The Structure Features and Improvement of Concrete Properties with Dead Jellyfish Mass

Abstract

Currently, there is an environmental problem associated with cleaning the seas and oceans from a large number of dead jellyfish thrown ashore and into the coastal zone, which is urgent and requires solutions. This research aims to study the formation and properties of cement and concrete with added jellyfish mass and to understand the effects of this addition. Tests were carried out on formulations containing dead jellyfish mass in amounts from 0.2% to 1.6%. This study focused on the density, shear stress, workability, water separation, strength, and water absorption of cement and concrete, which are the main properties that characterize cement and concrete in construction. Adding 0.6% dead jellyfish to this composition resulted in greater effectiveness compared to the control composition. With this dosage, the normal density of the cement paste decreased by 16.3%, there was a 32% decrease in ultimate shear stress, the workability expressed in the cone slump increased by 60.8%, the water separation of cement decreased by 19.7%, the increase in compressive strength was 10.6%, and water absorption decreased by 15.5%. An analysis of the structure showed that the modification of concrete with dead jellyfish mass reduces the defectiveness of a concrete structure compared to the composition of the control structure.

1. Introduction

Currently, improving the characteristics of both concrete and structures made from it is mainly achieved through the use of innovative materials [1,2]. At the same time, the global agenda within the framework of the concept of sustainable development posits new requirements for the careful treatment of the environment and production processes [3,4], the rational disposal of waste, and the production of sustainable construction materials [5,6]. One of the most important tasks in achieving sustainable development goals in the world is lean production and maintaining the environmental friendliness of reservoirs and aquaculture from the large number of dead jellyfish thrown ashore and in the coastal zone.

An important feature of the sustainable development of regions that are located near water bodies is the problem of recycling aquaculture waste—that is, waste that arises in connection with human activity or, conversely, its absence in coastal areas [7,8,9,10]. One of these environmental problems is the accumulation of waste, the so-called dead jellyfish mass. In many regions adjacent to marine areas, there are periods when hundreds of tons of dead jellyfish washed ashore pose a threat to environmental safety. The disposal of such an array of jellyfish causes a significant problem [11]. This problem is widely known and covered in scientific and economic sources, and currently, this problem has not been properly solved. At the same time, a number of research institutes and scientific and other organizations conduct large-scale research to study the possibilities and ways of recycling aquaculture waste, including dead jellyfish mass, in various sectors of production, economics, and management [12,13,14]. One of the promising areas for recycling dead jellyfish mass is in the construction industry. A work of research published in 1985 [15] described studies on the effect of adding dead jellyfish mass onto the structure formation and properties of fresh and hardened concrete. The study showed the positive effect of dead jellyfish mass on the rheological characteristics of the mixture, namely on mobility, as well as on the mechanical characteristics of hardened concrete. This study, as well as previously known research considering the use of dead jellyfish mass in other sectors of the economy [16,17,18,19], provided impetus for additional research to study the effect of using Black Sea dead jellyfish as a plasticizing additive in cement composites and the development of existing ideas about the structure formation and properties of concrete using dead jellyfish mass.

The use of plasticizing additives in the manufacture of prefabricated and monolithic reinforced concrete structures is an integral part of any construction process [20,21]. The introduction of plasticizing additives into a concrete mixture makes it possible to increase the physical and mechanical characteristics and durability of concrete composites, reduce cement consumption, and also regulate the rheological characteristics and viability of concrete mixtures and the process of their structure formation [22,23]. Today, polycarboxylate-based plasticizers are the most popular among chemical additives [24,25,26]. These types of plasticizers are adsorbed in particles of cement and microsilica, contributing to a significant increase in the workability of concrete. Also, studies [27,28,29,30] confirm that the introduction of additional components, such as methacrylic ester, aminosulfonic acid, protein retarder, hydroxypropyl methylcellulose, and others, into the composition of polycarboxylate superplasticizers helps to increase their effectiveness. No less popular are lignosulfonate-based plasticizing additives. These types of additives are obtained as a result of sulfite pulping processes. They are less effective in comparison with polycarboxylate-based additives, but, due to their low cost, they are competitive and have become quite widespread in the market of concrete additives [31]. For example, in [32], the use of modified lignosulfonates with increased molecular weight in cement composites improves their rheological properties. Improvement in the rheology of cement composites and their setting time with the addition of lignosulfonate-based plasticizers has also been confirmed by a number of other studies [33,34].

Based on the results of the literature review, it was established that all existing plasticizing additives differ in composition and content from dead jellyfish mass. Dead jellyfish mass is a gel that contains organic substances, including microelements (Cu, Fe, Mn, Zn, Va, Rb, Si), as well as inorganic compounds (calcium and sodium chlorides) [15]. The proteins that constitute the dead jellyfish mass have surface-active tension, and, due to the presence of polar and non-polar groups, proteins are easily adsorbed on various solid surfaces. Along with proteins and fats, the dead jellyfish mass contains glycogen (C₆H₁₀O₅). It is known that carbohydrates (monosaccharides and polysaccharides) are among the ionic hydrophilizing surfactants (surfactants) that dislocate in water to form surface-active anions, which include the carbohydrate part of the molecule. An adsorption coating of surface-active anions on cement particles retains a layer of water on the surface by molecular forces, stabilizing the cement suspension and preventing its coagulation [15,35,36]. Based on the foregoing, it can be assumed that the dead jellyfish mass has surface-active properties.

