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Avaliação das propriedades fisicas e mecanicas de concretos produzidos com os cimentos Portland de alta resistencia inicial e de alto-forno aditivados com silica ativa curados termicamente; Evaluation of physical and mechanical properties of steam cured concrete made with high early strenght Portland cement and blastfurnace slag cement containing silica fume

Paulo Sergio Bardella
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 19/01/2005 PT
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A durabilidade das estruturas de concreto depende da estrutura porosa e da impermeabilidade do concreto, uma vez que a entrada de água e de agentes deletérios iniciam os processos patológicos que diminuem a vida útil de uma estrutura de concreto. Dessa forma, o objetivo deste trabalho foi avaliar a resistência mecânica, permeabilidade, absorção e carbonatação natural de concretos submetidos a diferentes condições de cura. Os procedimentos de cura adotados são normalmente utilizadds em canteiros de obra e na produção de estruturas pré-moldadas de concreto: cura imersa até a idade de 7 dias, cura ambiente e cura térmica. A cura térmica foi realizada na temperatura de 60°C. Foram empregados concretos produzidos com cimento Portland de Alta Resistência Inicial (CP V ARI) e cimento Portland de Alto Forno (CP III) sem e com sílica ativa (em substituição ao cimento na proporção de 10% em massa) para cada um dos diferentes tipos de cura utilizados. Os resultados evidenciaram que o tipo de cura afeta o desempenho do concreto. A mudança do tipo de cura aplicada proporcionou variações nas propriedades mecânicas e na durabilidade dos concretos, principalmente no que diz respeito à sua estrutura porosa. Assim, um regime de cura adequado é essencial para garantir a resistência mecânica e a durabilidade dos concretos. A utilização de sílica ativa em substituição ao cimento melhorou o desempenho dos concretos...

Avaliação do desempenho de aglomerante a base de gesso com cimento portland de alto forno e silica ativa; Perfomance assessment of gypsum cement based rendering materials containing portland blast-furnce slag cement and condensed silica fume

Jose Antonio De Milito
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 07/02/2007 PT
Relevância na Pesquisa
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O gesso é um aglomerante que tem sido muito empregado em revestimento de paredes. Apresenta um bom desempenho, é econômico e de fácil aplicação, mas limitado ao uso interno devido a sua sensibilidade à água. Algumas tentativas têm sido realizadas para melhorar a sua utilização em ambientes sujeitos à umidade. Neste sentido, pesquisas avançam na tentativa de empregar diferentes adições como resinas epóxi, polímeros, cimentos, escórias, impermeabilizantes, entre outros. O objetivo desta tese foi avaliar o desempenho das misturas de gesso com cimento Portland de Alto Forno e sílica ativa nos revestimentos internos e externos sujeitos à umidade. Para isso verificaram-se as propriedades macroscópicas das misturas por meio de ensaios físicos, químicos, físico-químicos e também a avaliação microestrutural utilizando a microscopia eletrônica de varredura. As misturas foram aplicadas em revestimentos de painéis de alvenaria de blocos de concreto e observados visualmente por um período de cinco anos. Além da observação visual foi verificada a resistência de aderência das misturas aplicadas internamente e externamente. Dos resultados obtidos observou-se uma possível coexistência entre o gesso e o cimento e que a adição de sílica ativa na mistura reduz a formação de etringita...

