Carlos Leiva

Use of FGD gypsum in fire resistant panels

Gypsum from power plant flue gas desulphurization units (FGD gypsum) is a combustion by-product produced in high quantities. In this paper, gypsum panels composed of 100% FGD gypsum from two power plants have been subjected to different physico-chemical (density, pH, humidity), mechanical (flexural and compressive strength, surface hardness, impact resistance), fire resistance and environmental tests (leaching and radioactivity). The results obtained have been compared with the requirements established in some European standards for commercial gypsum and other standards for similar products. In addition, the panels manufactured have been compared with commercial gypsum panels in order to determine the recycling possibilities of this kind of material in this application.

Differential partitioning and speciation of Hg in wet FGD facilities of two Spanish PCC power plants

This paper evaluates the speciation and partitioning of mercury in two Spanish pulverised coal combustion power plants (PP1 and PP2), equipped with wet limestone-based flue gas desulphurisation facilities (FGD) operating with forced oxidation and re-circulation of FGD water streams. These plants are fed with coal (PP1) and coal/pet-coke blends (PP2) with different mercury contents. The behaviour, partitioning and speciation of Hg were found to be similar during the combustion processes but different in the FGD systems of the two power plants. A high proportion (86-88%) of Hg escaped the electrostatic precipitator in gaseous form, Hg2+ being the predominant mercury species (68-86%) to enter the FGD. At this point, a relatively high total Hg retention (72% and 65%) was achieved in the PP1 and PP2 (2007) FGD facilities respectively. However, during the second sampling campaign for PP2 (2008), the mercury removal achieved by the FGD was much lower (26%). Lab-scale tests point to liquid/gas ratio as the main parameter affecting oxidised mercury capture in the scrubber. The partitioning of the gaseous mercury reaching the FGD system in the wastes and by-products differed. In the low mercury input power plant (PP1) most of the mercury (67%) was associated with the FGD gypsum. Moreover in PP2 a significant proportion of the gaseous mercury reaching the FGD system remained in the aqueous phase (45%) in the 2007 sampling campaign while most of it escaped in 2008 (74%). This may be attributed to the scrubber operating conditions and the different composition and chemistry of the scrubber solution probably due to the use of an additive.

High fire resistance in blocks containing coal combustion fly ashes and bottom ash

Fire resistance recycled blocks, containing fly ash and bottom ash from coal combustion power plants with a high fire resistance, are studied in this paper by testing different compositions using Portland cement type II, sand, coarse aggregate and fly ash (up to 50% of total weight) and bottom ash (up to 30% of total weight). The fire resistance, physical-chemical (density, pH, humidity, and water absorption capacity), mechanical (compressive and flexural strength), and leaching properties are measured on blocks made with different proportions of fly ash and bottom ash. The standard fire resistance test is reproduced on 28cm-high, 18cm-wide and 3cm-thick units, and is measured as the time needed to reach a temperature of 180°C on the non-exposed surface of the blocks for the different compositions. The results show that the replacement of fine aggregate with fly ash and of coarse aggregate with bottom ash have a remarkable influence on fire resistance and cause no detriment to the mechanical properties of the product. Additionally, according to the leaching tests, no environmental problems have been detected in the product. These results lead to an analysis of the recycling possibilities of these by-products in useful construction applications for the passive protection against fire.

Use of co-combustion bottom ash to design an acoustic absorbing material for highway noise barriers

The present study aims to determine and evaluate the applicability of a new product consisting of coal bottom ash mixed with Portland cement in the application of highway noise barriers. In order to effectively recycle the bottom ash, the influence of the grain particle size of bottom ash, the thickness of the panel and the combination of different layers with various particle sizes have been studied, as well as some environmental properties including leachability (EN-12457-4, NEN-7345) and radioactivity tests. Based on the obtained results, the acoustic properties of the final composite material were similar or even better than those found in porous concrete used for the same application. According to this study, the material produced presented no environmental risk.

