A modified volcanic rock ultrafine composite admixture and its preparation method

Abstract

This invention discloses a modified volcanic rock ultrafine composite admixture and its preparation method, belonging to the technical field of building materials and solid waste resource utilization. The admixture is composed of volcanic rock, S95 grade mineral powder, fluorogypsum, silica fume, lime powder, nano-alumina, triisopropanolamine, and polycarboxylate superplasticizer in a specific ratio. The invention also discloses its preparation method, including drying, weighing, and co-grinding the raw materials to a D50 of 7.0-8.0 μm. Through the synergistic activation effect among the components, especially the depolymerization of the volcanic rock vitreous network by F⁻ in the fluorogypsum, the adjustment of the calcium-silicon ratio between the mineral powder and volcanic rock, and the combined effect of nanomaterials and chemical additives, the early and late-stage activity of the volcanic rock is significantly improved, and the water demand is reduced. The obtained admixture has a 7-day activity index ≥85%, a 28-day activity index ≥88%, and a water demand ratio ≤108%, and can directly replace traditional mineral powder and fly ash in concrete, solving the problem of the scarcity of high-quality admixtures in western regions, and has significant economic and social benefits.

Description

Technical Field

[0001] This invention belongs to the technical field of building materials and solid waste resource utilization, specifically relating to a modified volcanic rock ultrafine composite admixture and its preparation method. Background Technology

[0002] The demand for infrastructure construction in western China is growing. However, due to its distance from eastern industrial areas, the transportation costs of traditional mineral admixtures such as high-quality mineral powder and fly ash are high and the supply is unstable, making it urgent to develop localized, high-performance alternative materials.

[0003] The western region is extremely rich in volcanic rock resources, with reserves exceeding 5 billion tons. Its main components are SiO2, Al2O3, and CaO, providing a theoretical basis for its use as an active mineral admixture. Fully developing and utilizing local volcanic rock resources can not only solve the problem of admixture shortages but also reduce engineering costs and promote green and sustainable development.

[0004] However, volcanic rock glass networks have a high degree of polymerization, and unmodified volcanic rock powder has low activity. After conventional grinding, the activity index is generally below 50% after 28 days. Furthermore, the hydroxyl groups on the glass surface adsorb water molecules, resulting in a standard consistency water requirement of up to 130%, which is difficult to meet the performance requirements of modern concrete. Existing activation technologies, such as thermal activation (calcination at 800℃), have energy consumption as high as 120kWh / t, making them uneconomical; acid activation (H2SO4 treatment) produces corrosive byproducts, which does not meet the requirements of green building materials; alkali activation (NaOH solution) introduces soluble alkali, causing efflorescence and ASR risks in concrete; mechanical activation, with its limited activity improvement from single grinding.

[0005] Therefore, there is an urgent need for a composite activation method that can synergistically enhance the early activity of volcanic rock powder through multiple activation mechanisms and is suitable for industrial production. Based on this need, this invention proposes an efficient and stable composite activation scheme through systematic screening and orthogonal optimization. This aims to overcome the bottleneck of insufficient activity in natural volcanic rock powder and lay a solid technical foundation for its widespread application in remote areas. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a modified volcanic rock ultrafine composite admixture and its preparation method. The activity index of the modified admixture can reach more than 70% at 7 days and more than 85% at 28 days, and the water requirement ratio is less than 110%. It can be used as a high-quality admixture for the preparation of conventional concrete.

