CS201805B1 - Process for preparing rapid hardened cement mixture - Google Patents

Description

(54) Production of quick setting concrete mixture

The invention relates to the preparation of a concrete mixture with accelerated setting.

In the conventional method of concrete production, a hydraulic cementitious binder was mixed with aggregate and water. The mixture thus prepared was placed in molds and / or molds, respectively. formwork, where it compacted and allowed to solidify and harden. In order to be able to handle and compact the fresh concrete mixture, the setting of the hydraulic binder had to be artificially retarded and twice as much water had to be added to the concrete mixture as was necessary to hydrate the cement itself, since the water in the mixture also functioned as a plasticizer. In order to retard the setting of the hydraulic binder, gypsum, gypsum fragments or even boric acid were added to this setting retarding additive. The presence of additives to retard the setting of hydraulic binders as well as the excess amount of water influenced the negative strength of the concrete.

The principle of dry concreting is based on eg. PREPAKT concrete technology, which consists in placing and compacting the gravel mixture into which the cement slurry is injected. In Concrete Constručtion 14 no. 12, published in 1969, is a concrete casting technology of dry cement-sand mixture into which water has been infused. However, the technology used traditional cement containing solidification retardant, therefore the maturation cycles were relatively long 3 to 7 days.

These drawbacks due to the need to control the solidification rate of the hydraulic binders and the drawbacks of the conventional process for the production of concrete are overcome by the method of making the quick setting concrete composition according to the invention. Its essence is that in the process process a dry concrete mixture of aggregates is produced, to which a hydraulic binder is added without solidification retarding additives such as gypsum, gypsum chips, boric acid and others. The dry mixture thus prepared is placed in a mold or structure where it is first compacted. The compacted mixture is moistened with water e.g. by spraying with nozzles above the surface, sprinkling, steam, soaking or grouting.

The advantages of the process according to the invention are, in particular, that a highly active hydraulic binder can be used in which the control of the solidification is difficult or almost impossible, and also that the course of hydration is not influenced by the presence of solidifying retardants. that it is not necessary to add more water to the mass than is necessary for the actual hydration and, ultimately, that it is not necessary to accelerate the subsequent hardening of the concrete with respect to production cycles as used in the sensible manufacture of building components.

Example

In a forced-mixer with a useful capacity of 500 liters, a mixture consisting of:

gravel - fraction 8 to 16 mm 360 kg strk - fraction 4 to 8 mm 100 kg sand - fraction 0 to 4 mm 420 kg cement - MRVC 500 140 kg

The mixture is discharged, transported in a transport basket and placed in an individual mold on a thatched prefabricated piece of dimensions 290X180X X8 cm, in which the steel reinforcement is already prepared. In the mold, the mixture 75 is compacted from above

Claims (1)

SUBJECT Process for the production of a quick setting concrete composition, characterized in that, in the process for producing a dry concrete mixture, a hydraulic binder is added to the aggregate which does not contain additives which harden the vibration shield, whose plate is perforated. During the vibration through the nozzles the surface of the concrete mixture is irrigated with water in a total amount of 28 L. The compacted concrete mold is transferred to a mist chamber where the concrete hardens. After 6 hours, the mold is removed from the mist chamber, the precast is demolded and transferred to a warehouse. The compressive strength of the concrete, which in the case of demoulding is in the range of about 8 to 10 MPa, will increase to 25 MPa within 24 hours and to 40 to 45 MPa in 28 days. The process of producing the quick setting concrete composition according to the invention can be advantageously used in particular in the manufacture of prefabricated parts, where it is possible to comply with production cycles without the need for energy consumption to accelerate the hardening of the concrete. The mixture and the mixture thus obtained are compacted in form and the water required for hydration is introduced into the mixture by spraying or sprinkling, steaming, soaking, or injection.