CCNCRETE IiiiI TECHNa.OGY IIiII

ASSOCIATES

TEC HN ICAl BUllETIN 73-89

SEPTEMBER 1973

1123 PORT OF TACOMA ROAD !TACOMA. WASHINGTON 98421/ (206) 383-3545

ACCELERATED CURING

CTA2

17

18

INTRODUCTION

Current recommendations for accelerated curing generally reflect good practice and have a sound background; however, some specifications are overly restrictive and, in fact, may not result in high quality precast products.

This bulletin highlights the results of research at Francon limitee and Concrete Technology Corporation and makes recommendations for curing and controlling concrete at higher temperatures.

AC KNOWLED GMENT

We wish to thank Francon Limitee, in Montreal, Canada, for providing us all of the infor­mation gained from their five-year study of "Elevated Temperature Curing of Precast Concrete. Elements. "

SUMMARY AND RECOMMENDATIONS

Problems of low early strength are often found to be related to concrete materials, faulty

test procedures, or inadequate curing environment. The following recommendations refer to

these three problem areas:

Woter-Cement Ratio: Best results with accelerated curing are obtained with concrete

having a low water-cement ratio, i.e., less than 0.40 (4.5 gal;bag).

Ambient Temperature Curing: Concrete sections of fairly large mass, such as on AASHO

Type IV girder, may attain relatively high early strength when cured at ambient temperatures

above 70o

F. Tests described in this bulletin shaw that internal concrete temperatures reached

1500

F in AASHO beams and 1100

F in the less massive Washington State bridge grider with no

added heat. The heat of hydration should be retained in the concrete by insulating the

formwork with insulating blankets or by other means as described in CTA Bulletin 73-B2.

Accelerated Curing:

Short preheat times, i.e., less than 2 hours, are not detrimental provided the concrete

temperature remains below 120°F for 2 or 3 hours.

The rate of temperature rise is not critical except that it should stay below 200

F per

hour, if heat is applied immediately after casting.

Although the maximum concrete temperature can be taken as high as 180-200o

F, if

needed, for the sake of economy it should be limited to that necessary for early strength

development.

CTA-73-B9

19

Compressive Strength:

Early strength is related to the area under the time-temperature curve, i.e., maturity.

Accelerated curing to 170°F has little, if any, effect on the ultimate strength of con­

crete with low water-cement ratio.

Control Procedure:

Concrete temperature, rather than the surrounding air temperature, should be recorded

for control, because of the time lag and overshoot of concrete temperature.

Test cylinders do not follaw the same time-temperature curve as a large precast unit

and should, therefore, be cured in a separate curing chamber.

Schmidt test hammers can be used effectively to check concrete strength for prestress

release.

Steam vs. Dry Heat:

Concrete with a relatively high water-cement ratio (i .e., 0.45 or greater) will gain

approximately 10 per cent higher strengths when steam cured than when cured by dry

heat.

There is no significant difference in results of the two methods for concrete with low

water-cement ratios (below 0.40).

Material Properties: The behavior of cements and admixtures and the design of concrete

mixes to be cured at accelerated temperatures should be evaluated in order to determine

optimum procedures. The CTA staff can provide the following services:

Establish in-plant test programs and supervise them, if desired.

Evaluate your materials at CTA lab and submit recommendations.

Hot Concrete:

The use of hot concrete (concrete mixed and cured at temperatures up to 175°F) seems

to be limited to the fabrication of precast items requiring expensive molds and rapid

turnover.

Compressive strengths of about 4,000 psi are attainable within four hours of costing.

Hot concrete requires a large capital investment for mixing and rapid distribution systems.

The "pot life" of hot concrete is 15-25 minutes.

Cracking is a serious problem--molds and materials must be preheated.

High cement factors are required.

20

CTA-73-B9

FRANCON LlMITEE RESEARCH

In 19661 Francon undertook a very extensive and comprehensive study of elevated temper­

ature cud ng of precast elements. The research project, under the Industrial Research Program

of the National Research Council of Canada, took nearly five years to complete. The work

was reported in four phases:

Phose I

Phase II

Phose III

Phose IV

"Atmospheric Steam Curing of 6 X 12" Cylinders."

"Atmospheric Steam Curing of Type IV AASHO Girders and Companion 6X 12" Cylind."."

"Dry Heat Curing of Type IV AASHO Girders and Companion 6 X 12" and 4 X 8" Cylinders."