[0007] The technical solution adopted in this invention is: In a first aspect, the present invention provides a modified volcanic rock ultrafine composite admixture, which, by mass, is composed of the following components: 55-70 parts of volcanic rock, wherein the volcanic rock is a local volcanic rock from the western region, and its main chemical components are SiO2 53.1%, Al2O3 18.9%, Fe2O3 9.4%, CaO 9.5%, MgO 4.1%, K2O 2.5%, TiO2 0.93%, SO3 1.1%, with the balance being unavoidable impurities; 15-25 parts of S95 grade mineral powder, wherein the specific surface area of ​​the S95 grade mineral powder is 420 m² / kg, and its main components are SiO2 29.7%, Al2O3 14.1%, and CaO 42.4%; 10-20 parts of fluorogypsum, which is an industrial byproduct produced during the production of hydrogen fluoride. Its main component is anhydrous calcium sulfate with a content of 95%, and it contains 1.0%-1.5% fluorine. 1-4 parts of silica fume, wherein the silica fume contains 91% SiO2 and has a specific surface area of ​​22000 m² / kg; 1-2 parts of lime powder, wherein the lime powder contains 20%-30% CaO and 70%-80% Ca(OH)2; 0.1-0.5 parts of nano-alumina, wherein the nano-alumina is γ-type alumina with an average particle size of 10nm-20nm; 0.01-0.05 parts of triisopropanolamine; 0.05-0.2 parts of polycarboxylate superplasticizer.

[0008] Preferably, the polycarboxylate superplasticizer is a powdered polycarboxylate superplasticizer with a water reduction rate of 36%.

[0009] Preferably, the triisopropanolamine is an industrial-grade colorless liquid with an effective ingredient content of 85%.

[0010] Secondly, the present invention provides a method for preparing the above-mentioned modified volcanic rock ultrafine composite admixture, comprising the following steps: S1: Crush the volcanic rock and dry it together with fluorinated gypsum until the moisture content is less than 1%; S2: Weigh all components according to the above mass proportions; S3: Put all the weighed components into a ball mill and ball mill until the D50 particle size of the mixture is 7.0μm-8.0μm to obtain the modified volcanic rock ultrafine composite admixture.

[0011] Preferably, in the ball milling step, the D50 particle size of the mixture is 7.1 μm, 7.5 μm, or 7.8 μm.

[0012] Thirdly, the present invention provides a concrete characterized in that it comprises the above-mentioned modified volcanic rock ultrafine composite admixture.

[0013] The present invention has the following advantages over the prior art: 1. S95 grade mineral powder contains 42.4% CaO, which continuously releases Ca²⁺ in an alkaline environment (pH>12.5), maintaining the ion concentration gradient for CSH gel precipitation. Active Al₂O₃ (14.1%) and Al³⁺ dissolved from volcanic rock participate in the reaction, forming calcium aluminum silicate gel (CASH). Volcanic rock is rich in silicon (SiO₂>50%) and low in calcium (CaO<10%), while mineral powder is rich in calcium (CaO>40%) and high in aluminum (Al₂O₃>14%). The mixing of these two materials increases the calcium-to-silicon ratio, making it easier to form calcium aluminum silicate gel (CASH). Furthermore, the activation energy for glass dissolution of mineral powder is 62 kJ / mol (compared to 85 kJ / mol for volcanic rock), allowing for preferential hydration and providing nucleation sites for volcanic rock.

[0014] 2. Fluorogypsum dissolves and releases F⁻ ions, which replace O²⁻ in the silica-oxygen network of volcanic rocks, forming a weakly bonded Si-F structure. The Si-F bond energy (486 kJ / mol) is significantly lower than the Si-O bond energy (552 kJ / mol), resulting in a marked decrease in the depolymerization activation energy of the volcanic glass and making the reaction more likely. Simultaneously, it provides SO₄²⁻ to react with Al₂O₃ under alkaline conditions, rapidly generating needle-like ettringite crystals, consuming Ca²⁺ and Al³⁺ in the solution, disrupting the ion concentration balance, and promoting the dissolution of volcanic rocks and mineral powder.

[0015] 3. The particle size of silica fume (0.1μm-0.3μm) falls between that of volcanic rock and mineral powder micron-sized particles (1-10μm) and nano-Al2O3 (10-20nm), forming a gradient-graded filling. Simultaneously, silica fume (active SiO2 ≥ 90%) and nano-Al2O3 synergistically form a Si-O-Al bridging network, reacting with Ca²⁺ and OH⁻ released from silica fume powder and other materials to generate CASH gel, enhancing gel continuity.

