Vibration is a critical procedure in the production of cementitious materials to reduce porosity and improve compaction. However, the vibration energy of poker (inserted-type) vibrators exhibits spatial attenuation, which leads to pore distributive heterogeneity and results in uneven mechanical behavior of the material. The current study experimentally investigates the heterogeneity issue and quantifies the relevant efficient compaction zone (ECZ) for a single poker vibrator. Experimental results demonstrate that energy transmission of poker vibration becomes stable at 20s and forms the ECZ with only 53.9% coverage. The study confirms that certain difference of insertion depths between two adjacent vibrators can effectively improve the ECZ coverage and solve the corresponding heterogeneity problem. Subsequently, it formulates equations to determine the optimal depth difference and to develop a modified vibration mode. Compared to the conventional operation modes, the presented mode reduces the vertical porosity deviation from 2.46% to 0.90% and decreases the overall specimen porosity from 4.27% to 2.47%. And it achieves over 95% ECZ coverage. The findings and the proposed method have applications in promoting the precise vibration control for the on-site cementitious material production.

Alkali-activated materials (AAMs) have the potential to reduce carbon dioxide emissions in the cement industry. However, the complex preparation process for activator solutions and high production costs hinder their widespread application. This study developed a ternary one-part alkali-activated system composed entirely of waste materials, including coal-based synthetic natural gas slag (CSNGS), calcium carbide slag (CCS), and flue gas desulfurization gypsum (FGDG). The effect of the solid waste ratio and curing temperature on the mechanical properties of CSNGS-CCS-FGDG AAMs were investigated, and various characterization techniques were employed to study the synergistic mechanisms in the ternary alkali-activated system. The experimental findings revealed that the mechanical properties of AAMs were effectively improved by incorporating FGDG, and the 28-day compressive strength and flexural strength can reach up to 21.8 and 4.39 MPa, respectively. This is attributed to the increase in the gels formation within the reaction products, resulting from the dissolution of CSNGS facilitated by the presence of FGDG. It was also found that a reinforcement microstructure of cross-linked ettringite and gels was formed. Consequently, its bridging effects on the gels, as well as the connecting and filling effects, resulted in a matrix microstructure with good integrity and denseness. Furthermore, the curing temperature was a critical factor affecting the morphology and composition of the ettringite and gels reinforcement structure, with the suitable temperature sequence identified as 65 degrees C > 80 degrees C > ambient temperature > 95 degrees C for ettringite generation.

Pores are potential sources of internal defects in cementitious materials to substantially reduce material quality. Among various pore-related characteristics, porosity is the most critical feature affecting the structural performance of cementitious materials. To address this issue, this study proposes novel vibration methods for porosity optimization/reduction by involving ultrasonication. During the study, effects of different ultrasonic-assisted vibration (UAV) methods on the pore structure in cementitious mortar are explored. Test results demonstrate the effective reduction of porosity in cementitious mortar by ultrasonic treatment. Comparing with conventional vibration, two of the ultrasonic-mechanical coupling methods can significantly reduce cementitious mortar porosity by 40.83% and 60.79%, respectively. Moreover, ultrasonic treatment reduces the number of the most influential pores by 70% and the average pore radius by 30%. The ultrasonic effect is primarily localized in the region immediately below the probe. Microstructural observations further elucidate the underlying mechanism. Ultrasonic cavitation and acoustic streaming work together to break up entrapped bubbles and accelerate their upward migration.

