Moderate heat tensile cement and preparation method thereof

Abstract

The present invention relates to the technical field of medium-heat cement, and discloses a medium-heat tensile cement and a preparation method thereof, comprising calcium oxide, calcium silicate, dicalcium silicate, tricalcium silicate, tricalcium aluminate, tetracalcium aluminoferrate, metakaolin, iron ore powder, modified cotton stalk fiber, modified nano-silicon dioxide, sulfur trioxide and magnesium oxide. The present invention effectively improves the early compressive strength, flexural strength and splitting tensile strength of cement by using modified cotton stalk fiber, and reduces the damage of modified cotton stalk fiber under alkaline conditions by using nano-silicon dioxide, thereby improving the durability of cement. At the same time, the amide group grafted on the surface of the modified nano-silicon dioxide reacts with the hydroxyl group on the surface of the modified cotton stalk fiber to form a strong hydrogen bond, thereby further improving the tensile strength of cement and improving the mechanical properties of cement.

Description

Technical Field

[0001] The invention relates to the technical field of medium-heat cement, and in particular to medium-heat tensile cement and a preparation method thereof. Background Art

[0002] Medium-heat cement, as a type of cement with excellent performance under specific temperature conditions, has been widely used in the fields of construction and engineering. In terms of tensile strength, low-heat cement concrete has better crack resistance than medium-heat cement concrete. Cracks will occur when temperature stress exceeds the ultimate tensile strength of concrete. If the cracks are expanded into harmful cracks due to improper maintenance, they will cause irreversible damage to the safety of the concrete structure. Medium-heat cement is prone to cracks and fractures in certain environments. This is mainly because the thermal stress generated by its internal structure during the heating process cannot be effectively released. Due to its low tensile strength, medium-heat cement is prone to cracks when external forces act or the temperature changes drastically, which greatly limits its use in some high-demand application scenarios. Summary of the invention

[0003] Based on the above problems, the present invention provides a medium-heat tensile cement and a preparation method thereof, which can improve its early compressive strength, flexural strength, splitting tensile strength, and improve its mechanical properties under alkaline conditions.

[0004] In order to achieve the above technical effects, the technical solution adopted by the present invention is:

[0005] A medium-heat tensile cement comprises, by weight, 160-190 parts of calcium oxide, 3-15 parts of calcium silicate, 10-20 parts of dicalcium silicate, 20-30 parts of tricalcium silicate, 15-30 parts of tricalcium aluminate, 8-13 parts of tetracalcium aluminoferrite, 20-35 parts of metakaolin, 6-12 parts of iron ore powder, 3-8 parts of modified cotton stalk fiber, 17-28 parts of modified nano silicon dioxide, 4-8 parts of sulfur trioxide and 3-7 parts of magnesium oxide.

[0006] Furthermore, the preparation of the modified cotton stalk fiber comprises the following steps:

[0007] S11, drying and grinding cotton stalk fibers to obtain cotton stalk particles, wherein the moisture content of the cotton stalk particles is 7-10%;

[0008] S12, soaking the cotton stalk particles in a sodium hydroxide solution for 3-5 hours, washing with water after the soaking, and drying after the washing, wherein the mass concentration of the sodium hydroxide solution is 11-13%;

[0009] S13, spraying a sodium silicate solution onto the surface of the alkalized cotton stalk particles, and drying the cotton stalk particles at 60-70° C. for 16-20 hours after spraying, wherein the concentration of the sodium silicate solution is 1-2%, and the mass ratio of the sodium silicate solution to the cotton stalk particles is 2:3-4.

[0010] Furthermore, the mass loss rate of the cotton stalk particles after alkalization treatment is 94-98%;

[0011] Specific mass loss rate The calculation formula is , is the mass after immersion in sodium hydroxide, is the initial mass.

