Normal-temperature cured fiber-free seawater and sea sand alkali-activated ultrahigh-strength concrete

Abstract

The invention discloses fiber-free seawater and sea sand alkali-activated ultrahigh-strength concrete cured at normal temperature. Solid potassium carbonate and solid sodium metasilicate are used as composite excitants, under the condition that fibers are not doped, seawater and sea sand are used as water sand for mixing, industrial solid waste slag and silica fume are used as precursor materials, quartz powder is used as a filling material, borax is used as a retarder, the proportion of all raw material components is optimized, and a single-component forming mode is adopted, so that the fiber-reinforced concrete is prepared. The preparation of the ultrahigh-strength concrete can be realized under a normal-temperature sealed curing condition. According to the invention, the problem that the ultra-high strength performance and excellent flow / setting performance of the alkali-activated concrete are difficult to consider is effectively solved, and the popularization and application of the alkali-activated ultra-high strength concrete in actual engineering can be promoted. The technological process is simple, and the production energy consumption and cost are low; seawater and sea sand are used as water sand for mixing concrete, development and utilization of marine resources are promoted, dependence of concrete materials on freshwater river sand resources is reduced, and green and sustainable development of the building industry is facilitated.

Description

Technical Field

[0001] This invention belongs to the field of building materials technology, specifically relating to a fiber-free seawater sand alkali-activated ultra-high strength concrete that is cured at room temperature. Background Technology

[0002] China's large-scale infrastructure construction has driven a continuous increase in concrete production, leading to the massive consumption of freshwater and river sand, exacerbating freshwater shortages and causing damage to river ecosystems. Therefore, developing and utilizing abundant seawater sand resources to replace traditional freshwater river sand as construction sand is of great practical significance for alleviating resource consumption pressure and supporting marine engineering construction.

[0003] Meanwhile, the preparation of ultra-high-strength concrete using alkali-activated cementitious materials still faces key technological bottlenecks. This is due to the lack of water-reducing agents and retarders suitable for highly alkaline environments, resulting in poor flowability and excessively rapid setting time in alkali-activated ultra-high-strength concrete. Sodium metasilicate, as a commonly used alkaline activator, can enable cementitious materials to achieve rapid early strength and good mechanical properties, but it easily leads to excessively short setting time and significant loss of fluidity over time, which is detrimental to construction operations and engineering applications. In addition, the high cost of sodium metasilicate to some extent restricts its application as an activator. Summary of the Invention

[0004] This invention addresses the problems and shortcomings of existing technologies by providing a fiber-free, seawater sand-based alkali-activated ultra-high strength concrete that can be cured at room temperature. This invention uses potassium carbonate and sodium metasilicate as composite activators, without adding fibers, seawater sand as mixing water and sand, slag and silica fume as precursors, quartz powder as filler, and borax as a retarder. By adjusting the concrete mix proportions, the ultra-high strength, workability, and setting time of the alkali-activated concrete are synergistically optimized. In this system, sodium metasilicate rapidly activates the precursors, potassium carbonate improves the flowability of the slurry, and borax delays the slurry setting and hardening process. This allows for extended setting time and improved workability while ensuring strength development, effectively overcoming the problem of balancing workability and setting / hardening performance in seawater sand-based alkali-activated ultra-high strength concrete.

[0005] This invention uses a single-component method to prepare seawater-sand-alkali-activated ultra-high strength concrete, eliminating the need for activator solution preparation and improving practical application convenience. Compared with traditional high-temperature curing, room-temperature curing reduces energy consumption in preparing ultra-high strength concrete. It achieves ultra-high strength performance requirements without relying on fiber reinforcement, saving preparation costs and improving concrete workability.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A type of fiber-free seawater and sea sand alkali-activated ultra-high strength concrete material that can be cured at room temperature is composed of a precursor (composed of slag and silica fume), a composite activator (composed of potassium carbonate and sodium metasilicate), quartz powder, borax, seawater and sea sand.

[0007] Furthermore, the mass percentage ratio of slag to silica fume in the precursor is 75~85:25~15.

