CN114577657A - Method for measuring water absorption of recycled aggregate in cement base material - Google Patents
Method for measuring water absorption of recycled aggregate in cement base material Download PDFInfo
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- CN114577657A CN114577657A CN202011403823.0A CN202011403823A CN114577657A CN 114577657 A CN114577657 A CN 114577657A CN 202011403823 A CN202011403823 A CN 202011403823A CN 114577657 A CN114577657 A CN 114577657A
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- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 title claims abstract description 198
- 239000004568 cement Substances 0.000 title claims abstract description 196
- 239000000463 material Substances 0.000 title claims abstract description 102
- 238000010521 absorption reaction Methods 0.000 title claims abstract description 61
- 238000000034 method Methods 0.000 title claims abstract description 59
- 239000002002 slurry Substances 0.000 claims abstract description 60
- 238000002156 mixing Methods 0.000 claims abstract description 53
- 239000004567 concrete Substances 0.000 claims description 24
- 239000000203 mixture Substances 0.000 claims description 14
- 239000004570 mortar (masonry) Substances 0.000 claims description 13
- 239000002699 waste material Substances 0.000 claims description 13
- 238000005303 weighing Methods 0.000 claims description 9
- 239000011159 matrix material Substances 0.000 claims description 8
- QORWJWZARLRLPR-UHFFFAOYSA-H tricalcium bis(phosphate) Chemical compound [Ca+2].[Ca+2].[Ca+2].[O-]P([O-])([O-])=O.[O-]P([O-])([O-])=O QORWJWZARLRLPR-UHFFFAOYSA-H 0.000 claims description 8
- 239000003638 chemical reducing agent Substances 0.000 claims description 7
- 238000012216 screening Methods 0.000 claims description 7
- 238000003556 assay Methods 0.000 claims description 5
- 239000002245 particle Substances 0.000 claims description 5
- 230000000740 bleeding effect Effects 0.000 claims description 3
- 230000008569 process Effects 0.000 abstract description 19
- 238000011156 evaluation Methods 0.000 abstract description 4
- 230000009897 systematic effect Effects 0.000 abstract description 4
- 230000009286 beneficial effect Effects 0.000 abstract description 2
- 239000004566 building material Substances 0.000 abstract description 2
- 238000001514 detection method Methods 0.000 abstract description 2
- 238000011158 quantitative evaluation Methods 0.000 abstract description 2
- 238000005119 centrifugation Methods 0.000 description 8
- 238000010276 construction Methods 0.000 description 8
- 230000000052 comparative effect Effects 0.000 description 6
- 239000011083 cement mortar Substances 0.000 description 5
- 229920006395 saturated elastomer Polymers 0.000 description 5
- 239000000758 substrate Substances 0.000 description 5
- 239000011148 porous material Substances 0.000 description 4
- 238000011161 development Methods 0.000 description 3
- 238000005259 measurement Methods 0.000 description 3
- 238000000691 measurement method Methods 0.000 description 3
- 230000001276 controlling effect Effects 0.000 description 2
- 238000013461 design Methods 0.000 description 2
- 238000002791 soaking Methods 0.000 description 2
- 238000012546 transfer Methods 0.000 description 2
- 239000002253 acid Substances 0.000 description 1
- 230000033228 biological regulation Effects 0.000 description 1
- 230000008859 change Effects 0.000 description 1
- 230000006378 damage Effects 0.000 description 1
- 230000002950 deficient Effects 0.000 description 1
- 238000009826 distribution Methods 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 230000007613 environmental effect Effects 0.000 description 1
- 238000001704 evaporation Methods 0.000 description 1
- 238000002474 experimental method Methods 0.000 description 1
- 230000036571 hydration Effects 0.000 description 1
- 238000006703 hydration reaction Methods 0.000 description 1
- 230000006872 improvement Effects 0.000 description 1
- 238000004898 kneading Methods 0.000 description 1
- 230000014759 maintenance of location Effects 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 230000004660 morphological change Effects 0.000 description 1
- 239000012466 permeate Substances 0.000 description 1
- 238000002360 preparation method Methods 0.000 description 1
- 238000003825 pressing Methods 0.000 description 1
- 239000000047 product Substances 0.000 description 1
- 239000002994 raw material Substances 0.000 description 1
- 238000004064 recycling Methods 0.000 description 1
- 230000001105 regulatory effect Effects 0.000 description 1
- 230000000717 retained effect Effects 0.000 description 1
- 238000013341 scale-up Methods 0.000 description 1
- 238000000926 separation method Methods 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 238000010998 test method Methods 0.000 description 1
- 238000012360 testing method Methods 0.000 description 1
- 238000005406 washing Methods 0.000 description 1
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N5/00—Analysing materials by weighing, e.g. weighing small particles separated from a gas or liquid
- G01N5/02—Analysing materials by weighing, e.g. weighing small particles separated from a gas or liquid by absorbing or adsorbing components of a material and determining change of weight of the adsorbent, e.g. determining moisture content
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02W—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT
- Y02W30/00—Technologies for solid waste management
- Y02W30/50—Reuse, recycling or recovery technologies
- Y02W30/91—Use of waste materials as fillers for mortars or concrete
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- Life Sciences & Earth Sciences (AREA)
