Effect of Textile Layers and Hydroxypropyl Methylcellulose on Flexural Behavior of TRLC Thin Plates

Abstract

To examine the flexural toughness characteristics of textile-reinforced lightweight aggregate concrete (TRLC), a four-point bending test was conducted to assess the impact of varying numbers of textile layers and the inclusion of hydroxypropyl methylcellulose on the ultimate load-bearing capacity and deformation capacity of TRLC thin plates. Six groups of specimens were prepared for the experiment, and the bending capacity of the thin plates in each group was evaluated. The flexural toughness index was utilized to quantify the bending performance of TRLC thin plates. The findings revealed that increasing the number of textile layers improved the initial cracking load, initial cracking deflection, ultimate load, ductility, and flexural toughness of the thin plates. For the specimens without HPMC, the initial cracking load was increased by up to 36.1%, the ultimate load by up to 40.9%, and the flexural toughness index by up to 292% as the number of textile layers was increased. For specimens doped with HPMC, the initial cracking load was increased by up to 61.7%, the ultimate load by up to 246.7%, and the flexural toughness index by up to 65%. The TRLC thin plate containing hydroxypropyl methylcellulose exhibited a reduced initial cracking load yet displayed a stronger matrix consistency and good flexural toughness. Moreover, the enhancement in the ultimate load of TRLC thin plates with hydroxypropyl methylcellulose was more pronounced with an increased number of textile layers, resulting in a significantly higher number of cracks compared to TRLC without hydroxypropyl methylcellulose and an 11.40-fold increase in the flexural toughness index.

1. Introduction

Lightweight aggregate concrete refers to concrete formulated with light coarse aggregate, light sand (or ordinary sand), cementitious materials, admixtures, water, etc., and its dry apparent density is not greater than 1950 kg/m³. Light aggregate concrete is widely used in engineering practice due to its characteristics, such as light deadweight, but it needs to be optimized due to its disadvantages, such as brittleness and poor mechanical properties [1]. Research on textile-reinforced concrete (TRC) started in the late 1980s. Gardiner et al. [2] proved it is an effective reinforcement method by incorporating a fabric net with fixed intervals in the warp and weft yarns in cementitious materials. It also has been shown that the mechanical properties of concrete can be improved by incorporating textiles into the concrete [3,4,5]. The bonding strength between the textile and the concrete matrix influences the synergetic performance of the TRC [6]. The bonding performance of the TRC interface depends mainly on the mechanical properties and geometrical characteristics of the textile itself as well as on the strength of the concrete matrix [7,8]. To enhance the interface bonding performance, Xu and Yin [9,10,11] proved that epoxy impregnation and sand bonding, mixing of short-cut fibers, and applying pre-stressing can all enhance the bonding performance through a large number of experimental analyses, numerical simulations, and mechanism studies.

However, in practical structural engineering retrofitting and maintenance, the total weight of the structure cannot be significantly increased, as this may alter the inherent characteristics of the structure, such as the natural frequency, thereby adversely affecting the seismic behavior of the structure. Building on the previously discussed enhancement effect of textiles on the mechanical properties of concrete matrix, researchers have incorporated them into lightweight aggregate concrete to optimize its mechanical properties. Vast [12] designed a coffee table using textile-reinforced lightweight aggregate concrete (TRLC). Cibulka [13] et al. produced several thin-walled slabs reinforced with two-dimensional carbon and 3-dimensional glass textiles. The tests confirmed a significant increase in the strength of all reinforced specimens. Rozycki et al. [14] employed “Stikloporas” lightweight aggregate, which has a porosity of 41%, in the preparation of TRLC. They conducted experimental investigations on the flexural and compressive mechanical characteristics. The findings indicated that thinner specimens exhibited improved toughness and excellent interfacial bonding between glass fibers and the lightweight aggregate cement mortar matrix. Additionally, they utilized this TRLC material to design a canoe named “PKanoe”, showcasing the versatility and strength of the material. Naseri et al. [15] fabricated 18 TRLC thin plates using various textiles and subjected them to three-point bending tests. The findings revealed that the TRLC thin plates using nylon textiles exhibited good ductility but had a lower flexural load-bearing capacity. In contrast, the TRLC thin plates using steel fiber net displayed a high flexural load-bearing capacity and adequate energy absorption capabilities despite their limited ductility. Both thin-plate types demonstrated ample wind resistance, making them suitable for use in the construction of walls and roofs for prefabricated houses. Lightweight aggregate concrete is commonly employed in industrial and civil buildings, as well as other projects, to reduce structural weight and conserve materials. Incorporating textiles into lightweight aggregate concrete produces structures that are lightweight yet highly resilient. TRLC technology can be utilized in the production of walls, partition walls, heat insulation, roofs, insulation panels, floor slabs, staircases, pipes, bridges, and various other building components.

