Cement & concrete composites最新文献

英文中文

Carbon sequestration in aggregate and concrete by encapsulated biochar and carbonation: Experiment and simulation

IF 10.8 1区工程技术 Q1 CONSTRUCTION & BUILDING TECHNOLOGY

Cement & concrete composites

Pub Date : 2025-02-16 DOI: 10.1016/j.cemconcomp.2025.105990

Shuai Zou , Xi Chen , Man Lung Sham , Jian-Xin Lu , Chi Sun Poon

Biochar is emerging as a novel method for carbon sequestration in concrete to reduce its carbon footprint, however, the high volume incorporation of biochar would unavoidably deteriorate the concrete performance due to biochar's drawbacks in high water absorption and low strength. Facing this conflict, a novel biochar-enabled core-shell aggregate (BCSA) developed by encapsulating biochar with cementitious materials was proposed for firstly overcoming biochar's drawbacks and then utilizing in concrete for carbon sequestration. The results showed that the optimal BCSA performance achieved a loose bulk density of 857 kg/m³, a crushing strength of 8.05 MPa, and a strength efficiency of 9393 Pa m³/kg. These properties were better than commercial sintered aggregate, indicating the advantages of the core-shell design technology in developing artificial aggregate. The BCSA-based concrete attained a density of 1778 kg/m³ and a compressive strength of 35.8 MPa, which maintained concrete with structural performance and realized high biochar usage of 92.8 kg/m³. Comparatively, the utilization of biochar showed greater promising in carbon sequestration than carbonation curing. Direct carbonation curing the fresh BCSA attained higher carbonation degree and CO₂ uptake than firstly sealing and then carbonation curing, which can be explained by its higher moisture pore walls, which helped both CO₂ migration and adsorption as indicated by the molecular dynamics simulation. In sum, BCSA and BCSA-based concrete respectively realized total 250.4 kg/t and 247.1 kg/m³ CO₂ sequestration, which indicates a great carbon storage potential and puts a new way of using biochar for producing aggregate and concrete with promising engineering application potentials.

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引用次数: 0

Leaching behavior of lithium slag at various pH conditions

IF 10.8 1区工程技术 Q1 CONSTRUCTION & BUILDING TECHNOLOGY

Cement & concrete composites

Pub Date : 2025-02-13 DOI: 10.1016/j.cemconcomp.2025.105985

Chaowei Zheng , Zuhua Zhang , Yingcan Zhu , Qiang Ren , John L. Provis , Qianqian Wang , Zhengwu Jiang

To explore possible safe valorization routines for lepidolite lithium slags (LS) in different cement systems, this paper investigates their fundamental composition features and dissolution mechanisms under various pH conditions. Lepidolite LS is mainly divided into two types: high calcium LS with mineral phases mainly composed of anorthite and gypsum, and low calcium LS mainly comprising nosean and leucite, together with a higher amorphous phase content (

>

24 %). The main reaction product of LS in NaHCO₃ solution is calcite, while the products in NaOH solution are Ca(OH)₂ and (K, N)-A-S-(H). The dissolution of the amorphous LS phase in NaOH solution occurs in 0–3 h and generates (K, N)-A-S-(H) gels in 3–8 h. The shrinking core model can be used to describe the dissolution process of LS in NaOH solution, which is controlled by a reaction product layer diffusion. The leached quantity of Be, Tl, Ni, and Mn is negatively correlated with the solution pH, and the leaching rate increases with increasing temperature. The concentration of S in the LS leachate is higher than 300 mg/L, which may pose a threat to the volume stability of cement in concrete. Based on these characterization results, dissolution models of LS in neutral, weakly alkaline, and aggressive alkaline solutions have been proposed, providing theoretical guidance for understanding the hydration of LS in different binders, further its utilization in various cases.

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引用次数: 0

Improving the carbonation resistance of supersulfated cement by nano SiO2 and silica fume

IF 10.8 1区工程技术 Q1 CONSTRUCTION & BUILDING TECHNOLOGY

Cement & concrete composites

Pub Date : 2025-02-12 DOI: 10.1016/j.cemconcomp.2025.105984

Heng Chen , Zhongxu Song , Binbin Liu , Guilong Sun , Pengkun Hou , Qinfei Li , Yang Wang , Pengyu Zhang , Xin Cheng