[0012] Furthermore, the preparation of the modified nano-silicon dioxide comprises the following steps:

[0013] S21, grinding kaolin, calcining and keeping warm, and then cooling to room temperature;

[0014] S22, adding 15% by mass of hydrochloric acid to the first calcined kaolin, stirring continuously for 2 to 3 hours under a constant temperature water bath, and then washing, drying, and filtering;

[0015] S23, adding 20% ​​by mass sodium hydroxide solution to the kaolin treated by the first acidification, heating to 50-60° C., stirring continuously for 2-3 hours and then filtering;

[0016] S24, adding 10% by mass of hydrochloric acid to the kaolin treated with the first alkali to adjust the pH to 6-7, and then centrifuging and drying;

[0017] S25, calcining the kaolin subjected to the second acidification treatment at 500°C for 0.5-1h;

[0018] S26, add ethanol solution to the silica obtained by the second calcination treatment and stir; after dispersion is complete, add 8-10% by mass fraction of silane coupling agent LH-A110 solution dropwise thereto, and at the same time, heat to 120-140°C at a rate of 10-15°C / min, keep stirring for 1-2h, cool down, wash, and dry; the ethanol solution ;

[0019] S27. Dissolve sodium stearate in toluene, add silica powder modified by silane coupling agent, raise the temperature to 40-50°C and stir to react for 1-2 hours. After the reaction, centrifuge, wash, dry and grind to obtain modified nano-silica with a particle size of 16-20 nm; the amount of sodium stearate used is 12-15% of the amount of silica powder modified by silane coupling agent.

[0020] Furthermore, the first calcination of kaolin comprises the following steps:

[0021] S211, keeping the kaolin at 150-170° C. for 0.3-0.5 h to remove adsorbed water;

[0022] S212. Keep the kaolin from which adsorbed water has been removed at 300-400°C for 0.3-0.5h, and then raise the temperature to 800-850°C at a rate of 10-20°C / min.

[0023] Further, the following steps are included:

[0024] S1. Prepare, by weight, 160-190 parts of calcium oxide, 3-15 parts of calcium silicate, 10-20 parts of dicalcium silicate, 20-30 parts of tricalcium silicate, 15-30 parts of tricalcium aluminate, 8-13 parts of tetracalcium aluminoferrite, 20-35 parts of metakaolin, 6-12 parts of iron ore powder, 3-8 parts of modified cotton stalk fiber, 17-28 parts of modified nano-silicon dioxide, 4-8 parts of sulfur trioxide, and 3-7 parts of magnesium oxide;

[0025] S2, grinding the raw materials in step S1, the fineness of 0.08mm sieve residue is 19.0±1.5%, the 0.2mm sieve residue is 3.0%±0.8%; the raw material moisture content is ≤0.7%;

[0026] S3. Press the ground raw material into a test cake with a diameter of 10±2 cm and a thickness of 1±0.2 cm, calcine it at 1500~1600℃ for 20~30min, and cool it to room temperature to obtain cement.

[0027] Furthermore, the ratio of coal used at the head and tail of the kiln during the calcination process is controlled at 40%:60%; the clinker N value must match the kiln output; when clinker N = 3.50, the raw material feed into the kiln is 241 tons / hour and the clinker output is 3540 tons / day; when clinker N = 3.80, the raw material feed into the kiln is 204 tons / hour and the clinker output is 3250 tons / day; f-CaO is controlled at 0.5±0.3%; and the clinker loss on ignition is controlled within 0.6%.

[0028] Furthermore, the specific surface area of ​​the cement is 400-500m 2 / kg.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] 1. Modification of cement by cotton stalk fiber enhances its reinforcement strength, but it reduces the density of cement and increases the voids, which reduces its strength. Modification of cotton stalk fiber increases its compatibility with cement and bonding strength, improves the density and stiffness of the fiber, reduces the capillary channels and pores formed with cement, and provides more sufficient water for cement hydration reaction at the same water-cement ratio, effectively improving its early compressive strength, flexural strength, and splitting tensile strength. However, under alkaline conditions, its long-term degradation durability is low.

