CS250633B1 - Method of preparation of raw material production mixture - Google Patents

Abstract

A method of producing a mixture for aerated concrete while improving the cohesion of the solidified aerated concrete mass based on fly ash, in which at least 50% of the total amount of fly ash is saturated with water before being added to the mixture.

Description

The invention relates to a method of preparing a raw material production mixture for the production of aerated concrete based on power plant fly ash.

Aerated concrete is a building material made from a lightened water suspension of a silica component and a binder. The binder is made of lime, cement or a mixture thereof. According to the silica component used, we basically distinguish between aerated concrete made of sand, aerated concrete made of fly ash and aerated concrete made of Etruscan aerated concrete. The listed types of aerated concrete differ from each other in some physical and mechanical properties.

In terms of processing and technology, aerated concrete is produced from sand either by wet grinding of sand and separate dosing of the resulting sand slurry and binders into the mixer or by joint grinding of dried sand with a binder, or a mixture of binders. In the technology of producing aerated concrete from fly ash, joint dry grinding of fly ash or its part with a binder, which is made up of lime or its mixture with cement, is commonly used. The raw material production mixture prepared in this way is dosed into the mixer, after mixing and homogenizing with other dosed components, i.e. water, sulfate, surfactant and gas-forming additive, it is cast into molds. The ratio of dry matter and water in the casting is decisive for the subsequent technological process, where this water coefficient optimizes the consistency of the casting, as a decisive factor for stabilizing the process of rising and subsequent solidification of the risen mass in the mold. At this stage, the difference in the used silica component is manifested. If the ground sand in the production mixture is characterized by its specific surface area, then the value of the specific surface area is proportional to the size of its particles, or rather the degree of its miniaturization. This specific surface area is immediately after mixing increased by the required dose of code, the amount of which does not change further, only as a result of the reaction processes of hydration of the binders. A somewhat different process in this direction

250 633 occurs when using power plant or heating plant fly ash as a siliceous component of the production mixture. As a result of its formation, the fly ash grain can be characterized by its outer surface, which corresponds to the same particle size and morphology as sand, and by its inner surface, which is formed by micropores closed inside the fly ash grain and only partially opening onto its surface. This inner surface of the grains is, due to the nature of the comminution, only partially accessible to water for immediate wetting after mixing the fly ash mixture in water. The inner surface can be characterized by the absorbency of the fly ash, which depends on the type of coal used and the technology of its combustion. With regard to the gradually increasing casting temperature due to hydration of the binders and the time elapsed since mixing with water, water gradually penetrates into the closed pores of the fly ash, where it binds to the inner surface and fills the microcapillaries. This mechanism leads to a continuous loss of water from the casting suspension from the mixing of fly ash with water and the optimized consistency of the castings is disturbed. The castings thicken not only as a result of the hydration of the binders, the conditions for the rise of gas from the gas-forming additive and the formation of a porous macrostructure deteriorate, its defects and the formation of cavities occur, which worsen the physical and mechanical properties of the product. However, the loss of water in the system also reduces the water necessary for the hydration of the binders, in particular for ensuring such a crystalline structure of lime hydrate that will provide the necessary plastic properties to the risen and solidifying cast of aerated concrete. This hardened aerated concrete mass then appears relatively dry, poorly cohesive, brittle and very sensitive to mechanical damage. The effect of external mechanical forces leads to a violation of the integrity of products and an increase in the degree of damage and production rejects.

The above-mentioned shortcomings are eliminated by the method of preparing the raw material mixture according to the invention, the essence of which consists in saturating at least 50 l of the total amount of fly ash with water before dosing it into the mixture.

The invention therefore provides a method of preparing a raw material production mixture for the production of aerated concrete based on power plant fly ash, characterized in that at least 50% of the total amount of fly ash is saturated with water before being added to the mixture.

By saturating the fly ash with water before it is cast, it prevents further water binding to the ash during its further processing.

250 633 its inner surface, or rather into micropores and microcapillaries in its grains. The thickness will improve the conditions for the rheology of the hardened aerated concrete mass, which, by maintaining the consistency conditions of the casting, is optimized for the hydration of the binders and the process of rising and solidification. This fact will be reflected in an increase in the ratio of the bending and compressive strength of the hardened aerated concrete mass, which represents an evaluation criterion for the fragility of the mass.

Saturation of fly ash with water is achieved primarily by wet grinding and subsequent settling in sludge tanks or by simply wetting with water well in advance before dosing it into the mixer so that the desired effect is achieved. The necessary effect is also achieved by steaming the fly ash with steam, which, due to the increased temperature, accelerates the diffusion of water vapor into the porous structure of the fly ash. This effect can be used with advantage in pneumatic transport of fly ash, where air is replaced by pressurized steam. The degree of humidification necessary to achieve the necessary effect depends on the size of the internal surface of the fly ash particles and the content of closed pores, which are immediately wettable.

The effect of the process according to the invention is evident from the following example.

Two ©levy of aerated concrete mass for products - "3" with a bulk density of 550 kg.m . The recipe for casting A corresponds to the previous method, the mixture for casting B was prepared by the method according to the invention. The composition of both castings was otherwise the same, as shown in the following overview. The measured values of the strength of the solidified mass show that the strength parameter is more favorable for the casting according to the invention.

Composition of the production mixture, ground together A B

oement 50 kg 50 kg lime 100 kg 100 kg ash 350 kg 100 kg mixture dose 500 kg 250 kg ground fly ash sludge 0 450 liters sludge aging time 0 4 hours sludge density 0 1.26 kg/liter

250,633

A B technological water 300 liters 10 liters sulfate 10 kg 10 kg Al powder 0.35 kg 0.35 kg Surfactant Poron 0.4 liters 0.4 liters strength of solidified mass: in tension during bending 24 kPa 27 kPa under pressure 56 kPa 51 kPa strength parameter 0.43 0.53

Claims (3)

A process for the preparation of a raw material fly ash for the production of aerated fly ash, characterized in that at least 50% of the total amount of fly ash is saturated with water before being fed into the mixture. Method according to claim 1, characterized in that the fly ash is saturated with water by wet grinding and subsequent lying in sludge tanks. 3. The method of claim 1 wherein the fly ash is saturated with water by steaming.