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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
11

Uso da técnica de eletrocinética para estabilização de um solo arenoso

Fonini, Anderson January 2008 (has links)
A tentativa de modificar algumas propriedades dos solos é antiga. Alguns autores fazem considerações a tentativas ocorridas a três mil anos atrás. Com o crescimento populacional e o desenvolvimento de novos sistemas de produção ocorridos após a Revolução Industrial no século XVIII, houve uma intensa ocupação territorial exigindo obras de infra-estrutura e obras complementares, tornando cada vez mais comum o melhoramento de solos. Uma técnica in situ passível de aplicação para melhorar as propriedades mecânicas dos solos é a técnica de eletrocinética associada à injeção de soluções químicas. Esta é caracterizada pela aplicação de um baixo gradiente elétrico através de eletrodos num meio poroso inundado com soluções químicas. Nesta pesquisa, foram realizados ensaios associando as soluções de cloreto de cálcio com água carbonatada, cloreto de cálcio com bicarbonato de sódio além de cloreto de cálcio com silicato de sódio. Para verificação da ocorrência da cimentação entre as partículas de areia, após a saturação do corpo de prova com as devidas soluções, mas anterior à aplicação da diferença de potencial elétrico ao solo, foram realizados três ensaios de prospecção com um Miniature Cone, desenvolvido nesta pesquisa. Esses foram comparados a outros três ensaios que foram realizados após o período de aplicação da técnica. Todas as associações resultaram em regiões cimentadas não homogêneas, sendo que os melhores resultados foram obtidos com a associação das soluções de cloreto de cálcio e silicato de sódio. A aplicação da técnica de eletrocinética associada a injeções de soluções químicas mostrou se complexa e difícil de predizer devido ao número de variáveis que podem modificar o seu resultado final. / The attempt to change some soil properties of the soil is not new. Some authors describes attempts occurred three thousand years ago. With population growth and the new production systems development that occurred after the Industrial Revolution in the eighteenth century, there was an intense territorial occupation requiring infrastructure works and complementary works, becoming the soils improvement usual. One of the in situ soil improvement techniques is the eletrokinetics associated with injection of chemical solutions. This technique is characterized by the application of a low electrical gradient through electrodes in a porous media flooded with chemical solutions. In this study, tests were carried out associating the solutions of calcium chloride with soda water, calcium chloride with sodium bicarbonate, and calcium chloride with sodium silicate. To verify the occurrence of the cementation among the sand particles, after the samples flooded with the appropriate solutions, but prior to the application of electric potential difference in the soil, three exploration tests were performed with a Miniature Cone, developed in this study. These tests were compared to other three tests that were carried out after the application of the technique. All associations resulted in not homogeneous cemented regions, and the best results were obtained with the combination of the solutions of calcium chloride and sodium silicate. The application of the eletrokinetics technique associated with injections of chemical solutions is proved to be complex and difficult to be predicted due to the number of variables that can change its final result.
12

Efeito do silício e irrigação na produtividade do tomate de mesa no sudeste goiano / Estresse hídrico, evapotranspiração, silicato de sódio