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Abstract
The invention belongs to the technical field of building material detection, and particularly discloses a method for measuring water absorption of recycled aggregate in a cement base material. The determination method comprises the steps of firstly determining the centrifugable water content in the clean slurry under the preset water-cement ratio, then determining the centrifugable water content of the recycled cement base material containing the recycled aggregate under the same water-cement ratio, and deducting the background of the single clean slurry, so that the water absorption of the recycled aggregate in the cement base material can be calculated. The determination method only needs to control mixing of the clean slurry for two times under the condition of the same water-cement ratio and the same mixing and centrifuging process, overcomes the influence of systematic errors, is not limited to the specific value of the water-cement ratio, and has diversified and flexible application scenes. The determination method fully considers the difference of the water absorption capacity of the recycled aggregate in water and the cement base material, provides more quantitative evaluation operation, and is beneficial to improving the adjustment and evaluation of the working performance, the mechanical performance and the durability when the recycled aggregate is recycled to the cement base material.
Description
Technical Field
The invention belongs to the technical field of building material detection, and particularly relates to a method for measuring water absorption of recycled aggregate in a cement base material.
Background
With the rapid development of economy in China, infrastructure and major projects are being constructed on a large scale, and meanwhile, a large amount of construction waste is continuously discharged. Compared with developed countries, the comprehensive utilization level of the construction waste resources in China is lower, most of the construction waste resources are mainly treated in an open-air stacking and landfill mode, and the recycling technology is still in an exploration stage. On one hand, on the long run, the construction waste becomes soft ribs and hard injuries which influence the improvement of environmental quality and the development of economic society; on the other hand, natural materials for engineering construction are increasingly deficient, urban construction waste is reasonably and effectively utilized to prepare recycled materials, and the method has important significance for maintaining the sustainable and healthy development of economy in China.
After the construction waste is separated, the waste concrete is processed into recycled aggregate, a large amount of hardened cement mortar is adhered to the surface, microcracks are easily formed in the crushing process, and the high water absorption rate is caused. At present, the addition of additional water to common concrete is calculated according to the saturated water absorption rate of aggregate soaked in water for 24 hours, and in consideration of the high water absorption characteristic of recycled aggregate, researchers propose that the water absorption rate of 1 hour soaked in water or 90% of the saturated water absorption rate of 24 hours should be adopted as the calculation basis of the additional water consumption.
However, the recycled aggregate has a certain water absorption process, and the water absorption process in water is different from that in cement paste. Specifically, after the recycled aggregate is added into the cement paste, a part of the mixing water is adsorbed by the cement for adjusting the fluidity of the cement paste, and the other part of the mixing water is absorbed into capillary pores by the recycled aggregate. However, in this process, the recycled aggregate surface is surrounded by the slurry, and the resistance in the transfer passage is large, resulting in a decrease in the moisture transfer rate in the aggregate; in addition, compared with the cement paste directly soaked in water, the mixing water consumption in the cement paste is relatively less, the specific surface area of the cement is larger, and the water absorption rate is obviously higher than that of the recycled aggregate.
Based on the influence of the above two factors, the water absorption rate of the recycled aggregate in the cement paste is lower than that in water. Therefore, the calculation of adopting the saturated water absorption rate of 24h or the water absorption rate of 1h as the additional water consumption is only an estimated value and cannot reflect the actual water absorption capacity of the aggregate in the cement base material, and the water absorption capacity of the aggregate in different water cement ratio and bone ash ratio systems cannot be reflected, so that the evaluation of the mechanical property and the durability of the cement base material has deviation.
Disclosure of Invention
In order to solve the problems of the prior art, the invention provides a method for measuring the water absorption of a recycled aggregate in a cement base material, which can accurately measure the water absorption of the recycled aggregate in different cement base materials such as cement mortar or concrete and in different time periods, and provides a design basis for determining the additional water consumption in the cement base material when the recycled aggregate is recycled, thereby avoiding the loss of the workability of the cement base material caused by the high water absorption of the recycled aggregate.
