The capillary absorption capacity exerts an important effect on the durability of cement-based materials and is closely related to the pore structure. In this study, a variety of cement-based specimens were examined. The capillary water absorption and pore structure of the samples were determined using a gravimetric method and mercury intrusion porosimetry (MIP), respectively. The capillary water absorption coefficients for different water–binder ratios, diverse types and dosages of mineral admixtures, and various preloads were measured. The experimental results were analyzed and compared with data available in the current literature. The test results showed that the capillary water absorption performance of cement-based materials increased with an increasing water–binder ratio, first decreased and then increased with an increasing fly ash dosage, decreased with an increasing mineral power dosage, and decreased when the preload was less than a critical value and increased rapidly when the preload was greater than the critical value. The relationship between the capillary absorption coefficient and porosity was nearly linear. Water absorption by cement-based materials mainly correlated with pore diameters in the range of 10~1000 nm. The capillary water absorption coefficient increased continuously with the increase of pore fractal dimension.

The relation between slump flow and yield stress of ultra-high performance concrete (UHPC) mixtures was studied with theoretical analysis and experimentation. The relational expression between slump flow and yield stress of UHPC mixtures was built and then verified with a rheological test. The results showed that the prediction model, as a function of cone geometry of dimensionless slump flow and dimensionless yield stress of the UHPC mixtures, was constructed based on Tresca criteria, considering the geometric relation of morphological characterization parameters before and after slump of the UHPC mixtures. The rationality and applicability of the dimensionless prediction model was verified with a rheological test and a slump test of UHPC mixtures with different dosages of polycarboxylate superplasticizer. With increase in polycarboxylate superplasticizer dosage, yield stress of the two series of UHPC mixtures (large/small binding material consumption) gradually decreased, leading to a gradual increase in slump flow. Based on the prediction model of dimensionless slump flow and dimensionless yield stress, the relational expression between slump flow and yield stress of the UHPC mixtures was built. The comparison result showed that the calculated data was consistent with the experimental data, which provided a new method for predicting yield stress of UHPC mixtures with a slump test.

The tensile strength, crack behavior, and strain-hardening properties of ultra-high-performance concrete (UHPC) are mainly affected by the steel fibers distributed in the matrix. In this study, a mesoscopic model of UHPC was established using a numerical simulation method to study the effects of steel fibers on the crack propagation and tensile properties of UHPC. First, the exponential cohesive model was used to simulate the pull-out of a fiber embedded in a UHPC matrix. Then, the distribution and variation of the interfacial shear stress during the fiber pull-out process were obtained, and the UHPC fiber-pull-out load–displacement curve was obtained. Using the Monte Carlo method, a meso-scale finite element model of UHPC was established by modeling randomly distributed steel fibers in the UHPC matrix. After verification, the model was used to study the effects of fiber characteristics, interface strength, and matrix strength on the crack propagation path and tensile properties of UHPC. The results showed that the exponential cohesive constitutive model with a softening coefficient of –1 can effectively characterize the mechanical behavior of the interface between the steel fibers and matrix in UHPC. Affected by the random distribution of fibers, the main propagation mode of cracks in UHPC was that the cracks bypassed the fiber-dense area and extended to the fiber-sparse area, and the crack propagation path was mainly affected by the fiber distribution. The distribution of fibers significantly affected the tensile strength and peak strain of UHPC. When the fiber inclination angle was in the range of 15°–30°, the comprehensive tensile properties of UHPC were the best. With increasing fiber volume fraction and fiber length, UHPC gradually began to exhibit multi-cracking and strain hardening (when the fiber volume fraction was more than 2.5% or fiber length was more than 15.5 mm). The interface strength and matrix strength had little effect on the crack propagation path, but had significant effects on the tensile strength and toughness of the UHPC. The higher the strength of the UHPC matrix, the more fully the anti-cracking effect of the steel fiber that can be achieved.

To investigate the biaxial mechanical characteristics of reactive powder concrete (RPC), RPC plate specimens and bone‐shaped specimens were tested under compression‐compression and compression‐tension loadings, respectively. The strengths and strains of the specimens were recorded, and the crack patterns and failure modes in various stress states were examined. Based on the test data, the characteristics of biaxial strength were analyzed, and a biaxial failure criterion was established. The characteristics of major stress‐strain curves and failure modes in different biaxial stress states were determined. The results show that the ratio between the biaxial compression strength and the uniaxial compression strength was 1.44–1.58 for RPC. When the stress ratio under compression‐tension was −0.05, the tensile strength decreased by 48%. Under compression‐compression, the proportional limit of RPC was about 95%, and its peak strain was high. Under compression‐tension, as the compressive stress increased, the elastic modulus decreased, and the peak strain in the tensile direction increased. When the RPC specimens were under compression‐compression, the failure mode of RPC was splitting failure. Under compression‐tension, the failure mode changed from single‐crack tensile failure to multicrack compressive failure with increasing confining stress.