Fiber Reinforced Lightweight Aggregate Concrete Research Articles

Flexural behavior and serviceability of steel fiber-reinforced lightweight aggregate concrete beams reinforced with high-strength steel bars

Six beams reinforced with HRB600 bars and one reinforced with HRB400 bars fabricated using steel fiber-reinforced lightweight aggregate concrete (SFLWAC) were tested under a four-point bending load to investigate the load-carrying capacity and service performance, with different reinforcement ratios, clear span lengths, concrete strengths, and reinforcement strengths. The test results showed that cracks ran through lightweight aggregates and developed rapidly without an aggregate interlocking mechanism, and the specimens eventually failed in the mode that the compressive concrete was crushed following longitudinal bars yielded, with 3 ∼ 4 major cracks. The specimens satisfied the allowable deflection and crack width required in the codes, with a ductility coefficient exceeding 4.5, and 1/150 of the span length was recommended to be the maximum deflection at the serviceability limit state. Generally, the increasing reinforcement ratio significantly improved the flexural strength and serviceability but reduced the ductility, the linear stiffness decreased with the growing span length, and the SFLWAC strength mainly affected the cracking moment and ductility. Replacing HRB400 bars with equal strength of HRB600 bars led to a substantial drop in serviceability, while an equal area of HRB600 bars improved the ultimate moment by 38.7 %. The calculation results indicated that by neglecting the residual tensile strength, fracture characteristics, and bond properties of SFLWAC, the prediction equations in the Chinese, American, and European codes underestimated the ultimate moment and overestimated the crack width, and the Chinese code yielded the conservative deflection prediction. The analytical flexural models for HRB600-reinforced SFLWAC beams were derived by incorporating the effects of steel fibers, lightweight aggregate concrete, and bond stress, exhibiting accurate predictions.

Performance of steel fibre reinforced lightweight aggregate concrete in fresh and hardened state

Abstract There is a growing interest in the manufacture of lightweight aggregate concrete (LWC) due to its low density, which is below 2000 kg/m3. However, the trade-off for the lower density is a reduction in strength, leading to a drop in crack resistance. Therefore, steel fibre inclusion was implemented to augment the crack resistance of lightweight concrete (LWC). Thus, the present study aims to examine the impact of steel fibre on both the workability and mechanical properties of lightweight aggregate concrete (LWC) that incorporates lightweight expanded clay aggregate (LECA). Three varieties of concrete were fabricated, namely normal weight aggregate concrete (NC), lightweight concrete (LWC), and steel fibre lightweight concrete (SFWLC). The SFLWC incorporated hooked-end steel fibres as reinforcement, with fibre volume percentages of 1 % and 2 %. A strength assessment was undertaken to ascertain the concrete properties, with particular emphasis on compressive and tensile strength. The findings indicate that the incorporation of both LECA and steel fibre led to a notable reduction in the workability of concrete. Incorporating a 2 % steel fibre content into LWC yields a marginal enhancement in compressive strength. Steel fibre demonstrates enhanced efficacy when subjected to tension, with the most significant increase measured at around 152 %.

Seismic performance of precast steel fiber reinforced lightweight aggregate concrete shear walls assembled with a socket horizontal joint

In the context of constructing a precast shear wall structure, the connection of precast units plays a crucial role in ensuring structural safety and facilitating efficient construction, while the use of conventional concrete for heavy precast units leads to low lifting efficiency. It promotes the study of this paper, which proposed a novel type of socket horizontal joint for precast shear walls made of steel fiber reinforced lightweight aggregate concrete (SFRLAC). Three specimens were tested using the low-cyclic loading test: two reinforced SFRLAC shear walls assembled with a socket horizontal joint and a cast-in-place reinforced SFRLAC shear wall as a reference. The failure patterns and process of the shear walls were observed, while the load-displacement curves were obtained. Additionally, finite element (FE) numerical models were built to conduct parametric analysis on different influencing factors. The bearing capacity, energy dissipation capability, deformation ability, and stiffness degradation of the shear walls were studied. Results indicate that when the precast shear walls failed in bending-shear, the socket horizontal joint remained intact. The three shear walls exhibited fewer differences in seismic behaviors with relatively full hysteretic curves. The seismic mechanisms of the shear walls assembled with a socket horizontal joint are elucidated by analyzing the numerical distribution of stress in both SFRLAC and steel bars at different stress levels. Meanwhile, the study assesses the mechanical properties of precast shear walls by analyzing the impact of the shear to span ratio and the axial compression ratio.

