阅读说明：本技术 一种粉煤灰的改性方法及制得的改性粉煤灰 (Modification method of fly ash and prepared modified fly ash ) 是由 任思谦 马全章 王巍 王方 于 2021-08-25 设计创作，主要内容包括：本申请涉及外加剂的技术领域,具体公开了一种粉煤灰的改性方法及制得的改性粉煤灰,该改性方法包括以下步骤：预处理：将粉煤灰依次粉磨、干法球磨后过筛；粉煤灰液制备；氧化石墨烯液制备；改性：将粉煤灰液与2/3的氧化石墨烯液混合,调节pH至碱性,超声搅拌,得到混合液,然后将混合液与硅烷偶联剂混合,在60-70℃下搅拌反应5-8h；然后加入纳米二氧化硅,搅拌,加入三乙醇胺与剩余的氧化石墨烯液,搅拌,真空抽滤,烘干,得到改性粉煤灰。本申请还公开了一种由上述改性方法制得的改性粉煤灰。本申请具有提高粉煤灰的性能,改善其应用的混凝土早期强度低的问题。(The application relates to the technical field of additives, and particularly discloses a modification method of fly ash and prepared modified fly ash, wherein the modification method comprises the following steps: pretreatment: sequentially grinding the fly ash, performing dry ball milling and sieving; preparing fly ash liquid; preparing a graphene oxide solution; modification: mixing the fly ash liquid with 2/3 graphene oxide liquid, adjusting the pH value to be alkaline, performing ultrasonic stirring to obtain a mixed liquid, mixing the mixed liquid with a silane coupling agent, and stirring and reacting for 5-8h at the temperature of 60-70 ℃; and then adding nano silicon dioxide, stirring, adding triethanolamine and the rest graphene oxide solution, stirring, carrying out vacuum filtration, and drying to obtain the modified fly ash. The application also discloses the modified fly ash prepared by the modification method. The application has the advantages of improving the performance of the fly ash and improving the problem of low early strength of the applied concrete.)

1. The method for modifying the fly ash is characterized by comprising the following steps of:

pretreatment: sequentially grinding the fly ash, performing dry ball milling and sieving;

preparing fly ash liquid: then dispersing the fly ash in water, and ultrasonically stirring and dispersing to obtain a fly ash liquid;

preparing a graphene oxide solution: dissolving graphene oxide in water, and performing ultrasonic stirring to obtain a graphene oxide liquid;

modification: mixing the fly ash liquid with 2/3 graphene oxide liquid, adjusting the pH value to be alkaline, performing ultrasonic stirring to obtain a mixed liquid, mixing the mixed liquid with a silane coupling agent, and stirring and reacting for 5-8h at the temperature of 60-70 ℃;

and then adding nano silicon dioxide, stirring, adding triethanolamine and the rest graphene oxide solution, stirring, carrying out vacuum filtration, and drying to obtain the modified fly ash.

2. The method for modifying fly ash according to claim 1, wherein: in the modification step, dry ball milling operation is also carried out after drying.

3. The method for modifying fly ash according to claim 1, wherein: in the modification step, the drying operation is as follows: firstly drying for 2-3h at 35-40 ℃, then drying for 12-15h at 50-60 ℃, and drying under vacuum condition.

4. The method for modifying fly ash according to claim 1, wherein: the fly ash, the silane coupling agent, the graphene oxide, the nano silicon dioxide and the triethanolamine are sequentially 100 parts, 6-12 parts, 8-15 parts, 5-10 parts and 3-8 parts by weight.

5. The method for modifying fly ash according to claim 1, wherein: in the preparation step of the fly ash liquid, the mass ratio of fly ash to water is 1: (4-5);

in the step of preparing the graphene oxide liquid, the mass ratio of graphene oxide to water is 1: (2-3).

6. The method for modifying fly ash according to claim 1, wherein: in the pretreatment step, the fly ash with 400-800 meshes is obtained after sieving.

7. The method for modifying fly ash according to claim 1, wherein: the silane coupling agent is selected from one or more of KH550, KH570 and KH 560.

8. The method for modifying fly ash according to claim 1, wherein: in the modification step, the fly ash after vacuum filtration is washed by absolute ethyl alcohol and deionized water and then dried.

9. A modified fly ash is characterized in that: the fly ash is prepared by the modification method of the fly ash of any one of claims 1 to 8.

Technical Field

The application relates to the technical field of additives, in particular to a method for modifying fly ash and the modified fly ash prepared by the same.

