Reactive MgO cement (RMC) is a novel binder formed through the hydration and carbonation of MgO, but its low reactivity hinders its wider application. Preliminary research has suggested that citric acids can form compounds with Mg2+ that regulate these processes, but the mechanism is yet to be understood well. This study investigated the effects of citric acids on the fresh and hardened properties of RMC. Results showed that the shear yield stress and plastic viscosity of the RMC pastes decreased with the addition of citric acids. Under standard curing, 4 wt% and 8 wt% citric acids increased the compressive strength of RMC by ∼100 % at 14 days. The adsorption of citrate on MgO inhibited the formation of brucite, forming an amorphous network-like microstructure crystallised after 14 days. Under CO2 curing, the compressive strength of RMC with 8 wt% citric acids increased by 12 % at 14 days, which could be ascribed to the porous microstructure formed that promotes the uptake of CO2 and the densification of the microstructure.
{"title":"Regulating hydration and microstructure development of reactive MgO cement by citric acids","authors":"Huanhuan Wang , Shuang Liang , Xiangming Zhou , Pengkun Hou , Xin Cheng","doi":"10.1016/j.cemconcomp.2024.105832","DOIUrl":"10.1016/j.cemconcomp.2024.105832","url":null,"abstract":"<div><div>Reactive MgO cement (RMC) is a novel binder formed through the hydration and carbonation of MgO, but its low reactivity hinders its wider application. Preliminary research has suggested that citric acids can form compounds with Mg<sup>2+</sup> that regulate these processes, but the mechanism is yet to be understood well. This study investigated the effects of citric acids on the fresh and hardened properties of RMC. Results showed that the shear yield stress and plastic viscosity of the RMC pastes decreased with the addition of citric acids. Under standard curing, 4 <em>wt</em>% and 8 <em>wt</em>% citric acids increased the compressive strength of RMC by ∼100 % at 14 days. The adsorption of citrate on MgO inhibited the formation of brucite, forming an amorphous network-like microstructure crystallised after 14 days. Under CO<sub>2</sub> curing, the compressive strength of RMC with 8 <em>wt</em>% citric acids increased by 12 % at 14 days, which could be ascribed to the porous microstructure formed that promotes the uptake of CO<sub>2</sub> and the densification of the microstructure.</div></div>","PeriodicalId":9865,"journal":{"name":"Cement & concrete composites","volume":"155 ","pages":"Article 105832"},"PeriodicalIF":10.8,"publicationDate":"2024-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142562255","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-11-01DOI: 10.1016/j.cemconcomp.2024.105829
Qingsong Zhou , Amr Meawad , Wei Wang , Takafumi Noguchi
In this study, a two-step carbonation method is developed to control the formation of calcium carbonate (Cc) polymorphs on the surface of recycled hardened cement paste (RHCP) without the use of chemical additives. In the first step, RHCP undergoes semi-dry carbonation under controlled humidity conditions, followed by wet carbonation at various temperatures in the second step. The results show that vaterite and aragonite are stabilized during the wet carbonation process, forming primarily on the surface of RHCP particles. The stabilization of the metastable Cc phases is driven by the synergistic effect of existing Cc seeds in the RHCP and the reaction temperature. A temperature range of 9–48 °C promotes the formation of vaterite, while higher temperatures (60–90 °C) lead to its dissolution. The calcite seeds present in RHCP do not enhance the formation of vaterite and aragonite during wet carbonation. This method offers a potential practical approach for valorizing concrete waste while capturing CO₂ from the atmosphere.