Experimental study and modelling of flexural behaviour of continuous fibre-reinforced lightweight aggregate concrete one-way slab at ambient and elevated temperatures

An experimental study on the flexural behaviour of six fibre-reinforced lightweight aggregate concrete (FRLWAC) one-way slab strips under ambient and elevated temperatures is presented in this paper. Two slabs, one simply-supported and one continuous, were loaded to failure at ambient temperature as references for the fire tests, while another simply-supported and three continuous slabs with varying degrees of design moment redistribution were loaded and exposed to elevated temperatures until failure. The ambient tests showed that the steel fibre addition prevents premature flexural-compression failure commonly observed in lightweight aggregate concrete structures. The rotations of FRLWAC plastic hinges were concentrated in a single crack under ambient temperature and a few cracks under fire exposure. The fire tests revealed significant moment redistribution towards the hogging moment area in the continuous slabs due to restrained thermal-induced deflection. Furthermore, the reinforcement configuration that catered for moment redistribution towards the hogging area was found to enhance the fire resistance of continuous FRLWAC slabs. A fibre-reinforced concrete (FRC) plastic hinge model, based on the rigid-body rotation concept, was proposed and validated. This model predicts the moment-rotation behaviour of FRC hinges at ambient temperature and the fire resistance of FRLWAC one-way slabs with good accuracy.

Experimental and numerical study on seismic behavior of precast shear walls assembled with a socket vertical joint

In the development of precast shear wall structures, reliable and efficient connections of precast units are crucial for their seismic behavior. Meanwhile, the heavy precast units using conventional concrete bring a low lifting efficiency. Considering these issues, the paper proposed a novel type of socket vertical joint for precast shear walls made of steel fiber reinforced lightweight aggregate concrete (SFRLAC). Sixteen socket connection specimens, with four socket depths (100 mm, 150 mm, 200 mm, and 250 mm) and two interface treatments (smooth and exposed aggregate), underwent interface bonding performance tests using uniaxial tensile testing and finite element (FE) numerical models to determine the appropriate socket depth. Three specimens were tested using the low-cyclic loading test, including two reinforced SFRLAC precast shear walls assembled with a socket vertical joint and a cast-in-place reinforced SFRLAC shear wall as a reference. The failure patterns and process of the shear walls were observed, while the load-displacement curves were obtained. Additionally, a parametric analysis of different influencing factors was conducted using finite element (FE) numerical models. This analysis studied the bearing capacity, energy dissipation capability, deformation ability, and stiffness degradation of the shear walls. Results indicate that when the precast shear walls were damaged, the socket vertical joint was integrity and failed in bending-shear. The three specimens exhibited fewer differences in seismic behavior with relatively full hysteretic curves. The seismic mechanisms of the shear wall assembled with a socket vertical joint were elucidated by analyzing the numerical distribution of stress in both SFRLAC and steel bars at different stress levels. Furthermore, an expansion analysis was conducted to assess the impact of axial load ratios and shear to span ratios on the seismic behavior of precast shear walls.

Mechanical properties and stress-strain relationship of surface-treated bamboo fiber reinforced lightweight aggregate concrete

