CN112851250A - High-strength recycled concrete and preparation method and application thereof - Google Patents
High-strength recycled concrete and preparation method and application thereof Download PDFInfo
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- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B28/00—Compositions of mortars, concrete or artificial stone, containing inorganic binders or the reaction product of an inorganic and an organic binder, e.g. polycarboxylate cements
- C04B28/02—Compositions of mortars, concrete or artificial stone, containing inorganic binders or the reaction product of an inorganic and an organic binder, e.g. polycarboxylate cements containing hydraulic cements other than calcium sulfates
- C04B28/04—Portland cements
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- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B18/00—Use of agglomerated or waste materials or refuse as fillers for mortars, concrete or artificial stone; Treatment of agglomerated or waste materials or refuse, specially adapted to enhance their filling properties in mortars, concrete or artificial stone
- C04B18/04—Waste materials; Refuse
- C04B18/16—Waste materials; Refuse from building or ceramic industry
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- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B2201/00—Mortars, concrete or artificial stone characterised by specific physical values
- C04B2201/50—Mortars, concrete or artificial stone characterised by specific physical values for the mechanical strength
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- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02W—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT
- Y02W30/00—Technologies for solid waste management
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Abstract
The invention relates to the technical field of building materials, in particular to high-strength recycled concrete and a preparation method and application thereof, wherein the high-strength recycled concrete is prepared from the following raw materials in parts by weight: 290 portions of cement and 443 portions; 20-70 parts of fly ash; 20-70 parts of slag; 20-70 parts of silica fume; 20-70 parts of metakaolin; 650 portions and 750 portions of fine aggregate; 550 portions of natural coarse aggregate and 600 portions of natural coarse aggregate; 450 portions and 510 portions of recycled coarse aggregate; 4.0-7.0 parts of a water reducing agent; 140 portions of water and 160 portions. The invention designs and prepares a high-strength recycled concrete based on the service environment and the bearing requirements of a recycled concrete structure, wherein the mineral admixture comprises fly ash, slag, silica fume and metakaolin; the preparation method adopts a prewetting-double slurry coating method to carry out prewetting, slurry coating and multiple stirring treatments on the recycled aggregate, so that the internal microstructure of the concrete is enhanced, and the mechanical property of the recycled concrete and the durability of the recycled concrete in a composite salt corrosion environment are improved.
Description
Technical Field
The invention relates to the technical field of building materials, in particular to high-strength recycled concrete and a preparation method and application thereof.
Background
In recent 10 years, a large amount of waste concrete is generated in the urbanization process of China, and by 2017, the total amount of waste concrete generated in continents of China is 11.6 hundred million t, and the waste concrete is increased at a speed of 5-10% per year, and is expected to reach 17 hundred million t in 2020; at present, the treatment mode of waste concrete in China is mainly stacking and burying, and serious pollution is caused to the fragile ecological environment, so that the waste concrete is utilized to produce recycled aggregate and is used for preparing new concrete (recycled concrete), and the method has important value for promoting the recycling of the waste concrete; in recent years, under the strong support of provinces and cities in China, recycled concrete is gradually applied to newly built structures.
Different from natural aggregate, a large amount of old cement mortar is adhered to the surface of the recycled aggregate, and a multi-interface structure is generated in the stirring process, so that the recycled aggregate contains higher porosity and more microcracks, and the interface permeability is increased; in addition, moisture and erosion ions in the environment diffuse into the interface, loose products are generated through reaction, the interface structure is degraded, the interface strength is reduced, and the interface becomes a limiting phase of the mechanical property and durability of the recycled concrete, which is particularly prominent in the service environment of the concrete in northwest China. Therefore, in order to improve the performance of recycled concrete, it is necessary to reinforce the recycled aggregate and reinforce the internal microstructure of the recycled concrete.
In the existing scheme for improving the performance of the recycled concrete, the performance of the recycled concrete is improved well by adding mineral admixture in the mixing proportion and perfecting a concrete stirring method, for example, in a patent of C20-grade high-performance recycled concrete mixing proportion design method, the patent number CN 103086667 adopts I-grade fly ash doped with mineral admixture to replace part of P.I 42.5 portland cement to prepare the recycled concrete and improve the durability of the concrete; in patent "a construction waste recycled concrete and a preparation method thereof", patent No. CN 110282926a, sand and recycled coarse aggregate are fully stirred and mixed, then cement, class ii fly ash or class S95 slag are added, stirring and mixing are continued, and finally water and an additive are added, stirring and mixing are continued. Xie et al in the paper "Coupling effects of recycled aggregate and GGBS/metakaolin on physical properties of geopolymer cement" pre-wet and stir the recycled aggregate for 5min, then add the aggregate and the selected cementitious material to the concrete, continue stirring for 5min, and finally add the mixing water and stir for 3min by simultaneously adding slag and metakaolin mineral admixtures to replace part of the ordinary portland cement; vivian et al prepared recycled concrete by a double stirring method in a thesis of Microstructural analysis of recycled aggregate concrete from two-stage mixing approach, firstly stirred half water and recycled aggregate for 30s, then added with cement and stirred for 30s, finally added with coarse and fine aggregate, residual water and cementing material and stirred for 60s, and poured into a test mould after stirring; kong et al, in the paper "Effect and mechanism of surface-coating cementitious materials around aggregate and properties and ITZ microstructure of recycled aggregate concrete", prepared recycled concrete by a triple stirring method, first stirred with a portion of water and recycled aggregate for 15s, then stirred with a portion of mineral admixture for 15s, then stirred with cement for 30s, and finally stirred with the remaining cementitious material and aggregate for 60s, and poured into a test mold after stirring.
