Delft University of Technology

Stereological Methods In Cement-Based Materials TechnologyA Survey Of My Research Group’s Activities During The Past Half Of A CenturyStroeven, Piet

DOI10.5566/ias.2207Publication date2019Document VersionFinal published versionPublished inImage Analysis and Stereology

Citation (APA)Stroeven, P. (2019). Stereological Methods In Cement-Based Materials Technology: A Survey Of MyResearch Group’s Activities During The Past Half Of A Century. Image Analysis and Stereology, 38(3), 201-211. https://doi.org/10.5566/ias.2207

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Image Anal Stereol 2019;38:201-211 doi: 105566/ias.2207 Communications

201  

STEREOLOGICAL METHODS IN CEMENT-BASED MATERIALS TECHNOLOGY A survey of my research group’s activities during the past half of a century 

PIET STROEVEN Faculty of Civil Engineering and Geosciences, Delft University of Technology, Delft, the Netherlands e-mail: p.stroeven@tudelft.nl (Received June 23, 2019; revised October 27, 2019; accepted October 27, 2019)

ABSTRACT 

Four topics of high engineering relevance in which we were involved are introduced herein. Aggregate packing in concrete is of obvious relevance: denser packings lead to reduced cement demands, while modern developments in the (super) high performance range of cementitious materials are based on particle packing. Fiber reinforcement efficiency in concrete that we have studied extensively offers a relatively simple stereological problem for which Cauchy laid down the fundament. In the third problem of damage analysis the dispersion of small cracks in concrete is at issue. Insight into damage characteris-tics would be relevant in all (fracture) mechanical experiments. This topic can equally be linked to Cau-chy. In both cases, the data acquisition by stereological methods is indicated. The fourth topic is of high actual relevance. It involves porosimetry in computer-simulated (virtual) cementitious materials, ultimate-ly aiming permeability estimation. The stereological problems involved are indicated, and - again – Cauchy can be linked to finding solutions. Finally, new, mostly yet unpublished developments are indi-cated aiming for more economic procedures as well as improving reliability of permeability estimates by nano-packing of globules, so that ultimately this methodology could replace the laborious and expensive (and biased) experimental route.

Keywords: Cauchy, aggregates, fibers, cracks, pores

INTRODUCTION

This paper is intended as a “farewell message” to my dear colleagues and friends in the ISS community, focusing on what I personally learned in this ISS community and showing to which engineering problems I applied it in the concrete technology world during the past half of a century. Hence, I herewith want to show my gratitude to the very community: it enriched my life, as a concrete technologist and as a human being!

I enjoyed my first experiences with STEREOLO-GISTS in the ISS community during the Bern conference in 1971. I was involved in an extensive study in the concrete materials field for my PhD study that I completed in 1973. For most PhD committee members out of “my” field, the 329 pages of my dissertation were probably outside their capabilities, and the stereological approach made this an even more serious problem. Although I received my PhD degree –yet not without some overt animosity– for my colleagues in Delft I was considered for the rest of my

active life an outsider who always knew better… As a consequence, the appointment in 1997 to professor was due to cooperation partner Beijing Jiaotong University in China, not to my home institution…

So, I figured that as a young Dr. I should convince colleagues that stereology was a powerful tool for solving practical engineering problems in the field of concrete technology. A highly relevant field was steel fibre reinforced concrete (SFRC), which presented the simplest stereological conditions I could imagine: dispersed lineal elements in space. This task was supposedly easier than doing so for the damage analysis problems I had faced earlier in my PhD study. Motivation to accept this mission was also coming from serious violations to stereological concepts I had discovered in both fields.

