CN109320118B

CN109320118B - Dry-spraying or wet-spraying concrete nano-grade admixture and use method thereof

Info

Publication number: CN109320118B
Application number: CN201811330008.9A
Authority: CN
Inventors: 丁建彤; 雷英强; 杨森; 李晓华; 程安文; 李凤玉; 吴勇
Original assignee: Sinohydro Bureau 7 Co Ltd
Current assignee: Sinohydro Bureau 7 Co Ltd
Priority date: 2018-11-09
Filing date: 2018-11-09
Publication date: 2021-12-28
Anticipated expiration: 2038-11-09
Also published as: CN109320118A

Abstract

The invention discloses a dry-spraying or wet-spraying concrete nano-grade admixture and a use method thereof, wherein the admixture comprises the following components in percentage by weight: 94-99% of nano amorphous silicon dioxide powder, 1-4% of water reducing agent, 0.00-0.08% of thickening component and 0-2% of retarding component; the loose bulk density of the nano amorphous silicon dioxide powder is less than or equal to 400kg/m in a natural dry state³Preferably ≤ 300kg/m³Under a high-power electron microscope, the powder particles are in a dispersed single-particle state and have no obvious aggregate. When in use, the admixture and the coarse aggregate are stirred to promote the amorphous silicon dioxide powder to be further dispersed under the kneading of the coarse aggregate, and other materials are added. The comprehensive admixture and the innovation of the using method effectively shorten the initial setting time and the final setting time of the concrete, can effectively reduce the rebound rate and the dust amount of the concrete, improve the strength and the durability of the concrete, and are beneficial to reducing the comprehensive construction cost of the sprayed concrete.

Description

Dry-spraying or wet-spraying concrete nano-grade admixture and use method thereof

Technical Field

The invention relates to the technical field of production and use of concrete, in particular to a dry-spraying or wet-spraying concrete nano-grade admixture and a use method thereof.

Background

The sprayed concrete is widely used for underground engineering excavation support, rock engineering excavation support such as side slopes and foundation pits, repairing and reinforcing engineering and the like. According to the common spraying process, the concrete is divided into dry spraying (short for dry spraying or dry spraying), wet spraying (short for wet spraying or wet spraying), wet spraying (short for wet spraying or semi-wet spraying) and cement sand-coated sprayed concrete. The dry spraying concrete is prepared by mixing cement, sand and stone with natural water content according to a certain mixing ratio to obtain a dry-dispersed mixture, loading the mixture into a spraying machine, and conveying the concrete to a nozzle under the condition of 'micro-tide' (the water-cement ratio is 0.10-0.20) to be sprayed by adding water pressure. The wet spraying concrete is prepared by conveying a concrete mixture with a water-to-cement ratio of 0.30-0.60 and a slump of more than 100mm to a nozzle for pressurizing and spraying. The wet sprayed concrete is prepared by mixing cement, sand, stone and partial mixing water according to a certain mixing ratio to obtain a wet mixture (the water-cement ratio is 0.20-0.35), loading the wet mixture into a spraying machine, conveying the wet mixture to a nozzle, adding the rest mixing water, mixing and spraying. The cement sand-wrapped sprayed concrete is prepared by firstly adding part of sand into mixing water for pre-wetting (the water-cement ratio is 0.15-0.20), then adding cement into the sand for stirring, mixing the cement with coarse aggregate, then pumping the mixture to a nozzle, adding the rest mixing water into the nozzle for mixing, and then spraying the mixture.

Among the above modes, the dry spray rebound rate is the highest, generally reaching 20-40%, and the dust concentration is also the highest. The rebound rate and dust concentration of the wet spray are also higher.

The common measures in the prior art for reducing the rebound rate and high dust concentration of dry-sprayed and wet-sprayed concrete include adding silica fume (also called silica fume, micro silica fume) and nano SiO₂Admixture such as fly ash and chemical admixture such as water reducing agent and tackifier. However, the prior patent and literature documents do not mention the silica fume and the nano SiO₂The special requirements of the loose bulk density and the particle dispersibility of the nano-grade amorphous silica powder or the loose bulk density is considered to have no influence on the effect of the powder applied to the sprayed concrete.

For example, as for one of the common amorphous Silica powders such as Silica Fume, it is said in the report of "Silica Fume User guide" (Silica Fume User's Manual) published by the international Silica Fume association in 2005: "after years of testing, there is no data indicating which form of (silica fume) product is more effective in concrete mixes than the other forms".

