The production of cement leads to a large amount of CO2 emission. Using industrial waste slag, such as ceramic polishing powder (PP), to replace part of Portland cement can reduce the pollution ...caused by the cement industry and solid waste disposal. In order to use PP as a replacement for cement, its effects on the properties of cement paste need to be clarified. In this study, the effect of PP on the nucleation and growth of hydrates in cement paste at very early ages was investigated. Quartz was used as a reference. The interactions of their surface with various ions in cement paste solution, which has an important effect on the nucleation and growth of hydrates, were studied by using the zeta potential test. The morphology of the nucleus and crystal of hydrates was investigated by using SEM. The zeta potential measurements showed that the affinity of the surface of PP and quartz to ions in the pore solution of cement paste is similar. The image of SEM indicated that there is also not much difference in the crystallization of hydrates on the surfaces of PP and quartz. These evidences suggested that PP has similar surface charge properties as quartz, and its effects on the properties of cement paste are the same as that of quartz. From the viewpoint of the effect on very early hydration, PP can be used in cement paste, similar to quartz power.
This study presents the meso-mechanics models of the multi-scale fiber bridging constitutive law of ultra high-performance concrete (UHPC) under cyclic loading. First, an analytical fiber pullout ...model was improved by considering the effect of fiber inclination angle and embedded length. Second, the flexural behavior of the UHPC with various fiber volume fractions under quasi-static loading was predicted by performing meso-mechanics-based sectional analysis. Third, the relation between a single steel fiber and the crack opening displacement amplitude (ΔCOD) under cyclic loading was simulated. Importantly, regardless of the state of the single fiber in (debonding or sliding), the evolution of ΔCOD with different inclination angles and embedded lengths could be quantitatively analyzed during a cycle. Finally, the multi-scale fiber bridging constitutive law of the UHPC under cyclic loading was obtained, and the theoretical relation for the fiber bridging stress amplitude (Δσf) and ΔCOD during the entire cycle process could be quantitatively estimated. There was a slight of deviation between the predicted and experimental results for the UHPC under cyclic loading, because the effect of the UHPC matrix on the fatigue crack was neglected. Overall, the fiber bridging theoretical analysis model for the UHPC under cyclic loading showed good agreement with the experimental data.
Fatigue crack propagation behavior in ultra-high-performance concrete (UHPC) containing different volume fractions of steel fibers is investigated under cyclic flexural loading at various stress ...levels. Evolutions of the crack mouth opening displacement, crack tip strain, and crack propagation length are characterized during continuous loading cycles via digital image correlation. Test data are fit to smooth, continuous logarithmic functions to discern relationships between evolving crack length and the number of loading cycles. The crack propagation rates of different UHPC specimens are then determined from the first derivative of these logarithmic functions. A critical crack length of approximately 20 mm is found in UHPC containing a fiber volume fraction (Vf) of 0.5%, while that of other specimens (Vf = 1.0%, 1.5%, and 2.0%) is found to approach 60 mm under the stress levels of 0.80, 0.75, 0.70 and 0.65. Strain diagrams obtained via DIC reveal no obvious changes for the crack growth along the y-direction in UHPC specimens containing fiber volume fractions of 0.5% and 1.0%, while a tendency for strain concentrations oriented at 45° characterizes crack development in specimens containing 1.5% and 2.0% volume fractions of fiber. Crack propagation rates during the stable stage of crack propagation decrease upon reducing applied stress level and with increased content of steel fiber reinforcement, providing predominant means to enhance fatigue life.
•The fibers number per unit area for S0.5, S1.0, S1.5, and S2.0 were 7, 14, 21, and 31, respectively. The fiber pull-out length in cracked zone with different fiber-volume fractions was about ...3.56 mm.•The fiber orientation factor (ηθ) of S0.5, S1.0, S1.5, and S2.0 were 0.80, 0.79, 0.69 and 0.61 respectively.•A linear relationship between fiber pull-out number and equivalent bending stress, as well as between total fiber pull-out length and toughness, was established.•A quadratic relationship between the ηθ and the fiber pull-out number is proposed. The flexural-tensile strength ratio (β) is about 2.52 for UHPFRC exhibiting deflection hardening behavior.•The tri-linear softening curve analysis exhibited good agreement with the experimental results.
