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Article

Mechanical Properties and Microstructure of Lightweight Aggregate Concrete Incorporating Basalt Fiber

by
Xiaojiang Hong
1,*,
Yanqing Song
1 and
Jin Chai Lee
2
1
Department of Civil Engineering, Faculty of Civil and Hydraulic Engineering, Xichang University, Xichang 615013, China
2
Department of Civil Engineering, Faculty of Engineering, Technology and Built Environment, UCSI University, Kuala Lumpur 56000, Malaysia
*
Author to whom correspondence should be addressed.
Buildings 2025, 15(19), 3548; https://doi.org/10.3390/buildings15193548
Submission received: 29 August 2025 / Revised: 23 September 2025 / Accepted: 28 September 2025 / Published: 2 October 2025
(This article belongs to the Special Issue Application of Fiber-Reinforced Composite Materials in Building and Bridge Applications)
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Abstract

Basalt fiber (BF) can notably improve the mechanical properties of lightweight aggregate concrete (LWAC) through its crack-bridging and pull-out mechanisms, making it suitable for application in super high-rise buildings and large-span structures. This study assesses the influence of BF contents of 0%, 0.1%, 0.3%, 0.5%, and 0.7% (relative to the weight of cementitious materials) on the workability, mechanical properties, and microstructure of LWAC. The results showed that adding BF to LWAC can moderately weaken the slump, significantly enhance the mechanical properties, and lead to a maximum increase in specific strength of 7.3%. Compared with LWAC without BF, the maximum increases in compressive strength, flexural strength, and elastic modulus of LWAC with BF at 28 days were 24.7%, 33.9%, and 38.57%, respectively. In the microstructure, BF can connect the cracks in the internal structure of concrete, which is an important factor to consider when choosing a fiber to improve the mechanical properties of concrete. These conclusions provide a reference point for improving the mechanical properties of LWAC.