[0008] Furthermore, the amount of potassium carbonate used is 7% to 10% of the total weight of the precursor.

[0009] Furthermore, the amount of sodium metasilicate used is 9% to 16% of the total weight of the precursor.

[0010] Furthermore, the amount of quartz powder used is 10% to 20% of the total weight of the precursor.

[0011] Furthermore, the amount of borax used is 1.5% to 3.5% of the total weight of the precursor.

[0012] Furthermore, the sum of the amount of seawater used and the weight of water contained in sodium metasilicate and borax is 30% to 40% of the total weight of the precursor.

[0013] Furthermore, the amount of sea sand used is 80% to 120% of the total weight of the precursor.

[0014] Furthermore, the slag is S95 slag, with a specific surface area of ​​400~450 m². 2 / kg, density is 2.8~3.0g / cm³ 3 .

[0015] Furthermore, the silica fume has a fineness of 1500-2000 mesh and a SiO2 content greater than 94%.

[0016] Furthermore, the potassium carbonate has a purity of 99.0%.

[0017] Furthermore, the sodium metasilicate has a purity of 98.0% and a modulus of 1.0 to 2.0.

[0018] Furthermore, the quartz powder has a fineness of 300-600 mesh and a density of 1.3-1.6 g / cm³. 3 .

[0019] Furthermore, the purity of the borax is 99.5%.

[0020] Furthermore, the seawater in question is natural seawater.

[0021] Furthermore, the fineness modulus of the sea sand is 2.1~2.5, which meets the relevant requirements of the "Technical Specification for Application of Sea Sand Concrete" (JGJ206-2010) and "Sand for Construction" (GB / T14684-2011).

[0022] The preparation method of the fiber-free seawater sand alkali-activated ultra-high strength concrete material is as follows: weigh slag, silica fume, potassium carbonate, sodium metasilicate, quartz powder, borax, and sea sand according to the proportion, mix them and dry stir for 2 minutes, then add the seawater weighed according to the proportion, continue stirring for 5 minutes to form a slurry, then pour it into a concrete mold and vibrate to compact it, cover the surface of the mold with a layer of plastic wrap, place it in a constant temperature environment of 20℃ for 1 day, and then demold it. The resulting test block continues to be sealed and cured at room temperature in a 20℃ environment until the specified age.

[0023] Furthermore, the flow spread of the mixed slurry is greater than 200 mm, and the setting time is greater than 30 min.

[0024] Furthermore, the compressive strength of the obtained ultra-high strength concrete after 28 days is greater than 100 MPa.

[0025] Compared with commonly used alkali-activated concrete, the advantages of this invention are as follows: (1) The seawater sand alkali-activated ultra-high strength concrete prepared by the present invention makes full use of the resource advantages of seawater sand. Under normal temperature sealed curing conditions, it can achieve ultra-high strength performance without fiber addition and also has excellent workability and setting hardening performance.

[0026] (2) Potassium carbonate is widely available and inexpensive. The CO3 dissolved from it as an activator 2- It will react with the Ca released by the precursor 2+ The reaction produces calcium carbonate and potassium hydroxide. The generated potassium hydroxide can stimulate the precursor to react and generate alkaline-activated products such as CASH and hydrotalcite. Meanwhile, compared to sodium carbonate, potassium carbonate in the composite activator exhibits properties that contribute to improved flow properties of alkaline-activated materials. Compared to sodium carbonate... + K + The larger atomic ratio and lower charge density result in lower dipole forces and viscosity in its solution, while the K+ adsorbed on the surface of the negatively charged particles... + Than Na + The presence of more potassium carbonate creates a greater repulsive force between the two layers, reducing the rheological yield stress and plastic viscosity of the alkali-activated slurry. Potassium carbonate has limited alkali activation effect on precursors, resulting in a longer setting process for alkali-activated concrete, but it is relatively inexpensive. Sodium metasilicate, on the other hand, has a better alkali activation effect, but it tends to cause the slurry to set faster and is more expensive. Combining these two activators as a composite activator can "complement each other's advantages," delaying the setting and hardening process to a certain extent, improving the workability of alkali-activated concrete, and reducing production costs.

