P R O P E R T I E S OF C O N C R E T E IN CORES REMOVED FROM MASSIVE HYDRAULIC STRUCTURES* UDC 693.54:627.824.7.004.12
A. R. T o n k a
INTRODUCTION A gravity dam serves as the basic structure of the Toktogul hydraulic facility [i]. The concrete in the dam was prepared from aggregate consisting of 30% of carbonate rock. Two sand fractions and four gravel fractions were obtained by w e t - s c r e e n i n g the gravel mass. A special Grade 300 pozzolana portland cement (PPC), produced by the Kuvasay cement-shale combine, with a normalized mineralogical composition and restricted alkali content, in whose composition there is 27% of an active mineral additive (gliezh) was used as the binder for the concrete placed in the internal zone of the dam. H y d r o p h i l i z i n g (SDB) and air-entraining (SNV) agents were added to the concrete mix. Data on the concrete mix and the compositions of Grades 25018oV818oR1828 (Nos. i and 2), R1628 (Nos. 5-9), and R14=8 (Nos. 3, 4, and i0) concretes are presented in Table i. Carrying out of the method adopted for controlling the quality of concrete required that certain work be performed to improve the drill bit and to develop ment necessary for preparing the cores for testing [2].
from cores the equip-
From cores removed from the concrete in the internal zone of the dam, we studied the time dependence of a set of basic properties and characterized the homogeneity of the concrete in terms of strength, its moisture content, and the degree of hydration of the cement in the concrete at the time of testing. Most of the studies were conducted on cores (D = 300 mm) formed from concrete with cement contents of 200, 220, and 260 kg/m 3. Strength determinations were also run concurrently on cores with D = 130 and D = 150 mm, while permeability determinations were made only on small-diameter cores. The data cited below were obtained from tests conducted on more than 2000 cores, including ~ 1200 specimens with D = 300 mm. CONCRETE
STRENGTH
Cores of 28- to 730-day concrete with the ratio H:D = 3, 2, and I and 1-1.5 were subjected to compression and splitting-tension testing, respectively, and conversion factors R:/R= for strength as a function of specimen dimension were determined (Table 2). The variation in concrete strength (cores with D = 300 mm) with age is shown in Fig. I (cores with H:D = 2 were subjected to compression tests). One should note the rapid increase in compressive strength up to one year and even the somewhat greater increase in tensile strength as well as the 6% reduction in strength when the top-size diameter is reduced from 150 to 50 mm for the same cement factor (260 kg/m3). The time dependence of the relative concrete strength of cores 300 mm in diameter is shown in Table 3. Comparison of these data with the results obtained from tests conducted on the same concretes in the form of control specimens (a plant mix, cast on a vibratory platform in the laboratory, cured under standard conditions) [3] indicate that the rate of strength accumulation in the structure is higher. We studied the variation in the ratio of the tensile Rt to the compressive Rco strengths (cores 300 mm in diameter) with age. The minimum ratio Rt/Rco is produced at an age of 100-200 days. The introduction of SNV increases the ratio by 1-1.5%. One should note the
*The study was conducted under the direction and with the participation of Doctor of Technical Sciences, Professor A. A. Pariiskii, and Candidate of Technical Sciences, Yu. P. Inozemtsev. Translated
from Gidrotekhnicheskoe
Stroitel'stvo,
131
No. 2, pp. 17-19,
February,
1977.
132
A.R.
TONKA
TABLE i Consump. of materials, kg/ma gravel fractions, mm
sand
Com-
poation
artffiportlam cial lana
No. I
4
5---10
10--25
335 3OO 325
5O0
425 450 470 300 490 440 315 310
--
~0 205 205
~o
200 200 185
280 235
53 240 855 389 245 225 235 165
2~0 220 220 360 450 300 3OO
Core dimensions, mm type I type 2
R,/ R,
Compression 300 300 300 130 3O0 3O0
90:)
301
61)0 900 260 000 300
0.8I 0,92 0.8'3 0.91
300
300
300 600
300 130
130 2F~
130 130
0,80
130
i
30,3--450 130" I
130 130
]
130--200 !30
0,79
0,89
*The specxmens were split immediately after completion of permeability tests under m a x i m u m pressures of 9-25 kgf/ cm 2 .