1. Introduction

Lightweight aggregate concrete (LWAC) penetrates rapidly into high-rise and long-span structures because of its low unit weight, and it can effectively reduce the self-weight of buildings [1]. LWAC containing shale ceramsite (SC) has been proven to have a wide range of applications in modern bridges [2]. LWAC can also be used in prestressed structures. LWAC can be used as the structural material in post-tensioned members bearing high loads, showing high tensile strength on post-tensioned beams, with low shrinkage and creep [3]. In addition, in Europe, LWAC has been shown to improve the energy efficiency of buildings by reducing the thermal conductivity of building components [4]. It is worth mentioning that the recycled lightweight aggregate generated by recycling damaged LWAC blocks can replace up to 45% of the fine limestone aggregate, and the compressive strength of LWAC can reach 16.5–30.5 MPa, meeting engineering needs [5]. Furthermore, LWAC can be applied to the production of hollow blocks and precast slabs. Under the long-term action of actual load, these members show good structural performance [6]. Compared to normal-weight concrete (NWC), the density of structural LWAC typically ranges between 1600 and 2000 kg/m3, whereas conventional concrete has a density of 2300–2500 kg/m3, as reported in studies on lightweight expanded clay aggregate (LECA) concrete [7].
With the maturity of production technology, large quantities of environmentally friendly materials, including silica fume [8], fly ash [9], ceramsite [10], pottery sand [11], slag powder [12], lightweight expanded clay aggregate (LECA) [13], volcanic pumice [14], etc., are being used to prepare LWAC. In China, during the construction of infrastructure, a large amount of ordinary concrete is consumed, which not only leads to the depletion of natural resources but also seriously pollutes the environment. Notably, during the construction process, a large amount of shale waste soil is generated, and shale is an ideal raw material for preparing high-strength ceramic particles, which can be mass-produced. Using SC instead of traditional crushed stone as a concrete aggregate not only effectively reduces the weight of the structure but also reduces the exploitation of natural stone, thereby reducing the damage to the ecological environment, in line with the concepts of green building and sustainable development. However, LWAC prepared with shale ceramsite has low strength due to the porous nature of lightweight aggregates. Under tensile and shear forces, the aggregates are very prone to cracking [15].
To compensate for the strength of LWAC, current development processes need to improve the strength of the lightweight aggregate while ensuring that its mechanical parameters are within the qualified range. At present, the strength and toughness of LWAC are usually improved by adding fibers (e.g., steel fibers [16,17], carbon fibers [18], graphene oxide [19], extruded polystyrene [20,21], etc.) to LWAC. Compared with synthetic fiber, steel fiber has a higher elastic modulus and tensile strength and can share the tensile force in mortar to improve the compressive strength of concrete [22]. Libre et al. found that mixing steel fibers with polypropylene fibers in pumice LWAC can significantly improve its ductility properties. The study’s results showed that the tensile strength of concrete can be increased from 1.9 MPa to 4.1 MPa, an increase of 116%, by adding 1% steel fiber. At the same time, its flexural strength increased significantly from 2.1 MPa in the control group to 7.3 MPa, a growth rate of 284% [23]. However, steel fiber can easily increase the self-weight of concrete. It has been reported that a carbon fiber content of 0.4% can achieve the best comprehensive properties of concrete, with its compressive strength and tensile strength increased by 15.02% and 51.12%, respectively [24]. However, carbon fibers are difficult to disperse in concrete and are agglomerated. When the content of graphene oxide (GO) is 0.05%, the maximum increases in the 28-day elastic modulus, splitting tensile strength, flexural strength, and compressive strength of high-strength lightweight concrete are 15%, 17%, 20% and 24%, respectively [25]. There are a reasonable number of studies on nanomaterials in concrete. However, at present, due to the high cost of nanomaterials, their large-scale use in the construction industry is still limited [26]. Basalt fiber (BF) has a low cost and good creep resistance [27]. The production process of BF has obvious environmental advantages: its energy consumption is 40% lower than that of glass fiber, and no harmful by-products are produced. At the same time, the crushed BF concrete can be recycled as recycled aggregate, and the fiber can still play a reinforcing role through secondary utilization, realizing the closed-loop utilization of materials, embodying the green characteristics of the whole life cycle [28]. Meanwhile, BF can bond well with cement slurry and has been demonstrated to significantly enhance the mechanical performance of conventional concrete without increasing its own weight [29]. BF has higher tensile strength (≥2000 MPa) and elastic modulus (80–110 GPa) than glass fiber, and it is resistant to high temperatures of 600 °C and corrosion. As an environmental protection material, it can significantly improve the crack resistance, ductility, and interfacial bonding strength of concrete better than polypropylene fiber, making it an ideal concrete reinforcement material [30].
In recent decades, application-based research on BF in ordinary concrete has made remarkable progress. Jiang et al. demonstrated that BF incorporation effectively suppresses the propagation of cracks, and compared with the sample without BF, its compressive strength can be increased by about 50% [31]. Huang Zhang et al. investigated the mechanical behavior of BF-reinforced concrete materials with six volume contents, showing that incorporating BF modified the pore structure at the microscale, mitigating concrete brittleness [32]. The evidence showed that when the BF content was in the appropriate range, the compressive strength and splitting tensile strength of the specimen significantly improved. When the content of BF was 1%, both the compressive and splitting tensiles reached maximum values of 1.7 MPa and 0.8 MPa, respectively [33]. Abu Taqa et al. conducted related research on fly ash basalt concrete and found that compared with the control group, the optimal dosage can increase the flexural strength by 69.9% [34]. Similarly, BF was examined by Yasemin et al., incorporating it into kaolin clay to determine the optimal fiber ratio [35]. In terms of microstructure, a lower fiber content can strongly bond with the recycled aggregate concrete matrix to form an effective interface with minimal cracking [31]. At the same time, BF plays a bridging role in concrete, vertically crossing cracks, providing reverse stress, preventing the growth of existing cracks, and limiting the formation of new cracks [36]. Therefore, numerous studies have shown that the content of BF significantly impacts the mechanical properties of concrete. A content of 0.5–1.5% can increase the compressive strength by up to 25%, but when it exceeds 2%, the strength decreases due to fiber aggregation. The flexural strength continues to increase with the increase in dosage (an 18.4% increase at a 0.3% dosage), but the compressive strength may decrease by 5% at a 0.4% dosage due to uneven fiber dispersion [37,38]. Moreover, the literature on basalt fiber-reinforced LWAC is already rich with investigations into fiber length and content. As shown in Table 1, it is obvious that the typical lengths and contents of BF used in LWAC generally fall within the ranges of 6–18 mm and 0–1.5%, respectively. That said, this situation is particularly rare when using BF in LWAC with shale ceramic particles and shale clay sand as aggregates.
Currently, a large number of scholars are focusing on the application of BF with regard to the workability, mechanical properties, and microstructure of cement-based composite materials (including cement mortar and ordinary concrete) [34,45,46]. In summary, this situation is particularly rare when using BF in LWAC with shale ceramic particles and shale clay sand as aggregates. This research will add 0%, 0.1%, 0.3%, 0.5%, and 0.7% BF into LWAC to study the improvements in the workability, mechanical properties, and microstructure of LWAC caused by BF. In this study, the following three indicators were selected for comprehensive evaluation and verification: (1) the workability (slump) test was conducted according to the GB/T 14902-2012 specification; (2) a mechanical properties (compressive strength, flexural strength, and modulus of elasticity) test was conducted in accordance with GB/T 50081-2019; and (3) the microscopic morphology was assessed.

