# Ferrocement, Carbon, and Polypropylene Fibers for Strengthening Masonry Shear Walls

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## Abstract

**:**

## 1. Introduction

## 2. Materials and Experimental Method

#### 2.1. Unreinforced (URM) Walls

#### 2.2. Strengthened Walls

#### 2.2.1. Ferrocement Jacketing (FC)

^{2}to ensure a proper connection of the mesh to the wall. Care was taken during the process of mounting the steel mesh on the wall faces to ensure proper layering and to provide a clearance of 5–10 mm between the mesh and the bricks to fill with the mortar. The mortar mix was prepared using a volumetric ratio of Portland cement:sand of 1:4, and a water/cement ratio of 0.4. The average compressive and tensile strengths of the mortar coating were 19.30 MPa and 2.72 MPa, respectively.

#### 2.2.2. Polypropylene (PP) Reinforced Mortar Coating

#### 2.2.3. CFRP Epoxy-Bonded Sheet

#### 2.3. Test Method

_{s}was estimated using:

_{n}—net sectional area of the wall specimen:

_{70%}and G

_{33%}, respectively.

## 3. Numerical Modeling

_{n}) and shear stress (τ) to the normal interface displacement (u) and shear displacement (v), with a nominal width of 0.5 mm. In this model, eight plane stress elements and two interface elements were utilized. The mortar joints were the areas where cracks could be developed.

#### 3.1. Adopted Crack-Shear-Crush (CSC) Interface Material Model

- Tension cut-off criterion;
- Coulomb friction criterion;
- Elliptical compressive cap criterion (Figure 8).

#### 3.2. Assigning Material Properties

_{n}, shear stiffness, k

_{s}, [42] and bond strength, f

_{t}, were found in the existing scientific literature; Van der Pluijm [43] conducted extensive research on the determination of mechanical behavior of brick–mortar interfaces, where bond strength, f

_{t}, mode I and mode II fracture energies were determined together with other parameters such as internal friction angle, dilatancy coefficient, etc.

#### 3.3. Boundary Constraints

## 4. Results and Discussion

_{33%}increased between 69 and 189% compared to URM walls). However, this enhancement in stiffness is progressively reduced by increasing the shear load: this can be noted by looking at G

_{70%}values. These two indices (G

_{33%}and G

_{70%}) can be intended to represent the progression of the damage in the masonry material and the slippage at the bond between masonry and retrofit. In an ideal material, where both masonry and retrofit remain in the elastic phase, and their bond is perfect, the values of G should remain unchanged up to failure. The fact that the secant stiffness G decreases when calculated for higher values of the shear loads clearly indicates that phenomena of local cracking occur in the masonry (most likely in the mortar bed joints), and debonding develops in these regions. In this situation, the strengthened walls were still able to resist the diagonal loading by redistributing the tensile stresses from masonry to the retrofit, as common in statically indeterminate structures (known as progressive collapse).

#### Numerical vs. Experimental Results

## 5. Conclusions

- The behavior of the unreinforced shear walls was highly influenced by the strength of the mortar used in construction. In fact, only one type of failure was observed, namely, mortar cracking and debonding of the mortar from the bricks during shear testing of URM walls. Shear walls displayed considerable post-elastic deformation and energy dissipation and behaved in a quasi-ductile manner.
- Three different types of shear reinforcement were used and tested: (1) externally epoxy bonded CFRP sheets, (2) short polypropylene fibers embedded into a mortar coating, and (3) mortar jacketing reinforced with steel-wire mesh (ferrocement);
- Strengthening of unreinforced shear walls by the three methods contributed significantly to the shear performance of the walls, both increasing the lateral-load performance, shear stiffness, and ductility; the application of the different retrofits did not drastically change the wall’s failure mode: mortar in the head and bed joints cracked during shear testing, but the application of the surface retrofits could significantly produce a bridging effect to delay crack propagation in masonry. This has led to a substantial improvement of the lateral-load capacity and an ability to withstand the lateral load for higher levels of the wall’s shear deformation;
- According to the experimental findings, the ferrocement-strengthened panels exhibited a notable 546% increase in shear strength and a remarkable 680% improvement in deformation capacity compared to the control specimens. In contrast, the polypropylene-reinforced panels demonstrated a 382% enhancement in shear strength; however, they could only achieve 80% of the deformation capacity of the control specimens. The CFRP-reinforced panels exhibited a significant 444% increase in strength and a notable 370% improvement in ductility when compared to the unreinforced panels.
- To further investigate the performance of these techniques, a simplified numerical modeling was performed using commercially-available DIANA FEA software. It was noted that the numerical procedure was able to capture the structural response of both unreinforced and reinforced wall panels with acceptable reliability. The finite element analysis produced conservative results, with ferrocement exhibiting a 300% improvement in strength and an impressive 722% increase in ductility. In contrast, polypropylene showed a 200% enhancement.