As another example, an invention patent C, previously filed and granted by one of the inventors of the present inventionN201210343040.7 nanometer level sprayed concrete modified admixture, which is characterized in that₂Is SiO₂High activity nano-particle material with the content of more than or equal to 95 percent and the volume average diameter D (4,3) of nano-level sprayed concrete modified admixture powder particles is less than or equal to 150nm, and loose bulk density and particle dispersibility are not mentioned.

The invention patent application CN201810248219.1 ' an admixture for shotcrete ' comprises 50-80 parts of expanded superfine silicon powder ', but does not mention any characteristics of the silicon powder.

The silica fume contained in the composition of the invention patent application CN201510968974.3 ' early strength type sprayed concrete ' is characterized in that ' the specific surface area of the silica fume is 10000-30000 cm²However, the loose bulk density and particle dispersibility of the silica fume are not mentioned, and the rebound resilience of the concrete with the composition can only reach less than or equal to 15 percent and is still high.

The silica fume contained in the composition of invention patent application CN201810036120.5 ' A high-strength low-resilience shotcrete and its construction process ' is characterized by that ' the commercially available silica fume used for shotcrete preferably has an average particle size of 0.1-0.3 mu m and a specific surface area of 20m²/g～28m²Silica fume in g ", but the loose bulk density and particle dispersion of this silica fume are not mentioned. And the mixing amount of the high-performance.

The silica fume contained in the composition of "a cement specially used for shotcrete doped with an alkali-free liquid accelerator" of patent application CN201810189927.2 is characterized in that "said silica fume is ultrafine silica fume having an average particle diameter of 1.5 μm to 10 μm", but the loose packing density and particle dispersibility of this silica fume are not mentioned, and it is known from the examples thereof that even if this composition is used for wet shotcrete having a lower rebound rate than that of dry shotcrete or wet shotcrete, the rebound rate (not described as the comprehensive rebound rate or the side wall rebound rate) is as low as 10.4% or less and still higher.

The silicon powder contained in the composition of "a high-strength ultramicro shotcrete admixture" of the invention patent application CN201710085030.0 is characterized in that the expanded superfine silicon powder comprises silicon dioxide, ferric oxide and aluminum oxide, and the weight ratio of the three substances is 67.5-83.7: 4.5-5.6: 0.6-0.7 percent of the expanded superfine silicon powder, wherein the expanded superfine silicon powder comprises silicon dioxide, ferric oxide and aluminum oxide, and the weight ratio of the silicon dioxide to the ferric oxide to the aluminum oxide is 76.9: 4.9: 0.65 ' and ' the particle size of the expanded ultrafine silica fume is 1.5 to 10 mu m ', but the loose bulk density and particle dispersibility of the silica fume are not mentioned, and the specific rebound reduction effect of the admixture for dry-sprayed or wet-sprayed concrete is not mentioned.

The prior art relates to silicon powder and nano SiO₂The research of the nano amorphous silicon dioxide powder is mainly carried out aiming at the conventional cast concrete constructed by a non-spraying process. Compared with sprayed concrete, the conventional cast concrete has larger grain diameter and higher content of coarse aggregate, and grain aggregates in the powder are more easily scattered by the coarse aggregate in the stirring process, so that the influence of the difference of the particle dispersibility on the performance of the concrete is covered.

With respect to the water-reducing component of the admixture, the prior art does not specify the physical form of the powdered admixture used for dry-spray or wet-spray concrete or the water-reducing component of the admixture. In the processing of the powdery materials, if the liquid water-reducing component is used, the liquid water-reducing component is easy to adhere to other powdery components and agglomerate after being fed due to low mixing amount, and the mixing uniformity of the powdery materials is difficult to ensure.

In addition, the special requirement of dry-spraying or wet-spraying concrete on the dissolution rate of a water reducing agent when dry-hardening concrete with low water consumption is adopted is ignored in the prior art, the time for mixing dry or wet mixture mixed by a mixing plant with water in a spray gun is less than 1s, if the dry or wet mixture cannot be rapidly dissolved in the short time, the sprayed mixture has insufficient workability and cannot be well attached to a sprayed surface, so that the rebound is larger, the concrete is not uniform enough, the strength fluctuation is caused, and spray gun workers are forced to improve the workability of the mixture by adding more water, and the strength of the concrete is reduced.