2. Materials and Methods

2.1. Materials

The cementitious material used in this study was P.O42.5R ordinary Portland cement produced by Xichang Aerospace Co., Ltd., and its apparent density was determined to reach 3100 kg/m3. All coarse and fine aggregates were shale ceramsite (SC) and shale pottery sand (SPS), which were sourced from Hubei Huiteng Lightweight Aggregate Environmental Protection Products Co., Ltd. Their apparent densities were 1425 kg/m3 and 1638 kg/m3, respectively. Table 2 lists the physical property parameters of coarse and fine aggregates in detail, and Figure 1 visually shows their macro-morphological characteristics. Before mixing the mixture, SC was pre-wetted for 24 h to achieve the saturated surface dryness (SSD) condition. The high-purity BF purchased from Xichang Jishuntong Building Materials Co., Ltd., with a length of 6 mm, was a golden-brown chopped fiber. Table 3 shows the physical property parameters. As shown in Figure 2a, the BF surface was smooth and shiny, and obvious reflection could be seen. The mineral admixture used in the test was fly ash (FA) (Figure 2b) of grade II standard, and its specific surface area reached 350 m2/kg, and the loss on ignition was 2.34%. High-performance polycarboxylate superplasticizer (PS) was used, which had a water-reducing efficiency of 20%.

2.2. Mix Proportions

Based on the absolute volume method specified in the industry standard “Technical Standard for Application of Lightweight Aggregate Concrete” JGJ/T 12-2019, the control mix ratio (BF-0) was calculated, and its design compressive strength was 40 MPa. Moreover, the other four groups of test mixes were prepared by adding 0.1%, 0.3%, 0.5%, and 0.7% (relative to the weight of cementitious materials) of BF, and these mixes were named BF-1, BF-3, BF-5, and BF-7, respectively. It has been reported that mineral admixtures can partly replace cementitious materials to improve the fluidity and mechanical properties of concrete [47], and the replacement rate of FA in this research was 20%. The mix proportion used in this study is shown in Table 4.

2.3. Preparation and Curing

The mixing process was as follows: First, we wet the mixing equipment until the inner wall of the mixing drum was completely wet. Second, we added cement, SC, SPS, and FA and mixed at a low speed for 1 min. Third, we added BF in three batches, with a 10 s interval between each batch, and stirred for 2 min to form a uniform dry-mixed mixture. Finally, we added water and PS and mixed for 2 min until the slurry was uniform.
The process of mold installation and maintenance was as follows: We put the mixture into the standard-sized mold and vibrated it slowly on the vibrating table to increase the density of the mixture and reduce bubbles. The concrete was demolded after 24 h and then placed under standard conditions (temperature: 20 ± 2 °C, relative humidity: ≥95%) for curing for 3 days, 7 days, and 28 days. The detailed mixing process and experimental items are shown in Figure 3.
The mechanical properties test performed on concrete was carried out using the servo pressure testing machine (YAD-2015) according to the standard GB/T 50081-2019. Specifically, 100   m m   ×   100   m m   ×   100   m m cubic specimens were used to test the compressive strength at 3 days, 7 days, and 28 days, with a loading rate of 0.5–0.8 MPa/s; moreover, 100   m m ×   100   m m   ×   400   m m prismatic specimens were used for 28-day flexural strength testing, with a loading rate of 0.05–0.08 MPa/s. A cylindrical specimen with a diameter of 150 mm and a height of 300 mm was used for measuring the elastic modulus at 28 days. Meanwhile, regarding GB/T 50080-2016, the workability of fresh concrete was tested using the slump cone method, and its apparent density was determined. We tested three samples at each testing stage and took their average as the final estimated value to ensure the validity of the experimental data. To investigate the microstructure characteristics, the fracture of the sample was cut into about 10 × 10 × 5 mm3 after curing in water for 28 days and sprayed with thin gold on the surface of the sample to enhance the sample’s electrical conductivity. The crystal morphology characteristics were observed using a scanning electron microscope (SEM: Thermo Scientific Apreo 2C) with an acceleration voltage of 5.00 kV.

