1 Introduction

There are many cities in cold climates in the world that are located in areas with high risks of disasters. One of the major problems in these areas is temporary accommodation after disasters. Tents that are used for temporary accommodations are not appropriate insulation for the cold, rain, and snow penetration (Sukontasukkul 2009). The crisis management plays a very important role in organizing and providing temporary housing. To accelerate the process of temporary accommodation, it is necessary to use materials which are lightweight, easily transportable, and prefabricated (Kwon et al. 2015). Because of the effects of out-of-plane forces such as snow and wind, these materials should have suitable mechanical properties such as ductility and sufficient strength (Chen and Liu 2005; Gao and Sun 1997; Wasseman and Bentur 1997). The designers should consider enough out-of-plane strength, because it affects the structure’s behavior and reduces the damages of earthquake (Felice and Giannini 2001; Mohammadi Ghazimahalleh 2008). Lightweight concrete (LWC) has been successfully used in various constructions for many years. The main disadvantage of plain LWC panels is their low flexural strength. In order to improve this disadvantage, fiber/textile should be added to LWC panels so that their mechanical properties would be improved (Nishiwaki et al. 2012; Balendran et al. 2002; Merikallio et al. 1996; Reinhardt et al. 2003).

A comprehensive study of the polypropylene fiber-reinforced fly ash-based geopolymer is presented by Ranjbar et al. (2016a). The fiber–matrix interface and fiber surface were assessed in detail using field emission scan electron microscopy and also atomic force microscopy. Based on the present results, incorporation of PPF up to 3 wt% into the geopolymer paste reduces the shrinkage and enhances the energy absorption of the composites, while it might reduce the ultimate flexural and compressive strength of the material depending on the fiber content.

Failure prediction and reliability analysis of fibrocement composite structures by incorporating machine learning into acoustic emission monitoring technique are provided by Behnia et al. (2016). In this study, acoustic emission signal energy was first examined to find out the relation between damage progress and acoustic emission signal energy so that a damage index based on acoustic emission signal energy could be proposed. The results show that acoustic emission events with high energy were associated with activities in the fracture process zone. Moreover, the accuracy of a support vector regression technique in estimation of structural condition health as an intelligent method was presented in this study.

Effect of micro steel fibers incorporation on mechanical properties of fly ash-based geopolymer was investigated at different volume ratios of matrix by Ranjbar et al. (2016b). Various properties of the composite were compared and contrasted in terms of fresh state by flow measurement and hardened state by variation of shrinkage over time to assess performance of the composites subjected to flexural and compressive load. Test results confirmed that micro steel fibers additions could significantly improve both ultimate flexural capacity and also ductility of fly ash-based geopolymer, especially at early ages without an adverse effect on ultimate compressive strength.

Liu and Pantelides (2013) studied the behavior and shear capacity of LWC precast panels reinforced with glass fiber-reinforced polymer (GFRP) bars. In their study, the experimental results were compared with obtained formulation of ACI 440.IR (2006) regulations for panels made with LWC and normal weight concrete in which both panels were reinforced with GFRP. Results indicated that experimental shear capacity is different from shear capacity of ACI regulations. This difference is due to a disregard for concrete type in evaluating shear capacity by use of the ACI regulations formula. A reducing factor was added to the ACI formula, to compensate the mentioned difference (ACI 318–11 2001).

Seijo in his study on fiber-reinforced foam-based lightweight concrete precast wall panels obtained a relationship between the pressure applied to the walls and the capacity of deflection of the walls before reaching failure (Seijo 2001). The results confirmed the weak bond between steel reinforcement and concrete. Even though the behavior was ductile, the sudden detachment of wall panels indicates a need to improve the reinforcement in the joint between the floor slab and wall panels. This building prototype experienced a maximum pressure of 4.76 psi (0.33 kg/cm2) before failure. The results from this test were compared to normal weight concrete, and it showed that the developed panels behaved more ductile than the normal weight concrete.

