AU3253500A - Reactive powder concrete compositions - Google Patents

Description

-1-

AUSTRALIA

PATENTS ACT 1990 COMPLETE

SPECIFICATION

FOR A STANDARD

PATENT

ORIGINAL

Name of Applicant: MBT Holding AG Actual Inventor: Robert Alfred Marks and Kenneth William Fletcher Address for Service: BALDWIN SHELSTON WATERS MARGARET STREET SYDNEY NSW 2000 Invention Title: 'REACTIVE POWDER CONCRETE

COMPOSITIONS'

Details of Associated Provisional Application Nos. PQ0182 dated 05 May 1999 and PQ0799 dated 4 June 1999 The following statement is a full description of this invention, including the best method of performing it known to me/us:- File: 28019AUP00 TECHNICAL

FIELD

The present invention relates to reactive powder concrete compositions and in particular to such compositions which incorporate novel superplasticizers.

BACKGROUND

ART

Reactive Powder Concrete (RPC) is an ultra-high strength, low porosity material produced from powder composition cementitious materials. The material contains coarse aggregate and the fine aggregates are replaced by very fine sand with particle size in the range 150-600im. The entire material is therefore composed of very fine particles and for this reason it is called "Powder Concrete". The material also contains very large quantities of reactive cementitious material and the term "Reactive" has been added.

RPC has demonstrated very high compressive strengths in the range of 200-800MPa, flexural strengths of 25-50MPa and excellent durability. RPC usually incorporates large quantities of steel or synthetic fibres and has enhanced ductility and high temperature •performance, enabling structural members to be built entirely from this material to resist *15 all but direct primary tensile stresses A thorough understanding of High Performance Concrete and its component *materials led to the development of RPC. Traditional concrete is a heterogeneous material comprising aggregate in a cementitious continuous phase and the large particle size difference in the aggregate leads to a weak transition zone between the aggregate and the cement paste In RPC the homogeneity of the mix is improved by the relatively uniform size distribution of the fine particles. The microstructure in RPC is improved by the reduction in Ca(OH) 2 primarily due to the use of a supplementary cementitious material in the binder. By applying a heat treatment after setting, a pozzolanic reaction is activated and RPC is often cured at a high temperature such as 90C When ground quartz is added to the mix, even high curing temperatures, from 250'C to 400 0 C may be used. Samples cured at 350-400 0 C, without pressure have given compressive strengths of 488-524 MPa. With the application of a pressure technique, even higher strengths of up to 673MPa have been reported By increasing the compacted density of the dry solids the amount of water required for fluidising the mix can be reduced Optimisation of grain size and application of pressure can increase the compacted density of the dry solids. Usually ductility of RPC is achieved by the addition of large quantities of fibres. At the dosages used, usually, the material flexural strengths are also increased Currently, RPC is substantially more expensive than conventional concrete.

With such high ultimate strength and improved characteristics, however, it is often compared with steel sections and prestressed concrete beams. In some cases, due to the reduced thickness of member sizes required and speed of manufacture, RPC has provided more economic solutions when compared with steel and prestressed concrete.

Some actual practical applications include, cycle-pedestrian bridge in Canada, hazardous waste containers, precast floor beams, pipes, frames, cladding panels and tilt-up panels.

10 With the modification of the mixes with the view to reducing the binder content and faster production techniques, currently investigated, RPC may have more practical Sapplications.

The main advantages ofRPC include, significant weight reduction, superior ductility and hence greater structural reliability, enhanced abrasion resistance, reduced porosity and hence better durability, possible new structural shapes due to the absence of conventional reinforcement and the self-heating potential under cracking conditions due to a significant amount of unhydrated cementitious component in the finished product.

The areas which need attention may include working time available, autogenous •20 shrinkage and high temperature performance. These areas are currently being investigated. Scanning Electron Microscopic (SEM) studies have commenced to examine the morphology of hydration products under different curing conditions at early ages and to evaluate the long-term micro-structure of RPC.