This paper investigated the effect of steel fiber-volume fraction (0.5%, 1.0%, 1.5%, and 2.0%) and distribution on the flexural behavior of ultra-high performance fiber reinforced concrete (UHPFRC). Digital image correlation (DIC) was used to obtain the crack propagation behavior of UHPFRC under bending load. With increasing fiber-volume fraction, the crack-propagation path becomes more zigzagged. Based on the flexural response of UHPFRC and fiber distribution on the crack plane, a correlation between fiber distribution characteristics and flexural behavior was discussed. The fibers number per unit area for S0.5, S1.0, S1.5, and S2.0 were 7, 14, 21, and 31, respectively. The fiber pull-out length in cracked zone with different fiber-volume fractions was about 3.56 mm. The fiber orientation factor (ηθ) of S0.5, S1.0, S1.5, and S2.0 were 0.80, 0.79, 0.69 and 0.61 respectively. A quadratic relationship between the ηθ and the fiber pull-out number is proposed. The flexural-tensile strength ratio (β) is about 2.52 for UHPFRC exhibiting deflection hardening behavior. Finally, the post-cracking tensile behavior of UHPFRC was analyzed based on the matrix softening and fiber bridging curve models by the inverse analysis method. The tension softening curves obtained from the tri-linear softening curve analysis exhibited good agreement with the experimental results.
Abstract
The ability of the resistivity measurement to study the crack propagation behavior of the ultra‐high‐performance concrete (UHPC) under flexural loading was analyzed, and focused on ...investigating the effects of crack length and the fracture process zone (FPZ) on the change in electrical resistivity in the post‐cracking stage. The results indicated that the strain‐dependent resistivity characteristic was able to drawn by a linear‐fitting equation before the crack initiated (stage I). After the crack initiated, the change in electrical resistance of the UHPC can be good to reflect the crack development in the post‐cracking stages (II and III), then, the relationship between the crack propagation behavior and the fractional change in electrical resistance (FCR) can be quantitative analysis by using an exponential function. It was also found that the evolution of the crack length and FPZ also had an appreciable impact on the variation tendency of the FCR. The crack length increased dramatically at first and then increased smoothly with the increase of FRC, while the FPZ showed the reverse change trend.
Three combinations of single fibers and nine combinations of hybrid fibers were tested to analyze the mechanical properties and crack propagation behavior of ultra-high-performance concrete (UHPC) by ...digital image correlation. It was found that in comparison to single fibers, the long fibers had a more pronounced effect than short fibers. The hybrid combination of medium length fiber (Vf = 0.5%) and long fiber (Vf = 1.5%) generated a better flexural behavior in terms of post-crack strength, deflection, toughness, than the other hybridization series. A digital image correlation (DIC) technique was applied to record the evolution of surface deformation. The hybrid use of longer fiber replaced the shorter fiber, long fiber replaced medium length fiber and short fiber, medium length fiber replaced short at lower replacement ratios (0.5% and 1.0%), the crack shapes were presented linear variation and showed an abrupt change and did not have a constant increment at higher replacement ratios (1.5% and 2.0%).
Impact compression experiments for the steel fiber-reinforced high-strength concrete (SFRHSC) at medium strain rate were conducted using the split Hopkinson press bar (SHPB) testing method. The ...volume fractions of steel fibers of SFRHSC were between 0 and 3%. The experimental results showed that, when the strain rate increased from threshold value to 90 s -1, the maximum stress of SFRHSC increased about 30%, the elastic modulus of SFRHSC increased about 50%, and the increase in the peak strain of SFRHSC was 2-3 times of that in the matrix specimen. The strength and toughness of the matrix were improved remarkably because of the superposition effect of the aggregate high-strength matrix and steel fiber high-strength matrix. As a result, under impact loading, cracks developed in the SFRHSC specimen, but the overall shape of the specimen remained virtually unchanged. However, under similar impact loading, the matrix specimens were almost broken into small pieces.
