Concrete Casting Research Articles

Field test of internal visualization of deep-water pile foundation using ultrasonic waves

Early-age internal visualization is critical for timely assessing the quality of pile foundations, especially as super cross-sea bridges increase the diameter and length of pile foundations beyond the capabilities of traditional cross-hole sonic logging (CSL). This article introduces two innovations. First, ultrasonic instruments are specially developed to transmit waves through a concrete pile with a diameter of 4 m, a length of 92 m, and a water depth of 63 m, before the full hardening of concrete. Second, an imaging method is proposed to upgrade traditional CSL from 1D detection to 3D visualization. Both large-scale experiments and field tests are tested in the first 7 days after the concrete casting. The experiments successfully visualize typical construction defects, achieving a detection resolution of 18 cm for layered defects and 15 cm for void defects. During the field test, a low-pixel region is observed at the pile head, extending approximately 2.1 m deep, attributed to mud floating up during concrete casting into the steel casing. These developments in instrument technology and visualization methods provide essential tools for the quality evaluation of super pile foundations. Furthermore, the visualization data can support digital twin modeling in subsequent stages of construction and maintenance planning.

Vibration Position Detection of Robot Arm Based on Feature Extraction of 3D Lidar.

In the process of construction, pouring and vibrating concrete on existing reinforced structures is a necessary process. This paper presents an automatic vibration position detecting method based on the feature extraction of 3D lidar point clouds. Compared with the image-based method, this method has better anti-interference performance to light with reduced computational consumption. First, lidar scans are used to capture multiple frames of local steel bar point clouds. Then, the clouds are stitched by Normal Distribution Transform (NDT) for preliminary matching and Iterative Closest Point (ICP) for fine-matching. The Graph-Based Optimization (g2o) method further refines the precision of the 3D registration. Afterwards, the 3D point clouds are projected into a 2D image. Finally, the locations of concrete vibration points and concrete casting points are discerned through point cloud and image processing technologies. Experiments demonstrate that the proposed automatic method outperforms ICP and NDT algorithms, reducing the mean square error (MSE) by 11.5% and 11.37%, respectively. The maximum discrepancies in identifying concrete vibration points and concrete casting points are 0.059 ± 0.031 m and 0.089 ± 0.0493 m, respectively, fulfilling the requirement for concrete vibration detection.

Numerical and experimental study on reinforced 3DCP walls filled with light-weight concrete

This paper explores the structural viability of 3DCP as a novel additive manufacturing method in the construction industry, focusing on its integration and standardization challenges due to its emerging nature. With the construction industry's increasing interest in innovative materials and robotic construction, 3DCP's unique characteristics necessitate thorough investigation to understand its potential fully. This study aimed to assess the structural capacity of 3DCP walls, employing flexural tests on samples filled with lightweight concrete containing EPS, and comparing the outcomes with those of traditionally cast concrete. Through a comprehensive approach that combines experimental work with numerical analysis, this study intended to calibrate the material's properties based on small-scale tests to inform the design of larger structures. Macro and micro-scale numerical modeling methods were investigated for the analysis of 3DCP. The findings revealed that the inherent strength of 3DCP significantly depends on the material's composition and quality. Moreover, it was observed that the structural integrity of 3DCP walls was somewhat inferior to that of fully cast counterparts. However, a strong correlation between the numerical simulations and experimental data underscores the value of this research. By calibrating 3DCP's properties from small-scale experiments, the study provides a foundational basis for designing larger structures with enhanced reliability. Both numerical methods demonstrate high accuracy for the analysis of 3DCP and can be adopted for the analysis of larger structures.

