H.Kardumian, S.Kaprielov

A New Generation of Multicomponent Modifiers for Produ- cing High-Strength Concrete with Compensated Shrinkage and Expansion

As is known silica fume, metakaolin, slag, fly ash and highly effective superplasticizers are the canonical components of modern high-strength concrete. The combination of the mentioned materials makes it possible to govern the rheological properties of concrete mixtures and to modify the structure of the cement paste on the micro-level in such a way as to give to concrete the properties ensuring the high performance of structures. The gained properties of concretes are determined by the complex colloid-chemical and physical processes, which influence the phase composition, the porosity and the strength of the hardened cement paste [1,2]. Since the nineties of the last century the complex polyfunctional modifiers of MB series (MB-01 and MB-C) appeared on the construction market of Russia. They are powder- like materials with bulk weight about 800 kg/m3 and contain the components, which are necessary for high-strength concrete production, i.e. silica fume, fly ash, super-plasticizer on the base of sulfonated naphthalene-formaldehyde poly-condensates, hardening regulator, in various proportions. They are suitable for the large-scale production of concretes of new generation, providing high workability, high strength, low permeability and increased durability. Due to synergyc effect the several components of high-quality concrete in the form of united multicomponent product are more effective than the same materials, separately introduced into the concrete mixtures [3]. At the same time the powder-like form of the complex modifiers allows production of high strength concrete for any ready-mixed concrete plants without essential investment expenditures. The previous investigations showed that by varying composition and proportion of the MB modifiers in the concrete mixtures, it is possible to govern the deformation characteristics of concretes. In particular, it proved to be possible to obtain high-strength fine- grained concretes with the modulus of elasticity and creep, comparable to the characteristics of heavy-weight concrete with coarse aggregate of the similar strength class [2]. However, the attempts to influence the degree of shrinkage of the modified fine-grained concrete with the help of the modifiers MB, containing micro-silica, fly ash and superplasticizer, have not met with success. The unfavourable effect of shrinkage on the performance properties is known as a problem of great concern in the contemporary concrete technology. The essence of the problem is rather to prevent the processes causing the shrinkage of high-strength concrete than to remedy the negative consequences of shrinkage. The topical character of the problem of regulation of shrinkage deformations relates to the real possibility of large-scale production and employment of fine-grained and self- compacting high-strength concretes (which differ from the usual ones due to the increased consumption of the binding agents) in the contemporary construction. The outlined circumstance initiated the development of a new multicomponent organomineral modifier Embelit. Experiment

On the base of preliminary studies it has been assumed that metakaolin, which contains the amorphous SiO2 and Al203, can be used as a component of an expanding composition of sulfoaluminate type for obtaining the high-strength structure of the cement sys- tem with controllable shrinkage [4]. The idea of the experiment consisted in proportioning of the multicomponent modifier, which ensures obtaining high-strength concrete with controllable shrinkage. For the mineral part of the new modifier an expansive compound (EC) was propor- tioned on the basis of metakaolin and gypsum. Following the technology of the MB modifiers, the new types of the modifiers Embelit 6-50, Embelit 10-50, Embelit 0-100, Embelit 5-100, Embelit 6-100, Embelit 10-100 were prepared, which vary both in composition of the mineral part and in the amount of the superplasticizer (SP). In the mineral part of the Embelit modifiers silica fume (SF) and fly ash (FA) are replaced either totally or partially by the expansive compound. The influence of the composition of the mineral part, the amount of the organic part (SP) and the dosage of the complex modifier on the deformation and strength characteristics of high-strength fine-grained concretes were determined . The mineral part of the reference samples consisted of equal amounts of silica fume and fly ash, corresponding to the composition of the traditional modifier MB-C. Dosage of the modifiers in the concrete composition constituted 12.5% and 25% of the cement mass.

The following materials were used as the components of concrete mixtures: - Portland cement “PC500” conforming to the Russian Standard GOST 10178 with the characteristics presented in Table 1; - Concrete modifiers without the expansive compound (EC) of the type MB-50, the composition of which is presented in Table 2; - Concrete modifiers with different amount of the expansive compound of the type Embelit, the compositions of which are given in Table 2; - Quartz sand with the fineness modulus of 2.5; - Granite coarse aggregate of the fraction size of 5 to 10 mm with compressive strength of 120 MPa.