While the main objectives in developing RPC were to increase strength and ductility, it was also necessary to maintain mixing and casting procedures as close as possible to existing practice. As RPC has a very low water/binder ratio (typically around 0.15), high dosages of superplasticizer are required for it to be readily mixed and placed like conventional concrete There is thus a need for improved superplasticiser-containing RPC compositions with advantageous properties. The object of the present invention is to ameliorate at least some of the drawbacks of the prior art RPC compositions or to provide a useful alternative.

SUMMARY OF THE INVENTION The present invention makes use of a new generation of superplasticizers which, although previously known, have never been used in the preparation of Reactive Powder Concrete (RPC), to provide superior properties and characteristics. The superplasticizers which can advantageously be used in the present invention are of the polycarboxylic ether polymer-type. The detailed properties and characteristics of the superplasticizers used in the present invention are set out in Australian Patent Application No. 60516/96, which is incorporated in its entirety herein by reference.

According to a first aspect there is provided a reactive powder concrete 10 composition including a polycarboxylic ether polymer-type superplasticizer, wherein the superplasticizer has a weight average molecular weight (MW) in the range of 10,000 to 500,000 determined by gel permeation chromatography (GPC) with polyethylene glycol as standard, the difference between the peak top molecular weight of the superplasticizer and the weight-average molecular weight being from 0 to 8,000.

15 Preferably the superplasticizer used in the present invention is additionally characterised by being obtained by the co-polymerisation of: from 5-98% by weight of an (alkoxy)polyalkylene glycol mono(meth)acrylic ester type monomer represented by the general formula 1:

H

2

C-R

3 (1) wherein R' stands for hydrogen atom or a methyl group, R20 stands for one species or a mixture of two or more species of oxyalkylene group of 2 to 4 carbon atoms, providing two or more species of the mixture may be added either in the form of a block or in a random form, R 3 stands for a hydrogen atom or an alkyl group of 1 to 5 carbon atoms, and m is a value indicating the average additional mol number of oxyalkylenegroups which is an integer in the range of 1 to 100, (ii) 2 to 95% by weight of a (meth)acrylic acid type monomer represented by the general formula 2: H2- C- R 4

COOM

wherein R 4 stands for a hydrogen atom or a methyl group and M' stands for a hydrogen atom, a monovalent metal atom, a divalent metal atom, an ammonium group, or an organic amine group, and (iii) 0 to 50% by weight of other monomer copolymerizable with said monomers, provided that the total amount of (ii) and (iii) is 100% by weight.

Preferably the superplasticizer is present in the amount of from about 20 kg/m 3 to about 70kg/m 3 More preferably the amount is from about 30kg/m 3 to about 60kg/m 3 and even more preferred is an amount of about 30kg/m 3 According to a second aspect there is provided a paste or a structure formed from 10 a reactive powder concrete composition according to a first aspect.

Preferably the RPC composition has a water/binder ratio of from about 0.11 to about 0.14.

S' According to a third aspect there is provided a process for preparing a reactive powder concrete composition including intimately mixing reactive powder concrete components and a polycarboxylic ether polymer-type superplasticizer.

According to a fourth aspect there is provided a process for preparing a paste or a structure according to the fourth aspect including combining a composition according to ~the first aspect with water to obtain a homogeneous mixture.

Preferably the RPC prepared from the RPC composition is cured by high heat S 20 and even more preferred is high temperature water curing such as steam curing.

As used in the context of the present invention the term "composition" is intended to also include within its meaning mixes or mixtures of different components and may include dry mixtures or those including water or other fluids.