Life Cycle Assessment of Additively Manufactured Foundations for Ultratall Wind Turbine Towers

ABSTRACTWind energy production is rapidly growing in the United States and is expected to continue increasing as more and larger wind turbines are installed. To support these taller and heavier onshore turbines, new foundations must be designed and manufactured. One proposed method of reducing the total amount of concrete and steel in spread foundations is to utilize additive manufacturing to enable more material‐efficient designs. To compare these additively manufacturing‐enabled designs to conventional foundation designs, this study performs a life cycle impact assessment of four ultra‐tall wind turbine foundations: two foundations using 78‐MPa 3D printed stay‐in‐place concrete formwork cast with 35‐MPa ready‐mix concrete with reinforcements, and two conventional foundations cast entirely out of 35‐MPa concrete with reinforcements. The life cycle assessment investigates the environmental impacts of four different stages, including materials production, transportation, construction, and end‐of‐life. The materials production stage is found to dominate the life cycle results, contributing over 97% of the total CO2 emissions and over 88% of the fossil fuel depletion for each foundation. Compared to the conventional designs, the Short Flat Ribbed Beam foundation with 3D printed formwork has 22.4% lower CO2 emissions and 28.3% lower fossil fuel depletion than the Circular foundation, and 2.0% higher CO2 and 5.9% lower fossil fuel depletion compared to the Tapered foundation. Parametric studies indicate that reducing cement content and increasing recycled content in printed concrete can significantly reduce the overall life cycle impacts of the foundations.

Improvement of crushed returned concrete aggregates by wet carbonation

A considerable quantity of pre-mixed concrete is returned from construction sites which is usually dumped directly into pits. While this concrete may possess lower quality attributes due to inadequate compaction and curing, the crushed hardened concrete can be potentially used to produce recycled aggregates. Carbonation is regarded as a significant way of improvement of recycled concrete aggregates. This study investigated the effectiveness of wet carbonation method for the improvement of crushed returned concrete aggregates (CRCA) to reuse in concrete productions. Recycled concrete aggregate (RCA) obtained from crushing of old conventionally cast concrete was also subjected to the same treatment, and its properties were compared with those of CRCA to understand the improvement in each type of recycled aggregate. The effectiveness of wet carbonation was evaluated by the aqueous chemistry during carbonation, development of microstructure, depth of calcium carbonate deposition, the mineralogy, water absorption, and compressive strength for both treated and untreated CRCA and RCA for different carbonation durations. The results showed that, although the water absorptions of both uncarbonated and carbonated CRCA were higher than those of RCA, the rate of reduction of water absorption of CRCA after carbonation was higher than that in RCA. Due to the long exposure to open environment, CRCA showed less initial alkalinity and conductivity than RCA but at the end of carbonation, both pH and conductivity were almost same as those of RCA. Wet carbonation successfully produced well shaped calcite in both CRCA and RCA where the deposition depth of calcite was higher in CRCA than in RCA. Mineralogical analysis showed higher calcium carbonate formation in CRCA indicating its potential of sequestrating more CO2 than by RCA. The improvement of concrete compressive strength was more pronounced for CRCA, with a 28 % enhancement observed after 2 hours of carbonation, compared to an 18 % enhancement for RCA. These findings demonstrated that wet carbonation can be regarded as an effective strategy for enhancing CRCA.

Rheological, mechanical, and environmental performance of printable graphene-enhanced cementitious composites with limestone and calcined clay

As extrusion-based 3D concrete printing gains wider acceptance in construction, there is a growing imperative to incorporate supplementary cementitious materials (SCMs) into printable mixtures to address their high cement content and promote sustainability. Conventional SCMs like fly ash and slag are becoming increasingly scarce, underscoring the need for alternative solutions such as limestone and calcined clay. Additionally, the utilization of nanomaterials in printable mixtures holds potential for enhancing the mechanical properties of 3D printed structures. These properties are often compromised by interlayer interfaces and void formations during printing, resulting in lower mechanical performance compared to conventionally cast concrete. Graphene nanoplatelets (GNPs), with their high aspect ratios and exceptional mechanical characteristics, offer promising avenues for reinforcing printable cementitious composites. This study explores the rheological, mechanical, and environmental aspects of graphene-enhanced cementitious composites incorporating limestone and calcined clay. Graphene nanoplatelets (GNPs) were dispersed utilizing a surfactant-assisted sonication technique, and their dispersion characteristics were evaluated through absorbance, particle size, and zeta potential measurements. Then, the influence of varying GNP concentrations on the rheological properties of limestone-calcined clay (LC2) cementitious composites was assessed. Compressive and flexural strength tests were conducted on 3D-printed LC2 samples with different GNP ratios, alongside cast specimens for comparison. Microstructural examination of failed specimens was performed using scanning electron microscopy. Furthermore, a life cycle assessment was conducted to compare the environmental impacts of printable LC2 mixtures to conventional printable mixtures. Incorporating GNPs at a ratio of 0.05 % by weight of cement in printable LC2 mixtures enhances compressive strength by 23 %, leading to a reduction of approximately 31 % in environmental impacts compared to conventional printed mixtures.

