RU2562633C2 - Method of increasing heat capacity and heat-retaining capacity of concrete and mortar - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to production of building materials and can be used to increase specific heat capacity and heat-retaining capacity of concrete and mortar. The method of increasing heat capacity and heat-retaining capacity of concrete and mortar includes further adding to basic components at the step of preparing concrete or mortar a heat-retaining encapsulated aggregate, particularly a high-heat capacity aggregate in the form of capsules containing a heat-retaining substance in a durable chemically resistant shell while enabling temperature variation of the volume thereof. The heat-retaining substance used is refining effluent, wherein said aggregate is added in amount of 10-90 vol %.

EFFECT: high specific heat capacity and heat-retaining capacity of concrete and mortar to ensure high energy efficiency of construction facilities operating in a wide temperature range, including subzero temperatures, and recycling wastes.

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Description

The invention relates to the field of production of building materials and can be used to increase the specific heat and heat storage capacity of concrete and mortar.

A known method of producing heat-sensitive materials based on talc-magnesite, including obtaining 30-60% aqueous suspension of talc-magnesite by grinding talc-magnesite, mixing it with water, additional introduction of 5-15 wt.% Iron oxides, 0.5-4 wt.% Liquid glass into the suspension , 0.05-7 wt.% Cement, treatment in a rotary cavitation apparatus at a rotor speed of 3000-12000 per minute, temperature 15-70 ° C, the number of treatment cycles 5-50, molding the resulting mass under pressure and its heat treatment ( RF patent №2259974, priority date 03.24.2004, date pu of replication of 10.09.2005, the author of VP Shtager, RU).

A disadvantage of the known analogue is the complex chemical composition and manufacturing process of materials, a slight increase in specific heat, as well as the limited scope of its application, due to the limited raw material base in composition and the possibility of obtaining heat-sensitive materials based on talc magnesite, which indicates that the method is not universal .

Known concrete (GOST 7473, GOST 25192) or mortar (GOST 28013), characterized by a specific heat of 0.84 kJ / kg ° C (according to SP 50.13330.2012 "Thermal protection of buildings").

However, in order to evaluate and improve the energy efficiency of construction sites, it is important to take into account such thermal characteristics as the heat capacity and the heat storage capacity of building materials. In particular, the use of materials with high heat capacity and high heat storage ability allows you to slow down the change in temperature of the structure over a period of time with a change in ambient temperature. Thus, it seems possible to reduce the amplitude of the temperature fluctuation of the structure with phase shift of the peak temperature during, for example, night and day time. This effect, with economic feasibility, can be used in external and internal walling in the presence of an automated heating system, as well as in underfloor heating and structures of industrial refrigerators, taking into account the fact that the cost of electricity during periods of time with a minimum network load (usually night) lower.

As a prototype, a method has been adopted to increase the heat storage capacity of concrete building elements, characterized by the introduction of an encapsulated material having latent heat (enthalpy ΔH, [J / g]) of a phase transition, in particular a paraffin mixture or wax, into which it is encapsulated the material is added as a filler in the form of microcapsules with a shell of a polymer (RF Patent No. 2391319, priority date 04/21/2006, publication date 06/10/2010, authors WITTHON Michel et al., DE, pr prototype of).

The disadvantage of the prototype is the limited scope of heat storage materials obtained by the known method according to the prototype, due to the fact that the presence of paraffin microcapsules in the material provides a heat storage effect of up to 200 J / g due to the melting of paraffin in the temperature range from 22 ° C to 28 ° C, which determines their appropriate use in regions with a warm climate.

The objective of the invention is to obtain heat-consuming and heat-accumulating concrete and mortar to improve the energy efficiency of construction sites operated in a wide temperature range, including negative values.

To solve the problem in a method of increasing the heat capacity and heat storage capacity of concrete and mortar by adding to the main components at the stage of preparation of a concrete or mortar mixture a heat-storage encapsulated aggregate, in particular a heat-sensitive aggregate in the form of capsules containing a heat-accumulating substance in a durable chemically resistant shell with the possibility temperature changes in its volume, according to the invention, it uses encapsulated filling Nitel to the drains of the refining industry, having a high specific heat capacity than that of conventional concrete, the aggregate is administered encapsulated in an amount of from 10% to 90% by volume.

