Effect of the particle size range of construction and demolition waste on the fresh and hardened-state properties of fly ash-based geopolymer mortars with total replacement of sand

This study seeks the valorization of industrial residues (fly ash and construction and demolition waste (CDW)) through the production of geopolymer mortars. The effect of the sand substitution by CDW and the influence of the particle size range of CDW fine aggregates on the fresh and hardened properties of the mortars were evaluated. Geopolymer mortars were produced using biomass fly ash waste and metakaolin as a binder, CDW as fine aggregates, and an alkali solution of sodium silicate and sodium hydroxide as activator. The geopolymer mortars were characterized in fresh state by the flow table test and in the hardened state through chemical, physical/microstructural analyzes. The mortars produced with CDW showed lower flowability when compared to the ones prepared with sand. The compressive and flexural strength of hardened mortars, respectively, obtained with residues were higher when compared to sand: 40 MPa and 8.5 MPa with CDW, against 23 MPa and 3.1 MPa for sand-based samples. It was observed that mortars developed with recycled aggregate and natural aggregate present similar chemical and mineralogical compositions. The superior results obtained in the mechanical properties of mortars produced with CDW are related to the recycled aggregate-geopolymer paste interface.publishe

Impact of the absolute rutile fraction on TiO2 visible-light absorption and visible-light-promoted photocatalytic activity

Titanium dioxide is by far the most used semiconductor material for photocatalytic applications. Still, it is transparent to visible-light. Recently, it has been proved that a type-II band alignment for the rutile − anatase mixture would improve visible-light absorption. In this research paper we thoroughly characterised the real crystalline and amorphous phases of synthesised titanias – thermally treated at different temperatures to get distinct ratios of anatase-rutile-amorphous fraction – as well as that of three commercially available photocatalytic nano-TiO2. Optical spectroscopy showed that even a small fraction of rutile (2 wt%) is able to shift to lower energies the apparent optical band gap of an anatase-rutile mixed phase. But is this enough to attain a real photocatalytic activity promoted by merely visible-light? We tried to give an answer to that question. Photocatalytic activity was assessed in the liquid- and gas-solid phase (employing rhodamine B and 4-chlorophenol, and isopropanol, respectively, as the organic substances to degrade) using a light source irradiating exclusively in the visible-range. Photocatalytic activity results in the liquid-solid phase showed that a high surface hydroxylation led to specimen with superior visible light-promoted catalytic activity – i.e. dye and ligand-to-metal charge transfer complexes sensitisation effects, not photocatalysis sensu-strictu. On the other hand, the gas-solid phase results showed that a higher amount of the absolute rutile fraction (around 10 wt%), together with less recombination of the charge carriers, were more effective for both visible-light absorption and a “real” visible-light promoted photocatalytic oxidation of isopropanol.publishe

Biotechnologies and bioinspired materials for the construction industry : an overview

Published online: 16 Oct 2013Looking back to less than three centuries of industrialization, responsible for alarming levels of pollution and consumption of non-renewable resources that has led to the exhaustion of the earth’s capacity, the humankind only now begins to grasp the overwhelming potential of natural systems. During almost 40 million centuries, Nature has developed materials and processes with optimal performance which are totally biodegradable. Analysis of bioinspired materials requires the knowledge of both biological and engineering principles which are being a part of a large research area termed biotechnology. This hot area is one of the six strategic Key Enabling Technologies that will be funded under the EU Framework Programme Horizon 2020. This paper reviews the current knowledge on the potential of this emerging field, particularly in the development of materials and technologies for the construction industry. It covers the use of bacteria for enhancing concrete durability and for soil stabilization. It also covers bioinspired tough composite materials, bioinspired adhesives and coatings, and self-cleaning materials. Incorporation of biology basics in the civil engineering curriculum would ease the communication between biologists and civil engineers, helping to foster research on biotechnologies and bioinspired materials for the construction industry