3. Results and Discussion

3.1. Workability

The slump can directly show the fluidity and cohesion of the mixture. The slump values of basalt fiber-reinforced LWAC with contents of 0%, 0.1%, 0.3%, 0.5%, and 0.7% (referred to as BF-0, BF-1, BF-3, BF-5, and BF-7) were 110 mm, 102 mm, 93 mm, 79 mm, and 65 mm, respectively.
As shown in Figure 4, there is a strong decreasing linear fitting relationship between the content of BF and the slump of LWAC. It is particularly notable that LWAC (BF-0) without BF had the highest slump value of 110 mm. When the content of BF increased from 0% to 0.7%, the slump of the LWAC decreased from 110 mm to 65 mm, a reduction of 40.1%. When the slump of the LWAC was 50–75 mm, it could achieve a basic working performance [25]. If the slump of the LWAC was greater than 75 mm, its working performance was excellent. Correspondingly, all LWAC samples showed satisfactory performance.
Based on the notion that BF changes the internal structure and fluidity of concrete, the possible reasons for our results are as follows: BF restricted aggregate movement by increasing friction and mechanical interlocking between aggregates and formed a network structure in the slurry to inhibit fluidity [48]. The dispersion of BF inevitably consumed some of the cement slurry to form a coating layer, resulting in a decrease in the amount of cement slurry used for lubricating aggregates, leading to an increase in friction and a decrease in slump [49]. When the BF was added beyond a certain range, the excess BF formed local agglomeration due to uneven distribution, which hindered the fluidity of concrete and lowered the slump value [50]. Consequently, BF incorporation within an appropriate range can ensure the working performance of the concrete.

