High-early-strength quick-hardening cement-based material capable of being continuously hydrated at low temperature and preparation method of high-early-strength quick-hardening cement-based material

Abstract

The invention discloses a high-early-strength quick-hardening cement-based material capable of being continuously hydrated at a low temperature and a preparation method thereof. The cement-based material comprises the following components in parts by weight: 450 parts of sulphoaluminate cement, 50 parts of silica fume, 150 parts of water, 5-25 parts of sodium nitrate and 2 parts of a water reducing agent. The doping amount range of high-purity sodium nitrate (the purity is larger than 99%) is precisely regulated and controlled, the ionized water efficiency of the sulphoaluminate cement under the low-temperature (-10 DEG C) condition is activated, and it is guaranteed that the slurry has the excellent rheological property and densification characteristic in combination with the gradient optimized cementing material proportion and the synergistic plasticizing effect of the polycarboxylate superplasticizer; a foundation is built for early strength jump; the preparation process does not need preheating or complex temperature control procedures, and is directly adaptive to the conventional construction process.

Description

TECHNICAL FIELD

[0001] The application relates to a high-early-strength and fast-hardening cement-based material capable of sustainable hydration at low temperature and a preparation method thereof, in particular to a high-early-strength and fast-hardening sulphoaluminate cement composite material capable of sustainable hydration at-10 DEG C and a preparation method thereof, and belongs to the technical field of building materials. BACKGROUND

[0002] In the winter construction of infrastructure in cold regions, the low-temperature environment of-10 DEG C has become a key problem faced by concrete technology. Traditional antifreeze measures have failed in this working condition, and ordinary portland cement cannot be hydrated because all the internal free water is frozen at-10 DEG C. The effect of traditional antifreezes is almost zero at-10 DEG C, and there are mainly three problems: (1) the freezing point reduction efficiency of commercially available organic antifreezes (such as methanol and ethanol) decreases sharply at-10 DEG C. When the environmental temperature exceeds-8 DEG C, the antifreeze system completely loses the antifreezing ability; (2) under the condition of-10 DEG C, the free water in the concrete will freeze into ice in the early stage of hydration, resulting in hydration stagnation, and the early strength cannot be developed; (3) the existing antifreeze patent relies on a single organic component, and ignores the freezing point synergistic effect of inorganic salts.

[0003] Therefore, the sulphoaluminate cement system with a faster early hydration speed is used for the design of cold regions, and has the advantages of fast hydration heat release and good frost resistance. However, the sulphoaluminate cement system cannot work in the negative temperature environment of-10 DEG C, the hydration heat cannot be quickly released, the internal free water is frozen, and the hydration process is slowed down or even stopped. Therefore, it is urgent to develop inorganic admixtures applicable to the negative temperature environment of-10 DEG C, which can realize the gradient reduction of the freezing point of pore liquid, improve the low-temperature mass transfer condition, maintain the hydration continuity, and build a microstructure damage control mechanism. The development in this direction has a substantial promoting effect on the service safety application of major infrastructure in cold regions. SUMMARY

[0004] The first object of the present application is to provide a high-early-strength and fast-hardening cement-based material capable of sustainable hydration at low temperature, and the second object of the present application is to provide a preparation method of the high-early-strength and fast-hardening cement-based material capable of sustainable hydration at low temperature. In view of the extreme requirements of winter construction environment on the performance of cement-based materials, the present application breaks through the early strength and hydration rate, solves the problem of slow hardening of traditional portland cement in low-temperature environment, and has long-term stability which is superior to that of aluminate system, avoids the fluctuation defect of the late strength of aluminate cement, and ensures the continuous and stable strength growth. The present application has the capability of sustainable hydration in the environment of-10 DEG C without external heat source, thereby significantly expanding the engineering application boundary of the material in the extreme working conditions such as winter infrastructure, emergency repair and leakage rapid treatment.

[0005] Technical solution: The low-temperature sustainable hydration high early strength and fast hardening cement-based material comprises the following components in parts by weight: sulphoaluminate cement: silica fume: water: sodium nitrate: water reducing agent = 450: 50: 150: (5-25): 2.

