Pub Date : 2025-01-14DOI: 10.1016/j.cement.2025.100129
Neshable Noel, Tommy Mielke, Gustave Semugaza, Anne Zora Gierth, Susanne Helmich, Stefan Nawrath, Doru C. Lupascu
This paper aims to provide a thorough comprehension of the chemical transformations occurring during the thermal preparation of reactivated virgin cements (RVCes). X-ray Diffraction (XRD) analysis of RVCes reveals the reformation of the di-calcium mineral phases in two polymorphic forms: α/L-C2S and β-C2S, within the temperature range from 600 °C to 850 °C. We exactly quantify the two polymorphs α/L-C2S and α/H-C2S and distinguish their presence in the reactivation temperature range. This phase formation is corroborated by scanning electron microscopy (SEM) coupled with energy-dispersive X-ray spectroscopy (EDX). We further investigated the chemical changes that, after re-activation, take place during the 28-day rehydration period using differential scanning calorimetry (DSC), thermogravimetry (TG), XRD, and SEM, confirming the reformation of the typical hydration mineral phases. Mercury intrusion porosimetry (MIP) and compressive strength tests verified the development of strength-enhancing mineral phases in RVCs, exhibiting a mechanical strength recovery ranging from 50 % to 75 % compared to industrially produced virgin cement (VCe).
{"title":"Chemical transformations during the preparation and rehydration of reactivated virgin cements","authors":"Neshable Noel, Tommy Mielke, Gustave Semugaza, Anne Zora Gierth, Susanne Helmich, Stefan Nawrath, Doru C. Lupascu","doi":"10.1016/j.cement.2025.100129","DOIUrl":"10.1016/j.cement.2025.100129","url":null,"abstract":"<div><div>This paper aims to provide a thorough comprehension of the chemical transformations occurring during the thermal preparation of reactivated virgin cements (RVCes). X-ray Diffraction (XRD) analysis of RVCes reveals the reformation of the di-calcium mineral phases in two polymorphic forms: α<sup>/</sup><sub>L</sub>-C<sub>2</sub>S and β-C<sub>2</sub>S, within the temperature range from 600 °C to 850 °C. We exactly quantify the two polymorphs α<sup>/</sup><sub>L</sub>-C<sub>2</sub>S and α<sup>/</sup><sub>H</sub>-C<sub>2</sub>S and distinguish their presence in the reactivation temperature range. This phase formation is corroborated by scanning electron microscopy (SEM) coupled with energy-dispersive X-ray spectroscopy (EDX). We further investigated the chemical changes that, after re-activation, take place during the 28-day rehydration period using differential scanning calorimetry (DSC), thermogravimetry (TG), XRD, and SEM, confirming the reformation of the typical hydration mineral phases. Mercury intrusion porosimetry (MIP) and compressive strength tests verified the development of strength-enhancing mineral phases in RVCs, exhibiting a mechanical strength recovery ranging from 50 % to 75 % compared to industrially produced virgin cement (VCe).</div></div>","PeriodicalId":100225,"journal":{"name":"CEMENT","volume":"19 ","pages":"Article 100129"},"PeriodicalIF":0.0,"publicationDate":"2025-01-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143152060","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-01-13DOI: 10.1016/j.cement.2025.100130
H.C.B. Nascimento , N.B. Lima , S.D. Jesus , D.G. Rocha , H.S. Cavalcante , B.S. Teti , R. Manta , L.B.T. Santos , S. Campelo , N.B.D. Lima
The different temperatures associated with the climatic conditions of each continent and each biome directly influence the exposure properties of each material used in each region, including hydraulic cement, an important material widely employed in bridges, viaducts, and buildings worldwide. Despite being prepared at elevated temperatures, hydraulic cement is often stored and used under ambient conditions, posing challenges, particularly in tropical environments. The present work investigates the effects of different temperatures (10 °C, 30 °C, and 50 °C) on the deterioration of hydraulic cement and microstructural and mechanical behaviors. Kinect investigations were carried out to advance a chemical formalism of the deterioration of cement stored at different temperatures in a tropical climate. Signs of chemical deterioration of cement samples were investigated by XRD and SEM analyses, which revealed the presence of essential phases on the surface of the mortars, such as Portlandite, CSH, and Ettringite. The study incorporated gray residue into the mortar mixtures in two forms: addition (type B mortar) and substitution (type C mortar). For type B, 10 % of gray residue was added as an additive without reducing the cement content, while for type C, 10 % of the cement was replaced with gray residue to lower environmental impact. The presence of gray residue contributed to the hydration kinetics and microstructure, enhancing the formation of CSH phases, which are critical for mechanical strength. Mechanical performance revealed that type A (reference mortar) suffered a 6 % reduction in compressive strength after 90 days of storage at ambient conditions, while type B showed a 23 % increase due to the addition of ash residue, and type C, although with a 33 % reduction, balanced lower cement use with environmental benefits and mitigated losses related to chemical deterioration. Finally, sustainable mortars showed better mechanical performance than traditional ones, especially when the cement was stored at 50 °C, as predicted by the kinetic formalism (R² = 0.99 across storage conditions).