本研究开发了一种两步碳化法，可在不使用化学添加剂的情况下控制再生硬化水泥浆（RHCP）表面碳酸钙（Cc）多晶体的形成。第一步，RHCP 在可控湿度条件下进行半干碳化，第二步在不同温度下进行湿碳化。结果表明，在湿碳化过程中，脉石和文石得到稳定，主要在 RHCP 颗粒表面形成。在 RHCP 中现有 Cc 种子和反应温度的协同作用下，可稳定的 Cc 相得以稳定。9-48°C 的温度范围可促进钒铁矿的形成，而较高的温度（60-90°C）则会导致其溶解。在湿碳化过程中，RHCP 中存在的方解石种子不会促进钒钾矿和文石的形成。这种方法为混凝土废料的价值化提供了一种潜在的实用方法，同时还能从大气中捕获二氧化碳。
{"title":"Stabilization of metastable calcium carbonate polymorphs on the surface of recycled cement paste particles: A two-step carbonation approach without chemical additives","authors":"Qingsong Zhou , Amr Meawad , Wei Wang , Takafumi Noguchi","doi":"10.1016/j.cemconcomp.2024.105829","DOIUrl":"10.1016/j.cemconcomp.2024.105829","url":null,"abstract":"<div><div>In this study, a two-step carbonation method is developed to control the formation of calcium carbonate (<em>Cc</em>) polymorphs on the surface of recycled hardened cement paste (RHCP) without the use of chemical additives. In the first step, RHCP undergoes semi-dry carbonation under controlled humidity conditions, followed by wet carbonation at various temperatures in the second step. The results show that vaterite and aragonite are stabilized during the wet carbonation process, forming primarily on the surface of RHCP particles. The stabilization of the metastable <em>Cc</em> phases is driven by the synergistic effect of existing <em>Cc</em> seeds in the RHCP and the reaction temperature. A temperature range of 9–48 °C promotes the formation of vaterite, while higher temperatures (60–90 °C) lead to its dissolution. The calcite seeds present in RHCP do not enhance the formation of vaterite and aragonite during wet carbonation. This method offers a potential practical approach for valorizing concrete waste while capturing CO₂ from the atmosphere.</div></div>","PeriodicalId":9865,"journal":{"name":"Cement & concrete composites","volume":"155 ","pages":"Article 105829"},"PeriodicalIF":10.8,"publicationDate":"2024-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142562167","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-11-01DOI: 10.1016/j.cemconcomp.2024.105830
Yamei Cai , Xiaohong Zhu , Keke Sun , Kesheng Yin , Dongxing Xuan , Chi Sun Poon
This study compared the sulphate resistance of deionized water (DI)- and seawater (SW)-mixed cementitious materials based mainly on microstructural observations. The results show that, after a 450-day exposure to 50 g/L Na2SO4 solution, there was an increase in the mean chain length and polymerization degree of the remaining silicate chains in C-S-H gel for both DI- and SW-mixed pastes at a depth of 0–2 mm from the exposed surface. Notably, the Ca leaching of C-S-H gel in the SW-mixed paste at depths larger than 0.3 mm was slightly less than that in the DI-mixed one, despite the Ca leaching in both samples was comparable at a depth of 0.1 mm. For the aluminate phase, the mass loss and length change of the SW-mixed C3A mortar were lower than that of the DI-mixed C3A mortar, after immersing in 50 g/L Na2SO4 solution at different times. It seemed that more expansive product can be accommodated in the SW-mixed C3A matrix. Consequently, fewer cracks deposited by gypsum were observed in SW-mixed paste than in DI-mixed paste. The above were responsible for relatively less compressive strength loss of the SW-mixed mortars suffering from sulphate attack for 450 d.
{"title":"Degradation mechanism of seawater-mixed cementitious material subjecting to sulphate attack","authors":"Yamei Cai , Xiaohong Zhu , Keke Sun , Kesheng Yin , Dongxing Xuan , Chi Sun Poon","doi":"10.1016/j.cemconcomp.2024.105830","DOIUrl":"10.1016/j.cemconcomp.2024.105830","url":null,"abstract":"<div><div>This study compared the sulphate resistance of deionized water (DI)- and seawater (SW)-mixed cementitious materials based mainly on microstructural observations. The results show that, after a 450-day exposure to 50 g/L Na<sub>2</sub>SO<sub>4</sub> solution, there was an increase in the mean chain length and polymerization degree of the remaining silicate chains in C-S-H gel for both DI- and SW-mixed pastes at a depth of 0–2 mm from the exposed surface. Notably, the Ca leaching of C-S-H gel in the SW-mixed paste at depths larger than 0.3 mm was slightly less than that in the DI-mixed one, despite the Ca leaching in both samples was comparable at a depth of 0.1 mm. For the aluminate phase, the mass loss and length change of the SW-mixed C<sub>3</sub>A mortar were lower than that of the DI-mixed C<sub>3</sub>A mortar, after immersing in 50 g/L Na<sub>2</sub>SO<sub>4</sub> solution at different times. It seemed that more expansive product can be accommodated in the SW-mixed C<sub>3</sub>A matrix. Consequently, fewer cracks deposited by gypsum were observed in SW-mixed paste than in DI-mixed paste. The above were responsible for relatively less compressive strength loss of the SW-mixed mortars suffering from sulphate attack for 450 d.</div></div>","PeriodicalId":9865,"journal":{"name":"Cement & concrete composites","volume":"155 ","pages":"Article 105830"},"PeriodicalIF":10.8,"publicationDate":"2024-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142562166","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-10-30DOI: 10.1016/j.cemconcomp.2024.105816
