A design method of vvtm of cement stabilized solid waste recycled sand powder mixed with waste concrete recycled aggregate

Abstract

This invention discloses a design method for cement-stabilized solid waste recycled sand powder mixed with recycled aggregates from waste concrete. The method employs the Vertical Vibration Method (VVTM) and includes steps such as raw material inspection, aggregate gradation design, determination of optimal brick powder content, determination of optimal moisture content and maximum dry density, and determination of cement dosage. Data from the embodiments show that the strength of the cement-stabilized solid waste recycled sand powder mixed with recycled aggregates from waste concrete designed according to this invention can meet the design requirements of roadbeds of various grades. It can replace traditional backfill slag for roadbeds, realizing the transformation of construction waste into valuable resources and contributing to the ecological, environmentally friendly, and circular development of highway construction.

Description

Technical Field

[0001] This invention belongs to the field of solid waste recycled sand powder application in road water-stabilized layer technology, specifically involving a VVTM design method for cement-stabilized solid waste recycled sand powder mixed with waste concrete recycled aggregate. Background Technology

[0002] In recent years, with the rapid advancement of national development and urbanization, a large number of buildings are nearing the end of their service life, and the number of new construction, renovation, expansion, and decoration projects remains high, leading to a continuous and substantial increase in the amount of various types of construction solid waste, amounting to hundreds of millions of tons. Currently, construction solid waste accounts for 30% to 40% of the total urban solid waste. At the same time, the contradiction between sustainable, green, and high-quality development in the road transportation sector and the increasing shortage of sand and gravel materials is becoming increasingly prominent. my country's annual demand for sand and gravel aggregates in highway construction exceeds 10 billion tons, while the over-exploitation of natural aggregates has caused a series of ecological and environmental problems such as mountain destruction and soil erosion. In addition, the reserves of high-quality natural aggregates are becoming increasingly depleted. It is foreseeable that in the near future, the raw materials such as soil and stone required for highway construction will face a serious shortage of supply, and some areas have even experienced a situation where "sand is hard to find."

[0003] Currently, the following problems still exist in the use of cement-stabilized solid waste recycled sand powder in highway engineering: (1) The composition of recycled sand powder is complex and variable, usually containing bricks, concrete and ceramic tiles, etc., and the proportions of these components vary greatly, resulting in extremely unstable engineering quality; (2) Article 6.1.4 of JTG / T 2321-2021 "Technical Specification for the Utilization of Construction Waste in Highway Engineering" stipulates that "the blending rate of recycled aggregate in the base course shall not exceed 50%, and the blending rate in the subbase course shall not exceed 80%", and Article 6.1.6 states that "the largest material (20-30mm) should preferably use natural aggregate to form a high-strength skeleton". Obviously, the consideration of limiting the amount of recycled aggregate in the specification stems from the impact of the large variation in the composition of recycled aggregate on the quality of the project. However, the large-scale application of waste concrete recycled aggregates is inevitably affected by the stable quality of the recycled aggregates. (3) At present, the static pressing method is generally used to prepare specimens. However, the crushing value of waste concrete recycled aggregates is large. During the preparation of specimens by the static pressing method, the recycled coarse aggregates are easily crushed, which does not match the actual site of the project. As a result, the prepared specimens are difficult to reflect the actual project. Moreover, the adaptability of traditional design methods (test methods, aggregate gradation and strength standards) has not been effectively verified. (4) At present, the utilization rate of solid waste recycled sand powder in engineering practice is not high. JTG / T 2321-2021 does not involve the impact of waste concrete recycled aggregates on the road performance of solid waste recycled sand powder. However, the research found that solid waste recycled sand powder has the micro-aggregate filling effect and pozzolanic effect, and has strong activity. The composition of waste concrete recycled aggregates is stable. The combination of the two can improve the large variability of solid waste recycled sand powder composition and improve the problem of unstable construction. Summary of the Invention

[0004] The purpose of this invention is to provide a VVTM design method for cement-stabilized solid waste recycled sand powder mixed with recycled aggregates from waste concrete, to meet the design requirements of roadbeds of various grades, to replace the traditional backfill slag for roadbeds, to realize the transformation of construction waste into treasure, and to help the ecological, environmentally friendly and circular development of highway construction.

