A composite mineral admixture for mass raft concrete and a method for preparing the same
By combining fly ash and silica fume and applying a carbon coating to the surface, a composite mineral admixture was prepared, which solved the problem of excessive heat of hydration in large-volume raft concrete, achieving uniform control of heat of hydration and improving concrete performance.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- XIAN GAO KE XIN DA CONCRETE CO LTD
- Filing Date
- 2024-05-14
- Publication Date
- 2026-06-26
AI Technical Summary
Large-volume raft concrete generates a lot of heat of hydration during use, which prevents further improvement in concrete performance.
A composite mineral admixture was prepared by using fly ash and silica fume as a blend. By adjusting their mass ratio and particle size, and by combining the carbon coating treatment on the surface of fly ash, the generation and distribution of heat of hydration were controlled.
It effectively reduces the generation of heat of hydration, ensures uniform distribution of concrete at different stages, avoids cracking, and improves concrete performance.
Abstract
Description
Technical Field
[0001] This invention belongs to the field of building materials technology. More specifically, it relates to a composite mineral admixture for large-volume raft concrete and its preparation method. Background Technology
[0002] Massive raft concrete refers to a type of concrete slab used in foundation engineering, with a foundation beneath the slab and columns, walls, etc., on top. It is named for its raft-like appearance, resembling a raft floating on the ground. It possesses excellent integrity and is widely used in high-rise buildings.
[0003] Large-volume raft concrete is prone to generating a large amount of heat of hydration during use. This is mainly because the structure of large-volume raft concrete is large in size. Due to the large amount of concrete, the amount of cement used is relatively large. The cement hydration reaction in concrete is an exothermic reaction. The heat released by the hydration reaction accumulates in the interior of the concrete and is difficult to dissipate quickly, resulting in a significant increase in the internal temperature.
[0004] Therefore, special attention needs to be paid to the influence of hydration heat on large-volume raft concrete, and relevant measures should be taken to prevent it from significantly affecting the concrete performance and causing failure problems such as concrete cracking. Summary of the Invention
[0005] The technical problem to be solved by the present invention is to overcome the problem that the existing large-volume raft concrete generates a lot of heat of hydration during use, which prevents the concrete performance from being further improved. The present invention provides a composite mineral admixture for large-volume raft concrete and its preparation method.
[0006] The purpose of this invention is to provide a composite mineral admixture for large-volume raft concrete.
[0007] Another object of the present invention is to provide a method for preparing composite mineral admixtures for large-volume raft concrete.
[0008] The above-mentioned objective of this invention is achieved through the following technical solution:
[0009] A composite mineral admixture for large-volume raft concrete, comprising fly ash and silica fume;
[0010] The mass ratio of the fly ash to the silica fume is 2.5:1 to 3.5:1.
[0011] The fly ash has a D50 of 80-90 μm;
[0012] The D50 of the silica fume is 0.15-0.25 times that of the fly ash.
[0013] The above technical solution uses a mixture of fly ash and silica fume as mineral admixtures for large-volume raft concrete. This is achieved by controlling the mass ratio and particle size of the two materials. Specifically, the amount of fly ash added is greater than that of silica fume, while the D50 of silica fume is significantly smaller than that of fly ash. The rationale for this combination is that, overall, both fly ash and silica fume can participate in the hydration reaction of concrete, thus reducing the amount of cement used during concrete preparation and reducing the heat of hydration at its source. By combining two mineral admixtures of different sizes and properties synergistically, the mineral admixtures can more uniformly control the heat of hydration of the concrete and can control the heat of hydration at different stages of the overall concrete hydration process. Specifically, silica fume has higher activity than fly ash; by controlling its appropriate particle size and addition amount, it can participate more in the early stages of cement hydration in concrete. While hydration reactions reduce the heat of hydration, fly ash tends to participate in hydration reactions in the middle and later stages, continuously reducing the heat of hydration. Furthermore, the smaller particle size of silica fume allows it to flow and diffuse rapidly within the concrete system in the early stages of mixing, ensuring its uniform distribution. Moreover, the particle size of fly ash cannot be too small. If it is too small, the high surface energy silica fume will easily agglomerate during both the preparation of mineral admixtures and the concrete preparation process, affecting the uniform dispersion of mineral admixtures in the concrete. Choosing a fly ash particle size significantly larger than silica fume has the advantage that, in the early stages of concrete mixing, fly ash primarily acts as a carrier for small silica fume particles, and the van der Waals adsorption between the two is limited, making them easy to desorb under the external forces during concrete processing, thus dispersing within the concrete.