The mechanical performance of three types of FRLWC panels was investigated by Arisoy and Wu (2008). These panels were made of fiber-reinforced lightweight aggregate concrete, fiber-reinforced aerate concrete, and fiber-reinforced lightweight aggregate aerated hybrid concrete. Results showed that fiber-reinforced LWC, produced from a small amount of short polyvinyl alcohol fibers and lightweight aggregates, air-entraining agent, or a combination of both, exhibits strain hardening. Such fiber-reinforced concrete indicated a very large ductility and increase in ultimate flexural strength, in comparison with plain LWC.

Butler et al. (2009) studied durability of fiber–matrix interfaces in textile-reinforced concrete. Changes in the strength and toughness of textile-reinforced concrete with increasing age are determined essentially by the durability of the armoring fibers, the matrix itself, and the bond between the matrix and the fibers. The investigations were conducted on multi-filament yarns of AR-glass which were imbedded in matrices of varying alkalinity and hydration kinetics. Results indicated that measured reductions in the toughness of the composite material could be attributed to the diminishing protective effect of organic polymer sizing on the surface of the filaments as well as to the disadvantageous new formation of solid hydration phases in the fiber–matrix interface.

In this paper, the mechanical properties of F/TRLWC precast panels are studied. Different reinforcements are added or embedded to the LWC to improve the ductility and strength of panels. In order to evaluate the mechanical properties of various panels, a three-point bending test is performed. Based on these tests, the load–displacement and energy absorption curves are suggested. The main objective of this research was to study the flexural behavior of these panels and give appropriate recommendations for their possible application in temporary housing.

2 Materials and Methods

The paper presents the results of experimental tests carried out on thin panels made of a lightweight concrete matrix reinforced with either dispersed short fibers or textiles; both steel and polymeric reinforcements are considered. The important parameters in the present work, in order to prepare the panels, are based on the following: (1) four different kinds of reinforcements are used to improve ductility and flexural strength of panels as well as their performance; (2) lightweight materials are used to reduce the density.

2.1 Materials

The used materials in this investigation are LWA, cement, water, reinforcement, and fine aggregates. The important applications of LWA include building masonry blocks, wall panels, precast concrete elements, structural in situ concrete, screeding, and cladding. Due to cellular structure of LWA, the major advantages are thermal insulation and reduction of concrete’s dead load. One of the main problems of using LWA in concrete is high water absorption due to porous structure (Shannag 2011). Figure 1 shows photographs for the artificial LWA used in this investigation.

Fig. 1
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LWAs used in panel

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2.1.1 Reinforcement

Low modulus, high elongation fibers and high modulus and strength fibers are two types of fibers used in concretes (Kim et al. 2010; Barnett et al. 2010). Nylon, poly propylene, and polyethylene are subtypes of low modulus, high elongation fibers that are capable of large energy absorption characteristics. They impart toughness and resistance to impact and explosive loads; however, they do not improve strength. While steel, glass, asbestos, and carbon are from high modulus and strength fibers’ family. They improve strength, stiffness, and dynamics properties of the concrete. Fibers used in this paper are made of nylon and textile and include steel mesh, geogrid, and geonet.

2.1.1.1 Nylon Fibers

Nylon is a subtype of polypropylene fibers which can be used to produce burlap. Tensile force and elongation of fibers are about 60 N and 15 mm, respectively. A brief summary of the properties of Nylon fibers is presented in Table 1. Also, the nylon fibers used in panels and the force–displacement curve are given in Figs. 2 and 3, respectively.

Table 1 The properties of nylon fibers
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Fig. 2
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Nylon fibers used in panels

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Fig. 3
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Force–displacement curve obtained from the tested fiber prototype (20 cm)

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2.1.1.2 Steel Mesh

In this study, the diameter of used wires in steel mesh is about 0.8 mm, and the length of squares is about 1 cm, and measuring length of sample is 20 cm. Under tensile tests at laboratory, obtained force and elongation of wire mesh are about 140 N and 2 mm, respectively. The steel mesh used in this investigation is shown in Fig. 4, and the curve of load versus displacements for wire mesh is shown in Fig. 5.