[0027] (3) This invention effectively delays the setting and hardening process of ultra-high strength concrete activated by seawater sand using potassium carbonate / sodium metasilicate composite activator by adding an appropriate amount of borax. In an alkaline environment, borax reacts with the Ca of the alkali-activated concrete paste. 2+ The reaction forms calcium borate, which coats the surface of the cementitious particles, hindering water penetration into the particles and inhibiting the alkali-activated reaction. Additionally, borax can react with silicate groups in the alkali-activated concrete system to form a high-bond-energy BO-Al-O-Si structure, thus delaying the formation of the Si-O-Al tetrahedral structure. As the alkali-activated reaction proceeds, reaction products such as CASH increase, gradually destroying the initially formed calcium borate coating and re-promoting the alkali-activated reaction. Therefore, adding an appropriate amount of borax to the seawater sand alkali-activated ultra-high-strength concrete system using potassium carbonate / sodium metasilicate composite activator can both avoid the "rapid setting" phenomenon and ensure rapid early strength development of the alkali-activated concrete. Detailed Implementation

[0028] A type of room-temperature cured, fiber-free seawater-sand alkali-activated ultra-high-strength concrete material is composed of a precursor (composed of slag and silica fume), a composite activator (composed of potassium carbonate and sodium metasilicate), quartz powder, borax, seawater, and sea sand. The precursor comprises 75%–85% slag and 25%–15% silica fume, totaling 100%. Potassium carbonate accounts for 7%–10% of the total precursor weight. Sodium metasilicate accounts for 9%–16% of the total precursor weight. Quartz powder accounts for 10%–20% of the total precursor weight. Borax accounts for 1.5%–3.5% of the total precursor weight. The sum of the weights of seawater, water in sodium metasilicate, and water in borax accounts for 30%–40% of the total precursor weight. Sea sand accounts for 80%–120% of the total precursor weight.

[0029] The slag is S95 slag, with a specific surface area of ​​400~450m². 2 / kg, density is 2.8~3.0 g / cm³ 3 The silica fume has a fineness of 1500-2000 mesh and a SiO2 content greater than 94%. The potassium carbonate has a purity of 99.0%. The sodium metasilicate has a purity of 98.0% and a modulus of 1.0-2.0. The quartz powder has a fineness of 300-600 mesh and a density of 1.3-1.6 g / cm³. 3 The purity of the borax is 99.5%. The seawater is natural seawater. The fineness modulus of the sea sand is 2.1~2.5, which meets the relevant requirements of the "Technical Specification for Application of Sea Sand in Concrete" (JGJ206-2010) and "Sand for Construction" (GB / T14684-2011).

[0030] The following detailed description of various exemplary embodiments of the present invention should not be construed as limiting the invention, but rather as a more detailed description of certain aspects, features, and implementations of the invention.

[0031] The concrete prepared according to the mix proportions in Table 1, as shown in the examples and comparative examples, includes the following steps: 1) According to the mixing ratio in Table 1, weigh the powder of each component and sea sand (or river sand), and mix them dry for 2 minutes; 2) Add the weighed seawater according to the proportions in Table 1, and continue stirring for 5 minutes to prepare the mixture; 3) Pour the mixture into the concrete mold and vibrate to compact it; 4) Cover the mold surface with plastic wrap and seal it at room temperature to keep it moist. Place it in a constant temperature environment of 20℃ for 1 day before demolding. 5) After demolding, the test block is placed in a constant temperature environment of 20℃ and sealed for curing until the specified age.

[0032] Table 1. Mixing ratios of the examples and comparative examples ,

[0033] The test methods used for the mixed slurry or test blocks obtained in the examples and comparative examples are as follows: The compressive strength of specimens cured to the specified age was tested according to the test methods in "Test Method for Strength of Cement Mortar" (GB / T17671-1999); the setting time of the mixed grout was tested according to the test methods in "Standard for Test Methods of Basic Performance of Building Mortar" (JGJT70-2009); and the flowability of the mixed grout was tested according to the test methods in "Technical Specification for Application of Cement-based Grouting Materials" (GB / T50448-2015). The test results are shown in Table 2.