Thus, the purpose of this study is to investigate the process of structure formation and properties of fresh and hardened cement paste and concrete with the addition of dead jellyfish mass and to determine the qualitative and quantitative characteristics of this effect. The objectives of the study are as follows:

−

Conducting experimental studies with a preliminary determination of the initial factors and parameters influencing the recipe and technological effectiveness of the proposed methods;

−

An analysis of the results obtained and a comparison of these results with the results obtained by other additives, similar in effect and mechanism of action but having a different nature of origin;

−

Determining the possibility and feasibility of such a use of dead jellyfish mass and clarifying specific recommendations for the applied industry, as well as a conclusion about the effectiveness of using such environmentally and cost-effective methods.

The scientific novelty of this research is the systematization of new knowledge about the structure formation, properties, and dependencies occurring during the formation of concrete mixtures and concretes containing dead jellyfish mass, the rheological characteristics of the mixture, changes in its properties, as well as the mutual influence of the properties of the concrete mixture using dead jellyfish mass on the characteristics of the final concrete composite. The practical significance of this study is the development of a specific recipe and technological parameters of concrete based on dead jellyfish mass to solve the economic and environmental problems of coastal regions with the problem of the uncontrolled release of dead jellyfish mass onto the shore.

2. Materials and Methods

The following raw materials were used as the main raw materials for the manufacture of samples:

−

Portland cement CEM I 52.5N (PC) (Sebryakovcement, Volgograd, Russia);

−

Crushed sandstone (CS) (RostMed, Kamensk, Russia);

−

Quartz sand (S) (RostStroyMix, Rostov-on-Don, Russia)

The characteristics of the concrete components are presented in

Table 1. Characteristics of Portland cement.

Characteristics	Actual Value
Specific surface area (m2/kg)	341
Soundness (mm)	0.5
Fineness, passage through a sieve No 008 (%)	98.3
Setting times (min):
- start	180
- end	250
Compressive strength (MPa):
- 2 days	26.8
- 28 days	58.5
SiO2 (%)	17.6
Al2O3 (%)	5.3
Fe2O3 (%)	4.7
CaO (%)	65.7
MgO (%)	1.5
Alkali oxides in terms of
(Na2O + 0.658 K2O) (%)	0.5
Insoluble residue (%)	0.3
SO3 (%)	3.4
Cl− (%)	0.006
Loss on Ignition (%)	0.994

,

Table 2. Sand properties.

Characteristics				Actual Value
Bulk density (kg/m3)				1341
The content of dust and clay particles (%)				0.07
Content of clay in lumps (%)				0.11
Organic and contaminant content				No
Particle distribution
Sieve opening dimensions (mm)					Content (% by weight) of grains with a particle size of less than 0.16 mm	Fineness modulus
Partial residues on sieves (%)
Total residues on sieves (%)
2.5	1.25	0.63	0.315	0.16
1.9	1.4	11.7	44.6	36.1	4.7	1.76
1.9	3.3	15.0	59.6	95.7

and

Table 3. Properties of crushed stone.

Characteristics	Actual Value
Particle size (mm)	5–20
Bulk density (kg/m3)	1415
Apparent density (kg/m3)	2567
Resistance to fragmentation (wt %)	11.4
The content of lamellar and acicular grains (wt %)	8.3

and Figure 1 and Figure 2 (information received from manufacturers).

An additive in the form of dead jellyfish mass (DJM) was used as an additive to regulate the properties of concrete mixtures and concretes. The jellyfish mass was made from dead jellyfish of the Aurelia aurita species, collected on the Black Sea coast (Sochi, Russia) and preserved. The process of preparing canned dead jellyfish mass included the following main stages:

−

The collection of dead jellyfish mass washed ashore and in the coastal zone;

−

The transportation of dead jellyfish mass in closed containers with a small amount of sea water to the laboratory;

−

Cleansing the collected dead jellyfish mass by washing it under running water;

−

Bringing the cleaned dead jellyfish mass to a gel-like state by cutting with a knife and squeezing with a pestle in a porcelain mortar;

−

The mandatory conservation of dead jellyfish mass;

−

The storage of preserved dead jellyfish mass.

The need for the mandatory conservation of dead jellyfish mass is due to the fact that the organic substances it contains (proteins, fats, and carbohydrates) are a good nutrient medium for various microorganisms (bacteria, mold, yeast). Accordingly, the storage of dead jellyfish mass without the presence of preservatives is very limited in time and, at a temperature of 20 °C, is no more than two days. Preservation was carried out by introducing sodium nitrite in an amount of 0.2% of the mass of dead jellyfish.

The preserved dead jellyfish mass was stored in a closed container at a temperature of 20 °C. The reliability of preservation was visually determined by observing the absence of color change and odor formation. This preservation method allows for the preservation for dead jellyfish for up to 6 months.

The material and chemical composition of the tissues of the dead jellyfish mass is presented in

Table 4. Material composition of the tissues of dead jellyfish mass [12,15,37].

Name of Substance	Content (% by Raw Jellyfish Mass)
Water	95.5 ± 1.5
Protein	0.56 ± 0.12
Fat	0.02 ± 0.002
Glycogen	1.55 ± 0.34
Ash residue	2.37 ± 0.48

and

Table 5. Chemical composition of dead jellyfish mass [14].

Name of Chemical Element	Content in g/kg of Jellyfish Mass
Ca	12.1
P	0.61
Na	3.93
Cl	6.07

, respectively.

The appearance of all raw materials is shown in Figure 3.

Methods

To confirm the plasticizing properties of the canned dead jellyfish mass additive, indicators such as the normal consistency of the cement paste, the ultimate shear stress of the cement paste, and the workability of the concrete mixture were studied.