Furthermore, the prior art does not fully exert the water reducing function of the water reducing agent. But the admixture is only added into the admixture or admixture for dry-spraying or wet-spraying concrete in a general way, but the water reducing agent with higher water reducing rate is not realized for the dry and hard concrete with low water consumption, so as to reduce the water adding amount required by a spray gun mouth, reduce the water-cement ratio of the concrete, ensure the strength of the concrete, or increase the workability of the mixture under the same water adding amount, thereby reducing the resilience and dust. The water reducing rate of the common polycarboxylic acid water reducing agent sold in the market only meets the requirement that the water reducing rate is more than or equal to 25 percent in the national standard GB8076 concrete admixture, and most of the water reducing rate is 25 to 28 percent.

For example, in an invention of CN201210343040.7 patent CN201210343040.7, the inventor of the present invention has previously filed and granted "nano-level shotcrete modified admixture", the surfactant is characterized by being only "composed of one of organic powders such as polycarboxylic acids, naphthalene surfactants, aliphatic compounds, and sulfamates", and the physical form (liquid or powder) and technical properties of the polycarboxylic acid surfactant are not further described.

As another example, the water-reducing agent mentioned in patent application CN 200810044240.6 "shotcrete" (withdrawn) is characterized by "said concrete also comprises silica fume, water-reducing agent, said silica fume being 0-5% by weight of cement, and water-reducing agent being 0-0.8% by weight of cement", but the physical form (liquid or powder) and technical properties of this water-reducing agent are not mentioned.

For another example, the water reducing agent mentioned in patent application CN201710085030 "a high-strength ultra-micro shotcrete admixture" is characterized in that "the powder plasticizer is a polycarboxylic acid-based high-performance water reducing agent, and the solid content of the polycarboxylic acid-based water reducing agent is 97% -98%", but the physical form (liquid or powder) and the technical performance of the water reducing agent are not mentioned.

For another example, in patent application CN201711294401, "a special composite admixture for low-resilience and anti-corrosion shotcrete and application", the mentioned water reducing agent is characterized by "being any one or more of naphthalene-based water reducing agents, acetone and polycarboxylic acid-based water reducing agents", but the physical form (liquid or powder) and technical properties of the water reducing agent are not mentioned.

The prior art is silent as to the effect of these processes on dry-or wet-blown concrete resilience, strength and dust content with or without the use of nanoscale admixtures, with respect to the order of mixing and the standards for controlling mixture wetting. For example, GB 50086-.

Disclosure of Invention

The invention aims to overcome the defects of the prior art and provides a dry-spraying or wet-spraying concrete nano-grade admixture and a using method thereof, which can effectively shorten initial setting and final setting time, reduce the rebound rate and dust amount of concrete, improve the strength of the concrete and reduce the comprehensive construction cost.

The purpose of the invention is realized by the following technical scheme: a dry-spraying or wet-spraying concrete nano-scale admixture comprises the following components in percentage by weight: 94-99% of nano amorphous silicon dioxide powder, 1-4% of water reducing agent, 0.00-0.08% of thickening component and 0-2% of retarding component;

the nano amorphous silicon dioxide powder has loose bulk density of less than or equal to 400kg/m in a natural drying state³When the powder particles are observed under a high-power electron microscope, the powder particles are in a dispersed single-particle state and have no obvious aggregate.

SiO in the nano-scale amorphous silicon dioxide powder₂The content is more than or equal to 80 percent, and the particle diameter of the nano amorphous silicon dioxide powder is 0.1-1000 nm.

The nano amorphous silicon dioxide powder comprises silica fume and gas phase method nano SiO₂Precipitation method of nano SiO₂Chemical synthesis of nano SiO₂Any one or a combination of more of them.

The water reducing agent is a powdery high-performance water reducing agent, the powdery high-performance water reducing agent is obtained by using a polymer synthesized by a carboxyl unsaturated monomer and other monomers in a liquid phase as a matrix and performing spray drying, the water reducing rate is more than or equal to 25 percent, the dissolution rate is more than or equal to 95 percent, the dissolution time is less than 30s, the 40 mu m screen residue is less than or equal to 10 percent, and the 80 mu m screen residue is less than or equal to 5.0 percent.

The thickening component is a powdery thickening component, and the powdery thickening component comprises any one or combination of a plurality of water-soluble polymers of polyethylene oxide, polyacrylamide, polyvinyl alcohol, ethylene copolymerized carboxyl compound, degraded starch and derivatives thereof, cellulose derivatives, sodium alginate, natural guar gum, natural welan gum and natural xanthan gum.

