Research method for sulfate ion erosion path of recycled concrete

Abstract

The invention discloses a recycled concrete sulfate ion erosion path research method which comprises the following steps: firstly, preparing a sample which comprises a first new mortar block, an old mortar block, an old aggregate block and a second new mortar block which are sequentially arranged and are self-bonded into a whole; secondly, the bottom of the sample is soaked in a sulfate ion solution for an erosion test, all bonding faces vertically extend, and the sulfate ion solution erodes towards the upper portion of the sample under the action of the capillary effect; taking out the sample subjected to the erosion test, and slicing the sample along the direction of the bonding surface, wherein the slice is taken from a target part to be quantized; the quantitative contrastive analysis method for the sulfate erosion path of the recycled concrete has the remarkable effects that the quantitative contrastive analysis method for the sulfate erosion path of the recycled concrete is provided, and the quantitative contrastive analysis method for the sulfate erosion path of the recycled concrete can be used for accurately evaluating and comparing the erosion conditions of sulfate in different paths in the recycled aggregate; and a basis is provided for evaluating and comparing different modification methods and modification conditions to the sulfate corrosion resistance of the recycled aggregate.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of construction engineering, and particularly to a method for studying the salt particle erosion performance of recycled concrete. BACKGROUND

[0002] With the acceleration of urbanization and rapid economic development, a large amount of building materials is consumed. Some of the buildings have been built due to the inability to achieve the expected use function and are being rebuilt or demolished. At the same time, natural forces such as earthquakes, tsunamis, mudslides, floods, etc. have caused some damage to buildings. There are also building wastes generated in the construction of new houses, so there are a large amount of construction solid wastes. By 2020, the recycling rate of construction solid wastes is less than 10%. How to effectively recycle and utilize construction solid wastes, especially the utilization of waste concrete resources, is a new challenge faced by the current concrete industry, and it puts forward more urgent requirements for the application of recycled concrete.

[0003] For concrete structures in the water level fluctuation area, the deterioration damage is more severe due to the promotion of dry-wet cycle by sulfate erosion. Sulfate erosion damage will cause serious damage to the structure, and the safe service life of the structure is greatly reduced. The surface of recycled aggregate (old aggregate) is bonded with old mortar layer, which makes the apparent density, bulk density smaller, the strength lower, and the water absorption and porosity higher. The recycled concrete produced by using recycled aggregate (mainly recycled coarse aggregate) instead of natural aggregate has a complex internal microstructure, and the transmission channel of sulfate ions in the recycled concrete is increased, which makes it more susceptible to corrosion damage by harmful ions, thereby reducing its durability. Thus, the defects of recycled aggregate limit the application of recycled concrete in areas with high sulfate content.

[0004] In view of the defect problem of recycled concrete, many scholars found that the calcium carbonate and porous silica gel generated in the process of carbon sequestration treatment of recycled aggregate not only can improve the compactness and strength of the structure of recycled aggregate itself, but also can promote the hydration reaction of the interfacial transition zone of recycled concrete, reduce the thickness of the old mortar hydration film and the preferred orientation of high-sulfur type calcium sulphoaluminate and calcium hydroxide crystals in the interfacial transition zone, thereby improving the compactness and elastic modulus of the interfacial transition zone, reducing the water absorption, water content, crushing index and porosity of recycled aggregate, and further improving the compressive strength of recycled concrete.

[0005] In summary, combined with the characteristics of carbon sequestration recycled concrete and the characteristics of sulfate erosion, it can be predicted that carbon sequestration recycled concrete can improve the sulfate erosion resistance of recycled concrete. However, due to the long research period of sulfate erosion resistance test, there is still a lack of specific basis for the comparative analysis of the sulfate erosion path of recycled aggregate concrete or carbon sequestration recycled aggregate concrete at home and abroad. There is also a lack of specific quantitative analysis means for improving the sulfate erosion resistance of recycled concrete. SUMMARY

[0006] To solve the problems in the prior art, the application provides a quantitative analysis method for different erosion paths of sulfate in recycled concrete.

