DE2518799A1 - Rapidly setting concrete mixt. - prepd. from two premixes based on Portland cement and high alumina cement - Google Patents

Abstract

Prodn. of a hydraulically hardening mixt., esp. a concrete mixt. is improved by first preparing a premix contg. normal Portland cement and water, opt. with addn. of gravel, sand and other known additives and then admixing, before the beginning of the setting, another premix contg. a fused alumina cement and/or a cement predominantly consisting of 11 CaO. 7 Al2o3-CaX2 (in which X is Cl, Br, I or pref. F). The premixes alone set slowly (90 min.) but when they are mixed together the mixt. sets rapidly (within 3 min), and the concrete shows a considerable early strength. One or both premises can be heated so that the work can be carried out at temps. 0 degree C; additional heating is provided by heat liberation during the setting.

Description

Method of making a hydraulically hardening Zq ice chung The invention relates to a binder composition which quickly solidifies hydraulically and forms high strength early on.

In construction there is a great latent need for fast setting Cements present. This is mainly due to the advancing industrialization the precast concrete industry, where fast-setting cements are required for the production of concrete products in the continuous line process, but also in very large Quantities are used as shotcrete, e.g. in tunnel and tunnel construction.

Also the efforts of the construction industry, during the winter months in freezing weather Being able to work continuously through is partly due to the slow setting properties of the portlandsement currently in use, as the concrete mixes warmed up freeze through before they achieve sufficient strength.

A fast setting cement would be an advantage here and would bring it great economic benefit.

A characteristic of Portland cement is that after a Mixing the same with water this sets into a final product that is a sizeable one Has strength. However, such compositions have the property that the setting time compared to other cementitious products is very slow and that the initial set strength of the product is low and increases only relatively slowly during the setting period.

These relatively slow setting properties of the currently used Portland cement and the portland cement concretes have the consequence that the cycle for the molding, pouring and molding of concrete at least one and usually takes several days. A Portland cement whose setting time is controlled would speed up the construction process. There is also a big one The need for fast-setting concrete in concrete production plants in which such products are used such as blocks, pipes, architectural cladding, trusses, pillars, extruded products and various types of concrete sculptures are made. For example, if in a Such a plant rapidly sets, using three or four times a day instead of a single use per day, this would allow one Reduce the bulk of e-capital investments to a third to a quarter. With certain special uses, e.g. when repairing airport runways it would be desirable for a portland cement concrete to be available that would be in a Cast, peeled and sufficiently hardened in a shorter time than previously possible could.

In most of these cases it would set and harden quickly of concrete avoid many difficulties that traditionally slow set with a Concrete are connected. In many cases this would be the need for extensive Reduce wet curing times where the concrete is covering for the purpose of moisture retention or splashed, etc.

There are already a certain number of agents (so-called concrete admixtures) known that allow the usual Portland cement to solidify quickly. These are under called "solidification accelerator" available in building materials stores. These accelerators accelerate the setting and hardening of the concrete - measured in practical terms - but only insignificantly. Strong accelerators cause corrosion the reinforcing steel, so that apart from special areas of construction, could not prevail.

They are also fast in practice for narrowly limited areas of application hardening cements known, especially the so-called. Diibel cement made from a mixture consists of high-alumina cement and normal cement (see e.g. H.Kühl, "Zement-Chemie", VEB Verlag, Technology, Berlin). As the name of this cement suggests, it almost becomes used exclusively for setting dowels. The short solidification time of this Cements - 3 to 5 minutes after they have been mixed with water - leaves them for ruled out practical use in general concrete construction.

The same applies to modified Portland cements, which are considered to be accelerating acting clinker phase a calcium haloaluminate according to Dt OS 1929684 and the Dt OS 2124670 included and under the name nRegulated Set Cement "in the professional world have become known. However, these cements are only insignificantly longer-possible Processing times than the Lübelzemente (approx. 10 to 15 minutes) and could therefore also not enforce in practice.

However, there is, for example, the possibility of using dry gravel sand with each one of the two quick-release cements mentioned above (dowel cement, calcium haloaluminate cement) to mix and according to the known dry spraying process as shotcrete to process. In this process, the absolutely dry and therefore unlimited storable gravel-sand-cement premix pneumatically conveyed in a special system and - after adding water in the spray nozzle at the last moment of handling - was sprayed as a homogeneous, moist and hydraulically hardening concrete mixture. Due to the dry use of the gravel and cement premix and the addition of water in a special nozzle a few tenths of a second before the final installation of the finished In the concrete mix, the rapid setting time of the cements used is harmless.

Hygienic reasons - with the dry spraying process arises when using from absolutely dry gravel sand cement material always some dust - leave this procedure appear questionable in terms of health and work technology.

Furthermore, there are considerable costs involved in drying the in nature gravel sand extracted always moist. For economic reasons, this was absolutely necessary can also be used naturally moist.

Model calculations and practical explanations show that only the The process of drying the gravel sand makes this process uneconomical, so that it loses its practical importance.