Background

The fly ash is a main solid waste generated after coal combustion, and if the fly ash cannot be properly treated, a large amount of land resources are occupied, and meanwhile, dust can be generated to pollute the environment. At present, the main utilization modes of fly ash in China are additives of building materials such as cement, concrete, mortar and the like, but the early strength of the concrete is obviously reduced after the fly ash is mixed into the cement due to the slow hydration speed of the fly ash. It is required to improve it to improve the early strength of concrete to which it is applied.

Disclosure of Invention

In order to improve the performance of the fly ash and improve the problem of low early strength of concrete to which the fly ash is applied, the application provides a modification method of the fly ash and the prepared modified fly ash.

In a first aspect, the present application provides a method for modifying fly ash, which adopts the following technical scheme:

a modification method of fly ash comprises the following steps:

pretreatment: sequentially grinding the fly ash, performing dry ball milling and sieving;

preparing fly ash liquid: then dispersing the fly ash in water, and ultrasonically stirring and dispersing to obtain a fly ash liquid;

preparing a graphene oxide solution: dissolving graphene oxide in water, and performing ultrasonic stirring to obtain a graphene oxide liquid;

modification: mixing the fly ash liquid with 2/3 graphene oxide liquid, adjusting the pH value to be alkaline, performing ultrasonic stirring to obtain a mixed liquid, mixing the mixed liquid with a silane coupling agent, and stirring and reacting for 5-8h at the temperature of 60-70 ℃;

and then adding nano silicon dioxide, stirring, adding triethanolamine and the rest graphene oxide solution, stirring, carrying out vacuum filtration, and drying to obtain the modified fly ash.

By adopting the technical scheme, firstly, the fly ash is ground, so that a protective film on the surface of a glass body in the fly ash can be broken, the reaction contact area of the fly ash is increased, the chemical activity is improved, then, the ball milling is carried out, the surface condition of the fly ash is improved, then, the fly ash liquid is mixed with the graphene oxide liquid, and the silane coupling agent is added, a large amount of Si-O-Si bonds on the surface of the fly ash in the fly ash dispersion liquid are interacted with water to generate a large amount of hydroxyl groups, probably because one end of the silane coupling agent is ethoxy and hydrolyzed to generate silicon hydroxyl groups which are reacted with the hydroxyl groups on the surface of the fly ash to generate silicon oxygen bonds, the other end of the silane coupling agent is amidated with carboxyl functional groups on the surface of the graphene oxide to be grafted to the surface of the graphene oxide, the graphene oxide is grafted with the silicon dioxide by the silane coupling agent, and the nano silicon dioxide is added probably because the silicon oxygen bonds in the nano silicon dioxide are grafted to carboxylic acid groups on the surface of the graphene oxide, and further realizes the bonding of the surface chemical bonds of the nano silicon dioxide and the graphene oxide.

The triethanolamine can play a role of a catalyst in the cement hydration process, and the nano silicon dioxide can provide crystal nuclei in the cement hydration process, so that the triethanolamine has a good effect on the generation and growth of cement hydration products, and the graphene oxide has a certain positive effect on the hydration of cement-based materials. In addition, the graphene oxide is added twice, probably because the first addition is mainly that the graphene oxide is grafted with the fly ash through a silane coupling agent, and when the graphene oxide is added for the second time, probably because the graphene oxide can not only be grafted with the fly ash through the silane coupling agent, but also form a bonding effect with the nano silicon dioxide grafted on the graphene oxide, the finally obtained modified fly ash has better concrete performance, especially compressive strength.

Optionally, in the modification step, dry ball milling is performed after drying.

By adopting the technical scheme, the dry ball milling is carried out after the modification of the fly ash, the expression condition of the fly ash is improved, the defect of fluidity caused by the increase of viscosity or consistency in concrete due to the addition of the graphene oxide is overcome, and the fluidity of the concrete meets the construction requirement.

Optionally, in the modification step, the drying specifically comprises: firstly drying for 2-3h at 35-40 ℃, then drying for 12-15h at 50-60 ℃, and drying under vacuum condition.

By adopting the technical scheme, two-stage temperature drying operation is selected, the drying is carried out at low temperature firstly, and then the drying is carried out at high temperature, so that the condition that the performance of the applied concrete is reduced due to the broken bonds of molecular chains formed by grafting or bonding in the modified fly ash is prevented.

Optionally, the fly ash, the silane coupling agent, the graphene oxide, the nano silicon dioxide and the triethanolamine are 100 parts, 6-12 parts, 8-15 parts, 5-10 parts and 3-8 parts in sequence according to the parts by weight.