[0014] Furthermore, the surface of the fly ash includes a carbon coating layer; the carbon coating layer accounts for 10-12% of the mass of the fly ash.
[0015] By coating fly ash with carbon, the surface of fly ash can adsorb free water during concrete preparation. This helps to provide the necessary moisture for fly ash to participate in the hydration reaction, thus facilitating the full utilization of fly ash's function. If the carbon content is too low, the water retention effect will be limited and it will not be able to effectively support the function of fly ash. If the carbon content is too high, it will affect the contact between fly ash and components in concrete, and may even hinder the reaction.
[0016] Furthermore, the mass ratio of fly ash to silica fume is 2.5:1, the D50 of the silica fume is 0.15 times that of the fly ash, and the carbon coating layer is 12% of the mass of the fly ash.
[0017] Furthermore, the mass ratio of fly ash to silica fume is 3.5:1, the D50 of the silica fume is 0.25 times that of the fly ash, and the carbon coating layer is 10% of the mass of the fly ash.
[0018] Furthermore, the Fe element content in the silica fume is 0.010-0.015%.
[0019] Since silica fume is an industrial byproduct of the production of ferrosilicon, silicon steel, or other silicon metals, it often contains iron (Fe). Generally, the presence of Fe affects the pozzolanic activity of silica fume. However, the inventors surprisingly discovered that controlling the Fe content in silica fume within the aforementioned range can better utilize its properties. Specifically, if the silica fume content is too low, its pozzolanic activity will be too high. During use, due to its rapid reaction, it will be difficult for it to work synergistically with fly ash to fully reduce the heat of hydration throughout the entire cement hydration process. If the silica fume content is too high, the inhibition of silica fume activity will be too significant, affecting its early-stage heat of hydration control.
[0020] Furthermore, it also includes blast furnace slag powder with 20-25% silica fume by weight; the D50 of the blast furnace slag powder is 0.5-0.6 times that of the fly ash.
[0021] Furthermore, the porosity of the blast furnace slag powder is 40-50%; the porosity of the fly ash is 55-65%; and the porosity of the silica fume is 10-15%.
[0022] The above scheme further increases the amount of blast furnace slag powder and coordinates the dosage, porosity, and particle size of the three different mineral admixtures. In this way, the use of silica fume can avoid an excessive increase in the water demand of concrete. Furthermore, the matching of the three can further effectively control the heat of hydration at different time periods.
[0023] A method for preparing a composite mineral admixture for large-volume raft concrete, comprising the following specific preparation steps:
[0024] Weigh out the fly ash and silica fume of the corresponding specifications according to the formula;
[0025] The fly ash and silica fume are ultrasonically dispersed in water, then filtered and dried to obtain the composite mineral admixture.
[0026] Furthermore, the specific preparation steps also include:
[0027] Alkanes are used as carbon-containing gases to form a carbon-coated layer on the surface of fly ash through chemical vapor deposition.
[0028] Furthermore, the chemical vapor deposition includes:
[0029] Using nitrogen as the carrier gas and methane as the alkane, the volume ratio of nitrogen to methane is adjusted to 2.5:1-2.8:1. Chemical vapor deposition is performed at a temperature of 750-800℃ and a gas flow rate of 0.8-1.2 L / min. The quality of the carbon coating on the surface of fly ash is controlled by adjusting the deposition time. Detailed Implementation
[0030] The present invention will be further illustrated below with reference to specific embodiments, but the embodiments do not limit the present invention in any way. Unless otherwise specified, the reagents, methods, and equipment used in the present invention are conventional reagents, methods, and equipment in this technical field.
[0031] Unless otherwise specified, all reagents and materials used in the following examples are commercially available.
[0032] Example 1
[0033] Pretreatment of fly ash:
[0034] Fly ash was added to a carbonization furnace and heated to 790°C at a rate of 8°C / min. Nitrogen was used as the carrier gas, and methane was selected as the alkane. The volume ratio of nitrogen to methane was adjusted to 2.5:1 to form a mixed gas. Chemical vapor deposition was performed on the fly ash in the carbonization furnace at a gas flow rate of 0.8 L / min to coat the fly ash surface with carbon. The deposition time was controlled to be 3.8 h to obtain pretreated fly ash with a coating amount of 12% of the fly ash mass.