[0007] A research method for sulfate ion erosion paths in recycled concrete, the key of which lies in:

[0008] Step one, preparing a sample, the sample comprising a first new mortar block, an old mortar block, an old aggregate block and a second new mortar block arranged in sequence, the first new mortar block, the old mortar block, the old aggregate block and the second new mortar block being integrally bonded respectively, and the bonding surfaces of the first new mortar block, the old mortar block, the old aggregate block and the second new mortar block being parallel to each other;

[0009] Step two, soaking the bottom of the sample in a sulfate ion solution for erosion test, all the bonding surfaces extending vertically, and the sulfate ion solution eroding upward in the sample under the action of capillary effect;

[0010] Step three, taking out the sample after the erosion test and slicing along the bonding surface direction to obtain a first new mortar slice, a first new mortar-old mortar joint slice, an old mortar slice, an old mortar-old aggregate joint slice, an old aggregate slice and an old aggregate-second new mortar joint slice respectively;

[0011] Step four, determining the sulfate ion concentration of each slice and comparatively analyzing the sulfate erosion paths.

[0012] In the above method, the new mortar, the old mortar and the old aggregate are combined to form an integral whole, and the erosion test of the sulfate is simultaneously performed, compared with the erosion test of each part separately, the simultaneous erosion can reduce the variables to be controlled in the test process, and the test result is also more accurate. By slicing and analyzing the joint parts of each part, the transition interface of different materials against the sulfate erosion result can be determined, so that the research on the sulfate erosion path is no longer limited in the material interior. Finally, the quantitative determination of the sulfate concentration value of each slice can quantify the sulfate erosion result of different erosion paths. BRIEF DESCRIPTION OF DRAWINGS

[0013] Figure 1 It is a structural schematic diagram of the sample;

[0014] Figure 2 It is a state schematic diagram of the sample during the erosion test in a liquid tray;

[0015] Figure 3 It is an operation schematic diagram of slicing on the sample;

[0016] Figure 4 It is an appearance diagram of each sample after the erosion test for 15 days.

[0017] Figure 4 a is the appearance of RAC sample after 15 days of erosion test;

[0018] Figure 4 b is the appearance of FRAC-20% sample after 15 days of erosion test;

[0019] Figure 4 c is the appearance of CRAC-0.5 sample after 15 days of erosion test;

[0020] Figure 4 d is the appearance of FCRAC-20% sample after 15 days of erosion test;

[0021] Figure 5 is the appearance of each sample after 30 days of erosion test;

[0022] Figure 5 a is the appearance of RAC sample after 30 days of erosion test;

[0023] Figure 5 b is the appearance of FRAC-20% sample after 30 days of erosion test;

[0024] Figure 5 c is the appearance of CRAC-0.5 sample after 30 days of erosion test;

[0025] Figure 5 d is the appearance of FCRAC-20% sample after 30 days of erosion test;

[0026] Figure 6 is the sulfate ion erosion concentration-erosion path curve of each sample after 15 days of erosion;

[0027] Figure 6 a is the erosion concentration-path curve of RAC sample after 15 days of erosion;

[0028] Figure 6 b is the erosion concentration-path curve of FRAC-20% sample after 15 days of erosion;

[0029] Figure 6 c is the erosion concentration-path curve of CRAC-0.5 sample after 15 days of erosion;

[0030] Figure 6 d is the erosion concentration-path curve of FCRAC-20% sample after 15 days of erosion;

[0031] Figure 7 is the sulfate ion erosion concentration-erosion path curve of each sample after 30 days of erosion;

[0032] Figure 7 a is the erosion concentration-path curve of the RAC sample after 30 days of erosion;

[0033] Figure 7 b is the erosion concentration-path curve of the FRAC-20% sample after 30 days of erosion;

[0034] Figure 7 c is the erosion concentration-path curve of the CRAC-0.5 sample after 30 days of erosion;

[0035] Figure 7 d is the erosion concentration-path curve of the FCRAC-20% sample after 30 days of erosion. DETAILED DESCRIPTION

[0036] The application will be further described below in conjunction with the embodiments and the accompanying drawings.