The retarding component is powder retarding component, which comprises one or more of inorganic salts, hydroxy carboxylates, polyhydroxy carbohydrates, celluloses and lignosulfonates.

The inorganic salt retarding component comprises phosphate, borax and zinc sulfate;

the hydroxy carboxylate retarding component comprises sodium gluconate, citric acid, tartaric acid, malic acid, maleic acid, succinic acid and salts thereof;

the polyhydroxy carbohydrate retarding component comprises glucose, sucrose, molasses and maltodextrin;

the cellulose retarding component comprises methyl cellulose and carboxymethyl cellulose;

the lignosulfonate retarding component comprises calcium lignosulfonate, magnesium lignosulfonate and sodium lignosulfonate.

The use method of the dry-spraying or wet-spraying concrete nano-grade admixture comprises the following steps:

s1: uniformly stirring the admixture and the coarse aggregate to obtain a mixture;

s2: the cement, other additives to be added, sand and water are added to the mixture, and the total water content is controlled so that the total water content of each concrete including the water content of the sand and stone calculated on the basis of the dry state is 65kg to 90 kg.

The method for testing the loose bulk density of the nano amorphous silica powder comprises the following steps:

filling the powder into a container with a known volume, leveling, weighing to obtain the net weight of the nano amorphous silica powder, dividing the net weight by the volume of the container to obtain the loose bulk density, and taking the average value of at least two test results as the measurement result.

The invention has the beneficial effects that:

1) the admixture replaces cement in dry-sprayed or wet-sprayed concrete according to the doping amount of 8-12%, so that the initial setting and final setting time of the concrete can be shortened by over 50%, and the initial setting and final setting time is effectively shortened; the comprehensive rebound rate of the sprayed concrete is reduced by more than 70 percent, and the rebound rate and the dust content of the concrete are effectively reduced; the one-time spraying thickness can reach 50cm, the spraying construction speed is improved by 4-8%, the dust concentration is obviously reduced, and the comprehensive construction cost of the sprayed concrete is reduced; for dry-sprayed or wet-sprayed concrete with the water-cement ratio of 0.55-0.40 and doped with qualified products or first-class accelerators meeting the current standard specifications, the 12h strength can reach 8-12 MPa, the 1d strength can reach 15-20 MPa, and the 28d strength is improved by more than 30 percent compared with that of a water-cement ratio control group; for dry-spraying or wet-spraying concrete with the water-cement ratio of 0.39-0.28, the 1d strength can reach 20-30 MPa, and the 28d strength can reach 50-60 Mp, so that the strength of the concrete is effectively improved, and the durability is correspondingly improved.

2) The amorphous silica powder with small loose bulk density and highly dispersed particles is adopted, the physical adsorption and chemical activity effects of the nanoscale powder are fully exerted, and the cohesiveness and the adhesiveness of dry-sprayed or wet-sprayed concrete are improved, so that the key effects of shortening the setting time, reducing the rebound rate, increasing the thickness of a one-time sprayed layer and reducing dust are achieved.

3) The characteristic of high water reducing rate of the powdery high-performance water reducing agent is beneficial to reducing the water consumption and the water-cement ratio of dry-sprayed or wet-sprayed concrete, thereby improving the strength of the concrete; the characteristic of high dissolution rate is beneficial to ensuring that dry-sprayed or wet-sprayed concrete is quickly wetted and thinned after being stirred in a mixing plant and being mixed by adding water in a spray gun, and has good plasticity and adhesiveness, thereby reducing the resilience of the concrete and improving the homogeneity of the concrete.

4) The use method of the admixture can promote the amorphous silicon dioxide powder in the admixture to be further dispersed under the kneading of the coarse aggregate by adding the admixture and the coarse aggregate and then adding other materials, and can ensure that the total water content of each concrete including the water content of the sand stone calculated on the basis of the dry state is 65 kg-90 kg by controlling the water adding amount, control the wettability of the mixture, provide necessary water required by the dissolution of the water reducing agent in the admixture, enable the water reducing agent to play the wetting and plasticizing roles as soon as possible, be beneficial to reducing the rebound and dust of the concrete, reduce the water adding amount at a spray gun so as to improve the strength of the concrete and simultaneously prevent the spray pipe from being blocked due to over-wetting.

Drawings

FIG. 1 is a typical image of an amorphous silica powder according to the present invention observed under a high scanning electron microscope;

FIG. 2 shows the bulk density at 400kg/m³The above-mentioned particle dispersion state of the amorphous silica powder.