Supersulfated cement (SSC) is a low-carbon material with limited carbonation resistance due to its high content of easily carbonated components (AFt) and low content of carbonation-resistant components (C-(A)-S-H gel and portlandite). This study aims to utilize reactive siliceous materials (nano-silica (NS) and silica fume (SF)) to optimize the product composition of SSC and enhance its carbonation resistance. Incorporating 3 % of ultrasonic-dispersed/non-ultrasonic-dispersed NS and SF into SSC, this study explores their effects on the mechanical properties of SSC before and after carbonation, carbonation depth, phase composition, and micro-morphology. Results show that both SF and NS promote the hydration, increasing hydration products and compressive strength, with NS being more significantly. While SF increases the flexural strength, NS reduces it. NS could modify the morphology and structure of AFt and C-(A)-S-H gel, resulting in a better carbonation resistance effect than SF. Both ultrasonic-dispersed NS and non-ultrasonic-dispersed NS have almost the same effect on the performance of SSC, with undispersed NS slightly reducing flexural strength more. This study highlights the critical role of AFt in the flexural strength and reveals that increasing the content of C-(A)-S-H gel is crucial for enhancing carbonation resistance. Combination of NS and SF (or other ultrafine powders) offers a promising approach to improving the carbonation resistance of SSC.

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引用次数: 0

Enhancement mechanism of wet-carbonated recycled concrete aggregates subjected to calcium-rich and magnesium-rich industrial reclaimed wastewater sources

IF 10.8 1区工程技术 Q1 CONSTRUCTION & BUILDING TECHNOLOGY

Cement & concrete composites

Pub Date : 2025-02-12 DOI: 10.1016/j.cemconcomp.2025.105983

Ning Li, Cise Unluer

While efficient in enhancing recycled concrete aggregates' (RCAs) performance, wet carbonation demands significant amounts of water. Addressing this, we investigated carbonation of RCAs in tap-water (TW), concrete batching plant wash-water (WW), and reject brine (RB). Composition and microstructure of carbonated RCAs and their impact on reaction and mechanical properties of recycled aggregate concrete (RAC) were examined. Although the dissolution of Ca-containing components in RCAs was slower in WW, the high Ca(OH)₂ content in WW enhanced carbonation, leading to the formation of large calcite particles (1–2 μm). Despite a 56 % increase in RAC strength compared to the control, WW-RAC revealed slightly lower strengths than TW-RAC, which contained finer calcite particles (0.1–0.3 μm). The presence of Mg²⁺ in RB accelerated the dissolution of Ca components in RCAs due to the lower solubility product constant of Mg(OH)₂ compared to Ca(OH)₂, thereby promoting early-stage carbonation. As carbonation progressed, Mg²⁺ was recovered from the carbonation product into the solution, with a recovery rate of 94 %. This Mg-modification resulted in the formation of 0.1–0.3 μm calcite particles along with needle-shaped Mg-calcite, enhancing bond strength. Results demonstrated feasibility of using reclaimed industrial wastewater in enhancing CO₂ sequestration, while significantly improving RCAs’ properties.

湿法碳化虽然能有效提高再生混凝土骨料（RCA）的性能，但需要大量的水。为此，我们研究了在自来水（TW）、混凝土搅拌站冲洗水（WW）和废盐水（RB）中对 RCA 进行碳化的问题。研究了碳化 RCA 的成分和微观结构及其对再生骨料混凝土 (RAC) 的反应和机械性能的影响。虽然在 WW 中，RCA 中含钙成分的溶解速度较慢，但 WW 中的高 Ca(OH)2 含量增强了碳化作用，从而形成了大的方解石颗粒（1-2 μm）。尽管 RAC 强度比对照组提高了 56%，但 WW-RAC 的强度略低于 TW-RAC，因为 TW-RAC 中的方解石颗粒更细（0.1-0.3 μm）。由于 Mg（OH）2 的溶度积常数低于 Ca（OH）2，RB 中 Mg2+ 的存在加速了 RCA 中 Ca 成分的溶解，从而促进了早期碳化。随着碳化的进行，Mg2+ 从碳化产物中回收到溶液中，回收率高达 94%。这种镁改性形成了 0.1-0.3 μm 的方解石颗粒和针状镁方解石，增强了粘结强度。研究结果表明，利用回收的工业废水加强二氧化碳封存是可行的，同时还能显著改善 RCA 的性能。

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引用次数: 0

Hydration and physicochemical immobilization mechanisms of pozzolanic-hazardous waste in supersulfated cement

IF 10.8 1区工程技术 Q1 CONSTRUCTION & BUILDING TECHNOLOGY

Cement & concrete composites

Pub Date : 2025-02-10 DOI: 10.1016/j.cemconcomp.2025.105970

Jiaxing Ban , Jian-Xin Lu , Bin Ma , Ligang Peng , Hongjian Du , Dingqiang Fan , Jun Yao , Baoshan Xing , Chi Sun Poon

