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

Abstract

A method for producing a mixture for aerated concrete improving the cohesion of solidified aerated concrete fly ash-based masses at least 50% of the total amount of fly ash before by feeding it into the mixture with water.

Description

The present invention relates to a process for preparing a raw material feedstock for the production of aerated fly ash based on electric fly ash.

Cellular concrete is a building material made from a lightweight aqueous suspension of a dry silica component and a binder. The binder consists of lime, cement or a mixture thereof. Depending on the silica component used, we distinguish basically aerated concrete from sand, aerated concrete from fly ash and aerated concrete from etruska. These types of aerated concrete differ from each other by some physical-mechanical properties.

From the point of view of processing and technology, aerated concrete is made from sand either by wet grinding of sand and separate dosing of the resulting sand sludge and binders into a mixer or by joint grinding of dried sand with binder resp. mixture of binders. Common technology for the production of aerated concrete from fly ash is the common dry grinding of fly ash or its fly ash component, which is formed of lime or a mixture thereof with cement. The raw material mixture thus prepared is dosed into a mixer, after being mixed and homogenized with the other dosed components, ie water, sulfate, a surfactant and a gaseous additive, is cast into molds. The dry matter-to-water ratio in the outflow is decisive for the subsequent teohnologic process, where the water coefficient optimizes the outflow consistency as a decisive factor for stabilizing the progress of the acidification and subsequent solidification of the leavened mass in the mold. At this stage, the silica component used differs. If the ground sand in the production mixture is characterized by its specific surface area, then the specific surface area value is proportional to its particle size, resp. its diminutive. Immediately after mixing, this specific surface area is then coded with the required dose, the amount of which does not change any more, merely as a result of the binder hydration reaction processes. A slightly different process in this direction

250 633 occurs when power or heat fly ash is used as the siliceous component of the production mixture. As a result of its formation, the ash grain is characterized both by its outer surface, which corresponds, as in the case of sand of a particle size and its morphology, and by its inner surface, which consists of micropores enclosed within the fly ash and only partially flowing onto it. This inner grain surface is, according to the characteristics of diminishing, only partially accessible to water for immediate wetting after mixing the fly ash mixture in water. The inner surface is charac- terized by the absorption of fly ash, which depends on the type of coal used and the theology of its combustion. Due to the gradually increasing pouring temperature due to the hydration of the binders and the time elapsed since the actual mixing with water, the water gradually penetrates into the closed pore of the fly ash, where it binds to the inner surface and fills the microcapillaries. By this mechanism, since the fly ash is mixed with water, there is a continuous loss of water from the outflow suspension and the optimized outflow consistency is disrupted. The outflows densify not only as a result of hydration of the binders, the conditions for gassing from the gaseous additive deteriorate and the porous macrostructure is formed, it breaks down and forms cavities that impair the physical and mehanogenic properties of the product. However, the loss of water in the system also reduces the water necessary to hydrate the binders, in particular to provide a crystalline lime hydrate structure which provides the required and plasticized outflow of the aerated concrete. This solidified aerated concrete mass then appears externally as relatively dry, poorly cohesive, brittle and very sensitive to meo-hane damage. Due to the external mechanical forces, the product's jitteriness is violated and the degree of damage and rejectability of the production increases.

These drawbacks are overcome by the process for preparing the raw material composition according to the invention, characterized in that at least 50% of the total amount of fly ash is saturated with water before feeding into the mixture.

Accordingly, the present invention provides a process for preparing a raw fly ash raw material 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 fed into the mixture.

By saturating the fly ash with water before the actual outflow during its further processing, there is no further binding of water to

250 633 its inner surface, resp. into micropores and microcapillaries in its grains. This will improve the conditions for the rheology of the solidified aerated concrete, which is optimized for the hydration of the binders and the process of rising and solidification by maintaining the consistency of the outflow. This fact results in an increase in the ratio of flexural and compressive strength of the solidified cellular concrete, which is an evaluation criterion for the brittleness of the material.

Saturation of the fly ash with water is achieved mainly by its wet grinding and subsequent lying in sludge tanks or simply wetting it with water well before its dosing into the mixer so that the desired effect is achieved. The desired effect is also achieved by steaming the fly ash, which, due to the elevated temperature, accelerates the diffusion of water vapor into the porous structure of the fly ash matured. This effect can be advantageously used in the pneumatic conveying of fly ash, where the air is replaced by pressure steam. The degree of wetting required to achieve the desired effect is dependent on the size of the surface of the fly ash particles and the closed pore content, which are immediately wetted.

The effect of the process according to the invention can be seen from the example below.

Two pores of aerated concrete were prepared for products - "3 with a density of 550 kg.m". The recipe for the outflow A corresponds to the prior art, the raw material mixture for the outflow B was prepared according to the method according to the invention. The composition of both outflows was otherwise the same as shown in the following overview. It is apparent from the measured values of the strength of the solidified material that the strength parameter is more favorable for the outflow according to the invention.

Composition of the production mixture together ground A B

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

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AND (B) teohnol. water 300 liters 10 liters sulfate 10 kg 10 kg Al powder 0.35 kg 0.35 kg Poron 0.4 liter 0.4 liter solid state strength: in bending tension 24 kPa 27 kPa in 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.