Determinación del contenido de alúmina reactiva de las adiciones puzolánicas naturales y artificiales, por termogravimetría y por el método de Rietveld

Tanto el tema de esta investigación, como sus objetivos, fundamentos, materiales seleccionados y parte experimental para alcanzarlos, han sido promovidos por la situación y el estado de las construcciones de hormigón armado que se comenzaron a realizar en España a partir del año 1975, con hormigones y morteros de cemento que contenían cenizas volantes hasta un 20 %, en principio, y hasta un 35 %, más tarde, de su dosificación de cemento Portland (CP), los cuales y en contra de lo esperado, han demandado y continúan demandando, muy a pesar de sus aparentes bondades de todo tipo que se les atribuían, una necesidad de mejora de sus prestaciones, especialmente, debido a un nivel inesperadamente bajo de la durabilidad de algunas obras construidas con los mismos. Todo era debido, en definitiva, a que las adiciones puzolánicas, naturales y artificiales, tales como las cenizas volantes, referidas antes, se vienen utilizando reglamentariamente para la fabricación de cementos y/o de sus productos derivados, hormigones, morteros y pastas, en la mayor parte de los países industrializados, desde hace ya más de tres décadas aproximadamente, en las mismas condiciones e idénticos usos constructivos que los hormigones y morteros de CP puro, viniendo además, dictada dicha utilización de estos materiales residuales, hoy sub-productos industriales, por cuestiones medioambientales y/o económicas, principalmente, motivo por el cual esta Tesis Doctoral ha pretendido responder también, adecuadamente y de manera esquemática (en forma de diagrama de flujo), a los criterios que deben de tenerse en cuenta a la hora de su selección y caracterización normalizada y reglamentada de estas adiciones minerales activas, sobre todo, antes de su dosificación y uso en forma del denominado cemento Portland con puzolana, o con ceniza volante, o con esquistos calcinados o con puzolanas calcinadas o con humo de sílice, cemento Portland mixto, cemento puzolánico o cemento compuesto, para que dichos problemas no se le produzcan al hormigón armado ni en masa. De aquí el enfoque tan particular y especial de esta investigación, al haberla circunscrito únicamente a las puzolanas naturales y artificiales, por considerarlas todas ellas, independientemente de por su origen, como materiales constituidos por pequeñas fracciones cristalinas distribuidas aleatoriamente en una matriz mayoritariamente vítrea y/o amorfa, la cual es la que le confiere su reactividad con el hidróxido de calcio en forma de cal apagada o de portlandita procedente de la hidratación del CP. A su vez, dichas fracciones vítreas y/o amorfas están constituidas, en su mayor parte, por sílice reactiva, SiO2r-, alúmina reactiva, Al2O3r-, y óxido de hierro reactivo, Fe2O3r-, recibiendo además, en conjunto, el nombre específico de "factores hidráulicos" de la puzolana, los cuales, por lo común, difieren cuantitativamente de sus contenidos totales, determinados por fusión alcalina mediante procedimientos normalizados. De los tres óxidos reactivos mencionados y desde el punto de vista técnico, los más importantes por su mayor presencia en casi todas las puzolanas naturales y artificiales y, también, transcendencia en la durabilidad química que les pueden llegar a conferir al hormigón armado y en masa, mortero o pasta de cemento que las contenga, son la SiO2r- y la Al2O3r-. El primero de los dos, la SiO2r-, reacciona nada más que con la portlandita (y el Ca(OH)2) para formar geles C-S-H, más tarde transformados en tobermoritas o en jennitas, semejantes a los que originan la alita y la belita del CP en su hidratación. Y desde el punto de vista normativo, la presencia de esta fracción silícica reactiva en las puzolanas viene regulada por la norma EN 197-1, de modo general, siendo además referida por la norma EN 450-1:2006, en el contexto de las cenizas volantes en su adición al hormigón, como "un polvo fino de partículas principalmente de forma esférica y cristalina, procedentes de la combustión de carbón pulverizado, que tiene propiedades puzolánicas y que está compuesto fundamentalmente de SiO2 y Al2O3". Además y de acuerdo con la primera de las dos normas, "El contenido de dióxido de silicio reactivo (definido y determinado según la norma EN 196-2 o su equivalente la UNE 80225) no debe ser inferior al 25 % en masa". Por su parte, cuantiosos estudios experimentales realizados por Talero solo y con otros investigadores, han demostrado que si la puzolana no es adecuada en calidad ni en cantidad, la durabilidad del cemento del que forme parte, y, por consiguiente, de los productos derivados que con él se fabriquen, hormigones, morteros, pastas y prefabricados, puede llegar a ser anormalmente baja, porque la alúmina reactiva, Al2O3r-, o alúmina tetra- o penta-coordinada que la constituye, se implica como tal, de una forma muy directa y con resultados totalmente contrapuestos incluso, en los ataques químicos agresivos naturales que se les producen, provenientes de terrenos y aguas selenitosas (sulfatos, que atacan en su caso al propio material hormigón, mortero y pasta que la contiene para formar ettringita de rápida formación, ett-rf, la cual puede llegar incluso a provocar un ataque rápido del yeso), del rocío marino y de las sales de deshielo (cloruros, que atacan, en cambio, a las armaduras de acero del hormigón provocándoles su corrosión electroquímica por "picadura", si bien, en este otro ataque químico, dicha Al2O3r- lo que origina es sal de Friedel de rápida formación, sF-rf, también, cuyo efecto es, en cambio, colmatador y protector, en definitiva, de dicha corrosión electroquímica), del agua de mar (acción agresiva mutua de cloruros y sulfatos), de la carbonatación, de la reactividad árido-álcali, además de intervenir en la liberación del calor de hidratación, así como también, en el comportamiento reológico de sus pastas, etc., acortándoles de este modo su durabilidad prevista y, en ocasiones, muy seriamente incluso. Pero lo más paradójico de todo es, que a pesar de su referido comportamiento totalmente contrapuesto, frente a sulfatos y cloruros, - aún no se dispone de un método de análisis químico para su determinación cuantitativa, que sea además relativamente sencillo en su operatividad, veraz, preciso, de respuesta rápida, desde el punto de vista técnico de la construcción (no más de 28 días), repetible, reproducible, que no implique peligro alguno para la seguridad vital de las personas que lo tengan que manipular y poner en práctica, económico, y que sirva también tanto para investigación -vertiente científica-, como, sobre todo, para control de calidad -vertiente técnica-, - y ni mucho menos tampoco se dispone todavía, de especificación química alguna que precise el contenido máximo de Al2O3r- (%) que tiene que poseer una puzolana natural o artificial, para poder ser añadida al cemento Portland y/o al hormigón que va a estar sometido a un determinado ataque químico agresivo de los mencionados antes, y, en especial, a sulfatos, a cloruros o al agua de mar. Y para mayor justificación de ambas necesidades, se ha de decir también que la vigente Instrucción de Hormigón Estructural EHE-08 no contempla tampoco especificación química alguna sobre los "factores hidráulicos", en general, ni del contenido de Al2O3r-(%) de las cenizas volantes, muy en particular, en su Artículo 30º "Adiciones", ni en ningún otro Artículo, a pesar de que sí contempla, en cambio, - otras especificaciones químicas que carecen del necesario significado en cuanto a la necesidad de llevar explícita o implícitamente, el mensaje de la Durabilidad Química deseado, y - el Artículo 37º, el cual y para mayor abundamiento se titula paradójicamente "Durabilidad del hormigón y de las armaduras". Asimismo, tampoco se contempla en la última versión que acaba de publicarse de la norma EN 197-1 titulada: "Cementos. Parte 1: Composición, especificaciones y criterios de conformidad de los cementos comunes". Ni tampoco, en la norma EN 450-1:2006 titulada "Cenizas volantes para hormigón. Parte 1: Definiciones, especificaciones y criterios de conformidad", ni en la vigente Instrucción española para la Recepción de Cementos, RC-08, ni en la norma ASTM C618-03 tampoco. La única especificación química que ambas normas, la europea y la norteamericana, refieren es aquella que dice que la suma de los contenidos porcentuales de SiO2 total, Al2O3 total y Fe2O3 total, de la puzolana natural o artificial, ha de ser mayor o igual que 70 %, definiendo, además, a las puzolanas de este modo tan genérico: "materiales silíceos o silíceos y aluminosos, que por sí mismos no poseen valor cementante alguno, pero que finamente divididos y en presencia de humedad, reaccionarán químicamente con hidróxido de calcio a temperaturas ordinarias para formar compuestos que poseen propiedades cementantes". Por consiguiente y de acuerdo con todo lo anterior, el objetivo primordial de esta Tesis Doctoral ha sido: Diseñar y poner a punto un nuevo método analítico de utilidad técnica (que la duración máxima del ensayo no sea mayor de 28 días), para determinar el contenido