Nondestructive testing techniques for investigating mechanical property and porosity disparities in extrusion 3D printed concrete

ABSTRACT Three Dimensional Concrete printing (3DCP) stands at the forefront of modern construction methodologies, also named additive manufacturing, offering unparalleled time, cost, and labour savings compared to conventional approaches. The evaluation of fresh state parameters like extrudability and buildability through a specialised concrete extruder, combined with a methodical layer-by-layer deposition, ensures structural stability by precisely strengthening each layer. Mechanical strength evaluations highlight the printed material’s anisotropic nature, revealing extreme reductions of Fy = 27.94%, Fx = 19.07%, and Fy = 16.33% in compression, flexural, and split tensile strengths, respectively, compared to cast specimens. This emphasises the importance of direction-specific mechanical testing in understanding material behaviour completely. Non-destructive testing (NDT) methods, like Ultrasonic Pulse Velocity (UPV) testing, are crucial for the qualitative assessment of the integrity and mechanical strength of concrete structures, including both printed and cast specimens, by establishing a strong correlation with compressive strength without causing any damage. Limited research indicates that the microstructure of the material plays a significant role in its mechanical strength, particularly in printed specimens. This claim is reinforced by mercury intrusion porosimetry (MIP) results, which reveal that printed specimens have slightly higher overall porosity, concentrated between 1 µm and 0.1 µm, while cast specimens show higher porosity in pores smaller than 0.1 µm.

On the micro- and meso-structure and durability of 3D printed concrete elements

3D printed concrete (3DPC) creates opportunities, including a reduction in construction waste and time and increased design freedom. However, because of the differences in the construction technique compared to traditional concrete casting, the structures also perform differently; namely, the micro- and meso-structure and durability are shown to be different. For the 3DP technology to find its way to the market, one needs to be aware of these differences and needs to know how to quantify the above-mentioned properties, as differences in the testing methodologies impose themselves when characterizing printed instead of cast concrete. In this paper, we elaborate on the test methods to investigate the micro- and meso-structure and the durability of 3DPC. We start with a discussion on the micro- and meso-structure of the 3D printed concrete and how it is different from conventional mold-cast concrete. An in-depth discussion of the test methods to assess the durability of 3D printed concrete is outlined. Reported findings related to the two aforementioned properties are discussed. In addition, we report on the technologies proposed to improve the durability performance of 3DPC, and we highlight the remaining challenges and opportunities related to 3DPC.

Experimental investigation and fluid-structure interaction modelling of the casting of self-compacting concrete for CRTS III slab track in the curved segments

