Scanning electron microscopic (SEM) images of clay brick,
SBA15 and RHA15 specimens are shown in Fig. 27. Microstructure
of all the brick specimens incorporating SBA and RHA was porous
in nature, which is the main reason of their lesser unit weight than
the conventional bricks. Bricks incorporating SBA showed higher
porosity than clay bricks with RHA.
Control brick specimens showed homogenous and dense structure
under microscopic observations. However, RHA and SBA brick
specimens showed comparatively less binding and densification
along with open pores, which were irregular shaped and interconnected.
Presence of micro pores in all the specimens might be
related to the crystallization process [62]. SEM images are also consistent
with porosity and water absorption results. Increase in
porosity after incorporation of SBA and RHA reduced the compressive
strength of clay bricks.
Brick Color is an important parameter for aesthetics. Normally,
iron oxide is considered responsible for color [62]. Waste (SBA and
RHA) addition in burnt clay bricks did not affect the color of the
specimens. All the tested bricks were of red color because the ratio
of Fe2O3/Al2O3 was greater than 0.33 in all the raw materials [64].
Moreover, surface and black core defects were not observed in any
specimen.