Early-strength and rapid-hardening cementing material system free of heat curing at extremely low temperature and preparation method of early-strength and rapid-hardening cementing material system

Abstract

The invention discloses an early-strength quick-hardening cementing material system free of hot curing at an extremely low temperature and a preparation method thereof. The early-strength quick-hardening cementing material system comprises the following components in parts by weight: sulphate aluminium cement, coal ash, silica fume, water, calcium oxide and a water reducing agent in a ratio of 400: 50: 50: 150: (5-25): 2. The addition of CaO provides a large amount of heat for early hydration of the sulphoaluminate cement at an extremely low temperature (-20 DEG C), the peak temperature can reach 80 DEG C, the internal temperature is improved, the amount of water required by the hydration of the sulphoaluminate cement is increased, the liquid phase freezing point is greatly reduced, the freezing amount of the freezable water is effectively reduced, and the early hydration of the sulphoaluminate cement at an extremely low temperature (-20 DEG C) is facilitated. Continuous hydration of the sulphoaluminate cement at-20 DEG C is realized, and the defects of insufficient early strength and long-term stability of a traditional material are overcome. The preparation method provided by the invention is simple to operate, does not need complex pretreatment, and does not affect the construction period. Meanwhile, the industrial by-product fly ash is utilized, the resource utilization trend is met, energy is remarkably saved through the simplified maintenance process, and carbon emission is reduced.

Description

TECHNICAL FIELD

[0001] The application relates to an early-strength and fast-hardening cementitious material system under extremely low temperature without heat curing and a preparation method thereof, and belongs to the technical field of building materials. BACKGROUND

[0002] Under an extremely low temperature environment of-20 DEG C, concrete winter construction faces severe challenges. Although traditional heat preservation technologies such as the warm shed method and the electric blanket can maintain the curing temperature, thermodynamic analysis shows that the energy consumption exponentially increases with the decrease of the temperature, which leads to significant increase of carbon emission and decrease of energy utilization rate. At the same time, the conventional antifreeze agent system appears functional attenuation at this temperature, and it is difficult to effectively reduce the freezing point of the pore solution. For the sulphoaluminate cement (SAC) system, the condition of-20 DEG C will cause double failure: firstly, the rapid freezing of free water blocks the hydration reaction path, so that the hydration process on the surface of the cement particles is almost stagnant; secondly, the early strength development of the material is seriously hindered, and it cannot meet the core requirement of the concrete rapid formation of bearing capacity for the repair engineering in cold regions. Therefore, it is urgent to develop an innovative technical path suitable for the environment of-20 DEG C, to realize the coordinated development of the continuous hydration and early strength of the concrete under the premise of controlling the energy consumption and carbon emission, which has important significance for the emergency repair of major infrastructure and green construction. SUMMARY

[0003] The first object of the application is to provide an early-strength and fast-hardening cementitious material system under extremely low temperature without heat curing, and the second object of the application is to provide a preparation method of the early-strength and fast-hardening cementitious material system under extremely low temperature without heat curing. The problems of the existing Portland cement system in the negative temperature environment, such as the insufficient early strength and the immediate bearing requirement of the repair engineering, and the problems of the existing aluminate cement system, such as the unstable late strength growth and the long-term reliability requirement of the structure life, and the problems of the existing conventional material, such as the negative temperature hydration stagnation and the continuous operation requirement of the winter construction, are solved. The application synchronously realizes the super early strength, fast hardening and strength development sustainability by giving the material the self-activated negative temperature hydration capability, and provides a solution for the infrastructure and emergency engineering in cold regions.

[0004] Technical scheme: The early-strength and fast-hardening cementitious material system under extremely low temperature without heat curing comprises the following components in the weight ratio: sulphoaluminate cement: fly ash: silica fume: water: calcium oxide: water reducing agent = 400: 50: 50: 150: (5-25): 2.

