RU2795808C1 - Soil concrete for road construction - Google Patents

Abstract

FIELD: road building materials.

SUBSTANCE: invention relates soil concrete and can be used as an underlying layer of pavement or for the construction of layers of pavement bases. Soil concrete for road construction includes components in the following ratio, wt.%: light sandy loam 87.5-90.5, Portland cement 4.25-5.25, bitumen emulsion 4.25-5.25, acid fly ash 1-2.

EFFECT: improving the physical and mechanical properties: with high compressive strength, high flexural strength, low swelling.

1 cl, 5 tbl

Description

The invention relates to road building materials, namely soil concrete, and can be used as an underlying layer of pavement or for the construction of layers of pavement bases.

From the prior art, various compositions of soil-concrete for the construction of structural layers of roads based on clay soils are known, involving the use of binders of various types of hardening and additives, including industrial waste in the form of mineral raw materials.

Known compositions of mixtures for soil concrete (Patent RU No. 2392244, publ. 20.04.2010, bull. No. 17), containing clay soil, binder, additive and water, while the enzyme preparation "Dorzin" is used as a chemical additive, and as a binder – Portland cement with the following ratio of components, wt %: clay soil – 78–83; portland cement - 4–8; "Dorzin" - 0.03–0.06; water is the rest. The disadvantages of these mixtures include the high material consumption of traditional active reinforcing components - Portland cement to achieve the necessary physical and mechanical properties.

Known composition for the device of the lower layers of the bases of pavements (Pat. RU No. 2468139, publ. 27.08.2012, bull. No. 24), taken as a prototype, including a mineral binder - cement, ash and slag mixture, asbestos-cement production waste (OACP) and tall pitch at the following ratio of components, %: soil 52.0–60.0; cement 3.0–5.0; ash and slag mixture 12.0–18.0; ADC waste 5.0–7.0; water 14.0–22.0; saponified tall oil pitch 0.5–1.5 by weight of cement.

The disadvantages of the above composition is: insufficiently high physical and mechanical properties of soils reinforced with cement and complex additives, with a sufficiently high content of components for strengthening. In addition, among the characteristics of the final material, the effect of water on the reinforced soil is not taken into account, i.e. characteristics such as: compressive strength of water-saturated samples at a temperature of 20°C; tensile strength in bending of water-saturated samples at a temperature of 20°C; swelling.

The invention is directed to the development of soil concrete for road construction with improved physical and mechanical properties: high compressive strength, high flexural strength, low swelling.

This is achieved by the fact that the soil concrete for road construction includes clay soil, binders and an additive, while the clay soil is used in the form of light sandy loam, the mineral binder Portland cement and the organic binder bitumen emulsion are used as the binder, acid ash is used as the active mineral additive. entrainment, with the following ratio of components, wt.%:

light sandy loam 87.5-90.5 Portland cement 4.25-5.25 bituminous emulsion 4.25-5.25 acid fly ash 1-2

Component Feature:

1. Light sandy loam.

To study the possibility of producing soil concrete, a common natural soil was considered - light sandy loam. Its normalized physical and mechanical properties were studied in accordance with GOST 25100–2020, the granulometric composition and mineral composition of the soil according to X-ray phase analysis (Table 1).

2. Portland cement brand CEM I 42.5M., GOST 31108–2016.

3. Slowly disintegrating bitumen emulsion, its characteristics (table 2).

table 2

Properties of road bitumen emulsion brand EBDK-M

Index Values required by GOST R
58952.1–2020 Decay index when using quartz sand >260 Binder content with emulsifier, % 58–62 Residue on sieve No. 014, %, no more 0.25 Nominal viscosity at 40°C, s, no more thirty Residue on sieve No. 014, after storage for 7 days %, no more 0.30 Delamination resistance, 7 days storage, %, no more 5 Adhesion to mineral material, %, no more 50–100

4. Acid fly ash, for example, Troitskaya GRES.

Acid fly ash from the Troitskaya GRES was considered as an active mineral additive with a structuring effect, the physical and mechanical properties of which, in accordance with GOST 25818–2017, and the mineral phase composition are shown in Table 3.

Table 3

Physical and mechanical properties of acid fly ash

Troitskaya GRES and its mineral-phase composition

Physical and mechanical properties in accordance with GOST 25818–2017 Name of indicator Values Specific surface according to PSC, m ² /kg 495 Residue on sieve No. 008, wt. % 15 Water demand, % 73 Activity index for 28 days. 84 Activity index for 90 days. 95 Mineral-phase composition Component name Content, % Quartz 9.25 Mullit 18.69 Magnetite 1.87 RAS 70.19

To study the properties of soil concrete for road construction, the compositions of soil concrete mixtures given in Table 4 were considered.

