Durable brick waste
Replacing Portland cement with 20% ceramic waste powder could lead to superior and durable concrete for building applications, due to its pozzolanic properties.
Researchers at the University of Minho, Portugal, processed waste made up of bricks, and once and twice-fired white stoneware and sanitaryware in two grinding phases, to create a ceramic powder with a particle size of <75mm.
The team tested the use of ceramic waste in three phases – a 20% replacement of cement by ceramic powder, replacement of natural sand by ceramic sand, and finally by substituting coarse natural aggregates for coarse ceramic aggregates.
The highest quality of concrete has been achieved with ceramic powder, says Lead Researcher, Fernando Torgal.
To test durability, the team conducted mechanical, water performance, permeability and chloride diffusion tests.
Torgal explains, ‘A reduction of water absorption, permeability and chloride diffusion was shown, all of which are responsible for concrete degradation. For instance, chloride ion diffusion [in ceramic powder based concrete] was shown to be almost four times lower than standard concrete’.
To evaluate water absorption, water saturation of the sample under vacuum has been performed by cylindrical specimens four centimetre high and five centimetre in diameter and involved two main steps. One in which specimens are submitted to vacuum conditions (0.7 mbar) for three hours and another where the specimens are saturated with distilled water and again submitted to vacuum conditions for three hours.
Durability was further examined by an aging test, consisting of 12 cycles, where different phases were selected to simulate dry heat, cold weather and wet heat and cold.
‘[The material] also showed a better performance in aging tests than control concrete,’ notes Torgal.
Further probing looked at rapid change of temperature from 75ºC to -10ºC and then from -10ºC to 55ºC and dropping to -10 ºC in each cycle to simulate the thermal shock that concrete can suffer.
Torgal explains, ‘Using ceramic wastes in concrete can solve several environmental problems, by avoiding the extraction of large quantities of raw materials from the earth, reducing greenhouse gas emissions generated in the clinker production, and by reducing landfill. Yet research on the reuse of ceramic waste is scarce and does not evaluate durability performance, which is a key issue for the industry.’
However, although ceramic waste powder shows signs of a comparable alternative to cement, durability will depend on the quality of ceramic wastes being used. Torgal also notes that results using this replacement indicate a ‘minor compressive strength loss’.
Dr Charles Fentiman of Fentiman Consulting, UK, says, ‘Today, waste ceramics can be used as aggregates for the manufacture of some concrete blocks, but it is encouraging to see potential for more forms of ceramic waste. Research such as this is needed to re-establish routing use of waste ceramic in concrete as a viable alternative’.
The next research stage will look at further levels of ceramic waste for high performance concrete, and the use of ceramic waste with demolition and mine waste.