While the aforementioned studies have highlighted the potential of textiles as reinforcement in lightweight aggregate concrete, the precise bonding dynamics and synergistic performance between the lightweight aggregate concrete matrix and textiles remain ambiguous. The bonding properties between the textile and the concrete matrix significantly influence the structure’s mechanical properties. Lightweight aggregate concrete, characterized by numerous internal pores, high water content, and brittleness, presents unclear bonding properties with textiles. While hydroxypropyl methylcellulose exhibits a notable thickening effect and enhances the tensile bond strength of cement mortar, its impact on TRLC remains uncertain. Moreover, the effects of critical factors, such as the number of textile layers, on the mechanical properties of TRLC are not yet fully elucidated. Therefore, further investigation is necessary to explore the influence of varying numbers of textile layers and the external incorporation of hydroxypropyl methylcellulose into the matrix on the flexural behavior of TRLC thin plates. In this study, we conducted four-point bending tests on six sets of 36 TRLC thin plates to examine the impact of varying numbers of textile layers and external doping of the matrix with hydroxypropyl methylcellulose on the ultimate load-bearing capacity and deformation capacity of TRLC thin plates. Additionally, we utilized the bending toughness index to quantitatively assess the bending performance of TRLC thin plates. The results provide valuable insights into the bending capacity of TRLC thin plates and the potential effects of different material compositions on their mechanical properties.

2. Experimental Program

2.1. Specimen Design

In this study, the effect of the number of textile layers and the presence of hydroxypropyl methylcellulose in the cement mortar matrix on the flexural properties of a TRLC thin plate was examined. HPMC enhances the water retention of cement mortar and acts as a thickening agent in cement slurry. Studies have demonstrated that a 0.5% HPMC content can substantially improve the plastic viscosity and water retention of cement mortar [16]. Based on the proportion of TRC cement mortar matrix obtained from previous studies [17,18], the light aggregate concrete matrix proportion and experimental groups for this experiment are detailed in

Table 1. The proportion of light aggregate concrete matrix (kg/m³).

Cement	Fly Ash	Silica Fume	Shale Ceramic Sand	Mixing Water	Pre-Wetted Water	Superplasticizer
445	160	32	835	158	167	3.6

and

Table 2. Specimen index and main information.

Specimen	Number of Textile Layers	Hydroxypropyl Methylcellulose Dosage
Y1	1	0%
MY1	1	0.5%
Y2	2	0%
MY2	2	0.5%
Y3	3	0%
MY3	3	0.5%

Note: Y—epoxy-impregnated textile specimen; 1/2/3—number of textile layers; M—externally doped with 0.5% hydroxypropyl methylcellulose by mass ratio to cement.

, respectively. Six specimens were prepared for each experimental group.

Peled A [19] found that a 3 mm cement mortar protective layer was adequate to safeguard the textile in TRC members up to 30 mm thickness, effectively preventing cracks in the protective layer. To ensure the durability of TRC members, a 5 mm cement mortar protective layer is recommended. Consequently, all specimen dimensions were standardized to 500 mm × 100 mm × 16 mm, with the thickness of TRLC varying depending on the number of textile layers, as illustrated in Figure 1.