In a nutshell, the main disadvantages of the previously known are then Fast cements called: Possible processing time too short, hence transport and Processing of the fresh concrete is hardly possible in terms of time.

The quick-release cements already react with their own moisture Aggregate materials. Drying the aggregate is more economical Considerations in practice not taken into account.

Because whole mixed batches always have to be processed immediately an adaptation to the intermittent demand is difficult.

Due to the rapid strength development of the rapid cement concretes Concrete attachments to mixing and conveying tools arise during continuous operation, which will soon lead to operational disruptions.

In the case of machine malfunctions that are unavoidable from experience and subsequent If the concrete that has not been discharged becomes hard, serious difficulties arise, e.g. total loss of aggregates even with relatively harmless errors that occur when using normal Portland cement are negligible.

If there is already a slight delay in the solidification time, a longer one The handling time of the concrete is supposed to bring about, the strength development is equally so delayed that this Cements only have insignificant advantages compared to normal portland cement.

Additional heating - e.g. required when used for winter construction - leads to a further drastic reduction in the already short processing time.

On the other hand, low temperatures below 10 ° C (e.g. during winter construction) a strong delay in the reactivity of these cements, so that the "rapid effect" very much faded.

The present invention is therefore based on the object of a Find hydraulically hardening binder composition as a preparation mixture can be processed for a sufficiently long time in practice before the final installation, on the other hand Forms strength quickly after installation. A premix ~ or a partial premix with damp gravel sand, the premix should not solidify too early to lead.

A solution to this problem has surprisingly been found in this way that you can use a normal, moist portland cement mix that has not yet solidified a suspension or concrete mixture with high alumina cement or calcium haloaluminate cement mixed in as a binder.

This can be done, for example, by putting one into a dry spray gun instead of giving up a premix of naturally moist gravel sand and normal Portland cement of the added water in the special nozzle, however, is a suspension of high-alumina cement plus added water. Both the portland cement mix and the suspension alone have solidification times of approx. 90 minutes. Solidify accordingly mixed however, in a mixture of, for example, 80 parts Portland cement and 20 parts Alumina cement is made within 7 minutes.

There is another possibility of mixing together - e.g. in precast concrete plants - in that normal portland cement concrete, for example at the start a screw conveyor with a suspension of calcium haloaluminate cement and water is inoculated, then mixed in the screw during the conveying process, and the discharged material then has the desired fast-setting properties. Since only a negligible amount of material remains in the screw conveyor, it can be used Method intermittent needs can be met without difficulty.

The following are the main advantages of the new process called: The supply mixes of Portland cement and high-alumina cements are can be processed for a sufficiently long time.

As a result, preparation mixes are also made from moist gravel sand possible.

Machine malfunctions in spraying devices do not end in a problematic manner, because there are no rapidly hardening compounds in the device.

Because with the dry spray process the feed mixture is slightly damp can be (e.g. due to naturally moist aggregate), no dust is generated during the Spraying process and at the same time there is less tendency to segregate.

One or more of the premixes can be additionally heated, whereby winter concreting work is possible even in severe frost. The one that will start soon rapid development of strength - due to the chemical reaction - creates additional Amounts of heat free, so that the concrete mass cools down before it has sufficient strength won is avoided.

The same conditions apply to bodies of frost (permafrost, icing of water-bearing soils in tunnel construction).

Intermittent needs for shotcrete work can be satisfied. Waiting times do not require absolutely empty concrete storage tanks of the sprayer, because the supply mixes can be processed for a sufficiently long time.

The portland cement concrete - as the main component of the fast hardening Mixture - can, for example, be taken from parallel production branches in which no rapid curing is required; a separate mixing plant is therefore unnecessary.

The inventive concept is to be explained in more detail using a few examples and clarified: Example 1 Fast-hardening concrete mix for production of a precast element Composition: Preparation mix 1 normal Portland cement mix: Cement content: 300 kg / m) PZ 450F Water-cement ratio: 0.5 Gravel sand: grain size 0 - 32 mm Preparation mixture II high-alumina cement suspensions with water-cement value: 0.4 Approximately 50 minutes after preparing the preparation mixes I and II these are mixed together in a small mixer located above the part formwork and emptied directly into the formwork. The concrete mixture obtained in this way solidified approx.

3 minutes after mixing together. Test cubes according to DIN 1048 brought the following concrete compressive strengths: Age according to the compressive strength Mixing together kg! Cm2 1 hour 45 2 hours 95 7 days 335 28 days 360 The component could be removed and transported after 2 hours.

EXAMPLE 2 Fast-curing shotcrete.

Composition: Preparation mix I after separate premixing to be fed into the storage tank of the dry spray machine; normal portland cement bed onmi s chung with naturally moist gravel sand: Cement content: 300 kg / m3 PZ 450F gravel sand: Grain size 0 - 8 mm, naturally moist about 5% by weight inherent moisture Hitherto known quick-release cements would have reacted quickly with the water contained in the gravel sand mixture and rendered the mixture unusable.