Jun-Jie Zeng , Xianwen Hu , Hou-Qi Sun , Yue Liu , Wei-Jian Chen , Yan Zhuge
The layered deposition process of 3D concrete printing can lead to reduced mechanical properties at the interfaces between filaments. To address this limitation, external confinement devices, such as fiber-reinforced polymer (FRP) wrapping, have been proposed to enhance the strength of 3D-printed concrete concrete. Achieving this requires a solid understanding of the triaxial mechanical performance of 3D-printed concrete. This study presents an experimental investigation of the triaxial compressive behavior of 3D-printed PE fiber-reinforced ultra-high performance concrete (3DP-PEUHPC). A total of 16 pairs of concrete cubes were prepared, including mold-cast and 3D-printed specimens, and subjected to uniaxial and triaxial compression tests. The results revealed that the 3D-printed specimens exhibited either column-type or diagonal shear failures under triaxial compression. Weak bonding was observed at both filament-fusion and layer-fusion interfaces, with these weaker bonding interfaces, particularly when aligned parallel to the axial load, showing susceptibility to stress concentration and crack initiation. This led to a reduction in load-bearing capacity of the 3D-printed specimens compared to the mold-cast specimens. Importantly, as confining stresses increase, the difference in compressive strength between 3D-printed and mold-cast specimens decreases, highlighting the effectiveness of confinement in mitigating the directional weaknesses inherent in 3D-printed concrete. This paper also presents a modified model for predicting the axial stress-strain relationship of 3DP-PEUHPC under confinement, providing insights into the mechanism of FRP confinement on the compressive strength of 3D-printed concrete structures.
三维混凝土打印的分层沉积过程会导致长丝界面的机械性能降低。为解决这一局限性，有人提出了外部约束装置，如纤维增强聚合物（FRP）包裹，以增强三维打印混凝土的强度。要实现这一目标，需要对三维打印混凝土的三轴力学性能有扎实的了解。本研究对三维打印聚乙烯纤维增强超高性能混凝土（3DP-PEUHPC）的三轴抗压行为进行了实验研究。共制备了 16 对混凝土立方体，包括模铸试件和 3D 打印试件，并对其进行了单轴和三轴压缩试验。结果表明，三维打印试样在三轴压缩下表现出柱状或对角线剪切破坏。在丝融合和层融合界面上都观察到了较弱的粘合，这些较弱的粘合界面，尤其是与轴向载荷平行排列时，容易出现应力集中和裂纹萌生。这导致 3D 打印试样的承载能力低于模铸试样。重要的是，随着约束应力的增加，三维打印试样与模铸试样之间的抗压强度差异也在减小，这凸显了约束在减轻三维打印混凝土固有的方向性弱点方面的有效性。本文还提出了一个修正模型，用于预测约束下 3DP-PEUHPC 的轴向应力-应变关系，为了解 FRP 约束对 3D 打印混凝土结构抗压强度的影响机制提供了见解。
{"title":"Triaxial compressive behavior of 3D printed PE fiber-reinforced ultra-high performance concrete","authors":"Jun-Jie Zeng , Xianwen Hu , Hou-Qi Sun , Yue Liu , Wei-Jian Chen , Yan Zhuge","doi":"10.1016/j.cemconcomp.2024.105816","DOIUrl":"10.1016/j.cemconcomp.2024.105816","url":null,"abstract":"<div><div>The layered deposition process of 3D concrete printing can lead to reduced mechanical properties at the interfaces between filaments. To address this limitation, external confinement devices, such as fiber-reinforced polymer (FRP) wrapping, have been proposed to enhance the strength of 3D-printed concrete concrete. Achieving this requires a solid understanding of the triaxial mechanical performance of 3D-printed concrete. This study presents an experimental investigation of the triaxial compressive behavior of 3D-printed PE fiber-reinforced ultra-high performance concrete (3DP-PEUHPC). A total of 16 pairs of concrete cubes were prepared, including mold-cast and 3D-printed specimens, and subjected to uniaxial and triaxial compression tests. The results revealed that the 3D-printed specimens exhibited either column-type or diagonal shear failures under triaxial compression. Weak bonding was observed at both filament-fusion and layer-fusion interfaces, with these weaker bonding interfaces, particularly when aligned parallel to the axial load, showing susceptibility to stress concentration and crack initiation. This led to a reduction in load-bearing capacity of the 3D-printed specimens compared to the mold-cast specimens. Importantly, as confining stresses increase, the difference in compressive strength between 3D-printed and mold-cast specimens decreases, highlighting the effectiveness of confinement in mitigating the directional weaknesses inherent in 3D-printed concrete. This paper also presents a modified model for predicting the axial stress-strain relationship of 3DP-PEUHPC under confinement, providing insights into the mechanism of FRP confinement on the compressive strength of 3D-printed concrete structures.</div></div>","PeriodicalId":9865,"journal":{"name":"Cement & concrete composites","volume":"155 ","pages":"Article 105816"},"PeriodicalIF":10.8,"publicationDate":"2024-10-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142541710","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-10-30DOI: 10.1016/j.cemconcomp.2024.105827