de alúmina reactiva, vítrea o amorfa, Al2O3r-, de las puzolanas naturales y artificiales. Y una vez puesto a punto, validarlo a nivel de su repetibilidad, de acuerdo con parámetros estadísticos apropiados, poniendo especial énfasis en los criterios de aceptación establecidos por la American Association of Official Analytical Chemists (AOAC). Y para conseguirlo, la innovación de esta investigación se ha basado en los siguientes fundamentos generales, a saber: - Toda la alúmina de cualquier puzolana natural o artificial, capaz de ser atacada, disuelta y lixiviada en 28 días, por la portlandita o por el hidróxido de calcio, Ca(OH)2, en medio acuoso, es considerada como alúmina reactiva, Al2O3r-. - Dicha fracción alumínica reactiva de la puzolana natural o artificial se tiene que encontrar, además, en el estado físico-químico de poder reaccionar químicamente también, en presencia de hidróxido de calcio, cloruro de sodio y agua, para originar monocloro¿aluminato de calcio hidratado, C3A·CaCl2·10H2O, o sal de Friedel. Además, dicho estado físico-químico de la puzolana ha de ser acorde con la definición de alúmina reactiva adoptada en esta investigación en razón de las prestaciones reales de durabilidad química que le puede llegar a conferir a los cementos de mezcla y a sus productos derivados, hormigones, morteros y pastas, que se fabriquen con la misma. - La originalidad de este nuevo método analítico, respecto a los demás métodos ya existentes, reside en que la cuantificación de dicha fracción alumínica reactiva de la puzolana natural o artificial, se realiza mediante cálculo estequiométrico, basándose, para ello, en dicha reacción química de formación de sal de Friedel precisamente, tras 28 días de hidratación básica-salina acelerada de la puzolana natural o artificial, habiéndose realizado, además, en esta investigación dicha determinación cuantitativa de la cantidad de sal de Friedel originada por cada puzolana, mediante dos técnicas analíticas instrumentales que fueron las siguientes: el análisis termogravimétrico (variante I ó I-I en su caso) y el método de Rietveld con la difracción de Rayos X en polvo (variante II). - La reacción química de formación de sal de Friedel tras 28 días de hidratación básica-salina acelerada de las puzolanas que se analicen, se optimizó para asegurar que el único compuesto químico de aluminio y cloro formado fuese sal de Friedel nada más (dosificando para ello en cantidad adecuada los reactivos químicos necesarios: Ca(OH)2, NaCl y agua destilada), manteniendo, además y por otra parte, el compromiso apropiado entre el máximo rendimiento de dicha reacción química (ataque, disolución y lixiviación en 28 días, de toda la alúmina reactiva de la puzolana) y el modo y medios más adecuados de acelerarlo para conseguirlo fue a 40°C de temperatura, con agitación constante y cierre hermético del reactor. - La aplicabilidad y selectividad del nuevo método analítico, objeto de esta Tesis Doctoral, fue estudiada con una serie de puzolanas naturales y artificiales españolas, silíceas y/o silíceas y aluminosas en naturaleza, que fueron las siguientes: M0 (metacaolín 0), M1 (M0 con 50 % de cuarzo), C y L (puzolanas naturales de las Islas Canarias), CV10 y CV17 (cenizas volantes), A (puzolana natural de Almagro), O (puzolana natural de Olot) y HS (humo de sílice). - Todas las adiciones minerales anteriores cumplieron con los principales requisitos físicos y químicos que son preceptivos para poder considerarlas, antes de todo, como puzolanas, lo que era indispensable y de obligado cumplimiento, para poderles determinar su contenido total de Al2O3r- (%) mediante el nuevo método analítico. Estos condicionantes fueron los siguientes: grado adecuado de finura de molido o tamaño medio de partícula (según la norma EN 451-2), haber sido analizadas químicamente antes de todo (según la norma EN 196-2 ó la ASTM C311), con el fin de determinarles especialmente, sus contenidos totales de SiO2 (%), Al2O3 (%) y Fe2O3 (%), haberles determinado, además, su contenido de sílice reactiva, SiO2r- (%) (según la norma UNE 80225), y haber cumplido con el ensayo de puzolanicidad o de Frattini (según la norma EN 196-5) a la edad de 28 días al menos. Este último requisito, otrora de obligado cumplimiento hasta el año 1988, para cualquier puzolana natural y artificial que una fábrica de cementos pretendiera introducir en el proceso de fabricación de un nuevo cemento puzolánico o cemento tipo CEM IV, ha logrado así, que se tenga que volver utilizar de nuevo de forma obligada con esta Tesis Doctoral. Y los resultados obtenidos con el nuevo método analítico de los contenidos de Al2O3r-(%) de las puzolanas seleccionadas, fueron los siguientes: - Mediante su variante I: M0 29.9 %, M1 16.9 %, CV10 11.4 %, L 12.3 %, C 12.6 %, A 8.0 %, CV17 9.5 % y O 6.3 % de Al2O3r-, y - Mediante su variante II: M0 30.7 %, M1 15.4 %, CV10 14.7%, L 11.8 %, C 11.1 %, A 8.9 %, CV17 9.6 % y O 6.8 % de Al2O3r-. Finalmente, todos ellos fueron contrastados, además, mediante la calibración y validación del nuevo método analítico, con los valores de referencia obtenidos de esas mismas puzolanas, los cuales se les habían determinado mediante el método de Florentín, consistente en atacar, disolver y lixiviar también toda la fracción alumínica soluble de la puzolana (y además, aquella silícica y férrica que la constituyen a la par), pero, en especial, su contenido total de alúmina reactiva, mediante un ataque básico (con Ca(OH)2 en medio acuoso a temperatura del laboratorio, habiendo sido, además, su duración hasta 1 año), seguido de otro ácido (con HCl, d = 1.12), habiéndose obtenido esta vez los siguientes resultados de sus contenidos de Al2O3r- (%): M0 28.8 %, M1 16.7 %, CV10 9.7 %, L 11.2 %, C 12.2 %, A 13.0 %, CV17 10.6 % y O 9.5 %. Dicha validación realizada ha puesto de manifiesto, en términos generales, que el nuevo método analítico es más fidedigno que el de Florentín, por lo que resulta ser totalmente apropiado para obtener los resultados que se han pretendido, además de proporcionarlos en un espacio de tiempo relativamente corto (28 días a lo sumo) y a un coste económico razonable por no elevado (salvo error u omisión y libre de impuestos directos e indirectos, el coste económico estimado de la variante I estaría en torno a 800.00 - 900.00 €/puzolana -caso más probable-, y aproximadamente una tercera parte nada más, en el caso de que la edad máxima del ensayo acelerado sea 7 días nada más -caso menos probable-), y, por consiguiente, técnicamente aceptable, al cumplir, además, en todo el rango considerado de variabilidad posible de concentraciones o contenidos del analito buscado en la puzolana, con tales parámetros de validación como son: linealidad (los resultados obtenidos son directamente proporcionales a la señal-respuesta instrumental recibida), sensibilidad, precisión excelente, repetibilidad satisfactoria de los valores obtenidos de los contenidos de Al2O3r- de todas y cada una de las adiciones puzolánicas seleccionadas, confirmando, por ello, la universalidad de su uso. Finalmente, las ventajas del nuevo método analítico, respecto a los métodos ya existentes recopilados de la bibliografía (el método de Florentín, el método de López Ruiz -HF 40 % y HNO3 2N-, el método de Murat y Driouche para arcillas -HF 0.5M-, el método de Arjuan, Silbee y Roy para cenizas volantes -HF 1 %- y su modificación por Fernández-Jiménez y cols. -HF 1 %, 27Al NMR MAS y XRD (método de Rietveld)-, y el método de determinación de la relación SiO2r-/Al2O3r- para arcillas y cenizas volantes por Ruiz-Santaquiteria y cols. -HF 1 %, NaOH 8M y ICP-AES-) son, principalmente, estar exento de peligro alguno para la seguridad vital de las personas que lo tengan que manipular y poner en práctica, ser bastante apropiado para control de calidad además de para investigación, su considerable menor coste económico, su relativamente corto espacio de tiempo que se necesita para obtener la respuesta-resultado pretendida (28 días a lo sumo), así como su universalidad y selectividad, puesto que además, su aplicabilidad es para todo tipo de adiciones puzolánicas naturales o artificiales, como así lo demuestran los resultados obtenidos de los materiales puzolánicos naturales y artificiales seleccionados y analizados, en un rango de concentraciones del analito -contenido de alúmina reactiva, Al2O3r- (%)-, desde el 5 % hasta el 30 % en masa, rango éste que, por otra parte, comprende prácticamente TODAS las adiciones puzolanas naturales y artificiales existentes en el mercado transnacional y las aún por existir. Por consiguiente y de acuerdo con lo anterior, el nuevo método analítico, ya sea realizado mediante su variante I o la II, debido, - en primer lugar, a los fundamentados planteamientos relativos a su procedimiento experimental -modus operandi- el cual ha sido aplicado a una amplia gama de puzolanas naturales y artificiales, y - en segundo lugar, debido a la calidad de los resultados obtenidos con un grado de precisión y repetibilidad excelentes, ha demostrado poseer una gran utilidad científica -para investigación-, pero, sobre todo, técnica -para control de calidad de adiciones puzolánicas naturales y artificiales que se