Journal of the Ceramic Society of Japan

Microstructures

110 [6]535-540(2002) Paperof Hardened
SinteredIsao

TSUYUMOTO

Mortars
Using
SewageSludgeand Hiroshi

Eco-Cements

andUCHIKAWA

Division of Environmental Engineering, Kanazawa Institute of Technology,
7-1, Ohgigaoka, Nonoichi-machi, Ishikawa-gun, Ishikawa 921-8501

エ コセメン トと溶融下水汚泥 を使用 したモルタル硬化体 の微細構造
露 本 伊 佐 男

・内 川

金 沢工 業 大学 工学 部 環 境 系, 921‑8501石浩

川 県石 川郡 野 々市 町 扇 が丘7‑1

Strength development and microstructures were investigated for a hardened mortar using eco-cement
manufactured by replacing a part of the raw materials with incineration ash of urban waste and a waste-der
ived aggregate of sintered sewage sludge. Back-scattered electron images and X-ray image maps showedthat the porous zones of Ca(OH)2 usually observed at the interface between the normal Portland cement
paste and aggregate did not form in mortars using the eco-cements. The hydration processes of eco-cements
were discussed based on distribution maps of Cl, S, Mg, Na, K, Fe, Si, Al, Ca, and O.
[Received December 6, 2001; Accepted March 25, 2002]
Key-words: Eco-cement, Waste, Transition zone, Mortar, EPMA, HVRWC

eco-cement and the waste-derived aggregates will provide
great information on the utility of HVRWC.
In this paper we focused on the microstructures ofhardened mortars prepared from eco-cements, especially on
the interfacial zone structure between the cement paste andthe aggregate observed by means of scanning electron
microscopy (SEM) and electron probe microanalysis(EPMA)

1. Introduction
Discharges of incineration ash of urban refuses and indus
trial wastes have been increasing every year, and shortageof disposal centers has become a vital problem in environ
mental conservation. During recent years, substantial
efforts have been made in reducing and recycling thesewastes. In order to utilize such waste materials and at thesame time to preserve natural resources, techniques tomanufacture cements from the incineration ash of urban refuses and sewage sludge have been developed.1),2) These cements were called eco-cements after their environmental
load-reducing properties. Because of the difference in theraw materials, their mineralogical compositions and hydra
tion behavior differ from the normal Portland cement(NPC). However, the microstructures of hardened mortar
and concrete using eco-cements have not been clarified sofar.
The strength, gas and water permeability, ion penetrability, and durability of concrete are associated with the pore
structure, orientation, and crystal habit of Ca(OH)2 gener
ated at the transition zone formed at the interface between
the cement paste and the aggregate. As for the ordinary conCrete from NPC and natural aggregates, the texture and thecomposition of the transition zone have been elucidated, andthe techniques for the control of the hardened concrete
structure have been established.3)-5) However, there are noreports on the interface structures of the eco-cements between the cement paste and the aggregates. In order to veri
fy the durability sand the usefulness of the eco-cements, it isnecessary to elucidate their microstructures.
Furthermore,high-volume recycled waste concrete(HVRWC) containing several hundred kilograms or moreof waste derived.materials as aggregates per cubic meter; ofconcrete using, NPC zhas been proposed.6) The structure andthe strength of the hardened HVRWC have been reported
for various kinds and amounts of waste-derived aggregatessuch as incineration ash of urban refuse, sintered coal ash,sintered sewage sludge, and glass cullet.7) In view of en
vironmental conservation, it is highly desirable to prepare
HVRWC from both the eco-cement and the waste-derivedaggregate. The study of interfacial structures between the2.
2.1

SampleMortarr
pared

specimens

usingthree(160mm•~40mm•~40mm)
types(NPC),
normal-typeand
rapid-hardening(REC),andal Standard

Experimental

preparation

ofcement:

werenormal

eco-cement
with
type
eco-cement

cementlow chlorinewithhigh(NEC),chlorine

two typesof fine aggregates:
Japanese(JIS)naturalsand
and water-quenchedsewagesludgelogicalcomposition

(SS).

Table

1.

