Sustainable utilization of incinerated paper mill sludge ash for the manufacture of building bricks

Fly ash–lime–gypsum bricks are an environmentally friendly and energy-efficient alternative to burnt clay bricks. Nowadays, the scarcity of fly ash and lime adversely affects the production of fly ash bricks. To mitigate this, the current study examines incinerated paper mill sludge ash as a supplement to fly ash and lime. In the current study, in blend 1, coal fly ash is replaced by incinerated paper mill sludge ash (2.5–30 wt%), and in blend 2, lime is completely replaced by incinerated paper mill sludge ash (2.5–15 wt%). Based on Indian standards, bricks were tested for compressive strength, water absorption, weight density, percentage voids, efflorescence, drying shrinkage, dynamic modulus of elasticity, and impact energy. Before developing bricks, the materials have to be examined by X-ray diffraction, X-ray fluorescence, Fourier transform infrared spectroscopy, thermogravimetry differential thermal analysis, and scanning electron microscope techniques. Results from X-ray diffraction showed that higher replacement of incinerated paper mill sludge ash does not produce any phase transformation and merely improves porosity, which reduces weight. Higher replacement of incinerated paper mill sludge ash leads to a reduction in strength and a higher water requirement. The study found that incorporating incinerated paper mill sludge ash at replacement 2.5–15 wt% in blend 1 and 2.5–5 wt% in blend 2 satisfied the building brick requirements. By incorporating incinerated paper mill sludge ash into bricks, the brick industry can produce sustainable bricks that utilize resources effectively.