High performance concretes from Romania.

Buchman, Iosif ; Ignaton, Elemer

1. INTRODUCTION

The experimental researches regarding concrete development witnessed lately two significant stages.

The first stage consists in the perfecting of high performance concretes (Malier, 1990) characterized by a compression strength which exceeds 60 N/[mm.sup.2], as well as by other improved characteristics, such as the elasticity module, the contraction, the tranquil flow, the frost-thawing proof, the wear-proof, the impermeability, the resistance to aggressive chemical agents. They have been and are being studied in countries such as USA, Canada, France, Germany, Scotland, Norway, Japan, and are used at high buildings, large span bridges, marine structures, a.o.

The second stage included Western Europe, starting with the ninth decade of the last century. It refers to ultra high performance concretes, which, besides a very high compression strength of 200 N/[mm.sup.2], or even more, also have other performance characteristics, such as water tightness and gas proofness, placement without passive reinforcement, resistance to aggressive chemical agents, a.o.

High performance concretes are considered the present time concretes, and the ultra high performance ones are considered the concretes of the future.

Following two specializations attended by one of the authors in France, there has been initiated the research of these concretes types in Romania, as well.

This paper presents the theoretical studies and the experimental researches carried out by the authors concerning high performance concretes obtaining and some of their characteristics. Thus, there have been obtained and there have been studied high performance concretes with the average compression strength ranging within 60-80 N/[mm.sup.2].

2. COMPOSITION AND PREPARING

The specific components of the high and very high performance concretes are the superplasticizer additives and the ultrafine granular materials.

The first superplasticizer additives belonged, mostly, to one of the following categories of chemical compounds: sulphonated melamine resins and sulphonated naphthalenic resins. At present, in Romania, there are marketed other efficient types of superplasticizer additives.

The granular materials, such as the ultrafine silica, adds to the cement granulometry, namely reacts with Ca[(OH).sub.2] resulted at the cement hydration, there being obtained a very tight microstructure.

The establishing of the composition of a high or very high performance concrete is more complex than for the usual concrete, because there occur new parameters, namely: the superplasticizer additive and the ultrafine silica.

The authors' team has established that a very simplified way of establishing the composition of a high performance concrete supposes the following stages:

--there is established the composition of a usual concrete, whose class is 1.5 times smaller than the intended one for the high performance concrete, and this is completed with 10% silica fume (as compared to the cement mass) and 1-2% superplasticizer additive (as compared to the cement+silica mass);

--at preparing, the water quantity is reduced to make the high performance concrete have a consistency identical to that of the usual concrete, and after 28 days there is checked the compresion strength of the high performance concrete thus obtained, and, if needed there are applied corrections concerning the cement, ultrafine silica or superplasticizer ratios. The preparing of high performance concretes can be carried out with the same equipment employed for the usual concrete. To obtain a good homogeneity and to shorten the mixing time, there shall be used wet mixers with forced mixing provided with paddles and pugmill. The sequence of the mixing operations is as follows:

--cement mixing with the silica fume;

--the introduction of the aggregates and the dry mixing of the granular components;

--the adding of water in which there has been disolved the superplasticizer, followed by the mixing going on. The mixing time depends on the characteristics of the equipment employed. Compaction is obtained through vibration, as for the usual concrete.

3. COMPRESSION STRENGTH

Within the experimental researches that have been carried out (Buchman et al., 2001, 2003), there have been cast and compression tested 4 series of high performance concretes. The compositions have been established according to the presentation made at point 2.

There have been used the following materials:

--cement of CEM I 42.5 R type (series 1, 2), or of CEM I 42.5 type (series 3, 4 );

--river aggregates with [d.sub.max]=16 mm;

--silica fume from FEROM Tulcea;

--LOMAR D superplasticizer of foreign source (series 1, 2. 3), or FORTERA superplasticizer of indigenous source (series 4); Series 4 have been obtained only with indigenous materials. Table 1 showes that there have been obtained high performance concretes with on average compression strength, after 28 days, ranging within 63.5 and 84.9 N/[mm.sup.2].

4. THE ELASTICITY MODULE

The elasticity module (E) has been determined on 3 types of concrete: a usual reference concrete (a mark one) and 2 high performance concretes (one with Lomar D superplasticizer of foreign source, and the other with FORTERA superplasticizer of Romanian source). The results are presented in table 2. The researches concerning the elasticity module show larger values for the high performance concretes as compared to the usual concrete.

5. RESISTANCE TO AGGRESSIVE ENVIRONMENTS

The experimental researches carried out by the autors team (Buchman et al., 2003) studied the resistance in N[H.sub.4]N[O.sub.3] environment and the penetration of chlorine ions.