The normal consistency of cement paste with different contents of the dead jellyfish additive was determined in accordance with the requirements [38]. The normal thickness of the cement paste was considered to be a consistency at which the pestle of the Vicat device (Figure 4b), immersed in a ring filled with dough, did not reach 5–7 mm from the plate on which the ring is installed. The normal consistency of the cement paste was characterized by the amount of mixing water, expressed as a percentage of the mass of cement. Before starting the test, the free lowering of the Vicat instrument rod was checked, as well as the zero reading of the device, by contacting the pestle with the plate on which the ring is located. When deviating from zero, the instrument scale moved accordingly. Before testing, the ring and plate were lubricated with a thin layer of machine oil. To prepare cement dough manually, 400 g of cement were weighed out and poured into a bowl that had been previously wiped with a damp cloth. Then, a depression was made in the cement, into which water was poured in one step in the amount necessary (approximately) to obtain a cement paste of normal consistency. The depression was filled with cement and, 30 s after adding water, the resulting mixture was first carefully mixed and then vigorously rubbed with a spatula. The duration of mixing and rubbing was 5 min from the moment the water was added. After mixing was completed, the ring was quickly filled with cement paste in one go and shaken five to six times by tapping the plate on a solid base. The surface of the dough was leveled with the edges of the ring by trimming off the excess dough with a knife wiped with a damp cloth. Immediately after this, the pestle of the device was brought into contact with the surface of the dough in the center of the ring, and the rod was secured with a locking device, then quickly released, allowing the pestle to sink freely into the dough. Then, 30 s from the moment the rod was released, the immersion was counted on the scale. If the consistency of the cement paste was inappropriate, the amount of water was changed, and the dough was prepared again. The amount of added water to obtain a dough of normal consistency was determined with an accuracy of 0.25%.

The process of determining the normal density of cement paste with different contents of the DJM additive is presented in Figure 4.

Figure 2 shows the process of introducing mixing water containing the DJM additive into cement (Figure 4a) and determining the normal consistency of the resulting cement paste (Figure 4b). As is indicated in the image, the mixing water, after adding the DJM, acquires a cloudy, slightly grayish tint.

The method for determining the ultimate shear stress was as follows. A moistened viscometer was placed on a pre-moistened glass surface and filled with a cement slurry (water–cement ratio was 0.7) (Figure 5a). After filling, the viscometer cylinder was raised up, and the diameter of the spread was measured (Figure 5b). At each measurement, the density of the resulting suspension was recorded. Ultimate shear stress was calculated using the following formula:

$${\tau }_0=\frac{h\times d^2\times \rho \times g}{k\times D^2}$$

(1)

where ${\tau }_0$ is the ultimate shear stress of the suspension (Pa); h and d—height and diameter of the viscometer, respectively (m); ρ—suspension density (kg/m³); g—acceleration of gravity (m/s²); k—coefficient, taking into account the redistribution of stresses in viscoplastic bodies, equal to 2; and D is the diameter of the suspension spread (m) [39,40].

The process of determining the ultimate shear stress of cement paste with different DJM additive contents is presented in Figure 5.

Figure 5 demonstrates a viscometer filled with cement paste with the addition of DJM and the nature of the spreading of the cement paste after lifting the viscometer.

The workability of concrete mixtures was determined by the cone settlement in accordance with the requirements [41] (Figure 6).

Before testing, the supporting surface and cone were moistened. The cone was placed on a horizontal supporting surface. During the filling process, the cone was fixed to the supporting surface with clamping devices. The cone was filled in three stages; at each stage, approximately 1/3 of its height after compaction was filled. Each layer was compacted with 25 bayonet blows. The impacts were distributed evenly across the cross section of each layer. To compact the bottom layer, the bayonet was slightly tilted, and approximately half of the blows were made in a spiral towards the center. The bottom layer was compacted over its entire thickness without the bayonet touching the base. The middle and top layers were compacted throughout their entire depth so that impacts penetrated into the underlying layer. Before filling and compacting the top layer, the concrete mixture was applied above the top edge of the cone. If, during the compaction process, the concrete mixture settled below the top edge of the cone, then the concrete mixture was added to constantly maintain the level of the mixture above the top of the cone. After compacting the top layer, the excess was removed from the surface of the concrete mixture. The spilled concrete mixture was removed from the supporting surface. The cone was carefully removed by lifting it in a vertical direction. The time spent raising the cone ranged from 2 to 5 s. The entire process from the start of filling to the removal of the mold was carried out within 150 s without interruptions. Immediately after removing the mold, the settlement (h) was measured, that is, the difference between the height of the mold and the height of the highest point of the settled test sample.

The effect of the DJM additive on the process of water separation of cement was also assessed according to the method of [42]. The essence of this technique was as follows. A suspension of cement in water was prepared by mixing cement and water (water–cement ratio 1) in a glass measuring cylinder for 4 min. Then, the cylinder was placed on the table, and the volume of cement paste in cubic centimeters was noted. During the entire testing period, the cylinder remained motionless in a place where there was no air flow and where it was not subjected to shocks or shaking. The water loss of the cement was calculated using the formula:

$$W=\frac{a-b}{a}\times 100$$

(2)

where W—cement/water separation (%); a—initial volume of cement paste (cm³); and b—volume of settled cement paste (cm³).

The process of determining the water separation of cement with different contents of the dead jellyfish additive is presented in Figure 7.

Figure 7 clearly shows the boundary between the settled cement paste and the mixing water.

