Abstract
This paper presents the results of an experimental, numerical and analytical study of bending and shear behaviour of simply supported reinforced concrete beams with two layers of different grades of concrete. The top layer (1/3rd) concrete, mainly in compression, is higher grade, and the bottom (2/3rd) layer, in tension, is lower grade using rubber recycled aggregate concrete. A total of 8 tests were conducted. The results confirm that the two layer beam achieves the same bending resistance as the control reinforced concrete beam made entirely of the higher grade concrete.
In beams without shear reinforcement, the two layer beam attained lower shear resistance than the control beam. This was attributed to the unzipping effect: once the lower strength concrete has failed in shear, it loses its shear resistance and transfers the shear force from the failed lower strength concrete to the control concrete. Further FE simulations reveal that the top layer higher grade concrete plays no role in influencing the beam’s shear resistance. Therefore, when calculating shear resistance of concrete of the two layer beam, the lower concrete grade should be used. However, since the shear force in reinforced concrete beams is mainly resisted by shear links, the lower shear resistance of rubber recycled aggregate concrete has very minor implication on beam shear resistance.
The proposed construction facilitates wider adoption of recycled aggregate concrete without having to achieve the same mechanical properties of concrete made of fresh aggregates.
In beams without shear reinforcement, the two layer beam attained lower shear resistance than the control beam. This was attributed to the unzipping effect: once the lower strength concrete has failed in shear, it loses its shear resistance and transfers the shear force from the failed lower strength concrete to the control concrete. Further FE simulations reveal that the top layer higher grade concrete plays no role in influencing the beam’s shear resistance. Therefore, when calculating shear resistance of concrete of the two layer beam, the lower concrete grade should be used. However, since the shear force in reinforced concrete beams is mainly resisted by shear links, the lower shear resistance of rubber recycled aggregate concrete has very minor implication on beam shear resistance.
The proposed construction facilitates wider adoption of recycled aggregate concrete without having to achieve the same mechanical properties of concrete made of fresh aggregates.
| Original language | English |
|---|---|
| Article number | 20 |
| Pages (from-to) | 214 |
| Number of pages | 25 |
| Journal | Structures |
| Early online date | 12 Apr 2019 |
| DOIs | |
| Publication status | Published - 2019 |
Keywords
- Recycled aggregate; crumb rubber; rubber recycled aggregate concrete; two layer reinforced concrete beam, bending resistance, shear resistance.