In northwest areas, the deep habitation inland is far away from the sea, and in addition, the plateau and mountain land terrains are high, so that the resistance to humid air flow is caused, so that the rainfall is rare, the climate is drought, and the temperature is great in day worse and year worse due to the climate drought; in the northwest, only a few regions in the southeast are temperate monsoon climate, and most other regions are temperate continental climate and high-cold climate, which are severe cold and dry in winter and high in summer with little precipitation; in addition, most northwest regions are in a drought state and a semi-arid state, the precipitation amount is small, the evaporation amount is large, and salt dissolved in water is easy to accumulate on the surface layer of soil. At present, considering the service environment and the structural load-bearing requirements of recycled concrete in northwest China, the design and preparation of the mixing proportion of the recycled concrete with the strength grade of C20 cannot meet the engineering requirements, so that high-performance recycled concrete with higher strength grade needs to be prepared; secondly, in the actual preparation process of the recycled concrete, the final performance of the recycled concrete is often directly influenced by the difference between the combination mode and the mixing proportion of the mineral admixture, and in the prior art and research, most of the mineral admixture is fly ash, slag and silica fume, and the combination mode is relatively single (mostly single-mixing and double-mixing), so that the maximum improvement effect of the mineral admixture on the performance of the recycled concrete cannot be exerted; finally, the existing improvement technology of the recycled concrete preparation method is a simple improvement (such as a double stirring method and a triple stirring method) on the traditional stirring method, and the preparation process is not delicate and comprehensive.
Disclosure of Invention
Aiming at the technical defects, the invention aims to provide high-strength recycled concrete and a preparation method and application thereof, and the invention designs and prepares the high-strength recycled concrete based on the service environment and the bearing requirement of a recycled concrete structure, wherein the mineral admixture comprises fly ash, slag, silica fume and metakaolin; the preparation method adopts a prewetting-double slurry coating method to carry out prewetting, slurry coating and multiple stirring treatments on the recycled aggregate, thereby enhancing the internal microstructure of the concrete and improving the mechanical property of the recycled concrete and the durability of the recycled concrete in a composite salt corrosion environment.
In order to solve the technical problems, the invention adopts the following technical scheme:
the high-strength recycled concrete is prepared from the following raw materials in parts by weight: 290 portions of cement and 443 portions; 20-70 parts of fly ash; 20-70 parts of slag; 20-70 parts of silica fume; 20-70 parts of metakaolin; 650 portions and 750 portions of fine aggregate; 550 portions of natural coarse aggregate and 600 portions of natural coarse aggregate; 450 portions and 510 portions of recycled coarse aggregate; 4.0-7.0 parts of a water reducing agent; 140 portions of water and 160 portions.
Preferably, the feed is prepared from the following raw materials in parts by weight: cement 300-; 30-45 parts of fly ash; 30-45 parts of slag; 30-45 parts of silica fume; 30-45 parts of metakaolin; 720 parts of fine aggregate; 550 portions of natural coarse aggregate and 580 portions of natural coarse aggregate; 480 portions of regenerative coarse aggregate and 505 portions; 5.0-6.0 parts of a water reducing agent; 150 portions and 160 portions of water.
Preferably, the feed is prepared from the following raw materials in parts by weight: 311 parts of cement; 33 parts of fly ash; 33 parts of slag; 33 parts of silica fume; 33 parts of metakaolin; 705 parts of fine aggregate; 560 parts of natural coarse aggregate; 498 parts of recycled coarse aggregate; 5.54 parts of a water reducing agent; 155 parts of water.
Preferably, the cement is p.o42.5 portland cement;
the fly ash is II-grade F-type low-calcium fly ash;
the slag is granulated slag of grade S95;
the silica fume is 920U silica fume, and the volume density is 272kg/m3；
The metakaolin is prepared from calcined kaolin, and the activity index of the metakaolin in 7 days is 113%;
the fine aggregate is Weiriver sand with fineness modulus of 2.75;
the natural coarse aggregate is single-particle-size crushed stone with the particle size of 16-25 mm;
the recycled aggregate is a continuous graded recycled concrete aggregate with the particle size of 5-20 mm;
the water reducing agent is a PCA-I type polycarboxylic acid high-performance water reducing agent, the solid content is 30 percent, and the water reducing rate is 28 percent.