Optionally, in the step of preparing the fly ash liquid, the mass ratio of the fly ash to the water is 1: (4-5);

in the step of preparing the graphene oxide liquid, the mass ratio of graphene oxide to water is 1: (2-3).

Optionally, in the pretreatment step, the fly ash with 400-800 meshes is obtained after sieving.

By adopting the technical scheme, the concrete using the modified fly ash is better in performance by modifying the low-granularity fly ash.

Optionally, the silane coupling agent is selected from one or more of KH550, KH570 and KH 560.

Optionally, in the modification step, the fly ash subjected to vacuum filtration is washed by absolute ethyl alcohol and deionized water, and then dried.

By adopting the technical scheme, the excessive silane coupling agent in the fly ash is removed.

In a second aspect, the modified fly ash provided by the application adopts the following technical scheme:

modified fly ash prepared by the modification method.

Through adopting above-mentioned technical scheme, in being applied to the concrete through the modified fly ash that this application provided, show early strength and the later stage intensity that promotes the fly ash concrete.

In summary, the present application has the following beneficial effects:

1. the modified fly ash prepared by the modification method provided by the application can realize the grafting and/or bonding effect of the graphene oxide and the nano silicon dioxide on the fly ash due to the addition of the silane coupling agent, the nano silicon dioxide and the graphene oxide, so that the modification of the fly ash is realized, and the early strength of concrete is obviously improved when the modified fly ash is used for the concrete due to the influence of the modified fly ash on cement hydration;

2. in the application, the graphene oxide is added twice, probably because the grafting between the graphene oxide and the fly ash is realized, and the graphene oxide can be further bonded on the nano silicon dioxide grafted with the graphene oxide due to the chemical bonding effect, so that the structure of the graphene oxide-nano silicon dioxide-graphene oxide is realized, and the performance of concrete is further improved;

3. the modified fly ash is subjected to dry ball milling, so that the expression condition of the fly ash is improved, the defect of fluidity caused by the increase of viscosity or consistency in concrete due to the addition of graphene oxide is overcome, and the fluidity of the concrete meets the construction requirement;

4. the drying in the application selects two-stage temperature drying operation, firstly dries at low temperature, and then dries at high temperature, and prevents the performance reduction of the applied concrete caused by the bond breaking of molecular chains formed by grafting or bonding in the modified fly ash.

Detailed Description

The present application is further described in detail with reference to the following examples, which are specifically illustrated by the following: the following examples, in which specific conditions are not specified, were conducted under conventional conditions or conditions recommended by the manufacturer, and the starting materials used in the following examples are available from ordinary commercial sources unless otherwise specified.

KH550 was used as the silane coupling agent in the following examples.

Example 1

A modification method of fly ash comprises the following steps:

pretreatment: sequentially grinding the fly ash, performing dry ball milling and sieving to obtain the fly ash with 400-mesh and 800-mesh;

preparing fly ash liquid: dispersing 100kg of fly ash obtained after sieving in the pretreatment step into water, and performing ultrasonic dispersion in an ultrasonic stirring tank for 2 hours to obtain fly ash liquid, wherein the mass ratio of the fly ash to the water in the step is 1: 4;

preparing a graphene oxide solution: dissolving 8kg of graphene oxide in water, performing ultrasonic stirring dispersion in an ultrasonic stirring tank, and performing ultrasonic treatment for 0.5h to obtain a graphene oxide solution, wherein the mass ratio of the graphene oxide to the water in the step is 1: 2;

modification: mixing the fly ash liquid obtained in the fly ash liquid preparation step with the graphene oxide liquid with the total amount of 2/3 obtained in the graphene oxide preparation step in an ultrasonic stirring tank, adding ammonia water to adjust the pH value to 8, stirring, and performing ultrasonic treatment for 4 hours to obtain a mixed dispersion liquid;

then mixing the obtained mixed dispersion liquid with 6kg of silane coupling agent, and stirring and reacting for 8 hours at the temperature of 60 ℃;

then adding 5kg of nano silicon dioxide, stirring, adding 3kg of triethanolamine and the rest graphene oxide solution, stirring, carrying out vacuum filtration, then sequentially washing with absolute ethyl alcohol and deionized water, removing the excess silane coupling agent, drying, and then carrying out dry ball milling operation to obtain modified fly ash;

the specific operation of drying is as follows: drying at 35 deg.C for 3 hr, and drying at 50 deg.C for 15 hr.