Theirandchemical

surfaceThe

mineralogicalestimated

by

using

sumptionthatthe,compositions

C3S, C2S, C11A7•ECaCl2,andproperties

compositions

thefollowing

Industri
sinteredcomposition,

areaoffour

mineraareequationsof theprePortland

theshownREC

inwasbased

on

major

phasestheasareC4AF,%C3S=4.071CaO-2.852503-7.602SiO2- 5.718Fe2O3-3.519A1203-3.22001+3.683Na20+2.424K20(2.1)%C2S=2.867SiO2-0.7544C3S(2.2)%C11A7•ECaCl2=2.020A12O3-1.290Fe203(2.3)%C4AF=3.043Fe203
In

2.1,

the

suming

that

Na20

and

K20

reactwithcalciumcompoundliberate

CaO.

On

the

other

hand,

the

reaction

ofmostof

nottakenintodependently
ResultsofNa20andbecause

MgO

K20

duringhydration,

discussionsection.

The

aggregate:

water:

werecuredin water
Characterization

Bending

535of

account
asandcement:

mens
2.2terms

(2.4)

Eq.

strengthandwereaddedastoMgO

wasitdistributedin

asdiscussed

inmixing

ratio

was1:3:0.5,andat 20•Ž

accordingtocompressivebystrengthof mortar
thespeciJISR 5201.

tests

ofthe

Microstructures

536

of Hardened

Mortars

Using

Eco-Cements

and Sintered

SewageSludgeTable 1. Chemical and Mineralogical Compositions of the Cements and the Aggregates
NPC, Normal Portland Cement; NEC, Normal-Type Ecocement; REC, Rapid-Hardening Type Ecocement; SS, Sintered Sewage Sludge

mortarspecimens

and28d.

tions

andSEM
analysisof 28d.

Theat theacceleration

rentofwereandcarried

EPMAwerespecimens

carriedwerevoltage

outattheages(JXA-8800,ofoutof3,JEOL)

7,

onspecimensat thedry-polishedandcharacterized

15WV

and

the14,

observa

irradiation

age

cur

0.1ƒÊA.

3. Results and discussion
3.1 Mechanical strength
Figures 1 (a) and (b) show the compressivee and bending
strengths of the mortar specimens, respectively. As for thecompressive strength, the eco-cements showed very similar
strengths as the NPC at the age of 28 d though the earlystrengths of REC are higher than those of NPC and NEC,when the standard sand was used as aggregate. On the contrary, when the SS was used, the two types of eco-cements
showed slightly higher strengths than the NPC. The result
suggests that the combination of the eco-cements and SS is
comparable to that of NPC and sand after 28 d.
As for the bending strength, the specimens using the SS
were inclined to show lower strength, by about 10-20 per
cent, than those using the standard sand. This difference
can be ascribed to lower adhesive strength between the aggregate and the cement paste due to the glassy smooth surface of SS rather than to the strength of the aggregate itself.
The REC and the NEC using the SS showed higher
strengths than in the case of NPC using the SS. The influence of the surface smoothness of the SS on the bending
strengths was smaller in the case of eco-cements than in thecase of the NPC.
3.2

Microstructure

The observed
the microstructure
microstructurechangesin strength
are closely related
withof mortar,
especiallywith the interfacial
betweenthecementpaste.
andtheaggregate.4) Figure 2 (a) shows a back-scattered electron
image on the polished surface of hardened mortar using
NEC and standard sand. The white parts of the image cor
respondsto unhydrated calcium silicates since the X-ray im
age maps in Fig. 3 (a) showed high contents of calcium andsilicon at the part. The distribution of sodium coincides withthat of the unhydrates, indicating that most of the sodium
still exists in unhydrated solid solution. The distribution ofmagnesium does not necessarily correspond to those of theunhydrated calcium silicate or the chlorine, and part of themagnesium distribution correspond to that of iron. This in
dicates that the magnesium did not exist as a solid solutionof calcium silicate such as C54S16AM8)nor form chloride
during hydration; and that most of the magnesium exists aspericlase (MgO), brucite (Mg(OH)2) and the solid solutionof C4AF. It is exciting to note that the porous calcium-richphase mainly consisting of Ca(OH)2 usually observed
around the aggregate in the NPC mortars of water: cement
ratio of 0.4 or more4),5)was not observed in the present ones
having a water to cement ratio of 0.5. This indicates that thetransition zone is not formed at the conventional water: cement ratio in the mortar using the NEC. Therniogravimetry
and powder XRD measurement also indicated that the calci
um hydroxide did not form in the specimen at the age of 28d, and the formation of the ettringite was observed in theXRD profiles. These can mainly be ascribed to the lower
content of C3Sand C2Sin the eco-cement, and the calcium
hydroxide formed by thehydration of NEC is assumedito beeasily consumed to form ettringite.
Figures 2 (b) and 3 (b) show a backscattered electron image and an X-ray image rmp of mortar using the REC andthestandard sand respectively. The transitionzone was notobserved in Figs. 2 (b) and. 3 (b) similarly to the, case with
the NEC and the standard sandy These resultsindicate theIsao TSUYUMOTO

