FR2530614A1 - Process for the activation of the setting of hydraulic binders of pozzolanic nature. - Google Patents

Abstract

Binders of hydraulic or pozzolanic nature, such as granulated steelmaking slags, fly ash from coal combustion and pozzolana, set in the presence of water and an activator. The activation according to the invention is produced by a mixture of sulphocalcium ash (containing lime and sulphates) - for example the ash from the Gardanne thermal power station in France - with a strong base such as NaOH and KOH and optionally an accelerator of the gypsum or similar type. The mechanical strengths of the materials obtained are considerably higher (curve B) than when using the conventional process for activating the same binders with lime (curve A).

Description

 The present invention relates to the field of hydraulic binders and more specifically relates to a means of activating the setting of materials with hydraulic power such as in particular blast furnace slag and steelworks, fly ash for burning coal, natural pozzolans and, in general, all materials with pozzolanic power or character, that is to say setting in the presence of water and an activating agent.

Among the agents promoting the setting for binders of the aforementioned types, the most commonly used are lime and soda. It is known, for example, that in the case of granulated slag, hydration in basic medium gives rise to the formation of rapidly hardening products such as tetracalcium aluminate in the case of lime and a mixture of the latter and gelhenite when the activator is sodium,
The mechanical strengths of the compositions D such as mortars or the like, obtained by lime activation are interesting but the latter are even higher when using soda or products containing it such as sodium silicates or metasilicates, although that the use of such sodium agents entered certain subjugations.

 It has now been found that it was still possible to accelerate the setting of materials with pozzolanic power and to obtain mechanical resistances clearly greater than. those found in the aforementioned known techniques, by incorporating into the material a sulfocal ash that has determined characteristics, added with a strong base such as NaOH or KOH.

 The process for activating the setting of the hydraulic binder according to the invention therefore consists, in its most general definition, of adding, to a major proportion of the hydraulic binder, a minor proportion of an activating mixture consisting of a strong base and a sulphocalcic ash from a thermal power plant with a content of at least 20% in SiO2, 30% in CaO (including a part in free lime) and 10% in A1203.

 The strong base is advantageously constituted by sodium or potassium hydroxide and the incorporation of the activating mixture can be carried out at the time of kneading, in a kneader-doser, of the pozzolanic binder and possibly of the aggregates for obtaining mortars.

 The quantities of the aforementioned ingredients to be added to the hydraulic binder depend on various parameters such as: type of binder and subsequent aggregate for a mortar, desired setting time, short or longer term mechanical strength, etc. Generally, within the framework of the invention, for 100 parts of typepouzzalaniqie binder, approximately 1 to 20 parts of a mixture of 10 to 70% of sulfocalcic ash and 5 to 50 parts of strong base are used; the parts and the% being expressed by weight.

 In practice, all the components are preferably mixed in powder form, including the base (for example soda or potash in flakes) and mortars can be prepared by adding, in the mixer, Q aggregates sand to obtain construction materials including concrete blocks, tiles, bricks and compositions for the construction of roads and the stabilization-consolidation of soils.

According to an advantageous embodiment according to the invention, the pulverulent ash from the thermal power station of Sardane (France), the composition of which is as follows, is used as sulphoalcic ash.
CaO: 36 to 45% (including 10 to 25% of free lime); SiO2: 27 to 32%;
Al203: 10-16%; Fe203, MgO, S03: 10 to 20%
The other characteristics are the following, on average density: 2.9 g / cm3; BLAINE specific surface: 2800 cm2 / g; 80 micron sieve: 85%; average free lime, CaO content: 22%.

 In accordance with the invention, it has also been found that the activation could be further enhanced by adding to the mixture, in the mixer, accelerators of a type known per se such as: natural or artificial gypsum, phosphogypsum. One can also use other products such as: calcium chloride, activated silica, activated alumina. etc.

The proportion of accelerator can vary from 0 to 90% relative to the weight of the activating mixture added to the pozzolanic type binder.

Furthermore, when using a slag so derurgical, it is used in the form of granules of dimensions
0 to 5 mm or, better still, in the form of ground or ground slag such as for example ground slag having at least 10% (preferably 40 to 50%) of particles passing through a sieve of 80 microns and less than 10% of particles with a diameter greater than 200 microns. It is preferably arranged to comply with these particle sizes when replacing the slag with any of the other pozzolanic binders targeted by the invention.

By way of non-limiting example of carrying out the process, the results of comparative tests carried out on the basis of two compositions A and B each containing 79% by weight of fine sand and 20% of slag granule 0- will be indicated below. 1 mm, but with the following differences:
A also contained 1% added lime (expressed as CaO)
B contained, according to the invention 1% of a mixture of ash from Gardanne (60%) - NaOH (30%) - gypsum (10%)
Test pieces of diameter 50mm, height 100mm, were produced with static press pressures giving closing forces of 50 KN. We obtained series of compressive strengths, RC, expressed in megapascals MPa, which are illustrated on the diagram of the (single) figure attached.

 As can be seen, the activation process according to the invention (curve B) leads from the start to significant resistances and finally gives rise to products whose final resistance is 3 times higher than parallel compositions (A) according to the known technique.

Claims (6)

- CLAIMS -  1. Method for activating the setting of a hydraulic binder for the group consisting of granulated slag from the steel industry, fly ash from coal combustion and natural pozzolans or equivalent materials, characterized in that a proportion is added major of hydraulic binder, a mixture activating, in minor proportion, constituted by a sulfocalcic ash from thermal power plant having at least 20% in SiO2, 30% in CaO (of which a part in free lime) and 10% in Al203 and by a base strong.  2, Method according to claim 1, characterized in that the strong base is sodium or potassium hydroxide  3. Method according to any one of claims 1 or 2, characterized in that the mixing is carried out in a mixer-doser, all the ingredients used being introduced in powder form.  4. Method according to any one of claims 1 to 3 characterized in that one also incorporates into the activating mixture a setting accelerator chosen from the group: gypsum, phosphogypsum, calcium chloride, activated silica or alumina.  5. Method according to any one of claims 1 to 4, characterized in the shell is incorporated into 100 parts of the binder: 1 to 20 parts of a mixture containing 10 to 70% of sulfocalcic ash, 5 to 50% of NaOH or KOH and O at 90% of said accelerator (% by weight).  6. Method according to any one of claims 1 to 5. SiO2: 27 to 32%; Al203; 10 to 16; Fe2O3, MgO,: 10 to 20%; density: 2.9cm 3; specific surface (Blaine); 2800 cm; 80 micron sieve: 85% characterized in that the binder is a granulated or ground slag of particle sizes O to 1 mm and in that the sulfocalcic ash is constituted by the powdery ash from the Gardanne power station, of weight composition: CaO: 36 to 45% (of which 10 to 25% free lime);