Provisioning mixture II suspension of the composition: 100 parts by weight Water, 75 parts by weight calcium haloaluminate cement with over 96% by weight of the clinker phase 11 Ca 0.

7 A1203 CaF2 as the main component.

As before, the suspension became the added water by means of a submersible pump and hose line of the fuel nozzle supplied without any at the spray device Changes had to be made. The suspension replaces the usual pure water.

The sprayed concrete mix had the following properties: None Dust generation during spraying; Solidification: about 2 minutes possible processing of the Deployment Mix: 1 hour; The following compressive strengths were obtained using an impact hammer determined: after 1 hour 50 kg / cm2 after 2 hours 100 kg / cm2 after 28 days 340 kg / cm2 using suitable Accelerators known in the specialist world (e.g. addition of waterglass or hydrated lime for Portland cement mixture) even shorter setting times and even faster ones Achieve strength development.

EXAMPLE 3 Shotcrete in winter construction.

Composition of the preparation mixes as in Example 2.

Temperatures: Portland cement-gravel sand mixture: 1500 suspension: 35 ° C Formwork (14 cm thick wall): - 6 ° C Ambient temperature: - 600 The wall from normal Wooden formwork was filled with shotcrete.

The fresh concrete temperature is 20 ° C.

The mixture solidifies after 5 minutes.

Concrete compressive strength: Age according to the associated temperature Mixing ture of the concrete ° C ability kg / cm2 1 hour 25 45 2 hours 26 85 Hrs. 2 103

Claims (17)

Claims 3 / method for producing a hydraulically hardening Mixture, in particular a concrete mix, characterized in that a first premix (so-called preparation mix) of normal Portland cement and water, if necessary with a content of gravel, sand, additives known per se or additives another premix consisting of high-alumina cement before the respective start of solidification (TSZ) and / or a cement with predominantly clinker phase of type 11 CaO.7A1203.CaX2 to CaX (calcium haloaluminate cement, CHZ) where the symbol X, chlorine, fluorine, bromine or iodine means and water and optionally gravel admixed. 2. The method according to claim 1, characterized in that as further premix calcium fluoroaluminate of the formula 11 CaO. 7A1203 CaF2 is mixed in with water and, if necessary, gravel. 3. The method according to claim 1, characterized in that the both premixes broken down into portions and the individual portions are added separately. 4. Process according to Claims 1 to 3, characterized in that one or more premixes are added dry, i.e. without water, and the others Premixes contain all of the required mixing water. 5. Process according to Claims 1 to 4, characterized in that Premixes are used that contain pit-moist gravel, while the other premixes contain the added water. 6. Process according to Claims 1 to 5, characterized in that the proportion of the other cement types in each case is between 0 and 100%, preferably in the favorable excitation range known from the literature, namely between 20 and 35%. 7. Process according to Claims 1 to 6, characterized in that for better mutual stimulation of the cements forming the components from the Dowel cement production of one or more substances that are known to be effective Premixes such as Ca (OH) 2 are added between 15 and 0% of the total binder content or Ealziumzincat, tartaric acid, Calciumligninsulfonat, Wasserglasqund that in the known correspondingly acting doses also additions of gypsum or anhydrite. 8. Process according to Claims 1 to 7, characterized in that after the premixes have been mixed together, the solidification time of the total mixture is set at 200C between 10 seconds and 70 minutes. 9. Process according to Claims 1 to 8, characterized in that by known accelerators in one or more premixes and in The solidification time of the total mixture is reduced with the appropriate dosage and / or the strength development is accelerated; possibly with compensation the retarding effect of low temperatures, such as the addition of calcium chloride, Soda or sodium fluoril. 10. The method according to claims 1 to 9, characterized in that one or more premixes are preheated for the purpose of acceleration and then begins. 11. The method according to claims 1 to 10, characterized in that the heating of one or more premixes the rapid hydraulic hardening the processed total mixture at temperatures below + 10 ° O, but preferably at far below 0 ° C, if necessary while enabling sensible spraying on frost bodies, such as in subway construction. 12. The method according to claims 1 to 11, characterized in that by adding retarders known per se in one or more premixes exclusively or predominantly the possible availability time of the respective Premix is extended, for example by adding citric acid, organic Substances like sugar. 13, method according to claims 1 to 12, characterized9 that by using retarders known per se in one or more premixes postpones the solidification time of the overall mixture, for example through the use of Na2B0407, citric acid or Seignette salt. 14. The method according to claims 1 to 13, characterized in that the addition of retarder to a heated premix does not allow for the possible handling time of the premix, but has no retarding effect on the overall mix exercises. 15. The method according to claims 1 to 14, characterized in that the W / C value of the total binder content is 0.2 to 1.0, preferably 0.3 to 0.5, where the W / C value in the premixes may be significantly higher, 16. Process according to Claims 1 to 15, characterized in that the mixing together the premixing in mixers known per se, optionally also in continuous ones Mixer carries out, 17. The method according to claim 1 to 16, characterized in that that the premixes are sprayed separately from one another from several shotcrete nozzles, so that the total mixture occurs during the flight in the air or on the impact surface.