In order to achieve the purpose of the invention, the invention adopts the following technical scheme:
a method for measuring the water absorption of recycled aggregate in a cement base material is carried out based on a centrifugal tank, wherein the centrifugal tank comprises a slurry tank, a water-bearing cup communicated with the slurry tank and a filter layer arranged at the bottom of the slurry tank close to the water-bearing cup in a cushioning manner; the assay method comprises the steps of:
s1, respectively weighing first mixing water and first cement according to a preset water-cement ratio, and mixing to obtain first clean slurry;
s2, placing the first net slurry into the slurry tank and centrifuging, wherein the centrifugally separated water in the first net slurry enters the water-bearing cup through the filter layer, and the mass m of the centrifugally separated water is weighedw(ii) a Calculating the centrifugible water content W in the first clean slurry by adopting the formula 10：
Wherein, P0Is the mass of the first cement in the first net slurry in the slurry tank;
s3, respectively weighing second mixing water, second cement and recycled aggregate according to the water-cement ratio and the preset bone ash ratio in the step S1, firstly mixing the second cement and the second mixing water under the same condition as the first neat paste in the step S1 to obtain second neat paste, then adding the recycled aggregate into the second neat paste, continuously mixing and standing to obtain a recycled cement base material; wherein the recycled cement base material is recycled mortar or recycled concrete;
s4, placing the recycled cement base materials with different standing time t into the slurry tank, centrifuging under the same condition as the first clean slurry in the step S2, enabling the recycled cement base materials in the recycled cement base materials to centrifuge water to enter the water containing cup through the filter layer, and weighing the mass m of the centrifuged water of the recycled cement base materialsWt(ii) a Calculating the regenerated water by formula 2Water absorption W of mud base material under different standing times tt：
Wherein P is the mass of the second cement in the recycled cement base material in the slurry tank;
and G is the quality of the recycled aggregate in the recycled cement base material in the slurry tank.
Further, in step S3, the recycled aggregate is recycled fine aggregate obtained by crushing and screening the waste concrete into particles with a size of 0.16mm to 4.75 mm; the recycled cement base material is recycled mortar.
Further, in step S3, the volume ratio of the recycled aggregate to the second cement is 1:1 to 3: 1.
Further, a water reducing agent is added to the mixture of the first cement and the first mixing water or the mixture of the second cement and the second mixing water, so that the initial fluidity of the first net slurry and the recycled cement base material is larger than 160mm and is not weeping.
Further, in both of step S2 and step S4, at least two and an even number of the centrifuge tanks are employed, and a mass error between at least two and an even number of the centrifuge tanks containing the first neat paste or the reclaimed cement base is less than 0.20 g.
Or, further, in step S3, the recycled aggregate is recycled coarse aggregate obtained by crushing and screening waste concrete to a particle size of 4.75mm to 30 mm; the recycled cement base material is recycled concrete.
Further, in step S3, the volume ratio of the recycled aggregate to the second cement is 1:1 to 7: 1.
Further, adding a water reducing agent to the mixture of the first cement and the first mixing water so that the initial fluidity of the first neat paste is more than 160mm and the first neat paste does not bleed, or adding a water reducing agent to the mixture of the second cement and the second mixing water so that the initial expansion degree of the regenerated cement substrate is more than 400 mm.
Further, in both of step S2 and step S4, at least two and an even number of the centrifugal tanks are employed, and a mass error between at least two and an even number of the centrifugal tanks filled with the first net slurry or the reclaimed cement base material is less than 0.02 kg.
Preferably, the centrifugible moisture content W0And the water absorption WtThe average value is obtained by data obtained by at least two centrifugal tanks in even number.
Further, in step S4, the standing time t is calculated with the recycled aggregate added to the second neat paste as a starting point.
Preferably, the filter layer is a filter paper, a porous plate and a filter paper which are sequentially stacked.
Further preferably, the pore size of the filter paper is 50 μm.
