Ricardo Castelló

Influence of the calcination temperature of kaolin on the mechanical properties of mortars and concretes containing metakaolin

Abstract The effect of heating, to temperatures between 400 and 1200ºC, on the dehydroxylation of kaolin and the pozzolanic activity of the resulting amorphous material were determined by a variety of analytical techniques. Mixtures of concrete containing variable amounts of kaolin calcined at 700ºC were analysed and the results compared with those for concrete samples containing two different types of imported metakaolin. As shown in this work, Colombian kaolin can be used effectively as a raw material to obtain a highly active product (metakaolin). The optimum heating temperature for the kaolin is between 700 and 800ºC.

Influence of the Application Rate of an Organic Amendment (Municipal Solid Waste [MSW] Compost) on Gypsum Quarry Rehabilitation in Semiarid Environments

Rehabilitation of open-cast gypsum mines is made difficult by the permanent loss of the original soil resource. Soil development can be accelerated by using organic amendments (e.g., MSW compost), which provide both physical (structural) enhancement and chemical (nutrient) reinforcement. Excess of salts as a result of the effect of refuse application can lead to overfertilizing for some species and the species Atriplex halimus L. (Chenopodiaceae) can be considered an effective indicator of the optimum organic amendment rate. Four treatments of composted urban municipal solid waste (MSW compost) were applied to the top flat area of a gypsum spoil [soil-forming material (SFM)], being then the surface covered with natural topsoil layer coming from the head of the quarry. Soil and vegetation sampling was made over a four-year period. As a result of the physical and chemical effects of the organic amendment on soil properties, a close relationship existed between application rate and Atriplex halimus presence. Based on the results of this study, gypsum quarry rehabilitation in semiarid environments may be facilitated by the use of medium organic amendment rates. High rates caused halophyte species such as Atriplex halimus to grow in such a way that development of native gypsiferous species was hindered by the competitive processes. On the other hand, low rates seemed to have no beneficial effect on soil.

Laboratory alteration of gypsiferous materials below a landfill

Some urban solid waste landfill sites in Spain are located on geological substrates of gypsiferous lithology. Although this type of substrate is assumed to be of low permeability, it can develop secondary pores by dissolution and, under favourable environmental conditions, form a karstic system that may pose serious geotechnical problems in the medium and long term. The purpose of this work was to study alterations caused by selective tests in various sections of a gypsum lithological column obtained from the Colmenar de Oreja landfill site (Spain). The tests were used to assess the influence of individual environmental factors and involved the addition of milli-RO water, solutions containing a 1%, 5% or 10% concentration of landfill leachate, and 2, 5, 10 and 15mgl(-1) solutions of NaCl in successive immersion-drying cycles at -15, 20 or 60 degrees C. Differences in alterability between the six studied segments of the lithological column were found to be due to differences in lutite content, specific crystal habit and type of cement. Segments with specular gypsum were the strongest in the tests, while the segment with the highest amount of detrital materials was the most responsive to temperature and moisture changes. The treatments that produce greater alterations are those that contain only milli-RO water.