2.2. Raw Materials

In the preparation of TRLC thin plate specimens, PII 52.5 grade silicate cement and Class Ⅱ fly ash were employed in the light aggregate concrete matrix, and the relevant parameters are shown in

Table 3. Properties of fly ash.

Fineness (>45 μm, %)	Water Demand (%)	Loss on Ignition (%)	Moisture Content (%)	SO3 (%)	Free CaO (%)	28d Activity Index (%)
9.7	93	1.8	0.02	0.7	0.05	79

and

Table 4. Properties of silica fume.

Fineness (>45 μm, %)	SiO2 (%)	Loss on Ignition (%)	Moisture Content (%)	Moisture Content (kg/m3)
0.5	94	0.5	0.4	0.282

, respectively. The ceramic sand utilized was the 700-grade crushed shale ceramic sand manufactured by Hubei Yichang Guangda Ceramic Sand Co., Ltd. (Yichang, China), featuring a particle size ranging from 0 mm to 1.2 mm; a fineness modulus of 1.7, placing it in the category of fine sand in Zone II; an apparent density of 1740 kg/m³; and a water absorption rate of 20%. The superplasticizer used was a BASF polycarboxylic acid high-efficiency superplasticizer with a water-reducing rate of 27%. The thickening agent applied was hydroxypropyl methylcellulose (HPMC) from Fuqiang Chemical Industry (Jinzhou, China), characterized by a viscosity of 200,000 MPa.s. The light aggregate concrete matrix exhibited a 28-day compressive strength of 55.59 MPa and a 28-day flexural strength of 8.26 MPa.

The textile selected was crafted from basalt–glass fibers, with its overall morphology and fiber structure under electron microscope scrutiny depicted in Figure 2. This textile was a two-dimensional weave comprising basalt fiber bundles and glass fiber bundles, featuring a mesh size of 10 mm × 10 mm, a fiber bundle width of 1 mm, a fiber density of 1550 g/m², a fiber linear density of 0.80 g/m, a fiber mesh thickness of 0.2 mm, and individual fiber monofilaments with a diameter of approximately 13 μm, as discerned via SEM microscopy. We conducted five sets of mechanical property tests on basalt fiber bundles, and the results obtained are presented in

Table 5. Mechanical properties of basalt fiber bundles of textile.

	Sample 1	Sample 2	Sample 3	Sample 4	Sample 5	Average
Tensile strength (MPa)	512.7	427.3	482.2	445.6	586.0	490.8
Young’s Modulus (GPa)	29.5	26.7	26.9	28.6	27.2	27.8
Ultimate strain (%)	1.74	1.60	1.79	1.59	2.15	1.77

. As determined through testing, the ultimate tensile strength of the basalt fiber bundles ranged from 427 to 586 MPa, with an average value of 490.8 MPa and a standard deviation of 56 MPa. In addition, Young’s modulus was 27.8 GPa, and the ultimate tensile strain was 1.77%. The glass fibers, considered unstressed fibers, exhibited a measured monofilament tensile strength of 3100 MPa, Young’s modulus of 72 GPa, and an elongation at break of 4.5%. The test results showed some variation, which may be due to the difficulty of achieving complete consistency during material processing, transport, and storage. Additionally, as noted by Dai et al. [20], epoxy impregnation can notably bolster the tensile strength of fiber bundles. For instance, the basalt fiber bundles experienced a 170% surge in ultimate tensile strength post-impregnation compared to pre-impregnation levels. However, the extent of epoxy impregnation and its uniformity could not be precisely regulated, potentially contributing to the variability observed in the test results.