[0006] Further, the components comprise the following components in parts by weight: sulphoaluminate cement: silica fume: water: sodium nitrate: water reducing agent = 450: 50: 150: (10-20): 2. Most preferably, sulphoaluminate cement: silica fume: water: sodium nitrate: water reducing agent = 450: 50: 150: 10: 2. The sulphoaluminate cement meets the national standard 'Sulphoaluminate Cement' GB20472-2006. The silica fume is SF90 silica fume with a silicon dioxide content of not less than 90%. The purity of sodium nitrate is more than 99%. The water reducing agent is a polycarboxylic acid superplasticizer with an effective solid content of more than 20%. The low temperature is as low as -10 DEG C.

[0007] The preparation method of the low-temperature sustainable hydration high early strength and fast hardening cement-based material comprises the above steps.

[0008] (1) mixing sulphoaluminate cement and silica fume, stirring until uniform to obtain a composite cementitious material;

[0009] (2) dispersing sodium nitrate and water reducing agent in water, ultrasonic treatment to obtain a mixed solution containing admixtures;

[0010] (3) mixing the mixed solution containing admixtures with the composite cementitious material, low-speed stirring, then high-speed stirring to obtain a high early strength and fast hardening cement-based material slurry.

[0011] Further, in step (2), the ultrasonic power is 120-140 W and the ultrasonic time is more than 3 min. In step (3), the stirring equipment is a standard planetary cement paste stirrer, the low-speed stirring speed is 40-80 r / min, and the low-speed stirring time is 60-120 s. After low-speed stirring, stop for more than 15 s, scrape off the cement slurry adhered to the machine, then high-speed stir, the high-speed stirring speed is 100-150 r / min, and the high-speed stirring time is 60-120 s.

[0012] Technical mechanism: The sulphoaluminate cement system is under the condition of-10℃, the liquid phase has more ice, and has a lower hydration rate under negative temperature, which leads to easy freezing under negative temperature, produces less hydration product, appears more microcracks and interpenetration, and forms a loose sulphoaluminate cement microstructure. The addition of sodium nitrate under the condition of-10℃ increases the ion concentration in the sulphoaluminate cement system, reduces the freezing point of the liquid phase, has more hydratable water participating in hydration in the early hydration, and the size of the hydration product AFt growing on the cement particles is significantly larger and coarser, the hydration degree is greatly improved, the hydration products form a stable grid structure by mutual lapping, the microcracks in the microstructure are also significantly reduced, and therefore higher strength is obtained.

[0013] Beneficial effects: Compared with the prior art, the present application has the following significant advantages: (1) innovative construction of multi-component-10℃ synergistic system: sulphoaluminate cement contributes to fast hardening and early strength, SF90 silica ash optimizes the paste structure through the pozzolanic effect, water reducing agent realizes ultra-high water reducing rate (>20%) under low water-binder ratio, and high-purity sodium nitrate precisely regulates the dosage range of the core-10℃ catalyst and strength promoter to drive the whole process performance breakthrough; (2) the present application changes the traditional technology status, does not need preheating or complex temperature control program, and directly adapts to the conventional construction process; deeply integrates industrial solid waste resources, cooperates with the heat curing process to reduce energy consumption by 92%, realizes the dual transformation of green construction and engineering efficiency. BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1 The electron microscope graph of the cement-based material prepared in the comparative example 1 and the example 2 under the condition of-10℃ curing for 28 days;

[0015] Figure 2 The XRD graph of the cement-based material prepared in the comparative example 1 and the example 2 under the condition of-10℃ curing for 1 day and 7 days;

[0016] Figure 3 The TG-DTG curve graph of the cement-based material prepared in the comparative example 1 and the example 2 under the condition of-10℃ curing for 1 day and 7 days. 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 Polar Bear Building Material Co., Ltd., the chemical composition of which is shown in Table 1. The silica fume is SF90 grade silica fume, the important chemical composition of which is shown in Table 2. The sodium nitrate is produced by Shanghai Reagent Co., Ltd., with a purity of more than 99%. The polycarboxylate superplasticizer has an effective solid content of 28%, a pH value of 13.19, a specific gravity of 36.39, and a water solubility of 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 silica fume (mass ratio wt. %)

[0022]

[0023] Example 1

[0024] (1) Take the raw material components by weight parts: sulphoaluminate cement 450 parts, silica fume 50 parts, water 150 parts, sodium nitrate 5 parts, polycarboxylate superplasticizer 2 parts, and reserve;

[0025] (2) Add the sulphoaluminate cement and silica fume into a mixer and stir until uniform to obtain a composite cementitious material;

[0026] (3) Disperse the sodium nitrate and the superplasticizer uniformly in water, and obtain a mixed solution containing admixtures after ultrasonic treatment at an ultrasonic power of 120-140 W for 3 min;

[0027] (4) Add the mixed solution in step (3) and the composite cementitious material in step (2) into a standard planetary cement paste stirrer, stir at low speed (60 r / min) for 120 s, stop for 15 s while scraping the cement paste on the blade and the pot wall into the middle of the pot, and then stir at high speed (120 r / min) for 120 s, to obtain the high early strength fast hardening cement-based material slurry.

