CN108658533B - Sprayed concrete and preparation method thereof - Google Patents

Abstract

The invention relates to sprayed concrete which comprises the following raw materials in parts by weight: 415-475 parts of portland cement, 40-60 parts of fly ash, 820-860 parts of sand, 724-764 parts of crushed stone with the particle size of 5-10mm, 28-36 parts of an accelerator, 1.1-1.9 parts of a polycarboxylic acid water reducing agent, 1.2-2.0 parts of an organic coagulant, 2.3-2.7 parts of methylene bisacrylamide, 10-16 parts of a solvent and 182-190 parts of water. The sprayed concrete is quickly solidified after being sprayed on a sprayed surface, and the initial strength and the later strength of the sprayed concrete meet the construction requirements of the sprayed concrete.

Description

Sprayed concrete and preparation method thereof

Technical Field

The invention relates to the field of high-performance concrete, in particular to shotcrete and a preparation method thereof.

Background

The shotcrete is a kind of concrete which is formed by spraying concrete onto a sprayed surface at a high speed by a spraying machine and is rapidly solidified and hardened, and therefore, the shotcrete needs to have characteristics of good fluidity and high early strength.

In the construction process of the sprayed concrete, gypsum in the cement becomes sodium sulfate under the action of the accelerating agent, and the retarding effect is lost, so that C in the cement is promoted₃A is quickly hydrated and C is separated out₃The hydration product crystal of A and cement slurry are quickly hardened to achieve the early strength effect, and meanwhile, concrete doped with the accelerator can be initially set within five minutes and finally set within ten minutes. Although the strength of the concrete in the initial stage is improved by the cement paste with the aid of the accelerator, the strength of the concrete on the sprayed surface is remarkably reduced in the later stage.

Disclosure of Invention

The invention aims to provide the sprayed concrete which is quick in initial setting and high in early strength, and meanwhile, the later strength can reach the use standard.

The above object of the present invention is achieved by the following technical solutions:

the sprayed concrete comprises, by weight, 415-475 parts of portland cement, 40-60 parts of fly ash, 820-860 parts of sand, 724-764 parts of crushed stone with a particle size of 5-10mm, 28-36 parts of an accelerator, 1.1-1.9 parts of a polycarboxylic acid water reducing agent, 1.2-2.0 parts of an organic coagulant, 2.3-2.7 parts of methylene bisacrylamide, 10-16 parts of a solvent and 182-190 parts of water; the organic coagulant is a mixture of nitrohumic acid and sodium humate; the weight ratio of the nitro humic acid to the sodium humate is 3: 1.

Preferably, the raw materials comprise, by weight, 445 parts of portland cement, 50 parts of fly ash, 840 parts of sand, 744 parts of crushed stone with the particle size of 5-10mm, 32 parts of an accelerator, 1.5 parts of a polycarboxylic acid water reducing agent, 1.6 parts of an organic coagulant, 2.5 parts of methylene bisacrylamide, 13 parts of a solvent and 186 parts of water.

By adopting the technical scheme, the accelerating agent is added into a concrete system, namely CaSO in cement₄Becomes Na under the action of the accelerating agent₂SO₄The retardation is lost, thereby promoting C in the cement₃A is rapidly hydrated and combined with water to form C₃AH₆Crystals of, C₃AH₆The crystal is separated out, and the cement slurry is quickly hardened. The organic coagulant is complexed with metal ions in cement during the hydration of cement to form complex ions with stable structure, and the complex ions generate complex salt with low solubility in the hydration of cement and with C in the system₃AH₆The crystal is precipitated at the same time, and the early strength of the sprayed concrete is improved.

The methylene bisacrylamide is crosslinked and self-polymerized in the cement hydration heat release process, the amide groups in the molecules have strong polarity, part of the amide groups are dissociated into multi-charge anions with large molecular weight in the cement slurry, and the polymers which can be self-polymerized into linear molecules gradually agglomerate into a curve shape due to more charges on the anions, so that the viscosity of the cement slurry is increased. Meanwhile, complex ions generated in the cement slurry are combined with the self-polymerization product along with the generation of the self-polymerization product, and then the separated complex salt is adsorbed on the methylene bisacrylamide polymerization product.