adicionan habitualmente al cemento Portland en fábrica y/o a sus hormigones y morteros en planta-, además de ser representativos los valores obtenidos mediante el mismo respecto a la más que probable durabilidad química que cada una de ellas puede llegarle a conferir al hormigón armado y en masa, mortero y pasta del que forme parte, así como también su cantidad adecuada de sustitución parcial de cada cemento Portland para conseguirla, acorde con sus propias prestaciones químico-físicas o físico-químicas que puede llegarle a conferir, según sea su carácter químico (alumínico, alumínico-silícico, silícico-alumínico, silícico-férrico-alumínico o silícico), forma y tamaño medio de su partícula. Por último, el nuevo método analítico ha demostrado cumplir además, con todos los requisitos de obligado cumplimiento que establece la norma ISO/IEC 17025 sobre la calidad y fiabilidad de nuevos métodos o procedimientos analíticos no normalizados todavía, para poder ser propuesto en un futuro próximo, ante la Comisión de AENOR correspondiente, con objeto de comenzar un expediente para su certificación y normalización. ________________________________________________________________________________ Both the subject of this research, its objectives, fundamentals, materials selected and experimental part to achieve, have all been promoted by the situation and the state of reinforced concrete constructions that began performing in Spain from 1975, with concrete and mortars cement containing fly ash up to 20 %, in principle, and later, up to 35 % to its content of Portland cement, which and against expected, demanded a need to improve their performance, especially due to an unexpectedly low level of durability of some works built with them, despite, however, its apparent benefits of all kinds are ascribed to them. Ultimately, the natural or artificial pozzolanic additions, such as fly ash specially, referred to above, have been used with regulation to manufacture cements and/or its derivatives, concretes, mortars, cement pastes, in the most industrialized countries. More than three decades ago, under the same conditions and identical construction mainly uses concretes and mortars plain Portland cement, besides coming, given that use of these waste materials, industrial by-products today for environmental and/or economic issues. For this reason, this Doctoral Thesis aims to answer properly and schematically (in the form of flow chart), the criteria to be taken into account when selection and characterization standardized for these active mineral additions, especially prior to choosing and use in the so-called Portland Cement (PC) pozzolan, or with fly ash or with calcined shales or with calcined pozzolans or with silica fume or PC mixed or pozzolanic cement or compound cement, for that such pathology problems will not occur when reinforced concretes nor mass concretes are used for building. Hence the very particular and special focus about this research, having confined only to the natural or artificial pozzolans, considering them all, regardless of their origin, approach as materials consisting of small crystalline fractions randomly distributed in a largely vitreous and/or amorphous matrix, which confers their reactivity with calcium hydroxide in the form of slaked lime or portlandite from PC. In turn, these vitreous and/or amorphous fractions consist in its greater part, by reactive silica, SiO2r-, reactive alumina, Al2O3r-, and reactive iron oxide, Fe2O3r-, which also receive, in conjunction, the specific name of "hydraulic factors" of the pozzolan. Usually, they all differs in quantity of their respective total contents of the SiO2 (%), Al2O3 (%) and Fe2O3 (%) determined the pozzolan by alkaline fusion by means of standard procedures. Of the three above-mentioned oxides reagents and from the technical point of view, the most important for its increased presence in every one of the natural or artificial pozzolans and also significance in the chemical durability that can get them to give the concrete mortar or cement paste which contain them, are SiO2r- and Al2O3r-. From the first two, the SiO2r- reacts with portlandite only, released in the hydration of the PC (and with Ca(OH)2), to form C-S-H gels, transformed in tobermorites or jennites later on, similar to C-S-H gels also originating from the alite and belite hydration in the CP. From the standardization criteria point of view, the presence of this silicic fraction in pozzolans is regulated at first, by the European standard EN 197-1, in general, also being referred by the EN 450-1:2006, in the context of the fly ash in addition to the concrete, as a "fine powder of spherical particles mainly crystalline form. It is from the combustion of pulverized coal, which have pozzolanic properties and is mainly composed of SiO2 and Al2O3". In addition and according to the EN 197-1 standard, the reactive silica content (which can be defined and determined in accordance with EN 197-1 standard or its UNE 80225 standard) must not be lower than 25 % of its mass. Meanwhile, considerable experimental studies by Talero and Talero et al, have shown that if the pozzolan is not adequate in quality nor quantity, the durability of cement that is part and, therefore, of its derivative products, concretes, mortars and pastes cement, can become abnormally low because its reactive alumina, Al2O3r- (%), content or tetra- or penta-coordinated alumina which involves itself in a very direct and totally mixed and conflicting results even at all aggressive chemical attack natural to produce to the concrete, mortar and paste with inadequate natural and/or artificial pozzolans, such as those from the selenitous land and waters (sulfates, strikes if the material itself concrete, mortar and paste that contain them, for rapid forming ettringite form, ett-rf, which can even cause rapid gypsum attack to said concrete). In contrast, sea spray and de-icing salts (chlorides strikes the reinforced steel concrete causing them electrochemical corrosion by "bite", although in that other chemical attack, such Al2O3r- causes rapid Friedel's salt formation, Fs-rf, too, to cause protector effect of the electrochemical corrosion of reinforcements for these chlorides), seawater (mutual aggressive action of chlorides and sulfates), carbonation, alkali-silica reaction, and, in addition, to influence the release of hydration heat, as well as in the rheological behavior of the pastes, etc., decreasing/shorting them thus their expected durability and sometimes even very seriously. But the most ironic thing is, that despite its referral totally opposed, compared to sulfates and chlorides, behaviour, - far not available is, a chemical analysis method for its quantitative determination, which is also relatively simple in operation, accurate, precise, rapid response, from a technical point of view for building (no more than 28 days), repeatable, reproducible, not involving danger to life safety of the people who need to manipulate and implement, economic, and also serve for both scientific research and technical side, and - has yet to be any chemical specification that sets maximum levels for Al2O3r-(%) in the natural or artificial pozzolan to be added to the cement and/or to the concrete that will be subject to a particularly aggressive chemical attack from those mentioned above, and in particular, to sulphates, chlorides or sea water. And for the sake of and justification of this need, it has to be said that the current Spanish Instruction for Structural Concrete EHE-08 does not provide any specification on "hydraulic factors" in general, nor the content of Al2O3r- (%) in fly ash, very particular, as Article 30º "Additions", or any other Article, although does provide, however, other chemical specifications lacking the necessary meaning in terms of the message Chemical Durability mentioned, nor the Article 37º which and for greater sake, is paradoxically entitled "Durability of the concrete and of their reinforcements". It has also not contemplated in the latest version just released from EN 197-1 standard entitled "Cement Part 1: Composition, specifications and conformity criteria for common cements". Nor, in EN 450-1:2006 entitled "Fly ash for concrete Part 1: Definitions, specifications and conformity criteria", nor by current Spanish Instruction for Cement Reception, RC-08, nor the ASTM C618-03 Standard either. The only chemical specification that both Standards, European and American, refer is one that says that the sum of the total contents of SiO2 (%), Al2O3 (%) and Fe2O3 (%) of natural and artificial pozzolan, must be greater than or equal to 70 % , defining pozzolans thus: "siliceous or aluminous and siliceous materials, which themselves do not have any cementitious value but finely divided and in the presence of moisture it reacts with calcium hydroxide at ordinary temperatures to form compounds possessing cementitious properties". Consequently and according to everything related before, the primary objective of this Doctoral Thesis has been: To design and start-up a new quantitative analytical method of technical utility (the maximum test duration is not more than 