Tensile　failure　behavior　of　concrete　invariably　dominates　the　behavior　of　concrete　specimens　as　well　as　structural　elements　and　it　is　strongly　affected　by　loading　rate.　The　present　study　focuses　on　the　effects　of　loading　rate　and　heterogeneity　of　mesa-/micro-structure　on　the　failure　pattern　and　the　macroscopic　mechanical　properties　of　concrete.　For　simplicity,　concrete　is　regarded　as　a　two-phase　composite　composed　of　aggregate　and　mortar　matrix　at　meso-scale.　The　damaged　plasticity　theory　combined　with　strain-rate　effect　is　employed　to　describe　the　dynamic　mechanical　behavior　of　mortar　matrix,　and　the　aggregate　phase　is　assumed　to　be　elastic.　The　dynamic　tensile　failure　modes　of　a　single-edge　notched　concrete　specimen　and　the　L　specimen　under　different　loading　rates　are　numerically　investigated.　The　simulation　results　indicate　that　dynamic　failure　pattern　and　the　direction　of　crack　propagation　of　concrete　have　pronounced　loading　rate　sensitivity.　With　the　increase　of　loading　rate,　the　failure　mode　of　concrete　changes　from　mode-I　to　mixed　mode.　The　more　complex　the　mesa-structure　is,　the　higher　the　interaction　intensity　between　the　meso　components　has　and　the　more　complicated　the　crack　paths　are,　resulting　in　a　more　obvious　crack　branching　behavior.　Furthermore,　as　loading　rate　increases　much　more　branching　cracks　generate　within　concrete　and　the　width　of　the　damaged　region　increases,　implying　that　the　fracture　process　at　relatively　high　strain　rates　requires　more　energy　demand　to　reach　failure.　And　this　should　be　the　main　reason　for　the　improvement　of　the　dynamic　tensile　strength　of　concrete.　(C)　2013　Elsevier　Ltd.　All　rights　reserved.