1. Introduction
The current stage of the development of civilization is characterized by a deteriorating environmental situation, a lack of energy resources as well as natural and technological disasters [
1,
2,
3]. A person spends a significant part of his time surrounded by building materials that are designed to protect him from the negative effects of the environment [
4,
5,
6]. Natural or artificial aggregates are the main part (up to 90% by volume) of concrete and mortars; therefore, their quality and properties are largely determined by aggregates [
7,
8]. The problem arises in the difference in properties of aggregates obtained even from the same rock. For example, to save the binder, it is necessary that the strength of the aggregate is 1.2–1.5 times higher than the design class of concrete. This indicator mainly depends on the density and structure of the aggregate [
9]. The operational properties of aggregates are determined by the mineral and chemical compositions and water and frost resistance. The important characteristics of the aggregates also include the shape of the grains, the nature of the surface, structure, chemical composition, as well as economic indicators.
Many authors have worked on research to develop innovative sustainable concrete and/or mortar utilizing some aggregates. Longo et al. [
10] obtained lightweight solutions based on geopolymers for structural and energy upgrading of buildings. Cobo Ceacero et al. [
11] used marble slurry waste to produce sustainable materials in a circular economy. Torres et al. [
12] studied the incorporation of granite cutting and polishing waste into building materials. Tolstoy et al. [
13] studied in some detail the synergistic effects of different aggregates on the performance of green concrete. Klyuev et al. [
14] developed high-strength fiber-reinforced concrete based on Russian aggregates. Bessmertny et al. [
15] researched environmental thermal insulation composites using rock waste.
Of great importance is the cost of aggregates while taking care of the environment. An effective step along this path is the use of simultaneously produced rocks.
Granite, gravel, and limestone are the most popular and widespread sources of crushed stone, which are expensive, and their deposits are not available in all countries [
10]. The search for alternative rock sources distinguishes four groups: ore-containing quartzites, quartz sandstones (QS), crystalline schists, and dyke rocks. In terms of reserves and physicomechanical properties, QS are of great interest [
16]. In References [
17,
18,
19,
20], a detailed assessment was made of the quality of commonly available quartz-bearing rocks of sedimentary genesis: metamorphic, effusive igneous rocks, aluminosilicate rocks of the green shale degree of metamorphism, and carbonate rocks were studied. It has been established that with the identical mineral composition of rocks of the same name in petrographic groups, their energy potential can significantly differ [
21,
22]. The free internal energy contained in the structure of the raw material is determined by the imperfection of the crystal lattice of minerals, the inclusion of a mineral-forming medium, gas–air inclusions, the presence of an X-ray amorphous substance, surface morphology and texture, degree of crystallinity of minerals, dimension, etc. [
23,
24,
25].
The goal of the paper was to study the possibility of using quartz sandstone, which is simultaneously mined rock, as aggregate for greener high-strength concrete. To achieve this goal, the following tasks were solved, the determination of the activity of natural radionuclides of the QS aggregate, the development of greener high-strength concrete using quartz sandstone (screening as fine aggregate and crushed stone as coarse aggregate), and the study of the physicomechanical properties and durability characteristics of developed concrete.
3. Results and Discussion
3.1. Preparation of QS Aggregate
To maximize the disclosure of the stored energy of raw materials and their directed use while reducing the energy intensity of the technological process for producing building composites, the methods of chemical, thermal, and mechanical activation were used. The article used an energy-efficient, environmentally friendly method of non-thermal effects of electromagnetic pulses on the destruction mechanisms of quartz-containing raw materials. When current flows with extremely high power but moderately low energy through the matrix of mineral components, electrical breakdown channels as well as induced fracture zones are formed. This leads to the softening of mineral complexes with the formation of highly dispersed particles of increased activity and solves the problem of the destruction of raw materials. As a result, the number and nomenclature of hydration products increases and the density of the concrete increases; this leads to an increase in the mechanical properties of concrete.
According to the provisions of geomimetics science on the affinity of structures proposed by Lesovik [
32], for designing an optimal composite, it is necessary that its components have the same linear expansion coefficients, deformation characteristics, adhesive characteristics, etc. Therefore, taking into account the genesis of the raw materials, it is possible to form a composite structure of a given quality [
33].
