High-strength geopolymer mortar containing low-quality silica fume and method for preparing the same

Abstract

The present application relates to a kind of high-strength geopolymer mortar containing low-quality silica fume and its preparation method, belong to geopolymer mortar technical field.To solve the problem of low compressive strength of geopolymer mortar containing low-quality silica fume, the present application provides a kind of high-strength geopolymer mortar containing low-quality silica fume, components include gel material, aggregate, micro aggregate and alkali activator, gel material includes low-calcium fly ash, calcium aluminate cement, low-quality silica fume and nanometer silicon dioxide, aggregate includes quartz sand, micro aggregate includes steel fiber, and alkali activator includes solid sodium hydroxide, water glass solution and tap water.The present application utilizes the synergistic effect of low-quality silica fume and nanometer silicon dioxide, increases the active silicon dioxide content of overall system, plays a good reinforcing effect on the compressive strength of fly ash geopolymer mortar, so that the compressive strength of geopolymer mortar containing low-quality silica fume reaches 80.4MPa.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of geopolymer mortar, and particularly relates to a high-strength geopolymer mortar containing low-quality silica fume and a preparation method thereof. BACKGROUND

[0002] Geopolymer mortar is a new type of building material emerging in engineering in recent years, and is an inorganic gel material prepared by a silicate-aluminate active component under the action of an alkali activator. Compared with traditional Portland cement, geopolymer mortar has more excellent thermal stability and corrosion resistance. At the same time, the carbon emission and energy consumption in the production process of geopolymer mortar are 20% and 40% of those of ordinary Portland cement respectively, and therefore geopolymer mortar has significant low-carbon characteristics.

[0003] Industrial by-products such as silica fume, slag and fly ash have the potential to replace cement to become gel materials under the action of an alkali or acid activator. The activity of the powders such as silica fume, slag and fly ash is improved by using an alkali activator, and then a three-dimensional network structure of Si, Al and O is formed by polymerization. Therefore, high-quality silica fume and other materials are often used in the prior art to prepare high-strength geopolymer mortar, and few studies are conducted on low-quality silica fume.

[0004] Low quality refers to the fact that the main physical and chemical performance indicators of the mineral admixture do not meet the minimum requirements of the current standard, i.e., do not fall within the range of the standard grades. If these low-quality solid waste materials can be effectively utilized, they will play an important role in saving resources and protecting the environment. However, the use of low-quality silica fume often leads to a decrease in the performance of concrete. The patent application with the publication number CN104788060A, “Water permeable concrete prepared by complexly mixing low-quality active mineral admixtures and preparation method thereof”, uses low-quality silica fume and low-quality fly ash as raw materials to prepare concrete with a compressive strength of only 16.362 MPa. Therefore, it is urgent to solve the problem of the adverse effects of low-quality silica fume on the performance of geopolymer mortar and to improve the compressive strength of geopolymer mortar containing low-quality silica fume in the process of developing low-cost high-strength geopolymer. SUMMARY

[0005] To solve the problem of low compressive strength of geopolymer mortar containing low-quality silica fume, the application provides a high-strength geopolymer mortar containing low-quality silica fume and a preparation method thereof.

[0006] The technical scheme of the application is as follows:

[0007] A high-strength geopolymer mortar containing low-quality silica fume, components including gel material, aggregate, micro aggregate and alkali activator, the gel material including low-calcium fly ash, calcium aluminate cement, low-quality silica fume and nano-silica, the aggregate including quartz sand, the micro aggregate including steel fiber, the alkali activator including solid sodium hydroxide, water glass solution and tap water, the components being proportioned as follows: fly ash 732.6-941.4 parts, calcium aluminate cement 252.6 parts, low-quality silica fume 63.2-253 parts, nano-silica 6.3-25.3 parts, quartz sand 631.6 parts, solid sodium hydroxide 45.3 parts, water glass solution 360.9 parts and tap water 99 parts, the steel fiber being added in an amount of 2% of the volume of the high-strength geopolymer mortar.

[0008] Further, the low-calcium fly ash contains at least the following components in the following mass percentages: 35-50% of SiO2, 15-25% of Al2O3 and 9-10% of CaO.

