Rodrigo Henrique Geraldo

Gypsum Plaster Waste Recycling: Analysis of Calcination Time

The gypsum plaster is a material widely used in constructions around the world. It is a material with high versatility that can be applied from wall coverings to decorative ornaments. However, during its application in buildings, large amounts of waste materials are generated. The average values of waste during its application are higher than 45% of the gypsum amount used. A series of tests were conducted to develop a feasible methodology to reuse this waste material. The results collected at this stage indicated that it is possible to obtain a recycled product with low energy consumption. It was noted that after a certain number of procedures in which gypsum was subjected to recycling, there was a loss of workability; however, it did not present relevant changes in mechanical properties. This lack of workability avoids the recycled material maintain its properties in the fresh state as it is subjected to recycling. This work evaluates the calcination time of gypsum plaster waste for the production of a gypsum plaster with binder properties for using as components. The temperature of calcination was kept constant (150 °C), but the residence time in the stationary kiln was modified. The properties in the powder state (bulk density, fineness modulus, specific mass and sieve analysis), fresh state (mini-slump, setting times and kinetics of temperature) and in the hardened state (compressive strength and hardness) were analysed in order to have some answers about the performance of the recycled gypsum. In the fresh state, the recycled material showed good results for precast components. The initial setting times were good for all residence times and the final setting times for the material calcined in periods of 5 and 6 hours. In the hardened state, the best compressive strength results were obtained for all residence times, and hardness for calcination for 3, 4, 5 and 6 hours. All these results were satisfactory when compared to the commercial plaster took as reference. On the other hand, there was a lack of workability in those pastes indicating that an admixture is needed to adjust this property of the recycled material.

Estudo do desempenho de argamassas geopoliméricas produzidas com sílica das cinzas da casca do arroz

Introdução A produção de uma tonelada de cimento Portland (CP), um dos materiais mais consumidos do mundo, gera 1 tonelada de dióxido de carbono (CO2), o que levou a estudo de alternativas ao CP, como os geopolímeros1. Esta pesquisa avaliou o desempenho mecânico de argamassas geopoliméricas confeccionadas com o silicato de sódio produzido com a sílica da casca de arroz (CCA). Materiais e Métodos Os materiais utilizados na pesquisa foram o Cimento Portland CP II F40 para as argamassas convencionais com traço 1:3:0,48 (aglomerante: agregado miúdo: água). O Hidróxido de sódio, o metacaulim comercial e a Sílica da casca de arroz foram misturados para produzir as argamassas geopoliméricas. O silicato de sódio foi produzido seguindo a metodologia de Ferreira2 O agregado miúdo foi a areia natural, de rio. Corpos de prova prismáticos foram moldados e rompidos à compressão e à tração por flexão nas idades de 1, 7 e 28 dias. Corpos de prova cilíndricos foram moldados e submetidos à ensaio de absorção por capilaridade aos 28 dias. Resultados e Discussão Os resultados de resistência à tração na flexão e de resistência à compressão estão indicados nas Figuras 1 e 2, respectivamente. É possível notar que em ambos os casos, que o desempenho da argamassa geopolimérica foi de cerca de 60% do observado para a argamassa convencional.

Analysis of silica dissolution from rice husk ash for geopolymer production: the storage time

In the production of geopolymer the use of commercial sodium silicate is very common; however this material causes several environmental impacts during its production. The extraction of silica from rice husk ash by using the alkaline lixiviation method is an alternative. In this study the storage time was analysed in the production of a source of dissolved silica more environmental friendly. The results showed all these conditions are important in the production of the alternative sodium silicate.

Alkali-activation of rice husk ash to make building components

Abstract This work studied the development of geopolymer components with rice husk ash (RHA), which was used to make an alternative sodium silicate by the aqueous solution with NaOH. The mortars were produced using metakaolin as aluminosilicate source. The resulting mortars show compressive strength (cured at room temperature) in the range of 27-32 MPa, showing the sodium silicate with RHA had good performance. Such results suggest that geopolymer mortar and concrete can be made with waste materials and also replace Portland cement-based mixtures, minimizing social, economic and environmental impacts associated with its production.

Geopolymers Studies in Brazil: A Meta-Analysis and Perspectives

Geopolymers have stimulated a great interest since it appeared years ago. Many researchers are investigating the structures, characteristics and the formation processes of this promising technology. These materials are a type of binder that in its production sends less carbon dioxide to the atmosphere and requires lower energy consumption when compared to the Ordinary Portland Cement; moreover, it can demonstrate excellent mechanical properties. Brazilian scientific community is also developing researches in this field, and the new policy about the management and disposal of waste, the high growth of the civil construction, among other facts, tends to increase the interest about geopolymers in the country. The aim of this work is to make a meta-analysis of the literature about geopolymers, showing some studies and perspectives about this theme in Brazil.