* '

CaGKTITI0U3 inOf-CiilliS 0? S.TTALHIaOICAl GS

S'̂lr

A dissertation presented to the Faculty c Engineering,

University of the Vitwatersranu

in fulfilment of tne requirements for the Degree

of

KAfTZR OF 3CIZHCE IN £NGIft£. ROG

by

Robert Eortey Coale, Xet. 2.

1971

3 T fl 0 ? * I .1

An investigation was sade into the cenentiticus properties of

metallurgical sl-i~a which fsll in the four-comconer.t system 'iP^-Al^C^-

MgC-CaC, notably those slags t'ron the iron biset furruce. A aeries of

slags have been chosen arsed on the following criteria:

SiO., : 2 0 - 5 0 Per cent

Al.Oj : 10 - 55 Per cert

MgO : 0 ' 35 cent

CaC : 10-50 Per cent

Liquidus temperature le33 than 160C°C.

These -iriteria result in 101 3lags which best reflect the slags available

for the nanufacture of cement.

The slars were prepared by melting the pure oxide components and

quenching them into water. The quenched slags were ground and subjected

to various tests:

1. True liquidus temperature determination

2. Primary Phase determination

3. Pate of quenching required to prevent crystallisation,

Small test cylinders were made by mixing the ground slag with

sand and Ca(0K)2 activator and moulding the mixture. These were tested

at various intervals 17, 1̂ , 2 % and 56 days) to determine their cr"'-

pressional strength.

Iso-strergth curves, relating corapressional strength to com­

position, were drawn on pseudo-terr. try diagroms at constant A^2®3 ^ev®^8*

These provide a mejins for rapidly assessing tin hydraulic strength of a

slag based on composition.

Two statistical approaches, a correlation matrix and a multiple

linear regression analysis, wero made to determine if a linear relation-

-rrrjf

C O N T S ' I T S

CHAPTER I asrrsaAL cc::.~I33ra?icik1.1 Introduction 1

1.2 Slag Cea^nt 1

1.3 Assessment of the ''ydraulic Properties of 3Slags

1.** Me tallurgical 31a ,-s k

1.1*.1 Iron 31ast Furnace Sla^i 61.*t.2 Steelnaking Sla~s 61 .4 .3 Ferro-alloy 31a ~s 7

1.5 Granulation of 8

CHAPTER II sxPsair-r̂ JTAi prccsotse - s l a m

2.1 Selection of Slag Compositions 9

2.2 Slag Preparation 17

2 .3 31* g Melting 17

2.4 Grinding of Slags 21

2.5 Liquidus Te~por?tuie Measurement 21 ■

2.5.1 Micro-Jiffere '.ial Themal Analyzer 21

2.5.2 Thermocouple Fabrication 23■ :-

2.5.3 Sea pie Dead ?rereration 232.5> Liquidu* Temperature Determination 252.5.5 Results of Liquidus Temperature Determination 252.6 Determination of '.uenching 3ehaviour 352.6.1 Homogeneous Mucleat-on-Crystallization 352.6.2 Heterogeneous Hucleation-Crystallization 77

2.6.3 Non-equilibrium Conditions 372.6.4 Rate of Crystallization 382.6.5 Quenching Procedure 382.7 Primary Phase Determination *♦0

CHAPTER III sx?̂ Rr::..".TAL pscczdc?*: - ssmswt

3.1 Hydraulic Properties *♦2

3 .1 . i Hydration of Portl-,u»j Cement 42

3.1.1. i Hydration of C,S and 3eta-C2S 42

3 .1 .1 .2 Other Hydration Reaction* <♦3

3 .1 .1 .3 Hydration Products 44

CC-ITT" (Continued)

C ir ? ”:?, h i

3.1.2

3.1.33.2 3.2.1

3.2.2

3.3 3.^

hydraulic Properties of Crystalline Slags Hydraulic Properties of Glassy -'lags Activation Requirements of a Slag Determination of Activator Hequireoer.ts Activation of Sample Slaja Preparation of Test Cylinders Compressive strength Determination

Page

*5k6

V?V7585860

f;.