[0009] Further, the calcium aluminate cement contains at least the following components in the following mass percentages: 70-80% of Al2O3 and 20-30% of CaO.

[0010] Further, the low-quality silica fume contains at least the following components in the following mass percentages: 50-85% of SiO2, 0-20% of Al2O3 and 0-20% of K2O.

[0011] Further, the nano-silica has a particle size of 5-20 nm, and is dispersed by ultrasonic treatment before being mixed into the geopolymer mortar, the ultrasonic power being 100 W and the ultrasonic dispersion treatment time being 30 min.

[0012] Further, the quartz sand has a particle size of 180-380 μm.

[0013] Further, the steel fiber has a diameter of 0.12 mm, a length of 13 mm and a density of 7850 kg / m 3 .

[0014] Further, the water glass solution has a modulus of 2.3 and a solid content of 43.5%.

[0015] A preparation method of a high-strength geopolymer mortar containing low-quality silica fume, first preparing an alkali activator from solid sodium hydroxide, water glass solution and tap water, and then standing at room temperature; mixing and stirring low-calcium fly ash, calcium aluminate cement, low-quality silica fume and nano-silica, then adding quartz sand and continuing to stir to make them uniformly mixed, finally adding the alkali activator after standing and continuing to stir, slowly adding steel fiber during stirring to make it more uniformly dispersed, and finally obtaining a high-strength geopolymer mortar with good fluidity.

[0016] Further, the specific preparation method of the alkali activator is as follows: the sodium hydroxide particles are prepared into a sodium hydroxide solution with a concentration of 10.5 mol / L according to the water-gel ratio of 0.24 to calculate the water amount, the sodium hydroxide solution is mixed with the water glass solution to stir, and the alkali activator with a modulus of 1.3 is obtained.

[0017] The beneficial effects of the present application are as follows:

[0018] The high-strength geopolymer mortar containing low-quality silica fume provided by the present application utilizes the synergistic effect of low-quality silica fume and nano-silicon dioxide to increase the active silicon dioxide content of the overall system, which plays a good reinforcing role on the compressive strength of the fly ash geopolymer mortar, overcomes the adverse effect of low-quality silica fume on the strength of the geopolymer mortar, and makes the compressive strength of the geopolymer mortar containing low-quality silica fume reach 80.4 MPa.

[0019] The present application makes the low-quality silica fume well applied in the high-strength geopolymer mortar, which not only effectively utilizes the low-quality silica fume and reduces the pollution to the environment, but also greatly reduces the production cost of the high-strength geopolymer mortar, so that the high-strength geopolymer mortar can replace cement and be widely promoted and used. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 The 28-day XRD diagram of the geopolymer neat paste test block prepared in Examples 1-4 and Comparative Example 1;

[0021] Figure 2 The 28-day SEM micro-morphology diagram of the geopolymer neat paste test block prepared in Example 1;

[0022] Figure 3 The 28-day SEM micro-morphology diagram of the geopolymer neat paste test block prepared in Example 2;

[0023] Figure 4 The 28-day SEM micro-morphology diagram of the geopolymer neat paste test block prepared in Example 3;

[0024] Figure 5 The 28-day SEM micro-morphology diagram of the geopolymer neat paste test block prepared in Example 4;

[0025] Figure 6 The 28-day SEM micro-morphology diagram of the geopolymer neat paste test block prepared in Comparative Example 1. DETAILED DESCRIPTION

[0026] The technical solutions of the present application are further described below with reference to the examples, but are not limited thereto, and any modification or equivalent replacement of the technical solutions of the present application without departing from the spirit and scope of the present application shall be encompassed in the protection scope of the present application. The process equipment or device not specifically mentioned in the following examples is the conventional equipment or device in the art, and the raw materials used in the examples of the present application are commercially available if not specifically indicated; and the technical means used in the examples of the present application is the conventional means well known to those skilled in the art if not specifically indicated.

[0027] Example 1

[0028] The present example provides a high-strength geopolymer mortar containing low-quality silica fume, and the components include a gel material, aggregate, micro aggregate and an alkali activator.