## Author Contributions

## Funding

## Institutional Review Board Statement

## Informed Consent Statement

## Data Availability Statement

## Acknowledgments

## Conflicts of Interest

## References

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**Figure 1.**Common failure modes of masonry members under horizontal loading: (

**a**) in-plane failure; (

**b**) out-of-plane rocking mechanism.

**Figure 2.**Steel mesh reinforcement of shear walls: the mesh is embedded into a cement mortar coating applied to one or both sides of the shear walls. The mortar coatings are typically connected to each other with transversal ribbed steel rebars inserted into holes drilled into the wall: (

**a**) Reinforcement photo; (

**b**) detail.

**Figure 3.**The plastering with ferrocement jacketing: (

**a**) installment of the mesh; (

**b**) application of the first plaster layer; (

**c**) application of the second layer; (

**d**) details of the mesh, connector, and the mesh-wall connection.

**Figure 4.**The plastering process with polypropylene fibers: (

**a**) polypropylene fibers; (

**b**,

**c**) before and after application to brickwork walls.

**Figure 5.**Application of carbon fiber reinforced polymer (CFRP): (

**a**) placing of the CFRP sheet; (

**b**) application of epoxy; (

**c**) finished panel.

**Figure 7.**DIANA 9.6 elements used for modeling: (

**a**) Q8MEM, plane stress element; and (

**b**) CL12I, interface element [40].

**Figure 12.**The failure mode of polypropylene strengthened wall panels: (

**a**) W7-PP; (

**b**) W8-PP; (

**c**) W9-PP.

**Figure 13.**The failure mode of wall panels reinforced with carbon fibers: (

**a**) W10-CFRP; (

**b**) W11-CFRP; (

**c**) W12-CFRP.

**Figure 16.**Comparison between experimental and numerical stress–strain curves: (

**a**) unreinforced walls; (

**b**) carbon fiber reinforcement; (

**c**) polypropylene fiber reinforcement.

Mesh Type | Galvanized Welded Wires |
---|---|

Mesh size (mm) | 12 × 12 |

Nominal wire diameter (mm) | 1 |

Weight (kg/m^{2}) | 0.3 |

Young’s modulus (GPa) | 170 |

Yield strength (MPa) | 200 |

Ultimate strength (MPa) | 550 |

Chemical Base | 100% Polypropylene Fiber |
---|---|

Specific gravity (g/cm³) | 0.91 |

Fiber length (mm) | 12 |

Fiber diameter (mm) | 18 |

Melting point (°C) | 160 |

Fiber tensile strength (MPa) | 300–400 |

Fiber Young’s modulus (MPa) | ~4000 |

Specific surface area of fiber (m^{2}/kg) | 250 |

Fiber Type | Carbon |
---|---|

Orientation | unidirectional |

Fiber dry weight density (g/m^{2}) | 230 |

Fiber tensile strength (MPa) | 4300 * |

Fiber Young’s modulus (GPa) | 238 * |

Fiber elongation at break (%) | 1.8 |

Epoxy resin tensile strength (MPa) | 30 |

Epoxy resin flexural elastic modulus (GPa) | 3.8 |

Epoxy resin tensile elastic modulus (GPa) | 4.5 |

