Steel slag stability detection method based on steel slag aggregate concrete in full particle size range

Abstract

The invention provides a steel slag stability detection method based on full-particle-size-range steel slag aggregate concrete. The steel slag stability detection method comprises the following steps: step 1, preparing steel slag aggregate; step 2, preparing a concrete test piece and detecting compressive strength; 3, autoclaving treatment: carrying out autoclaving treatment on the steel slag-doped aggregate concrete test block by using an autoclave, and naturally cooling after the autoclaving treatment is finished; 4, comparing strength, and calculating the compressive strength change rate of the steel slag aggregate-doped concrete before and after autoclaving; and 5, evaluating the stability of the steel slag, namely evaluating the stability according to the compressive strength change rate in the step 4, if the compressive strength change rate of the steel slag aggregate-doped concrete before and after autoclaving is smaller than a rated ratio, determining that the stability of the steel slag is unqualified and cannot be used as an aggregate to prepare concrete, otherwise, determining that the steel slag is qualified. The method can quickly, effectively, accurately and reliably detect the stability of the steel slag aggregate as the concrete, and promotes the resource utilization of the steel slag as the concrete aggregate.

Description

Technical Field

[0001] The present invention relates to the technical field of recycling of bulk solid waste, and particularly relates to a method for detecting the soundness of concrete prepared with steel slag as aggregate. Background Art

[0002] Restricted by factors such as poor homogeneity and poor volume soundness, steel slag is one of the most difficult-to-utilize industrial solid wastes in metallurgical slag. There has been no substantial progress in the research on the soundness of steel slag as concrete aggregate in China, and the soundness performance of steel slag aggregate concrete in actual engineering still has great uncertainty.

[0003] In the prior art, there are many detection methods and evaluation indexes for the soundness of steel slag at home and abroad. However, there are significant differences between the test conditions of specimens and the actual engineering application routes and service environment conditions, and the results obtained by each detection method cannot truly and effectively reflect the soundness performance of steel slag aggregate in concrete engineering.

[0004] In addition, most of the domestic standards for steel slag as concrete aggregate are recommended national standards and metallurgical industry standards. Different industries in the engineering field often implement the standards formulated by themselves, lacking unified and effective evaluation indexes for the soundness of steel slag aggregate concrete and clear limit regulations, which seriously affects the comprehensive utilization of steel slag as concrete aggregate. Summary of the Invention

[0005] In view of the above situation, the present invention provides a method for detecting the soundness of steel slag based on concrete with steel slag aggregate in the full particle size range, which can accurately detect the soundness of steel slag as concrete aggregate and provides a reliable detection method for the application of steel slag in concrete aggregate.

[0006] According to one aspect of the present invention, there is provided a method for detecting the soundness of steel slag based on concrete with steel slag aggregate in the full particle size range, including the following steps:

[0007] Step 1. Preparation of steel slag aggregate: Crush and screen the steel slag to be tested to obtain steel slag aggregate particles in different particle size ranges.

[0008] Step 2. Preparation of concrete specimens and detection of compressive strength: Replace the natural aggregate of the corresponding particle size with the steel slag aggregate of different particle sizes obtained in Step 1 in equal volume according to a certain ratio to prepare concrete with steel slag aggregate, and perform compressive strength detection after curing.

[0009] Step 3. Autoclave treatment: Perform autoclave treatment on the concrete specimens with steel slag aggregate, and then cool naturally after completion.

[0010] Step 4. Strength comparison: Determine the compressive strength of the autoclaved concrete test blocks with steel slag aggregate. Calculate the change rate of the compressive strength of the concrete with steel slag aggregate before and after autoclaving based on the compressive strength determined in Step 4 and the compressive strength detected in Step 2.

[0011] Step 5. Evaluation of steel slag soundness: Evaluate the soundness according to the change rate of the compressive strength in Step 4 to determine the soundness of the applied particle size of steel slag.

[0012] In an alternative embodiment, in Step 4, determining the compressive strength of the autoclaved concrete test blocks with steel slag aggregate includes: If the autoclaved concrete test blocks with steel slag aggregate are significantly damaged as a whole or completely fragmented and pulverized from the inside to the outside, and their strength is completely lost, the compressive strength of the autoclaved test blocks is 0 MPa. If the appearance of the autoclaved concrete test blocks with steel slag aggregate is intact or slightly damaged as a whole, the compressive strength test is performed again.