The invention also provides a preparation method of the high-strength recycled concrete, which comprises the following steps:
(1) weighing: weighing the following raw materials in parts by weight: 290 portions of cement and 443 portions; 20-70 parts of fly ash; 20-70 parts of slag; 20-70 parts of silica fume; 20-70 parts of metakaolin; 650 portions and 750 portions of fine aggregate; 550 portions of natural coarse aggregate and 600 portions of natural coarse aggregate; 450 portions and 510 portions of recycled coarse aggregate; 4.0-7.0 parts of a water reducing agent; 140 portions of water and 160 portions for standby;
(2) pre-wetting recycled aggregate: prewetting the recycled coarse aggregate dried to constant weight to obtain prewetted recycled aggregate;
(3) preparing a cementing material: uniformly mixing cement, fly ash, slag, silica fume and metakaolin to obtain a cementing material, and then dividing the cementing material into an M1 cementing material and an M2 cementing material by mass, wherein the M1 cementing material accounts for 45-55% of the total mass;
(4) preparing a water reducing agent solution: dividing water into W1 water and W2 water by mass, and uniformly mixing the W2 water with a water reducing agent to obtain a water reducing agent solution, wherein the W2 water accounts for 45-55% of the total amount;
(5) preparing the pulp-coated recycled aggregate: mixing the pre-wetted recycled aggregate in the step (2), the M1 cementing material in the step (3) and the W1 water in the step (4) for 30-50s to obtain a pulp-coated recycled aggregate;
(6) preparing primary stirring recycled concrete: adding natural fine aggregate into the pulp-coated recycled aggregate in the step (5) and stirring for 50-70s to obtain primary stirred recycled concrete;
(7) preparing the cementing material slurry-wrapped concrete: adding an M2 gelled material into the primary stirring recycled concrete in the step (6), and stirring for 25-35s to obtain gelled material slurry-coated concrete;
(8) preparing high-strength recycled concrete: adding natural coarse aggregate into the cementing material slurry-wrapped concrete in the step (7), stirring, adding a water reducing agent solution within 15-30s, and continuously stirring for 35-45s to obtain high-strength recycled concrete;
and discharging internal bubbles from the high-strength recycled concrete in the test mould, and maintaining after floating.
Preferably, the mass of the pre-wetting water in the step (2) is 90% of the water absorption of the recycled coarse aggregate.
Preferably, the curing method in the step (8) is as follows: curing the film for 24h at room temperature, adding saturated Ca (OH)2Curing in the solution for 28 days, and then curing for 90 days under natural conditions.
The invention also protects the application of the high-strength recycled concrete in the salt corrosion environment construction engineering in the northwest region.
Compared with the prior art, the invention has the beneficial effects that:
1. according to the invention, the fly ash-slag-silica fume-metakaolin mineral admixture is added into the concrete mixing ratio to replace part of ordinary portland cement, so that the production cost of the concrete is reduced, the greenness of the concrete is improved, the microstructure of an interface region of the recycled concrete is improved, the mechanical property and the durability of the recycled concrete are improved, and the improvement effect of four mineral admixtures and different mixing ratios on the performance of the recycled concrete is clarified. The first mineral admixture and the fourth mineral admixture have different particle sizes, so that the particle accumulation in the recycled concrete can better accord with the closest accumulation principle; the second and the fourth mineral admixtures have different action effects and different activities in the concrete and can supplement each other; thirdly, the secondary hydration reaction of the mineral admixture can obviously improve the microstructure of the interface transition zone of the recycled concrete and reduce the communication porosity of the recycled concrete; fourthly, the mineral admixture secondary hydration reaction consumes calcium hydroxide and generates erosion-resistant hydration products, and the durability of the recycled concrete is improved. In conclusion, the four mineral admixtures are used together to adjust the microstructure and hydration product mineral composition in the recycled concrete, and the mechanical property and durability of the recycled concrete are obviously improved.
2. The preparation process of the recycled concrete adopts a pre-wetting-double slurry coating method, and the pre-wetting-double slurry coating method is used for carrying out pre-wetting, slurry coating and concrete multiple-time stirring treatment on the recycled aggregate, so that the microstructure of the recycled concrete is improved, and the mechanical property of the recycled concrete and the durability of the recycled concrete in a composite salt corrosion environment are improved; when the curing period is 28d, the compressive strength of the recycled concrete with the recycled aggregate substitution rate of 50 percent can reach 68.8MPa, and reaches the standard of high-strength concrete.
3. The invention adopts a mode of 'four-doped mineral admixture' + 'prewetting-double slurry wrapping method' for the recycled concrete, improves the mechanical property of the recycled concrete, and reaches the standard of high-strength concrete. Firstly, the water reducing effect of the fly ash in the four-doping process is mutually promoted with the high pozzolanic property and the filling effect of slag, silica fume and metakaolin to generate a secondary hydration reaction product, and the secondary hydration reaction product greatly improves the internal microstructure of concrete; secondly, the recycled aggregate is subjected to pre-wetting, slurry wrapping and multiple stirring treatment of concrete in a pre-wetting-double slurry wrapping method, so that the slurry wraps the aggregate more tightly, the hardness of a recycled aggregate interface is improved better, and meanwhile, the aggregate and the slurry in the concrete are distributed more uniformly and the pore grading is better due to multiple stirring.
