The chemical resistance of an ultra-high performance concrete.

Buchman, Iosif ; Ignaton, Elemer

Abstract: The paper presents the laboratory researches that have been carried out on special industrial concrete (SIC) for the checking of its chemical resistance. The concrete samples, with a compression strength of about 200 N/[mm.sup.2], have been kept for 600 days in a solution of ammonium nitrate with 62.2% concentration. Although the ammonium nitrate solution has been very concentrated, and the attack period has been very long, the special industrial concrete samples have lost only 10% of the compression strength

Key words: chemical resistance, ammonium nitrate, attack period, compression strength, silica fume

1. INTRODUCTION

The objectives most often attacked regarding the ammonium ions are the units of production, transport, storage, handling, and use of the chemical compounds with N[H.sub.4.sup.+]; the residual water treatment stations or the buildings which are in the neighbourhood of these units.

The damage may affect the following elements:

--buildings foundations (store-houses, production shops etc.);

--concrete platforms (for handling, loading-unloading);

--supporting pillars;

--the basin walls of residual water treatment stations; concrete sewers (for rain water flow or for residual industrial solutions discharge);

--approaches (roads, bridges);

--dams, etc.

The corrosion brought about by the ammonium salt on concrete may lead to the generation of calcium salts soluble in water and ammonia. These compounds are easily removed causing the increase of concrete porosity, bringing about a series of negative consequences, among which the reduction of mechanical strength and of the resistance to subsequent chemical attacks (Buchman & Fagadar, 2003).

The paper synthesizes the authors' researches regarding the ammonium nitrate attack (N[H.sub.4]N[O.sub.3]) on special industrial concrete with a compression strength of about 200 N/[mm.sup.2] (looked upon as ultra-high performance concrete).

The aim was the reduction of the compression strength following the samples keeping, for 600 days, in an ammonium nitrate solution with 62.2% concentration (Buchman & Badea, 2005).

2. EXPERIMENTAL PROGRAMME. RESULTS

There have been obtained and tested 3 types of materials:

--special industrial concrete;

--mark concrete for the special industrial concrete (without steel fibres);

--standard mortar for the cement class.

The compositions of these materials and the characteristics of the components are given in the tables 1, 2, and 3. The cement, the silica, the sand, and the gravel are from Romania, and the sand for the standard mortar from France, the steel fibres from Belgiue, and the superplasticizer are from Germani (Fig. 4).

Concretes preparing has been carried out with a wet mixer with forced mixing. The mixing technology consisted in:

--the cement mixing with silica in the wet mixer tank;

--the introducing of water and superplasticizer and then mixing with reduced speed for 1 minute followed by the mixing with high speed for 1 minute;

--the 0...4 mm sand adding followed by mixing with reduced speed for 1 minute;

--the 4...8 mm gravel adding followed by mixing with high speed for 1 minute;

For the special industrial concrete with steel fibers, there has first been prepared the concrete without steel fibers, according to the above shown technology, and then, the steel fibers have been manually introduced, as follows:

--the addition of 1/2 of the fibers quantity, followed by reduced velocity mixing for 30 seconds;

--the addition of the other 1/2 of the fibers quantity, followed by reduced velocity mixing for 30 seconds.

The standard mortar preparing has followed up the technology provided by the norms in force (EN 196/1).

Out of each composition there have been cast 6 prismatic samples of 40x40x160 mm. Mould compaction has been made through vibration. The samples have been kept, for 28 days, in water at the temperature of 20[degrees]C.

Following hardening and drying, there have been used 3 samples out of each composition to establish the apparent density and the compression strength after 28 days. The other samples have been kept in laboratory conditions (20[degrees]C and about 60% relative humidity) in a solution of ammonium nitrate (N[H.sub.4]N[O.sub.3]) of 62.2% concentration, for 600 days, and then there has been defined the compression strength.

The compression test has been made according to the technology used for the defining of cements class.

The apparent density and the compression strength are presented in table 5 (Buchman & Badea, 2005).

The visual examination of the samples, which have undergone the chemical attack, has not highlighted any sign of their damage. The compression test has led to the results from table 6 (Buchman, 1999).

