STUDY AND SCIENTIFIC JUSTIFICATION OF THE EFFECT OF MATERIALS USED FOR COLORED CONCRETE ON THE PROPERTIES OF COLORED CONCRETE

ABSTRACT

This article analyzes modern approaches to the production of colored concrete using local materials. It was determined that the use of pigments and chemical admixtures not only improves the decorative properties of concrete but also enhances its physical, mechanical, and performance characteristics. The study revealed that a rational selection of mixture composition increases economic efficiency by reducing the consumption of colored cement and optimizing the use of fillers. The feasibility of applying effective methods for developing optimal concrete mix designs was substantiated in order to ensure durability, technological reliability, and competitiveness.

АННОТАЦИЯ

В статье проанализированы современные подходы к производству цветного бетона с использованием местных материалов. Определено, что применение пигментов и модифицирующих химических добавок позволяет не только улучшить декоративные свойства бетона, но и повысить его физико-механические и эксплуатационные характеристики. Выявлено, что рациональный подбор состава смеси способствует повышению экономической эффективности за счёт снижения расхода цветного цемента и оптимизации использования наполнителей. Обоснована целесообразность применения эффективных методов формирования состава бетонной смеси для обеспечения её долговечности, технологичности и конкурентоспособности.

Keywords: Colored concrete, coarse aggregate, fine aggregate, colored aggregate, gravel, chemical additives, plasticizers, pigments.

Ключевые слова: Цветной бетон, крупный заполнитель, мелкий заполнитель, цветной заполнитель, гравий, химические добавки, пластификаторы, пигменты.

Introduction

Selection of the optimal composition of fine and coarse aggregates for colored concrete: In the production of colored concrete, pigments are added to white cement depending on the desired color, resulting in colored concrete. However, in some cases, to achieve certain shades of colored concrete, it is necessary to use not only pigments but also colored fine and coarse aggregates. [1]

When calculating the concrete mix with colored aggregates, it is necessary to determine the properties of the aggregates used. First, the bulk density, true density, fineness modulus, and porosity of the colored fine aggregates are determined. [2]

Table 1.

The bulk density of the coarse aggregate used for colored concrete was determined

The true density of gravel particles is determined using a pycnometer. If the sample size is larger than 10 mm, 0.5 kg is taken; up to 10 mm, 1 kg is taken; for 40 mm, 2.5 kg is taken; and for 70 mm, 5 kg is taken. Dust and dirt from the sample are cleaned with a brush, and the sample is crushed to a size not exceeding 5 mm. Then, 150 g is weighed on a balance, crushed to a size not exceeding 1.25 mm, and 30 g is taken. The obtained powder is dried at a temperature of 105-110 °C until its mass becomes constant. From the dried gravel powder, two portions of 10 g each are weighed and placed into separate pycnometers. The pycnometers must be clean, dry, and pre-weighed on a balance.

Each filled pycnometer is then weighed. Afterwards, distilled water is added to about two-thirds of the volume, and the mixture is stirred. The pycnometers are placed at an angle in a sand or water bath. To remove air bubbles from the gravel powder particles, the water (or sand) in the pycnometer is boiled. Once the air bubbles are completely released, the pycnometer is wiped with a cloth and cooled to room temperature. Additional distilled water is added (up to the calibration mark on the neck), and the pycnometer is weighed again. Then, the water and gravel powder are removed, the pycnometer is thoroughly rinsed, refilled with distilled water up to the calibration mark, and weighed once more.

The true density of the gravel particles is calculated with an accuracy of 0.01 g/cm³. The true density of the gravel was found to be 2.6 g/cm³. [5]

P^g_x= 2.6 g/sm³

The voids between gravel particles are determined based on the previously calculated density of the gravel. The density of gravel (in volume percentage) is calculated using a formula with an accuracy of up to 0.1%.

Bulk density of crushed stone -. 1416  kg/m³. Average bulk density of gravel - .2.6  g/sm³. Space (by volume)- . . . %.