28 days), to determine the content of reactive alumina content, Al2O3r- (%), vitreous or amorphous alumina, of natural and artificial pozzolans. And once designed, validate at repeatability level and in accordance with appropriate statistical parameters with special emphasis on the acceptance criteria established by the American Association of Official Analytical Chemists (AOAC). And to achieve this, the innovation of this research has been based on the following general principles, namely: - All the alumina in any pozzolan, natural or artificial, that can be attacked, dissolved and leached by portlandite or calcium hydroxide, Ca(OH)2, in aqueous medium, is considered reactive alumina, Al2O3r-. - This aluminic fraction of natural or artificial pozzolan to analyze and study, has to be in such physical-chemical state that it can react in the presence of calcium hydroxide, sodium chloride and water status and to cause monochloro-aluminate hydrated calcium, C3A·CaCl2·10H2O or Friedel's salt. Moreover, such physical-chemical state of the pozzolan must be consistent with the definition of reactive alumina adopted in this research because of the actual performance of chemical durability that can reach confer on blended cements and their derivatives, concretes, mortars and pastes that are manufactured with the same. - The originality of this new analytical method, compared to the other methods for determining reactive alumina existing (collected in abbreviated form in the state of the art of this report), is the quantification of such aluminic fraction of natural or artificial pozzolans is performed by stoichiometric calculation based on this, in the chemical reaction of Friedel's salt formation after 28 days of the analysis of saline-basic hydration accelerated natural or artificial pozzolan also performed in this research, and the quantitative determination of the Friedel's salt has been performed by two instrumental analytical techniques known as thermogravimetric analysis (variant I), and Rietveld method with X-ray powder diffraction (variant II). - The chemical reaction of Friedel's salt formation after 28 days of accelerated saline-basic hydration of the selected natural and artificial pozzolan, was optimized to ensure that the single chemical compound of aluminium and chlorine formed was Friedel's salt only (dosing for this purpose in amount suitable chemical reagents: Ca(OH)2, NaCl and distilled water), and, on the other hand, maintaining the appropriate compromise between the highest yield from the chemical reaction (attack, dissolution and leaching in 28 days, all reactive alumina of pozzolan) and to accelerate the etching media, which were 40°C temperature, constant stirring and sealing the reactor. - The applicability and selectivity of the new analytical method, the subject of this Doctoral Thesis, was studied with a series of Spanish natural and artificial pozzolans, siliceous or siliceous and aluminous in nature, which were as follows: M0 (metakaolin 0), M1 (M0 with 50 % quartz), L and C (natural pozzolans of the Canary Islands), CV10 (fly ash 10), CV17 (fly ash 17), A (natural pozzolan of Almagro), O (natural pozzolan of Olot), and HS (silica fume). - All mineral admixtures were selected satisfied the physical and chemical requirements proposed to consider them as pozzolan, which was mandatory, so its Al2O3r- (%) content can determine by the new analytical method. These conditions were as follows: adequate degree of fineness of grind or average particle size (according to EN 451-2 standard), have been analyzed chemically (according to EN 196-2 or ASTM C311 standards), in order to determine their total contents of SiO2 (%), Al2O3 (%) and Fe2O3 (%), mainly, having also determined its reactive silica content, SiO2r- (%) (UNE 80225 standard), and fulfilled with testing of pozzolanicity or Frattini test (according to EN 196-5 standard) at 28 days age at least. The last criteria was mandatory until 1988, for any natural and artificial pozzolan to a factory intended to introduce cements in the manufacturing process of a new Portland cement type CEM IV pozzolanic additions, and with this Doctoral Thesis has made is to be used once again mandatory. And the results obtained using the new analytical method, of the Al2O3r- (%) content for each selected pozzolan, were as follows: - by its variant I: M0 29.9 % , M1 16.9 % , CV10 11.4 % , L 12.3 % , C 12.6 % , A 8.0 % , CV17 9.5 % and O 6.3 % of Al2O3r-, and - by its variant II: M0 30.7 % , M1 15.4 % , CV10 14.7% % , L 11.8 % , C 11.1 % , A 8.9 % , CV17 9.6 % and O 6.8 % of Al2O3r-. Finally, they would all be further contrasted by the calibration and validation of new analytical method, with reference values obtained from these same natural and artificial pozzolans, which had been given by the method of Florentin, consisting of attack, dissolve and leached with a basic attack (with Ca(OH)2 in aqueous medium and laboratory temperature, having also been its duration up to 1 year), followed by another acid attack (HCl, d = 1.12), all soluble aluminic fraction of pozzolan, and in particular their total content of reactive alumina, Al2O3r-(%), was this time as follows: M0 28.8 %, M1 16.7 %, CV10 9.7 %, L 11.2 %, C 12.2 %, A 13.0 %, CV17 10.6 % and O 9.5 % (and their siliceous and iron contents that are at par). This validation has shown on the new analytical method is more reliable than Florentin method, so it turns out to be entirely appropriate to get the results that have been tried by the same, besides providing them a relatively short space of time (28 days at most) and reasonably no high economic cost (unless mistake -free direct and indirect taxes, such economic cost would be between 800.00 - 900.00 €/pozzolan (most likely case), and about an one-third part around, in the event that the maximum age of the accelerated test is 7 days only (less likely case). So it is technically acceptable, to consider the range of possible variability of concentrations or contents pozzolan analyte with validation parameters such as: linearity (the results obtained are directly proportional to the instrumental response signal received), excellent sensitivity and accuracy, satisfactory repeatability values from the contents of each and Al2O3r- (%) each selected pozzolan, confirming therefore universal use. Finally, the advantages of the new analytical method over existing methods compiled from literature (Florentin method , the Lopez Ruiz method -HF and HNO3 40 % 2N-, the method of Murat and Driouche for clays -0.5M HF-, the method of Arjuan, Roy and Silbee for fly ash -HF 1 %- and its modification by Fernández-Jiménez et al -HF 1 %, 27Al MAS NMR and XRD (Rietveld method)-, and the method for determining the SiO2r-/Al2O3r- clay and fly ash ratio of Santaquiteria Ruiz et al -HF 1 %, NaOH 8M and ICP-AES-) are primarily and relatively short time get the result intended answer (28 days at most), its considerable lower cost, free from danger to the life safety of the people who need to manipulate and put in practice as well as its universality and selectivity, since it is applicable for all types of natural or artificial pozzolans, as it has been shown by the results of selected natural and artificial pozzolanic materials and analyzed in a range of analyte concentrations -reactive alumina, Al2O3r- (%) content- from 5 % to 30 % by mass, this range, on the other hand, includes virtually ALL existing transnational market in natural and artificial pozzolans and still exist. Therefore and in accordance with the above, the new analytical method is already performed by the variant I or II, because, - firstly, grounded to experimental approaches concerning its experimental procedure -"modus operandi"- which has been applied to a wide range of natural and artificial pozzolans, and - secondly, due to the quality of the results obtained with a great degree of accuracy and repeatability, it has been shown to possess significant scientific value in the research, but especially technical value -for quality control of natural and artificial pozzolans commonly added to Portland cement factory and/or directly to their concrete and mortar in plant-, and also be representative enough of the values obtained by the same probable chemical durability that each of them can reach out to give the concrete mortar and paste to which it belongs, as well as proper amount of partial replacement of Portland cement. To get in line with their own chemical-physical or physical-chemical features which can come to confer, as its chemical character (aluminic, silicic-aluminic, aluminic-silicic, aluminic-ferric-silicic or ferric-silicic), form and medium size of its particle is. Finally, the new analytical method has proven to meet all mandatory requirements established by ISO/IEC 17025 on the quality and reliability of new methods or analytical procedures are not standardized yet, in order to be considered appropriate this new analytical method, in this Doctoral Thesis it is to be proposed in the near future, before the corresponding AENOR (Spanish Association for Standardization and Certification) Commission, to start a procedure for certification and standardization.

