Portland cement is considered an excellence building material. This is due mainly to its high performance, its good quality/price ratio and the raw materials from which it is made can be found almost everywhere in the world. However, the development of alternative Portland cements obtained through processes involves lower emission of CO2 into the atmosphere is a priority research and great interest worldwide. Alkaline activation constitutes an alternative to Portland cement, preferably amorphous or vitreous aluminosilicates and alkaline activator (such as NaOH, Na2CO3 or sodium silicates hydrates). The aluminosilicates may be natural products such as metakaolin or industrial by-products such as blast furnace slag or aluminosiliceous fly ash. These cements and concretes obtained by alkali activating aluminosilicates are characterised by high mechanical strength, low heat of hydration and high impermeability, as well as resistance to high and low temperatures and sulphate, seawater and acid attacks. Moreover, the preparation of these alkaline cements requires lower energy than in the manufacturing process of Portland cement. However, we still cannot say or establish that alkaline cements (alkali activated materials or geopolymers) are based on a clean chemical to the environment, due to production processes of alkaline solutions such as sodium silicates emit large amounts of CO2 into the atmosphere. This article aims to make a trip back in time to the origins of the alkali activation to explain the most characteristic and important chemical concepts.
Pozzolans have demonstrated to be highly efficient mineral additions in the concrete industry, because they reduce the environmental impact generated by the cement manufacture, improve the physical, chemical and mechanical properties of blends, and reduce costs. Calcined clays have been recognized as very good pozzolans, because they improve the durability and compressive strength of mortars and concretes. However, data reported by different authors show a very high variability that makes its modelling difficult. In the same way, and based on a review of the scientific literature, the relationship between morphologic characteristics, thermal treatments and mineral composition of clays and its pozzolanic reactivity is shown; as well as with the chemical, thermal and mechanical methods for improving that reactivity.
There are few studies on the behavior of historic structures of adobe and rammed earth in Latin America, which has contributed to the deterioration of these buildings, which are part of our architectural and cultural heritage. Colombia has 90% of its heritage buildings made of earth and most of them are located in high and intermediate seismic risk zones. The town halls of the colonial era (made of adobe or rammed earth) are part of this Colombian architectural heritage and still kept 11 of these houses in the Department of Cundinamarca. This article presents the results of a study conducted by research groups GRIME and Estructuras & Construcción, where the objective was to study a method of rehabilitation of town halls of rammed earth through confinement wooden elements. The research is based on shake table tests on scale models (1:20), with and without reinforcement with confinement wooden elements. The results suggest that the reinforced model had less seismic displacements (69% less than the model without reinforcement) and that the wooden confinement elements diminishes the cracking of the rammed earth walls.
The behavior in flexural fatigue tests of concrete containing metal fibers has not been extensively studied. Therefore, this study was considered to determine the effect of incorporating metal fibers in concrete paving in flexural fatigue tests. A concrete mix was designed with modulus of rupture of 4.1 MPa at 28 days, which is dosed metal fibers 35 mm long and 0.5 mm in diameter in three proportions: 20 kg/m3, 40 kg/m3 and 80 kg/m3 and left to a non-corresponding control mixture addition. The fatigue tests were performed on 68 specimens of 100 x 100 x 350 mm, at a frequency of 8 Hz, and stresses between 80% and 90% of the modulus of rupture of each mixture. The Weibull probability distribution were used to calculate the fatigue curves with different failure probabilities. For the stresses ranges studied, the fatigue life does not increase for the mix with fiber content of 20 kg/m3 and increased by 6% to 40 kg/m3 (0.5%) and 25% to 80 kg/m3 (1%) compared to the Control mixture.
En este artículo se evalúa la influencia de dos ambientes corrosivos a corto plazo, y de la dosificación de fibras sobre el desempeño a flexión del concreto reforzado con fibras de acero, CRFA. El programa experimental comprendió el ensayo de 54 especímenes de concreto reforzado con fibras de acero que tienen relación longitud/diámetro de 65 y dosificaciones de fibras de 30 kg/m3 y 60 kg/m3. En cuanto a los ambientes corrosivos, cilindros y vigas fueron sometidos a la acción de un medio acuoso y un medio de solución NaCl al 3.5%, por un periodo de 60 días. Los resultados fueron comparados con aquellos cilindros y vigas que permanecieron en condiciones inalteradas. Para dicho tiempo de exposición que corresponde a la fase de iniciación de la corrosión, se observó que los iones cloruro presentes en el medio salino (NaCl al 3.5%) ocasionan degradación en el desempeño mecánico del concreto con fibras de acero, por ejemplo, pérdida aproximada del 10% en la resistencia a flexión y disminución del 11% de la tenacidad en flexión. No obstante para la fase de iniciación de la corrosión, la exposición al medio salino provoca un incremento de la capacidad de deflexión del CRFA que puede mejorar su ductilidad y la capacidad de adherencia entre la matriz y las fibras de acero embebidas. Finalmente, se han propuesto ecuaciones que permiten describir el efecto de ambientes acuosos y salinos en la fase de iniciación de la corrosión sobre el CRFA sometido a esfuerzos de flexión.
The article aims to describe, identify and classify application forms for Open Innovation, delivering specific cases for its justification. The methodology consisted of a critical review of the main theoretical fundamentals presented in the statement about art, the concept of Open Innovation, its evolution and application. The concept of Open Innovation and its implementation is a matter that occurs in practice, where methodologies have not been determined to define the application mechanism that best suits the organization. The document has four sections. The first discusses the evolution of the concept of Open Innovation. The second classifies this concept, then in the third we present specific application fields and its main mechanisms or application tools, application examples and at the end of the last section findings and input on prospective studies are delivered.
Dynamic characteristics of structures determine the methods to be used for their analysis and design against environmental loads such as wind. In some structures, the effect of the energy contained in gusts sequences must be attended, emphasizing the fluctuating components of the gusts that resonate with them. In these cases, dynamic methods in time domain are frequently used. Numerical simulation of wind loads is a tool that has been widely developed and applied. The aim of this study is to perform a literature review to determine the necessary parameters for simulating wind time series as well as the existing numerical methods for this purpose, emphasizing in tropical cyclone-prone region.
This work presents a numeric study using the Finite Element Method for castellated beams manufactured from Brazilian steel rolled I-sections, which collapse by web post buckling. After the beam analysis for the limit buckling state, other analyses were carried out, adding web post stiffeners in the region that would suffer the buckling. The results show significant influence of the stiffeners in the bearing capacity and in the collapsing mode presented in the analyzed beams.
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