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
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
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