[0037] A method for studying the sulfate ion erosion path of recycled concrete, as shown in Figure 1 、 2 , 3, comprising the following steps:

[0038] Step one, preparing a sample, the sample comprising a first new mortar block, an old mortar block, an old aggregate block and a second new mortar block arranged in sequence, the first new mortar block, the old mortar block, the old aggregate block and the second new mortar block being respectively bonded into one whole, the bonding surfaces of the first new mortar block, the old mortar block, the old aggregate block and the second new mortar block being parallel to each other;

[0039] The first new mortar block and the second new mortar block are both formed by white cement curing, the old mortar block is formed by Portland cement P·O 42.5R curing, and the old aggregate block is formed by granite cutting; the white cement, the Portland cement and the granite are respectively used for simulating new mortar, old mortar and old aggregate; the first new mortar block and the second new mortar block are consistent in composition;

[0040] The length, width and height of the first new mortar block and the second new mortar block are all 35mm×40mm×100mm;

[0041] The length, width and height of the old mortar block are 25mm×15mm×100mm;

[0042] The length, width and height of the old aggregate block are 25mm×10mm×100mm;

[0043] The preparation method of the sample is as follows: first, old mortar is cast on the side surface corresponding to one width direction of the old aggregate block, and after curing, the old mortar is solidified into an old mortar block; then, new mortar is cast on the outer side surface corresponding to the width direction of the old aggregate block and the old mortar block, respectively, and after curing, the new mortar is solidified into a first new mortar block and a second new mortar block, respectively;

[0044] After obtaining the sample, the sample is dried in a blast drying oven at 105 DEG C for 48 hours until the weight is constant, and then the erosion test is performed;

[0045] The sample can be adjusted according to the object to be analyzed. When the carbon sequestration recycled concrete is subjected to a sulfate erosion path analysis, or the sample is subjected to an erosion test after being subjected to carbon sequestration treatment, or the first new mortar block, the second new mortar block and the old mortar block are all subjected to carbon sequestration treatment, or the first new mortar block and the second new mortar block are subjected to carbon sequestration treatment, or the old mortar block is subjected to carbon sequestration treatment. When the sulfate erosion resistance of fly ash replacing part of the mortar is to be studied, or fly ash is mixed in the first new mortar block, the second new mortar block and the old mortar block, or fly ash is mixed in the first new mortar block and the second new mortar block, or fly ash is mixed in the old mortar block.

[0046] Step two, the bottom of the sample is soaked in a sulfate ion solution for erosion test, all the bonding surfaces extend vertically, and the sulfate ion solution erodes upward to the upper part of the sample under the action of capillary effect;

[0047] A specific embodiment is that the sulfate ion solution is contained in a liquid tray, a raised net rack is placed in the liquid tray, the sulfate ion solution submerges the raised net rack, and the bottom of the sample is placed on the raised net rack to ensure that the sample is suspended and has sufficient sulfate ion solution at the bottom;

[0048] The sulfate ion solution can be a sodium sulfate solution, the concentration of the sodium sulfate solution is 5%, and the soaking depth of the bottom of the sample is 10 mm; during the soaking process, the sodium sulfate solution is added to the liquid tray every 3 days to keep the concentration of the sodium sulfate solution at about 5%, and the sodium sulfate solution needs to be stirred after being added.

[0049] Step three, the sample after completing the erosion test is taken out and sliced along the bonding surface direction, the slice is taken from the target part to be quantified, and the target part can be a new mortar part, a new mortar-old mortar joint part, an old mortar part, an old aggregate-new mortar joint part, an old aggregate part, or an old aggregate-new mortar joint part; thus, a first new mortar slice, a first new mortar-old mortar joint slice, an old mortar slice, an old mortar-old aggregate joint slice, an old aggregate slice, and an old aggregate-second new mortar joint slice can be obtained.

[0050] It should be noted that each of the slice size remains equal for subsequent determination of the relative better calculation.

[0051] The size of the slice (length, width, height) is recommended to be 25mm x 3mm x 100mm.