et al.

Journal of the Ceramic Society of,Japan

110 [6]

2002537

Fig. 1. Compressive strength (a) and bending strength (b) of themortar specimens using three types of cements and two types offine aggregates. NPC, normal Portland cement; NEC, normal typeeco-cement; REC, rapid-hardening type, eco-cement; SS, sinteredsewage sludge.

adhesionsandbetween

were

the

two

satisfactory,types

andof eco-cement

thiscorresponds

their28

d strengths

werecomparable

to those

The

REC

contains

0.9%

ofchlorine

andcanbeshown
age

in Tablemap.

1, andThecontent

white

this
parts

of theunhydrated

calcium

caseof NEC(Figs.

is confirmed

by

these

distributions

orC2S•

theCaC12

areformed

ofunhydrated

calciumthehydration

tion

activity

thancalcium

silicate

is notclear

so farwhether

thisproceeds

muchty is caused

by

the

differenceandcrystalstructures

suchThedistribution

sulfurandaluminum,
areofandestimatedinvidessignificant

information

cal

compositionsoflittlealinite

due

to

higher
and

hydra
NPC.

compositionsorin specificcorresponds

30%,ontoarea.
thoseof chlorine,and(3CaO•
A1203•E3CaSO4•E32H2O)
are 4.3
in monosulfate
hydrate(3Ca0•EAl203•

This

products.
sulfurof

sulfur,regionrespectively.

hydrationIt

activichlorine-concentrated

9 andaluminumThein hydration

distortion,It(C3S
becauseits

in mineralogicalthesimilar

3 (a)).

in NECdifference

concentrations

5,

that

aFig.

is smaller

The1.5,inandeco-cements.9)

almostcalciumassilicates
2 (a)

phase

high

chlorine,

in thechlorine

aluminum.

imcontain

silicate
more

as

as

the

containhardly

NPC.
S03

which

andsize

theofimage,in theCaC12)

of8.5%

byastothethat

confirmed

calciummannersilicon

and
fact

also

ofcorresponded

andpasteto the

in

pro

Chemi
ettringite

and 7.7%,
andCaSO4•E12H20)

thoseareFig. 2. Back scattered electron images on the polished surface ofthe mortars from (a) NEC and sand, (b) REC and sand, (c) NEC
and sintered sewage sludge, and (d) REC and sintered sewage
sludge.

538

Microstructuresof Hardened

Mortars

Using Eco-Cements

and Sintered

SewageSludgeConcentration (%)

(b)

(a)

8.7

andandsulfur

5.1%,

thoseofmonosulfate,monosulfate

hydrate.

inFriedel'sThus

theormorechlorinethatrespectively.

in thecompositions

indicating
The

salt

the

chemicalFriedel'saluminum

aresimilarsulfurmostly

salt,

salt

regionwhichwasof

concentrated

the12.7%.

in theregion

Fromcanforms

iscontains

estimated

toof chlorine(3CaO•EA12O3•ECaC12•E10H2O)

composition

schemeofregioncompositions

chlorine-concentratedof Friedel'shydration

The

chlorine-concentrated

by

10%

dividing

theregiontheseresults,

beproposed

12.7%.

about
1.5%
part
asbyof thefollows.

After mixing with water, ettringite is formed by hydrationof calcium chloroaluminate C11A7•CaCI2,with gypsum, andit converts into monosulfate hydrate with time. In theprocess of hydration, about 10% or more of the monosulfate
hydrate reacts with Cl-liberated from C11A7•CaC12to form
Friedel's salt.
Figures 2 (c) and (d) show back scattered electron images of hardened mortars using the SS as aggregate withNEC and REC, respectively. The surface of the SS was
found to be smooth compared with that of the sand, and theIsao TSUYUMOTO

et al.