[0013] In an alternative embodiment, in Step 4, the change rate of the compressive strength is as follows:

[0014]

[0015] Where: Pr - the change rate of the compressive strength of the test block, %;

[0016] P - the compressive strength of the autoclaved test block, MPa;

[0017] P0 - the compressive strength of the test block before autoclaving, MPa;

[0018] The numerical values of the compressive strength of the test blocks before and after autoclaving are the average values of three test blocks.

[0019] In an alternative embodiment, in Step 5, if the change rate of the compressive strength of the test block is less than the rated ratio, the soundness of the applied particle size of steel slag is unqualified and it cannot be used as aggregate to prepare concrete. If the change rate of the compressive strength of the test block is greater than or equal to the rated ratio, the soundness of the applied particle size of steel slag is qualified. The rated ratio is -18% to -20%.

[0020] In an alternative embodiment, in Step 1, the steel slag aggregate particles in different particle size ranges include steel slag fine aggregate with a particle size of 0 - 5 mm (including 5 mm), steel slag coarse aggregate with a particle size of 5 - 10 mm (including 10 mm), and steel slag coarse aggregate with a particle size of 10 - 20 mm (including 20 mm).

[0021] In an alternative embodiment, in Step 1, the crushing and screening operations are as follows:

[0022] (1) Use a jaw crusher to perform coarse and fine two-stage crushing on the steel slag to be tested. Before the second-stage crushing, pass it through a vibrating screen with a screen hole size of 9.5 - 19.0 mm for 3 minutes of vibration time to obtain steel slag coarse aggregate with a particle size of 10 - 20 mm (including 20 mm).

[0023] (2) The undersize material is subjected to three-stage crushing by a cone crusher. Before the three-stage crushing, pass it through a vibrating screen with a screen hole size of 4.75 - 9.5 mm for 3 minutes of vibration time to obtain steel slag fine aggregate with a particle size of 0 - 5 mm (including 5 mm) and steel slag coarse aggregate with a particle size of 5 - 10 mm (including 10 mm).

[0024] In an alternative embodiment, in step (2), the prepared strength grade of the concrete with steel slag aggregate is C30, and the formula is: 325 - 375 parts of cement, 80 - 120 parts of fly ash, 780 - 1200 parts of fine aggregate, 930 - 1300 parts of coarse aggregate, 200 - 230 parts of water, and 0 - 13 parts of water reducing agent. Among them, the weight ratio of the 5 - 10 mm (including 10 mm) particles to the 10 - 20 mm (including 20 mm) particles is 1:2.

[0025] In an alternative embodiment, in step (2), the steel slag aggregate with a certain particle size is one or more of the steel slag fine aggregate with a particle size of 0 - 5 mm (including 5 mm), the steel slag coarse aggregate with a particle size of 5 - 10 mm (including 10 mm), and the steel slag coarse aggregate with a particle size of 10 - 20 mm (including 20 mm); the replacement ratio of the steel slag aggregate in each particle size range for the natural aggregate with the corresponding particle size is 80% - 100% (including 100%).

[0026] In an alternative embodiment, in step (2), the size of the concrete specimen with steel slag aggregate is 100 mm × 100 mm × 100 mm, the curing temperature is 18 - 22 °C, the curing humidity ≥ 95% RH, and the curing time is 28 d.

[0027] In an alternative embodiment, in step (3), the autoclave steam pressure is 0.8 - 1.2 MPa, corresponding to a temperature of 159 - 188 °C; the autoclave time is 3.5 - 5.5 h, and the pressure change is divided into three stages:

[0028] (1) In the pressure increase stage, after setting the temperature according to the target pressure value, the autoclave body starts to heat up, and the pressure in the autoclave rises to the target value after 60 - 90 minutes.

[0029] (2) In the constant pressure stage, after reaching the target pressure, the autoclave is kept at a constant temperature for 2.5 - 3.5 h, and the pressure in the autoclave is constant.

[0030] (3) In the pressure reduction stage, after setting the autoclave time to end, stop heating, and the pressure in the autoclave drops below 0.1 MPa within 30 minutes.

[0031] The beneficial effects of the present invention are as follows: By utilizing the conditions of high temperature and high pressure, the hydration reaction of the expansive components in steel slag can be effectively accelerated. The feasibility of using various gradations as concrete aggregates is judged by the change rate (Pr) of the compressive strength of the concrete with steel slag aggregates before and after autoclaving, and the soundness test of using steel slag as concrete aggregates can be accurately carried out.

[0032] The autoclaving conditions adopted in the present invention are relatively appropriate for the damage degree of the appearance of the concrete with steel slag aggregates, and will not cause serious damage to the structure or performance of the concrete; and it can moderately magnify the damage caused by expansion to make it easy to identify, and keep the change rate of the concrete compressive strength within a relatively reasonable range; and the autoclaving treatment time is relatively short, with good timeliness. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only the embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained according to the provided drawings without creative efforts.