[0005] To achieve the above objectives, the technical solution adopted by this invention is: a VVTM design method for cement-stabilized solid waste recycled sand powder mixed with recycled aggregates from waste concrete, specifically implemented according to the following steps: Step 1, Inspect raw materials: Select representative samples from the materials actually used in the project for inspection, including cement, recycled coarse aggregate, recycled fine aggregate, and recycled sand and powder from solid waste; Step 2: Determine the optimal amount of recycled aggregate from waste concrete: The particle size of the recycled fine aggregate from waste concrete should be less than 4.75 mm, and the particle size of the recycled coarse aggregate should be between 4.75 mm and 10 mm. The recycled fine aggregate is weighed according to different proportions of the total mass of the mixture; the recycled coarse aggregate is weighed according to different proportions of the total mass of the mixture, and is used to replace the recycled sand powder in the mixture. VVTM molded specimens are used and their 7-day unconfined compressive strength is tested. The relationship curve between the representative value of the 7-day unconfined compressive strength and the amount of recycled aggregate is plotted. The amount of recycled aggregate corresponding to the highest strength point is the amount of recycled aggregate. Finally, the proportion of each aggregate specification is determined. Step 3, determine the maximum dry density and optimum moisture content: VVTM is used to determine the maximum dry density and optimum moisture content of mixtures with different cement dosages. The cement dosage for the subgrade is 1.0%, 1.5%, 2.0%, 2.5%, and 3.0% water. Step 4, determine cement dosage: Use VVTM to form mixture specimens with different cement dosages. After standard curing for 7 days, test the unconfined compressive strength of the mixture, plot the relationship curve between the representative value of the 7-day unconfined compressive strength and the cement dosage, and determine the cement dosage according to the strength design standard.

[0006] The technical solution of the present invention also has the following characteristics: As a preferred technical solution of the present invention, in step 1, the recycled coarse aggregate and recycled fine aggregate are obtained by crushing and screening waste concrete, and the recycled solid waste sand powder is the powder and aggregate produced by the process of removing impurities, crushing and screening recycled materials. The particle size of the recycled coarse aggregate is 4.75~10mm, the nominal maximum particle size of the recycled fine aggregate is ≤4.75mm, and the particle size of the recycled solid waste sand powder is 0~10mm.

[0007] As a preferred embodiment of the present invention, in step 1, the crushing value of the recycled coarse aggregate is ≤35%, and the sand equivalent of the recycled fine aggregate is ≥40%.

[0008] As a preferred technical solution of the present invention, in step 2, the VVTM specimen has a diameter of 150mm and a height of 150mm, and the VVTM test parameters are: working frequency 30 Hz±1 Hz, static eccentric torque 0.215kN·m±0.005kN·m, upper vehicle mass 120 kg±1 kg, lower vehicle mass 180 kg±1 kg, and vibration time 120s.

[0009] As a preferred embodiment of the present invention, the method for determining the maximum dry density and optimum moisture content in step 3 is as follows: Step 4.1: Take one part of cement and one part of dried sample, mix them evenly to obtain a dry mixture. m k Add mass of m k × w i Add water, mix well, and you will get 1 part of wet mixture. w i It ranges from 6% to 12%; Step 4.2: Use VVTM to form a cylindrical specimen with a diameter of 150 mm and a height of 120 mm, and calculate the dry density and moisture content of the specimen; Step 4.3: After obtaining 3 to 5 sets of valid data from the experiment, plot the relationship curve between dry density and moisture content with the mixing moisture content as the abscissa and dry density as the ordinate. The abscissa and ordinate of the peak value of the curve are the optimum moisture content and the maximum dry density, respectively. The dry density of the sample should be calculated according to formula (1): (1) In the formula: ρ di —Dry density of the sample during the i-th test, in g / cm³ 3 ; m di —The mass of the sample during the i-th test, in grams; h i —The height of the sample during the i-th test, in cm; w i —Moisture content of the sample during the i-th test, in units of %.