"Hot Concrete; Rapid Curing of Concrete Elements Cast with Concrete Mixed at Elevated Temperatures."

The four reports cover over 325 pages of text and approximately 570 pages of tables and

graphs. Tests were conducted on over 3,500 cyl inders and more than J I 000 cores taken from 64

Type IV AASHO girders and over 20,3' X 3' X 8" test panels.

The preceding statistical summary of the Francon prl?iect is given only to point out that this

paper can merely highlight Some of the results of this research.

CONCRETE TECHNOLOGY CORPORATION RESEARCH

Most of the accelerated curing procedures at eTC were developed from frequent controlled

production testing. Additional information was obtained from development work related to

electric curing of precast concrete at eTe (see Technical Bulletin 73-B2, February 1973). More

recent Iy, CT A laboratory investigati ons have yielded much j nformati on regardi ng the effects of

concrete mQterials on optimum accelerated curing procedures.

The Francon project and the eTA work are complementary I covering nearly all methods of

accelerated curing and a full range of curing cycles. Overlapping areas of work at the two firms

yielded generally the same conclusions. In a few cases, which will be pointed out in this text,

test results were contradi ctory.

CT A- ""'3-89

21

PRINCIPLES OF ACCELERATED CURING

Concrete curing iS r by definition, a procedure which controls temperature and moisture

movement in and out of the concrete. The objective of curing is to keep concrete saturated, or

nearly saturated, until the original water-filled spaces in the fresh cement paste are filled to

the desired extent with the products of hydration of cement.

Moisture loss:

It should be emphasized here that it is extremely important for manufacturers of

precast concrete products to maintain saturation in concrete while curing. Only about

one-half of the water present in the cement paste can be used for chemical hydration, if

no water movement to or from the paste is permitted. Woter is lost internally in concrete

by self-desiccation, i ,e., the products of hydration are colloidal and will adsorb free water.

Most precast concrete contains less than 5 gallons per bog NV/C = 0.45). It can be seen

that self-desiccation could result in relatively weak and porous concrete, since 2 1/2 to

23/4 gallons per bag is required for full hydration. Therefore l moisture loss from precast

concrete should be prevented and, in some cases, additional moisture must be added.

Effects of Curing Temperature:

The chemical reactions of cement hydration take place more rapidly with increased

curing temperatures. This, of course, results in greater early strengths for more rapid

turnover of precast products. The necessity for controlled curing temperatures exists for

the following reasons:

1) Early heat appl ication and a high rate of temperature r·ise can adversely influence

the strength and other structural properties of concrete.

2) An optimum maximum curing temperature exists, above which there is no appreciable

benefit to early strength and possible detriment to later strength.

3) Uniform temperatures within the product and from day to day are necessary to prevent

differential shrinkage and for good camber control.

Accelerated Curing Methods:

Concrete! as a material, reacts only to surrounding form and air temperatures and to

the relative humidity at exposed surfaces. It is completely unaware of the heat source, be

it steam, hot oil, or electricity, except as these energy sources affect temperature and

humidity. Thus, it is pointless to argue the advantages of one system over the other on any

other basis than these and, of course, economic considerations. The decision as to which

method to use must be based on several factors, including:

CTA-73-B9

22

I) Size and shape of product.

2) location of forms or beds.

3) Energy output required.

4) Degree of control needed.

5) Maintenance required.

6) Etc.

This bul~etin will be concerned with three basic methods of accelerating curing temperatures:

a) low presslXe steam.

b) Dry heat, i.e., radiant heat at low humidity, such as circulating hot water or hot oil

and electric form heat.

c) Hot concrete.

FACTORS INFLUENCING OPTIMUM ACCELERATED CURING

Major consideration is given to compressive strength when trying to optimize curing cyles.

Fortunately, the factors which have the most influence on compressive strength are the SOme as

those which affect other concrete properties, such as modulus of elasticity, tensile strength,

shrinkage and creep. These controlling factors are:

0) Preheating time and temperature.

b) Maximum temperature in enclosure.

c) Rate of temperature rise.

d) Moisture loss (or gain) in concrete.

The first three aspects of optimum curing are identified in Fig. 1, a graphical description

of on accelerated curing cycle. Some of the time-temperature curves from the AASHO beam

tests Qt Francon ore shO'Nn in Figs. 2-7. These curves will help to identify the relationships

o.f air, beam conCrete and cylinder temperatures to each other, even though top and bottom

flange concrete temperatures are somewhat inconsistent.