[0029] The gel material in the present example includes low-calcium fly ash, calcium aluminate cement, low-quality silica fume and nano-silica, wherein the composition of the low-calcium fly ash contains 49.61% of SiO2, 18.49% of Al2O3, 9.57% of CaO, 10.55% of Fe2O3, 5.70% of MgO, 2.52% of K2O, 2.58% of Na2O, 0.61% of TiO2, and the balance is impurities; the composition of the calcium aluminate cement contains 71.12% of Al2O3, 27.42% of CaO, 0.6% of SiO2, 0.32% of Na2O, 0.28% of MgO, 0.16% of Fe2O3, 0.03% of TiO2, and the balance is impurities; the composition of the low-quality silica fume contains 53.13% of SiO2, 17.88% of Al2O3, 18.09% of K2O, 0.123% of CaO, 1.27% of Na2O, 1.09% of Fe2O3, 1.07% of TiO2, and the balance is impurities; the nano-silica has a particle size of 5-20 nm, and is dispersed by ultrasonic treatment before being added into the geopolymer mortar, with an ultrasonic power of 100 W and an ultrasonic dispersion treatment time of 30 min.

[0030] In the present example, the aggregate is quartz sand with a particle size of 180-380 μm, and the micro aggregate is steel fiber with a diameter of 0.12 mm, a length of 13 mm and a density of 7850 kg / m 3 The alkali activator is prepared by mixing solid sodium hydroxide, water glass solution and tap water in a certain proportion, wherein the solid sodium hydroxide is a flaky solid particle with a purity of more than 99%; the modulus of the water glass solution is 2.3, and the solid content is 43.5%, mainly composed of SiO2 and Na2O.

[0031] The components in the high-strength geopolymer mortar of the embodiment are proportioned by weight as follows: fly ash 941.4 parts, calcium aluminate cement 252.6 parts, low-quality silica fume 63.2 parts, nano-silicon dioxide 6.3 parts, quartz sand 631.6 parts, solid sodium hydroxide 45.3 parts, water glass solution 360.9 parts, tap water 99 parts, and the addition amount of steel fiber is calculated as 2% of the volume of the high-strength geopolymer mortar.

[0032] The preparation method of the high-strength geopolymer mortar of the embodiment is as follows:

[0033] First, an alkali activator is prepared using solid sodium hydroxide, water glass solution, and tap water as raw materials, and the water amount is calculated according to a water-binder ratio of 0.24. Sodium hydroxide particles are prepared into a sodium hydroxide solution with a concentration of 10.5 mol / L. The sodium hydroxide solution is mixed and stirred with the water glass solution to obtain an alkali activator with a modulus of 1.3, which is left to stand at room temperature for 24 hours.

[0034] Low-calcium fly ash, calcium aluminate cement, low-quality silica fume, and nano-silicon dioxide are added to a blender and stirred at low speed for 2 minutes. Quartz sand is then added and stirred for another 2 minutes to mix them evenly. Finally, the alkali activator after standing is added and stirred for another 4 minutes. Steel fiber is slowly added during stirring to make it more evenly dispersed. Finally, a high-strength geopolymer mortar with good fluidity is obtained.

[0035] In order to detect the performance of the obtained high-strength geopolymer mortar, the obtained high-strength geopolymer mortar paste is poured into a 50mm×50mm×50mm mold, and is vibrated on a vibrating table to make it more compact. After vibration, the mold is wrapped with plastic wrap to prevent water loss from the paste. The prepared test block is demolded after curing at room temperature for 24 hours, and finally the test block is placed in a standard curing room with a temperature of 20±2℃ and a relative humidity of 95%. The compressive strength of the test block is tested after 28 days.

[0036] Example 2

[0037] The embodiment provides a high-strength geopolymer mortar containing low-quality silica fume, which includes gel material, aggregate, micro aggregate, and alkali activator.