[0052] Step four, determine the concentration of sulfate ions of each slice, from which the amount of sulfate ions under different erosion paths can be obtained, so as to quantify and compare the erosion ability of sulfate under different erosion paths.

[0053] As a more detailed comparative analysis method: the slice can be cut along the direction of sulfate ion erosion, and the concentration of sulfate ion is determined again. Thus, the amount of sulfate ion erosion at different heights of each slice can be obtained, so as to quantify and compare the erosion height of sulfate under the same erosion path.

[0054] The determination method of the concentration of sulfate ions of each slice is as follows:

[0055] Step 4.1, place any of the slices in an oven at 65℃ for 24 hours, then grind them into powder using a mortar and weigh them to obtain the powder mass m p ;

[0056] Step 4.2, pour the powder into a beaker, add an appropriate amount of deionized water 1moL / L hydrochloric acid solution and stir to exclude the interference of calcium carbonate ions;

[0057] Step 4.3, place the beaker in a 90-100℃ water bath for 5 minutes, and continuously stir with a glass rod during heating to make the sulfate ions fully dissolve in the solution.

[0058] Step 4.4, filter the mixture in the beaker using fast qualitative filter paper, and rinse the beaker and filter paper with deionized water for 8-10 times to obtain the filtrate;

[0059] Step 4.5, concentrate the filtrate (such as: reduce pressure concentration) to 250mL, then heat it in a 90-100℃ water bath for 5 minutes, and finally add 10mL of 10% mass fraction barium chloride to obtain a barium sulfate solution;

[0060] Step 4.6, let the barium sulfate solution stand at room temperature for 24h to allow the generated barium sulfate to naturally precipitate;

[0061] Step 4.7, filter the barium sulfate solution using slow qualitative filter paper, and weigh the mass of the slow qualitative filter paper before filtration as m t ;

[0062] Step 4.8, dry the slow qualitative filter paper, and weigh the total mass of the slow qualitative filter paper and the precipitate as m g; and finally the mass fraction of sulfate ions ζ is calculated according to the following formula:

[0063]

[0064] ζ: mass fraction of sulfate ions;

[0065] m p : mass of the powder after drying of the slice;

[0066] m t : mass of the slow qualitative filter paper;

[0067] m g : total mass of the slow qualitative filter paper and the precipitate;

[0068] Step 4.9: Steps 4.1-4.8 are repeated to determine the sulfate ion concentration of the other slices.

[0069] Example 2:

[0070] A method for studying the sulfate ion erosion path of recycled concrete is prepared according to the method of step one in Example 1 as follows:

[0071]

[0072] RAC: represents a recycled concrete sample that has not undergone solid-state treatment and has no fly ash replacement;

[0073] FRAC-20%: represents a recycled concrete sample that has not undergone solid-state treatment, and fly ash replaces 20% of the white cement in the first and second new mortar;

[0074] CRAC-0.5: represents a recycled concrete sample that has undergone carbon fixation treatment at a pressure of 0.5 MPa, and has no fly ash replacement;

[0075] FCRAC-20%: represents a recycled concrete sample that has undergone carbon fixation treatment at a pressure of 0.5 MPa, and fly ash replaces 20% of the white cement in the first and second new mortar.

[0076] The above samples are then immersed in a sodium sulfate solution and subjected to a sulfate ion erosion test according to the method of step two in Example 1:

[0077] In the sulfate erosion concrete test, the capillary water absorption characteristics cause the upper half of the sample to be in a non-saturated state, and water will continue to evaporate and be absorbed from below. During the process of capillary water absorption, sodium sulfate spreads upward with the flow of water, and sodium sulfate crystals will precipitate when the concentration of sodium sulfate is too high. The amount of crystals reflects the capillary water absorption capacity, and the faster the capillary water absorption, the poorer the pore structure of the concrete.

[0078] After immersion for 15 days, record and observe the appearance of each sample. The results are as follows: Figure 7 (include Figure 7 a. Figure 7 b. Figure 7 c. Figure 7 d).

