RESUMO Este trabalho estuda o efeito da forma de tratamento termomecânico (calcinação e moagem) do resíduo de ardósia com foco na ativação das propriedades pozolânicas. O programa experimental consistiu em avaliar as propriedades físicas, químicas, minerais e morfológicas do resíduo. O material foi cominuído por 1 hora e 45 minutos, peneirado e, em seguida, as amostras passantes em 45 µm foram submetidas ao tratamento térmico, as quais foram expostas a temperatura 1000ºC, mantendo-se constante por um período de até 5 horas e foram moídas novamente. As análises cristalográficas demonstraram que processo de calcinação gerou uma redução da cristalinidade pela diminuição dos picos e formação de um possível halo de amorfização. Os resíduos de ardósia após tratamento térmico, aumentaram o tamanho médio devido ao efeito de aglomeração pela fusão das partículas o que interferiu no efeito da ativação pozolânicas, sendo que uma maior moagem garantiu um ótimo resultado de ativação, comprovando que a granulometria mais elevada interfere na reatividade do material. Ficou evidenciado que para ativação do resíduo de ardósia se faz necessária a utilização de moagem antes do processo de aquecimento (partículas menores de 45 µm) e após (partículas menores de 38 µm).

ABSTRACT This paper studies the effect of thermomechanical treatment (calcination and grinding) of slate waste focusing on the activation of pozzolanic properties. The experimental program consisted in evaluating the physical, chemical, mineral and morphological properties of the residue. The material was comminuted for 1 hour and 45 minutes, sieved, and then samples passing through 45 μm were subjected to heat treatment, which were exposed at 1000 °C temperature, remaining constant for up to 5 hours and were ground again. Crystallographic analyzes demonstrated that the calcination process generated a reduction in crystallinity by reducing the peaks and forming a possible amorphization halo. The slate waste after thermal treatment, increased the average size due to the effect of agglomeration by the melting of the particles, which interfered in the pozzolanic activation effect, and a greater grinding ensured an excellent activation result, proving that the higher granulometry interferes in the material reactivity. It was evidenced that for the slate residue activation it is necessary to use grinding before the heating process (particles smaller than 45 μm) and after (particles smaller than 38 μm).

In this work we analyzed the "residual" performance of Portland cement concretes heat-treated at 600 °C after cooling down to room temperature. Concretes with characteristic compressive strength at 28 days of 45 MPa and of 60 MPa were studied. The heat-treatment was carried out without any imposed load. We measured the residual compressive strength and modulus of elasticity. The geometry of the structure was described by mercury intrusion porosimetry and nitrogen sorption tests. We observed a decrease of residual compressive strength and modulus of elasticity, with the raise of heat-treatment temperature, as a result of heat-induced material degradation. The results also indicated that the microstructural damage increased steadily with increasing temperature. Based on the results of this experimental work we concluded that residual mechanical properties of concrete are dependent of their original non heat-treated values.

We evaluated the "residual" thermal conductivity of Portland cement concretes (with characteristic compressive strength at 28 days, f ck, of 20 MPa and 50 MPa) at room temperature after heat-treating at 180 °C, 300 °C and 600 °C. The description of the geometry of the structure was carried out using mercury intrusion porosimetry and nitrogen sorption. The results showed a decreasing tendency of residual thermal conductivity, which we attributed to heat-induced concrete degradation. Furthermore, the results from mercury intrusion porosimetry and nitrogen sorption tests showed that a coarser pore structure is produced with the raise of heat-treatment temperatures.