Table 4

Soil concrete compositions for road construction

Component name Quantity, % Prototype Composition 1 Composition 2 Composition 3 Composition 3 Priming 52 89.25 87.5 89 90.5 Cement 5.0 6.25 5.25 4.75 4.25 fly ash - - 1 1.5 2 bituminous emulsion - 4.5 5.25 4.75 4.25 ZShS 12 - - - - OACP 9 - - - - Tallow pitch (depending on cement content) 1.5 - - - -

For experimental verification of the proposed optimal composition of soil concrete for road construction, various variants of mixtures based on clay soil were made with a combination of all components both within the proposed compositions and outside the indicated values.

The preparation of a soil-concrete mixture with the addition of mineral and organic components for complex strengthening was carried out as follows. Cement and fly ash were added sequentially to a sample of soil 87.5-90.5 g with obligatory mixing. It should be noted that fly ash was introduced instead of a part of the cement (20–30% by weight of cement, in 5% increments). After obtaining a homogeneous mass, the calculated amount of bituminous emulsion was introduced and mixing was continued for 2-3 minutes. Physical and mechanical parameters were determined in accordance with GOST 30491–2012 Sample preparation and equipment were used in accordance with GOST 12801–98. Samples were molded from the obtained soil-concrete mixture in the form of cylinders with dimensions of 50×50 cm and beams with dimensions of 4×4×16 cm, which, after storage in natural conditions for 28 days, were tested to determine: compressive strength; ultimate strength in bending; compressive strength of water-saturated samples at a temperature of 20°C; tensile strength in bending of water-saturated samples at a temperature of 20°C; frost resistance coefficient; swelling. The results of comparative tests are shown in table 5.

Table 5

Physical and mechanical properties of soil concrete compositions

Properties Name of soil concrete composition: Proto
-type Composition No. 1 Composition No. 2 Composition No. 3 Composition No. 3 Compressive strength, MPa 5.59 6.04 5.99 5.95 4.89 Bending strength, MPa 0.97 1.78 1.89 1.95 1.68 Shrinkage, mm/m 0.6 0.5 0.5 0.4 0.9 Compressive strength at 20°C, MPa - 4.91 4.79 4.75 4.28 Compressive strength of water-saturated samples at a temperature of 20°C, MPa - 2.92 3.03 3.14 2.81 Tensile strength in bending of water-saturated samples at a temperature of 20°C, MPa - 1.73 1.82 1.91 1.64 Frost resistance coefficient - 1 1.1 1.2 0.9 Swelling, % by volume - 1.1 1 0.9 1.2

Thus, soil-concrete samples for road construction were obtained and tested on the basis of clay soil - light sandy loam with the use of Portland cement, bitumen emulsion and an active mineral additive with a structuring effect - acid fly ash from the Troitskaya GRES under the influence of different loads under different conditions. The developed soil concrete in comparison with the prototype has an increased compressive strength (by 6%); ultimate strength in bending (2 times); reduced shrinkage value (30%). At the same time, the improvement of the physical and mechanical properties of the developed soil concrete in comparison with the prototype is ensured at lower resource costs, and the use of fly ash instead of part of the cement makes it possible to reduce its consumption. In addition, compared with the composition of soil concrete without the use of fly ash (table 5, composition 1), the developed soil concrete (table 5, composition 3) has improved: compressive strength of water-saturated samples at a temperature of 20 ° C (by 7%); tensile strength in bending of water-saturated samples at a temperature of 20°C (12%); frost resistance coefficient by (20%); swelling (by 5%).

The proposed composition (Table 5, Composition 3) of the mixture allows achieving the stated result - improving the physical and mechanical properties of soil concrete - due to the fact that a complex of binders is used in combination with an active mineral additive (which is a key feature), which acts as a structure formation regulator, in the form of acidic fly ash Troitskaya GRES in the amount of 1.5% by weight of the mixture.

The introduction of a larger amount of an active mineral additive in the form of acid fly ash from the Troitskaya GRES is impractical, as it leads to a decrease in strength indicators, the introduction of a smaller amount of the structure formation regulator of the additive does not allow achieving the necessary activity of cement and redistribution of bitumen after emulsion breakdown due to insufficient concentration of the additive, which leads to to reduce the physical and mechanical properties of soil concrete.

The role of fly ash is to regulate the structure formation of soil concrete. At the optimal ratio in the system “soil + cement + bitumen emulsion + fly ash”, free portlandite is bound to acid fly ash as a result of a pozzolanic reaction with the formation of a developed network of hydrate compounds of various composition and morphology, unreacted ash acts as selective centers of adsorption of the emulsion, providing a uniform distribution of bituminous films in the volume of the composite without physical sorption by clay particles. This circumstance contributes to the achievement of the necessary physical and mechanical parameters of the structural layers for pavement made of soil concrete. It should be noted that fly ash is used in its natural form without additional activation.

Claims (2)

Ground concrete for road construction, including clay soil, binders and an active mineral additive, characterized in that clay soil is used in the form of light sandy loam, the mineral binder Portland cement and organic binder - bitumen emulsion are used as the binder, acid ash is used as the active mineral additive. entrainment, with the following ratio of components, wt.%: light sandy loam 87.5-90.5 Portland cement 4.25-5.25 bituminous emulsion 4.25-5.25 acid fly ash 1-2