阅读说明：本技术 一种天然水镁石纤维改性石灰-偏高岭土复合砂浆的制备方法 (Preparation method of natural brucite fiber modified lime-metakaolin composite mortar ) 是由 宋彦军 陶隆凤 刘云贵 于 2020-05-11 设计创作，主要内容包括：本发明公开了一种天然水镁石纤维改性石灰-偏高岭土复合砂浆的制备方法,具体包括天然水镁石纤维预处理和天然水镁石纤维改性L-MK砂浆,石灰-偏高岭土胶凝材料是将熟石灰与活性偏高岭土按一定比例混合后制成的具有水硬性的无机胶凝材料,其中偏高岭土是L-MK胶凝材料中的主要活性成分,因此,L-MK胶凝材料既保留了石灰与古建筑基体良好兼容性的同时又具有水泥的水硬性,在砖石及岩土质古建筑的修护工作中具有不可忽略的优势,此外,其原料石灰石与高岭土资源丰富、加工便利、价格低廉,煅烧温度低,硬化过程中还会吸收大气环境中的CO2,因而L-MK胶凝材料还是一种低能耗的环境友好型材料。(The invention discloses a preparation method of natural brucite fiber modified lime-metakaolin composite mortar, which specifically comprises natural brucite fiber pretreatment and natural brucite fiber modified L-MK mortar, wherein the lime-metakaolin cementing material is an inorganic cementing material with hydraulicity prepared by mixing hydrated lime and active metakaolin according to a certain proportion, wherein metakaolin is a main active component in the L-MK cementing material, therefore, the L-MK cementing material not only keeps good compatibility of lime and ancient building matrixes, but also has the hydraulicity of cement, has non-negligible advantages in repairing and protecting masonry and rock-soil ancient buildings, in addition, the raw materials of limestone and kaolin have rich resources, convenient processing and low price, the calcination temperature is low, and CO2 in the atmospheric environment can be absorbed in the hardening process, therefore, the L-MK cementing material is also an environment-friendly material with low energy consumption.)

1. A preparation method of natural brucite fiber modified lime-metakaolin composite mortar is characterized by comprising the following steps:

(1) selecting natural brucite fibers with the fiber length specification of 1-6 mm and the relative density of about 2.44, screening the fibers, and drying the natural brucite fibers in a constant-temperature drying oven at 60 ℃ for 24 hours;

(2) adding the fiber and the dispersing agent into water according to the mass ratio of the fiber to the dispersing agent to the water of 10:1.5:200, and repeatedly stirring by using a stirrer to further loosen the fiber;

(3) the turbid liquid is filtered to remove redundant water, and is kept to be dried in a constant-temperature drying oven for 24 hours for later use;

(4) mixing slaked lime and high-activity metakaolin according to the mass ratio of 1:1, adding a polycarboxylic acid high-efficiency water reducing agent after mixing the slaked lime and the high-activity metakaolin, adding standard sand with the total mass ratio of the slaked lime to the metakaolin being 1:3, and stirring for 3min by using a stirrer to obtain mixed powder after mixing;

(5) the blending amount of the brucite fibers is 0%, 2%, 4%, 6%, 8% and 10% of the total mass of the hydrated lime and the metakaolin, then 150-160mm is taken as a fluidity standard, and then a proper amount of water and the loosened brucite fibers are mixed and stirred for 10 min;

(6) adding the previously mixed slaked lime, metakaolin, water and the loosened brucite fiber powder, stirring at a low speed for 5min by using a stirrer, scraping the blades and the mortar on the pot wall into the middle of the pot by using a scraper, and then stirring at a high speed for 5min to fully and uniformly mix;

(7) pouring the mixed slurry into a triple membrane of 40X 160mm, vibrating and compacting, scraping the surface, placing the triple membrane in a room, standing for 24 hours, demoulding, and finally placing the demoulded sample under standard conditions for curing.

2. The method for preparing natural brucite fiber modified lime-metakaolin composite mortar according to claim 1, wherein in the step (1), the raw material fibers are elutriated by a 60-mesh standard sieve to remove surface impurities and fibers with too short length.

3. The method for preparing natural brucite fiber modified lime-metakaolin composite mortar according to claim 1, wherein a direct current mixer is used as the mixer in the step (2).