Preheating Time and Temperature:

Concrete which hydrates rapidly under higher temperatures forms a more porous physicol

structure than one which undergoes a slower initial hydration at lower temperatures. Con­

sequently, the compressive strength of concrete which reaches 120°F in less than about

2 or 3 hours is adversely affected. The degree to which the compressive strength suffers

depends on the:

CTA-73-B9

23

1) Cement. 2) Admixtures, if any. 3) Initial concrete temperature.

Fig. 8 compares relative compressive strengths of bottom cores from AAS HO beams cured

at varying maximum enclosure temperatures with preheat times of 1, 3, 5 and 7 hours. The

effect of early heat application (l-hour delay) reduced the 18-hour core strergth by a maximum

of about 5 per cent and the 28-day core strength by a maximum of about 10 per cent. Early

heat application in these tests was not extremely detrimental because the actual concrete

temperature logged approximately 3 to 4 hours behind the enclosure temperature in the first

few hours after heat application. Thus, in all of the tests on AASHO beams at Francon, the

concrete temperatures did not reach 1200

F until at least 4 or 5 hours after costirg. This oc­

curred, even in the most severe case, where steam was injected on the girder after 1 hour

at 80°F /haur up to 170°F (see F;g. 7).

We do not recommend the application of heat sooner than two hours after casting, unless

concrete temperatures are monitored to make certain that they do not reach 1200

F before

2 or 3 hours. Some manufacturers have established a practice of delaying heat application

until after initial set is reached. Initial set, of course! is dependent on the cement and ad­

mixtures used, as well as concrete temperature, and can be measured as discussed in eTA

Bulletin 73-B8.

Maximum Enclosure Temperature:

Researchers generally agree that the early strength of concrete improves with increasing

maximum curing temperature even up as high as 200o

F. In many cases, the early strength

seems to be optimum at about 1500

F with little apparent gain at temperatures above that.

Most recommendations suggest maximum concrete temperatures of 1500

F to 1600

F to insure

minimum sacrifice of strength at later ages.

An extensive test program at CTC revealed that the 16-hour strength of concrete increased

linearly with temperature up to at least 180°F (see Fig. 9). These tests also showed that

° ° 28-day strengths of concrete cured at 170 F were equal to that cured at 70 F, as long as the

water-cement ratio remained below 0.40 (4.5 gal/bag). Fig. 10 illustrates that as the woter­

cement ratio increased, the relative 28-day strength of the concrete decreased when cured at

1700

F. The relative strength loss at higher water-cement ratios is due to the incomplete

filling of the water capillaries with hydration products as explained below.

CTA-73-B9

24

Strength Reduction:

The reduction of strength at later ages due to accelerated curing occurs when an im­

permeable coating forms around cement grains and restricts further hydration. The coating

develops from the early hydration of the tricalcium aluminate (C3

A) compound in the cement,

A premature "honeycomb-like" structure occurs when insufficient gypsum (503) is present

in solution to fully retard the C3

A hydration, Higher temperatures accelerate the hydration

of C3

A and lower the solubility of gypsum. Therefore, cements low in C3

A and with higher­

than-normal optimum 503 tend to perform better under accelerated curing conditions than

those high in C3

A (greater than 8%) with low 5°3

,

Some precast conCrete manufacturers add gypsum to their concrete to relieve this

detrimental action. This must be done only after careful investigation because excess gypsum

leads to expansion and disrupt ion of paste set.

This premature aluminate hydrotion can also occur in concretes mixed and placed at

high temperatures, e.g., Summer conditions or hot concrete, which explains the reduction

in their potential strength gain.

Further investigations are being carried on in the CTA lab to determine the benefits of

additional gypsum or retarders used in accelerated concrete.

Rate of Temperature Rise:

The relative la-hour strengths of cores from Francon beams are plotted in Fig. 11 versus

rates of temperature rise for each maximum temperature reached. It appears from these

results that the rate of temperature increase has little effect on compressive strength for pre­

heat times of one hour or more. As stated in CTA Bulletin 73-B2, however/ if heat is

applied immediately after casting, the rate of temperature rise should be kept below 200

F

per hour.

QUALITY CONTROL PROCEDURES

Maturity Concept of Strength Development:

The concept of "maturity" is a useful tool for predicting early compressive strength.