[0038] The gel material in the embodiment comprises low calcium fly ash, calcium aluminate cement, low quality silica fume and nano-silica, wherein the low calcium fly ash comprises 49.61% of SiO2, 18.49% of Al2O3, 9.57% of CaO, 10.55% of Fe2O3, 5.70% of MgO, 2.52% of K2O, 2.58% of Na2O, 0.61% of TiO2, and the rest is impurities; the calcium aluminate cement comprises 71.12% of Al2O3, 27.42% of CaO, 0.6% of SiO2, 0.32% of Na2O, 0.28% of MgO, 0.16% of Fe2O3, 0.03% of TiO2, and the rest is impurities; the low quality silica fume comprises 53.13% of SiO2, 17.88% of Al2O3, 18.09% of K2O, 0.123% of CaO, 1.27% of Na2O, 1.09% of Fe2O3, 1.07% of TiO2, and the rest is impurities; the nano-silica has a particle size of 5-20 nm, and is dispersed by ultrasonic wave before being mixed into the geopolymer mortar, the ultrasonic power is 100 W, and the ultrasonic dispersion time is 30 min.

[0039] In the embodiment, the aggregate is quartz sand with a particle size of 180-380 μm, and the micro aggregate is steel fiber with a diameter of 0.12 mm, a length of 13 mm and a density of 7850 kg / m 3 The alkali activator is prepared by mixing solid sodium hydroxide, water glass solution and tap water in a certain proportion, wherein the solid sodium hydroxide is flaky solid particle with a purity of more than 99%; the modulus of the water glass solution is 2.3, and the solid content is 43.5%, which mainly comprises SiO2 and Na2O.

[0040] In the high-strength geopolymer mortar, the components are mixed in the following proportions by weight: 871.9 parts of fly ash, 252.6 parts of calcium aluminate cement, 126.4 parts of low quality silica fume, 12.6 parts of nano-silica, 631.6 parts of quartz sand, 45.3 parts of solid sodium hydroxide, 360.9 parts of water glass solution, 99 parts of tap water, and the addition amount of steel fiber is 2% of the volume of the high-strength geopolymer mortar.

[0041] The preparation method of the high-strength geopolymer mortar is as follows:

[0042] First, the alkali activator is prepared by using solid sodium hydroxide, water glass solution and tap water as raw materials, and the water amount is calculated according to the water-binder ratio of 0.24, the sodium hydroxide particles are prepared into a sodium hydroxide solution with a concentration of 10.5 mol / L, the sodium hydroxide solution is mixed with the water glass solution to obtain an alkali activator with a modulus of 1.3, and the mixture is stirred and then left to stand at room temperature for 24 h.

[0043] The low-calcium fly ash, calcium aluminate cement, low-quality silica fume and nano-silica were added into a blender and stirred at low speed for 2 min, then the quartz sand was added and stirred for 2 min to make them mix uniformly, finally the alkali activator after standing was added and stirred for 4 min, and the steel fiber was slowly added and stirred to make it disperse more uniformly during the stirring, and finally the high-strength geopolymer mortar with good fluidity was obtained.

[0044] In order to detect the performance of the obtained high-strength geopolymer mortar, the obtained high-strength geopolymer mortar paste was cast in a 50mmx50mmx50mm mold, and was vibrated on a vibrating table to make it more compact. After vibration, the mold was wrapped with plastic wrap to prevent water loss from the paste. The prepared test block was demolded after curing at room temperature for 24 hours, and finally the test block was placed in a standard curing room with a temperature of 20±2℃ and a relative humidity of 95%, and the compressive strength of the test block was detected after 28 days.

[0045] Example 3

[0046] The present embodiment provides a high-strength geopolymer mortar containing low-quality silica fume, and the components include gel material, aggregate, micro aggregate and alkali activator.

[0047] The gel material in the present embodiment includes low-calcium fly ash, calcium aluminate cement, low-quality silica fume and nano-silica, wherein the composition of the low-calcium fly ash is 49.61% of SiO2, 18.49% of Al2O3, 9.57% of CaO, 10.55% of Fe2O3, 5.70% of MgO, 2.52% of K2O, 2.58% of Na2O, 0.61% of TiO2, and the balance is impurities; the composition of the calcium aluminate cement is 71.12% of Al2O3, 27.42% of CaO, 0.6% of SiO2, 0.32% of Na2O, 0.28% of MgO, 0.16% of Fe2O3, 0.03% of TiO2, and the balance is impurities; the composition of the low-quality silica fume is 53.13% of SiO2, 17.88% of Al2O3, 18.09% of K2O, 0.123% of CaO, 1.27% of Na2O, 1.09% of Fe2O3, 1.07% of TiO2, and the balance is impurities; the particle size of the nano-silica is 5-20nm, and it is dispersed by ultrasonic before being added into the geopolymer mortar, the ultrasonic power is 100W, and the ultrasonic dispersion treatment time is 30min.