Study of the decalcification process in mortars degraded by NH4NO3 by using ultrasonic techniques; Estudio del proceso de descalcificación en morteros degradados en NH4NO3 empleando técnicas ultrasónicas

Segura Pérez, Ignacio; Moragues, A.; Macphee, Donald E.; Anaya Velayos, José Javier; Molero Armenta, Miguel Ángel
Fonte: Conselho Superior de Investigações Científicas Publicador: Conselho Superior de Investigações Científicas
Tipo: Artículo Formato: 2033543 bytes; application/pdf
SPA; ENG
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Artículo enviado y aceptado para próxima publicación en la revista Materiales de Construccion.; [EN] Water takes part in most if not all of the degradation processes experienced by cement-based materials during their service-life. The effect of pure water usually is not of primary concern as it involves very lengthy degradation diffusion controlled processes; aqueous solutions are more aggressive, promoting increased solubility of matrix components and microstructure modification due to leaching. The ability to monitor such changes non-destructively presents a number of challenges as, often, conventional characterisation techniques require sample preparation likely to modify the properties of interest. In this study, ultrasonic pulse velocity profiles have provided a non-destructive means of monitoring microstructural changes during aggressive leaching of blastfurnace slag cement mortars with ammonium nitrate solutions. These data are compared with corresponding analyses by destructive techniques including mercury intrusion porosimetry (MIP), water porosity measurements, X-ray diffraction (XRD) and scanning electron microscopy (SEM). By analysing degraded ultrasonic velocity profiles it has been possible to calculate degraded depths in the samples...

Mechanical and hydration properties of ground granulated blastfurnace slag pastes activated with MgO-CaO mixtures

Gu, Mai; Jin, Fei; Al-Tabbaa, Abir; Shi, Bin; Liu, Jin
Fonte: Elsevier Publicador: Elsevier
Tipo: Article; accepted version
EN
Relevância na Pesquisa
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This is the accepted manuscript version. The final version is available from Elsevier at http://www.sciencedirect.com/science/article/pii/S0950061814007569.; Since alkali-activated slag using conventional activators suffers from economical and technical problems, other alternative activators should be explored. This paper reports the results of an investigation into the activation of ground granulated blastfurnace slag by using 10% (by weight) reactive MgO, CaO and their mixtures with various ratios. The mechanical and hydration properties of pastes were examined up to 90 days. It was found that the strength of slag pastes activated with MgO?CaO mixtures decreased with the increasing ratio of MgO to CaO in the early age while a much steeper strength gain was observed in pastes with MgO/CaO higher than 19/1 after 28 days and longer. The addition of small amount of CaO in MgO can greatly accelerate the hydration of slag in the early age by increasing the pH of pore solution. However, pastes showed small difference in strength development at each period when MgO/CaO was less than 1. The main hydration products, analysed by XRD, TGA and SEM/EDS, were C?S?H and hydrotalcite-like phases. While CaO accelerated the formation of C?S?H in the early age...

Strength and hydration properties of reactive MgO-activated ground granulated blastfurnace slag paste

Jin, Fei; Gu, Kai; Al-Tabbaa, Abir
Fonte: Elsevier Publicador: Elsevier
Tipo: Article; accepted version
EN
Relevância na Pesquisa
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This is the accepted manuascript for a paper published in Cement and Concrete Composites, Volume 57, March 2015, Pages 8?16, doi:10.1016/j.cemconcomp.2014.10.007; Ground granulated blastfurnace slag (GGBS) is widely used as a partial replacement for Portland cement or as the major component in the alkali-activated cement to give a clinker-free binder. In this study, reactive MgO is investigated as a potentially more practical and greener alternative as a GGBS activator. This paper focuses on of the hydration of GGBS, activated by two commercial reactive MgOs, with contents ranging from 2.5% to 20% up to 90 days. The hydration kinetics and products of MgO?GGBS blends were investigated by selective dissolution, thermogravimetric analysis, X-ray diffraction and scanning electron microscopy techniques. It was found that reactive MgO was more effective than hydrated lime in activating the GGBS based on unconfined compressive strength and the efficiency increased with the reactivity and the content of the MgO. It is hence proposed that reactive MgO has the potential to serve as an effective and economical activator for GGBS.; The authors are grateful to Cambridge Trust and China Scholarship Council (CSC) for their financial help of the PhD studentship for the first author.

