DE2039196A1 - Fly ash building material - Google Patents

Abstract

Fly ash has a content of 3-15% by weight SO3 and 40-90% active ingredients which are SO3 free & 100% active. The latter comprises by weight %, 8-25 SiO2, 18-45 Al2O3 + Fe2O3, and 35-75 CaO + MgO. The mixture is bound with water at 50-90 C, pref. 60-80 C, & the building material is obtained in less than 24 hrs. Specifically, the fly ash is lignite or oil shale filter ash.

Description

Process for the utilization of fly ash, in particular for production of building materials The invention relates to a method for utilizing lime-rich fly ash. Lime-rich fly ashes with a binding agent character are produced alone or in a mixture with known aggregates to aggregates (pellets, ash concrete grit), concrete ware, Different types of construction elements and mass concrete are processed or are used for soil reinforcement (Soil stabilization).

It is known that fly ash, in particular lignite and oil shale filter ashes, the more than 8% CaO in the form of free and bound to silicates and aluminates klk contain, are characterized by a more or less pronounced hardening capacity, i.e. they solidify and harden after being mixed with water, similar to an industrial one manufactured binder, It has therefore not been tried in the past lacking the binding properties of these cheaply available ashes in the Practice to use.

However, these efforts are faced with undesirable properties of ashes contrary, so that overall, the degree of utilization before all lime-rich ashes Ashes that remain low are subject to dependency in a power plant in the state of accumulation the location of the attack and the time of removal generally strong fluctuations in the chemical-mineralogical and physical composition. These are due to the changes in the quality of the Brennstallbess the operation caused by the firing and the dedusting system. As a result, change too the binder-technical properties of the ashes, which have a positive effect varying amounts of hydraulic and latent hydraulic components considered harmful Applicable components CaSO4 and CaO (free) burned between 900 and 1400 o contain. By hydration or delayed chemical reactions of these Sooner or later, constituents of the hardened ash can show signs of growth or disintegration occur that a sole use of the ashes as a binder so far has been strong shocked. Procedures have already been proposed which do it in spite of what is set out Disadvantages of the ashes in their accumulation state allow their binding properties to be used.

In addition to purely physical measures to increase the utility value the ashes by homogenizing. Selecting particularly suitable batches from the Total ash from a power station, or grinding, were mainly chemical measures suggested.

In individual and this 1. Mixing or grinding the Aachen n with binders never burnt or slaked lime, cement, gypsum and / or latent hydraulic Substances (blast furnace slag, siliceous Residues from the Aluminum sulphate production from clay, trass, brick powder). This is intended to be used by the specific Disadvantages of the ashes largely freed mixed binders are produced in the generally contain between 20 and 70% ash.

2. Elimination of the harmful constituents that give rise to drifting CaO (free) and CaSO4, which are burnt and difficult to hydrolyze should. CaO is made by soaking the ashes for a long time or treating them with water vapor at a pressure of up to 20 at or by introducing moist air into dry air Ashes cleared.

CaSO4 should either be converted to CaS04 by steam pressure treatment. 21120 hydrolyzed or by conversion with equivalent amounts of Sr, Ba or Pb salts to form sparingly soluble Sulphates are implemented. Additions of NaOH or alumina hydrate are also said to drive the sulfate switch off.

Perner was suggested by immediately storing by pressing manufactured stones under water, the timely hydration of the harmful components bring about.

3. Adjust the mortar pH value to the range 11 to 12 Neutralization of the excess lime with hydrochloric acid. This measure is based on the theory that the hustle and bustle of the lime-rich brown coal miners caused by ettringite transformation. Also treating the ashes for several days with 2N hydrochloric acid is known.

4. Influencing the processability of the ashes and improving them the quality of the building materials through joint processing of the ashes with additives of NaOH, Na2HPO4, Na3PO4, NaHSO4, H2SO4, Na2CO3, NaHCO3. Water glass, alum, aluminum powder, ground aluminum dross, Al2 (SO4) s, CaCl2 (1 to 3%) and recently also MgCl2 in quantities of up to 100 g per 1 kg of fly ash. Through the use of chemicals of the same quality should compensate for the strongly fluctuating binding agent properties of the ashes and space, water and frost resistance of the materials manufactured in this way will.