4. Research shows that the sodium sulfate-magnesium sulfate-sodium chloride composite solution (with the concentration of 20%) is used as an erosion medium, and after the wet and dry alternation is carried out for 180 times, the loss rate of the relative dynamic elastic modulus of the recycled concrete is 3.52%, the loss rate of the quality is 0, the loss rate of the compressive strength is 4.93%, and the loss rate of the splitting tensile strength is 2.75%. Has higher salt corrosion resistance, and meets the durability requirement of the composite salt corrosion environment regenerated concrete structure in northwest regions.
Drawings
FIG. 1 is a graph showing the comparative relationship between the cubic compressive strength and the curing time of recycled concrete prepared in example 3, comparative example 1 to comparative example 3 of the present invention;
FIG. 2 is a graph showing the comparison between the cleavage tensile strength and the curing time of recycled concrete prepared in example 3, comparative example 1 to comparative example 3 of the present invention;
FIG. 3 is a diagram of samples soaked in a corrosion resistance test according to example 3, comparative example 1 to comparative example 3 of the present invention;
FIG. 4 is a sample graph of samples of example 3, comparative example 1 to comparative example 3 of the present invention dried in a corrosion resistance test;
FIG. 5 is a graph showing the dynamic elastic modulus test experiment of the samples of example 3 of the present invention, comparative example 1 to comparative example 3;
FIG. 6 is a graph showing mechanical property test experiments of samples of example 3 of the present invention and comparative examples 1 to 3.
Detailed Description
The following description of the preferred embodiments and accompanying fig. 1-6 are used in conjunction with the accompanying drawings in the embodiments of the invention to illustrate the preferred embodiments.
Example 1
A preparation method of high-strength recycled concrete comprises the following preparation steps:
(1) weighing: weighing the following raw materials in parts by weight: 290 parts of cement; 20 parts of fly ash; 70 parts of slag; 20 parts of silica fume; 70 parts of metakaolin; 650 parts of fine aggregate; 600 parts of natural coarse aggregate; 510 parts of regenerated coarse aggregate; 4.0 parts of a water reducing agent; 140 parts of water for later use;
(2) pre-wetting recycled aggregate: prewetting the dried recycled coarse aggregate with constant weight, wherein the mass of prewetting water is 90% of the water absorption of the recycled coarse aggregate, so as to obtain prewetted recycled aggregate;
(3) preparing a cementing material: uniformly mixing cement, fly ash, slag, silica fume and metakaolin to obtain a cementing material, and then dividing the cementing material into an M1 cementing material and an M2 cementing material by mass, wherein the M1 cementing material accounts for 45% of the total mass;
(4) preparing a water reducing agent solution: dividing water into W1 water and W2 water by mass, and uniformly mixing the W2 water with a water reducing agent to obtain a water reducing agent solution, wherein the W2 water accounts for 45% of the total amount;
(5) preparing the pulp-coated recycled aggregate: mixing the pre-wetted recycled aggregate in the step (2), the M1 cementing material in the step (3) and the W1 water in the step (4) for 30s to obtain slurry-coated recycled aggregate;
(6) preparing primary stirring recycled concrete: adding natural fine aggregate into the pulp-coated recycled aggregate in the step (5) and stirring for 70s to obtain primary stirred recycled concrete;
(7) preparing the cementing material slurry-wrapped concrete: adding an M2 cementitious material into the primary stirring recycled concrete in the step (6), and stirring for 25s to obtain cementitious material slurry-coated concrete;
(8) preparing high-strength recycled concrete: adding natural coarse aggregate into the cementing material slurry-wrapped concrete in the step (7), starting stirring, adding the water reducing agent solution within 30s of stirring, and continuing stirring for 35s to obtain high-strength recycled concrete;
discharging internal bubbles from the high-strength recycled concrete in a test mould, leveling and maintaining, wherein the maintenance method comprises the following steps: curing the coated film at normal temperature for 24h, demoulding, and adding saturated Ca (OH)2Curing in the solution for 28 days, and then curing for 90 days under natural conditions.