The results which have been obtained witness a very good behaviour of the special industrial concrete. Although the ammonium nitrate solution was very concentrated and the period of attack was very long, the samples of special industrial concrete have lost only 10% of the compression strength, while the samples of the other materials have lost 13.4 % (the mark without fibres), and even 74.9% of the the initial strength (the standard mortar).

[FIGURE 1 OMITTED]

[FIGURE 2 OMITTED]

3. 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 chemical strength of the special industrial concrete at the attack of ammonium ions is a high one.

* The studied samples have lost only 10% of the compression strength, although they have undergone a very severe chemical attack with ammonium nitrate.

* The special industrial concrete is recommended for small dimensions elements, precompressed or not, resistant to aggressive environments, but suppositions may be advanced of its future use at art works, high buildings, chimneys, cooling towers and other.

* The special industrial concrete has been used in France at the restoring of an atomic station instead of reactive powders concretes (RPC 200), the former having the advantage that they do not require thermal treatment (Richard & Cheyrezy, 1995, Fiche technique, 1998).

4. REFERENCES

Buchman, I. (1999). Ultra-high performance concretes, University Horizons Publishing House, ISBN Timisoara

Buchman, I., Badea, C. & Fagadar, g. (2003). Ultra-high performance concretes, Final report, GRANT, CNCSIS contract, U.P. Timisoara

Buchman, I., Badea, C. (2005). Ultra-high performance concretes, Final report, GRANT, CNCSIS contract, U.P. Timisoara

Richard, P. & Cheyrezy, M. (1995). Les betons de poudres reactives, Annales de l'Institut Technique du Batiment et des Travaux Publics, No.532, Paris

*** Betons Un B 150 coule en place, Fiche technique, Maitre d'ouvrage: EDF, CNEPE Tours, France, 1998.

*** FM 40 superfluidizer, technical sheet no. kind 10955, Heidelberg Bauchemie, Marke Addiment

Tab. 1. The silica fume composition

%Si[O.sub.2] %[Fe.sub.2] %[Al.sub.2] %CaO %MgO %MnO
 [O.sub.3] [O.sub.3]

91.07 1.83 4.63 0.50 0.50 1.04

Tab. 2. The materials composition

 Material

Component Special Mark concrete Standard
 industrial for the mortar
 concrete special
 industrial
 concrete

Cement CEM 1 1053 1053 502
42.5 R, kg/[m.sup.3]

Silica fume 161 161 --
(SUIT), kg/[m.sup.3]

Sand 0 ... 4 mm, 558 558 --
kg/[m.sup.3]

Gravel 4 ... 8 454 454 --
mm, kg/[m.sup.3]

Sand for the -- -- 1506
standard mortar,
kg/[m.sup.3]

Steel fibres, 1 = 230 -- --
13 mm, d = 0.16
mm, kg/[m.sup.3]

Superplasticizer 57.5 57.5 --
FM 40
(solution),
kg/[m.sup.3]

Water, kg/[m.sup.3] 195.5 195.5 251

W/C 0.19 0.19 10.5

W/(C+SUF) 0.16 0.16 --

Tab. 3. The (FM 40) superplasticizer characteristics

Characteristic Technical data

Aspect Liquid

Color Brown

Density 1.05 [+ or -] 0.02 g/[cm.sup.3]
 (la 20[degrees]C)

The basic active polycarboxilateter
substance

Chlorides contents [less than or equal to] 0.1%

Tab. 4. The steel fibers characteristics

Characteristic Technical data

Aspect Circular, smooth, straight section

Carbon content (0.69 ... 0.76)

Tensile minimum strength 2000 N/mm2

Diameter 0.16 mm

Length 13 mm

Source Steel dead-drawn wire

Tab. 5. The apparent density and the compression strength

Material Apparent density, Compression
 kg/[m.sup.3] strength,
 N/[mm.sup.2]

Special industrial 2575 204
concrete

Mark concrete for the
special industrial 2315 141.7
concrete (without
fibres)

Standard mortar 2145 41.1

Tab. 6. Compression strength after 600 days of attack with
N[H.sub.4]N[O.sub.3]

Material Compression Strength
 strength, reduction,
 N/[mm.sup.2] %

Special industrial 183.5 10
concrete

Mark concrete for the 122.7 13.4
SIC (without fibres)

Standard mortar 10.3 74.9