Viana, Débora Macedo Paronetto 24 June 2015 (has links)
Submitted by Marlene Santos (marlene.bc.ufg@gmail.com) on 2016-08-18T21:15:21Z No. of bitstreams: 2 Dissertação - Débora Macedo Paronetto Viana - 2015.pdf: 1160036 bytes, checksum: 74179969a46784eda015c0776c564c67 (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) / Approved for entry into archive by Luciana Ferreira (lucgeral@gmail.com) on 2016-08-19T13:06:52Z (GMT) No. of bitstreams: 2 Dissertação - Débora Macedo Paronetto Viana - 2015.pdf: 1160036 bytes, checksum: 74179969a46784eda015c0776c564c67 (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) / Made available in DSpace on 2016-08-19T13:06:52Z (GMT). No. of bitstreams: 2 Dissertação - Débora Macedo Paronetto Viana - 2015.pdf: 1160036 bytes, checksum: 74179969a46784eda015c0776c564c67 (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Previous issue date: 2015-06-24 / The use of silicon shows promising results in productivity of crops. However, its effectiveness on minimizing the effects of water stress on tomato crop is incipient and should be studied. The objective of this study was to evaluate sodium silicate doses through foliar application on tomato (Solanum lycopersicum) and to evaluate the negative effects of water stress under greenhouse conditions. The quality (length, fruit diameter and weight, shell thickness and number of fruits per plant) of tomato was quantified, along with fruit productivity parameters. Plants of the salad group were subjected to four watering rounds (3, 6, 9, 12 days), and three concentrations of sodium silicate (Na2SiO3) (0.0% Si L-1, 0.2% Si L-1 and 0.4% Si L-1) through foliar application. The values stipulated for irrigation intervals correspond to levels ranging from a sufficient water supply to plants to water deficit. The irrigation management was carried out with the aid of an evaporimeter, or mini-tank class A. The experimental design was a randomized block design with a factorial 3x4 (sodium silicate doses x irrigation intervals), totaling 12 treatments with four replications each. In general, the irrigation interval alone influenced more the productivity parameters than the fruit quality parameters. As the plants were growing older, it was detected more significant effect of silicon on parameters evaluated. / O uso de silício apresenta resultados promissores em função de produtividade das culturas, entretanto, a sua eficácia ou não, em minimizar os efeitos do estresse hídrico na cultura do tomate são incipientes e devem ser estudadas. O objetivo deste trabalho foi avaliar doses de silicato de sódio via aplicação foliar em plantas de tomate Solanum lycopersicum e avaliar os efeitos negativos do estresse hídrico sob condições de cultivo protegido. A qualidade (comprimento, diâmetro e peso médio dos frutos, espessura da casca e número de frutos planta-1) do tomate foram quantificadas, além de parâmetros de produtividade dos frutos submetidos aos tratamentos. Plantas de tomate grupo salada foram submetidas a quatro turnos de rega (3, 6, 9, 12 dias), e três concentrações de silicato de sódio (Na2SiO3) (0,0 % Si L-1, 0,2 % Si L-1 e 0,4 % Si L-1) via aplicação foliar. Os valores estipulados de turno de rega compreenderam níveis variando desde a suficiente oferta de água à planta até o déficit hídrico. O manejo da irrigação foi realizado com o auxílio de um evaporimetro, ou mini tanque classe A. O delineamento experimental utilizado foi em blocos casualizados, em esquema fatorial 3x4 (doses de silicato de sódio x turno de rega), totalizando doze tratamentos com quatro repetições. De maneira geral, o turno de rega considerando-o de forma isolada influenciou mais em parâmetros de produção do que nos de qualidade do fruto. A partir do momento em que as plantas de tomate foram tornando-se mais velhas ocorreu maior significância do fator silício nos parâmetros avaliados.
13

Zinc Silicate Based Pigments for Corrosion Inhibition of Cold Rolled Steel

Pemmaraju, Prajyula January 2018 (has links)
No description available.
14

Properties of geopolymers sourced from construction and demolition waste: A review

Alhawat, Musab M., Ashour, Ashraf, Yildirim, Gurkan, Sahmaran, M. 13 April 2022 (has links)
Yes / Geopolymers have been recognised as a viable replacement to ordinary Portland cement (OPC), providing a cleaner solution since it can significantly reduce greenhouse gas emissions as well as accomplishing effective waste recycling. Construction and demolition waste (CDW) has been recently identified as raw materials for geopolymers due to its availability and high contents of silica and alumina. This paper aimed at reviewing the current state-of-the-art on the geopolymer paste, mortar, and concrete production and their properties, with special attention paid to geopolymers incorporating CDWs. The review covers brief assessment of using CDWs in concrete, the mix design of geopolymer mixtures in addition to identification of the main factors influencing the performance of geopolymer containing CDW. The most recent data related to the mechanical and durability properties of CDW-based geopolymers are presented, while the cost and environmental impacts of using recycled materials in producing geopolymer concretes are also discussed. Geopolymer concretes have a vast range of possible applications, however, there are still several barriers facing commercialisation of geopolymers in construction industry. The review indicated that it is possible to produce geopolymer concretes from CDW-based materials with properties comparable to OPC-based ones; however, the selection of proper material composition should be carefully considered, especially under normal curing conditions.
15

