AC'I 'IVA'~ION OF PIIGH-CALCIUM FLY ASH : PRELIMITVARY INVESTIGA'I 'IONS

4.1 INTRODUCTION

This chapter reports and discusses the experimental study in which lime and gypsum

have been used as 'activators' of high-calcium fly ash, in mortar and concrete.

Compressive strength attained at normal and at later-ages has been chosen as the

principal parameter for comparing the effect of the above activators on the various fly

ash-based mortars and collcretes. The effect of three different 'curing regimes' on the

strength characteristics have also been studied and reported.

4.2 PLAIN FLY ASH

4.2.1 Plain Fly ash Paste

Consistency and setting times were determined for plain fly ash paste. It was

observed that the consistency was 23.5% and the initial and final setting times were 9

and 17 minutes, respectively. Plain fly ash paste specimens were cast with water

content equal to its consistency. The above quantity of water was added to fly ash and

the mixture was hand mixed and kneaded well to obtain a homogenous mix and the

paste was cast into 70.7mni cubes in three layers with 25 tampings for each layer, as

specified in IS: 1727-1967. The specimens were then kept under moist jute cloth untiI

the time of testing. Compressive strength of the above paste specimens evaluated at

3,7,14 i r E 1 1.2, 12.0, and 12.0 MPa, respectively 4

4.2.2 Plain Fly ash Mortar

As the fly ash is of self-hardening type, the first study was made with plain fly ash

mortar without addition of extra lime. As it was also proposed to compare the strength

of these mixes with that of fly ash mortars activated with lime and gypsum, it was

decided to adopt the same test procedure as that of lime reactivity test for fly ash as

per IS 1727-1 967, except curing, which was done at the laboratory temperature.

Binder to standard sand ratio was maintained as 1 :3 (by wt.) and the required quantity

)f water was dctcrrnincd based on the 'flow test'. 'She specimens after dc~noulding

vere transf'errcd lo a humid~ty cabmet. After 7 days of 'hulnld curing' at 27* C and

,O% RI-I. the compressive strcngth of thc above specimens. was determined by the

,tandard procedure and presented in Table 4.1. Crushed satnples from the specimens

vere kept soaked in acetone in order to arrest hrther hydration and preserved for

{RD and SEM analysis.

<RD d'ffiactogram of the hydrated fly ash mortar sample is shown in the previous t* Zhaptercn Pig. 3.P It is observed that, C ~ A C H I I , c~A'SIHX, MgO, CSH, c ~ A % .

-

:ttringite, and C5S2S, could be identified. Hydrated of fly ash particles are seen in

3EM micrographs, shown in Figs. 4.1 and 4.2.

1.3 FLY ASH - LIME

1.3.1 Fly ash-Lime Paste

2onsistency and setting tests were carried out on the fly ash-lime blends with the lime

;ontent varied between 10% to 30% (by wt.). It was observed that the corresponding

;onsistency values of the F-L blends, varied between 37.5% to 76.67% and the initial

md final setting times, 6 to 9 minutes and 9 to 15 minutes, respectively. Fly ash-lime

~ a s t e specimens were cast for various lime contents and their co~npressive strength ma

determined as detailed in Section 4.2. It was found thatkmaximum strength was

3btained at a lime content of 18.5% (by wt. of total binder). Compressive strength of

F-L pastes at 3,7,14 and 28 days arei8.4, 9.6 11.5 and 11.6 MPa, respectively.

Estimafion of Tlieoretical Lime Required

The actual quantity of lime required for the complete hydration of fly ash is usually

difficult to estimate. which is due to the fact that complex compounds are formed

during hydration. However, an approximate estimate of the lime required to hydrate

completely a unit quantity of a given fly ash is possible. The procedure outlined by

Anne Roja (1996), which is very simple and provides reasonably a good estimate of

lime required, has been followed. The above procedure is described below:

The main reactionary compounds due to the hydration of fly ash-lime blend are:

&ydrates of calcium silicate, calcium aluminate, and calcium ferrite. The reactions can

6e represented as follows:

3C'aO I 2SiO2 -t 3 1-120 3Ca0.2Si02.3 1-120 (C-S-[I) . . . 4.1 ( a )

I ' ! 0 1 - 0 I A 9 1 I ( - 1 j . . . 4. i t b j

3CaO t- Fe20.7 + 6 H z 0 3Ca0 . Fe203.6 H20 (C-F-H) ... 4.1 (c)

The molecular weights of the diffcrcnt compounds are :

From equation 4. ](a), one can obtain that one gram of SiOz requires 1.4 grams of

CaO to forni C-S-H. Similarly from equation 4.1 (b), it can be seen that, one gram of

A1203 requires 2.2 grams of CaO to form C-A-H. Equation 4.1 (c) gives that one gram

of Fez03 requires 1.05 grams of CaO. Thus, one gram of fly ash requires

(1.4+2.2+ 1.05) = 4.65 granis of CaO, for its complete hydration.