Table 1 Physical and Chemical Characteristics of Cement

Physical properties Specific surface Water demand of cement Setting time Activity, area, m2/kg paste of normal consisten- (initial/final), min MPa cy, % 318 25,4 160/360 51,0 Composition of basic oxides, %

SiO2 Al2O3 CaO Fe2O3 MgO SO3 Na2O K2O other 20,5 5,5 64,4 4,6 0,7 2,6 0,2 0,5 1,0

Table 2 Composition of Concrete Modifiers

Mass proportion of the components, % expansive compound Super-plas- No. Types of modifiers silica fume fly ash (metakaolin + gypsum) ticizer (SF) (FA) (EC) (SP) 1 MB 6-50C 47.0 47.0 - 6 2 MB10-50C 45.0 45.0 - 10 3 Embelit 6-50 23.5 23.5 47.0 6 4 Embelit 10-50 22.5 22.5 45.0 10 5 Embelit 0-100 - - 100.0 - 6 Embelit 5-100 - - 95.0 5 7 Embelit 6-100 - - 94.0 6 8 Embelit 10-100 - - 90.0 10

The influence of the composition of the mineral part on the characteristics of concrete was studied on fine-grained concrete prepared with the mixture proportion of 1:1 (cement : sand) by mass and the water-binder (water/(cement + modifier) ratio equal to 0.25-0.28. Two series of testing were carried out. Firstly the multicomponent modifiers corresponding to the proportions No.2, No.4 and No.8 (Table 2) were used. They differ by the quantity of the expansive compound: 0%, 45% and 90%, correspondingly. The amount of the superplasticizer in these modifiers is identical and makes up 10% of the mass of the mineral part. The influence of the organic part (SP) of the new modifier on the properties of concrete was studied dealing with the compositions with the dosage of 5% and 10% of SP. The reference specimens were prepared without the superplasticizer. For this series of testing the modifiers with the proportions No.5, No.6 and No.8 (Table 2) were used. The dosage of the modifiers in the concrete was constant and equal to 25% of the cement mass. Properties of the mixtures and characteristics of the concretes are presented in Table 3.

Table 3 Characteristics of Fine-grain Concrete with various Modifiers corresponding to 25% of the cement mass

Properties Properties of fine-grain concrete with the proportion of 1:1 No. of of mixtures No. of the Serie pro- Self- Compressive strength, MPa, modifiers Water- Cone Linear s por- -stress- at … days (Table 2) binder flow, expansion, tion ing, S , ratio mm % p MPa 1 7 28 90 1 2 0.25 255 - - 29.0 69.4 79.7 94.6 2 4 0.25 190 0.02 0.9 32.7 69.4 90.7 99.7 I 3 8 0.25 142 0.10 1.8 34.7 68.6 96.6 104 4 5 0.28 130 0.18 2.1 26.0 74.1 94.7 103 5 6 0.22 155 0.12 2.0 38.2 98.0 99.4 109 II 6 8 0.22 180 0.09 1.6 35.4 98.0 102 105

To study the influence of proportioning of the new modifier Embelit on the deformation and compressive strength properties of concrete the compositions were designed for fine-grain concretes of the compressive strength grades B70-B80 from high-workability concrete mix (slump of in the range of 21 to 25 cm). The binder-aggregate (sand) ratio was 1:1.6, the water-binder ratio was 0.28. Different multicomponent modifiers MB-50 and Embelit were employed with different portions of the expansive compound in the mineral part (0%, 45 – 47% and 90 – 94%) and the content of SP (from 6% to 10%). It allows obtaining concretes of equal strength from mixtures of equal workability with different proportioning of the modifiers (No.1, No.2, No.3, No.4, No.7 and No.8 ac- cording to Table 2). The dosage of modifiers was 25% and 12.5% of the cement mass. Composition and properties of the concrete mixtures are presented in Table 4.