Waste glass from end-of-life fluorescent lamps as raw material in geopolymers

Nowadays the stunning volume of generated wastes, the exhaustion of raw materials, and the disturbing greenhouse gases emission levels show that a paradigm shift is mandatory. In this context, the possibility of using wastes instead of virgin raw materials can mitigate the environmental problems related to wastes, while reducing the consumption of the Earth’s natural resources. This innovative work reports the incorporation of unexplored waste glass coming from end-of-life fluorescent lamps into geopolymers. The influence of the waste glass incorporation level, NaOH molarity and curing conditions on the microstructure, physical and mechanical properties of the geopolymers was evaluated. Results demonstrate that curing conditions are the most influential factor on the geopolymer characteristics, while the NaOH molarity is less important. Geopolymers containing 37.5% (wt) waste glass were successfully produced, showing compressive strength of 14 MPa (after 28 days of curing), suggesting the possibility of their use in non-structural applications. Porous waste-based geopolymers for novel applications were also fabricated

Desarrollo de pigmentos cerámicos basados en residuos

Se presenta la preparación de pigmentos cerámicos empleando residuos industriales como fuente de materias primas. Se detallan el uso de barros ricos en aluminio obtenidos en los tratamientos de depuración de aguas de plantas industriales de anodizado y barros de galvanizados de chapados de Cr/Ni. Los pigmentos cerámicos se prepararon empleando reacción en estados sólido a partir del barro rico en metal. Los principales pigmentos estudiados son orquídea casiterita de cromo-estaño (Sn,Cr)O2, malayita rojo de cromo-estaño Ca(Sn,Cr)SiO3, granate verde victoria Ca3Cr2Si3O12, y corindón rosa/verde de cromo alúmina (Cr,Al)2O3. Los pigmentos fueron caracterizados y ensayados después de ser vidriados en cerámicas estándares. Se presentan las condiciones de trabajo y el desarrollo de color

Effect of nano-SiO2 and nano-TiO2 addition on the rheological behavior and the hardened properties of cement mortars

This paper reports on the use of nano-SiO2 (nS) and nano-TiO2 (nT) in cement pastes and mortars. Samples with 0–3 wt.% nS, 0–12 wt.% nT and 0.5 water/binder weight ratio were prepared. Rheological and flow table measurements were carried out. In addition, the design of experiments was applied to validate the results found. The temperature of hydration and compressive strength with 28 days was also determined. In general, mortars exhibited noticeable differences in the rheological behavior, but less evident in temperature of hydration and compressive strength. The values of torque, yield stress and plastic viscosity of mortars with nanoadditives increased significantly, reducing the open testing time in rheology tests. Meanwhile, the flow table values reduced. In addition, spread on table and initial yield stress exhibited a power correlation, while the spread on table and plastic viscosity did not show any special relationship. The results of kinetics of hydration followed the same tendency found by rheology, in which samples with higher amounts of nS and nT showed remarkable changes in relation to the samples without nanoadditives. Mechanical properties were not significantly affected by nanoparticles in the range considered in this work

Setting behaviour of waste-based cements estimated by impedance spectroscopy and temperature measurements

Este trabajo describe el estudio del desarrollo de fases durante el fraguado de diferentes formulaciones de clinker preparados con residuos industriales o subproductos, denominados barros (generados en los procesos de recubrimientos industriales por anodizado de Al, en procesos de filtración/depuración de agua potable y en procesos de corte de mármol) y arenas de fundición. Con el objeto de comparar, se prepararon formulaciones similares a partir de materias primas comerciales de alta pureza y procesadas en idénticas condiciones. Para sortear las restricciones experimentales de inherentes a la aguja de Vicat (esto es, grandes cantidades de material), se realizaron medidas de resistividad eléctrica en corriente alterna (a.c.) de espectroscopía de impedancia para seguir el proceso de hidratación y fraguado. Durante el fraguado, la evolución de la temperatura de las pastas de agua/cemento se registró. Los estudios de espectroscopía de impedancia mostraron ser un método fiable y en algunos casos, pueden emplearse como técnica sensible para detectar el inicio de las reacciones de hidratación