Pietro Lura , Nikolajs Toropovs , Janis Justs , Mahdieh Shakoorioskooie , Beat Münch , Michele Griffa
In this study, a number of different fibers - namely kenaf, jute, abaca, coir and sisal - were investigated as natural alternatives to polypropylene (PP) fibers for reducing plastic shrinkage cracking. The risk of plastic shrinkage cracking of mortars with water-to-cement ratio 0.5 containing either 0.6 or 0.9 kg/m3 of natural fibers was assessed according to the ASTM C1579-21 standard and compared with plain mortars and mortars with PP fibers. The water absorption of the natural fibers was low enough that (at the employed dosages) the effect on the workability and on other fresh properties was small. The natural fibers also had no measurable influence on cement hydration in the examined mortars, as revealed by isothermal calorimetry.
The best performance in reducing the width of plastic shrinkage cracks was shown by kenaf and jute fibers at the dosage of 0.6 kg/m3, which outperformed even a higher dosage of PP fibers (0.9 kg/m3). Kenaf fibers in pellets, which are advantageous for dosing and mixing, performed similarly as loose fibers. The distribution of both loose and pelletized kenaf fibers in the mortars was studied by X-ray tomography, showing no substantial difference between the two ways of delivering the fibers.
{"title":"Mitigation of plastic shrinkage cracking with natural fibers - kenaf, abaca, coir, jute and sisal","authors":"Pietro Lura , Nikolajs Toropovs , Janis Justs , Mahdieh Shakoorioskooie , Beat Münch , Michele Griffa","doi":"10.1016/j.cemconcomp.2024.105827","DOIUrl":"10.1016/j.cemconcomp.2024.105827","url":null,"abstract":"<div><div>In this study, a number of different fibers - namely kenaf, jute, abaca, coir and sisal - were investigated as natural alternatives to polypropylene (PP) fibers for reducing plastic shrinkage cracking. The risk of plastic shrinkage cracking of mortars with water-to-cement ratio 0.5 containing either 0.6 or 0.9 kg/m<sup>3</sup> of natural fibers was assessed according to the ASTM <span><span>C1579-21</span><svg><path></path></svg></span> standard and compared with plain mortars and mortars with PP fibers. The water absorption of the natural fibers was low enough that (at the employed dosages) the effect on the workability and on other fresh properties was small. The natural fibers also had no measurable influence on cement hydration in the examined mortars, as revealed by isothermal calorimetry.</div><div>The best performance in reducing the width of plastic shrinkage cracks was shown by kenaf and jute fibers at the dosage of 0.6 kg/m<sup>3</sup>, which outperformed even a higher dosage of PP fibers (0.9 kg/m<sup>3</sup>). Kenaf fibers in pellets, which are advantageous for dosing and mixing, performed similarly as loose fibers. The distribution of both loose and pelletized kenaf fibers in the mortars was studied by X-ray tomography, showing no substantial difference between the two ways of delivering the fibers.</div></div>","PeriodicalId":9865,"journal":{"name":"Cement & concrete composites","volume":"155 ","pages":"Article 105827"},"PeriodicalIF":10.8,"publicationDate":"2024-10-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142541707","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-10-30DOI: 10.1016/j.cemconcomp.2024.105828
Zhenyu Tao , Minghong Qiu , Kay Wille , Yanping Zhu , Rensheng Pan , Zhao Li , Xudong Shao
This study aims to investigate the effects of specimen thickness and fiber length on the tensile and cracking behaviors of ultra-high-performance fiber-reinforced concrete (UHPFRC). To this end, a uniaxial tensile test was conducted with three specimen thicknesses (30, 50, and 100 mm) and two fiber lengths (13 and 20 mm), and the fiber orientation, dispersion and specimen void were quantitatively evaluated based on image recognition. The test results indicated that fiber orientation was improved with the decreased specimen thickness and increased fiber length. Meanwhile, the initial cracking and peak stress, capacity to limit cracking were enhanced with the decreased specimen thickness. A modified prediction model considering the wall effect, flattening and squeezing effect was developed to predict the probability density function p(θ) of fiber orientation angle. Additionally, the uniformity factor μ2 was introduced to predict crack number, and the relationship between the μ2 and parameter ψ = (Vf × lf/df)/t was determined. Furthermore, a model was developed to convert the main crack width into uniaxial tensile strain. All models and relationships were validated using test data. A micromechanical model that considered the predicted p(θ) and conversion model was established to predict the uniaxial tensile response of UHPFRC, which was also successfully validated using test data.