The assessment of the physical and mechanical characteristics of concrete with different contents of the dead jellyfish additive included the determination of compressive strength [43,44,45] and water absorption [46] in accordance with the requirements of the methods. When testing for compression, cube samples were installed with one of the selected faces on the lower support plate of the test press centrally relative to its longitudinal axis, using marks applied to the press plate. After installing the sample on the support plates of the press, it was loaded until failure at a constant rate of load increase (0.6 ± 0.2) MPa/s. Compressive strength was calculated using the following formula:

$$R=\alpha \frac{F}{A}$$

where:

• F—breaking load (N);
• A—working section area of the sample (mm²);
• α—the scale factor for reducing the strength of concrete to the strength of concrete in samples of basic size, with the shape measured at 0.95.

To determine water absorption, the concrete samples were placed in a container filled with water so that the water level in the container was approximately 50 mm above the top level of the laid samples. Every 24 h, the water-saturated samples were weighed, and the test itself lasted until the results of two consecutive weighings differed by no more than 0.1%. Water absorption was calculated using the following formula:

$$W=\frac{m_w-m_d}{m_d} ·100$$

where:

• m_w—the mass of the water-saturated sample (g);
• m_d—dry sample weight (g).

The process of determining the compressive strength of concrete with different contents of the dead jellyfish additive is presented in Figure 8. The designs of experimental concrete mixtures are presented in

Table 6. Concrete mix designs.

Composition Type	Concrete Mixture Proportion per 1 m3
	PC (kg/m3)	W (l/m3)	CS (kg/m3)	S (kg/m3)	Dead Jellyfish Mass (% by Weight of Cement)
C	361	205	985	738	0
DJM0.2	361	205	985	738	0.2
DJM0.4	361	205	985	738	0.4
DJM0.6	361	205	985	738	0.6
DJM0.8	361	205	985	738	0.8
DJM1.0	361	205	985	738	1.0
DJM1.2	361	205	985	738	1.2
DJM1.4	361	205	985	738	1.4
DJM1.6	361	205	985	738	1.6

Note: PC is Portland cement; W is water; CS is crushed stone; S is sand.

.

The production of the concrete mixture included the following main steps. The first stage was the dosing of all raw materials. At the second stage, dry cement and sand were loaded into a concrete mixer and mixed. At the third stage, mixing water with the DJM additive was introduced into the dry cement–sand mixture. And at the fourth stage, crushed stone was added to the resulting cement–sand mortar, and the mixture was mixed until homogeneous. Next, the resulting concrete mixture was placed into metal molds with dimensions of 100 × 100 × 100 mm, which were then vibrated for 60 s. After 24 h, concrete samples of a control composition and with different contents of the DJM additive were removed from the molds and placed in a normal hardening chamber for 27 days at a temperature of 20 ± 2 °C and a relative humidity of 95% [47].

The main equipment for producing concrete with the DJM additive included, as follows:

−

Laboratory concrete mixer BL-10 (ZZBO, Zlatoust, Russia);

−

Laboratory scales HT-5000 (NPP Gosmetr, St. Petersburg, Russia);

−

Cube shapes 2FK-100 (RNPO “RusPribor”, St. Petersburg, Russia);

−

Normal curing chamber KNT-1 (RNPO RusPribor, St. Petersburg, Russia);

−

Laboratory vibration platform (IMash, Armavir, Russia).

The experimental research program is presented in Figure 9.

The structure of the concrete samples was analyzed using a stereoscopic microscope MBS-10 (Measuring equipment, Moscow, Russia) with 10× magnification. The methodology of the study using a microscope consists primarily of analyzing the structure, which is considered at the micro- and macro-level. The nature of the phase boundaries is studied, first of all, as well as the defectiveness and porosity of the material structure. The nature of porosity, changes in texture, and other characteristics of concrete are also analyzed, which may indicate the positive or negative impact of certain changes that are made to the formulation of the material, thereby influencing the properties and formation of the structure of concrete with different zones and sections of phase boundaries.

3. Results and Discussion

The results of determining the plasticizing properties of composites with the addition of dead jellyfish mass are presented in Figure 10, Figure 11 and Figure 12. Figure 10 shows the graphical dependence of the normal consistency of cement paste on the dosage of the dead jellyfish mass.

The influence of the dosage of the dead jellyfish mass additive (x) on the normal consistency of the cement paste was approximated by a polynomial function of a 3rd degree with determination coefficient R², shown as follows:

$$NC=28.6-12.81x+9.63x^2-1.210x^3,\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}{R}^2=0.973$$

(3)

Based on the results of determining the normal consistency of cement paste with different DJM contents, the following basic patterns were established. When introducing the DJM additive in dosages from 0.2% to 0.6%, an increasing plasticizing effect was observed, expressed by a decrease in the percentage of normal consistency. At 0.2% DJM, the normal consistency of the cement paste decreased by 9.4%, and, at 0.4% and 0.6% DJM, it decreased by 13.5% and 16.3%, respectively. However, at dosages from 0.8% to 1.2% DJM, a stabilization of the plasticizing effect was observed. The decrease in the normal consistency of the cement paste at dosages of the DJM additive of 0.8%, 1.0%, and 1.2% was 15.6%, 15.3%, and 14.9%, respectively, compared to the control composition. At 1.4% and 1.6% DJM, the plasticizing effect decreased. At 1.4% DJM, the decrease in the normal consistency of the cement paste was 8.7%, and, at 1.6% DJM—3.1%. The material and chemical composition of the dead jellyfish mass, including the influence of their function in concrete as the main factor, has a number of important aspects. One of these important aspects is the formed structure and, as a result, the improved or preserved characteristics of concrete as a stone structural material. At the same time, Figure 10 presents another side of the beneficial effect of dead jellyfish mass on the process of manufacturing concrete structures. These are the rheological characteristics of the mixture, which directly depended on the characteristics of the binder used, as well as on the water-binding relationship. The normal consistency of the cement paste was characterized, among other things, by the water requirement of the Portland cement used and showed the predicted rheological characteristics of the concrete mixture as a whole. In view of the good results obtained at the stage of studying the cement paste, we can say that the mechanisms for the formation of the rheological properties of concrete composites directly depend on the presence of appropriate chemicals in the composition of the dead jellyfish mass, as well as on its material composition, and the good compatibility of these components and substances with other components of concrete mixture and cement paste. The stages of introducing dead jellyfish mass, depending on its dosage, can be divided into three conventional sections. The first stage is an insufficient rational amount of jellyfish mass. The point is that a component is introduced into the composition that needs wetting but, nevertheless, does not have time to influence the improvement of the rheological properties. When a rational amount of jellyfish mass is achieved (second stage), it acts as a plasticizer and water-reducing additive, and less water is required, taking into account the improvement in the general properties of the concrete mixture as a whole. When the cement mixture is supersaturated beyond the rational amount (third stage), more water is required to wet the surface of the introduced DJM, and their plasticizing effect no longer covers this amount of water. Thus, the rational amount of DJM was determined to be 0.6%.

