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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. • Bamboo fiber (BF)-reinforced lightweight aggregate concrete (LWAC) was examined. • BFs significantly improved the splitting tensile strength and ductility of LWAC. • The failure modes of specimens were analyzed based on SEM images and DIC technology. • The stress-strain models of BF-reinforced LWAC were established. [ABSTRACT FROM AUTHOR]

• Lightweight cellular concrete (LCC) filled with fly ash (LCCFFA) is developed. • Strengthening mechanism of LCCFFA is revealed from microstructure point of view. • 25% content of fly ash is recommended with the Si/Ca ratio as a judging criterion. Fly ash has been used to fill the lightweight cellular concrete (LCC) as the primary admixture to promote comprehensive engineering applications. However, the strengthening mechanism of LCC resulted from fly ash is not well understood. In this paper, the strengthening mechanism of LCC filled with fly ash (LCCFFA) was investigated with respect to the microstructures including porosity and skeleton characteristics. The variation rules of average pore size (PS), pore roundness value (PRV), and fractal dimension of pore distribution (FDPD) with different fly ash contents were explained. The relationship between microscopic parameters of PS, PRV, and FDPD and the overall compressive strength, along with the wet bulk density was established. Furthermore, the difference of skeleton structure evolution mechanism between LCC and LCCFFA was investigated with the results showing that the difference comes from the effects of ball and particle filling of fly ash when before 28 days. While after 28 days, the pozzolanic reaction of fly ash and hydration reaction of cement mutually promote the densification of skeleton structure. Finally, the SEM energy spectrum diagram was analyzed to further reveal the strengthening mechanism. From the perspective of characteristic pore parameters and skeleton hydration products, the recommended content of fly ash is approximately 25%. The ratio between Si and Ca (Si/Ca) can determine the degree of reaction of fly ash, and can therefore be used as a judging criterion to determine whether the content of fly ash is appropriate. [ABSTRACT FROM AUTHOR]

• Micromechanics-based finite-element model of LCC is developed. • Various roles of microstructural porosity are quantified with different mixture ratio. • Effects of porosity characteristics are demonstrated on the ultrasonic pulse velocity. While nondestructive ultrasound-based methods are suitable for evaluating the physical and mechanical properties of lightweight cellular concrete (LCC) materials, the quantitative relation between porosity characteristics and acoustic parameters is not well understood. In this study, the micromechanics-based finite-element models are rebuilt using the real porous microstructure of LCC. Various roles of porosity characteristics are analyzed, including equivalent pore radius, pore sphericity value and fractal dimension of pore distribution with different mixture ratios. Effects of porosity characteristics are quantitatively demonstrated on the ultrasonic pulse velocity. It is shown that the ultrasonic pulse velocity is positively correlated with equivalent pore radius and fractal dimension of pore distribution, and negatively correlated with pore sphericity value and porosity. As the orientation of pores increases, the ultrasonic pulse velocity initially drops, followed by the increase. The quantitative understanding of porosity characteristics on ultrasonic responses helps improve the accuracy of ultrasonic detection on LCC properties. Comparisons between simulation results and experimental data of ultrasonic pulse velocities demonstrate good agreement. This study represents an effective quantitative method to explore the ultrasound propagation in LCC. [ABSTRACT FROM AUTHOR]