RU2106327C1 - Method and process line for manufacturing especially-high-strength cement concrete - Google Patents

Abstract

FIELD: manufacture of building materials. SUBSTANCE: concrete mix is prepared from fine and coarse fillers, high-strength cement, superplasticizer, and tempering water. Mix is cast and compacted prior to harden, temperature and time conditions being strictly observed. Fillers are preliminarily freed from weak grains and impurities and are separated into fractions. As fine filler, sand with crushability index 5-30% is utilized, and, as coarse filler, crushed rock with desired parameters at cement/sand/crushed rock volume ratio 1:(1.00-1.45):(2.00-3.00). Amount of tempering water is determined from empirical-theoretical dependence for calculating planned concrete strength. Water to cement ratio is maintained within (0.24-0.28):1 range and superplasticizer is added to mix in amount 0.5-1.0% on cement weight. So prepared concrete mix components are placed into concrete mixer, which is filled with tempering water. Watered mix is agitated and resultant concrete mortar is cast into structure and kept under desired conditions to form especially high- strength concrete. EFFECT: optimized process parameters. 4 cl, 4 dwg, 3 tbl

Description

 The invention relates to the construction, in particular, to methods of manufacturing particularly strong cement concrete of classes B 105-B 135 and higher, used in the construction of nuclear power plants / nuclear power plants /, high-rise buildings, civil defense structures, hydraulic structures and tunnels for various purposes.

A known method of manufacturing high-strength cement concrete with a strength of up to 110 MPa, including the preparation of concrete mix from Portland cement grade M 700 (685 kg / m ³ ), basalt gravel, river sand, plasticizing additives SSB with a water-cement ratio W / C = 0.26 and hardness mixtures 240 s, layer-by-layer laying of concrete mixture in a mold, compaction of layers of a mixture with a load and hardening (O. Ya. Berg, E.N. Sherbakov, G.N. Pisarenko, High-strength concrete. M: Stroyizdat, 1971, p. 52-56).

 The disadvantage of this technical solution is that the concrete mixture in the specified method of manufacturing cement concrete is particularly rigid, and its practical use in concrete and reinforced concrete products is impractical.

 In addition, the reproduction of the composition of the mixture to obtain concrete strength of more than 100 MPa is impossible due to the lack of quantitative characteristics of the mechanical properties of the components that make up the concrete mixture.

There is also known a method of manufacturing high-strength cement concrete with a strength of 150 - 160 MPa, including the preparation of concrete mix from a binder in the form of high-strength and quick-hardening Portland cement and quartz flour, aggregates in the form of high-strength quartz and silicon-containing rocks with a maximum grain size of 8 mm and superplasticizer, laying and hardening in an autoclave in the following modes:
exposure at a temperature of 15 - 20 ^o C 8 - 10 hours;
raising the temperature to 60 ^o C at a rate of 0.7 ^o C / min 1 - 2 hours;
holding at a temperature of 60 ^o C and a pressure in the autoclave of 0.1 - 0.2 MPa / 1st stage / 5 - 8 hours;
temperature rise to 180 - 200 ^o C and pressure to 1.0 MPa 4 to 6 hours;
holding at a temperature of 180 - 200 ^o C and pressure up to 2.0 MPa for 15 hours;
keeping the samples after autoclaving at a temperature of about 20 ^o C and a relative humidity of 100% for 7 days.

The technological line for the manufacture of high-strength cement concrete according to the specified method, including such typical elements as aggregate crushers, metering devices and a mixer, additionally contains an autoclave with temperature regulators (Tognon G., Urstella P. and Copetti G. Design and properties of concrete with strength over 1500 kg / sm ^3. Gournal of American Concrete Jnstitute, 180, 1977, N 3, pp. 171 - 178).

 However, when obtaining high strength characteristics of concrete, this technology has drawbacks, it is energy-intensive, time-consuming and expensive.

The closest in technical essence and the achieved result is a method of manufacturing particularly strong cement concrete, including the preparation of concrete mix from fine and coarse aggregates / quartz sand and basalt crushed stone /, high-strength cement, superplasticizer and mixing water, laying concrete mixture and hardening. The concrete mixture is laid in four-layer molds, each of which is compacted with a 2.0 MPa load. Sealing is repeated after 30 minutes. Hardening of samples is carried out in three stages: the first day at a temperature of 5 ^o C, the next 6 days. at a temperature of 10 ^o C, the next 35 days. at a temperature of 20 ^o C. 28 days. from the start of production, the samples hardened in water. (Walz K, Uber die Hersteellung von Beton hochster Festig keit Beton, 16, 1966, H. 8. ss. 320 - 321).