4. The preparation method of the natural brucite fiber modified lime-metakaolin composite mortar according to claim 1, wherein the polycarboxylic acid high-efficiency water reducing agent is added in the step (4) to make the total mass be 0.5%.

5. The method for preparing natural brucite fiber modified lime-metakaolin composite mortar according to claim 1, wherein the mixer in the step (6) is a planetary cement mortar mixer.

6. The method for preparing natural brucite fiber modified lime-metakaolin composite mortar according to claim 1, wherein the standard conditions in the step (7) are the temperature of 20 +/-2 ℃ and the relative humidity of 95% +/-5%.

Technical Field

The invention relates to composite mortar, in particular to a preparation method of natural brucite fiber modified lime-metakaolin composite mortar.

Background

Ancient architecture sites are important components of human historical cultural heritage, and witness the development of human culture and the progress of science and technology. At present, China keeps a large number of ancient sites of brick, stone and rock-soil buildings, such as city walls, graves, stone carving statues, rock painting murals and the like, and the key of the site protection work is whether the adopted repairable cementing material is proper or not. When the building cementing material is used for building, the overall mechanical property of a building structure is concerned, and when the building cementing material is used as plastering slurry, the exchange of moisture and substances of an inner layer and an outer layer is also controlled, so that the repairing adopted cementing material needs to have good compatibility with an ancient building body in physical property, mechanical property, chemical property and even appearance. The cement-based cementing materials widely used in modern building industry are not suitable for repairing ancient buildings due to the disadvantages of large mechanical strength and cohesive force, poor water and air permeability, salt secretion and the like, but can cause irreversible damage to the ancient buildings after repair, and in addition, the appearance of the cement cured is mostly cold gray, so that the irreconciliation of repaired and non-repaired parts in appearance is obviously caused, and the aesthetic value of architectural sites is seriously damaged. Therefore, the development of suitable ancient building repair materials is always the research focus of scholars related to the ancient building repair field. At present, a great deal of research on L-MK repairing mortar is carried out in developed countries in Europe and America. In contrast, the research on the L-MK repairing mortar is started later in China, and relatively few researches are carried out at present.

Disclosure of Invention

The invention aims to provide a preparation method of natural brucite fiber modified lime-metakaolin composite mortar, so as to solve the problems in the background technology.

In order to achieve the purpose, the invention provides the following technical scheme: a preparation method of natural brucite fiber modified lime-metakaolin composite mortar specifically comprises the following steps:

(1) selecting natural brucite fibers with the fiber length specification of 1-6 mm and the relative density of about 2.44, screening the fibers, and drying the natural brucite fibers in a constant-temperature drying oven at 60 ℃ for 24 hours;

(2) adding the fiber and the dispersing agent into water according to the mass ratio of the fiber to the dispersing agent to the water of 10:1.5:200, and repeatedly stirring by using a stirrer to further loosen the fiber;

(3) the turbid liquid is filtered to remove redundant water, and is kept to be dried in a constant-temperature drying oven for 24 hours for later use;

(4) mixing slaked lime and high-activity metakaolin according to the mass ratio of 1:1, adding a polycarboxylic acid high-efficiency water reducing agent after mixing the slaked lime and the high-activity metakaolin, adding standard sand with the total mass ratio of the slaked lime to the metakaolin being 1:3, and stirring for 3min by using a stirrer to obtain mixed powder after mixing;

(5) the blending amount of the brucite fibers is 0%, 2%, 4%, 6%, 8% and 10% of the total mass of the hydrated lime and the metakaolin, then 150-160mm is taken as a fluidity standard, and then a proper amount of water and the loosened brucite fibers are mixed and stirred for 10 min;

(6) adding the previously mixed slaked lime, metakaolin, water and the loosened brucite fiber powder, stirring at a low speed for 5min by using a stirrer, scraping the blades and the mortar on the pot wall into the middle of the pot by using a scraper, and then stirring at a high speed for 5min to fully and uniformly mix;

(7) pouring the mixed slurry into a triple membrane of 40 multiplied by 160mm for vibration compaction, scraping the surface, placing the triple membrane in a room, standing for 24 hours, and then demoulding; and finally, placing the demolded sample under standard conditions for curing.