3.2. Mechanical Property

3.2.1. Compressive Strength

The compression failure mode of 100 mm × 100 mm × 100 mm concrete after 28 days of curing under standard conditions is shown in Figure 5. At the initial loading stage of the pressure testing machine, the LWAC was at the linear elastic stage, the stress distribution was uniform, and the internal micro-cracks had not yet penetrated [51]. Adding BF can effectively inhibit crack propagation, and its high tensile strength causes the fiber to span cracks and slow down crack development. With the increase in load, the concrete entered the nonlinear stage, and micro-cracks expanded and formed macro-cracks. BF dispersed stress through restraint and the fiber–matrix interface bonding force to delay structural damage. After reaching the ultimate compressive strength, the concrete failed [52], but the random distribution of BF can cause concrete to transition from brittleness to ductility, enhance the toughness, improve the deformation ability, and indirectly improve the compressive strength.
Obviously, after being subjected to compression failure, local fragmentation occurred on both the top and side surfaces of BF-0, and some concrete fragments peeled off from the main structure, with the irregular distribution of peeling areas. Moreover, BF-1 exhibited vertical macroscopic cracks, and the crack width gradually expanded with increasing load. BF-5 and BF-7 had continuous small cracks. It is worth noting that BF-3 only exhibited microscopic cracks, and the degree of crack development was significantly lower than for other groups.
Table 5 lists the compressive strengths of different BF contents at corresponding ages. According to the JGJ 51-2002 standard, under standard curing conditions, when the 28-day cube compressive strength of the specimen reaches 40 MPa, it is defined as concrete with a strength grade of LC40, ensuring sufficient strength reliability. When the BF content increases from 0% to 0.7%, the compressive strength of LWAC exhibits a nonlinear pattern of first increasing and then decreasing. This indicates that there is an optimal amount of added BF that enables concrete to achieve maximum compressive strength. The compressive strength of one test block with added BF (BF-3) is the highest, and the compressive strength at 28 days can reach 51.03 MPa. In comparison, for the test block without BF (BF-0), the maximum increase is 24.7%. Therefore, the optimal dosage of BF in this study is 0.3% (BF-3). When the length of BF was fixed at 6 mm, the optimal dosage of BF for producing LWAC using industrial waste circular ceramsite [41], lytag [44], and expanded polystyrene [45] was determined to be 1%, 1.5%, and 0.5%, respectively. This difference was mainly due to the physical properties of the aggregates.
There are several possible reasons for the increase and then decrease in compressive strength. BF forms a network structure in concrete, suppressing the propagation of micro-cracks through the fiber-bridging effect [53]. Its high tensile strength and interfacial pull-out work shift the failure process from brittleness to quasi-plasticity, indirectly improving compressive strength [54]. However, when the content of basalt exceeds its optimal value (0.3%), BF struggles to disperse evenly during the concrete mixing process and form local fiber constraints, enabling the expansion of micro-cracks near the fibers [55]. Thus, the compressive strength of concrete gradually decreases. As a result, it is necessary to reasonably control the dosage of BF.
The densities of LWAC with BF contents of 0%, 0.1%, 0.3%, 0.5%, and 0.7% after 28 days of curing are 1438.4, 1573.7, 1668.8, 1700.7, and 1753.6 kg/m3, respectively. The reason for this phenomenon is the filling effect of BF. Additionally, the density of BF is greater than that of the aggregates [56]. The densities of these concrete samples are all less than 1950 kg/m3, categorizing them as LWAC [57]. Additionally, the specific strength (C/D in Table 5) refers to the ratio of the average compressive strength of concrete to its dry apparent density [58], which is a key indicator of structural performance. The reference specimen (without BF) exhibited a specific strength of 28.44 kN·m/kg, whereas the specimen with 0.03% BF content demonstrated a 7.5% higher value of 30.58 kN·m/kg. According to [59], when using oil palm shell to prepare concrete, the specific strength of this lightweight concrete is 30.9 kN·m/kg. Moreover, a study has found that the specific strength of LECA concrete is 20.18 KN·m/kg, higher than that of ordinary concrete [58].
Figure 6 presents the compressive strength data of BF concrete with different dosages under standard curing for corresponding ages. With the increase in concrete age, the compressive strength of LWAC increased significantly. It can be clearly seen that the compressive strengths of test blocks with added BF at all ages are greater than those of the test blocks without added fibers, indicating that BF significantly improves compressive strength.

3.2.2. Flexural Strength

Figure 7 shows the influence of different BF contents on the flexural strength of a concrete specimen with dimensions of 150 mm × 150 mm × 550 mm after 28 days of standard curing. The research showed that the flexural strength of the concrete with BF was greater than that of the concrete without BF after 28 days of curing, indicating that BF greatly improved its flexural strength. With the increase in BF content from 0% to 0.7%, the flexural strength first increased and then decreased. The flexural strengths of BF-0, BF-1, BF-3, BF-5, and BF-7 were 3.84 MPa, 4.43 MPa, 5.14 MPa, 4.36 MPa, and 4.16 MPa, respectively. Compared with BF-0, the flexural strengths of BF-1, BF-3, BF-5, and BF-7 increased by 0.59 MPa, 1.3 MPa, 0.52 MPa, and 0.32 MPa, respectively. It is worth noting that BF-3 increased by 33.9%. Therefore, the optimal content of BF for improving the flexural strength of LWAC was 0.3%.
The possible reasons why the flexural strength first increased and then decreased are as follows: BF enhanced the flexural strength of concrete by absorbing tensile stresses and improving its tensile damage resistance [36]. Additionally, BF transferred the stress to the surrounding concrete at cracks, reduced the stress concentration in the concrete, effectively inhibited crack propagation, and, thus, reduced the damage in the concrete [60,61]. However, when the content of basalt exceeded its optimal range, excessive fiber content formed micro-cracks and pores due to aggregation, and the flexural strength reduced accordingly.
In addition, the ratio of flexural strength to compressive strength is called flexural compression ratio (F/C in Table 6) [62]. The flexural ratios of all LWACs investigated in this study were within the range of 9.38% to 10.01%. Some research has indicated that BF significantly enhances the flexural strengths of cement-based composite materials [63,64,65]. Chiadighikaobi et al. found in their study of lightweight expansive clay concrete that BF with a length of 20 mm and a dosage of 1.6% can increase the flexural strength of concrete by 1.612 MPa [63]. Qin and Wu found that the flexural strength can be increased by 6.3% when adding BF at a content of 2 kg/m3 and a length of 24 mm [66]. Thus, the scope of our study is acceptable.