Age, days
Type of test
61 90
Cement Tension Same Compression
No. of s~ecimens"
Strength,* Coeff. of kgf/cm z variation,*
content, 220 kg/mZ 17/36 , 23.2,25.6,
51/22 [ 21/I7
25,9132,6 181/199.8
[
400
400 200 250 440 450 500 575
SNV
water
0.55 0.63 0,55 0.55 033 0130 0,20 0,20 0,20 0,38
--
120 115 120 123 119 112 116 If6 114 II0
Cent / factog A d d i t i v e kg/ma/ 200 J" SD~
220 22o 200 Mean
SDB 'S DB SDB' SDB~
-/~72~
24.7/45.3 T_/378
0,022
0.36 0,36 0,37 0,30 0,32 0,29
0.57 0,60
0.27 0.26 0.26
0,58 0,58
0,27
Rel. strength* at age, days 90
180
366
1.64/I.55 1,74/I ,7~ 1.6o/ 1.66 1.94/1 .~)
1,85/I.71 1.95j 1.81 2.0'2/2.07 2.17/I.96 2.40/2.17 2.08/1.94
2,05/1,94 2.14/2.04 2.22/2.35 2.41/2.20 2.73/2.50 2.31/2.22
1.74/1.65
730 2,17/2,05 2,26/2,15 2,34[2,46 2,53/2,31 2,8~/2,61 2.43/2,32
*Compressive strengths are listed in the numerator, tensile in the denominator. #The concrete was p r e p a r e d from gravel with Dtop size = 50 mm; in the remaining cases, Drop size = 150 mm.
5
2351100
-/13,313'8/15'5
*Results obtained on cores 300 mm in diameter and 130 and 150 mm in diameter are presented in the numerator and denominator, respectively. tConcrete prepared from Grade 400 cement.
Weight, kg/% prior to after freezing freezing
Strength, (kgf/cm z )/% at equiv, after age freezing
,3,4/2o.3
112/15124.4/24,6111,0/16.1 22..27 22.9/30.3 13.7/16.4
Same 18o15~ C~mpression
-0.033 0.030 0.040 0,040 0,040
0,46 0,44 0,55 0.56 0,54 0,56
3
14,2/15,u 15,9/20.U
Cement content, 200 kg/m 3 90
~00
TABLE
4
311Tension
SDB
0,80
Tension
9O
800 900 900 620 710 700 550 500 600 555
TABLE
TABLE 2
300 130"
25---,50 50--130
0.2--1.2 I 1,2--5,0
260 260 220 220 220
5 6 7 8 9 10
w/c
natural frao-
tion, mm
cement
2 3
TABLE
Fraction of sand in dry aggregate mix
additive
Pozzo-
254/100 272/100
300-ram diam., 90-day concrete tAfter 100 cycles 248/105.3 I 51.921100 51,86199.9 fter 150 cycles I 266/104 5 | 52.72/100 52,88/100.3 fter 200 '@clesl 272/100
I
51.75/100
51,25/100
150-ram diam., 235-day concrete fter 150 cycles I 3151100 430/100
ter
Wycle8 1 347162
t
6.55jloo
6. ,/06.2
6.43/100
6,43/100
extreme character of the dependence of Rt/Rco on the cement content: the maximum corresponds to a concrete containing 220 kg/m 3 of binder. The dependence of strength and its uniformity, which is characterized by the coefficient of variation, on the core diameter is shown in Table 4. Analysis of the data in the table indicates that the strength and its uniformity are functions of core diameter. The coefficient of v a r i a t i o n C v of the concrete from small-diameter cores is 4-6% greater as compared with the test r e s u l t s obtained for specimens 300 mm in diameter.
PROPERTIES
OF CONCRETE IN CORES
133
kgf/cm 2
IR 300
2../
co
3\ I
-
-
ZOO
~50
I
I00 00 I170 kgf 'crn 2
ZOO
3~
~
500
600
700 t, days
a
R
kgf/cmz
Z~_.f
c
"z/// Z5
.':-"
x o o
ooo o o% o
-
o ~
o
co o
o
o
20 ////J
Ig Q
IpO
200
500
~00
Fig.
