Recycling and reusing ceramic construction and demolition waste (CCDW) is a way forward to a circular economy. Today, the utilization of CCDW is low, mainly due to the lack of systematic collection systems. Usually, much of typical whiteware ceramic waste (sanitaryware, tableware, and ceramic tiles) is mixed with demolition waste, e.g., concrete and bricks. However, as the traditional whiteware ceramics used in construction consist of compounds produced in high-temperature reactions, these energy-intensive materials are feasible as secondary raw materials for several new recycling applications. This study explored the influence of different whiteware ceramic waste materials on the strength development of cement-based mortars.
Samples of used/end-of-life sanitaryware, tableware, and ceramic tiles were collected. The oxide composition was determined by SEM/EDS analysis. The mineral composition and the amount of crystalline and amorphous phases were determined by XRD measurements.
The ceramic waste was milled and sieved to fractions less than 1 mm, 100 µm, and 30 µm. The particle size distribution of the raw materials was determined by laser diffraction measurements. The pozzolanic effect of substituting ceramic waste for cement was estimated. To verify the results and to exclude the impact of particle size distribution, inert quartz sand in similar fractions and amounts were also substituted for cement.
Mixtures of cement, aggregates (0-2 mm) of quartz and gravel, ceramic particles and water were cast into moulds (50*50*50 mm) and demoulded after 1 day. After that, the samples were immersed in water until the strength measurements. The compression strength of the samples was determined after 7, 28, and 91 days. The morphology of the samples was examined by SEM/EDS.
Substituting ceramic waste particles for cement did not develop the desired strength after 7 days of water immersion. However, the strength had significantly improved after 28 days. The reactivity of the ceramic waste-based fractions depended on their particle size distribution and phase composition. The results also suggest that ceramic waste can be utilized to substitute the coarser filler aggregates of natural gravel and sand in concrete/mortars. However, the particle size distribution of the natural aggregates significantly impacted the strength development of the mortars. Finally, the ceramic waste materials showed a pozzolanic effect and thus could be used as a partial substitute for cement in concrete/mortars.