Below, Figure 11 shows the effect of the amount of dead jellyfish added on the ultimate shear stress of the cement paste.

The dependence of the ultimate shear stress of the cement paste on the dead jellyfish additive dosage (x) shown in Figure 11 was approximated by this 3rd degree polynomial:

$${\tau }_0=28.5-24.6x+20.03x^2-3.061x^3,\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}{R}^2=0.958$$

(4)

In Figure 11, it can be seen that the introduction of the addition of dead jellyfish mass into the composition of the cement paste in an amount from 0.2% to 0.8% made it possible to reduce the ultimate shear stress. The most effective dosage of the additive was 0.6%, at which the ultimate shear stress decreased by 32%. At 0.2% and 0.4% DJM, the ultimate shear stress decreased by 13.4% and 23.2%. At the same time, at 0.8%, 1.0%, and 1.2% DJM, a stabilization of this indicator was observed. The ultimate shear stress of these compositions was less by 26.1%, 25.7%, and 24.3%, respectively, in comparison with the control composition. Furthermore, when the dosage of the DJM additive was increased to 1.4–1.6%, a decrease in the plasticizing effect was observed. At 1.4% DJM, the ultimate shear stress was 9.9% less and 2.5% less at 1.6% DJM compared to the control composition. The effect of reducing the ultimate shear stress when introducing the dead jellyfish mass additive was associated with a decrease in friction forces in the cement system due to the adsorption of protein and glycogen molecules on cement particles and the formation of a polymolecular membrane on them [15,48]. A dependence measure of the slump of the concrete mixture on the amount of dead jellyfish mass is shown in Figure 12.

The influence (Figure 12) of the dosage of the dead jellyfish mass additive (x) on the workability of the concrete mixture is shown in Equation (5):

$$S_l=4.88+9.05x-8.478x^2+1.88x^3,\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}{R}^2=0.905$$

(5)

Based on the results of determining the slump of concrete mixtures with different contents of dead jellyfish mass in them, as presented in Figure 12, it was found that the introduction of DJM had a positive effect on the rheology of concrete mixtures. It could be seen that, at dosages from 0.2% to 0.6%, there was an increase in cone settlement. The most effective dosage is 0.6%, at which the cone settlement increased by 60.8% compared to the control mixture. Such a significant increase in cone settlement was primarily due to the fact that the addition of dead jellyfish mass, in an amount of 0.6% of the cement mass, exhibited a maximum plasticizing effect, which occurred due to the fact that the mixture was fully saturated with molecules of surfactants and was expressed in increasing friction forces between the main components of the concrete mixture. At 0.2% and 0.4% DJM, the cone settlement increased by 15.7% and 43.1%, respectively. At an amount of 0.8%, 1.0%, and 1.2% DJM, a stabilization of the workability index was observed, and its increases were 45.1%, 41.2%, and 39.2%, respectively. At 1.4% and 1.6% DJM, a decrease in the plasticizing effect was observed, which was expressed in a decrease in cone settlement and a decrease in settlement increments of 13.7% and 7.8%, respectively, in comparison with the control composition.

Improvement in rheological characteristics (the normal thickness of the cement paste, the ultimate shear stress of the cement paste, the workability of concrete mixture) with a dead jellyfish mass content of 0.2–0.6% of the binder mass might have been due to a decrease in friction forces in the cement system due to the adsorption of surfactant molecules (proteins, glycogen) on cement particles and the formation of a polymolecular film on them. The stabilization of the plasticizing effect at DJM dosages from 0.8% to 1.2% can be explained by the fact that cement particles and hydrate formations were completely saturated with surfactant molecules. As for the reduction in the plasticizing effect at 1.4% and 1.6% DMM, this was due to the fact that the dead mass of jellyfish contained an excess of unsaturated fatty acids, which contributed to an increase in the viscosity of the medium [15,49].

In general, the mechanism of the plasticizing effect of adding dead jellyfish mass in the studied ranges from 0.2% to 1.6% of the binder mass can be divided into three stages. The first stage is an increase in the plasticizing effect, which is associated with the fact that in DJM dosages of up to 0.6% surfactant molecules are completely adsorbed in the initial phase (cement particles) with the formation of monomolecular and polymolecular membranes and on new hydrate formations. The second stage is the stabilization of the plasticizing effect at DJM dosages of 0.8–1.2%, which is caused by complete saturation with surfactant molecules in the initial phase of both cement grains and hydrate formations. The third stage is a decrease in the plasticizing effect at a DJM dosage of more than 1.2%, which is primarily associated with an increase in the viscosity of the medium [15].