[0035] Ingredients:
[0036] Weigh the raw materials according to a mass ratio of pretreated fly ash to silica fume of 2.5:1;
[0037] Weigh blast furnace slag powder equal to 20% of the mass of the silica fume;
[0038] The fly ash has a D50 of 80 μm; the fly ash referred to here is the raw fly ash before carbon coating pretreatment.
[0039] The D50 of the silica fume is 0.15 times that of the fly ash;
[0040] The D50 of the blast furnace slag powder is 0.5 times that of the fly ash;
[0041] The porosity of the blast furnace slag powder is 40%; the porosity of the fly ash is 55%; the porosity of the silica fume is 10%; the fly ash mentioned here is the raw fly ash before carbon coating pretreatment.
[0042] Mixing:
[0043] The pretreated fly ash, silica fume, and blast furnace slag powder are sequentially added to water, wherein the mass of water is 10 times the total mass of the pretreated fly ash, silica fume, and blast furnace slag powder. After ultrasonic dispersion at 45°C and 75kHz for 2 hours, the mixture is filtered, the filter cake is collected, and the filter cake is washed twice with deionized water. The washed filter cake is then transferred to an oven and dried at 100°C to constant weight. The resulting material is a composite mineral admixture for use in large-volume raft concrete.
[0044] Example 2
[0045] Pretreatment of fly ash:
[0046] Fly ash was added to a carbonization furnace and heated to 760°C at a rate of 8°C / min. Nitrogen was used as the carrier gas, and methane was selected as the alkane. The volume ratio of nitrogen to methane was adjusted to 2.6:1 to form a mixed gas. Chemical vapor deposition was performed on the fly ash in the carbonization furnace at a gas flow rate of 0.9 L / min to coat the fly ash surface with carbon. The deposition time was controlled to be 3.8 h to obtain pretreated fly ash with a coating amount of 11.5% of the fly ash mass.
[0047] Ingredients:
[0048] Weigh the raw materials according to a mass ratio of pretreated fly ash to silica fume of 2.9:1;
[0049] Weigh blast furnace slag powder, which accounts for 22% of the mass of the silica fume.
[0050] The fly ash has a D50 of 85 μm; the fly ash referred to here is the raw fly ash before carbon coating pretreatment.
[0051] The D50 of the silica fume is 0.18 times that of the fly ash;
[0052] The D50 of the blast furnace slag powder is 0.56 times that of the fly ash;
[0053] The porosity of the blast furnace slag powder is 46%; the porosity of the fly ash is 58%; the porosity of the silica fume is 12%; the fly ash mentioned here is the raw fly ash before carbon coating pretreatment;
[0054] Mixing:
[0055] The pretreated fly ash, silica fume, and blast furnace slag powder are sequentially added to water, wherein the mass of water is 10 times the total mass of the pretreated fly ash, silica fume, and blast furnace slag powder. After ultrasonic dispersion at 48°C and 75kHz for 3 hours, the mixture is filtered, the filter cake is collected, and the filter cake is washed three times with deionized water. The washed filter cake is then transferred to an oven and dried at 100°C to constant weight. The resulting material is a composite mineral admixture for use in large-volume raft concrete.
[0056] Example 3
[0057] Pretreatment of fly ash:
[0058] Fly ash was added to a carbonization furnace and heated to 780°C at a rate of 8°C / min. Nitrogen was used as the carrier gas, and methane was selected as the alkane. The volume ratio of nitrogen to methane was adjusted to 2.75:1 to form a mixed gas. Chemical vapor deposition was performed on the fly ash in the carbonization furnace at a gas flow rate of 0.86 L / min to coat the fly ash surface with carbon. The deposition time was controlled to be 3.6 h to obtain pretreated fly ash with a coating amount of 10% of the fly ash mass.
[0059] Ingredients:
[0060] Weigh the raw materials according to a mass ratio of pretreated fly ash to silica fume of 3.5:1;
[0061] Weigh blast furnace slag powder, which accounts for 25% of the mass of the silica fume.
