GB2114107A - Sepiolite concrete additive - Google Patents

Abstract

A process for producing a concrete additive to improve the flow properties thereof involves: a) selection of sepiolite mineral by probing before extraction, b) weathering to reach a humidity between 30% and 40%, c) reduction to a particle mesh size of 3 mm, d) rotary drum drying at 75 DEG to 80 DEG C to reach humidity content of 13% to 15%, and e) sieve screening until 95% of the particles are between 125 and 437 microns. s

Description

SPECIFICATION Manufacturing process for a concrete additive for improving its flow properties The term additive is applied to all products, excepting cement, aggregates and water which are added to fresh concrete to achieve an improvement in its properties.

A large number of substances serve as additives according to their properties-they may be classified under the headings of organic and inorganic. Among the inorganic additives there are the powders such as kieselguhr, bentonite, diatomaceous earth, fat limes, fly ash and ground pozzolana volcanic rock; salts such as chlorides, carbonates, silicates and aluminates; mineral oils; colourants such as titanium dioxide, ferric oxide or chromium hydroxide and silicones. Among the organic additives there are the ligno-sulphates, soaps, carbon hydrates and resins.

The action exerted by these products upon the concrete is of a physical and physico-chemical nature, and they are used as setting-speed regulators, plasticizers, aerators, plasticising-aerators, water-proofing agents, expanding agents, gasifying agents, surface hardeners, colourants, corrosion inhibitors, insecticides, fungicides and anti-frost media, their addition rate is generally less than 5% of the weight of cement and requires special care, since an incorrect rate may have an undesirable influence upon the concrete, sometimes opposing the original purpose of the additive. All additives impart secondary properties to the concrete, which may of a prejudicial nature. Every care must be taken to ensure that the intensity of such perturbations, is prevented from countering the advantages achieved by the addition.

The additives modify the properties of the concrete at difference stages of utilisation: 1. In fresh concrete, for instance: plasticisers, aerators and plasticiser-aerators.

2. During setting and drying, for instance: setting-speed modifiers, in the form of accelerators or retarders, and anti-frost media.

3. In hardened concrete, for instance: water-proofers, hardeners, corrosion inhibitors, etc.

According to the invention there is provided a process for concrete additive to improve its flow properties and characterised by the use of the mineral known as sepiolite forming a basic ingredient of the product, its production involving the following operations: a) selection of the mineral by sensors before extraction, b) weathering of the mineral until it reaches a humidity of 30% to 40%.

c) subsequent reduction to a particle size averaging 3 mm, d) drying in rotary drum at a temperature of 75--800C until a humidity level between 13% and 15% is achieved, e) sizing by means of sieves, down to a particle size level at which 95% is between 1 25 and 437 microns.

The product thus obtained is in the form of a fine powder. The development of the material flow properties is achieved by means of two processes: by simple dispersion or by pre-gelling. In this way, a non-Newtonian, pseudo-plastic and specifically thixotropic fluid is achieved.

On the basis of this product a 10% aqueous dispersion is formed by prior stirring before adding to the concrete mixer. The stirring may be manual or mechanical, the flow properties of the product being improved by greater stirring. In the event of manual stirring, this is achieved over 1 5 minutes at 4060 rpm. In the event of mechanical stirring, the optimum conditions are 1000-1 700 rpm for 3 minutes, the stirrer being located at an angle of 600 in relation to the surface of the dispersion. In both cases, stirring continues during the integration of the additive during the concrete production process, together with the remainder of the ingredients.

A pre-gel may be formed by a pre-gelling operation of a 1 5%-25% suspension, obtained by stirring the product at 3000 rpm for 20 minutes, followed by subsequent dilution of the pre-gel and subsequent addition to the concrete-mixer, ensuring a considerable increase in flow properties of the concrete, as compared with direct addition or dispersed addition. The additive thus obtained consists of 5% to 25% sepiolite, the balance being water.

The product may also be applied in dry form, though the yields obtained are inferior to those obtained with the previous processes.

The main effects of the product upon the concrete are as follows: 1). Improved concrete flow 2). Elimination of segregation of the various concrete ingredients 3). Maintenance of an adequate suspension of concrete ingredients.

The product reacts mainly on fresh concrete and hardened concrete.

In the first case it has several functions:- as plasticiser: increasing the workability and handling of the concrete, facilitating its use.

as homogeniser: maintaining a stable suspension of concrete ingredients in water, avoiding segregation and decanting.

as pumping aid: exercising two different actions. In normal and lean concrete, since the plasticity conferred by the additive maintains a stable suspension during pumping. In light aggregate concretes, it serves as an aggregate water-prcofer, eliminating their water absorption during pumping.