 The disadvantage of this method of manufacturing particularly durable cement concrete is that it is complex, energy-intensive, time-consuming and expensive.

 The production line of especially strong cement concrete closest in technical essence and achieved result contains crushing plants for fine and coarse aggregates, batchers for concrete mix components, a mixer with forced mixing, means of transporting the concrete mix and laying it in a structure with the possibility of maintaining it in a given mode ( see USSR author's certificate N 478726, B 28 B 5/04, 1973).

 The disadvantage of this production line is its low productivity and reliability.

 The basis of the present invention is the task of increasing the strength of cement concrete and hardening the manufacturing technology of highly durable cement concrete with a reduction in the cost of its manufacture by choosing the optimal parameters that make up the concrete mix and using standard equipment in concrete plants.

где

- проектная прочность бетона, МПа;
R_ц - активность цемента, МПа;
K_в - поправочный коэффициент удобоукладываемости бетонной смеси, равный 1,15 для жесткой смеси и 1,05 для литой;
Ц - расход цемента, кг/м³;
A₁ - коэффициент, учитывающий фактическую прочность песка, определяемую по показателю дробимости, равный 0,92 - 1,1;
A₂ - коэффициент, учитывающий фактическую прочность щебня, определяемую по показателю дробимости, равный 0,9 - 1,07;
A₃ - коэффициент, учитывающий состояние поверхности и загрязненность мелкого заполнителя, равный 0,87 - 1,0 для природного песка и 1,0 для дробленного песка,
водоцементное отношение при этом выдерживаю в пределах В/Ц = 0,24 - 0,28, суперпластификатор вводят в смесь в количестве 0,5 - 1,0% от массы цемента, приготовленные компоненты бетонной смеси подают в бетоносмеситель, заполняют его водой затворения, принудительно перемешивают приготовленную бетонную смесь, укладывают в конструкцию и выдерживают в заданном режиме.The essence of the invention lies in the fact that in a new method of manufacturing particularly strong cement concrete, including the preparation of concrete mix from fine and coarse aggregates, high-strength cement, superplasticizer and mixing water, laying concrete mix, its compaction and hardening with exposure to temperature and time conditions, aggregates pre-prepared with the removal of weak grains, impurities and separation into fractions, while sand is used as a fine aggregate and crushing index 5 - 30%, and as coarse aggregate - crushed stone of fractions of 5 - 10 mm or 5 - 10 and 10 - 20 mm in a ratio of 30 - 50% and 50 - 70%, respectively, with a crushing index of 4 - 8% with a volumetric ratio of cement, sand and gravel
V _c : V _p : V _n = 1.0: / 1.0 - 1.45 /: / 2.0 - 3.0 /,
moreover, the amount of mixing water is determined by the following relationship:

Where

- design strength of concrete, MPa;
R _c - cement activity, MPa;
K _in - correction coefficient of workability of the concrete mixture, equal to 1.15 for a rigid mixture and 1.05 for a cast;
C - cement consumption, kg / m ³ ;
A ₁ - coefficient taking into account the actual strength of the sand, determined by the crushing index, equal to 0.92 - 1.1;
A ₂ - coefficient taking into account the actual strength of crushed stone, determined by the crushing index, equal to 0.9 - 1.07;
A ₃ - coefficient taking into account the surface condition and the contamination of the fine aggregate, equal to 0.87 - 1.0 for natural sand and 1.0 for crushed sand,
while the water-cement ratio is maintained within the range of W / C = 0.24 - 0.28, the superplasticizer is introduced into the mixture in an amount of 0.5 - 1.0% by weight of the cement, the prepared components of the concrete mixture are fed into the concrete mixer, filled with mixing water, forcibly mix the prepared concrete mixture, lay in the structure and maintain in the given mode.

 In the new technological line for the production of especially durable cement concrete, containing crushing plants for fine and coarse aggregates, batchers for concrete mix components, a mixer with forced mixing, means for transporting concrete mix components, as well as concrete mix and laying it in the structure, installed during the technological process with the ability to withstand in a given mode, crushing plants are made in the form of two devices for dry enrichment of small and large aggregates their separation into fractions, which are mounted to dispensers for components of the concrete mix and the conveyors are connected to them.