Ensuring the casting quality of self-compacting concrete (SCC) is crucial for the operational safety and durability of China railway track system (CRTS) III slab track. However, the mechanisms of key factors influencing flow behaviors of SCC and structural responses remain insufficiently understood, nor is the relationship between flow behaviors and structural responses during casting. In this study, fluid-structure interaction (FSI) models of SCC casting were developed and verified by full-scale physical tests, comprising slump flow, L-box flow and casting of SCC in an actual track at the field of Laixi-Rongcheng high-speed railway. Through in-depth analysis on the casting process of SCC in curved segments with a super elevation of 80 mm, the relationship between flow behaviors and structural responses was established. Furthermore, the influence mechanisms of key factors on flow behaviors and structural responses were investigated systematically. Results show that during gravity-fed SCC casting, its flow velocity diminishes, thus increasing the static pressure and the forces exerted on the slab by SCC. These vertical and lateral forces increase to 147.16 and 7.83 kN through three stages of development, acceleration and stabilization, resulting in commensurate structural responses. At the end of casting process, the central region of the slab exhibits maximum vertical deformation of 0.95 mm and tensile stress of 1.07 MPa. The tension rods at the side with lower elevation bear greater vertical and lateral forces than the ones at the side with higher elevation. The rise of funnel height from 1.05 to 1.35 m accelerates the casting process but increases the forces exerted by SCC by up to 26 % and augments the associated response of entire structures, whereas the funnel diameter shows little effect. Increasing yield stress of SCC from 9.3 to 49.3 Pa produces a more uniform flow morphology and thus higher static pressure and force by SCC in the middle region of the slab, impacting the structural responses by up to 15 %. The growth of plastic viscosity from 59 to 99 Pa⋅s significantly affects the volume rate and casting time by up to 66 % but has little effect on the flow morphology, fluid pressure and structural responses. In order to ensure high quality casting of SCC, five clamping beams are suggested with two beams positioned at either side of the slab and the other three evenly placed along the middle region of the slab.

Time-dependent behaviour of 3D printed fibre-reinforced limestone calcined clay cement concrete under sustained loadings

The evolution of 3D-printed concrete (3DPC) structures has made remarkable impacts in the construction industry and academia for prospective engineering practice globally. This is due to promising outcomes of various investigations on its construction coupled with several advantages it offers over conventional cast concrete. However, the time-dependent deformation of 3DPC under sustained loading is still unknown and requires extensive research. Quasi-static studies have also shown that creep could be of great concern due to its production technique involving layer stacking, which eventually leads to weak interlayer bond strength. This paper experimentally investigates the time-dependent behaviour of fibre-reinforced printed concrete (FRPC) containing limestone calcined clay cement (LC3) under sustained tensile and flexural loadings. The experimental tests conducted on LC3-FRPC specimens in two orthogonal directions were individual creep and shrinkage to determine other parameters associated with creep responses, including creep fracture. The specimens for tensile and flexural creep were subjected to sustained stresses of 40, 60 and 80 % of the tensile and 40 % flexural strength results obtained from quasi-static tests. The quantified creep is compared in terms of the difference in stress levels, as the results revealed that none of the specimens fractured under sustained loadings. Instead, higher direct tensile strengths were recorded for the creep specimens after 225 days loaded at different stress levels. Then, it is postulated that direct tensile tests on similar LC3-FRPC specimens without creep loading may confirm that the monotonic stress-strain response at the age at which the tests are terminated forms an envelope for creep fracture.

Impact of groove-and-tongue parameters on the bonding behavior between 3d-printed UHP-SHCC and cast normal concrete

The utilization of 3D-printed formworks represents a significant advancement in traditional construction practices, offering the potential to enhance structural capacity and effectively address reinforcement challenges in 3D concrete printing. Ensuring strong bonding between formwork and cast concrete is critical for structural integrity. In this study, 11 composite specimens with varying groove-and-tongue parameters including the layer number, spacing, length, and thickness of tongues undergo splitting tests. Results reveal that increasing the tongue’s layer number enhances the interfacial splitting tensile strength, whereas tongue spacing has minimal impact on interfacial strength, and a thicker tongue negatively affects the interfacial splitting tensile strength. An optimized groove-and-tongue configuration can significantly increase the interfacial splitting tensile strength from 2.10 MPa to 3.66 MPa, with a maximum increase rate of 70.4% and achieving a higher value (20.8%) than that of fully cast normal concrete. A splitting tensile strength model is proposed, with predictions aligning well with experimental results.

