CN101187265A - Method for reducing cement base material internal temperature adopting prefilling phase-change material - Google Patents

Abstract

The invention belongs to the material application field, which provides a method which adopts built-in phase-change material to lower temperature rise in cement-based material, phase-change material with temperature 28 to 40 degrees and energy-storage intensity 170 to 290 J/g is injected in ducts under the temperature which is higher than critical point, and the temperature of which is lowered under critical point after being packed, and the phase-change material is changed to solid state, the ducts with solid-state phase-change material are built in the cement-based material in the process of concreting, when the temperature in the material rises to the critical point in the process of cement hydration, the phase-change material is phase-changed, which absorbs a large amount of heat, wherein the dosage of phase-change material is calculated with (A) type. The burying amount of PCM is designed according to requirements, and peak value and temperature rise speed of temperature in concrete can be effectively controlled, and concrete cracking which is caused by the over high temperature rise. The PCM is beforehand packed, the influence to the property of directly adding cement-based material is avoided, the material source is wide, and the invention provides a method of lowering inner temperature rise of the cement-based material in low price.

Description

Adopt pre-landfill phase-change material to reduce the method for cement-based material internal temperature rise

Technical field

The invention belongs to the material applied technical field, particularly a kind of reduction cement-based material internal temperature rise delays the temperature peak time of occurrence, avoids occurring the method for thermal cracking.

Background technology

After cement-based materials such as concrete were built, the heat of hydration of cement rose the material internal temperature.Because the surface is different with inner radiating condition, forms bigger internal-external temperature difference, make the material surface layer produce tensile stress.At the hydrated cementitious initial stage, the modulus of elasticity of cement-based material is less, and tensile strength is lower, and the tensile stress that the temperature difference produces surpasses the tensile strength of material easily, makes material surface produce the crack, and serious the penetrability crack will occur.The crack not only can reduce the rigidity and the globality of structure, and will aggravate corrosion of steel bar and carbonization, causes the reduction of performances such as freeze thawing resistance, antifatigue, antiseepage, waterproof, has a strong impact on durability of structures.So must be controlled to the internal temperature rise of large volume cement-based material.

The technology of existing control cement-based material internal temperature rise mainly contains:

1. set up cooling water recirculation system

Build at cement-based material and to arrange pipeline in the process, recirculated water is provided in pipeline in hydration process, the heat of hydration of part cement is derived, thereby regulate and the control concrete internal temperature.This method is present the most frequently used method, but also has a lot of shortcomings, and outstanding behaviours exists: in the water flowing process, there are the temperature difference in water temperature and material internal, when excessive temperature differentials, when cooling velocity is too fast, easily produce the crack, are commonly called as " cold hitting "; The temperature difference of recirculated water and cement-based material, water-flowing amount are in different times difference to some extent, and variations in temperature is not mild; The influence that temperature control effect is changed by ambient temperature.

2. add the retarding agent microcapsules

Admixture is that wall material, retarding agent are the microcapsules of core with paraffin in cement-based material, and the paraffin thawing discharges retarding agent in the temperature rise process, the hydration rate of slowing down cement, thus reduce internal temperature rise speed and temperature peak.But this method can make concrete early strength reduce greatly, influences construction speed; Paraffin melts the back also not to be goed deep into the research of cement-based material long-term behaviour influence.

3. directly in concrete, add phase-change material (Phase Change Materials is called for short PCM)

Phase-change material is meant in phase transition process can absorb or emit a large amount of heats, and keeps the metastable material of temperature in this process.Phase-change material is a development in recent years new material rapidly, is widely used in storage of solar energy, industrial waste heat recovery, electronic device heat management, heating and fields such as air-conditioning system and building external envelope structure.Because PCM latent heat height, variations in temperature is little in the phase transition process, so can utilize these characteristics to control the variation of ambient temperature.Directly add solid phase change material in the concrete whipping process, the heat that hydration reaction is produced has certain absorption, thereby concrete internal temperature is had certain control action, reduces the probability that concrete thermal cracking produces.The shortcoming of the method is: the weight that directly adds phase-change material is limited, and cooling-down effect is limited; Phase-change material has potential hazard to the durability of cement-based material; And the stability of phase-change material physicochemical properties under alkaline environment also needs further research.