Table 4 lists the deformative characteristics of quartz sandstone, allowing its use for aggregate in heavyweight concrete.
3.2. Ecological Safety of Quartz Sandstone
The environmental indicators of aggregate from quartz sandstone of simultaneously mined rocks from the Lebedinsky deposit were determined. The specific effective activity of natural radionuclides
Aeff was determined. In order to obtain the value of
Aeff, the specific activity of radium
226Ra—
ARa, thorium
232Th—
ATh, and potassium
40K—
AK was measured and summarized according to the formula:
Aeff =
ARa + 1.31
ATh + 0.085
AK (
Table 5). It was found that the activity of natural radionuclides of the tested aggregate from quartz as was almost three times lower than that of the granite crushed stone of the Novopavlovsk deposit and four times lower than that of gabbro diabase. This indicates the indisputable advantage of the studied aggregate made of QS for use in cement systems.
3.3. Physicomechanical Properties of Concrete
In order to identify the influence of the type of coarse aggregate on the physicomechanical properties of concrete, the compositions were assigned according to
Table 3 from the condition of ensuring equal consumption of crushed stone of three types. At the same time, the ratio of the mass of fine aggregate to the total mass of aggregates was taken to be 0.4 to ensure maximum packing density. Concretes of classes C 25 and C 30 were taken as targets to ensure the specified strength characteristics (
Table 6).
The density of concrete mixes with quartz sandstone coarse aggregate was higher than in the case of granite and gabbro diabase. Thus, with constant consumption of materials, the replacement of the traditional coarse aggregate with quartz sandstone one reduces the weight of the structure, increasing its capacity for multi-story construction. At the same time, there was no increase in water demand and, as a result, a noticeable increase in the water–cement ratio. This eliminated the possibility of segregation of the concrete mix. In addition, there was an increase in compressive strength of 10–12% and flexural one by 15–25% compared with control specimens.
However, for specimens using quartz sandstone screening as a fine aggregate, there was a slight increase in water consumption. Obviously, this was due to the fact that the obtained quartz sandstone aggregates had more microcracks, which in turn increased the absorbent area for water. At the same time, in the next section, it is proved that due to the fact of these microcracks, a better adhesion strength of the cement paste to the aggregate—that is, a denser interfacial transition zone (ITZ)—is ensured.
3.4. Interfacial Transition Zone
Granite consists of 30–35% quartz, approximately 60% feldspars, and the rest is mica. The cleavage of feldspars is perfect, but that of mica is very perfect. The adhesion to cement paste for feldspars and mica is very low, so granites cannot be used to produce high-strength concrete [
17,
18]. Gabbro diabase is an intrusive main rock consisting of plagioclase, augite, titanomagnetite, pyroxenes, and amphiboles [
18,
19]. These minerals also show low adhesion compared to quartz sandstone. The SEM images and XRF data explain the higher strength of concrete on quartz sandstone compared with the strength of concrete on granite crushed stone (
Figure 4,
Figure 5,
Figure 6 and
Figure 7). This is because quartz contained in QS has crystal lattice defects that are present in granite quartz in much smaller quantities. Therefore, the quartz of QS has a greater energy intensity and reactivity which determines its properties in comparison with granite. This is confirmed by testing prototypes of concrete on a crushed stone from quartz sandstone and granite. The structure of concrete with QS is characterized by the high density and strength of the interfacial transition zone (
Figure 4a). By the finish of the hydration process, the pores are almost completely overgrown with crystals of hydrosilicate, hydroaluminate, and hydroferritic phases (
Figure 4b), which perform a monolithic and reinforcing function, creating a strong network structure around the aggregate grains (
Figure 4c). On the XRF pattern (
Figure 5), the reflections of the new growths confirm the presence of calcium hydrosilicates and the absence of portlandite in the ITZ with crushed stone.
