Search Results (150)

Quarry dust (QD) landfill causes environmental issues that cannot be ignored. In this study, we systematically explore its potential application as a supplementary cementitious material (SCM) in cemented paste backfill (CPB), revealing the activated mechanism of modified QD (MQD) and exploring the hydration process and workability of CPB containing QD/MQD. The experimental results show that quartz, clinochlore and amphibole components react with CaO to form reactive dicalcium silicate (C₂S) and amorphous glass phases, promoting pozzolanic reactivity in MQD. QD promotes early aluminocarbonate (M_c) formation through CaCO₃-derived CO₃²⁻ release but shifts to hemicarboaluminate (H_c) dominance at 28 d. MQD releases active Al³⁺/Si⁴⁺ due to calcination and deconstruction, significantly increasing the amount of ettringite (AFt) in the later stage. With the synergistic effect of coarse–fine particle gradation, MQD-type fresh backfill can achieve a 161 mm flow spread at 20% replacement. Even if this replacement rate reaches 50%, a strength of 19.87 MPa can still be maintained for 28 days. The good workability and low carbon footprint of MQD-type backfill provide theoretical support for—and technical paths toward—QD recycling and the development of low-carbon building materials. Full article

This study systematically investigates the effects of shell ash (SA) content (0–10%) on early moisture evolution, pore structure, and hydration kinetics in cement paste using LF-NMR and NG-I-D hydration kinetic models. Key findings include the following: (1) Increased SA content significantly alters moisture phase distribution. Low contents (≤8%) consume free water through rapid CaO hydration, promoting C-S-H gel densification. However, 10% SA causes reduced moisture in 0.16–0.4 μm gel micropores (due to hindered ion diffusion) and abrupt increases in 0.63–2.5 μm pores. (2) Porosity first decreases then increases with SA content, reaching minimum values at 3–5% and 8%, respectively. The 10% content induces abnormal porosity growth from localized over-densification following polynomial fitting (R² = 0.966). (3) Krstulovic–Dabic model analysis reveals three consecutive hydration stages: nucleation–growth (NG), phase boundary reaction (I), and diffusion control (D). The NG stage shows the most intense reactions, while the D stage dominates (>60% contribution), with high model fitting accuracy (R² > 0.9). (4) SA delays nucleation/crystal growth, inducing needle-like crystals at 3% content. Mechanical properties exhibit quadratic relationships with SA content, achieving peak compressive strength (18.6% increase vs. control) at 5% SA. This research elucidates SA content thresholds governing hydration kinetics and microstructure evolution, providing theoretical support for low-carbon cementitious material design. Full article

Recycled wood fiber (RWF) obtained through the multi-stage processing of waste wood serves as an eco-friendly green construction material, exhibiting lightweight, porous, and high toughness characteristics that demonstrate significant potential as a cementitious reinforcement, offering strategic advantages for environmental protection and resource recycling. In this study, high-performance sulfoaluminate cement (SAC)-RWF composites prepared by modifying RWFs with nano-silica (NS) and a silane coupling agent (KH560) were developed and their effects on mechanical properties, shrinkage behavior, hydration characteristics, and microstructure of SAC-RWF composites were systematically investigated. Optimal performance was achieved at water–cement ratio of 0.5 with 20% RWF content, where the KH560-modified samples showed superior improvement, with 8.5% and 14.3% increases in 28 d flexural and compressive strength, respectively, compared to the control groups, outperforming the NS-modified samples (3.6% and 8.6% enhancements). Both modifiers improved durability, reducing water absorption by 6.72% (NS) and 7.1% (KH560) while decreasing drying shrinkage by 4.3% and 27.2%, respectively. The modified SAC composites maintained favorable thermal properties, with NS reducing thermal conductivity by 6.8% through density optimization, whereas the KH560-treated specimens retained low conductivity despite slight density increases. Micro-structural tests revealed accelerated hydration without new hydration product formation, with both modifiers enhancing cementitious matrix hydration product generation by distinct mechanisms—with NS acting through physical pore-filling, while KH560 established Si-O-C chemical bonds at paste interfaces. Although both modifications improved mechanical properties and durability, the KH560-modified SAC composite group demonstrated superior overall performance than the NS-modified group, providing a technical pathway for developing sustainable, high-performance recycled wood fiber cement-based materials with balanced functional properties for low-carbon construction applications. Full article

