▁chem istry ▁is ▁known ▁also ▁as ▁Port land ite . ▁In ▁comparison ▁to ▁calci um ▁sil icate ▁hyd rate , ▁Port land ite ▁is ▁relatively ▁por ous , ▁per me able ▁and ▁soft ▁( 2 ▁to ▁ 3 , ▁on ▁Moh s ▁scale ). ▁It ▁is ▁also ▁sect ile , ▁with ▁flexible ▁cle av age ▁fla kes . ▁Port land ite ▁is ▁sol ub le ▁in ▁water , ▁to ▁yield ▁an ▁al kal ine ▁solution ▁which ▁can ▁comprom ise ▁a ▁concrete ' s ▁resistance ▁to ▁acid ic ▁attack . ▁ ▁Port land ite ▁makes ▁up ▁about ▁ 2 5 % ▁of ▁concrete ▁made ▁with ▁Port land ▁c ement ▁without ▁po zz olan ic ▁c ement it ious ▁materials . ▁In ▁this ▁type ▁of ▁concrete , ▁carbon ▁dio x ide ▁is ▁slowly ▁absor bed ▁to ▁convert ▁the ▁Port land ite ▁into ▁ins ol ub le ▁calci um ▁carbon ate ▁( Ca CO 3 ), ▁in ▁a ▁process ▁called ▁carbon at ation : ▁ ▁Ca ( OH ) 2 ▁+ ▁CO 2 ▁-> ▁Ca CO 3 ▁+ ▁H 2 O ▁ ▁In ▁min eral ▁form , ▁calci um ▁carbon ate ▁can ▁exhib it ▁a ▁wide ▁range ▁of ▁hard ness ▁depending ▁on ▁how ▁it ▁is ▁formed . ▁At ▁its ▁soft est , ▁calci um ▁carbon ate ▁can ▁form ▁in ▁concrete ▁as ▁ch alk ▁( of ▁hard ness ▁ 1 . 0 ▁on ▁Moh s ▁scale ). ▁Like ▁Port land ite , ▁calci um ▁carbon ate ▁in ▁min eral ▁form ▁can ▁also ▁be ▁por ous , ▁per