[0016] 4. Triisopropanolamine (TIPA) provides a grinding aid effect; the tertiary amine group (-N-) of TIPA reacts with the Si on the volcanic rock surface. 4 The formation of coordinate bonds at vacancies reduces the energy required for new bond breaking and the surface energy required for particle crack formation, making grinding easier. Simultaneously, the adsorption of isopropyl groups (-CH(CH3)2) creates a steric hindrance effect, preventing fine powder agglomeration and enhancing grinding efficiency. Furthermore, the trihydroxy structure of TIPA forms a soluble chelate with Ca²⁺, disrupting the Ca²⁺ double layer, increasing the dissolution rate of the mineral powder glass, and releasing more Al³⁺. The released Al³⁺ then reacts with SiO₄ dissolved from volcanic rock. 4The formation of CASH gel also promotes the hydration of volcanic rocks.

[0017] 5. The addition of polycarboxylate superplasticizer can increase the fluidity of the above admixtures, ensuring that they have good workability when used in concrete.

[0018] After modification by the present invention, the activity of the prepared volcanic rock ultrafine composite admixture is significantly improved compared with that of volcanic rocks from pure regions, and the water demand ratio is also significantly reduced. It can be used as a high-quality concrete admixture, which to some extent solves the predicament of lack of fly ash and mineral powder in these regions, can promote infrastructure construction, and has good social and economic benefits. Detailed Implementation

[0019] The embodiments of the present invention are described in detail below. The embodiments are implemented based on the technical solution of the present invention, and detailed implementation methods and specific operation processes are given. However, the protection scope of the present invention is not limited to the following embodiments. Example

[0020] The raw materials, by weight, are as follows: volcanic rock 63.58, S95 grade mineral powder 20, fluorogypsum 13, silica fume 2, lime powder 1, nano alumina 0.3, triisopropanolamine 0.02, and polycarboxylate superplasticizer 0.1.

[0021] The volcanic rock was crushed and dried together with fluorinated gypsum until the moisture content was less than 1%. Then, all materials were accurately weighed according to the above mass ratio and put together into a ball mill. The mixture was ball-milled until the material D50 was 7.1 μm to obtain the above-mentioned admixture. Example

[0022] The raw materials, by weight, are as follows: volcanic rock 61.93, S95 grade mineral powder 20, fluorogypsum 15, silica fume 1, lime powder 1.5, nano alumina 0.4, triisopropanolamine 0.02, and polycarboxylate superplasticizer 0.15.

[0023] The volcanic rock was crushed and dried together with fluorinated gypsum until the moisture content was less than 1%. Then, all materials were accurately weighed according to the above mass ratio and put into a ball mill. The mixture was ball-milled until the material D50 was 7.5 μm to obtain the above-mentioned admixture. Example

[0024] The raw materials, by weight, are: volcanic rock 66.72, S95 grade mineral powder 15, fluorogypsum 12, silica fume 4, gray calcium powder 2, nano alumina 0.2, triisopropanolamine 0.03, and polycarboxylate superplasticizer 0.05.

[0025] The volcanic rock was crushed and dried together with fluorinated gypsum until the moisture content was less than 1%. Then, all materials were accurately weighed according to the above mass ratio and put together into a ball mill. The mixture was ball-milled until the material D50 was 7.8 μm to obtain the above-mentioned admixture. Example

[0026] The raw materials, by weight, are: volcanic rock 56.28, S95 grade mineral powder 23, fluorogypsum 17, silica fume 2, gray calcium powder 1, nano alumina 0.5, triisopropanolamine 0.02, and polycarboxylate superplasticizer 0.2.

[0027] The volcanic rock was crushed and dried together with fluorinated gypsum until the moisture content was less than 1%. Then, all materials were accurately weighed according to the above mass ratio and put into a ball mill. The mixture was ball-milled until the material D50 was 7.5 μm to obtain the above-mentioned admixture.