The deposition of silica on titanium dioxide surfaces

Furlong, Donald Neil January 1975 (has links)
The deposition of amorphous silica from aqueous solution on to rutile particles has been studied with the aim of elucidating the nature of the silica-titania interactions occurring and of following the progressive build up of the silica coating. The coating process, which involves the addition of an aqueous sodium silicate solution to an aqueous dispersion of titanium dioxide, has been investigated by performing a series of controlled preparations and using the technique of microelectrophoresis. Prepared silica-coated rutile samples ranging from partial to full silica coatings have been characterized using transmission electron microscopy, microelectrophoresis and nitrogen, argon and water sorption. Nitrogen and argon adsorption isotherms have been analysed using the equation of Brunauer, Emmett and Teller (BET). Differential energies of adsorption of nitrogen and argon have been determined calorimetrically. Water sorption isotherms have been analysed using the BET equation and the Frenkel - Halsey - Hill (FHH) equation. It has been shown that uniform silica coatings can be produced if adsorption of monomeric silica is followed by polymerization of silica at the solid/liquid interface. Surface cations on rutile may be hydroxylated or co-ordinately bound to water molecules and it appears that monomeric silica adsorbs preferentially by replacing ligand water molecules. Rutile particles with silica coatings thicker than approximately 2.5nm exhibit characteristics typical of silica and not of the base rutile. Silica coatings deposited at pH 10 contain narrow channels which are accessible to water molecules but not to nitrogen or argon. Neutralization to pH 7 reduces the volume in the coating accessible to water molecules.
16

Silício no manejo pré e pós-colheita da podridão parda (monilinia fructicola) no pessegueiro / Silicon in management pre and postharvest brown rot (monilinia fructicola) in peach