Bamboo fiber (BF) possesses advantages such as environmental friendliness, renewability, economic viability, and favorable mechanical properties, making it a promising material for improving the brittleness and tensile strength of concrete. Previous investigations have demonstrated a limited exploration of BF-reinforced lightweight aggregate concrete (LWAC). Current study concentrates on investigating the mechanical properties and stress-strain relationship of BF-reinforced LWAC. To achieve this, 7 groups of BF-reinforced LWAC specimens were subjected to compressive tests, splitting tensile tests, and prism compressive tests. The influence of BF content and length on the compressive performance, failure modes and stress-strain curves was studied. BFs effectively suppressed the development of internal cracks in LWAC, playing a role in crack resistance and toughness enhancement. Furthermore, BFs significantly improved the splitting tensile strength of concrete, while the compressive strength slightly decreased with the increase of BF content. After adding BFs, the splitting tensile strength of concrete increased by 8.2∼23.7%, and the compressive strength decreased by 3.6∼11.1%. Moreover, the BF length had almost no effect on the compressive strength of concrete, while when the BF length was 10–30 mm, the tensile strength increased by 5.3∼17.6%. Based on existing researches, strength conversion equations and stress-strain constitutive models of BF-reinforced LWAC were proposed, and the models provide a theoretical basis for the calculation and analysis of BF-reinforced LWAC components and structures.

The Evaluation of the Effectiveness of Biomineralization Technology in Improving the Strength of Damaged Fiber-Reinforced LWAC.

Concrete cracks and local damage can affect the bond performance between concrete and steel bars, thereby reducing the durability of reinforced concrete structures. Compared with general concrete crack repair methods, biomineralization repair not only has effective bonding capabilities but is also particularly environmentally friendly. Therefore, this study aimed to apply biomineralization technology to repair damaged fiber-reinforced lightweight aggregate concrete (LWAC). Two groups of LWAC specimens were prepared. The experimental group used lightweight aggregates (LWAs) containing bacterial spores and nutrient sources, while the control group used LWAs without bacterial spores and nutrient sources. These specimens were first subjected to compression tests and pull-out tests, respectively, and thus were damaged. After the damaged specimen healed itself in different ways for 28 days, secondary compression and pull-out tests were conducted. The self-healing method of the control group involved placing the specimens in an incubator. The experimental group was divided into experimental group I and experimental group II according to the self-healing method. The self-healing method of experimental group I was the same as that of the control group. The self-healing method of experimental group II involved soaking the specimen in a mixed solution of urea and calcium acetate for two days, and then taking it out and placing it in an incubator for two days, with a cycle of four days. The test results show that in terms of the relative bond strength ratio, the experimental group II increased by 17.9% compared with the control group. Moreover, the precipitate formed at the cracks in the sample was confirmed to be calcium carbonate with the EDS and XRD analysis results, which improved the compressive strength and bond strength after self-healing. This indicates that the biomineralization self-healing method used in experimental group II is more effective.

Experimental evaluation of fracture toughness of basalt macro fiber reinforced high performance lightweight aggregate concrete

High performance lightweight aggregate concrete has become a popular topic for the development of green concrete due to the incorporation of various industrial wastes to substitute aggregate. However, its brittleness has gradually emerged as an issue with the increasing of compressive strength. To address this concern, the authors in this paper investigated the influence of basalt macro fiber (BMF) on the compressive and splitting tensile strengths of lightweight aggregate concrete at different fiber volume contents and lengths. Moreover, the three-point bending test on notched beams, with the help of acoustic emission and digital image correlation, was also carried out to evaluate the fracture toughness of basalt macro fiber reinforced lightweight aggregate concrete. Finally, the softening constitutive model was determined in the present study. The results showed that the addition of BMF increased the compressive strength of lightweight aggregate concrete and the maximum increase reached 9.03%. As for splitting tensile strength, the maximum increase was 39.88%. In addition, it was observed that the incorporation of basalt macro fiber significantly improved the initial cracking toughness and unstable fracture toughness of plain specimen. The fracture energy of BMF reinforced lightweight aggregate concrete was also increased, and the largest improvement was seen in BMF-0.5–22.5 group, 8.5 times that of plain specimen.