Example 2

A method for modifying fly ash is carried out according to the method in the embodiment 1, except that,

pretreatment: sequentially grinding the fly ash, performing dry ball milling and sieving to obtain the fly ash with 400-mesh and 800-mesh;

preparing fly ash liquid: dispersing 100kg of fly ash obtained after sieving in the pretreatment step into water, and performing ultrasonic dispersion in an ultrasonic stirring tank for 2 hours to obtain fly ash liquid, wherein the mass ratio of the fly ash to the water in the step is 1: 4;

preparing a graphene oxide solution: dissolving 12kg of graphene oxide in water, performing ultrasonic stirring dispersion in an ultrasonic stirring tank, and performing ultrasonic treatment for 0.5h to obtain a graphene oxide solution, wherein the mass ratio of the graphene oxide to the water in the step is 1: 2;

modification: mixing the fly ash liquid obtained in the fly ash liquid preparation step with the graphene oxide liquid with the total amount of 2/3 obtained in the graphene oxide preparation step in an ultrasonic stirring tank, adding ammonia water to adjust the pH value to 8, stirring, and performing ultrasonic treatment for 4 hours to obtain a mixed dispersion liquid;

then mixing the obtained mixed dispersion liquid with 9kg of silane coupling agent, and stirring and reacting for 5-8h at 65 ℃;

then adding 8kg of nano silicon dioxide, stirring, adding 5kg of triethanolamine and the rest graphene oxide solution, stirring, carrying out vacuum filtration, then sequentially washing with absolute ethyl alcohol and deionized water, removing the excess silane coupling agent, drying, and then carrying out dry ball milling operation to obtain modified fly ash;

the specific operation of drying is as follows: drying at 35 deg.C for 3.5 hr, and drying at 55 deg.C for 14 hr.

Example 3

A method for modifying fly ash is carried out according to the method in the embodiment 1, except that,

pretreatment: sequentially grinding the fly ash, performing dry ball milling and sieving to obtain the fly ash with 400-mesh and 800-mesh;

preparing fly ash liquid: dispersing 100kg of fly ash obtained after sieving in the pretreatment step into water, and performing ultrasonic dispersion in an ultrasonic stirring tank for 2 hours to obtain fly ash liquid, wherein the mass ratio of the fly ash to the water in the step is 1: 5;

preparing a graphene oxide solution: dissolving 15kg of graphene oxide in water, performing ultrasonic stirring dispersion in an ultrasonic stirring tank, and performing ultrasonic treatment for 0.5h to obtain a graphene oxide solution, wherein the mass ratio of the graphene oxide to the water in the step is 1: 3;

modification: mixing the fly ash liquid obtained in the fly ash liquid preparation step with the graphene oxide liquid with the total amount of 2/3 obtained in the graphene oxide preparation step in an ultrasonic stirring tank, adding ammonia water to adjust the pH value to 8, stirring, and performing ultrasonic treatment for 4 hours to obtain a mixed dispersion liquid;

then mixing the obtained mixed dispersion liquid with 12kg of silane coupling agent, and stirring and reacting for 5 hours at 70 ℃;

then adding 10kg of nano silicon dioxide, stirring, adding 3kg of triethanolamine and the rest graphene oxide solution, stirring, carrying out vacuum filtration, then sequentially washing with absolute ethyl alcohol and deionized water, removing the excess silane coupling agent, drying, and then carrying out dry ball milling operation to obtain modified fly ash;

the specific operation of drying is as follows: drying at 40 deg.C for 2 hr, and drying at 60 deg.C for 12 hr.

Example 4

A method for modifying fly ash is carried out according to the method in the embodiment 2, and the difference is that:

in the modification step, ball milling is not carried out after drying, and the modified fly ash is directly obtained.

Example 5

A method for modifying fly ash is carried out according to the method in the embodiment 2, and the difference is that:

the specific operation of drying is as follows: drying in a vacuum drying oven at 50 deg.C for 17.5 h.

Example 6

A modification method of fly ash is carried out according to the method in the embodiment 2, and the difference is that the specific operation of drying is as follows: drying in a vacuum drying oven at 35 deg.C for 24 h.

Comparative example

Comparative example 1

A method for modifying fly ash, which comprises the following steps of example 2:

in the modification step, the addition of the graphene oxide liquid is performed once, that is, the fly ash liquid obtained in the fly ash liquid preparation step and the graphene oxide liquid obtained in the graphene oxide preparation step are directly mixed in an ultrasonic stirring tank, and the rest of the operations are the same as those in example 2.

Comparative example 2

A modification method of fly ash is carried out according to the method in the embodiment 2, and the difference is that nano silicon dioxide is replaced by graphene oxide in an equivalent manner in the modification step.

Comparative example 3

A modification method of fly ash is carried out according to the method in the embodiment 2, except that the nano-silica is replaced by triethanolamine in an equivalent manner in the modification step.