Thus, the study of a number of rheological characteristics confirmed the plasticizing effect of the additive and made it possible to establish the relationship between the degree of the plasticizing effect and the dosage of dead jellyfish mass. According to the results of experimental studies in the form of dependencies presented in Figure 10, Figure 11 and Figure 12, the maximum plasticizing effect was recorded at a dosage of dead jellyfish mass of 0.6%, which made it possible to reduce the normal consistency of the cement paste by 16.3% and the ultimate shear stress of the cement paste by 32.0% and increase the workability of the concrete mixture by 60.8%.

As is known, water separation negatively affects concrete mixtures during transportation and promotes separation. The most rational way to reduce water separation of concrete mixtures is by the introduction of surfactant additives, which has been confirmed by a number of studies [15,49]. Surfactants adsorbed on the surface of cement grains have the ability to retain fairly thick layers of water close to them, which helps reduce the amount of separated water as a result of sedimentation phenomena. The influence of the dosage of the dead jellyfish mass additive on the process of water separation of cement is reflected in the form of a dependence measure in Figure 13.

The effect of the dosage of the dead jellyfish mass additive (x) on cement water separation, shown in Figure 13, was approximated using Equation (6):

$$W_C=22.28-11.70x+8.25x^2-0.757x^3,\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}{R}^2=0.96$$

(6)

Based on the results of determining the water separation of cement, it was found that cement particles in suspensions with the addition of dead jellyfish mass in an amount of 0.2% to 1.6% settled more slowly in comparison with the control suspension. The lowest water separation value was recorded for the suspension with 0.6% DJM, and it was 19.7% less than the control composition. At 0.2%, 0.4%, 0.8%, 1.0%, 1.2%, and 1.6%, the DJM of cement water loss reduction was 8.1%, 17.5%, 17.9%, 17.5%, 17.0%, 11.7%, and 2.2%, respectively. The decrease in cement water separation can be explained by the fact that the addition of dead jellyfish mass slowed the process of the sedimentation of cement grains and immobilized water [15,50]. The surface-active properties of the jellyfish mass were primarily ensured by the protein content in it. Proteins, due to the presence of polar and non-polar groups, are easily adsorbed on solid particles. An adsorption coating of surface-active anions on cement particles held a layer of water on the surface with molecular forces, stabilizing the cement suspension, thereby reducing water separation in concrete mixtures.

Based on the results of a study of the rheological properties of cement compositions and cement water separation, it is possible to conclude that the use of the dead jellyfish mass additive in an amount of 0.2% to 1.2% is most preferable, since it is in this amount of DJM that the most pronounced plasticizing effect was observed. At a dosage of 1.4% DJM, the plasticizing effect of the additive began to decrease, and, further on, at a dosage of 1.6% DJM, the rheological characteristics of cement composites were approximately comparable to those of the control composition (without DJM).

Furthermore, Figure 14 and Figure 15 show the dependence measures of the physical and mechanical characteristics of concrete mixtures on the different content of dead jellyfish mass in them. Figure 14 shows the compressive strength values depending on the amount of dead jellyfish mass added to the mixture.

The effect of the dosage of the dead jellyfish additive (x) on the compressive strength of concrete, as shown in Figure 14, was approximated using Equation (7):

$$R=40.4+12.38x-12.2x^2+3.03x^3,\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}{R}^2=0.929$$

(7)

As can be seen from Figure 14, the introduction of the dead jellyfish mass additive promoted an increase in strength characteristics while maintaining the same level of the water–cement ratio (W/C). It is worth noting that, for all the variants of the considered dosages, an increase in compressive strength was observed. And the curve of change in compressive strength can be described as follows: intensive growth at dosages of 0.2% and 0.4%, where the increases in compressive strength were 4.7% and 7.9%, compared to the control composition, and a peak at around 0.6% with an increase of 10.6%. Furthermore, at dosages of 0.8%, 1.0%, and 1.2%, a stable, almost identical increase in compressive strength was observed, which amounted to 7.7%, 7.2%, and 6.4%, respectively. At dosages of 1.4% and 1.6%, the opposite situation was observed, expressed in a decrease in compressive strength. Therefore, in comparison with the control composition, the increases were 5.2% and 1.7%. Thus, we can conclude that the use of a dead jellyfish mass additive of more than 1.4% is ineffective and irrational. The increase in the strength of concrete with the introduction of dead jellyfish can primarily be associated with the structural and phase changes that occur in cement composites with the introduction of surfactants. As is known, the main products of hydration and the subsequent carbonization of Portland cement clinker concrete without surfactant additives are represented by calcium hydrosilicates of two types of CSH and C₂SH, calcium hydroaluminates C₃AH₆, as well as calcium oxide hydrate Ca(OH)₂, and calcite CaCO₃. And when a surfactant is introduced into the concrete composition, the main hydration products are represented by hydrosilicates of the CSH type, calcium hydroaluminates C₃AH₆, calcium oxide hydrate, and calcite. The introduction of a surfactant reduces the concentration of CaO in the liquid phase of the system, which in turn contributes to the intensive formation of low-basic CSH silicates. Thus, the formation of cement stone with a reduced basicity in calcium hydrosilicates causes an increase in compressive strength [15,51,52].

Figure 15 shows a dependence measure of the water absorption of concrete on the content of dead jellyfish mass in its composition.