Effects of fiber characteristics and specimen sizes on static and dynamic split-tensile failures of BFLAC: 3D mesoscopic simulations

In this study, a three-dimensional mesoscopic numerical model considering concrete heterogeneity and explicit modelling of basalt fibers was established to simulate the static and dynamic split-tensile failures of basalt fiber-reinforced lightweight aggregate concrete (BFLAC), with a special focus on the influences of structure sizes (D = 100, 200, 300 and 400 mm), basalt fiber contents (Vf = 0.1 %, 0.2 % and 0.3 %), fiber lengths (Lf = 6, 12, 18, 24 mm) and loading strain rates (ε̇ = 10-5/s ∼ 100/s) on split-tensile failure patterns, deformation characteristic and failure strengths. Simulation results indicate that as the fiber length increases, split-tensile strength of BFLAC enhances first and then remains unchanged. As the fiber content increases, both static and dynamic split-tensile strengths enhance, showing a fiber reinforcement effect which increases with the rising strain rate rise and reaches a threshold when the strain rate exceeds 1/s. Under static and low strain rates, the size effect on split-tensile strength of BFLAC is reduced by the addition of basalt fiber content; while there is a reverse size effect under high strain rates and it is strengthened with the increasing fiber content. Besides, the strain rate effect of BFLAC is stronger with the increasing basalt fiber content. A unified TDIF formula of BFLAC considering the influence of basalt fiber content was proposed, which can provide a valuable reference for the dynamic performance simulations and calculations.

Evaluation of pore and fiber distribution characteristics of hybrid fiber reinforced lightweight aggregate concrete using X-ray computed tomography

The contribution of lightweight aggregate (LWA) and fibers to the mechanical performance of concrete is still controversial due to the unclear understanding of the enhancing mechanism. Clarifying pore structure and fiber orientation characteristics is the key to it. In this study, pore characteristics and fiber distribution properties as well as their correlations with concrete strengths were evaluated. To separate the effect of LWA's internal pores and LWA's internal curing, pore parameters were calculated in two ways, i.e., containing and excluding LWA. Results show that the internal pores of LWA are detrimental to the overall pore structure while the internal curing optimizes the pore distribution by decreasing porosity and pore size and increasing sphericity. Pore sphericity has a positive linear correlation with compressive strength only when LWA's internal pores are included. When the inner pores of LWA are excluded, sphericity is positively correlated with flexural strength. It indicates that LWA's internal pores have a more significant effect on compressive strength while LWA's internal curing effect has a more prominent impact on flexural strength. In addition, adding fibers benefits pore characteristics given that more pores are in the spheroid shape with higher sphericity. Furthermore, fibers are well distributed in this study with a mean orientation coefficient of 0.59, which exhibits a positive correlation with flexural strength but an insignificant correlation with compressive strength.

An investigation of the hybrid effect of pre-absorbed lightweight aggregate and basalt-polypropylene fiber on concrete performance

Although fibers have been extensively adopted to modify the mechanical performance of concrete containing lightweight aggregate (LWA), the composite impact of fibers and LWA’s internal curing has not been addressed yet. In this study, a comprehensive investigation of basalt-polypropylene (BF-PF) fiber reinforced lightweight aggregate concrete was carried out to investigate the interactions between BF-PF fibers and LWA’s internal curing, considering multiple LWA contents and BF:PF ratios. Results showed that adding LWA benefited the flexural strength but lowered the compressive strength, as the multi-pore structure of LWA increased the porosity and pore size of concrete while the internal curing of LWA optimized the overall pore structure. Nonetheless, adding BF-PF fibers could alleviate LWA’s negative effect on compressive strength given that a positive hybrid effect was identified between LWA and BF-PF fibers. The discharged water from LWA benefited cement hydration and contributed to an increased Ca(OH)2 content in the paste and a lowered Ca/Si ratio in the interfacial transition zone, thereby enhancing the bond between BF-PF fibers and the paste. Given a fixed fiber volume, increasing the PF ratio was more conducive to concrete’s post-cracking behavior while increasing the BF ratio benefited concrete’s pore structure. Furthermore, a multi-dimensional evaluation accommodating fresh properties, mechanical performance, pore characteristics, cost and environmental sustainability indicated that a mix of 20% LWA and 0.20% fiber at a BF:PF ratio of 3:1 was the optimum one. The results demonstrate the enhancing mechanism of fiber reinforced lightweight aggregate concrete, providing insight into concrete design in practical engineering.

