Tailoring Light-Weight Aggregates for Concrete 3D Printing Applications

Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Peer Review Share Icon Share Twitter Facebook Reddit LinkedIn Tools Icon Tools Reprints and Permissions Cite Icon Cite Search Site Citation R. T. Bonnecaze, J. F. Brady; Yield stresses in electrorheological fluids. Journal of Rheology 1 January 1992; 36 (1): 73–115. https://doi.org/10.1122/1.550343 Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentThe Society of RheologyJournal of Rheology Search Advanced Search |Citation Search

The study herein was intended to evaluate the rheological properties of cemented gangue backfill material (CGBM). For this purpose, the rheological test of CGBM with fractal aggregate particle size distribution was carried out, and variations of static yield stress, dynamic yield stress, and plastic viscosity were investigated as a function of fractal dimension and time. The results reveal that aggregate particle size distribution exerts a significant influence upon the rheological properties of CGBM, and with the escalation of the fractal dimension of the aggregate, the yield stress and plastic viscosity initially decline and then increase. In addition, with elapsing time, the correlation between the static yield stress and the fractal dimension of CGBM specimens increases, while the correlations between the dynamic yield stress and the plastic viscosity and the fractal dimension decrease. The relationships between rheological parameters and fractal dimensions at different times are established based on the experimental results. The influence mechanism of aggregate particle size distribution on CGBM is analyzed from the perspective of the aggregate packing state. This study can provide a basis for the ratio design of CGBM in backfill mining.

This study investigates the use of demolition waste as recycled coarse aggregates (RCAs) to replace natural coarse aggregates (NCAs), and the use of ground granulated blast slag (GGBS) and limestone filler (LF) as a supplementary cementitious material, in self-compacting concrete (SCC), with proportions of 150 kg/m3 for GGBS and 180 kg/m3 for LF. Various SCC mixtures were prepared with RCA proportions of 0, 25, 50, 75, and 100%, while maintaining fixed dosages of LF and GGBS. Initially, RCA was incorporated in a dry state, followed by a water dosage adjustment for mixtures containing 100% RCA, equivalent to 20 min of RCA absorption. The experimental investigation evaluated the evolution of flow properties through tests such as slump flow, flow time (T500), L-box, sieve stability, fresh density, and air content. The static yield stress and plastic viscosity were also calculated using mathematical models. Additionally, hardened properties, including short-term and long-term compressive strength and capillary water absorption, were assessed. An environmental impact analysis of using demolition waste was conducted, revealing that a total NCA replacement with RCA is viable for both fresh and hardened states, provided that the RCA water absorption is managed and a reactive mineral additive is incorporated. For a 50% replacement of natural aggregates with recycled aggregates, this approach significantly reduces environmental impacts, lowering fossil fuel consumption by up to 35% and greenhouse gas emissions by up to 32%.

A case study on examining the fresh-state behavior of self-compacting mortar containing waste powders from various sources

This study delves into the influence ofwater film thickness (WFT) on the rheological characteristics, particularly the yield stress, of cement paste incorporating limestone powder. Employing an Anton Paar MCR 102 rheometer, precise measurements of both the static and dynamic yield stress were conducted. Artificial neural networks (ANN) were then applied to explore the relationship between WFT and yield stresses. The findings reveal an approximate linear growth pattern in the shear stress-shear rate profile of cement-limestone paste, with an intensified shear thickening observed as limestone powder content increases. The augmentation of limestone powder and specific surface area notably enhances both static and dynamic yield stresses, with the latter reaching 70.26 Pa in the case of a paste containing 50% Class III limestone powder (1088 m2/kg). The WFT of cement-limestone paste particles is contingent on the ratio of solid particle packing density to total specific surface area, exhibiting an increase with rising solid particle packing density. Both static and dynamic yield stresses exhibit a negative correlation with WFT. Artificial neural networks demonstrate efficacy in predicting static and dynamic yield stresses based on mix ratio parameters and WFT, with a higher prediction accuracy for static yield stress, reflected in an R2 value of 0.9745.

Oscillation experiments, creep tests and shear stress ramps have been performed to analyze the yield stress and its time dependency. It has to be distinguished between iso-structural, dynamic and static yield stress. The iso-structural yield stress occurs immediately after shearing. Since the slurry structure remains unchanged, it is equivalent to the structure during shearing. At rest an internal structure builds up, this leads to an increase of the yield stress, which is referred to as the dynamic yield stress. It increases until its maximum value, the static yield stress, is reached.

The Chinese Knot inspired anisotropic TC4 lattice Structures: Ultra-high specific strength in engineering materials

The use of bamboo as an aggregate replacement is one of the efforts to reduce the density and static load of structural elements, sincethe structural strength of bamboo is high. This study focus on the issue of the using bamboo as aggregate concrete with flowing method on a review of specific gravity and compressive strength of the concrete. This study uses bamboo as a percentage of the aggregate at 0% (normal), 20%, 40%, 60%, 80% and 100% of the conventional split and using additional silicafume aggregates. Specimens used in this study is the concrete cylinder (diameter 15 cm and height 30 cm). The identification and testing of tap density after 14 days of treatment.Results show that using more bamboo aggregate will result lower slump value, higher water absorption, decreasing in both specific gravity and compressive strength.