The invention determines the centrifugal water content in the cement paste under the water-cement ratio by firstly removing the centrifugal water in the cement paste under the determined water-cement ratio, because the centrifugal water content W in the cement paste with the fixed water-cement ratio0And then obtaining the water absorption capacity of the recycled aggregate in the recycled cement base material under the water cement ratio after obtaining the recycled cement base material under the same mixing process and centrifugal process, thereby obtaining the water absorption rate by calculation. The determination method only needs to control the mixing of the clean slurry for two times under the same water cement ratio and the same mixing and centrifuging process, overcomes the influence of systematic errors brought by the water cement ratio, the mixing and centrifuging process, is not limited to a specific set value of the water cement ratio, is not limited to application in various cement base materials such as cement mortar or concrete, can also determine the water absorption rate of the recycled aggregate in the recycled cement base materials under different standing times, and has diversified and more flexible application scenes. The determination method fully considers the difference of the water absorption capacity of the recycled aggregate in water and the cement base material, provides more quantitative evaluation operation, has more accurate determination result, and can design the raw material proportion of the recycled aggregate recycled to different cement base materials such as cement mortar or concrete, especially the recycled aggregateThe determination of the additional water consumption of the material provides more accurate data support, and is beneficial to improving the adjustment and evaluation of the working performance, the mechanical property and the durability when the recycled aggregate is recycled to the cement base material.
Drawings
The above and other aspects, features and advantages of embodiments of the present invention will become more apparent from the following description taken in conjunction with the accompanying drawings, in which:
FIG. 1 is a schematic view showing the structure of a centrifuge tank in the measuring method according to the present invention;
FIG. 2 is a graphical representation of the morphological changes of the recycled cement matrix before and after mixing in the assay method according to the present invention.
Detailed Description
Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. This invention may, however, be embodied in many different forms and should not be construed as limited to the specific embodiments set forth herein. Rather, these embodiments are provided to explain the principles of the invention and its practical application to thereby enable others skilled in the art to understand the invention for various embodiments and with various modifications as are suited to the particular use contemplated. In the drawings, the shapes and sizes of elements may be exaggerated for clarity, and the same reference numerals will be used throughout to designate the same or similar elements.
It is noted that the terms first, second and the like in the description and in the claims of the present application are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It will be appreciated that the data so used may be interchanged where appropriate.
Based on the fact that the prior art is based on the water absorption rate of the recycled aggregate when being recycled, and the influence of factors such as different absorption processes in water and a cement base material, faster water absorption speed of the cement in the cement base material than the recycled aggregate and the like is not considered, so that the measurement result has a large deviation, the inventor of the invention provides a brand-new method for measuring the water absorption rate of the recycled aggregate in the cement base material. The determination method fully considers the water absorption process of the recycled aggregate in the cement base material, can deduct the background and eliminate the system error only by controlling the same mixing and centrifuging process under the fixed water cement ratio, can determine the water absorption of the recycled aggregate in the cement base material under different water cement ratios, and can also be applied to various cement base materials such as cement mortar or concrete; meanwhile, the determination method can also determine the water absorption of the recycled aggregate under different blending time, and provides theoretical basis for meeting the requirement of carrying out the working performance regulation and control of construction in different pouring time.
The above-described measurement method of the present invention will be described in detail below with reference to the accompanying drawings.
The determination method is based on the fact that the water absorption of the recycled aggregate in the recycled cement base material is obtained by centrifuging the centrifugable water in the separate cement paste and the recycled cement base material, respectively, followed by a subtraction, and thus the process is carried out in a centrifuge tank. Referring specifically to fig. 1, the centrifuge tank includes a slurry tank 11, a water receiving cup 12 communicating with the slurry tank, and a filter layer 13 padded at the bottom of the slurry tank 11 near the water receiving cup 12.
More specifically, the slurry tank 11 is used to house a separate cement paste or recycled cement base material in the assay process and to perform a centrifugal operation; the water-bearing cup 12 is used for bearing separate cement paste or centrifuged water which is thrown out by centrifuging the regenerated cement base material. The bottom of the slurry tank 11 has a water outlet 111 through which the water-holding cup 12 communicates into the slurry tank 11, and through which the centrifuged water is "thrown" into the water-holding cup 12 through the water outlet 111. In the centrifugal separation process of the single cement paste or the regenerated cement base material, in order to prevent other components in a centrifugal system from being separated by centrifugation, a filter layer 13 is padded at the bottom of the paste tank 11, and the filter layer 13 is about to block the water outlet 111.
Preferably, the filter layer 13 includes filter paper, a porous plate and filter paper, which are sequentially stacked, and the filter paper preferably has a pore size of 50 μm to ensure that centrifuged water freely permeates through the water outlet 111 into the water receiving cup 12.
Firstly, the quality of the water-bearing cup 12 is respectively weighedAmount is m0And the mass of the centrifuge tank is m1。
Then, according to the preset water-cement ratio CW/CAnd respectively weighing mixing water and cement, and mixing to obtain the clean slurry.
