Reactive powders concrete.

Buchman, Iosif ; Ignaton, Elemer

1. INTRODUCTION

Since 1990, in France (Richard, 1995), there is being studied a concrete with special performance called reactive powders concrete (RPC), characterized by an ultra-high resistance to compression, tightness to water and gases, placement without passive reinforcement, and other.

Reactive powders concretes (RPC) are obtained from powders: fine sand, cement, ground quartz, ultrafine silica, having grains which do not exceed 0.6 mm.

They are prepared in conditions similar to those used for the usual concrete, but with a very small quantity of water.

The RPC special performance is obtained by applying four principlies:

--the improvement of the material homogeneity by eliminating large aggregates;

--the increase of compactness through granular mixture optimization and, if possible, through pressing before and during setting;

--the improvement of the microstructure through thermal treatment;

--the increase of ductility through steel wire fibres adding. There have been identified two types of reactive powders concretes:

--RPC 200, which are obtained through thermal treatment at 90 [degrees]C;

--RPC 800, which are obtained through pressing and a thermal treatment at 250 [degrees]C applied after setting.

2. THE EXPERIMENTAL PROGRAMME

The experimental programme has been carried out in France, at The Superior Normal School from Cachan, in The Building Materials Laboratory, led by associate professor Gerard Bernier, Ph.D.

The programme included the obtaining and testing of two concretes made up of reactive powders concretes, without and with steel wire fibres, of RPC 200 type.

Each concrete type has been used to obtain cylindrical specimens of 70 mm diameter and 140 mm height, and prismatic specimens of 40x40x160 mm.

On the hardened specimens, there have been established the following: the apparent density, the compression strength (on cylinders), stretching strength from bending (on prisms), the [sigma]

--[sigma] diagram at compression, the elasticity module at compression (on cylinders).

3. TECHNICAL ASPECTS OF THE SPECIAL INDUSTRIAL CONCRETE

3.1 The materials and compositions used for this concrete manufacture

Reactive powders concrete has been obtained in L'ENS Cachan Laboratory (France), having in its composition the following foreign materials:

Cement: of CPA 55 HTS type, with high content of silicates;

Sand: siliceous of 0.25 mm grains dimension;

Silica fume: produced by SEPR firm (*** 1996);

Superplasticizer: of MAPEFLUID X 404 type (*** 1996);

Steel wire fibres: produced by BEKAERT firm (*** 1997),

having the following characteristics:--carbon content: 0.690.76%;

--minimum stretching strength: 2000 N/[mm.sup.2]; length/dimeter

ratio: 13/0.16=81;--source: dead-drawn steel wire. The compositions of the tested reactive powders concretes have been established on the basis of the data that exist in the literature (Dugat et al. 1995), and they are presented in table 1.

3.2 Concretes obtaining

The RPC have been manufactured by using the standard paddle mixer for the establishing of the cement class, the paddle being modified in case of steel wire fibres RPC to prevent fibres aglomeration.

The sequence of the mixing operations at RPC without fibres has been as follows:

--the manual mixing of the materials in the wet mixer tank granulation (cement, sand, SUF);

--wet mixer operation and low speed mixing of the granular materials for 10 seconds, at the same time with the introduction of water in which there has been previously mixed the superplasticizer solution;

--the mixing is continued with middle speed for 10 seconds, and then with high speed for 30 seconds.

For the RPC with steel wire fibres, there has been prepared first the RPC without fibres by observing the sequence of the mixing operations presented above, and then there have been manually introduced the fibres by means of a screen, followed by low speed mixing for 15 seconds, middle speed mixing for 15 seconds, and high speed mixing for 30 seconds. The concretes hardening conditions (thermal treatment) are presented in table 2.

3.3 The apparent density, the compression strength, the stretching strength from bending

The apparent density, the compression strength, and the stretching strength from bending have been carried out according to the standards in force.

The average values of the characteristics that have been obtained for the hardened RPC are given in table 3 and table 4. The analysis of the results from table 3 shows that, for reactive powders concrete with steel wire fibres, there have been obtained the following results: for compression strength 186.12 N/[mm.sup.2], for stretching strength from bending 35.67 N/[mm.sup.2], and an apparent density of 2366 kg/[m.sup.3]. The strengths thus obtained comply with the values highlighted by the literature for the RPC 200 type, which are of 170--230 N/[mm.sup.2] for the compression strength, and of 30--60 N/[mm.sup.2] for the stretching strength. The steel wire fibres have led to the increase of the compression strength with 17.65% and of the stretching strength from bending with 106.50%.