The concretes resistances after the chemical attack are given in table 3.

For the chlorine ions penetration, the concretes samples (CC and HPC) have been kept 90 days in NaCl solution of 2.5 g/l concentration. The penetration depth of the chlorine ions determining has been carried out according to SR 13380(1997).

6. CONCLUSION

Following the experimental studies and researches that have been made so far, there can be drawn out the conclusions given below:

* The high performance concretes preparing and placement can be carried out by using the same equipment and procedures employed for the usual concrete.

* The high performance concretes have, besides the compression strength, other improved characteristics, as well, namely: the elasticity module, the contraction, the tranquil flow, the frost-thawing proof, the impermeability, the resistance to aggressive chemical agents.

* The own experimental researches have led to the obtaining of some high performance concretes with a compression strength ranging within 63.5 and 84.9 N/[mm.sup.2], one of the compositions having been obtained only from indigenous materials.

* The researches concerning the elasticity modules show larger values for these modules for the high performance concretes as compared to those for the usual concrete.

* The BIP resistance to the attack of N[H.sub.4]N[O.sub.3] (the ammonium ions) is significantly increased. After 90 days of keeping in concentrated solution of N[H.sub.4]N[O.sub.3] (62.2%), the BIP compression strength lowered with only 7.8%, while the compression strength of the usual concrete (mark) lowered with 25.6%.

* The penetration depth of the chlorine ions is much smaller at BIP: the penetration depth has been of 0--1 mm at BIP and 3-5 mm at BO.

7. REFERENCES

Buchman I., Bob C., Jebelean E., Badea C. (2001) High performance concretes. Documentary study and experimental researches concerning high performance concretes obtaining. Work synthesis. Grant A, UP Timisoara contract nr.34977/2001, theme 9 code CNCSIS 872, Timisoara, 8 pages

Buchman I., Bob C., Jebelean E., Badea C. (2003) High performance concretes. Determining of the wearing resistance, the frost-thawing proof, and of the resistance in an aggressive environment. The work synthesis. Grant A, UP Timisoara contract nr.33501/2002, theme 7, code CNCSIS 504, Timisoara, 8 pages

De Larrard F., Malier Y. (1990) Proprietes constructives des betons a tres hautes performances--de la micro a la macrostructure. v.Malier (1990), 107-138

Tab. 1. Concretes ratios and some of their characteristics

 Dosage, (kg/[m.sup.3])

Series C W Ag SUF SP W/L

1 CC 580 235 1585 -- -- 0,40
 HPC 587 181 1607 58,7 6,4 0,28
2 CC 588 223 1609 -- -- 0,38
 HPC 588 179 1608 58,8 6,4 0,28
3 CC 566 232 1602 -- -- 0,41
 HPC 586 188 1660 58,6 6,4 0,29
4 CC 639 227 1509 -- -- 0,35
 HPC 642 203 1517 64,2 7,2 0,29

 [[rho].sub.a] [R.sub.c] [R.sub.c.sup.HPC]/
Series Kg/[m.sup.3] N/[mm.sup.2] [R.sub.c.sup.CC]

1 CC 2382 55,2 1,41
 HPC 2419 77,6
2 CC 2335 56,3 1,51
 HPC 2356 84,9
3 CC 2279 37,1 1,71
 HPC 2370 63,5
4 CC 2326 48,5 1,57
 HPC 2385 76

Obs.: 1). HPC--high performance concretes; CC--conventional concretes
(blank test); 2). C, W, Ag, SUF, SP, L--cement, water, aggregates,
silica fume, superplascizer and binding agent (cement + silica fume).

Tab. 2. The elasticity module

 Compression strength
 (N/[mm.sup.2])
The concrete Age
type (days) Cubic Prismatic

CC 28 55,2 36,6
HPC with LOMAR 28 77,6 67,6
HPC with FORTERA 28 73,2 66,5

 The
The concrete elasticity [E.sup.HPC]
type module [E.sup.CC]

CC 30 690 --
HPC with LOMAR 33 230 1,09
HPC with FORTERA 32 430 1,06

Tab. 3. Concretes resistance before and after the attack with
N[H.sub.4]N[O.sub.3]

The The initial
concrete The solution- [R.sub.c]
type concentration, (%) (N/[mm.sub.2])

BO 62.2 48.5
BIP 76.0

The The [R.sub.c]
concrete after the attack [DELTA]
type (N/[mm.sup.2]) [R.sub.c] (%)

BO 36.1 25.6
BIP 70.1 7.8

The results thus obtained are presented in table 4.

Tab. 4. Penetration depth of the CL ions

Concrete type Penetration depth, mm

Usual concrete (mark) 3-5

High performance 0-1
concrete