Method for preparing roadbed material based on reclaimed water plant sludge

Abstract

The invention discloses a method for preparing a roadbed material based on reclaimed water plant sludge, the method comprises the step of curing and modifying the reclaimed water plant sludge, and the curing and modification specifically comprises the following steps: adding a curing agent and an alkali activator into the reclaimed water plant sludge; wherein the mixing mass ratio of the reclaimed water plant sludge to the curing agent to the alkali activator is (12-50): (40-80): (8-10). According to the method disclosed by the invention, on one hand, rapid resource utilization of the sludge (solid waste) of the reclaimed water plant can be realized, and on the other hand, the obtained roadbed material has high unconfined compressive strength and good water stability.

Description

Technical Field

[0001] The invention relates to a method for preparing roadbed materials based on sludge from a reclaimed water plant. Background Art

[0002] The existing sludge from recycled water plants is mostly disposed of by "sludge concentration + centrifugal dehydration + outsourcing". However, the moisture content of the dehydrated sludge is still relatively high, resulting in large volume and volume of transported sludge, and low transportation efficiency. In addition, the dehydrated sludge needs to be disposed of by a third-party general solid waste disposal unit, which takes a long time and has a high cost of about 220 yuan per ton. Moreover, if the sludge is not removed in time and piled up for a long time, it will cause corruption and odor, causing secondary pollution to the environment. At present, the resource utilization of sludge from recycled water plants is mainly concentrated in building materials such as cement and concrete, mainly by firing. The firing process will bring carbon emissions and cause environmental pollution.

[0003] When the sludge from the reclaimed water plant is directly used as a roadbed material, it has the problems of high water content, high organic matter content, too high liquid limit, and low unconfined compressive strength, which does not meet the requirements of the Highway Roadbed Design Code (JTG D30-2015) for roadbed filling, so it cannot be directly used as a roadbed material. The Highway Roadbed Design Code (JTG D30-2015) clearly stipulates that organic soil and fine-grained soil with a liquid limit greater than 50% shall not be directly used as embankment fill. When the soil moisture content is too high, the soil becomes viscous and difficult to compact, resulting in a decrease in compaction quality, affecting the stability and bearing capacity of the soil. Excessive organic matter content will weaken the binding force between soil particles, resulting in loose soil structure, prone to collapse and landslides. The liquid limit refers to the boundary moisture content between the plastic state and the flow state of clay soil, that is, the upper limit moisture content of the plastic state. When the water content of the soil increases to exceed the liquid limit, the soil changes from a plastic state to a flowing state, there is almost no bonding force between the soil particles, and the strength of the soil decreases. In addition, when the sludge from the recycled water plant is directly used as a roadbed material, its water stability is poor. If it is infiltrated by groundwater and surface water, it will become loose. Summary of the invention

[0004] Purpose of the invention: The purpose of the present invention is to provide a method for preparing roadbed materials based on recycled water plant sludge. On the one hand, this method can realize the rapid resource utilization of recycled water plant sludge (solid waste), and on the other hand, it can make the obtained roadbed material have high unconfined compressive strength and good water stability.

[0005] Technical solution: The method for preparing roadbed materials based on reclaimed water plant sludge described in the present invention includes solidifying and modifying the reclaimed water plant sludge, and the solidification and modification are specifically: adding a solidifying agent and an alkali activator to the reclaimed water plant sludge; wherein the mixing mass ratio of the reclaimed water plant sludge, the solidifying agent and the alkali activator is 12-50:40-80:8-10.

[0006] Wherein, the curing agent is at least one of fly ash, cement or gypsum; and the alkali activator is one of quicklime, cement clinker or slaked lime.

[0007] Wherein, the particle size of the quicklime is less than 75 microns; the particle size of the fly ash is 0.5 to 300 microns.

[0008] The quicklime is grade three quicklime, which can reduce the cost in terms of the technology of ensuring the performance of the roadbed material.

[0009] Among them, the mixing mass ratio of the reclaimed water plant sludge, the solidifying agent and the alkali activator is 44-45:48-50:8-10.

[0010] Wherein, the moisture content of the sludge in the reclaimed water plant is 50-70%.