Summary of the invention

The present invention is directed to above-mentioned shortcoming a kind of appearance that can effectively avoid thermal cracking is provided, avoid direct admixture to the cement-based material Effect on Performance, the temperature control amplitude is controlled, and material source is extensive, the method for cheap reduction cement-based material internal temperature rise.

Technical scheme of the present invention is: a kind of method that adopts pre-landfill phase-change material to reduce the cement-based material internal temperature rise, be to be 28～40 ℃ with phase transition temperature, energy storage density is that the phase-change material of 170～290J/g is under being higher than the temperature of transformation temperature in the flow in pipes, cool under the phase point temperature after the encapsulation, it is solid-state that phase-change material is become, the pipeline landfill that will contain solid phase change material in the process of building is in cement-based material, in cement hydration process, when the material internal temperature is increased to transformation temperature, phase-change material undergoes phase transition, absorb a large amount of heat, wherein the phase-change material consumption is calculated as follows:

$M_p=\frac{\mathrm{C\ρQ}(M_c+K{M}_F)\mathrm{\α}}{\mathrm{C\ρ}[C_1\left({T-t}_0\right)+q-C_1^{\′}T]+C_1(1-\mathrm{\α})(M_c+K{M}_F)Q}.$

Following mask body is set forth the calculating of phase-change material consumption down:

Under the adiabatic condition, the maximum thermal insulation warming of cement-based material can be expressed as:

$T_{\max }=\frac{(M_C+K{M}_F)Q}{\mathrm{C\ρ}}---\left(1\right)$

The PCM landfill in the cement-based material after, the heat that absorbs in temperature-rise period is:

Q′＝C ₁MX(T-t ₀)+M _Pq+C ₁′M _P(T _max′-T) (2)

This part heat that PCM absorbs has been equivalent to reduce the heat that causes the cement-based material internal temperature rise.The maximum thermal insulation warming theoretical calculation formula of the concrete of pre-landfill PCM can be expressed as:

$T_{\max }^{\′}=\frac{(M_C+K{M}_F)Q-[C_1{M}_p\left({T-t}_0\right)+M_{p}q+C_1^{\′}{M}_p(T_{\max }^{\′}-T)]}{\mathrm{C\ρ}}$

So the maximum thermal insulation warming behind the landfill PCM is:

$T_{\max }^{\′}=\frac{(M_c+K{M}_F)Q-M_p[C_1(T-t_0)}{\mathrm{C\ρ}+C_1^{\′}{M}_p}---\left(3\right)$

After adding PCM, in identical cement-based material inside, the reduction amplitude (in percentage) of theoretical thermal insulation warming is

$\mathrm{\α}=(1-\frac{T_{\max }^{\′}}{T_{\max }})\×100\%---\left(4\right)$

Formula (1) and formula (3) (4) formula of bringing into are got:

$\mathrm{\α}=\{1-\frac{\mathrm{C\ρQ}(M_c+K{M}_F)-C{\mathrm{\ρM}}_p[C_1(T-t_0)+q-C_1^{\′}T]}{(C+C_1{M}_p)(M_c+K{M}_F)Q}\}\×100\%---\left(5\right)$

The pre-amount of landfill of PCM is

$M_p=\frac{\mathrm{C\ρQ}(M_c+K{M}_F)\mathrm{\α}}{\mathrm{C\ρ}[C_1\left({T-t}_0\right)+q-C_1^{\′}T]+C_1(1-\mathrm{\α})(M_c+K{M}_F)Q}---\left(6\right)$

In the above-mentioned formula

M _c: the quality of cement in the unit volume concrete; M _F: the quality of admixture in the unit volume concrete;

K: refer to reduction coefficient, for flyash, K=0.25, for slag micropowder, K=0.3;

Q: the heat of hydration of unit cement;

Q ': the PCM landfill in the concrete after, the heat that absorbs in the temperature-rise period

C: concrete specific heat; ρ: concrete density;

C ₁: the specific heat C of solid-state PCM ₁': the specific heat of liquid PCM

M _p: the energy storage density of the weight q:PCM of PCM

The phase transition temperature t of T:PCM ₀: concrete initial temperature

T _Max': concrete maximum thermal insulation warming behind the pre-landfill PCM;

T _Max: the maximum thermal insulation warming of cement-based material;

α: thermal insulation warming reduces amplitude

The present invention's beneficial effect compared to existing technology is:

1. utilize pre-landfill PCM control cement-based material internal temperature rise, the temperature control amplitude can design the amount of landfill of PCM as requested, can effectively control concrete internal temperature peak value and temperature rise rate, has avoided the concrete cracking that causes because of temperature rise is too high.