Example 2
A preparation method of high-strength recycled concrete comprises the following preparation steps:
(1) weighing: weighing the following raw materials in parts by weight: 300 parts of cement; 45 parts of fly ash; 45 parts of slag; 30 parts of silica fume; 30 parts of metakaolin; 680 parts of fine aggregate; 580 parts of natural coarse aggregate; 480 parts of regenerated coarse aggregate; 5.0 parts of a water reducing agent; 150 parts of water for later use;
(2) pre-wetting recycled aggregate: prewetting the dried recycled coarse aggregate with constant weight, wherein the mass of prewetting water is 90% of the water absorption of the recycled coarse aggregate, so as to obtain prewetted recycled aggregate;
(3) preparing a cementing material: uniformly mixing cement, fly ash, slag, silica fume and metakaolin to obtain a cementing material, and then dividing the cementing material into an M1 cementing material and an M2 cementing material by mass, wherein the M1 cementing material accounts for 48% of the total mass;
(4) preparing a water reducing agent solution: dividing water into W1 water and W2 water by mass, and uniformly mixing the W2 water with a water reducing agent to obtain a water reducing agent solution, wherein the W2 water accounts for 52% of the total amount;
(5) preparing the pulp-coated recycled aggregate: mixing the pre-wetted recycled aggregate in the step (2), the M1 cementing material in the step (3) and the W1 water in the step (4) for 35 seconds to obtain slurry-coated recycled aggregate;
(6) preparing primary stirring recycled concrete: adding natural fine aggregate into the pulp-coated recycled aggregate in the step (5) and stirring for 65s to obtain primary stirred recycled concrete;
(7) preparing the cementing material slurry-wrapped concrete: adding an M2 cementitious material into the primary stirring recycled concrete in the step (6), and stirring for 30s to obtain cementitious material slurry-coated concrete;
(8) preparing high-strength recycled concrete: adding natural coarse aggregate into the cementing material slurry-wrapped concrete in the step (7), starting stirring, adding the water reducing agent solution within 20s of stirring, and continuing stirring for 40s to obtain high-strength recycled concrete;
discharging internal bubbles from the high-strength recycled concrete in a test mould, leveling and maintaining, wherein the maintenance method comprises the following steps: curing the coated film at normal temperature for 24h, demoulding, and adding saturated Ca (OH)2Curing in the solution for 28 days, and then curing for 90 days under natural conditions.
Example 3
A preparation method of high-strength recycled concrete comprises the following preparation steps:
(1) weighing: weighing the following raw materials in parts by weight: 311 parts of cement; 33 parts of fly ash; 33 parts of slag; 33 parts of silica fume; 33 parts of metakaolin; 705 parts of fine aggregate; 560 parts of natural coarse aggregate; 498 parts of recycled coarse aggregate; 5.54 parts of a water reducing agent; 155 parts of water for later use;
(2) pre-wetting recycled aggregate: prewetting the dried recycled coarse aggregate with constant weight, wherein the mass of prewetting water is 90% of the water absorption of the recycled coarse aggregate, so as to obtain prewetted recycled aggregate;
(3) preparing a cementing material: uniformly mixing cement, fly ash, slag, silica fume and metakaolin to obtain a cementing material, and then dividing the cementing material into an M1 cementing material and an M2 cementing material by mass, wherein the M1 cementing material accounts for 50% of the total mass;
(4) preparing a water reducing agent solution: dividing water into W1 water and W2 water by mass, and uniformly mixing the W2 water with a water reducing agent to obtain a water reducing agent solution, wherein the W2 water accounts for 50% of the total amount;
(5) preparing the pulp-coated recycled aggregate: mixing the pre-wetted recycled aggregate in the step (2), the M1 cementing material in the step (3) and the W1 water in the step (4) for 40s to obtain slurry-coated recycled aggregate;
(6) preparing primary stirring recycled concrete: adding natural fine aggregate into the pulp-coated recycled aggregate in the step (5) and stirring for 60s to obtain primary stirred recycled concrete;
(7) preparing the cementing material slurry-wrapped concrete: adding an M2 cementitious material into the primary stirring recycled concrete in the step (6), and stirring for 30s to obtain cementitious material slurry-coated concrete;
(8) preparing high-strength recycled concrete: adding natural coarse aggregate into the cementing material slurry-wrapped concrete in the step (7), starting stirring, adding the water reducing agent solution within 20s of stirring, and continuing stirring for 40s to obtain high-strength recycled concrete;
discharging internal bubbles from the high-strength recycled concrete in a test mould, leveling and maintaining, wherein the maintenance method comprises the following steps: curing the coated film at normal temperature for 24h, demoulding, and adding saturated Ca (OH)2Curing in the solution for 28 days, and then curing for 90 days under natural conditions.