Unlocking the efficacy of cement-shell encapsulation for microbial self-healing process of concrete cracks

Oxygen supply and bacterial viability are crucial for efficient calcium carbonate precipitation in concrete crack healing processes. However, the open deliverance of oxygen-releasing compounds (ORCs) and bacterial spores during concrete mixing and casting poses a threat to spore viability and limits oxygen availability. To address these challenges, we developed an innovative approach integrating an oxygen self-supply strategy with bacterial strain B6. As such, B6 spores, along with Ca(OH)2 and CaO2 as oxygen sources and essential nutrients, were embedded within cement-shell microcapsules to build a microbial self-healing system. The result shows that in the presence of oxygen source and nutrients, B6 group (BPN) exhibits successful crack repair, achieving a repair ratio of approximately 100% after 30 days, while other control groups show less effective repair rates (20–60%). Moreover, water permeability significantly improves in the BPN specimens after crack repair, reaching 0 ml/cm−2·min, highlighting the efficacy of the developed self-healing system. Encapsulating the healing agent within cement shell effectively mitigates the reactivity between ORCs (CaO2) and water, thereby facilitating stable oxygen supply and safe delivery of microbial agents during crack healing. Furthermore, in-situ micromorphology and composition identification of crack repair materials affirm the presence of calcium carbonate precipitation to seal the concrete cracks. The encapsulation of healing material within cement shell stands out as an innovative approach, demonstrating an efficient self-healing process of concrete cracks. These findings might unveil new possibilities for bio-concrete to be used in sustainable and resilient construction practices, particularly in environments prone to cracking and water ingress.

3D Printed Concrete: Fresh and Hardened Properties

3D concrete printing (3D CP) is an advanced form of additive manufacturing (AM), that allows for the creation of complex geometrical structures using concrete. This technology has the potential to reduce construction time and labour costs while minimizing material waste. However, there are also challenges related to material properties, structural integrity, and standardization of construction practices. The primary challenge in developing 3D printable cementitious materials lies in engineering specific fresh properties that enable extrusion-based printing. Unlike cast concrete, where formwork provides dimensional stability during the printing process, the absence of formwork in 3D printing necessitates fresh mixtures with low-slump and high-thixotropy to be suitable for concrete 3D printing. Additionally, the orthotropic nature of the resulting 3D printed object due to the extrusion process impacts its mechanical properties. Therefore, this research aims to study the effect of water content and loading directions on 3D printed concrete. A pre-mix material from Sika was used in this study. Three mixes were prepared by using three different water to dry material (w/d) ratios, 0.140 l/kg, 0.145 l/kg and 0.150 l/kg. The experiments focused on analysing flowability, green strength, mechanical properties (compressive strength, flexural strength, and modulus of elasticity), water absorption, porosity, and chemical transformations at high temperatures through thermoanalytical measurement. The results showed that the mixture containing 0.145 l/kg (w/d) exhibited satisfactory 3D printability, optimal mechanical performance, lower porosities compared with mixtures 0.140 and 0.150, and same total porosity compared with cast specimen.

Experimental investigations on the flexural behavior of compression-cast seawater sea-sand concrete beams reinforced with CFRP bars

To address the corrosion problems, environmental concerns, and achieve green and sustainable civil engineering practices, this study designed several compression-cast seawater sea-sand concrete (SSC) beams reinforced with corrosion-resistant carbon fiber-reinforced polymer (CFRP) bars (i.e., FRP-SSC beams) and their flexural behavior was experimentally investigated through four-point bending tests. Twelve FRP-SSC beams were designed, including three normal-cast and nine compression-cast ones. The critical parameters included the concrete casting forms, water-to-cement (w/c) ratios, and reinforcement ratios of CFRP bars (ρf). Effects of the concrete casting methods, w/c ratios, and ρf on the flexural responses of FRP-SSC beams were comprehensively studied. In addition, the flexural theorems were used to derive the prediction models of the equivalent stress block parameters (i.e., εcm, α1, and β1) and flexural strength (Mu) of compression-cast FRP-SSC beams. Moreover, based on the experimental results, effectiveness and accuracy of the proposed flexural strength design models were verified by using the existing design specifications. Finally, the results indicate that, (1) compression-cast FRP-SSC beams with the larger ρf (1.78 %) exhibited bending failure featured by compression concrete crushing, whereas that with the smaller ρf (0.75 %) shown splitting failure; (2) The cracking moments of compression-cast FRP-SSC beams increased significantly owing to the higher compressive strength and elastic modulus of compression-cast concrete (CCC); (3) Because of the pronounced brittleness of CCC, the improvement of the ultimate flexural capacity of compression-cast FRP-SSC beams was limited; (4) Under the same moment level, the maximum crack widths of compression-cast FRP-SSC beams were smaller than their normal-cast counterparts; and (5) the proposed flexural strength design models could yield more accurate, safer, and conservative predictions of flexural strength for both normal- and compression-cast FRP-SSC beams.