As the hydration of the cement enters the later stage, the unhydrated part of the cement generates Ca when meeting water²⁺Ca is generated²⁺The complex ions are formed again and adsorbed on the polymer of methylene-bisacrylamide, Ca (OH) in the concrete₂The content is reduced, the expansion degree of the concrete volume is greatly reduced, the strength of the concrete is continuously increased in the cement hydration process, and the later strength of the concrete is improved.

The fly ash has fine particle size, replaces part of cement, promotes the conversion of cement hydration products, and improves the strength of sprayed concrete; meanwhile, the fly ash has adhesiveness after meeting water and strong adhesive force, and the resilience of concrete is effectively reduced. In addition, the fly ash has the slight expansion effect, so that the drying shrinkage of the concrete is compensated to a certain extent, and the strength of the sprayed concrete is improved.

Preferably, the accelerating agent is a mixture of polyaluminium sulfate, sodium carbonate and quick lime.

Preferably, the weight ratio of the polyaluminium sulfate to the sodium carbonate to the quicklime is 0.5:1: 0.5.

By adopting the technical scheme, the accelerator is an important additive for early strength of concrete production, and promotes gypsum in cement to generate Na₂SO₄The cement slurry loses the retarding effect, wherein the polyaluminium sulfate overcomes the defect of short storage period of the aluminum soil.

Preferably, the polycarboxylate water reducer is a mixture of a maleic anhydride polycarboxylate water reducer and an acrylic polycarboxylate water reducer.

Through adopting above-mentioned technical scheme, maleic anhydride polycarboxylate water reducing agent and acrylic acid polycarboxylate water reducing agent are high efficiency water reducing agent, have fine dispersion effect to cement, and maleic anhydride polycarboxylate water reducing agent and acrylic acid polycarboxylate water reducing agent can adjust the pH valve in the cement slurry simultaneously, prevent that the accelerator of adding makes cement slurry basicity too high.

Preferably, the solvent is a mixture of ethylene glycol and ethyl acetate.

By adopting the technical scheme, the solvent is a mixture of ethylene glycol and ethyl acetate, polyaluminium sulfate, sodium carbonate and quick lime are dispersed in the solvent, and the accelerator is favorable for dispersing in the cement slurry when being mixed with the cement slurry.

The invention also aims to provide a preparation method of the shotcrete.

The above object of the present invention is achieved by the following technical solutions: a preparation method of shotcrete comprises the following steps:

s1: weighing portland cement and fly ash according to the specification, adding the portland cement and the fly ash into a stirrer, and stirring for l0min to obtain a mixture;

s2: weighing sand and crushed stone with the particle size of 5-10mm according to the specified weight, adding the weighed sand and crushed stone into the mixture obtained in S1, stirring for 15min, then adding water, and continuing stirring for 7min to obtain a mixture;

s3: weighing a polycarboxylate superplasticizer according to a specified weight, adding the polycarboxylate superplasticizer into the mixture obtained in S2, stirring for 9min, then adding an organic coagulant, and stirring for 5min to obtain a mixture;

s4: weighing the accelerating agent, the methylene bisacrylamide and the solvent according to the specified weight, adding the accelerating agent and the methylene bisacrylamide into the solvent, and stirring for 3min to obtain a mixture;

s5: and (3) loading the mixture obtained in the step (S3) into a sprayer, conveying the mixture to a spray head by using high-pressure air, introducing the mixture obtained in the step (S4) into the spray head of the sprayer, mixing the mixture obtained in the step (S3) with the mixture obtained in the step (S4), and spraying the mixture onto a sprayed surface at a high speed from the spray head.

By adopting the technical scheme, the cement and the fly ash are uniformly dispersed in water under the action of the polycarboxylate water reducer, the accelerator and the methylene acrylamide are firstly dispersed in the solvent, then the solvent is added into the sprayer of the sprayer and mixed with cement slurry sprayed out of the sprayer, and the two aggregates are sprayed on a sprayed surface after being temporarily combined. The concrete sprayed on the sprayed surface precipitates a large amount of crystals at the initial stage of cement hydration, and the sprayed concrete is immediately hardened. And after the spraying is finished, curing and forming the sprayed concrete to reach the use strength standard.