**Table 4.**Material properties used for the model [40].

Masonry | Young’s Modulus E (MPa) | Shown in Table 5 |
---|---|---|

Poisson’s ratio n (−) | 0.15 | |

Linear normal stiffness D_{11} (N/mm^{3}) | 10^{4} | |

Cracks | Linear tangential stiffness D_{12} (N/mm^{3}) | 10^{3} |

Linear normal stiffness D_{11} (N/mm^{3}) | 83.0 | |

Linear tangential stiffness D_{12} (N/mm^{3}) | 36.0 | |

Mortar tensile strength f_{t} (MPa) | 0.268 | |

Fracture energy G_{f} (N/mm) | 0.018 | |

Cohesion c (MPa) | 0.35 | |

Friction angle tan φ | 0.75 | |

Dilatancy angle tan ψ | 0.60 | |

Joints | Residual friction coefficient Φ | 0.75 |

Confining normal stress for ψ_{0}, σ_{u} (MPa) | −1.3 | |

Exponential degradation coefficient δ | 5.0 | |

Mortar compressive strength f_{c} (MPa) | 2.816 | |

Shear traction control factor C_{s} | 9.0 | |

Compressive fracture energy G_{fc} (N/mm) | 5.0 | |

Equivalent plastic relative displacement K_{p} | 0.093 | |

Fracture energy factor b | 0.05 |

Masonry Young’s Modulus E (MPa) | Masonry Shear Modulus G (MPa) | |
---|---|---|

URM | 530 | 212 |

Ferrocement | 1218 | 487 |

Polypropylene | 1265 | 506 |

Wall Panel | P_{max} (kN) | S_{s} (MPa) | δ (%) | G_{70%} (MPa) | G_{33%} (MPa) |
---|---|---|---|---|---|

W1 | 49.8 | 0.117 | 0.384 | 68 | 415 |

W2 | 54.8 | 0.129 | 0.343 | 264 | 1096 |

W3 | 64.8 | 0.153 | 0.281 | 305 | 1620 |

W-average | 56.5 | 0.133 | 0.336 | 212 | 1044 |

W4-FC | 279.0 | 0.657 | 1.872 | 567 | 1508 |

W5-FC | 299.0 | 0.704 | 2.676 | 646 | 1759 |

W6-FC | 348.7 | 0.822 | 2.311 | 248 | 2025 |

FC-average | 308.9 | 0.728 | 2.286 | 487 | 1764 |

FC vs. URM | 5.469 | 6.805 | 2.29 | 1.69 | |

W7-PP | 199.3 | 0.470 | 0.426 | 368 | 2657 |

W8-PP | 239.1 | 0.564 | 0.259 | 916 | 3985 |

W9-PP | 209.2 | 0.493 | 0.211 | 234 | 2405 |

PP-average | 215.9 | 0.509 | 0.299 | 506 | 3016 |

PP vs. URM | 3.822 | 0.888 | 2.38 | 2.89 | |

W10-CFRP | 234.2 | 0.552 | 0.889 | 65 | 3346 |

W11-CFRP | 259.1 | 0.611 | 1.813 | 34 | 960 |

W12-CFRP | 259.1 | 0.611 | 1.034 | 59 | 1036 |

CFRP-average | 250.8 | 0.591 | 1.245 | 53 | 1781 |

CFRP vs. URM | 4.443 | 3.706 | 0.25 | 1.71 |

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**MDPI and ACS Style**

Mustafaraj, E.; Corradi, M.; Yardim, Y.; Luga, E.; Codur, M.Y.
Ferrocement, Carbon, and Polypropylene Fibers for Strengthening Masonry Shear Walls. *Materials* **2023**, *16*, 4597.
https://doi.org/10.3390/ma16134597

**AMA Style**

Mustafaraj E, Corradi M, Yardim Y, Luga E, Codur MY.
Ferrocement, Carbon, and Polypropylene Fibers for Strengthening Masonry Shear Walls. *Materials*. 2023; 16(13):4597.
https://doi.org/10.3390/ma16134597

**Chicago/Turabian Style**

Mustafaraj, Enea, Marco Corradi, Yavuz Yardim, Erion Luga, and Muhammed Yasin Codur.
2023. "Ferrocement, Carbon, and Polypropylene Fibers for Strengthening Masonry Shear Walls" *Materials* 16, no. 13: 4597.
https://doi.org/10.3390/ma16134597