Bsr '

Eft*

chapter Vi istsrp.ctatic?* a:;d pi-srsr.xc? c? its4 .1 Graphical interpretation of Results It.2 Statistical Interpretation of Results I*,2.1 Correlation Coefficient Analysis U.2.1.1 Anorthite Phase Field4.2.1 .2 orstcrite Phase Pield4.2.1.3 Melilite Phese Pield **«2.1.k Spinel Phase PieldI*.2.1.5 Samples Exhibiting a Compressive strength

Greater than 1800 N x 10H/a24.2.2 Multiple Linear 'egression Analysis4.2 .3 Discussion of Statistical Result*l±mx R e la tio n sh ip s O ther than Com positional

4.3.1 "nmple Selection4.3 .2 Thermo-gravimetric Analysis4.3 .3 X-ray Diffraction Analysis4.3.4 Discussion of P.esults of Non—evaporoble

Water Tests

CHAPTER V CC'iCLrJSIC:iS

667*»

3385?591

95

9S107110110

111

1 1*+11^

115

'RKFPREMC2S 119

I . G Z ” Z 3 A I. ; C M S I D ?. A T I G ?! 3

1.1 Introduction

As world production of metals increases, so does production of

esscci'ited metallurgical sla-s. Although new processes and technology

have reduced the quantity of slag per unit of metal produced, increased

demands for metals have increased the tctal amount of slag formed.

Although slags are formed during a number of pyrometallurgical

processes, the major proportion of 3lag is derived from the iron and

steel industry and ferro-alloy production. Sla'js themcelves, if free

from metal values, have little further use metallurgically, except

when used as a fluxing material. Hence large quantities of slags must

be disposed of by various metal producers. Several different industries

have found slags to be a useful raw nrterial for various applications.

Perhaps the most common use of raw, unprocessed slags is as ag­

gregate, either as a concrete filler or as roadway and railway found­

ation material. Other uses of slags include slag ceramics wiiich are

produced by n proccss of controlled devitrification, slag wool for use

as insulation material, foamed slag for use as a light-weight aggregat-.?,

and, depending upon their composition, as fertilizers. Slaps are aldo

frequently used for the manufacture of cement or as an addition to

Portland cement constituents. The subject of this thesis is the use of

sl^gs as cement.

1.2 Slag CementBlast furnace sing has been used as a raw material for the manu­

facture of cement for about 100 years (1). These slags, which fall

into the quaternary system SiO^-Al^-MgC-CaO may vary greatly in

their hyclraulic properties depending upon their chemical cccpositiou,

the presence of constituents other than those in the quaternary sys­

tem, the amount of crystalline material in the quenched slag, and

other considerations.

31ast furnace sl-sg can be utilized as a ceaent with the ad­

dition cT an activator, or, Tore commonly, as an addition to portland

cement in varying proportions, Clag additions to Portland cemer.'c c m

either be trade to the cement clinker prior to grinding or as an ad­

dition to the mortar mix. The Corner results in ar. unequal particle

size distribution between the cement and the slag, as the softer clinker

will be preferentially ground. Addition of the slag to tho mortar nix

necessitates separate grinding of the two constituents.

Mixtures of portland cem»rt and blast furnace slaga fall gen­

erally into three cate-orics depending upon the weight ratio of the (2 )tw'j constituents

Specification Per Cent 'Jilast ?u~nace 31^g

Blast furnajt- ce-*>r.t 35 <35

Blast furnace cement 35/^0 35 -

Ciment de laitier au Portland > 85

Unassociated MgO (p~riclase) in portland cement clinkers has

been shown to be dele’erious to the cement because of the volume in­

crease experienced when this constituent hydrates to form brucite .