[0062] The fly ash has a D50 of 90 μm; the fly ash referred to here is the raw fly ash before carbon coating pretreatment.
[0063] The D50 of the silica fume is 0.25 times that of the fly ash;
[0064] The D50 of the blast furnace slag powder is 0.6 times that of the fly ash;
[0065] The porosity of the blast furnace slag powder is 50%; the porosity of the fly ash is 65%; the porosity of the silica fume is 15%; the fly ash mentioned here is the raw fly ash before carbon coating pretreatment;
[0066] Mixing:
[0067] The pretreated fly ash, silica fume, and blast furnace slag powder are sequentially added to water, wherein the mass of water is 10 times the total mass of the pretreated fly ash, silica fume, and blast furnace slag powder. After ultrasonic dispersion at 50°C and 80kHz for 4 hours, the mixture is filtered, the filter cake is collected, and the filter cake is washed 4 times with deionized water. The washed filter cake is then transferred to an oven and dried to constant weight at 100°C. The resulting material is a composite mineral admixture for use in large-volume raft concrete.
[0068] Example 4
[0069] The difference between this embodiment and embodiment 1 is that the mass ratio of fly ash to silica fume is different, while the other conditions remain unchanged. Specifically, the mass ratio of pretreated fly ash to silica fume is 3:1, while the other conditions remain unchanged.
[0070] Example 5
[0071] The difference between this embodiment and embodiment 1 is that the coating amount is different, while the other conditions remain the same. Specifically, the coating amount is 9.5%, and the other conditions remain the same.
[0072] Example 6
[0073] The difference between this embodiment and embodiment 1 is that the coating amount is different, while the other conditions remain the same. Specifically, the coating amount is 13.5%, while the other conditions remain the same.
[0074] Example 7
[0075] The difference between this embodiment and embodiment 1 is that no blast furnace slag powder was added, while the other conditions remained unchanged.
[0076] Example 8
[0077] The difference between this embodiment and Embodiment 1 is that the porosity of the three mineral admixtures is different. Specifically, the porosity of the blast furnace slag powder is 40%; the porosity of the fly ash is 55%; and the porosity of the silica fume is 17%. The fly ash mentioned here is the raw fly ash before carbon coating pretreatment.
[0078] Example 9
[0079] The difference between this embodiment and Embodiment 1 is that the porosity of the three mineral admixtures is different. Specifically, the porosity of the blast furnace slag powder is 35%; the porosity of the fly ash is 52%; and the porosity of the silica fume is 10%. The fly ash mentioned here is the raw fly ash before carbon coating pretreatment.
[0080] Comparative Example 1
[0081] The difference between this comparative example and Example 1 is that no silica fume was added, while all other conditions remained unchanged.
[0082] Comparative Example 2
[0083] The difference between this comparative example and Example 1 is that the D50 of the silica fume is 0.1 times that of the fly ash, while the other conditions remain unchanged.
[0084] Comparative Example 3
[0085] The difference between this comparative example and Example 1 is that the D50 of the silica fume is 0.3 times that of the fly ash, while the other conditions remain unchanged.
[0086] The products obtained in Examples 1-9 and Comparative Examples 1-3 were subjected to performance tests. The specific test methods and results are as follows:
[0087] The concrete uses 42.5# ordinary Portland cement. The coarse aggregate is crushed stone with a particle size distribution of 5-25mm and a mud content of less than 1%. The fine aggregate is medium sand with an average particle size of 0.5mm and a mud content of less than 5%. The specific raw material composition of the concrete is as follows (by weight):
[0088] Water: 180 parts, cement: 260 parts, fine aggregate: 750 parts, coarse aggregate: 1000 parts, water-reducing agent: 5 parts, composite mineral admixture prepared by the above embodiments or comparative examples: 120 parts;
[0089] After the above raw materials are mixed evenly, they are transferred to the pump truck for layered pouring. The first layer is 8m long and 45cm thick, with the slope angle controlled at 10°. The pouring proceeds horizontally forward from the top of each layer, using natural flow to form a slope, continuously advancing in a zigzag pattern and rising evenly along the height. During the pouring process, temperature monitoring points are set at each layer, a total of 5 points, evenly distributed in both the vertical and horizontal directions. Specific temperature test results are shown in Table 1. After pouring is completed, thermal curing is applied, specifically by covering with cotton blankets for 14 days.
