Alkali-free and fluorine-free liquid accelerating agent and preparation method thereof

Abstract

The present invention provides an alkali-free and fluorine-free liquid accelerating setting agent and a preparation method thereof, and belongs to the technical field of concrete admixtures. The accelerating setting agent comprises the following components: 25-35 parts of aluminum sulfate, 5-15 parts of ferrous sulfate, 3-4 parts of compounded alcohol amine, 3-4 parts of pH adjusting agent, and 33-36 parts of deionized water. By optimizing the alcohol amine ratio, the present invention can achieve the coordination of the setting time and initial compressive strength of cement materials by a ternary accelerating setting system consisting of only ferrous sulfate / ferrous sulfate, aluminum sulfate, and alcohol amine without adding additional reinforcing components, and solves the problem that the above-mentioned ternary accelerating setting system is difficult to meet the performance requirements of GB / T35159-2017 for accelerating setting agents. The accelerating setting agent prepared by the present invention has the characteristics of low cost, simple process, and can be prepared at room temperature and has good stability of the product.

Description

Technical Field

[0001] The invention relates to the technical field of concrete admixtures, and in particular to an alkali-free and fluorine-free liquid quick-setting agent and a preparation method thereof. Background Art

[0002] Cement accelerating agent is a chemical admixture that can make cement or concrete set and harden quickly. It is also called accelerator. It is the key to the construction of shotcrete and has been widely used in tunnel support, slope reinforcement and other fields.

[0003] Traditional alkali-containing quick-setting agents have the disadvantages of threatening the health of construction workers and inducing alkali-aggregate reaction. Therefore, more efficient aluminum sulfate-based alkali-free quick-setting agents have been rapidly developed. However, in the production of such quick-setting agent products, fluoride is often an indispensable and important component. Fluoroaluminum complexes are often obtained by reacting hydrofluoric acid with aluminum-containing compounds, and then mixed with aluminum sulfate, alcohol amines, inorganic / pH regulators, and amides to prepare liquid alkali-free quick-setting agents. Alternatively, fluorides such as sodium fluoride, magnesium fluorosilicate, aluminum fluorosilicate, etc. are directly heated and stirred with the above-mentioned aluminum sulfate, alcohol amines, inorganic / pH regulators, and amides in an aqueous solution to prepare alkali-free quick-setting agents. Among them, the first preparation method will quickly release heat and generate a large amount of white smoke after adding hydrofluoric acid to aluminum-containing compounds. This process will cause fluoride to volatilize and overflow. Operators will be at risk of poisoning after short-term and large-scale contact. Even if they are in trace contact, they will cause fluorosis in the long run. In addition, no matter which of the above schemes is used to prepare the quick-setting agent, there is a risk of fluoride leaching after the construction is completed. In the paper ("Leaching behavior and environmental safety evaluation of fluorine ions from shotcrete with high-fluorine alkali-free liquid accelerator" Yang R, et al. Environmental science and pollution research international, 2021. DOI: 10.1680 / adcr.2005.17.1.1), it is clearly pointed out that concrete with the addition of accelerators has the phenomenon of fluorine ion leaching, which poses a risk of groundwater and soil pollution. It can be seen that although fluorine-containing alkali-free liquid accelerators have a good accelerating effect, the health, safety and environmental hazards they cause cannot be ignored.