Based on the micro-structure of wollastonite (WS) and bamboo flour (BF), a series of PP/WS/BF ternary composite materials are prepared using blending, twin-screw melt extrusion, and injection molding processes. The experiment shows that the formulation and processing technology play a significant impact on the structure, thermal, and mechanical properties of the composites. BF has a significant impact on the nucleation and crystallization of PP, while WS has almost no effect on PP. BF improves tensile strength and enhances the strength of composites; WS improves the bending strength and flexural modulus and enhances the rigidity of composites. Taking the W-B-30-1:3 sample as an example, its tensile performance is the highest at 23.33 MPa, as well as bending strength and flexural modulus of 26.23 and 904.67 MPa, respectively. The combination of BF and WS leads to an increase in storage modulus, a decrease in loss modulus, a decrease in loss factor, an increase in glass transition temperature, and a decrease in bonding factor of ternary composite materials. This work can enrich the scope of PP composite materials, and the composite materials are expected to have potential applications in the fields of automotive interior parts with lightweight.Highlights Heterogeneous bonding among fillers enhances crystallization of composites. Wollastonite is more conducive to improving the thermal stability of composites. Adding fillers can more effectively enhance mechanical properties. The use of fillers increases interfacial compatibility and bonding performance.

In present work, citric acid was used as a cross-linking agent to perform surface hydrophobization of magnesium oxysulfate (MOS) whiskers and bamboo flour (BF), producing PP/MOS/BF ternary composites via melt extrusion and injection molding processes. The results show that MOS increase the crystallization temperature, melting temperature, and degree of crystallinity of the composites, acting as heterogeneous nucleation agents. BF inhibits the crystallization process of PP, but when compounded with MOS, it enhances the crystallization performance of the ternary composites, leading to an increase in crystallinity. Additionally, the rigidity of MOS and the flexibility of BF synergistically enhance the adhesion between PP and the filler, thereby improving the mechanical properties of the ternary composites. Furthermore, the storage modulus and loss modulus of the ternary composites increase, while the loss factor and bonding factor decrease, with no significant change in the glass transition temperature. The good compatibility and bonding strength generated between MOS whiskers, BF, and PP result in optimal dynamic mechanics. For the M-B-30-3:1 sample, its tensile performance reaches 33.74 MPa, as well as bending strength and notched impact strength of 28.87 MPa and 9.77 kJ/m2, respectively.

Binder jetting 3D printing (BJ3DP) of cementitious material exhibits remarkable dexterity in printing complex or customer-tailored architectural components due to the support of powder. The length distribution and content of basalt fibers are optimized to achieve uniform dispersion of long fibers in cement powder and the synergy between printability and mechanical enhancement of composite materials. A high-speed mixer is used to break and disperse fibers into cement powder. Effect of working parameters, such as the mixing time, original fiber length and content, on printability and mechanical properties are exploited. Different post-processing methods are attempted to enhance the strength of the printed specimens. The successful printing of highly complex hollow thin-wall structures demonstrates the dexterity and high accuracy of BJ3DP using fiber reinforced cementitious materials. Test results show that higher fiber content and fiber length tend to negate spreadability of powders and the dimensional accuracy of printed specimens. The directional alignment of fibers is more remarkable for longer fibers. The printed specimens with 12mm fibers (1.5%) show maximum flexural strength of 13.52MPa, which is 62.5% higher than non-reinforced control specimens. The basalt fiber-reinforced specimens show obvious anisotropy in compressive strength and ultrasonic wave velocity due to basalt fiber orientation. The post-processing method of SiO2 particles in silica sol impregnation adhere each other and fill voids in the matrix and result in a denser material, thus effectively enhancing the flexural and compressive strengths to 14.27MPa and 37.67MPa, respectively.

Cavitation damage often happens inside high-pressure ball valves, causing the sealing failure of valve balls and lower seats. This paper applied the standard k - epsilon turbulence model and mixture multiphase flow model to explore the cavitation behaviour inside the ball valve. It identified the relationship between the cavitation flow and the failure of high-pressure ball valves. The cavitation states under the different opening degrees were analyzed to predict the locations prone to cavitation corrosion. As one of the main reasons for sealing failure, the unbalanced forces of the valve seat were also examined. Results show that the cavitation intensity increases with the rise of inlet pressure. The maximum volume fraction increases from 0.699 to 0.993, and the distribution area of cavitation enlarges by about 50 %. When the inlet pressure rises to 35 MPa, the valve cavity begins to happen cavitation. Increasing outlet pressure helps to reduce the vapor phase in the outlet flow channel. In the valve closing process, the cavitation of the outlet channel is much more severedue to the action of the unbalanced force of the lower valve seat. The average pressure difference of the monitoring points on the cavitation and non-cavitation sides may reach 20.64 MPa. This study provides an effective cavitation failure analysis method and improves the safety performance of valves.