Within the hardened and set concrete it has the following effects:- water-proofing: occupying the concrete capillary network thus preventing the flow of water.

shrinkage-reducer, allowing the laying of slabs measuring 25x5 m without risk of fissures.

absence of negative reaction upon compression strength for a same given water/cement ratio.

Examples of product obtained 1. Fresh concrete' 1.1 Consistency The consistency measure according to the Abrams method, clearly show the transition of the concrete from a plastic to a dry consistency. It must be taken into account that the consistency is not of a true nature, since if the test were carried out on a jolt table, a plastic consistency would be achieved.

Table 1 shows the consistency results obtained for concrete without additive and a concrete to which different amounts of additive have been made.

Table 1 Concrete consistencies Concrete Water/Cement Cone control 0.65 12 +0.3% additive 0.65 +0.15% ,, 0.65 6-7 +0.6% ,, 0.75 7 +0.3% ,, 0.75 9 +0.4% " 0.85 3 +0.46% ,, 1.00 7-8 1.2 Handling The combination of properties ensure the workability of the concrete on site. As a result of the plasticity contributed by the additive, the concrete is easier to handle, even when using crushed aggregates.

1.3 Homogeneity This is the most important property contributed by the additive to concrete, since it avoids segregation of ingredient materials or any decantation.

1.4 Specific gravity In view of the uniformity of the concrete, it remains constant and practically equal to that of normal concretes.

Example: Specific gravity Concrete 2.451 Control 2.430 With additive (equals cone) 2.417 With additive (equals water/cement) 2. Application Concrete obtained with an additive addition has a better yield, owing to the easier handling and workability conferred by the additive. The concrete surface is smooth and uniform without further treatment. In the event of trowel-smoothing, the finish is extremely good.

3. Setting This has to be achieved with great care in the case of concrete without an additive, since the water loss is extremely slow.

4. Hardened concrete 4.1 Shrinkage It is lower than in concretes without the product. As an example two unreinforced slabs measuring 25x5 m were laid.

A) In the first test a premixed concrete was used, supplied by Pioneer and metered by the Bolomey procedure, according to the following formulation: Valderribas PA 350 cement 250 kg Sand 820 kg Gravel 500 kg Coarse sand 690 kg Total water 228 1 Additive 5 kg Concrete required: 250-D-40 Consistency: smooth Handling: pump, Bombeher automatic pump, 15 cm piping Pumping pressure: 50 kg/cm2 Specification conditions: medium finish Sampling, Abrams cones, preparation and breaking of test-pieces by the cement supplier laboratory, according to the following standards: 1). Instructions for manufacture and supply of premix concrete (EHPRE) 2). Abrams cone. UNE 7.103 Std.

3). Preparation and storage of test-pieces. UNE 7.240 standard for cylindrical testpieces 1 5 cmx30 cm high.

4). Breaking of test-pieces. UNE 7.242 std. for the same test-pieces.

Results: water/cement ratio 0.91 Abrams cone base 8 cm compression resistance 7 days 1 35 kg/cm2 compression resistance 28 days 1 90 kg/cm2 Pumping achieved without problems or breaks, greatly reducing the pumping pressure.

The slab showed a good finish with a smooth, uniform and crack-free surface.

B. Test carried out with concrete of similar properties to previous case, of the following formulation: Valderribas PA-350 cement 200 kg Sand 870 kg Gravel 500 kg Coarse sand 690 kg Total water 1901 Additive 6.6 kg Concrete required: 200-D-40 Consistency: smooth Handling: same as A) Pumping pressure 50 kg/cm2 Specification conditions: medium finish Sampling and tests: as for A) Results: water/cement ratio 0.99 Abrams cone base 6 cm compression resistance 7 days 79 kg/cm2 compression resistance 28 days 1 20 kg/cm2 Pumping without problems or breaks, reducing the pumping pressure. The slab finish was good, with a smooth, uniform and crack-free surface.

4.2 Compression resistance With a lower water/cement ratio the concrete containing additive has a smaller cone, and an increased resistance of up to 20%, in various cases observed and according to the type of cement used. Using equal cones, and with a higher water/cement ratio, the sepiolite-bearing concrete has the same resistance.