Strength and drying shrinkage of slag paste activated by sodium carbonate and reactive MgO

Jin, Fei; Gu, Kai; Al-Tabbaa, Abir
Fonte: Elsevier Publicador: Elsevier
Tipo: Article; accepted version
EN
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This is the accepted manuscript for a paper published in Construction and Building Materials, Volume 81, 15 April 2015, Pages 58?65, doi:10.1016/j.conbuildmat.2015.01.082; This paper investigates the potential of combining Na2CO3 and reactive MgO as a sustainable activator for ground granulated blastfurnace slag. Two very different reactivity MgOs were added at 5?10 % and the Na2CO3 content varied from 4% to 8% by the weight of slag. The strength and drying shrinkage of the activated slag pastes were tested up to 90 d. It was found that the optimum reactive MgO addition was 5% regardless of the MgO type and Na2CO3 content. MgO with the higher reactivity significantly increased the early strength of the paste but had almost no effect on the strength at 90 d. On the other hand, the effect of the lower reactivity MgO on the strength was more profound at later ages and low Na2CO3 dosage. In terms of drying shrinkage, increasing the Na2CO3 content from 4% to 6% caused a remarkable decrease of drying shrinkage while increasing it from 6% to 8% had negligible effect. X-ray diffraction and thermogravimetric analysis revealed that the major hydration products were calcium silicate hydrate gel and hydrotalcite-like phases, similar to those in conventional alkali-activated slag cements. There was also a large quantity of calcite formed especially in the 8% Na2CO3 pastes due to causticisation. It was concluded that the combination of reactive MgO and Na2CO3 could serve as a potential sustainable activator for slags.; The first author is grateful to Cambridge Trust and China Scholarship Council (CSC) for sponsoring his Ph.D. studentship.

Time-dependent performance of soil mix technology stabilised/ solidified contaminated site soils

Wang, Fei; Wang, Hailing; Al-Tabbaa, Abir
Fonte: Elsevier Publicador: Elsevier
Tipo: Article; accepted version
EN
Relevância na Pesquisa
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This is the author accepted manuscript. The final version is available from Elsevier via http://dx.doi.org/doi:10.1016/j.jhazmat.2015.01.007; This paper presents the strength and leaching performance of stabilized/solidified organic and inorganic contaminated site soil as a function of time and the effectiveness of modified clays applied in this project. Field trials of deep soil mixing application of stabilization/solidification (S/S) were performed at a site in Castleford in 2011. A number of binders and addictives were applied in this project including Portland cement (PC), ground granulated blastfurnace slag (GGBS), pulverised fuel ash (PFA), MgO and modified clays. Field trial samples were subjected to unconfined compressive strength (UCS), BS CN 12457 batch leaching test and the extraction of total organics at 28 days and 1.5 years after treatment. The results of UCS test show that the average strength values of mixes increased from 0?3250 kPa at 28 days to 250?4250 kPa at 1.5 years curing time. The BS EN 12457 leachate concentrations of all metals were well below their drinking water standard, except Ni in some mixes exceed its drinking water standard at 0.02 mg/l, suggesting that due to varied nature of binders, not all of them have the same efficiency in treating contaminated soil. The average leachate concentrations of total organics were in the range of 20?160 mg/l at 28 days after treatment and reduced to 18?140 mg/l at 1.5 years. In addition...

The role of brucite, ground granulated blastfurnace slag, and magnesium silicates in the carbonation and performance of MgO cements

Unluer, C.; Al-Tabbaa, A.
Fonte: Elsevier Publicador: Elsevier
Tipo: Article; accepted version
EN
Relevância na Pesquisa
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This is the author accepted manuscript. The final version is available from Elsevier via http://dx.doi.org/10.1016/j.conbuildmat.2015.07.105; This study focuses on the enhancement of the technical and environmental performance of MgO cements through the inclusion of brucite, GGBS, talc and serpentine as partial MgO substitutes in concrete blocks. The influence of these additives on the microstructure, hydration, carbonation, and mechanical performance of blocks cured under natural and elevated CO2 conditions is presented. An optimum replacement level was determined for each composition via unconfined compressive strength (UCS), scanning electron microscopy (SEM), x-ray diffraction (XRD), thermogravimetric analysis (TGA) and acid digestion. Mixes subjected to accelerated carbonation indicated up to 100% carbonation in 7 days. Results highlight the suitability of each additive in replacing MgO without compromising performance.