[0079] from Figure 7 It can be seen that:

[0080] RAC specimens ( Figure 7 a) A large amount of sodium sulfate crystals precipitated on the left and right sides and the top, with the largest amount of crystals in the first and second new mortar parts;

[0081] FRAC-20% sample ( Figure 7 b) Compared with the RAC specimen, fewer crystals were analyzed in the first and second new mortar parts;

[0082] CRAC-0.5 sample ( Figure 7 c) Compared with the RAC specimen, the old mortar part has less crystals, while the first and second new mortar parts still have more crystals;

[0083] FCRAC-20% sample ( Figure 5 d) Compared with the previous three samples, the amount of precipitated crystals is the least.

[0084] This shows that fly ash mainly modifies the pore structure of the new mortar, and carbon fixation modifies the pore structure of the old mortar. The modification is best when the two act at the same time.

[0085] After immersion for 30 days, record and observe the appearance of each sample. The results are as follows: Figure 5 (include Figure 5 a. Figure 5 b. Figure 5 c. Figure 5 d). Figure 5 It can be seen that:

[0086] The distribution of sodium sulfate crystals after precipitation is not much different from that at 15 days, and the precipitation of all four samples is more than that at 15 days. This shows that as the soaking time increases, the crystal precipitation becomes more obvious. Among the four samples, FCRAC-20% sample ( Figure 5 d) The best performance, RAC sample ( Figure 6 a) The most crystals are precipitated.

[0087] Further, according to the method of step three and step four in embodiment 1, the samples immersed for 15 days and 30 days were sectioned in segments, specifically: each section was evenly divided into four segments (0-25mm segment, 25-50mm segment, 50-75mm segment, 75-100mm segment) along the extension direction of the bonding surface, and the sulfate ion concentration was measured respectively, and the sulfate ion concentration and section height line graph was drawn, and the results were as follows Figure 6 (consisting of Figure 6 a, Figure 6 b, Figure 6 c, Figure 7 d) and Figure 7 (consisting of Figure 7 a, Figure 7 b, Figure 6 c, Figure 6 d) as shown.

[0088] In order to simplify the name and mark, the first new mortar section is abbreviated as "XJ";

[0089] The "first new mortar-old mortar joint section" is abbreviated as "XJ-LJ";

[0090] The "old mortar section" is abbreviated as "LJ";

[0091] The "old mortar-old aggregate joint section" is abbreviated as "LJ-LG";

[0092] The "old aggregate-second new mortar joint section" is abbreviated as "LG-XJ";

[0093] ①, 15-day sulfate erosion path analysis

[0094] From Figure 6 It can be seen that:

[0095] For RAC samples ( Figure 6a): at the depth of 0-25mm, the concentration of sulfate ions is ranked as: LG-XJ > XJ-LJ > XJ > LJ-LG > LJ; at the depth of 25-50mm, the concentration of sulfate ions is ranked as: LG-XJ > XJ-LJ > XJ > LJ-LG > LJ; at the depth of 50-75mm, the concentration of sulfate ions is ranked as: LG-XJ > XJ-LJ > XJ > LJ-LG > LJ; at the depth of 75-100mm, the concentration of sulfate ions is ranked as: LG-XJ > XJ-LJ > XJ > LJ-LG > LJ. At all depths, the concentration of LG-XJ path is always the highest among all paths, indicating that the RAC specimen is most easily eroded in this path and has the worst resistance to sulfate ion erosion. The second is the XJ-LJ path, and its concentration is close at the depth of 0-25mm and 25-50mm, slightly lower than that of LG-XJ path. In each depth range, the concentration of XJ path changes little and is at a medium level. In comparison, the concentration of LJ path is always the lowest among all paths, especially at deeper erosion depths (such as 50-75mm and 75-100mm), which shows a significant lower concentration. This indicates that the LJ path has the best resistance to sulfate ion erosion. Without any treatment, LG-XJ, XJ-LJ and XJ are more easily eroded in the new mortar part of the recycled concrete than in the old mortar part, mainly because the hydration time of the new mortar cement is shorter and the hydration degree is not complete compared with the old mortar, while the secondary hydration of the standard curing of the old mortar is basically complete, and its structure is more compact and has higher strength. The Vickers hardness of the five intervals is further tested, and the results show that LJ > LJ-LG > XJ > LG-XJ > XJ-LJ, and the strength size order is almost the same as the sulfate ion erosion path order. The reason for the difference may be that the cut granite is relatively smooth, and the bonding ability is worse than that of the irregular limestone in the Vickers hardness test.