In conclusion, the invention has the following beneficial effects:

1. accelerating the generation of Na in gypsum in the early stage of cement hydration by using an accelerator₂SO₄The retarding effect is lost, thereby promoting the precipitation of a large amount of C from the cement₃AH₆The crystal and the concrete meet the initial setting requirement. Meanwhile, the organic coagulant is complexed with metal ions in the cement during the hydration of the cement, along with C in the cement system₃AH₆The crystal is separated out at the same time, and the early strength of the concrete sprayed on the sprayed surface is higher.

2. Along with the hydration and heat release process of cement, methylene bisacrylamide begins to generate self-polymerization reaction, and simultaneously, due to the strong polarity of amide groups, precipitated crystals are promoted to be attached to a self-polymerization product, so that the later strength of concrete sprayed on a sprayed surface is improved.

Detailed Description

All materials referred to in the examples of the present invention are commercially available.

The specifications of the samples used in the examples are shown in table 1.

TABLE 1 specification of samples used in the following examples

The raw material ratios used in the examples are shown in Table 2.

TABLE 2 component contents in the examples

The preparation method of the shotcrete in each of the above examples is as follows:

s1: weighing portland cement and fly ash according to the specification, adding the portland cement and the fly ash into a stirrer, and stirring for l0min to obtain a mixture;

s2: weighing sand and crushed stone with the particle size of 5-10mm according to the specified weight, adding the weighed sand and crushed stone into the mixture obtained in S1, stirring for 15min, then adding water, and continuing stirring for 7min to obtain a mixture;

s3: weighing a polycarboxylate superplasticizer according to a specified weight, adding the polycarboxylate superplasticizer into the mixture obtained in S2, stirring for 9min, then adding an organic coagulant, and stirring for 5min to obtain a mixture;

s4: weighing the accelerating agent, the methylene bisacrylamide and the solvent according to the specified weight, adding the accelerating agent and the methylene bisacrylamide into the solvent, and stirring for 3min to obtain a mixture;

s5: and (3) loading the mixture obtained in the step (S3) into a sprayer, conveying the mixture to a spray head by using high-pressure air, introducing the mixture obtained in the step (S4) into the spray head of the sprayer, mixing the mixture obtained in the step (S3) with the mixture obtained in the step (S4), and spraying the mixture onto a sprayed surface at a high speed from the spray head.

The evaluation indexes and the detection methods adopted by the shotcrete prepared in the above examples are as follows:

compressive strength: when the sprayed concrete is constructed, the concrete is sprayed into a mould which is made into a standard test block according to GB/T50010 concrete structure design specification, and the compressive strength with 95% of guarantee rate is measured on the 1 st day, the 7 th day, the 14 th day and the 28 th day.

Initial setting time: when the sprayed concrete is constructed, the concrete is sprayed into the slurry containing cup, and timing is started from the concrete spraying into the slurry containing cup until the time that the 300g steel needle can not penetrate to the bottom just by freely falling.

Final setting time: when the sprayed concrete is constructed, the concrete is sprayed in the slurry containing cup, and timing is started from the concrete spraying in the slurry containing cup until the time that a steel needle of 300g freely falls and can not penetrate into the surface of the concrete just.

The performance indexes of the above examples are shown in table 3.

TABLE 3 Performance test results of shotcrete prepared in each example

As can be seen from the table, the shotcrete can reach initial setting within 3min and final setting within 5min, and the initial strength and the later strength of the shotcrete meet the construction specification requirements of the shotcrete through a compressive strength performance test.

The raw material ratios used in the respective ratios are shown in Table 4.

TABLE 4 component contents in the respective proportions

The preparation of each comparative example was identical to example 1.

The performance indexes of the above respective proportions are shown in Table 5.

Table 5 results of performance test of concrete prepared in each comparative example

As can be seen from the above table, in comparative example 1 no organic setting accelerator was added and the cement had only C during hydration₃AH₆Crystal precipitation, auto-polymerization of methylene bisacrylamide with continuous cement hydration, C₃AH₆The adsorption ability of the crystals to the self-polymerized product was reduced, and therefore, the early strength and the late strength of the concrete prepared in comparative example 1 were lower than those of the concrete prepared in example 1.