 In addition, the device for dry enrichment and separation into fractions of fine and coarse aggregates is made up of a high-pressure fan connected to each other with a storage chamber, inside of which heaters are installed, a storage chamber with a booster pipe, on which a loading pipe is installed, a booster pipe with a separation chamber in which a tumbler type glass plate is installed, while the separation chamber in its lower part is connected via elastic ties to the hopper, inside of which a vibrator installed, closed top wall and between the partition and the sieve baffle plate so as to form two unloading pipes, podsitovogo space connected with the suction pipe system, and isolating the desired fractions of aggregates.

 Moreover, the gaps in the screens for small and large aggregates are made equal to from 1.0 to 5.0 mm and from 5.0 to 20.0 mm, respectively.

The set of essential features presented above is aimed at achieving a technical result and is in a causal relationship with it, because allows
to increase the strength of cement concrete, since aggregates are preliminarily prepared with the removal of weak grains, extraneous impurities and fractionated, and they are also used with an optimal crushing index for a certain volume ratio of cement, sand and crushed stone, with a certain amount of superplasticizer and mixing water with water-cement a ratio of W / C = 0.24 - 0.28;
to simplify the manufacturing technology of highly durable cement concrete, since the production line mainly uses standard equipment and optimally selected concrete mix according to the components, which will reduce the cost of manufacturing concrete.

 In addition, the invention is industrially applicable, as it can be used in construction.

 Thus, we can conclude that the claimed technical solution meets the conditions of patentability of the invention.

In FIG. 1 shows a graph of the workability of concrete mix / OK / on the correction empirical coefficient K _b : figure 2 is a diagram of a production line for the manufacture of highly durable cement concrete; figure 3 - node a in fig. 2; figure 4 is a section aa in figure 3.

 The manufacture of particularly durable cement concrete is as follows.

 At the first stage, a concrete mixture is prepared.

 Upon receipt of concrete with a strength of 120-150 MPa, it is necessary to carefully consider all factors affecting the strength and relating to both the composition of concrete and the method for its preparation.

For the manufacture of such concrete, high-strength cements are used, for example, Portland cement grades 500 and 600 of the Belgorod plant with activity R _C = 49.5 MPa and 60 MPa, respectively.

 Fine aggregate, sand, must have a grain strength higher than the stresses occurring in concrete. Aggregate grains are stress concentrators when a load is applied to structures, and in the case of insufficient sand strength, the concrete strength will be reduced, therefore, it is necessary to enter the sand strength indicator in the calculation formula for the design concrete strength.

 The strength of the sand can be estimated by the crushability of sand, determined by the test method similar to that used for crushing crushed stone. It was experimentally established that crushability should not exceed 30% for concrete with a strength of 100 - 150 MPa.

The strength of the sand is taken into account in the formula for calculating the design strength of concrete in the form of a coefficient A ₁ , the relationship of which with the crushing index is shown in Table 1.

For concrete with a strength of 100 ... 150 MPa, the value of A ₁ is 0.92 ... 1.10.

 The stress concentrator is also a large aggregate - crushed stone, the dimensions of which in the framework of the present invention should be 5 ... 10 mm or 5. ..10 and 10 ... 20 mm in the ratios 30 ... 50% and 70 ... 50 % respectively. It is necessary that the strength of crushed stone exceeds the strength of concrete in the loading stage close to the ultimate. This fact is known and taken into account in GOST 10268 "Aggregates for heavy concrete". However, GOST requirements for crushed stone strength are, as our studies have shown, overpriced, which increases the cost of concrete.

 It was experimentally and theoretically revealed that the optimum strength of crushed stone should exceed the strength of concrete in the range of its classes B105 ... B150 / grade M120. . .M150 / not less than 1.7 times. In addition, it was found that with sufficiently high strengths of fine aggregate / sand / and cement, a 1.5 times excess of crushed stone strength over concrete strength is sufficient.

 For a practical assessment of the strength of the rock suitable for processing into crushed stone, crushing values are used for fractions of crushed stone selected for this concrete.