[0004] At present, relevant research has been conducted on the development of fluorine-free and alkali-free liquid accelerating agents, and the basic measure adopted is to seek alternatives to fluoride. The research results show that both ferrous sulfate and ferric sulfate can replace fluoride, but the ternary system consisting of ferrous sulfate / ferric sulfate, aluminum sulfate, and alcohol amine has a quick-setting effect, but the early strength deteriorates seriously, and excessive alcohol amines are usually added, resulting in the hydration of the silicate phase in the cement clinker being hindered, making it difficult to meet engineering requirements. In the prior art, it is often necessary to introduce additional reinforcing components such as aluminum sol, hydrated magnesium silicate, magnesium sulfate, magnesium hydroxide, lithium hydroxide, and calcium formate into the above system to re-accelerate the hydration of the silicate phase clinker. This operation will undoubtedly increase the cost of the accelerating agent and also make the preparation process more complicated. Summary of the invention

[0005] The invention aims to provide an alkali-free and fluorine-free liquid accelerating setting agent and a preparation method thereof, aiming to solve the problems of the existing fluorine-free and alkali-free liquid accelerating setting agent, such as complex components, high cost and poor stability.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is:

[0007] An alkali-free and fluorine-free liquid quick-setting agent comprises the following components by weight: 25-35 parts of aluminum sulfate, 5-15 parts of ferrous sulfate, 3-4 parts of compound alcohol amine, 3-4 parts of pH regulator and 33-36 parts of deionized water.

[0008] Furthermore, the following components are included, by weight: 31-34 parts of aluminum sulfate, 8-12 parts of ferrous sulfate, 3.4-3.6 parts of compound alcohol amine, 3.3-3.7 parts of pH regulator, and 34-35 parts of deionized water.

[0009] Further, the compounded alcoholamine is selected from any one of triethanolamine and diethanolamine, and any one of n-propanolamine and isopropanolamine. Further preferably, the alcoholamine is formed by mixing triethanolamine with n-propanolamine or isopropanolamine in a mass ratio of 1-3:10, or the alcoholamine is formed by mixing diethanolamine with n-propanolamine or isopropanolamine in a mass ratio of 3-7:10.

[0010] In the multi-component system of the accelerator, the action mechanisms of different alcohol amines are different. For example, triethanolamine has the best effect on promoting the reaction of aluminate cement clinker, but also has the most obvious inhibitory effect on silicate phase clinker. Diethanolamine is inferior to triethanolamine in both promoting the aluminate cement clinker and inhibiting the silicate phase clinker. Propanolamine has a poor effect on aluminate, but has a more obvious promoting effect on silicate clinker. The present invention realizes the simultaneous promotion of the reaction of aluminate and silicate cement clinkers by compounding triethanolamine / diethanolamine with propanolamine, thereby achieving the purpose of simplifying the material components of the accelerator.

[0011] Furthermore, the pH adjuster includes but is not limited to lactic acid, oxalic acid, and phosphoric acid.

[0012] The acidic environment provided by the pH regulator can inhibit the hydrolysis of aluminum ions, thereby avoiding the occurrence of precipitation. In addition, the essence of ferrous sulfate is the same as that of aluminum sulfate, both of which are sulfates. The former can partially replace the aluminum sulfate with lower solubility in the accelerator system, which is also conducive to enhancing the stability of the liquid accelerator.

[0013] Ferric ions are more likely to replace aluminum ions in cement hydration product ettringite than divalent ferrous ions, thereby replacing aluminum ions to form ettringite. Therefore, the use of a pH regulator to oxidize ferrous ions into ferric ions in the present application technology plays a role in promoting the hydration of cement clinker tricalcium aluminate, thereby shortening the setting time.

[0014] The present invention also provides a preparation method of the alkali-free and fluorine-free liquid accelerating setting agent, comprising the following steps: firstly, adding an alcohol amine into deionized water to obtain an alcohol amine solution, which is recorded as solution A; then, adding aluminum sulfate into solution A, stirring until it is completely dissolved, to obtain solution B; adding ferrous sulfate into solution B, stirring until it is completely dissolved, to obtain solution C; finally, adding a pH regulator into solution C, adjusting the pH to 2-3, to obtain the alkali-free and fluorine-free liquid accelerating setting agent.

[0015] Furthermore, the stirring is stirring at room temperature.

[0016] The present invention has no special provisions on stirring time and stirring speed.

