Search Results (29)

Currently, in hydrotechnical engineering, such as oil and gas platform construction, floating docks, and other floating structures, the need to develop new lightweight composite building materials is becoming an important problem. Expanded clay concrete (ECC) is the most common lightweight concrete option for floating structures. The aim of this study is to develop effective composite ECC with improved properties and a coefficient of structural quality (CCQ). To improve the properties of ECC, the following formulation and technological techniques were additionally applied: reinforcement of lightweight expanded clay aggregate by pre-treatment in cement paste (CP-LECA) with the addition of microsilica (MS) and dispersed reinforcement with basalt fiber (BF). An experimental study examined the effect of the proposed formulation and technological techniques on the density and cone slump of fresh ECC and the density, compressive and flexural strength, and water absorption of hardened ECC. A SEM analysis was conducted. The optimal parameters for LECA pretreatment were determined. These parameters are achieved by treating LECA grains in a cement paste with 10% MS and using dispersed reinforcement parameters of 0.75% BF. The best combination of CP-LECA10MS-0.75BF provides increases in compressive and flexural strength of up to 50% and 61.7%, respectively, and a reduction in water absorption of up to 32.8%. The CCQ increases to 44.4%. If the ECC meets the design requirements, it can be used in hydraulic engineering for floating structures. Full article

This study evaluates the rheological behavior and mechanical performance of Ultra-High-Performance Fiber-Reinforced Concrete (UHPFRC) mixes with varying superplasticizer dosages, aiming to optimize their use in pavement rehabilitation overlays on sloped surfaces. A reference self-compacting UHPFRC mix was modified by reducing the superplasticizer-to-binder ratio in incremental steps, and the resulting mixes were assessed through rheometry, mini-Slump, and Abrams cone tests. Key rheological parameters—static and dynamic yield stress, plastic viscosity, and thixotropy—were determined using the modified Bingham model. The results showed that reducing superplasticizer content increased yield stress and viscosity, enhancing thixotropic behavior while maintaining ultra-high compressive (≥130 MPa) and flexural strength (≥20 MPa) at 28 days. A predictive model was validated to estimate the critical yield stress needed for overlays on slopes. Among the evaluated formulations, the SP-2 mix met the stability and performance criteria and was successfully tested in a prototype overlay, demonstrating its viability for field application. This research confirms the potential of rheology-tailored UHPFRC as a high-performance solution for durable and stable pavement overlays in demanding geometric conditions. Full article

The presence of free muscovite in tailings can negatively affect the mechanical strength and rheological properties of cemented paste backfill, as has been observed for several cementitious materials. The aim of this study is to evaluate the influence of free muscovite content in tailings on the consistency and rheology of cemented paste backfill. For this purpose, cemented paste backfill mixtures were prepared from two different tailings. The mixtures were prepared at solids contents between 70% and 74% and with the addition of 5% GU (general use Portland cement)/slag binder. In addition, the influence of muscovite was studied by varying the muscovite content of the tailings from about 14% to 25%. Abrams cone slump tests and rheological analyses were carried out for each recipe. The results show a decrease in slump height and an increase in yield stress, Herschel–Bulkley flow index, and infinite shear rate Cross viscosity with increasing muscovite content for a given solids content. Therefore, water should be added to maintain the required flowability of cemented paste backfill, which increases the water/binder ratio and may affect the mechanical strength. A method is presented for determining the amount of binder to be incorporated to maintain the water/binder ratio of the original cemented paste backfill recipe. Full article

A cementitious paste fill (CPF) ensures the long-age stability of underground cavities. Recently, superplasticizers, specifically ones that are polycarboxylate ether-based, have been incorporated to enhance CPF performance, yet their long-term effects on permeability, mechanical properties, and microstructures remain unclear. This study investigates these effects with CPF samples containing varying superplasticizer dosages (0%, 1%, 3%, 5%) that have been cured for up to 150 days. Rheological assessments (slump cone, vane shear tests), unconfined compressive strength testing, microstructural characterization (MIP, SEM), and hydraulic conductivity measurements were performed alongside XRD and thermal analyses (TAns) on high w/c (2) cement paste samples. The results showed that superplasticizer addition reduced CPF water content by 23% and yield stress by six times, aiding slurry transport. Long-term strength was enhanced by up to 2.4 times compared to the control samples, indicating improved underground stability. Superplasticizers altered the CPF samples stress–strain responses, increasing their load-bearing capacity. TG/DTG and XRD analyses revealed that hydration product development increased and porosity decreased in the presence of a superplasticizer. Hydraulic conductivity and permeability also decreased significantly. SEM and MIP analyses showed that the superplasticizer enhanced denser microstructures with fewer pores and fractures. These findings offer promising implications for designing CPFs with improved strength, durability, and environmental sustainability. Full article