In order to distinguish the mixing water, cement, and the resulting neat paste used in the below-described process for producing a recycled cement base material, the three in this step are referred to as a first mixing water, a first cement, and a first neat paste, respectively. Generally, the first slurry is mixed in a slurry mixer, and the mixture is slowly mixed until the mixture is uniform.
And thirdly, placing the obtained first clean slurry in a centrifugal tank and centrifuging.
Preferably, in order to keep the stability and error of the data controllable, at least two and even number of centrifuge cans with equal distribution used in the same centrifuge can be used to operate simultaneously, and finally the data can be averaged. Thus, the first clean slurry is poured into a plurality of centrifugal tanks equally and uniformly until the volume is about 2/3 of the slurry tank 11; meanwhile, the mass errors of a plurality of centrifugal tanks filled with the first clean slurry are not more than 0.20g when the regenerated mortar is prepared, and the mass error of the regenerated concrete is not more than 0.02kg due to scale-up control.
Weighing the centrifuge tank filled with the first clean slurry to obtain a mass m2Mass m of the first net slurry in each centrifuge tankPComprises the following steps:
mP＝m2-m1
during the centrifugation, the centrifuged water in the first purified pulp enters the water-bearing cup 12 through the filter layer 13, and the mass m of the centrifuged water is weighed and calculatedw. Specifically, after the centrifugation is finished, the mass of the water receiving cup 12 at that time is weighed to be m3(ii) a Meanwhile, the mass m of partial centrifugal water absorbed by the two pieces of filter paper due to the centrifugal water of the filter pulp is calculated4Obtaining the mass m of the centrifugal water of the clean pulpWComprises the following steps:
mW＝m3-m0+m4
calculating the centrifugible water content W in the first clean slurry using the following formula 10：
Wherein, P0Is the mass of the net slurry cement in the net slurry of cement in the slurry tank 11, i.e.
Fourthly, respectively weighing m mass according to the water-cement ratio of the first clean slurry and a preset bone ash ratioWThe mixing water has a mass of mCCement of mass mGThe recycled aggregate of (1).
In this step, in order to distinguish the above-described corresponding substances, the second mixing water and the second cement are referred to, respectively, and the obtained neat paste is referred to as a second neat paste.
And firstly, mixing second cement and second mixing water to obtain second clear paste, then adding the recycled aggregate into the second clear paste, continuously mixing and standing to obtain the recycled cement base material.
The recycled cement substrate may be recycled mortar or recycled concrete.
The recycled aggregate can be recycled fine aggregate with the grain diameter of 0.16-4.75 mm after crushing and screening waste concrete, and the recycled cement base material obtained by the method is recycled mortar; or crushing and screening the waste concrete to obtain recycled coarse aggregate with the grain diameter of 4.75-30 mm, wherein the obtained recycled cement base material is recycled concrete.
Wherein the bone ash ratio is the volume ratio of the recycled aggregate to the second cement. When the recycled aggregate is recycled fine aggregate, the bone ash ratio is generally controlled to be 1: 1-3: 1, and when the recycled aggregate is recycled coarse aggregate, the bone ash ratio is controlled to be 1: 1-7: 1.
Typically, the blending of the reclaimed cement substrate is performed in a blender. It should be noted that, in order to avoid systematic errors caused by different mixing processes, the mixing conditions are maintained in the same manner as the first neat paste during the mixing stage of the second neat paste. And then, adding the recycled aggregate, continuously mixing until the mixture is uniform, and standing according to different time requirements.
Here, the standing time t is calculated from the time when the recycled aggregate is added to the second neat paste. If the water absorption at different standing times t needs to be measured, the mixer can be treated with a moisture retention measure to prevent the water in the recycled cement base material from evaporating during the standing process.
Figure 2 is a simplified depiction of the change in conditions encountered by cement and recycled aggregate in a recycled cement matrix under mixing water. When the recycled aggregate c is added into the clean slurry containing the mixing water a and the cement b, a part of the mixing water a is absorbed by the recycled aggregate c, and the rest unabsorbed water is the recycled cement substrate centrifugal water.
And finally, placing the regenerated cement base materials obtained after different standing times t into a centrifugal tank and centrifuging.