Detailed Description

The technical solutions of the present invention will be described clearly and completely with reference to the following embodiments, and it should be understood that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be obtained by a person skilled in the art without inventive effort based on the embodiments of the present invention, are within the scope of the present invention.

A dry-spraying or wet-spraying concrete nano-scale admixture comprises the following components in percentage by weight: 94-99% of nano amorphous silicon dioxide powder, 1-4% of water reducing agent, 0.00-0.08% of thickening component and 0-2% of retarding component.

The nanometer amorphous silicon dioxide powder comprises silica fume (also called silica powder, micro silica powder) and gas phase method nanometer SiO₂Precipitation method of nano SiO₂Chemical synthesis of nano SiO₂The silicon ash is produced by smelting industrial silicon and ferrosilicon in an industrial electric furnace at high temperatureThe smoke and dust escaping with the waste gas is collected and processed by a special collecting device to form powder.

SiO in the nano-scale amorphous silicon dioxide powder₂The content is more than or equal to 80 percent, and SiO in the optimized nano-scale amorphous silicon dioxide powder₂The content is more than or equal to 90 percent, and the loose bulk density is less than or equal to 400kg/m in a natural dry state³Preferably, the loose bulk density is less than or equal to 300kg/m³When the nano-grade amorphous silicon dioxide powder is observed under a high-power electron microscope, the particle diameter of the nano-grade amorphous silicon dioxide powder is 0.1-1000 nm, and the powder particles are in a dispersed single-particle state and have no obvious aggregate.

The amorphous silicon dioxide powder has small loose bulk density and highly dispersed particles, and effectively reduces the rebound rate of sprayed concrete; the powder with the dispersion characteristic has no obvious granular feeling when fingers are twisted because no large particle cluster is formed by aggregating small particles.

An example of the particle highly dispersive characteristics of the amorphous silica powder is shown in fig. 1, which is an image observed under a high power (5 ten thousand times) scanning electron microscope, and individual particles can be clearly distinguished. The powder with the dispersion characteristic has no obvious granular feeling when fingers are twisted because no large particle cluster is formed by aggregating small particles. In contrast, the bulk density shown in FIG. 2 is 400kg/m³The amorphous silicon dioxide powder has obvious granular feel when being visually inspected and twisted by fingers, larger particles with the diameter of about 1mm can be seen in the falling process, the powder is large in loose bulk density and poor in particle dispersibility, particle aggregates with the nominal particle size being larger are formed although the particle size of each particle is also nanoscale, and the particle aggregates cannot be redispersed under the simple stirring process of dry spraying or wet spraying concrete, so that the function of huge specific surface area of nanoscale materials cannot be exerted.

The amorphous silicon dioxide powder plays a role in physical adsorption and chemical activity of nano-scale powder and plays a key role in increasing the cohesiveness and the adhesiveness of dry-sprayed or wet-sprayed concrete, thereby shortening the setting time, reducing the rebound rate, increasing the thickness of a one-time sprayed layer and reducing dust.

The water reducing agent is a powdery high-performance water reducing agent, the powdery high-performance water reducing agent is obtained by taking a polymer synthesized by a carboxyl unsaturated monomer and other monomers in a liquid phase as a matrix and performing intermediate-temperature rapid (within 10 s-20 s) spray drying at 90-110 ℃, the water reducing rate detected by GB8076 concrete admixture is more than or equal to 25%, preferably, the water reducing rate is more than or equal to 30%, the water reducing rate is high, the dissolution rate in water at 5-35 ℃ is more than or equal to 95%, the dissolution time is less than 30s, the dissolution rate is rapid, the 40 mu m screen residue is less than or equal to 10%, and the 80 mu m screen residue is less than or equal to 5.0%.

The characteristic of high water reducing rate of the powdery high-performance water reducing agent is favorable for reducing the water consumption and the water-cement ratio of dry-sprayed or wet-sprayed concrete, thereby improving the strength of the concrete; the characteristic of high dissolution rate is beneficial to ensuring that dry-sprayed or wet-sprayed concrete is quickly wetted and thinned after being stirred in a mixing plant and being mixed by adding water in a spray gun, and has good plasticity and adhesiveness, thereby reducing the resilience of the concrete and improving the homogeneity of the concrete.

The thickening component is a powdery thickening component, and the powdery thickening component comprises polyethylene oxide, polyacrylamide, polyvinyl alcohol and ethylene copolymerized carboxyl compound which take ethylene as raw material, semi-artificially synthesized degraded starch and derivatives thereof, cellulose derivatives, sodium alginate, and any one or combination of more water-soluble polymers of natural guar gum, welan gum and xanthan gum.

