CN115613595A

CN115613595A - Application of waste concrete as backfill material and backfill construction method thereof

Info

Publication number: CN115613595A
Application number: CN202211416205.9A
Authority: CN
Inventors: 汤泽华; 杨旭; 贾岳伟; 代学然; 李军; 何强; 王康; 张智强; 杜兴
Original assignee: China Railway No 2 Engineering Group Co Ltd; Shenzhen China Railway Second Bureau Engineering Co Ltd
Current assignee: China Railway No 2 Engineering Group Co Ltd; Shenzhen China Railway Second Bureau Engineering Co Ltd
Priority date: 2022-11-12
Filing date: 2022-11-12
Publication date: 2023-01-17

Abstract

The invention relates to an application of waste concrete as backfill material and a backfill construction method thereof, belonging to the technical field of waste concrete utilization.A blocky waste concrete is used as backfill material, waste concrete blocks are backfilled, and then regenerated cement foam slurry is injected into a concrete block layer in a manner of embedding and grouting by a conduit, so that the concrete blocks and the regenerated cement foam slurry are fully gelled and combined to form a semi-rigid backfill system, and the load or vibration of a main body structure can be transmitted to the backfill layer by utilizing the buffering and energy absorption effects of the regenerated cement foam slurry with density; and the waste concrete blocks are cemented and wrapped by the recycled cement foam slurry, so that the load of the main body structure is greatly reduced, and the effects of shock resistance and sinking resistance are achieved.

Description

Application of waste concrete as backfill material and backfill construction method thereof

Technical Field

The invention belongs to the technical field of waste concrete utilization, and particularly relates to application of waste concrete as a backfill material and a backfill construction method thereof.

Background

In the process of building urban underground spaces and roads, in order to ensure the excavation/tunneling progress, the safety of constructors, the arrangement of construction machinery and reduce the influence on the passing of surrounding people and vehicles, temporary support enclosing structures including temporary support beams, columns, retaining walls and the like need to be built in the bright/dark construction space. The temporary support enclosure structure is mostly of a reinforced concrete structure, and the strength grade of concrete is the same as or similar to that of the permanent support enclosure structure. When the engineering main structure is formally built, the temporary support enclosure structure needs to be cut and dismantled step by step in advance, and after the cut and dismantled reinforced concrete is roughly broken and separated into reinforcing steel bars on site, the rest inorganic non-metal waste is treated according to the common construction waste, or is transported to landfill or further processed for regeneration and recycling. Different from the construction waste generated by the conventional civil building demolition, the inorganic non-metallic waste generated by the temporary support enclosure demolition is mainly made of waste concrete, and basically no brick/tile/building block, wallboard, glass, ceramic and the like exist.

At present, the waste concrete after the temporary support enclosure is dismantled is further crushed, modified and ground to obtain regenerated coarse/fine aggregate or regenerated micro powder. However, in the crushing and grinding processes, the integrity of the waste concrete structure is further broken, the original aggregate and the cement mortar are also damaged, and a large amount of surface, microcrack or other defects are generated and exposed, so that the mechanical property of the regenerated material is greatly reduced, and the water absorption rate is greatly improved; and because the volume ratio of the bone substance to the mass in the concrete is higher, the regenerated micro powder has more hydration inertia and lower activity. Therefore, the recycled aggregate and the recycled micro powder of the waste concrete have the problems of complex recycling processing technology, high processing and modifying cost, low quality performance and difficult large-dosage application at present.

