PSI - Issue 45

Yipu Guo et al. / Procedia Structural Integrity 45 (2023) 66–73 Yipu Guo et al. / Structural Integrity Procedia 00 (2019) 000 – 000

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uniaxial test is 0.1 mm/min. For triaxial test, the loading regimen contains two stages. In the first stage, the axial load and lateral confining pressure were applied at the identical loading rate of 0.2 MPa/s until the predesigned load magnitude. In the second stage, the axial load was applied at a loading rate 0.1 mm/min until specimen was damaged or axial deformation was too large. 3. Results and discussions 3.1 Peak stress Fig. 1 (a) illustrates the normalized results of peak stress ( ) and lateral confining pressure ( ), where represents the peak stress of the specimens under uniaxial compression. The lateral confining pressure has an important influence on peak stress. The peak stress increases with the increase of confining pressure, but the increasing rate is slightly declined at higher confining pressure. Similar results were reported in RAC (Chen et al., 2019) and polyvinyl alcohol fiber reinforced RAC (Chen et al., 2022) with various RA substitution rates. The transverse expansion tensile initiates unstable cracks, which is the primary cause of concrete compression failure (Chen et al., 2019). The transverse expansion tensile deformation is suppressed by lateral confining pressure and subsequently delays the development of cracks, thereby improving the axial compressive strength of the specimen and weakening the negative impact from Multi-RA defects. Compared to RAC, additional recycling cycles induce more defects zones such as extra ITZs, and negatively affect the chemical cementing force of Multi-RAC (Zhu et al., 2019). Under the smaller confining pressure, the compensating reinforcement effect to the defect zones brought by lateral confining pressure is more pronounced. When lateral confining pressure increases, this compensating effect is weakened because of the initiation of more microcracks, thus the increasing rate of peak stress is slightly declined.

1.6

4.5

RACI

RACII

RACIII

NAC RACI RACII RACIII

4.0

1.4

3.5

1.2

3.0

2.5

s g /s 0

s v / f co

1.0

2.0

0.8

1.5

0.6

1.0

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.5

0.4

0

5

10

15

20

s w / f co

s w (MPa)

(a) Relationship between peak stress and lateral confining pressure

(b) Peak stress variation

Fig. 1. Correlation between peak stress and confining pressure. Fig. 1 (b) illustrates the peak stress variation of Multi-RAC after sequential recycling cycles. and 0 denote peak stress of Multi-RAC for different generations and NAC, respectively. Generally, the peak stress variation shows a downward trend, but the magnitude of decreasing rate shows a distinctive discrepancy under different levels of confining pressure. The decreasing rate is evidently lower when lateral confining pressure is applied, implying the positive role of lateral confining pressure in delaying the development of the crack. Compared to RACI, RACII and RACIII show higher peak stress when confining pressure is smaller than 10 MPa. Previous studies confirmed that presaturated RCA particles with porous characteristics could enable the internal curing effect and therefore contribute to improved interfacial adhesion strength of ITZs (Abate et al., 2018). However, under higher confining pressure, the improved adhesion due to internal curing effect is impaired due to the initiation of more microcracks.

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