The strength development of concrete is proportional to the area under the time-temperature

curve. This area, or product of time and temperature, down to on arbitrary datum of 11 OF

is referred to as maturity in degree hours. A maturity curve for concrete at eTC is shown In

Fig. 12. This curve was developed from the same data as used to construct the f' vs. c

CTA-73-B9

25

temperature curve in Fig. 9. These maturity-strength relationships usually apply only to

concretes using the same materials and preheat times. However, once they are established

for each case, they can be used to predict the strength for concrete cured for shorter or

longer periods of time, or at higher or lower temperatures than normal.

Curing Cycle:

The contribution of the heat of hydration to internal concrete temperatures was dis­

cussed in CTA Bulletin 73-82 and was found to be significant in an I-Beam. See Fig. 13,

which shOW's time versus concrete temperature in a Washington State Highway beam cured

at 65°F ambient, and compare this to Fig. 14 for an AASHO rv girder from the Francon

study which was cu-ed at 750

F.

It is obvious that this internal heat buildup is responsible for the overshoot of the top

and bottom flange temperatures above surrounding air temperatures in Figs. 2-7, where heat

is applied. These figures also show the variotion of the concrete temperatures behind (or

ahead of) the air temperature depending on preheat time.

Therefore, the curing cycle should be controlled by monitoring temperatures within the

concrete mass rother than the temperature of air outside the form. Once the air temperature

versus concrete temperature has been established for a partic'ular product, it should suffice

to measure air temperature with only periodic checks of concrete temperature.

Measuring Concrete Strength:

Perhaps one of the greatest mysteries to a precast concrete producer is whether or not

the test cylinder, broken in the morning truly reflects the strength of concrete in the product.

Conclusions reached in the Francon and CTA studies are that cylinders cured with correspond­

ing precast units generally have a much different time-temperature cycle and, therefore,

do not accurately represent the strength of product for purpose of prestress release or

stripping.

In Figs. 2-7, the temperatures of cylinders cured with the beam are plotted along with

top and bottom fla"ge temperatures. The strengths of these cylirders are shown in Fig. 15

compared to bottom flange core strengths. The variations here are ~ 15%. Tests at eTA

show that the difference can be as great as 25% for other methods of curi ng.

We would recommend two alternate solutions to this problem of determining actual

compressive strengths prior to stripping or release:

CTA-73-B9

26

1) Cure cylinders in a separate curing chamber, programmed to put the cylinders

through the same time-temperature cycle as the precast unit.

2) Cure cylinders with the precast unit, having established the usual strength dis­

crepancy with the product, or having established the strength-maturity relationships.

The actual strength of the product will then need to be estimated.

In either case, the precast unit should be checked with the Schmidt test 'hammer prior

to release or stripping. Proper use of the hammer is described in CTA Bulletin 73-BS. One

word of caution: hammer rebound readings should be token on formed surfaces after the

surface moisture has disappeored, which is usually 30-60 minutes after stripping. Rebound

readings on a hot, damp surface will yield significantly lower results.

STEAM VERSUS DRY),EAT

The Francon research included several AASHO IV girders cured with dty heat using curing

cycles identical to some of the steam-cured specimens. Results of compressjve str~ngth tests on

dry heat specimens are shown in Fig. 16.

Compressive strength comparisons between cores from similarly cured beams show that steam

curing produced 5-12% higher compressive strength than dry-heat curing. Dry-heat curing

reduced 28-day strengths about 8-12% more than did steam curing.

The average relative splitting tensile strengths of the bottom flange cores from steam-cured

beams were4% higher than those from dry heat-cured beams.

An explanation for lower strengths in dry-heat-cured beams may be loss of moisture due to

self-desiccation and drying at the upper, exposed surface. No moisture barrier was applied over

the top flange in the Francon dry-heat tests, apparently.

However, as stated earlier, the role that the water-cement ratio plays in obtaining good

strength development is of the most importance. Many beams have been cured under dry heat

conditions at eTC where tests indicate that little, if any, strength is lost relative 'to that of

companion 28-day standard moist-cured cylinders. These beams were manufactured with concrete

containing less than 4 gallons of water per bag rN/C = 0.36 or less).

Neville* states that, when hydration is complete, the original water-filled p·ores in concrete

are just about completely filled with the products of hydration at a water-cement ratio of 0.38,

or below, even though not all of the cement is hydrated. Above wjC:::: 0.38, some of the pores

remain empty leading to lO'Ner strength and higher permeability.