Pavanello, Elizandra Pivotto 24 February 2016 (has links)
Conselho Nacional de Desenvolvimento Científico e Tecnológico / Brown rot is the main diseases of peaches, with pre and postharvest losses. Control it is difficult because the fungus infect fruit and remain latent until conditions are favorable to its manifestation. Therefore, to understand the role of latent infection of the disease incidence and find strategies to minimize losses, with low environmental impact, is essential for sustainable crop management. This thesis consists of four papers that resulted from work with the following objectives: to study the relationship between latent infection and the occurrence of postharvest brown rot; to evaluate the effect of preharvest fungicide application on the Monilinia fructicola control during storage and marketing of peaches; to investigate the pre and postharvest applications of silicon on the brown rot control in peach. They were used peaches of Eldorado and Pepita cultivars, in field experiments involving preharvest spraying of fungicides and pre and postharvest applications of silicon and experiments in refrigerated storage conditions at -0.5 ° C. Iprodione, tebuconazole and difenoconazole are effective in brown rot control in the field conditions, while in postharvest, the incidence was controlled in 96.2% with iminoctadine. These products decreased the incidence of injuries resulting from latent infections. There is a high correlation between the presences of latent infections in preharvest with the incidence of the disease in postharvest, with most of the damage after cold storage resulting from the latent infections of Monilinia fructicola. Foliar application of 6 g L-1 sodium silicate or sodium metasilicate is effective in controlling the disease without causing phytotoxicity to the plants. Six sodium silicate applications had the same effect as six fungicides applications to brown rot control in peaches Eldorado . Postharvest sodium metasilicate application, in 6 g L-1, reduced the diseases incidence but caused fruit skin darkening. Physical defense mechanisms of the plants are affected by silicon application, because it increased the element content in the leaves and fruits, and increased skin texture. However, the effect of silicon on the biochemical defense mechanisms may involve the synthesis of polyphenols, because in the one year of search we found a higher content of these compounds in fruit treated with silicon. In general, products based on silicon, applied alone or intercalated with fungicides, control the disease in pre and postharvest, allowing a decrease in fungicide use and production cost. / A podridão parda do pessegueiro é a doença de maior importância para a cultura, com danos em pré e pós-colheita. O controle é dificultado devido à habilidade do fungo de infectar os frutos e permanecer latente até que as condições tonarem-se favoráveis à sua manifestação. Portanto, compreender o papel da infecção latente na incidência da doença, bem como encontrar estratégias que minimizem as perdas, com baixo impacto ambiental, é fundamental para o manejo sustentável da cultura. Esta tese é composta por quatro artigos científicos que resultaram de trabalhos com os seguintes objetivos: estudar a relação da infecção latente com a ocorrência da podridão parda em pós-colheita; avaliar o efeito da aplicação pré-colheita de fungicidas no controle do fungo Monilinia fructicola durante o armazenamento e comercialização de pêssegos; investigar o potencial do silício em pré e pós-colheita no controle da podridão parda do pessegueiro. Foram utilizados pêssegos das cultivares Eldorado e Pepita em experimentos a campo envolvendo pulverizações pré-colheita de fungicidas e aplicações pré e pós-colheita de produtos à base de silício e experimentos em condições de armazenamento refrigerado a 0,5 ºC. Os fungicidas iprodione, tebuconazole e difenoconazole foram eficazes no controle da podridão parda a campo, enquanto que em pós-colheita, a incidência foi controlada em 96,2% com iminoctadina. Esses produtos também reduziram a incidência de lesões decorrentes de infecções latentes. Há uma alta correlação entre a presença de infecções latentes em pré-colheita com a incidência da doença em pós-colheita, sendo a maior parte das lesões após o armazenamento refrigerado decorrentes das infecções latentes do fungo Monilinia fructicola. Aplicação foliar de 6 g L-1 de metassilicato de sódio ou de silicato de sódio foram eficazes no controle da doença sem causar fitotoxidez às plantas. Seis aplicações de silicato de sódio tiveram o mesmo efeito que seis aplicações de fungicidas no controle da podridão parda em pêssegos cv. Eldorado. A aplicação de metassilicato de sódio em pós-colheita, na dose de 6 g L-1, reduziu a incidência da doença, mas causou escurecimento da epiderme dos frutos. Os mecanismos físicos de defesa das plantas são afetados pelo Si, pois houve aumento do conteúdo do elemento nas folhas e frutos e aumento da textura da epiderme, entretanto, o efeito do silício sobre os mecanismos bioquímicos de defesa pode envolver a síntese de polifenóis, pois em um dos anos da pesquisa verificou-se maior conteúdo destes compostos em frutos tratados com silício. Em geral, produtos à base de silício, aplicados isoladamente ou intercalados com fungicidas, controlam a doença em pré e pós-colheita proporcionando redução no uso de fungicidas e no custo de produção.
17

[pt] ESTUDO DO PROCESSO DE GELIFICAÇÃO DO SILICATO DE SÓDIO E SEU CONTROLE ATRAVÉS DO USO DE MICROCÁPSULAS / [en] STUDY OF THE SODIUM SILICATE GELATION PROCESS AND ITS CONTROL THROUGH THE USE OF MICROCAPSULES