[0005] Further, the components are included in the following ratio by weight parts: sulphoaluminate cement: fly ash: silica fume: water: calcium oxide: water reducing agent = 400: 50: 50: 150: (5-15): 2. Most preferably, the ratio is sulphoaluminate cement: fly ash: silica fume: water: calcium oxide: water reducing agent = 400: 50: 50: 150: 10: 2. The sulphoaluminate cement meets the national standard "Sulphoaluminate Cement" GB20472-2006. The fly ash is F-class 1st grade fly ash. The silica fume is SF90 grade silica fume. The purity of the calcium oxide is above 99%. The water reducing agent is a polycarboxylic acid high efficiency water reducing agent, and the effective solid content of the water reducing agent is above 20%. The very low temperature refers to as low as -20℃.

[0006] The preparation method of the early strength and fast hardening cementitious material system under very low temperature without heat curing, comprises the above steps:

[0007] (1) mixing sulphoaluminate cement, fly ash, silica fume and calcium oxide, and slowly stirring with an Eirich R type strong mixing stirrer until uniform to obtain a composite cementitious material;

[0008] (2) dispersing a water reducing agent in water to obtain a mixed solution containing an additive;

[0009] (3) mixing the mixed solution containing the additive with the composite cementitious material, slowly stirring, and then rapidly stirring to obtain a high early strength and fast hardening cement-based material slurry.

[0010] Further, in steps (1) and (3), the rotating speed of the mixer of the stirrer is 30-50 r / min, the rotating speed of the rotor is 150-200 r / min, the rotating directions of the mixer and the rotor are opposite, and the slowly stirring time is 30-60 s. In the rapid stirring, the rotating speed of the mixer of the stirrer is 30-50 r / min, the rotating speed of the rotor is 300-350 r / min, the rotating directions of the mixer and the rotor are opposite, and the rapid stirring time is 60-90 s.

[0011] Technical mechanism: the addition of CaO provides a large amount of heat for the early hydration of sulphoaluminate cement under very low temperature (-20℃), increases the internal temperature, increases the amount of water required for the hydration of sulphoaluminate cement, greatly reduces the freezing point of the liquid phase (-7.2℃), and realizes the continuous hydration of sulphoaluminate cement under negative temperature conditions. From the results of XRD refinement and chemical combined water content, the early hydration degree is obviously increased, more hydration products AFt are produced to fill the pore of sulphoaluminate cement stone, a dense microstructure is formed, and therefore higher strength is obtained.

[0012] Beneficial effects: Compared with the prior art, the present application has the following remarkable advantages: (1) After adding CaO, a huge exothermic peak appears in the early hydration stage, and the peak temperature can reach 80℃. The exothermic peak can delay the freezing of the liquid phase in the cement to a certain extent, so that the cement continues to hydrate at an environmental temperature of-20℃. At the same time, the freezing point of the sulphoaluminate cement is reduced to-7.2℃, the platform stage of the curve is sharply shortened, the ice freezing amount is effectively reduced, and the negative effect of early frost damage of the sulphoaluminate cement is smaller. (2) The compressive strength of the cementitious material system of the present application is 15.47MPa after curing at-20℃ for 24 hours, which is far higher than the threshold value of the demolding strength in cold regions. (3) The preparation method provided by the present application is simple to operate, does not require complex pretreatment, and will not affect the construction period. At the same time, the industrial by-product fly ash is used, which conforms to the resource utilization trend, the simplified curing process significantly saves energy, and reduces carbon emissions. BRIEF DESCRIPTION OF DRAWINGS

[0013] Figure 1 Microstructure diagram of the cement-based material prepared for Comparative Example 1 and Example 2, which is cured at-20℃ for 28d;

[0014] Figure 2 Temperature-time curve diagram of the hydration at-20℃ in the cement-based material prepared for Comparative Example 1 and Example 2;

[0015] Figure 3 XRD diagrams of the cement-based material prepared for Example 2, Example 5 and Comparative Example 1, which are cured at-20℃ for 1d and 7d respectively;

[0016] Figure 4 TG-DTG curve diagrams of the cement-based material prepared for Example 2 and Comparative Example 1, which are cured at-20℃ for 1d and 7d respectively. DETAILED DESCRIPTION

[0017] The technical solutions of the present application will be further described below in combination with the drawings.