[0048] The aggregate in the present embodiment is quartz sand with a particle size of 180-380μm, and the micro aggregate is steel fiber with a diameter of 0.12mm, a length of 13mm and a density of 7850kg / m 3The alkali activator is prepared by mixing solid sodium hydroxide, water glass solution and tap water in proportion, wherein the solid sodium hydroxide is in the form of flaky solid particles with a purity of more than 99%; the water glass solution has a modulus of 2.3 and a solid content of 43.5%, and is mainly composed of SiO2 and Na2O.

[0049] In the high-strength geopolymer mortar of the embodiment, the components are proportioned as follows by weight: fly ash 802.4 parts, calcium aluminate cement 252.6 parts, low-quality silica fume 189.5 parts, nano-silicon dioxide 19 parts, quartz sand 631.6 parts, solid sodium hydroxide 45.3 parts, water glass solution 360.9 parts, and tap water 99 parts. The amount of steel fiber added is calculated as 2% of the volume of the high-strength geopolymer mortar.

[0050] The preparation method of the high-strength geopolymer mortar of the embodiment is as follows:

[0051] First, the alkali activator is prepared by using solid sodium hydroxide, water glass solution and tap water as raw materials. The amount of water is calculated according to a water-binder ratio of 0.24. The sodium hydroxide particles are prepared into a sodium hydroxide solution with a concentration of 10.5 mol / L. The sodium hydroxide solution is mixed with the water glass solution and stirred to obtain an alkali activator with a modulus of 1.3. The mixture is left to stand at room temperature for 24 hours.

[0052] The low-calcium fly ash, calcium aluminate cement, low-quality silica fume and nano-silicon dioxide are added to a stirrer and stirred at low speed for 2 minutes. Then the quartz sand is added and stirred for another 2 minutes to make the mixture uniform. Finally, the alkali activator after standing is added and stirred for 4 minutes. During the stirring, steel fiber is slowly added to make it more evenly dispersed. Finally, a high-strength geopolymer mortar with good fluidity is obtained.

[0053] In order to detect the performance of the obtained high-strength geopolymer mortar, the obtained high-strength geopolymer mortar paste is poured into a 50mm×50mm×50mm mold and vibrated on a vibrating table to make it more compact. After vibration, the mold is wrapped with plastic wrap to prevent water loss from the paste. The prepared test block is demolded after curing at room temperature for 24 hours. Finally, the test block is placed in a standard curing room with a temperature of 20±2℃ and a relative humidity of 95% for curing. The compressive strength of the test block is tested after 28 days.

[0054] Example 4

[0055] The embodiment provides a high-strength geopolymer mortar containing low-quality silica fume, which comprises gel material, aggregate, micro aggregate and alkali activator.

[0056] The gel material in the embodiment comprises low calcium fly ash, calcium aluminate cement, low quality silica fume and nano-silica, wherein the low calcium fly ash comprises 49.61% of SiO2, 18.49% of Al2O3, 9.57% of CaO, 10.55% of Fe2O3, 5.70% of MgO, 2.52% of K2O, 2.58% of Na2O, 0.61% of TiO2, and the rest is impurities; the calcium aluminate cement comprises 71.12% of Al2O3, 27.42% of CaO, 0.6% of SiO2, 0.32% of Na2O, 0.28% of MgO, 0.16% of Fe2O3, 0.03% of TiO2, and the rest is impurities; the low quality silica fume comprises 53.13% of SiO2, 17.88% of Al2O3, 18.09% of K2O, 0.123% of CaO, 1.27% of Na2O, 1.09% of Fe2O3, 1.07% of TiO2, and the rest is impurities; the nano-silica has a particle size of 5-20 nm, and is dispersed by ultrasonic wave before being mixed into the geopolymer mortar, the ultrasonic power is 100 W, and the ultrasonic dispersion time is 30 min.