2.3. Specimens and Preparation

To streamline the mass production of TRLC thin plate specimens, wooden mold frames measuring 650 mm × 500 mm were utilized. As illustrated in Figure 3, wooden molds of varying thicknesses—3 mm, 5 mm, 6 mm, and 8 mm—were crafted, with each frame combination capable of producing six specimens. The specimen fabrication process unfolds as follows:

(1)

Pre-treatment: Affix the textile onto the mold using adhesive, ensuring that the radial basalt fibers align parallel to the 500 mm side during textile placement to preserve their utility as tensile fibers post-cutting into thin plates later. In addition, the subsequent cutting position was calculated to avoid cutting into the basalt fiber bundles. A mixture of epoxy resin and hardener in a 1:1 ratio was prepared, adding 1/4 to 1/5 xylene as a thinner based on the external temperature conditions. The textile was cured for 24 h before the subsequent pouring of the cement mortar matrix began.

(2)

Specimen production: First, we fixed the wooden frame on the base plate and mixed the light aggregate concrete, in which the hydroxypropyl methylcellulose was mixed with the dry powder and stirred evenly. The protective layer of light aggregate concrete was poured first, then the mold with the textile was fixed, and finally, the light aggregate concrete was poured. After 24 h of initial setting, the mold was removed, and the specimens were cured. The specimen preparation process is shown in Figure 3.

(3)

Specimen processing: After the molded specimens were cured for 28 d, the specimens were cut into standard bending specimens of 500 mm × 100 mm using a cutting machine, as shown in Figure 4.

2.4. Testing Method

The four-point bending test was conducted by the “Standard for test methods of concrete physical and mechanical properties” (GB/T 50081-2019) [21] and the “Standard test methods for fiber reinforced concrete” (CECS 13:2009) [22]. The INSTRON universal testing machine was employed for the loading tests. The length of the thin plate measured 500 mm and a span of 300 mm to preserve the length of the pure moment section as much as possible and the shear span of 100 mm on each side. Displacement loading control was adopted, with a loading speed set at 0.5 mm/min. When the textile was pulled off or pulled out, or when the specimen was severely damaged, the loading was stopped. Linear variable displacement transducers (LVDT) were positioned at the span center and span end. The schematic diagram of the loading device is shown in Figure 5.

3. Test Results and Analysis

3.1. Characterization of Damage at Various Stages of Loading

The load-deflection relationship curves for the six groups of tests are shown in Figure 6. As shown in the figures, the trends of the load-deflection curves are relatively consistent, but the results still differ between specimens. In this study, the fiber bundles were impregnated with epoxy resin to improve the bonding properties of the fiber bundles. However, the degree of epoxy resin impregnation and its uniformity could not be precisely controlled in advance, resulting in a relatively discrete tensile strength of the fiber bundles [20]. This may be one of the reasons for the differences in the test results. In order to make a more scientific comparison, an average curve was obtained for each test group for subsequent analysis.

The initial cracking point is the first spike of the load on the curve. After the cracking of the specimen, there was a sudden drop in the load, and due to the bonding and bridging effect between the textile and the concrete matrix, the specimen was not completely damaged despite the sudden drop in the load. The textile began to be tensed, and the load continued to increase. With the increase in the number of textile layers and the incorporation of hydroxypropyl methylcellulose, the initial cracking load and ultimate load of the specimen increased. The damage of the specimen showed a tendency for multi-seam cracking. The damage mode of the TRLC thin plate can be divided into four stages. The first is the concrete matrix cracking; thereafter, due to the bridging effect of the textile, the TRLC thin plate is synergistically stressed, forming a state of multi-seam cracking. As the load continues to increase, a certain main crack appears to bear the main stress. As the deflection increases, it continues to expand, and finally, the final damage occurs along the main crack. The damage form of the TRLC thin plate is mainly realized in the form of textile pulling off, and thus the overall fracture. The specific load-deflection behavior and crack development state are shown in Figure 7.

The initial cracking load, initial cracking deflection, peak load, and ultimate deflection for each test group are shown in

Table 6. Test results of each specimen group.