[0011] When modifying the sludge from the reclaimed water plant, the present invention selects quicklime and fly ash as modifiers. After the fly ash and lime are mixed, with the participation of free water in the sludge, a water-hardening cementitious material can be generated, namely, hydrated calcium silicate and hydrated calcium aluminate containing crystal water. As the volcanic ash reaction proceeds, the cementitious material continuously transitions to a crystal body and is effectively cemented together to form an overall structure, thereby improving the compactness of the gel structure. This process can reduce the water content, organic matter and liquid limit of the sludge from the reclaimed water plant. In addition, the calcium hydroxide in the sludge from the reclaimed water plant can also exert a solidification effect in the soil, so that the prepared roadbed material has higher unconfined compressive strength and water stability, and the structure is not easily destroyed.

[0012] The roadbed material obtained by the above method is used in the construction of secondary trunk roads and branch roads.

[0013] During the application process, when the mixture is mixed in the process of forming the roadbed, water is added to the roadbed material to make the moisture content of the mixture the optimal moisture content ±1% to 2%. After the roadbed is formed, it is maintained. When the ambient temperature is above 20°C, the maintenance time is not less than 7 days; when the ambient temperature is between 5 and 20°C, the maintenance time is not less than 14 days.

[0014] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages:

[0015] (1) The present invention utilizes the sludge from the reclaimed water plant as raw material to prepare the roadbed material, thus realizing the resource utilization of the sludge from the reclaimed water plant. This not only solves the problems of sludge transportation and stacking, but also effectively reduces the consumption of traditional roadbed materials such as stone, pond residue, cement and lime, thus saving natural resources.

[0016] (3) The roadbed material prepared from the modified reclaimed water plant sludge of the present invention has low organic matter content, low liquid limit and high CBR, and specifically meets the following technical indicators: organic matter content (0.0% to 1.6%); liquid limit (39.6% to 44.4%); CBR (134.5% to 242.7%), all of which meet the technical requirements of the "Highway Roadbed Design Code" (JTG D30-2015) for the roadbed and embankment of secondary highways; and has good water stability (the unconfined compressive strength after immersion in water for 8 days does not decrease significantly), indicating that the strength of the roadbed material is less affected by the infiltration of groundwater and surface water.

[0017] (3) The roadbed material prepared from the modified reclaimed water plant sludge of the present invention has a high unconfined compressive strength and is not easily damaged. The present invention solves the problem that the existing reclaimed water plant sludge has a high water content, a high organic matter content, an excessively high liquid limit and a low unconfined compressive strength, and thus cannot be directly used as a roadbed material;

[0018] (4) In the field pilot test of the roadbed material prepared from the modified recycled water plant sludge of the present invention, the compaction degree meets the standard, and the deflection value and rebound modulus are better than the standard, reaching the following technical indicators: compaction degree ≥ 93%; the representative value of deflection is 87.50 (0.01mm); the rebound modulus value is 64Mpa, which is suitable for the roadbed of Class II and below highways, as well as low-grade roads such as villages and towns. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 The water stability test results of the roadbed material of Example 2 in the small test section test piece;

[0020] Figure 2 is a photograph of the roadbed material of Example 2;

[0021] Figure 3 An unconfined compressive strength specimen formed based on the roadbed material of Example 2;

[0022] Figure 4 The water stability test results of the roadbed material of Example 2 in the field test section are shown. DETAILED DESCRIPTION

[0023] In the present invention, the source of the sludge in the reclaimed water plant is the sludge produced after the circulating cooling water in the water company undergoes coagulation and sedimentation. The fly ash is provided by the thermal power plant.

[0024] Example 1

[0025] The invention discloses a method for preparing roadbed materials based on sludge from a reclaimed water plant, which specifically comprises the following steps: adding 40 parts by weight of fly ash and 10 parts by weight of quicklime to 50 parts by weight of sludge from the reclaimed water plant; and mixing and stirring the mixture to obtain the roadbed materials.

[0026] The moisture content of the above-mentioned roadbed material is 21.3%, the organic matter content is 1.3%, the liquid limit is 44.4%, the plasticity index is 10.9, the minimum bearing ratio (CBR) of the unconfined compressive specimen formed is 242.7%, and the 7d unconfined compressive strength is 2.0Mpa.