[0057] In the embodiment, the aggregate is quartz sand with a particle size of 180-380 μm, and the micro aggregate is steel fiber with a diameter of 0.12 mm, a length of 13 mm and a density of 7850 kg / m 3 The alkali activator is prepared by mixing solid sodium hydroxide, water glass solution and tap water in a certain proportion, wherein the solid sodium hydroxide is flaky solid particle with a purity of more than 99%; the modulus of the water glass solution is 2.3, and the solid content is 43.5%, which mainly comprises SiO2 and Na2O.

[0058] In the high-strength geopolymer mortar of the embodiment, the components are mixed in the following proportions by weight: 732.6 parts of fly ash, 252.6 parts of calcium aluminate cement, 253 parts of low quality silica fume, 25.3 parts of nano-silica, 631.6 parts of quartz sand, 45.3 parts of solid sodium hydroxide, 360.9 parts of water glass solution and 99 parts of tap water, and the amount of steel fiber is calculated as 2% of the volume of the high-strength geopolymer mortar.

[0059] The preparation method of the high-strength geopolymer mortar in the embodiment is as follows:

[0060] First, the alkali activator is prepared by using solid sodium hydroxide, water glass solution and tap water as raw materials, and the water amount is calculated according to the water-binder ratio of 0.24, the sodium hydroxide particles are prepared into a sodium hydroxide solution with a concentration of 10.5 mol / L, the sodium hydroxide solution is mixed with the water glass solution and stirred to obtain an alkali activator with a modulus of 1.3, and the mixture is left to stand at room temperature for 24 h.

[0061] The low-calcium fly ash, calcium aluminate cement, low-quality silica fume and nano-silica were added into a blender and stirred at low speed for 2 min, then the quartz sand was added and stirred for 2 min to make them mix uniformly, finally the alkali activator after standing was added and stirred for 4 min, and the steel fiber was slowly added and stirred to make it more uniformly dispersed during the stirring, and finally the high-strength geopolymer mortar with good fluidity was obtained.

[0062] In order to detect the performance of the obtained high-strength geopolymer mortar, the obtained high-strength geopolymer mortar paste was cast in a 50mmx50mmx50mm mold, and was vibrated on a vibrating table to make it more dense. After vibration, the mold was wrapped with plastic wrap to prevent water loss from the paste. The prepared test block was demolded after curing at room temperature for 24 hours, and finally the test block was placed in a standard curing room with a temperature of 20±2°C and a relative humidity of 95%, and the compressive strength of the test block was detected after 28 days.

[0063] Comparative Example 1

[0064] The present comparative example provides a geopolymer mortar without low-quality silica fume and nano-silica, and the components include gel material, aggregate, micro aggregate and alkali activator.

[0065] The gel material in the present comparative example includes low-calcium fly ash and calcium aluminate cement, wherein the composition of the low-calcium fly ash is 49.61% of SiO2, 18.49% of Al2O3, 9.57% of CaO, 10.55% of Fe2O3, 5.70% of MgO, 2.52% of K2O, 2.58% of Na2O, 0.61% of TiO2, and the balance is impurities; the composition of the calcium aluminate cement is 71.12% of Al2O3, 27.42% of CaO, 0.6% of SiO2, 0.32% of Na2O, 0.28% of MgO, 0.16% of Fe2O3, 0.03% of TiO2, and the balance is impurities.

[0066] The aggregate in the present comparative example is quartz sand with a particle size of 180-380μm, and the micro aggregate is steel fiber with a diameter of 0.12mm, a length of 13mm and a density of 7850kg / m 3 The alkali activator is prepared by mixing solid sodium hydroxide, water glass solution and tap water in proportion, wherein the solid sodium hydroxide is a flaky solid particle with a purity of more than 99%; the modulus of the water glass solution is 2.3, and the solid content is 43.5%, mainly composed of SiO2 and Na2O.

[0067] The components in the high-strength geopolymer mortar of the comparative example are proportioned by weight parts as follows: fly ash 1010.9 parts, calcium aluminate cement 252.6 parts, quartz sand 631.6 parts, solid sodium hydroxide 45.3 parts, water glass solution 360.9 parts, and tap water 99 parts. The amount of steel fiber added is calculated as 2% of the volume of the high-strength geopolymer mortar.