The rheological behavior of cementitious paste plays a pivotal role in determining the workability, pumpability, and uniformity of fresh concrete. Classical rheological models often struggle to capture the complex flocculation and hydration effects inherent in cement-based systems, and they typically depend on parameters that are difficult to measure directly, limiting their practical utility. This study presents a novel composition-based constitutive model that introduces a virtual maximum packing fraction (${\varphi }_{max}$) to account for interparticle flocculation and entrapped water effects. By establishing quantitative relationships between powder characteristics—such as particle size and specific surface area—and rheological parameters, the model enables physically interpretable and measurable predictions of yield stress and plastic viscosity. Our validation against 65 paste formulations with varying water-to-binder ratios, mineral admixture types and dosages, and superplasticizer contents demonstrates strong predictive accuracy (R² > 0.98 for plain pastes and >0.85 for blended systems). The influence of superplasticizers is effectively captured through modifications to ${\varphi }_{max}$, allowing the model to remain both robust and parameter efficient. This framework supports forward prediction of paste rheology from raw material properties, offering a valuable tool for intelligent mix design in high-performance concrete applications such as self-consolidating and 3D-printed concrete. Full article

Alkali-activated binders (AAB) are a suitable and sustainable alternative to ordinary Portland cement (OPC), with reductions in natural resource usage and environmental emissions in regions where the necessary industrial residues are available. Despite its potential, the lack of mix design methods still limits its applications. This paper proposes a systematic parametric validation for AAB mix design applied to pastes and concretes, valorizing steel slag as precursors. The composed binders are based on coal fly ash (FA) and Basic Oxygen Furnace (BOF) steel slag. These precursors were activated with sodium silicate (Na₂SiO₃) and sodium hydroxide (NaOH) alkaline solutions. A parametric investigation was performed on the mix design parameters, sweeping the (i) alkali content from 6% to 10%, (ii) silica modulus (SiO₂/Na₂O) from 0.75 to 1.75, and (iii) ash-to-slag ratios in the proportions of 75:25 and 50:50, using parametric intervals retrieved from the literature. These variations were analyzed using response surface methodology (RSM) to develop a mechanical model of the compressive strength of the hardened paste. Flowability, yield stress, and setting time were evaluated. Statistical analyses, ANOVA and the Duncan test, validated the model and identified interactions between variables. The concrete formulation design was based on aggregates packing analysis with different paste contents (from 32% up to 38.4%), aiming at self-compacting concrete (SCC) with slump flow class 1 (SF1). The influence of the curing condition was evaluated, varying with ambient and thermal conditions, at 25 °C and 65 °C, respectively, for the initial 24 h. The results showed that lower silica modulus (0.75) achieved the highest compressive strength at 80.1 MPa (28 d) for pastes compressive strength, densifying the composite matrix. The concrete application of the binder achieved SF1 fluidity, with 575 mm spread, 64.1 MPa of compressive strength, and 26.2 GPa of Young’s modulus in thermal cure conditions. These findings demonstrate the potential for developing sustainable high-performance materials based on parametric design of AAB formulations and mix design. Full article

The microstructure of cement paste is governed by the hydration of its major component, tricalcium silicate (C₃S). Quantitative analysis of C₃S microstructural images is critical for elucidating the microstructure-property correlation in cementitious systems. Existing image segmentation methods rely on image contrast, leading to a struggle with multi-phase segmentation in regions with close grayscale intensities. Therefore, this study proposes a weighted K-means clustering method that integrates intensity gradients, texture variations, and spatial coordinates for the quantitative analysis of hydrated C₃S microstructure. The results indicate the following: (1) The deep convolutional neural network with guided filtering demonstrates superior performance (mean squared error: 53.52; peak signal-to-noise ratio: 26.35 dB; structural similarity index: 0.8187), enabling high-fidelity preservation of cementitious phases. In contrast, wavelet denoising is effective for pore network analysis but results in partial loss of solid phase information. (2) Unhydrated C₃S reflects optimal boundary clarity at intermediate image relative resolutions (0.25–0.56), while calcium hydroxide peaks at 0.19. (3) Silhouette coefficients (0.70–0.84) validate the robustness of weighted K-means clustering, and the Clark–Evans index (0.426) indicates CH aggregation around hydration centers, contrasting with the random CH distribution observed in Portland cement systems. Full article