[0018] In the following examples, the sulphoaluminate cement is a fast-hardening composite sulphoaluminate cement (R·SAC) of 42.5 strength grade produced by Tangshan Beijiaohu Bear Materials Co., Ltd., and the chemical composition thereof is shown in Table 1. The fly ash is F-class I-grade fly ash, and the important chemical components thereof are shown in Table 2. The silica fume is SF90-grade silica fume, and the important chemical components thereof are shown in Table 3. The calcium oxide is produced by Shanghai Gaoke Chemical Reagent Co., Ltd., and the purity is greater than 99%. The effective solid content of the polycarboxylate superplasticizer is 28%, the PH value is 13.19, the specific gravity is 36.39, and the water solubility is 0.38. The water is Wahaha pure water.

[0019] Table 1 Chemical composition of cement (mass ratio wt. %)

[0020]

[0021] Table 2 Chemical composition of fly ash (mass ratio wt. %)

[0022]

[0023] Table 3 Chemical composition of silica ash (mass ratio wt. %)

[0024]

[0025] Example 1

[0026] (1) Take raw material components by weight parts: sulphoaluminate cement 400 parts, fly ash 50 parts, silica ash 50 parts, water 150 parts, calcium oxide 5 parts, polycarboxylic acid superplasticizer 2 parts, standby;

[0027] (2) Mix sulphoaluminate cement, fly ash, silica ash and calcium oxide, slowly stir to uniformity with Liebher R type strong mixing stirrer, to obtain composite cementitious material;

[0028] (3) Disperse polycarboxylic acid superplasticizer uniformly in water, to obtain mixed solution containing superplasticizer;

[0029] (4) Add mixed solution in step (3) and composite cementitious material in step (2) into Liebher R type strong mixing stirrer, control the rotating speed of mixer of stirrer at 40 r / min, rotating speed of rotor at 150 r / min, rotating direction of mixer opposite to that of rotor, slowly stir for 30 s. Then control the rotating speed of mixer of stirrer at 40 r / min, rotating speed of rotor at 300 r / min, rotating direction of mixer opposite to that of rotor, quickly stir for 90 s, to obtain early strength and fast hardening cementitious material system free of heat curing under -20 ℃ environment.

[0030] Example 2

[0031] Take raw material components by weight parts: sulphoaluminate cement 400 parts, fly ash 50 parts, silica ash 50 parts, water 150 parts, calcium oxide 10 parts, polycarboxylic acid superplasticizer 2 parts.

[0032] Preparation method is same as example 1.

[0033] Example 3

[0034] Take raw material components by weight parts: sulphoaluminate cement 400 parts, fly ash 50 parts, silica ash 50 parts, water 150 parts, calcium oxide 15 parts, polycarboxylic acid superplasticizer 2 parts.

[0035] Preparation method is same as example 1.

[0036] Example 4

[0037] The raw material components were taken by weight parts: sulphoaluminate cement 400 parts, fly ash 50 parts, silica ash 50 parts, water 150 parts, calcium oxide 20 parts, polycarboxylic acid superplasticizer 2 parts.

[0038] The preparation method was the same as that of Example 1.

[0039] Example 5

[0040] The raw material components were taken by weight parts: sulphoaluminate cement 400 parts, fly ash 50 parts, silica ash 50 parts, water 150 parts, calcium oxide 25 parts, polycarboxylic acid superplasticizer 2 parts.

[0041] The preparation method was the same as that of Example 1.

