堆石混凝土(RFC)的抗拉性能是保障坝体抗裂、防渗及长期稳定性的核心指标,其力学特性与破坏规律随龄期显著变化,直接影响工程结构安全与服役寿命。为探究早龄期RFC的劈裂抗拉宏观力学性能及其损伤演化规律,利用声发射技术,对边长为450 mm的RFC立方体试件开展了不同养护龄期(3、7、14、28 d)下的劈裂抗拉试验。结果表明:①不同龄期RFC的荷载-位移曲线变化趋势一致,劈裂抗拉强度随养护龄期的增加而增加,7、14、28 d龄期下劈裂抗拉强度较3 d的增幅为24.44%、137.78%和160%;②不同龄期下RFC表面裂缝主要沿加载方向扩展,断面呈现沿自密实混凝土(SCC)、块石、SCC-块石界面破坏类型,块石破坏的占比分别为0%、10.53%、27.78%和29.41%;③微裂纹扩展和裂纹稳定扩展阶段的累计振铃计数缓慢增长,失稳阶段的振铃计数发生突变,峰值时刻累计振铃计数随龄期增加而递增,RFC破坏所需的能量显著增加,7、14、28 d龄期较3 d龄期所需的能量分别增长60.20%、102.47%和178.05%;④RFC劈裂抗拉破坏以拉伸裂纹为主,声发射事件的分布与RFC表面裂缝分布一致,集中在225±25 mm,此外,幅值>65 dB声发射事件与块石破坏在数量和空间分布上呈现良好的对应关系。

[Objective] The tensile properties of early-age concrete significantly influence the crack evolution of Rock-filled Concrete (RFC). To investigate the macroscopic splitting tensile mechanical properties and damage evolution laws of early-age RFC, we conducted splitting tensile tests on RFC cubic specimens at curing ages of 3 d, 7 d, 14 d, and 28 d using acoustic emission (AE) technology. The mechanical responses and AE characteristics of RFC at different ages were systematically analyzed. [Methods] The splitting tensile performance indicators, including load-displacement curves, splitting tensile strength, and failure morphology, as well as acoustic emission characteristic parameters such as ring count, RA-AF distribution characteristics, and event location points, were obtained. [Results] (1) The load-displacement curves of specimens at different ages exhibit a consistent trend, with splitting tensile strength increasing with curing age. Compared to the 3 d age, the strength gains at 7 d, 14 d, and 28 d are 24.44%, 137.78%, and 160%, respectively.(2) Cracks primarily propagate parallel to the loading direction, accompanied by micro-crack development on the specimen surface. Failure modes can be categorized into three types: failure through the self-compacting concrete (SCC) matrix, failure through the rock block, and failure along the SCC-rock bonded surface. With increasing curing age, the proportion of rock block failure increases progressively, accounting for 0%, 10.53%, 27.78%, and 29.41%, respectively.(3) Based on ring count characteristics, the splitting process can be divided into four stages: initial compaction, micro-crack propagation, stable crack propagation, and unstable failure. The cumulative ring count increased slowly during the micro-crack propagation and stable crack propagation stages, while it underwent a sudden change during the instability stage. The cumulative ring count at the peak increased with age, and the energy required for RFC failure increased significantly, rising by 60.20%, 102.47%, and 178.05% at 7, 14, and 28 d, respectively, compared to 3 d.(4) In terms of crack evolution, tensile cracks dominate during the splitting process of RFC. The distribution of acoustic emission events corresponds to the distribution of surface cracks in RFC, with a concentration at 225 ± 25 mm. Furthermore, there is a strong correlation between AE events with amplitudes greater than 65 dB and rock failure in terms of both quantity and spatial distribution. [Conclusions] With increasing curing age, the degree of cement hydration gradually deepens, enhancing both the strength of the SCC matrix and its bond interface with rock blocks. Consequently, the splitting tensile strength of RFC increases, and the cooperative deformation capacity between rock blocks and SCC is improved. The experimental results demonstrate that acoustic emission characteristic parameters, including ring-down count, RA-AF, and spatial distribution, exhibit strong consistency with macroscopic test results such as load-displacement curves, splitting tensile strength, and failure morphology. The crack-arresting effect of rock blocks is more prominent at curing ages of 3 d and 7 d, where the failure surfaces are predominantly characterized by debonding at the SCC-rock block interface. Beyond 7 d, rock block failure begins to emerge on the fracture surfaces, accompanied by an increase in the energy required for specimen failure. At the curing age of 28 d, rock block fracture is evident on the failure surfaces, with a marked increase in failure energy, a notable enhancement in splitting tensile strength, and a corresponding rise in the proportion of tensile cracks. Moreover, the damaged regions on the specimen surface are generally consistent with the clustering locations of acoustic emission events, and acoustic emission events with amplitudes exceeding 65 dB show favorable correspondence with rock block failure in both quantity and spatial distribution.