An actual scientific problem in current concrete science is poor knowledge of the problem of modifying concrete with plant waste. At the same time, plant waste benefits from other types of waste because it is a recycled raw material. A promising technological approach to modifying concrete with plant waste is the introduction of components based on the processing of coffee production waste into concrete. This study aims to investigate the use of biochar additives from spent coffee grounds (biochar spent coffee grounds—BSCG) in the technology of cement composites and to identify rational formulations. A biochar-modifying additive was produced from waste coffee grounds by heat treatment of these wastes and additional mechanical grinding after pyrolysis. The phase composition of the manufactured BSCG additive was determined, which is characterized by the presence of phases such as quartz, cristobalite, and amorphous carbon. The results showed that the use of BSCG increases the water demand for cement pastes and reduces the cone slump of concrete mixtures. Rational dosages of BSCG have been determined to improve the properties of cement pastes and concrete. As a result of the tests, it was determined that the ideal situation is for the BSCG ratio to be at a maximum of 8% in the concrete and not to exceed this rate. For cement pastes, the most effective BSCG content was 3% for concrete (3%–4%). The compressive and flexural strengths of the cement pastes were 6.06% and 6.32%, respectively. Concrete’s compressive strength increased by 5.85%, and water absorption decreased by 6.58%. The obtained results prove the feasibility of using BSCG in cement composite technology to reduce cement consumption and solve the environmental problem of recycling plant waste. Full article

Low-grade limestone (LGL) is not used to produce cement clinker, but this leftover material in cement quarries increases the water demand when used as a filler in concrete production. In this study, the effect of six commercial superplasticizers on the performance of cement mixes containing 35% LGL and 2% gypsum was investigated. The optimal doses of these superplasticizers were found in a range of different water/binder (w/b) ratios by conducting several Marsh cone and mini-slump tests. The addition of a superplasticizer with a higher active solid content produced a maximum cement flow, regardless of the w/b ratios. The LGL-based mortar samples admixed with this superplasticizer obtained a maximum compressive strength of about 36 MPa at the end of 28 days. SEM and XRD results showed the formation of a new calcium-rich mineral in their microstructure. These findings highlight the impact of the type and properties of superplasticizers on the performance of concrete mixes containing LGL as a supplementary cementitious material. Full article

One fascinating concept for enhancing the durability and lifespan of concrete buildings involves the use of self-healing concrete. This study focuses on the effect of crystalline admixtures and coatings on various properties of self-healing concrete and provides a comparison with traditional concrete. Four different concrete mixtures were prepared to assess their effectiveness in bridging crack openings, their flexural and compressive strengths, and water absorption. Various testing methods, including destructive, semi-destructive, and non-destructive tests, were used in this research. The capacity of the mixes to repair themselves was assessed on the destroyed and semi-destroyed test specimens using crack-healing and microstructure testing. Additionally, all mixtures were also subjected to the slump cone test and air content test in order to investigate the characteristics of the concrete in its fresh state. The findings demonstrate that crystalline coating and admixture combinations have significant potential for healing concrete. The compressive and bending strengths of self-healing concrete mixtures were shown to be slightly higher compared to traditional concrete when the additive dose was increased. Self-healing concrete mixtures also exhibited much lower water absorption, a tightly packed and improved microstructure, and signs of healed gaps, all of which indicate greater durability. Full article

Understanding the transient properties of cementitious pastes is crucial for construction materials engineering. Computational modeling, particularly through Computational Fluid Dynamics (CFD), offers a promising avenue to enhance our understanding of these properties. However, there are several numerical uncertainties that affect the accuracy of the simulations using CFD. This study focuses on evaluating the accuracy of CFD simulations in replicating slump flow tests for cementitious pastes by determining the impact of the numerical setup on the simulation accuracy and evaluates the transient, viscosity-dependent flows for different viscous pastes. Rheological input parameters were sourced from rheometric tests and Herschel–Bulkley regression of flow curves. We assessed spatial and temporal convergence and compared two regularization methods for the rheological model. Our findings reveal that temporal and spatial refinements significantly affected the final test results. Adjustments in simulation setups effectively reduced computational errors to less than four percent compared to experimental outcomes. The Papanastasiou regularization was found to be more accurate than the bi-viscosity model. Employing a slice geometry, rather than a full three-dimensional cone mesh, led to accurate results with decreased computational costs. The analysis of transient flow properties revealed the effect of the paste viscosity on the time- and shear-dependent flow progress. The study provides an enhanced understanding of transient flow patterns in cementitious pastes and presents a refined CFD model for simulating slump flow tests. These advancements contribute to improving the accuracy and efficiency of computational analyses in the field of cement and concrete flow, offering a benchmark for prospective analysis of transient flow cases. Full article