[0028] Comparative Example 1 100 parts of volcanic rock were crushed and dried until the moisture content was <1%, and then ground with a ball mill until the material D50 was 7.5 μm.

[0029] Comparative Example 2 The only difference from Example 1 is that the material was ball-milled until the D50 was 6.0 μm.

[0030] Comparative Example 3 The only difference from Example 1 is that the material was ball-milled until the D50 was 10.0 μm.

[0031] Comparative Example 4 The only difference from Example 4 is that S95 grade mineral powder is not added, and the extra 23 parts are added to the volcanic rock.

[0032] Comparative Example 5 The only difference from Example 4 is that fluorinated plaster is not added, and the extra 17 parts are added to the volcanic rock.

[0033] Comparative Example 6 The only difference from Example 4 is that silica fume is not added, and the extra 2 parts are added to the volcanic rock.

[0034] Comparative Example 7 The only difference from Example 4 is that no lime powder is added, and the extra 1 part is added to the volcanic rock.

[0035] Comparative Example 8 The only difference from Example 4 is that nano-alumina and triisopropanolamine are not added, and the extra 0.52 parts are added to the volcanic rock.

[0036] Comparative Example 9 The only difference from Example 4 is that no polycarboxylate superplasticizer is added, and the extra 0.2 parts are added to the volcanic rock.

[0037] According to the standard "Test Method for Strength of Cement Mortar (ISO Method)" (GB / T 17671-2021), reference group mortar was prepared using reference cement that conforms to the "Specification for Concrete Admixtures" (GB 8076-2025). After demolding for 24 hours, it was cured under standard curing conditions (20±2℃, 95%±5% relative humidity). The compressive strength at 7 days and 28 days was tested and used as the reference strength value for calculating the volcanic rock activity index.

[0038] According to the standard "Technical Specification for Application of Mineral Admixtures" (GB / T 51003-2014), the admixtures prepared in Examples 1-4 and Comparative Examples 1-9 were uniformly mixed with the same reference cement at a mass ratio of 3:7 to prepare mortar strength test specimens. After curing for 24 hours, the specimens were demolded and cured under standard curing conditions (20±2℃, 95%±5% relative humidity). The compressive strength at 7 days and 28 days was tested. Using the 28-day compressive strength of the reference group mortar as the benchmark value, the activity index of the admixtures prepared in Examples 1-4 and Comparative Examples 1-9 was calculated. Simultaneously, the water requirement ratio of the admixtures prepared in Examples 1-4 and Comparative Examples 1-9 to the reference cement was also tested according to this standard.

[0039] The test results are shown in Table 1 below:

[0040] As can be seen from the table above, Comparative Examples 1, 2, and 3 did not have any added modifying materials; they were simply activated by mechanical force, which had little effect. The finer particle size did not significantly improve the activity; on the contrary, it increased the water requirement.

[0041] The 28-day activity index of Comparative Example 4 was only 69.3%, a decrease of 19.3 percentage points compared to Example 4 (88.6%). This demonstrates that the CaO and Al2O3 ionic components in the S95 mineral powder form a crucial hydration synergistic network with the active SiO2 in the volcanic rock—the absence of this component hinders the depolymerization of silicon-oxygen tetrahedra in the volcanic rock, reducing the nucleation efficiency of the gel phase (CASH) by approximately 40%. The 7-day compressive strength of Comparative Example 4 (24.4 MPa) was 18.9% lower than that of Example 4 (30.1 MPa). This is attributed to the preferential hydration of the S95 mineral powder glass, which provides nucleation sites; its absence prolongs the hydration induction period of the volcanic rock.

[0042] The 28-day activity index of Comparative Example 5 (75.2%) decreased by 15.1% compared to Example 4 (88.6%), indicating that the absence of fluorogypsum led to the interruption of the supply of key ions (SO4²⁻, Ca²⁺), hindering the formation of the gel network. At the same time, the lack of F- reduced the depolymerization activation capacity of the volcanic glass, resulting in a decrease in its reactivity.

