CEMENT最新文献

英文中文

Effect of ultrasonication on sucrose structure and its influence on controlled retardation of earth-based alkali-activated materials

CEMENT

Pub Date : 2024-12-20 DOI: 10.1016/j.cement.2024.100127

Pitabash Sahoo, Souradeep Gupta

Excavated soil from construction and demolition activities can be stabilized by alkali-activated binders to manufacture low-carbon construction materials. This research attempts to investigate the efficacy of non-sonicated (S) and sonicated sucrose (USS) as a controlled retarder in alkali-activated materials containing excavated lateritic soil (EAAM) (clay content of 42.5 %). Influences of sucrose dosage and sonication on hydration kinetics, setting, and structural build-up of EAAM have been investigated. Findings from isothermal calorimetry show 30 – 65 % retardation in hydration kinetics leading to a 50 – 60 % delay in setting and slower structural build-up of EAAM during the initial 12 h. This results in higher flowability and superior flow retention for longer duration than the control (0 % sucrose). By decoupling the effect on hydration of GGBS and FA, it is found that sucrose has a more dominant retarding effect on GGBS compared to FA, attributed to its stronger interaction with calcium-rich sites than aluminates. The addition of 2 % USS to EAAM results in higher retardation compared to 2 %S. This is attributed to the formation of acidic byproducts due to sonication-induced breakdown of sucrose molecules, leading to reduced pH and electrostatic repulsion. The densified microstructure of EAAM with USS compared to that with S results in a noticeable improvement in strength retention under wet conditions, suggesting reduced moisture sensitivity. Due to enhanced hydration at later ages, sucrose-EAAM possesses 30 – 48 % higher wet compressive strength than the control EAAM at the 28-day mark. Overall, sucrose, which can be prepared from waste biomass through “green” processes, can be a potential chemical admixture for earth-based alkali-activated constructions.

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引用次数: 0

Synergistic effects of silica fume, nanomaterials and inorganic salts on the hydration and compressive strength of low-density oil well cement slurry

CEMENT

Pub Date : 2024-12-19 DOI: 10.1016/j.cement.2024.100125

Kenedy Geofrey Fikeni , Xueyu Pang , Yukun Zhao , Shenglai Guo , Jie Ren , Kaihe Lv , Jinsheng Sun

During offshore cementing at shallow depth, the low-temperature environment at the bottom of the sea and the low-density requirement of the cement slurry significantly hinder the strength development of oil well cement systems. Hence there is always a strong need to take various measures to enhance the strength development of low-density oil well cement systems. During this study, potential synergistic effects of silica fume, nanomaterials (C-S-H nano-seeds, nano-silica, nano-alumina), and inorganic salts (CaCl₂, NaCl, Na₂SiO₃) to improve the strength of low-density well cement slurry were investigated. Water-to-cement ratio (w/c) was varied between 1.04 and 1.28 to obtain a constant slurry density of 1.5 g/cm³. Test results revealed that the addition of silica fume altered the rheology and flow behavior of low-density cement slurries, resulting in flat rheology profiles at high shear rates. The Bingham plastic model can describe the rheological behavior of cement slurries without silica fume, whereas the Power-law model is more suitable to cement slurries with silica fume. High-dosage silica fume (30 %) is shown to have similar acceleration capability as the strongest nanomaterial accelerator (i.e. C-S-H nano-seeds) at 2 % dosage. However, adding nanomaterials to silica-fume-enriched slurries cannot further increase the hydration rate of cement (i.e. no synergistic effect), possibly due to their similar acceleration mechanism. In contrast, adding chloride-based inorganic salts to silica-fume-enriched slurries further increased the hydration rate of cement significantly, exhibiting a strong synergistic effect. Based on the 7-day compressive strength test results at 15°C, the addition of silica fume or nanomaterials individually can increase the strength of neat cement by up to 92 %, while the combined addition of silica fume and NaCl can increase its strength by 306 %.