Evaluation of sulfate resistance of calcined dolomite activated ground granulated plastfurnace slag

Gu, Kai; Jin, Fei; Al-Tabbaa, Abir; Shi, Bin; Tang, Chaosheng
Fonte: American Society of Civil Engineers Publicador: American Society of Civil Engineers
Tipo: Article; accepted version
EN
Relevância na Pesquisa
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This is the author accepted manuscript. The final version is available from ASCE via http://dx.doi.org/10.1061/(ASCE)MT.1943-5533.0001392; Aggressive environments significantly influence the durability and serviceability of hardened cement and concrete. This paper presents an evaluation of the resistance of ground granulated blastfurnace slag (GGBS) activated with calcined dolomite, as a novel alkali activator, to 5% sodium sulfate attack and 5% magnesium sulfate attack. Two calcined dolomites, D800 and D1000, were prepared in the laboratory at 800 ?C and 1000 ?C respectively. The results demonstrated the good potential of using calcined dolomite activated slag in resisting sulfate attack. Immersion in Na2SO4(aq) led to an increase in strength in both the D800 (D800S) and the Portland cement CEM I 52.5N (PCS) activated slag, with a more pronounced effect in the former, while a decrease in the D1000 (D1000S) activated slag. On the other hand, calcined dolomite activated slag 25 had less strength loss than PCS after MgSO4 attack. The products of sulfate attack and the deterioration processes are also analyzed by a range of tests including pH, weight change, corroded depth, XRD, TGA and SEM/EDS. After Na2SO4 attack, the main product on D800S and D1000S was gypsum with a larger amount in the later. Gypsum...

Incorporation of reactive magnesia and quicklime in sustainable binders for soil stabilisation

Gu, Kai; Jin, Fei; Al-Tabbaa, Abir; Shi, Bin; Liu, Chun; Gao, Lei
Fonte: Elsevier Publicador: Elsevier
Tipo: Article; accepted version
EN
Relevância na Pesquisa
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This is the author accepted manuscript. The final version is available from Springer at http://www.sciencedirect.com/science/article/pii/S0013795215001799.; The utilisation of reactive magnesia or quicklime as novel activators for slag offers a range of technical and environmental benefits over conventional caustic alkali activators and showed great potential in soil stabilisation. This paper investigates the mechanical and microstructural properties of two model soils, i.e., a clayey soil and a slightly silty clayey sand, stabilised by ground granulated blastfurnace slag (GGBS) using various techniques including unconfined compressive strength (UCS) test, thermogravimetric analysis (TGA) and scanning electron microscopy (SEM). A number of MgO and CaO mixtures with different MgO/CaO ratios were adopted for slag activation. The activator to GGBS ratio was 1:3 and the dosage of the binder (including MgO, CaO and GGBS) was 12% by weight of the dry soil. The result demonstrated that the increasing MgO/CaO ratio in the binder led to an increase in the UCS of the stabilised clayey soil up to 90 days, due to the increased homogeneity of C?S?H gel structure, the decreased Ca/Si ratio of C?S?H gel and the increased amount of voluminous hydrotalcite-like phases. On the other hand...