Compressive and flexural toughness indices of lightweight aggregate concrete reinforced with micro-steel fibers

There remains a lack of comprehensive investigations examining ductility of the fiber-reinforced lightweight aggregate concrete (LWAC) elements, necessitating a deeper exploration. The purpose of this study is to assess the effect of micro-steel fibers on the compressive and flexural toughness capacities of LWAC. A total of twenty-one LWAC mixtures were prepared, varying the test parameters of the compressive strength of concrete and fiber volume fraction. The toughness capacities of fiber-reinforced LWAC were calculated using the stress–strain curves in compression and flexural load–deflection curves measured for each specimen, in accordance with ASTM C1018. These were compared with those of the previous normal-weight concrete and LWAC specimens reinforced by single macro-steel fibers or a combination of macro-steel fibers and micro synthetic fibers. The effect of numerous fiber parameters on the toughness of concrete was considered as a function of the fiber reinforcing index. Simple closed-form equations from the literature were modified to reliably determine the compressive and flexural toughness indices of micro-steel fiber-reinforced LWAC. Additionally, the relationship between equivalent flexural strength ratio and flexural toughness indices was formulated from a regression analysis using test datasets. Test results showed that the addition of only 0.25% micro-steel fibers significantly enhanced strength and toughness in compression and flexure. Moreover, better dispersion of steel microfibers enabled greater LWAC strength and toughness increases through a denser restriction of crack propagation.

Local bond-slip behaviour of reinforcing bars in fibre reinforced lightweight aggregate concrete at ambient and elevated temperatures

This paper presents an experimental investigation of the bond-slip behaviour of reinforcing bars in fibre-reinforced lightweight aggregate concrete (FRLWAC) at ambient and elevated temperatures. Sixty-four bond-slip specimens with four target temperature exposures, two concrete covers and four steel fibre contents were tested to failure. The experimental results showed that exposure to elevated temperature shifted failure pattern from more ductile pull-out to brittle splitting modes, and reduced the peak bond strength and toughness of bond-slip behaviour. Scanning electron microscope (SEM) images of the concrete-steel interface showed that thermal mismatch induced microcracks contributed to degradation of bond strength, in addition to temperature induced degradation of concrete materials. The temperature exposure also negated beneficial effect of concrete cover in enhancing bond behaviour. Addition of steel fibre helped in preventing brittle failure mode, enhancing bond strength in specimens with small concrete cover and improving the post-peak bond-slip behaviour at all target temperatures. A simple semi-analytical bond-slip model that considers different failure modes and incorporates fibre-reinforced concrete tensile behaviour from Swedish Code SS 812310 was proposed and validated based on the test results in this study.

Experimental study on compression failure characteristics of basalt fiber-reinforced lightweight aggregate concrete: Influences of strain rate and structural size

This paper presents systematic experimental investigations on the combined influences of loading strain rate and structural size on uniaxial-compression failure characteristics of LAC and basalt fiber-reinforced lightweight aggregate concrete (BFLAC), in terms of workability, failure morphology, deformation curve, failure strength, elastic modulus and energy absorption, with a special focus on the size-dependence of strain rate effect. Results indicate that the uniaxial-compression strength, elastic modulus, compression toughness as well as specific toughness are increased when the basalt fibers with 0.3% volume content is added in LAC, which can be ascribed to the synergistic effect of three working modes of basalt fibers in restricting the crack propagation and fracture failure. As the strain rate increases, specimens with larger size perform a stronger strain rate effect, resulting in that the influence of structural size on uniaxial-compression failures is weakened. The addition of basalt fibers can also weaken the size-dependence on uniaxial-compression strength, compression toughness and specific toughness, which contributes to the promotion and application of basalt fibers in LAC, especially for large-scale engineering structures. The dynamic increase factor (DIF) empirical formulas of LAC and BFLAC with various structural sizes have been obtained, which can provide a reasonable reference for structure safety design and numerical computation of LAC and BFLAC.