BRIEF DESCRIPTION OF THE FIGURES Figure 1: Flow characteristics of RPC at different mixing temperatures Figure 2: Cube strength development of RPC (Mix 1) Figure 3: Comparison of cube and cylinder strength (75mm size cubes and diameter cylinders) Figure 4: Load-deflection characteristics of prisms (cross-section: 50x50mm; span: 300mm) Figure 5: Testing of prototype beam sections Figure 6: Residual load-deflection curves of prisms (50x50x600mm) subjected to 500 0

C

DESCRIPTION OF THE PREFERRED

EMBODIMENTS

The present invention is based on the observation that certain superplasticizers can be effectively used in RPC compositions to provide superior properties, for example to minimise porosity, reduce binder content and achieve higher strengths with adequate ductility using readily available ingredients. Different types of cement, and three •different types of fibres were investigated. The cements used included Type GP, and two micro-cements with fineness of 650m2/kg and 900m 2 /kg. Fibres used were straight 10 steel, crimped polypropylene and PAN based carbon (see Experimental section). The 0. influence of grading of fine aggregate was investigated by assessing the suitability of four different types of sand. The curing of RPC was identified as critical and therefore the effect of different curing regimes, particularly, high temperature curing was investigated. The age at which high temperature curing commenced was considered an important factor influencing strength development. Details of the curing regimes adopted are given in Table 1.

Some high temperature tests were carried out in a furnace, heating the specimens up to 1000°C, to assess the fire resistance and residual strength characteristics of the material.

Table 1. Curing Regimes Used in the Experimental Investigation Curing Regime Description Condition 1 Demoulded after 24 hours and cured at 23C in water for up to 3 or 7 days Condition 2 Demoulded after 24 hours, cured at 90/95°C hot water/steam up to 2 or 7 days and then stored in water at 23 0 C until testing Condition 3 Demoulded after 3 hours and cured at 23°C in water for 1, 3 or 7 days Condition 4 Demoulded after 3 hours, cured at 90/95 0 C hot water/steam for 1 or 7 days and then stored in water at 23 0 C until testing Condition 5 Demoulded after 21/24 hours and cured at 80°C in hot water up to 3 or 7 days Condition 6 Demoulded after 21/24 hours, cured at 160 0 C autoclaving for 6 hours and then stored in water at 23°C until testing Condition 7 Demoulded after 21/24 hours, cured at 225°C autoclaving for 4 hours and then stored in water at 23 C until testing The present invention will now be described in more detail with reference to specific embodiments, by way of example only.

EXPERIMENTAL

Example 1: Materials Cement Most of the investigation was carried out using Type GP cement. A limited number of specimens made with two micro-cements with specific surface areas 650m 2 /kg and 900m 2 /kg were also investigated.

Silica Fume 10 The silica fume used was an Australian silica fume with the characteristics given in Table 2. In some mixes precipitated silica was used instead ofundensified silica fume.

Table 2. Physical Properties of Cement and Silica Fume Used *o 9 9* Physical Type GP Micro Micro Undensified Properties (Type A) Cement 1 Cement 2 Silica fume Cement Specific Gravity 3.15 2.20 Fineness (Surface 360 625-675 875-950 19,000 2 Area)m /kg Compressive 41 45-52 strength at 28 days (MPa) Aggregates For most mixes Sydney sand with particle sizes between 100 to 400tm was used.

This is similar to the sand recommended by Richard and Cheyrezy for RPC production. They used a sand with particles sizes between 150-400|tm. In the present investigation a sand with a similar particle size distribution was used to produce the specimens. In some mixes a ground silica flour with particle sizes less than 4|tm was used to replace part of cement.

8 Superplasticizer In the initial investigations, a beta-naphthalene sulphonate-formaldehyde condensate-based superplasticizer was used. Water/binder ratios of 0.14 could be achieved with this superplasticizer but with a considerably long mixing time. The use of the new generation modified polycarboxylic ether polymer superplasticizer led to easier production of RPC compositions of the present invention and w/b ratios of 0.11-0.14 can be consistently achieved. The superplasticizers most suitable for use in the present invention are generally described in Australian Patent Application No. 60516/96, incorporated herein in its entirety by reference. Briefly, the polycarboxylic ether 10 polymer-type superplasticizers have a weight-average molecular weight (MW) in the range of 10,000 to 500,000, determined by gel permeation chromatography (GPC) with polyethylene glycol as standard. For the purpose of exemplifying the present invention the superplasticizer used was FC 900 (MW 25,000-33,000, obtainable from Nippon Shokubai, Japan).