* Properties of Concrete, A. M. Neville, John Wiley and Sons, Inc., pp. 22f.

CTA-73-B9

27

It is possible, then, that fewer water capillary pores remain empty at higher water-cement

ratios when cured with steam than when cured with dry heat, because of more complete hydration.

(Note: the water-cement ratio of concrete in the Francon study was 0.49).

In summary, it is best to steam-cure concrete containing more than 4.5 gallons of water per

bag IyV/C ~ 0.40).

EFFECT OF CONCRETE MATERIALS

Portland cement and water-reducing admixtures are of great significance when considering

materials for concrete to be cured at accelerated temperatures. Please refer to eTA Bulletin 73-85,

~ High-Strength Concrete" for a discussion of these materia Is.

The behavior of each cement and water-reducer combined in concrete should be studied as

to effects on setting time, early stiffening, early strength development, and ultimate strength

development.

OTHER CONCRETE PROPERTIES

Tensile strength, flexural strength, and modulus of elasticity of concrete cured at accelerated

temperatures ore affected similarly to its compressive strength.

Often overlooked is the contribution of accelerated curing to the re~uction of creep and

shrinkage in precast concrete. Creep, shrinkage, and prestress losses can be 50 per cent lower

thon in normally cured concrete.

HOT AND COLD WEATHER CONCRETING

The placing of concrete at high temperatures Can adversely affect strength development, as

was pointed out eQrlier. Every effort should be made to keep initial concrete temperature as

lOY.' as possible. This may necessitate continuous sprinkling of coarse aggregate stockpiles and

the use of ice water in the mix.

Preheating of forms to 7Q-90oF in cold weather is advisable. Extremely cold air temperatures

sometimes necessitate longer preheat times.

HOT CONCRETE

Defi nit ion;

The term "hot" concrete is used here to describe concrete which ,is mixed Qnd cured at

high temperatures up to 17SoF. In research conducted at Froncon limitee, the mix was

heated by low pressure steam injected in the mixer. Curing temperatures were maintained

CTA.73-B9

28

through preheating forms and the use of a curing chamber.

Hot concrete offers the possibility of developing high strengths in just a few hours,

permitting rapid turnover of production facilities. The Francon study aimed at reaching the

highest strengths possible within the shortest period of time. The cement type and factor I

the temperature, and the dlA'ation of curing were treated as variables. Specimens were

monitored for their strength-time properties, workability of the mix, and durability.

Results:

Fig. 17 shows the compressive strengths attained by laboratory-hatched 4 X 8 cylinders

using Type I cement. The following general observations can be made:

Compressive Strength.

Concrete strengths in the range of 3000-4500 psi are attainable within four hours of

casting. Twenty-eight day strengths, however, are sUbstantially less for hot concrete

specimens than for control specimens of the same mix cast at 70oF. The sacrifice in

u It imate strength is 20-50 per cent.

Duration of Curing.

Increases in the duration of rapid curing produce higher early and 28-day compressive

strengths up to and including six hours. The rate of gain of strength is most dramatic

between two and four hours.

Temperature of Curing.

Early strength increases with the curing temperature between 1000

F and 1750 F with no

optimum occuring in that range.

Cement Factor.

The early strength of hot concrete specimens increases with increasing cement content.

Rather high cement factors are necessary For safe handling strengths in four hours.

Durabi I ity.

Neither hot concrete nor control specimens displayed adequate resistance to freezing

and thawing (per ASTM designation C 291-67). However, both the hot concrete and

control specimens performed well in freeze-thaw tests when an air-entraining admixture

was used.

Workability.

Workability of plant-produced concrete (2" slump) remained good for one-holf hour.

CTA-73-B9

29

Retardant.

A test mix containing a retarding admixture (Plastiment) exhibited no extension

in time of workability. There was, however, approximately two hours retardation

in strength gain following which the normal pattern was restored.

Bond Pin Pullout Test.

The following results were obtained fron the bond pin pullout test:

White Cement.

Setting Time

Initial Final

3.5 hrs 4.5 hrs

0.8 hrs ) .0 hr,

Since white cement is of maior importance in manufacturing architectural components,

tests were made on specimens cast with a white cement mix.. The results paralleled

those of Type III mix specimens. Workability remained good for an average of thirty

minutes. Twenty-eight day strengths of control cylinders exceeded those of hot

concrete specimens, and the pattern of strength gain with rapid curing followed that

of Type II).