Wherein, only nitrohumic acid and sodium humate are respectively added in the comparative examples 2 and 3, the pH value in the concrete system can not be adjusted, and Ca can be caused²⁺Direct precipitation of (2) to form Ca (OH)₂Or the quick setting effect of the quick setting agent on cement, the strength of the shotcrete prepared in comparative example 2 and comparative example 3 is reduced and the setting time is increased compared with example 1.

Comparative example 4 without addition of methylenebisacrylamide, only C is precipitated during hydration of the cement under the action of the accelerator₃AH₆Although the early strength of the concrete is not much different from that of example 1 due to the crystals and the complex salt having a stable structure, the late strength of the concrete is greatly reduced from that of example 1 as the concrete is hardened. Comparative example 5 instead of using fly ash for a portion of the cement, shotcrete was prepared having a lower strength than in example 1 and a higher viscosity than the concrete prepared in example 1The coagulation time increases.

In comparative example 6, the setting accelerator was preliminarily dispersed without using a solvent, and the cement slurry and the setting accelerator dry material were mixed at the head of the spray machine and then sprayed onto the sprayed surface, and since the mixing time of the two was short, the setting accelerator could not be well dispersed in the cement slurry, and the setting could be agglomerated in the cement slurry, and the setting accelerator of the concrete on the sprayed surface was unevenly distributed, resulting in the decrease in the strength of the concrete.

The present embodiment is only for explaining the present invention, and it is not limited to the present invention, and those skilled in the art can make modifications of the present embodiment without inventive contribution as needed after reading the present specification, but all of them are protected by patent law within the scope of the claims of the present invention.

Claims (7)

1. A shotcrete is characterized in that: the raw materials comprise the following components in parts by weight:

the organic coagulant is a mixture of nitrohumic acid and sodium humate; the weight ratio of the nitro humic acid to the sodium humate is 3: 1.

2. The shotcrete of claim 1, wherein: the raw materials comprise the following components in parts by weight:

3. shotcrete according to claim 1 or 2, wherein: the accelerating agent is a mixture of polyaluminium sulfate, sodium carbonate and quick lime.

4. The shotcrete of claim 3, wherein: the weight ratio of the polyaluminium sulfate to the sodium carbonate to the quicklime is 0.5:1: 0.5.

5. Shotcrete according to claim 1 or 2, wherein: the polycarboxylate superplasticizer is a mixture of a maleic anhydride polycarboxylate superplasticizer and an acrylic polycarboxylate superplasticizer.

6. Shotcrete according to claim 1 or 2, wherein: the solvent is a mixture of ethylene glycol and ethyl acetate.

7. A method of preparing shotcrete as claimed in claim 1 or claim 2, wherein: the method comprises the following steps:

s1: weighing portland cement and fly ash according to the specification, adding the portland cement and the fly ash into a stirrer, and stirring for 10min to obtain a mixture;

s2: weighing sand and crushed stone with the particle size of 5-10mm according to the specified weight, adding the weighed sand and crushed stone into the mixture obtained in S1, stirring for 15min, then adding water, and continuing stirring for 7min to obtain a mixture;

s3: weighing a polycarboxylate superplasticizer according to a specified weight, adding the polycarboxylate superplasticizer into the mixture obtained in S2, stirring for 9min, then adding an organic coagulant, and stirring for 5min to obtain a mixture;

s4: weighing the accelerating agent, the methylene bisacrylamide and the solvent according to the specified weight, adding the accelerating agent and the methylene bisacrylamide into the solvent, and stirring for 3min to obtain a mixture;

s5: and (3) loading the mixture obtained in the step (S3) into a sprayer, conveying the mixture to a spray head by using high-pressure air, introducing the mixture obtained in the step (S4) into the spray head of the sprayer, mixing the mixture obtained in the step (S3) with the mixture obtained in the step (S4), and spraying the mixture onto a sprayed surface at a high speed from the spray head.