3.2.3. Elastic Modulus

Table 7 shows the test values for the elastic modulus of concrete with different BF contents after 28 days of standard curing. The research showed that the elastic modulus of concrete with BF was greater than that of concrete without BF after 28 days of curing, indicating that BF greatly improved its elastic modulus. The elastic modulus of concrete without BF was 17.63 GPa, significantly lower than that of ordinary concrete [67]. With the increase in BF content (0–0.7%), the elastic modulus first increased and then decreased. The elastic moduli of BF-0, BF-1, BF-3, BF-5, and BF-7 were 17.63 GPa, 20.61 GPa, 24.43 GPa, 22.27 GPa, and 19.80 GPa, respectively. Compared with BF-0, BF-1, BF-3, BF-5, and BF-7 increased by 16.90%, 38.57%, 26.32%, and 12.31%, respectively. Based on these changes, the peak value of the elastic modulus was achieved by BF-3 (i.e., fiber content was 0.3%), and the elastic modulus reached 24.43 GPa, 38.57% higher than that of BF-0. An appropriate BF content can fill the micropores in concrete, thereby improving the compactness and elastic modulus. However, when the BF content exceeds the optimal value, excessive BF formed aggregates, resulting in a weak interface, thereby reducing the compactness and elastic modulus.

3.3. Microstructure

The effect of BF on LWAC can be further studied by analyzing the microstructure characteristics of LWAC. A scanning electron microscope (SEM) can be used to more clearly investigate the surface morphology characteristics of hydrated cement-based composites [34]. Figure 8 presents SEM micrographs of mixtures with varying BF contents, acquired by randomly selecting samples from the mixture. Figure 9 shows the microscopic morphology of BF failure in the compressive and flexural states of the sample.
Figure 8a shows the LWAC (BF-0) without BF. At this stage, there were large voids and cracks in the sample, increasing the permeability of the sample and making it easy for external substances to penetrate it [61]. After adding BF, as shown in Figure 8b, the end of the BF penetrated and filled the internal pores, which were closely combined with the cement matrix, effectively reducing porosity in the concrete. Strengthening the pore structure made the concrete matrix more compact, thereby improving its overall performance [68]. The fibers in Figure 8b showed that the mechanical bite effect inside the structure may have been strengthened by friction between BF and cement-based materials, providing physical constraints to enhance the mechanical properties [69,70]. With the increase in fiber content, as shown in Figure 8c, the integrity of concrete improved, and the internal structure became denser. However, when the fibers gathered into clusters, as shown in Figure 8d,e, the voids inside the concrete increased, and the structural integrity became low.
Figure 9a shows that BF is completely connected inside the concrete before compression failure. Furthermore, when the pressure gradually increases, vertical cracks appear inside the concrete. As shown in Figure 9b, BF can cause lateral tension on both sides of the crack. As the vertical crack continues to increase and exceeds the tensile strength of BF, the fiber is broken. Figure 9c,d shows the microscopic morphology of the bottom of the concrete. BF bears the tensile force in a manner akin to steel bars, which is the purpose of reinforcement. As the stress increases, the fiber is broken.
SEM confirmed that BF can play a bridging role. Appropriate amounts of BF can increase the density of the microstructure, thereby improving the performance of LWAC. However, excessive basalt fiber weakens the reinforcing performance due to agglomeration.