Experimental Characterization of Anisotropic Mechanical Behaviour and Failure Mechanisms of Hardened Printed Concrete.

Extrusion-based printing of cementitious materials represents an innovative technology in civil engineering. The additive manufacturing process significantly influences the material properties in the hardened state, leading to anisotropic behaviour in terms of stiffness and strength compared to conventionally cast concrete. This experimental study aims to deepen the understanding of the mechanical behaviour of hardened printed concrete. Beam-like specimens with varying printing patterns, loading orientations and lengths are investigated within three-point bending tests (3PBT) and uniaxial compression tests (UCT). Homogenized material parameters such as Young's modulus, compressive and flexural tensile strength and density are statistically evaluated using optically measured displacement and strain fields on the specimen surface. The qualitative and quantitative results demonstrate a strong dependency of material properties and failure mechanisms on the printing pattern. The interfilamental and interlayer areas with weak adhesion are identified as the main reason for anisotropy.

Effects of concrete strength and joint stirrup ratio on seismic behavior of precast RCS joint with simple detail

Extensive research showed that RC column-steel beam (RCS) joints had sufficient seismic resistance. However, the combination of complicated strengthening details led to more workloads of welding and difficulties in concrete casting. A new RCS joint with whole column-section diaphragm was proposed in this research to address the shortcomings of constructability. The steel web did not pass through the joint, which was convenient for placing the reinforcement and horizontally casting the concrete. Since no additional steel plate was embedded in the joint region, the joint strength was mainly contributed by the concrete and stirrups. This paper aimed to study the effect of concrete strength and joint stirrup ratio on joint behavior. Five interior joint specimens were tested under cyclic loading. Joint shear failure occurred in each specimen. The joint shear strength improved by 88 % when the concrete strength increased from 33 MPa to 63 MPa. Since the joint stirrups had not fully yielded at the peak load point, the joint stirrup had a limited effect on the joint strength, represented by a 10 % increase in joint strength when the joint stirrup ratio changed from 0.5 % to 1.1 %. Nevertheless, the joint stirrups played a crucial role in confining the joint. With the increase of joint stirrup ratio, the growth of joint shear deformation could be restrained and the ductility of the joint would be improved. In addition, the shear strengths of the proposed joints were calculated according to typical methods. The results showed that nearly 90 % of joint strength was contributed by the concrete according to Nishiyama method, while the contribution of concrete represented 60 % to 80 % of total joint strength by using the Chinese specification. Improving the mechanical properties of concrete could effectively enhance the joint behavior. In Chinese specification, the contribution of stirrups may be overestimated since all the stirrups were assumed to reach the yield strength. This research could provide a reference for the future design and application of the proposed joint.

Development of Models Relating Screw Conveying Capacity of Concrete to Operating Parameters and Their Use in Conveyor Operating Strategies to Consider Batch Production

The screw conveyor is the key equipment used to realize the casting and forming of concrete in prefabricated components (PC), and its performance affects the PC shape, quality, and cost. In batch production, there is a process variable, the residence time. It is affected by the quality of the downstream vibration process. This also results in operating parameters that are difficult to match to the time scales. Eventually, it can lead to problems such as low casting efficiency or poor molded quality. In this paper, the DEM simulation method is used to explain and quantify the relationship between the screw conveying capacity and three important operating parameters: the screw’s outer diameter, residence time, and screw speed. The axial and radial velocity vectors are used as features to analyze the changing rule of particle motion trajectory and mass flow rate. Based on the simulation data, the operating parameters and the mass flow rate are forward-fitted to establish the prediction model of the screw conveying capacity. In addition, the residence time is backward fitted from the screw speed and mass flow rate. It is used to estimate the concrete workability. Furthermore, the fitted forward and backward models explore how to propose feasible operational strategies to achieve automatic discharge during batch production.