2. the variations in temperature of cement-based material and PCM is synchronous, can effectively avoid excessive " cold the hitting " of causing of local temperature difference.

3. because the liquid density of the PCM that selects for use less than solid-state density, undergoes phase transition when solid-state so handle through cooling, volume can not increase, and can effectively avoid the compressive stress that produces because of volume expansion.

4.PCM, avoided direct admixture that the cement-based material performance is impacted through encapsulation in advance.

5.PCM of a great variety, material source is extensive, and is cheap, range of choice is big.

6.PCM after absorbing heat, become liquid state, can derive recyclingly by pipeline, economy is environmental protection again.

Description of drawings

Fig. 1 adopts pre-landfill phase-change material to reduce the control flow chart of cement-based material internal temperature rise.

Fig. 2 is the pipe arrangement schematic diagram that adopts PCM control cement-based material internal temperature rise.

Wherein: 1 insulation layer; 2 plastic foils; 3 cement-based materials; 4 pipes; 5PCM; A places the thermocouple of PCM; B places the thermocouple at cement-based material center; C places the thermocouple of cement-based material sidewall.

Fig. 3 is the influence of PCM amount of landfill to the maximum thermal insulation warming of concrete of different cement consumptions.

Fig. 4 is the relation that pre-amount of landfill of PCM and maximum thermal insulation warming reduce amplitude.

Fig. 5 is the influence of pre-landfill PCM to cement paste half thermal insulation warming.

Fig. 6 is the influence of pre-landfill PCM to cement mortar half thermal insulation warming.

The specific embodiment

Below in conjunction with accompanying drawing the present invention is made and to specify.

Fig. 1 is the flow chart of technical scheme of the present invention, referring to Fig. 1 as can be seen the present invention be when being higher than the temperature of transformation temperature, to carry out encapsulation process in liquid PCM flow in pipes or the container, be cooled to below the phase point temperature then, it is solid-state that PCM is changed into by liquid state in pipeline or container, and the temperature below transformation temperature is stored standby.During use again by certain way with pipeline or container landfill in concrete in mass, when the concrete heat of hydration makes that internal temperature reaches phase transition temperature, PCM with the absorption portion heat of hydration by the solid-state liquid state that becomes, concrete internal temperature peak value and temperature rise rate are effectively reduced, avoided the concrete cracking that causes because of temperature rise is too high; The variations in temperature of cement-based material and PCM is synchronous, can effectively avoid excessive " cold the hitting " of causing of local temperature difference; PCM becomes liquid state after absorbing heat, can be recycling by the pipeline derivation by valve switch control, and economy is environmental protection again.

Fig. 2 is the wherein a kind of pipe arrangement schematic diagram that adopts the method for the invention, this pipe arrangement is that steel pipe 4 or vinyl tube 4 that constant weight PCM 5 is housed are arranged evenly that by crawling privileged sites can suitably be adjusted according to structure situation in cement-based material.Arrange that at center, edge and the PCM material internal of cement-based material thermocouple B, C, A carry out thermometric respectively.Two ends at pipeline are provided with valve, can carry out the PCM derivation of liquid state recycling.The cement-based material body can be provided with insulation layer 1, can intercept with plastic foil 2 in the insulation layer 1.

Suppose that the heat of hydration that the final aquation of cement is emitted is 400J/g, cement-based material density 2400kg/m ³, specific heat is 0.96J/g ℃.The pre-amount of landfill of PCM is 0 of cement weight～40% o'clock, and the maximum thermal insulation warming of cement-based material reduces along with the increase of the pre-amount of landfill of PCM, as shown in Figure 3.The reduction amplitude relation of the maximum thermal insulation warming of the pre-amount of landfill cement-based material of PCM as shown in Figure 4, the pre-amount of landfill of PCM is big more, the amplitude that thermal insulation warming reduces is big more.The cement consumption of cement-based material is 400kg/m ³The time, the pre-amount of landfill of PCM is 10% of cement weight～20% o'clock, and maximum thermal insulation warming descends 6.17 ℃～11.66 ℃, and fall is 8.89%～16.79%.So will improve the reduction amplitude of PCM as can be seen to the cement-based material thermal insulation warming by Fig. 3 and Fig. 4, can strengthen the pre-amount of landfill of PCM, select suitable pre-burying method, can be chosen in the higher cement-based material of cement consumption simultaneously and use.