The effect of the dosage of the dead jellyfish mass additive (x) on the water absorption of concrete, shown in Figure 15, is presented in Equation (8):

$$W=5.83-2.59x+2.201x^2-0.40x^3,\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}{R}^2=0.970$$

(8)

The curve describing the nature of changes in the water absorption of concrete with different contents of dead jellyfish mass, presented in Figure 14, can be described as follows. In the DJM dosage range from 0.2% to 0.6%, a decrease in water absorption with a peak of 0.6% was observed at 5.2%, 12.1%, and 15.5%, in comparison with the control composition. At 0.8%, 1.0%, and 1.2% DJM, a stabilization of concrete water absorption was observed, and its decrease was 13.8%, 12.1%, and 10.3%, respectively, in comparison with the control composition. When adding 1.4% and 1.6% DJM to the concrete mixture, the opposite trend was visible, expressed in an increase in water absorption. In comparison with the control composition, the water absorption of concrete with 1.4% DJM decreased by 6.9%, and, for concrete with 1.6% DJM, it decreased by 1.7%. The introduction of the dead jellyfish mass additive helped reduce water absorption. This can be explained by the fact that the introduction of dead jellyfish mass into the composition of the composite helps to reduce the overall porosity and makes the structure of the composite denser [15,51].

In general, based on the results of determining the compressive strength and water absorption of concrete with the addition of the dead jellyfish mass, it was established that the use of this additive in a rational dosage from 0.2% to 1.2% was justified and helped to improve these properties. An increase in compressive strength with the same W/C value indicates the potential for saving cement in the production of concrete with dead jellyfish mass.

For a comparative assessment of the structural features of the developed composites, concrete samples of a control composition and a composition with 0.6% DJM were selected. Photographs of the structure of concrete samples are presented in Figure 16 and Figure 17.

The structure of concrete of the control composition shown in Figure 16 was characterized by the following features. Numerous pores and voids were visible in the contact zones “cement-sand mortar - aggregate”. The structure of the sample was represented by a large number of pores. The pores were predominantly spherical or elongated with jagged edges. The introduction of DJM into the concrete mixture affected the process of the formation of the structure of the hardened composite. As can be seen from Figure 17, concrete mixtures with 0.6% DJM had a denser structure, and the observed pores were spherical and isolated from each other. There were no significant defects or voids observed in the contact zone.

The effectiveness of using the DJM supplement can be explained as follows. The proteins that comprise DJM have surface-active properties, and their solutions have low surface-active tension. Due to the presence of polar and non-polar groups, the protein is easily adsorbed on various solid surfaces. Some proteins, such as egg albumin, also have the ability to spread on the surface of water, forming an elastic monomolecular layer. Protein is a hydrophilic colloid; its molecules in an aqueous solution behave like hydrophilic particles, dissolving in water [53]. However, it should be noted that the surface layers of proteins at various boundary surfaces are anisotropic in hydrophilicity. When adsorbed on the surface of solid particles, an ellipsoidal protein particle, entering the phase interface, undergoes profound changes in its structure, turning into a two-dimensional planar figure. Thus, the adsorption of the molecules of organic substances that form the dead jellyfish mass (protein, glycogen, fat) on cement grains with the formation of hydrodynamic lubrication will cause a decrease in the internal friction of the components of the concrete mixture during its laying and compaction. A denser packing of the components forming the conglomerate will reduce the overall porosity of the material, as well as the average pore size [54].

When assessing the effect of the organic substances that form DJM, it was found that the dead jellyfish mass also had surface-active properties. Based on the analyzed literature [28,29,30,31,32,33,34,35,36,37,55], the feasibility of using surfactants in concrete and concrete mixtures can be reflected in the form of an Ishikawa cause-and-effect diagram presented in Figure 18.

From Figure 18, it can be seen that the use of plasticizing additives of various types in rationally selected quantities made it possible to improve the mechanical (branch 1), rheological (branch 2), and physical (branch 3) characteristics of cement-containing compositions, as well as the economic and energy efficiency of their production (branch 4). Surfactant additives improved the structure of concrete at the macro and micro levels.

As noted earlier, there are no currently relevant scientific studies on the use of dead jellyfish mass as a plasticizing additive for the production of concrete mixtures, with the exception of work [15]. When analyzing the results obtained in [15] and comparing them with the results obtained in this study, we can conclude that they are comparable and in good agreement. In this regard, to conduct a comparative analysis with other studies, it would be rational to consider research work devoted to the use of natural organic biodegradable components as a plasticizer for the preparation of concrete mixtures. For example, in [56], the use of modified starch as a plasticizing additive in an amount of 0.5% in concrete makes it possible to reduce the water–cement ratio to 0.4 and increase the compressive strength to 40% in comparison with reference samples. Research conducted in [57] confirms that the use of cellulose ether in cement composites can reduce capillary porosity and reduce water absorption. The use of extracted starch from cassava and corn in concrete, in amounts from 0.5% to 2.0%, helps improve strength characteristics [58]. In [59], the use of biodegradable additives based on modified polysaccharides makes it possible to obtain characteristics of mortars and concretes comparable to similar compositions made using additives based on polycarboxylates. In our case, the use of dead jellyfish mass in an amount of 0.2% to 1.2% as a plasticizing additive allowed us to improve the rheological characteristics of concrete mixtures and the compressive strength and water absorption of hardened composites. The peak effectiveness of the dead jellyfish mass supplement was recorded at a dosage of 0.6%.

Figure 18. The feasibility of using surfactants in concrete and concrete mixtures [18,19,20,21,22,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,60].

Figure 18. The feasibility of using surfactants in concrete and concrete mixtures [18,19,20,21,22,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,60].