As a further scheme of the invention: and (2) elutriating the raw material fibers by using a 60-mesh standard sieve in the step (1) to remove surface impurities and fibers with too short length.

As a further scheme of the invention: and (3) selecting a direct current stirrer as the stirrer in the step (2).

As a further scheme of the invention: and (3) adding a polycarboxylic acid high-efficiency water reducing agent in the step (4) to make the total mass be 0.5%.

As a further scheme of the invention: and (5) the stirrer in the step (6) is a planetary cement mortar stirrer.

As a still further scheme of the invention: the standard conditions in the step (7) are that the temperature is 20 +/-2 ℃ and the relative humidity is 95% +/-5%.

Compared with the prior art, the invention has the beneficial effects that:

the lime-metakaolin cementing material is an inorganic cementing material with hydraulicity prepared by mixing hydrated lime and active metakaolin according to a certain proportion, wherein the metakaolin is a main active ingredient in the L-MK cementing material, is a thermodynamically metastable amorphous silica-alumina compound formed by calcining and dehydrating natural clay mineral kaolin at 600-900 ℃, has strong pozzolan activity, can react with calcium hydroxide which is a main ingredient in the hydrated lime in the presence of water to generate a hydration product with certain structural strength, reduces volume shrinkage while ensuring that the material obtains hydraulicity, and improves mechanical properties. Therefore, the L-MK cementing material not only keeps the good compatibility of the lime and the ancient building matrix, but also has the hydraulicity of cement, and has the advantages of being not negligible in the repairing work of the masonry and geotechnical ancient buildings. In addition, the raw materials of limestone and kaolin have rich resources, convenient processing, low price and low calcination temperature, and can absorb CO2 in the atmospheric environment in the hardening process, so that the L-MK cementing material is an environment-friendly material with low energy consumption.

Drawings

FIG. 1a is a schematic drawing of a 1000 Xpicture of a raw brucite fiber;

FIG. 1b is a 10000 Xpicture schematic diagram of a raw material brucite fiber;

FIG. 1c is a schematic view of a 1000 Xpicture of a washed brucite fiber;

FIG. 1d is a 10000 Xpicture schematic diagram of brucite fiber after washing;

FIG. 1e is a schematic drawing of a 1000 Xpicture of a disintegrated brucite fiber;

FIG. 1f is a 10000 Xpicture schematic of a disintegrated brucite fiber;

FIG. 2a is a schematic view of test pictures of flexural strength of different brucite fiber doped L-MK mortars;

FIG. 2b is a schematic view of a test picture of the influence of different brucite fiber content L-MK mortar compression strength;

FIG. 3 is a three-point anti-breaking strength appearance photograph of fiber modified L-MK mortar (upper) and pure L-MK mortar (lower);

FIG. 4a is a schematic view of a cross section of SMS-1, 5000 Xpicture;

FIG. 4b is a schematic drawing of a cross section of SMS-1, 2500 Xpicture;

FIG. 4c is a cross-section of SMS-1, 10000 Xpicture.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious 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 derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Referring to fig. 1 to 4, in the embodiment of the invention, a method for preparing natural brucite fiber modified lime-metakaolin composite mortar is provided, in which hydrated lime, high-activity metakaolin, standard sand and water are mixed in a certain proportion, and then a certain amount of natural brucite fibers subjected to washing and loosening treatment are added to prepare the brucite fiber modified lime-metakaolin composite mortar, specifically including natural brucite fiber pretreatment and natural brucite fiber modified L-MK mortar.

Firstly, the natural brucite fiber pretreatment concrete method is as follows, adding a certain amount of brucite fiber into L-MK mortar, so that the mechanical strength, shrinkage resistance and other properties of the composite mortar produced by the L-MK mortar and the brucite fiber can be further improved, the method is better suitable for repairing ancient architecture sites of masonry and rock-soil texture, but the fiber pretreatment, the adding mode and the adding amount can generate different influences on the properties of the final mortar, the natural brucite fiber is usually produced in a fiber bundle mode, the bonding among the fibers is very tight, commercial fibers sold in the market are crushed, loosened and screened in mines, but still contain a large amount of coarse fiber bundles and impurities, so the natural brucite fiber is difficult to be uniformly dispersed in the mortar in the process of adding the mortar and stirring, the fibers cannot be fully contacted with the mortar, and the overall utilization rate of the fibers is reduced, the reinforcing and toughening effects of the composite mortar on the material cannot be fully exerted, so that the method firstly performs the loosening treatment on the natural brucite fiber. The specific treatment process is as follows:

(1) the selected fiber length specification is 1-6 mm, the relative density is about 2.44, the natural brucite fiber is in a light green flocculent appearance, then a 60-mesh standard sieve is used for elutriating the raw material fiber to remove surface impurities and fibers with too short length, and after completion, a part of fiber samples are taken and placed in a 60-DEG C constant-temperature drying oven for drying for 24 hours;

(2) then adding fibers and a dispersing agent (dioctyl sodium sulfosuccinate (OT)) into water according to the mass ratio of the fibers to the dispersing agent to the water of 10:1.5:200, stirring for 30min by using a direct current stirrer, wherein the rotating speed of the direct current stirrer is about 1500r/min, oscillating the uniformly stirred suspension for 30min by using ultrasonic waves, specifically, generating dispersion effect on the fibers by using micro-vibration and bubbles generated by the ultrasonic waves, simultaneously enabling the dispersing agent to better infiltrate the surfaces of the fibers, mechanically stirring the oscillated suspension for 15min, and finally enabling the rotating speed of the direct current stirrer to be about 1500r/min, and further loosening the fibers;

(3) filtering the suspension with 60 mesh sieve to remove excessive water, and drying in 60 deg.C constant temperature drying oven for 24 hr;

the natural brucite fiber modified L-MK mortar is further included, and due to the fact that the addition of brucite and sepiolite fibers can obviously improve the water demand for mixing, a polycarboxylic acid high-efficiency water reducing agent is added to reduce the water consumption for mixing, the natural brucite fibers after being loosened are added into the L-MK mortar through wet adding, and the specific steps are as follows:

(1) mixing slaked lime and high-activity metakaolin according to the mass ratio of 1:1, wherein the content of Ca (OH)2 in the slaked lime is more than 95 percent, the average particle size of the metakaolin is 2.4 mu m, the balance of the metakaolin is 0.1 percent through a 325-mesh sieve, the volcanic ash activity index in 28 days is 122 percent, the specific surface area is 16m2/g, and the sum of the SiO2 and the Al2O3 is more than 98 percent of the total mass, adding a polycarboxylic acid high-efficiency water reducing agent with the total mass of 0.5 percent after the slaked lime and the high-activity metakaolin are mixed, adding standard sand with the total mass ratio of 1:3 of the slaked lime and the metakaolin, mixing the mixture and stirring the standard sand for 3min by a stirrer;

(2) the content of the brucite fibers is 0%, 2%, 4%, 6%, 8% and 10% of the total mass of the hydrated lime and the metakaolin, then a proper amount of water and the loosened brucite fibers are taken to mix and stir for 10min by taking 150-160mm as a fluidity standard, and the specific proportion of the brucite fiber modified L-MK mortar is shown in the following table.

Brucite fiber modified L-MK mortar proportioning table

(3) Adding the previously mixed slaked lime and metakaolin, stirring at low speed for 5min by using a planetary cement mortar stirrer, scraping the blades and the mortar on the wall of the pot into the middle of the pot by using a scraper, and stirring at high speed for 5min to fully and uniformly mix the materials;

(4) pouring the mixed slurry into a triple membrane of 40 multiplied by 160mm for vibration compaction, scraping the surface, placing the surface in a room for 24 hours, demoulding, and finally placing the demoulded sample under the standard condition that the temperature is 20 +/-2 ℃ and the relative humidity is 95 +/-5%;