On the other hand, the underground space and the road construction process also relate to the backfill of an upper cushion layer with huge engineering quantity, the replacement and filling of a foundation, the filling of a excavated area, the backfill of a culvert, a fertilizer trough and the like. The conventional method for the engineering backfilling is to stabilize sand/broken stone/soil by cement or adopt cement mortar with high fluidity, wherein, the coarse and fine aggregates such as sand, broken stone and the like are mostly new aggregates. In consideration of the requirements of load, vibration transmission reduction and the like of the foundation and the main structure, a semi-rigid backfill system with relatively low compressive strength or density is generally selected for engineering backfill so as to reduce the settlement effect of self weight on the foundation and buffer the vibration from the upper part or the main structure. Also, therefore, recycled aggregate could theoretically be used, but in view of the quality performance deficiencies of recycled aggregate, it is generally not more than 30% in replacement of virgin aggregate in backfill engineering. On one hand, the backfill engineering quantity is huge, the aggregate demand is large, the natural resource consumption is large, and the cost is high; on the other hand, the processing technology of the recycled aggregate is complex, the cost is higher than that of the traditional aggregate, but the quality performance of the recycled aggregate has great defects, the recycled aggregate is used for backfilling projects with less consumption, and the whole manufacturing cost is higher than that of the traditional system for ensuring the project quality. This results in that the treatment and disposal of the used concrete of the temporary support enclosure structure are still mainly carried out, and a large amount of fresh aggregate is still purchased for the backfill of the engineering.

Disclosure of Invention

In order to overcome the problems in the background art, the invention provides an application of waste concrete as a backfill material and a backfill construction method thereof, wherein waste concrete blocks are used as the backfill material, the structural integrity of the waste concrete can be reserved, the defect generated by the crushing treatment of the existing waste concrete is avoided, when in backfill, the waste concrete blocks are backfilled firstly, and then regenerated cement foam slurry is injected into a concrete block layer in a manner of embedding a conduit for grouting, so that the concrete blocks and the regenerated cement foam slurry are fully gelatinized and combined, and a semi-rigid backfill system with the compression strength of a backfill layer larger than 1.2 MPa is formed, so that the utilization of the waste concrete is realized while the original structure and mechanical property of the waste concrete are reserved, and the requirement of engineering backfill quality is also met.

Accordingly, a first object of the present invention is to provide an application of a waste concrete in a block form as a backfill material, and a second object of the present invention is to provide a construction method for engineering backfill of a waste concrete in a block form.

Wherein, when the waste concrete is used as the callback material, the maximum radial dimension is larger than 300mm.

The backfill construction method using the waste concrete as a backfill material comprises the following steps:

(1) Backfilling: and accumulating the waste concrete blocks in the backfilling space.

(2) Burying and pouring a conduit: and embedding a slurry pouring conduit in the waste concrete block accumulation layer.

(3) Pouring: and pumping and pouring the regenerated cement foam slurry through the pouring guide pipe until the surface of the accumulated waste concrete blocks is discharged and covers the accumulated layer of the waste concrete blocks.

Further, the maximum radial dimension of the concrete block is greater than 300mm; the single stacking thickness of the waste concrete blocks is more than 0.8m and less than 3 m; pouring the slurry on the surface of the stacked waste concrete blocks, and covering the slurry on the top by about 10 to 20 mm.

Further, the method also comprises step (4) of film coating and curing, specifically, the film coating and curing lasts for more than 7 days.

Further, repeating the steps (1) to (4) until the backfill height requirement is met.

Furthermore, the waste concrete blocks account for 50-60% and the regenerated cement foam slurry accounts for 40-50% by volume percentage.

Further, the recycled cement foam slurry comprises cement, a foaming agent, recycled sand powder, a mineral admixture and water.

Further, the distance between the outlet at the lower part of the pouring guide pipe and the backfill bottom is not more than 300mm, and the outlet pressure of the pouring guide pipe is 0.8 to 1.2 MPa.

Further, the mass ratio of cement to regenerated sand powder in the regenerated cement foam slurry is 2:1.

further, the slump of the recycled cement foam slurry is 280-320 mm, the expansion degree is 720-750 mm, and the wet density is not more than 630 kg/m.

The invention has the beneficial effects that:

(1) According to the invention, the waste concrete is directly sieved into large blocks and spread in the backfill space, further crushing, grinding or modification is not needed, the original performance of the waste concrete is retained, the treatment is simpler, and the cost is lower.