[0034] Figure 1 It is a flow schematic diagram of a method for detecting the soundness of steel slag based on concrete with steel slag aggregates in the full particle size range provided by the present invention;

[0035] Figure 2 It is an overall schematic diagram of a method for detecting the soundness of steel slag based on concrete with steel slag aggregates in the full particle size range provided by the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0036] To make the objectives, technical solutions and advantages of the present invention clearer, the following will clearly and completely describe the technical solutions of the present invention in conjunction with the specific embodiments and corresponding drawings of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the protection scope of the present invention.

[0037] According to another aspect of the present invention, a method for detecting the soundness of steel slag based on concrete with steel slag aggregates in the full particle size range is provided:

[0038] Step 1: Preparation of steel slag aggregates: The steel slag to be tested is crushed and screened to obtain steel slag aggregate particles in different particle size ranges.

[0039] Step 2: Preparation of concrete specimens and detection of compressive strength: Using steel slag aggregates of a certain particle size, replacing the natural aggregates of the corresponding particle size by equal volume according to a certain proportion to prepare concrete with steel slag aggregates, and performing compressive strength detection after curing.

[0040] Step 3 Autoclave treatment: Use an autoclave to perform autoclave treatment on the steel slag aggregate concrete test blocks, and then let them cool naturally after completion.

[0041] Step 4 Strength comparison: Observe the appearance of the test specimens. If the corners and sides of the test specimens show severe defects, or obvious deep cracks appear on the surface, or the steel slag aggregate concrete is completely fragmented and pulverized from the inside to the outside, record it as 0 MPa; if the appearance of the test specimens is intact or slightly damaged, conduct compressive strength testing, and calculate the change rate of the compressive strength of the steel slag aggregate concrete before and after autoclaving according to the following formula. The compressive strength values of the test specimens before and after autoclaving are the average values of three test specimens.

[0042]

[0043] Where: Pr - the change rate of the compressive strength of the test specimen, %;

[0044] P - the compressive strength of the test specimen after autoclaving, MPa;

[0045] P0 - the compressive strength of the test specimen before autoclaving, MPa.

[0046] Step 5 Soundness evaluation: If Pr is less than the rated ratio (-18% to -20%), it can be determined that the soundness of the steel slag with the applied particle size is unqualified and cannot be used as an aggregate to prepare concrete; otherwise, it is qualified.

[0047] Example

[0048] In this example, steel slags produced by three steel mills are selected, and after crushing, they are screened into fine aggregates of 0 - 5 mm (including 5 mm), and coarse aggregates of 5 - 10 mm (including 10 mm) and 10 - 20 mm (including 20 mm).

[0049] The composition mix ratio of the steel slag aggregate concrete can be seen in Table 1. The numbers S1 - S10 are 10 specific examples.

[0050] Table 1 Mix ratio of steel slag aggregate concrete

[0051]

[0052] The different particle size ranges of the steel slag aggregates to be tested used in the above-mentioned Examples S1 to S4 were all produced by Steel Mill A. In S1, the natural sand in the concrete was completely replaced by the fine steel slag aggregate to be tested; in S2, the 5 - 10 mm (including 10 mm) natural gravel in the natural coarse aggregate of the concrete was completely replaced by the 5 - 10 mm (including 10 mm) coarse steel slag aggregate to be tested; in S3, the 10 - 20 mm (including 20 mm) natural gravel in the natural coarse aggregate of the concrete was completely replaced by the 10 - 20 mm (including 20 mm) coarse steel slag aggregate to be tested; in S4, the natural coarse aggregate of the concrete was completely replaced by the 5 - 20 mm (including 20 mm) coarse steel slag aggregate to be tested, and the natural fine aggregate of the concrete was completely replaced by the fine steel slag aggregate to be tested. The autoclave treatment conditions for the specimens were: autoclave steam pressure 1 MPa, autoclave time 4 h.

[0053] The different particle size ranges of the steel slag aggregates to be tested used in the above-mentioned Examples S5 to S7 were all produced by Steel Mill B. In S5, 90% of the natural sand in the concrete was replaced by the fine steel slag aggregate to be tested; in S6, 90% of the 5 - 20 mm (including 20 mm) natural gravel in the 5 - 20 mm (including 20 mm) natural coarse aggregate of the concrete was replaced by the 5 - 20 mm (including 20 mm) coarse steel slag aggregate to be tested; in S7, 90% of the natural coarse aggregate of the concrete was replaced by the 5 - 20 mm (including 20 mm) coarse steel slag aggregate to be tested, and 90% of the natural fine aggregate of the concrete was replaced by the fine steel slag aggregate to be tested. The autoclave treatment conditions for the specimens were: autoclave steam pressure 0.8 MPa, autoclave time 5.5 h.