according to the test results generated by all the steps, the early strength of the mortar can be effectively improved by adding the polycarboxylate superplasticizer, the flexural strength and the compressive strength of the JSJ sample after being cured for 7 days are 2.7MPa and 7.5MPa, and are respectively improved by 50.0 percent and 72.8 percent compared with 1.8MPa and 4.3MPa of the standard L-MK sample, so that the flexural strength and the compressive strength of the standard L-MK sample reach 64.3 percent and 44.4 percent of the self 28-day age strength, and the flexural strength and the compressive strength of the standard L-MK sample after being cured for 7 days are respectively 41.9 percent and 24.6 percent of the 28-day strength; but the strength of the mortar in 28 days is slightly reduced by adding the polycarboxylic acid water reducing agent, the flexural strength and the compressive strength of a JSJ sample in 28 days are respectively 4.2MPa and 16.9MPa, and the flexural strength and the compressive strength of the JSJ sample in 28 days are slightly reduced by 3.5% compared with the flexural strength and the compressive strength of a reference L-MK sample which are both 4.3MPa and 17.5MPa, which shows that the polycarboxylic acid water reducing agent has a certain catalytic action on hydration reaction in the mortar, and can promote the formation of the early strength of the mortar, but the water supply of later hydration reaction is insufficient due to the reduction of the total mixing water consumption of the mortar, so the strength is reduced; after the brucite fibers are added, the 7-day strength value of the mortar is lower than that of the sample SJS, but the total strength is higher than that of the reference L-MK sample, the fact that the disordering components of the fibers in the slurry can generate certain obstruction on the catalytic effect of the water reducing agent is presumed, the 28-day strength of the mortar is in a descending trend along with the increase of the fiber mixing amount, wherein the effect is the best when the fiber mixing amount is 2%, the 28-day folding strength and the 28-day compressive strength are respectively 4.8MPa and 18.4MPa, are respectively increased by 11.6 percent and 4.6 percent compared with the reference L-MK sample, and are gradually reduced after the effect is obtained.

In addition, after the fiber modified L-MK mortar is subjected to a three-point bending strength test, although a sample is greatly deformed and cracked but is not completely broken, fibers can obviously cross two sides of the crack at the crack to present a phenomenon of 'coupling and breaking of filaments', and the fracture mode is determined to be a non-catastrophic fracture mode, particularly, the fibers have higher tensile strength than that of a matrix, so that the slippage and extraction effects of a large number of fibers in the L-MK matrix fracture process are caused by large consumption of fracture energy, and compared with the fracture mode, the fracture of a benchmark L-MK sample is catastrophic, namely the sample is completely fractured into two sections, which shows that the reliability of the material in the application process can be effectively improved by adding the brucite fibers.

A section scanning electron microscope of the solidified mortar with the brucite fiber content of 2% hardly finds the existence of brucite fibers in the undamaged area of the mortar through 5000-time amplification, the compactness of the whole structure is good, the brucite fibers mainly exist on the fracture surface of a matrix in a large amount in a pulling-out state on the stressed crack surface of the mortar, the fibers which are not completely pulled out exist on two sides of the fracture surface in a bridging mode, and only a small amount of fibers are pulled out, so that the brucite fibers can be well loosened and dispersed in the mortar matrix when the brucite fiber content is low, and when the composite mortar is stressed, the large amount of brucite fibers are distributed between the fracture surfaces to block further crack propagation.

In conclusion, the method considers that the natural brucite fibers have a certain effect of improving the mechanical strength of the solidified L-MK mortar, and the optimal proportion is as follows: under the requirement of 150-mm fluidity of freshly mixed mortar, the mass ratio of hydrated lime to high-activity metakaolin is 1:1, the mortar-to-mortar ratio is 1:3, the addition amount of a polycarboxylic acid water reducing agent is 0.5% of the total mass of the hydrated lime and the metakaolin, the natural brucite fiber is added by a wet method, the addition amount of the natural brucite fiber is 2% of the total mass of the hydrated lime and the metakaolin, the brucite fiber needs to be subjected to loosening treatment and modified by the brucite fiber, the flexural strength and the compressive strength of the L-MK mortar after 28 days of curing are respectively improved by 11.6% and 4.6% compared with those before modification, the catastrophic fracture of the mortar can be effectively avoided, and the reliability of the material in the application process is effectively improved.

In the description of the present invention, it should be noted that, unless otherwise explicitly specified or limited, the terms "mounted," "connected," and "connected" are to be construed broadly, e.g., as meaning either a fixed connection, a removable connection, or an integral connection; can be mechanically or electrically connected; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meaning of the above terms in the present invention can be understood by those of ordinary skill in the art through specific situations.

Although the present invention has been described in detail with reference to the foregoing embodiments, it will be apparent to those skilled in the art that various changes in the embodiments and/or modifications of the invention can be made, and equivalents and modifications of some features of the invention can be made without departing from the spirit and scope of the invention.