# Influence of Polyformaldehyde Monofilament Fiber on the Engineering Properties of Foamed Concrete

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## Abstract

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^{3}densities were produced by the insertion of four varying percentages of PFF (1%, 2%, 3%, and 4%). The properties assessed were splitting tensile, compressive and flexural strengths, workability, porosity, water absorption, and density. Furthermore, the correlations between the properties considered were also evaluated. The outcomes reveal that the foamed concrete mix with 4% PFF attained the highest porosity, with approximately 13.9% and 15.9% for 600 and 1200 kg/m

^{3}densities in comparison to the control specimen. Besides, the mechanical properties (splitting tensile, compressive and flexural strengths) increased steadily with the increase in the PFF percentages up to the optimum level of 3%. Beyond 3%, the strengths reduced significantly due to poor PFF dispersal in the matrix, leading to a balling effect which causes a degraded impact of scattering the stress from the foamed concrete vicinity to another area of the PFF surface. This exploratory investigation will result in a greater comprehension of the possible applications of PFF in LFC. It is crucial to promote the sustainable development and implementation of LFC materials and infrastructures.

## 1. Introduction

^{3}[4]. This distinction results in a decrease in the total dead load of the structural components, as well as a decrease in the costs of manufacturing and labor during the transportation and construction processes [5].

^{3}and 1200 kg/m

^{3}were achieved.

## 2. Materials and Methods

#### 2.1. Mix Constituents

^{3}and particle sizes ranging from 0.15 to 2.36 mm, as well as Portland cement that complied with the specifications of the British Standards Institution (1996). The entire required fine river sand quantity underwent a sieve examination to fit the coarse aggregate standard specification, as per what was stated in ASTM-C33. Figure 1 shows the result of the sand grading curve. Besides, using a protein-based surfactant, stable foam with a density of 70 kg/m

^{3}was produced. It was attenuated in the mortar slurry at a ratio of 1:34 and then aerated using a TM-1 foam generator. Then, four different weight fractions of polypropylene fibrillated fiber (Figure 2) in a range from 1% to 4% were added to the foamed concrete mixtures. Table 1 displays the physical and mechanical characteristics of polypropylene fibrillated fiber (PFF).

#### 2.2. Mix Proportions

^{3}were cast. The cement-to-sand ratio was held at 1:1.5, and the water-to-cement proportion was maintained at 0.45 for all mixtures. Five distinct PFF weight fractions of 1%, 2%, 3% and 4% were selected for addition to foamed concrete mixtures. Table 2 displays the proportions of the created foamed concrete mixture.

## 3. Results

#### 3.1. Flow Table Test

#### 3.2. Porosity Test

#### 3.3. Water Absorption Test

#### 3.4. Compression Test

#### 3.5. Flexural Test

#### 3.6. Splitting Tensile Test

## 4. Discussion

#### 4.1. Spreadability

^{3}densities of the control specimens, respectively. Spreadability was reduced by adding PFF to foamed concrete, and this effect was proportional to the amount of PFF added. Foamed concrete mixes with 4% PFF had the lowest spreadability when compared to the other foamed concrete mixes. Spreadabilities were measured to be 206 mm for 600 kg/m

^{3}and 187 mm for 1200 kg/m

^{3}. Because PFF tends to absorb water, there is a consistent decrease in spreadability when it is are present; the external segment of PFF presents significant porosity, which benefits the bond to the matrices, and thus the spreadability of the foamed concrete decreases. In addition, the cementitious matrices aggregate on the PFF’s large specific surface area, increasing the foamed concrete’s viscosity and causing a decrease in spreadability at greater PFF weight fractions. As the air bubbles are forced out of the cementitious matrix, the slump diameter of the foamed concrete will decrease as a result of the free flow of the intermittent stage above the capacity of the stable spreading form. Mortar must additionally cover the smooth PFF membrane in addition to the fine filler (sand). The spreadability of foamed concrete was reduced as the percentage of PFF was raised from 1% to 4%, indicating that greater quantities filling mortar was required to cover the additional zone of PFF. Furthermore, PFF increases the inner abrasion between foamed concrete components, which in turn causes more cement matrix to diminish the inner resistance, hence reducing the workability of foamed concrete. A similar finding, that increasing the fiber’s weight fraction in concrete reduced its workability, was previously described by Mohseni et al. [29].