Material extrusion technologies have been extending the frontier of manufacturing technologies due to their high flexibility and low cost. Several studies have fulfilled lightweight designs, such as heterogeneous and conformal lattice structures and continuum optimized structures. The existing methods should be further improved according to the technical characteristics of material extrusion. To improve the mechanical performance and manufacturability of material extrusion structures, an integrated design method is proposed in this study. The design domain is discretized into a coarse mesh, and its nodes are connected to generate beam elements. A barrier function algorithm is introduced to find the optimum structural layout with minimum compliance. The design domain is filled by a globally continuous path to optimize the printing process. Various cases and experimental results validate the feasibility of the proposed algorithm. This research paves a new way for lightweight structural design with high printability and mechanical performance.

3D printed ultra-high performance concrete (3DP-UHPC) acting as the reinforcement to in-process reinforce 3D printed concrete (3DP-C) can significantly improve the load-bearing capacity of 3DP-C. This method (3DP-UIRC) is achieved via a dual 3D printing procedure in which 3DP-UHPC as inner core is wrapped by 3DP-C and extruded together. However, lack of printing synergism between 3DP-C and 3DP-UHPC in deposition parameters, such as deposition layer height, printing speed and deposition rate, may result in heterogeneity of composite materials, and thus negates the overall mechanical strength of the structure. Therefore, parameters of nominal proceeding error (NPE) and co-printing factor (CF) are suggested to characterize the simultaneous manufacturing precision of 3DP-UIRC. The two suggested indicators are practically geometrical parameters to reflect the 3D concrete printing quality. Correspondingly, the printing precision error e and area ratio r are defined based on the experimentally measured values for comparison with NPE and CF, respectively. The printing precision error e and the area ratio r are calculated to be 0.37 and 0.163 by evaluating the practical syncing printing results with different layer height and extrusion volumetric flow rates of 3DP-C and 3DP-UHPC. They are approximately equal to NPE of 0.4 and CF of 0.16 with deviations of 7.5% and 2.5%, respectively. This study provides a new concept and quality assessment method for simultaneous printing of 3DP-UIRC. It also provides ideas and scientific references for promoting the application of 3DP-UIRC in 3D printing structured applications.

The final setting time (FST) and uniaxial compressive strength (UCS) are critical parameters for designing the mixture proportions of alkali-activated materials (AAMs). To understand the influence of the mixture composition on FST and UCS of AAMs, two datasets containing 616 samples for UCS and 278 samples for FST were compiled from published literature. A random forest (RF) model was developed on these datasets to predict FST and UCS of AAMs. The hyperparameters of the RF model were optimized using the Genetic Algorithm (GA). Results show that the hybrid GA-RF model achieved the highest prediction accuracy on the test set of UCS (0.932) and FST (0.997), compared to other machine learning models. The developed model was then used to interpret the influence of mixture composition on FST and UCS. The curing time and water content significantly influenced the UCS, while Na/Al and water contents were more important to FST. The microstructure development of the AAMs was affected by Ca/Si, Na/Al and Si/Al ratios. To achieve better UCS, the recommended Ca/Si varied from 1 to 2; Na/Al was slightly lower than 1 and Si/Al ratios changed between 2.5 and 3.5. This study can facilitate the mixture optimization for FA-slag based AAMs.