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引用次数: 0

Sanitary ware waste in eco-friendly Portland blended cement: Potential use as supplementary cementitious material

CEMENT

Pub Date : 2024-12-19 DOI: 10.1016/j.cement.2024.100126

Vitor Affonso Lopes Silveira, Domingos Sávio de Resende, Augusto Cesar da Silva Bezerra

The sanitary ware industry led to significant waste generation with a long biodegradation period. To produce eco-friendly Portland blended cement, partial Portland cement (PC) substitution is proposed, reducing clinker consumption and mitigating adverse environmental impacts. This paper assessed the pozzolanic activity and the filler effect of clay-based sanitary ware waste (CSW) to study its feasibility of reutilization as a supplementary cementitious material (SCM). After being collected, the samples underwent a preparation process consisting of drying and sieving. The waste replaced 0 to 25 wt% PC. The CSW powder was characterized by laser diffraction granulometry, X-ray diffraction (XRD), X-ray fluorescence, and scanning electron microscopy (SEM). The pozzolanic activity was assessed by compressive strength test, isothermal calorimetry, and electrical conductivity. Durability was considered by acid attack, and the hardened mortar proprieties were shown. The utilization of CSW blended with PC is feasible for producing eco-friendly binders.

引用次数: 0

Potential of Saudi Arabian bauxite to produce low-carbon cement

CEMENT

Pub Date : 2024-12-14 DOI: 10.1016/j.cement.2024.100124

S. Pavia , O. Alelweet

To produce calcium aluminate cement (CAC), bauxites are usually fused with lime/limestone at high temperature (1600 °C). At this temperature, the bauxite´s hydrates of alumina break down - dehydroxylation - and combine with calcium forming monocalcium aluminate (CA), the principal active phase in CAC.

A previous study evidenced that the Saudi bauxite begins dehydroxylation at low temperature (300 °C). This paper investigates whether low temperature can produce a cement, to reduce the carbon footprint of cement production. Cements are sintered by fusing the bauxite with calcium sources (limestone and quicklime) at temperatures from 600 to 1200 °C.

The results evidenced that limestone fusion is the most efficient method, as it renders hydraulic phases at 800 °C (C₁₂A₇) and 1000 °C (haüyne). The early release of Ca²⁺ from the limestone acts as a flux, lowering the breakdown point of the bauxite´s components. C₁₂A₇ (mayenite) which can speed up hydration and setting, appears widely in the limestone-bauxite cements, beginning at 800 °C and remaining stable up to 1200 °C.

The bauxite´s gypsum released sulphur, affording the sintering of calcium-sulfoaluminate (haüyne) at 1000 °C. Therefore, the bauxite can produce sulfoaluminate cement, a green cement which can reduce carbon emissions and fight climate change.

The bauxite´s high silica content and the breakdown of its kaolinite polymorph nacrite, facilitate the production of hydraulic calcium silicate clinkers (belite, andradite, gehlenite, wollastonite and prehnite) which afford strength on hydration.

The fluxing action of iron, aluminium and sulphur, significant in the bauxite, lowered the clinkering temperature.

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引用次数: 0

Workability, compressive strength, and efflorescence characteristics of one-part mix alkali-activated circulating fluidised bed combustion fly ash-based mortars

CEMENT

Pub Date : 2024-12-01 DOI: 10.1016/j.cement.2024.100123

Jason Shun Fui Pei , Chung Siung Choo , Deni Shidqi Khaerudini , Sing Muk Ng , Dominic Ek Leong Ong , Melvina Tan , Jaka Sunarso