#### 4.2. Density

^{3}for all foamed concrete mixes that included PFF in different percentages. For instance, for mixes PF0%, PF1%, PF2%, PF3% and PF4%, the discrepancies between final dry densities and planned dry densities of 600 kg/m

^{3}density were ±2 kg/m

^{3}, ±5 kg/m

^{3}, ±10 kg/m

^{3}, ±19 kg/m

^{3}and ±24 kg/m

^{3}, respectively. The foamed concrete properties are entirely reliant on the dry density [30].

#### 4.3. Porosity

^{3}densities, respectively. It is possible that this is because of the high packing capacity that PFF has in the cementitious matrix of foamed concrete. A porosity value of 64.9% was observed for the foamed concrete mix, with a density of 600 kg/m

^{3}and a percentage of PFF of 4%, whereas a porosity value of 75.4% was recorded for the control sample. Microcracks formed on the surface of the foamed concrete while it was still in its fresh state condition. At the same time, the surface moisture was rapidly evaporating, which resulted in significant dry shrinkage. When PFF is added to foamed concrete mixes, the segregation can be reduced, and this also helps to reduce the amount of water that is lost through evaporation. In addition to this, the use of PFF has been shown to effectively stop the spread of cracks in foamed concrete that start on the surface and move inward [31]. The morphology of the control foamed concrete specimen, which has a density of 1200 kg/m

^{3}, is shown in Figure 11a. It was clear that there were a great number of huge pores that were attached to one another, which resulted in a high porosity value. With the presence of 4% PFF, the compactness of the foamed concrete is improved, and the number of pores that are both large and interconnected is reduced significantly. As the PF was incorporated into the cementitious matrix, as seen in Figure 11b, the internal structure became denser and a homogenous microstructure was achieved, all while decreasing the foamed concrete porosity value.

#### 4.4. Water Absorption

#### 4.5. Water Absorption—Porosity Relationship

^{3}densities, correspondingly.

#### 4.6. Compressive Strength

^{3}densities, corresponding with the insertion of various percentages of PFF, are shown in Figure 14 and Figure 15 (the dataset can be found in Appendix A, Table A1). Generally, adding PFF to foamed concrete limited in the growth of the material’s compressive strength. For both densities, the optimal percentage of PFF was 3%. PFF was added to foamed concrete, which resulted in a decrease in the amount of entrapped air voids, capillary pores, and entrained air voids. All three of these factors contribute to a rise in the foamed concrete compressive strength. The compressive strengths of the foamed concrete on days 7, 28, and 56 with the inclusion of PFF were greater than the control specimen strength, regardless of the density of the foamed concrete. In comparison to the control specimen, which only achieved compressive strengths of 1.37 MPa (600 kg/m

^{3}) and 4.34 MPa (1200 kg/m

^{3}), the optimal compressive strengths achieved on day 56 were 2.26 MPa and 7.83 MPa, with the inclusion of a 3% and 4% weight fraction of PFF for the 600 and 1200 kg/m

^{3}densities, respectively. When an optimal percentage of PFF is evenly scattered in foamed concrete cement paste, the hydrated products of cement amass around the PFF. This is due to their superior surface energy, as their surface behaves as a nucleation site. As the foamed concrete contracts, the PFF membrane absorbs tensile energy through the boundary between the PFF and the foamed concrete cementitious matrix. It then transfers this energy to the neighboring matrix, thereby reducing the amount of concentrated tensile stress and increasing the foamed concrete’s resistance to cracking [36]. Poor PFF dispersal in the foamed concrete cementitious matrix results in a balling effect when the percentage of PFF in the foamed concrete exceeds 3%. This creates a deteriorated impact by scattering the tensile stress from the vicinity of the foamed concrete to another place on the PFF surface. This explanation lends credence to the idea that a decline in compressive strength occurred when the weight fractions of PFF increased to a level greater than 3%.

#### 4.7. Flexural Strength

^{3}are shown in Figure 16 and Figure 17, respectively (the dataset can be found in Appendix A, Table A1). These densities correspond with different weight fractions of PFF. It is clear from looking at Figure 16 and Figure 17 that the inclusion of PFF in foamed concrete led to a rise in flexural strength. For both densities considered in this study, the best weight fraction of PFF was 3%. The flexural strengths of the foamed concrete with the presence of PFF on days 7, 28, and 56 were greater than the flexural strength of the control specimen, regardless of the density of the foamed concrete. In contrast to the control specimen, which only achieved flexural strengths of 0.38 MPa (600 kg/m

^{3}) and 1.04 MPa (1200 kg/m

^{3}), the ideal flexural strengths that were attained at day 56 were 0.63 MPa and 1.66 MPa, with the addition of a 3% of PFF for the 600 kg/m

