The chapter focuses on the reinforcement of foamed concrete with polypropylene fibers and geotextiles for geotechnical applications. It begins by defining foamed concrete and its key properties, including low density and good insulation parameters. The study then introduces two reinforcement solutions: polypropylene fibers and geotextiles of varying weights. Through extensive testing, the authors demonstrate that the addition of polypropylene fibers significantly enhances the splitting tensile strength of foamed concrete, transforming its failure mode from brittle to ductile. Similarly, the use of geotextiles increases the flexural strength of foamed concrete, with the improvement proportional to the weight of the geotextile. These findings suggest that reinforced foamed concrete could be suitable for applications such as road pavement subsoil systems. The chapter concludes with a discussion on the potential of reinforced foamed concrete and its relevance to broader research projects in the field.
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Abstract
Foamed concrete is known as lightweight or cellular concrete. It is commonly defined as a cementitious material with a minimum of 20% (by volume) mechanically entrained foam in the mortar mix where air-pores are entrapped in the matrix by means of a suitable foaming agent. Although the foamed concrete has been patented in 1923, it is mainly used as a filling or leveling material. The use of foamed concrete has been limited e.g. for backfilling retaining walls. As a material used in contact with the ground, it is a relatively new material. In order to use foamed concrete in road construction as a replacement for hydraulically bound mixtures, the improvement of foamed concrete was considered. The article presents the two different type of polypropylene reinforced of foamed concrete. Polypropylene fibers with content of 0.3 kg/m3 and 6.37 kg/m3 were used. For foamed concrete samples with addition of 6.37 kg/m3 PP fibers, the splitting tensile strength increased. In second case, the polypropylene geotextiles with weight 150 g/m2, 200 g/m2 and 500 g/m2 were used. It can be observed that flexural strength for foamed concrete reinforced with geotextile samples was higher compared to the base (unreinforced) foamed concrete sample. On this basis, the suitability of using reinforced foamed concrete in the road pavement-subsoil system was determined.
1 Introduction
Foamed concrete is known as lightweight or cellular concrete. It is commonly defined as a cementitious material with a minimum of 20% (by volume) mechanically entrained foam in the mortar mix where air-pores are entrapped in the matrix by means of a suitable foaming agent (protein or synthetic). The most important features of foamed concrete include low density (from approximately 100 kg/m3 to 1800 kg/m3 [1‐3]), good insulation parameters (thermal conductivity coefficient λ ranging from approximately 0.05 W/(m·K) to 1 W/(m·K) K) [4‐8]), speed and ease of implementation and low cost of production. However, although the foamed concrete has been patented in 1923, it is mainly used as a filling or leveling material. The use of foamed concrete has been limited e.g. for backfilling retaining walls. As a material used in contact with the ground, it is a relatively new material (Figs. 1 and 2). In addition, the use of a structure or building element in contact with the ground, as is the case, among others, in road pavement or floors on the ground, requires specific material and strength properties related to the soil and water conditions occurring in a given area [9‐14].
Applications of foamed concrete in the construction of a parking lot in Trencin, Slovakia: in section (a) and in view (b) [16]
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In this purpose special test stand was created at the Faculty of Civil Engineering of the University of Žilina (FCE Uniza) [17, 18]. In order to use a foamed concrete layer in the lower subbase layer, it is necessary to meet the requirements for tensile stresses at the bottom of this layer. The reinforced foamed concrete is rarely presented in the literature. The aim of the article is to attempt to improve foamed concrete through various types of reinforcement: by using polypropylene fibre (first solution (I)) and polypropylene geotextile (solution II).
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2 Materials and Methods
2.1 Case I—Foamed Concrete Reinforced with PP Fiber
The tests in case I have been performed on foamed concrete with density of 800 kg/m3. The materials used in this study were Portland cement, water and synthetic foaming agent. The industrial cement was Portland cement CEM I 42.5 R, according to PN-EN 197–1:2011 [19].
Polypropylene fiber with a length of 13 mm was used (Fig. 3). The fiber content was 0.30 kg/m3 and 6.37 kg/m3.
Fig. 3.
Used polypropylene fiber
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The splitting tensile strength of foamed concrete reinforced with PP fiber was performed according to PN-EN 12390–6 [20], but loading speed was equal 0,05 ± 0,01 MPa/s.
2.2 Case II—Foamed Concrete Reinforced with PP Geotextile
The tests in case II have been performed on foamed concrete with density of 500 kg/m3. The materials used in this study were cement, ground granulated blast-furnace slag (GGBS), aggregate with fraction of 0/2 mm, clean water without chemical residues and protein foaming agent. The Portland cement CEM I 42.5 R according to EN 197–6:2023 [21] was used.
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Used reinforcement was polypropylene geotextile with a tree different weight: 150 g/m2, 200 g/m2 and 500 g/m2, see Fig. 4. The parameters of geotextile were presented in Table 1 and in Fig. 5. The geotextile is made of cut polypropylene fibers with density of 0.91 kg/dm3 and melting temperature of 165 ℃ connected in the needling process.
