Technical and economical aspects of the special industrial concrete from Romania.

Buchman, Iosif ; Ignaton, Elemer

1. INTRODUCTION

The special industrial concrete SIC (Buchman, 1999) belongs to the family of ultra high performances concretes (strength to very high compression (200-800 N/[mm.sup.2]), tightness to water and gases, placement without passive reinforcements, resistance to aggressive chemical agents, etc., namely: reactive powder concrete RPC (Richard & Cheyrezy, 1995), compacted concrete with steel fibers (CCSF), the concrete from steel fibers felting injected with paste CSFFIP. The special industrial concrete can be used both for prefabricated parts, and for monolith elements. This work presents the technical-economic aspects of this concrete.

2. TECHNICAL ASPECTS OF THE SPECIAL INDUSTRIAL CONCRETE

2.1 The materials and compositions used for this concrete manufacture

The special industrial concrete has been obtained by using the following indigenous materials: cement of superior quality, silica fume, aggregates of 0...7 mm dimension, superplasticizer, water, and steel fibers. The materials sources and characteristics were as follows:

Cement: from CARPATCEMENT, Deva, of CEM I 42.5 R type;

Silica fume: from SC: FEROM SA., Tulcea, with the oxide composition as presented in table 1.

Sand: from Sag--Timiseni gravel pit, the maximum grains dimension being of 7.1 mm.

Superplasticizer: from Sika--Timisoara Subsidiary, with the commercial dimension of FM 40.

Steel fibers: from the Belgian firm BEKAERT with the following characteristics:

--carbon content: 0.69-0.76 %;

--minimum tensile strength: 2000 N/[mm.sup.2];

--length-diameter ratio: 13 mm/0.16 mm = 81;

--steel fiber: steel dead-drawn wire.

Water: from the public water supply network.

The special industrial concrete has been produced by using two compositions, each of them having two series of samples: a witness sample without steel fibers, and a sample with steel fibers. The compositions are presented in tables 2 and 3.

2.2 The technology for concrete obtaining

The special industrial concrete has been produced by using the wet mixer with standard arm for the establishing of the cement class.

The manufacture technology of the witness concrete without fibers has been as follows:

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

--the mechanical mixing of the cement with the silica for 1 minute with reduced speed;

--the adding of water and superplasticizer solution, and the mixing with reduced speed for 1 minute, and then the mixing with high speed for 1 minute;

--the adding of the 0/3.15 mm aggregate, and the mixing with reduced speed for 1 more minute; then the adding of the 3.15/7.1 mm aggregate, followed by the mixing with high speed 1 more minute.

The special industrial concrete with steel fibers manufacture was first preceded by the preparing of the concrete without fibers according to the technology described above, followed by the manual introduction of the steel fibers, as shown below:

--the adding of 54 of the fibers quantity, followed by the mixing with reduced speed for 30 seconds;

--the adding of the other half of the fibers quantity, followed by another mixing with reduced speed for 30 s.

Out of each composition, there have been poured 2 series of 3 prismatic samples of 40x40x160 mm each series, which have been kept after shuttering removal (1 day after casting) under laboratory conditions (20 [C.sup.0], relative humidity under 60 %) until the age of 28 days.

2.3 Experimental results

The samples have been tested at the age of 28 days according to the cements class testing methodology. The prisms have been subjected to bending, and the resulted prisms halves have been used for the compression test.

Following the tests, there have been obtained the values of the mechanical strengths presented in table 4.

As shown in the tables, there has been obtained compression strength of 200 N/[mm.sup.2] and a tensile strength from bending of up to 45.9 N/[mm.sup.2].

The steel fibers have determined the increase of the compression strength of up to 1.5 times, and the increase of tensile strength from bending of up to 2.3 times. The best results have been obtained with composition 1. The presentation so far shows an important increase of the technical efficiency (the compression strength and the tensile strength) of the special industrial concrete, as compared to the witness concrete.

3. ECONOMICAL ASPECTS OF THE SPECIAL INDUSTRIAL CONCRETE

The cost of the special industrial concrete determining, in compliance with Norm C, has been carried out through price analyses of the concrete compositions, the results being presented in table 5.

Table 6 presents the analytical cost estimate for composition 1. For composition 2, the cost estimate 2683,94 lei/[m.sup.3].

Making the ratio strength/total cost SIC, there results 0.076, and for the concrete of 50 N/[mm.sup.2], there results 0.095. Analysing these ratios [(0.095 - 0.076)/0.095 = 0.2], there results that SIC concrete is cheaper with 20%.

4. CONCLUSION

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

1. The laboratory tests enabled the obtaining of the special industrial concrete in Romania, as well, a concrete with a compression strength of 200 N/[mm.sup.2], and a tensile strength of up to 45,9 N/[mm.sup.2], the materials used for it being mostly indigenous ones.

2. The preparing technology used in laboratory can also be adopted in production, if there are used wet mixers with forced mixing (with arms). The steel fibers incorporation can be easily made due to the concrete thinning by the FM 40 superplasticizer additive. The mixing length, i.e. the vibration length, can be reduced by using a larger percentage of superplasticizer.

3. The mechanical strengths, as well as the ductility are highly improved by the presence of the steel fibers, which also enable the obtaining of some elements without passive reinforcements.