The filling rule of the recycled cement base material at this time is in accordance with that of the aforementioned individual cement paste. After filling, the mass of the centrifuge bowl containing the recycled cement substrate is weighed to m5Mass m of the recycled cement matrix in the centrifuge tankAComprises the following steps:
mA＝m5-m1
in the process of centrifugation, the centrifuged water of the regenerated cement base material in the regenerated cement base material enters the water bearing cup 12 through the filter layer 13, and the mass m of the centrifuged water of the regenerated cement base material is weighed and calculatedWt. Specifically, after the centrifugation is finished, the mass of the water receiving cup 12 at that time is weighed to be m6(ii) a Meanwhile, the mass m of partial centrifuged water of the regenerated cement base material absorbed by the two pieces of filter paper due to the filtered centrifuged water of the regenerated cement base material is calculated7Obtaining the mass m of the centrifugal water of the recycled cement base materialWtComprises the following steps:
mWt＝m6-m0+m7
calculating the water absorption W of the recycled aggregate in the recycled cement base material at different standing times t by adopting the following formula 2t：
Where P is the mass of the second cement in the recycled cement matrix in the slurry tank 11, i.e. P is the mass of the second cement in the recycled cement matrix
G is the mass of recycled aggregate in the recycled cement matrix in the slurry tank 11, i.e.
It is worth noting that the same centrifugation conditions of the recycled cement matrix as the cement paste alone are also maintained in order to avoid systematic errors due to different centrifugation processes. The centrifugation is preferably carried out in a high-speed refrigerated centrifuge.
In the centrifugal operation, the rotation speed is related to the centrifugal radius of the rotor and the maximum radius of the capillary pores of the recycled aggregate, and the centrifugal rotation speed is generally calculated by the following formula 3 under the condition that the recycled aggregate is kept in a saturated surface dry state, and the determination method of the invention is not particularly limited, and can be selected according to specific equipment parameters:
where ω represents the angular velocity (ω 2 π n, n is the centrifuge rate in rpm), ρ represents the water density in the well, and 1000kg/m is taken3(ii) a Gamma is the surface tension and takes the value of 72.75mN/m at 20 ℃, R represents the centrifuge radius (i.e. the distance from the centre of the centrifuge, i.e. the centre of the combination of a plurality of centrifuge cans, to the can filling). When preparing recycled concrete, it is generally sufficient to control the volume of the centrifugal tank to be at least 10 times larger than the maximum size of the recycled coarse aggregate, and it is not particularly limited herein, and it is sufficient for those skilled in the art to determine the volume according to the general selection rules in the prior art.
In the above-described measuring method, in order to ensure the operability of the measurement, it is generally necessary to ensure good fluidity of cement paste alone, as well as recycled mortar obtained by adding recycled fine aggregate, or recycled concrete obtained by adding recycled coarse aggregate. The initial fluidity of the individual cement paste and the recycled mortar is preferably regulated to be more than 160 mm; if the fluidity is not satisfied due to the water-cement ratio, a water reducing agent can be added into the cement paste or the reclaimed mortar alone to ensure the fluidity of more than 160mm and a non-bleeding state. And similarly, controlling the initial expansion degree of the recycled concrete to be more than 400 mm.
It should be noted that, when the recycled aggregate is recycled to the cement base material, the recycled aggregate is generally substituted for the natural aggregate in equal proportion in practical application, that is, in the obtained recycled cement base material, the aggregate composition may be only the recycled aggregate or the mixed aggregate of the recycled aggregate and the natural aggregate. The water absorption of the common natural coarse aggregate is less than 1 percent, and can be ignored in engineering, while the water absorption of the natural fine aggregate is more than 2 percent, which influences the working performance of the recycled cement base material to a certain extent. Therefore, if the recycled cement base material is prepared using the mixed aggregate, it is necessary to calculate the water absorption rate of the recycled aggregate in the recycled cement base material in the mass ratio of the natural aggregate to the recycled aggregate. I.e. several parameters in each formula in the measurement method of the present invention need to be adapted.
Specifically, if a recycled cement base material is prepared using a mixed aggregate of natural aggregate and recycled aggregate, the above-mentioned bone ash ratio is obtained as the total amount of the mixed aggregate, wherein the mass m is obtained by subtracting the amount of the natural aggregate usedGThe recycled aggregate of (4); meanwhile, the mass G of the recycled aggregate in the slurry tank 11 in equation 2 should be calculated by deducting the mass of the natural aggregate again. Further, if the recycled mortar is prepared by adopting the mixed fine aggregate of the natural fine aggregate and the recycled fine aggregate, the blending water amount absorbed by the natural fine aggregate is supplemented to the molecule part in the formula 2 so as to obtain the blending water amount absorbed by the natural fine aggregate independently; and finally, after the additional water consumption corresponding to the recycled fine aggregate is obtained through calculation, the additional water consumption required by the natural fine aggregate is added, and the sum of the two additional water consumption is the additional water consumption required in the preparation of the recycled mortar.