[0068] The preparation method of the geopolymer mortar of the comparative example is as follows:

[0069] First, an alkali activator is prepared using solid sodium hydroxide, water glass solution, and tap water as raw materials. The amount of water is calculated based on a water-binder ratio of 0.24. Sodium hydroxide particles are prepared into a sodium hydroxide solution with a concentration of 10.5 mol / L. The sodium hydroxide solution is mixed with the water glass solution and stirred to obtain an alkali activator with a modulus of 1.3. The mixture is left to stand at room temperature for 24 hours.

[0070] Low-calcium fly ash and calcium aluminate cement are added to a mixer and stirred at low speed for 2 minutes. Quartz sand is then added and stirred for another 2 minutes to ensure uniform mixing. Finally, the alkali activator after standing is added and stirred for 4 minutes. Steel fibers are slowly added and stirred during the stirring process to ensure more uniform dispersion. The geopolymer mortar is obtained.

[0071] To test the performance of the obtained geopolymer mortar, the geopolymer mortar bodies obtained in Examples 1-4 and Comparative Example 1 are poured into 50mm x 50mm x 50mm molds and vibrated on a vibrating table to make them more compact. After vibration, the molds are wrapped with plastic wrap to prevent water loss from the mortar body. The prepared test blocks are demolded after curing at room temperature for 24 hours. Finally, the test blocks are placed in a standard curing room with a temperature of 20±2°C and a relative humidity of 95% for curing. After 28 days, the compressive strength, bulk density, and porosity of the test blocks are tested, and the results are shown in Table 1.

[0072] Table 1

[0073]

[0074]

[0075] From the data in Table 1, it can be observed that when the low-quality silica fume content in the gel material is 20wt.%, and the nano-silica content is 2wt.%, the 28-day compressive strength of the geopolymer mortar is the highest, reaching 80.4MPa. Silica fume and nano-silica provide more active silicon for geopolymerization. Their particle sizes are relatively small, and some particles that do not participate in geopolymerization can fill the voids between fly ash and calcium aluminate cement as aggregate, making the matrix more compact.

[0076] The incorporation of steel fiber has a certain negative impact on the workability of geopolymer mortar, but with the incorporation of silica fume and nano-silica, the fluidity gradually increases, which improves the workability of geopolymer mortar.

[0077] The porosity gradually decreases with the increase of the content of silica fume and nano-silica, and the simulation of the particle size of geopolymer mortar precursor by the close packing density model shows that the packing density gradually increases with the increase of the content of silica fume and nano-silica, which is positively correlated with the compressive strength and negatively correlated with the porosity.

[0078] Figure 1 The 28-day XRD patterns of the geopolymer paste test blocks prepared in Examples 1-4 and Comparative Example 1; from Figure 1 It can be seen that when no silica fume is added, the main crystal phase remains stable after geopolymerization, but due to carbonization, the 29.5° crystal phase of fly ash geopolymer without silica fume is observed to be calcite phase, and there are also quartz diffraction peaks in the product. When silica fume is added, the calcite phase peak disappears, and with the addition of low-quality silica fume and nano-silica, the geopolymer produces a halo at 20°-40° 2θ angle. This halo represents the formation of sodium aluminum silicate gel (N-A-S-H), which is believed to be the cause of the strength development of geopolymer materials. The diffraction peaks of quartz and calcium aluminate cement are observed at 2θ of 26.5° and 35.5°, indicating the presence of unreacted fly ash and calcium aluminate cement in the reaction product. The diffraction peak at 2θ = 29.4° is related to the formation of C-S-H gel. The formation of C-S-H gel in alkali-activated fly ash systems or aluminate cement systems has also been observed in previous studies. In addition to the coexistence of N-A-S-H gel and C-S-H gel, a small amount of hydrocalumite and hydrated calcium silicate was also identified. SF wrapping leads to a decrease in the intensity of quartz-related peaks, indicating that more Si content is dissolved during the alkali activation process.