4. Conclusions

In this study, LWAC with a strength grade of 40 MPa was prepared by using SC and SPS. The slump and mechanical properties of LWAC mixed with 0%, 0.1%, 0.3%, 0.5%, and 0.7% BF were measured, and the microstructure was observed through SEM. The conclusions are as follows:
  • The slump of the LWAC decreases with the increase in the BF due to interfacial adsorption between fibers and cement slurry. Simultaneously, the fibers within the mixture interweave with one another to establish a three-dimensional network configuration, thereby increasing the internal frictional resistance of the system and markedly diminishing the flowability of the composite mixture. The slump variation in all experimental groups ranges from 110 mm to 65 mm, meeting the requirements of JGJ 51-2002 for the workability of LWAC. The slump of 0.7% BF was 65 mm, 40.1% lower than that of BF-0. However, BF causes the slump of the LWAC to drop within a reasonable range that does not excessively affect the working performance of the LWAC mixture.
  • Compared to compressive strength, the reinforcement effect of BF on the LWAC is more prominent in terms of bending and deformation resistance because the fiber forms a network structure in concrete to suppress crack propagation. After adding BF, the 28-day compressive strength, flexural strength, and elastic modulus of LWAC increased by 24.7%, 33.9%, and 38.57%, respectively. When the BF content was 0.3%, the specific strength and flexural ratio of LWAC were 30.53 kN·m/kg and 10.01%, respectively. The results also show that a basalt content of 0.3% is the best value for improving the mechanical properties of the LWAC.
  • Microscopic tests show that BF penetrates through the pore structure, and its end is firmly bonded with the cement matrix. BF improves the concrete bond and fills the pores. This may help to further improve the mechanical properties of the LWAC. In subsequent research, it will be necessary to adopt microstructure characterization techniques and interfacial transition zone to further delve into the potential mechanisms for enhancing mechanical performance.