Specimen	Initial Cracking Load (N)	Initial Cracking Stress (MPa)	Initial cracking Deflection (mm)
Y1	670.24 (71.75)	11.78 (1.26)	0.40 (0.13)
Y2	693.22 (117.78)	12.19 (6.49)	0.41 (0.13)
Y3	912.16 (50.7)	16.03 (0.89)	0.37 (0.09)
MY1	283.11 (23.43)	4.98 (2.74)	0.20 (0.03)
MY2	317.40 (10.58)	5.58 (0.18)	0.17 (0.01)
MY3	457.79 (36.62)	8.05 (0.65)	0.34 (0.09)
Specimen	Peak Load (N)	Peak Stress (MPa)	Ultimate Deflection (mm)	Number of Cracks (Average Value)
Y1	670.24 (71.75)	11.78 (1.26)	3.37 (0.77)	1.00
Y2	719.08 (81.04)	12.64 (1.59)	6.42 (1.32)	1.50
Y3	944.38 (78.3)	16.60 (1.38)	6.17 (0.62)	1.33
MY1	378.51 (55.93)	6.65 (0.99)	8.43 (1.12)	3.33
MY2	665.32 (46.08)	11.7 (0.81)	8.00 (1.57)	4.40
MY3	1312.33 (92.16)	23.07 (1.62)	9.62 (0.39)	6.33

Note: Each data point is taken as the average of the test results of the six specimens in the same experimental group, with standard deviations in parentheses. Peak load and peak stress correspond to the maximum load during loading, and the ultimate deflection is the deflection corresponding to the last peak point on the load-deflection curve.

. All data in Table 5 are averages of the results from each group. To quantify the bending stress, the equivalent bending stress σ was introduced and calculated as follows:

$$\sigma =\frac{3PL}{2{bh}^2}$$

(1)

where P is the peak load, L is the distance between the hinge supports in Figure 5, b is the width of the thin plate, and h is the thickness of the TRLC thin plate.

The ideal state of cracking under the bending load is multi-seam cracking in TRLC thin plates. The cracking of thin plates in the different experimental groups is given in Figure 8, and the average values of the crack number statistics for the pure bending section are given in Table 6. The results show that the enhancement of the number of textile layers increases the likelihood of the occurrence of the number of multi-cracks, and its effect is more pronounced on the HPMC-doped TRLC thin plate. The number of cracks also tends to increase due to the rise in bond strength between the textile and the concrete matrix.

3.2. Effect of the Number of Textile Layers on the Bending Properties of TRLC Thin Plate

Figure 9 illustrates the load-deflection curves for TRLC thin plates with varying numbers of textile layers, and the average curves of each group were taken for comparison.

Due to the bonding and bridging interaction between the textile and the concrete matrix, the concrete retained the capability to distribute the external loads with the textile even after cracking occurred. As the number of textile layers increased, the residual stress following the initial concrete cracking also rose, leading to a higher incidence of cracks, improved ultimate load-carrying capacity and ductility in the TRLC thin plate, and a more favorable damage pattern. The transition from one to two textile layers resulted in a more substantial increase in the initial cracking load and damage load. Upon reaching three textile layers, multiple cracks emerged in the thin plate post-initial cracking, allowing for a greater energy absorption capacity. Relative to the Y1 specimens, the initial cracking loads of Y2 and Y3 were elevated by 3.4% and 36.1%, the ultimate loads by 7.3% and 40.9%, and the ultimate deflections by 90.5% and 83.1%, respectively. The number of textile layers had little effect on the initial cracking deflection of the specimens in group Y. Relative to the MY1 specimens, the initial cracking loads of MY2 and MY3 were elevated by 12.1% and 61.7%, and the ultimate loads by 75.8% and 246.7%, respectively. The ultimate deflection of the MY2 specimens is slightly lower than that of the MY1 specimens. The reason for this may be that the addition of HPMC has significantly increased the ultimate deflection of the specimens, and the increase in the number of textile layers from one to two has a very limited effect on the ultimate deflection at this point. When the number of layers was increased to three, the ultimate deflection of the group’s MY3 specimens increased by 14% compared to the group’s MY1 specimens.