The retarding component is a powdery retarding component, the powdery retarding component comprises any one or a combination of more of inorganic salts, hydroxycarboxylic acid salts, polyhydroxy carbohydrates, celluloses and lignosulfonate, the inorganic salt retarding component comprises phosphate, borax and zinc sulfate, the hydroxycarboxylic acid salt retarding component comprises sodium gluconate, citric acid, tartaric acid, malic acid, maleic acid, succinic acid and salts thereof, and the polyhydroxy carbohydrates retarding component comprises glucose, sucrose, molasses and maltodextrin; the cellulose retarding component comprises methyl cellulose and carboxymethyl cellulose; the lignosulfonate retarding component comprises calcium lignosulfonate, magnesium lignosulfonate and sodium lignosulfonate.

Control group

The raw materials used are P.O 42.5 ordinary portland cement, granite pea stone with nominal grain diameter of 10mm, granite artificial sand with fineness modulus of 2.7 and stone powder content of 12%, powdery low-alkali setting accelerator with alkali content of 12% and tap water.

The mixing proportion of the used dry-spraying concrete is P.O 42.5 ordinary portland cement: sand: and (3) bean stones: blending materials: water: powdery low-alkali setting accelerator (397): 882: 882: 43: 185: 21.5, using a rated capacity of 5m³And (3) constructing by a PZ-5D type dry spraying machine, testing the comprehensive rebound rate of the spray on 1 section of III-type surrounding rock with the length of 3m and the height of 5m and a U-shaped chamber side top arch with a steel bar hanging net, and taking a large plate to test the compressive strength of the core sample.

The properties of the concrete obtained are shown in Table 1.

Example one

A dry-spraying or wet-spraying concrete nano-scale admixture comprises the following components in percentage by weight: 99 percent of silica fume and 1 percent of powdery polycarboxylic acid high-performance water reducing agent.

Other raw materials used for shotcrete were the same as those used for the control group.

The preparation process of the sprayed concrete comprises the following steps: the method comprises the steps of firstly uniformly stirring the nanoscale admixture and coarse aggregate in a double-horizontal-shaft forced stirrer for 30s, then adding cement, sand and a certain amount of water to enable the total water content of concrete in each direction including the water content of sand and stone (calculated on the basis of a dry state) to be 65kg, wherein the wettability of the concrete after uniform stirring reaches the degree that the concrete can be kneaded into a cluster by hands and does not slump in 1-2 seconds after the fingers are loosened.

With a rated capacity of 5m³And (3) constructing by a PZ-5D type dry spraying machine, testing the comprehensive rebound rate of the spray on 1 section of III-type surrounding rock with the length of 3m and the height of 5m and a U-shaped chamber side top arch with a steel bar hanging net, and taking a large plate to test the compressive strength of the core sample.

The properties of the concrete obtained are shown in Table 1.

Example two

A dry-spraying or wet-spraying concrete nano-scale admixture comprises the following components in percentage by weight: 98% of silica fume, 1% of powdery polycarboxylic acid high-performance water reducing agent and 1% of sodium citrate.

The preparation process of the shotcrete was the same as in the first example.

The properties of the concrete obtained are shown in Table 1.

EXAMPLE III

A dry-spraying or wet-spraying concrete nano-scale admixture comprises the following components in percentage by weight: 98.99 percent of silica fume, 1 percent of powdery polycarboxylic acid high-performance water reducing agent and 0.01 percent of 10 ten thousand molecular weight cellulose ether.

The preparation process of the shotcrete was the same as in the first example.

The properties of the concrete obtained are shown in Table 1.

Example four

A dry-spraying or wet-spraying concrete nano-scale admixture comprises the following components in percentage by weight: 90.92% of silica fume and gas phase method nano SiO₂5 percent of powdery polycarboxylic acid high-performance water reducing agent and 0.08 percent of 10 ten thousand molecular weight cellulose ether.

The preparation process of the shotcrete was the same as in the first example.

With a rated capacity of 5m³Construction and test injection of PZ-5D type dry spraying machineAnd (3) obtaining 1 section of 3m long and 5m high comprehensive resilience rate of the III-type surrounding rock and the U-shaped chamber side arch with the steel bar hanging net, and taking a large plate to test the compressive strength of the core sample.

The properties of the concrete obtained are shown in Table 1.