4. The special industrial concrete does not require thermal treatment, and thus it becomes a serious competitor of the concrete with reactive powders from BRP 200 range, and consequently, the special industrial concrete can be used at the manufacture of monolith elements.

5. As compared to the 50 N/[mm.sup.2] concrete, the special industrial concrete is cheaper with 20%, and its exceptional technical characteristics recommend it to be used in Romania.

As a conclusion, we can assert that the special industrial concrete can also be manufactured in Romania, and its exceptional technical characteristics recommend it to be used both at prefabricated parts, and at monolith elements.

5. REFERENCES

Buchman, I. (1999). Betoane de ultra inalte performante, Ultra High Performance Concrete, Editura Orizonturi Universitare, ISBN 973-9400-55-8, 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

Tab. 1. Composition of silica fume

% Si[O.sub.2] [Fe.sub.2][O.sub.3] % [Al.sub.2][O.sub.33]

91,07 1,83 4,63

% Si[O.sub.2] % CaO % MgO % MnO

91,07 0,50 0,50 1,04

Tab. 2. Special industrial concrete--composition 1

Materials Mixture ratios
 SIC without SIC with
 fibers fibers

Cement CEM I 42,5 R, kg/[m.sub.3] 1030 1027

Silica fume (SF), kg/[m.sub.3] 154 (15 % of the 154 (15 % of
 cement) the cement)

River siliceous 0/3,15 mm 544 543
aggregate, 3,15/7,1 mm 443 443
kg/[m.sup.3]

Steel fibers (l=13 mm; d = 16 mm) -- 224 (2,85 %
kg/[m.sub.3] in volume)

Superplasticizer Dry 10,5 (0,9% of 10,5 (0,9%
FM 40 substance the of the
(solution 30 cement+SF) cement+SF)
%), kg/[m.sup.3] Water 24,5 24,5

Mixing water, 190 189
kg/[m.sup.3]

Total water 214,5 213,5
[W.sub.t], kg/
[m.sup.3]

[W.sub.t]/C 0,21 0,21

[W.sub.t]/ 0,18 0,18
(C + UFS)

Total, kg 2396 2615

Tab. 3. Special industrial concrete--composition 2

Materials Mixture ratios

 SIC without SIC with
 fibers fibers

Cement CEM I 42,5 R, kg/[m.sup.3] 1083 1053

Silica fume (SF), kg/[m.sup.3] 162(15 % of 158 (15 % of
 the cement) the cement)

River siliceous 0/3,15 mm 572 556,4
aggregate, kg/ 3,15/7,1 mm 465,4 454,1
[m.sup.3]

Steel fibers (l=13 mm; d= 16 mm) -- 229,8 (2,9 %
kg/[m.sup.3] in volume)

Superplasticizer Dry 11,1 (0,9% of 10,9 (0,9%
FM 40 substance the of the
(solution 30 cement+SF) cement+SF)
%), kg/[m.sup.3] Water 26,0 25,3

Mixing water, kg/[m.sup.3] 173,5 168,5

Total water [W.sub.t], kg/[m.sup.3] 199,5 193,8

[W.sub.t]/C 0,18 0,18

[W.sub.t]/(C + UFS) 0,16 0,16

Total, kg 2493 2656

Tab. 4. Mechanical strength of the experimental concretes

Composition Mechanical strengths, N/[mm.sup.2]

 Compression Tensile strength
 strength from bending

 [R.sub.c]/ [R.sub.i]/
 [R.sub.c] [R.sub.cm] [R.sub.i] [R.sub.im]

 1 Without fibres 134,2 1.5 19,8 2,3
 With fibres 200,2 45,9
 2 Without fibres 129,2 1.5 17,4 2,2
 With fibres 199,7 ,37,7

Tab. 5. Cost of special concrete

Concrete cost Composition Composition Concrete of
 1 2 50 N/[mm.sup.2]
 (lei/[m.sup.3)] (lei/[m.sup.3]) (lei/[m.sup.3])

Materials 1879,25 l 1928,27 526,48
Manual labour 0,68 0,68 0,68
Equipment 4,49 4,49 4,49

Tab. 6. Analytical cost estimate

SYIMBOL QUANTITY MATERIALS TOTAL
U.M. ARTICLE MANUAL VALUES
ARTICLE NAME LABOUR TOTAL
 EQUIPMENT WEIGHT
 TRANSP. CF (T)
 GR.MAT./UM

NL--CZ011 1 1879,25 1879,25
mc 0,68 0,68
Special industrial 4,49 4,49
concrete preparing 1884,42
 0,00 0,00
 2,31600 2,31600

--Social insurance 0,68 x 0,19750= 0,13

--Unemployment 0,68 x 0,02500= 0,02
wages

--Health fund 0,68 x 0,07000= 0,05

--Accidents and 0,68 x 0,01000= 0,01
professional
illnesses

--Other expenses 0,68 x 0,01000= 0,01

--Indirect 1884,42 0,08000= 150,76
expenses

--Profit 2035,18 0,08000= 162,81

TOTAL 2197,99

--VAT 2197,99 0,19000= 417,62

TOTAL with 2625,61
VAT