[0031] 2. Adding nano-silicon dioxide to cement, it reacts with it under alkaline conditions to generate silicon-silicon bonds, which self-assemble on the surface of the hydrated phase to form a three-dimensional molecular film, reducing the damage of alkaline conditions to the modified cotton stalk fiber and improving the durability of cement. However, the dispersibility of nano-silicon dioxide in cement is low and it is easy to agglomerate. Surface modification is performed to make it have good dispersibility, greatly improving the performance of cement while facilitating construction. At the same time, the amide group grafted on the surface of the modified nano-silicon dioxide reacts with the hydroxyl group on the surface of the modified cotton stalk fiber to generate a strong hydrogen bond, further improving the tensile strength of the cement and improving the mechanical properties of the cement. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is a SEM image of the fusion bonding of the hardened cement paste cotton stalk fiber and cement in the cement mortar test block in Example 2;

[0033] Figure 2 This is the SEM image of the nano-silicon dioxide film formed on the surface of the cotton stalk fiber modified by the hardened cement slurry in the cement mortar test block in Example 2. DETAILED DESCRIPTION

[0034] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with embodiments and drawings. The exemplary embodiments of the present invention and their description are only used to explain the present invention and are not intended to limit the present invention.

[0035] Embodiment 1:

[0036] A medium-heat tensile cement comprises, by weight, 160-190 parts of calcium oxide, 3-15 parts of calcium silicate, 10-20 parts of dicalcium silicate, 20-30 parts of tricalcium silicate, 15-30 parts of tricalcium aluminate, 8-13 parts of tetracalcium aluminoferrite, 20-35 parts of metakaolin, 6-12 parts of iron ore powder, 3-8 parts of modified cotton stalk fiber, 17-28 parts of modified nano silicon dioxide, 4-8 parts of sulfur trioxide and 3-7 parts of magnesium oxide.

[0037] The preparation method of modified cotton stalk fiber comprises:

[0038] S11, drying and grinding cotton stalk fibers to obtain cotton stalk particles, wherein the moisture content of the cotton stalk particles is 7-10%;

[0039] S12, soaking the cotton stalk particles in a sodium hydroxide solution for 3-5 hours, washing with water after the soaking, and drying after the washing, wherein the mass concentration of the sodium hydroxide solution is 11-13%;

[0040] S13, spraying a sodium silicate solution onto the surface of the alkalized cotton stalk particles, and drying the cotton stalk particles at 60-70° C. for 16-20 hours after spraying, wherein the concentration of the sodium silicate solution is 1-2%, and the mass ratio of the sodium silicate solution to the cotton stalk particles is 2:3-4.

[0041] The preparation method of modified nano silicon dioxide comprises:

[0042] S21, grinding kaolin, calcining and keeping warm, and then cooling to room temperature;

[0043] S22, adding 15% by mass of hydrochloric acid to the first calcined kaolin, stirring continuously for 2 to 3 hours under a constant temperature water bath, and then washing, drying, and filtering;

[0044] S23, adding 20% ​​by mass sodium hydroxide solution to the kaolin treated by the first acidification, heating to 50-60° C., stirring continuously for 2-3 hours and then filtering;

[0045] S24, adding 10% by mass of hydrochloric acid to the kaolin treated with the first alkali to adjust the pH to 6-7, and then centrifuging and drying;

[0046] S25, calcining the kaolin subjected to the second acidification treatment at 500°C for 0.5-1h;

[0047] S26, add ethanol solution to the silica obtained by the second calcination treatment and stir; after dispersion is complete, add 8-10% by mass fraction of silane coupling agent LH-A110 solution dropwise thereto, and at the same time, heat to 120-140°C at a rate of 10-15°C / min, keep stirring for 1-2h, cool down, wash, and dry; the ethanol solution ;

[0048] S27, dissolving sodium stearate in toluene, adding silica powder modified by silane coupling agent, heating to 40-50°C and stirring for reaction for 1-2h, centrifuging, washing, drying and grinding after the reaction to obtain modified nano-silicon dioxide with a particle size of 16-20nm; the amount of sodium stearate used is 12-15% of the amount of silica powder modified by silane coupling agent;

[0049] The first calcination of kaolin comprises the following steps:

[0050] S11, keeping the kaolin at 150-170° C. for 0.3-0.5 h to remove adsorbed water;

[0051] S12. Keep the kaolin from which adsorbed water has been removed at 300-400°C for 0.3-0.5h, and then heat it to 800-850°C at a rate of 10-20°C / min to increase its reaction activity with acid for modification.