{"title":"A molecular formalism of the hydraulic cement deterioration stored at different temperatures and its impact on the mechanical behavior","authors":"H.C.B. Nascimento , N.B. Lima , S.D. Jesus , D.G. Rocha , H.S. Cavalcante , B.S. Teti , R. Manta , L.B.T. Santos , S. Campelo , N.B.D. Lima","doi":"10.1016/j.cement.2025.100130","DOIUrl":"10.1016/j.cement.2025.100130","url":null,"abstract":"<div><div>The different temperatures associated with the climatic conditions of each continent and each biome directly influence the exposure properties of each material used in each region, including hydraulic cement, an important material widely employed in bridges, viaducts, and buildings worldwide. Despite being prepared at elevated temperatures, hydraulic cement is often stored and used under ambient conditions, posing challenges, particularly in tropical environments. The present work investigates the effects of different temperatures (10 °C, 30 °C, and 50 °C) on the deterioration of hydraulic cement and microstructural and mechanical behaviors. Kinect investigations were carried out to advance a chemical formalism of the deterioration of cement stored at different temperatures in a tropical climate. Signs of chemical deterioration of cement samples were investigated by XRD and SEM analyses, which revealed the presence of essential phases on the surface of the mortars, such as Portlandite, CSH, and Ettringite. The study incorporated gray residue into the mortar mixtures in two forms: addition (type B mortar) and substitution (type C mortar). For type B, 10 % of gray residue was added as an additive without reducing the cement content, while for type C, 10 % of the cement was replaced with gray residue to lower environmental impact. The presence of gray residue contributed to the hydration kinetics and microstructure, enhancing the formation of CSH phases, which are critical for mechanical strength. Mechanical performance revealed that type A (reference mortar) suffered a 6 % reduction in compressive strength after 90 days of storage at ambient conditions, while type B showed a 23 % increase due to the addition of ash residue, and type C, although with a 33 % reduction, balanced lower cement use with environmental benefits and mitigated losses related to chemical deterioration. Finally, sustainable mortars showed better mechanical performance than traditional ones, especially when the cement was stored at 50 °C, as predicted by the kinetic formalism (R² = 0.99 across storage conditions).</div></div>","PeriodicalId":100225,"journal":{"name":"CEMENT","volume":"19 ","pages":"Article 100130"},"PeriodicalIF":0.0,"publicationDate":"2025-01-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143152663","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-12-20DOI: 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.
{"title":"Effect of ultrasonication on sucrose structure and its influence on controlled retardation of earth-based alkali-activated materials","authors":"Pitabash Sahoo, Souradeep Gupta","doi":"10.1016/j.cement.2024.100127","DOIUrl":"10.1016/j.cement.2024.100127","url":null,"abstract":"<div><div>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.</div></div>","PeriodicalId":100225,"journal":{"name":"CEMENT","volume":"19 ","pages":"Article 100127"},"PeriodicalIF":0.0,"publicationDate":"2024-12-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143152059","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-12-19DOI: 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 %.