CTA-73-B9

30

CYCLE, 3 - 20 - 125 \ '-MAXIMUM CURING TEMPERATURE IN . "- CHAMBER ("Fl

RATE OF TEMPERATURE RISE (OF / HR.l -----PRE-HEAT PERIOD (HRS.)

I - P~E-HEATING PERIOD 2 - TEMPERATURE RISE PERIOD 3 - MAXIMUM TEMPERATURE PERIOD 4 - TOTAL HEATING TIME 5 - CURING CYCLE (t - to) 6 - TIME AT WHICH HdT IS ADMITTED INTO CURING CHAMBER 7 - TIME AT WHICH HEAT IS SHUT - OFF. TO - TEMPERATURE OF CURING CHAMBER BEFORE HEATING. to - TIME OF CONCRETE BATCHING TI - MAXIMUM CHAMBER TEMPERATURE t. - END OF STEAM CURING CYCLE

4

5

TIME ELAPSE FROM BATCHING

FIG. 1- DESCRIPTION OF TYPICAL ACCELERATED CURING CYCLE.

31

FIG. 2 200 ,

u. o

- 150 UI a: ::l I­<l a: UI 100 Cl. :E UI I-

I- , 50

o

/

LI

2

200 FIG, :3 I- '

~

• 150 UI a: ::l

~ a: ~ 100 :E UI I-

50

I-

~

~

./

o 2

CYCLE' 1-20-125 , , , , , ,

....... bottOIll flango

. ..--.~-.--,- top flan~:--·-·· ----I

- __ ~cyllndln

.' --. -----__ ..1

/ I ,-II ./

-, , , , , , 4 6 8 10 12 14 16

DURATION OF CYCLE, HRS.

CYCLE, I - 80-125 , , , , , ,

r-'- -'-.. -~ '-'-.;::::: , . -~ -1/1 ---I ----I . ----__

I f f / .

./ ......

-, , , , I , , 4 6 8 10 12 14 16

DURATION OF CYCLE, HRS.

FIG. 2 a :3 - TIME VS TEMPERATURE CURVE FOR AASHOTESTS ® 125°F.

32 FRANCON TESTS

200 FIG. 4

l-u. 0

150 I-

• w a: :::> I-<[ a:

100 w 0.. ~ W I-

2

200 FIG. 5 I- '

u. o

" 150 w a: :::> I­<[ a: ~ 100 ~ W I-

50

I-

c-

-I

o 2

CYCLE ,3-40-150 , " '_" I

top flanlle-:/o-o '-'-'-._.: I / bottom flonge .

j,--~-L::'CYllnders If" I I

I 'j I / , II I

/ II 1/

/ " 1/ / " .- ./

I , , I I , I , .

4 6 8 10 12 14 16

DURATION OF CYCLE, HRS.

CYCLE, 3-60-150 I , I I r -,

--~ /' - .-._-- .. I -- --. I /'~ ------__ •

I . 1/ '/ • I

I II I

. L II / I

. IL. -

I I , , , , 4 6 8 10 12 14 16

DURATION OF CYCLE, HRS.

FIG. 48t 5 - TIME VS TEMPERATURE CURVE FOR AASHO BEAM TESTS (Q) 150°F

33 FRANCON TESTS

IJ.. • ~

llJ a: ::> !;t a: llJ 0.. ::l1 w I-

IJ.. • ~

w a: ::> !;t a: w 0.. ::l1 llJ I-

FIG. 6 200

1-"""

I-

I-150 I-

I-l-I-l-

100 L..

50 o

,

2

FIG 7 200

l-150

~

l-

100 I

CYCLE, 3- 20-170 -T , ,

lop flange .~.-.-.-

.... ;:;-.;.... _ _ bottom flange ------'" 'l'

"'A cylinders -t' IAil ~

i /i II I

/ /~

1//

, , ,

4 6 8 10 12· 14 16

DURATION OF CYCLE, HRS.

CYCLE·I-80-170 _. "-'/ Tf-:" ., . . . ( --I . -------------

I I ! '/ '/

I /

. .7 ;,

t-

50 o

'A .

,

2

. , , , , ,

4 6 8 10 12 14 16

DURATION OF CYCLE, HRS.

FIG. 6 a 7 - TI ME VS TEMPERATURE FOR AASHO BEAM TESTS ® 170°F

34 FRANCON r'STS

:t: I-(!) Z UJ 0: I-(f)

UJ > (f) (f)

UJ 0: Q. :;: 0 (.)