[0027] The moisture content is determined by the drying method specified in the "Highway Geotechnical Test Code" (JTG 3430-2020) T 0103-2019. The organic matter content is determined by the weight method specified in the "Urban Sewage Treatment Plant Sludge Inspection Method" (CJ / T221-2005). The limit moisture content (liquid limit and plastic limit) test is carried out in accordance with the provisions of T0118-2007 Liquid Limit and Plastic Limit Combined Determination Method in the "Highway Geotechnical Test Code" (JTG 3430-2020). The bearing ratio CBR test is carried out in accordance with the provisions of T 0134-2019 Bearing Ratio (CBR) Test in the "Highway Geotechnical Test Code" (JTG 3430-2020). The preparation of unconfined compressive strength test specimens is carried out in accordance with the provisions of the "Test Code for Inorganic Binder Stabilized Materials for Highway Engineering (Draft for Comments)".

[0028] Example 2

[0029] The present invention discloses a method for preparing roadbed materials based on sludge from a reclaimed water plant, which specifically comprises the following steps: adding 48 parts by weight of fly ash and 8 parts by weight of quicklime to 44 parts by weight of sludge from the reclaimed water plant; and mixing and stirring the mixture to obtain the roadbed materials.

[0030] The water content of the above-mentioned roadbed material is 21.9%, the organic matter content is 1.6%, the liquid limit is 40.7%, the plasticity index is 7.8, the minimum bearing ratio of the unconfined compressive specimen formed is 134.5%, and the 7d unconfined compressive strength is 1.8Mpa; the zinc leaching content is 0.12mg / L. The zinc leaching detection method of roadbed material is "Determination of 22 Metal Elements in Solid Waste by Inductively Coupled Plasma Emission Spectrometry" (HJ 781-2016).

[0031] The roadbed material of the present invention utilizes SiO2, Al2O3, Fe2O3, CaO, and MgO in quicklime, fly ash, and sludge to combine with OH- in water to generate Ca(OH)2, hydrated calcium silicate (CSH) gel, and hydrated magnesium silicate (MSH) gel. These substances have adsorption properties and can absorb heavy metal Zn in raw materials. 2+It has a good solidification effect (heavy metals in the raw materials will be dissolved through the penetration of rainwater during actual road use, causing harm to the surrounding environment), thereby effectively controlling the leaching of heavy metals in roadbed materials; the environmental safety performance meets the technical requirements for the utilization of solid waste building materials in the "Technical Guidelines for Pollution Prevention and Control of Solid Waste Recycling" (HJ1091-2020).

[0032] The unconfined compressive strength of the roadbed formed by the above roadbed material after 8 days of immersion is still 1.6 MPa, and the unconfined compressive strength does not decrease with the increase of the number of days of immersion, indicating that the roadbed material of Example 2 has good water stability. Figure 3 It is demonstrated that the unconfined compression specimen based on the roadbed material of Example 2 has good formability.

[0033] Example 3

[0034] The present invention discloses a method for preparing roadbed materials based on sludge from a reclaimed water plant, which specifically comprises the following steps: adding 64 parts by weight of fly ash and 8 parts by weight of quicklime to 28 parts by weight of sludge from the reclaimed water plant; and mixing and stirring the mixture to obtain the roadbed materials.

[0035] The moisture content of the above-mentioned roadbed material is 10.4%, the organic matter content is 0.8%, the liquid limit is 39.6%, the plasticity index is 10.8, the minimum bearing ratio of the unconfined compressive specimen formed is 177.8%, and the 7d unconfined compressive strength is 1.6Mpa.

[0036] Example 4

[0037] The invention discloses a method for preparing roadbed materials based on sludge from a reclaimed water plant, which specifically comprises the following steps: adding 80 parts by weight of fly ash and 8 parts by weight of quicklime to 12 parts by weight of sludge from the reclaimed water plant; and mixing and stirring the mixture to obtain the roadbed materials.

[0038] The moisture content of the above-mentioned roadbed material is 1.9%, the organic matter content is 0.1%, the liquid limit is 43.8%, the plasticity index is 7.7, the minimum bearing ratio of the unconfined compressive specimen formed is 208.5%, and the 7d unconfined compressive strength is 1.8Mpa.

[0039] Table 1 shows the performance of the sludge from the reclaimed water plant and the roadbed materials of Examples 1 to 4 prepared based on the sludge from the reclaimed water plant and the unconfined compressive test pieces formed therefrom.

[0040]

[0041]

[0042] Water stability testing is not a mandatory requirement for roadbed filling in the Highway Roadbed Design Specification (JTG D30-2015). Only Example 2 was selected for water stability testing.