This study employed fly ash, blast furnace slag and steel slag to synthesize ternary-blended alkali-activated materials (AAMs) in order to make full use of the industrial solid wastes and improve the mechanical performance by synergistic effects of the precursors. However, peudo-brittle nature is still the main problem of ternary-blended AAMs. To solve this problem, the effect of hybrid fibers consisting of high-modulus steel (ST) fiber and low-modulus Polyvinyl Alcohol (PVA) fiber on the mechanical properties of the ternary-blended AAMs was evaluated by testing their setting time, flowability, uniaxial compressive strength (UCS), indirect tensile strength (IDT), uniaxial tensile strength (UTS), and three-point bending strength (3PBS). Also, the microstructure of the matrix and fibers were analyzed using a scanning electron microscope. The results show that the flowability and setting time increased with the increasing replacement of PVA fiber by ST fiber. At the PVA/ST fiber volume ratio of 1:1, the AAMs cured for 28 days achieved the highest UCS, IDT, UTS, and 3PBS, which were 32 %, 91 %, 80 % and 114.7 % higher than the AAMs without fiber reinforcement, respectively. The fracture pattern and microstructure illustrated that the best synergistic effect of hybrid fibers was achieved at the PVA:ST fiber ratio of 1:1, at which the small-sized PVA fibers and large-sized ST fibers can inhibit the propagation of micro- and macro-cracks at early and late deformation processes. Furthermore, the ultimate elongation of the composite was improved from 2.62 % to 4.21 % and 5.3 % by modifying the PVA fiber with acrylic polyurethane copolymer and replacing the PVA fiber with polyethylene fiber, respectively, implying the significance of surface hydrophilicity of low-modulus fiber on the ductility of AAMs. This study provided a guide for synthesizing and tailoring the mix design of hybrid-fiber-reinforced ternary AAMs with better strength and ductility.

Fly ash-slag based geopolymer has excellent mechanical performance with low carbon footprints, which has emerged as a promising alternative to Portland cement. The optimization of geopolymers requires trade-offs between multiple objectives (strength, cost, and CO2 emission) while considering a large number of highly nonlinear variables. To solve this multi-objective optimization (MOO) problem, this study developed a MOO model combining the tree-based ensemble learning algorithm and non-dominated sorting genetic algorithm (NSGA-II). The MOO model was trained on a database collected from published literature with 676 mixture proportions. The chemical components as well as their contents and the curing conditions were selected as the input variables, while the uniaxial compressive strength (UCS) was the output variable. The UCS of fly ash-slag based geopolymers were modeled using the random forest regressor, extra trees regressor, gradient boosted regressor and extreme gradient boosting regressor. The results show that the gradient boosted regressor has the highest prediction accuracy with R (0.966) and RMSE (5.295 MPa) on the testing set. The analysis of the variable importance by the developed model indicates that the curing age, contents of slag and sodium silicate are more important to the strength development of the binary blended geopolymer. The MOO model developed based on the gradient-boosted regressor and NSGA-II successfully found the cost-UCS and CO2 emission-UCS Pareto fronts of the bi-objective optimization problem, as well as the cost-UCS-CO2 emission Pareto front of the tri-objective optimization problem. This developed framework improves the efficiency of geopolymer design and can be applied to the mixture optimization of other construction materials.

