Title:
Application of SEM-EDS to do Micro- and Nano-structural Characterization and Durability Evaluation of Cementous System
Author(s):
Mukhopadhyay
Publication:
Web Session
Volume:
Issue:
Appears on pages(s):
Keywords:
DOI:
Date:
10/23/2022
Abstract:
The extensive use of Scanning Electron Microscopy (SEM) equipped with Energy Dispersive Spectroscope (EDS) to do micro- and nano-scale characterization and durability evaluation of different constructional materials (e.g., cement, aggregate, paste, mortar, and concrete) is a very common practice. In SEM, a specimen is scanned under a high vacuum with a focused beam of electrons and black and white good quality images form with higher magnification (good up to 50,000X-70,000X) and good resolution (~2nm). An EDS is used to detect the x-ray emitted from the specimen [secondary electrons (SE) with fractured surface specimens and backscattered electrons (BSE) from polished specimens] and identify the phases present based on their characteristic elemental compositions. Both bulk and power sample can be tested. Specimen surface shall be flat and smooth when the BSE mode is used. Compared to SE, BSE has a much higher energy. The sample size is usually small (e.g., several square inches to 1-4 cm2) in SEM evaluation. It must be remembered that the larger the size of the specimen, the longer it takes to reach the required level of vacuum. Cement paste / mortar / concrete specimens shall be coated with a thin electrically conductive material. This presentation will cover the application of SEM-EDS to (i) characterize the morphology and chemical composition of C-S-H phase in cement paste matrix (CPM), (ii) characterize nature and distribution of CH, ettringite and monosulfate crystals in CPM and interfacial transition zone (ITZ), (iii) do microstructural characterization of ITZ, (iv) evaluate pore (especially capillary pores) distribution in CPM and ITZ, (v) study the effects of adding mineral and chemical admixtures on concrete micro-and nano-structures such as matrix densification, improvement in ITZ, and reduction in porosity and permeability, and (vi) investigate the cause and extent of deterioration in concrete due to different internal and external deleterious agents.