550
~00
~c___~o
700 t, days
/gu
b
1
zoo
300
5UUkgf/cm2 Fig.
2
Fig. i. Time dependence of compressive (a) and tensile (b) strength of concrete placed in dam. Cement factor: I, 2) 260 kg/m3; 3, 4) 220 kg/m~; 5) 200 kg/m3; top size of gravel: i) 50 mm; 2-5) 150 mm; additives: 1-3) SDB; 4, 5) SNB. Fig. 2. Relationship E = f(Rpr). O) Concrete cores removed from Toktogul hydroelectric plant dam; A) same from Bratsk hydroelectric plant; x) same from Hungry Horse h y d r o e l e c t r i c plant; []) large control specimens formed from concrete used in Toktogul plant dam. Analysis of the relationship Rt = f(Rco) and comparison of the data we obtained with the test results of concretes from other structures [4] demonstrated that the character of the relationship is similar, but the curve for the concrete in the dam lies above the rest of the curves; this suggests the high extensibility of the concrete in the Toktogul dam. The initial static elastic modulus E of the concrete was determined on cores 300 mm in diameter and 900 mm high (a base of 300 mm) in load increments o = (0.2=0.3)Rpr, where Rpr is the compressive prismatic strength of the concrete, which is obtained from failure of the specimens; E is also determined thus; and o is the stress at which strain measurements were obtained. The curve in Fig. 2 is a representation of the relationship E = f(Rco) according to Construction Norms and Specifications II-V.1-62. The disposition of the experimental points for the concrete in the Toktogul and other dams above the curve suggests a higher elastic modulus of the concrete in the structure. In our opinion, this is explained not only by the increased content of the stone component in the concrete and the scale factor, but also by the effect of the temperature--moisture conditions of the mass and its stress state on the development of concrete properties. Poisson's ratio ~ was determined with ~ = (0.2-0.7)Rpr. Transverse deformations were measured in two planes located in the median section of the specimen and spaced 60 mm apart. The test results indicate a certain increase in ~ with increasing O/Rpr within the range from 0.2 to 0.4. The value of ~ for the concrete placed in the Toktogul dam, which has a cement factor of 180-260 k g / m 3 and one or two additives, ranges from 0.14 to 0.20 at an age of from one month to four years.
134
A.R.
TONKA
The coefficient of linear thermal expansion ~ of the concrete in the dam (cores 300 mm in diameter and 900 mm high), which has a cement factor of 200-260 k g / m 3 and one or two additives and which was produced from gravel with a top size of 150 mm, is (5.2-6.6)'106/ deg C in the temperature range from 50-17~ at an age of 3-40 months. The comparatively small value of ~ is explained by the significant content of carbonates in the aggregate, the low cement factor, and the increased content of coarse aggregate in the concrete. The unit weight of the concrete placed in the dam was determined from cores and other concrete specimens removed from the structure. Data on its dependence on the type of vibratory consolidation, layer thickness, concrete composition, and the location of the specimen that we removed in the structure were published earlier [5]. Frost resistance was studied on cores 150 and 300 mm in diameter, which were drilled with a diamond bit (Table 5). We tested gravel concrete with a top-size aggregate of 150 mm, a cement content of 200 kg/m ~, and a 0.02% additive of SNV. The data in Table 5 indicate that the concrete cores removed from the structure by diamond drilling, which had aged for not less than 90 days at the start of the tests, successfully endured 200 cycles of alternate freezing and thawing, despite the fact that pozzolana portland cement was employed as the binder for its preparation. The high frost resistance of the concrete is explained primarily b y the introduction of the SNV air-entraining agent, the favorable effect of which on the resistance of concrete to alternate freezing and thawing is well known. The fact that the laboratory specimens are distinguished from the cores by an increased content of mortar and grout in the surface layer of the specimen due to the "wall" effect during their casting is, in the opinion of the author, critical. The loss of strength and weight during frost-resistance tests occurs primarily as a result of the failure of precisely these components in the surface layer of