Influencia de los requisitos de seguridad a la fatiga en el dimensionamiento de puentes mixtos de carretera

El fenómeno de fatiga es uno de los condicionantes más importantes en el diseño de puentes metálicos y mixtos bajo la acción cíclica de fuertes sobrecargas reales. Hoy en día, ha tomado mayor relevancia en el ámbito de puentes de carretera debido al aumento sustancial de la intensidad de tráfico y el peso de los vehículos. La evolución de las normativas actuales, que recogen su cálculo a partir del ELU de seguridad a fatiga, debe ir dirigida, hacia una mayor simplicidad de aplicación y un mayor rigor técnico. A partir del análisis de seis puentes mixtos de carretera proyectados recientemente (2007-2011) se pretende establecer una comparación, tanto cualitativa como cuantitativa, entre los métodos simplificados de la normativa española (antigua RPM/RPX 95 y actual EAE) y el Eurocódigo frente al Método del Daño Acumulado, caracterizado por ser más complicado de aplicar pero más riguroso. A través del análisis efectuado, se obtienen reglas prácticas sencillas y fiables para el dimensionamiento o verificación de elementos estructurales a fatiga según características principales como la tipología de la sección o la longitud de vano, entre otros. En conclusión, el trabajo que se propone desarrollar combina el análisis crítico de la base teórica con el estudio aplicado de casos reales y pretende sentar las bases para profundizar en esta área de gran interés para proyectistas. Fatigue is one of the most determining factors in the design of steel and composite bridges with dynamic loads subject to cyclic live loads. Nowadays, it has taken relevance in the field of roadway bridges due to considerable increase in the intensity of traffic and the weight of vehicles. The evolution of the current design codes, which include an analysis of the ultimate limit state of fatigue, should aim for greater ease of application and technical rigour. Based on the analysis of six composite road bridges designed recently (2007-2011), a comparison has been made, both qualitative and quantitative, between the simplified methods of the Spanish codes (current EAE and old RPM/RPX95) and Eurocode with regard to the Cumulative Damage Method, characterised for being more difficult to apply but more rigorous. Through an exhaustive analysis, a set of practical and reliable rules have been obtained for the sizing or verification of structural elements according to main characteristics such as the tipology of the cross section or the length of span, among others. In conclusion, the work developed combines the critical analysis of the theory with the applied study of real cases and sets out to lay the foundations for deepening into this area of great interest to designers.