As the fly ash sample used in this study, has the following chemical composition,

namely, SiOz = 34.18%; Al203= 24.09% and Fe203= 10.78%, the lime required per

gram of fly ash has been computed as, equal to 1.18 gm igm of fly ash. The above

quantity is valid only, when the components participating in the reactions are 100%

'reactive'. Since, most of the Indian fly ashes have only 27-34 % of 'reactive silica? as

reported by Sharma (1990), the lime required for various reactivity levels of fly ash

(5% to 40%), was computed proportionately and presented in Table 4.2.

Corresponding to the reactivity of the fly ash used in this study, (i.e. 16 %), the

theoretical quantity of lime required for the hydration of fly ash-lime blend is 0.1 89

gm 1 gm of fly ash. The CaO content already present in the fly ash sample is 16.9 gm /

gm. llcnce, thc additional quantity of linlc rcquircd will only bc vcry small. In

addition to the above 'major' compounds participating in the hydration of fly ash-

lime, other 'minor' compounds present in fly ash, may also participate in the reactions

with lime. Hence, the actual lime required is likely to be somewhat higher than the

quantity theoretically s

~eterrniilatioll of Actual Qzrarrtity of Lime Rey ztired

In order to determine the actual quantity of lime to be added to the fly ash sample,

compressive strength of fly ash-lime mortars was determined, using the procedure

detailed in Section 4.2. Taking into consideration the theoretical quantity of lime

required for the fly ash and the small additional quantity of lime required for the

hydration of minor compounds in fly ash, it was decided to add 4 - 16 % lime (reagent

grade) to the mix (by weight). The compressive strength of the such fly ash-lime

mortars are presented in Table 4.3. Lumps of the crushed specimens were powdered,

soaked in acetone and preserved for conducting XRD and SEM analysis.

Compressive strength results obtained indicate that there is only a marginal increase in

strength with increase in lime and that the maximum strength obtained is about 15%

higher than the reference mortar strength at an additional lime of 16%. Corresponding

XRD ( Fig. 4.3) also does not indicate much variation with respect to that obtained

without additional lime (Fig. 3.3). Only notable factor is the pronounced formation of

C4AH3 and CSH. SEM micrographs (Figs. 4.4 and 4.5) indicate the formation of

relatively denser hydrated products in the system with probably a few calcium

hydroxide cubical crystals. As the increase in the compressive strength is not

significant, considering the quantity of lime added, it is inferred that the fly ash

sample has the potential to impart good strength, without addition of (external) lime.

4.4 FLY ASH - GYPSUM (F-G)

4.4.1 Fly ash -Gypsum Paste

Gypsum content was varied between 10/o to 13% in fly ash - gypsum (F-G) blends.

Consistency of the F-G blends corresponding to the above gypsum content, showed

water content variation between 22.5% to 29%; initial and final setting times of the

above F-G blends showed a variation of 10 to 12 minutes, and 18 to 30 minutes,

respectively. F-G paste specimens cast with various gypsum contents and tested as

detailed in section 4.2, attained the maximum strength at a gypsum content of 6.25%

,(by wt. of total binder). Compressive strength of the above blends observed at 3,7,14

and 28 days are: 14.0, 19.2,24.0 and 24.0 MPa, respectively.

4.4.2 Fly ash - Gypsum Mortar

Studies ca t~ lcd out cullier tiad indicated that there was no dimensional instability of

the matrix, ~ ~ p t o a gypsLlm content of about 15% in F-L-G system [Karasimha and

~thers (1998, 1998, 2001 ); Jagannathan and others (1996)] . As, the focus at this stage

of the study was on F-G systems, it was decided to vary the gypsum content between

0 - 28 Oh, in order to understand better, the role of gypsum, in the system. Mortar cube

specimens (70.07 11irn) wcrc prepared and their compression strength determined, as

outlined in Scction 4.2. Thc results obtained are presented in Table 4.4 and in Fig. 4.6.

Lumps of the crushed specimens were, powdered and soaked in acetone and preserved

for carrying out XRD and SEM analysis. Compressive strength results (as given in

Table 4.4) indicate that the addition of gypsum to fly ash increases the strength upto

8% of it and that the maximum strength attained is 60 % higher than the strength of

reference fly ash mortar. But, when the gypsum content is increased beyond 8%,

strength reduction with respect to the maxiniuni value is observed. This indicated that

all the gypsum added could not be utilized for the formation of hydrated (i.e, strength-

giving) products, when its content is very high. Moreover, some of the gypsum added

may act as 'soft intrusions' in the rigid skeleton of the hydrated products.

From the compressive strength results of the fly ash-gypsum mortars, it can be

inferred that addition of gypsum to the high-calcium fly ash is advantageous, in

preference to the addition of lime, as substantial increases in compressive strength

can be obtained, provided, gypsum is not in excess quantities. Addition of gypsum

beyond 8% to the high-calcium fly ash, is not expected to contribute to maximizing

the strength.