UJ 0: ::> (.)

I-(f)

0 :;:

~ 0

CD N

lL. 0

I-Z UJ (.) 0: UJ Q.

DRY HEAT

100

90

70

60. .

50'--------' 125 150

28 d cor ••

18 hr. cores

125

STEAM HEAT

,.,"~

I PRE-HEAT'

<11- I hr. G- a hrs. 0- 5 hrs. 0-7hrs.

150

MAXIMUM TEMPERATURE, OF

170

28 d cor ••

18 hr. cor ••

FIG. 8 - EFFECT OF MAXIMUM CURING TEMPERATURE ON RELATIVE COMPRESSIVE STRENGTH - DRY HEAT a STEAM (w/C = 0.49)

35 FRANCON as~s

. ui a:

8000

'I.' 000 ~ C!l Z L1J

1=6000 en L1J > ~5000 L1J a: £l. ~

84000

a: :I:

<D -3000

2000

1000

•

• •

50 70

• • • •

• • ;

• • • ,

•

CONCRETE MIX DATA' W/C • 0.36:1; Slump· 3/4- .. I 1/2-

•

•

Initial Concrete Temp.· 55·-70·F Cylinder Pre"t. 2 hra. @ 65e F 1 Total Cur. TlrM· 15 hrl .

90 110 130 150 CURING TEMPERATURE, of

170

FIG. 9 - CURING TEMPERATURE VS f~

eTA TESTS 36

en (l. ~

:I: I-(.!) 100 z W II:: I-en w > 80 en en w II:: (l.

:. 0 60 0

W II:: => 0

I-!!? 100 0 :. >-<[ 0 CD 80 '" IJ.. 0

I-Z 60 w 0

II:: W (l.

, I

... I HOUR PREHEAT -I- 3 HOUR PREHEAT -~ - -

I- -I- -

~-~ ---~?7&~!-> <;18--• ..a - --

- -r

5 HOUR PREHEAT - 7 HOUR PREHEAT

- -

~--~ 2:8 -110:

~ I 2:60

i!O" '*- -4011< 20

I I I

125 150 170 125 150 170 MAXIMUM TEMPERATURE, Of

FIG_ II - EFFECT OF RATE OF TEMPERATURE RISE ON 18 HOUR RELATIVE CORE STRENGTH w/c = 0_49

FRANCON TESTS

38

en (l. ~

:I: I-(.!) 100 z W II:: I-en w > 80 en en w II:: (l.

:. 0 60 0

W II:: => 0

I-!!? 100 0 :. >-<[ 0 CD 80 '" IJ.. 0

I-Z 60 w 0

II:: W (l.

, , , ,

l- I HOUR PREHEAT -- 3 HOUR PREHEAT -

f- l-

f- -f- -

I---~ • > <;18--

..a

f----~?--- ;;§!-f-

-

- - f- -

5 HOUR PREHEAT -f- 7 HOUR PREHEAT -

- -~ -

~--~ :;;;;:8 •

110:-I ?-:~-rm =

20

., , , , , 125 150 170 125 150 170

MAXIMUM TEMPERATURE, Of

FIG_ II - EFFECT OF RATE OF TEMPERATURE RISE ON 18 HOUR RELATIVE CORE STRENGTH w/c = 0_49

FRANCON TESTS

38

w ~

<J) 0.. -:x: l-t!) Z UJ a: I-<J)

UJ > <J) <J) UJ a: 0.. :Ii 0 0

a:: :x: III

10000 rl ---------r-----,---------,----,

'" :I ! J -~

/' /'

8000 L II

6000

4000

r- -~-·-i,-; D.lum

NOTE' Sam. 1 .. 11 .1 In Flg.9

...J

J !

J : ,~ ___ ..J

TOO

•

2000 I r 200 500 1000

Are. (d.V- h ... .l· M.lu,IIy

• •

• • •

•

2000 3000

MATURITY (LOG SCALE), DEGREE-HOURS

FIG_ 12- 16-HOUR COMPRESSIVE STRENGTH VS MATURITY

eTA TESTS

~

160r, ------,------,------,------,------,------,------,------,

LL •

140

• UJ 120 0::

~ 0:: UJ Q. 100 ::e

~

:: .. • ~ ..

t e. I

.. ". I!-II!

