Effects of using tea waste as an additive in the production of solid bricks in terms of their porosity, thermal conductivity, strength and durability

In this paper, we investigated the use of tea waste as an additive in the production of traditional bricks. This could provide several environmental and economic benefits, as well as improving thermal insulation in construction. To this end, we produced brick samples with 0, 5 and 10 w% of tea waste mixed with a clayey material from Teruel (Spain) that was rich in quartz and phyllosilicates and had smaller amounts of carbonates. These samples were fired at 800, 950 and 1100 °C in an electric oven. We then analysed and discussed their chemical, mineralogical, textural and physical-mechanical behaviour and evaluated their durability in response to salt crystallization. The pore system of the bricks was examined using a combination of different analytical techniques (hydric tests, mercury intrusion porosimetry and digital image analysis). We also evaluated their thermal conductivity and observed that an increase in the firing temperature and the amount of tea waste altered the texture of the bricks, increasing their porosity. This happened above all at 1100 °C, where it led to the appearance of a new family of pores and increased the porosity to about 39% for bricks made with 10 w% added tea waste. The increased porosity made the bricks lighter. The bricks made with tea waste showed higher levels of water absorption and poorer mechanical strength. Our results suggest that the addition of tea residues strongly decreases the thermal conductivity and heat diffusion capacity of the bricks. They could therefore be used as lightweight bricks for the thermal insulation of buildings.