[0017] Compared with the prior art, the present invention has the following beneficial effects: the present invention solves the problem that the ternary coagulation accelerating system composed of ferrous sulfate / ferrous sulfate, aluminum sulfate and alcohol amine is difficult to meet the performance requirements of GB / T35159-2017 for the accelerating agent. By optimizing the alcohol amine ratio, the above-mentioned ternary coagulant can achieve the coordination of the setting time and initial compressive strength of the cement material without adding additional reinforcing components. The alkali-free and fluorine-free liquid accelerating agent prepared in this way has the characteristics of low cost, simple process, can be prepared at room temperature and has good stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is an electron microscope image of cement paste without accelerator after curing for 24 hours;

[0019] Figure 2 This is an electron microscope image of cement paste containing 7wt% alkali-free and fluorine-free liquid accelerating agent after curing for 24 hours;

[0020] Figure 3 The figures are the state diagrams of the fluorine-free and alkali-free liquid quick-setting agent prepared in Example 1 of the present invention when it is just prepared and after being placed at room temperature for 3 months. DETAILED DESCRIPTION

[0021] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work belong to the scope of protection of the present invention.

[0022] The experimental methods or test methods described in the following examples are conventional methods unless otherwise specified; the raw materials and auxiliary agents are obtained from conventional commercial channels or prepared by conventional methods unless otherwise specified.

[0023] Example 1

[0024] A method for preparing an alkali-free and fluorine-free liquid accelerating setting agent, the specific steps are as follows:

[0025] (1) Weighing 3.4 g of a composite alcohol amine and dissolving it in 35 g of deionized water to obtain an alcohol amine solution, referred to as solution A, wherein the alcohol amine is prepared by mixing diethanolamine and n-propanolamine in a mass ratio of 6:10;

[0026] (2) Add 34 g of aluminum sulfate to solution A and stir at room temperature until the solid particles are completely dissolved to obtain solution B;

[0027] (3) adding 9.2 g of ferrous sulfate to solution B, and continuing to stir at room temperature until the solid particles are completely dissolved to obtain solution C;

[0028] (4) Finally, 3.5 g of lactic acid was added to solution C, and the mixture was stirred at room temperature for 10 min. The pH of the solution was adjusted to 2-3, and the ferrous ions were oxidized to trivalent ferrous ions to obtain an alkali-free and fluorine-free liquid accelerating setting agent.

[0029] The alkali-free and fluorine-free liquid accelerating setting agent prepared in this embodiment was added to cement paste (water-cement ratio 0.35) at a mass ratio of 6wt%-9wt% to test the setting time, and was added to mortar (water-cement ratio 0.5) to measure the compressive strength (for specific test regulations, see GB / T 35159-2017 Accelerating setting agent for shotcrete).

[0030] The test results are shown in Table 1

[0031] Table 1

[0032]

[0033] It can be seen from Table 1 that the alkali-free and fluorine-free liquid accelerator prepared in this embodiment has good applicability to silicate cement from different manufacturers. In the range of 6wt%-9wt% of addition, the initial setting time of cement paste is <5min, and the final setting time is <12min; the 1-day compressive strength of mortar is >7MPa, and the 28-day compressive strength ratio (%) is >90%, which meets the requirements of GB / T 35159-2017 for accelerators for shotcrete.

[0034] By comparing the SEM results of neat cement paste and neat cement paste with 7wt% alkali-free and fluorine-free liquid accelerator, it can be seen that the neat cement paste with 7wt% accelerator obviously produces more amorphous gel material, making the microstructure of the stone body more compact. At the same time, the accelerator also helps to form large-sized ettringite, indicating that the hydration reaction of aluminate and silicate cement clinker is accelerated. The combined effect of the two makes the cement material coagulate rapidly and improves its mechanical properties (see Figure 1 and Figure 2 ).