Our primary objective is to correlate damping predictions from a quasi-steady Bingham plastic damper analysis with experimentally measured steady state damping levels for a magnetorheological (MR) fluid damper. We seek to characterize damper properties of yield force and post-yield damping, and relate the damper parameters to effective MR fluid properties of dynamic yield stress and plastic viscosity. This characterization is done as a function of applied field and frequency. The damper was mounted in a mechanical scotch-yoke type damper dynamometer. The damper shaft was displaced sinusoidally with 1 inch of stroke and the resulting steady state force was measured as a function of applied current and frequency. The resulting force vs. displacement and force vs. velocity data is used to characterize the damper. The nonlinear hysteretic biviscous model is used to identify four physical parameters of the MR damper from the force vs. velocity diagram due to sinusoidal input displacements: pre-yield damping, post-yield damping, yield force, and zero-force velocity intercept. The post- yield damping and the yield force are used to calculate effective MR fluid properties of plastic viscosity and dynamics yield stress, respectively, from the damper data. Using the effective dynamic yield stress and the effective plastic viscosity, the Bingham plastic model is used to predict the damping, and these predictions are correlated with measurements from the force vs. displacement hysteresis cycle. The damping coefficient is the ratio of the damping with the field ON, to the Newtonian damping associated with the plastic viscosity. The resulting damping coefficient vs. nondimensional plug thickness diagram successfully predicts the damping behavior of the MR damper.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

3D printing with concrete has been accounted as a foremost strategy to mitigate low productivity, workforce shortage, and high waste generation in the construction industry. However, substantial environmental impacts related to high cement content in printable mixtures have received minor concern so far. An interesting prospect is the use of recycled concrete powders (RCP) to decrease cement content through their fineness and high specific surface area, which can potentially enhance rheological properties for 3D printing. However, their effects on cementitious mixtures greatly depend on their origin. This research investigated two distinct RCPs to replace 50% of Portland cement in pastes. On cementitious pastes, rotational rheometry, isothermal calorimetry, and a Life Cycle Inventory assessment were conducted. Printability tests on mortars evaluated the effects of RCP on extrudability and buildability. The results showed intensified early hydration for RCP pastes and up to a three-fold increase in static yield stress and higher dynamic yield stresses, regardless of origin. The viscosity of RCP pastes varied in relation to packing density. Extrudability and buildability can be compromised using RCP due to higher yield stress. The LCI assessment indicated a potential decrease of up to 62% in CO2 emissions using RCPs. Therefore, if adequate rheological adjustments are employed in the mix design of RCP mixtures, this material emerges as a feasible strategy to formulate 3D printable mixtures with a lower environmental footprint.

In the paper, the structure and static and dynamic mechanical properties of ultrafine-grained A5083 alloy (Al-Mg-Mn) produced by high-pressure torsion (HPT) are reported. The static yield stress and tensile strength were determined in tensile tests at a strain rate of ~ 10−3 s−1, and the dynamic yield stress and spall strength were calculated from free-surface velocity histories obtained during shock-wave loading at a strain rate of 105 s−1. The HPT technique provides strong grain refinement. The average grain size of the alloy after HPT is 100-180 nm and depends on the accumulated true strain. HPT significantly improves the static strength properties of the alloy. The static yield stress is increased by 360-390% and the static ultimate tensile strength by 166-182%. It is shown that the dynamic yield stress improved by 168-181%, while the dynamic spall strength was not improved by HPT. Moreover, the nanostructured alloy with a grain size of ~ 100 nm demonstrates the lowest spall strength.

