Marble stone waste as raw material for autoclaved sand-lime bricks

A representative fine marble waste sample was heated to produce active lime (through calcination of CaCO3, which is the main constituent of marble) which was then used to prepare sand-lime briquettes. The raw mix for the sand-lime units consisted of different lime/sand ratios (20/75, 25/70, 30/65 and 35/60) combined with constant 5 mass-% clay. Different autoclaving periods (4, 6, and 8 h) at 10 bars were applied. The physico-mechanical properties of the prepared briquettes were studied. XRD and DTA techniques were used for phase determination. SEM imaging was used for microstructural evaluation of selected briquettes. Under these experimental conditions, the 25 mass-% lime-containing mix possessed optimum compressive strength (318-336 kg/cm2) compared to the other mixes. Fibrous CSH was the predominant binder phase in the optimal mix. Lower mechanical properties were associated with the appearance, indicated by XRD, of free calcium hydroxide.