RUBIA DE ALBUQUERQUE E VASCONCELOS BODAS 26 August 2021 (has links)
[pt] Em um reservatório de petróleo, a eficiência do deslocamento do óleo é bastante reduzida pela presença de fraturas e camadas de alta permeabilidade. Quando uma fase aquosa é injetada, esta flui preferencialmente por caminhos de baixa resistência, deixando grandes volumes do reservatório não afetados pelo processo de injeção. Uma alternativa para minimizar esse problema é bloquear as fraturas com um sistema líquido que forma um gel após algum tempo, forçando a fase aquosa a fluir pela matriz porosa. Os géis de silicato de sódio são uma das formulações que podem ser utilizadas para esse fim. No entanto, a cinética do processo de formação do gel de silicato é difícil de controlar, pois depende de muitas variáveis. Essa incerteza do processo de gelificação pode levar à formação de uma fase de gel fora da posição desejada, levando a diversos problemas, como perda de injetividade. Uma formulação líquida utilizando microcápsulas é uma proposta com um método inovador que tem como objetivo controlar o tempo de liberação do agente ativador e, consequentemente, melhorar o controle sobre o início do processo de gelificação. O primeiro passo no desenvolvimento desta técnica foi estudar a evolução da reologia do gel formado a partir do silicato de sódio com ácido clorídrico para avaliar a taxa de formação do gel em função de diferentes parâmetros do processo, como a concentração de Na-Si e HCl. Os resultados mostram que o processo de gelificação é função do pH da solução e que o tempo de gelificação é menor quanto maior a concentração de ácido clorídrico. No método proposto, a solução de ácido clorídrico é encapsulada e a gelificação só se inicia após o rompimento do invólucro da cápsula, que é desencadeado pela imposição de um gradiente de pressão osmótica. / [en] In an oil reservoir, the efficiency of oil displacement is greatly reduced by the presence of fractures and high permeability layers. When an aqueous phase is injected, it flows preferentially through low resistance paths, leaving large volumes of the reservoir not affected by the injection process. An alternative to minimize this problem is to block fractures with a liquid system that forms a gel after some time, forcing the water phase to flow through the porous matrix. Sodium silicate gels are one of the formulations that can be used for this purpose. However, the kinetics of the silicate gel formation process is difficult to control, since it depends on many different variables. This uncertainty of the gelation process in the subsurface may lead to the formation of a gel phase away from the desired position, leading to many different problems, such as loss of injectivity. A liquid formulation using microcapsules is proposed as an innovative method designed to control the release time of the activating agent and, consequently, to improve control over the start of the gelation process. The first step in the development of this technique was to study evolution of the rheology of the gel formed from sodium silicate with hydrochloric acid in order to evaluate the rate of the gel formation as a function of different process parameters, such as the concentration of Na-Si and HCl. The results show that the gelation process is a strong function of the solution pH and that the gelation time is shorter the higher the concentration of hydrochloric acid. In the proposed method, the hydrochloric acid solution is encapsulated and the gelation only starts after the bursting the capsule shell, which is triggered by imposing a gradient of osmotic pressure.
18

Effects Of Source Water Blending Following Treatment With Sodium Silicate As A Corrosion Inhibitor On Metal Release Within A Wat