EXAMPLE five

A dry-spraying or wet-spraying concrete nano-scale admixture comprises the following components in percentage by weight: 84% of silica fume and chemical synthesis method of nano SiO₂10 percent of powdery polycarboxylic acid high-performance water reducing agent and 2 percent of sodium gluconate.

The preparation process of the shotcrete was the same as in the first example.

The properties of the concrete obtained are shown in Table 1.

TABLE 1 shotcrete Properties with nanoscale admixtures

As can be seen from Table 1: compared with the examples, the concrete of the control group has the lowest 24h compressive strength and 28d compressive strength, and the final setting time and the rebound rate of the sprayed concrete are far higher than those of the concrete of the examples, so that the material cost waste and the time waste are great.

In the first embodiment, the amorphous silicon dioxide powder and the powdery high-performance water reducing agent are added on the basis of the control group, the initial setting time, the final setting time and the rebound rate of the sprayed concrete are all lower than those of the control group, and the 24h compressive strength and the 28d compressive strength are all higher than those of the control group, so that the concrete performance of the control group is improved.

In the second embodiment, amorphous silica powder, a powdery high-performance water reducing agent and a powdery retarding component are added on the basis of a control group, and the initial setting time, the final setting time, the rebound rate, the 24h compressive strength and the 28d compressive strength of the sprayed concrete are slightly larger than those in the first embodiment.

In the third embodiment, amorphous silica powder, a powdery high-performance water reducing agent and a powdery thickening component are added on the basis of a control group, the initial setting time, the final setting time and the resilience rate of sprayed concrete are all lower than those of the first embodiment, the 24h compressive strength and the 28d compressive strength are all slightly higher than those of the first embodiment, and the performance of the concrete in the first embodiment is improved.

Example four addition of gas phase method-containing nano SiO based on control group₂The initial setting time, the final setting time and the rebound rate of the sprayed concrete are all lower than those of the third embodiment, and the 24h compressive strength and the 28d compressive strength are all slightly higher than those of the third embodiment, so that the performance of the concrete of the third embodiment is improved.

EXAMPLE V addition of chemical synthesis-containing Nano SiO on the basis of control group₂The initial setting time, final setting time and rebound rate of the sprayed concrete are all lower than those of the fourth example, and the 24h compressive strength and 28d compressive strength are all slightly higher than those of the fourth example

Example four, the concrete performance of example four was improved, and the best concrete performance was obtained in six experimental groups.

s1: and uniformly stirring the admixture (the mixing amount of the admixture is 8-12% of the total amount of the rubber material) and the coarse aggregate (generally 20-60 s, and the specific time depends on the efficiency of a stirrer) to obtain a mixture.

S2: adding cement, other additives, sand and water which need to be added into the mixture, and controlling the total water content, so that the total water content of each concrete including the water content of the sand and stone calculated on the basis of a dry state is 65 kg-90 kg, the specific water content is such that the wettability of the uniformly stirred concrete is better that the concrete can be kneaded into a mass by hands and cannot be wholly slumped within 1-2 seconds after the fingers are loosened, the wettability of the mixture is controlled, the necessary water required for dissolving the water reducing agent in the admixture can be provided, the water reducing agent can play a role in wetting and plasticizing as soon as possible, the rebound and dust of the concrete can be reduced, the water adding amount at a spray gun can be reduced, the strength of the concrete can be improved, and the spray gun cannot be blocked due to over-wetting.

The use method can promote the amorphous silicon dioxide powder in the admixture to be further dispersed under the kneading of the coarse aggregate by adding the nano amorphous silicon dioxide powder and the coarse aggregate and stirring the mixture and then adding other materials.

The admixture replaces cement, coal ash and other cementing materials in dry-sprayed or wet-sprayed concrete according to the doping amount of 8-12%, so that the initial setting time and the final setting time of the concrete can be shortened by more than 50%, the comprehensive rebound rate of sprayed concrete is reduced by more than 70% (the comprehensive rebound rate refers to the average rebound rate of a crown arch and a side wall of a typical tunnel, if parts such as side slopes mainly sprayed in the horizontal direction, the rebound rate can be reduced to less than or equal to 5%), the once-spraying thickness (the maximum thickness of once continuous spraying under the condition of spraying in the vertical direction of the crown arch of the tunnel and the like) can reach 50cm, the spraying construction speed is improved by 4-8%, the dust concentration is obviously reduced, and the comprehensive construction cost of the sprayed concrete is reduced. For dry-sprayed or wet-sprayed concrete with the water-cement ratio of 0.55-0.40 and doped with qualified products or first-class accelerators meeting the current standard specifications, the 12h strength can reach 8-12 MPa, the 1d strength can reach 15-20 MPa, and the 28d strength is improved by more than 30 percent compared with that of a water-cement ratio control group; for dry-spraying or wet-spraying concrete with the water-to-glue ratio of 0.39-0.28, the 1d strength can reach 20-30 MPa, and the 28d strength can reach 50-60 MPa.