Ordinary Portland cement (OPC) is a versatile cement binder suitable for solidifying hazardous wastes, while its production induces significant carbon emissions. This study developed a novel low-carbon supersulphated phosphogypsum slag cement (SPSC) with the inclusion of pozzolanic-hazardous waste and investigated the synergetic mechanism of its pozzolanic reaction and immobilization behavior. The hydration characteristics of SPSC were explored using ionic chromatography, XRD, and hydration heat tests. The study also assessed the effectiveness of SPSC in immobilizing hazardous waste using toxicity characteristic leaching procedure and sequential extraction procedure tests, and explored these mechanisms through XRD, SEM, Zeta potential, NMR, and progressive leaching tests. The results indicate that the SPSC system is more effective in immobilizing hazardous waste than OPC. This superior performance is attributed to the lower Ca/Si ratio and higher Al/Si ratio in SPSC, which results in the formation of hydrates with more negative charges than OPC and thus stronger physical adsorption of heavy metals. Additionally, the longer gel chains with larger interlayer zones in SPSC contribute to better solidification of heavy metals. Larger amounts of ettringite in SPSC also aids the immobilization by facilitating the exchange of Al ions for heavy metals. The excess SO₄²⁻ in the pore solution of SPSC binder could help immobilize heavy metals by sulfate precipitation. Overall, this study provides new insights into the sustainable immobilization of hazardous waste by adopting SPSC.

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引用次数: 0

Optimization and performance regulation of pipe piles based on nano-calcium silicate hydrated (n-C-S-H)

IF 10.8 1区工程技术 Q1 CONSTRUCTION & BUILDING TECHNOLOGY

Cement & concrete composites

Pub Date : 2025-02-07 DOI: 10.1016/j.cemconcomp.2025.105977

Xiaofeng Han , Penggang Wang , Zijun Ling , Rihong Zhang , Zhenxing Du , Mengzhuo Sun , Xiaomeng Sui , Dongxuan Wei

Prestressed high-strength concrete (PHC) pipe piles are widely used in various construction projects. However, higher steam curing temperatures and times in the preparation of pipe piles severely affect material performance, while increasing cost and environmental pollution. This study investigates the use of nanoscale calcium-silicate-hydrate (n-C-S-H) to reduce curing temperature and time, ensuring high demoulding strength and short demoulding time of pipe piles. Samples with n-C-S-H content of 0 %, 1 %, 2 % and 4 % were examined under curing times of 6 and 8 h and temperatures of 60 °C and 80 °C. The results show that it is feasible to solve the problem of reduced strength of samples due to reduced temperature by adding n-C-S-H, and increasing the n-C-S-H content while decreasing the steam curing times is favourable to the compressive strength of the samples. Through lowering the curing temperature, time and n-C-S-H addition both optimize the pore structure of the samples and the delayed ettringite formation (DEF) can be prevented, also contributes greatly to the improvement of sample durability. The results provide valuable insights into the preparation of cementitious materials for pipe piles and contribute to the development of more durable and sustainable infrastructure materials.

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引用次数: 0

Digital-volume-correlation-assisted crack extraction using X-ray computed tomography images of cementitious materials

IF 10.8 1区工程技术 Q1 CONSTRUCTION & BUILDING TECHNOLOGY

Cement & concrete composites

Pub Date : 2025-02-07 DOI: 10.1016/j.cemconcomp.2025.105968

Shuxian Hong , Zhongbo Yuan , Disheng Pan , Chuan Kuang , Biqin Dong , Shengxin Fan

The image segmentation results for microcrack detection suffer from poor continuity and integrity due to noise, grayscale inhomogeneity, and the very small size of microcrack voxels. Strain information is introduced to aid crack recognition and reduce the impact of image accuracy on crack detection. A new crack detection method is proposed that combines image processing and digital volume correlation (DVC). This method detects and extracts microcracks with specific propagation directions, distinguishing them from pseudo-cracks. It also enhances the integrity of crack morphology analysis by incorporating both image and mechanical information (DVC) data. Furthermore, analysis of X-ray computed tomography (XCT) images of fractured rubber concrete specimens, along with optical microscope verification, demonstrates that this method is effective for visualizing and quantifying fracture patterns.