[0043] The mechanical properties and environmental safety performance results of the unconfined compression test pieces formed based on the sludge from the reclaimed water plant and the roadbed materials of Examples 1 to 4 are shown in the table above. The liquid limit of the sludge from the reclaimed water plant is 51.6%, which does not meet the requirement that fine-grained soil with a liquid limit greater than 50% and a plasticity index greater than 26 cannot be directly used as embankment filler. The results also show that the organic matter content of the sludge is greater than 10%. It is an organic soil and does not meet the requirement that the organic matter content of the embankment material should be less than 10%. The unconfined compressive strength of the sludge from the reclaimed water plant is 0.5MPa, which does not meet the requirement that the roadbed filler should not be less than 0.6MPa in the "Highway Roadbed Design Code" (JTG D30-2015). Therefore, the sludge cannot be used directly as embankment filler, so the sludge needs to be solidified, and the unconfined compression test piece made of the sludge from the reclaimed water plant is loose when exposed to water. The results of Example 2, Example 3 and Example 4 show that when the fixed amount of quicklime added is 8%, as the amount of fly ash added increases, the moisture content and organic matter content gradually decrease, and the unconfined compressive strength and CBR gradually increase. It can be seen that when the fixed amount of quicklime added is 8%, the increase in the amount of fly ash added can make more fly ash excited by quicklime, and more fly ash will undergo a volcanic ash reaction. In Example 1, the amount of quicklime added is 10%, and its unconfined compressive strength and CBR are relatively high, indicating that the increase in the proportion of quicklime can fully dissolve the moisture in the sludge, increase the reaction temperature, and facilitate the reaction.

[0044] Example 5

[0045] The roadbed material of Example 2 was subjected to a pilot test under the same experimental conditions:

[0046] On the basis of indoor small-scale tests, a field pilot test of roadbed materials was carried out based on a regional test road project. The filling parts of the test roadbed materials were the roadbed and the embankment. On-site sampling was carried out on the solidified sludge filling roadbed to test whether the unconfined compressive strength met the road use requirements. The compaction degree and other related tests were carried out on the formed roadbed, and its road performance was analyzed and evaluated.

[0047] The scale of the field test site is 200m in length, 9m in width and 1.65m in thickness (200m of field pilot test).

[0048] The construction process of the on-site test section is as follows:

[0049] Construction preparation - Mixing and transportation of mixture - Paving, shaping and rolling - Roadbed maintenance - Inspection and acceptance.

[0050] It can be seen from Table 2 that the compaction degree of the roadbed material embankment meets the requirement of not less than 93% for expressways and trunk roads in the "Code for Construction and Quality Acceptance of Urban Road Engineering" (CJJ1-2008), and the roadbed meets the requirement of not less than 93% for secondary trunk roads.

[0051] Table 2 is a table showing the degree of compaction of the roadbed material in Example 5.

[0052]

[0053] Deflection value and rebound modulus test

[0054] 14 days after the completion of the above-mentioned roadbed construction, the deflection value and rebound modulus of the roadbed top surface were tested. The test results are shown in Table 3. The representative deflection value is 87.50 (0.01mm), which meets the design deflection value requirement of 179.1 (0.01mm). The rebound modulus value is 64MPa, which meets the requirement of not less than 30MPa for expressways and trunk roads in the "Criteria for Construction and Quality Acceptance of Urban Road Engineering" (CJJ1-2008).

[0055] Table 3 is the calculation table of deflection value

[0056]

[0057] Water stability test

[0058] The water stability test results of the field test section are as follows: Figure 4 As shown, the figure shows the relationship between the unconfined compressive strength and the number of days of immersion in water for the indoor test and outdoor test section samples. The results show that the unconfined compressive strength after immersion in water for 5 days and 8 days does not decrease with the increase of the number of days of immersion in water. As the immersion time of the roadbed material in the field test section increases, its unconfined compressive strength stabilizes between 1.7 and 1.9 MPa (the increase in strength may be due to the more complete reaction of sludge, fly ash and quicklime after immersion in water, which increases the strength of the roadbed material). It shows that the volcanic ash reaction and carbonation produced in the roadbed material play a key role in the water stability of the roadbed material. Therefore, the water stability of the roadbed material in Example 5 is good.