In the case of the HPMC-doped TRLC thin plate (Groups MY), the enhanced bonding between the concrete matrix and textile resulted in a stronger bridging effect post-initial cracking. This effect hindered crack propagation and promoted the development of multiple cracks in the TRLC thin plate. All specimens within this group exhibited damage characterized by multiple cracks, a preferred form of structural damage. The addition of more textile layers notably improved the flexural properties, leading to an increase in crack formation, as well as enhancements in the initial cracking load and ultimate load.

Figure 10 illustrates the linear relationship between the number of textile layers and the ultimate load of groups Y and groups MY. In examining the correlation between the ultimate load and the number of textile layers, it is observed that for a standard lightweight aggregate concrete matrix, an increase in the number of textile layers can indeed boost the ultimate load of the TRLC thin plate. A positive correlation is noted between the number of textile layers and the ultimate load within the test group. Specifically, a higher number of textile layers resulted in a considerable increase in the ultimate load within the test group.

On the whole, augmenting the number of textile layers proves to be a beneficial strategy for enhancing the flexural properties of TRLC thin plates. This enhancement is primarily evident in several aspects: (1) enhancement of the initial cracking load and initial cracking deflection; (2) improvement in residual stress post-initial cracking to prevent premature damage; (3) promotion of multi-crack formation following initial cracking, thereby improving the ductility of the thin plates; and (4) delaying textile pull-out or pull-off, consequently enhancing the ultimate load capacity of the thin plates.

3.3. Effect of HPMC Doping on Flexural Properties of TRLC Thin Plate

Two types of concrete matrix were selected for this research: a standard lightweight aggregate concrete matrix and a lightweight aggregate concrete matrix with HPMC. Figure 11 illustrates the load-deflection curves of TRLC thin plates with varying concrete matrices, and the average curves of each group were taken for comparison. The graph indicated a significant decrease in the initial cracking load and stress of the HPMC-doped thin plate under bending stress. This decline can be attributed to the presence of voids within the HPMC-doped thin plate itself, resulting in lower stiffness and an earlier onset of initial cracking. Moreover, the bond strength between the HPMC-doped matrix and the textile was notably robust. Following the initial cracking, the textile exhibited enhanced bridging capabilities, impeding crack propagation and leading to the formation of multiple cracks in the TRLC thin plate. As the number of cracks increased, the thin plate demonstrated improved load-bearing capacity and enhanced ductility. To validate the aforementioned analysis and elucidate the impact of HPMC on TRLC thin plates at a microscopic level, two additional TRLC thin plates were prepared without epoxy resin impregnation on the textile to emphasize the influence of HPMC. Images of the interfaces of these two TRLC thin plates examined under an electron microscope are presented in Figure 12 and Figure 13, respectively.

In Figure 12, it is evident that at the interface under 100 times magnification, the HPMC-doped specimen exhibits a notably higher presence of minute bubbles and holes compared to the undoped HPMC specimen. The internal structure appears loosely packed, leading to reduced stiffness at the initial loading stage, consequently causing a decrease in the initial cracking load in comparison to the undoped HPMC specimen.

In Figure 13, it is apparent that the hydration reaction at the interface of the HPMC-doped specimens is more pronounced. This improved reaction could be attributed to the water retention properties of HPMC, facilitating better hydration of the cement at the interface that may have been inadequately wetted otherwise. As a result, the interfacial adhesion is bolstered to a certain degree. Additionally, the hydration products of cement penetrated into the fiber bundles, filling the gaps between the fiber filaments and augmenting the frictional forces.