15 Steel Fibres An 18mm long straight steel fibre with ends modified, having a cross-section of 0.6 x 0.4mm, was used for the steel fibre reinforced mixes.

Polypropylene Fibres A crimped, new type of polypropylene fibre with an effective length of 20 was used.

Carbon Fibres A PAN (Polyacrylonitrile) based fibre with a modulus of238GPa was used. The length of the fibres was either 6mm or 12mm having a diameter of 7pm.

Example 2: Mix Proportions Several mixes with different compositions, as shown in Table 3, were investigated in order to obtain an optimum mix. Most of the results reported here are obtained on Mix 1.

9 Table 3. Details of Mix Proportions of RPC Materials Mix Proportions (kg/m 3 1 2 3 4 5 6 CementType GP 955 955 955 Micro-cement 1 875 660 (650m 2 /kg) Micro-cement 2 660 (900m 2 /kg) 6 6 0 Silica Fume 240 240 240 220 220 220 Water 170 170 170 370 290 290 Water/binder 0.14 0.14 0.14 0.33 0.33 0.33

I

ine Aggregate 1100 1100 1100 1010 1305 1305 Superplasticizer 30 30 30 60 60 (litres) S: teel Fibres 190 175 175 175 Polypropylene Fibres 26 S (kg) Carbon (kg) 12 Example 3: Preparation and Curing of Specimens The mixing sequence of Mix 1 is described below: A Hobart or similar mortar mixer was used for the bulk of the investigation. For large scale casting a pan mixer was used. In order to standardise the mixing procedure with the Hobart mixer, among the Sthree laboratories participating in this investigation in Sydney, the following mixing :sequence was adopted. First, water and superplasticizer were mixed together and introduced into the mixing bowl. Saturated surface dry (SSD) sand was then introduced followed by the silica fume. The mixing of the above materials was carried out within 2 minutes. The cement was then added and the mixing continued for a further 5 minutes.

During this 5 minute period, the steel fibres were added.

The flow test was carried out immediately after mixing, and thereafter at minute intervals. After the initial flow test, the batch was left in the bowl of the Hobart mixer and covered to minimise evaporation. Just prior to the 30 min. test period, the bowl was uncovered and the material given a 15 seconds re-mixing before checking the flow. For flow tests at different temperatures, a control plain mix (identical to Mix 1 but without fibres), a mix with steel fibres (Mix 1) and a mix with polypropylene fibres (Mix 2) were used.

Cubes (50 mm size) were cast for the compression test, from the different mixes.

It was decided to use cubes due to the difficulties in capping cylinders of such a high strength material. The smaller size for cubes was chosen for development purposes of the mixes and due to the smaller size particles in RPC. Load capacities of testing machines was also a consideration. For flexural strength determination, 50x50x600mm, long prisms were cast. However, limited number of large cubes 1 00mm size) and cylinders (75mm diameter) were also cast and the results compared. Special beam moulds were used to cast the 600mm long prototype beams.

Different curing conditions were used and the main curing conditions are shown in Table 1.

Example 4: Properties and characteristics of RPC mixes Flow Characteristics and Plastic State Properties 10 The flow of the Control Mix (without fibres) immediately after mixing and flow S" retention characteristics are presented in Fig. 1. Initially, the mix had a flow of 70%. A few minutes after mixing, the control RPC mix appeared to stiffen due to the high thixotropy induced by the low water/binder ratio and high silica fume content. The material, however, showed a significant flow once agitated or vibrated as seen by the extended flow retention times. Within the temperature range of 13-33°C, good flow characteristics can be maintained for more than 1 hour after mixing.

The flow, plastic density, air content, initial set and final set of three mixes (control, Mix 1 and Mix 2) at 23 0 C, are compared in Table 4. Even at high fibre contents with steel and polypropylene fibres, similar flow characteristics were observed at room temperature.