I

I e. , Bottom Flang.

/Top Flang.

80 _----..J-.-,.,.,. ---- ..-... -... k-.....,,-----..... ---...... T

""".:.:-:::::::.:--o_o_._._o_._._oL .. , Cyllnd.r.

UJ I-

.......... ...... - .-.......... ......... .... .... . ................ ... c.. Ambl. , ••• •••••• n . ..... .. 60 LI ______ L-____ -L ______ ~ ____ ~ ______ ~ ____ ~L_ ____ _L ____ ~

o 2 4 6 8 10 12 14 16

DURATION OF CYCLE, HRS.

FIG. 13 - AMBIENT CURING: TIME VS TEMPERATURE FOR WSHD 100 - SERIES GIRDERS ( TYPE m CEMENT) w/c = 0.36

CTA TESTS

..

160,1------.------,,------.------,-------,------,,------,------.

lL. •

140

~ 120 a:: ::l l-e:( a:: w Q. 100 :::t lIJ I-

80

20'

• .. • '\ / ..

I" 0"

• • !!! t" .. .,

t-=-... t-/ "-...

27

Bottom Flange

.""".----.,/ --, --

/

/ Top Flano. 7 ---

I --

.I / I T .. t Cyllnderl

,I /'-'-' 1 ,/ /' -'-

--

,'/ /' '-. ..,,/ / '-. .,,/ . -~:;.- / -.,

~"" ./_ Ambient

............. -.~ . - .. , ................................ ~ ---. .. .. "...................... ................ . ..... \ .. . ............................ _ ........ .

601~------~----~------~----~------~----~------~----~ o 2 4 6 8 10 12 14 16

DURATION OF CYCLE. HRS.

FIG.14- AMBIENT CURE: TEMPERATURE VS TIME FOR AASHO TYPE nz: GIRDERS (TYPE m CEMENT) w/c = 0.49

FRANCON TESTS

.... z ~ 0::

'" Q.

110

100

90

80

70

60

50

110

100

90

80

70

60

50

110

100

90

80

70

60

50

7 HOURS

2.' {cor •• y

a' "

to ""","

./- ' ~ , .. ~. 18ht.

~ lc,U

,

~/ ~ -~

PRE-STEAM TIME

5 HOURS 3 HOURS I HOUR

---MAXIMUM TEMPERATURE - 125°F

I I ......J ! I I L..--L_'---'

: ~

'\ ~ .... , I ~ I

/ ~ I ., '.; ",

~PE ATURE - 150°F . MIAXIMUM TE I I I I

r

-

M1AXIMUM TE1MPE ATURE - 17 OF

20 40 60 80 20 40 60 80 20 40 60 80 20 40 60 80

10 HOURS

FIG. 15- RELATIVE CONCRETE

RATE OF TEMPERATURE RISE, OF/HR. 12 HOURS 14 HOURS 16 HOURS TOTAL STEAMING TIME

COMPRESSIVE STRENGTH OF STEAM-CURED (TYPE m CEMENT) - w/c = 0.49

FRANCOM TESTS

42

FIG. 16 - RELATIVE DRY-HEAT CEMENT)

COMPRESSIVE STRENGTH OF CURED CONCRETE (TYPE m

FRANCON TESTS 43

f:

NOTE, 6000 r, -,---.,-----,

- Coner ••• mldd a cured C!O Indlca'ed '"mp.

-Initial til" on 4x8-ln. cyll. C!Il 4 or 6 hro. 5000

-28 d tIlt, on 4Jt8 In. cyl •. rapid-cured a 'hln .tored <lb 70°F, 40 % RH.

4000

If) 0-

0

J: 3000 I-(!) Z lIJ a: Iii lIJ 2000 > C/l C/l

~ 0-

S 1000

."......--' ........

/'

.... ..... --­.....

o ·L_....L_L----1

_-.P---......... -

/ /

I

/

I /

, ..... /

100 125 150 175 100 125 150 175 MAXIMUM CURING

510 605 CEMENT CONTENT,

,.

/

,," I

"'./

/ 100 125 150 175

TEMPERATURE, of 720

LBS.! CY

" ~28d

,.

6 hr. RIC

,-, I .....

flNITIAL

I I I

I I I r 4 hr. RIC

I I

/

100 125 150 175

820

FIG. 170 LABORATORY BATCHED HOT CONCRETE - TYPE I CEMENT FRANCON TESTS