5. Simultaneous use of several of the items described under 1., 2. and 4. Measure.

The well-known processes for the recovery of lime-rich As practice shows, fly ash adhere to @economic and / or qualitative defects at. It is therefore a widespread, sustained use of lime-rich ashes in the building materials industry despite many years of effort.

The mixed binder production is generally due to the expenditures Too expensive for transport and technology, especially when compared to standard cements decreased Quality parameters of the mixed binders accepted Need to become. In addition, those for making mixed binders are preferred required high fey slag economically more appropriate for the production of Metallurgical cements used.

The hydration of the burned CaO and CaSO4 of the ashes works at normal temperature, e.g. when swamping, with an undesirable, premature Hydration of valuable hydraulic components goes hand in hand. It becomes an ash mortar received, which is no longer suitable for the production of high-quality ash building materials. The disadvantages are to be avoided by extinguishing with tensioned water vapor. However, the outlay on equipment required for this is great. Also occurs in the in most cases there is late rub caused by the formation of ettringite. The CaSO4 bond is due to the expensive and toxic Sr, Ba or Pb compounds cannot introduce oneself; the storage of freshly pressed moldings in water for Avoidance of later driving turned out to be due to the appearance of decay as impracticable.

Also the setting of a certain mortar pH value through precise Hydrochloric acid dosage to avoid drifting has become more difficult when venturing out Working with hydrochloric acid on construction sites and because of the required chemical monitoring every ash batch cannot enforce.

In practice it was found that when using an ashes a certain Power plant and an empirically found chemical additive (i.e. the listed Salts, alkalis, etc.) building materials with good quality characteristics can definitely be obtained could. If the results are transferred to other ashes or if there are fluctuations however, the quality of the ash type originally used was generally evident quickly the limited applicability of the procedure: structural damage occurs The proposed Processing of lime-rich ashes of a defined chemical quality range with MgCl2, preferably in the form of the cheaply available final liquors from Potash industry, represented a significant advance in this context, as this made it possible to directly dispose of large quantities of fly ash in the accumulation state in a manner customary with the use of cement, but using a To use saline solution as mixing liquid. Despite good early and final strengths this fly ash-MgCl2 concrete and the permissible relatively large fluctuations in the This process could not be used due to the fact that it only occurred after 2 to 5 days Water and frost resistance of the products not in all suggested areas of application introduce. The initially existing insufficient water and frost resistance of the products requires that a dispatch only after several days of protected Interim storage can be done. This causes an increased need for storage space and in-house Transport and burdens the economy of the fly ash-MgCl2 concrete.

The invention is based on the object of high-lime fly ash alone or to process with the addition of known additives to building materials or for To use soil reinforcement, with the technical and economic Defects are to be avoided. The ashes should preferably be used in the state of attack, i. without prior extinguishing in the autoclave. Mix with conventional binders and / or chemicals are used. The building materials should be used immediately after completion of production, be room, water and frost-resistant at the latest 24 hours after the start of production, whereby At the same time, the early and final strengths of the building materials corresponding to the state of the art should be guaranteed.

At the same time should be achieved by the invention that the Changes in ash quality caused by fluctuations in coal quality do not affect the parameters of the products to such an extent that their quality is questioned.

The object is achieved according to the invention in that ashes are used will contain at least 40% and a maximum of 90% active ingredients, corresponding to a Contains inert substances from 10 to 60%. Among active ingredients will This means that when boiling for 10 minutes, 1.00 g of ash in 50 ml of a Mixture of concentrated hydrochloric acid and water prepared from equal parts go into solution.