[0010] As a preferred technical solution of the present invention, in step 4, the strength design standard for recycled aggregate cement stabilized solid waste recycled sand powder mixed with waste concrete is as follows: 7-day unconfined compressive strength of base course ≥ 4.0 MPa, 7-day unconfined compressive strength of subbase course ≥ 3.0 MPa, and CBR of subgrade ≥ 20%.

[0011] The beneficial effects of this invention are as follows: The VVTM design method for cement-stabilized recycled sand powder with recycled aggregate from waste concrete proposed in this invention can quickly and accurately determine the optimal amount of recycled aggregate from waste concrete, the optimal moisture content, the maximum dry density, and the cement dosage. The resulting cement-stabilized recycled sand powder with recycled aggregate from waste concrete has good road performance and can replace traditional backfill materials for roadbed structures. Attached Figure Description

[0012] Figure 1 This is a graph showing the relationship between the representative value of the 7-day unconfined compressive strength and the brick powder content in Example 1 of the present invention.

[0013] Figure 2 This is a graph showing the relationship between the representative value of the 7-day unconfined compressive strength and the cement dosage in Example 1 of the present invention.

[0014] Figure 3 This is the vertical vibration meter used in VVTM in Embodiment 1 of the present invention.

[0015] Figure 4 This is a photograph of the VVTM specimen in Example 1 of the present invention. Detailed Implementation

[0016] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0017] Example 1 The present invention discloses a VVTM design method for recycled aggregates from waste concrete and recycled sand powder from cement-stabilized solid waste, which is implemented according to the following steps: Step 1, raw material inspection.

[0018] Representative samples were selected from the materials actually used in the project for testing, including cement, recycled coarse aggregate, recycled fine aggregate, and recycled sand and powder from solid waste.

[0019] The cement used has a strength grade of 42.5, which complies with the relevant provisions of the current "General Portland Cement" (GB 175).

[0020] The technical specifications of the recycled aggregates used are shown in Table 1, which comply with the relevant provisions of the current "Technical Specification for the Utilization of Construction Waste in Highway Engineering" (JTG / T 2321-2021).

[0021] Table 1 shows the technical specifications for recycled aggregates. Step 2: Determine the optimal brick powder content.

[0022] Weigh out recycled coarse aggregate at different proportions (30%, 35%, 40%, 45%, and 50% of the total mass of the mixture) to replace recycled sand powder from solid waste in the mixture. Use VVTM to form specimens and test their 7-day unconfined compressive strength. Plot the relationship curve between the representative value of the 7-day unconfined compressive strength and the amount of brick powder. The amount of recycled coarse aggregate corresponding to the highest strength point is the optimal amount of recycled coarse aggregate.

[0023] like Figure 1 As shown, when the content of recycled coarse aggregate is 40%, the 7-day unconfined compressive strength of the mixture is the largest. The optimal brick powder content is determined to be 40%. At this time, the ratio of aggregates of various sizes in the mixture is: 5~10mm waste concrete recycled aggregate: 0~10mm brick powder = 4:6.

[0024] Step 3: Determine the maximum dry density and optimum moisture content.

[0025] Before the test, aggregates of various specifications were dried in an oven to constant weight. Five to six samples of the dried aggregates were then prepared according to the required proportions. The mass of each sample was... m k For a weight of 4800g~5500g, prepare 5~6 parts of cement, each part weighing [weight missing]. m k × P s , P s This is the preset cement dosage.