Lintereur, Phillip 01 January 2008 (has links)
A study was conducted to investigate and quantify the effects of corrosion inhibitors on metal release within a pilot distribution system while varying the source water. The pilot distribution system consisted of pre-existing facilities from Taylor et al (2005). Iron, copper, and lead release data were collected during four separate phases of operation. Each phase was characterized by the particular blend ratios used during the study. A blended source water represented a water that had been derived from a consistent proportion of three different source waters. These source waters included (1) surface water treated through enhanced coagulation/sedimentation/filtration, (2) conventionally treated groundwater, and (3) finished surface water treated using reverse osmosis membranes. The corrosion inhibitors used during the study were blended orthophosphate (BOP), orthophosphate (OP), zinc orthophosphate (ZOP), and sodium silicate (Si). This document was intended to cite the findings from the study associated with corrosion treatment using various doses of sodium silicate. The doses were maintained to 3, 6, and 12 mg/L as SiO2 above the blend-dependent background silica concentration. Sources of iron release within the pilot distribution system consisted of, in the following order of entry, (1) lined cast iron, (2) un-lined cast iron, and (3) galvanized steel. Iron release data from these materials was not collected for each individual iron source. Instead, iron release data represented the measurement of iron upon exposure to the pilot distribution system in general. There was little evidence to suggest that iron release was affected by sodium silicate. Statistical modeling of iron release suggested that iron release could be described by the water quality parameters of alkalinity, chlorides, and pH. The R2 statistic implied that the model could account for only 36% of the total variation within the iron release data set (i.e. R2 = 0.36). The model implies that increases in alkalinity and pH would be expected to decrease iron release on average, while an increase in chlorides would increase iron release. The surface composition of cast iron and galvanized steel coupons were analyzed using X-ray photoelectron spectroscopy (XPS). The surface analysis located binding energies consistent with Fe2O3, Fe3O4, and FeOOH for both cast iron and galvanized steel. Elemental scans detected the presence of silicon as amorphous silica; however, there was no significant difference between scans of coupons treated with sodium silicate and coupons simply exposed to the blended source water. The predominant form of zinc found on the galvanized steel coupons was ZnO. Thermodynamic modeling of the galvanized steel system suggested that zinc release was more appropriately described by Zn5(CO3)2(OH)6. The analysis of the copper release data set suggested that treatment with sodium silicate decreased copper release during the study. On average the low, medium, and high doses decreased copper release, when compared to the original blend source water prior to sodium silicate addition, by approximately 20%, 30%, and 50%, respectively. Statistical modeling found that alkalinity, chlorides, pH, and sodium silicate dose were significant variables (R2 = 0.68). The coefficients of the model implied that increases in pH and sodium silicate dose decreased copper release, while increases in alkalinity and chlorides increased copper release. XPS for copper coupons suggested that the scale composition consisted of Cu2O, CuO, and Cu(OH)2 for both the coupons treated with sodium silicate and those exposed to the blended source water. Analysis of the silicon elemental scan detected amorphous silica on 3/5 copper coupons exposed to sodium silicate. Silicon was not detected on any of the 8 control coupons. This suggested that sodium silicate inhibitor varied the surface composition of the copper scale. The XPS results seemed to be validated by the visual differences of the copper coupons exposed to sodium silicate. Copper coupons treated with sodium silicate developed a blue-green scale, while control coupons were reddish-brown. Thermodynamic modeling was unsuccessful in identifying a controlling solid that consisted of a silicate-based cupric solid. Lead release was generally decreased when treated with sodium silicate. Many of the observations were recorded below the detection limit (1 ppb as Pb) of the instrument used to measure the lead concentration of the samples during the study. The frequency of observations below the detection limit tended to increase as the dose of sodium silicate increased. An accurate quantification of the effect of sodium silicate was complicated by the observations recorded below detection limit. If the lead concentration of a sample was below detection limit, then the observation was recorded as 1 ppb. Statistical modeling suggested that temperature, alkalinity, chlorides, pH, and sodium silicate dose were important variables associated with lead release (R2 = 0.60). The exponents of the non-linear model implied that an increase in temperature, alkalinity, and chlorides increased lead release, while an increase in pH and sodium silicate dose were associated with a decrease in lead release. XPS surface characterization of lead coupons indicated the presence of PbO, PbO2, PbCO3, and Pb3(OH)2(CO3)2. XPS also found evidence of silicate scale formation. Thermodynamic modeling did not support the possibility of a silicate-based lead controlling solid. A solubility model assuming Pb3(OH)2(CO3)2 as the controlling solid was used to evaluate lead release data from samples in which lead coupons were incubated for long stagnation times. This thermodynamic model seemed to similarly describe the lead release of samples treated with sodium silicate and samples exposed to the blended source water. The pH of each sample was similar, thus sodium silicate, rather than the corresponding increase in pH, would appear to be responsible if a difference had been observed. During the overall study, the effects of BOP, OP, ZOP, and Si corrosion inhibitors were described by empirical models. Statistically, the model represented the expected value, or mean average, function. If these models are to be used to predict a dose for copper release, then the relationship between the expected value function and the 90th percentile must be approximated. The USEPA Lead and Copper Rule (LCR) regulates total copper release at an action level of 1.3 mg/L. This action level represents a 90th percentile rather than a mean average. Evaluation of the complete copper release data set suggested that the standard deviation was proportional to the mean average of a particular treatment. This relationship was estimated using a linear model. It was found that most of the copper data sub-sets (represented by a given phase, inhibitor, and dose) could be described by a normal distribution. The information obtained from the standard deviation analysis and the normality assumption validated the use of a z-score to relate the empirical models to the estimated 90th percentile observations. Since an analysis of the normality and variance (essentially contains the same information as the standard deviation) are required to assess the assumptions associated with an ANOVA, an ANOVA was performed to directly compare the effects of the inhibitors and corresponding doses. The findings suggested that phosphate-based inhibitors were consistently more effective than sodium silicate when comparing the same treatment levels (i.e. doses). Among the phosphate-based inhibitors, the effectiveness of each respective treatment level was inconsistent (i.e. there was no clear indication that any one phosphate-based inhibitor was more effective than the other). As the doses increased for each inhibitor, the results generally suggested that there was a corresponding tendency for copper release to decrease.
19

Properties of cementless mortars activated by sodium silicate.