As depicted in Figure 11, the ultimate loads of all test groups externally treated with HPMC exhibited an increase, except group Y1. The specimens in group Y demonstrated a sharp rise in the peak load at initial cracking, following which subsequent peak loads on the curve showed minimal increments. Conversely, the specimens in group MY exhibited a lower load at initial cracking, attributed to the presence of voids in the externally treated HPMC, resulting in reduced stiffness. However, as the textile progressively engaged during the loading process, the peak loads on the curve continued to rise. In the case of groups MY1 and MY2, where the initial cracking load experienced a significant decrease, a single or double layer of textile had a limited impact on the ultimate load of the specimens; thus, the ultimate loads in groups MY1 and MY2 remained unaffected by the HPMC treatment of the matrix. Conversely, in group MY3, the presence of multiple textile layers led to a noticeable enhancement in load, consequently increasing the ultimate load as well. For the group MY3 specimens, the effect of adding HPMC is very obvious, the ultimate load increased by 367.95 N with an increase of 40.0%. Although the addition of HPMC did not raise the ultimate loads of specimens in groups M1 and M2, it raised their ultimate deflections for all three sets of specimens. For one, two, and three textile layers, the ultimate deflection is increased by 150%, 24.6%, and 55.9%, respectively.

4. Flexural Toughness of TRLC Thin Plate

The flexural properties of the TRLC thin plate are related to both the ultimate deflection and ultimate load of the specimen. Therefore, the flexural toughness index is used to define the energy dissipation capacity of a material or structure from the onset of the load action to the cessation of damage. Various methodologies exist for determining the flexural toughness index, including those outlined by the American Concrete Institute (ACI 544) [23], the Japanese Society of Civil Engineering (JSCE G552) [24], and the American Society for Testing and Materials (ASTM C 1018) [25].

The simplified ASTM C 1018 standard is employed for the calculation in this test [25]. The flexural toughness index is defined as follows: the area under the curve corresponding to the initial cracking deflection is denoted as S₀, representing the initial cracking energy consumption, while the area under the curve corresponding to the ultimate deflection is denoted as S₁, representing the ultimate energy consumption. The calculation for S₀ or S₁ is conducted, as shown in Equation (2), with a visual representation provided in Figure 14.

$$S_0={\displaystyle \int P_{0}df}$$

(2)

where P₀ is the corresponding load at initial cracking or ultimate, and f is the corresponding deflection.

The flexural toughness index (I) is expressed as the ratio of the ultimate energy consumption to the energy consumption at the first crack and is calculated as follows:

$$I=S_1/S_0$$

(3)

where, S₀ and S₁ are the measured values of toughness (N·mm) when the deflection in the span is the initial crack and the limit, respectively.

The flexural toughness index I of the TRLC thin plate under various conditions is presented in

Table 7. Calculated values of S₀, S₁, and I for TRLC thin plates.

Specimen	S0 (N∙mm)	S1 (N∙mm)	I
Y1	125.20 (35.13)	610.09 (92.31)	5.19 (1.99)
Y2	134.2 (12.73)	2527.68 (743.28)	18.85 (5.06)
Y3	147.32 (32.25)	2932.26 (535.56)	20.33 (4.57)
MY1	30.78 (3.79)	2179.45 (602.88)	64.38 (18.46)
MY2	30.02 (2.00)	3093.28 (254.45)	103.17 (7.9)
MY3	76.26 (4.64)	8086.29 (612.22)	105.97 (2.18)

Note: The data in the table are expressed as the means (standard deviation).