Fig. 4
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Steel mesh

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Fig. 5
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Force–displacement curve obtained from tensile test

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2.1.1.3 Geogrid

The cross section width, thickness, and the length of squares of the sample are 3 mm, 1 mm, and 20 mm, respectively. Geogrid specimen is shown in Fig. 6. The measuring length of sample is 20 cm. Rupture force and elongation are obtained 1400 N and 7 mm, respectively. Geogrid tensile test result is shown in Fig. 7.

Fig. 6
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Geogrid specimen

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Fig. 7
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Force–displacement curve obtained from tensile test for geogrid

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2.1.1.4 Geonet

Geonet is from geosynthetic family, and it is used in soil, rock, or other branches of engineering. Geonet is different from geotextile in construction, appearance, and performance. The mesh holes’ length is about 2 cm, and the average diameter of geonet wire is about 2 mm. The rupture force and elongation obtained from the tensile test for single fiber are about 350 N and 50 mm, respectively. Tensile test result and geonet specimen are shown in Figs. 8 and 9, respectively. The details of all fibers are listed in Table 2.

Table 2 Details of all fibers
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Fig. 8
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Force–displacement relationship obtained of tensile test for geonet

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Fig. 9
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Geonet specimen

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2.2 Mix Proportions

Due to various parameters, mixing the lightweight aggregate concrete is different from normal weight concrete (Butler et al. 2009). To obtain the final mix and improve the workability, density, and strength, the ratio of used materials in concrete must be optimized which occurs after casting several mixes and making necessary variations. To increase the workability of concrete, the LWA should be saturated before preparing concrete. The details of these mixes are listed in Table 3. These values are adjusted after applying the correction factor. It illustrates that fresh concrete density for different mixing is varied from 1300 to 1410 kg/m3, e.g., in case 1, fresh concrete density is 1410 kg/m3 while air dry density and oven dry density are obtained about 1300 kg/m3 and 1150 kg/m3, respectively.

Table 3 Mix design
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The tilting drum mixer of 0.12 m3 capacity is used to prepare concrete mixes. To prepare concrete mixes, first the LWA fractions are mixed dryly with fine aggregates and cement and then the proper amount of water is poured into it and finally the fibers are added, while in textile-reinforced LWC panels, the mesh is imbedded inside the concrete after the mix is ready. The concrete mixes are poured in formwork and compacted using a vibration table at low speed. Pouring concrete into the formwork is shown in Fig. 10, 11. After casting, the panels are covered with wet burlap and kept at 23 °C at laboratory for 24 h and then demolded and again are covered with wet burlap for 28 days.

Fig. 10
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Pouring of concrete into the formwork

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Fig. 11
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Reinforcement details of specimens

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2.3 Test Methods

In this study, the produced panel had dimensions of 8 × 50 × 230 cm3 (see Fig. 12). The numbers and types of panels are shown in Table 4. After 28 days of production, the panels are subjected to three-point bending test (see Fig. 13). A hydraulic jack of 5 tons is used to apply pressure. At each step of the applied force, the midspan deflection is measured by linear displacement transducers (LVDT). The data acquisition system was used to transfer and convert the data readings from load cell and LVDT to computer language. Loading is continued until the occurrence of a significant deep crack (Tables 5, 6, 7).

Table 4 The numbers and types of panels
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Table 5 Flexural strength and flexural load of all panels
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Table 6 Distributed load of all panel
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Table 7 Value of maximum forces and displacement for all panels
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Fig. 12
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Fiber/textile-reinforced LWC panels

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Fig. 13
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Setup used in bending test

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3 Experimental Results and Discussion