[0028] Example 2

[0029] Take the raw material components by weight parts: sulphoaluminate cement 450 parts, silica fume 50 parts, water 150 parts, sodium nitrate 10 parts, polycarboxylate superplasticizer 2 parts.

[0030] The preparation method is the same as that in Example 1.

[0031] Example 3

[0032] The raw material components are taken by weight parts as follows: sulphoaluminate cement 450 parts, silica fume 50 parts, water 150 parts, sodium nitrate 15 parts, polycarboxylic acid superplasticizer 2 parts.

[0033] The preparation method is the same as that of Example 1.

[0034] Example 4

[0035] The raw material components are taken by weight parts as follows: sulphoaluminate cement 450 parts, silica fume 50 parts, water 150 parts, sodium nitrate 20 parts, polycarboxylic acid superplasticizer 2 parts.

[0036] The preparation method is the same as that of Example 1.

[0037] Example 5

[0038] The raw material components are taken by weight parts as follows: sulphoaluminate cement 450 parts, silica fume 50 parts, water 150 parts, sodium nitrate 25 parts, polycarboxylic acid superplasticizer 2 parts.

[0039] The preparation method is the same as that of Example 1.

[0040] Comparative Example 1

[0041] (1) The raw material components are taken by weight parts as follows: sulphoaluminate cement 450 parts, silica fume 50 parts, water 150 parts, polycarboxylic acid superplasticizer 2 parts, ready for use;

[0042] (2) The sulphoaluminate cement and silica fume are added into a mixer and stirred until uniform to obtain a composite cementitious material;

[0043] (3) The water-reducing agent is uniformly dispersed in water, and after being treated for 3 min at an ultrasonic power of 120-140 W, a mixed solution containing an additive is obtained;

[0044] (4) The mixed solution in step (3) and the composite cementitious material in step (2) are added into a standard planetary cement paste stirrer, and stirred at a low speed (60 r / min) for 120 s, and after stopping for 15 s while scraping the cement paste on the blade and the pot wall into the middle of the pot, the cement-based material paste is obtained by stirring at a high speed (120 r / min) for 120 s.

[0045] The cement-based materials prepared in Comparative Example 1 and Example 2 are subjected to scanning electron microscope analysis after being cured at -10℃ for 28 days, 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 and cured at -10℃ for 28 days, wherein a is Comparative Example 1, and b is Example 2. From the images, it can be seen that the cement-based material prepared in Example 2 has a better microstructure than that prepared in Comparative Example 1. Figure 1It can be found that there are needle-like and small-sized AFt crystals and some amorphous hydration products in Comparative Example 1, but the structure is loose, and the microstructure has many holes and even interpenetrating microcracks, which is related to the freezing of the cement sample at negative temperature. Compared with Comparative Example 1, the hydration product AFt crystal size in Example 2 is obviously increased and the crystal becomes thick, and no obvious holes and cracks are observed in multiple SEM pictures, indicating that the addition of sodium nitrate significantly improves the microstructure of the cement system at negative temperature.

[0046] The cement-based materials of Examples 1-5 and Comparative Example 1 above were directly placed in a curing temperature of -10℃ for curing, and then tested, mainly 1d, 3d, 7d compressive strength. The test results are shown in Table 3 below.

[0047] Table 3 Compressive strength test results of cement-based materials of Examples 1-5 and Comparative Example 1 at -10℃ (unit: MPa)

[0048]

[0049]

[0050] As can be seen from Table 3, when the curing temperature is -10℃, the early hydration degree of the sulfoaluminate cement in Comparative Example 1 is low under negative temperature conditions. With the addition of sodium nitrate in Examples 1-5, it can be found that the strength at each age under -10℃ has a significant improvement effect. The strength of Examples 1-5 gradually decreases after increasing, among which, the mechanical properties of Example 2 with a sodium nitrate content of 2% are the best, and the 1d, 3d, 7d strengths are increased by 186%, 377% and 358% respectively compared with Comparative Example 1.