Journal of the Ceramic Society of Japan

110 [6]

2002539

Fig. 3. X-ray image maps of mortars from (a) NEC and sand, (b) REC and sand, (c) NEC and sintered sewage sludge, and (d) REC andsintered sewage sludge.

transition zones were not observed also for these mortars.
The surface smoothness of SS is due to the deposit of glass
phase in the treatment process of sintering and waterquenching.10) Although the absence of the transition zone isfavorable to strength, the surface smoothness of the ag
gregates can cause a reduction of the adhesive strength andconsequently the lowering of the strengths, especially thebending. As shown in Figs. 3 (c) and (d), the behavior of
the cement pastes were almost the same as the cases using
the standard sand. The same discussions on the distribu
tions of each element are possible, and this indicates thatchemical components affecting the hydration of cement do
not elute from the waste-derived aggregate.

(1)

The

strengths

ments

werecomparable

in strengths,
ingSS

strength

4.
and theConclusions
microstructuresof hardenedmortars using
eco-cements
and the waste-derived
aggregateswere investigated.
Results
obtained
are summarized
as follows:The

transition

cementThisofCa(OH)2

form
did

(4)
formeddidhavinga water

betobytheto theirinmore
thewasnottocement

hydrationthat(MgO),
The
notin thethebrucite

distribution
existinmostof(Mg(OH)2)

ofand

that

in

the

ratio

of0.5.

toof C3S andhardened

thesolidC2S.

mortar, of calcium
andmagnesium
existedandofformed

eco-cementsof chlorine
indicatedalinite(C3S•ECaC12)
or

eco-cements,

a porousmortars

consumption

contents
inus

surface.

as
NPC

accelerated

lower

eco-cedecreasesmoothobserved

aggregateortheTheof mortars

glassyThe
distributionof magnesium
necessarily
correspondto those

indicating

periclaseof C4AF.
rine

owing

NPC.

strengths,
its

usuallydueusingof thetothe0.4

produced

ettringite

(3)
notto

due

zone
ofmortars

is consideredbearoundratio

specimens

thosebendingtozoneeco-cement

con,

The

thought

(2)

theto

particularly

wascalcium-richwater:ofsili
assolutionthatlittle chlo
C2S• CaC12 are

it is incorporated

into

540

Microstructuresof Hardened

Mortars

Using

Friedel's salt produced by reaction with 10% or more ofmonosulfate ,hydrate.
(5) The size of the calcium silicate of the REC which
remained unhydrate was smaller than that of the NEC ,showing its high reactivity.
(6) Chemical components affecting the hydration of ce
ment are deduced not to be eluted from the waste-derived
aggregate.
References
1) Uchikawa,
H. and Obana, H., World Cement, 26 , 33-40(1995).
2) Uchikawa, H. and Hanehara, S., "Waste Materials and Industrial By-Product in Concrete Manufacturing," Noyer Publica
tions (1997) pp. 430-553.
3) Uchikawa, H., "Concrete Technology, Ceramic Transactions

Eco-Cements

4)
5)
6)
7)

8)
9)
0)

and Sintered

SewageSludgeVol. 40," Ed. by Grantner, E. M . and Uchikawa, H., Am.
Ceram. Soc. (1994) pp. 143-86 .
Uchikawa, H., "Pros. of 3rd CANMET/ACI Int . Sym. on
Adv. in Concrete Technol." (1997) pp. 109-29 .
JUchikawa, H., Concrete Engineering , 33, 5-17 (1995) [inapanese].
Uchikawa,
H., J. Materials in Civil Engineering , 12, 320-29(2000).
Uchikawa,
CANMET/ H., Hanehara, S. and Hirao , H., "Proc. of 4th
ACI Int. Sym, on Adv. in Conrete Technol."(1998) pp. 23-37.
Jeffery, J. W., Acta Cryst., 5, 26 (1952).
Kurdowski, W. and Miskiewicz, K., Cem. Concr. Res., 15,785-92 (1985).
Imaoka,1M., "Advances in Glass Technology Part I ," Plenum,
New York (1962) pp. 149-64.