{"title":"Synergistic effects of silica fume, nanomaterials and inorganic salts on the hydration and compressive strength of low-density oil well cement slurry","authors":"Kenedy Geofrey Fikeni , Xueyu Pang , Yukun Zhao , Shenglai Guo , Jie Ren , Kaihe Lv , Jinsheng Sun","doi":"10.1016/j.cement.2024.100125","DOIUrl":"10.1016/j.cement.2024.100125","url":null,"abstract":"<div><div>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 (CaCl<sub>2</sub>, NaCl, Na<sub>2</sub>SiO<sub>3</sub>) 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/cm<sup>3</sup>. 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 %.</div></div>","PeriodicalId":100225,"journal":{"name":"CEMENT","volume":"19 ","pages":"Article 100125"},"PeriodicalIF":0.0,"publicationDate":"2024-12-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143152665","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-12-19DOI: 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.
{"title":"Sanitary ware waste in eco-friendly Portland blended cement: Potential use as supplementary cementitious material","authors":"Vitor Affonso Lopes Silveira, Domingos Sávio de Resende, Augusto Cesar da Silva Bezerra","doi":"10.1016/j.cement.2024.100126","DOIUrl":"10.1016/j.cement.2024.100126","url":null,"abstract":"<div><div>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.</div></div>","PeriodicalId":100225,"journal":{"name":"CEMENT","volume":"19 ","pages":"Article 100126"},"PeriodicalIF":0.0,"publicationDate":"2024-12-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143152666","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-12-14DOI: 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.
{"title":"Potential of Saudi Arabian bauxite to produce low-carbon cement","authors":"S. Pavia , O. Alelweet","doi":"10.1016/j.cement.2024.100124","DOIUrl":"10.1016/j.cement.2024.100124","url":null,"abstract":"<div><div>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.</div><div>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.</div><div>The results evidenced that limestone fusion is the most efficient method, as it renders hydraulic phases at 800 °C (C<sub>12</sub>A<sub>7</sub>) and 1000 °C (haüyne). The early release of Ca<sup>2+</sup> from the limestone acts as a flux, lowering the breakdown point of the bauxite´s components. C<sub>12</sub>A<sub>7</sub> (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.</div><div>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.</div><div>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.</div><div>The fluxing action of iron, aluminium and sulphur, significant in the bauxite, lowered the clinkering temperature.</div></div>","PeriodicalId":100225,"journal":{"name":"CEMENT","volume":"19 ","pages":"Article 100124"},"PeriodicalIF":0.0,"publicationDate":"2024-12-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143152664","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-12-01DOI: 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.
{"title":"Workability, compressive strength, and efflorescence characteristics of one-part mix alkali-activated circulating fluidised bed combustion fly ash-based mortars","authors":"Jason Shun Fui Pei , Chung Siung Choo , Deni Shidqi Khaerudini , Sing Muk Ng , Dominic Ek Leong Ong , Melvina Tan , Jaka Sunarso","doi":"10.1016/j.cement.2024.100123","DOIUrl":"10.1016/j.cement.2024.100123","url":null,"abstract":"<div><div>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 (Na<sub>2</sub>SiO<sub>3</sub>) 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 Na<sub>2</sub>SiO<sub>3</sub>-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.</div></div>","PeriodicalId":100225,"journal":{"name":"CEMENT","volume":"18 ","pages":"Article 100123"},"PeriodicalIF":0.0,"publicationDate":"2024-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143154827","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-11-15DOI: 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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Pub Date : 2024-11-06DOI: 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。
{"title":"Downstream processing of End-of-Life concrete for the recovery of high-quality cementitious fractions","authors":"A.T.M. Alberda van Ekenstein , H.M. Jonkers , M. Ottelé","doi":"10.1016/j.cement.2024.100121","DOIUrl":"10.1016/j.cement.2024.100121","url":null,"abstract":"<div><div>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.</div></div>","PeriodicalId":100225,"journal":{"name":"CEMENT","volume":"18 ","pages":"Article 100121"},"PeriodicalIF":0.0,"publicationDate":"2024-11-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142657538","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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.
{"title":"The impact of relative humidity on the nanoindentation relaxation in calcium silicate hydrates","authors":"Zhao Chen , Jessy Frech-Baronet , Hang Tran , Luca Sorelli","doi":"10.1016/j.cement.2024.100120","DOIUrl":"10.1016/j.cement.2024.100120","url":null,"abstract":"<div><div>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.</div></div>","PeriodicalId":100225,"journal":{"name":"CEMENT","volume":"18 ","pages":"Article 100120"},"PeriodicalIF":0.0,"publicationDate":"2024-10-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142530219","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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