Since expansion nay occur a considerable length of time after the cement

hfiS set, thus disrupting the entire matrix, the amount of periclase

allowed in cement clinker is regulated by various specifications, gen­

erally to less than five por cent. This specification has also been(3,^,5,6)applied to blast furnace slag cements, although various workers

have shown that when maintained in the glcssy state the MgO in blast

furnace slags is not harmful.The risk of lime unsoundness has also led to certain restrictions

being imposed on the CzO content of blast furnace slag cements. Lime

unsoundnesa results from the phase change beta to gamma dicalciun jil-

j'.cate (2CaO.SiC2) and is accompanied by a volume increase of the slag.

- 2 -

---- '■ \mmm aim.nmnm I— . W n Wi V M k

- 3 -

Several workers have proposed composition speci.ficitior.s of the slag(7 P Qlwhich will prevent "falling" because of lice unsoundness ’ *>/,

and it has b°en shown that rapid quenching of a blast furnace si-'*;

prevents the crystallization of diePicture silicate and thus preclu.es

the possibility of the phase change.

1 .3 ‘-ssessMfrnt of the Hydraulic Properties of "la.-s

Sone investigations have been m-de into the suitability of high-

ma-̂ nesia or high-line slags for cement production however the

entire range of slag compositions available for cement manufacture has

not been st.-died to determine the extent of those slsgs suitable for

cement.

Various composition formulae have been proposed for the assess­

ment cf a slar bnsed on its composition. Cf tr.tse, the modulus

CaC ♦ UgO + 1/3 A1 0 {5) _________________-— - 1 has been one of the most popular *SiC2 + 2/3 Al^Oj

CaO + KgO ♦ A1205 , a0Other related formulae include c.(r, — > 1, - —• j> 1.2,

2 S:.02CaO + Al-,0, + CaS + KgO

a„ j _______ ______________"-» 1.5. T^ese formulae are based on*nC SiC2 ♦ MnOexperience and have been used to indicate the hydraulic value of %

slag. The validity of these formulae over a wide compositional range

has not been established.One of the most important criteria for assessing slags for use

as cement is that they do not contain more than about 15 per cent

crystalline material, "ot only might crystalline material lead to

unsoundness as discussed above, but crystalline slag possesses little

or no hydraulic properties (1C). For this reason, slags which cannot

be successfully quenched to yield a glassv product sill be unsuitable

for cement manufacture. Therefore, a determination of the quenching

characteristics is necessary.

Parker ar.d Nurse have combined b^th a composition modulus

and the percentage glas3 into 3 strength

I = 0.3?G (K - + 75.0

where

I = Strength index of a 6;/35 portlnnd cement/slag fixture

G = Per ccnt glass

CeO ♦ HgO + 1/3A1207 r1 = SiO? ♦ 2/3*igC3 ' *

It is therefore proposed to examine a nuaber of slags rc-

spect to not only their hydraulic capabilities but also to their over­

all suitability as cement.

1. U Ketallur^ir -P. 31a~s

Slars which might be considered for use as ceaent come from three

main sources:

a. iron blast furnace

b. steelmaking processes

c. ferro-alloy production.

All of these sla^s fall basically into the quaternary system

SiO -A1.0,-Ca0-"g0 but contain varyirg amounts of other material. In 2addition to those slags lisced above, non-ferrous slags may also fall

generally into this quaternary system, but these slags usually cost- m

significant amounts (mere than 10 per cent) of material not falling

into the Si0..-Al-0,-f'f,O-Ca0 system, which would probably affect theC. d j

g; \nulation behaviour and the ceaentitious properties of the slag.

Table I is 1 tabulation of the analyses of several types of

metallurgical slags which have a composition suited to war. a.it -heir

application as a constituent oi lenient.

Author Coale R D Name of thesis Cementitious properties of Metallurgical slags 1971

PUBLISHER: University of the Witwatersrand, Johannesburg

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