Mitigating the brittle behavior of compression cast concrete using polypropylene fibers

Compression casting enhances mechanical properties, durability, and microstructure of concrete while reducing cement usage and carbon emissions. However, its brittleness restricts its widespread use. This study aims to mitigate the brittleness of compression cast concrete (CCC) through fiber reinforcement. Eleven concrete mixes with varied volumetric ratios (0, 0.05, 0.1, 0.15, 0.2, and 2 %) and aspect ratios (250, 313, and 396) of polypropylene fibers were prepared. Both compressed and uncompressed specimens were analyzed for compressive stress-strain behavior, compressive strength, modulus of elasticity, toughness, specific toughness, and microstructure. Results show that CCC specimens have steeper and shorter descending segments on their compressive stress-strain curves than uncompressed concrete, indicating brittleness. Adding polypropylene fibers significantly reduces this brittleness by enhancing the post-peak compressive stress-strain behavior of CCC. Fiber reinforced CCC specimens exhibit significant enhancements in compressive strength, modulus of elasticity, and toughness (up to 68 %, 34 %, and 38 % respectively) compared to uncompressed plain concrete. Mercury intrusion porosimetry, scanning electron microscopy, and backscattered electron imaging confirm that compression casting strengthens the interfacial transition zone of both plain and fiber reinforced CCC. Proposed empirical models accurately forecast the modulus of elasticity, compressive strength, and peak compression strain for both types of CCC. Comparisons with existing models show that Nematzadeh and GB50010–2010 models effectively predict the ascending part of the compressive stress-strain curves of plain and fiber reinforced CCC. These findings affirm that polypropylene fibers effectively reduce the brittleness of CCC, promoting its practical application.

Pumping-less 3D concrete printing using quick nozzle mixing

Nozzle technologies for 3D concrete printing have been evolving to balance the conflicting demands of buildability and pumpability. This study introduces a simplified approach that eliminates the need for pumping by developing a customized system, the parameters of which were evaluated. The effect of process parameters (i.e., the flow rates of liquid and solid materials) and mixture proportions (i.e., the ratios of powder to sand and liquid to solid) on the extrudability and print quality was explored. Furthermore, the mechanical properties and microstructure of concrete printed using the Quick Nozzle Mixing system were examined. Results show that Quick Nozzle Mixing Technology not only enables high-quality printing but also exhibits the potential for achieving better process efficiency and higher aggregate content. The water-to-solid ratio is a critical factor influencing extrudability and buildability. Due to anisotropy caused by this new method, printed concrete has a lower strength than cast concrete.

Enhancing sustainability in concrete production: A novel compression casting technique for optimizing cement usage

Cement manufacturing is a major source of carbon dioxide (CO2) emissions. This study focuses on using the compression casting method to reduce the cement content in concrete manufacturing. No such work is present in the existing literature. For this purpose, five concrete mix designs of normal concrete (NC) and compression cast concrete (CCC), targeting compressive strengths of 50 MPa, 30 MPa, 25 MPa, 20 MPa, and 15 MPa, were considered. Moreover, considering the reduced cement content, five additional concrete mixes of NC and CCC were also prepared. All concrete specimens were tested in axial compression to study the stress-strain behavior. The findings reveal that CCC specimens exhibit higher stress-strain curves compared to NC specimens for the same mix design. The post-peak behavior of CCC specimens is observed to be more brittle than that of NC specimens. The reduction in density, compressive strength, and elastic modulus with the increase in the water-to-cement (w/c) ratio is more pronounced in NC specimens than in CCC specimens. The results indicate that the compression casting method allows for a reduction in cement content by approximately 25–50 % while achieving the desired compressive strengths, ranging from 30 to 50 MPa. A correlation is clearly demonstrated to determine the potential cement savings for specific concrete strengths. In summary, adopting compression casting technology effectively lowers cement requirements, leading to cost and carbon emission reductions in the construction sector and significantly enhancing the durability of concrete materials.