Method to determine composition of dry construction mix for concrete

FIELD: construction.

SUBSTANCE: previously prepared samples with various quantity of a filler in a highly dispersed condition for a dry construction mix are placed into a hollow part of metal washers, placed on a metal plate, are compacted by any available method under permanent load of up to 5 MPa per 1 cm2 of sample surface for 10-15 seconds, then marks are applied on the surface of each sample in the form of drops of a solution of various concentration, wetting angles of samples are measured θ, a curve of dependence is built cosθ-1=f(1/σl), where σl - surface tension of the liquid, they determine the angle of inclination of this functional dependence a for each sample of different composition, the curve of dependence a is built on quantity of mix components, and by the point of break of the curve of dependence they define the optimal content of a modifier in the tested object.

EFFECT: reduced number of tests and higher accuracy of mixture composition selection.

2 cl, 2 dwg, 1 tbl

 

The invention relates to methods for determining the composition of the dry mix mortar for concrete filler in finely dispersed condition, which includes technological measures for measuring material properties in order to increase the strength and / or other performance characteristics of the concrete.

The optimum content of the filler in the composition of dry construction mixes for concrete is often determined experimentally.

There is a method of determining the composition of the dry mix mortar for concrete by measuring the mobility of mortar [GOST 31357-2007. A mixture of dry construction with cement binder. General specifications; GOST 5802-86. The mortars. Test methods]. In accordance with GOST 5802-86 the method includes a preliminary selection of the composition, mixing the starting components, preparation of mortar and based on the dependence of the mobility of the construction of the mortar mix and the magnitude of the depth of immersion of the standard metal cone relative to the surface of the mixture. This method is resource-demanding, less accurate and requires a large number of experimental tests.

There is a method of determining the flow of fine and coarse aggregate in the concrete mix by the values of bulk density and average protectionary and coefficient of separation of the grains of the coarse aggregate with a solution of [RU, patent 2014305, C04B 28/00, 1994]. This method relates to a method of operational control concrete mix, including the selection of the composition of the starting components, but it is very cumbersome, multi-stage, includes a large amount of experimental tests and inspections, adjustments calculations. This method is adopted for the prototype.

The task of the invention is to reduce the amount of experimental testing and improving the accuracy of the determination of the dry mixes for concrete.

Sample preparation is carried out as follows. Conducted selection and mixing of the original main components of dry building mix: aggregate (sand), binder (cement), water, and optional components: filler in fine condition, modifier, etc., In this particular case as a source of additional component was used filler in fine condition. The prepared samples with different amount of filler in fine condition for dry building mixtures are placed in a hollow part of the metal washers that are located on a metal plate, compacted by any known method under a constant load of 5 MPa on 1 cm2the sample surface for 10-15 seconds.

The determination is performed following the way. Prepare standard solutions of liquid, in this case water-alcohol solutions of ethanol of different concentrations. The sample is put a drop of wetting liquid. Parameters drops measure the contact angle of the surface θ. Formulate dependence

cosθ-1=f(1/σW),

determine the slope of this dependenceafor each sample of different composition. Build a dependency graphafor each sample, and the breakpoint graph dependencies define the optimum filler content in the tested object.

The surface tension of the standard liquid σWinstall any known method Rehbinder, method account drops and so on [Surface phenomena and surfactants: a Handbook/ by A. A. Abramson, L. E. Bobrov, L. P. Zaichenko, etc. - L.: Chemistry, 1984, 392 S., ill.]. In our case, we used a method of hanging drops, implemented on the installation Easy Drop intended for measuring surface tension, interfacial tension between two liquids, and also for measuring the wetting angle between the liquid and the solid surface. The measurement results of the surface tension of the liquid range of water-alcohol solutions ethanol are shown in table 1.

The invention is illustrated in the drawing, where Fig.1 presents zobrazeniearly, received by highlighting on the one hand, recording the camcorder (digital photography, observation under a microscope) and transfer to a computer for determining the contact angle of the surface of the test material. In this particular case was used in the laboratory setup Easy Drop, the measuring principle of which is based on highlighting drops on one side of the lifting table. Using DSA1 software analyzes the shape of the drop and is determined by the boundary angle. Calculate the cosine of the contact angle, build a dependency graph cosθ-1=(1/σW) determine the slope of this dependenceandproduce similar measurements and calculations for all of the subjects, objects with different filler contents. According to the data obtained for different percentage content of the filler in dry mixes build functional dependence ofafor each sample, and the break point of this graph determine the optimum content of the components of the test object (Fig.2).

The contact angle of the water-alcohol solutions of different concentrations to determine the installation Easy Drop on the phase boundary.

The surface tension of the water-alcohol solutions determined by the method of hanging drops. The tests were empirically selected physical parameters of the droplets, the diameter of the capillary ,821 mm Table 1 presents the results obtained values of the surface tension of water-ethanol solutions σW. All experiments were conducted at 22±1°C.

Table 1
№ p/pWater content,%vol.Wof ±0.02)×103N/m
1424,74
21026,61
32027,34
43028,11
54028,42
65031,31

According to the obtained values build a graph of functional dependencies

cosθ-1=f(1/σW).

This dependence is described by the equation of the straight line. Determine the slope of this functional dependenceand.

Similar experimental tests are conducted for all test objects with different content of fill who I am. Sample preparation is carried out analogously.

According to the data obtained for different percentage content of the filler in a dry building mix build dependencyafor each sample, and the break point of this graph determine the optimum content of the components of the test object.

The application of the method of determining the optimal composition of dry construction mixes for concrete filler in fine condition allows to obtain such a mixture, which increases the strength of the samples and / or other performance characteristics of the concrete, without the need for multiple, material-intensive and time-consuming experimental tests.

1. The method of determining the composition of the dry mixes for concrete, including the selection of the composition and mixing the starting components of the mixture, characterized in that the surface of the test object put labels liquid drops, measure the angles of wetting the samples θ, build a graph of functional dependencies
cosθ-1=f(1/σW), where σW- the surface tension of the liquid, determine the slope of this dependenceandbuild a dependency graphandthe number of mixture components, and the break point of this graph determine the optimum content of the components of the test object.

2. The method according to p. 1, characterized in that the when asked liquids used are water-alcohol solutions of different concentrations.



 

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