Strain Hardening Cementitious Composite (SHCC) is one kind of engineered materials designed based on the principles of mesoscale and fracture mechanics. It exhibits a tensile strain capacity of up to 3%-8%, which are approximately 300~800 times greater than ordinary concrete. SHCC has been successfully used in the rehabilitation of dams and bridge decks in Japan owing to its excellent mechanical properties. These structures withstand not only static loads but also potential dynamic impact loads during service. To accelerate the application of SHCC in seismic-resistant structures, blast-resistant structures and other critical infrastructure, it is essential to have knowledge of its dynamic mechanical properties and failure mechanisms. Therefore, this study characterized the mechanical behavior and failure modes of SHCC under high strain rate loading using Split Hopkinson Pressure Bar (SHPB) testing, with high-speed digital image correlation (DIC) capturing full-field strain evolution on specimen surfaces during impact tests. X-ray computed tomography (X-CT) technology was used to observe the internal damage of SHCC after high strain rate loading. The influences of strain rate on the dynamic peak stress, energy absorption capacity, dynamic growth factor, full-field dynamic strain distribution, internal damage form and microstructure of SHCC were investigated.

This study adopted Ordinary Portland cement 42.5 (GB175—2023, with an average particle size of 27 μm and the particles of 3-30 μm account for about 70%) and Class I fly ash (GB1596—2017, with a particle size less than 10 μm account for more than 80%) as cementitious materials. The quartz sands with a maximum particle size of 0.3 mm were used as fine aggregates. SHCC samples were prepared using PVA fiber produced by Kuraray, Japan. Meanwhile, the polycarboxylate superplasticizer (provided by Nanjing Subote New Materials Co., Ltd.) was added to enhance the workability, ensuring uniform fiber dispersion of the slurry.

After mixing, the slurry was cast into molds, followed by vibration, and demolded after a 24 h curing period under standard laboratory conditions. Specimens were then cured under standard conditions until testing age. Static compression tests were employed using 70.7 mm cube specimens. Moreover, dynamic properties were evaluated using a SHPB system with ϕ48×25 mm cylindrical specimens. During impact loading, high-speed industrial camera was used to captured specimen deformation for subsequent VIC-2D digital image correlation analysis. The damaged SHCC samples after high strain rate loading were scanned using X-ray computed tomography and observed with scanning electron microscope (SEM).

The dynamic compressive stress-strain curve of SHCC presents typical three-stage characteristics under high strain rate loading: linear elastic deformation stage, nonlinear strain hardening stage and damage softening stage. Dynamic compressive stress-strain curves of SHCC exhibit strong dependence on strain rate. At higher strain rates, the dynamic compressive response of SHCC exhibits significant strain hardening, primarily governed by fiber bridging effects and secondarily enhanced by compaction of micro-defects. The dynamic peak stress of SHCC increases significantly with strain rate, demonstrating a pronounced strain rate sensitivity. Simultaneously, the dynamic peak stress of SHCC increases substantially at high strain rates. This enhancement primarily arises from the significantly shorter stress wave propagation time compared to the characteristic relaxation time of internal defects under high strain rate loading. Consequently, stress waves preferentially propagate through high-strength regions (e.g., matrix grains and fiber reinforcements), inducing localized stress concentrations. The energy absorption capacity of SHCC increases with the increase of strain rate. When the strain rate exceeds 180 s^-1, E_d shows an approximate exponential growth trend, reaching 546.12 kJ/m³ at 188 s^-1, with a relative increase of about 106.42%, demonstrating exponential growth behavior and significant strain rate strengthening. This energy absorption surge primarily stems from synergistic multi-scale damage mechanisms. At identical strain rates, the dynamic increase factor for stress demonstrates both a higher mean value and greater variability than that for energy, reflecting its stronger dependence on strain rate effects. This indicates greater strain rate sensitivity in dynamic peak stress than energy absorption capacity, confirming the dynamic peak stress is more susceptible to strain rate.

The main conclusions of this paper are summarized as following. SHCC exhibits strain rate sensitivity of dynamic mechanical properties, with both peak stress and energy absorption capacity increasing significantly under high strain rate loading. The sensitivity of dynamic stress to strain rate is significantly greater than that energy absorption capacity. DIC analysis shows that the vertical expansion of the specimen is substantially more significant than the lateral compression. X-CT analysis reveals significantly denser crack distribution near specimen edges compared to the central region. Moreover, multiple cracks appear at the same crack point, which is an essential reason for the excellent dynamic mechanical properties of SHCC.