[0052] In the present embodiment, cement is modified by cotton stalk fiber, and its reinforcement strength is enhanced, but it makes the compactness of cement decrease, and the space increases, so that its strength is reduced, and by modifying cotton stalk fiber, its compatibility and bonding strength to cement are increased, and the density and rigidity of fiber are improved, and the capillary channel and pore formed with cement are reduced, and under the same water-cement ratio, it provides more sufficient water for cement hydration reaction, effectively improves its compressive strength, flexural strength, splitting tensile strength in early stage, but under alkaline conditions, its long-term deterioration durability is lower. Nano silicon dioxide is added to cement, and it reacts with it under alkaline conditions to generate silicon oxygen silicon bond, and self-assembly forms a three-dimensional molecular film on the hydration phase surface, reduces the damage of alkaline conditions to modified cotton stalk fiber, and improves the durability of cement. But the dispersibility of nano silicon dioxide in cement is lower, and it is easy to reunite, and surface modification is carried out to it, so that it has good dispersibility, greatly improves the performance of cement, and is easy to construct. At the same time, the amide groups grafted on the surface of modified nano-silica react with the hydroxyl groups on the surface of modified cotton stalk fibers to generate strong hydrogen bonds, further improving the tensile strength of cement and improving the mechanical properties of cement.

[0053] Embodiment 2:

[0054] Cement samples for the test group and three control groups were prepared for use.

[0055] Test group: The cement components prepared in this test group have the following specific preparation process:

[0056] S1. Prepare, by weight, 160-190 parts of calcium oxide, 3-15 parts of calcium silicate, 10-20 parts of dicalcium silicate, 20-30 parts of tricalcium silicate, 15-30 parts of tricalcium aluminate, 8-13 parts of tetracalcium aluminoferrite, 20-35 parts of metakaolin, 6-12 parts of iron ore powder, 3-8 parts of modified cotton stalk fiber, 17-28 parts of modified nano-silicon dioxide, 4-8 parts of sulfur trioxide, and 3-7 parts of magnesium oxide;

[0057] S2, grinding the raw materials in step S1, the fineness of 0.08mm sieve residue is 19.0±1.5%, the 0.2mm sieve residue is 3.0%±0.8%; the raw material moisture content is ≤0.7%;

[0058] S3. Press the ground raw material into a test cake with a diameter of 10±2 cm and a thickness of 1±0.2 cm, calcine it at 1500~1600℃ for 20~30min, and cool it to room temperature to obtain cement.

[0059] The ratio of coal used at the head and tail of the kiln during the calcination process is controlled at 40%:60%; the clinker N value should match the kiln output; when clinker N = 3.50, the raw material input into the kiln is 241 tons / hour, and the clinker output is 3540 tons / day; when clinker N = 3.80, the raw material input into the kiln is 204 tons / hour, and the clinker output is 3250 tons / day; f-CaO is controlled at 0.5±0.3%; the clinker ignition loss is controlled within 0.6%. The specific surface area of ​​the cement is 400~500m 2 / kg.

[0060] The preparation method of modified cotton stalk fiber comprises:

[0061] S11, drying and grinding cotton stalk fibers to obtain cotton stalk particles, wherein the moisture content of the cotton stalk particles is 7-10%;

[0062] S12, soaking the cotton stalk particles in a sodium hydroxide solution for 3-5 hours, washing with water after the soaking, and drying after the washing, wherein the mass concentration of the sodium hydroxide solution is 11-13%;

[0063] S13, spraying a sodium silicate solution onto the surface of the alkalized cotton stalk particles, and drying the cotton stalk particles at 60-70° C. for 16-20 hours after spraying, wherein the concentration of the sodium silicate solution is 1-2%, and the mass ratio of the sodium silicate solution to the cotton stalk particles is 2:3-4.

[0064] The mass loss rate of the cotton stalk particles after alkalization treatment is 94-98%;

[0065] Specific mass loss rate The calculation formula is , is the mass after immersion in sodium hydroxide, is the initial mass.