In this study, one-part alkali-activated mortars are formulated using circulating fluidised bed combustion (CFBC) fly ash, derived from lignite (brown coal) combustion, as the precursor, and sodium hydroxide (NaOH) and sodium metasilicate (Na₂SiO₃) as the solid activators. Experimental findings indicate that an increase in solid activator-to-precursor ratio correlates with improved workability and compressive strength of the mortars. The influence of Na₂SiO₃-to-NaOH ratio on the compressive strength of the mortars is apparent only in mixes with a high solid activator-to-precursor ratio of 0.4 and 0.5, indicating its relatively lesser significance compared to the solid activator-to-precursor ratio. The mechanism through which an increase in the solid activator-to-precursor ratio improves the compressive strength of the mortars is elucidated using attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy. The results indicate that increasing the solid activator-to-precursor ratio enhances the degree of alkali-activation for fly ash, thereby improving the compressive strength with increasing solid activator-to-precursor ratio.

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引用次数: 0

Co-calcination to produce a synergistic blend of bauxite residue and low-grade kaolinitic clay for use as a supplementary cementitious material 通过共煅烧产生铝矾土渣和低品位高岭土的协同混合物，用作胶凝补充材料

CEMENT

Pub Date : 2024-11-15 DOI: 10.1016/j.cement.2024.100122

Arne Peys , Athina Preveniou , David Konlechner , Guilherme Rubio , Maria Georgiades , Rupert J. Myers , Natalia Pires Martins , Efthymios Balomenos , Panagiotis Davris , Ruben Snellings , Ken Evans

New sources of reactive supplementary cementitious materials (SCMs) are essential to help the cement industry to further lower CO₂ emissions. A co-calcination process in which bauxite residue (BR) is mixed with kaolinitic clay before calcination can deliver such SCM. The main novelty of the work discussed here is that acceptable reactivity as a SCM can be reached when co-calcining the BR with clays having only 40 wt% of kaolinite. The use of such low-grade kaolinitic clay greater increases the process economics and therefore likely increases overall feasibility. A high inherent reactivity of the desilication products present in the BR is the cause of this ability of using low-grade kaolinitic clays. Cement mortars were made with 30 wt% replacement of CEM I, which showed adequate strength at 28 days and increased strength in comparison with calcined clays or other SCMs in the literature at early age (2–7 days). A wide process temperature window with relatively constant reactivity was observed, but a range of 700–750 °C is recommended for process stability. In addition, a life-cycle assessment underlines that at these conditions a sufficiently low embodied CO₂ relative to Portland clinker production is obtained.

要帮助水泥行业进一步降低二氧化碳排放量，必须要有新的活性胶凝补充材料（SCM）来源。矾土渣（BR）在煅烧前与高岭土混合的共煅烧工艺可以提供这种 SCM。本文所讨论的工作的主要新颖之处在于，当铝矾土渣与仅含 40 wt% 高岭石的粘土进行共煅烧时，可以达到可接受的反应活性，作为一种 SCM。使用这种低品位的高岭土可以提高工艺的经济性，从而提高整体可行性。BR 中存在的脱硅产物的高固有反应性是使用低级高岭土的原因。用 30 wt%的 CEM I 替代物制作水泥砂浆，28 天时强度足够，与文献中的煅烧粘土或其他单质材料相比，在早期龄期（2-7 天）强度更高。观察到的工艺温度窗口较宽，反应活性相对稳定，但为了工艺稳定性，建议温度范围为 700-750 °C。此外，生命周期评估强调，在这些条件下，相对于波特兰熟料生产，二氧化碳的体现量足够低。

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引用次数: 0

Downstream processing of End-of-Life concrete for the recovery of high-quality cementitious fractions 对报废混凝土进行下游处理以回收优质胶凝组分