Test methods

Properties of concrete mixtures and concretes were evaluated in accordance with the Russian standards. The shrinkage-expansion deformations were determined with the use of specimens of 4040160 mm and 100100400 mm. Self-stressing was determined from consideration of the expansion-deformation of specimens of 4040160 mm and 5050200 mm under restrictions of one-dimension- al elastic state set up by dynamometric conductors. Compressive strength of concrete was determined by testing of specimens of 100100100 mm. Watertightness of concrete was determined by testing of cylindrical specimens with di- ameter of 150 mm. All specimens were cured at a temperature of 202оС during one day in the forms under the cover, further 6 days at the relative humidity (RH) of 100% and from 7 to 120 days – at RH of 60%. For all the test-cases the kinetics of concrete hardening was compared as well as the development of shrinkage-expansion. Self-stressing was determined for those specimens, which contained modifier with the expansive compound.

Table 4 Composition and Properties of Concrete mixtures containing modifiers at dosages of 25% and 12.5% of the cement mass

Mixture proportion, kg/m3 Properties of concrete mixtures Type of Binder (B) Air modi- № modifier Sand Water Slump, entrai- ρ, fiers ce- W/B B/S (S) (W) cm ned kg/m3 (Table 2) ment kg % % 1 1 650 163 1300 228 21.0 6.8 0.28 1:1.6 2340 2 3 650 163 25 1300 228 23.0 6.0 0.28 1:1.6 2335 3 7 650 163 1300 228 20.0 5.5 0.28 1:1.6 2336 4 2 720 90 1300 227 21.0 6.3 0.28 1:1.6 2320 5 4 720 90 12.5 1300 227 23.0 5.8 0.28 1:1.6 2318 6 8 720 90 1300 227 24.0 5.5 0.28 1:1.6 2321

Results and Discussion In the first test series at the equal strength level (about 30 MPa at 1 day and about 100 MPa at 90 days) the fine-grain concretes showed an increase in the expansion, which is obviously due to the enlarged amount of SP in the mineral part of the modifier Embelit. The same effect was observed for the deformations of self-stressing (Table 3, Fig.1 and 2). , % 0,18 Embelit 0-100 0,16

0,14

n Embelit 5-100

o 0 ,1 2

s n

a 0 ,10 p

x Embelit 10-100 E 0 ,0 8 0 ,0 6

0 ,0 4 Embelit 10-50

0 ,02 e

g MB 10-50C a

k 0

i r

h -0,0 2 S 0 1 2 3 7 10 14 28 , d ay s Fig.1. Deformations of linear expansion

Sp , M Pa Embelit 0-100 2,1 Embelit 5-100 1 ,8 Embelit 10-100

1 ,5

1 ,2

Embelit 10-50 0 ,9

0 ,6

0 ,3

0 0 1 2 3 7 10 14 28 , days

Fig.2. Self-stressing of specimens

In the second test series the hardening kinetics data showed a higher (30%) compressive strength level in the earlier period of hardening for the concretes with the modifiers, which includes SP (Table 3). In the subsequent period of hardening the strength characteristics of the modified concretes (with and without SP) level off. It is known that the use of SP makes it possible to reduce the water-binder ratio considerably and improve the strength parameters of concretes. Deformation characteristics of EC (linear expansion and self-stressing) are intimately related to the strength parameters of concretes. The study of deformations showed that the stabilization of the expansion processes for all concrete comes after 14 days of hardening. The measured final values of deformations showed considerable variation and made up 0.18%, 0.12% and 0.09% for the compositions with the modifier EMBELIT without SP, with 5% of SP and 10% of SP, correspondingly. As for the self-stressing the variation for the concretes was not significant (within the range of 2 MPa to 1.6 MPa) (Table 3). All the specimens of fine-grain concretes (their compositions are given in Table 4) showed similar kinetics of hardening and the resulting values of the compressive strength. The tests results are presented in Table 5.

Table 5 Hardening Kinetics of Concretes with various Modifiers

Type of modifiers Dosage of Compressive strength at … days, MPa N (Table 2) modifiers 1 3 7 28 90 1 1 48.4 67.0 78.1 101.3 108.1 2 3 25% 48.6 65.2 85.2 103.1 106.4 3 7 49.9 60.3 85.5 103.2 114.6 4 2 40.9 60.1 76.2 99.1 103.4 5 4 12.5% 42.1 60.9 78.0 100.4 106.8 6 8 44.1 71.0 91.5 103.7 112.9

It was interesting to consider the expansion-deformations of concretes of equal-strength prepared from mixtures of equal-workability with different amount of modifiers. The test results are presented in Fig.3.