3.5. Weather Resistance
In the granite structure, quartz does not have as many crystal lattice defects as in quartz sandstone, which explains its lower reactivity. The ITZ is less dense; microcracks are present in it (
Figure 6). This is confirmed by the nature of the new growths that are represented not only by calcium hydrosilicates but also by a significant amount of portlandite in the interfacial transition zone of crushed granite (
Figure 7), which has a lower adhesion to the surface of the aggregate. Thus, a high degree of adhesion of the cement paste to the surface of the aggregate made of quartz sandstone was established in comparison with crushed granite.
For structural materials operating in environmental conditions, weather resistance is of great importance, which affects the durability characteristics.
Table 7 lists the results of determining the freeze–thaw resistance and water resistance of the concrete. It was established that utilization of crushed stone from quartz sandstone provided greater freeze–thaw resistance and water resistance compared to the gabbro diabase or granite specimens. The test results indicated high durability of the obtained concrete. When cement consumption was 350 kg/m
3, the water resistance of concrete corresponded to the W6 grade, and with an increase in cement consumption to 400 kg/m
3, it increased to W12–W14. The freeze–thaw resistance of the concrete complied with grades F200 and F300.
Thus, concrete with a crushed stone from quartz sandstones exceeds a similar type of concrete from granite or gabbro diabase crushed stone in strength. The value of compressive strength corresponded to classes C25 and C30. An increase in compressive strength by 14% in concrete with quartz sandstone indicates the possibility of reducing the consumption of cement in such concrete.
It was established that the use of crushed stone from quartz sandstone provided greater freeze–thaw resistance and water resistance compared to the gabbro diabase or granite specimens. The test results indicated high durability of the obtained concrete. When cement consumption was 350 kg/m3, the water resistance of the concrete corresponded to the W6 grade, and with an increase in cement consumption to 400 kg/m3, it increased to W12–W14. The freeze–thaw resistance of the concrete complied with grades F200 and F300. Thus, concrete with crushed stone from quartz sandstones exceeded similar types of concrete with granite or gabbro diabase crushed stone in strength. The value of compressive strength corresponded to classes C25 and C30. An increase in compressive strength by 14% in concrete with quartz sandstone indicates the possibility of reducing the consumption of cement in such concrete.
3.6. Economic Efficiency
The economic efficiency of the results of the work was to reduce the cost of aggregates through the use of mine waste. In addition to the fact that this waste had no value, it can also generate income for the one who is utilizing it. The environmental objective achieved along with this makes it possible to consider the developed material with the use of aggregates from mine waste as cost-effective and environmentally effective.
4. Conclusions
Quartz sandstone is a mine waste; therefore, its use in construction allows both for reducing the cost of the concrete and contributing to the utilization of waste. The novelty of this study is the identification of models of the effect of QS aggregate on the physicomechanical, durability characteristics, and eco-safety of concrete. In the investigation campaign, the properties of greener high-strength concrete made with QS aggregate was investigated, bearing in mind the provisions of geomimetics science on the affinity of microstructures. Results were obtained on the properties of aggregate made of quartz sandstones activated by non-thermal effects of electromagnetic pulses as well as the heavyweight concrete based on it. On the basis of the results obtained, the following conclusions are listed:
- −
Quartz sandstone, which is a mine waste, can be used as aggregate for a high-strength, greenest concrete;
- −
The activity of natural radionuclides of the tested aggregate from quartz sandstone is 3–4 times lower than that of traditional types of crushed stone: granite and gabbro diabase;
- −
The use of a crushed stone from QS provides concrete with strength corresponding to grades C25 and C30. Mechanical properties of cement composite with coarse aggregate from quartz sandstone are 12–15% higher compared to concrete from traditional ones;
- −
The freeze–thaw and water resistance of concrete on crushed stone from QS provides a sufficient level of durability. The indicators of freeze–thaw and water resistance of concrete with a cement consumption of 300 kg/m3 corresponded to grades F200 and W8, respectively, and with a cement consumption of 400 kg/m3 corresponded to grades F300 and W14, respectively.
Furthermore, the perspectives for further scientific research can be directed to the possibility of obtaining aggregates from incidentally mined rocks for the creation of various building products. This will contribute to the expansion of the range of local raw materials used to obtain concrete components and the expansion of the field of research in the direction of studying the features of the processes of structure formation of composites using various fine and coarse aggregates.