[0096] For FRAC-20% samples Figure 6b) : At the depth of 0-25mm, the concentration order is LJ-LG > LG-XJ > XJ-LJ > XJ > LJ; at the depth of 25-50mm, the concentration order is XJ-LJ > LG-XJ > XJ > LJ-LG > LJ; at the depth of 50-75mm, the concentration order is XJ-LJ > LG-XJ > XJ > LJ-LG > LJ; at the depth of 75-100mm, the concentration order is XJ-LJ > LG-XJ > XJ > LJ-LG > LJ. At the depth of 0-25mm, in the soaking zone, the concentration of LJ-LG path is the highest, and the erosion is the most serious, followed by LG-XJ and XJ-LJ paths, and then XJ path, and the concentration of LJ path is the lowest. It shows that in the shallow layer, the sulfate ion transmission of LJ-LG path is the easiest. At the depth of 25-50mm to 75-100mm, as the erosion depth increases, the concentration order basically remains the same. The XJ-LJ path is always in the first place among all the paths, indicating its strong erosion ability. The concentration of LG-XJ path remains stable. The concentration of XJ path is in the middle, and it shows a slight rebound in the deeper erosion layer (50-75mm and 75-100mm). The concentration of LJ-LG path gradually decreases, and is always lower than that of XJ-LJ and LG-XJ paths, while the concentration of LJ path is always the lowest among all the paths and is the least eroded.

[0097] For the CRAC-0.5 sample Figure 7 c) : At the depth of 0-25mm, the concentration order is LG-XJ > XJ > XJ-LJ > LJ-LG > LJ; at the depth of 25-50mm, the concentration order is LG-XJ > XJ > XJ-LJ > LJ-LG > LJ; at the depth of 50-75mm, the concentration order is XJ > LG-XJ > XJ-LJ > LJ-LG > LJ; at the depth of 75-100mm, the concentration order is LG-XJ > XJ > XJ-LJ > LJ-LG > LJ. From the overall trend, the LG-XJ path shows strong sulfate ion erosion ability in the erosion layers of 0-25mm and 75-100mm, and always remains in the top two. The XJ path reaches the highest concentration at the depth of 50-75mm, and shows relatively stable at other depths, and is in a relatively high position. The concentration of XJ-LJ path basically remains stable at each depth, and is always in the middle position. The concentration of LJ-LG path is generally low, and fails to break through the concentration of other paths, especially in deep erosion, its concentration gradually decreases. The LJ path always shows the weakest erosion, and has the lowest concentration.

[0098] For the FCRAC-20% sample Figure 7d) : at the depth of 0-25mm, the concentration of erosion path was ranked as LG-XJ > XJ > XJ-LJ > LJ > LJ-LG; at the depth of 25-50mm, the concentration of erosion path was ranked as LG-XJ > XJ > XJ-LJ > LJ > LJ-LG. At the depth of 50-75mm, the concentration of erosion path was ranked as XJ-LJ > XJ > LJ-LG > LG-XJ > LJ. At the depth of 75-100mm, the concentration of erosion path was ranked as XJ-LJ > LG-XJ > XJ > LJ-LG > LJ. From the above ranking results, it can be seen that with the increase of erosion depth, the change trend of sulfate ion concentration in different transmission paths is not completely consistent. In the shallow depth (0-25mm and 25-50mm), the concentration of LG-XJ path is relatively high, while in the deeper layer (50-75mm and 75-100mm), the XJ-LJ path shows higher sulfate ion concentration.

