Materials and Structures最新文献

In this study, reaction products and reactivity of carbonation-cured limestone-calcined clay cement (LC³) were investigated. The LC³ pastes were prepared by introducing Portland cement, metakaolin, and limestone. The LC³ samples with various water-to-binder ratios were normally or carbonation-cured for 28 days. The mechanical properties and microstructural changes over time were evaluated by analyzing the flexural strength, compressive strength, thermogravimetry, X-ray diffraction, and ²⁹Si nuclear magnetic resonance results. The test results revealed that the carbonation-cured LC³ samples commonly experienced a rapid rate of carbonation ingress and low mechanical strength compared to the samples composed solely of Portland cement. The use of LC³ with a high water-to-binder ratio increased the CO₂ uptake level in the sample. In addition, the reaction degrees of the Portland cement clinkers and metakaolin in the LC³ samples were significantly enhanced upon carbonation curing.

This study develops a novel soil suitability criterion for compressed earth block (CEB) production, addressing the shortcomings of existing methods. Soils with distinct physical properties were sourced from five deposits and their fine particles were assessed using X-ray diffraction, sedimentation, and methylene blue value analysis. By systematically modifying their granulometries, 50 soil samples with controlled properties were produced. The static optimum moisture content (OMC) for each sample was determined, guiding the production of CEBs. These blocks were tested for compressive strength, and select samples were further analyzed for drying shrinkage. Building on the obtained findings, empirical models predicting compressive strength and shrinkage were developed, enabling the formulation of an objective soil suitability criterion based on desired levels for minimum compressive strength and maximum drying shrinkage thresholds. The model demonstrated consistent results when soils from other regions were evaluated, highlighting the robustness of the established criteria. The proposed criterion is easy to implement, saves time, and offers flexibility by allowing soil suitability to be assessed based on any desired values for CEB strength and shrinkage.

Rammed earth is a layered construction technique, making it essential to examine both material and interlayer properties to understand the behaviour of rammed earth structures. In particular, understanding how the layers are able to resist shear is critical for the design of structures that are resilient to lateral loadings such as those due to earthquakes. This study evaluates the material and interlayer properties of rammed earth specimens using unconfined compression tests and shear wedge tests, complemented by Digital Image Correlation and numerical simulations. Unconfined compression strength tests revealed that mechanical properties such as compressive strength and Young’s modulus are significantly influenced by environmental conditions as expected. Compressive strength was found to decrease with higher relative humidity and lower temperature. Compression fracture energy of rammed earth was evaluated, a parameter which has not received attention in the past. The numerical simulation of the unconfined compression test using Concrete Damaged Plasticity model showed good agreement with the experimental results. The shear wedge tests with measurements undertaken using digital image correlation were used to determine interlayer properties such as cohesion and friction angle. Further, these tests helped in the evaluation of shear and normal stiffnesses not previously determined. The use of digital image correlation permitted location of failure planes in the rammed earth material as well as interlayers. It also provided variation of displacement and strain fields. To the best of the author’s knowledge, the shear wedge test was numerically simulated for the first time; demonstrating the suitability of the constitutive model, Surface Based Cohesive Behaviour, employed for rammed earth interlayer. These findings support the use of the shear wedge test as a practical method for determining the interlayer properties of equilibrated rammed earth.