The composition of the active ash content converted to SO3-free (set equal to 100%) must also be within the limits of SiO2 8 to 25% by mass Al2O3 + F2O3 18 to 45 mass% CaO + MgO 35 to 75 mass% lie, corresponding to the Fig. 1 indicated area I in the three-component system SiO2; Al2O3 + FeO3; CaO + MgO. area II identifies the ashes that cannot be used for the process, unless they are classified as not self-hardening aggregates known per se are used. The SO3 content of the raw ashes which, according to analysis and calculation, correspond to area I, may be in the Limits are 3 to 15% by mass.

According to the invention, those identified as suitable must continue to be Ash at elevated temperature in the range from 50 to 90 ° C, preferably between Harden at 60 to 80 ° C under hydrothermal conditions; d. H. who prepared with ashes Building material mixtures must be used during the hardening time provided in the manufacturing process be kept in this temperature range. This can be done in a known manner by steaming and / or preheating of the feed materials happen, space, water and frost resistance of these building materials are dependent on the ash quality and the selected processing conditions within 1 to 20 hours after reaching the hardening temperature achieved, with the pre-storage time of the materials at Temperatures <50 ° C must not exceed 5 hours after shaping.

If the specified temperature limit of 90 ° C is exceeded Depending on the extent of the exceedance, a considerable reduction in the quality parameters (e.g.

Strengths) of the building materials, even with ashes with the invention Composition can lead to room, water and frost resistance not more are guaranteed. This is due, among other things, to an incipient thermal degradation of the Hardening carrier ettringite attributed. At hardening temperatures <50 ° C When processing ashes, the mentioned quality parameters of space, Water and frost resistance usually not achieved.

It has been found that the relationships known from cement chemistry between hardening temperature, hardening time and the achievable strengths cannot be used when processing Schen.

The processing of the ashes can be done alone or mixed with known Aggregates or earth materials, such as gravel sand, fine sand, wood chips, xylitol from raw lignite, not with Water-setting ash and slag, clay or marl take place. The use of air entrainment agents is permitted.

An addition of conventional binders (lime, cement, gypsum) as well Salts, acids and bases can be done. However, to solve the inventive Task not required; on the contrary, when ashes harden under normal conditions known positive additives, such as. B. KOH or CaCl can be used in the invention specified temperature range have a quality-reducing effect.

The ashes selected and processed according to the invention are suitable for the production of light, heavy and wood-concrete-like building materials and aggregates, by bearing and hardening the pellets in the specified temperature range or by breaking up ash concrete produced according to the invention. The method is also suitable for the production of filling compounds with soil of any kind, if on early strength and fast water and frost resistance the masses are valued.

Generally, the ashes become as they are or after homogenization used in larger quantities in natural fineness. The invention extends the application possibilities for the so far insufficiently used industrial waste plug ash, whereby the ashes in the antall state can be used. Previously common There is no need for costly pre-treatments, e.g. in mills and autoclaves. By ensuring the water and frost resistance of the products immediately after Completion of the production, the economy of building material production is favorably influenced, since temporary storage or material damage due to weather influences now omitted.

In general, 1 t of Portland cement is required to achieve the same strength 1.2 to 2 t of fly ash of a quality that is higher than that of cement is available much cheaper, replaceable.

The invention is illustrated below by way of examples for the preparation of various Building materials are explained.

Example 1: Ash concrete In a compulsory mixer, 600 kg Raw gravel (approximately grading curve E) and 150 kg lignite filter ash (composition in% by mass): Inert substance content: 21.8% SO3 a 6.8% active substance t 16.3 s S102 26.8% Al2O3 + FeO3 56.9% CaO + MgO with the addition of 24 liters of water to achieve this mixed to a stiff consistency.

Reinforced construction site slabs were made from this. The mixture it was usually compacted in steel molds and the pormen then in a steam chamber brought in. After a heating time of 2 h, 75 ° C. were held for 6 h, the The temperature in the ash concrete during the trial production was controlled by a remote thermometer became.

The panels were demolded after a cooling time of 4 hours and im Stored outdoors.