^{3}and 1200 kg/m

^{3}. PFF is a hydrophilic substance, and as a result, it possesses great adhesion when combined with cement paste. After the PFF percentage was increased to 4%, the flexural strength of foamed concrete drastically dropped for both densities that were taken into consideration for this investigation. Because it is difficult to disperse the PFF evenly and because it might cause agglomeration, the flexural strength will be lowered if the percentage of PFF is too high. This is because PFF can cause agglomeration. During the process of the crack spreading out, the PFF will gradually become separated from the matrix until the bond strength is completely exceeded. This will continue until the fracture has completely spread out. Although the matrix is damaged, it is still capable of maintaining its fundamental form. The presence of PFF in foamed concrete plays a significant role in both the strengthening of the foamed concrete cementitious matrix, and the modification of the material’s physical characteristics from a brittle state to a ductile one. Both of these effects are the result of the material’s transition from a brittle to a ductile state. Because an appropriate percentage of PFF can bond with the hydration products and unhydrated constituents in the foamed concrete matrix to build a three-dimensional grid structure, incorporating an appropriate weight fraction of PFF can efficiently increase the flexural strength of foamed concrete. This is because the three-dimensional network structure can create a subsidiary effect and boost the foamed concrete flexural strength [37].

#### 4.8. Splitting Tensile Strength

^{3}(the dataset can be found in Appendix A, Table A1). It is clear from the whole trend that with the rise in PF percentages, the splitting tensile strength of both foamed concrete densities at different ages all exhibit an upward trend. This is the case because the PFF percentages are increasing as the trend continues. In most cases, the splitting tensile strength progressively increases with the growth in the percentages of PFF up to 3%. In comparison to the control specimen, which achieved compressive strengths of 0.24 MPa (600 kg/m

^{3}) and 0.64 MPa (1200 kg/m

^{3}), the optimal splitting tensile strengths attained at day 56 were 0.39 MPa and 0.93 MPa, with the inclusion of a 3% PFF for the 600 and 1200 kg/m

^{3}densities. Because of the enhanced foamed concrete robustness, helped along by the presence of PFF, the enhancement of splitting tensile strengths was accomplished for both materials that were taken into consideration throughout this investigation. PFF will gradually form a fiber grid skeleton inside the foamed concrete as it goes through the process of hardening. This can improve the brittle state of the foamed concrete matrix by governing the growth and propagation of cracks when it is subjected to external tensile stress, preventing the cracks from leading to an explosive failure. It became apparent that the PFF could be uniformly disseminated when the PFF percentage was 3%, which resulted in a growth in the bonding strength between the cement matrix and the PFF. The PFF is dispersed throughout the foamed concrete matrix in a manner that is nearly homogeneous and does not show any significant signs of buildup. In the presence of a tensile load, foamed concrete demonstrates elastic linear tension prior to the onset of plastic deformation, which occurs after the appearance of the first crack in the material. The addition of PFF membrane to foamed concrete, on the other hand, causes the membrane to take on the role of fastening when the foamed concrete cracks. This ensures that the matrix elastic modulus does not immediately drop to zero when the direct boundary strain is reached [38,39,40]. When cracks appear in the PFF membrane, the membrane will bear all the tension and then gradually transmit it to the matrix [8,41,42,43,44,45].

#### 4.9. Compressive—Flexural Strengths Relationship

^{3}of foamed concrete was used in the execution of a correlation between the compressive and flexural strengths of the material. For the purpose of this investigation, all curing periods were taken into account. The connection between the flexural and compressive strengths of foamed concrete with various percentages of PFF is demonstrated in Figure 20. It seems that they found out that there is a direct expanding, relationship that can be differentiated in the compressive strength and flexural strength of foamed concrete. From Figure 20, it can be seen that an R-squared value of 0.9588 was obtained, which indicates a highly linear relationship between the two strength parameters. This implies that variations in the predictors are interrelated to deviations in the response variable and that the achieved prediction models explain a significant portion of the response’s inherent variability. Because of this relationship, it is clear that the flexural strength of foamed concrete increases as the compressive strength of the concrete increases. This regression model makes it possible to approximate the flexural strength of foamed concrete, based on its axial compressive strength, for the range of values that was investigated in this exploration.

