The introduction of teaching innovations into the traditional teaching of construction and building materials

The traditional teaching methods used for training civil engineers are currently being called into question as a result of the new knowledge and skills now required by the labor market. In addition, the European Higher Education Area is requesting that students be given a greater say in their learning. In the subject called Construction and Building Materials at the Civil Engineering School of the Universidad Politécnica de Madrid, a path was set three academic years ago to lead to an improvement in traditional teaching by introducing active methodologies. The innovations are based on cooperative learning, new technologies, and continuous assessment. The writers’ proposal is to offer their experience as a contribution to the debate on how students can be encouraged to acquire the skills currently demanded from a civil engineer, though not overlooking solid, top-quality training. From the outcomes obtained, it can be concluded that using new teaching techniques to supplement a traditional approach provides more opportunities for students to learn while boosting their motivation. In our case, the introduction of these changes has resulted in an increased pass rate of 29% on average, when such a figure is considered in the light of the mean value of passes during the last decade

Experiencias docentes en innovación educativa como mejora de una enseñanza tradicional de los materiales de construcción

En este trabajo se presentan los resultados de una experiencia docente en la asignatura de Materiales de Construcción incorporando metodologías activas como lo sugiere el Espacio Europeo de Educación Superior (EEES). Desde el curso 2006-07 se inició una mejora de la enseñanza tradicional, basada en la utilización del aprendizaje cooperativo, evaluación continua y las nuevas tecnologías. En los últimos tres cursos ha habido un aumento notable del número de aprobados, un 32% de aumento sobre alumnos matriculados, respecto a cursos anteriores. De los resultados obtenidos se puede concluir que el uso de técnicas docentes activas como complemento de la enseñanza tradicional mejora el aprendizaje de los alumnos y potencia su motivación. Sin embargo, requiere mayor dedicación del profesor y mayor dedicación del alumno en su aprendizaje

Stress relaxation losses of prestressing steel wires

Prestressed structures are susceptible to relaxation losses which are of significant importance in structural design. After being manufactured, prestressing wires are coiled to make their storage and transportation easier. The possible deleterious effects of this operation on the stress relaxation behavior of prestressing steel wires are usually neglected, though it has been noticed by manufacturers and contractors that when relaxation tests are carried out after a long-time storage, on occasions relaxation losses are higher than those measured a short time after manufacturing. The influence of coiling on the relaxation losses is checked by means of experimental work and confirmed with a simple analytical model. The results show that some factors like initial residual stresses, excessively long-time storage or storage at high temperatures, can trigger or accentuate this damage. However, it is also shown that if the requirements of standards are fulfilled (minimum coiling diameters) these effects can be neglected

Bond Modelling of prestressed concrete during the prestressing force release

This paper presents an analytical model for simulating the bond between steel and concrete, in precast prestressed concrete elements, during the prestressing force release. The model establishes a relationship between bond stress, steel and concrete stress and slip in such concrete structures. This relationship allows us to evaluate the bond stress in the transmission zone, where bond stress is not constant, along the whole prestressing force release process. The model is validated with the results of a series of tests and is extended to evaluate the transmission length. This capability has been checked by comparing the transmission length predicted by the model and one measured experimentally in a series of tests

Modelling of non-uniform corrosion-induced cover cracking in reinforced concrete

Cover cracking and spalling in concrete due to corrosion of reinforcement bars is one of the major concerns for durability of reinforced concrete structures and has been widely researched during recent years. Most approaches to the problem are based on a uniform corrosion and expansion pressure around the rebar. However, corrosion rust tends to accumulate around the steel circumference that faces the concrete cover. From this outer part of the rebar, the corrosion front gradually advances to the inner, which entails a non-uniform expansive pressure around the rebar. The purpose of the study is to simulate the effect of non-uniform rust distribution around the corroded rebar, taking advantage of an embedded cohesive crack finite element. The objective is to develop more realistic models for the estimation of the service life of reinforced concrete structure

