Tarrahan Parseh Transportation Research Institute International Journal of Transportation Engineering 2322-259X 13 1 2025 07 01 Microstructure Study of Ordinary Concrete Containing High Grade Portland Cement 2119 2129 226813 10.22119/ijte.2025.517813.1694 EN Mohammadhossein Mansourghanaei Ph.D. in Civil Engineering, Department of Civil Engineering, Chalous Branch, Islamic Azad University, Chalous, Iran 0000-0003-4644-104X Journal Article 2025 04 19 In this experimental study, a mixture design of ordinary concrete containing Portland cement (OPCC) with a grade of 500 kg/m³ was made and compressive strength tests were performed at 7, 28 and 90 days of curing, and X-ray diffraction spectrometer (XRD) and scanning electron microscopy (SEM) imaging were performed on concrete samples at 90 days of curing at 21 ℃ to evaluate the microstructure of the concrete and to compare it with the test results of this study. Increasing the curing age due to the progress of the polymerization process (hydration) improved the results of the concrete compressive strength test. In this regard, at 90 days of curing, a compressive strength of 64.92 MPa was obtained, which was an increase of 79.48% compared to 7 days. SEM and XRD results indicate that a large part of the polymerization process has been completed and a high volume of hydrated calcium aluminosilicate gel called ettringite gel (C-A-S-H) and hydrated calcium silicate gel called tobermorite gel (C-S-H) has been produced in the concrete mix. The reduction in the amount of calcium hydroxide (Ca(OH)₂) crystals in the XRD results indicates that this product has a good contribution to the hydration process and the production of hydrated gels. The high grade of cement used has played a significant role in increasing the volume of C-S-H gel production (as the main product of the chemical reaction process in OPCC) and filling the pores, cracks and capillary pores in the microstructure matrix of OPCC. http://www.ijte.ir/article_226813_ff2ace384f966a1baf7155bb179b199a.pdf