[0099] ②, sulfate erosion path analysis for 30 days

[0100] Combined Figure 7 It can be seen that:

[0101] For RAC samples ( Figure 7 a) : the concentration of LG-XJ path is the highest, and the concentration at different erosion depths is relatively high, especially in the concentration of 0-25mm and 25-50mm. The concentration of XJ-LJ path is followed, which is relatively high as a whole, especially in the concentration of 0-25mm and 25-50mm. The concentration of LJ path is obviously lower, and its concentration basically remains stable, which belongs to the minimum. The concentration of other paths falls in the middle range, among which the concentration of LJ-LG path gradually changes, which is always lower than that of XJ and XJ-LJ paths. The concentration of erosion path is ranked as LG-XJ > XJ-LJ > XJ > LJ-LG > LJ, and the overall concentration is improved compared with that of 15 days immersion.

[0102] For FRAC samples ( Figure 7 b) : the concentration change law of its four depth segments is consistent with that of 15 times immersion 0-25mm concentration is the highest. The overall concentration ranking is XJ-LJ > LG-XJ > XJ > LJ-LG > LJ, and the sulfate ion concentration of XJ-LJ and LG-XJ is not much different.

[0103] For CRAC-0.5 samples ( ​c) : The concentration of the erosion path of 0-25mm, 25-50mm, 50-75mm, 75-100mm is LG-XJ > XJ > XJ-LJ > LJ-LG > LJ. It is consistent with 15 days immersion. It is illustrated that the sulfate ions are more easily eroded and damaged from the LG-XJ and XJ part in the sulfate erosion of the CRAC-0.5 sample.

[0104] For the FCRAC-20% sample, ​ d) : The erosion concentration of each path is lower than that of each path of the other three single aggregate concrete, which illustrates that the combination of carbon sequestration and fly ash can effectively inhibit the sulfate ion erosion of each path.

[0105] In this embodiment, five sulfate ion erosion paths are designed, and the main conclusions are as follows:

[0106] (1) In the partial immersion test, the salting-out phenomenon occurs, and it is observed that sodium sulfate crystals are more easily salting-out in the new mortar part, which illustrates that the new mortar is also a weak area in the recycled concrete.

[0107] (2) In the RAC sample, the sulfate ions are more easily eroded from the LG-XJ, XJ-LJ and XJ paths; in the CRAC-0.5 sample, the sulfate ions are more easily eroded from the LG-XJ and XJ paths; in the FRAC-20% sample, the sulfate ions are more easily eroded from the LG-XJ and LJ-XJ paths; and in the CFRAC-20% sample, the sulfate ion concentration of each path is lower, that is, the sulfate ion erosion resistance of the concrete is the best.

[0108] (3) Based on the comparison and analysis of the sulfate ion concentration in the same path and different samples, it is illustrated that the fly ash acting on the recycled concrete can reduce the sulfate ion concentration of the LG-XJ, LJ-XJ and XJ three paths; the carbon sequestration acting on the recycled concrete can reduce the sulfate ion concentration of the XJ-LJ, LJ and LJ-LG three paths; when both of them act on the recycled concrete, the sulfate ion concentration of the XJ, XJ-LJ, LJ, LJ-LG and LG-XJ five paths is reduced; when the XJ-LJ path is simultaneously affected by the carbon sequestration and the fly ash, the sulfate ion concentration is reduced the most.

[0109] It can be known from the above description that the present application has the following beneficial effects: a quantitative comparative analysis method of the sulfate erosion path of the recycled aggregate concrete or the carbon sequestration recycled aggregate concrete is proposed, which provides a basis for accurately evaluating the erosion of the sulfate in the different paths of the recycled aggregate and evaluating the sulfate erosion resistance of the recycled aggregate under different modification methods and modification conditions.

[0110] Finally, it should be noted that the above description is only for the preferred embodiments of the present application, and those of ordinary skill in the art can make various similar expressions under the inspiration of the present application without departing from the purpose and scope of the present application, and such changes fall within the protection scope of the present application.