The parameters of the discrete element simulation model for rice field soils serve as valuable data references for investigating the dynamic characteristics of the walking wheel of high-speed precision seeding machinery in paddy fields. The research specifically targets clay loam soil from a paddy field in South China. Calibration of essential soil parameters was achieved using EDEM_2022 software (and subsequent versions) discrete element simulation software, employing the Edinburgh Elasto-Plastic Adhesion (EEPA) nonlinear elastic-plastic contact model. The tillage layer and plough sub-base layer underwent calibration through slump and uniaxial compression tests, respectively. Influential contact parameters affecting slump and axial pressure were identified through a Plackett–Burman test. The optimal contact parameter combinations for the discrete element model of the tillage layer and plough sub-base layer were determined via a quadratic rotational orthogonal test. The accuracy of the discrete element simulation model’s parameters for paddy field soils was further validated through a comparative analysis of the simulation test’s cone penetration and the field soil trench test. Results indicate that the Coefficient of Restitution, surface energy, Contact Plasticity Ratio, and Tensile Exp significantly influence slump (p < 0.05). Additionally, the Coefficient of Restitution, Contact Plasticity Ratio, coefficient of rolling friction, and Tangential Stiff Multiplier significantly impact axial pressure (p < 0.05). Optimal contact parameters for the plough layer were achieved with a particle recovery coefficient of 0.49, a surface energy of 18.52 J/m², a plastic deformation ratio of 0.45, and a tensile strength of 3.74. For the plough subsoil layer, optimal contact parameters were a particle recovery coefficient of 0.47, a coefficient of interparticle kinetic friction of 0.32, a plastic deformation ratio of 0.49, and a tangential stiffness factor of 0.31. Results from the cone penetration test reveal no significant disparity in compactness between the actual experiment and the simulation test. The calibrated discrete element model’s contact parameters have been verified as accurate and reliable. The findings of this study offer valuable data references for understanding the dynamic characteristics of the walking wheel of the entire machinery in high-speed precision seeding in paddy fields. Full article

Currently, there is an environmental problem associated with cleaning the seas and oceans from a large number of dead jellyfish thrown ashore and into the coastal zone, which is urgent and requires solutions. This research aims to study the formation and properties of cement and concrete with added jellyfish mass and to understand the effects of this addition. Tests were carried out on formulations containing dead jellyfish mass in amounts from 0.2% to 1.6%. This study focused on the density, shear stress, workability, water separation, strength, and water absorption of cement and concrete, which are the main properties that characterize cement and concrete in construction. Adding 0.6% dead jellyfish to this composition resulted in greater effectiveness compared to the control composition. With this dosage, the normal density of the cement paste decreased by 16.3%, there was a 32% decrease in ultimate shear stress, the workability expressed in the cone slump increased by 60.8%, the water separation of cement decreased by 19.7%, the increase in compressive strength was 10.6%, and water absorption decreased by 15.5%. An analysis of the structure showed that the modification of concrete with dead jellyfish mass reduces the defectiveness of a concrete structure compared to the composition of the control structure. Full article

This paper deals with the optimization of reactive powder concrete mixtures with respect to the addition of silica fume and the type of polycarboxylate superplasticizer used. First, the properties of reactive powder concrete with eight different commercial polycarboxylate superplasticizers were tested in terms of workability, specific weight, and mechanical properties. It was found that different commercially available superplasticizers had significant effects on the slump flow, specific weight, and compressive and flexural strengths. The optimal superplasticizer (BASF ACE430) was selected for further experiments in order to evaluate the influences of silica fume and superplasticizer content on the same material properties. The results showed that the silica fume and superplasticizer content had considerable effects on the mini-cone slump flow value, specific weight, flexural and compressive strengths, and microstructure. There were clearly visible trends and local minima and maxima of the measured properties. The optimal reactive powder concrete mixture had a composition of 3.5–4.0% superplasticizer and 15–25% silica fume. Full article

Nano-SiO₂ (NS) is widely used in cement-based materials due to its excellent physical properties. To study the influence of NS content on a cement paste and the interfacial transition zone (ITZ), cement paste samples containing nano content ranging from 0 to 2% (by weight of cement) were prepared, and digital image correlation (DIC) technology was applied to test the mechanical properties. Finally, the optimal NS content was obtained with statistical analysis. The mini-slump cone test showed that, with the help of superplasticizer and ultrasonic treatment, the flowability decreased continuously, as the NS content increased. The DIC experimental results showed that NS could effectively improve the mechanical properties of the cement paste and the ITZ. Specifically, at the content level of 1%, the elastic modulus of cement paste and ITZ was 20.95 GPa and 3.20 GPa, respectively. When compared to that without nanomaterials, the increased amplitude was 73.50% and 90.50%, respectively. However, with the further increase in NS content, the mechanical properties decreased, which was mainly caused by the agglomeration of nanomaterials. Additionally, the NS content did not exhibit a significant effect on the thickness of the ITZ, and its value was maintained at 76.91–91.38 μm. SEM confirmed that NS would enhance the microstructure of both cement paste and ITZ. Full article