[0042] Comparative Example 1

[0043] (1) The raw material components were taken by weight parts: sulphoaluminate cement 400 parts, fly ash 50 parts, silica ash 50 parts, water 150 parts, polycarboxylic acid superplasticizer 2 parts, for standby;

[0044] (2) The sulphoaluminate cement and fly ash were added into a mixer and stirred until uniform to obtain a composite cementitious material;

[0045] (3) The polycarboxylic acid superplasticizer was uniformly dispersed in water to obtain a mixed solution containing an additive;

[0046] (4) The mixed solution in step (3) and the composite cementitious material in step (2) were added into a high-speed mixer of a type R of Eirich, the rotating speed of the mixer was controlled at 40 r / min, the rotating speed of the rotor was controlled at 150 r / min, the rotating directions of the mixer and the rotor were opposite, and slow stirring was carried out for 30 s. Then the rotating speed of the mixer was controlled at 40 r / min, the rotating speed of the rotor was controlled at 300 r / min, the rotating directions of the mixer and the rotor were opposite, and fast stirring was carried out for 90 s to obtain a cement-based material slurry.

[0047] The cement-based materials prepared in Example 2 and Comparative Example 1 were subjected to scanning electron microscope analysis after being cured at -20℃ for 28 d, and the results are shown in Figure 1 . Figure 1 The SEM images of the cement-based materials prepared in Comparative Example 1 and Example 2 after being hydrated at -20℃ for 28 d, wherein a is Example 2 and b is Comparative Example 1. It can be seen from Figure 1 that there are a large number of AFt crystals in the form of needles and rods and some amorphous hydration products in Example 2, the AFt crystals form a skeleton by lapping with each other and fill the pores of the cement stone, so the performance is more excellent. There are many cracks and obvious pores in Comparative Example 1, and the size of the AFt crystals is also smaller, so the mechanical properties are poor.

[0048] The cement-based materials obtained in Examples 1-5 and Comparative Example 1 were directly placed in a curing temperature of -20°C to be cured, and then tested and measured, mainly the 1d, 3d and 7d compressive strengths. The test results are shown in Table 4 below.

[0049] Table 4 Compressive strength test results of cement-based materials of Examples 1-5 and Comparative Example 1 at -20°C (unit: MPa)

[0050]

[0051] As can be seen from Table 4, when the curing temperature is -20°C, the strength of Comparative Example 1 is extremely low and develops slowly with the age. The water used for cement hydration has already frozen at an environmental temperature of -20°C, and the hydration reaction at negative temperature is forced to stop. When CaO is added in Examples 1-5, the early strength is increased to different degrees compared with Comparative Example 1. Compared with Comparative Example 1, the strength increasing effect of Examples 1-3 is obvious, especially the 1d, 3d and 7d strengths of Example 2 are increased by 3.51 times, 2.38 times and 3.14 times respectively, and the 1d strength can be increased from 3.53 MPa to 15.47 MPa, which can reach the critical strength required in the specification.

[0052] Figure 2 The hydration temperature-time curves of the cement-based materials prepared in Comparative Example 1 and Example 2 at -20°C are shown in Figure 2. Figure 2 As can be seen from Figure 2, Example 2 has a huge exothermic peak at the initial hydration stage, and the peak temperature can reach 80°C, which is caused by the exothermic reaction of CaO and water to generate Ca(OH)2. The existence of the exothermic peak can delay the freezing of ice in the cement to some extent, so that the cement can continue to hydrate at an environmental temperature of -20°C. Example 2 not only reduces the freezing point of the cement system to -7.2°C, but also sharply shortens the platform stage of the curve, indicating that the ice freezing amount is effectively reduced, and the negative effect of early frost damage of the cement is smaller, so Example 2 can effectively reduce the freezing point of the cement system and increase the mechanical properties