{"title":"Effects of specimen thickness and fiber length on tensile and cracking behavior of UHPFRC: Uniaxial tensile test and micromechanical modeling","authors":"Zhenyu Tao , Minghong Qiu , Kay Wille , Yanping Zhu , Rensheng Pan , Zhao Li , Xudong Shao","doi":"10.1016/j.cemconcomp.2024.105828","DOIUrl":"10.1016/j.cemconcomp.2024.105828","url":null,"abstract":"<div><div>This study aims to investigate the effects of specimen thickness and fiber length on the tensile and cracking behaviors of ultra-high-performance fiber-reinforced concrete (UHPFRC). To this end, a uniaxial tensile test was conducted with three specimen thicknesses (30, 50, and 100 mm) and two fiber lengths (13 and 20 mm), and the fiber orientation, dispersion and specimen void were quantitatively evaluated based on image recognition. The test results indicated that fiber orientation was improved with the decreased specimen thickness and increased fiber length. Meanwhile, the initial cracking and peak stress, capacity to limit cracking were enhanced with the decreased specimen thickness. A modified prediction model considering the wall effect, flattening and squeezing effect was developed to predict the probability density function <em>p</em>(<em>θ</em>) of fiber orientation angle. Additionally, the uniformity factor <em>μ</em><sub>2</sub> was introduced to predict crack number, and the relationship between the <em>μ</em><sub>2</sub> and parameter <em>ψ</em> = (<em>V</em><sub><em>f</em></sub> × <em>l</em><sub><em>f</em></sub>/<em>d</em><sub><em>f</em></sub>)/<em>t</em> was determined. Furthermore, a model was developed to convert the main crack width into uniaxial tensile strain. All models and relationships were validated using test data. A micromechanical model that considered the predicted <em>p</em>(<em>θ</em>) and conversion model was established to predict the uniaxial tensile response of UHPFRC, which was also successfully validated using test data.</div></div>","PeriodicalId":9865,"journal":{"name":"Cement & concrete composites","volume":"155 ","pages":"Article 105828"},"PeriodicalIF":10.8,"publicationDate":"2024-10-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142541709","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-10-28DOI: 10.1016/j.cemconcomp.2024.105826
Ying Wei , Ziwei Chen , Marcus Yio , Christopher Cheeseman , Hailong Wang , Chi Sun Poon
The porous lightweight aggregates in concrete experience a process of water absorption and desorption. This study aims to improve the performance of water-sensitive low water/binder (w/b) systems by effectively utilizing these water regulations. The effects of expanded shale (ES) substitutions and saturation levels (dry, half saturation, and saturation) on the fresh and hardened properties of mixtures with a w/b of 0.18 were investigated. The results indicated that, during the fresh stage, water absorption reduced workability and shortened the setting time. In the hardening stage, the released water improved hydration, increased internal relative humidity, and caused volumetric expansion, which reduced autogenous shrinkage. A comprehensive evaluation revealed that the optimal condition for ES was half-saturation with 4.0 wt% pre-absorbed water. This condition achieved the best internal curing effect, improved workability, and optimal structural efficiency (strength/density). This study provides practical insights for the effective integration of porous aggregates in the mixture design and engineering applications.