[0066] The preparation method of modified nano silicon dioxide comprises:

[0067] S21, grinding kaolin, calcining and keeping warm, and then cooling to room temperature;

[0068] S22, adding 15% by mass of hydrochloric acid to the first calcined kaolin, stirring continuously for 2 to 3 hours under a constant temperature water bath, and then washing, drying, and filtering;

[0069] S23, adding 20% ​​by mass sodium hydroxide solution to the kaolin treated by the first acidification, heating to 50-60° C., stirring continuously for 2-3 hours and then filtering;

[0070] S24, adding 10% by mass of hydrochloric acid to the kaolin treated with the first alkali to adjust the pH to 6-7, and then centrifuging and drying;

[0071] S25, calcining the kaolin subjected to the second acidification treatment at 500°C for 0.5-1h;

[0072] S26, add ethanol solution to the silica obtained by the second calcination treatment and stir; after dispersion is complete, add 8-10% by mass fraction of silane coupling agent LH-A110 solution dropwise thereto, and at the same time, heat to 120-140°C at a rate of 10-15°C / min, keep stirring for 1-2h, cool down, wash, and dry; the ethanol solution ;

[0073] S27, dissolving sodium stearate in toluene, adding silica powder modified by silane coupling agent, heating to 40-50°C and stirring for reaction for 1-2h, centrifuging, washing, drying and grinding after the reaction to obtain modified nano-silicon dioxide with a particle size of 16-20nm; the amount of sodium stearate used is 12-15% of the amount of silica powder modified by silane coupling agent;

[0074] The first calcination of kaolin comprises the following steps:

[0075] S11, keeping the kaolin at 150-170° C. for 0.3-0.5 h to remove adsorbed water;

[0076] S12. Keep the kaolin from which adsorbed water has been removed at 300-400°C for 0.3-0.5h, and then heat it to 800-850°C at a rate of 10-20°C / min to increase its reaction activity with acid for modification.

[0077] Control group 1: Different from the experimental group, the cement component prepared in this control group does not contain modified cotton stalk fiber, and the formula and preparation method include:

[0078] S1. Prepare, by weight, 160-190 parts of calcium oxide, 3-15 parts of calcium silicate, 10-20 parts of dicalcium silicate, 20-30 parts of tricalcium silicate, 15-30 parts of tricalcium aluminate, 8-13 parts of tetracalcium aluminoferrite, 20-35 parts of metakaolin, 6-12 parts of iron ore powder, 17-28 parts of modified nano-silicon dioxide, 4-8 parts of sulfur trioxide, and 3-7 parts of magnesium oxide;

[0079] S2, grinding the raw materials in step S1, the fineness of 0.08mm sieve residue is 19.0±1.5%, the 0.2mm sieve residue is 3.0%±0.8%; the raw material moisture content is ≤0.7%;

[0080] S3. Press the ground raw material into a test cake with a diameter of 10±2 cm and a thickness of 1±0.2 cm, calcine it at 1500~1600℃ for 20~30min, and cool it to room temperature to obtain cement.

[0081] The ratio of coal used at the head and tail of the kiln during the calcination process is controlled at 40%:60%; the clinker N value should match the kiln output; when clinker N = 3.50, the raw material input into the kiln is 241 tons / hour, and the clinker output is 3540 tons / day; when clinker N = 3.80, the raw material input into the kiln is 204 tons / hour, and the clinker output is 3250 tons / day; f-CaO is controlled at 0.5±0.3%; the clinker ignition loss is controlled within 0.6%. The specific surface area of ​​the cement is 400~500m 2 / kg.

[0082] The preparation method of modified nano silicon dioxide comprises:

[0083] S21, grinding kaolin, calcining and keeping warm, and then cooling to room temperature;

[0084] S22, adding 15% by mass of hydrochloric acid to the first calcined kaolin, stirring continuously for 2 to 3 hours under a constant temperature water bath, and then washing, drying, and filtering;

[0085] S23, adding 20% ​​by mass sodium hydroxide solution to the kaolin treated by the first acidification, heating to 50-60° C., stirring continuously for 2-3 hours and then filtering;

[0086] S24, adding 10% by mass of hydrochloric acid to the kaolin treated with the first alkali to adjust the pH to 6-7, and then centrifuging and drying;

[0087] S25, calcining the kaolin subjected to the second acidification treatment at 500°C for 0.5-1h;

[0088] S26, add ethanol solution to the silica obtained by the second calcination treatment and stir; after dispersion is complete, add 8-10% by mass fraction of silane coupling agent LH-A110 solution dropwise thereto, and at the same time, heat to 120-140°C at a rate of 10-15°C / min, keep stirring for 1-2h, cool down, wash, and dry; the ethanol solution ;