The primary limitation of today’s lightweight structural alloys is that specific yield strengths (SYS) higher than 200MPa x cc/g (typical value for titanium alloys) are extremely difficult to achieve. This holds true especially at a cost lower than 5dollars/kg (typical value for magnesium alloys). Recently, high-entropy alloys (HEA) have shown promising SYS, yet the large composition space of HEA makes screening compositions complex and time-consuming. Over the course of this 2-year project we started from 150 billion compositions and reduced the number of potential low-density (<5g/cc), low-cost (<5dollars/kg) high-entropy alloy (LDHEA) candidates that are single-phase, disordered, solid-solution (SPSS) to a few thousand compositions. This was accomplished by means of machine learning to guide design for SPSS LDHEA based on a combination of recursive partitioning, an extensive, experimental HEA database compiled from 24 literature sources, and 91 calculated parameters serving as phenomenological selection rules. Machine learning shows an accuracy of 82% in identifying which compositions of a separate, smaller, experimental HEA database are SPSS HEA. Calculation of Phase Diagrams (CALPHAD) shows an accuracy of 71-77% for the alloys supported by the CALPHAD database, where 30% of the compiled HEA database is not supported by CALPHAD. In addition to machine learning, and CALPHAD, a third tool was developed to aid design of SPSS LDHEA. Phase diagrams were calculated by constructing the Gibbs-free energy convex hull based on easily accessible enthalpy and entropy terms. Surprisingly, accuracy was 78%. Pursuing these LDHEA candidates by high-throughput experimental methods resulted in SPSS LDHEA composed of transition metals (e.g. Cr, Mn, Fe, Ni, Cu) alloyed with Al, yet the high concentration of Al, necessary to bring the mass density below 5.0g/cc, makes these materials hard and brittle, body-centered-cubic (BCC) alloys. A related, yet multi-phase BCC alloy, based on Al-Cr-Fe-Ni, shows compressive strain >10% and specific compressive yield strength of 229 MPa x cc/g, yet does not show ductility in tensile tests due to cleavage. When replacing Cr in Al-Cr-Fe-based 4- and 5-element LDHEA with Mn, hardness drops 2x. Combined with compression test results, including those on the ternaries Al-Cr-Fe and Al-Mn-Fe suggest that Al-Mn-Fe-based LDHEA are still worth pursuing. These initial results only represent one compressive stress-strain curve per composition without any property optimization. As such, reproducibility needs to be followed by optimization to show their full potential. When including Li, Mg, and Zn, single-phase Li-Mg-Al-Ti-Zn LDHEA has been found with a specific ultimate compressive strength of 289MPa x cc/g. Al-Ti-Mn-Zn showed a specific ultimate compressive strength of 73MPa x cc/g. These initial results after hot isostatic pressing (HIP) of the ball-milled powders represent the lower end of what is possible, since no secondary processing (e.g. extrusion) has been performed to optimize strength and ductility. Compositions for multi-phase (e.g. dual-phase) LDHEA were identified largely by automated searches through CALPHAD databases, while screening for large face-centered-cubic (FCC) volume fractions, followed by experimental verification. This resulted in several new alloys. Li-Mg-Al-Mn-Fe and Mg-Mn-Fe-Co ball-milled powders upon HIP show specific ultimate compressive strengths of 198MPa x cc/g and 45MPa x cc/g, respectively. Several malleable quarternary Al-Zn-based alloys have been found upon arc/induction melting, yet with limited specific compressive yield strength (<75 MPa x cc/g). These initial results are all without any optimization for strength and/or ductility. High-throughput experimentation allowed us to triple the existing experimental HEA database as published in the past 10 years in less than 2 years which happened at a rate 10x higher than previous methods. Furthermore, we showed that high-throughput thin-film combinatorial methods can be used to get insight in isothermal phase diagram slices. Although it is straightforward to map hardness as a function of composition for sputtered, thin-film, compositional gradients by nano-indentation and compare the results to micro-indentation on bulk samples, the simultaneous impact of composition, roughness, film density, and microstructure on hardness requires monitoring all these properties as a function of location on the compositional gradient, including dissecting the impact of these 4 factors on the hardness map. These additional efforts impact throughput significantly. This work shows that a lot of progress has been made over the years in predicting phase formation that aids the discovery of new alloys, yet that a lot of work needs to be done to predict phases more accurately for LDHEA, whether done by CALPHAD or by other means. More importantly, more work needs to be done to predict mechanical properties of novel alloys, like yield strength, and ductility. Furthermore, this work shows that there is a need for the generation of an empirical alloy database covering strategic points in a multi-dimensional composition space to allow for faster and more accurate predictive interpolations to identify the oasis in the dessert more quickly. Finally, this work suggests that it is worth pursuing a ductile alloy with a SYS > 300 MPa x cc/g in a mass density range of 6-7 g/cc, since the chances for a single-phase or majority-phase FCC increase significantly. Today’s lightweight steels are in this density range.

Preparation and characterization of mesophase-pitch-based foam/natural graphite composites

Ambient temperature cured ‘just-add-water’ geopolymer for 3D concrete printing applications

Pervious concrete is one of the concrete types that contain no or little fine aggregate to obtain the void between aggregate particles for permitting passage of water through and reducing the risk of flooding. This article deals with the preparation of two sets of sustainable pervious concrete by using waste glass granular, lightweight pumice aggregate as a partial replacement of single-size coarse aggregate with six different ratios, including 0, 5, 10, 20, 30, and 50%, for finding their effect on the mechanical properties, permeability, and abrasion resistance. The second group used waste glass granular as a partial replacement of coarse aggregate with the same rate of pumice aggregate to find their effect on the abrasion resistance ability of the previous concrete and compare them together. The obtained result showed that using lightweight aggregate as a partial replacement of coarse aggregate with a single size (9.5–12.5 mm) increased the mechanical properties and permeability of pervious concrete. The usage of LWA compared to the WGG in the previous concrete showed that LWA provided lower abrasion resistance ability (toughness) compared to the WGG.