. From the data in Table 7, it can be seen that the flexural toughness index increases with the number of layers of the textile. The flexural toughness index of the Y2 and Y3 specimens was increased by a factor of 2.63 and 2.92, respectively, compared to the Y1 specimens. The flexural toughness index of the MY2 and MY3 specimens was increased by 60% and 65%, respectively, compared to the MY1 specimens. In order to further analyze the relationship between the number of textile layers and the flexural toughness index of the specimens, the best fit was conducted using linear regression analysis. The fitting results are shown in Figure 15. The coefficients of regression were 0.82 for the specimens in group Y and 0.80 for the specimens in group MY. The fitting results indicated a correlation between the flexural toughness index and the number of textile layers. When the number of textile layers was increased from one to two, the flexural toughness index increased by 263% and 60% for the group Y and group MY specimens, respectively. When the number of textile layers was increased from two to three, the flexural toughness index of the specimens in groups Y and MY increased by only 7.9% and 2.7%, respectively. This shows that when the number of textile layers is increased from one to two, it is effective in increasing the flexural toughness of the specimens. However, increasing the number of textile layers after reaching two textile layers has a very limited effect on the flexural toughness of the specimens. This may explain the small correlation coefficients in Figure 15.

The incorporation of HPMC is also an important factor affecting the flexural toughness index. On average, the initial cracking energy consumption of the HPMC-doped TRLC thin plate decreased by 67% compared to the non-HPMC-doped TRLC thin plate. This decline can be attributed to the presence of voids within the HPMC-doped thin plate itself, resulting in lower stiffness and an earlier onset of initial cracking. However, the flexural toughness index increased significantly by 11.40, 4.47, and 4.21 times for one, two, and three textile layers, respectively. It is noteworthy that the effect of HPMC doping in the matrix had a far more pronounced effect on the flexural toughness index of the specimens than the number of textile layers.

5. Conclusions and Recommendations

In this study, the synergistic effect between basalt textiles and lightweight aggregate concrete was investigated by employing four-point bending tests on six groups of 36 TRLC thin plates with and without the addition of HPMC to the matrix and the number of textile layers as parameters. In addition, the effect of the above parameters on the flexural properties of TRLC thin plates was quantitatively assessed using the flexural toughness index. Moreover, we focused on a single HPMC doping content and exclusively analyzed the flexural behavior of TRLC specimens. Despite these constraints, the following conclusions can be drawn.

(1)

The increase in the number of textile layers elevates the initial cracking load, initial cracking deflection, residual stress after initial cracking, the possibility of multi-crack development after initial cracking, and the ultimate load and ductility of the TRLC thin plate.

(2)

The mechanical properties of the HPMC-doped TRLC thin plate exhibited a reduction. While the initial cracking load decreased, the matrix consistency was enhanced. Furthermore, the increase in the ultimate load of the TRLC thin plate due to HPMC incorporation was more significant when a higher number of textile layers were present. For the group MY3 specimens, the effect of adding HPMC is very obvious, the ultimate load increased by 367.95 N with an increase of 40.0%.

(3)

Multi-seam cracking represents a more favorable bending damage mode for TRLC thin plates. The quantity of cracks serves as a key indicator of bending performance, influenced by the number of textile layers and the presence of hydroxypropyl methylcellulose. In HPMC-doped TRLC thin plates, the number of cracks is notably higher compared to non-HPMC-doped plates.

(4)

The impact of matrix doping with HPMC on the flexural toughness index of the specimens was significantly more pronounced compared to the influence of the number of textile layers. On average, the initial cracking energy consumption of TRLC thin plates doped with HPMC decreased by 67%, while the flexural toughness index showed consistent increases, with some reaching up to 11.40 times higher values.

(5)

In this study, we focused solely on particular textile types and HPMC doping ratios, analyzing only the bending behavior of the specimens. Future research could explore the impact of various textile varieties and diverse doping ratios of HPMC on TRLC. Additionally, other dynamic properties of TRLC could be investigated beyond the bending characteristics.

Based on the experimental and theoretical results outlined in this paper, the multi-layer textile-reinforced lightweight aggregate concrete with HPMC exhibits characteristics of being lightweight and possessing high toughness. This material can be effectively utilized in the fabrication of assembly wall panels, fulfilling the criteria for lightweight assembly components while also enhancing the mechanical properties of the panels due to their high toughness. These attributes suggest a broad range of potential applications in civil engineering.