Frost resistance of pavement concrete is closely related to air void structure. Traditionally, such a structure is assessed by measuring chord lengths according to the guidelines provided in the PN-EN 480-11 standard. In recent years, increased attention has been given to analyzing pore diameters (2D) on the surface of concrete samples. The measurement procedure employed in the surface method should enable accurate identification of small pores formed by modern air-entraining admixtures. Researchers suggest only pores under 300 µm significantly impact frost resistance, raising the question of whether pores over 1000 µm should be considered in measurements. This study attempts to define the measurement frame parameters required to obtain satisfactory results. Additionally, a comparative analysis of air void structure parameters from 2D and 1D methods was conducted. Geometrical models of air voids distributed within cement paste using the Monte Carlo method based on air void structure data derived from real concrete were created. Analysis of these models demonstrated good agreement between the 2D and 1D results. It was concluded that satisfactory results require the analysis of either three measurement frames of 50 × 50 mm or four frames of 40 × 40 mm, with a resolution of at least 3 µm/px. Full article

Clay soils are known to have a high swelling pressure with an increase in water content. This behavior is considered a serious hazard to structures built upon them. Various mechanical and chemical treatments have historically been used to stabilize the swelling behavior of clay soils. This work investigates the potential use of shredded plastic waste to reduce the swelling pressure and compressibility of clay soils. Two types of highly plastic clay (CH) soils were selected. Three different dimensions of plastic waste pieces were used, namely lengths of 0.5 cm, 1.0 cm, and 1.5 cm, with a width of 1 mm. A blend of plastic–cement waste with a ratio of 1:5 by weight was prepared. Different fractions of the plastic–cement waste blend with a 2 wt.% increment were added to the clay soil, which was then remolded in a consolidometer ring at 95% relative compaction and 3.0% below the optimum. The zero swell test, as per ASTM D4546, was conducted on the remolded soil samples after three curing periods: 1, 2, and 7 days. This method ensures the accurate evaluation of swell potential and stabilization efficiency over time. The experimental results showed that the addition of 6.0–8.0% of the blend significantly reduced the swelling pressure, demonstrating the mixture’s effectiveness in soil stabilization. It also reduced the swell potential of the expansive clay soil and had a substantial effect on the reduction in its compressibility, especially with a higher aspect ratio. The compression index decreased, while the maximum past pressure increased with a higher plastic–cement ratio. The 7-day curing time is the optimum time to stabilize expansive clay soils with the plastic–cement waste mixture. This study provides strong evidence that plastic waste can enhance soil mechanical properties, making it a viable geotechnical solution. Full article

Previous research on cement aging mainly focuses on construction cement, exploring the mechanisms through which aging conditions affect cement properties. However, the impact of aging on oil well cement remains understudied. Aging of cement under high-humidity conditions leads to significant alterations in its properties, indicating that the cement formulation needs to be adjusted to reduce the negative effects during cementing operations. The effect of aging on particle size, mineral composition, and early hydration behavior of oil well cement after 0, 7, 14, and 28 d at 90% relative humidity (±3%RH) and 25 °C (±2 °C) was investigated. The results showed that, during the aging process, the uptake of H₂O and CO₂ from the surrounding atmosphere by cement leads to slight hydration. This process was associated with a reduction in the specific surface area and surface energy. The contents of hydration products ettringite (AFt) and calcium hydroxide (CH) increased, whereas the amounts of C₃S and C₃A decreased. Consequently, the early hydration rate of cement decreased along with a reduction in the cumulative heat release. As the aging time increased, the compressive strength and thickening time of the cement pastes decreased, and the rheological properties deteriorated. Under the experimental temperature and humidity conditions, the permissible aging time without significant deterioration should not exceed 7 d, with a maximum permissible aging time of 14 d. Full article