Análisis experimental de la pérdida de adherencia hormigón-acero en hormigones sometidos a altas temperaturas

En el conjunto de materiales de construcción habituales en la edificación y las obras de ingeniería, el hormigón destaca entre otras razones por su excelente comportamiento frente a las altas temperaturas y la exposición al fuego. El presente estudio se centra en la adherencia residual entre el hormigón y las barras de acero corrugado soldable tras exponer probetas a altas temperaturas y enfriarlas hasta temperatura ambiente por convección natural. El estudio incluye hormigones de resistencia convencional, hormigones de alta resistencia y hormigones reforzados con fibras de polipropileno y fibras de acero. La adherencia hormigón-acero se ha medido mediante el conocido ensayo de pull-out. La campaña experimental también ha incluido la resistencia a compresión y la resistencia a tracción indirecta. Parte de las probetas se han ensayado a 28 días de edad a temperatura ambiente. A 60 días de edad se han repetido los ensayos a temperatura ambiente y se han realizado esos mismos ensayos en probetas calentadas en un horno industrial hasta tres rangos de temperatura: 450°C, 650°C y 825°C. Previo al proceso de calentamiento han sido sometidas durante 3 horas a un escalón de secado a 120°C. Mediante la metodología propuesta ha sido posible caracterizar la evolución de la pérdida de adherencia residual entre el acero y el hormigón conforme se exponen los especímenes a temperaturas más elevadas. La adición de fibras no tiene una influencia clara en la adherencia a temperatura ambiente. Sin embargo, sí se ha conseguido determinar una mejora sustancial de la adherencia residual en los hormigones, reforzados con fibras de acero sometidos a altas temperaturas.

Cyclopedia of architecture, carpentry, and building : a general reference work ... /

"Authorities consulted" at beginning of each volume.