{"title":"Advanced moisture control in porous aggregates for improved lightweight high-performance concrete","authors":"Ying Wei , Ziwei Chen , Marcus Yio , Christopher Cheeseman , Hailong Wang , Chi Sun Poon","doi":"10.1016/j.cemconcomp.2024.105826","DOIUrl":"10.1016/j.cemconcomp.2024.105826","url":null,"abstract":"<div><div>The porous lightweight aggregates in concrete experience a process of water absorption and desorption. This study aims to improve the performance of water-sensitive low water/binder (w/b) systems by effectively utilizing these water regulations. The effects of expanded shale (ES) substitutions and saturation levels (dry, half saturation, and saturation) on the fresh and hardened properties of mixtures with a w/b of 0.18 were investigated. The results indicated that, during the fresh stage, water absorption reduced workability and shortened the setting time. In the hardening stage, the released water improved hydration, increased internal relative humidity, and caused volumetric expansion, which reduced autogenous shrinkage. A comprehensive evaluation revealed that the optimal condition for ES was half-saturation with 4.0 wt% pre-absorbed water. This condition achieved the best internal curing effect, improved workability, and optimal structural efficiency (strength/density). This study provides practical insights for the effective integration of porous aggregates in the mixture design and engineering applications.</div></div>","PeriodicalId":9865,"journal":{"name":"Cement & concrete composites","volume":"155 ","pages":"Article 105826"},"PeriodicalIF":10.8,"publicationDate":"2024-10-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142519673","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-10-26DOI: 10.1016/j.cemconcomp.2024.105810
Yan Yu, Guoqing Geng
Quantitative microstructure analysis of supplementary cementitious material (SCM) - blended paste through backscattered electron (BSE) imaging has long been intractable owing to the sophisticated micro phase distribution and overlapped greyscale histogram. This study explores the use of Convolutional Neural Network (CNN) based supervised semantic segmentation methods for quantifying phase assemblage in BSE images of blank cement paste and SCM-blended cement pastes. Four types of SCMs, namely limestone, slag, quartz and metakaolin, were separately blended with WPC and OPC paste for analysis. U-Net architecture with and without ResNet backbones were trained to perform pixel-level image segmentation of anhydrous cement and SCM particles. The results indicate that deep learning models can robustly segment anhydrous cement particles from BSE images and achieve same level of precision as QXRD. For limestone, quartz and slag, deep learning models show strong potential for semi-quantitative segmentation. While metakaolin cannot be reliably segmented based solely on graphic information.
{"title":"Deep learning methods for phase segmentation in backscattered electron images of cement paste and SCM-blended systems","authors":"Yan Yu, Guoqing Geng","doi":"10.1016/j.cemconcomp.2024.105810","DOIUrl":"10.1016/j.cemconcomp.2024.105810","url":null,"abstract":"<div><div>Quantitative microstructure analysis of supplementary cementitious material (SCM) - blended paste through backscattered electron (BSE) imaging has long been intractable owing to the sophisticated micro phase distribution and overlapped greyscale histogram. This study explores the use of Convolutional Neural Network (CNN) based supervised semantic segmentation methods for quantifying phase assemblage in BSE images of blank cement paste and SCM-blended cement pastes. Four types of SCMs, namely limestone, slag, quartz and metakaolin, were separately blended with WPC and OPC paste for analysis. U-Net architecture with and without ResNet backbones were trained to perform pixel-level image segmentation of anhydrous cement and SCM particles. The results indicate that deep learning models can robustly segment anhydrous cement particles from BSE images and achieve same level of precision as QXRD. For limestone, quartz and slag, deep learning models show strong potential for semi-quantitative segmentation. While metakaolin cannot be reliably segmented based solely on graphic information.</div></div>","PeriodicalId":9865,"journal":{"name":"Cement & concrete composites","volume":"155 ","pages":"Article 105810"},"PeriodicalIF":10.8,"publicationDate":"2024-10-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142519263","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-10-26DOI: 10.1016/j.cemconcomp.2024.105817
Kaiyin Zhao , Hengrui Liu , Lucen Hao , Shuangshuang Liu , Shipeng Zhang , Chi Sun Poon
The study aimed to elucidate the mechanism behind rheological modification due to CO2 mixing at the mixing and post-mixing stages from an electrochemical perspective. The results indicated that CO2 mixing reduced the flowability while increasing penetration resistance and static yield stress. The electrostatic attraction between particles with opposite surface charges and the bridging effect of calcium carbonate constitute the primary factors for influencing the rheological properties of mortar at an early age. The altered surface charge of carbonized cement particles, primarily resulting from CO2 injection lowering the pH and ion concentration, reversed the zeta potential of particles from the traditionally negative charge (−3.59 mV) to a positive value (+13.3 mV). Furthermore, CO2 mixing further enhanced the dissolution of cement particles and accelerated the hydration process, thereby increasing the rate of structural build-up. CO2 mixing was demonstrated to be a potential rheological modifier for 3D-printed concrete applications.