XRD diffractogram, for 8% of gypsum addition (Fig. 4.7), shows the formation of

calcium aluminate hydrate, calcium alumino silicates, calcium alumino sulphates,

calcium sulpho silicates, apart from calcium silicate hydrates and ettringite. For a

higher gypsum content of 1496, the XRD diffractogram shown in Fig. 4.8, indicates

the formation of all the above compounds, except, calcium alumino sulphates. SEM

Corresponding to the above two blends are shown in Figs. 4.9 to 4.12.

4.5.1 Fly ash - Lirne - Gypsurn Paste

~ l y ash was blended with both the activators, namely, lime and gypsum and their

consistency and setting times determined. It was found that the consistency of the

above pastes varied between 55% to 64%, and the initial and final setting times was

found to vary between 8 - 15 minutes and 24- 30 minutes, respectively. Maximum

compressive strength, i.e. 10.8 MPa, was observed for the F-L-G blend of 70:20: 10

(fly ash : lime : gypsum) at 7 days.

4.5.2 Fly ash - Lime - Gypsum Mortar

Comparing the compressive strengths obtained for fly ash-lime mortars and fly ash-

gypsum mortars (Tables 4.3 and 4.4), it can be concluded that the fly ash used in this

study, could give higher strength with gypsum, than, with lime. But, the behavior of

the above type of fly ash, when both lime and gypsum are added, also needs to be

studied, before determining the best act~vator for the high - calcium fly ash used in

this study.

Hence, it was decided to carryout preliminary investigations on a few trial mixes by

adding lime to the fly ash - gypsum blend. Various combinations of fly ash (GO-80%),

lime (0-35%) and gypsum (0 -35s ) were selected and mortar cubes cast and tested as

mentioned in Section 4.2. Casting of specimens were done at different points of time,

partly to study the repeatability of results, and partly to takc into account matcr~al

variability, if any. These are indicated here as Series - I to Series - IV. Details of the

lrial mixes of the above series, are given in Appendix - D. 'The corresponding

compressive strength of the above F-L-G mortars, are presented in Tables 4.5 - 4.8.

From the critical analysis of the above results, following inferences are drawn :

(i) As the lime - content increases, the gypsum that can be added, also increases. The

above trend is in accordance with the observations of Lea [ 19711.

(ii) the lime - content increases, the compressive strength increases, upto a lime

of about 20:% iuf tile total biend) in ali tne Lur scrlcs of mixes. i-jo::,.cvcr,

strength - loss is observed, when the lime content exceeds 20 %.

(iii) The results also indicate that the maximum compressive strength of F-G mortar is

about 50% higher than the maximum strength of F-L mortar and it is almost equal

to the maximum strength obtained for F-L-G mortar.

Therefore, F-L-G system is not superior to either F-L or F-C; system. Interference i n

the hydration process, formation of unstable con~pounds are possible causes for the

lower strengths in F-L-G system [Sarkar (1995); Bhanumathidas (1989,

1992), Roja (1 99t~)I.

Hence, it can be concluded that the high-calcium lignite-based fly ash used in this

study, is more sensitive to the addition of gypsum and that the addition of (external)

lime, may not be necessary. However, the behaviour of the various fly ash-based

blends in concrete, needs to be studied.

4.6 F - L - G CONCRETE

4.6,l General

In order to understand the strength development characteristics of the various fly ash-

based blends in concrete as distinct from mortars, compressive strength of fly ash-lime

concretes, fly ash-gypsum concretes and fly ash-lime-gypsum concretes, were also

studied. The details of the above investigation, the results obtained and important

observations on the strengths dcvclopcd, arc presented in this section.

4.6.2 Materials Used

Apart fiom the fly ash, lime and gypsum, fine and coarse aggregates were used in F-

L-G concretes. Locally available, wcII - graded fine aggregate (sand) and crushed

granite coarse aggregates, were used, Aggregates were oven dried at 105- 1 10' C for

24 hours before their use. Salient physical properties of the aggregates including their

gradation are presented in Tables 4.9(a) and 4.9 {b).

AS the objective at this stage of the study was to understand the relative strengths that

can bc obtained using the above fly ash blends in concrete, it was decided to use only

nominal mix for casting concrete specimens. Moreover, a WIB ratio which is neither

too-low, nor too-high, but which will yield a workable mix for the various binders,

was selected. Accordingly, the nominal mix of 1:2:4, with a W/B ratio equal to 0.5

was selected for casting (cube) specinlens of the above concretes. Compressive

of the above specimens were determined after various ages of moist curing.

Relatively smaller quantities of lime (0-6%) were added to the fly ash and the

maximum content of gypsum was also restricted to 16%. The above values were

chosen considering the trends and results obtained earlier, as detailed in Section 4.3 to

4.5. The various combination of fly ash-based binders and their ranges, considered for

the compressive strength studies of the above concretes, are given in Table 4.10.