Hybrid mathematical and informational modeling of beam-to-column connections

The analysis of steel and composite frames has traditionally been carried out by idealizing beam-to-column connections as either rigid or pinned. Although some advanced analysis methods have been proposed to account for semi-rigid connections, the performance of these methods strongly depends on the proper modeling of connection behavior. The primary challenge of modeling beam-to-column connections is their inelastic response and continuously varying stiffness, strength, and ductility. In this dissertation, two distinct approaches—mathematical models and informational models—are proposed to account for the complex hysteretic behavior of beam-to-column connections. The performance of the two approaches is examined and is then followed by a discussion of their merits and deficiencies. To capitalize on the merits of both mathematical and informational representations, a new approach, a hybrid modeling framework, is developed and demonstrated through modeling beam-to-column connections. Component-based modeling is a compromise spanning two extremes in the field of mathematical modeling: simplified global models and finite element models. In the component-based modeling of angle connections, the five critical components of excessive deformation are identified. Constitutive relationships of angles, column panel zones, and contact between angles and column flanges, are derived by using only material and geometric properties and theoretical mechanics considerations. Those of slip and bolt hole ovalization are simplified by empirically-suggested mathematical representation and expert opinions. A mathematical model is then assembled as a macro-element by combining rigid bars and springs that represent the constitutive relationship of components. Lastly, the moment-rotation curves of the mathematical models are compared with those of experimental tests. In the case of a top-and-seat angle connection with double web angles, a pinched hysteretic response is predicted quite well by complete mechanical models, which take advantage of only material and geometric properties. On the other hand, to exhibit the highly pinched behavior of a top-and-seat angle connection without web angles, a mathematical model requires components of slip and bolt hole ovalization, which are more amenable to informational modeling. An alternative method is informational modeling, which constitutes a fundamental shift from mathematical equations to data that contain the required information about underlying mechanics. The information is extracted from observed data and stored in neural networks. Two different training data sets, analytically-generated and experimental data, are tested to examine the performance of informational models. Both informational models show acceptable agreement with the moment-rotation curves of the experiments. Adding a degradation parameter improves the informational models when modeling highly pinched hysteretic behavior. However, informational models cannot represent the contribution of individual components and therefore do not provide an insight into the underlying mechanics of components. In this study, a new hybrid modeling framework is proposed. In the hybrid framework, a conventional mathematical model is complemented by the informational methods. The basic premise of the proposed hybrid methodology is that not all features of system response are amenable to mathematical modeling, hence considering informational alternatives. This may be because (i) the underlying theory is not available or not sufficiently developed, or (ii) the existing theory is too complex and therefore not suitable for modeling within building frame analysis. The role of informational methods is to model aspects that the mathematical model leaves out. Autoprogressive algorithm and self-learning simulation extract the missing aspects from a system response. In a hybrid framework, experimental data is an integral part of modeling, rather than being used strictly for validation processes. The potential of the hybrid methodology is illustrated through modeling complex hysteretic behavior of beam-to-column connections. Mechanics-based components of deformation such as angles, flange-plates, and column panel zone, are idealized to a mathematical model by using a complete mechanical approach. Although the mathematical model represents envelope curves in terms of initial stiffness and yielding strength, it is not capable of capturing the pinching effects. Pinching is caused mainly by separation between angles and column flanges as well as slip between angles/flange-plates and beam flanges. These components of deformation are suitable for informational modeling. Finally, the moment-rotation curves of the hybrid models are validated with those of the experimental tests. The comparison shows that the hybrid models are capable of representing the highly pinched hysteretic behavior of beam-to-column connections. In addition, the developed hybrid model is successfully used to predict the behavior of a newly-designed connection.

Desenvolvimento e caracterização de um compósito matriz metálica (CMM): aço EUROFER97 reforçado com Carbeto de Tântalo - TaC

Steel is an alloy EUROFER promising for use in nuclear reactors, or in applications where the material is subjected to temperatures up to 550 ° C due to their lower creep resistance under. One way to increase this property, so that the steel work at higher temperatures it is necessary to prevent sliding of its grain boundaries. Factors that influence this slip contours are the morphology of the grains, the angle and speed of the grain boundaries. This speed can be decreased in the presence of a dispersed phase in the material, provided it is fine and homogeneously distributed. In this context, this paper presents the development of a new material metal matrix composite (MMC) which has as starting materials as stainless steel EUROFER 97, and two different kinds of tantalum carbide - TaC, one with average crystallite sizes 13.78 nm synthesized in UFRN and another with 40.66 nm supplied by Aldrich. In order to improve the mechanical properties of metal matrix was added by powder metallurgy, nano-sized particles of the two types of TaC. This paper discusses the effect of dispersion of carbides in the microstructure of sintered parts. Pure steel powders with the addition of 3% TaC UFRN and 3% TaC commercial respectively, were ground in grinding times following: a) 5 hours in the planetary mill for all post b) 8 hours of grinding in the mill Planetary only for steel TaC powders of commercial and c) 24 hours in the conventional ball mill mixing the pure steel milled for 5 hours in the planetary mill with 3% TaC commercial. Each of the resulting particulate samples were cold compacted under a uniaxial pressure of 600MPa, on a cylindrical matrix of 5 mm diameter. Subsequently, the compressed were sintered in a vacuum furnace at temperatures of 1150 to 1250 ° C with an increment of 20 ° C and 10 ° C per minute and maintained at these isotherms for 30, 60 and 120 minutes and cooled to room temperature. The distribution, size and dispersion of steel and composite particles were determined by x-ray diffraction, scanning electron microscopy followed by chemical analysis (EDS). The structures of the sintered bodies were observed by optical microscopy and scanning electron accompanied by EDS beyond the x-ray diffraction. Initial studies sintering the obtained steel EUROFER 97 a positive reply in relation to improvement of the mechanical properties independent of the processing, because it is obtained with sintered microhardness values close to and even greater than 100% of the value obtained for the HV 333.2 pure steel as received in the form of a bar

Projeto e Construção de um Veleiro Autónomo, utilizando materiais compósitos, Impressão a 3D e Aprendizagem Máquina

Este trabalho consistiu no projeto e construção de um veleiro autónomo de pequena escala. No início do trabalho, é feito um estudo acerca dos diferentes tipos de veículos autónomos, dando mais enfase aos veleiros. Em seguida, é iniciado o projeto do casco do veleiro, aplicando conceitos básicos de Arquitetura Naval. A forma do casco é desenhada com recurso ao programa DELFT Ship Free, onde são realizados estudos hidrodinâmicos do mesmo. Posteriormente é retratado a construção do casco projetado, com recurso a materiais compósitos e impressão 3D de componentes do veleiro. São ainda descritos os sensores, controladores, atuadores e programação desenvolvida para o veleiro. É também realizado um estudo sumário da estimativa de consumos e autonomia do sistema. No final, encontram-se os resultados obtidos das provas de mar efetuadas ao veleiro.

Vibration characteristics of concrete-steel composite floor structures

This paper discusses the vibration characteristics of a concrete-steel composite multi-panel floor structure; the use of these structures is becoming more common. These structures have many desirable properties but are prone to excessive and complex vibration, which is not currently well understood. Existing design codes and practice guides provide generic advice or simple techniques that cannot address the complex vibration in these types of low-frequency structures. The results of this study show the potential for an adverse dynamic response from higher and multi-modal excitation influenced by human-induced pattern loading, structural geometry, and activity frequency. Higher harmonics of the load frequency are able to excite higher modes in the composite floor structure in addition to its fundamental mode. The analytical techniques used in this paper can supplement the current limited code and practice guide provisions for mitigating the impact of human-induced vibrations in these floor structures.

Lateral movements in composite high-rise buildings under seismic action

Daring human nature has already led to the construction of high-rise buildings in naturally challenging geological regions and in worse environments of the world. However; literature review divulges that there is a lag in research of certain generic principles and rules for the prediction of lateral movement in multistorey construction. The present competitive trend orders the best possible used of available construction material and resources. Hence; the mixed used of reinforced concrete with structural steel is gaining prevalence day by day. This paper investigates the effects of Seismic load on composite multistorey building provided with core wall and trusses through FEM modelling. The results showed that increased rigidity corresponds to lower period of vibration and hence higher seismic forces. Since Seismic action is a function of mass and response acceleration, therefore; mass increment generate higher earthquake load and thus cause higher impact base shear and overturning movement. Whereas; wind force depends on building exposed, larger the plan dimension greater is the wind impact. Nonetheless; outriggers trusses noticeably contribute, in improving the serviceability of structure subjected to wind and earthquake forces.