该研究旨在从电化学角度阐明二氧化碳在混合和混合后阶段造成流变性改变的机理。结果表明，二氧化碳混合降低了流动性，同时增加了渗透阻力和静屈服应力。表面电荷相反的颗粒之间的静电吸引和碳酸钙的架桥效应是影响早期砂浆流变性能的主要因素。碳化水泥颗粒表面电荷的改变主要是由于二氧化碳的注入降低了 pH 值和离子浓度，使颗粒的 zeta 电位从传统的负电荷（-3.59 mV）逆转为正值（+13.3 mV）。此外，二氧化碳混合进一步促进了水泥颗粒的溶解，加速了水化过程，从而提高了结构形成的速度。二氧化碳混合被证明是 3D 打印混凝土应用中一种潜在的流变改性剂。
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Pub Date : 2024-10-25DOI: 10.1016/j.cemconcomp.2024.105814
Samuel Adu-Amankwah , Ben Douglas , Leslie Arkless , Nina Cardinal , Maciej Zajac
Over 35 % of the CO2 associated with cement production comes from operational energy. The cement industry needs alternative fuels to meet its net zero emissions target. This study investigated the influence of hydrogen mixed with biofuels, herein designated net zero fuel as an alternative to coal, on the clinker quality and performance of cement produced in an industrial cement plant. Scanning electron microscopy, X-ray diffraction and nuclear magnetic resonance were coupled to study the clinker mineralogy and polymorphs. Hydration and microstructure development in plain and slag blended cements based on the clinker were compared to commercial cement equivalent. The results revealed a lower alite/belite ratio, but a significant proportion of the belite was of the α′H-C2S polymorph. These reacted faster and compensated for the alite/belite ratio. Gel and micro-capillary pores were densified, which reduced total porosity and attained comparable strength to the reference plain and blended cement. This study demonstrates that the investigated net zero fuel-produced clinker meets compositional and strength requirements for plain and blended cement, providing a feasible pathway for the cement industry to lower its operational carbon significantly.
{"title":"-Mixed hydrogen and biofuels cement clinker: Characterisation, microstructure, and performance","authors":"Samuel Adu-Amankwah , Ben Douglas , Leslie Arkless , Nina Cardinal , Maciej Zajac","doi":"10.1016/j.cemconcomp.2024.105814","DOIUrl":"10.1016/j.cemconcomp.2024.105814","url":null,"abstract":"<div><div>Over 35 % of the CO<sub>2</sub> associated with cement production comes from operational energy. The cement industry needs alternative fuels to meet its net zero emissions target. This study investigated the influence of hydrogen mixed with biofuels, herein designated net zero fuel as an alternative to coal, on the clinker quality and performance of cement produced in an industrial cement plant. Scanning electron microscopy, X-ray diffraction and nuclear magnetic resonance were coupled to study the clinker mineralogy and polymorphs. Hydration and microstructure development in plain and slag blended cements based on the clinker were compared to commercial cement equivalent. The results revealed a lower alite/belite ratio, but a significant proportion of the belite was of the α′<sub>H</sub>-C<sub>2</sub>S polymorph. These reacted faster and compensated for the alite/belite ratio. Gel and micro-capillary pores were densified, which reduced total porosity and attained comparable strength to the reference plain and blended cement. This study demonstrates that the investigated net zero fuel-produced clinker meets compositional and strength requirements for plain and blended cement, providing a feasible pathway for the cement industry to lower its operational carbon significantly.</div></div>","PeriodicalId":9865,"journal":{"name":"Cement & concrete composites","volume":"155 ","pages":"Article 105814"},"PeriodicalIF":10.8,"publicationDate":"2024-10-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142489213","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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