Table 2 Water/cement Cone 28 day resistance Additive 0.3% 0.85 10 195/201 Additive 0.3% 0.72 8 234/234 Control 0.72 10 194/197 4.3 Homogeneity Breaking of the test-pieces showed the good distribution of the aggregate throughout hardened concrete.

Pumpability Concretes of various resistances and types were test-pumped.

5.1 Concretes of typical resistances in excess of 175 kg/cm2 Where concretes without additive are used without problems, the addition of additive nevertheless shows: a) lower pumping pressure b) aggregate homogeneity c) better pumping yield d) easier slab working properties 5.2 Concretes of typical resistances between 175 and 150 kg/cm2 Although containing certain other additives, these are subject to pumping problems. Addition of the additive ensures freedom from problems and retention of all properties.

5.3 Concretes of typical resistances below 150 kg/cm2 It has not been possible to pump these concretes to date. As a result of the addition of the product, concretes of 80 kg/cm2 strength have been pumped.

5.4 Concretes with arlites The problems presented by these concretes lie in their increased water absorption capacity when subjected to high pressures, thereby causing the drying of the concrete and consequently blockages in piping.

The additive eliminates the problem, covering the arlite particles with a light coating avoiding water absorption during pumping.

Examples: Various concrete compositions were pumped in spirals as follows: a. pump type BP- 8 100 PA 350 cement 248 kg Sand 498 kg Arlite 583 1 Water 1711 Additive 4.6 kg Volume pumped 5.797 m3 Result: The mixture is pumpable, though the 6,0 m3 took 1 hour to pump and a final total of 350 1 of water had to be added.

b. pump type BP- (b 125 PA 350 cement 240 kg Sand 480 kg Arlite 567 1 Water 1961 Additive 4.3 kg Volume pumped 6.148 m3 Result: Similar to the previous test, though with the addition of only 120 1 and a considerably shorter pumping time.

6. Exuded mortar This factor is decisive in the pumpability and setting of concrete.

Table 3 Exuding of mortars with and without additive Exuding rate Exuding capacity Mixture reference (cm3/cm2-s) x 10~5 (cm3/cm3)x 1 O-) dispersed additive 0,5% 1.3 5.0 dispersed additive 1,0% 1.1 4.5 It was found in tests carried out with mortars that as a rule the addition of the product to the mortar favourably modifies the exuding capacity and speed.

7. Other industrial applications 1. The product may be used as an additive for concrete pre-cast products (tubing, fibro-cement, beams, etc.) improving their properties.

b. As an additive for industrial flooring, specified in Ince Building Standard Specifications, in the following cases: b1. Surface treatment of hardened concrete consisting of the application of a special mortar facing consisting of special aggregates, cement and resins. The use of the additive in this special mortar reduces differential stresses between a hardened concrete and a fresh concrete.

b2. Surface treatment of a fresh concrete. The use of the additive in this type of aggregates allows larger slabs to be produced, owing to reduced shrinkage and improved handling.

c. As internal stress regulator medium between concretes of different types (movement joins, etc.).

d. As an additive to hydraulic mixtures and ingredients of whatsoever type.

Claims (6)

Claims

1. Manufacturing process for concrete additive to improve its flow properties and characterised by the use of the mineral known as sepiolite forming a basic ingredient of the product, its production involving the following operations during its production: a) selection of the mineral by sensors before extraction, b) weathering of the mineral until it reaches a humidity of 30% to 40%.

c) subsequent reduction to a particle size averaging 3 mm, d) drying in rotary drum at a temperature of 75-800C until a humidity level between 13% and 15% is achieved, e) sizing by means of sieves, down to a particle size level at which 95% is between 125 and 437 microns.

2. Manufacturing process for a concrete additive according to claim 1, and characterised by the formation of a 10% aqueous dispersion by prior stirring before adding to the concrete mixer.

3. Manufacturing process according to claim 2 wherein stirring is carried out manually and is continued for 15 minutes at 40-60 rpm.

4. Manufacturing process according to claim 2 wherein stirring is carried out mechanically and optimum conditions are 1 000--1 700 rpm for 3 minutes and with the stirrer forming an angle of 60C in relation to the surface of the dispersion.

5. Manufacturing process for concrete additive, according to claim 1, and characterised by the formation of a pre-gel by way of a pre-gelling procedure using a 1 5-25% suspension, obtained by stirring the product at 3000 rpm for 20 minutes, with subsequent dilution of the pre-gel and subsequent addition to the concrete-mixer, thus obtaining a considerable increase in the flow of the concrete.

6. Manufacturing process for concrete additive to improve its flow properties substantially as herein described.