(2) The backfill construction of the invention does not need any fresh aggregate, and the main raw material is waste material generated in the engineering field, thereby being beneficial to ensuring the engineering progress, reducing the engineering consumption and reducing the waste discharge.

(3) In the invention, a small part of fine particles with the particle size of less than 5mm generated in the process of cutting, dismantling and crushing the recycled steel bars of the temporary support enclosure structure concrete on site are utilized in the regenerated cement foam slurry, thereby not only reducing the cement consumption of the regenerated cement foam slurry, but also further consuming the waste concrete fine particles.

(4) The regenerated cement foam slurry can adopt the excavated waste soil, residue soil and dust which are generated in engineering sites and have the greatest resource utilization difficulty as mineral additives.

(5) The invention changes the traditional backfilling mode, adopts the mode of paving the waste concrete blocks with the percentage of at least 50 vol, and then adopts the mode of pumping and injecting the regenerated cement foam, thereby saving the stirring engineering quantity with the percentage of at least 50 vol.

(6) The wet density of the regenerated cement foam slurry adopted by the invention is lower and far lower than that of waste concrete, so that the waste concrete blocks cannot float upwards, the pipe is adopted to penetrate into the waste concrete blocks for pumping and pouring, the bottom layer pouring plumpness is ensured by virtue of the pump pressure, and the low-density regenerated cement foam slurry is easy to fill gaps from bottom to top by virtue of the advantage of light self weight.

(7) In the invention, the waste concrete blocks are cemented in the setting and hardening regenerated cement foam slurry to form a semi-rigid backfill system. On one hand, the load or vibration of the main body structure can be transmitted to the backfill layer by means of the buffering and energy absorption effects of the low-density regenerated cement foam slurry; on the other hand, the waste concrete blocks are cemented and wrapped by the recycled cement foam slurry, and the load of the waste concrete blocks on the main body structure is greatly reduced.

Drawings

FIG. 1 shows a backfill layer after casting according to the present invention;

FIG. 2 is a cross-section of a backfill layer cast in accordance with the present invention;

FIG. 3 shows a backfill layer poured by the construction method of comparative example 1;

FIG. 4 is a cross-section of a backfill layer cast according to the construction method of comparative example 1.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention clearer, the technical solutions of the present invention will be described in detail below, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all the embodiments. Other embodiments that can be obtained by persons skilled in the art without making any creative effort based on the embodiments of the present invention belong to the protection scope of the present invention.

The waste concrete blocks used for temporarily supporting the enclosure structure are used as backfill materials, the quality requirement of engineering backfill is met while the mechanical structure of concrete is not damaged, the concrete blocks are firstly filled, and then the regenerated cement foam slurry is injected into the concrete block layer in a manner of embedding the conduit for grouting, so that the concrete blocks and the regenerated cement foam slurry are fully gelatinized and combined, and the load or vibration of a main body structure can be transmitted to a backfill layer by utilizing the buffering and energy absorption effects of the low-density regenerated cement foam slurry; and the waste concrete blocks are cemented and wrapped by the recycled cement foam slurry, so that the load on the main body structure is greatly reduced, and the effects of shock resistance and sinking resistance are achieved.

The backfill construction method comprises the following steps:

s1, accumulating the waste concrete blocks in a backfilling space. The waste concrete blocks may include concrete blocks produced by processing the temporary support envelope, and the maximum radial dimension of the waste concrete blocks is greater than 300mm.

And S2, dividing grids on the top plane of the accumulated waste concrete blocks, and burying a slurry pouring guide pipe in the center of the grids. The function of dividing the net is in order to guarantee to bury the pouring pipe underground in the old and useless concrete piece accumulation layer evenly, guarantees the homogeneity of follow-up pouring regeneration cement foam slurry, makes regeneration cement foam slurry even, synchronous shaping in the same horizontal plane of old and useless concrete piece accumulation layer, and then guarantees the fastness and the stability of the backfill layer after pouring, guarantees the mechanical properties of the backfill layer after pouring.

