing 0% coarse RA. In the failure tests, the experimental results were between 1.5 and 3 times higher than the required values. The elastic behavior of both SCC mixes was also very similar in those tests, regardless of the amount of coarse RA, due to the robust design of the water and superplasticizer content of the SCC, which balanced the decreased flowability and the lower compressive strength of SCC that resulted from the additions of coarse RA. The SCC mix with 100% RA showed a lower load‐bearing capacity after failure and narrow compliance margins with the deflection limits of the long‐term‐deflection test. Even though the SCC mix with 100% RA met all the standard technical specifications of the precast‐concrete manufacturer, reference should always be made to the serviceability limit states that are applicable at the time of the structural design phase.

“…[4][5][6][7] However, according to previous studies, the material properties of RAC are different from natural aggregate concrete (NAC). 8 It is shown that: recycled coarse aggregate (RCA) usually has greater porosity, water absorption, and lower strength at the same ratio; RAC has a low modulus of elasticity and greater dispersion of parameters [9][10][11] ; RAC is more brittle than NAC 12,13 ; RAC has a damage evolution is more complex than that of NAC. 14 The above research proved that there are some differences in the properties of RAC compared with NAC after crushing.…”

Section: Introductionmentioning

confidence: 99%

Mechanical properties of short polypropylene fiber enhanced recycled concrete under cyclic compression

Zhu

Chen

et al. 2023

Self Cite

This study investigated the mechanical properties and stress–strain relationship of polypropylene fiber recycled aggregate concrete (PFRAC) subjected to uniaxial cyclic compression. A total of 78 cylindrical specimens were designed for uniaxial cyclic compression test with coarse aggregate replacement rate, polypropylene fiber volume fraction, and loading rate as variation parameters. The failure process of the specimens under cyclic loading was observed and recorded. The stress–strain curve of PFRAC was summarized. The important mechanical properties of PFRAC were obtained, such as plastic strain, accumulated energy dissipation. The microstructure of PFRAC was analyzed by scanning electron microscopy, and the crack resistance mechanism of PFRAC under cyclic loading was revealed. The results show that the PFRAC under cyclic loading appeared oblique splitting failure. The compressive stress–strain curve envelope of PFRAC subjected to cyclic loading exhibited similarity to the monotonic counterpart. The addition of polypropylene fibers can improve the peak stress, peak strain, residual stress, post‐peak ductility, and accumulated energy dissipation of the recycled concrete. In addition, a constitutive relation formula for the PFRAC stress–strain curve under cyclic loading is proposed, and the fitting result is good.