Looking backwards, the research efforts in the previous period involved four major engineering topics with stereological background. The two selected ‘promotion’ topics (SFRC and damage analysis) are nowadays quite established. Other contributions came from all over the world. The ‘French school’ can

 

 

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particle packphysical (vanMore materialpacking of paralready proodiscussed subj

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Our firstmethod involv

ifferent fiberatios by weig

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2'L AP L

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L FIBRE CRETE

rmulated in nology. The oe problem” isould readily pression by we analyzed

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t applicationved the anar types in SFght (w/c=0.4 e aggregate ximum grainmodulus (FM

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REINFO

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ograph of a “mm (top). Co

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f=3.89), we8 mm. Note thmpirical figu

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point bendinsile tests wn characteristctions. This

y, 1882). Oneacture plane, tto the bottommple, that fibeven concept

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ing ere tics

is e of the

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Nin sp

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ned by addinn aggregate rees, and dividimens, measurolled testedved from thet of about ted from eacVisualizationottom) of pying orthogoneven, 1979c

even and Da; Stroeven ang other thinorcement effindered possvior of the SF

The remainining experimegth tests in eiific informatiibution parameven, 1979c

even and Da).

0 in this case)was in vertica

case a mixturs), was directle strength at7) (Stroeven

e.g., Stroever relevant corcement in c

Note further tpace and in

hods in cemen

ng the total petained on eacing the sum

uring 70x200d to beyon

testing machequally size

ch full-size sn was by waypre-loaded cnal grids. For; 2009; Stro

alhuisen, andnd Słovik; Sngs, it proviiciency of theible to inte

FRC specimen

ng prisms weents and the cither one of oion on crack

meters of the ; 2009; Stro

alhuisen, 199

) of a test-loaal direction. A

re of 2D and tly reflected bt increasing vn and Babut,n (2009) for ontributions

concrete.

that in SFRC n the forthco

nt-based mater

ercentages ofch of a specif

m by 100. A 0x1000 mm, nd ultimate,hine and sectied prismaticspecimen (Fy of X-rayingconcrete sper detailed infooeven and S

d Stroeven 1Stroeven andided informae different fiberpret phenoens in structur

ere subjectedcubes to spli

orthogonal dirk developmen

full-size speoeven and S

96; Stroeven

aded (and craAnalysis is by

3D “randomby anisotropyvolume fracti, 1986; Stroea large selecto the fie

C we deal withoming dama

rials

f the samplefied series of

total of 48 were strain- thereupon ioned so that c specimens ig. 6 at the

g slices (Fig. cimens and ormation see Shah, 1978;996; Babut,

d Hu, 2007).ation on the ber types and menological ral terms.

d to 3-point itting tensile rections. For nt and fiber ecimens, see Shah, 1978;

and Babut,

acked) SFRC y orthogonal

mly” oriented y in splitting ion of fibers even, 1993). ction of also ld of fiber

h line length age analysis

Image Anal Stereol 2019;38:201-211 

205  

approach with surface area in space. Cauchy provided the relationships that are at the basis of counting observations and determination of total line length (SFRC) and total surface area (Damage analysis), respectively (Cauchy, 1882).

Fig. 7. Anisometry in steel fiber dispersion (top) and anisotropy of splitting tensile strength fs in N/mm2 of steel fiber reinforced cubes at increasing fiber volume fraction Vf (bottom).

For the fibre case of Fig. 6, upon application of the Stroeven concept of a mixture of 2D and 3D fibre portions, the following equation is obtained (Stroeven, 1979c; 2009)

' 1 2 1

2 2V VL L

(2)

where is the total length ratio of the 2D fibre portion over that of the total amount of fibres. Mono-size fibers are assumed in this case, however, also for multi-size and curved fibers, similar models have been expanded. In eq. (2), LV is the total fiber length per unit of volume and LV’ the component in the plane of the 2D portion; so, in the case of Fig. 6 oriented perpendicular to the compaction direction of the prismatic specimen. Consequently, it is the effective part of the fiber reinforcement because loading direction will be perpendicular to the plane of the X-ray image.

DAMAGE ANALYSIS

Buffon/Saltikov provided also the basis for quantitative analysis of cracks in concrete. By as well adopting the Stroeven concept for spatial crack development (combining at maximum, 1D, 2D and 3D portions), the orthogonal measurements of intersections of line grids with the cracks can be interpreted in spatial terms. Fig. 8 concerns the case of direct compression, requiring only a 3D and 1D portion, the latter having its axis of orientation coinciding with that of the loading. Hence, the solution for the spatial interpretation of cracking can be based on a section parallel to the loading direction in which the orthogonal observations LP Pand LP suffice (Fig. 8, at the left).