With the advantages of fast hardening, high early strength, excellent bonding strength and room temperature curing, magnesium phosphate cement (MPC) is highly preferable for powder-based 3D concrete printing. In this paper, a systematic approach via comprehending parametric analysis, visualizing techniques (SEM, XRD and X-Ray CT) and mechanical testing is developed to evaluate and optimize printability and printing quality of powder-based 3D MPC printing. The test printing results show that appropriately mapped proportions of ingredients will orient the specific properties towards the target objectives through navigating different combinations of proportions comprehensively. Specifically, 1,2-propylene glycol is able to significantly increase the viscosity of the binder, and Surfynol 465 can substantially reduce the surface tension of the binder. 25 wt% quartz sand can remarkably improve spreadability and surface flatness of the powder bed. In addition, the penetration and diffusion of the binder in the powder bed is effectively controlled by appropriate content of polyvinyl alcohol (PVA) due to the properties of high viscosity and good film-forming, thus remarkably improves printing accuracy. The compactness and hydration degree of the powder-based 3D printed MPC are optimized by 5 wt% PVA (MPC5) with the total porosity reduced by 2.86% compared to that of MPC0 (without PVA). High printing precision of the printed complex geological canyon river model indicates that MPC with appropriate contents of modulators, such as 1,2-propylene glycol and Surfynol 465 for binder and PVA and quartz sand for base powder, is desirable powder-based 3D printable material.

Microcable reinforcement has been demonstrated as a promising solution for enhancing the mechanical properties of three-dimensional (3D) printed concrete. Generally, inadequate interfacial bonding between simultaneously entrained microcables and concrete matrix limits the general application of microcable reinforcement. This paper proposes a method of automatically including expansive cementitious materials (ECMs) in the cable–concrete interface in the printing process to improve the cable bond in 3D concrete printing to improve cracking resistance. A pull-out device is designed and developed in the lab to assess the cable–matrix bonding properties with respect to different bond lengths. Four-point bending tests of a microcable-reinforced beam are also conducted. The crack evolution during these tests is monitored by digital image correlation. The test data are compared with calculated cracking and ultimate loads, crack spacing, and crack width, and a small difference of 15% is found. The experimental results exhibit a 44%–67% increase in the bond strength and a 30%–50% reduction in crack width, demonstrating the effectiveness of the currently proposed method in improving both the cable bond and cracking resistance. Scanning electron microscopy observations reveal that the improvements can be attributed to the lowered porosity or denser microstructure at the cable–ECM interface realized by the addition of the ECMs.

In extrusion-based additive manufacturing, path filling patterns may significantly affect the printing process. To overcome printing defects incurred by path discontinuity, a Globally Continuous Hybrid Path (GCHP) is developed to solidly fill or partially fill connected domains. Discontinuous contour paths and single zigzag paths are constructed to generate locally continuous paths. These paths are subsequently connected by contour paths to render global continuity. To reduce underfilled areas without breaking path continuity, the boundaries of gap areas are evenly clipped and merged with the path. Sharp turns are optimized by fillet edges to alleviate the reduction in printing velocity. The construction results of variable shapes indicate that GCHP can continuously fill domains. The printing quality and mechanical performance of the proposed path are better than those of the previous scheme based on contour parallel paths. This study paves a new way to fabricate models using hybrid paths for extrusion-based additive manufacturing.

Reliable composite material parameter identification is of practical engineering significance in view of the extensive applications of composite materials in high-tech industries, such as aerospace, automobile industry and medical fields, etc. Efficient and easy-to-use computational tools are needed, and a new theoretical framework of two-way TrumpetNets have been proposed recently. It can solve both the forward and inverse problems effectively. The striking beauty of this theory is that the solution of the inverse problem is expressed by direct weight inversion (DWI) approach in an explicit formula. This study extends and implements the explicit inverse solution using two-way TrumpetNets for identification of material parameters of composite laminates. We successfully inversely identify up to seven parameters for composite laminates, which is essentially a 7-Dimensional inverse problem. It is found that by application of the two-way TrumpetNets, regularization parameters are not required in the DWI formula due to the intrinsic regularization by the least square formulation. The influence of different network structures, i.e., the number of hidden layers and the number of each layer, on the inverse result is explored. For similar composite material parameter identification, the computational efficiency is significantly improved in view of that, for inverse identification of composite parameters, it takes only 20 min computational time by two-way TrumpetNets. While this computational time is one sixth of that by the traditional inverse neural network using the same desktop computer, the computational accuracy is not compromised.