Experimental investigation on splitting-tension failures of basalt fiber-reinforced lightweight aggregate concrete: Effects of strain rate and structure size

The incorporation of basalt fibres in lightweight aggregate concrete (LAC) is a potentially effective approach to ameliorate failure strength and ductility, which has been extensively applied in concrete structures. This paper investigates the comprehensive effects of strain-rate (ranging from 10−5 to 10−2s−1) and structure size (ranging from 70 to 300 mm) on splitting-tension fracture failures of LAC and basalt fibre-reinforced lightweight aggregate concrete (BFRLAC) via a systematic experiment, in terms of failure modes, deformation curves, peak fracture strengths and microstructure mechanisms. Results indicated that the incorporation of basalt fibres with 0.30% volume fraction in LAC enhanced the splitting-tension strength by 27.3–38.0% at quasi-static strain-rate while it increased to 42.3–53.4% at low strain-rate rising to 10−2s−1, which can be attributed to the change of dominated action mode of basalt fibres in bridging and toughening effect and the superior tensile properties of basalt fibres being made the best use. Both LAC and BFRLAC with larger structure sizes performed higher dynamic increase factors (DIFs), showing a stronger strain-rate effect. LAC and BFRLAC performed a dropping trend in splitting-tension strength with the growing structure size but the drop was reduced as strain-rate rose. The incorporation of basalt fibres could reduce the sensitivity of splitting-tension strength to structure size, which caused 13.3% reduction in size effect at quasi-static strain-rate while up to 51.7% reduction at strain-rate rising to 10−2s−1. The DIF equations captured through regressive analysis on test results could reasonably describe the strain-rate effect of LAC and BFRLAC considering the influence of structure size and offer a valuable guidance for optimal structure designs and simulation calculations.

Strength attributes of fiber-reinforced lightweight aggregate concrete incorporating Lytag ceramsite under freeze-thaw environment

The property of high strength of lightweight aggregate concretes (LWACs) makes them widely applicable in construction. However, a low-temperature environment could accelerate the properties degradation of LWACs. In this paper, the effects of freeze-thaw cycles on the strength behavior of basalt fiber (BF) and polyacrylonitrile fiber (PANF) reinforced lightweight aggregate concrete with Industrial waste ceramsite-Lytag investigated, including cubic and axial compressive strength, splitting tensile strength, flexural strength, and shear strength. Mass loss, relative dynamic elastic modulus (RDEM), scanning electron microscopy (SEM), and computed tomography (CT) were used to analyze the impact of freeze-thaw damage on strength performance and microstructure. The results showed that BF and PANF incorporation significantly affected the residual strength due to their ability to suppress crack growth. The specimens with higher BF and PANF volume fracture had better freeze-thaw resistance properties. Moreover, BF-reinforced LWACs exhibited better freeze-thaw resistance than PANF-reinforced LWACs because BF has superior mechanical properties. The flexural strength indicated the fastest degradation rate after freeze-thaw cycles, while the RDEM revealed the least damage. The freeze-thaw resistance durability of fiber-reinforced LWACs is evaluated based on strength degradation, and the corresponding environment partition of specimens is produced. In order to estimate the strength behavior, the equal-damage strip calculation model is proposed by considering size and loading type effects. The comparison analysis of calculation and test results of strength after freeze-thaw cycles suggested applying the four-sides calculation model for predicting the strength behavior of LWACs.

Experimental Study on Size Effect and Fracture Properties of Polypropylene Fiber Reinforced Lightweight Aggregate Concrete

In this experimental research, the effects of polypropylene fibers on size effect and fracture properties of lightweight aggregate concrete were studied. Two methods, including size effect method and work of fracture method, were used to investigate and analyze the size effect and fracture properties on different sizes of notched beams. The polypropylene fiber contents were 0.5%, 0.75%, and 1% by volume fraction. The obtained results revealed that increasing the polypropylene fibers in lightweight aggregate concrete relatively decreased the dependence of strength on the size effect parameter, while the addition of polypropylene fibers exhibited significant influence on decreasing the size dependency of ductility and fracture energy in lightweight aggregate concrete. Moreover, the increase of polypropylene fibers improved the total fracture energy (GF), initial fracture energy (Gf), characteristic length (lch), length of fracture process zone (cf), and critical stress intensity factor (KIc) of lightweight aggregate concrete in both size effect method and work of fracture method. This increase was more significant in work of fracture method because of considering the post-peak behavior. The size effect method was suitable and accurate for plain lightweight aggregate concrete. The GF ⁄ Gf ratio increased from 2.88 in plain lightweight aggregate concrete to 12.26 in polypropylene fiber reinforced lightweight aggregate concrete.