To obtain extra strong concrete, the crushability of Dr should be 4 - 8%. In the formula for calculating the design strength of concrete, crushed stone strength is introduced in the form of a coefficient A ₂ , the relationship of which with the crushing index Dr is given in Table 2.

Coefficient A ₃ takes into account the surface roughness of natural sand and its contamination. This coefficient is determined experimentally and is equal to 1.0 for crushed sand and 0.87 - 1.0 for natural sand.

 Of the factors in the process of preparing concrete, the most important is the choice of the cement-water ratio C / B, which determines the amount of mixing water - B. The ratio C / B is determined, in turn, by the workability of the mixture and the size of the sand. Table 3 shows the values of C / B for various workability and size of sand.

To accurately calculate the design strength of concrete, you must enter the correction factor K _in , determined empirically and associated with the value of workability, OK. To find it, the graph shown in FIG. 1. For a tough mixture, K _in is 1.15; for cast - 1.05.

,
где

- проектная прочность бетона, МПа;
R_ц - активность цемента, МПа;
K_в -поправочный коэффициент удобоукладываемости бетонной смеси;
Ц - расход цемента, кг/м³;
В - количество воды затворения;
Ц/В - цементо-водное отношение;
A₁- коэффициент, учитывающий фактическую прочность песка;
A₂ - коэффициент, учитывающий фактическую прочность щебня;
A₃ - коэффициент, учитывающий состояние поверхности и загрязненность мелкого заполнителя.Given the composition of the concrete mixture and knowing the characteristics of the components and the value of workability, you can calculate the design strength of concrete by the formula

,
Where

- design strength of concrete, MPa;
R _c - cement activity, MPa;
K _{in -} correction coefficient of workability of concrete mixture;
C - cement consumption, kg / m ³ ;
In - the amount of mixing water;
C / B - cement-water ratio;
A ₁ - coefficient taking into account the actual strength of the sand;
A ₂ - coefficient taking into account the actual strength of crushed stone;
A ₃ - coefficient taking into account the condition of the surface and the contamination of the fine aggregate.

.Given, in turn, the necessary strength of concrete, you can calculate the amount of mixing water according to the formula

.

 When choosing cement, the following experimentally established ratios should also be considered. For concrete with a strength of 120 - 150 MPa, the ultimate deformability of cement stone should exceed by 10 - 30% the maximum deformability of the mortar, and the latter should be 20-30% higher than the ultimate deformability of concrete. Thus, the compressive strength of concrete, mortar and cement stone for particularly strong concrete should be maintained in a ratio of 0.7: 0.8: 1.0.

 Example.

For the manufacture of concrete, the following mixture components were selected:
Portland cement M600 with activity R _c = 58.5 MPa;
fractionated natural sand with a maximum crushability index of 9%;
basalt crushed stone with a grain crushing index of not more than 5%;
superplasticizer C-3, representing the complex additive "Liquefier C-3", consisting of the condensation product of naphthalene sulfonic acid and formaldehyde, sodium sulfate and lignosulfonate as a plasticizer.

The quantitative composition of the mixture per 1 m ³ : crushed stone consumption is 1380 kg, sand - 650 kg, cement - 530 kg, superplasticizer - 3.8 kg.

 Workability of concrete mix OK = 4, .0 cm.

 According to the table 1 - 3 and the graph in figure 1 set the values of the coefficients and parameters characterizing the concrete mix and included in the equation for calculating the design strength of concrete.

They are: K _in = 1,15; D / W = 3.92; A ₁ = 1.06, A ₂ = 1.07, A ₃ = 1.0.

проектную прочность бетона

. Величина прочности

= 154,7 МПа.Calculated by the formula

design strength of concrete

. Strength value

= 154.7 MPa.

 A method of manufacturing highly durable cement concrete is being implemented on a production line for highly durable cement concrete.

 The technological line for the manufacture of particularly durable cement concrete is / FIG. 2 / from the device 1 installed during the technological process for dry concentration and separation of fine aggregate (sand) into fractions, parallel device 2 for dry concentration and separation of large aggregate (crushed stone) into fractions, conveyors 3 and 4 for enriched and divided into large fractions and fine aggregates, respectively, batchers 5 for concrete mix components / sand, gravel, Portland cement and superplasticizer /, conveyor 6 for metered concrete mix components, concrete mixer 7 with concrete mixer which / is not shown / for mixing the concrete mixture with mixing water, rail tracks 8, means of transportation 9 of the concrete mixture and for laying it in the structure 10 with subsequent exposure to it in a given mode.