Claims

1. A method for studying the sulfate ion erosion path of recycled concrete, characterized in that: Step 1, preparing a sample, the sample comprising a first new mortar block, an old mortar block, an old aggregate block and a second new mortar block arranged in sequence, the first new mortar block, the old mortar block, the old aggregate block and the second new mortar block being bonded into one whole respectively, the bonding surfaces of the first new mortar block, the old mortar block, the old aggregate block and the second new mortar block being parallel to each other; Step 2, immersing the bottom of the sample in a sulfate ion solution for erosion test, all the bonding surfaces extending vertically, the sulfate ion solution eroding upward of the sample under the action of capillary effect; Step 3, taking out the sample after the erosion test and slicing along the bonding surface direction, the slices being taken from the target site to be quantified; Step 4, determining the sulfate ion concentration of each slice and comparatively analyzing the sulfate erosion path. In the step 1, the first new mortar block and the second new mortar block are both formed by white cement solidification, the old mortar block is formed by ordinary Portland cement solidification, and the old aggregate block is formed by granite cutting. 3.The method for studying the sulfate ion erosion path of recycled concrete according to claim 2, characterized in that: the first new mortar block, the second new mortar block and the old mortar block all undergo carbon sequestration treatment; and the first new mortar block, the second new mortar block and the old mortar block all contain fly ash. The sample is prepared as follows: first, pouring old mortar on one side of the old aggregate block, curing the old mortar to form the old mortar block, then pouring new mortar on the outer side of the old aggregate block and the old mortar block respectively, and curing the new mortar to form the first new mortar block and the second new mortar block respectively. After the sample is completely solidified, it is dried to constant weight before the erosion test.

2. The method of claim 1, wherein: In the step 2, the sulfate ion solution is contained in a liquid tray, and a raised net rack is placed in the liquid tray, the sulfate ion solution submerging the raised net rack, and the bottom of the sample being placed on the raised net rack. In the step 2, the sulfate ion solution is a sodium sulfate solution, the concentration of the sodium sulfate solution being 5%, and the immersion depth of the bottom of the sample being 10mm. In the step 3, the sizes of the slices are equal. The slices are cut in segments along the sulfate ion erosion direction, and the sulfate ion concentration is determined in segments.

4. The method for studying the sulfate ion ingress path in recycled concrete according to claim 2 or 3, characterized in that, In the step 4, the sulfate ion concentration of each slice is determined as follows:

5. The method of claim 2 or 3, wherein: Step 4.2, pouring the powder into a beaker, adding 1moL / L hydrochloric acid solution and stirring; 6. The method of claim 1, wherein: Step 4.3, placing the beaker in an environment of 90-100℃ for 5 minutes, continuously stirring during the heating process, so that the sulfate ions are fully dissolved in the solution.

7. The method of claim 1, 2, 3, or 6, wherein: Step 4.4, filtering the mixture in the beaker using rapid qualitative filter paper, and rinsing the beaker and filter paper with deionized water for 8-10 times to obtain a filtrate; 8. The method of claim 1, 2, 3, or 6, wherein: Step 4.5, concentrating the filtrate to 250mL, heating in an environment of 90-100℃ for 5 minutes, and finally adding 10mL of barium chloride with a mass fraction of 10% to obtain a barium sulfate solution; 9. The method of claim 1, 2, 3, or 6, wherein: ​ 10. The method of claim 1, 2, 3, or 6, wherein, ​ Step 4.1: Place any of the slices in an oven at 65°C and dry for 24 hours, then grind them into powder and weigh them to obtain a mass of m p ; ​ ​ ​ ​ Step 4.6, the barium sulfate solution is left to stand at room temperature for 24 h, and the generated barium sulfate is allowed to naturally precipitate; Step 4.7, filter the barium sulfate solution using slow qualitative filter paper, before filtering, weigh the mass of the slow qualitative filter paper as m t ; Step 4.8, dry the slow qualitative filter paper, weigh the total mass of the slow qualitative filter paper and the precipitate as m g ; and finally the mass fraction of the sulfate ion ζ is calculated according to the following formula; ζ: mass fraction of sulfate ions; m p : mass of the powder after drying of the slice; m t : quality of slow qualitative filter paper; m g : total mass of slow qualitative filter paper and sediment; Step 4.9, steps 4.1-4.8 are repeated to determine the sulfate ion concentration of other sections.

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