In practical applications, the maximum volumetric content of the heat-intensive aggregate in concrete (mortar) depends on the particle size distribution of the aggregate and the required thermophysical properties of concrete (mortar) and may be less than 90%. A volumetric content of aggregate of less than 10% does not significantly affect the increase in specific heat and heat storage capacity in concrete and mortar.

In addition, water or saline solutions, which also increase the heat capacity and heat storage capacity of concrete and mortar, can be used as a heat-storage substance in an encapsulated aggregate. In addition, it is advisable to use encapsulated aggregate with saline solutions, the heat capacity and state of aggregation of which does not change at low temperatures, in contrast to other liquid materials.

The introduction into the composition of a concrete or mortar mixture of an encapsulated aggregate with any specified liquid highly heat-sensitive substance at the stage of preparation of the mixtures leads to an increase in the specific heat capacity and heat storage capacity of concrete and mortar.

In practice, the heat capacity of the encapsulated aggregate of cement concrete can be changed to a considerable extent and at the same time use materials with a changing phase state, which are very promising from the standpoint of energy conservation and energy efficiency. The effectiveness of the use of such materials is estimated by the amount of latent energy released or absorbed during crystallization, melting, evaporation and condensation.

Concrete compositions are usually calculated by absolute volumes. The estimated value of the density of concrete ρ containing less dense, but having a much higher heat capacity aggregate (encapsulated water and its salt solutions) can be determined as the sum of the densities of the mortar and aggregate multiplied by the corresponding fractions of their content in 1 m ^{3 of} concrete:

where ρ _m is the density of the hardened mortar part of the concrete in which the aggregate is distributed; ρ _L is the density of the heat-intensive aggregate; φ _m is the volume fraction of the mortar in concrete.

Thus, knowing the calculated concrete density ρ, heat capacity of the mortar part c _m and aggregate c _L , the total heat capacity of the system C can be calculated by the formula

In this case, the density and heat capacity of the capsule are neglected.

Examples of the implementation of methods for producing heat-consuming and heat-accumulating concrete and mortar are based on the fact that at the stage of preparing a concrete or mortar mixture, a filler is introduced from a highly heat-sensitive substance enclosed in capsules with a strong and chemically resistant shell, for example, from polymer.

The results are summarized in the following tables: table 1 - thermophysical properties of concrete with a matrix of heavy concrete and encapsulated water; table 2 - thermophysical properties of concrete with a matrix of lightweight concrete and encapsulated water; table 3 - thermophysical properties of concrete with encapsulated saline with a density of 1.28 kg / m ³ ; table 4 - thermophysical properties of concrete with encapsulated saline with a density of 1.38 kg / m ³ .

Example 1. As a well-known highly heat-sensitive substance, water was used (specific heat of 4.2 kJ / kg ° C and heat storage capacity (ΔH is the phase transition enthalpy) up to 333 J / g at n.o.) or its salt solutions.

According to the above expression (2) and table 1, which reflects the dependence of the thermophysical properties of concrete on the volumetric content of the aggregate, it follows that the presence of encapsulated highly heat-resistant aggregate with water in a volume of 10 to 90% in 1 m ^{3 of} concrete with a matrix of heavy concrete can increase the heat capacity of the system 4.7 times, and the heat-accumulating effect, characterized by the magnitude of the phase transition enthalpy, is up to 300 J / g due to crystallization of water or melting of ice at a temperature of about 0 ° C.

