Study on the bond properties between basalt fiber-reinforced spontaneous combustion coal gangue concrete and BFRP bars

Microstructural characterization of spontaneous combustion coal gangue (SCCG), the hydration products and mechanism of spontaneous combustion coal gangue concrete (SCCGC) were discerned through microscopic analysis. The bond performance was assessed employing a central pull-out test on samples variably substituted with SCCG (0%, 25%, 50%, 75%, and 100%) and augmented with basalt fiber (BF) (0%, 0.1%, 0.15%, and 0.2%). The failure mode and bonding mechanism were also revealed by this test. The bond-slip curves were fitted by various bond-slip constitutive models and a suitable model was found for each section. As indicated by the results, SCCGC possessed a lower carbon content and higher Al and Si element contents. These elements would undergo secondary hydration reactions with CH, which could enhance the strength of the ITZ and the compactness of the bond interface between BFRP bars and concrete. The failure modes were splitting and pull-out. An inverse correlation was observed between bond strength and the increment in SCCG aggregate substitution, ranging from a decline of 2.6% to 23.1%. As the BF content increased, the bond strength and peak slip increased by 3.9% ∼ 19.7% and 4.0% ∼ 14.6%, respectively. Furthermore, the reinforcing effect of BF on bond strength increased from 3.9% ∼ 10.3% to 8.8% ∼ 19.7% as the SCCG replacement rate increased, which was noticeable. The Malvar model and the Continuous Curve model were the best fitting models for the ascending and descending sections of bond-slip curves, respectively, while the residual stage was well fitted by the Hao Qingduo model.</p

Experimental investigation of bond performance between BFRP and different strength recycled-aggregate concrete

In recent years, there has been a large number of studies on recycled-aggregate concrete as a potential solution to the problem of a scarcity natural resources. This study investigated the bonding performance of a new reinforcement material employed in medium and high-strength recycled aggregate concrete. The pull-out test was carried out by employing basalt fiber-reinforced polymer (BFRP) bars with different diameters (12, 14, and 20 mm) in medium and high-strength concrete with different ratios of recycled coarse aggregate replacement (0, 25, 50, 75, and 100%). Based on the concrete bond damage, the failure modes were identified, the corresponding bond mechanism was analyzed and the bond stress–slip characteristics were summarized. The effect of each parameter on the failure mode, bond strength, and the bond-slip curve between recycled-aggregate concrete and BFRP bars was evaluated. Results indicated that as the diameter of the BFRP bar increased, the failure mode was shifted, the uneven distribution of bond stress became more pronounced, and the bond strength showed a decreasing trend. Two distinct situations of medium to high-strength concrete with very different relative bond strengths at different replacement ratios were found. The relative bond strength of medium-strength concrete increased at first and then decreased with the increase of the replacement ratio of recycled coarse aggregate. A non-linear relationship between the bond strength of recycled concrete and its compressive strength was found. The two-stage model was proposed to describe the bonding behaviour more accurately between BFRP bar and medium to high-strength recycled aggregate concrete.</p