Example 4
A preparation method of high-strength recycled concrete comprises the following preparation steps:
(1) weighing: weighing the following raw materials in parts by weight: 320 parts of cement; 30 parts of fly ash; 30 parts of slag; 45 parts of silica fume; 45 parts of metakaolin; 720 parts of fine aggregate; 550 parts of natural coarse aggregate; 505 parts of recycled coarse aggregate; 6.0 parts of a water reducing agent; 160 parts of water for later use;
(2) pre-wetting recycled aggregate: prewetting the dried recycled coarse aggregate with constant weight, wherein the mass of prewetting water is 90% of the water absorption of the recycled coarse aggregate, so as to obtain prewetted recycled aggregate;
(3) preparing a cementing material: uniformly mixing cement, fly ash, slag, silica fume and metakaolin to obtain a cementing material, and then dividing the cementing material into an M1 cementing material and an M2 cementing material by mass, wherein the M1 cementing material accounts for 52 percent of the total mass;
(4) preparing a water reducing agent solution: dividing water into W1 water and W2 water by mass, and uniformly mixing the W2 water with a water reducing agent to obtain a water reducing agent solution, wherein the W2 water accounts for 48% of the total amount;
(5) preparing the pulp-coated recycled aggregate: mixing the pre-wetted recycled aggregate in the step (2), the M1 cementing material in the step (3) and the W1 water in the step (4) for 45s to obtain slurry-coated recycled aggregate;
(6) preparing primary stirring recycled concrete: adding natural fine aggregate into the pulp-coated recycled aggregate in the step (5) and stirring for 65s to obtain primary stirred recycled concrete;
(7) preparing the cementing material slurry-wrapped concrete: adding an M2 cementitious material into the primary stirring recycled concrete in the step (6), and stirring for 30s to obtain cementitious material slurry-coated concrete;
(8) preparing high-strength recycled concrete: adding natural coarse aggregate into the cementing material slurry-wrapped concrete in the step (7), starting stirring, adding the water reducing agent solution within 25s of stirring, and continuing stirring for 35s to obtain high-strength recycled concrete;
discharging internal bubbles from the high-strength recycled concrete in a test mould, leveling and maintaining, wherein the maintenance method comprises the following steps: curing the coated film at normal temperature for 24h, demoulding, and adding saturated Ca (OH)2Curing in the solution for 28 days, and then curing for 90 days under natural conditions.
Example 5
A preparation method of high-strength recycled concrete comprises the following preparation steps:
(1) weighing: weighing the following raw materials in parts by weight: 443 parts of cement; 70 parts of fly ash; 20 parts of slag; 70 parts of silica fume; 20 parts of metakaolin; 750 parts of fine aggregate; 550 parts of natural coarse aggregate; 450 parts of recycled coarse aggregate; 7.0 parts of a water reducing agent; 160 parts of water for later use;
(2) pre-wetting recycled aggregate: prewetting the dried recycled coarse aggregate with constant weight, wherein the mass of prewetting water is 90% of the water absorption of the recycled coarse aggregate, so as to obtain prewetted recycled aggregate;
(3) preparing a cementing material: uniformly mixing cement, fly ash, slag, silica fume and metakaolin to obtain a cementing material, and then dividing the cementing material into an M1 cementing material and an M2 cementing material by mass, wherein the M1 cementing material accounts for 55% of the total mass;
(4) preparing a water reducing agent solution: dividing water into W1 water and W2 water by mass, and uniformly mixing the W2 water with a water reducing agent to obtain a water reducing agent solution, wherein the W2 water accounts for 55% of the total amount;
(5) preparing the pulp-coated recycled aggregate: mixing the pre-wetted recycled aggregate in the step (2), the M1 cementing material in the step (3) and the W1 water in the step (4) for 50s to obtain slurry-coated recycled aggregate;
(6) preparing primary stirring recycled concrete: adding natural fine aggregate into the pulp-coated recycled aggregate in the step (5) and stirring for 50s to obtain primary stirred recycled concrete;
(7) preparing the cementing material slurry-wrapped concrete: adding an M2 cementitious material into the primary stirring recycled concrete in the step (6), and stirring for 35 seconds to obtain cementitious material slurry-coated concrete;
(8) preparing high-strength recycled concrete: adding natural coarse aggregate into the cementing material slurry-wrapped concrete in the step (7), starting stirring, adding the water reducing agent solution within 15s of stirring, and continuing stirring for 45s to obtain high-strength recycled concrete;
discharging internal bubbles from the high-strength recycled concrete in a test mould, leveling and maintaining, wherein the maintenance method comprises the following steps: curing the coated film at normal temperature for 24h, demoulding, and adding saturated Ca (OH)2Curing in the solution for 28 days, and then curing for 90 days under natural conditions.
Comparative example 1
The preparation method of the high-strength recycled concrete is the same as the preparation steps of the embodiment 3, and is different in that the raw materials are weighed according to the following parts by weight: 443 parts of cement, 717 parts of fine aggregate, 569 parts of natural coarse aggregate, 506 parts of recycled coarse aggregate, 5.54 parts of water reducing agent and 155 parts of water.
Comparative example 2
The preparation method of the high-strength recycled concrete is the same as the preparation steps of the embodiment 3, and is different from the preparation method of the embodiment in that 33 parts of fly ash is used; 33 parts of slag; 33 parts of silica fume; 33 parts of metakaolin; replacing 66 parts of fly ash; 22 parts of slag; 22 parts of silica fume; and 22 parts of metakaolin.
Comparative example 3
The preparation method of the high-strength recycled concrete is the same as the preparation steps of the embodiment 3, and is different from the preparation method of the embodiment in that 33 parts of fly ash is used; 33 parts of slag; 33 parts of silica fume; 33 parts of metakaolin; replacing by 44 parts of fly ash; 22 parts of slag; 22 parts of silica fume; 44 parts of metakaolin.
