RESEARCH ARTICLE A preliminary assessment of microstructural and compositional characteristics of two variants of precarbonated and postcarbonated concrete mixes Shwetambara Verma 1 | Somesh Sengupta 2 | Srinivasan Varadharajan 1 | Arun Kumar 1 1 Department of Civil Engineering, Amity University, Noida 201313Uttar Pradesh, India 2 Department of Civil and Environmental Engineering, Birla Institute of Technology, Mesra, Ranchi 835215, India Correspondence Shwetambara Verma, Department of Civil Engineering, Amity University, Uttar Pradesh, Noida 201313, India. Email: sverma10@amity.edu; The hydration, precarbonation, and postcarbonation microstructural and compositional attributes of 2 variants of concrete were studied using scanning electron microscope, energy dispersive spectroscopy, and X‐ray diffraction tech- niques. Results obtained showed presence of large number of diffraction peaks indicative of SiO 2 as major phase. Higher pH, alkalinity, and absence of effects of carbonation were suggested from the presence of portlandite peaks. Evidence of effect of carbonation was studied through the analysis of the experimental diffraction peaks obtained postexposure to accelerated carbonation in a controlled environment. Presence of all the 3 polymorphs of calcium carbonate (CaCO 3 ) such as aragonite, vaterite, and calcite depending upon the moisture content and the material constituting the concrete sample were envisaged signi- fying carbonation. Precipitation of these CaCO 3 crystals was responsible for depletion of CH as well as calcium–silicate–hydrate, ettringite with the progress of carbonation as suggested by their absence in the X‐ray diffraction diffractograms of the carbonated samples. The crystal structure of the newly formed minerals in both the variants of concrete sample was highly controlled by the stages of carbonation, with development of amorphous CaCO 3 (amal- gamated with that of calcium hydrates) in early stages of carbonation as well as fully developed rhombohedral CaCO 3 crystals in later stages. 1 | INTRODUCTION Concrete is the most used material in the construction industry as of today in the entire world. Cement paste (water and cement mix) binds together inert aggregate such as sand or crushed gravel forming concrete. [1] In India, the use of concrete has witnessed sharp growth in the recent past. The concrete structures are of prime importance owing to the fact that the concrete being versatile material with properties such as foldability can be designed for desired property, robustness, lower life cycle cost, and so forth. However, concrete structures exposed to aggressive environments, durability is a major concern. [2] The concrete structures are subject to deterioration and consequent damage due to a number of factors in their service life. One of the major factors for the aforesaid deterioration is that of carbonation‐ induced reinforcement corrosion. Concrete carbonation is a physical–chemical process that comprises the diffusion of CO 2 through the concrete pores and its response with hydration products such as calcium hydroxide and calcium silicate hydrates. [3,4] It is a process by which atmospheric carbon dioxide reacts with the hydration products of the cement to form calcium carbonate, which lowers the alkalinity of the concrete. [5] Carbonation rates vary depending on factors such as type and amount of cement used, concrete poros- ity, curing time, and type and quantity of minerals Received: 26 October 2017 Revised: 5 January 2018 Accepted: 15 February 2018 DOI: 10.1002/xrs.2839 X‐Ray Spectrometry. 2018;1–10. Copyright © 2018 John Wiley & Sons, Ltd. wileyonlinelibrary.com/journal/xrs 1