Systematic approach for evaluation and optimization of spray-based 3D (S-3D) mortar printing technology are explored. Effects of different fly ash (FA), silica fume (SF) and water-binder (W/B) ratios on the rheological properties of mortar are firstly evaluated by orthogonal tests. The mortar with excellent rheological properties is then adopted to assess the S-3D printability. The test results show that proper additions of FA, SF and W/B can prolong the printing window to 120-135 min as well as improve the printing accuracy. Single layer and accumulative thickness tests are innovatively used to quantify the morphological sustainability of S-3D printed mortar. The mechanical strengths of S-3D printed mortar are remarkably higher than those of the cast counterparts in view of maximum increase of 72.64% compressive, 45.83% flexural and 33.33% splitting strengths, respectively. The high spraying pressure of S-3D printing procedure avails small pore size, therefore the compactness of the internal microstructure of S-3D printed mortar. A special-configured convex nameplate "HEBUT" with size of 2200mm x 500mm x 30 mm (X x Z x Y directions) is successfully printed on a vertical platform, which proves the applicability and dexterity of S-3D printing technology in spatial context.

The study on geopolymers blended with silica fume is scant. This study investigates the effects of silica fume (SF) on the compressive strength of geopolymer-based ultra-high-performance concrete (G-UHPC) subject to ambient curing. Low-calcium fly ash (LCFA) and calcium aluminate cement (CAC) were activated by a combination of sodium hydroxide and sodium silicate solution to produce geopolymer binders. Effects of the CAC content, alkaline solution to binder (A/B) ratio, and sodium hydroxide (SH) concentration on the flowability and compressive strength of geopolymer binders were studied. The SF dosage varied from 5% to 30% of the total binder weight, and the Taguchi method was used to determine the optimum mix proportions. The incorporation of SF showed a complicated influence on the compressive strength, depending on the CAC content. For mixes with 20% CAC content, the compressive strength increased with increasing SF dosage. But for mixes with 10% CAC content, a high SF dosage (>10%) negatively influenced the compressive strength. The mechanisms for this contradictory behavior were discussed based on the X-ray diffraction and scanning electron microscopy analyses. The inclusion of steel fibers has a positive influence on the mechanical properties of G-UHPC. The G-UHPC mix with 1.5 vol% steel fibers achieved a compressive strength of 139.1 MPa and flexural strength of 13.5 MPa at 28 days.

In spite of anisotropy and layer interface weakness intrinsic to the 3D printing procedure, 3D printed ultra-high performance concrete (3DP-UHPC) exhibits excellent mechanical performance due to fiber alignment. For the first time, 3DP-UHPC slab, 3DP-UHPC reinforced normal concrete (PURN) slabs are tested against contact explosions. Explosion resistances with regard to different reinforcing methods, layer thickness ratios and construction methods for base materials are investigated. Specifically, PURN, steel bar reinforced 3DP-UHPC (RU), steel bar reinforced normal concrete (RC), and normal concrete (NC) slabs of similar sizes are constructed to compare the explosion resistances. Different reinforcing layer thickness are attempted. From the contact explosion tests, it exhibits that the extrusion-based 3D printing procedure enhances the explosion resistance substantially via fiber orientation alignment. With the layer thickness ratio of 40% (PURN6) as the watershed, both the top and bottom surface crater diameters of PURN slabs increase first and then decrease with increasing reinforcing layer thickness. In particular, crater diameters and failure modes for PURN8 and PURN15 are consistent with those of RC and RU, respectively. The underlying mechanism for the fibers to be aligned by the 3D printing procedure is theoretically analyzed to support the conclusions. The material costs of all the slabs are compared. The costs of PURN8 and PURN15 are 1.7 and 0.8 times of those for RC and RU, respectively. Thus, it can be stated that the 3D extrusion-based printing procedure will avail explosion resistance for 3DP-UHPC. Current test results prove the feasibility and cost-effectiveness of PURN for protective structures.