4.6.4 Preparation and Casting of F - L - G Concrete Specimens

One of the important steps in the preparation and casting of F-L-G specimens, is the

use of a pan mixer for grinding the ingredients of F-L-G concrete. In the present

study, a pan mixer was specially fabricated for the above purpose based on the

suggestions outlined by Bhanumathidas and others (1989). A brief description of the

pan mixer used, is given below.

Details of Part Mixer

A grinding-type pan mixture was used to ground the F-L-G blend. A few views of the

pan mixer are shown in Figs. 4.13 - 4.14. It consists of a pair of heavy cast iron

wheels at the ends of a horizontal beam, which rotates about a vertical shaft fixed at

the center of the drum. The shaft is powered by a 5 HP induction type motor

(Kirlosker make). The rotation of the shaft is adjusted so as to deliver 45 rpm, using a

gear system. Baffle plates fixed to the beam helps to achieve a homogenous mixing.

Cusfi,lg altd C'rtri~ig c!f'Specinie~is

'Jhe dry bleticl of' iiy ash, ~ ~ P S L I I I ~ , iitr~e iind s;~:rd bere c}rar.ged i l l to the pan lllixcr ?lrld

Mixed for 15 nlinutcs. The required (i.e. calculated) quantity of watcs is then poured

into the pan mixer and grinding continued for a further period of 10 minutes. Dry

coarse aggregates arc then charged and hand-mixed with the already ground mortar,

but without grinding. The concrete mix thus prepared was then taken out for casting

specimens. The specilnens were demouldcd after 24 hours and kept wrapped under

wet jute cloth. Water was periodically sprinkled over the wet jute cloth and this type

of 'moist curing' was continued until the required age of testing. All the curing was

done at laboratory tcrnperdtures. Three specimens were cast for each agc and mix and

a total of 504 specimens of concrete were cast.

Test and Test Methods

Compressive strength of various concretes cast and cured as above were tested at

various ages (i.e. at 3,7,14,28,56 and 90 days) in a 1000 kN con~pression testing

machine following IS standard test procedure.

Influelzce of tlze Activators on the Compressive Strengtlz

The results of the compressive strength of various fly-based concretes are presented in

Figs. 4.1 5 to 4.23 and in Table 4.1 I. From the above, it can be seen that compressive

strength of concretes prepared with only fly ash as binder, has increased from 3.7 MPa

to 12.4 MPa between 3 and 90 days. When a small quantity of lime (i.e. 2 - 6% by

weight of fly ash) was added to the fly ash, the compressive strength of concrete was

observed to be in the rangc of 4.0 to 12.0 MPa betwccn 3 and 30 days. 1-Iowcvcs,

instead of lime, when gypsum was added (6 -16 % by weight of fly ash) compressive

strength of concrete ranging from 8.7 to 26.3 MPa was obtained at identical ages.

Compressive strength o f concrete, with both the activators, namely, gypsum and lime,

were not very encouraging, when compared to the compressive strength attained by

F-G concretes.

It can be inferred from Figs. 4-17 to 4.23 that addition of (external) lime to the high-

n91nium fly ash does not influence the compressive strength of plain fly ash in

a n the other hand, addition of gypsum to thc fly ash influences the

comprcsslvc srrcr~g[h of rile concrctc, s~gniiiiantiy. wit11 thc Ilrcrcasc In tile

of gypsum, the compressive strength also increases. However, when thc

gypsum content cxceeds 12%, strength inversion was obscrvcd, which is similar to

the observation made and discussed earlier. Hence, it can be inferred that the quant~ty

ofgypsum required to activate the high-calcium fly ash is in the range of 6 - 12% (of

the total bindcr content).

4.7 OPTIMUM QUANTITY AND DESIRED CURING FOR F-G BINDERS

4.7.1 General

The results of the compressive strengths of various fly ash-based concrete given in the

earlier sections, have revealed that fly ash-gypsum based concretes have yielded better

and consistent results, compared to F-L-G or F-L concretes. Hence, it was decided to

use gypsum alone to activate fly ash for further studies. Moreover, the optiniuni

quantity of gypsum that will yield the maxin~um strength, the most desirable and

appropriate method of curing for fly ash-gypsum based mortars, were further

investigated in detail. The details of the above investigations and the results obtained

are presented in this section.

4.7.2 Mix Proportion and their Physical Properties

Blends Selected

Gypsum content in the blend was varied from 4% to 14% and the consistency and

setting times were evaluated for each combination of blend. The above results arc

presented in Table 4.1 2. Fine aggregate and water used were same as those for earlier

studies on F-G blends, mortars and concretes, discussed and presented earlier. The

required quantity of water for mortar content was evaluated as per IS: 1727- 1967. As,

not much variation in the consistency of the various F-G blends was observed (Table

4.12), the water content was maintained constant at 0.38 for all the blends of F - G

mortar which corresponds to a flow value of 75k5 %.