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. Full article

Air-void characteristics are defined in the EN-480-11 test method. The primary criticism of Powers’ model comes from the fact that the spacing factor is calculated with the average chord length, without taking into account the chord length distribution. The aim of this study is to determine whether an analysis of the chord length distribution can provide a more accurate estimate of the spacing factor. A data set containing 110 air-entrained concretes with various characteristics was analyzed. The artificial neural network method was applied to develop a model that determines the relationship between the spacing factor, L2, and the parameters of the air-void structure. The input parameters for the ANN-L2 model included the following: A, d, and W—characteristics of the chord size distribution, P—cement paste content, and N5—number of large pores. The ANN model allows for a sufficiently accurate estimation of the spacing factor, L2. The most significant factors that influenced L were the peak amplitude, A; peak width, W; and cement paste content, P. There was a strong correlation between the results of the ANN model and the standard spacing factor L2, indicating that both calculation methods produced comparable results. Finally, a simple method for using the ANN model to calculate the spacing factor in Excel is demonstrated. Full article

Concrete printing in three dimensions is believed to be an innovative construction method. Numerous researchers conducted laboratory experiments over the past decade to examine the behavior of concrete mixtures and the material properties that are pertinent to the 3D concrete printing industry. Furthermore, the global warming effect is being further exacerbated by the increased use of cement, which increases carbon dioxide (CO₂) emissions and pollution. Various standards endorse the utilization of Portland-composite cement in construction to mitigate CO₂ emissions, particularly cement CEM II/A-P. This research provides an experimental and numerical study to examine the evolution of cementitious composite utilizing cement CEM II/A-P for three-dimensional concrete printing, combining three different types of synthetic fiber. The thorough experimental analysis includes three combinations integrating diverse fiber types (polypropylene, high-modulus polyacrylonitrile, and alkali-resistant glass fibers) alongside a reference mixture devoid of fiber. The three distinct fiber types in the mixtures (polypropylene, high modulus polyacrylonitrile, and alkali-resistant glass fibers) were evaluated to assess their impact on (i) the flowability of the cementitious mortar and the slump flow test of fresh concrete, (ii) the concrete compressive strength, (iii) the uniaxial tensile strength, (iv) the splitting tensile strength, and (v) the flexural tensile strength. Previous researchers designed a cylinder stability test to determine the shape stability of the 3D concrete layers and their capacity to support the stresses from subsequent layers. Furthermore, the numerical analysis corroborated the experimental findings with the finite element software ANSYS 2023 R2. The flexural performance of the examined beams was validated using the Menetrey–Willam constitutive model, which has recently been incorporated into ANSYS. The experimental data indicated that the incorporation of synthetic fiber into the CEM II/A-P mixtures enhanced the concrete’s compressive strength, the splitting tensile strength, and the flexural tensile strength, particularly in combination including alkali-resistant glass fibers. The numerical results demonstrated the efficacy of the Menetrey–Willam constitutive model, featuring a linear softening yield function in accurately simulating the flexural behavior of the analyzed beams with various fiber types. Full article