#### 4.10. Compressive—Splitting Tensile Strengths Relationship

^{3}density foamed concrete with different PFF percentages is shown in Figure 21. The compressive strength was mapped against the foamed concrete’s splitting tensile strength. According to Figure 21, data dissemination supports the existence of a strong correlation between the splitting tensile and compressive strengths of foamed concrete. In a similar trend, the splitting tensile strengths rose with increasing compressive strength for all curing periods. With an R-squared value of 0.9646, a strong linear connection is evident. The splitting tensile strength was approximately 15% of its strength under compression conditions for the total specimens evaluated in this investigation.

## 5. Conclusions

^{3}densities were made. Compressive, splitting tensile and flexural strengths were assessed. Additionally, the workability, porosity, water absorption, and density of products were evaluated as well. Additionally, the correlations between the considered properties were analyzed. When PFF is added to foamed concrete, spatial networks are formed and cement paste is incinerated to cover the PFF, resulting in reduced spreadability versus foamed concrete without fibers. However, all foamed concrete mixes exhibited spreadabilities greater than 187 mm, indicating a significant capacity for self-flow. In contrast to the control specimen, the dry density of the foamed concrete decreases as the PFF weight fractions rise from 1% to 4%. The control specimen had the highest dry density of foamed concrete, whereas the 4% PFF inclusion product had the lowest density. Due to the intricacy of the compaction process, which produces porous foamed concrete, the dry density decreased at larger weight fractions of PFF. With the presence of PFF, the foamed concrete porosity grows gradually up to 4%. Foamed concrete mixes containing 4% PFF achieved the optimal porosity with a reduction of around 13.9% and 15.9% for 600 and 1200 kg/m

^{3}densities correspondingly. This is most likely because foamed concrete’s cement matrix has strong PFF packing capabilities. As the PFF percentages rose from 1% to 4%, foamed concrete water absorption was increased. With the addition of 4% PFF, the highest water absorption capacity was achieved. When PFF is added to foamed concrete, the fissures are less noticeable and finer than they are in foamed concrete that does not contain PFF. The foamed concrete flexural, compressive, and splitting tensile strengths were increased by the addition of PFF. The ideal percentage of PFF for both densities was 3%. The foamed concrete’s compressive, flexural, and breaking tensile strengths considerably decreased above the 3% PFF. It is difficult to spread the PFF uniformly, and agglomeration is caused if the PFF weight fractions are too large.

## Author Contributions

## Funding

## Conflicts of Interest

## Appendix A

Specimen | 600 kg/m^{3} | 1200 kg/m^{3} | |||||
---|---|---|---|---|---|---|---|

7 Day | 28 Day | 56 Day | 7 Day | 28 Day | 56 Day | ||

Compressive Strength (MPa) | Control | 0.98 | 1.22 | 1.37 | 3.11 | 3.88 | 4.35 |

1% | 1.21 | 1.51 | 1.69 | 4.16 | 5.20 | 5.83 | |

2% | 1.40 | 1.76 | 1.97 | 4.47 | 5.59 | 6.26 | |

3% | 1.61 | 2.02 | 2.26 | 5.34 | 6.68 | 7.48 | |

4% | 1.47 | 1.87 | 2.10 | 4.57 | 5.67 | 6.35 | |

Flexural Strength (MPa) | Control | 0.27 | 0.34 | 0.38 | 0.74 | 0.93 | 1.04 |

1% | 0.34 | 0.43 | 0.48 | 0.93 | 1.16 | 1.30 | |

2% | 0.38 | 0.48 | 0.54 | 1.04 | 1.31 | 1.46 | |

3% | 0.45 | 0.56 | 0.63 | 1.19 | 1.48 | 1.66 | |

4% | 0.40 | 0.49 | 0.55 | 1.02 | 1.28 | 1.44 | |

Splitting Tensile Strength (MPa) | Control | 0.17 | 0.21 | 0.24 | 0.46 | 0.57 | 0.64 |

