Does the type of sand affect the durability of bricks
The hypothesis that coarse sand particles make more durable bricks than those made of fine sand particles is proven to be true.
Bricks have been used in the construction of homes for hundreds of years. Their high thermal properties have also made them suitable for use to line the walls of furnaces used in glass manufacturing and metallurgy.
The science fair project can be repeated by varying the ratios of the materials used to make the bricks or by varying the materials used to make the bricks.
You might also want to consider testing how much compression or weight the bricks are able to bear.
Brick - http://www.enotes.com/how-products-encyclopedia/brick
Composition of bricks - http://chestofbooks.com/architecture/Construction-Superintendence/215-Composition-of-Bricks.html
Basic safety requirements