Analyzing the already generalized results of the study and their discussion, it is worth noting a number of important aspects identified during this work. The theoretical and scientific significance of the article is the almost complete lack of data, both empirical and fundamental, in the global literature devoted to research on the use of dead jellyfish masses in the production of building materials. This study partially eliminated the scientific deficit in establishing the relationships between the composition, structure formation, and properties of cement concrete using dead jellyfish mass. The main patterns of the influence of dead jellyfish mass on the structure formation and properties of concrete have been identified and compared at the micro- and macro-levels. The type of influence of the addition of dead jellyfish mass on the cement–concrete conglomerate was explained; the essence and nature of the addition of dead jellyfish mass in the formation of a new material were determined. The results previously obtained by other authors were clarified; new promising directions of research on the use of dead jellyfish mass in cement concrete—both in dense structures and structures of another type, differing in density and component composition—were identified. An application has been made for the use of the resulting technology in industrial production. The promise of technology was determined by the obvious environmental benefits of using this method, as well as the predicted economic effect in the case of replacing expensive construction chemicals with organic waste in the form of dead jellyfish. Of course, the use of such a technology and method is more appropriate in regions where there is an environmental problem concerning the release of dead jellyfish from water bodies. The main environmental agenda of this study is the possibility of clearing the shore and coastal zone of the Black Sea from a significant number of dead jellyfish. The process of the degradation of dead jellyfish is accompanied by the release of large amounts of nitrogen and a decrease in pH, which has a detrimental effect on sea water and, as a result, leads to a disruption of the marine ecosystem.

The plasticizing additive based on dead jellyfish mass that was developed in this study is a complex natural additive based on a surfactant and, indeed, has some limitations associated with its practical use. First of all, this is a limited territory. The production and use of this additive in concrete production technology is only rational and appropriate in coastal regions suffering from the massive invasion and death of jellyfish. Note that, from a technical point of view, the process of introducing the technology of using a plasticizing additive from dead jellyfish mass into the process of making a concrete mixture is quite simple and includes three main stages: the collection of dead jellyfish mass from the shore and coastal zone; grinding; and conservation. Thus, with the right approach to the practical application of this technology, it is possible to solve the environmental problem associated with the pollution of sea water by the decaying bodies of jellyfish in the coastal zone.

As a result of this research, an applied result was obtained, which consists, firstly, of the development of a technology that allows for the use of dead jellyfish waste, which is a cheap renewable raw material for concrete. Secondly, a workable, effective concrete composition has been proposed, allowing for the production of structures with specified properties. A qualitative and quantitative picture of the influence of a rational dosage of dead jellyfish mass introduced into a concrete composition has been tested and identified, which makes it possible to characterize the specifically obtained product from the dead jellyfish mass as a special additive that improves the properties of concrete. Summarizing the information above and taking into account the technological, economic, and recipe aspects, the applied significance of the research and the applicability of the resulting additive in concrete technology in the practical construction of objects located near coastal zones that have a sufficient amount of corresponding dead jellyfish mass, which is a precursor for the concrete mixture, are formulated with improved characteristics.

Because the effectiveness of the proposed formulation of the composition and technology still needs approbation experiments and pilot development on original objects in concrete structures, it is recommended to carefully study this issue before introducing these recommendations and composition into continuous production at construction sites. These recommendations are limited in practice because of the geographical location. Thus, there is a need for an additional systematization of knowledge about such concrete and a standardization of this issue with the definition of regulatory and technical documents of local or industry significance at the first stage.

Further developments in studying the possibilities of using jellyfish mass are important, as this provides an advantage in a competitive sense, since dead waste is used, and this helps to reduce the cost of the work.

The sustainable nature of this study also follows. Using dead jellyfish waste, prohibited from development in terms of waste disposal, is a new development in lean manufacturing technologies, reducing the burden on the environment and being, in principle, a sensible approach to the use of aquaculture waste.

Thus, the scientific novelty, practical significance, and relevance of this research are confirmed.

4. Conclusions

The conducted studies revealed the feasibility and effectiveness of using dead jellyfish mass as an additive to concrete. This will simultaneously solve two important problems: environmental, which consists of the disposal of dead jellyfish washed ashore in large quantities; and technological, which consists of improving the rheological and strength characteristics of concrete. Based on the results obtained in this study, the following conclusions were drawn:

(1)

Dead jellyfish mass is a natural complex additive based on surfactants. The surface-active properties of the additive and its hydrophilicity were due to the presence of organic substances in the composition—protein and glycogen.

(2)

Based on the results of the experimental studies, the optimal range for using the dead jellyfish mass additive in concrete was established, which varied from 0.2% to 1.2% by weight of cement. The greatest effectiveness was shown by the addition of dead jellyfish mass in an amount of 0.6%.

(3)

DJM improved the rheological characteristics of the cement paste. At 0.6% DJM, the normal consistency of the cement paste was reduced by 16.3%, and the ultimate shear stress was reduced by 32% compared to the control composition; the workability of the concrete mixture, expressed in its slump, improved by 60.8%; the water separation of the cement was reduced by 19.7%.

(4)

The strength of concrete with 0.6% DJM increased by 10.6%, and water absorption decreased by 15.5% compared to the control samples.

(5)

The modification of the concrete structure with dead jellyfish mass reduced the overall porosity and made the structure denser.

The use of dead jellyfish mass in cement concrete provides an obvious environmental benefit and has a predictable economic effect in the case of replacing expensive construction chemicals with organic waste in the form of dead jellyfish. The use of such a technological technique is more appropriate in regions where there is an environmental problem with the release of dead jellyfish from water bodies. The study of the addition of dead jellyfish mass in variotropic concrete is promising [47,55]. Dead jellyfish mass can be used for the manufacture of concrete and reinforced concrete structures operated in air-dry conditions, water, and aggressive solutions, as well as sea water, in order to improve the technological properties of concrete mixtures, increase the strength of concrete, and reduce cement consumption.