[0034] Table 2

[0035] As can be seen from Table 2, Examples 5 and Comparative Examples 1-11 show that, when seawater sand alkali-activated ultra-high strength concrete using sodium carbonate / sodium metasilicate, sodium carbonate / potassium silicate, potassium carbonate / sodium metasilicate, and potassium carbonate / potassium silicate composite activators is added with an appropriate amount of borax, although its compressive strength and flow spread are slightly reduced, its setting time is delayed from 21 min, 16 min, 18 min, and 14 min to 29 min, 32 min, 33 min, and 22 min, respectively. In contrast, the setting time of seawater sand alkali-activated ultra-high strength concrete using potassium hydroxide / sodium silicate and potassium hydroxide / potassium silicate composite activators before adding an appropriate amount of borax is 13 min and 13 min, respectively, and the setting time after adding an appropriate amount of borax is 14 min and 13 min, respectively. This indicates that adding an appropriate amount of borax can effectively delay the setting time of ultra-high strength concrete prepared using carbonate / silicate composite activators. Among them, the ultra-high strength concrete using potassium carbonate / sodium metasilicate composite activators has the best delaying effect (i.e., in Example 5, adding 3% borax can double the setting time), while it has almost no retarding effect on ultra-high strength concrete using potassium hydroxide / silicate composite activators.

[0036] As can be seen from Examples 5 and Comparative Examples 7-9, the flow spreads of ultra-high strength concrete prepared using sodium carbonate / sodium metasilicate, sodium carbonate / potassium silicate, potassium carbonate / sodium metasilicate, and potassium carbonate / potassium silicate composite activators were 130 mm, 175 mm, 210 mm, and 240 mm, respectively. This demonstrates that using potassium carbonate instead of the corresponding sodium carbonate to form a composite activator helps improve the workability of seawater-sand-alkali-activated ultra-high strength concrete (although the flow spread of Example 5 was inferior to that of Comparative Example 9, it still exceeded 200 mm, showing excellent performance, and its compressive strength and setting hardening properties were also superior to those of Comparative Example 9). Furthermore, Comparative Examples 10 and 11, using potassium hydroxide / sodium metasilicate and potassium hydroxide / potassium silicate composite activators, both had a flow spread of only 111 mm, and their workability did not meet the requirements for engineering applications.

[0037] Furthermore, a comparison between Example 5 and Comparative Examples 7-11 shows that the ultra-high strength concrete prepared using the potassium carbonate / sodium metasilicate composite activator exhibits superior strength development compared to ultra-high strength concrete prepared using sodium carbonate / sodium metasilicate, sodium carbonate / potassium silicate, potassium carbonate / potassium silicate, potassium hydroxide / sodium metasilicate, and potassium hydroxide / potassium silicate composite activators, i.e., both early compressive strength and 28-day compressive strength are better.

[0038] A comparison of Examples 1-3 and Comparative Examples 12-14 shows that the compressive strength, fluidity, and setting time of alkali-activated ultra-high strength concrete using seawater sand at various ages are basically equivalent to those of the corresponding alkali-activated ultra-high strength concrete using freshwater river sand. This indicates that using seawater sand instead of freshwater river sand as the preparation water and sand has a relatively limited impact on the compressive strength development and mixing performance of alkali-activated ultra-high strength concrete. Using seawater sand to prepare alkali-activated ultra-high strength concrete can reduce concrete production costs while ensuring strength development.

[0039] A comparison of Example 6 with Comparative Examples 15 and 16 shows that high-temperature curing can improve the early-age compressive strength of seawater-cure alkali-activated ultra-high-strength concrete, but this effect gradually weakens with age. The compressive strength of seawater-cure alkali-activated ultra-high-strength concrete cured at room temperature for 28 days is basically equivalent to that cured at high temperatures (40 ℃ and 60 ℃), meeting the requirements for ultra-high-strength concrete performance. Furthermore, seawater-cure alkali-activated ultra-high-strength concrete cured at 60 ℃ exhibits strength reduction with increasing age.