CEMENT

Pub Date : 2024-11-06 DOI: 10.1016/j.cement.2024.100121

A.T.M. Alberda van Ekenstein , H.M. Jonkers , M. Ottelé

The clinker in cement largely determines the environmental footprint of concrete. Therefore, concrete recycling should focus on retrieving high-quality cementitious fractions to replace clinker. This requires a shift from current traditional recycling techniques towards innovative recycling methods, enabling recovery of not only clean secondary aggregates, but also residual cementitious fines (RCF), potentially eliminating the carbon dioxide emissions associated with them. The production and upcycling of RCF offer new implementation routes that were previously deemed unfeasible. However, the properties of RCF may vary based on their origin, affecting their replacement and upcycling potential. Consequently, assessing the original concrete quality, with a focus on the binder type, before demolition is important. A handheld x-ray fluorescence technique appears promising for this purpose. To achieve effective separation of clean secondary aggregates from the original cementitious content, innovative crushing and separation techniques are needed. Additionally, electrostatic separation shows significant research potential for further optimizing RCF.

水泥中的熟料在很大程度上决定了混凝土的环境足迹。因此，混凝土回收应侧重于回收高质量的胶凝组分来替代熟料。这就要求从目前的传统回收技术转向创新的回收方法，不仅能够回收干净的二次骨料，还能回收残余胶凝细粒（RCF），从而消除与之相关的二氧化碳排放。RCF 的生产和升级再循环提供了新的实施途径，这在以前被认为是不可行的。然而，RCF 的特性可能因其来源而异，从而影响其替代和再循环潜力。因此，在拆除之前评估原始混凝土质量（重点是粘合剂类型）非常重要。手持式 X 射线荧光技术在这方面似乎大有可为。为了从原始胶凝成分中有效分离出干净的二次集料，需要采用创新的破碎和分离技术。此外，静电分离技术在进一步优化 RCF 方面也具有巨大的研究潜力。

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引用次数: 0

The impact of relative humidity on the nanoindentation relaxation in calcium silicate hydrates 相对湿度对硅酸钙水合物纳米压痕松弛的影响

CEMENT

Pub Date : 2024-10-16 DOI: 10.1016/j.cement.2024.100120

Zhao Chen , Jessy Frech-Baronet , Hang Tran , Luca Sorelli

Despite extensive research efforts, understanding the time-dependent behavior of concrete remains an enigma due to the complex nature of cement microstructure. In this study, the statistical nanoindentation was employed to investigate the influence of relative humidity (RH) on the relaxation behavior of calcium silicate hydrates (C-S-H) in a cement paste. Our experiments, performed at RH levels of 33 % and 86 %, revealed significant enhancements in both the indentation modulus and hardness of the C-S-H as RH increased. Remarkably, the internal water exerted a significant influence on the asymptotic relaxation behavior, displaying a clear power-law fashion. Further analysis identified the presence of short- and long-term viscoelastic behaviors within the C-S-H, distinguished by a transition observed within the initial seconds. These findings advance the understanding of nanoscale mechanisms driving concrete creep under different humidity conditions.

尽管进行了大量研究，但由于水泥微观结构的复杂性，对混凝土随时间变化的行为的理解仍然是一个谜。本研究采用统计纳米压痕法研究相对湿度（RH）对水泥浆中硅酸钙水合物（C-S-H）松弛行为的影响。我们在相对湿度为 33% 和 86% 的条件下进行的实验表明，随着相对湿度的增加，C-S-H 的压痕模量和硬度都有显著提高。值得注意的是，内部水分对渐进松弛行为产生了重大影响，呈现出明显的幂律模式。进一步分析发现，C-S-H 中存在短期和长期粘弹性行为，并在最初几秒钟内出现了过渡。这些发现加深了人们对不同湿度条件下混凝土徐变的纳米级驱动机制的理解。

引用次数: 0

Low-grade fly ash in portland cement blends: A decoupling approach to evaluate reactivity and hydration effects 硅酸盐水泥掺合料中的低标号粉煤灰：评估反应性和水化效应的解耦方法