~ ~ ~ ~ ~ r c h c n s i v c conlprcssivc strength studies were carried out on F-C mortar

specimcn~ preparcd ~lsing the pan mixer and the procedure detailed in Section 4.6.4.

specimens thus cast were cured under three curing regimes, namely,(i) moist curing;

(ii) immersed curing atid ( i i i ) accelerated curing (i.e. 'boiling water method' as given

in [S : 9013-1975).

The results of the con~prcssivc strength of various blends of the mot-tar specimens

under the three curing regimes and at various ages (0 to 120 days) are presented in

Tables 4.13 to 4.1 5 and in Figs. 4.24 to 4.27. Comparison of the cotnpressive strength

of F-G mortars at 28 days for all the three types of curing, is presented in Table 4.16.

From the results obtained, it can be seen that the maximum compressive strength for

F-G mortars were obtained when the gypsum content is 8% of the total binder content.

The above phenon~enon is independent of the type of curing and the age of curing.

Moreover, addition of gypsum beyond 8 - 10 % does not seem to improve the

strength. From the Figs. 4.20 and 4.23, it can be observed that higher gypsum contents

(i.e. >lo%) have contributed to the early-age strength (i.e. say upto 7 days), but,

strength - gain with later - ages is low, when compared with the strengths of F-G

mortars with gypsum contents upto 10%. Apart from the above phenomena, mortar

specimens with higher percentage of gypsum, (i.e. above 10 %), showed 'excessive

leaching' of calcium sulphate and that crystals of calcium sulphate were seen to grow

into small heaps on the surface of the above specimens, which is highly undesirable.

Hence, from the 'durability' point of view as well, it can be concluded that the

Optimum Gypsum Content.(OGC) for the fly ash under consideration, is about 8 -

10%. But, the above value of OGC may slightly vary, even for the same fly ash

depending on the 'lime content' at the time of procurement.

Normally, almost all OPC based elements require 'immersed curing' at ambient

temperature for attaining appropriate strength and that the strengths attained are

highly sc~is~tlvc to the vari;ltlaii in tlic curing regimes for such elements. [3~1t, F -- (; . .

!nosthi. h P C ~ l i i l C l l S iild 1101 h i l O \ ~ 11111~il L '11 ldiitiir l i ; t h f : c ' c ) l : i ; ) : . ~ ~ ~ i ~ ~ cngih a[ralllcci

,-,vcr ~~ornial to Inter-ages. with respect to the various types of curing rcgil~ics

cotlsidcr~d 111 this stltdy. 111 fhct, the strength obtained with 'moist curing' is

higher than that with 'inimcssed curing'. 'The above results indicate that

the F - G binder is less-sensitive to the above two types of curing, normally adopted.

In this chapter, linie and gypsuni wcsc uscd as activators of the fly ash. It is observed

that the addition of lime to the fly ash has increased the water demand but did not

affect the initial and final setting tinics, significantly. However, addition of gypsum

did influence the setting times significantly, but, did not influencc the water demand.

On the other hand, addition of both liine and gypsum to the fly ash has influenced

both the water demand, as well as, the setting times, of the paste significantly.

Compressive strengths of various fly ash-based mortar specimens have revealed that

the high-calcium fly ash is more sensitive to the addition of gypsum, rather than lime

and hence, addition of lime niay not be necessary to the fly ash ~ ~ n d e r consideration.

Mortar cubes of various F - L - G blends were cast and their compressive strengths

evaluated at various points of time to study the repeatability and the consistency of

results. The strength characteristics of F-L-G based concretes were also investigated in

detail and i t was observed that this system did not contribute much to the strength of

concrete, rather, there seems to be some loss of strength compared with F-L of F-G

mortars or concretes. Hence, it was decided to use only gypsum to activate the high-

calcium fly ash, soirced from Neyveli, Tamil Nadu, India. Studies were also carried

out to obtain Optimum Gypsum Content (OGC) and the compressive strength

characteristics of F-G concrete based on three different 'curing regimes'. The results

obtained have indicated that the OGC is about 8 to 12% of the binder content and that

the compressive strength of F - G blends are not very sensitive to the type of curing.

.[‘able 4. I : ('ompt-cssivc strength o f plain fly ash mortar

Tablc 4.2: Lime required Vs reactivity of fly ash

Table 4.3: Compressive strength of fly ash-lime mortar ( 1 :3)

- Reactivity o f

Lime

- Standard sand (gm)

- ------ GOO --- GOO 600 600 600

5

Lime requireincnt (gm per 100 gm of fly ash)

I I I I - (*) - k t e r content adjusted to obtain a constant flow as specif.ied in IS: 1727. (**) - t fe rence mortar strength of fly ash using standard sand.

