CS240653B1 - Pressure dispersion reinforcement - Google Patents

Abstract

The invention relates to a pressure dispersion reinforcement for structural concretes, made of coarse aggregate, cement mortar and steel spacers and made of concrete mixtures with a low water to cement ratio, and mixtures in which the settlement of the steel spacers is prevented. The steel spacers have a slenderness ratio of length to diameter of 10 to 20 and are evenly dispersed in the concrete

Description

The invention relates to a pressure dispersion reinforcement for structural concretes made of coarse aggregate and cement mortar. The purpose of the invention is to improve some important mechanical properties of concrete, in particular to reduce the volume changes of commonly produced structural concretes with a volume, weight of approximately 2,300 kg/m^.

Concretes produced so far show volume changes that are not negligibly small and significantly affect the design and calculations of structures. These changes are determined according to standards that necessarily take these properties into account and determine their calculation values. In the last ten years, concrete reinforced with tensile dispersion reinforcements, mainly made of thin steel fibers, has experienced significant development. The use of these reinforcements shows that there is still a search for improvements in the composition and structure of concrete so that adverse properties are reduced or eliminated. Dispersion reinforcement is inserted into these concretes in order to prevent the formation and development of cracks in concrete, which leads to an increase in some physical and mechanical properties of concrete, especially tensile strength. The parameters of steel dispersion reinforcements range from diameters of 0.1 mm to 0.8 mm with lengths of 50 to 150 diameters. In world literature, these parameters are given as the ratio of length to diameter, i.e. 1/d = 50 to 100.

The above-mentioned shortcomings are eliminated by the pressure dispersion reinforcement for structural concretes, made of coarse aggregate, cement mortar and steel spacers and made of concrete mixtures with a low water-to-cement ratio and mixtures in which the settlement of the steel spacers is prevented, according to the invention. Its essence lies in the fact that the steel spacers have a slenderness ratio of length to diameter of 10 to 20 and are evenly dispersed in the concrete.

240,853

The basic effect of the reinforcement according to the invention consists in reducing and limiting the unfavorable properties of cement stone in concrete, which leads to a reduction in the volume changes of concrete, in particular shrinkage and creep.

The arrangement of this reinforcement in the concrete structure is such that it 'spans the individual grains of coarse aggregate arranged in the space of the structure by bridging their distance through the cement mortar'.

Short and relatively strong dispersion reinforcements act in the concrete structure as spacers between individual grains of coarse aggregate, i.e. they concentrate the compressive stresses in the mortar, which arise in the structure, on themselves and transfer them between the expanded grains of coarse aggregate through the areas of cement stone - mortar. The spacers thus create a spatial lattice framework in the concrete structure, which, by expanding the grains of coarse aggregate, reduces the volume changes occurring mainly in the mortar, i.e. in particular shrinkage and creep.

Experimental tests were carried out on test specimens with dimensions 10/10/10, 15/15/15 and 10/10/40 in several consecutive series and in variants - plain concrete and concrete with spacers. The number of samples was chosen in threes, only in the case of cubes 10/10/10 in six pieces. After processing the resulting 28-day compressive strengths of concretes, a 10% to 20% increase in strength was shown in samples made of concrete with spacers. In the samples on which shrinkage was measured, it was found in the final phase of measurement that shrinkage in concrete with spacers is 25% to 55% less. Shrinkage measurements were carried out continuously at intervals given by standards for a period of two months.

The spacer reinforcement according to the invention is further described in more detail with examples of embodiments, which can be seen from the table below.

example

Composition of the mixture

Spacer mixture /plain concrete/

Mixture with spacers cement water

471

212 kg

458

206 kg

- 3,240,053

sand /0-4/ 1226 kg 1191 kg gravel /12-16/ 451 kg 451 kg liquefier /UMAFORM/ 6.6 kg 6.4 kg spacer reinforcement /soft wire jaf 1.2 mm/ m _a - length 7 mm - 20 kg mfc - length 15 mm - 87 kg m _c - length 22.5 mm - 82 kg

The spacers were calculated as the shortest connecting lines between the largest grains of coarse aggregate /gravel 12-16/, which are considered as ideal spheres with a mean diameter of 14 mm with uniform dispersion in a cubic arrangement. The number of spacers indicates:

mg - quantity in the edges of the cubes πη-, - quantity in the walls of the cubes m _c - quantity in the solid diagonals.

As part of the experimental investigation, the following were made from the mixture:

and 6 pcs 3 pcs - á 3 pcs cubes 100/100/100 mm cubes 150/150/150 mm beams 100/100/400 mm Measured values:

cube-shaped fortresses - without spacers

- with spacers, shrinkage of beams after 56 days

- without spacers

- with spacers approx.

100%

115 to 120%

100%

The use of spacer reinforcements therefore reduces the volume changes of concrete. The use of concretes with smaller volume changes will find great application in construction practice not only from the point of view of technical needs, such as in tanks for liquefied gases, nuclear reactors, etc., but also from the point of view of saving materials in prestressed structures by reducing losses due to shrinkage and creep.

The specific use of spacer reinforcement is expected in concrete mixtures with a low water to cement ratio and in mixtures where their composition will prevent the spacer reinforcement from settling during processing and thus ensure their uniform dispersion in the concrete structure.

- 4 240 0S3

As a starting material for spray reinforcement, it is possible to use industrial waste that meets the parameters of spray reinforcement, such as from a nail factory.

Claims (1)

SUBJECT OF THE INVENTION Pressure dispersion reinforcement for structural concretes ^made of coarse aggregate, cement mortar and steel spacers and made of low-water-to-cement concrete mixtures and mixtures where the spacers are prevented from settling, characterized in that the steel spacers have a slenderness ratio of length to a diameter of 10 to 20 and are evenly dispersed in the concrete.