They were room, water and frost resistant after completion of the production. Compressive strengths were found on comparative cubes 20 cm x 20 cm x 20 cm treated in the same way of 180 kg / cm² (completion of production) or 283 kg / cm² after 28 days of storage in a damp room.

Example 2: Hollow blocks using heavy aggregates Mixtures made from raw gravel and ash in a mass ratio of 4: 1 as in Example 1 were on a semi-automatic, block maker to 2000 3-chamber hollow blocks 24 cm x 30 cm x 23.8 cm and these after a production-related pre-storage time cured for 0 to 2 h in a steam chamber (heating time 2 h, holding time 2 h at 70 ° C, chamber opened after a further 10 h).

The stones were resistant to space, water and frost. 25 stones were made Tested for compressive strength 1 day after completion of production, of which 2 stones 44 kp / cm² 8 "46 13" 48 2 "50.

Density, dry: 2.0 kg / dm³ Example 3t hollow blocks using of ash concrete demolition ash concrete, as described in Examples 1 and 2 was manufactured, although the type and dimensional accuracy of the forms are irrelevant is broken in conventional crushers and sieved into grain fractions disassembled. In comparison to the raw gravel originally used (bulk density in the dry state 1.8 kg / dm³) a reduced bulk density (1.1 to 1.4 kg / dm³ depending on the fraction) and can be used, among other things, to produce lighter hollow blocks will.

600 kg ash concrete chippings with a grain size of 2 to 5 mm (bulk density 1.2 kg / dm3) are processed with 150 kg of ash similar to Example 2.

After completion of production, room water and frost-resistant are obtained Hollow blocks, which in the dry state only have a bulk density of 1.50 kg / dm³ exhibit.

25 stones were tested for compressive strength 1 day after completion of production investigated, resulting in the following strength distribution: 3 stones a 40 kp / cm2 18 "b 42 6" c 44 "The example shows the possibility of manufacturing more standardized Hollow blocks from heavy aggregates and ashes in the state of attack, the total seen from 1 part by mass of ash to 3 parts by mass of gravel sand. Example 4: Aggregate pellets ash the composition oxygen content z 24.5% SO3 t 7.1% active substance s 11.2 % SiO2 29.3% Fe2O3 + Al2O3 59.5% CaO + MgO became more common on a turntable Construction using 22% water by mass (based on the ash weight) in granulated in a known manner.

The granules were stored in a steam chamber without prior storage heated to 70 ° C. in 2 h. The hardening time was 2 hours; the cooling time also 2 H. Space, water and frost-resistant granules were obtained, their bulk density (Fraction 5 to 12.5 mm in diameter) was 1.1 kg / m3. The cylinder compressive strength is 56 5 parts by mass of ash granulate were with 1 part by mass of ash in this Example, marked quality in the manner described in Example 2, see below Hollow blocks processed, with stones with a dry bulk density of 1.53 kg / dm³ and an average 1 day compressive strength of 32 kgf / cm². They were resistant to the effects of water and frost.

Claims (3)

Claims 1. Process for the recovery of fly ash, alone or in combination with known surcharges, in particular for the production of building materials, characterized in that that ashes with an SO3 content of 3 to 15 mass% and a content of 40 to 90% active ingredients converted to SO3-free and 100% active substance between 8 and 25 mass% SiO2 18 and 45 mass% Al2O3 + Fe2O3 and 35 and 75 mass% Must contain CaO + MgO, preferably with water at temperatures of 50 to 90 ° C 60 bia 800C set under hydrothermal conditions, creating within a period of time Resistant to room, water and frost changes within less than 24 hours after the start of production Building materials are preserved. 2. The method according to claim 1, characterized in that the ash alone or in a mixture with known additives in granulated form the hardening conditions be subjected. 3. The method according to claim 1, characterized in that the water and frost-resistant ash concrete in well-known crushing units to grit with bulk densities from 0.6 to 1.4 kg / dm³ is broken up.