 Devices 1 and 2 for dry enrichment and separation into fractions of fine and coarse aggregates are structurally similar and consist (see Figs. 3 and 4) of a high pressure fan 11, a storage chamber 12, heaters 13, a loading pipe 14, an acceleration pipe 15, distribution chamber 16, at the end of which a jack plate 17 of the glass type is installed. A hopper 19 is connected to the lower part of the distribution chamber 16 through elastic connections 18, on which a vibrator 20 is located, closed on top by a partition 21. A sieve 22 with openings 23 of various sizes for small and large aggregates is installed between the baffle plate 17 and the partition 21. The vibrator 20 divides the hopper 19 into two discharge pipes 24 and 25. The suction space 26 is connected through a dust fan 27 to an aspiration system. The sizes of the spaces in the devices for enrichment and separation into fractions of fine and coarse aggregates range from 1 to 5 mm and from 5 to 20 mm, respectively.

 The production line for highly durable cement concrete works as follows.

 The small and coarse aggregates coming from the quarries are fed into the loading nozzles 14 of the device 1 for dry enrichment and separation into fractions of fine aggregate and the device 2 for dry enrichment and separation into fractions of coarse aggregate. Turn on the heaters 13 in the accumulation chambers 12, start the high-pressure fans 11 and open the shutters (not shown) of the loading nozzles 14. The fillers fall into the booster pipes 15 and, with the high-speed pressure from the fans 11, move to the distribution chambers 16 in warm air flows and hit the chimneys plates 17 glass type, where they are cleaned of impurities. The cleaned aggregates through sieves 22 with openings 23 / for small aggregates from 1 to 5 mm in size, for large aggregates from 5 to 20 mm / are classified into the required fractions and fed to discharge nozzles 24, of which small aggregate enters conveyor 4, and large aggregate - onto conveyor 3 and then into batchers 5 for concrete mix components. Unclassified aggregates through the discharge pipes 25 enter the waste. Small particles and dust with dust fans 27 from the suction spaces 26 are sent to the suction system. The dosed components of the concrete mixture, including small and large aggregates, Portland cement and superplasticizer in the required quantities (proportions) are transferred to the mixer 7 using the conveyor 6, where they are forcedly mixed with mixing water in compliance with the optimal water-cement ratio. After that, the concrete mixture along the rail tracks 8 is moved in a means of transportation 9 to the workshop 10 for the manufacture of concrete structures, where it is laid in the structure, compacted and maintained in a given mode.

- 120 - 155 МПа
призменная прочность (R_в) - /0,80 - 0,90/

модуль упругости (E_в) - /50 - 60/ МПа
предельная деформативность продольного сжатия (ε_ив) - /2,4 - 2,8/ • 10^-3
границы микротрещинобразования - -R^осгс = /0,62 - 0,78/ P_в - -Rν сгс = (0,82 - 0,95)P_в
коэффициент Пуасона ν - 0,19 - 0,23
масштабный коэффициент (K_m) - 1,00
коэффициент прироста прочности во времени:
к 1 году - K_τ = 1,10 - 1,20
к 5 годам - K_τ = 1,15 - 1,35
морозостойкость /F/ - более 800 циклов
водонепроницаемость (W) - более 1,2 МПа
коэффициент вариации (C_ν)
механических свойств - до 5%
физических свойств - до 12%
объемная масса (ρ_в) - 2,65 - 2,72 т/м³
Применение особо прочного цементного бетона позволит снизить массу центрально сжатых конструкций в 2 раза, внецентренно сжатых - на 20 - 30%, изгибаемых элементов - до 30%. Использование особо прочных бетонов в армированных конструкциях позволяет либо увеличить прочность конструкции, либо уменьшить количество и стоимость металла, вводимого в армированный бетон. Появляется возможность создания армированных конструкций с прочностью на сжатие 250 - 300 МПа. Открываются возможности создания сооружений нового технического уровня.The following are the main mechanical and physical characteristics of especially durable cement concrete made on a technological line of the claimed method:
cubic strength at the age of 28 days.