The loose bulk density of the nano amorphous silicon dioxide powder does not have a standard test method at present, and in consideration of the reliability and repeatability of the test, the test method adopted by the invention comprises the following steps:

the method comprises the steps of filling powder into a container with a known volume (the calculation error can be reduced by adopting a container with a larger volume) with a volume of more than or equal to 5L, leveling, weighing to obtain the net weight of the nano amorphous silica powder, dividing the net weight by the volume of the container to obtain the loose bulk density, and taking the average value of at least two test results as a measurement result.

Specifically, a cylindrical container with the volume of 5L is adopted, nanoscale amorphous silicon dioxide powder is scooped into the container by a circular spoon with the opening diameter of 8-10 cm and filled in the container, then the container is stricken off by a straight ruler, the mass of the nanoscale amorphous silicon dioxide powder is weighed, the volume of the container calibrated by water in advance is divided, the loose bulk density is obtained, and the average value of two test results is used as the measurement result.

The foregoing is illustrative of the preferred embodiments of this invention, and it is to be understood that the invention is not limited to the precise form disclosed herein and that various other combinations, modifications, and environments may be resorted to, falling within the scope of the concept as disclosed herein, either as described above or as apparent to those skilled in the relevant art. And that modifications and variations may be effected by those skilled in the art without departing from the spirit and scope of the invention as defined by the appended claims.

Claims

1. A dry-spraying or wet-spraying concrete nano-scale admixture is characterized in that: comprises the following components in percentage by weight: 94-99% of nano amorphous silicon dioxide powder, 1-4% of water reducing agent, 0.00-0.08% of thickening component and 0-2% of retarding component;

the nano amorphous silicon dioxide powder has loose bulk density of less than or equal to 400kg/m in a natural drying state³When the nano-grade amorphous silicon dioxide powder is observed under a high-power electron microscope, the powder particles are in a dispersed single-particle state and have no obvious aggregate, and the particle diameter of the nano-grade amorphous silicon dioxide powder is 0.1-1000 nm; the nano amorphous silicon dioxide powder is nano SiO by chemical synthesis₂；

The water reducing agent is a powdery high-performance water reducing agent, the powdery high-performance water reducing agent is obtained by taking a polymer synthesized by a carboxyl unsaturated monomer and other monomers as a matrix and spray drying the matrix at 90-110 ℃ within 10-20 s, the water reducing rate is more than or equal to 25%, the dissolution rate is more than or equal to 95%, the dissolution time is less than 30s, the 40 mu m screen residue is less than or equal to 10%, and the 80 mu m screen residue is less than or equal to 5.0%.

2. The nanoscale admixture for dry-or wet-blown concrete according to claim 1, wherein: SiO in the nano-scale amorphous silicon dioxide powder₂The content is more than or equal to 80 percent.

3. The nanoscale admixture for dry-or wet-blown concrete according to claim 1, wherein: the thickening component is a powdery thickening component, and the powdery thickening component comprises any one or combination of a plurality of water-soluble polymers of polyethylene oxide, polyacrylamide, polyvinyl alcohol, ethylene copolymerized carboxyl compound, degraded starch and derivatives thereof, cellulose derivatives, sodium alginate, natural guar gum, natural welan gum and natural xanthan gum.

4. The nanoscale admixture for dry-or wet-blown concrete according to claim 1, wherein: the retarding component is powder retarding component, which comprises one or more of inorganic salts, hydroxy carboxylates, polyhydroxy carbohydrates, celluloses and lignosulfonates.

5. The nanoscale admixture for dry-or wet-blown concrete according to claim 4, wherein: the inorganic salt retarding component comprises phosphate, borax and zinc sulfate;

6. The method of using a dry-or wet-blown concrete nanoscale admixture according to any one of claims 1 to 5, characterized in that it comprises the following steps:

7. Use according to claim 6, characterized in that: the method for testing the loose bulk density of the nano amorphous silica powder comprises the following steps: