CN114577657B - Method for measuring water absorption rate of recycled aggregate in cement base material - Google Patents
Method for measuring water absorption rate of recycled aggregate in cement base material Download PDFInfo
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- 239000004568 cement Substances 0.000 title claims abstract description 195
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 title claims abstract description 192
- 239000000463 material Substances 0.000 title claims abstract description 106
- 238000010521 absorption reaction Methods 0.000 title claims abstract description 62
- 238000000034 method Methods 0.000 title claims abstract description 42
- 239000002002 slurry Substances 0.000 claims abstract description 61
- 238000002156 mixing Methods 0.000 claims abstract description 42
- 239000004567 concrete Substances 0.000 claims description 25
- 239000000203 mixture Substances 0.000 claims description 21
- 238000000691 measurement method Methods 0.000 claims description 16
- 239000004570 mortar (masonry) Substances 0.000 claims description 14
- 239000002699 waste material Substances 0.000 claims description 11
- 238000005303 weighing Methods 0.000 claims description 10
- 239000003638 chemical reducing agent Substances 0.000 claims description 8
- 239000002245 particle Substances 0.000 claims description 7
- 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 7
- 230000000740 bleeding effect Effects 0.000 claims description 4
- 238000012216 screening Methods 0.000 claims description 4
- 239000000758 substrate Substances 0.000 claims description 4
- 238000007873 sieving Methods 0.000 claims 1
- 230000008569 process Effects 0.000 abstract description 11
- 230000009897 systematic effect Effects 0.000 abstract description 5
- 238000011156 evaluation Methods 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
- 230000000052 comparative effect Effects 0.000 description 6
- 238000010276 construction Methods 0.000 description 6
- 239000011083 cement mortar Substances 0.000 description 5
- 238000005259 measurement Methods 0.000 description 5
- 229920006395 saturated elastomer Polymers 0.000 description 5
- 241000190070 Sarracenia purpurea Species 0.000 description 4
- 239000011159 matrix material Substances 0.000 description 4
- 238000011049 filling Methods 0.000 description 3
- 239000011148 porous material Substances 0.000 description 3
- 238000003556 assay Methods 0.000 description 2
- 230000005540 biological transmission Effects 0.000 description 2
- 238000013461 design Methods 0.000 description 2
- 238000011161 development Methods 0.000 description 2
- 238000002360 preparation method Methods 0.000 description 2
- 238000004064 recycling Methods 0.000 description 2
- 238000012360 testing method Methods 0.000 description 2
- 238000012935 Averaging Methods 0.000 description 1
- 239000002253 acid Substances 0.000 description 1
- 230000000903 blocking effect Effects 0.000 description 1
- 239000002639 bone cement Substances 0.000 description 1
- 230000008859 change Effects 0.000 description 1
- 238000004891 communication Methods 0.000 description 1
- 230000001276 controlling effect Effects 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 238000001704 evaporation Methods 0.000 description 1
- 230000008020 evaporation Effects 0.000 description 1
- 238000002474 experimental method Methods 0.000 description 1
- 238000001914 filtration Methods 0.000 description 1
- 230000036571 hydration Effects 0.000 description 1
- 238000006703 hydration reaction Methods 0.000 description 1
- 230000008595 infiltration Effects 0.000 description 1
- 238000001764 infiltration Methods 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 230000003020 moisturizing effect Effects 0.000 description 1
- 230000004660 morphological change Effects 0.000 description 1
- 238000003825 pressing Methods 0.000 description 1
- 238000012545 processing Methods 0.000 description 1
- 239000002994 raw material Substances 0.000 description 1
- 230000001105 regulatory effect Effects 0.000 description 1
- 238000000926 separation method Methods 0.000 description 1
- 238000002791 soaking Methods 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
- 238000003756 stirring Methods 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 238000010998 test method Methods 0.000 description 1
- 238000005406 washing Methods 0.000 description 1
Classifications
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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
-
- 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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- Physics & Mathematics (AREA)
- Health & Medical Sciences (AREA)
- Life Sciences & Earth Sciences (AREA)
- Chemical & Material Sciences (AREA)
- Analytical Chemistry (AREA)
- Biochemistry (AREA)
- General Health & Medical Sciences (AREA)
- General Physics & Mathematics (AREA)
- Immunology (AREA)
- Pathology (AREA)
- Preparation Of Clay, And Manufacture Of Mixtures Containing Clay Or Cement (AREA)
Abstract
The invention belongs to the technical field of building material detection, and particularly discloses a method for measuring water absorption rate of recycled aggregate in a cement base material. The method comprises the steps of firstly measuring the centrifugally water content in the clean slurry under a preset water-cement ratio, then measuring the centrifugally water content of the recycled cement base material containing the recycled aggregate under the same water-cement ratio, and subtracting the background when the clean slurry is alone, so that the water absorption rate of the recycled aggregate in the cement base material can be calculated and obtained. The determination method only needs to control the mixing of the purified pulp for two times under the same water-cement ratio and the same mixing and centrifuging process, overcomes the influence of systematic errors, is not limited to a 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 in the cement base material, provides more quantitative evaluation operation, and is beneficial to improving the adjustment and evaluation of the working performance, mechanical property and durability of the recycled aggregate 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 rate of recycled aggregate in a cement base material.
Background
With the rapid development of the economy in China, large-scale construction of infrastructure and major engineering is being developed, and the recycling technology of the construction waste resources in China is still in an exploration stage. The urban construction waste is reasonably and effectively utilized to prepare the regenerated material, and the method has important significance for keeping economic, sustainable and healthy development in China.
After the construction waste is separated, the waste concrete is used for processing the construction waste into recycled aggregate, a large amount of hardened cement mortar is adhered to the surface of the recycled aggregate, microcracks are easy to form in the crushing process, so that the recycled aggregate has high water absorption rate, and additional water is required to be added when the concrete is prepared so as to meet the requirement of working performance. At present, the addition of the additional water of the common concrete is calculated according to the saturated water absorption rate of the aggregate soaked in water for 24 hours, and in consideration of the high water absorption characteristic of the recycled aggregate, a learner proposes that the water absorption rate soaked in water for 1 hour or 90% of the saturated water absorption rate soaked in water for 24 hours is adopted as the calculation basis of the additional water consumption.
However, since recycled aggregate has a certain water absorption course, and the water absorption course in water is different from that in cement slurry. Specifically, when recycled aggregate is added to the cement slurry, a part of the mixing water is adsorbed by the cement for adjusting the fluidity of the cement slurry, and the other part is absorbed into the capillary holes by the recycled aggregate. However, in the process, the surface of the recycled aggregate is surrounded by slurry, so that the resistance in the transmission channel is high, and the transmission rate of moisture in the aggregate is reduced; in addition, compared with the cement slurry which is directly soaked in water, the cement slurry has relatively less mixing water consumption, the specific surface area of the cement is larger, and the water absorption rate is obviously faster than that of the recycled aggregate.
Based on the influence of the two factors, the water absorption rate of the recycled aggregate in the cement slurry is lower than that in water. Therefore, the calculation of adopting the 24h saturated water absorption rate or the 1h water absorption rate as the additional water consumption is only a predicted value, the actual water absorption capacity of the aggregate in the cement base material cannot be reflected, and the water absorption capacity of the aggregate in different water cement ratios and bone cement ratio systems cannot be reflected, so that the evaluation of the mechanical property and the durability of the cement base material is deviated.
Disclosure of Invention
In order to solve the problems in the prior art, the invention provides a method for measuring the water absorption rate of recycled aggregate in cement base materials, which can accurately test the water absorption rate of the recycled aggregate in different cement base materials such as cement mortar or concrete and in different time periods, and provides design basis for determining the additional water consumption in the cement base materials when the recycled aggregate is recycled, thereby avoiding the working loss of the cement base materials caused by the high water absorption rate of the recycled aggregate.
In order to achieve the aim of the invention, the invention adopts the following technical scheme:
The method for measuring the water absorption rate of the recycled aggregate in the cement base material is 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 measuring method comprises the following steps:
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 purified pulp into the pulp tank and centrifuging, wherein the centrifuged water in the first purified pulp enters the water bearing cup through the filter layer, and the mass m w of the centrifuged water in the purified pulp is weighed; calculating the centrifugable moisture content W 0 in the first net slurry using formula 1:
Wherein P 0 is 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 in the step S1 and the preset bone ash ratio, firstly mixing the second cement and the second mixing water under the same condition as the first clean pulp in the step S1 to obtain second clean pulp, then adding the recycled aggregate into the second clean pulp, continuing 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 regenerated cement base materials under different standing time t in the slurry tank, centrifuging under the same condition as the first clean slurry in the step S2, enabling the centrifugally-produced water of the regenerated cement base materials in the regenerated cement base materials to enter the water bearing cup through the filter layer, and weighing the centrifugally-produced water of the regenerated cement base materials to obtain the mass m Wt; the water absorption W t of the recycled cement base material at different rest times t was calculated using 2:
Wherein P is the mass of the second cement in the recycled cement base material in the slurry tank;
G is the quality of the recycled aggregate in the recycled cement base material in the slurry tank.
Further, in the step S3, the recycled aggregate is recycled fine aggregate of which the particle size is 0.16-4.75 mm after the waste concrete is crushed and screened; 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 mix water or to the mixture of the second cement and the second mix water so that the initial fluidity of the first net slurry and the recycled cement base material is greater than 160mm and no bleeding occurs.
Further, in both step S2 and step S4, at least two and even number of the centrifugal tanks are employed, and a mass error between at least two and even number of the centrifugal tanks filled with the first paste or the recycled cement base material is less than 0.20g.
Or further, in the step S3, the recycled aggregate is recycled coarse aggregate of which the particle size is 4.75-30 mm after the waste concrete is crushed and screened; 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, a water reducing agent is added to the mixture of the first cement and the first mix water so that the initial fluidity of the first net slurry is greater than 160mm and no bleeding occurs, or a water reducing agent is added to the mixture of the second cement and the second mix water so that the initial expansion of the recycled cement base material is greater than 400mm.
Further, in both step S2 and step S4, at least two and even number of the centrifugal tanks are employed, and a mass error between at least two and even number of the centrifugal tanks filled with the first paste or the recycled cement base material is less than 0.02kg.
Preferably, said centrifugable moisture content W 0 and said water absorption W t are each found by averaging data obtained from at least two and even number of said centrifuge tanks.
Further, in step S4, a standing time t is calculated with the recycled aggregate added to the second net slurry as a starting point.
Preferably, the filter layer is filter paper, a porous plate and filter paper which are sequentially stacked.
Further preferably, the pore size of the filter paper is 50 μm.
The invention firstly removes the centrifugally-controllable water in the cement paste with the determined water-cement ratio, and determines the content of centrifugally-controllable water in the cement paste with the determined water-cement ratio, and the water absorption of the recycled aggregate with the water-cement ratio in the recycled cement base material can be obtained after the recycled cement base material is obtained under the same mixing process and centrifugal process because the content W 0 of centrifugally-controllable water in the cement paste with the fixed water-cement ratio is fixed, thereby calculating and obtaining the water absorption rate. 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, and overcomes the influence of systematic errors caused by the water-cement ratio and the mixing and centrifuging process, so that the determination method is not limited to a specific set value of the water-cement ratio, is also not limited to application in various cement base materials such as cement mortar or concrete, and can also determine the water absorption rate of the recycled aggregate in the recycled cement base materials under different standing time, and the application scene is diversified and more flexible. The determination method fully considers the difference of the water absorption capacity of the recycled aggregate in water and in the cement base material, provides more quantitative evaluation operation, has more accurate determination results, can design the raw material proportion when the recycled aggregate is recycled to different cement base materials such as cement mortar or concrete, and particularly provides more accurate data support for determining the additional water consumption of the recycled aggregate, and is beneficial to improving the adjustment and evaluation of the working performance, mechanical performance and durability of the recycled aggregate 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 when taken in conjunction with the accompanying drawings in which:
FIG. 1 is a schematic diagram of the structure of a centrifuge bowl in an assay method according to the invention;
FIG. 2 is a schematic representation of the morphological changes of a recycled cement substrate before and after blending in an assay method according to the 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 so that others skilled in the art will be able to understand the invention for various embodiments and with various modifications as are suited to the particular use contemplated. In the drawings, the shape and size of elements may be exaggerated for clarity, and the same reference numerals will be used throughout to designate the same or similar elements.
It should be noted that the terms "first," "second," and the like in the description and in the claims are used for distinguishing between similar objects 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 method for measuring the water absorption rate of recycled aggregate in recycling is based on the water absorption rate immersed in pure water in the prior art, the method for measuring the water absorption rate of the recycled aggregate in the cement base material is not considered to be influenced by factors such as different absorption processes in water and in the cement base material, and the water absorption rate of cement in the cement base material is faster than that of the recycled aggregate, so that the problem of larger deviation of measurement results is caused. 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 systematic error only by controlling the same mixing and centrifuging process under the condition of fixed water-cement ratio, not only can determine the water absorption rate of the recycled aggregate in the cement base material under different water-cement ratios, but also can be applied to various cement base materials such as cement mortar or concrete; meanwhile, the determination method can also determine the water absorption rate of the recycled aggregate at different mixing time, and provides a theoretical basis for the adjustment and control of the working performance of construction at 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 method is based on a centrifuge tank, in which the water absorption of recycled aggregate in the recycled cement base material is obtained by separately centrifuging the centrifuged water in the separated cement paste and the recycled cement base material, followed by a differential. Referring specifically to fig. 1, the centrifuge bowl includes a slurry bowl 11, a water receiving cup 12 in communication with the slurry bowl, and a filter layer 13 that is padded to the bottom of the slurry bowl 11 near the water receiving cup 12.
More specifically, the slurry tank 11 is used to house the individual cement paste or recycled cement base materials during the measurement and is subjected to centrifugation; and the water receiving cup 12 is used for receiving the separate cement paste or recycled cement base material and separating the centrifuged water which is thrown away by centrifugal operation. The bottom of the slurry tank 11 is provided with a water outlet 111, the water receiving cup 12 is communicated into the slurry tank 11 through the water outlet 111, and the centrifugally-arranged water is 'thrown' into the water receiving cup 12 through the water outlet 111. In the course of centrifugal separation of individual cement paste or recycled cement base material, in order to prevent other components in the centrifugal system from being separated together, a filter layer 13 is arranged at the bottom of the paste tank 11, and the filter layer 13 is used for blocking the water outlet 111.
Preferably, the filter layer 13 comprises a filter paper, a porous plate and a filter paper, which are arranged in sequence, the filter paper preferably having a pore size of 50 μm, to ensure free infiltration of centrifuged water into the basin 12 via the outlet 111.
First, the mass of the water receiving cup 12 was m 0 and the mass of the centrifuge bowl was m 1, respectively.
And then, respectively weighing mixing water and cement according to a preset water-cement ratio C W/C, and mixing to obtain the clean slurry.
In order to distinguish between the mix water, cement, and the resultant clean slurry used in the preparation of the recycled cement base material described below, the three in this step are designated as first mix water, first cement, and first clean slurry, respectively. Generally, the first paste is stirred in a paste mixer, and the first paste is stirred slowly until the first paste is uniform.
Third, the first net slurry obtained is placed in a centrifuge tank and centrifuged.
Preferably, in order to keep the stability and error of the data controllable, at least two and even number of centrifugal tanks which are uniformly distributed in the same centrifugal machine can be adopted to operate simultaneously, and finally the data can be averaged. Thus, the first net slurry is equally and uniformly poured into a plurality of centrifugal tanks until the volume is about 2/3 of the volume of the slurry tank 11; meanwhile, the quality error of a plurality of centrifugal tanks filled with the first clean mortar is ensured not to exceed 0.20g when the regenerated mortar is prepared, and the mass error is controlled not to exceed 0.02kg when the regenerated concrete is prepared.
The mass of the centrifugal tanks filled with the first net pulp is weighed to be m 2, and then the mass m P of the first net pulp in each centrifugal tank is as follows:
mP＝m2-m1
During centrifugation, the net pulp centrifuged water in the first net pulp enters the water receiving cup 12 via the filter layer 13, and the mass m w of the net pulp centrifuged water is weighed and calculated. Specifically, after centrifugation is completed, weighing the water cup 12, wherein the mass of the water cup is m 3; meanwhile, calculating the mass m 4 of part of the water which is absorbed by the two pieces of filter paper due to the filtering of the water which can be centrifuged by the water, and obtaining the mass m W of the water which can be centrifuged by the filter paper, wherein the mass m W is:
mW＝m3-m0+m4
The centrifuged water content W 0 in the first net slurry was calculated using the following formula 1:
wherein P 0 is the mass of the net slurry cement in the slurry tank 11, i.e
And fourthly, respectively weighing mixing water with the mass of m W, cement with the mass of m C and recycled aggregate with the mass of m G according to the water-cement ratio of the first paste and the preset bone ash ratio.
In this step, in order to distinguish the above-mentioned corresponding substances, they are respectively denoted as second mix water, second cement, and the resultant net slurry is denoted as second net slurry.
Firstly, mixing the second cement and the second mixing water to obtain second clean slurry, then adding recycled aggregate into the second clean slurry, continuing mixing and standing to obtain the recycled cement base material.
The recycled cement base material may be recycled mortar or recycled concrete.
The recycled aggregate can be recycled fine aggregate of waste concrete with the particle size of 0.16-4.75 mm after crushing and screening, 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 particle size of 4.75-30 mm, and obtaining the recycled cement base material, namely the 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.
In general, the blending of the recycled cementitious substrate is performed in a blender. It should be noted that, in order to avoid systematic errors caused by different mixing processes, first, in the mixing stage of the second paste, the same mixing conditions as those of the first paste are maintained. And then adding the recycled aggregate, continuing to stir until uniform, and standing according to different time requirements.
The rest time t is calculated here starting from the time when recycled aggregate is added to the second paste. If it is desired to determine the water absorption at different rest times t, the mixer may be treated with a moisturizing measure to prevent evaporation of the water in the recycled cement matrix during the rest.
Fig. 2 depicts briefly the change in state of cement and recycled aggregate encountering mixing water in a recycled cement matrix. After adding recycled aggregate c to the clear slurry containing mix water a and cement b, a portion of mix water a is absorbed by cement b, a portion is absorbed by recycled aggregate c, and the remainder is unabsorbed, i.e., recycled cement base material centrifugally water.
And finally, placing the regenerated cement base material obtained after different standing times t in a centrifugal tank and centrifuging.
The filling rules of the recycled cement base material are consistent with the independent cement paste. After filling, the mass of the centrifugal tank filled with the recycled cement base material is weighed to be m 5, and then the mass m A of the recycled cement base material in the centrifugal tank is as follows:
mA＝m5-m1
During centrifugation, the centrifuged water of the recycled cement base material in the recycled cement base material enters the water receiving cup 12 through the filter layer 13, and the mass m Wt of the centrifuged water of the recycled cement base material is weighed and calculated. Specifically, after centrifugation is completed, weighing the water cup 12, wherein the mass of the water cup is m 6; meanwhile, the mass of the centrifugally-usable water of the part of the regenerated cement base material absorbed by the two pieces of filter paper due to the centrifugally-usable water of the filtered regenerated cement base material is calculated as m 7, and the mass m Wt of the centrifugally-usable water of the regenerated cement base material is obtained as follows:
mWt＝m6-m0+m7
the water absorption W t of the recycled aggregate in the recycled cement base material at different rest times t was calculated using the following formula 2:
Wherein P is the mass of the second cement in the recycled cement matrix in the slurry tank 11, i.e G is the mass of recycled aggregate in the recycled cement matrix in slurry tank 11, i.e./>
It is worth noting that in order to avoid systematic errors from different centrifugation processes, the same centrifugation conditions of the recycled cement base material as the cement paste alone are also maintained. The centrifugation is preferably performed in a high-speed refrigerated centrifuge.
In the case of performing the centrifugal operation, the rotational speed is related to the centrifugal radius of the rotor and the maximum radius of the capillary of the recycled aggregate, and the centrifugal rotational speed is generally obtained by calculating the following formula 3 in a state where the recycled aggregate is kept in a saturated surface dry state, and the measurement method of the present invention is not particularly limited, and may be selected according to specific equipment parameters:
Wherein ω represents angular velocity (ω=2ρn, n is centrifugal rate in rpm), ρ represents density of water in the pores, 1000kg/m 3; gamma is the surface tension, which at 20 ℃ takes a value of 72.75mN/m, R represents the centrifuge radius (i.e. the centrifuge center, i.e. the distance from the center of a combination of a plurality of centrifuge tanks to the tank filling). When preparing recycled concrete, the volume of the centrifugal tank is generally controlled to be at least 10 times larger than the maximum size of the recycled coarse aggregate, which is not particularly limited herein, and may be determined by one skilled in the art according to general selection rules in the prior art.
In the above measurement method, in order to ensure the workability of measurement, it is generally necessary to ensure good fluidity of the cement paste alone, and the recycled mortar obtained by adding the recycled fine aggregate or the recycled concrete obtained by adding the recycled coarse aggregate. Preferably, the initial fluidity of the independent cement paste and the regenerated mortar is regulated to be more than 160mm; if the fluidity is not satisfied due to the cement ratio, a water reducing agent may be added to the cement paste or the recycled mortar alone to ensure a fluidity of more than 160mm and a bleeding-free state. The initial expansion degree of the recycled concrete is controlled to be larger than 400mm in the same way.
In the actual application, the recycled aggregate is generally replaced with the natural aggregate in equal proportion when recycled aggregate is recycled into the cement base material, that is, the recycled cement base material obtained may have the aggregate composition of only recycled aggregate or may be a mixture of recycled aggregate and natural aggregate. The water absorption rate of the natural coarse aggregate is generally less than 1%, the engineering is negligible, and the water absorption rate of the natural fine aggregate is more than 2%, so that the working performance of the recycled cement base material is affected 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 terms of the mass ratio of both the natural aggregate and the recycled aggregate. That is, several parameters in the respective formulas in the measurement method of the present invention need to be adaptively adjusted.
Specifically, if a recycled cement base material is prepared by using a mixed aggregate of natural aggregate and recycled aggregate, the above bone ash ratio is obtained by subtracting the amount of the natural aggregate used from the total amount of the mixed aggregate, and then obtaining recycled aggregate with a mass of m G; meanwhile, the mass G of the recycled aggregate in the slurry tank 11 in formula 2 should be subtracted from the mass of the natural aggregate. Further, if the mixed fine aggregate of the natural fine aggregate and the recycled fine aggregate is adopted to prepare the recycled mortar, the molecular part in the formula 2 should be supplemented with the blending water amount absorbed by the natural fine aggregate 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 calculated and obtained, adding the additional water consumption required by the natural fine aggregate, wherein the sum of the two additional water consumption is the additional water consumption required by the preparation of the recycled mortar.
The above-described measurement method of the present invention will be embodied by specific examples. In the following examples 1 to 4, in consideration of the experimental scale and site limitation, the recycled aggregate was obtained by crushing, screening and washing the laboratory concrete block after the strength test, the concrete strength grade was C30, and the aggregate particle size range was 0.60mm to 4.75mm, that is, the recycled fine aggregate was used in the following examples to prepare recycled mortar. The fluidity of the prepared regenerated cement base material is adjusted by adopting the polycarboxylic acid type high-performance water reducer, the solid content is 20%, and the water reducing rate is 15%.
In each of examples 1 to 4 below, two centrifuge tanks were used for parallel measurement, and the total mixing volume of the recycled cement base material was 1L, and the standing time t of the recycled cement base material was set to 1min, 5min, 10min, 30min and 60min, respectively, when the measurement of the recycled cement base material was performed.
The slurry tank inner diameter of the centrifuges used in examples 1 to 4 was 5cm, the centrifugal radius was 8.10cm, and the mixing speed of 4000r/min and the centrifugal time of about 2min were obtained by calculation.
The following table 1 shows the blending ratios of the regenerated cement base materials in examples 1 to 4.
TABLE 1 mixing ratio kg/m of recycled Cement base materials in examples 1 to 4 3
Table 2 shows the water absorption of recycled aggregate in examples 1 to 4 in different recycled cement substrates and at different rest times.
Meanwhile, in order to embody the measurement method of the present invention when applied to a cement base material in which recycled aggregate has different water absorption courses in the cement base material and in water, an experiment of the water absorption rate of recycled aggregate in water under the same standing time as described above was also performed as a comparative example.
In this comparative example, recycled aggregate was immersed in pure water at normal temperature for various times (i.e., various rest times), and the water absorption thereof was measured. The water absorption results in the comparative examples are also shown in Table 2.
Table 2 water absorption of recycled aggregate in different recycled cement base materials and comparative examples at different standing times in water for recycled aggregate in examples 1 to 4
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As can be seen from table 2, when the recycled aggregate was placed in pure water, the water absorption was higher than that in 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 progress of water absorption caused by these two environments was evident. It is obvious that in the prior art, the water absorption measured by immersing the recycled aggregate in water for 1h or the 90% of the saturated water absorption measured by 24h is generally used as the calculation basis of the additional water consumption, and is inaccurate; when the water absorption rate is larger, which is obtained by soaking in pure water, in practical application, the additional water consumption is obviously increased, and the water-cement ratio of the regenerated cement base material system is finally larger than a preset value, so that the adjustment and evaluation of the working performance, mechanical property and durability of the obtained regenerated cement base material are affected.
In order to evaluate the accuracy of the above measurement method of the present invention, the system centrifugable water was measured on the cement base material by the following method, and it was found that the data of the centrifugable water measured by the above measurement method of the present invention was reliable, and the result of the calculation of the water absorption was also reliable.
The reliability and accuracy of the above measurement method provided by the invention are verified by adopting the following test methods mature in the art, and the specific operations are as follows: placing the mixed recycled cement base material on a square-hole sieve, slightly pressing with force to enable the cement paste in the recycled cement base material to pass through the square-hole sieve, and retaining the recycled aggregate on the sieve; and (3) placing the screened cement paste in a 1050 ℃ high-temperature furnace to be baked to constant weight, wherein the quality difference of the cement paste before and after high-temperature treatment is the moisture content of the cement paste, and the moisture content of the cement paste comprises the free water content and the combined water content of hydration products. And the total amount of the weighed mixing water is differed from the water content in the cement paste, so that the consumption of part of the mixing water absorbed by the recycled aggregate is obtained, and the water absorption rate of the recycled aggregate in the recycled cement base material is calculated.
Table 3 below calculates the water absorption calculated from the centrifuged water content of each recycled aggregate at different rest times t in each of the above examples and comparative examples according to the above conventional measurement method, and the error between the water absorption obtained by the measurement method according to the present invention in the above table 2.
Table 3 error in centrifugally water content of recycled aggregate in different recycled cement base materials and recycled aggregate in comparative example in different standing times in water to reversely push water absorption rate in examples 1 to 4
As can be seen from Table 3, the water absorption data obtained by the measurement method provided by the invention have an error range within + -1%, which means that the measurement method is accurate and reliable.
The above measurement method of the present invention is performed based on the dried recycled aggregate, however, generally the recycled aggregate may have a certain initial water content, and thus, when the above measurement method is applied to the recycled cement base material to calculate the additional water consumption required for the recycled aggregate, the initial water content value thereof should be subtracted.
While the invention has been shown and described with reference to certain embodiments, those skilled in the art will appreciate 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. The method for measuring the water absorption rate of the recycled aggregate in the cement base material is 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 method is characterized by comprising the following steps:
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 purified pulp into the pulp tank and centrifuging, wherein the centrifuged water in the first purified pulp enters the water bearing cup through the filter layer, and the mass m w of the centrifuged water in the purified pulp is weighed; calculating the centrifugable moisture content W 0 in the first net slurry using formula 1:
Wherein P 0 is 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 in the step S1 and the preset bone ash ratio, firstly mixing the second cement and the second mixing water under the same condition as the first clean pulp in the step S1 to obtain second clean pulp, then adding the recycled aggregate into the second clean pulp, continuing mixing and standing to obtain a recycled cement base material; wherein the recycled aggregate is dry recycled aggregate, and the recycled cement base material is recycled mortar or recycled concrete;
S4, placing the regenerated cement base materials under different standing time t in the slurry tank, centrifuging under the same condition as the first clean slurry in the step S2, enabling the centrifugally-produced water of the regenerated cement base materials in the regenerated cement base materials to enter the water bearing cup through the filter layer, and weighing the centrifugally-produced water of the regenerated cement base materials to obtain the mass m Wt; the water absorption W t of the recycled cement base material at different rest times t was calculated using 2:
Wherein P is the mass of the second cement in the recycled cement base material in the slurry tank;
G is the quality of the recycled aggregate in the recycled cement base material in the slurry tank.
2. The method according to claim 1, wherein in the step S3, the recycled aggregate is recycled fine aggregate obtained by crushing and sieving waste concrete to a particle size of 0.16-4.75 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 measuring according to claim 2, wherein a water reducing agent is added to the mixture of the first cement and the first mix water or the mixture of the second cement and the second mix water so that the initial fluidity of the first net slurry and the regenerated cement base material is more than 160mm and no bleeding occurs.
5. The method according to any one of claims 1 to 4, wherein in both step S2 and step S4, at least two and even number of said centrifugal tanks are used, and the mass error between at least two and even number of said centrifugal tanks filled with said first paste or said recycled cement substrate is less than 0.20g.
6. The method according to claim 1, wherein in the step S3, the recycled aggregate is recycled coarse aggregate obtained by crushing and screening waste concrete to a particle size of 4.75-30 mm; the recycled cement base material is recycled concrete.
7. The method according to 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 method according to claim 6, wherein a water reducing agent is added to the mixture of the first cement and the first mixed water so that the initial fluidity of the first net slurry is more than 160mm and no bleeding occurs, or a water reducing agent is added to the mixture of the second cement and the second mixed water so that the initial expansion of the regenerated cement base material is more than 400mm.
9. The method according to any one of claims 1, 6 to 8, wherein in each of step S2 and step S4, at least two and even number of the centrifugal tanks are used, and a mass error between at least two and even number of the centrifugal tanks filled with the first paste or the recycled cement base material is less than 0.02kg.
10. The measurement method according to claim 1, wherein in step S4, the standing time t is calculated from the time when the recycled aggregate is added to the second paste.
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