And S3, continuously pumping and pouring the regenerated cement foam slurry through the pouring guide pipes, wherein the distance between every two adjacent pouring guide pipes is not more than 3 m, the distance between a lower outlet of each pouring guide pipe and the bottom of the backfilling space is not more than 300mm, and the pressure of the lower outlet of each pouring guide pipe is 0.8 to 1.2 MPa. Pouring until the surface of the stacked waste concrete blocks is subjected to slurry discharge and covering the top by about 10 to 20 mm. The regenerated cement foam slurry comprises cement, a foaming agent, regenerated sand powder, a mineral admixture and water. The mineral admixture can be any one of excavation waste soil, slag soil and dust or a combination of a plurality of the excavation waste soil, the slag soil and the dust in any proportion. The blowing agent may be a surfactant physically blown foam.

The traditional rock-fill concrete adopts the way of firstly stacking rock and then self-compacting concrete/mortar surface pouring, the self gravity and the high fluidity of the self-compacting concrete/mortar are relied on for filling and compacting, the bottom layer pouring plumpness is difficult to guarantee in the way, and the rock-fill can float in the mortar.

And S4, covering the film and maintaining for more than 7 days to finish backfilling.

Before the step S1, the backfilling space is cleaned on the working face, and a supporting template can be set up as required. When the waste concrete blocks are stacked in the backfill space in the step S1, the waste concrete blocks can be paved by a machine firstly and naturally stacked in the backfill space, and the waste concrete blocks can be stacked at the boundary by manual assistance.

The waste concrete blocks adopted in the step S1 are coarse blocks with the radial maximum size larger than 300mm generated in the process of on-site cutting, dismantling and crushing of concrete of the temporary support envelope structure of C30 or above grade and recycling of reinforcing steel bars. The compression strength of the drill core sample before the temporary support envelope concrete is removed is not less than 35 MPa, so that the backfilled material can meet the requirement of the compression strength.

During backfilling, waste concrete blocks with the radial maximum size larger than 300mm are directly screened and spread in a backfilling space, and the method is simple in treatment and disposal and low in cost. The waste concrete blocks do not need to be further crushed, ground or modified, so that a large amount of defects can be avoided from being generated and exposed in the secondary processing process, the original performance of the waste concrete of the temporary support enclosure structure is reserved to the maximum extent by the large-size concrete blocks, and the secondary processing cost of the waste concrete is also saved.

The slump of the regenerated cement foam slurry can be 280-320 mm, the expansion degree can be 720 to 750 mm, wet density is not greater than 630 kg/m.

When the waste concrete blocks are stacked in the backfill space, the single stacking thickness is more than 0.8m and less than 3 m. If the thickness of the waste concrete blocks accumulated at a single time exceeds 3 m, the pouring plumpness is difficult to ensure when the pouring guide pipe is used for continuously pumping and pouring the regenerated cement foam slurry, and the compressive strength of the whole backfilling project is influenced; if the thickness of the waste concrete blocks is less than 0.8m in single accumulation, the backfilling times are increased for the engineering with high backfilling thickness, so that the backfilling engineering quantity is large, and the construction period is long.

The used waste concrete blocks and the regenerated cement foam slurry are calculated according to the volume percentage, the waste concrete blocks are 50 to 60 vol percent, the regenerated cement foam slurry is 40 to 50 vol percent, namely, when the waste concrete blocks are stacked, the waste concrete blocks which are 50 to 60 vol percent are firstly paved, and then the concrete blocks are continuously pumped and poured into the regenerated cement foam slurry which is 40 to 50 vol percent.

And under the condition that the required thickness of the backfill is not reached after the backfill is completed in the step S4, continuously repeating the steps S1 to S4 until the required thickness of the backfill is reached.