Recycled blocks with improved sound and fire insulation containing construction and demolition waste

The environmental problem posed by construction and demolition waste (C&D waste) is derived not only from the high volume produced, but also from its treatment and disposal. Treatment plants receive C&D waste which is then transformed into a recycled mixed aggregate. The byproduct is mainly used for low-value-added applications such as land escape restoration, despite the high quality of the aggregate. In the present work, the chemical composition properties and grading curve properties of these aggregates are defined. Furthermore, the resulting recycled concrete with a high proportion of recycled composition, from 20% to 100% replacement of fine and coarse aggregate, is characterized physically and mechanically. An environmental study of the new construction material when all aggregates are substituted by C&D waste shows a low toxicity level, similar to that of other construction materials. The new material also has improved properties with respect to standard concrete such as high fire resistance, good heat insulation, and acoustic insulation.

Development of fly ash boards with thermal, acoustic and fire insulation properties

This paper presents an experimental analysis on a new board composed of gypsum and fly ashes from coal combustion, which are mutually compatible. Physical and mechanical properties, sound absorption coefficient, thermal properties and leaching test have been obtained. The mechanical properties showed similar values to other commercial products. As far as the acoustic insulation characteristics are concerned, sound absorption coefficients of 0.3 and 0.8 were found. The board presents a low thermal conductivity and a fire resistance higher than 50 min (for 4 cm of thickness). The leaching of trace elements was below the leaching limit values. These boards can be considered as suitable to be used in building applications as partitions.

Radiological, Leaching, and Mechanical Properties of Cocombustion Fly Ash in Cements

AbstractWastes are used increasingly as construction materials to make the building industry more sustainable. In this regard, the European standards indicate the characteristics to be met by fly a...

Assessing durability properties of noise barriers made of concrete incorporating bottom ash as aggregates

Abstract This research analyses the durability of a noise barrier using coal bottom ashes as aggregates in a high proportion (80%wt of bottom ash). A concrete noise barrier is composed by a combination of a porous sound absorbing face and a standard concrete in order to increase the mechanical properties of the barrier. The bottom ash was sieved at 2.5 mm, a porous concrete with the coarse fraction of bottom ashes and a standard concrete with the fine fraction of bottom ashes were made. This paper analyses the water absorption, resistance to acid attacks, resistance to sulphate attacks and resistance to freeze-thaw cycles, determining mechanical and acoustical properties of the porous concrete. When the materials are subjected to acid and sulphate attacks, the compressive strength is reduced to 20% and the noise absorption to 40% from initial baseline. When all the materials are subjected to freeze-thaw cycles, a mass loss higher than 15% at 30–40 cycles was observed, the compressive strength of materials with a high particle size drops at 20–30 cycles for natural and bottom ashes aggregates, and the noise absorption of bottom ash materials present a lower drop than natural aggregates.

Recycling of Wastes into Construction Materials

Construction activity generates a large amount of waste, causing environmental and economic impacts due to waste elimination without recycling or reusing these materials. In this research, the incorporation of wastes from different sectors (biomass, power plants, construction and demolition process) in concrete with good fire resistance is studied. The chemical composition and grading curve of these wastes are determined. Fire resistance blocks are manufactured with a high percentage of waste in their composition. The new materials are then subjected to several tests in order to analyse their fire resistance, mechanical properties, thermal conductivity, leaching, and radioactivity. A new facade solution is developed by changing traditional materials for some of the new recycled materials, and their technical features are compared. All four wastes studied decreased the density and mechanical strength of a 28-day-old block, and a higher water ratio is needed for block preparation. On the other hand, the blocks’ fire resistance increased, decreasing their thermal conductivity. The properties of the new materials validate their possible usage for nonstructural applications such as blocks or prefabricated concrete panels for facades and inside partitioning, showing good mechanical and thermal performance. Their use does not represent a significant risk to the environment.