Light fine-grained fibrous concrete for small architectural forms

The selection of the composition of a highly mobile concrete mixture for manufacturing small architectural forms has been performed, and the strength characteristics of light fine-grained fibrous concrete have been studied. It has been experimentally established that the optimal ratio of the Portland cement to microsilica is 1: 1. The introduction of basalt fiber in the amount of 0.5% of the mass of solids contributes to the increase in bending strength of fine-grained concrete to 70%. The construction process involves working not only with heavy structural elements, but also with decorative concrete products designed for decoration and decoration of facades and building interiors, and used as small architectural forms. Small architectural forms (SAF) have a great impact on the emotional state of a person. Their use allows to fill the empty space in the room or on the ground, embodying many ideas architects and designers have. SAF specificity is the production of thin-walled products of complex configuration with an abundance of small elements. This makes it difficult to use hard concrete mixes. The use of highly movable (cast) concrete mixtures based on traditional materials contradicts the need to ensure strength and durability [1]. The analysis of the literature sources [1-21] made it possible to establish that the use of industrial by-products and dispersed-reinforcing additives in fine-grained concretes makes it possible to increase their strength characteristics. The aim of the paper is to select the composition of a highly mobile concrete mixture for the preparation of light fine-grained fibrous concrete with increased strength characteristics. The following materials were used in the studies: Portland cement CEM II / A-III 32.5B (PC 400 D20) with a bulk density of ρn = 880 kg/m being produced by the “Angarskcement” JSC; White cement of the company “Cimsa” CEM I 52,5 R (PC 600) with a bulk density of ρn = 1440 kg/m (Turkey); Microsilica from filters of dust collectors made by the Silicon JSC with bulk density of ρn = 600 kg/m; * Corresponding author: baranova2012aa@mail.ru © The Authors, published by EDP Sciences. This is an open access article distributed under the terms of the Creative Commons Attribution License 4.0 (http://creativecommons.org/licenses/by/4.0/). MATEC Web of Conferences 212, 01008 (2018) https://doi.org/10.1051/matecconf/201821201008 ICRE 2018

The construction process involves working not only with heavy structural elements, but also with decorative concrete products designed for decoration and decoration of facades and building interiors, and used as small architectural forms.
Small architectural forms (SAF) have a great impact on the emotional state of a person. Their use allows to fill the empty space in the room or on the ground, embodying many ideas architects and designers have.
SAF specificity is the production of thin-walled products of complex configuration with an abundance of small elements. This makes it difficult to use hard concrete mixes. The use of highly movable (cast) concrete mixtures based on traditional materials contradicts the need to ensure strength and durability [1].
The analysis of the literature sources  made it possible to establish that the use of industrial by-products and dispersed-reinforcing additives in fine-grained concretes makes it possible to increase their strength characteristics.
The aim of the paper is to select the composition of a highly mobile concrete mixture for the preparation of light fine-grained fibrous concrete with increased strength characteristics.
The following materials were used in the studies: -Portland cement CEM II / A-III 32.5B (PC 400 D20) with a bulk density of ρn = 880 kg/m 3 being produced by the "Angarskcement" JSC; -White cement of the company "Cimsa" CEM I 52,5 R (PC 600) with a bulk density of ρn = 1440 kg/m 3 (Turkey); -Microsilica from filters of dust collectors made by the Silicon JSC with bulk density of ρn = 600 kg/m 3 ; -Chalk MTD-2 with bulk density of ρn = 525 kg/m 3 (Belgorod region); -Chalk CALCITEC V / 40S with a bulk density of ρn = 875 kg / m 3 (Italy); -Hyperplasticizer based on polycarboxylates "MC-Power-Flow-3100" with a density of 1.09 g/cm 3 (Germany); -Basalt fiber "Vulcan" (Perm city). The research method was as follows. The concrete mix was kneaded by hand. The water ratio was chosen in such a way as to ensure the uniform mobility of concrete mixtures with different component ratios. It is known from the previous work [22] that, due to the high water demand of microsilica, it is expedient to use it together with plasticizing additives. The amount of hyperplasticizer was taken constant. Compositions of concrete mixtures made on Portland cement CEM II / A-III 32.5B (PC 400 D20) are listed in Table 1. From uniformly mobile concrete mixtures size were molded the samples of 40x40x160 mm. On the third day, the samples were formed and placed in a normal hardening chamber. After 28 days of normal hardening, the samples were dried to constant weight and tested for bending and compression according to a standard procedure. The results are shown in Table  2. It can be seen from Table 2 that an increase in the amount of microsilica in a concrete mixture leads to a decrease in the mechanical characteristics of fine-grained concrete. The introduction of 10% of the mass of solid components into the composition of chalk MTD-2 makes it possible to increase the compressive strength of concrete by 4÷19% and the bending strength by 7 ÷ 42.5%; with the addition of chalk CALCITEC V/40S, the compression ratio was from 1 to 8% and with bendingfrom 11 to 32.5% [23].
Further studies were continued with composition No. 3 (Table 2), which has the largest coefficient of constructive quality.
To study the effect of the Portland cement brand on the strength properties of fine-grained concrete from concrete mixtures on different binders ( Table 3), samples of 40x40x160 mm were made. After 28 days of normal hardening, the samples were dried to constant weight and tested for bending and compression according to a standard procedure. The test results are shown in Figures 1 and 2.   It can be seen from Figures 1 and 2 that the use of high-strength Portland cement in the composition of light fine-grained concrete contributed to an increase in its strength characteristics: bending strength increased by 28%, compressive strengthby 37%.
To determine the influence of the amount of basalt fiber on the strength of bending finegrained concrete from concrete mixes with different percentage of basalt fiber (from 0.125% to 0.5% of the mass of solids), samples of 40x40x160 mm were made. After 28 days of normal hardening, the samples were dried to constant weight and tested for bending according to a standard procedure. The test results are shown in Figure 3. From the graph shown in Figure 3, it can be seen that the introduction of basalt fiber in an amount of 0.5% of the mass of solids contributes to an increase in strength when bending light fine-grained concrete to 70%.
It was experimentally established that: -The optimum ratio of Portland cement to microsilica is 1: 1; -The addition of chalk in an amount of 10% of the mass of solids to the composition of concrete mixtures has a positive effect on the mechanical properties of the finished concrete; -The introduction of a dispersive-reinforcing additive (basalt fiber) in an amount of 0.5% of the mass of solids contributes to an increase in the bending strength of fine-grained concrete to 70%.
The replacement of a sandy aggregate with microsilica by fine-grained concrete leads to a decrease in its average density to 900÷1040 kg/m 3 , which is approximately two times lower than the average density of fine-grained concrete on natural sand, which, according to the author's data [1], is 2058 kg/m 3 .