The excavation waste soil, the slag soil and the dust generated in the engineering field are the most difficult to recycle, and the main components of the excavation waste soil, the slag soil and the dust are soil or earth, which has great influence on the working performance, the mechanical performance and the durability of the traditional concrete, so that the excavation waste soil, the slag soil and the dust can only be dumped and buried at present. However, the invention can be used as a mineral admixture for regenerated cement foam slurry, because the soil or mud in the excavated spoil, muck and dust has water absorption and retention properties, the consistency of the slurry can be increased, so that the stability of the prefabricated foam in the slurry with high water content is higher, and the slurry with high fluidity and high expansion degree does not generate layered segregation bleeding in the pumping and pouring process.

The regenerated sand powder is fine particles with the particle size of less than 5mm generated in the process of cutting and dismantling-crushing recycled steel bars on site for temporary support enclosure structure concrete with the grade of C30 or above. Therefore, a small part of fine particles with the particle size smaller than 5mm generated in the process of cutting, dismantling and crushing the temporary support enclosure structure concrete on site and recycling the reinforcing steel bars are applied to the regenerated cement foam slurry, so that the cement consumption of the regenerated cement foam slurry can be reduced, and the waste concrete fine particles can be further consumed.

In order to more clearly illustrate the present invention, the following specific examples are given below in detail.

Example 1

The concrete block backfill construction method comprises the following steps:

(1) After the temporary support enclosure structure is cut and removed, reinforcing steel bars are crushed and recycled on site, and waste concrete blocks with the radial maximum size larger than 300mm and regenerated sand powder with the particle size smaller than 5mm are collected respectively.

(2) And (4) cleaning the operation surface of the on-site backfill space, and erecting a supporting template according to the requirement.

(3) And collecting excavation spoil, muck and dust on the cutting, dismantling and crushing and working face cleaning site as mineral additives.

(4) Paving waste concrete blocks with the radial maximum size larger than 300mm mechanically, naturally stacking the waste concrete blocks in the backfilling space, manually and auxiliarily stacking the waste concrete blocks at the boundary, wherein the stacking thickness of the waste concrete blocks is 1.5 m, and the volume of the backfilling space is 50 percent vol.

(5) And dividing grids on the top plane of the accumulated waste concrete blocks, burying a regenerated cement foam slurry pouring guide pipe at the center of the grids, wherein the distance between adjacent pouring guide pipes is 3 m, and the distance between the lower outlet of each pouring guide pipe and the bottom of a backfill space is 300mm.

(6) According to the weight proportion of 300 kg/m cement, 150 kg/m regenerated sand powder with the grain size smaller than 5mm, 30 kg/m mineral admixture, 30 kg/m surfactant physical foaming foam and 120 kg/m water for carrying out thin film plantation, the regenerated cement foam slurry is prepared on site, meanwhile, the slump of the regenerated cement foam slurry is controlled to be 280-320 mm, the expansion degree is 720-750 mm, and the wet density is 630 kg/m thin film plantation.

(7) Setting the outlet pressure of the regenerated cement foam slurry at 1.0 MPa, continuously pumping and pouring directly through a pouring conduit, and stopping pouring the regenerated cement foam slurry when the surface of the piled waste concrete blocks is discharged and covers about 10-20 mm above the top, wherein the regenerated cement foam slurry occupies 50 vol of the backfill space volume.

(8) And after 7 days of film covering and maintenance, core drilling and sampling are carried out, and the compressive strength of the completed backfill material is 1.8 MPa.

Example 2

The concrete block backfilling construction method comprises the following steps:

(2) And (5) cleaning the operation surface of the on-site backfill space, and erecting a supporting template according to the requirement.

(4) And mechanically paving the waste concrete blocks with the radial maximum size larger than 300mm, naturally stacking the waste concrete blocks in the backfilling space, manually assisting and stacking the waste concrete blocks at the boundary, wherein the stacking thickness of the waste concrete blocks is 2.5 m, and the waste concrete blocks account for about 50 vol% of the backfilling space volume.

(5) And dividing grids on the top plane of the accumulated waste concrete blocks, burying a recycled cement foam slurry pouring guide pipe at the central position of the grids, wherein the distance between adjacent pouring guide pipes is 2 m, and the distance between the lower outlet of each pouring guide pipe and the bottom of a backfill space is 300mm.