The results of all tested panels were recorded and analyzed in terms of their load–displacement curves as shown Fig. 14. The panels with textile and nylon fibers showed superior behavior compared to samples without reinforcement in the core matrix. The panels with the nylon fiber initially developed flexural cracks at midspan at lower loads; as the load increased, the width and depth of the cracks gradually increased. The maximum load is dependent on the tensile strength of reinforcing fibers in addition to the pullout response of the fibers. The crack spacing was larger for samples with nylon fibers as compared to the textile. This is due to the lower stiffness of the nylon fibers, a weaker matrix/fiber mechanical bond, and a less-than-optimum load transfer mechanism. The panel with steel mesh, geogrid, and geonet represents the behavior of uncracked sample under increasing loading; it ends with the cracking of the matrix at the notch. Because of the specimen’s less-than-critical fiber content, the reinforcement cannot bear the imposed high load after the matrix has cracked, so that a sudden drop in force (so-called “snap-back”) occurs. The magnitude of the “snap-back” depends mainly on the stiffness of test apparatus and bond characteristics between multi-filament yarn and matrix. Filaments with a very intensive bond to the matrix do not have much ductility and suddenly collapse (Fig. 15).

Fig. 14
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Force–displacement curves for different panels

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Fig. 15
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Crack pattern in nylon fiber panel

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Evaluating the results at hand, it can be concluded that the ductility and load-bearing capacity of plain LWC panels are much less than those of the fiber/textile-reinforced LWC panels whereas ductility of nylon fiber-reinforced panels is much more than the rest of the panels and thus the failure occurs. Load-bearing capacity of two-layered steel mesh-reinforced panels is more than the rest, but their failure occurs due to brittleness because the bond between filaments and matrix is very intensive and matrix cannot represent much ductility and will suddenly collapse.

Load-bearing capacity of geogrid-reinforced panels is less than the fiber/textile-reinforced LWC panels and their failure occurs due to brittleness. Therefore, the use of this type of mesh does not improve the load-bearing capacity and ductility properties significantly.

3.1 Comparison of Panels’ Energy Absorptions

In building structures, ductility and energy absorption capacity decrease the damages of the earthquake. The amount of this energy can be obtained from calculating the area under force–displacement curve for different structures. Energy absorption diagrams for different panels are shown in Fig. 16.

Fig. 16
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Energy absorption of different panel

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It can be seen that the energy absorption of plain LWC panels, due to low ductility and strength, is much less than the fiber/mesh-reinforced LWC panels as well as geogrid-reinforced panels which have lower energy absorption in comparison with the fiber/mesh-reinforced ones. Thus, adding fiber/mesh increases the energy absorption capacity of LWC panels.

4 Conclusion

This paper presents the experimental results conducted from investigations into the structural behavior of fiber/textile-reinforced LWC panels. To investigate the panel flexural behavior up to failure, 18 panel specimens of 0.50 m width and a selected span of 2.30 m were put under three-point bending test. Based on the experimental results, the following conclusions can be made:

  1. 1.

    Plain LWC precast panels have low load-bearing capacity, flexural strength, ductility, and energy absorption. So, by adding proper fibers/textile, the mechanical properties of these panels could be improved.

  2. 2.

    Panels reinforced with nylon fibers have great ductility but low load-bearing capacity. Therefore, for using these fibers, they should be combined with other meshes to improve strength properties.

  3. 3.

    The steel mesh used in this study has low ductility; therefore, based on this study, steel mesh with adequate ductility can be used to improve the mechanical properties of panels.

  4. 4.

    Two-layered steel mesh-reinforced panels have the highest energy absorption. Therefore, by placing layer(s) of mesh on each side of the panels, they can be used as structural components and ferrocement.

  5. 5.

    According to the diagram of bending test results, it can be concluded that the load-bearing capacity of two-layered and one-layered steel mesh-reinforced panels is more than the rest of the fiber/textile-reinforced LWC panels studied here, but their failure occurs due to brittleness because of the intensive bond between filaments and matrix.

  6. 6.

    Geonet, two-layered, and one-layered steel mesh-reinforced panels are suitable to be used as roofs in the obtained total load of snow and asphalt roof coating studied here.

  7. 7.

    In this study, all panels are resistant against the obtained wind pressure. Therefore, they can be used as proper wall elements.