The stability of cement slurries under high-temperature conditions poses a significant engineering challenge in cementing operations. This study explored the development of a novel tetrameric thermosensitive thickening polymer (TTSTC) as a solution to this problem. Aqueous free radical polymerization was employed to synthesize the polymer. The base monomers 2-acrylamido-2-methylpropanesulfonic acid (AMPS) and acrylamide (AM) were employed, in conjunction with the long-chain thermosensitive monomers octadecyldimethylallylammonium chloride (C18DMAAC) and N-vinylpyrrolidone (NVP). The optimal synthesis conditions were determined by orthogonal experiments as follows: monomer molar ratio (AM:AMPS:C18DMAAC:NVP) = 15:10:5:5, initiator concentration of 16 wt%, cross-linker concentration of 0.45 wt%, pH 6, and polymerization temperature of 60 °C. The chemical structure of TTSTC was characterized by Fourier transform infrared spectroscopy (FT-IR), proton nuclear magnetic resonance (1H-NMR), gel permeation chromatography, scanning electron microscopy, Zeta potential, and particle size measurement. The results verified the successful synthesis of the target polymer. Its thermal stability, thermosensitive thickening behavior, and salinity resistance were systematically investigated. Furthermore, the impact of TTSTC on the settling stability, rheological characteristics, and compressive strength of cement paste was assessed. The experimental findings demonstrated that TTSTC displayed noteworthy thermosensitive thickening properties at temperatures up to 279 °C, pH values ranging from 11 to 13, and NaCl/CaCl₂ concentrations between 0.05 and 0.5 g/L. The optimal performance of TTSTC was observed at mass fractions ranging from 0.6 to 0.8 wt%. When incorporated into the slurry at 0.6–1.0 wt%, TTSTC significantly improved the slurry settling stability, thickening properties, and 28d compressive strength at elevated temperatures compared with the control. When comparing the temperature-sensitive thickening performance of the newly developed treatment agent with that of the commercially available xanthan gum thickener, the results showed that for the cement slurry system containing the new treatment agent at a mass fraction of 0.6%, the reduction in consistency was 30.9% less than that of the cement slurry system with xanthan gum at a mass fraction of 0.6%. These findings indicate that TTSTC has the potential to function as a highly effective additive in cementing operations conducted in extreme environments, thereby enhancing the stability and dependability of such operations. Full article

To apply the cementitious capillary crystalline waterproof materials (CCCWs) in real engineering practice, the mechanical properties and related mechanism of cement after adding CCCW are investigated in this study. By using a combination of techniques including X-ray diffraction, Fourier-transform infrared spectroscopy, thermogravimetric analysis, scanning electron microscopy, and mercury intrusion porosimetry, the effect of Penetron (PNC, a kind of CCCW) content on the microstructure and compressive strength of cement with different water-to-bind (w/b) ratio were studied. The results show that the high-water content definitely decreased the mechanical properties of cement pastes. The addition of PNC appeared to play a detrimental role in the 7 d compressive strength due to the lower reactivity of PNC than cement. As the PNC content increased from 0% to 1.5%, the 28 d compressive strength of cement pastes increased despite the w/b ratio. For cement pastes with a w/b ratio of 0.50, its 28 d compressive strength increased from 24.6 MPa to 32.9 MPa. This can be attributed to the sulfate/carbonate-containing species in PNC to react with cement to form suitable ettringite. Consequently, the microstructure became denser, and porosity decreased. As PNC content increased to a further 2.5%, the compressive strength of cement pastes decreased gradually. The excessive PNC caused the excess ettringite, which destroyed the microstructure and increased the porosity of cement pastes. This study demonstrated that the PNC and its dosage affected the microstructure and the mechanical properties of cement paste. Suitable content, normally 1.5%, is recommended to apply in cement paste considering the mechanical properties despite the w/b ratio. Full article

In this work, we propose a Navier–Stokes-Informed Neural Network (NSINN) as a surrogate approach to predict the localized flow behavior of cementitious materials for advancing 3D additive construction technology to gain fundamental insights into multiscale mechanisms of cement paste rheology. NS equations are embedded into the NSINN to interpret the flow pattern in the 3D printing barrel. The results show that the presented NSINN has a higher accuracy compared to a traditional artificial neural network (ANN) as the Mean Square Errors (MSEs) of the u, v, and p predicted by NSINN are $1.25\times {10}^{-4}$, $1.85\times {10}^{-5}$, and $3.91\times {10}^{-3}$, respectively. Compared to the ANN, the MSE of the predictions are $5.88\times {10}^{-2}$, $4.17\times {10}^{-3}$, and $1.72\times {10}^{-2}$, respectively. Moreover, the mean prediction time used in the NSINN, the ANN, and Computational Fluid Dynamics (CFD) are 0.039 s, 0.014 s, and 3.37 s, respectively. That means the method is more computationally efficient at performing simulations compared to CFD which is mesh-based. The NSINN is also utilized in studying the relationship between geometry and extrudability. The ratio (R = 0.25, 0.5, and 0.75) between the diameter of the outlet and that of the domain is studied. It shows that a larger ratio (R = 0.75) can lead to better extrudability of the 3D concrete printing (3DCP). Full article