Yang, Keun-Hyeok, Song, J-K., Ashour, Ashraf, Lee, E-T. 09 1900 (has links)
yes / The present paper reports the testing of 12 alkali-activated mortars and a control ordinary portland cement (OPC) mortar. The main aim is to develop cementless binder activated by sodium silicate powder. An alkali quality coefficient combining the amounts of main compositions of source materials and sodium oxide (Na2O) in sodium silicate is proposed to assess the properties of alkali activated mortars, based on the hydration mechanism of alkali-activated pastes. Fly ash (FA) and ground granulated blast-furnace slag (GGBS) were employed as source materials. The ratio of Na2O-to-source material by weight for different mortars ranged between 0.038 and 0.164; as a result, alkali quality coefficient was varied from 0.0025 to 0.0365. Flow loss of fresh mortar, and shrinkage strain, compressive strength and modulus of rupture of hardened mortars were measured. The compressive strength development of alkali activated mortar was also compared with the design equations for OPC concrete specified in ACI 209 and EC 2. Test results clearly showed that the flow loss and compressive strength development of alkali-activated mortar were significantly dependent on the proposed alkali quality coefficient. In particular, a higher rate of compressive strength development achieved at early age for GGBS-based alkali-activated mortar and at long-term age for FA-based alkali-activated mortar. In addition, shrinkage strain and modulus of rupture of alkali-activated mortar were comparable to those of OPC mortar.
20

Effects of Fly Ash on the properties of Alkali Activated Slag Concrete

Kothari, Ankit January 2017 (has links)
This master thesis presents the effects of fly ash on the properties of alkali activated slag concrete, commonly referred as Geopolymer concrete (GPC). Cement manufacturer are major producers of CO2 which negatively affects the environment. Due to the increased construction activities and environmental concern, it is necessary to introduce alternative and eco-friendly binders for concrete. Slag and fly ash based concrete, which is by-product from industrial waste, is probably the best replacement for OPC concrete due to less or nil environmental issue. Most of the researchers have already concluded that slag and fly ash can be used as binders in concrete by activating them with alkali activator solution (e.g. by sodium silicate or sodium carbonate). In the present work concretes were produced by varying the proportion of slag to fly ash (40:60, 50:50, 60:40 & 80:20); amount of alkali activators (5, 10 & 14) and chemical modulus of sodium silicate (Ms) (0.25, 0.5 & 1).  Setting times and compressive strength values were evaluated. Results showed that decrease in fly ash content irrespective of % of alkali activators and alkali modulus (Ms), the compressive strength was increasing and setting time was getting shorter. The produced concretes showed increasing compressive strength with increase in % of alkali activator for Ms 0.5 and 1, while for Ms=0.25 the strength was decreasing with increase in % of alkali activators. From this it can be concluded that, Ms=0.5 was the optimum point below which the reaction got slower. Based on the initial investigations, mix S8:F2-SS10(1) and S8:F2-SS10(0.5) showed most promising results in terms of fresh and hardened concrete properties and were easy to handle. Consequently, the above mentioned mixture was chosen to be studied in more detail. The experimental program for these mixes included determination of slump flow, compressive strength (7, 14, 28 days) and shrinkage (drying and autogenous). The results shows that, strength increased with time and comparatively mix with Ms=0.5 showed higher compressive strength than mix with Ms=1, due to higher alkalinity of the pore solution. Mix with Ms=1 showed higher drying shrinkage compared to mix with Ms=0.5, which was explained by higher alkalinity of the solutions (Ms=0.5) leading to rapid formation of aluminosilicate gel. Autogenous shrinkage appeared to be higher for mix with Ms=0.5. This was associated with lower modulus which leads to densification of concrete microstructure at early ages. Pore diameter decrease and the water trapped in the pores exerted increasing tensile stress resulting for higher autogenous shrinkage.

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