% 0 0

1 n

= n

o i

H i s

R s

x e 0% e =6 RH

RH=100%

r h

h RH=60%

s s

МB 6 -50С Embelit 6-50 Embelit 6-100 МB 10 -50С Embelit 10-50 Embelit 10-100

Fig.3. Expansion-shrinkage of Concrete with various types of Modifiers vs Relative Humidity

An increase in the value of linear expansion-deformation in water conditions is determined by the increased portion of the EC in the mineral part of the modifier. The EC in amounts of 12.5% in the mineral part of the modifier Embelit 6-50, which also contains SF and FA, allows one to consider this concrete as the concrete with compensated shrinkage after curing in air-dry conditions. The same amount of the expansive compound (12.5%) in the modifier Embelit 10-100 with the mineral part consisting of EC alone, shows a stable permanent expansion even after curing in air-dry conditions. The obtained results showed that employment of modifiers with the EC of sulfoaluminate type makes it possible to achieve (at high compressive strength of fine-grain concretes) permanent self-stressing and linear expansion after curing in air-dry conditions. Replacing the mineral part of the traditional modifier MB-50 by 50% of the expansive compound of metakaolin and gypsum (to say, the presence of EC in amounts of 12.5% of the cement mass) allows to reduce considerably shrinkage (2 times) at the equal strength level of fine-grain concretes. Normal concretes prepared from concrete mixtures of high-workability with the use of different types of the designed modifiers, in particular, Embelit 10-50 and Embelit 10- 100 were tested and compared with concretes containing MB-50. The compositions and properties of the concretes are presented in Table 7. The presented test results (Table 7) confirm in full measure the effects found in the tests with fine-grain concretes. Organomineral modifiers EMBELIT allow (at high strength and extra-low permeability of concretes from mixtures of high-workability) not only eliminating shrinkage, but also providing expansion and self-stressing of the concretes.

, Table 7 p S

Mixture Proportions and Properties of Concretesg n i s s e t r t 3 n Compressive W s

Concrete composition, kg/m e % - s

f , s

No. of m l strength m  e e e

c e c n , S t n

modifiers t - (MPa), , a r Binder a o h r p i e g P d e g t

№ (in accor- s t i

e days n m a t n r a M a - u a g dance with r l S W p W g e

Ce- Modi- S t o x i A Table 2) 7 28 a t

ment fier a r W 1 2 450 90 734 980 145 22 0.32 - - 68.4 92.4 20 2 4 451 92 735 978 146 24 0.32 0.04 0.8 70.4 91.1 > 20 3 8 448 87 733 977 144 25 0.32 0.10 1.9 71.1 93.0 > 20

Conclusion

On the basis of results obtained a new multicomponent modifier has been developed, which enables producing high-strength concretes , especially fine-grain ones, with re- duced and compensated shrinkage or with expansion and self-stressing. The modifier, which is named EMBELIT, contains metakaolin, silica fume, fly ash, natural gypsum and super-plasticizer. It is a powder-like product with bulk weight 750-800 kg/m3 with an optimised proportion of the above-mentioned components.

References

1. Kaprielov S.S. General regularities of forming the structure of the cement paste and concrete with ultra-dispersed admixtures. Concrete and Reinforced Concrete, No.4, 1995, pp.16-20 (in Russian). 2. Kaprielov S.S., Karpenko N.I., Sheinfeld A.V., Kuznetsov E.N. Influence of the organomineral modifier MB-50C on the structure and deformability of the cement paste and the high strength concrete. Concrete and Reiforced Concrete, No.3, 2003, pp.2-7. (in Russian). 3. Kaprielov S.S., Sheinfeld A.V., Batrakov V.G. Properties of Concrete with Complex Modifier Based on Silica Fume and Superplasticizer.// Fifth CANMET/ACI International Conference on Superplasticizers and Other Chemical Admixtures in Concrete, Rome, October 7-10. 1997, Supplementary Papers, p.р. 123-136. 4. Kardumian H., Kaprielov S. Shrinkage Controlling of Self-Compacting High-Strength Concrete. – 15 Internationale Baustofftagung, Weimar, Deutschland, 2003. – Band 2, pp.513-523.