Vertical greening systems are a promising solution to the increasing demand for urban green spaces, improving environmental quality and addressing biodiversity loss. This study facilitates the development microbially greened algal biofilm facades, which offer a low maintenance vertical green space. The study focuses on concrete as a widely used building material and explores how physical surface characteristics impact its bioreceptive properties. Concrete samples, produced from the same mix but differing in surface structure, were subjected to a laboratory weathering experiment to assess their bioreceptivity. A novel inoculation method was employed, involving a single initial inoculation with either alga (Jaagichlorella sp.) alone, or a model biofilm consisting of a combination of the alga (Jaagichlorella sp.) with a fungus (Knufia petricola). The samples underwent four months of weathering in a dynamic laboratory setup irrigated with deionized water to observe subaerial biofilm attachment and growth. The formation of subaerial biofilms was monitored with high resolution surface imaging, colorimetric measurements and Imaging Pulse Amplitude Modulated Fluorometry (Imaging PAM-F), with Imaging PAM-F proving the most effective. Statistical analysis revealed that by impacting surface pH value and water retention capability, surface structures significantly influence microbial growth and that the concrete’s bioreceptivity can be influenced through thoughtful design of the materials surface. The inoculation of algae combined with a fungus facilitated the formation of a stable subaerial biofilm, enabling algae to colonize a surface structure that it could not colonize alone. This finding highlights the importance of modelling synergistic interactions present in natural biofilms.

The growing use of recycled aggregates in concrete represents a sustainable strategy to reduce the environmental impact of construction, but their influence on structural behaviour remains insufficiently understood. This study presents a numerical investigation of steel–concrete composite slabs incorporating recycled aggregate concrete (RAC), aimed at reproducing the experimental results obtained on twelve full-scale specimens with different aggregate replacement ratios (0–100%) and span lengths (2.4–3.2 m). Advanced non-linear finite element models were developed in ABAQUS to simulate the load–deflection response and interface debonding between the concrete and steel sheeting. A cohesive interaction law was implemented to capture progressive bond degradation and shear transfer. The comparison between numerical and experimental data demonstrates that the models accurately predict the load-bearing capacity and stiffness trends, while highlighting the beneficial effect of recycled aggregates on interface adhesion due to their increased surface roughness. The study confirms the potential of cohesive modelling as a reliable and cost-effective tool for analysing and designing composite slabs made with recycled concrete.

This paper presents an experimental program on the notched timber-concrete composite (TCC) connections with glued-in rod (GIR) to investigate the effects of test configurations and loading protocols on the shear performance of the connections. A total of twenty-seven notched TCC connections with GIR were designed to experience shear tests. The test results indicated that the double-shear specimens exhibited a higher load capacity but generally a lower slip modulus compared to the single-shear specimens. The load-carrying capacity of both the single- and double- shear specimens showed a non-linear increase to the notch length, specifically the increase of load-carrying capacity slows down once the notch length reaches 100mm. While their coefficients of ductility decreased by 47.5% and 82.2%, respectively, as the notch length increased from 50 to 150 mm. The loading rate showed slight effect on both the failure modes and the load-carrying capacity of specimens but significantly influenced their slip modulus and ductility. The analytical approximations of shear-slip response indicate that the proposed shear-slip response formula can capture the shear-slip behaviour, especially the post-peak behaviour of the connections effectively. Finally, a calculation model was developed for predicting the load-carrying capacity of the connections. The results indicate that the proposed calculation model can predict the shear capacity of the single-shear specimens effectively but underestimates the shear capacity of the double-shear specimens obviously.

The determination of the activity concentration of ²²²Rn is related to its emanation and the equilibrium reached with its short-lived gamma-emitting progeny, ²¹⁴Pb and ²¹⁴Bi. Previous studies conducted with hybrid and alkali-activated cements, both utilizing fly ash (FA), reflected ²²⁶Ra/²¹⁴Pb ratios significantly greater than 1. This study further investigates this disequilibrium by determining the ²²⁶Ra/²¹⁴Pb ratios in different cement pastes: (i) magnesium phosphate, (ii) blended with FA, (iii) hybrid with FA, (iv) alkali-activated with FA and metakaolin (MK) using various alkaline activators. The samples were measured by gamma spectrometry both in solid form and after grinding. The results showed ²²⁶Ra/²¹⁴Pb ratios of 1.3 for the ground pastes manufactured with 100% FA and using NaOH as the activator at different molarities (8 M, 10 M, and 12 M). Measurement of the samples with the addition of 2% (w/w) activated carbon showed that this effect was neutralized, resulting in ratios of 1, indicating equilibrium between ²²⁶Ra and ²¹⁴Pb. The measurement of the emanation coefficient (F_e) for the powdered solids obtained from the ground cubes showed that the emanations were higher than those of the anhydrous materials (cement (C), FA, and MK). This high emanation is primarily caused by NaOH activation, which induces microstructural changes in the cement pastes, leading to increased radon release. The highest emanations were 36.2% for samples derived from pastes alkali-activated with NaOH. Additionally, it was observed that ²²²Rn was lost by 5% from the cylindrical containers used for gamma spectrometry measurements when the F_e was 0.20 (20% emanation).