- 120 - 155 MPa
prismatic strength (R _in ) - / 0.80 - 0.90 /

modulus of elasticity (E _in ) - / 50 - 60 / MPa
ultimate deformability of longitudinal compression (ε _iv ) - / 2.4 - 2.8 / • 10 ^-3
microcracking boundaries - -R ^о sgs = / 0.62 - 0.78 / P _in - -Rν sgs = (0.82 - 0.95) P _in
Poisson's ratio ν - 0.19 - 0.23
scale factor (K _m ) - 1.00
strength gain over time:
by 1 year - K _τ = 1.10 - 1.20
5 years old - K _τ = 1.15 - 1.35
frost resistance / F / - more than 800 cycles
water resistance (W) - more than 1.2 MPa
coefficient of variation (C _ν )
mechanical properties - up to 5%
physical properties - up to 12%
bulk density (ρ _in ) - 2.65 - 2.72 t / m ³
The use of particularly durable cement concrete will reduce the weight of centrally compressed structures by 2 times, eccentrically compressed - by 20 - 30%, bending elements - up to 30%. The use of particularly strong concrete in reinforced structures allows either to increase the strength of the structure, or to reduce the amount and cost of the metal introduced into the reinforced concrete. There is the possibility of creating reinforced structures with a compressive strength of 250 - 300 MPa. Opportunities for creating structures of a new technical level are opening up.

Claims (4)

1. A method of manufacturing particularly durable cement concrete, comprising preparing a concrete mixture of fine and coarse aggregates, high-strength cement, superplasticizer and mixing water, laying the concrete mixture, compacting and hardening it with temperature and time conditions, characterized in that the aggregates are pre-prepared with removal of weak grains, extraneous impurities and fractionation, while sand is used as a fine aggregate with a crushing index of 5 - 30%, and as a large about the filler - crushed stone fractions of 5 - 10 mm or 5 - 10 and 10 - 20 mm in a ratio of 30 - 50% and 50 - 70%, respectively, with a crushing index of 4 - 8% with a volume ratio of cement, sand and crushed stone
V _c : V _p : V _n = 1.00: 1.00 - 1.45: 2.00 - 3.00,
moreover, the amount of mixing water is determined by the following relationship:

Where

- design strength of concrete, MPa;
R _c - cement activity, MPa;
K _in - correction coefficient of workability of the concrete mixture, equal to 1.15 for a rigid mixture and 1.05 for a cast;
C - cement consumption, kg / m ³ ;
A ₁ - coefficient taking into account the actual strength of the sand, determined by the crushing index, equal to 0.92 - 1.10;
A ₂ - coefficient taking into account the actual strength of crushed stone, determined by the crushing index, equal to 0.90 - 1.07;
A ₃ - coefficient taking into account the surface condition and the contamination of fine aggregate, equal to 0.87 - 1.00 for natural sand and 1.00 for crushed sand;
the water-cement ratio is maintained within the range of W / C = 0.24 - 0.28, the superplasticizer is introduced into the mixture in an amount of 0.5 - 1.0% by weight of the cement, the preparation of the components of the concrete mixture is fed into the concrete mixer, filled with mixing water, forcedly mixed and the prepared concrete mixture is laid in the structure and maintained in a given mode.  2. A technological line for the production of especially durable cement concrete, containing crushing plants for fine and coarse aggregates installed during the technological process, batchers for concrete mix components, a mixer with forced mixing, means of transporting concrete mix components, as well as concrete mix and laying it in structures with the ability to withstand in a given mode, characterized in that the crushing plants are made in the form of two devices for dry enrichment of small and round Nogo fillers and separate them into fractions which are mounted to dispensers for components of the concrete mix and the conveyors are connected to them.  3. The line according to claim 2, characterized in that the device for dry enrichment and separation of fine and coarse aggregates into fractions is made of a high-pressure fan connected in series with a storage chamber, inside of which heaters are installed, a storage chamber with an accelerating pipe, on which a loading pipe is installed, an acceleration pipe with a separation chamber, in which a glass-type breaker plate is installed, while the separation chamber in its lower part is connected via elastic ties to a hopper, inside of which a vibrator is installed, closed on top by a partition, and a sieve between the partition and the baffle plate with the possibility of forming two discharge pipes, a filler space connected by a pipeline to the aspiration system, and isolating the required aggregate fractions.  4. The line according to claims 2 and 3, characterized in that the openings in the screens for fine and coarse aggregates are made equal to from 1 to 5 mm and from 5 to 20 mm, respectively.

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