the specimens. The surface of the cores is formed to a significant degree by aggregate grains. The failure of specimens exhibiting this structure in the surface zone will therefore be delayed. The permeability was determined on 130- and 150-mm diameter cores formed from concrete ranging in age from one to 36 months. Despite the fact that pressures of from 9 to 25 kgf/ cm 2 were employed in the testing process, through seepage of water was moted only in a small number of specimens. The test results suggest that in addition to the SDB, the introduction of SNV air-entraining agent in the mix gives rise to an increase in impermeability [6]. The increase in impermeability is attained not only by the use of the SNV and adequately coarse gravel, but also owing to the high density of the concrete in the structure, which was obtained as a result of the use of batteries of heavy-duty modern vibrators. According to design requirements, the concrete in the thrust face of the dam (grade V8) should be the most impermeable. The test results indicated that the comcrete placed in the structure with the SDB agent and a cement factor of 220 kg/m 3 satisfies this requirement in just one month~ The moisture content as determined by weight for the concrete that we tested varied within a small interval, diminishing from 4.5 to 3% with increasing age from i to 36 months. The amount of water chemically bonded with the cement increased in this case (from 16 to 22%). The use of modern technology for the preparation, placement, and quality control of the concrete made it possible to reduce the percentage of sand and the cement content in the dam concrete to 180 kg/m 3 with a continuous increase in the plan dimensions of the blocks and in the height of the concreted layers. CONCLUSIONS i. The results of core tests indicate that use of the Toktogul method of concreting massive dam structure [i] makes it possible to provide high-quality concrete and its placement. 2. The high efficiency of the use of gliezh-portland cement and the combination of an SDB hydrophilizing additive and an SNV hydrophobizing additive in stiff mixes for the dam's internal zone is shown. In combination with the use of controlled screening of the gravel and an aggregate containing six fractions, dam concrete corresponding to the design requirements (250180 V8~8o R16=8 and 25018oV81soR1428) is produced with grade 300 pozzolana
PROPERTIES OF CONCRETE IN CORES
135
portland cement contents of 200 and 180 kg/m 3, respectively (a content of purely clinker portland cement of 145 and 130 kg/m3). 3. A rapid increase in strength during the first year and one-half, exceedence of the modulus of elasticity as compared with data presented in the Construction Norms and Specific cations, an extremely high degree of impermeability, and a high crack resistance are characteristic for the concrete of the internal zone. All this is explained by an increase in the content of the colloidal phase in the hydration products stemming from formation of calcium hydrosilicates during interaction between the calcium hydroxide and siliceous gliezh, and also by the effect of favorable conditions of the mass and the specifics of the procedure of concreting by the Toktogul method on the development of these properties in the concrete. LITERATURE CITED i. 2. 3.
4. 5.
6.
L . A . Tolkachev and V. B. Sudakov, The Toktogul Method of Concreting Massive Structures [in Russian], Energiya, Moscow (1973). L . A . Tolkachev, V. S. Shangin, and Yu. P. Inozemtsev, "A diamond bit used for the quality control of dam concrete," Sint. Almazy, No. 4 (1974). Yu. P. Inozemtsev, S. N. Semenenok, and R. S. Tilles, "Certain design composition characteristics of the low-cement concrete used for the basic structures of the Toktogul hydroelectric power plant," in: Proceedings of Coordination Conferences on Hydraulic Engineering [in Russian], No. 95, Energiya, Leningrad (1974). V . M . Malhotra, "Relations between splitting tensile, flexural, and compression strengths of concrete," Eng. I., 52, No. 5 (1969). Yu. P. Inozemtsev, A. Ya. Luksin, A. A. Ravkin, and A. R. Tonka, "Quality control of concrete consolidation in constructing the dam for the Toktogul hydroelectric power plant," Energ. Stroit., No. II (1973). R. Milens, "The use of surface-active substances in concrete," in : Fifth International Congress on the Chemistry of Cement [in Russian], Stroiizdat, Moscow (1973).