[0054] The different particle size ranges of the steel slag aggregates to be tested used in the above-mentioned Examples S8 to S10 were all produced by Steel Mill C. In S8, 80% of the natural sand in the concrete was replaced by the fine steel slag aggregate to be tested; in S9, 80% of the 5 - 10 mm (including 10 mm) natural gravel in the 5 - 10 mm (including 10 mm) natural coarse aggregate of the concrete was replaced by the 5 - 10 mm (including 10 mm) coarse steel slag aggregate to be tested; in S10, 80% of the natural coarse aggregate of the concrete was replaced by the 5 - 20 mm (including 20 mm) coarse steel slag aggregate to be tested, and 80% of the natural fine aggregate of the concrete was replaced by the fine steel slag aggregate to be tested. The autoclave treatment conditions for the specimens were: autoclave steam pressure 1.2 MPa, autoclave time 3.5 h.

[0055] The following test results were obtained:

[0056] Table 2 Detection and Calculation Results of the Appearance and Compressive Strength of Concrete with Steel Slag Aggregates

[0057]

[0058]

[0059] From the mixture ratios and test results of Examples S1 to S10, it can be seen that for the steel slag aggregate concrete S1 to S4 prepared with the steel slag produced by Steel Plant A, the compressive strength loss does not exceed 1%, that is, the soundness of the fine aggregate of 0 to 5 mm (including 5 mm), the coarse aggregate of 5 to 10 mm (including 10 mm) and 10 to 20 mm (including 20 mm) is good. The three gradations of steel slag can be used alone as aggregates to prepare concrete, or can be used together to prepare the full-graded steel slag aggregate concrete.

[0060] Among the steel slag aggregate concrete S5 to S8 prepared with the steel slag produced by Steel Plant B, the compressive strength losses of S5 and S7 both exceed 20%, and S6 has no loss. It can be seen that the soundness of the steel slag sand produced by Steel Plant B is poor and it cannot be used as the fine aggregate of concrete to prepare concrete, while the soundness of the coarse aggregate of 5 to 20 mm (including 20 mm) is qualified.

[0061] Among the steel slag aggregate concrete S8 to S10 prepared with the steel slag produced by Steel Plant C, the compressive strength losses of S8 and S10 both exceed 20%, and the compressive strength loss of S9 does not exceed 5%. It can be seen that the soundness of the steel slag sand produced by Steel Plant C is poor, while the soundness of the coarse aggregate of 5 to 10 mm (including 10 mm) is qualified.

[0062] The above are only the embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the scope of the claims of the present invention.

Claims

1. A method for detecting the stability of steel slag based on steel slag aggregate concrete with a full range of particle sizes, characterized in that: The steps include: Step 1. Preparation of steel slag aggregate: crushing and screening the steel slag to be tested to obtain steel slag aggregate particles with different particle size ranges; Step 2. Preparation of concrete specimens and compressive strength test: the steel slag aggregates of different particle sizes obtained in step 1 are replaced by natural aggregates of corresponding particle sizes in a certain proportion and equal volume to prepare concrete mixed with steel slag aggregates, and the compressive strength test is performed after curing; Step 3. Autoclave treatment: autoclave the concrete test block mixed with steel slag aggregate, and then cool it naturally after completion; Step 4. Strength comparison: determine the compressive strength of the steel slag aggregate concrete test block after autoclaving, and calculate the compressive strength change rate of the steel slag aggregate concrete before and after autoclaving based on the compressive strength determined in step 4 and the compressive strength detected in step 2; Step 5. Evaluate the stability of steel slag. Perform a stability evaluation based on the compressive strength change rate in step 4 to determine the stability of the steel slag of the applicable particle size.

2. The method for detecting the steel slag stability of steel slag aggregate concrete based on a full-size range of steel slag aggregates as claimed in claim 1, characterized in that: In the step 4, the compressive strength of the autoclaved concrete block with steel slag aggregate is determined. If the concrete block with steel slag aggregate has obvious overall defects, or is completely broken and powdered from the inside to the outside, and its strength is completely lost, the compressive strength of the autoclaved concrete block is 0 MPa. If the appearance of the concrete specimen mixed with steel slag aggregate is intact or slightly damaged overall, the compressive strength test shall be carried out again.