[0090] According to the temperature tests mentioned above, the highest temperature after the raft foundation concrete was poured was T1, and the corresponding time of its occurrence is also recorded in Table 1; the maximum temperature difference between the inside and outside was T2; and during the curing process and within 30 days after completion, the surface was observed to see if there were any obvious cracks.
[0091] Table 1: Product Performance Test Results
[0092] T1 / ℃ On which day did it appear? T2 / ℃ Surface cracking Example 1 41.5 Day 5 22.0 No obvious cracks Example 2 42.0 Day 5 22.1 No obvious cracks Example 3 41.3 Day 5 21.5 No obvious cracks Example 4 42.5 Day 5 22.6 No obvious cracks Example 5 41.8 Day 6 22.0 No obvious cracks Example 6 42.2 Day 5 22.3 No obvious cracks Example 7 42.4 Day 5 22.5 No obvious cracks Example 8 42.1 Day 5 22.2 No obvious cracks Example 9 42.7 Day 6 22.8 No obvious cracks Comparative Example 1 46.8 Day 5 25.6 Slight cracks Comparative Example 2 42.8 Day 5 24.8 Slight cracks Comparative Example 3 44.5 Day 5 23.9 Slight cracks
[0093] As shown in Table 1, the test results indicate that the product obtained by this invention can effectively control the heat of hydration generated during the hydration process of concrete, and the relative temperature difference between the inside and outside is lower. The concrete product has excellent performance and no obvious cracks are generated.
[0094] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.
Claims
1. A composite mineral admixture for large-volume raft concrete, characterized in that, Including fly ash and silica fume; The mass ratio of the fly ash to the silica fume is 2.5:1 to 3.5:
1. The fly ash has a D50 of 80-90 μm; The D50 of the silica fume is 0.15-0.25 times that of the fly ash.
2. The composite mineral admixture for large-volume raft concrete according to claim 1, characterized in that, The surface of the fly ash includes a carbon coating layer; the carbon coating layer accounts for 10-12% of the mass of the fly ash.
3. A composite mineral admixture for large-volume raft concrete according to claim 2, characterized in that, The mass ratio of fly ash to silica fume is 2.5:1, the D50 of silica fume is 0.15 times that of fly ash, and the carbon coating layer is 12% of the mass of fly ash.
4. A composite mineral admixture for large-volume raft concrete according to claim 2, characterized in that, The mass ratio of fly ash to silica fume is 3.5:1, the D50 of the silica fume is 0.25 times that of the fly ash, and the carbon coating layer is 10% of the mass of the fly ash.
5. A composite mineral admixture for large-volume raft concrete according to any one of claims 3 or 4, characterized in that, The Fe element content in the silica fume is 0.010-0.015%.
6. A composite mineral admixture for large-volume raft concrete according to claim 5, characterized in that, It also includes blast furnace slag powder with 20-25% silica fume by weight; the D50 of the blast furnace slag powder is 0.5-0.6 times that of the fly ash.
7. A composite mineral admixture for large-volume raft concrete according to claim 6, characterized in that, The porosity of the blast furnace slag powder is 40-50%; the porosity of the fly ash is 55-65%; and the porosity of the silica fume is 10-15%.
8. A method for preparing a composite mineral admixture for large-volume raft concrete as described in any one of claims 1-7, characterized in that, The specific preparation steps include: Weigh out the fly ash and silica fume of the corresponding specifications according to the formula; After ultrasonically dispersing the fly ash and silica fume in water, the mixture is then filtered and dried to obtain the composite mineral admixture.
9. A method for preparing a composite mineral admixture for large-volume raft concrete according to claim 8, characterized in that, The specific preparation steps also include: Alkanes are used as carbon-containing gases to form a carbon-coated layer on the surface of fly ash through chemical vapor deposition.
10. A method for preparing a composite mineral admixture for large-volume raft concrete according to claim 9, characterized in that, The chemical vapor deposition includes: Using nitrogen as the carrier gas and methane as the alkane, the volume ratio of nitrogen to methane is adjusted to 2.5:1-2.8:
1. Chemical vapor deposition is performed at a temperature of 750-800℃ and a gas flow rate of 0.8-1.2 L / min. The quality of the carbon coating on the surface of fly ash is controlled by adjusting the deposition time.