Fig. 4.
Used geotextile Filtek 500 non-woven PP geotextile ironed (a) and detail (b)
Table 1.
Parameters of geotextiles
Parameter
Geotextile with weight of:
150 g/m2
200 g/m2
500 g/m2
tensile strength (kN/m−)
• longitudinal direction
• transversal direction
3.4 ± 0.4
9.5 ± 1.0
12.0 ± 1.0
7.5 ± 1.0
33 ± 2
19 ± 2
ductility (%)
• longitudinal direction
• transversal direction
120 ± 35
80 ± 20
75 ± 15
115 ± 15
70 ± 20
115 ± 15
dynamic puncture resistance (mm)
19 ± 4
14 ± 2
6 ± 2
static puncture resistance (N)
850 ± 150
1400 ± 200
3600 ± 300
Fig. 5.
Load-Tensile strain curves of geotextile with weight 500 kg/m3 for longitudinal (a) and transversal direction (b)
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The flexural strength of foamed concrete reinforced with PP geotextile was determined in a four-point flexural test in accordance with the EN ISO 12390–5 standard [22]. The reinforced foamed concrete beam with dimensions of 100 mm x 100 mm x 400 mm was tested.
3 Results and Conclusions
3.1 Case I – Foamed Concrete Reinforced with PP Fiber
The effect of the polypropylene fiber content on the splitting tensile strength for foamed concrete (without the addition of sand) is shown in Fig. 6. For a density of 800 kg/m3, the addition of polypropylene fibers in the amount of 0.30 kg/m3 (approximately 0.1% of the cement mass) does not improve the splitting tensile strength of foamed concrete. However, the addition of polypropylene fibers in the amount of 6.37 kg/m3 (approximately 2% of the cement mass) is characterized by approximately 30% higher splitting tensile strength compared to the value obtained for foamed concrete without the addition of fibers. Similar results were obtained by Bing et al. [23], who showed an increase in splitting tensile strength by 31.7% by using the addition of polypropylene fibers compared to foamed concrete without fibers.
Fig. 6.
The effect of polypropylene fiber content on splitting tensile strength for foamed concrete with a density of 800 kg/m3
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Moreover, the use of fibers in foamed concrete, in addition to strengthening it, also changes the nature of the degradation of foamed concrete samples, from brittle to ductile (Fig. 7).
Fig. 7.
Degradation of samples in the splitting tensile strength test for foamed concrete with a density of approximately 750 kg/m3 without the addition of fibers (a) and with the addition of polypropylene fibers in the amount of 6.37 kg/m3 (b)
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3.2 Case II—Foamed Concrete Reinforced with PP Geotextile
Figure 8 presents result of four-point flexural test of foamed concrete with density of 500 kg/m3. It can be observed that flexure strength increased for foamed concrete with geotextile. Increase in flexural strength of foamed concrete with geotextile is proportional to weight of the geotextile. Flexural strength increased by about 11%, 20% and 56% compared to the unreinforced foamed concrete sample for the geotextile with weight of 150 g/m2, 200 g/m2 and 500 g/m2, respectively.
Fig. 8.
Flexural strength of foamed concrete with density of 500 kg/m3 without and with the PP geotextile with different weight
Fig. 9.
Degradation of samples in the flexural test for foamed concrete with a density of approximately 500 kg/m3 without (a) and with the geotextile with weight of 500 g/m3 (b)
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A different nature of degradation of foamed concrete with geotextile compared to the base sample (without reinforcement) was demonstrated, see Fig. 9.
4 Conclusions
The research aimed to assess the possibility of using propylene reinforcement as an improvement for foamed concrete. For this purpose, two different types of PP reinforcement were assumed. Propylene fibers with a length of 13 mm and a content of 0.3 kg/m3 and 6.37 kg/m3 were used (Case I). In addition, geotextiles of three different weights (150 g/m2, 200 g/m2 and 500 g/m2) were used (Case II). The positive effect of polypropylene reinforcement in improvement foamed concrete has been demonstrated. Each time, the tensile strength was higher, and the nature of failure changed from brittle to ductile. The following conclusions from the research described above can be drawn:
for foamed concrete samples with addition of 6.37 kg/m3 PP fibers, the splitting tensile strength increased,
increase in flexure strength of foamed concrete with geotextile is proportional to weight of the geotextile.
On this basis, the suitability of using reinforced foamed concrete in the road pavement-subsoil system was determined. Moreover, the article is part of a wider research project aimed at assessing reinforced foamed concrete.
Acknowledgements
The results presented in this article are the result of the scientific internship and to conduct classes in the frame of the Personal exchange program for students and scientists as part of bilateral cooperation—mobility offer for the academic year 2021/2022 financed by the NAWA (Polish National Agency for Academic Exchange) No. PPN/BIL/2020/1/00318/U/01 and the result of the research project No. VEGA 1/0484/20 ‘Experimental and numerical analysis of base layers of foamed concrete reinforced with geosynthetics’.
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