The above-described measurement method of the present invention will be described below by way of specific examples. In the following examples 1 to 4, in consideration of the experimental scale and site restrictions, the recycled aggregate was obtained by crushing, screening and washing a laboratory concrete sample after strength testing, the concrete strength grade was C30, and the aggregate particle size ranged from 0.60mm to 4.75mm, i.e., recycled mortar was prepared using recycled fine aggregate in the following examples. The fluidity of the prepared recycled cement base material is adjusted by adopting a polycarboxylic acid type high-performance water reducing agent, the solid content is 20%, and the water reducing rate is 15%.
In each of examples 1 to 4 described below, parallel measurement was performed using two centrifuge tanks, and when the recycled cement base material was measured, the total volume of the recycled cement base material mixed was kept at 1L, and the standing time t of the recycled cement base material was set to 1min, 5min, 10min, 30min, and 60min, respectively.
Further, the following examples 1 to 4 were carried out by using a centrifuge having a slurry tank inner diameter of 5cm and a centrifugal radius of 8.10cm, and calculating to obtain a kneading rotation speed of 4000r/min and a centrifugal time of about 2 min.
Table 1 below shows the mixing ratio of each of the recycled cement base materials in examples 1 to 4 below.
TABLE 1 blending ratio of the reclaimed cement base materials in examples 1 to 4
kg/m3
Table 2 shows the water absorption rates of the recycled aggregates in examples 1 to 4 in different recycled cement base materials and different standing times.
Meanwhile, in order to embody the present invention, when the measuring method is applied to a cement base material in which the recycled aggregate has different water absorption courses in the cement base material and in water, an experiment of water absorption rate of the recycled aggregate in water at the same standing time as described above was also performed as a comparative example.
In this comparative example, the recycled aggregate was immersed in pure water at normal temperature for various times (i.e., various standing times), and the water absorption thereof was measured. The water absorption results in the comparative example are also shown in table 2.
Table 2 water absorption rates of the recycled aggregate in examples 1 to 4 in different recycled cement base materials and the recycled aggregate in comparative example in water at different standing times
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As can be seen from table 2, when the recycled aggregate was placed in pure water, the water absorption rate was higher than that of the cement base material in examples 1 to 4 of the present invention at the same standing time, which also confirmed that the difference in the water absorption process by these two environments was significant. Obviously, the recycled aggregate is generally inaccurate by taking the water absorption measured by soaking the recycled aggregate in water for 1 hour or 90% of the saturated water absorption measured for 24 hours as the basis for calculating the additional water consumption in the prior art; when the high water absorption rate obtained by soaking in pure water is actually applied, the water-cement ratio of the regenerated cement base material system is larger than a preset value due to the fact that the use of additional water consumption is obviously increased, and therefore the adjustment and evaluation of the working performance, the mechanical performance and the durability of the obtained regenerated cement base material are affected.
In order to evaluate the accuracy of the above-described measuring method of the present invention, the following method was used to measure the system-centrifuged water on the cement base material, and it was found that the measured data of the centrifuged water by the above-described measuring method of the present invention was reliable, and the result of the water absorption rate obtained by the calculation was also reliable.
The following test methods mature in the field are adopted to verify the reliability and accuracy of the determination method provided by the invention, and the specific operation is as follows: placing the mixed recycled cement base material on a square-hole sieve, and slightly pressing with force to enable cement paste in the recycled cement base material to pass through the square-hole sieve, and enable recycled aggregate to be retained on the sieve; and placing the screened cement paste in a high-temperature furnace at 1050 ℃ to be dried to constant weight, wherein the mass difference of the cement paste before and after high-temperature treatment is the water content of the cement paste, and the water content comprises the free water content and the combined water content of hydration products. Therefore, the difference is made between the total amount of the weighed mixing water and the moisture content in the cement paste, the using amount of partial mixing water absorbed by the recycled aggregate is obtained, and then the water absorption of the recycled aggregate in the recycled cement base material is calculated.
Table 3 below calculates the water absorption calculated from the centrifugable water content at different standing times t of the recycled aggregates of the above examples and comparative examples according to the above conventional measuring method, and the error between the water absorption obtained according to the measuring method of the present invention in table 2 above.