A kind of method that adopts pre-landfill phase-change material to reduce the cement-based material internal temperature rise, be to be that 28～40 ℃, energy storage density are that the phase-change material of 170～290J/g is under being higher than the temperature of transformation temperature in the flow in pipes with phase transition temperature, cool under the phase point temperature after the encapsulation, it is solid-state that phase-change material is become, the pipeline landfill that will contain solid phase change material in the process of building is in cement-based material, in cement hydration process, when the material internal temperature is increased to transformation temperature, phase-change material undergoes phase transition, absorb a large amount of heat, wherein the phase-change material consumption is calculated as follows:

$M_p=\frac{\mathrm{C\ρQ}(M_c+K{M}_F)\mathrm{\α}}{\mathrm{C\ρ}[C_1(T-t_0)+q-C_1^{\′}T]+C_1(1-\mathrm{\α})(M_c+K{M}_F)Q}.$

Wherein the phase transition temperature of phase-change material is optional between 28～40 ℃, can comprise in the described scope each number between the minimum and maximum value and all number and/or part for 28 ℃, 30 ℃, 31 ℃, 37 ℃, 40 ℃.Energy storage density is the arbitrary numerical value between 170～290J/g, comprises each number between the minimum and maximum value and whole number and/or part number in the described scope, as gets 170J/g, 173J/g, 180J/g, 200J/g, 240J/g up to 290J/g.

Embodiment 1

Adopt Na ₂SO ₄10H ₂O is as pre-landfill phase-change material, and its physical property is as shown in table 1.

The physical property of table 1 PCM

Molecular formula	Energy storage density J/g	Fusing point ℃	Solid-state specific heat J/g ℃	Liquid specific heat J/g ℃
					Na 2SO 4·10H 2O	241	32.4	1.76	3.30

The cement paste employing trade mark is that the cement of PO42.5 is mixed system, and water ash mass ratio is 0.3: 1.Under half thermal insulation warming condition, pre-landfill is the PCM of 0,3%, 6% weight of cement weight in clean slurry respectively, starches the internal temperature rise curve only as shown in Figure 5.Figure as can be known thus: landfill PCM is 3% of cement weight～6% o'clock, and comparing not, the temperature peak of landfill PCM cement paste reduces by 13 ℃～20 ℃, time lengthening 1.5h～2.5h that temperature peak occurs; Half thermal insulation warming curve of cement paste tends towards stability along with the increase of PCM amount of landfill; In temperature is that temperature curve breaks up about 32 ℃.

Scatter and disappear because incubator has the part heat in cement hydration process, so the temperature that records is the temperature under cement-based material half adiabatci condition, it is lower than calculated value that temperature rise reduces amplitude.

Embodiment 2

Adopt Na ₂SO ₄10H ₂O is as pre-landfill phase-change material, and its physical property is as shown in table 1.Cement mortar adopts PO42.5 cement and siliceous river sand to mix system, and water ash mass ratio is 0.4: 1, and the sand-lime mass ratio is 1: 3.Under half thermal insulation warming condition, pre-landfill accounts for the PCM of 0,3%, 6% quality of cement mortar weight in cement mortar respectively, and mortar internal temperature rise curve as shown in Figure 6.Figure as can be known thus: landfill PCM is 3% of cement weight～6% o'clock, and comparing not, the temperature peak of landfill PCM mortar reduces by 4 ℃～6 ℃, time lengthening 2h～5h that temperature peak occurs; Half thermal insulation warming curve of mortar tends towards stability along with the increase of PCM amount of landfill; In temperature is that temperature curve breaks up about 32 ℃.

Scatter and disappear because incubator has the part heat in cement hydration process, so the temperature that records is the temperature under cement-based material half adiabatci condition, it is lower than calculated value that temperature rise reduces amplitude.

Embodiment 3

Adopt Na ₂HPO ₄12H ₂O is as pre-landfill phase-change material, and its physical property is as shown in table 2.