CEMENT

Pub Date : 2024-10-04 DOI: 10.1016/j.cement.2024.100119

Qingxu Jin , Wenyu Liao , Xiaoqiang Ni , Hongyan Ma

Fly ash with low glass content is often prohibited from use in concrete due to the low reactivity and/or the inclusion of contaminants. However, the scarcity of high-quality fly ash promotes the evaluation of the feasibility of using fly ash with low glass content (e.g., low-grade fly ash) in concrete. This study proposes a decoupling method to quantitatively estimate the degree of reaction of fly ash with extremely low glass content, which partially replaces cement, and the degree of hydration of the hosting cement, simultaneously. The estimation is derived from the contents of calcium hydroxide and chemically bonded water in hydrated binary cement pastes, which can be determined by thermogravimetric analysis-based experiments and theoretically validated stoichiometric parameters. The results exhibit that the fly ash tends to retard the early-age hydration of cement but promotes its later-age hydration, resulting in a higher ultimate degree of reaction of cement than the reference paste. The microstructural and porosity evaluation shows that the fly ash, though has relatively low degrees of reaction due to its low glass content, can result in a more tortuous pore network of the hydrated pastes, which could be potentially more resistant to the penetration of water and aggressive chemicals.

玻璃含量低的粉煤灰由于反应活性低和/或含有污染物，通常被禁止用于混凝土中。然而，优质粉煤灰的稀缺促进了对在混凝土中使用低玻璃含量粉煤灰（如低等级粉煤灰）可行性的评估。本研究提出了一种解耦方法，可同时定量估算部分取代水泥的玻璃含量极低的粉煤灰的反应程度和宿主水泥的水化程度。估算值来自水化二元水泥浆中氢氧化钙和化学键水的含量，可通过基于热重分析的实验和理论验证的化学计量参数确定。结果表明，粉煤灰往往会延缓水泥的早期水化，但会促进其后期水化，从而使水泥的最终反应度高于参考浆体。微观结构和孔隙率评估结果表明，粉煤灰虽然因其玻璃含量低而反应度相对较低，但却能使水化浆料的孔隙网络更加曲折，从而可能更能抵御水和侵蚀性化学品的渗透。

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引用次数: 0

Accelerating effect of low replacements of carbonaceous materials in cement paste and mortar 水泥浆和砂浆中碳质材料低替代率的加速效应

CEMENT

Pub Date : 2024-09-30 DOI: 10.1016/j.cement.2024.100118

Victor Brial, Thomas Duplessis, Claudiane M. Ouellet-Plamondon

This study investigated the effect of incorporating small amounts of carbonaceous materials in cement paste and mortar systems at a low dosage. The materials studied include industrial graphite, natural graphite, carbon black, activated charcoal, and decolorized charcoal. The effect of this material on cement hydration through different techniques such as compressive strength mortar, TGA, SEM, isothermal calorimetry, rheology, and calcium isotherm adsoprtion. These tests studied the influence of carbonaceous materials’ properties on cement hydration. With the exception of industrial graphite G1, the carbonaceous materials showed an acceleration of setting after 1 day by favoring the nucleation of hydrates, reducing the porosity, and improving the mechanical properties. On the other hand, traces of this acceleration are no longer visible beyond 28 days. The accelerating effect of different carbons sources appears to be less dependent of crystallinity, mineralogy, or particle size, but rather on surface chemistry and the quality of particle dispersion.

本研究调查了在水泥浆和砂浆系统中加入少量低剂量碳质材料的效果。研究的材料包括工业石墨、天然石墨、炭黑、活性炭和脱色炭。通过不同的技术，如抗压强度砂浆、热重分析、扫描电镜、等温量热、流变学和钙等温吸附等，研究了这些材料对水泥水化的影响。这些测试研究了碳质材料的特性对水泥水化的影响。除工业石墨 G1 外，其他碳质材料在 1 天后通过促进水化物成核、降低孔隙率和改善机械性能，显示出加速凝结的作用。另一方面，这种加速的痕迹在 28 天后就不再明显。不同碳源的加速效果似乎与结晶度、矿物学或颗粒大小的关系不大，而是取决于表面化学和颗粒分散的质量。

引用次数: 0

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