Table 1. Thermophysical properties of concrete with a matrix of heavy concrete and encapsulated water No. p / p Volume fraction of aggregate The density of concrete, kg / m ³ System heat capacity Enthalpy of phase transition, J / g Specific heat, J / kg · ° C × 10 ^-3 Volumetric heat capacity, J / m ³ · ° C × 10 ^-6 one 0.9 1138 3,476 3,956 300 2 0.8 1278 2,926 3,741 266 3 0.7 1419 2,485 3,525 233 four 0.6 1559 2,123 3,309 200 5 0.5 1699 1,821 3,094 167 6 0.4 1839 1,565 2,878 133 7 0.3 1979 1,345 2,663 one hundred 8 0.2 2120 1,155 2,447 67 9 0.1 2260 0.987 2,232 33

Table 2. Thermophysical properties of concrete with lightweight concrete matrix and encapsulated water No. p / p Volume fraction of aggregate The density of concrete, kg / m ³ System heat capacity Enthalpy of phase transition, J / g Specific heat, J / kg · ° C × 10 ^-3 Volumetric heat capacity, J / m ³ · ° C × 10 ^-6 one 0.9 958 3,971 3,805 300 2 0.8 918 3,744 3,438 266 3 0.7 879 3,496 3,071 233 four 0.6 839 3,224 2,705 200 5 0.5 799 2,926 2,338 167 6 0.4 759 2,596 1,971 133 7 0.3 719 2,230 1,604 one hundred 8 0.2 680 1,821 1,238 67 9 0.1 640 1,361 0.871 33

According to the above expression (2) and Table 2, which reflects the dependence of the thermophysical properties of concrete on the volumetric content of aggregate, it follows that the presence of encapsulated highly heat-resistant aggregate with water in a volume of 10 to 90% in 1 m ^{3 of} concrete with a matrix of lightweight concrete allows to increase the heat capacity of the system 4.5 times, and the heat-accumulating effect, characterized by the magnitude of the phase transition enthalpy, is up to 300 J / g due to crystallization of water or melting of ice at a temperature of about 0 ° C.

Example 2. As a high-heat aggregate used industrial wastes, in particular aqueous saline solutions, obtained as a result of disposal of effluents from the refining production of the plant of OJSC “Krastsvetmet” in the city of Krasnoyarsk:

- 360 мг/л, Cl^- - 147000 мг/л, $$N{O}_3^{-}$$

- 111000 мг/л, Ca⁺ - 31600 мг/л, Fe - 0,78 мг/л, Cu - 0,141 мг/л, Ni - 0,0078 мг/л, Zn - 1,14 мг/л, Pb - 8,6 мг/л.1 - saline solution with a density of 1.28 kg / m ³ , pH is 8.2, having a specific heat of at least 3 kJ / kg · ° C, does not crystallize upon cooling (does not freeze) to minus 30 ° C, with the chemical composition: $$S{O}_{\mathrm{four}}^{-}$$

- 360 mg / l, Cl ^- - 147000 mg / l, $$N{O}_3^{-}$$

- 111000 mg / L, Ca ⁺ - 31600 mg / L, Fe - 0.78 mg / L, Cu - 0.141 mg / L, Ni - 0.0078 mg / L, Zn - 1.14 mg / L, Pb - 8.6 mg / l.

Table 3. Thermophysical properties of concrete with encapsulated saline based on refining effluents with a density of 1.28 kg / m ³ No. p / p Volume fraction of aggregate The density of concrete, kg / m ³ System heat capacity Specific heat, J / kg · ° C × 10 ^-3 Volumetric heat capacity, J / m ³ · ° C × 10 ^-6 one 0.9 1392 2628 3658 2 0.8 1504 2311 3475 3 0.7 1616 2038 3293 four 0.6 1728 1800 3110 5 0.5 1840 1591 2928 6 0.4 1952 1407 2746 7 0.3 2064 1242 2563 8 0.2 2176 1094 2381 9 0.1 2288 961 2198

According to the above expression (2) and table 3, which reflects the dependence of the thermophysical properties of concrete on the volumetric content of the aggregate, it follows that the presence of encapsulated highly heat-resistant aggregate from the presented salt solutions in a volume of 10 to 90% in 1 m ^{3 of} concrete with a matrix of heavy concrete can increase the heat capacity of the system is 4.35 times.