Comparative example 4

A modification method of fly ash is carried out according to the method in the embodiment 2, and the difference is that triethanolamine is replaced by graphene oxide in an equivalent manner in the modification step.

Comparative example 5

A modification method of fly ash is carried out according to the method in the embodiment 2, and the difference is that triethanolamine is replaced by nano silicon dioxide in the modification step in an equivalent manner.

Comparative example 6

A method for modifying fly ash was carried out as in example 2, except that,

pretreatment: sequentially grinding the fly ash, performing dry ball milling and sieving to obtain the fly ash with 400-mesh and 800-mesh;

modification: and (3) directly mixing and grinding 100kg of fly ash obtained after sieving in the pretreatment step and 5kg of triethanolamine.

Performance detection

1. Early compressive strength

The modified fly ash and the unmodified fly ash prepared in the examples and the comparative examples of the application are used for preparing test blocks according to test mortar in a fly ash strength activity index test method in GB/T1596-2017 fly ash for cement and concrete, the test blocks are prepared by using the comparative mortar according to the method, then the test mortar and the comparative mortar are subjected to 7d and 28d compression strength and strength activity index detection, and the detection results are shown in the following table 1.

Table 1:

detecting items	Example 1	Example 2	Example 3	Example 4	Example 5	Example 6	Comparative example 1
								7d compressive strength/MPa	24.1	25.7	23.3	25.1	22.7	24.9	20.3
28d compressive strength/MPa	37.2	38.3	36.8	38.0	36.0	37.5	33.8
								Strength activity index/%)	76.5	78.8	75.7	78.2	74.1	77.2	69.5
Detecting items	Comparative example 2	Comparative example 3	Comparison ofExample 4	Comparative example 5	Comparative example 6	Unmodified fly ash	Comparative mortar
								7d compressive strength/MPa	16.8	14.2	18.2	20.1	19.3	20.8	32.8
28d compressive strength/MPa	30.7	28.5	32.9	33.4	32.7	34.2	48.6
								Strength activity index/%)	63.2	58.6	67.7	68.7	67.3	70.4	—

As can be seen from table 1 above, the strength activity indexes of the modified fly ash prepared in the embodiment of the present application are all greater than 70%, and referring to the detection results of the embodiments 2 and 5, it can be seen that the activity of the modified fly ash obtained when two-stage drying is adopted in the drying step is stronger, and the detection result of the embodiment 6 is combined, so that the method in the embodiment 2 is adopted, not only the drying time is shorter, but also the activity of the obtained modified fly ash is higher.

Referring to the detection results of example 2 and comparative example 1, the activity of the modified fly ash obtained by adding graphene oxide twice is higher, and referring to the detection results of comparative examples 2 to 3, it can be seen that the activity is lower when only graphene oxide and triethanolamine are used as the activating agents selected in the process of modifying fly ash, and the activity is lower when only graphene oxide and silicon dioxide are used but triethanolamine is not added, as can be seen from the detection results of comparative examples 4 and 5. The modified fly ash obtained by adopting the graphene oxide, the nano silicon dioxide and the triethanolamine in the embodiment has better performance.

2. Fluidity of concrete

Since the addition of the graphene oxide has a certain influence on the viscosity and/or consistency of the cement mortar, the application of the graphene oxide to the fluidity detection of concrete is also carried out, and the modified fly ash and the unmodified fly ash obtained in the application and the comparative example are mixed according to the following ratio in the table 2 to prepare the concrete, wherein the polycarboxylic acid water reducer is available from the chemical industry ltd.

Table 2:

cement	Fly ash	Fine aggregate	Coarse aggregate	Additive agent	Water (W)
						P.O42.5	—	Washing river sand (Fine modulus 2.5-3.0)	5-25mm graded broken stone	Polycarboxylic acid water reducing agent	—
300g	65g	450g	650g	1g	85g

The concrete prepared in the examples and the comparative examples was tested for slump according to GB/T14902-2012, and the test results are shown in Table 3 below.

Table 3:

detecting items	Example 1	Example 2	Example 3	Example 4	Example 5	Example 6	Comparative example 1
								Slump/mm	125	130	125	110	125	130	125
Detecting items	Comparative example 2	Comparative example 3	Comparative example 4	Comparative example 5	Comparative example 6	Unmodified fly ash	—
								Slump/mm	120	125	120	130	135	140	—

As can be seen from the above Table 3, the modified fly ash prepared by the method has good fluidity and meets the construction requirements.

The present embodiment is only for explaining the present application, and it is not limited to the present application, 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 application.