3.4 The [sigma]--[epsilon] diagram and the elasticity module at centric compression

The [sigma]-[epsilon] diagrams on the cylindrical samples tested at compression have been established by using an automatic logging. The [sigma]-[epsilon] curve for the RPC without steel wire fibres is presented in fig. 1, and that for the RPC with steel wire fibres is presented in fig.2.

[FIGURE 1 OMITTED]

[FIGURE 2 OMITTED]

Comparing these curves with those obtained by other researchers (Dugat et al. 1995), there can be observed a good agreement regarding both quality and quantity. The use of steel wire fibres has contributed to the increase of the breaking stress and ultimate strain. The j-s diagrams have enabled the calculation of the elasticity modules. Their average values are given in table 4.

4. CONCLUSION

The analysis of the results obtained for the reactive powders concrete that has been achieved leads to the following conclusions:

1. the strengths, at the compression of 186.12 N/[mm.sup.2] and at the stretching of 35.67 N/[mm.sup.2], comply with the values highlighted by the literature, which for the BPR 200 type are as follows: 170--230 N/[mm.sup.2] for the compression strength, and 30--60 N/[mm.sup.2] for the stretching strength;

2. the comparison of the obtained [sigma]--[epsilon] curves with those reported by other researchers indicates a good agreement regarding both quality and quantity;

3. the values for the elasticity modules are near to those from the literature;

4. the reactive powders concretes with steel wire fibres are adequate for structures without passive reinforcements, bent elements, lattice structures, and by their use at precompressed elements there can be obtained much more lighter structures than those achieved from the usual concrete.

5. REFERENCES

Dugat J., Roux N., Bernier G., Etude experimental de la deformation sous contrainte et du comportement a la ruptura du beton de poudres reactives, Annales de L'Institut Technique du Batiment et des Travaux Publics, No. 532, Paris, Mars-Avril, 1995

Richard P., Cheyrezy M., Les betons de poudres reactives, Annales de L'Institut Technique du Batiment et des Travaux Publics, No. 532, Paris, Mars-Avril, 1995

*** Silice thermique, Specification technique SEPR SP ST 01, France, Fevrier, 1996

*** Superplastifiant de conception nouvelle pour beton, Prospect MAPEFLUID X 404, No. 724/12.96

*** Straigth steel wire fibres, Specification BEKAERT AS-10-03, France, Mars, 1997

Tab. 1. Reactive powders concretes compoziton

 RPC 200 RPC 200
Component materials (without fibres) (with fibres)

Cement CPA 55 HTS, 950 950
kg/[m.sup.3]

Silica fume (SUF), 237 237
kg/[m.sup.3] (25% of the (25% of the
 cement mass) cement mass)

Siliceous sand with 997 997
[d.sub.med] = 0,25
mm, kg/[m.sup.3]

Steel wire fibres -- 146
with d = 0,16 mm (1,86% in
si l = 13 mm, volume)
kg/[m.sup.3]

Superplasticizer 17 17
MAPEFLUID X 404 (1,43% din (1,43% din
(dry substance), cement+SUF) cement+SUF)
kg/[m.sup.3]

Water, kg/[m.sup.3] 180 180

W/(C + SUF) 0,15 0,15

Tab. 2. The RPC hardening conditions

 In moulds
 covered with In water
Preserving polyethyle up to
conditions ne foils 20 [degrees]C

Durata 2 days 7 days

 In water and In drying
 in drying chamber
 chamber at at 90 [dgrees]C
 90 [degrees]C and and 50%
Preserving 80% relative relative
conditions humidity humidity

Durata 4 days 2 days

Tab. 3. The RPC characteristics in hardened state

 Stretching
 Compression strength
 Apparent strength from
Concrete density, [f.sub.c], bending ft, [f.sub.c]/
type kg/[m.sup.3] N/[mm.sup.2] N/[mm.sup.2] [f.sub.t]

RPC 2227 158,20 17,27 9,16
without
fibres

RPC 2366 186,12 35,67 5,22
with
fibres

Tab. 4. The elasticity modules for RPC

 Compression The elasticity
 strength, module,
Concrete type N/[mm.sup.2] N/[mm.sup.2]

RPC 158,20 51 400
without fibres

RPC 186,12 55 610
with fibres