Jorge Iván Tobón

An Opportunity for Environmental Conservation: Evaluation of Test Material for Construction of Artificial Reefs Modules Trainers Made of Ecological Concrete

As a result of the degradation of coral reefs around the world and given that conservation efforts alone are not enough, artificial reefs have been proposed as a tool for the conservation of these ecosystems and recovery. As part of an initiative to develop modules forming artificial reefs made of concrete to promote the ecological conservation of the biodiversity of the Colombian Caribbean, this work constitutes a starting point. During eight months two trapezoidal plates were submerged in the waters surrounding the Bajo Grande (Isla Palma) archipelago de San Bernardo in the Colombian Caribbean; the plates were fabricated in concrete with Portland cement and waste ceramic. Seeking a more ecological product, aggregates were replaced entirely by ceramic waste. After making biological and physicochemical evaluations of the material exposed to the marine environment it was concluded that this is a favorable substrate for the development of coral reefs; and the plates were colonized on more than 30% of its surface by marine organisms, their structure was found internally stable and there were no adverse effects on marine biota near the test site.

RESISTENCIA A LA COMPRESIÓN DE MORTEROS PIGMENTADOS CON AZUL ULTRAMAR

Ultramarine Blue (sodium polisulphurated aluminesilicate, UB) is an inorganic pigment used in different industries (automovilistic, polymers, soap and detergents). Strength in mortars with traditional pigments and with Ultramarine Blue was evaluated in this investigation; we found that UB increase it until 54% to seven days of setting time. However, the mineralogical analysis does not show to UB as a classic pozzolane because the CH drop does not increase the tobermorite quantity, but yes the ettrigite quantity. The ettringite is the responsible of strength increase.

Performance and Microstructural Analysis of Lightweight Concrete Blended with Nanosilica under Sulfate Attack

The influence of two lightweight aggregates (LWA) on concrete and the effects of cement substitution for nanosilica (NS) on the interfacial transition zone (ITZ) and cementitious matrix of concrete in resistance to attacks by magnesium sulfate (MgSO4) are researched in this work. The aggregates evaluated were perlite, which is a lightweight aggregate of open porous structure, and expanded clay (aliven) with closed porous structure. The variables included in the study were replacement percentage of coarse aggregates by lightweight coarse aggregates (0 and 100% by volume) and replacement percentage of cement by nanosilica (0 and 10% by weight). In the dosage of the mixtures, water/cementitious-material ratio constant of 0.35 was used. The LWA were characterized by XRD, XRF, and SEM techniques. Compressive strength, water absorption, and volume change in magnesium sulfate solution (according to ASTM C1012 for a period of 15 weeks) of lightweight concretes were evaluated. It was found that the nanosilica had effect on refinement in the pore system; however, the main incidence on the compressive strength and durability of lightweight concrete (LWC) was defined by the characteristics of lightweight aggregate used in its preparation.

Reduction of CO2 Emissions by Chemical Synthesis Processes in the Cement Industry

Portland cement is obtained by a conventional synthesis process from a mixture of limestone and clay at high temperature (1450°C). This work reports the possibility to obtain cement silicates via alternative methods like Solution Combustion Synthesis (SCS), which optimize both time and temperature, and the consequences to energy efficiency and mitigation of CO2 emissions. The production of one ton of cement emits between 0.62 and 0.97 tons of CO2 into the atmosphere. In this process the CO2 emissions are between 21 and 59%. The combustion methods are chemical redox processes in which, at high temperature, a self-sustaining and fast wave is generated from using chemical precursors and organic fuels.

Efectos de algunas adiciones minerales colombianas en la fabricación del clínker para cemento pórtland i

En esta investigacion se usaron minerales de origen colombiano tal y como son producidos en sus respectivas minas. Se experimento con la fluorita (Santander), el feldespato (Antioquia) y el manganeso (Antioquia) en cantidades del 0,0%, 0,2%, 0,5%, 1,0%, 1,5% y 2,0%. Se aplicaron varias tecnicas como difraccion de rayos X, fluorescencia de rayos x, microscopia electronica de barrido y microscopia optica para caracterizar los materiales utilizados y analisis termico diferencial para determinar la temperatura de clinkerizacion y se evaluo mineralogicamente el clinker obtenido. Se encontro que el mejor resultado se logro con la adicion de 0,5% de la fluorita al permitir la mayor formacion de alita y la disminucion en el contenido de cal libre. El feldespato y el manganeso (braunita) utilizados no tuvieron un comportamiento apropiado.