引用次数: 0

New insights into the retardation mechanism of phosphorus slag on the early cement hydration

IF 10.8 1区工程技术 Q1 CONSTRUCTION & BUILDING TECHNOLOGY

Cement & concrete composites

Pub Date : 2025-02-07 DOI: 10.1016/j.cemconcomp.2025.105963

Shiyu Zhuang , Qiang Wang , Yichen Shan , Ruiquan Jia , Zihan Zhou

Phosphorus slag (PS) is widely reported to retard the cement hydration due to the existence of phosphorus and fluorine in it. However, the key role and its corresponding mechanism have not been fully reported. In this study, the effects of PS on the early cement hydration were investigated from the insights of solid phases, aqueous species and microstructures evolution. Results show that PS remarkably prolongs the induction period and setting time, and delays the microstructure evolution of cement paste. PS retards the early hydration of C₃S, inhibiting the precipitation of C-S-H and portlandite, but promotes the hydration of C₃A. It is likely that the insoluble phosphorus-fluorine compound in PS plays a more important role in the retardation. The doping of calcium or silicon in the phosphorus-fluorine compound can restrict its retarding effect on the early cement hydration.

引用次数: 0

Development of 3D-printable alkali-activated GGBFS and fly ash binder-based mortars with concrete demolition waste as aggregates

IF 10.8 1区工程技术 Q1 CONSTRUCTION & BUILDING TECHNOLOGY

Cement & concrete composites

Pub Date : 2025-02-06 DOI: 10.1016/j.cemconcomp.2025.105954

M. Gurunandan , Aparna Sai Surya Sree Nedunuri , Jayant Tanwar , Prakash Nanthagopalan , Salman Muhammad

3D-printable alkali-activated mortar mixtures using concrete demolition waste (CDW) as aggregates, which are pumpable, extrudable, buildable up to 1000 mm with an open time of 180 minutes were developed in this study. The mixtures provided a minimum compressive strength of 50 MPa at 28 days age. The effect of various parameters such as binder composition, water-to-binder ratio, molar modulus and activator dosage on workability of the mixtures was investigated. The mixtures were assessed for pumpability, extrudability and buildability in fresh state and for compressive and splitting tensile strength in hardened state. The high workability mixtures (spread diameter>180 mm) recorded lower pumping pressure (<6 bar) and higher extrusion test discharge (>25 cm³/s at 25 rpm) inferring that they were easier to pump and extrude. However, they possessed lower strength (<1 kg) and stiffness (<2 kg/mm) at 20^th minute in empirical buildability test, leading to lower buildable height (100 mm). The mixtures with spread diameter of 135–165 mm having static yield stress of 1.8–2.4 kPa, were apt for 3D-printing as it was buildable (>500 mm) without compromising on pumpability and extrudability. FTIR, XRD and TGA studies revealed that the prolonged workable time was due to the formation of sodium carbonate resulting from the reaction of carbonate phases in CDW with sodium hydroxide. The printing process has not affected the mechanical properties of the mixtures and there is no cold joint formed between subsequently printed layers. The 3D-printed specimens exhibited an anisotropic index of less than 0.30 indicating that they were isotopic in compression.

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引用次数: 0

Tensile behavior simulation of ECC/SHCC at subzero temperatures based on a fiber/interface combination constitutive model

IF 10.8 1区工程技术 Q1 CONSTRUCTION & BUILDING TECHNOLOGY

Cement & concrete composites

Pub Date : 2025-02-06 DOI: 10.1016/j.cemconcomp.2025.105969

Yanlin Huo , Xiaoyu Han , Chunran Wu , Dong Lu , Huayang Sun , Zhitao Chen , Yingzi Yang , Victor C. Li

The performance degradation of Engineered Cementitious Composites/Strain-hardening cementitious composites (ECC/SHCC) at subzero temperatures is becoming a widespread concern. However, experimental testing and data acquisition in cold environments are very difficult and demanding. It is an inevitable trend to use numerical simulation for research. In this paper, a finite element model based on a fiber/interface combination constitutive model was proposed to simulate the tensile behavior of SHCC at subzero temperatures. While the validity of the model was verified using 16 groups of tests, the reduction in multiple cracking and the increased proportion of fiber and interface failures induced with decreasing temperature were explored. The effect of matrix cracking strength on the tensile properties of SHCC was further compared. It was found that a lower matrix cracking strength could help SHCC to maintain high ductility at −60 °C, and the tensile strain capacity could reach 6.58 %. Therefore, it is crucial to control the matrix cracking strength in the design and application of SHCC in cold regions. The simulation method in this paper is expected to provide new insights for the development of high ductility SHCC in winter climate.

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引用次数: 0

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