1% | 0.21 | 0.26 | 0.30 | 0.57 | 0.71 | 0.80 | |

2% | 0.24 | 0.30 | 0.33 | 0.62 | 0.78 | 0.87 | |

3% | 0.28 | 0.35 | 0.39 | 0.66 | 0.83 | 0.93 | |

4% | 0.25 | 0.31 | 0.34 | 0.61 | 0.76 | 0.85 |

Specimen | 600 kg/m^{3} | 1200 kg/m^{3} | |
---|---|---|---|

Workability (mm) | Control | 255 | 230 |

1% | 235 | 210 | |

2% | 225 | 202 | |

3% | 214 | 194 | |

4% | 206 | 185 | |

Density (kg/m ^{3}) | Control | 600 | 1200 |

1% | 594 | 1195 | |

2% | 589 | 1190 | |

3% | 580 | 1185 | |

4% | 574 | 1181 | |

Porosity (%) | Control | 75.4 | 54.5 |

1% | 69.1 | 51.1 | |

2% | 68.3 | 50.4 | |

3% | 67.5 | 49.3 | |

4% | 64.9 | 45.8 | |

Water Absorption (%) | Control | 46.4 | 25.9 |

1% | 48.4 | 26.5 | |

2% | 49.2 | 27.3 | |

3% | 50.0 | 28.1 | |

4% | 50.7 | 29.2 |

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**Figure 14.**Compressive strength of foamed concrete of 600 kg/m

^{3}density with varying PFF percentages.

**Figure 15.**Compressive strength of foamed concrete of 1200 kg/m

^{3}density with varying PFF percentages.

**Figure 16.**Flexural strength of foamed concrete of 600 kg/m

^{3}density with varying PFF percentages.

**Figure 17.**Flexural strength of foamed concrete of 1200 kg/m

^{3}density with varying PFF percentages.

**Figure 18.**Splitting tensile strength of foamed concrete of 600 kg/m

^{3}density with varying PFF percentages.

**Figure 19.**Splitting tensile strength of foamed concrete of 1200 kg/m

^{3}density with varying PFF percentages.

Properties | Value |
---|---|

Elastic modulus (GPa) | 7.25 |

Tensile strength (MPa) | 915 |

Elongation at failure (%) | 19.3 |

Thermal conductivity (W/mK) | 0.255 |

Specific heat capacity (J/kgK) | 1335 |

Melting temperature (°C) | 160 |

Specific weight (g/cm^{3}) | 0.89 |

Thickness (mm) | 0.25 |

Length (mm) | 19 |

Density (kg/m ^{3}) | PFF (%) | Cement (kg/m^{3}) | Sand (kg/m^{3}) | Water (kg/m^{3}) | Foam (kg/m^{3}) | PFF (kg/m ^{3}) |
---|---|---|---|---|---|---|

600 | 0 | 230.2 | 345.4 | 103.6 | 43.2 | 0.0 |

600 | 1 | 230.2 | 345.4 | 103.6 | 43.2 | 7.2 |

600 | 2 | 230.2 | 345.4 | 103.6 | 43.2 | 14.4 |

600 | 3 | 230.2 | 345.4 | 103.6 | 43.2 | 21.7 |

600 | 4 | 230.2 | 345.4 | 103.6 | 43.2 | 28.9 |

1200 | 0 | 446.9 | 670.4 | 201.1 | 24.4 | 0.0 |

1200 | 1 | 446.9 | 670.4 | 201.1 | 24.4 | 13.4 |

1200 | 2 | 446.9 | 670.4 | 201.1 | 24.4 | 26.9 |

1200 | 3 | 446.9 | 670.4 | 201.1 | 24.4 | 40.3 |

1200 | 4 | 446.9 | 670.4 | 201.1 | 24.4 | 53.7 |

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## Share and Cite

**MDPI and ACS Style**

Mydin, M.A.O.; Abdullah, M.M.A.B.; Mohd Nawi, M.N.; Yahya, Z.; Sofri, L.A.; Baltatu, M.S.; Sandu, A.V.; Vizureanu, P.
Influence of Polyformaldehyde Monofilament Fiber on the Engineering Properties of Foamed Concrete. *Materials* **2022**, *15*, 8984.
https://doi.org/10.3390/ma15248984

**AMA Style**

Mydin MAO, Abdullah MMAB, Mohd Nawi MN, Yahya Z, Sofri LA, Baltatu MS, Sandu AV, Vizureanu P.
Influence of Polyformaldehyde Monofilament Fiber on the Engineering Properties of Foamed Concrete. *Materials*. 2022; 15(24):8984.
https://doi.org/10.3390/ma15248984

**Chicago/Turabian Style**

Mydin, Md Azree Othuman, Mohd Mustafa Al Bakri Abdullah, Mohd Nasrun Mohd Nawi, Zarina Yahya, Liyana Ahmad Sofri, Madalina Simona Baltatu, Andrei Victor Sandu, and Petrica Vizureanu.
2022. "Influence of Polyformaldehyde Monofilament Fiber on the Engineering Properties of Foamed Concrete" *Materials* 15, no. 24: 8984.
https://doi.org/10.3390/ma15248984