In mathematical terms, it is found that the crack surface area per unit of volume, SV, is related to orthogonal measurements in the mid-section of the compressed specimen by

41

2V L LS P P

P (3)

In tension testing, a combination of 3D and 2D portions is required. Again, an axial section can be sampled by an orthogonal line grid. For methodological details and results of applications, see (Stroeven, 1973; 1979b; Stroeven and Słovik; Stroeven and He, 2011a; 2011b). Of course, any (fracture) mechanical investigation on cementitious materials can profit from the structural research efforts discussed herein, since it will promote the understanding of the recorded phenomenological behavior.

Note that these labour-intensive contributions to the aforementioned topics had to be terminated at the end of last century, because physical experimenting became too expensive. Therefore, I figured we should instead use modern computer facilities. So, the last subject is hot, actual and highly relevant. My PhD student and son, Martijn, developed the first professional Discrete Element Method (DEM) - SPACE - in our group that became operational around the millennium break (Stroeven, M., 1999). During the next years, a series of my PhD students have used it (and an upgraded version, HADES) in studies on virtual cementitious materials (compucrete). Particle packing problems (as discussed earlier) and particularly permeability estimation were the issues of interest and engineering relevance.

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our engineeri

EABILITY

pts for 3D atural analysis. More recenand predicti

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206

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n to show stefor solving enon this topic y of Techno

ui, 2001). Of imately relate(due to the

ength of a liace, by av

ll topics - asesulted in seuch as in IAS; Hu and

ong others wrand new devas simulating ment paste cd in fractal-ligists! Yet, r

to economation using oned in this pvik).

ally be stresd topics werethose years. ned here, bec

n of “hard” tem the discusssustainabilit

t la letter”. ASri Lanka wile laboratoryof cooperatio

with Viete Dutch Gochanges in th

accepted projetive was to rPortland cem

nt-based mater

al life” startinto extensi

ork of my PhDle packing ate) and ther

RC. It resulteof hundred

in journals inds available ereology a vengineering prwas Shui Zh

ology who rf course, damed in stereolotwo Cauchy ine or area o

veraging of

s already meeries of pubS (Stroeven, Stroeven, 20

with Kai Li, velopments ca

the outer hydconsisting oike “arms” (Frecently, we

omic develo– again – Ca

paper (see als

ssed that thee not the onlAt least, one

cause it may oechnology acsed topics. Tty aspects

Application foith Architect

y research waon with Tanztnam. The overnment (he country reect) in signifreduce CO2 e

ment by fine-

rials

ted when I ive physical D study (i.e.and damage reupon with ed over the

papers in n the SFRC worldwide),

ery practical roblems. My honghe from received his

mage analysis ogical terms concepts of

of a surface, their total

entioned for blications in et al., 2012; 006). Some

are still in an hereby be dration layer

of nano-size Fig. 11); real

have given opments in auchy’s 3-D

so: Stroeven;

e mentioned ly ones that e other topic offer nuance ctivities that

This one was in concrete ocussed on a tural student as conducted zania, Brazil

latter was (1982-2002), sulted in our

ficant budget emissions by grained rice

Image Anal Stereol 2019;38:201-211 

209  

husk ash (Bui, 2001) or non-commercial metakaolin (Vu, 2002). Mind that this was significantly before such CO2 emissions were internationally declared leading to global warming, hence it was hard in our case to find moral and, particularly, financial support. Note that the given examples are particle packing-driven. This illustrates again the actual relevance of the first topic discussed herein!

At the final end of this paper it should be men-tioned that promotion of stereology in my field was also explicitly in my mind during the many years that I participated in the ISS community as “regional representative” and as Editorial Board member for Acta Stereologica and Image Analysis and Stereology.

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