Steel bars identification in reinforced concrete structures by using ANN and magnetic fields

This work proposes a methodology for non destructive testing (NDT) of reinforced concrete structures, using superficial magnetic fields and artificial neural networks, in order to identify the size and position of steel bars, embedded into the concrete. For the purposes of this paper, magnetic induction curves were obtained by using a finite element program. Perceptron Multilayered (PML) ANNs, with Levemberg-Marquardt training algorithm were used. The results presented very good agreement with the expect ones, encouraging the development of real systems based upon the proposed methodology.

Vibration characteristics of slender structures under human induced loads

This paper presents the outcome of investigations and studies of the vibratioon characteristics and response of low frequency structural systems for a composite concrete steel floor plate and a reverse profiled cable tensioned foot bridge. These highly dynamic and slender structure are the engineering response to planning, aesthetic and environmental influences, but are prone to excessive and complex vibration. A number of design codes and practice guides provided information to engineers for vibration mitigation However, they are limited to very simple load function applied to a few uncoupled translational modes of excitation. Motivated by the need to address the knowledge gaps in this area, the investigations described in this paper focused on synchronous multi-modal and coupled excitation of the floor plate and footbridge with considerations for torsinal effects. The results showed the potential for adverse dynamic response from multi-modal and coupled excitation influenced by patterned loading, structure geometry, stiffness distribution, directional effects, forcing functions based on activity frequency and duration of foot contact, and modal participation. It was also shown that higher harmonics of the load frequency can excite higher modes in the composite floor structure. Such responsive behaviour is prevalent mainly in slender and lightweight construction and not in stiffer and heavier structural systems. The analytical techniques and methods used in these investigations can supplement the current limited code and best practice provisions for mitigating the impact of human induced vibrations in slender structural systems.

Investigation of hybridized polyurethane, glass fibre reinforced cement and steel laminate in structural floor plate systems

Sandwich components have emerged as light weight, efficient, economical, recyclable and reusable building systems which provide an alternative to both stiffened steel and reinforced concrete. These components are made of composite materials in which two metal face plates or Glassfibre Reinforced Cement (GRC) layers are bonded and form a sandwich with light weight compact polyurethane (PU) elastomer core. Existing examples of product applications are light weight sandwich panels for walls and roofs, Sandwich Plate System (SPS) for stadia, arena terraces, naval construction and bridges and Domeshell structures for dome type structures. Limited research has been conducted to investigate performance characteristics and applicability of sandwich or hybrid materials as structural flooring systems. Performance characteristics of Hybrid Floor Plate Systems comprising GRC, PU and Steel have not been adequately investigated and quantified. Therefore there is very little knowledge and design guidance for their application in commercial and residential buildings. This research investigates performance characteristics steel, PU and GRC in Hybrid Floor Plate Systems (HFPS) and develops a new floor system with appropriate design guide lines.

Static and dynamic performance of lightweight hybrid composite floor plate system

In the modern built environment, building construction and demolition consume a large amount of energy and emits greenhouse gasses due to widely used conventional construction materials such as reinforced and composite concrete. These materials consume high amount of natural resources and possess high embodied energy. More energy is required to recycle or reuse such materials at the cessation of use. Therefore, it is very important to use recyclable or reusable new materials in building construction in order to conserve natural resources and reduce the energy and emissions associated with conventional materials. Advancements in materials technology have resulted in the introduction of new composite and hybrid materials in infrastructure construction as alternatives to the conventional materials. This research project has developed a lightweight and prefabricatable Hybrid Composite Floor Plate System (HCFPS) as an alternative to conventional floor system, with desirable properties, easy to construct, economical, demountable, recyclable and reusable. Component materials of HCFPS include a central Polyurethane (PU) core, outer layers of Glass-fiber Reinforced Cement (GRC) and steel laminates at tensile regions. This research work explored the structural adequacy and performance characteristics of hybridised GRC, PU and steel laminate for the development of HCFPS. Performance characteristics of HCFPS were investigated using Finite Element (FE) method simulations supported by experimental testing. Parametric studies were conducted to develop the HCFPS to satisfy static performance using sectional configurations, spans, loading and material properties as the parameters. Dynamic response of HCFPS floors was investigated by conducting parametric studies using material properties, walking frequency and damping as the parameters. Research findings show that HCFPS can be used in office and residential buildings to provide acceptable static and dynamic performance. Design guidelines were developed for this new floor system. HCFPS is easy to construct and economical compared to conventional floor systems as it is lightweight and prefabricatable floor system. This floor system can also be demounted and reused or recycled at the cessation of use due to its component materials.

Blast response and safety evaluation of a composite column for use as key element in structural systems

This paper presents the blast response, damage mechanism and evaluation of residual load capacity of a concrete–steel composite (CSC) column using dynamic computer simulation techniques. This study is an integral part of a comprehensive research program which investigated the vulnerability of structural framing systems to catastrophic and progressive collapse under blast loading and is intended to provide design information on blast mitigation and safety evaluation of load bearing vulnerable columns that are key elements in a building. The performance of the CSC column is compared with that of a reinforced concrete (RC) column with the same dimensions and steel ratio. Results demonstrate the superior performance of the CSC column, compared to the RC column in terms of residual load carrying capacity, and its potential for use as a key element in structural systems. The procedure and results presented herein can be used in the design and safety evaluation of key elements of multi-storey buildings for mitigating the impact of blast loads.

Effect of bond length on the behaviour of CFRP strengthened concrete-filled steel tubes under transverse impact

Concrete-filled steel tubular (CFST) columns have shown great potential as axial load carrying member and used widely in many mission critical infrastructures. However, attention is needed to strengthen these members where transverse impact force is expected to occur due to vehicle collisions. In this work, finite element (FE) model of carbon fibre reinforced polymer (CFRP) strengthened CFST columns are developed and the effect of CFRP bond length is investigated under transverse impact loading. Initially the numerical models have been validated by comparing impact test results from literature. The validated models are then used for detail parametric studies by varying the length of externally bonded CFRP composites. The parameters considered for this research are impact velocity, impact mass, CFRP modulus, adhesive type, and axial static loading. It has been observed that the effect of CFRP strengthening is consistent after an optimum effective bond length of CFRP wrapping. The effect of effective bond length has been studied for above parameters. The results show that, under combined axial static and transverse impact loads CFST columns can successfully prevent global buckling failure by strengthening only 34% of column length. Therefore, estimation of effective bond length is essential to utilise the CFRP composites cost effectively.