- 3000 мг/л, $$S{O}_4^{-}$$

- 45 мг/л, Cl^- - 210000 мг/л, $$N{O}_3^{-}$$

- 260000 мг/л, Ca⁺ - 126000 мг/л, Fe - 0,88 мг/л, Cu - 3,5 мг/л, Ni - 0,52 мг/л, Zn - 5,8 мг/л, Pb - 0,63 мг/л.2 - saline solution with a density of 1.38 kg / m ³ , pH is 5.2, having a specific heat of at least 3 kJ / kg · ° C, does not crystallize upon cooling (does not freeze) to minus 60 ° C, with the chemical composition: $$N{H}_{\mathrm{four}}^{+}$$

- 3000 mg / l $$S{O}_{\mathrm{four}}^{-}$$

- 45 mg / l, Cl ^- - 210,000 mg / l, $$N{O}_3^{-}$$

- 260,000 mg / L, Ca ⁺ - 126,000 mg / L, Fe - 0.88 mg / L, Cu - 3.5 mg / L, Ni - 0.52 mg / L, Zn - 5.8 mg / L, Pb - 0.63 mg / L.

Table 4. Thermophysical properties of concrete with encapsulated saline based on refining effluents with a density of 1.38 kg / m ³ No. p / p Volume fraction of aggregate The density of concrete, kg / m ³ System heat capacity Specific heat, J / kg · ° C × 10 ^-3 Volumetric heat capacity, J / m ³ · ° C × 10 ^-6 one 0.9 1482 2650 3928 2 0.8 1584 2345 3715 3 0.7 1686 2078 3503 four 0.6 1788 1840 3290 5 0.5 1890 1629 3078 6 0.4 1992 1439 2866 7 0.3 2094 1267 2653 8 0.2 2196 1111 2441 9 0.1 2298 970 2228

According to the above expression (2) and table 4, which reflects the dependence of the thermophysical properties of concrete on the volumetric content of the aggregate, it follows that the presence of encapsulated highly heat-resistant aggregate from the presented salt solutions in a volume of 10 to 90% in 1 m ^{3 of} concrete with a matrix of heavy concrete can increase the heat capacity of the system is 4.67 times.

The results of the study of the heat storage capacity of cement concretes (mortars) are presented in the figure in the form of graphical dependencies (1-5), reflecting the accumulation of thermal energy when heated by water and concrete of various compositions, including concrete with a volumetric content of heat-sensitive aggregate with water of 80%. The graphs given refer to water (specific heat 4.2 kJ / kg ° C) (1), heat-intensive heavy concrete (specific heat 2.93 kJ / kg ° C) (2), heat-sensitive light concrete (specific heat 3.74 kJ / kg ° C) (3), ordinary heavy concrete (specific heat 0.84 kJ / kg ° C) (4) and ordinary light concrete (specific heat 0.84 kJ / kg ° C) (5). On the graphs (1-5) it is seen that the specific amount of heat accumulated during heating by the developed compositions is less than that of water, however, it is much more than that of ordinary compositions of heavy and light concrete. A greater accumulation of thermal energy by heat-intensive materials compared to conventional materials will allow us to level the extreme values of temperature changes (on the surface and in the whole volume) of concrete, accumulate thermal energy and, thus, save electrical and thermal energy during the operation of construction sites.

To implement the method, it is preferable to use a spherical encapsulated aggregate with sizes from 0.3 mm to 5 mm, which can be obtained in known installations, for example, according to RF patent No. 2420350. The size of the aggregate is selected in accordance with the required thermophysical properties of concrete or mortar and depends on its volumetric content in the mixtures.

The proposed method for increasing the heat capacity and heat storage capacity is universal and can be used for concrete and mortar of various compositions.

Claims (1)

A method of increasing the heat capacity and heat storage capacity of concrete and mortar by adding to the main components at the stage of preparation of a concrete or mortar mixture a heat-storage encapsulated aggregate, in particular a heat-sensitive aggregate in the form of capsules containing a heat-accumulating substance in a durable chemically resistant shell with the possibility of temperature variation of its volume, characterized in that it uses an encapsulated aggregate with effluent refining drains plants having a greater specific heat capacity than conventional concrete, and encapsulated aggregate is introduced in an amount of from 10% to 90% of the volume.

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