In designing a porous concrete, containing a high volume of air pores, the effects of its mesoscale phases on its macro level properties have to be known. For this purpose, porous concretes having different aggregate gradings and cement paste compositions were investigated through macro-scale strength tests. The tests showed that aggregate grading had a predominant effect on the properties of porous concrete in comparison with cement paste composition. Replacing cement by silica fume even slightly lowered the strength values of the porous concretes which was explained by the presence of agglomerates. Meso-scale tension tests were also conducted to determine the tensile strength of the ITZ. The tests at the two different scales revealed that, even though the ITZ phase did not become weaker with the presence of silica fume with the inclusion of agglomerates, the strengths of macro-size samples were lowered due to the bulk cement paste phase being degraded.