[0026] Prepare samples according to the predetermined moisture content. Take one part of cement and one part of dried sample, mix them evenly to obtain a dry mixture, and add a mass of... m k ×(1+ P s )× w i After mixing the water thoroughly, one part of wet mixture is obtained. Generally, w i It ranges from 6% to 12%.

[0027] Place the spacer block inside the mold, ensuring the bottom is level. Place a circular filter paper on the spacer block. Then, fill the mold with the well-mixed wet mixture using the quartering method, tamping it down along the mold wall at least six times, and record the mass of the wet mixture filled. m s After fixing the test mold on the base of the vertical vibratory compactor, lower the vibratory hammer and bring it into contact with the material to be compacted. Set the vibration frequency to 30 Hz and the vibration time to 120 s, and then perform vibration compaction.

[0028] After vibration compaction, remove the mold, push the sample out using a demolding device, and weigh it, recording the weight as follows: mdi The height of the test sample was measured in four symmetrical directions using vernier calipers, and the average value was taken as the sample height. h i If the sample height exceeds the requirement of 120 mm ± 5.0 mm, it should be discarded, and the requirements should be adjusted accordingly based on the sample height. m s The sample was then re-prepared.

[0029] Plot a curve showing the relationship between dry density and moisture content, with the mixing moisture content on the x-axis and dry density on the y-axis. The x-axis and y-axis of the peak value of the curve are the optimum moisture content and the maximum dry density, respectively.

[0030] The maximum dry density and optimum moisture content of recycled aggregates from waste concrete and cement-stabilized solid waste recycled sand powder are shown in Table 2.

[0031] Table 2 shows the maximum dry density and optimum moisture content of recycled aggregates from waste concrete, cement-stabilized solid waste, and recycled sand powder. Step 4: Determine the cement dosage.

[0032] VVTM was used to form mixture specimens with different cement dosages. After standard curing for 7 days, the unconfined compressive strength of the mixture was tested. The relationship curve between the representative value of the 7-day unconfined compressive strength and the cement dosage was plotted. The cement dosage was determined according to the strength design standard.

[0033] The 7-day unconfined compressive strength test results of recycled aggregates from waste concrete and cement-stabilized solid waste recycled sand powder are shown in Table 3. The average compressive strength, C V The deviation coefficient, R c0.95 This represents the compressive strength. Strength testing was conducted according to T 0805-1994 in JTG E51-2009.

[0034] Table 3 shows the 7-day unconfined compressive strength and representative values. Based on the data in Table 3, the relationship between recycled aggregates in waste-admixed concrete, cement-stabilized solid waste, recycled sand powder, and cement dosage is plotted. Figure 2 .

[0035] Depend on Figure 2 It is known that the minimum cement dosage corresponding to a base layer design strength of 7.0 MPa is 1.5%. Considering factors such as on-site mixing and construction technology, it is recommended that the cement dosage be 2.5% for the sake of safety.

[0036] VVTM uses a vertical vibration meter such as Figure 3As shown in the photos, the specimens are made from recycled aggregates from waste concrete, cement-stabilized solid waste, and recycled sand powder. Figure 4 As shown.

Claims

1. A VVTM design method for cement-stabilized solid waste recycled sand powder mixed with recycled aggregates from waste concrete, characterized in that, The specific steps are as follows: Step 1, Inspect raw materials: Select representative samples from the materials actually used in the project for inspection, including cement, recycled coarse aggregate, recycled fine aggregate, and recycled sand and powder from solid waste; Step 2: Determine the optimal amount of recycled aggregate from waste concrete: The particle size of the recycled fine aggregate from waste concrete should be less than 4.75 mm, and the particle size of the recycled coarse aggregate should be between 4.75 mm and 10 mm. The recycled fine aggregate is weighed according to different proportions of the total mass of the mixture; the recycled coarse aggregate is weighed according to different proportions of the total mass of the mixture, and is used to replace the recycled sand powder in the mixture. VVTM molded specimens are used and their 7-day unconfined compressive strength is tested. The relationship curve between the representative value of the 7-day unconfined compressive strength and the amount of recycled aggregate is plotted. The amount of recycled aggregate corresponding to the highest strength point is the amount of recycled aggregate. Finally, the proportion of each aggregate specification is determined. Step 3, determine the maximum dry density and optimum moisture content: VVTM is used to determine the maximum dry density and optimum moisture content of mixtures with different cement dosages. The cement dosage for the subgrade is 1.0%, 1.5%, 2.0%, 2.5%, and 3.0% water. Step 4, determine cement dosage: Use VVTM to form mixture specimens with different cement dosages. After standard curing for 7 days, test the unconfined compressive strength of the mixture, plot the relationship curve between the representative value of the 7-day unconfined compressive strength and the cement dosage, and determine the cement dosage according to the strength design standard.