[0040] As can be seen from the above analysis, this invention uses seawater sand instead of freshwater river sand as the mixing sand, potassium carbonate / sodium metasilicate as a composite activator, slag and silica fume as precursors, quartz powder as admixture, borax as a retarder, and no fibers are added. Under normal temperature and sealed curing conditions, seawater sand alkali-activated ultra-high strength concrete with both excellent workability and setting hardening performance can be prepared. This breaks through the bottleneck of traditional alkali-activated concrete, which is difficult to balance ultra-high strength performance with excellent workability / setting hardening performance.

[0041] The above embodiments illustrate the technical solution of the present invention. The present invention is not limited to the illustrated embodiments. Those skilled in the art can make various adjustments and variations based on the embodiments of the present invention, but any variations that are the same as or similar to the present invention fall within the scope of the present invention.

[0042] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made within the scope of the claims of the present invention should be included in the scope of the present invention.

Claims

1. A type of fiber-free seawater sand alkali-activated ultra-high strength concrete material that can be cured at room temperature, characterized in that: The concrete material is composed of a precursor, a composite activator, quartz powder, borax, seawater, and sea sand; wherein the precursor is a compound of slag and silica fume; and the composite activator is composed of potassium carbonate and sodium metasilicate.

2. The room-temperature cured, fiber-free seawater sand alkali-activated ultra-high strength concrete material according to claim 1, characterized in that: The mass percentage ratio of slag to silica fume in the precursor is 75~85:25~15.

3. The room-temperature cured, fiber-free seawater sand alkali-activated ultra-high strength concrete material according to claim 1 or 2, characterized in that: The slag is S95 slag, with a specific surface area of ​​400~450m². 2 / kg, density is 2.8~3.0 g / cm³ 3 The silica fume has a fineness of 1500-2000 mesh and a SiO2 content greater than 94%.

4. The room-temperature cured, fiber-free seawater sand alkali-activated ultra-high strength concrete material according to claim 1, characterized in that: The amount of potassium carbonate in the composite activator is 7% to 10% of the total weight of the precursor, and the amount of sodium metasilicate is 9% to 16% of the total weight of the precursor.

5. The room-temperature cured, fiber-free seawater sand alkali-activated ultra-high strength concrete material according to claim 1 or 4, characterized in that: The potassium carbonate has a purity of 99.0%; the sodium metasilicate has a purity of 98.0% and a modulus of 1.0 to 2.

0.

6. The room-temperature cured, fiber-free seawater sand alkali-activated ultra-high strength concrete material according to claim 1, characterized in that: The quartz powder has a fineness of 300-600 mesh and a density of 1.3-1.6 g / cm³. 3 Its dosage is 10% to 20% of the total weight of the precursor.

7. The room-temperature cured, fiber-free seawater sand alkali-activated ultra-high strength concrete material according to claim 1, characterized in that: The amount of borax used is 1.5% to 3.5% of the total weight of the precursor.

8. The room-temperature cured, fiber-free seawater sand alkali-activated ultra-high strength concrete material according to claim 1, characterized in that: The sum of the amount of seawater used, the water content of sodium metasilicate, and the water content of borax is 30% to 40% of the total weight of the precursor.

9. The room-temperature cured, fiber-free seawater sand alkali-activated ultra-high strength concrete material according to claim 1, characterized in that: The fineness modulus of the sea sand is 2.1 to 2.5, and its amount is 80% to 120% of the total weight of the precursor.

10. The room-temperature cured, fiber-free seawater sand alkali-activated ultra-high strength concrete material according to claim 1, characterized in that: The preparation method is to weigh out slag, silica fume, potassium carbonate, sodium metasilicate, quartz powder, borax, and sea sand according to the proportion, mix them and dry stir for 2 minutes, then add the seawater weighed according to the proportion, continue stirring for 5 minutes to form a slurry, then pour it into a concrete mold and vibrate to compact it, cover the surface of the mold with a layer of plastic wrap, place it in a constant temperature environment of 20℃ for 1 day and then demold it. The resulting test block continues to be sealed and cured at room temperature in a 20℃ environment until the specified age.

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