[0059] The cost of entrusting a third party to dispose of the sludge from the reclaimed water plant is 220 yuan / ton, and the actual construction cost of using it as roadbed material is about 86.9 yuan / m 3 The construction cost of using mountain gravel as roadbed material is about 144 yuan / m 3 The method of the present invention can effectively reduce the treatment cost of sludge in a reclaimed water plant and the preparation cost of roadbed materials.

[0060] Comparative Example 1

[0061] A method for preparing roadbed materials based on reclaimed water plant sludge, specifically comprising: adding 22.2 parts by weight of fly ash, 10 parts by weight of quicklime, 5.1 parts by weight of cement and 0.2 parts by weight of gypsum to 62.5 parts by weight of reclaimed water plant sludge; mixing and stirring evenly to obtain roadbed materials.

[0062] The moisture content of the above-mentioned roadbed material is 45.4%, the organic matter content is 3.3%, the liquid limit is 47.8%, the plasticity index is 13.7, the minimum bearing ratio of the unconfined compressive specimen formed is 111.4%, and the 7d unconfined compressive strength is ≥2.5Mpa (exceeding the maximum range of the instrument).

[0063] Comparative Example 2

[0064] A method for preparing roadbed material based on recycled water plant sludge, specifically: adding 33.0 parts by weight of fly ash, 14.6 parts by weight of quicklime, 3.3 parts by weight of cement, 0.3 parts by weight of gypsum, 0.5 parts by weight of water plant sludge 1 and 23 parts by weight of water plant sludge 2 to 25.3 parts by weight of recycled water plant sludge; mixing and stirring evenly to obtain roadbed material. Wherein, water plant sludge 1 and water plant sludge 2 are both produced by concentrating and dehydrating wastewater discharged from river water through a high-density clarifier and a V-type filter.

[0065] The moisture content of the above-mentioned roadbed material is 29.4%, the organic matter content is 4.0%, the liquid limit is 40.1%, the plasticity index is 12.6, the minimum bearing ratio of the unconfined compressive specimen formed is 114.3%, and the 7d unconfined compressive strength is ≥2.5Mpa (exceeding the maximum range of the instrument).

[0066] By comparing Comparative Examples 1 to 2 with Example 2, the roadbed material of the present invention has lower organic matter and liquid limit, and higher minimum bearing ratio.

Claims

1. A method for preparing roadbed materials based on sludge from a reclaimed water plant, characterized in that: The method comprises solidifying and modifying the sludge from the reclaimed water plant, wherein the solidifying and modifying comprises: adding a solidifying agent and an alkali activator to the sludge from the reclaimed water plant; wherein the mixing mass ratio of the sludge from the reclaimed water plant, the solidifying agent and the alkali activator is 12-50:40-80:8-10.

2. The method for preparing roadbed materials based on sludge from a reclaimed water plant according to claim 1, characterized in that: The curing agent is at least one of fly ash, cement or gypsum.

3. The method for preparing roadbed materials based on recycled water plant sludge according to claim 1, characterized in that: The alkali activator is one of quicklime, cement clinker or slaked lime.

4. The method for preparing roadbed materials based on sludge from a reclaimed water plant according to claim 3, characterized in that: The quicklime is grade 3 quicklime.

5. The method for preparing roadbed material based on sludge from a reclaimed water plant according to claim 2 or 3, characterized in that: The particle size of the quicklime is less than 75 microns; the particle size of the fly ash is 0.5 to 300 microns.

6. The method for preparing roadbed materials based on sludge from a reclaimed water plant according to claim 1, characterized in that: The mixing mass ratio of the sludge, solidifying agent and alkali activator in the reclaimed water plant is 44-45:48-50:8-10.

7. The method for preparing roadbed materials based on recycled water plant sludge according to claim 1, characterized in that: The water content of the sludge in the reclaimed water plant is 50-70%.

8. Use of the roadbed material obtained by the method according to claim 1 in the construction of secondary trunk roads and branch roads.

9. The use according to claim 8, characterized in that: When the mixture is mixed during the process of forming the roadbed, water is added to the roadbed material to make the moisture content of the mixture within the optimum moisture content ±1% to 2%.

10. The use according to claim 8, characterized in that: After the roadbed is formed, maintenance shall be carried out. When the ambient temperature is above 20℃, the curing time shall be no less than 7 days; when the ambient temperature is between 5 and 20℃, the curing time shall be no less than 14 days.

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