2. The VVTM design method for cement-stabilized solid waste recycled sand powder mixed with recycled aggregates from waste concrete according to claim 1, characterized in that, In step 1, the recycled coarse aggregate and recycled fine aggregate are obtained from waste concrete through crushing and screening. The recycled solid waste sand powder is the powder and aggregate produced during the process of removing impurities, crushing, and screening the recycled material. The particle size of the recycled coarse aggregate is 4.75~10mm, the nominal maximum particle size of the recycled fine aggregate is ≤4.75mm, and the particle size of the recycled solid waste sand powder is 0~10mm.

3. The VVTM design method for cement-stabilized solid waste recycled sand powder mixed with recycled aggregates from waste concrete according to claim 2, characterized in that, In step 1, the crushing value of recycled coarse aggregate is ≤35%, and the sand equivalent of recycled fine aggregate is ≥40%.

4. The VVTM design method for cement-stabilized solid waste recycled sand powder mixed with recycled aggregates from waste concrete according to claim 3, characterized in that, In step 2, the VVTM specimen has a diameter of 150 mm and a height of 150 mm. The VVTM test parameters are: operating frequency 30 Hz ± 1 Hz, static eccentric torque 0.215 kN·m ± 0.005 kN·m, upper vehicle mass 120 kg ± 1 kg, lower vehicle mass 180 kg ± 1 kg, and vibration time 120 s.

5. The VVTM design method for cement-stabilized solid waste recycled sand powder mixed with recycled aggregates from waste concrete according to claim 4, characterized in that, In step 3, the method for determining the maximum dry density and optimum moisture content is as follows: Step 4.1: Take one part of cement and one part of dried sample, mix them evenly to obtain a dry mixture. m k Add mass of m k × w i Add water, mix well, and you will get 1 part of wet mixture. w i It ranges from 6% to 12%; Step 4.2: Use VVTM to form a cylindrical specimen with a diameter of 150 mm and a height of 120 mm, and calculate the dry density and moisture content of the specimen; Step 4.3: After obtaining 3 to 5 sets of valid data from the experiment, plot the relationship curve between dry density and moisture content with the mixing moisture content as the abscissa and dry density as the ordinate. The abscissa and ordinate of the peak value of the curve are the optimum moisture content and the maximum dry density, respectively. The dry density of the sample should be calculated according to formula (1): （1） In the formula: ρ di —Dry density of the sample during the i-th test, in g / cm³ 3 ; m di —The mass of the sample during the i-th test, in grams; h i —The height of the sample during the i-th test, in cm; w i —Moisture content of the sample during the i-th test, in units of %.

6. The VVTM design method for cement-stabilized solid waste recycled sand powder mixed with recycled aggregates from waste concrete according to claim 5, characterized in that, In step 4, the specific design standard for the strength of recycled aggregate cement stabilized solid waste recycled sand powder mixed with waste concrete is as follows: 7-day unconfined compressive strength of base course ≥ 4.0 MPa, 7-day unconfined compressive strength of subbase course ≥ 3.0 MPa, and CBR of subgrade ≥ 20%.

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