(6) According to 290 kg/m cement, 145 kg/m reclaimed sand powder with the grain size smaller than 5mm, 45 kg/m mineral admixture, 30 kg/m surfactant physical foaming foam and the proportion of 120 kg/m water for carrying out thin film plantation, the reclaimed cement foam slurry is prepared on site, meanwhile, the slump of the reclaimed cement foam slurry is controlled to be 280-320 mm, the expansion degree is 720-750 mm, and the wet density is 630 kg/m thin film plantation.

(7) Setting the outlet pressure of the regenerated cement foam slurry at 1.2 MPa, continuously pumping and pouring directly through a pouring guide pipe, and stopping pouring the regenerated cement foam slurry when the surface of the accumulated waste concrete blocks is discharged and covers about 10-20 mm above the top, wherein the regenerated cement foam slurry occupies about 50 vol of the backfill space volume.

(8) And after 7 days of film covering and maintenance, core drilling and sampling are carried out, and the compressive strength of the completed backfill material is 1.7 MPa.

Example 3

(1) After the temporary support enclosure structure is cut and removed, the reinforcing steel bars are crushed and recycled on site, and waste concrete blocks with the radial maximum size larger than 300mm and regenerated sand powder with the particle size smaller than 5mm are respectively collected.

(3) Collecting the excavated waste soil, dregs and dust on the cutting, dismantling, crushing and working face cleaning sites as mineral additives.

(4) Mechanically paving the waste concrete blocks with the radial maximum dimension larger than 300mm, naturally stacking the waste concrete blocks in the backfilling space, manually assisting the stacking of the waste concrete blocks at the boundary, wherein the stacking thickness of the waste concrete blocks is about 1m, and the waste concrete blocks occupy 60% vol of the volume of the backfilling space.

(5) And dividing grids on the top plane of the accumulated waste concrete blocks, burying a regenerated cement foam slurry pouring guide pipe at the center of the grids, wherein the distance between adjacent pouring guide pipes is 2.5 m, and the distance between a lower outlet of each pouring guide pipe and the bottom of a backfill space is 300mm.

(6) According to 280 kg/m cement, 140 kg/m grain size is less than 5 mm's regeneration sand powder, 60 kg/m mineral admixture, 30 kg/m surfactant physical foaming foam, the mix proportion of 120 kg/m water, prepare regeneration cement foam slurry on the spot, control regeneration cement foam slurry slump is 280-320 mm, the expansion is 720-750 mm, wet density is 600 kg/m.

(7) Setting the outlet pressure of the regenerated cement foam slurry at 0.8MPa, directly and continuously pumping and pouring through a pouring guide pipe, and stopping pouring the regenerated cement foam slurry when the surface of the accumulated waste concrete blocks is discharged and covers about 10-20 mm above the top, wherein the regenerated cement foam slurry occupies 40 vol of the space volume of the backfill system.

(8) And after 7 days of film covering and maintenance, core drilling and sampling are carried out, and the compressive strength of the completed backfill material is 1.3 MPa.

The backfill layer and the backfill layer cross-section obtained in this example are shown in fig. 1 and fig. 2.

Comparative example 1

The concrete block backfill construction method comprises the following steps:

(4) According to the weight proportion of 280 kg/m cement, 140 kg/m regenerated sand powder with the grain size smaller than 5mm, 60 kg/m mineral admixture, 30 kg/m surfactant physical foaming foam and 120 kg/m water for carrying out thin film planting, preparing regenerated cement foam slurry on site, and meanwhile controlling the slump of the regenerated cement foam slurry to be 280-320 mm, the expansion degree to be 720-750 mm and the wet density to be 600 kg/m for carrying out thin film planting. Injecting the recycled cement foam slurry into a backfill space, wherein the grouting thickness is about 0.41m, putting the waste concrete blocks in the step (1) into a grouting layer, the waste concrete blocks occupy about 60 vol% of the volume of the backfill space, and the total height of the backfill layer is about 1m.