10

- Water*

- 60.00 -- 62.60 65.20 67.79 70.38

11.8

Compressive strength of mortar cubes gi) 10 days (MPa) - - - . . -- ~ .GO*- - - -- - - - - - . - - - 7.64- 7.72 8.69 8.75

15

41.34 47.24 17.72

30 2 0

--

2 5

I I - - - - - -Ti --

35.43 23.62 29.53

t I (1711 ) strengtl~

i (M 1%) 6 0 0

6 1 200 000 0 3 1 1 . 1 1 200 1 6 000 0 0 9.05

24 0 0 0 0 8 6.37 28 0 0 0 7 1 5.40

* -Water content adjusted to n~aintain constant flow as specified in IS: 1727 ** eferer~ce mortar strength of'fly ash using standard sand.

C

Table 4..5: Compressive strength of F-L-G mortars( 1 :3) (Series-I)

' S1. No.

1 2 3

4 5 6

Fly ash ('2,)

83.50 81 .OO 79.00

76.00 71.25

Lime I

. -- 11.50 13.50 16.00

19.00 23.75

I 63.50 31.50

11.00 13.00 15.00

7 8 9

L - A

Gypsum (%)

5.0 5.0 5.0

5.0 5.0

79.00 77.00 75.00

compressive Strength@.10 days (M 1%)

7 .O 3.2

5.0

10.0 10.0 10.0

j 10 I 1 12

13 14 15

16 17 18

hence, the results are not available.

* --P- (ii)&ndicates that the specimens have crumbled after casting and partial curing and

4.8

3.6 2.2 7.0

10.6- 10.0 10.0

15.0 15.0 15.0

15.0 15.0 15.0

8.0 10.4

4.4 3.4 8.2

8.0 11.2 *

Note: (i) F-fly ash; L-lime; G-gypsum

72.00 67.50 60.00

74.50 73.00 71 .OO

68.00 63.75 56.50

18.00 22.50 30.00

10.50 12.00 14.00

17.00 21.25 28.50

'1 able 4.0. C 'or~ ipr~ss~~es t rength of F-I,-G mor-tars ( 1 : 3 ) (Series -11 )

--- l;ly ash ('XI) ('XI) ('XI) Strength ((0 10

S1 No

75 00 20.00 5 00 3.3

82.00 10.00 7.50 3 .6 78.25 14.30 7.50 4.5 72.50 20.00 7.50 5 5

Table 4.7: Compressive strength of F-L-G mortars ( 1 :3) (Series -I 1 I )

Table 4.8: Compressive strength of F-L-G mortars ( 1 :3) (Series -1V)

, S1. No.

1 2 3

Fly ash (%)

85.75 8 1.30 77.00

r- Sl. No.

1 2 3

4 5 6

7

L ~ m e ("10)

4.25 8.65 13 .O

Fly :~sh (%)

66.80 66.70 57.00

73.50 66.70 53.40

40.00

Gypsum (%)

10.0 10.0 10.0

8

Cotnpressive Strength c4 10 days (M Pa) 4.10 11.3 11.9

Compresc;ive Strength @ 10 days (M Pa) 4.70 7.50 8.50

9.00 9.90 8.30

8.00

I ime

26.60 20.00 28.50

7.50 13.30 26.60

28.00 53.40 11.90

Gypsum

6.60 13.30 14.50

19.00 20.00 20.00

32.00 13.30 33.30

'J'ablc .t.O(a): Propertics of fine atid coarse aggregates

Dcscr~ptior~ Obscrved Val~lc F ~ n e aggregate --

- - --

2 3 4

Table 4.9(b): Sieve analysis of aggregates

Coarse aggregate

L- i

5 6

2.37 --- Specific gravity

Bulk density Water absorption

Table 4.10: Combination of binders and their ranges

Rodded density Grading

S ~ e v e size, mrn

2 0 10 4.75 2.36 1.18 0.6 0.3 0.15

2.64 1.59glcc

1 (YO

1 Total numb; of mixes studied 28 1 Note: (i) B1 - only fly ash; B2-fly ash-lime; B3-fly ah-gypsum; B4-fly ash-lime-gypsum

1.4 1 glcc 0.5% I

1.73gJcc Zone I1

Cumulative percentage passing

/Type Range of values (%) No. of mixes

(ii) All the above mlxes were cast and tested for their compressive strength. Rut only those mixes which gave the highest strength values for a given type of binder have been chosen for reporting.

1.55gIcc --

Coarse aggregate 100 13 2 0 0 0 0 0

Fine aggregate 100 100 100 97.8 87.8 46.7 4.9 1.3

studied F L G

'I'ahlc 4. I I : ('ompressive strength of 1:-I .-G concretes ( 111 M Pa)

- - - - -- - - . Age in days

bincicr .- -

Table 4.12: Consistency and setting time of F - G blends

- LB3 e4 {'. 8.8 -- --

Table 4.13: Compressive strength of F - G mortar cubes [ W/(F + G) = 0.38; Sand / (F + G ) = 0.67; Curing = "MOIST"]

Note: ( I ) 'l'he values given above are the maxlmuni In each of the blend ( 1 1 ) 'The correspond~ng llme or 1 and gypsum are also ~ndicated.