Table 3 error in the back-reckoned water absorption of the centrifugalizable water content of the recycled aggregate in different recycled cement base materials in examples 1 to 4 and the recycled aggregate in the comparative example in water at different standing times
As can be seen from Table 3, the water absorption data obtained by the method provided by the invention has a deviation within + -1%, which indicates that the method is accurate and reliable.
The above-described measuring method of the present invention is performed based on dried recycled aggregate, however, the recycled aggregate may have a certain initial water content, and therefore, when the above-described measuring method is applied to a recycled cement base material to calculate an additional water amount required for the recycled aggregate, the initial water content value should be subtracted.
While the invention has been shown and described with reference to certain embodiments, those skilled in the art will understand that: various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims and their equivalents.
Claims (10)
1. A method for measuring the water absorption of recycled aggregate in a cement base material is carried out based on a centrifugal tank, wherein the centrifugal tank comprises a slurry tank, a water-bearing cup communicated with the slurry tank and a filter layer arranged at the bottom of the slurry tank close to the water-bearing cup in a cushioning manner; characterized in that the determination method comprises the steps of:
s1, respectively weighing first mixing water and first cement according to a preset water-cement ratio, and mixing to obtain first clean slurry;
s2, placing the first net slurry into the slurry tank and centrifuging, wherein the centrifugally separated water in the first net slurry enters the water-bearing cup through the filter layer, and the mass m of the centrifugally separated water is weighedw(ii) a Calculating the centrifugible water content W in the first clean slurry by adopting the formula 10：
Wherein, P0Is the mass of the first cement in the first net slurry in the slurry tank;
s3, respectively weighing second mixing water, second cement and recycled aggregate according to the water-cement ratio and the preset bone ash ratio in the step S1, firstly mixing the second cement and the second mixing water under the same condition as the first neat paste in the step S1 to obtain second neat paste, then adding the recycled aggregate into the second neat paste, continuously mixing and standing to obtain a recycled cement base material; wherein the recycled cement base material is recycled mortar or recycled concrete;
s4, placing the recycled cement base materials with different standing time t into the slurry tank, centrifuging under the same condition as the first clean slurry in the step S2, enabling the recycled cement base materials in the recycled cement base materials to centrifuge water to enter the water containing cup through the filter layer, and weighing the mass m of the centrifuged water of the recycled cement base materialsWt(ii) a Calculating the water absorption W of the recycled cement base material under different standing times t by adopting a formula 2t：
Wherein P is the mass of the second cement in the recycled cement base material in the slurry tank;
and G is the quality of the recycled aggregate in the recycled cement base material in the slurry tank.
2. The measuring method according to claim 1, wherein in step S3, the recycled aggregate is recycled fine aggregate obtained by crushing and screening waste concrete to a particle size of 0.16mm to 4.75 mm; the recycled cement base material is recycled mortar.
3. The method according to claim 2, wherein in step S3, the volume ratio of the recycled aggregate to the second cement is 1:1 to 3: 1.
4. The method of claim 2 wherein a water reducing agent is added to the mixture of the first cement and the first blending water or the mixture of the second cement and the second blending water to provide an initial fluidity of the first neat paste and the reclaimed cement base of greater than 160mm and no bleeding.
5. The assay method according to any one of claims 1 to 4, wherein in each of step S2 and step S4, at least two and an even number of the centrifuge tanks are used, and the mass error between at least two and an even number of the centrifuge tanks containing the first neat paste or the reclaimed cement-based material is less than 0.20 g.
6. The measuring method according to claim 1, wherein in step S3, the recycled aggregate is recycled coarse aggregate obtained by crushing and screening waste concrete to a particle size of 4.75mm to 30 mm; the recycled cement base material is recycled concrete.
7. The method of claim 6, wherein in step S3, the volume ratio of the recycled aggregate to the second cement is 1:1 to 7: 1.
8. The assay of claim 6 wherein a water reducing agent is added to the mixture of the first cement and the first mix water to provide an initial fluidity of the first neat paste of greater than 160mm without bleeding, or to the mixture of the second cement and the second mix water to provide an initial spread of the reclaimed cement matrix of greater than 400 mm.
9. The method according to any one of claims 1 and 6 to 8, wherein at least two and an even number of the centrifugal tanks are used in each of the steps S2 and S4, and a mass error between at least two and an even number of the centrifugal tanks containing the first neat paste or the recycled cement base material is less than 0.02 kg.
10. The measuring method according to claim 1, wherein in step S4, a standing time t is calculated from the time when the recycled aggregate is added to the second neat paste.
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