Table 4. Plastic State Properties of RPC at 23°C Control Mix 1 (with Mix 2 (with (Plain) steel fibres) polypropylene fibres) Flow 65 64 60.5 Air Content 8.4 9.2 8.6 Plastic Density 2260 2370 2210 Initial Set (min) 330 Final Set (min) 430 The air contents at plastic state can be further reduced by the addition of a chemical admixture. A further reduction in the air content is expected to significantly improve the strength characteristics. Methods to reduce air contents are currently being investigated.

Compressive Strength Development Selection of the appropriate type of cement for RPC can influence the strength development of RPC. Since RPC is (generally) subjected to heat treatment, the type and morphology of hydration products and the stability of the paste system with time will be governed by the type of cement. With the appropriate heat treatment applied at a chosen age, Type GP cement can be used for RPC. Micro-cement 1, with a reduced C 3

A

content and 650m 2 /kg fineness, also appears to be a viable alternative for the production of RPC.

Four different sand types (Kumell sand, Anna Bay sand, Ottawa sand and 10 Normalised sand) were investigated. A Sydney sand with particle sizes varying from .50-600tm was also investigated. Particle sizes up to 600 tm can be utilised for RPC and a cube strength of 189 MPa can be obtained (with a naphthalene formaldehyde superplasticizer) at the age of 7 days for specimens cured at 90 0 C hot water. To further examplify the present inbvention sand having particle sizes varying from 100- 4 00gm 15 was used.

Compressive strength development of cubes cured in hot water at (Condition 2 in Table 1) is shown in Figure 2. It is possible to achieve 200MPa cube compressive strength with Mix 1, at 28 days of age, and these values are higher than those reported by Collepardi et al for 90°C steam-cured cube specimens. The high temperature curing commenced at 24 hours of age. Specimens where the hot temperature curing commenced at the age of 3 hours after casting (Condition 4 in Table 1) showed somewhat lower results. Early age hot temperature curing, beating the specimens gradually up to 80°C, is currently being investigated to simulate steam-curing conditions. Prolonged curing in hot water for 28, 56 and 128 days did not show any benefits and in some cases prolonged heat curing may cause harmful effects such as the development of micro-cracks. Specimens cured for 3 or 7 days at 90 0 C maintained their strength values up to 128 days. Further long-term testing is currently under way.

On selected specimens, high temperature autoclaving was carried out at 160 0 C and 225°C (Conditions 6 and 7 in Table It is generally not advisable to apply such high temperature curing at 3-4 hours after casting due to the development of cracks, expansion and failure of specimens. It is, however, possible to apply this technique at 24-72 hours after casting. At 3 days of age, heat treatment at 160°C improved the compressive strength by 20-60% of the strength of specimens cured at room temperature.

Hence for precast products with RPC, autoclaving at a high temperature can offer advantages. Heat treatment at 225 0 C is currently being investigated.

A comparison of cube and cylinder strengths of RPC specimens cured in hot water at 90 0 C is shown in Figure 3. The ratio of cylinder strength/cube strength for these RPC mixes is in the range of 0.843 to 0.886. These values are slightly higher than the values reported for normal strength concrete.

Modulus of Elasticity Static modulus of elasticity on 75mm diameter cylinders and dynamic modulus 10 of elasticity on 50x5x600mm prisms (using fundamental resonant frequency method) were determined and these results are shown in Table 5. These are non-standard size S specimens. However, for development work and high temperature testing, it was not possible to test larger size specimens with the existing capacity of test machines and e v muffle furnaces.

ce• 15 Table 5. Modulus of elasticity of RPC (cured at 90'C hot water) at different ages Age of Concrete Static Chord Modulus (GPa)* Dynamic Modulus (GPa)+ (Days) 3 45.68 50.67 7 48.81 28 49.63 52.24 56 51.76 54.90 Average of 3 specimens Average of 4 specimens The variation of results among specimens for the static modulus test was high, possibly due to preparing the 75mm cylinders for testing capping), and as a result the dynamic modulus of elasticity was determined. The dynamic modulus results are very consistent (The values for the 4 specimens are 54.66, 51.30, 52.59 and 50.41 GPa) and relatively easy to obtain. For normal concrete mixes, the dynamic modulus is higher than the static chord modulus. With RPC also slightly higher values for the dynamic modulus was observed. The modulus values are comparable to very high strength concrete mixes but RPC mixes do not have coarse aggregates which contribute considerably to the modulus of elasticity of concrete.