12.4

10.5

r-

24.8

11.2

Blend Designation

R 0

S1. No. 1 2

13 4 5 6 7

25.7

13.7

Fly ash (%)

1 00

Note (i) C* - Tested immediately after demould (ii) ~ * j dtrengths indicated above are based on the Average of five cubes (iii) BO refers to the use of only fly ash and it is taken as the reference mortar.

Blend

B0 B1 B2 B3 B4 B5 BG -.

Age at testing (in days) 0* 3.6 4.2 4.8 5.2 5.7 3 3.4

26.3

12.5

Gypsum (%)

0

12% gypsum

2'%L and 8% G

Consistency (%)

44

1

4.1 6.4 6.0 6.5 6.3 7.0 7.5

Setting Time (min) -

Initial / Final 4 5 / 210

7

5.4 7.7 8.0 12.3 9.4 7.7 8.0

3 4.4 6.8 7.2 8.0 7.3 7.3 7.8

28 6.5 7.9 10.8 16.3 9.8 10.9 8.7

56 9 10.9 11.9 23.7

9 0 9.4 14.8 15.3 23.2

120 9.6 '

13.9 17.5 25.6

I able 4.14: ~ ' o 1 ~ 1 i x c s s s l v ~ strength I; - (; mot-tar. cubes [ A 8 ! + : ~ j ? , y , can4 , :,; 1;()7,( ~ , , , , , g - ' ' !~;~~!i, i<,$I~~;' 1

-- SI 1 13lcntl 1 Agc a t Icstlng (in days)

- --

3 7 28 56 ' 90 .-

120 8 10.3

7 6.6 6.8 I 9.7 10.8 11.9 12.9 6 6.9 7.5 12.0 1 14.3 15 19

5.2 6.5 7.6 11.4 16.5 ' 20.4 23 24 B 4 5.7 0.1 10 12 18 2 1

16.3 3.4 6.6 5.5 7.6 10.3 8.4 15.4 16.4

\,, -7 ' ,-u.-.. ....... I......"., U I I V . U"I.."UIU

( 1 1 ) @*I -strengths mdicated above are based on the Average of five cubes (111) BO refers to the use of only fly ash and ~t IS taken as the reference mortar

Table 4.1 5 Average compressive strength F - G mortar cubes [w/(I'+ G) ~ 0 . 3 8 ; Sand 1 (F; G) = O.67,Curing = "BOll.lNc; WA.I ER**"]

I SI. No. / Blend / Compressive strength I

Note: (1) i*I - Strength Indicated above are based on average offifteen cubes I I I

(11k4 - Spec~rnens were demould after 24 hours of moist curing and Immersed In boiling water for 3% hours. They are then alr cured for one hour and then thelr compressive strength evaluated

Table 4.1 6: Comparison of the compressive strength of F -- G mortars (under various curing conditions)

S1. No. 1 2 3 4 5 6 7 -

116

Blend

BO B1 B2 B3 B4 B5 B6

28 days Compressive strength ( M Pa) Accelerated Curing 7.6 9.7 13.9 14.8 9.7 9.4 9.1

Moist Curing 6.50 11.8 10.8 16.3 9.80 10.9 8.70

Immersed Curing 7.50 9.70 12.60 16.5 10.0 10.50 10.30

Fig. 4.1 : Hydrated products of plain fly ash surrounding a fly ash particle Ohyh.k-p+-)

, Fig. 4.2: Hydrated products of plain fly ash surrou~iding ;I siind pwin cs iw -w+)

10 20 30 40 5 0 60 7 0

Two theta value

7 days

- A -.Ixpb -2 " ,d&--h-.-~..P\ ~~

Fig. 4.3: XRD diffractogram of fly ash-lime blend

I

Legend 1 - Quartz; 2 - Calcite; 3 - Mullite; 4 - C6AS3H,r ; 5 - CSH; 6 - C4AH3; 7 - Ettringite

I I I

Fig. 4.4: Hydration products of fly ash and lime blend csw h u l ~ r p k )

Fig. 4.5: Hydration products of fly ash lime blend (at higher magnification)

c-rw ~ s r p r r " )

z! COMPRESSIVE STRENGTH (M Pa) 90

- Quartz; 2 - C6 ~ $ 3 ~ 3 ~ ; 3 - Ettringite; 4 - CSH; 5 - cS; 6 - C ~ A C H ~ I; 7 - C ~ A & - c5s2S

10 20 30 40 50 60 70

Two theta value

Fig. 4.8 : XRD Spectra of fly ash - gypsum hydration (1 4%)

1 - Quartz; 2 - Calcium sulphate; 3 - CIS2S; 4 - C4ACHI 1; 5 - CSH; 6 - Ettringite

Fig. 4.9: Hydration products of fly ash and gypsum blend (at 8% gypsum) C-Y t4-h)

Fig. 4.10: Hydration products of fly ash gypsum blend ( at 8% gypsum) (at higher magnification) C S ~

Fig.