3. The method for detecting the steel slag stability of steel slag aggregate concrete in a full range of particle sizes as claimed in claim 1, characterized in that: In the step 4, The compressive strength change rate is: Where: Pr——Change rate of compressive strength of specimen, %; P——compressive strength of specimen after autoclave, MPa; P0——compressive strength of specimen before autoclave, MPa; The compressive strength values ​​of the specimens before and after autoclaving were taken as the average value of three specimens.

4. The method for detecting the steel slag stability of steel slag aggregate concrete in a full-size range according to claim 1, characterized in that: In the step five, if the change rate of the compressive strength of the specimen is less than the rated ratio, the stability of the applied particle size steel slag is unqualified and cannot be used as aggregate to prepare concrete. If the change rate of the compressive strength of the specimen is greater than or equal to the rated ratio, the stability of the applied particle size steel slag is qualified, and the rated ratio is -18% to -20%.

5. The method for detecting the steel slag stability of steel slag aggregate concrete based on a full-size range of steel slag aggregates as claimed in claim 1, characterized in that: In the step 1, the steel slag aggregate particles of different particle size ranges include steel slag fine aggregate with a particle size of 0 to 5 mm (including 5 mm), steel slag coarse aggregate with a particle size of 5 to 10 mm (including 10 mm), and steel slag coarse aggregate with a particle size of 10 to 20 mm (including 20 mm).

6. A method for detecting the stability of steel slag based on full-size range steel slag aggregate concrete as claimed in claim 5, characterized in that: In the step 1, the crushing and screening operations are as follows: (1) The steel slag to be tested is crushed in two stages, namely coarse and fine crushing, by a jaw crusher. Before the secondary crushing, the steel slag is passed through a vibrating screen with a sieve size of 9.5 to 19.0 mm for a vibration time of 3 minutes to obtain steel slag coarse aggregate with a particle size of 10 to 20 mm (including 20 mm); (2) The material under the screen is crushed in three stages by a cone crusher. Before the crushing, it is passed through a vibrating screen with a mesh size of 4.75 to 9.5 mm for a vibration time of 3 minutes to obtain steel slag fine aggregate with a particle size of 0 to 5 mm (including 5 mm) and steel slag coarse aggregate with a particle size of 5 to 10 mm (including 10 mm).

7. The method for detecting the steel slag stability of steel slag aggregate concrete based on a full-size range of steel slag aggregates as claimed in claim 1, characterized in that: In the step 2, the strength grade of the concrete mixed with steel slag aggregate is C30, and the formula is: 325-375 parts of cement, 80-120 parts of fly ash, 780-1200 parts of fine aggregate, 930-1300 parts of coarse aggregate, 200-230 parts of water, and 0-13 parts of water reducer, wherein the weight ratio of 5-10 mm (including 10 mm) particles to 10-20 mm (including 20 mm) particles is 1:

2.

8. The method for detecting the steel slag stability of steel slag aggregate concrete in a full range of particle sizes as claimed in claim 1, characterized in that: In the step 2, the steel slag aggregate of a certain particle size is one or more of steel slag fine aggregate with a particle size of 0 to 5 mm (including 5 mm), steel slag coarse aggregate with a particle size of 5 to 10 mm (including 10 mm), and steel slag coarse aggregate with a particle size of 10 to 20 mm (including 20 mm); the proportion of steel slag aggregate in each particle size range replacing natural aggregate of the corresponding particle size is 80% to 100% (including 100%).

9. The method for detecting the steel slag stability of steel slag aggregate concrete based on a full-size range of steel slag aggregates as claimed in claim 1, characterized in that: In the step 2, the size of the concrete specimen mixed with steel slag aggregate is 100 mm×100 mm×100 mm, the curing temperature is 18-22° C., the curing humidity is ≥95% RH, and the curing time is 28 days.

10. The method for detecting the steel slag stability of steel slag aggregate concrete in a full range of particle sizes according to claim 1, characterized in that: In step 3, the autoclave steam pressure is 0.8-1.2 MPa, corresponding to a temperature of 159-188° C.; the autoclave time is 3.5-5.5 h, and the pressure change is divided into three stages: (1) During the pressure-raising stage, after the temperature is set according to the target pressure value, the kettle body begins to heat up, and the pressure in the kettle rises to the target value after 60 to 90 minutes; (2) Constant pressure stage: after reaching the target pressure, the autoclave is kept at a constant temperature for 2.5 to 3.5 hours, and the pressure inside the autoclave is constant; (3) Depressurization stage: After the set autoclave time is over, heating is stopped and the pressure in the autoclave drops below 0.1 MPa within 30 minutes.

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