The crack characteristics of polypropylene concrete and plain concrete are investigated in the SHPB test. The relation between the character on the Crack Surface of Concrete and material properties ...and the impact pressure is analyzed. Also the multifractal characteristics are given on the Crack Surface of Concrete. The crack distributions of steel fiber reinforced concrete and polypropylene concrete are investigated. The crack resistance effects of fiber are analyzed from the degree of closenness and uniformity.
Metal halide perovskites represent a family of the most promising materials for fascinating photovoltaic and photodetector applications due to their unique optoelectronic properties and much needed ...simple and low‐cost fabrication process. The high atomic number (Z) of their constituents and significantly higher carrier mobility also make perovskite semiconductors suitable for the detection of ionizing radiation. By taking advantage of that, the direct detection of soft‐X‐ray‐induced photocurrent is demonstrated in both rigid and flexible detectors based on all‐inorganic halide perovskite quantum dots (QDs) synthesized via a solution process. Utilizing a synchrotron soft‐X‐ray beamline, high sensitivities of up to 1450 µC Gyair−1 cm−2 are achieved under an X‐ray dose rate of 0.0172 mGyair s−1 with only 0.1 V bias voltage, which is about 70‐fold more sensitive than conventional α‐Se devices. Furthermore, the perovskite film is printed homogeneously on various substrates by the inexpensive inkjet printing method to demonstrate large‐scale fabrication of arrays of multichannel detectors. These results suggest that the perovskite QDs are ideal candidates for the detection of soft X‐rays and for large‐area flat or flexible panels with tremendous application potential in multidimensional and different architectures imaging technologies.
The direct detection of soft‐X‐ray‐induced photocurrent in both rigid and flexible detectors based on all‐inorganic halide perovskite quantum dots is reported. Utilizing inexpensive inkjet printing, perovskite film is printed homogeneously on various substrates to demonstrate large‐scale fabrication. These types of detectors are ideal candidates for applications in the detection of soft/hard X‐rays and for large‐area flat/flexible imaging technologies.
Agricultural ecosystems are facing increasing environmental changes. Revealing ecological stability of belowground organisms is key to developing management strategies that maintain agricultural ...ecosystem services in a changing world. Here, we collected soils from adjacent pairs of maize and rice fields along large spatial scale across Eastern and Southeast China to investigate the importance of core microbiota as a predictor of resistance of soil microbiome (e.g. bacteria, fungi and protist) to climate changes and nutrient fertilization, and their effect on multiple ecosystem functions, representing key services for crop growth and health in agro‐ecosystems. Soil microbiome in maize soils exhibited stronger resistance than that in rice soils, by considering multiple aspects of the resistance index, for example, community, phylogenetic conservation and network complexity. Community resistance of soil microbiome showed a geographic pattern, with higher resistance at lower latitudes, suggesting their stronger resistance in warmer regions. Particularly, we highlighted the role of core phylotypes in enhancing the community resistance of soil microbiome, which was essential for the maintenance of multifunctionality in agricultural ecosystems. Our results represent a significant advance in linking core phylotypes to community resistance and ecosystem functions, and therefore forecasting agro‐ecosystems dynamics in response to ongoing environmental changes. These suggest that core phylotypes should be considered a key factor in enhancing agricultural sustainability and crop productivity under global change scenarios.
Agricultural ecosystems are facing increasing environmental changes. In the present study, we revealed the importance of core phylotypes in community resistance of soil microbiomes, which were essential for the maintenance of multifunctionality in agricultural ecosystems. In addition, soil microbiome in maize soils exhibited stronger resistance than that in rice soils, by considering multiple aspects of resistance in soil microbiome. Our study represents a considerable advance in linking core phylotypes to community resistance and ecosystem functions, and therefore forecasting agro‐ecosystems dynamics in response to ongoing environmental changes, knowledge of which could be used to enhance agricultural sustainability and crop productivity.
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