The influence of fly ash as substitute of cement in the durability of concrete

Limitation of transport capacity through the concrete is one of the key points in the improvement of the material’s durability. The use of fly ash as an admixture to concrete is widely extended; a general consensus has been established due to the pore size reduction produced by the ashes. Nevertheless, the importance of the micro-structural and composition changes in mechanical and durable properties is not well defined. In the present study the use of fly ash has been considered as substitute of cement in the design limits. The concrete mechanical properties and its porous structure were evaluated. The tests included porosimetry and water permeability tests. In order to characterize the hydration products and its evolution with time TG and DTA analysis were performed. This work studies the fly ash concrete hydration process, their influence in the porous distribution, and the mechanical and durable properties of the material

Estudio del comportamiento mecánico y frente a corrosión de armaduras pasivas de acero revestidas con resina epoxi

La Instrucción EHE-08 prevé una vida útil para las estructuras de hormigón armado habituales de 50 ó 100 años. En ambientes en los que el hormigón esté expuesto a la acción de cloruros el recubrimiento de la armadura necesario resulta excesivo, por lo que se recomienda el empleo de medidas especiales de protección de la armadura frente a corrosión. Una medida eficaz es el revestimiento de la armadura con resina epoxi. Esta solución plantea dos dudas: 1) la eficacia real de la protección frente a la corrosión, y 2) la posible alteración de la adherencia acero-hormigón. Este artículo presenta los resultados de los ensayos de corrosión acelerada y arrancamiento de barras (?pull-out?) de estas barras y los compara con los obtenidos con barras iguales no revestidas. Se han ensayado barras de diámetros 8, 16 y 25 mm. Además, en los ensayos de corrosión acelerada, se ha estudiado la influencia de los defectos en la capa de resina epoxi, producidos por golpes en la superficie, así como la eficacia de la posible reparación en obra. Los resultados obtenidos muestran la gran eficacia de este tipo de protección frente a los ensayos de corrosión acelerada y la prácticamente nula influencia que tiene la capa de resina epoxi en los resultados de los ensayos de arrancamien

Caracterización del comportamiento en fractura de paneles sandwich de placas de yeso laminado y lana de roca

En esta comunicación se presenta el trabajo realizado para la caracterización experimental de un panel sándwich de yeso laminado y lana de roca, así como de cada uno de sus componentes: placa de yeso laminado, placa de yeso, lana de roca y papel. Para ello se diseñó una campaña de ensayos destinados a obtener las propiedades resistentes de los materiales estudiados, así como la energía específica de fractura, GF, y las curvas completas de carga aplicada frente a desplazamientos. A partir de los resultados experimentales se ha observado que la energía de fractura está muy condicionada por el espesor de la lana de roca, y no tanto por el de la placa. Para simular numéricamente el comportamiento en fractura del panel se ha utilizado un modelo de elementos finitos con fisura embebida basado en la fisura cohesiva en el que se introducen como entrada los parámetros obtenidos a partir de la experimentación, obteniéndose una buena aproximació

Finite element simulation of sandwich panels of plasterboard and rock wool under mixed mode fracture

This paper presents the results of research on mixed mode fracture of sandwich panels of plasterboard and rock wool. The experimental data of the performed tests are supplied. The specimens were made from commercial panels. Asymmetrical three-point bending tests were performed on notched specimens. Three sizes of geometrically similar specimens were tested for studying the size effect. The paper also includes the numerical simulation of the experimental results by using an embedded cohesive crack model.The involved parameters for modelling are previously measured by standardised tests

Creep and shrinkage of self compacting concrete of medium-strenght

Self-compacting concrete (SCC) is an innovative concrete that does not require vibration for placing and compacting. SCC, developed in Japan in the 1980s, provides a present-day and attractive challenge for many researchers, as the long list of papers on the topic corroborates. Nevertheless, the durability of SCC, especially medium-low strength SCC, provides the researcher with opportunities for study in depth. This paper deals with the shrinkage and creep of SCC: three SCC mixtures, with 30 MPa compressive strength, are studied. The main differences among the SCCs involve the type of the cement: one SCC with type I cement and two SCCs with blended cements. The shrinkage and creep of the three SCCs are studied and compared. Fresh properties and mechanical properties are also evaluated. The shrinkage strains and creep are calculated by means of ACI 209 and Eurocode 2 models. These models overestimate the shrinkage strains and undervalue the creep for the studied concretes