[0035] Depend on Figure 3 It can be seen that the alkali-free and fluorine-free liquid quick-setting agent prepared in this embodiment is a light yellow transparent liquid with good stability. Even after being placed for 3 months, it is still transparent and has no precipitation.

[0036] Comparative Examples 1-5

[0037] The difference from Example 1 is that the raw material composition and compounding ratio of the alcohol amine are different, the cement is PC42.5 silicate cement produced by Southwest Cement, and the remaining steps are the same as Example 1. The performance of the accelerated setting agent with an addition amount of 8wt% is tested.

[0038] The performance test results of the quick-setting agents of Comparative Examples 1-5 are shown in Table 2.

[0039] Table 2

[0040]

[0041] As can be seen from Table 2, when triethanolamine or n-propanolamine is used alone, or the two alcoholamines are compounded but not within the ratio range specified in the present invention, the setting time and compressive strength are difficult to simultaneously meet the performance requirements of GB / T35159-2017 for alkali-free and fluorine-free liquid accelerating setting agents. However, alcoholamines within the ratio range specified in the present invention can effectively solve this problem.

[0042] Comparative Examples 6-9

[0043] The difference from Example 1 is that only the ratio of diethanolamine to n-propanolamine is changed, PC42.5 silicate cement produced by Southwest Cement is used, and the remaining steps are the same as Example 1. The performance of the accelerated setting agent with an addition amount of 8 wt % is tested.

[0044] The performance test results of the quick-setting agents of Comparative Examples 6-9 are shown in Table 3.

[0045] Table 3

[0046]

[0047]

[0048] As shown in Table 3, when diethanolamine is used alone, the cement setting time is long and the early strength is difficult to meet the requirements of GB / T35159-2017 for alkali-free liquid accelerating agents. After compounding n-propanolamine according to the ratio given in the present invention, the above-mentioned shortcomings are successfully solved.

[0049] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. An alkali-free and fluorine-free liquid accelerating agent, characterized in that: The composition comprises the following components by weight: 25-35 parts of aluminum sulfate, 5-15 parts of ferrous sulfate, 3-4 parts of compound alcohol amine, 3-4 parts of pH regulator, and 33-36 parts of deionized water; The compounded alcohol amine is selected from any one of triethanolamine and diethanolamine, and any one of n-propanolamine and isopropanolamine; The compound alcohol amine is prepared by mixing triethanolamine and n-propanolamine or isopropanolamine in a mass ratio of 1-3:

10.

2. The alkali-free and fluorine-free liquid quick-setting agent according to claim 1, characterized in that: The composition comprises the following components by weight: 31-34 parts of aluminum sulfate, 8-12 parts of ferrous sulfate, 3.4-3.6 parts of compound alcohol amine, 3.3-3.7 parts of pH regulator and 34-35 parts of deionized water.

3. The alkali-free and fluorine-free liquid quick-setting agent according to claim 1, characterized in that: The compound alcohol amine is prepared by mixing diethanolamine and n-propanolamine or isopropanolamine in a mass ratio of 3-7:

10.

4. The alkali-free and fluorine-free liquid quick-setting agent according to any one of claims 1 or 2, characterized in that: The pH adjuster includes lactic acid, oxalic acid and phosphoric acid.

5. The method for preparing the alkali-free and fluorine-free liquid accelerating setting agent according to claim 1, characterized in that: The following steps are involved: First, the compound alcohol amine is added into deionized water to obtain a compound alcohol amine solution, which is recorded as solution A; Aluminum sulfate is then added to solution A, stirred until completely dissolved, to obtain solution B; ferrous sulfate is added to solution B, stirred until completely dissolved, to obtain solution C; finally, a pH adjuster is added to solution C, and the pH is adjusted to 2-3 to obtain an alkali-free and fluorine-free liquid accelerating setting agent.

6. The method for preparing the alkali-free and fluorine-free liquid accelerating setting agent according to claim 5, characterized in that: The stirring is stirring at room temperature.

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