The demand for sustainable construction materials has driven the exploration of various innovative approaches to enhance the properties of concrete for reducing its environmental impact. The present study examines the effects of incorporating recycled concrete aggregate (RCA), slag cement, alccofine, and glass fibers into concrete mixtures. In the present study, it has been observed that recycled concrete aggregate (RCA) exhibits inferior properties, including higher water absorption and poorer performance, when compared to natural coarse aggregate. Various replacement levels of RCA were utilized in this study to assess its impact on concrete performance. Alccofine, a supplementary cementitious material, is used to partially replace the binding material. Additionally, glass fibers were added to enhance the flexural and tensile behavior of the concrete. The concrete mixtures were designed to meet the required strength and durability specifications. A comprehensive testing program was conducted to evaluate the fresh and hardened properties of the concrete. A slump cone test was performed for assessing the workability of fresh concrete. For hardened concrete, compressive strength, flexural strength, and split tensile strength are evaluated. The results demonstrated that incorporating RCA, slag cement, alccofine, and glass fibers into the concrete mixtures improved mechanical properties. The use of RCA led to a reduction in natural resource consumption, namely natural coarse aggregate in concrete. On the other hand, the generated construction and demolition (C&D) waste is used effectively. Portland slag cement (PSC) and alccofine (A) improved the long-term strength of concrete. The addition of glass fibers significantly enhanced the tensile and flexural performance of the concrete, resulting in improved crack resistance and overall performance. This study introduces a novel concept by exploring the potential utilization of recycled concrete aggregate, slag cement, alccofine, and glass fibers in combination as sustainable and high-performance components in concrete mixtures. Previous research has not extensively studied this combination of materials, making it a unique and innovative approach. These findings contribute to the development of eco-friendly construction practices and provide insights for engineers, researchers, and practitioners aiming to incorporate recycled materials and supplementary cementitious materials into concrete construction. Full article

In the production of 3D printable mortar (3DPM), numerous efforts have been made globally to effectively utilise various cementitious materials, admixtures, and fibres. The determination of rheological and material strength properties is crucial for successful 3D concrete printing because the materials used in 3DPM must possess the unique characteristic of making mortar flowable while being strong enough to support the weight of subsequent layers in both fresh and hardened states. The complexity of the required characteristics makes it challenging to develop an optimised mix composition that satisfies both the rheological and material strength requirements, given the wide range of available admixtures, supplementary cementitious materials, and fibres. Fly ash, basalt fibre and superplasticiser when blended with cement can help to improve the overall performance of 3DPM. The objective of this research is to optimise the rheological properties and material strength of 3D printable mortars (3DPM) containing cement, fly ash, basalt fibre, and superplasticiser. This study aims to produce 3DPM with an optimised mix composition to meet the requirements of both rheological and material strength characteristics using the factorial design approach and desirability function. Different dosages of cement, fly ash, basalt fibre, and superplasticiser are chosen as the primary design parameters to develop statistical models for the responses of rheological and material strength properties at 7 and 28 days. The results expressed in terms of the measured properties are valid for mortars made with cement ranging from 550 to 650 kg/m³, fly ash from 5% to 20% (of cement), superplasticiser from 2 to 4 kg/m³, and basalt fibre from 1 to 3 kg/m³. The rheological properties are evaluated using slump flow, cone penetrometer, and cylindrical slump tests, while the mechanical strength is evaluated using a three-point bending test and compressive test. A full factorial design experiment (FoE) is used to determine the significant parameters effecting the measured properties. Prediction models are developed to express the measured properties in terms of the primary parameters. The influence of cement, fly ash, basalt fibre, and superplasticiser is analysed using polynomial regression to determine the main effects and interactions of these primary parameters on the measured properties. The results show that the regression models established by the factorial design approach are effective and can accurately predict the performance of 3DPM. Cement, fly ash, and superplasticiser dosages have significant effects on the rheological and mechanical properties of mortar, while basalt fibre is able to influence the static yield stress and flexural strength of 3DPM. The utilisation of regression models and isoresponse curves allows for the identification of significant trends and provides valuable insight into the behaviour of the material, while desirability function is useful to optimise overall performance of mix proportions to meet the desired performance objective at fresh and hardened states. Full article

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