0@

S

00 5 eSS *0

S

C 0 0 00 S

S

0, 0500 Flexural Strength Flexural strength and load-deflection curves were obtained on 50x50x600mm prisms. The water/binder ratio in this mix was 0.13 and the water-cement ratio was 0.16.

These results are summarised in Table 6 while a typical load-deflection curve of Mix 1 is given in Figure 4.

Table 6. Flexural Strength Development of RPC (cured at 90C water) (Mix 1) Age of Concrete (Days) Flexural Strength (MPa)* 3 30.08 7 34.29 28 35.2 Average of 3-4 specimens The flexural strengths obtained from the prisms compare well with the 28-day results reported on 40x40x160mm prisms by Collepardi et al for 90°C steam-curing.

These high flexural strengths together with high toughness indices make RPC an ideal material for pipes, panels and floor beams. Structures subjected to impact loading such as explosion chambers are also possible applications. In a typical pipe design, for example, it is expected to allow a hoop tensile stress of up to O1MPa, resulting in a significant reduction in the production cost Other thin wall products can also result 15 in economic designs. To verify this, two prototype beam sections shown in Fig.5 were wet-cast with external vibration and tested in flexure, under two point loading, with a span of 450mm. In these sections flexural strengths in excess of 25 MPa have been achieved. These values are higher than the values reported by Collepardi et al on 150xl50x600mm prisms (about 20MPa) cured under similar conditions.

The high compressive and flexural strengths of RPC make it an ideal material for certain structural applications. Currently, code provisions, world over, do not cover such high strength materials and hence structural components have to be carefully designed with special design manuals.

High Temperature Performance of RPC Since the matrix of RPC is very dense, it is important to assess the fire rating and high temperature performance of RPC mixes. Mixes with steel and carbon fibres have been tested up to 500 0 C at this stage. Testing is continuing up to 1000 0 C. A panel of about 930x775x50mm in size will also be tested for fire resistance. Some preliminary results at high temperatures are shown in Fig.6. Carbon fibre reinforced mixes with 12kg/m 3 and 20kg/m 3 performed better than metallic fibres in terms of retaining higher residual strengths and ductility after subjecting them to 500C.

With the materials available currently in Australia, with Type GP cement, and the polycarboxylic ether polymer-type superplasticizer, it is possible to produce RPC mixes with cylinder compressive strengths of 175MPa (cube strengths of above 200MPa).

Sands having particles sizes up to 600plm can be used for the production of RPC. Only a high temperature curing, such as steam curing, is adequate to produce the above compressive strength.

Application of high temperature water curing and autoclaving have a beneficial effect on strength development. The heat treatment to be used, however, depends on the age ofRPC, and type of cement.

S* Static modulus of elasticity above 50GPa can be achieved. This is slightly higher than the values recorded for high strength concrete mixes. Flexural strengths of 35MPa can be achieved for RPC with steel fibres, and these values are more than twice the flexural strengths of high strength concrete mixes. Toughness of RPC is also considerably high enabling this material to be used without conventional reinforcement 00 "in certain applications. In prototype beam sections flexural strengths of 25MPa have .00.been achieved.

High temperature explosive spalling can be controlled by appropriate type and quantities of fibres. The behaviour of RPC appears to be similar to very high strength concrete mixes.

Possible applications of RPC can include precast pipes, panels, floor beams, tiltup construction, culverts, sheet piles, etc..

Although the present invention has been described with reference to preferred embodiments, it will be understood that variations which are in keeping with the spirit and intent of the invention are also contemplated and fall within its scope.

REFERENCES

1. Richard, P. and Cheyrezy, M.H. (1994). Reactive Powder Concretes with High Ductility and 200-800MPa Compressive Strength, ACI Spring Convention, San Francisco. ACI SP 144-24, pp507-518.