1. The following is a composition comparison of comparative examples 1 to 3 of the present invention with the high strength recycled concrete prepared in example 3, as shown in table 1:
recycled concrete formulation (kg/m) as designed in Table 13)
Compared with example 3, comparative example 1 contains only cement and no other mineral admixtures; the mineral admixture ratio of comparative example 2 is 3:1:1:1, the mineral admixture ratio of comparative example 3 is 2:1:1:2, and the mineral admixture ratio of example 3 is 1:1:1: 1; the influence of the mineral admixture on the high-strength recycled concrete is researched, and the specific test method is as follows:
according to the standard of the test method for the mechanical properties of common concrete (GB/T50081-2019), testing the compressive strength and the splitting tensile strength of a cubic standard test piece of the recycled concrete, wherein the testing age comprises 1d (only including the compressive strength), 3d, 7d, 28d, 60d and 90d, the testing result of the compressive strength is shown in figure 1, and the testing result of the splitting tensile strength is shown in figure 2; the mechanical properties of the four formulations are shown in table 2:
TABLE 2 recycled concrete mechanical Properties (MPa)
The results show that the compressive strength and the splitting tensile strength of the concrete are obviously improved along with the prolonging of the curing time, and the compressive strength and the splitting tensile strength of the high-strength recycled concrete prepared in the embodiment 3 are the most excellent; when the high-strength recycled concrete in the embodiment 3 is in the curing age of 28d, the compressive strength of the recycled concrete with the recycled aggregate substitution rate of 50 percent can reach 65.6MPa, the splitting tensile strength reaches 4.26MPa, and the standard of the high-strength concrete is met. The result shows that the doping and proportion of the mineral admixture have very important influence on the strength of the recycled concrete, the mechanical property obtained by the proportioning of the mineral admixture in the embodiment 3 of the invention is optimal, and the high-performance recycled concrete which can reach the standard of high-strength concrete is also obtained.
2. Recycled concrete durability study
Durability was studied with Na2SO4-MgSO4NaCl Complex salt solution as an aggressive Medium (Na in it)2SO47.5 percent of MgSO4The mass fraction is 7.5%, the mass fraction of NaCl is 5%, so the total concentration of the composite salt solution is 20%), the dynamic elastic modulus, the mass, the compressive strength and the splitting tensile strength of the recycled concrete are tested after 180 times of dry-wet alternation, and the specific implementation process is as follows:
(1) placing the recycled concrete test piece which is maintained for 90 days in an air-blast drying oven to be dried for 48 hours at the temperature of 60 ℃, and then cooling to room temperature in the oven;
(2) testing the initial dynamic elastic modulus, the quality, the compressive strength and the splitting tensile strength of the test piece;
(3) placing the test piece in water to be soaked for 4 days to saturate the concrete test piece with water;
(4) placing the water-saturated test piece in a composite salt solution to carry out a dry-wet alternation test, wherein the dry-wet alternation operation comprises the following steps: na (Na)2SO4-MgSO4Soaking in NaCl complex salt solution for 15 hours, airing for 1 hour indoors, drying for 7 hours at 60 ℃, and cooling for 1 hour indoors, wherein the total time is 24 hours; testing the pH value of the compound salt solution by using a handheld pH meter every 7 days, adjusting the pH value of the solution to 7.0 +/-0.5 by using analytically pure concentrated sulfuric acid, and replacing the solution every 30 days;
(5) after the dry-wet alternation is carried out for 180 times, the test piece is dried for 48 hours at the temperature of 60 ℃, the dynamic elastic modulus, the quality, the compressive strength and the splitting tensile strength of the test piece are tested again, and the relative value of each index is calculated; the tests are shown in fig. 3 to 6, and the durability index of the recycled concrete is shown in table 3:
TABLE 3 recycled concrete durability index
The results show that compared with the corresponding physical mechanical indexes of the non-eroded recycled concrete test piece, the mechanical property and the relative dynamic elastic modulus of the recycled concrete eroded for a long time have certain losses, after the dry-wet alternation is carried out for 180 times, the loss rate of the relative dynamic elastic modulus of the recycled concrete test piece prepared in the embodiment 3 of the invention is 3.52 percent, the loss rate of the mass is 0, the loss rate of the compressive strength is 4.93 percent, and the loss rate of the cleavage tensile strength is 2.75 percent, although the mechanical property of the recycled concrete prepared in the embodiment 3 of the invention is reduced, the performance is not obviously reduced, which indicates that the recycled concrete prepared in the embodiment 3 of the invention has excellent corrosion resistance, and is obviously superior to that of the recycled concrete prepared in the comparative examples 1 to 3; meanwhile, compared with the comparative example 1, the mechanical property, the mass loss rate and the relative dynamic elastic modulus are obviously superior to those of the comparative example 1, which shows that the addition of the mineral admixture has a positive effect on the corrosion resistance of the recycled concrete; the comparison of comparative examples 1 to 3 shows that the proportion of mineral admixtures also has a very important influence on the corrosion resistance.
In summary, the applicant provides the optimum recycled concrete mass mix ratio, which is shown in table 4:
TABLE 4 final preferred recycled concrete mass mix ratio
It will be apparent to those skilled in the art that various changes and modifications may be made in the present invention without departing from the spirit and scope of the invention. Thus, if such modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include such modifications and variations.