[0043] Comparative Example 6 shows that silica fume has a compacting effect, and that active silica can synergistically promote the hydration of mineral powder to generate hydrated calcium silicate gel, providing nucleation sites and indirectly promoting the hydration of volcanic rocks.

[0044] Comparative Examples 7 and 8 show that the absence of lime powder provides Ca2+ and alkalinity, while nano-alumina provides active Al2O3. The chelating effect of triisopropanolamine weakens the breaking of Al-O and Si-O bonds in mineral powder and volcanic rock to some extent, reducing the degree of hydration and macroscopically manifesting as a decrease in the activity index.

[0045] Comparative Example 9 shows that polycarboxylate superplasticizer can significantly reduce the water requirement ratio.

[0046] To further evaluate the effect of the admixture described in this invention on the performance and mechanical strength of concrete, C30 concrete was prepared using Example 4, and its mixing performance and mechanical properties were tested. The test results are shown in Table 2 below:

[0047] Table 3:

[0048] As can be seen from the table above, using the admixture of this invention to replace conventional fly ash and mineral powder in the preparation of C30 concrete has virtually no impact on the workability and strength of the concrete, and can meet the requirements of concrete for conventional admixtures.

[0049] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A modified volcanic rock ultrafine composite admixture, characterized by: By weight, it consists of the following components: 55-70 parts of volcanic rock, which are local volcanic rocks from the western region, have the following main chemical components: SiO2 53.1%, Al2O3 18.9%, Fe2O3 9.4%, CaO 9.5%, MgO 4.1%, K2O 2.5%, TiO2 0.93%, SO3 1.1%, with the balance being unavoidable impurities; 15-25 parts of S95 grade mineral powder, wherein the specific surface area of ​​the S95 grade mineral powder is 420 m² / kg, and its main components are SiO2 29.7%, Al2O3 14.1%, and CaO 42.4%; 10-20 parts of fluorogypsum, which is an industrial byproduct produced during the production of hydrogen fluoride. Its main component is anhydrous calcium sulfate with a content of 95%, and it contains 1.0%-1.5% fluorine. 1-4 parts of silica fume, wherein the silica fume contains 91% SiO2 and has a specific surface area of ​​22000 m² / kg; 1-2 parts of lime powder, wherein the lime powder contains 20%-30% CaO and 70%-80% Ca(OH)2; 0.1-0.5 parts of nano-alumina, wherein the nano-alumina is γ-type alumina with an average particle size of 10nm-20nm; 0.01-0.05 parts of triisopropanolamine; 0.05-0.2 parts of polycarboxylate superplasticizer.

2. The modified volcanic rock ultrafine composite admixture according to claim 1, characterized in that: The polycarboxylate superplasticizer is a powdered polycarboxylate superplasticizer with a water reduction rate of 36%.

3. The modified volcanic rock ultrafine composite admixture according to claim 1, characterized in that: The triisopropanolamine is an industrial-grade colorless liquid with an effective ingredient content of 85%.

4. A method for preparing a modified volcanic rock ultrafine composite admixture as described in any one of claims 1-3, characterized in that, Includes the following steps: S1: Crush the volcanic rock and dry it together with fluorinated gypsum until the moisture content is less than 1%; S2: Weigh all components according to the mass proportions described in claim 1; S3: Put all the weighed components into a ball mill and ball mill until the D50 particle size of the mixture is 7.0μm-8.0μm to obtain the modified volcanic rock ultrafine composite admixture.

5. The preparation method according to claim 4, characterized in that: In the ball milling step, the D50 particle size of the mixture is 7.1 μm, 7.5 μm, or 7.8 μm.

6. A type of concrete, characterized in that, It contains the modified volcanic rock ultrafine composite admixture as described in any one of claims 1-3.

Images