Aggregate content plays a critical role in governing both the rheological behavior and mechanical performance of 3D printed concrete (3DPC). This study investigates the impact of varying the aggregate-to-binder (A/B) ratio from 0.5 to 1.5, while maintaining a constant water-to-binder ratio, on the printability, mechanical behavior, and volumetric stability of 3DPC. A dual-parameter framework based on flowability and shape retention is proposed to define printability across different A/B ratios, offering a practical and generalizable alternative to rheometer-based evaluation. The experimental results demonstrate that the proposed dual-parameter framework effectively enables rapid evaluation of 3DPC printability. When both flowability and shape retention are maintained within appropriate ranges, 3DPC exhibits good printing performance. Mechanical testing reveals that increasing the A/B ratio above 1.25 reduces both compressive and flexural strength due to weakened matrix–aggregate bonding and interfacial failure. Furthermore, anisotropy in strength distribution emerges at extreme A/B values due to variable interlayer cohesion. Drying shrinkage is significantly reduced at higher A/B ratios, with a threshold of A/B ≥ 1.0 ensuring compliance with ACI volumetric stability standards. Notably, the binder contributes approximately 89% of the total CO₂ emissions associated with 3DPC. Consequently, the overall carbon emissions decrease markedly as the A/B ratio increases. An optimal A/B ratio of 1.25 is recommended for designing 3DPC, as it provides a well-balanced performance across mechanical strength, volumetric stability, and environmental sustainability.

This study investigates the hydration and mechanical properties of ternary blends incorporating metakaolin and various carbonates with different dissolution kinetics, including limestone, coral sand and dolomite. The hydration behavior and microstructure of these blends were analyzed using isothermal calorimetry, X-ray diffraction (XRD), thermogravimetric analysis (TGA), and mercury intrusion porosimetry (MIP). Results show that coral sand, primarily composed of aragonite with a faster dissolution rate, exhibits higher reactivity in ternary systems, demonstrating a more pronounced accelerating effect on the early hydration of cement compared to limestone and dolomite. Similar to limestone, the incorporation of coral sand promotes the formation of more carboaluminates and enhances ettringite stabilization compared to the dolomite-modified system, which predominantly forms strätlingite due to the lower dissolution rate of dolomite. The ternary blends containing coral sand and limestone achieved final comparable compressive strength to the dolomite-modified system, but exhibited higher flexural strength and lower brittleness coefficients. These findings suggest that, in ternary blends, the formation of carboaluminates play a more critical role for enhancing flexural strength and toughness of cementitious materials than for contributing to compressive strength.

Geopolymers typically exhibit low yield stress, which is beneficial in most conventional applications but poses limitations for emerging technologies such as 3D printing. This study investigates the use of quaternary ammonium compounds, each differing in the length and number of aliphatic chains, as admixtures to modify the rheological properties of metakaolin-based geopolymers. These admixtures caused a slight increase in the plastic viscosity, but a substantial increase in the yield stress up to 20 times. Time-dependent rheological measurements showed rapid structural recovery of the modified fresh geopolymer paste, which is particularly favourable for 3D printing applications. The dosage and number of long aliphatic chains played a critical role, with double-chained molecules proving more effective than their single-chained counterparts. The interactions of the admixtures with the particles in the fresh geopolymer paste were studied by surface tension and zeta potential measurements, as well as molecular dynamics simulations, which supported the observed rheological behaviour.