Determination of Aggregate Surface Morphology at the Interfacial Transition Zone (ITZ)

Summary

Hereby, we proposed a protocol to illustrate the effect of aggregate surface morphology on the ITZ microstructure. The SEM-BSE image were quantitatively analyzed to obtain ITZ's porosity gradient via digital image processing and a K-means clustering algorithm was further employed to establish a relationship between porosity gradient and surface roughness.

Abstract

Here, we present a comprehensive method to illustrate the uneven distribution of the interfacial transition zone (ITZ) around the aggregate and the effect of aggregate surface morphology on the formation of ITZ. First, a model concrete sample is prepared with a spherical ceramic particle in roughly the central part of the cement matrix, acting as a coarse aggregate used in common concrete/mortar. After curing until the designed age, the sample is scanned by X-ray computed tomography to determine the relative location of the ceramic particle inside the cement matrix. Three locations of the ITZ are chosen: above the aggregate, on the side of the aggregate, and below the aggregate. After a series of treatments, the samples are scanned with a SEM-BSE detector. The resultant images were further processed using a digital image processing method (DIP) to obtain quantitative characteristics of the ITZ. The surface morphology is characterized at the pixel level based on the digital image. Thereafter, K-means clustering method is used to illustrate the effect of surface roughness on ITZ formation.

Introduction

At the mesoscopic scale, cement-based materials can be regarded as a three-phase composite comprised of the cement paste, the aggregate, and the interfacial transition zone (ITZ) between them^1,2. The ITZ is often treated as a weak link since its increased porosity could act as channels for the ingress of aggressive species^3,4 or provide easier pathways for crack growth^5,6,7,8,9,

Protocol

1. Preparation of the model concrete with a single ceramic particle

1. Mold preparation
   1. Use a brush to clean the mold (25 mm x 25 mm x 25 mm) and ensure that the inner surfaces of the mold are impurity-free.
   2. Use another brush to uniformly apply diesel oil on the inner surfaces of the mold for easier mold-release.
      NOTE: Here, we did not use the common mold for mortar or concrete preparation. As the ceramic particle is around 15 mm in diameter, a cubic plastic mold around 30 mm in length is used for sample preparation. Ensure that the size of plastic mold is larger than the ceramic particle.
2. Molding the model....

Results

The porosity distribution of ITZ regions above the aggregate, on the side of the aggregate, and below the aggregate are compared and shown in Figure 4³². The porosity of the ITZ above the upper surface appears to be smaller than that on the side or above the aggregate, indicating a denser ITZ microstructure, while the ITZ below the aggregate is always the most porous due to micro-bleeding. Figure 4³² shows that eve.......

Discussion

The X-CT technique was applied to roughly determine the geometrical center of the ceramic particle to ensure that the analyzed surface is through the equator of the particle. Thus, the overestimation of the ITZ thickness caused by the 2D artifacts could be avoided³⁸. Herein, the accuracy of obtained results is highly dependent on the flatness of the examined surfaces. Generally, a longer grinding and polishing time contributes to an adequately smooth surface for testing. However, due to the varyin.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Auto Sputter Coater	Cressington	108 Auto/SE
Automatic polishing machine	Buehler	Phoenix4000
Brush	Huoniu	3#
Cement	China United Cement Corporation	P.I. 42.5
Cement paste mixer	Wuxi Construction and Engineering	NJ160
Ceramic particle	Haoqiang	Φ15 mm
Cling film	Miaojie	65300
Cold mounting machine	Buehler	Cast N' Vac 1000
Conductive tape	Nissin Corporation	7311
Cup	Buehler	20-8177-100
Cutting machine	Buehler	Isomet 4000
Cylindrical plastic mold	Buehler	20-8151-100
Diamond paste	Buehler	00060210, 00060190, 00060170
Diesel oil	China Petroleum	0#
Electronic balance	Setra	BL-4100F
Epoxy resin	Buehler	20-3453-128
Hardener	Buehler	20-3453-032
High precision cutting machine	Buehler	2215
Image J	National Institutes of Health	1.52o
Isopropyl alcohol	Sinopharm	M0130-241
Matlab	MathWorks	R2014a
Paper	Deli	A4
Plastic box	Beichen	3630
Plastic mold	Youke	a=b=c=25mm
Polished flannelette	Buehler	242150, 00242050, 00242100
Release agent	Buehler	20-8186-30
Scanning Electron Microscopy	FEI	Quanta 250
Scrape knife	Jinzheng Building Materials	CD-3
SiC paper	Buehler	P180, P320, P1200
Ultrasonic cleaner	Zhixin	DLJ
Vacuum box	Heheng	DZF-6020
Vacuum drying oven	ZK	ZK30
Vibrating table	Jianyi	GZ-75
Wooden stick	Buehler	20-8175
X-ray Computed Tomography	YXLON	Y.CT PRECISION S