(5) And after 7 days of film covering and maintenance, core drilling and sampling are carried out, and the compressive strength of the completed backfill material is 0.8MPa.

The cross-sections of the backfill layers and the backfill layers are shown in figures 3 and 4, respectively. The section of the backfill layer can show that the waste concrete block is not completely wrapped by cement mortar, and the backfill quality is poor. The backfill layer and the section thereof shown in fig. 1 and fig. 2 are poured by the backfill construction method of the invention, and the section of the backfill layer shows that the recycled cement foam slurry can well wrap the waste concrete blocks and the waste concrete blocks are uniformly distributed. If the regenerated cement foam slurry is poured firstly and then the concrete block is put into the regenerated cement foam slurry, the cementation effect of the concrete block and the regenerated cement foam slurry is obviously poor.

The backfill construction method has good effect, the waste concrete removed by the temporary support enclosure structure is efficiently utilized, and the working performance and the mechanical property of the formed backfill material are higher than the requirements of backfill engineering.

In conclusion, the waste concrete adopted by the invention is a coarse block obtained by removing the coarse crushing recycled steel bars on the site of the temporary support enclosure structure, does not need deep processing, can be directly accumulated in a backfill space, simplifies the regeneration processing procedure and process of the waste concrete, and simultaneously completely replaces natural or machine-made crushed stone; the regenerated sand powder is added into the regenerated cement foam slurry in a large amount and used as a filling cementing material, so that the cement consumption is further reduced. The invention provides a simple, practical, economic and feasible way for the treatment and disposal of the demolished temporary support enclosure concrete on the engineering site, and realizes the high-efficiency, low-cost and safe construction of the backfill engineering.

Finally, it is noted that the above-mentioned preferred embodiments illustrate rather than limit the invention, and that, while the invention has been described in detail with reference to the above-mentioned preferred embodiments, it will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the scope of the invention as defined by the appended claims.

Claims

1. The application of the waste concrete is characterized in that the waste concrete is in a block shape and is used as a backfill material.

2. The backfill construction method using the waste concrete as the backfill material is characterized by comprising the following steps:

(1) Backfilling: accumulating the waste concrete blocks in a backfill space;

(2) Burying and pouring a conduit: embedding a slurry pouring conduit in the waste concrete block accumulation layer;

3. The backfill construction method according to claim 2, wherein the concrete block has a maximum radial dimension greater than 300mm; the single stacking thickness of the waste concrete blocks is more than 0.8m and less than 3 m; and pouring the cement foam slurry to the surface of the stacked waste concrete blocks for slurry discharge, and covering the top by 10 to 20 mm.

4. The backfill construction method according to claim 2, further comprising a step (4) of film coating maintenance, in particular, film coating maintenance for more than 7 days.

5. The backfill construction method according to claim 4, wherein the steps (1) to (4) are repeated until the backfill height requirement is met.

6. The backfill construction method according to any one of claims 2 to 5, wherein the waste concrete blocks account for 50% to 60% and the recycled cement foam slurry accounts for 40% to 50% by volume.

7. The backfill construction method according to any one of claims 2 to 5, wherein the recycled cement foam slurry is a mixture of cement, foaming agent, recycled sand powder, mineral admixture and water.

8. The backfill construction method according to any one of claims 2 to 5, characterized in that the distance from the outlet at the lower part of the pouring conduit to the backfill bottom is not more than 300mm, and the outlet pressure of the pouring conduit is 0.8 to 1.2 MPa.

9. The backfill construction method according to claim 7, wherein the mass ratio of the cement to the reclaimed sand powder in the reclaimed cement foam slurry is 2:1.

10. the backfill construction method according to claim 7, wherein the slump of the recycled cement foam slurry is 280-320 mm, the expansion degree is 720-750 mm, and the wet density is not more than 630 kg/m for carrying out the method.