Author Contributions

Conceptualization, Y.S., X.H., and J.C.L.; methodology, Y.S. and X.H.; formal analysis, X.H.; investigation, Y.S. and X.H.; resources, Y.S. and X.H.; writing—original draft preparation, Y.S. and X.H.; writing—review and editing, Y.S. and X.H.; visualization, X.H.; supervision, J.C.L. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the Doctoral Research Foundation of Xichang University (YBZ202144).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The original contributions presented in this study are included in the article. Further inquiries can be directed to the corresponding author.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. Images of the aggregates: (a) SC; (b) SPS.
Figure 1. Images of the aggregates: (a) SC; (b) SPS.
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Figure 2. Images of the admixture: (a) BF; (b) FA.
Figure 2. Images of the admixture: (a) BF; (b) FA.
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Figure 3. The mixing procedure and experimental items.
Figure 3. The mixing procedure and experimental items.
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Figure 4. The relationship between slump and the dosage of basalt fiber.
Figure 4. The relationship between slump and the dosage of basalt fiber.
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Figure 5. The compression failure mode of concrete after 28 days of standard curing: (a) BF-0; (b) BF-1; (c) BF-3; (d) BF-5; (e) BF-7.
Figure 5. The compression failure mode of concrete after 28 days of standard curing: (a) BF-0; (b) BF-1; (c) BF-3; (d) BF-5; (e) BF-7.
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Figure 6. The compressive strength results for LWAC.
Figure 6. The compressive strength results for LWAC.
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Figure 7. The flexural strengths for different BF contents.
Figure 7. The flexural strengths for different BF contents.
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Figure 8. SEM images of different mix proportions at 28 days: (a) BF-0; (b) BF-1; (c) BF-3; (d) BF-5; (e) BF-7.
Figure 8. SEM images of different mix proportions at 28 days: (a) BF-0; (b) BF-1; (c) BF-3; (d) BF-5; (e) BF-7.
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Figure 9. SEM images of BF failure: (a) intact fibers (0.3%) under compressive stress; (b) broken fibers (0.3%) under compressive stress; (c) intact fibers (0.7%) under flexural stress; (d) broken fibers (0.7%) under flexural stress.
Figure 9. SEM images of BF failure: (a) intact fibers (0.3%) under compressive stress; (b) broken fibers (0.3%) under compressive stress; (c) intact fibers (0.7%) under flexural stress; (d) broken fibers (0.7%) under flexural stress.
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Table 1. A summary of the literature on the length and content of BF.
Table 1. A summary of the literature on the length and content of BF.
No.Aggregates for LWACLength of BF
(mm)		Range of BF
(%)		Optimal Value of BF (%)Ref.
(1)Industrial waste circular ceramsite60.5–1.51[39]
(2)Sintered fly ash180–0.250.25[40]
(3)Volcano slag15–170–0.40.1[41]
(4)Lytag60.5–1.51.5[42]
(5)Expanded polystyrene60.2–0.80.5[43]
(6)Silica fume180.1–0.30.3[44]
Table 2. The physical properties of the aggregates.
Table 2. The physical properties of the aggregates.
Physical PropertiesSPSSC
Water absorption (24 h) (%)1.364.6
Water absorption (3 h) (%)1.232.9
Bulk density (kg/m3)974835
Apparent density (kg/m3)16381425
Table 3. The property parameters of BF.
Table 3. The property parameters of BF.
Physical
Properties		Density
(kg/m3)		Tensile Strength
(MPa)		Elastic Modulus
(GPa)		Elongation at Break
(%)		Maximum Operating Temperature
(℃)		Length
(mm)
Parameter29403000–480091–1101.5–3.26506
Table 4. Mix proportion (kg/m3).
Table 4. Mix proportion (kg/m3).
No.CementBF 1FA 2SC 3SPS 4WaterPS 5
BF-0368092667568174.85.52
BF-13680.4692667568174.85.52
BF-33681.3892667568174.85.52
BF-53682.3092667568174.85.52
BF-73683.2292667568174.85.52
1 BF: basalt fiber; 2 FA: fly ash; 3 SC: shale ceramsite; 4 SPS: shale pottery sand; 5 PS: polycarboxylate superplasticizer.
Table 5. The results for and analysis of density and mechanical properties.
Table 5. The results for and analysis of density and mechanical properties.
Mix No.BF-0BF-1BF-3BF-5BF-7
Density (kg/m3)1438.41573.71668.81700.71753.6
3-day compressive strength (MPa)17.4323.9628.8324.1323.98
7-day compressive strength (MPa)32.5639.1944.5539.3439.15
28-day compressive strength (MPa)40.9145.1751.0347.7545.49
Compressive strength growth rate (%)-10.424.716.711.2
C/D 1 (KN·m/kg)28.4428.7030.5328.0825.94
1 C/D: the ratio of the 28-day compressive strength of concrete to its dry apparent density.
Table 6. The results for and analysis of flexural strength.
Table 6. The results for and analysis of flexural strength.
Mix No.BF-0BF-1BF-3BF-5BF-7
Flexural strength (MPa)3.844.435.144.764.36
Compressive strength (MPa)40.9145.1751.0347.7545.49
Flexural strength growth rate (%)-15.433.923.913.5
F/C 1 (%)9.389.8110.019.979.58
1 F/C: the ratio of the 28-day flexural strength to the 28-day compressive strength.
Table 7. The results for and analysis of the elastic modulus.
Table 7. The results for and analysis of the elastic modulus.
Mix No.BF-0BF-1BF-3BF-5BF-7
28-day elastic modulus (GPa)17.6320.6124.4322.2719.80
Elastic modulus growth rate (%)-16.9038.5726.3212.31
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Hong, X.; Song, Y.; Lee, J.C. Mechanical Properties and Microstructure of Lightweight Aggregate Concrete Incorporating Basalt Fiber. Buildings 2025, 15, 3548. https://doi.org/10.3390/buildings15193548

AMA Style

Hong X, Song Y, Lee JC. Mechanical Properties and Microstructure of Lightweight Aggregate Concrete Incorporating Basalt Fiber. Buildings. 2025; 15(19):3548. https://doi.org/10.3390/buildings15193548

Chicago/Turabian Style

Hong, Xiaojiang, Yanqing Song, and Jin Chai Lee. 2025. "Mechanical Properties and Microstructure of Lightweight Aggregate Concrete Incorporating Basalt Fiber" Buildings 15, no. 19: 3548. https://doi.org/10.3390/buildings15193548

APA Style

Hong, X., Song, Y., & Lee, J. C. (2025). Mechanical Properties and Microstructure of Lightweight Aggregate Concrete Incorporating Basalt Fiber. Buildings, 15(19), 3548. https://doi.org/10.3390/buildings15193548

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