Fig.

4.1 1: Hydration products of fly ash and gypsum blend (at 14% gypsum) (2-4 ~-fpyA;I

4-12: Hydration products of fly ash gypsum blend ( at 14 % gypsum) (at higher magnification) c . ~ ~w

Fig. 4.13: A view of the pan mixer

Fig. 4.14: A view showing the mixing of F-G mortar in the pan mixer

Extra lime added % of lotal b~nder

I *llhoul I ~ m t

i ! 2 % lime

A 4 % lime

6% lime

0 20 40 60 80 100 AGE ( IN DAYS)

Fig 4.15: Compressive strength of B 1 and B2 series concrete at various ages and external lime content 0 - 6% ( 0% Gypsum)

x t- I /: '

15 3 *; B [L

%' l- V)

W / MIX 1:2:4 W/F-L-G = 0.5 1 I

V) GYPSUM CONTENT % OF BINDER '

w K 1 1 % I 0 I X 8%

8 .S 10% 5 I I

0 20 40 60 80 100 AGE (IN DAYS)

Fig. 4.16: Compressive strength of B3 series concrete at various ages and gypsum content upto 10% ( 0% lime)

1 GYPSUM CONTENT % OF BINDER

I 16% I

i '12%

5

0 20 40 60 80 100 AGE (IN DAYS)

Fig. 4.17: Compressive strength of B3 series concrete at various ages and gypsum content 12 - 16 % ( 0% lime)

A 20 , I m

1 ' I Lime added, %of binder I n. 1 1 2 %

I

E 0 6 %

!

I !

I- ' A 4 % I

15 : I 1

t / * ~ l h out L!me 5 I I PC +- -t- I- V) ; \ I W (,' I ,& t \ v, 10 I

V) .-A a P. E 0

i)

O r - I - , 1 1 1 I I 1 0 20 40 60 80 100

AGE (IN DAYS)

Fig 4.18: Compressive strength d B 4 series concrete at various ages and external lime content 0 - 6%( 6% Gypsum)

0 I I I

I

0 20 40 60 80 100 AGE (IN DAYS)

Fig 4.19: Compressive strength of B4 series concrete at various ages and external lime content 2 - 6% ( 8% Gypsum)

MIX 1 2 4 WIF4.G - 0 5 1 LIME ADDED PERCETAGE OF BINDE 1 I I I 0 %

I

0 1 1 1 . 7 - f I I 0 20 40 60 80 100

AGE (IN DAYS) Fig 4.20: Compressive strength of B4 series concrete at various ages and

external lime content 0 - 6% ( 10% Gypsum)

Mlr -1 ' 2 4 ~ / F . L . G . 0 5 LIME ADDED % OF BINDER

' 0 %

2 %

4 %

1 6 %

0 20 40 60 80 100 AGE (IN DAYS)

Fig 4.2 1 : Compressive strength of 8 4 series concrete at various ages and external lime content 0 - 6% ( 12% Gypsum)

Mlx=l : 2: 4 WIF.L.0 r 0.5 LIME ADDED qL OF BINDER

f 0 %

I ' 2 %

4 %

6 %

i I

O I ' 1 . 1 - 1 - 1 I I i

0 20 40 60 80 100 AGE (IN DAYS)

Fig 4.22: Compressive strength of B4 series concrete at various ages and external lime content 0 - 6% ( 14% Gypsum)

M I - 1 2 4 W I F L G - 0 5 ' LIME ADDED% OF BINDER

I I 0 %

20 ' 2 %

a 5 , 6 %

I + " 15 T .- 3 K

i 1

I I

0 20 40 60 80 100 AGE (IN DAYS)

Fig 4.23: Compressive strength of B4 series concrete at various ages and external lime content 0 - 6% ( 16% Gypsum)

0 - I i T [- ' 0 4 8 12

I 16

GYPSUM CONTENT (w

Fig. 4.24: Compressive strength of F -G mortars at various gypsum contents ( MOIST CURING)

CURING PEROID

I I I

4 8 12 16 GYPSUM CONTENT (%)

Fig 4.25. Compressive strength of F -G mortars at vanous gypsum contents ( IMMERSED CURmG)

30

Gypsum content :

I wllh out xypmm

1 Y 4 % I

40 60 80 AGE (IN DAYS)

Fig. 4.26: Compressive strength of F -G mortars at various ages and gypsum contents (4 - 12 %) ( IMMERSED CURING)

I , GYPSUM CONTENT

I k 4 %

8 %

:i 1 2 %

h 20 wllh out Gypsurn

P E V I

0 . I 7 - I 1 - ' I 0 I

0 40 80 120 AGE IN DAYS

Fig. 4.27: Compressive strength of F -G mortars at various ages and gypsum contents (4 - 12 941) ( MOIST CURING)