[0053] The XRD analysis of the cement-based materials prepared in Example 2, Example 5 and Comparative Example 1 was carried out after curing at -20°C for 1d and 7d respectively, and the results are shown in Figure 3. Figure 3 Figure 3 Figure 3 is the XRD graphs of the cement-based materials prepared in Example 2, Example 5 and Comparative Example 1 cured at -20°C for 1d and 7d respectively, wherein a is 1d, b is 7d, E represents ettringite, Y represents anhydrous calcium sulphoaluminate, G represents gypsum, and M represents magnesium oxide. As can be seen from Figure 3, Figure 3 ​It can be seen that the content of CaO has a significant effect on the intensity of the main peak of AFt. Whether it is 1d or 7d, the intensity of the ettringite diffraction peak of Example 2 at -20℃ is significantly increased, and the unhydrated calcium sulphoaluminate diffraction peak is also the smallest. The low reactant peak and high product peak indicate that there is a higher degree of hydration in the sulphoaluminate cement system with the addition of 2% CaO. In addition, the intensity of the AFt diffraction peak increases with the age, indicating that the sulphoaluminate cement system can undergo normal hydration under the negative temperature environment of -20℃.

[0054] The cement-based materials prepared in Example 2 and Comparative Example 1 were subjected to micro-thermal gravimetric analysis after being cured at -20℃ for 1d and 7d respectively, and the results are shown in Figure 4 Figure 4 TG-DTG curves of the cement-based materials prepared in Example 2 and Comparative Example 1 cured at -20℃ for 1d and 7d respectively, wherein a is 1d and b is 7d. It can be seen from Figure 4 that the total weight loss of Example 2 is lower than that of Comparative Example 1, indicating that Example 2 produces more hydration products to fill the pores of the cement under the condition of -20℃ compared to Comparative Example 1, and the pore structure of the cement paste is more compact.​

Claims

1. An early-strength and fast-hardening gelling material system that does not require heat curing at extremely low temperatures, characterized in that: The composition includes the following components in proportion by weight: sulphoaluminate cement: fly ash: silica fume: water: calcium oxide: water reducer = 400:50:50:150:(5-25):

2.

2. The early-strength and fast-hardening gelling material system without heat curing at extremely low temperature according to claim 1, characterized in that: The composition includes the following components in proportion by weight: sulphoaluminate cement: fly ash: silica fume: water: calcium oxide: water reducer = 400:50:50:150:(5-15):

2.

3. The early-strength and fast-hardening gelling material system without heat curing at extremely low temperature according to claim 1, characterized in that: Sulphoaluminate cement complies with the national standard "Sulphoaluminate Cement" GB20472-2006.

4. The early-strength and fast-hardening gelling material system without heat curing at extremely low temperature according to claim 1, characterized in that: The fly ash is Class F 1 fly ash, and the silica fume is SF90 grade silica fume.

5. The early-strength and fast-hardening gelling material system without heat curing at extremely low temperature according to claim 1, characterized in that: The purity of calcium oxide is above 99%.

6. The early-strength and fast-hardening gelling material system without heat curing at extremely low temperature according to claim 1, characterized in that: The water reducer is a polycarboxylic acid high-efficiency water reducer.

7. The early-strength and fast-hardening gelling material system without heat curing at extremely low temperature according to claim 1, characterized in that: The effective solid content of the water reducer is more than 20%.

8. The method for preparing the early-strength and fast-hardening gelling material system without heat curing at extremely low temperature according to any one of claims 1 to 7, characterized in that: Including the above steps: (1) Sulphoaluminate cement, fly ash, silica fume and calcium oxide are mixed and slowly stirred until uniform to obtain a composite cementitious material; (2) dispersing the water reducer in water to obtain a mixed solution containing the admixture; (3) The mixed solution containing the admixture is mixed with the composite cementitious material, stirred slowly, and then stirred rapidly to obtain a high early strength and fast hardening cement-based material slurry.

9. The method of preparation according to claim 8, characterized in that: In step (1) and step (3), the mixer rotation speed of the stirrer used for slow stirring is 30 to 50 r / min, the rotor rotation speed is 150 to 200 r / min, and the mixer and rotor rotate in opposite directions; the slow stirring time is 30 to 60 s.

10. The preparation method according to claim 8, characterized in that: In step (3), during rapid stirring, the mixer rotation speed of the stirrer is 30 to 50 r / min, the rotor rotation speed is 300 to 350 r / min, the mixer and the rotor rotate in opposite directions, and the rapid stirring time is 60 to 90 s.

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