[0079] Figures 2-6are 28-day SEM micro-morphology images of geopolymer paste test blocks prepared in Examples 1-4 and Comparative Examples, and it can be observed from the images that the SEM image of the geopolymer paste of Comparative Example 1 without adding silica fume and nano-silica shows a large amount of unreacted fly ash and calcium aluminate cement, and the internal voids are large, making the overall structure less dense, resulting in low compressive strength. With the addition of silica fume and nano-silica, due to their small particle size and high activity, part of them participate in the geopolymerization reaction to form a more dense substance, and the unreacted silica fume and nano-silica particles can fill the pores between fly ash and calcium aluminate cement due to their small particle size, making the geopolymer matrix structure gradually more dense, the cracks gradually reduced, and the reaction more complete. The matrix interface gradually becomes smooth, making the geopolymer paste structure more dense, indicating that the synergistic effect of low-quality silica fume and nano-silica effectively improves the microstructure of the geopolymer paste, which is beneficial to the improvement of the compressive strength.

Claims

1. A high-strength geopolymer mortar containing low-quality silica fume, the components comprising a geopolymeric material, aggregates, micro-fines and an alkali activator, characterised in that, The gel material comprises low calcium fly ash, calcium aluminate cement, low quality silica fume and nano-silica, the aggregate comprises quartz sand, the micro aggregate comprises steel fiber, the alkali activator comprises solid sodium hydroxide, water glass solution and tap water, the components are proportioned by weight parts as follows: low calcium fly ash 732.6~941.4 parts, calcium aluminate cement 252.6 parts, low quality silica fume 63.2~253 parts, nano-silica 6.3~25.3 parts, quartz sand 631.6 parts, solid sodium hydroxide 45.3 parts, water glass solution 360.9 parts and tap water 99 parts, the addition amount of the steel fiber is calculated as 2% of the volume of the high-strength geopolymer mortar; The low quality silica fume contains at least the following components with the mass percentage: 50~85% of SiO2, 0~20% of Al2O3 and 0~20% of K2O, the particle size of the nano-silica is 5~20 nm, and the nano-silica is dispersed by ultrasonic before being mixed into the geopolymer mortar, the ultrasonic power is 100 W, and the ultrasonic dispersion treatment time is 30 min.

2. The high-strength geopolymeric mortar containing low-quality silica ash according to claim 1, characterized by, The low calcium fly ash contains at least the following components with the mass percentage: 35~50% of SiO2, 15~25% of Al2O3 and 9~10% of CaO.

3. The high-strength geopolymer mortar containing low-quality silica ash according to claim 1 or 2, characterized by, The calcium aluminate cement contains at least the following components with the mass percentage: 70~80% of Al2O3 and 20~30% of CaO.

4. The high-strength geopolymeric mortar containing low-quality silica ash according to claim 3, characterized by, The particle size of the quartz sand is 180~380 μm.

5. The high-strength geopolymeric mortar containing low-quality silica ash according to claim 4, characterized by, The steel fibers have a diameter of 0.12 mm, a length of 13 mm, and a density of 7850 kg / m 3 .

6. The high-strength geopolymeric mortar containing low-quality silica ash according to claim 5, characterized by, The modulus of the water glass solution is 2.3, and the solid content is 43.5%.

7. A method of producing a high-strength geopolymer mortar containing low-quality silica ash according to any one of claims 1 to 6, characterized by, First, the alkali activator is prepared by using solid sodium hydroxide, water glass solution and tap water as raw materials and standing at room temperature; the low calcium fly ash, calcium aluminate cement, low quality silica fume and nano-silica are mixed and stirred, then the quartz sand is added and continuously stirred to make them uniformly mixed, finally the alkali activator after standing is added and continuously stirred, the steel fiber is slowly added during stirring to make it more uniformly dispersed, and finally the high-strength geopolymer mortar with good fluidity is obtained.

8. The method of claim 7, wherein the high-strength geopolymer mortar containing low-quality silica fume is prepared by mixing the following components: a geopolymer binder, a silica fume, a fine aggregate, a coarse aggregate, a superplasticizer, a water reducer, a water, and a curing agent. The specific preparation method of the alkali activator is as follows: the water amount is calculated according to the water-binder ratio of 0.24, the sodium hydroxide particles are prepared into a sodium hydroxide solution with a concentration of 10.5 mol / L, the sodium hydroxide solution is mixed and stirred with the water glass solution to obtain an alkali activator with a modulus of 1.3.

Images