Thermo-mechanical efficiency of fibre-reinforced structural lightweight aggregate concrete

The construction industry must consider not only the mechanical performances of structural materials but also their thermal performances for energy-efficient buildings. There exist conflicting thermal and mechanical properties between normal weight concrete (NWC) and lightweight aggregate concrete (LWAC). NWC with high mechanical strength exhibits poor thermal efficiency but LWAC possesses low mechanical strengths but high thermal efficiency. The inclusion of fibres in the mixture of LWAC could provide a solution to its weaknesses in mechanical properties however its thermal performance was not well fully understood. To produce an energy-efficient building material, this study was conducted to determine thermo-mechanical performances of steel (ST) and polypropylene (PP) fibre-reinforced LWACs that meet the structural code requirements with good thermal properties. Lightweight expanded clay aggregate was used to make a structural LWAC and polypropylene and steel fibres were used as the reinforcement. Test results revealed that structural LWAC reinforced ST fibre with 1.0% dosage has the best mechanical and thermo-mechanical efficiency whilst PP fibre with 0.3% dosage has the best thermal performance.The ST fibre has a positive influence on the compressive and tensile strength than PP fibre. In terms of overall thermal performance and cost, LWAC containing 0.3% PP fibre was the most desirable. The PP fibre has a more positive influence on thermal properties than ST fibre. The equations had been proposed with a good correlation of R2 > 0.7979 to predict the thermal properties against density for ST and PP fibres. The new merit Mo equation provides a novel way to measure the thermo-mechanical efficiency of the building materials for the construction industry. ST fibre is better than PP fibre in enhancing the mechanical efficiency but PP fibre is more efficient than ST in enhancing the thermal efficiency of fibre-reinforced LWAC.

Influence of Different Ambient Temperatures on the Thermal Properties of Fiber-Reinforced Structural Lightweight Aggregate Concrete

This study reports the influence of different climatic ambient temperatures on the thermal properties of fiber-reinforced lightweight aggregate concrete (LWAC). Lightweight expanded clay aggregates (LECA) with steel (ST) and polypropylene fibers were used in the mix proportions. The steady-state thermal test was performed on concrete samples at the oven-dry state with the measurement taken at six different climatic ambient temperatures of 0 °C, 10 °C, 20 °C, 30 °C, 40 °C, and 50 °C. The results show a linear dependence of thermal conductivity, specific heat, thermal diffusivity and thermal effusivity of fiber-reinforced LWACs against the different ambient temperatures. These ambient temperature variations are discussed as a function of the thermal properties of fiber-reinforced LWAC. The thermal conductivity and thermal diffusivity decrease linearly between 0 °C and 50 °C, whilst the specific heat and thermal effusivity increase linearly between 0 °C and 50 °C. Equations with strong correlations to predict thermal properties of fiber-reinforced LWAC were proposed based on the results of this study. The significance of this research is to propose the dynamic ambient temperature-dependent thermal properties equations that can be used in the energy analysis of the buildings.

Stress-Strain Model for Lightweight Aggregate Concrete Reinforced with Carbon-Polypropylene Hybrid Fibers.

This research aimed to investigate the hybrid effects of carbon and polypropylene fibers on the stress–strain behavior of lightweight aggregate concrete (LWAC). The considered test variables were two fiber volume fractions of 0.2% and 0.4% and two water/binder ratios of 0.27 and 0.30. Eighteen groups of prisms fabricated with fiber-reinforced LWAC were tested under axial compressive load. Experimental studies were carried out to analyze the influence of different fiber combinations on the complete stress–strain behavior. It was found that the carbon–polypropylene hybrid fibers led to toughness enhancement that was numerically more significant than the sum of individual fibers, indicating a positive synergistic effect between them. Finally, a mathematical expression of the stress–strain curve accounting for the fiber combinations was developed. Compared with existing stress–strain models, the proposed model shows better accuracy in predicting the effect of carbon and polypropylene fibers in both single and hybrid forms on the stress–strain curve of LWAC.