The physical property of table 2 PCM

Molecular formula	Energy storage density J/g	Fusing point ℃	Solid-state specific heat J/g ℃	Liquid specific heat J/g ℃
					Na 2HPO 4·12H 2O	279	40	1.56	1.95

The cement paste employing trade mark is that the cement of PO42.5 is mixed system, and water ash mass ratio is 0.3: 1.Under half thermal insulation warming condition, pre-landfill is the PCM of 0,3%, 6% weight of cement weight in clean slurry respectively, clean slurry internal temperature rise is 3% of cement weight～6% o'clock at landfill PCM, that compares that the temperature peak of landfill PCM cement paste not reduces wants big, and the time that temperature peak occurs also obtains prolonging.

Embodiment 4

Adopt CaCl ₂6H ₂O is as pre-landfill phase-change material, and its physical property is as shown in table 3.

The physical property of table 3 PCM

Molecular formula	Energy storage density J/g	Fusing point ℃	Solid-state specific heat J/g ℃	Liquid specific heat J/g ℃
					CaCl 2·6H 2O	170.0	29.0	1.46	2.13

The cement paste employing trade mark is that the cement of PO42.5 is mixed system, and water ash mass ratio is 0.3: 1.Under half thermal insulation warming condition, pre-landfill is the PCM of 0,3%, 6% weight of cement weight in clean slurry respectively, clean slurry internal temperature rise is 3% of cement weight～6% o'clock at landfill PCM, that compares that the temperature peak of landfill PCM cement paste not reduces wants big, and the time that temperature peak occurs also obtains prolonging.

Embodiment 5

Adopt Na ₂CO ₄10H ₂O is as pre-landfill phase-change material, and its physical property is as shown in table 4.

The physical property of table 4 PCM

Molecular formula	Energy storage density J/g	Fusing point ℃	Solid-state specific heat J/g ℃	Liquid specific heat J/g ℃
					Na 2CO 4·10H 2O	267	32	1.99	3.34

The cement paste employing trade mark is that the cement of PO42.5 is mixed system, and water ash mass ratio is 0.3: 1.Under half thermal insulation warming condition, pre-landfill is the PCM of 0,3%, 6% weight of cement weight in clean slurry respectively, clean slurry internal temperature rise is 3% of cement weight～6% o'clock at landfill PCM, that compares that the temperature peak of landfill PCM cement paste not reduces wants big, and the time that temperature peak occurs also obtains prolonging.

Claims (6)

1. method that adopts pre-landfill phase-change material to reduce the cement-based material internal temperature rise, it is characterized in that 28～40 ℃ of phase transition temperatures, energy storage density is that the phase-change material of 170～290J/g is under being higher than the temperature of transformation temperature in the flow in pipes, cool under the phase point temperature after the encapsulation, it is solid-state that phase-change material is become, the pipeline landfill that will contain solid phase change material in the process of building is in cement-based material, in cement hydration process, when the material internal temperature is increased to transformation temperature, phase-change material undergoes phase transition, absorb a large amount of heat, wherein the phase-change material consumption is calculated as follows:

$M_p=\frac{\mathrm{C\ρQ}(M_c+K{M}_F)\mathrm{\α}}{\mathrm{C\ρ}[C_1\left({T-t}_0\right)+q-C_1^{\′}T]+C_1(1-\mathrm{\α})(M_c+K{M}_F)Q}.$

2. the pre-landfill phase-change material of employing as claimed in claim 1 reduces the method for cement-based material internal temperature rise, and the liquid density that it is characterized in that phase-change material is less than solid-state density.

3. the pre-landfill phase-change material of employing as claimed in claim 1 reduces the method for cement-based material internal temperature rise, it is characterized in that evenly arranging by crawling in cement-based material at the pipeline that contains solid phase change material.

4. the pre-landfill phase-change material of employing as claimed in claim 3 reduces the method for cement-based material internal temperature rise, it is characterized in that the pipe ends that contains solid phase change material stretches out outside the cement-based material, be provided with the valve gauge tap, when phase-change material becomes liquid state, can flow out.

5. the pre-landfill phase-change material of employing as claimed in claim 1 reduces the method for cement-based material internal temperature rise, it is characterized in that being provided with thermocouple in center, edge and the phase-change material inside of cement-based material respectively.

6. reduce the method for cement-based material internal temperature rise as the pre-landfill phase-change material of the arbitrary described employing of claim 1～5, it is characterized in that phase-change material is Na ₂SO ₄10H ₂O, Na ₂HPO ₄12H ₂O, CaCl ₂6H ₂O, Na ₂CO ₃10H ₂O's is arbitrary.

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