2. Gowripalan N. and Te Strake (1998), Feasibility of manufacturing Reactive Powder Concrete (160-800 MPa) in Australia (in press), pp 3. HDR Dateline (1994), News Letter of HDR Inc., Omaha, NE, USA, 4pp.

4. Dowd, W.M. and Dauriac, C.E. (1998), Development of Reactive Powder Concrete (RPC) Precast Products for the United States Market, International Symposium S 10 on High Performance and Reactive Powder Concretes, Edited by Pierre-Claude Aitcin and Yves Dela, August, Sherbrooke, Quebec, Canada. pp 37-48.

Collepardi,S., Coppola,L., Troli,R. and Collepardi,M. (1997), Mechanical Properties of Modified Reactive Powder Concrete. Superplasticizers and Other Chemical Admixtures in Concrete. Proceedings of Fifth CANMET/ACI International Conference.

Rome. Italy. ACI- 173. pp 1-21 oo *oooo ooo go

Claims (10)

1. Reactive powder concrete composition including a polycarboxylic ether polymer- type superplasticizer, wherein the superplasticizer has a weight average molecular weight in the range of 10,000 to 500,000 determined by gel permeation chromatography (GPC) with polyethylene glycol as standard, the difference between the peak top molecular weight of the superplasticizer and the weight-average molecular weight being from 0 to 8,000.

2. The composition according to claim 1, wherein the superplasticizer is obtained by the co-polymerisation of: S 10 from 5-98% by weight of an (alkoxy)polyalkylene glycol mono(meth)acrylic ester type monomer represented by the general formula 1: H2--C- R COO(R20)mR3 wherein R' stands for hydrogen atom or a methyl group, R20 stands for one species or a mixture of two or more species of oxyalkylene group of 2 to 4 carbon atoms, providing 15 two or more species of the mixture may be added either in the form of a block or in a random form, R 3 stands for a hydrogen atom or an alkyl group of 1 to 5 carbon atoms, and m is a value indicating the average additional mol number of oxyalkylenegroups which is an integer in the range of 1 to 100, (ii) 2 to 95% by weight of a (meth)acrylic acid type monomer represented by the general formula 2: H 2 R 4 COOM (2) wherein R 4 stands for a hydrogen atom or a methyl group and M 1 stands for a hydrogen atom, a monovalent metal atom, a divalent metal atom, an ammonium group, or an organic amine group, and (iii) 0 to 50% by weight of other monomer copolymerizable with said monomers, provided that the total amount of(i), (ii) and (iii) is 100% by weight.

3. The composition according to claim 1 or claim 2, wherein the superplasticizer is present in the amount of from about 20 kg/m 3 to about 70kg/m 3 P-4519.DOC -17-

4. The composition according to claim 3, wherein the superplasticizer is present in the amount of from about 30kg/m 3 to about 60kg/m 3 The composition according to claim 3, wherein the superplasticizer is present in the amount of about 30kg/m 3

6. The composition according to any one of claims 1 to 5, having a water/binder ratio of from about 0.11 to about 0.14.

7. The composition according to any one of claims 1 to 6, further including fibres selected from the group consisting of steel fibres, carbon fibres and polypropylene fibres.

8. A paste or a structure formed from a reactive powder concrete composition according to any one of claims 1 to 7.

9. A process for preparing a reactive powder concrete composition including i* intimately mixing reactive powder concrete components and a polycarboxylic ether polymer-type superplasticizer. S*

10. A process for preparing a paste or a structure according to claim 8 including combining a composition according to any one of claims 1 to 7 with water to obtain a homogeneous mixture.

11. A process according to claim 10, wherein the homogeneous mixture is cured by high temperature. S12. A process according to claim 11, wherein the homogeneous mixture is cured by steam. DATED this 5th day of May 2000 MBT HOLDING AG Attorney: IVAN A RAJKOVIC Fellow Institute of Patent Attorneys of Australia of BALDWIN SHELSTON WATERS P-4519.DOC