en Research Paper Research Paper <p style="margin: 0cm 0cm 0pt; text-align: justify; line-height: 200%;"><span font-size:="" lang="EN" mso-ansi-language:="" mso-ascii-theme-font:="" mso-bidi-theme-font:="" mso-hansi-theme-font:="" new="" style="color: rgb(34, 34, 34); line-height: 200%; font-family: " times="">Microscopic studies has shown that</span><span font-size:="" mso-ascii-theme-font:="" mso-bidi-theme-font:="" mso-hansi-theme-font:="" new="" style="color: rgb(34, 34, 34); line-height: 200%; font-family: " times=""> adjacent to </span><span font-size:="" lang="EN" mso-ansi-language:="" mso-ascii-theme-font:="" mso-bidi-theme-font:="" mso-hansi-theme-font:="" new="" style="color: rgb(34, 34, 34); line-height: 200%; font-family: " times="">the interface between cement paste and aggregate, there exists an area with high porosity and low binding compounds that is referred to as interfacial transition zone (ITZ). ITZ in concrete and mortar imposes a number of negative effects, including flexural and compressive strengths reduction and permeability enhancement. That&rsquo;s why many research attempts have been devoted to limit ITZ and its negative effects. The present study investigates the possibility of utilizing fine Portland cement (PC) clinker as a reactive aggregate in mortar for the same purpose. For this, natural quartz sand in normal mortar (NM) was totally replaced with PC clinker of the same particle size distribution and the most important engineering properties of the new mortar referred to as Reactive Aggregate Mortar (RAM) were measured and compared with NM as control. The results of compressive strengths measurements represented 65% and 21% increases at curing ages of 7 and 90 days, respectively, for RAM compared to NM. Chloride penetration depth in RAM displayed reductions by about </span><span font-size:="" mso-ascii-theme-font:="" mso-bidi-theme-font:="" mso-hansi-theme-font:="" new="" style="color: rgb(34, 34, 34); line-height: 200%; font-family: " times="">33</span><span font-size:="" lang="EN" mso-ansi-language:="" mso-ascii-theme-font:="" mso-bidi-theme-font:="" mso-hansi-theme-font:="" new="" style="color: rgb(34, 34, 34); line-height: 200%; font-family: " times="">% and 26% after 14 and 28 days of exposure, respectively. The effect of PC clinker reactivity on the microstructure and size of ITZ was studied by using scanning electron microscopy.</span></p> Portland cement clinker, Compressive strength, Chloride penetration depth,Interfacial transition zone,Mortar,Portland cement clinker,Compressive strength,Chloride penetration depth 40 47 http://ijmse.iust.ac.ir/browse.php?a_code=A-10-294-6&slc_lang=en&sid=1 Jafar Shafaghat shafaghatjafar70@gmail.com 1800319475328460012789 1800319475328460012789 No Research Laboratory of Inorganic Chemical Process Technologies,School of Chemical Engineering, Iran University of Science and Technology, Narmak Ali Allahverdi ali.allahverdi@iust.ac.ir 1800319475328460012790 1800319475328460012790 Yes Iran university of Science and Technology