Calculation formula: organized the =(1-1.416/2.6)·100%=43.8%

Materials and Methods

In calculating the composition of colored concrete, the composition of ungraded gravel particles (coarse aggregate without fraction separation) was determined. [4]

Depending on the particle size of the gravel, 1000 g was taken and divided into the following fractions: 5-10 mm, 10-20 mm, 20-40 mm, and 40-70 mm. The particle size distribution of ungraded, unwashed colored gravel was determined by sieving the aggregate sample while simultaneously soaking and washing it. The sample is then dried: for instance, 420 g of gravel with a particle size of 10 mm, 300 g of gravel with a particle size of 20 mm, and so on. The sample is usually passed through sieves with mesh openings of 70 mm, 40 mm, 20 mm, 10 mm, and 5 mm. The residue retained on each sieve is calculated, and Table2 is filled in accordingly.[3]

Table 2.

Average size of the colored aggregate

It was found that M_k=A₇₀+A₄₀+A₂₀+A₁₀+A₅/100=30+72+94/100=1.96 cm or 19.4 mm. As a fine aggregate for colored concrete, the properties of sand obtained by crushing colored stones are determined.

Aggregates make up the main part of concrete. They account for 80–85% of the concrete volume, thereby forming the solid skeleton of the concrete, reducing shrinkage during drying, and preventing cracking.

Natural sands are classified according to their origin as river sand, sea sand, and pit (mountain) sand. The particles of river and sea sands are generally rounded in shape, while the particles of pit (mountain) sand are angular. Such angular particles bond well with concrete. However, pit sands usually contain more harmful impurities compared to river and sea sands.[5]

To calculate the composition of colored concrete, determine the volume of voids between sand particles, as well as for tasks such as sand transportation, designing storage facilities for aggregates, and similar calculations, the bulk density of the sand was determined. The results are presented in Table 3.[3]

Results and Discussio

Table 3.

Bulk density of the sand used for colored concrete

It was determined that the average bulk density of the sand, measured under laboratory conditions, is 1.392 g/cm³.

Table 4.

Absolute density of the sand used for colored concrete

It was determined that the density of the fine aggregate required for the composition of colored concrete is 2.56 g/cm³.

Table 5.

Moisture content of the sand used for colored concrete

The moisture content of the sand was found to be 3.6%. When calculating the composition of colored concrete, it was determined that this 3.6% moisture in the sand must be considered, and the water consumption should be reduced accordingly.[4]  In calculating the composition of colored concrete to achieve the desired strength, the properties of the white cement used must be determined.[2]

Table 6.

Effect of the pigment used for colored concrete on the normal consistency of white cement

As a result of the experiment, it was determined that the pigment added to white cement affects its normal consistency. The results showed that the pigment reduced the amount of water required in the cement mix by an average of 6.25%.

The setting times of cement paste were determined in accordance with GOST 310.3-76, and the obtained results are presented in Table 7.[1]

Table 7.

Effect of the pigment on the normal consistency of white cement

It was found that as the amount of pigment added to white cement increases, the setting time becomes longer. [2]

Conclusion

The conducted research has shown that the use of pigments and locally available colored aggregates significantly improves both the decorative and mechanical properties of colored concrete. The optimal selection of aggregate fractions and pigment dosage leads to better homogeneity, reduced water demand, and enhanced strength and durability. It was also observed that increasing pigment content extends the setting time of white cement, which must be considered in practical applications. Overall, the experimental results confirm that by applying a scientifically justified composition and using local raw materials, it is possible to produce high-quality colored concrete that is cost-effective, durable, and aesthetically superior.

References:

1.  Baranov E.V., Ph.D. (Eng.), Assoc. Prof., Shelkovnikova T.I., Ph.D. (Eng.), Assoc. Prof., modified decorative fine-grained concrete with plasticizer and filler additives.
2.  Batrakov V.G., D.Sc. (Eng.), Prof., Kaprielov S.S., D.Sc. (Eng.), modified concrete in modern construction practice.
3. Akramov X.A., Nuriddinov X.I., Raximov Sh.T., Turopov M.T., "Beton to’ldiruvchilari texnologiyasi". O’quv qo’llanma. T., Taki, 2010-167b.
4.  A.Akramov, H.N.Nuridinov. “Beton va temir-beton buyumlar ishlab chiqarish texnologiyasi”. Toshkent 2011. 593 b.
5.  Qosimov E., Samig‘ov N.«Qurilish ashyolaridan tajriba ishlari». Oliyo‘quv yurtlari talabalari uchun qo‘llanma.Toshkent-2010. -34-37b.