Comparison of reactive magnesia-, carbide slag-activated ground granulated blastfurnace slag and Portland cement for stabilisation of a natural soil

Yi, Yaolin; Zheng, Xu; Liu, Songyu; Al-Tabbaa, Abir
Fonte: Elsevier Publicador: Elsevier
Tipo: Article; accepted version
EN
Relevância na Pesquisa
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This is the accepted manuscript. The final version is available at http://www.sciencedirect.com/science/article/pii/S0169131715001325.; In this study, reactive magnesia (MgO)- and carbide slag (CS)-activated ground granulated blastfurnace slag (GGBS) were used to stabilise a natural soil in comparison to Portland cement (PC). X-ray diffraction (XRD), scanning electron microscopy (SEM) and unconfined compressive strength (UCS) test were employed to investigate the microstructural and mechanical properties of stabilised soils. The results indicated that the main hydration products of CS-GGBS stabilised soil included calcium silicate hydrates (CSH), calcium aluminate hydrates (CAH) and ettringite. For MgO-GGBS stabilised soils, CSH was the only hydration product detected. These hydration products had different microstructure and binding ablility, affecting the strength of stabilised soils. There was an optimum MgO or CS content, in a range of 10-20%, for yielding the highest UCS of MG-GGBS or CS-GGBS stabilised soil at the same age. The 90-day UCS of the optimum MgO-GGBS and CS-GGBS stabilised soils was 3.0-3.2 and 2.4-3.2 times that of the PC stabilised soil, respectively.; The authors appreciate the funding provided by National Natural Science Foundation of China (41330641) and Jiangsu Province (BY2014120).

Deformation and mechanical properties of quaternary blended cements containing ground granulated blastfurnace slag, fly ash and magnesia

Mo, Liwu; Liu, Meng; Al-Tabbaa, Abir; Deng, Min; Lau, Wai Yuk
Fonte: Elsevier Publicador: Elsevier
Tipo: Article; accepted version
EN
Relevância na Pesquisa
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This is the accepted manuscript. The final published version is available from Elsevier at http://www.sciencedirect.com/science/article/pii/S0008884615000319.; Shrinkages of cementitious materials may lead to cracking under restrained conditions. This study was motivated to develop non-shrinkage quaternary blended cements through blending slag and fly ash with Portland cement containing reactive MgO. The hydration process, autogenous shrinkage at early age, long-term volume deformation, mechanical properties, and microstructure of cement specimens were investigated. Results showed that the autogenous shrinkage of the cement pastes was effectively mitigated due to the compensation of the MgO present and the reduction of cement content owing to the partial replacements with slag and fly ash. The mechanical strengths of the blended cement mortars were lower than that of the corresponding plain Portland cement mortars at early age of 3 d, but increased significantly to be similar or higher at late ages of 28 d and 90 d. This is attributed to the microstructure densification and the interface microstructure enhancement due to the reaction of SCMs with clinker phases.; The financial support from the Royal Academy of Engineering UK/China Exchange (12/13RECI013)...

The performance of blended conventional and novel binders in the in-situ stabilisation/solidification of a contaminated site soil

Wang, Fei; Wang, Hailing; Jin, Fei; Al-Tabbaa, Abir
Fonte: Elsevier Publicador: Elsevier
Tipo: Article; accepted version
EN
Relevância na Pesquisa
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F. Wang et al. Journal of Hazardous Materials 285 (2015) 46?52, http://dx.doi.org/10.1016/j.jhazmat.2014.11.002 NOTICE: this is the author?s version of a work that was accepted for publication in the Journal of Hazardous Materials. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in the Journal of Hazardous Materials, [285, 46-52, (2015)] 10.1016/j.jhazmat.2014.11.002; This paper presents an investigation of the effects of novel binders and pH values on the effectiveness of the in-situ stabilisation/solidification technique in treating heavy metals and organic contaminated soils after 1.5-year treatment. To evaluate the performance of different binders, made ground soils of SMiRT site, upto 5 m depth, were stabilised/solidified with the triple auger system and cores were taken for laboratory testing after treatment. Twenty four different binders were used including Portland cement (PC), ground granulated blastfurnace slag (GGBS), pulverised fuel ash (PFA), MgO and zeolite. Unconfined compressive strength (UCS)...