Claims (8)
1. The high-strength recycled concrete is characterized by being prepared from the following raw materials in parts by weight: 290 portions of cement and 443 portions; 20-70 parts of fly ash; 20-70 parts of slag; 20-70 parts of silica fume; 20-70 parts of metakaolin; 650 portions and 750 portions of fine aggregate; 550 portions of natural coarse aggregate and 600 portions of natural coarse aggregate; 450 portions and 510 portions of recycled coarse aggregate; 4.0-7.0 parts of a water reducing agent; 140 portions of water and 160 portions.
2. The high-strength recycled concrete according to claim 1, which is prepared from the following raw materials in parts by weight: cement 300-; 30-45 parts of fly ash; 30-45 parts of slag; 30-45 parts of silica fume; 30-45 parts of metakaolin; 720 parts of fine aggregate; 550 portions of natural coarse aggregate and 580 portions of natural coarse aggregate; 480 portions of regenerative coarse aggregate and 505 portions; 5.0-6.0 parts of a water reducing agent; 150 portions and 160 portions of water.
3. The high-strength recycled concrete according to claim 1, which is prepared from the following raw materials in parts by weight: 311 parts of cement; 33 parts of fly ash; 33 parts of slag; 33 parts of silica fume; 33 parts of metakaolin; 705 parts of fine aggregate; 560 parts of natural coarse aggregate; 498 parts of recycled coarse aggregate; 5.54 parts of a water reducing agent; 155 parts of water.
4. A high-strength recycled concrete according to any one of claims 1 to 3,
the cement is P.O42.5 portland cement;
the fly ash is II-grade F-type low-calcium fly ash;
the slag is granulated slag of grade S95;
the silica fume is 920U silica fume, and the volume of the silica fumeThe density was 272kg/m3；
The metakaolin is prepared from calcined kaolin, and the activity index of the metakaolin in 7 days is 113%;
the fine aggregate is Weiriver sand with fineness modulus of 2.75;
the natural coarse aggregate is single-particle-size crushed stone with the particle size of 16-25 mm;
the recycled aggregate is a continuous graded recycled concrete aggregate with the particle size of 5-20 mm;
the water reducing agent is a PCA-I type polycarboxylic acid high-performance water reducing agent, the solid content is 30 percent, and the water reducing rate is 28 percent.
5. The method for preparing high-strength recycled concrete according to claim 1, comprising the following steps:
(1) weighing: weighing the following raw materials in parts by weight: 290 portions of cement and 443 portions; 20-70 parts of fly ash; 20-70 parts of slag; 20-70 parts of silica fume; 20-70 parts of metakaolin; 650 portions and 750 portions of fine aggregate; 550 portions of natural coarse aggregate and 600 portions of natural coarse aggregate; 450 portions and 510 portions of recycled coarse aggregate; 4.0-7.0 parts of a water reducing agent; 140 portions of water and 160 portions for standby;
(2) pre-wetting recycled aggregate: prewetting the recycled coarse aggregate dried to constant weight to obtain prewetted recycled aggregate;
(3) preparing a cementing material: uniformly mixing cement, fly ash, slag, silica fume and metakaolin to obtain a cementing material, and then dividing the cementing material into an M1 cementing material and an M2 cementing material by mass, wherein the M1 cementing material accounts for 45-55% of the total mass;
(4) preparing a water reducing agent solution: dividing water into W1 water and W2 water by mass, and uniformly mixing the W2 water with a water reducing agent to obtain a water reducing agent solution, wherein the W2 water accounts for 45-55% of the total amount;
(5) preparing the pulp-coated recycled aggregate: mixing the pre-wetted recycled aggregate in the step (2), the M1 cementing material in the step (3) and the W1 water in the step (4) for 30-50s to obtain a pulp-coated recycled aggregate;
(6) preparing primary stirring recycled concrete: adding natural fine aggregate into the pulp-coated recycled aggregate in the step (5) and stirring for 50-70s to obtain primary stirred recycled concrete;
(7) preparing the cementing material slurry-wrapped concrete: adding an M2 gelled material into the primary stirring recycled concrete in the step (6), and stirring for 25-35s to obtain gelled material slurry-coated concrete;
(8) preparing high-strength recycled concrete: adding natural coarse aggregate into the cementing material slurry-wrapped concrete in the step (7), stirring, adding a water reducing agent solution within 15-30s, and continuously stirring for 35-45s to obtain high-strength recycled concrete;
and discharging internal bubbles from the high-strength recycled concrete in the test mould, and maintaining after floating.
6. The method for preparing high-strength recycled concrete according to claim 5, wherein the pre-wet water mass in the step (2) is 90% of the water absorption of the recycled coarse aggregate.
7. The method for preparing high-strength recycled concrete according to claim 5, wherein the curing in the step (8) is performed by: curing the film for 24h at room temperature, adding saturated Ca (OH)2Curing in the solution for 28 days, and then curing for 90 days under natural conditions.
8. The use of a high strength recycled concrete according to claim 1 in construction works in salt-corrosion environments in the northwest region.
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