[0051] The cement-based materials prepared in Comparative Example 1 and Examples 2 and 5 were cured at -10℃ for 1 day and 7 days, and XRD analysis was performed, and the results are shown in Figure 2 . Figure 2 XRD patterns of cement-based materials prepared in Comparative Example 1 and Example 2 cured at -10℃ for 1 day and 7 days, wherein a is 1d and b is 7d, in the figure, E represents ettringite, Y represents anhydrous calcium sulfoaluminate, G represents gypsum, and M represents magnesium oxide. Figure 2Comparing the effect of the intensity of the phase material diffraction peak of Example 2, Example 5 and Comparative Example 1 at 1d and 7d, it can be found that the intensity of the main diffraction peak of calcium alumite of Example 2 at 1d and 7d is significantly increased, and the unhydrated calcium sulphoaluminate diffraction peak is also the smallest. The low intensity of the reactant diffraction peak and the high intensity of the product diffraction peak can indicate that there is a higher degree of hydration in Example 2, which produces more hydration products to fill the pores and provide strength for the sulphoaluminate cement system. In addition, the intensity of the AFt diffraction peak is continuously enhanced with the increase of the age, which indicates that the sulphoaluminate cement system can carry out normal hydration under the condition of -10℃ environment.

[0052] The cement-based materials prepared in Comparative Example 1 and Examples 2 and 5 were cured at -10℃ for 1 day and 7 days, and micro-thermal gravimetric analysis was carried out, and the results are shown in Figure 3 Figure 3 The TG-DTG curves of the cement-based materials prepared in Comparative Example 1 and Example 2 cured at -10℃ for 1 day and 7 days are shown in the figure, wherein a is 1d and b is 7d. From the weight loss peak in the curve, it can be seen that the results are consistent with the XRD diffraction pattern, mainly containing hydration products AFt, amorphous C-S-H gel and AH3, etc., and a small amount of CH only appears in the later stage. By comparing the total weight loss of the TG curve, it can be seen that the total weight loss of Example 2 and Example 5 after adding NaNO2 is reduced, among which Example 2 is the lowest, indicating that the addition of 2% NaNO2 in the three dosage groups produces the most hydration products to fill the pores, making the pore structure of the sulphoaluminate cement system after hydration more compact.​

Claims

1. A high early strength and fast hardening cement-based material that can be sustainably hydrated at low temperatures, characterized in that: The composition comprises the following components in proportion by weight: sulphoaluminate cement: silica fume: water: sodium nitrate: water reducing agent = 450:50:150:(5-25):

2.

2. The high early strength and fast hardening cement-based material that can be sustainably hydrated at low temperatures according to claim 1, characterized in that: The composition includes the following components in proportion by weight: sulphoaluminate cement: silica fume: water: sodium nitrate: water reducing agent = 450:50:150:(10-20):

2.

3. The high early strength and fast hardening cement-based material that can be sustainably hydrated at low temperatures according to claim 1, characterized in that: Sulphoaluminate cement complies with the national standard "Sulphoaluminate Cement" GB20472-2006.

4. The high early strength and fast hardening cement-based material that can be sustainably hydrated at low temperatures according to claim 1, characterized in that: The silica fume is SF90 silica fume with a silica content of more than 90%.

5. The high early strength and rapid hardening cement-based material capable of sustainable hydration at low temperatures according to claim 1, characterized in that: The purity of sodium nitrate is above 99%.

6. The high early strength and rapid hardening cement-based material capable of sustainable hydration at low temperatures according to claim 1, characterized in that: The water reducer is a polycarboxylic acid high-efficiency water reducer.

7. The high early strength and rapid hardening cement-based material capable of sustainable hydration at low temperatures according to claim 1, characterized in that: The effective solid content of the water reducer is more than 20%.

8. The method for preparing a high early strength and fast hardening cement-based material capable of sustainable hydration at low temperature according to any one of claims 1 to 7, characterized in that: Including the above steps: (1) mixing sulphoaluminate cement and silica fume and stirring until uniform to obtain a composite cementitious material; (2) dispersing sodium nitrate and a water reducer in water, and ultrasonically treating the water to obtain a mixed solution containing the admixture; (3) The mixed solution containing the admixture is mixed with the composite cementitious material, stirred at a low speed, and then stirred at a high speed 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 (2), the ultrasonic power is 120-140 W, and the ultrasonic time is more than 3 minutes.

10. The preparation method according to claim 8, characterized in that: In step (3), the equipment used for mixing is a standard planetary cement slurry mixer.

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