[0089] S27, dissolving sodium stearate in toluene, adding silica powder modified by silane coupling agent, heating to 40-50°C and stirring for reaction for 1-2h, centrifuging, washing, drying and grinding after the reaction to obtain modified nano-silicon dioxide with a particle size of 16-20nm; the amount of sodium stearate used is 12-15% of the amount of silica powder modified by silane coupling agent;

[0090] The first calcination of kaolin comprises the following steps:

[0091] S11, keeping the kaolin at 150-170° C. for 0.3-0.5 h to remove adsorbed water;

[0092] S12. Keep the kaolin from which adsorbed water has been removed at 300-400°C for 0.3-0.5h, and then heat it to 800-850°C at a rate of 10-20°C / min to increase its reaction activity with acid for modification.

[0093] Control group 2: Different from the experimental group, the cement component prepared in this control group does not contain modified nano-silicon dioxide, and the formula and preparation method include:

[0094] S1. Prepare, by weight, 160-190 parts of calcium oxide, 3-15 parts of calcium silicate, 10-20 parts of dicalcium silicate, 20-30 parts of tricalcium silicate, 15-30 parts of tricalcium aluminate, 8-13 parts of tetracalcium aluminoferrite, 20-35 parts of metakaolin, 6-12 parts of iron ore powder, 3-8 parts of modified cotton stalk fiber, 4-8 parts of sulfur trioxide, and 3-7 parts of magnesium oxide;

[0095] S2, grinding the raw materials in step S1, the fineness of 0.08mm sieve residue is 19.0±1.5%, the 0.2mm sieve residue is 3.0%±0.8%; the raw material moisture content is ≤0.7%;

[0096] S3. Press the ground raw material into a test cake with a diameter of 10±2 cm and a thickness of 1±0.2 cm, calcine it at 1500~1600℃ for 20~30min, and cool it to room temperature to obtain cement.

[0097] The ratio of coal used at the head and tail of the kiln during the calcination process is controlled at 40%:60%; the clinker N value should match the kiln output; when clinker N = 3.50, the raw material input into the kiln is 241 tons / hour, and the clinker output is 3540 tons / day; when clinker N = 3.80, the raw material input into the kiln is 204 tons / hour, and the clinker output is 3250 tons / day; f-CaO is controlled at 0.5±0.3%; the clinker ignition loss is controlled within 0.6%. The specific surface area of ​​the cement is 400~500m 2 / kg.

[0098] The preparation method of modified cotton stalk fiber comprises:

[0099] S11, drying and grinding cotton stalk fibers to obtain cotton stalk particles, wherein the moisture content of the cotton stalk particles is 7-10%;

[0100] S12, soaking the cotton stalk particles in a sodium hydroxide solution for 3-5 hours, washing with water after the soaking, and drying after the washing, wherein the mass concentration of the sodium hydroxide solution is 11-13%;

[0101] S13, spraying a sodium silicate solution onto the surface of the alkalized cotton stalk particles, and drying the cotton stalk particles at 60-70° C. for 16-20 hours after spraying, wherein the concentration of the sodium silicate solution is 1-2%, and the mass ratio of the sodium silicate solution to the cotton stalk particles is 2:3-4.

[0102] The mass loss rate of the cotton stalk particles after alkalization treatment is 94-98%;

[0103] Specific mass loss rate The calculation formula is , is the mass after immersion in sodium hydroxide, is the initial mass.

[0104] Control group 3: Different from the test group, the cement component prepared in this control group does not contain modified cotton stalk fiber and modified nano-silicon dioxide, and the formula and preparation method include:

[0105] S1. Prepare, by weight, 160-190 parts of calcium oxide, 3-15 parts of calcium silicate, 10-20 parts of dicalcium silicate, 20-30 parts of tricalcium silicate, 15-30 parts of tricalcium aluminate, 8-13 parts of tetracalcium aluminoferrite, 20-35 parts of metakaolin, 6-12 parts of iron ore powder, 4-8 parts of sulfur trioxide, and 3-7 parts of magnesium oxide;

[0106] S2, grinding the raw materials in step S1, the fineness of 0.08mm sieve residue is 19.0±1.5%, the 0.2mm sieve residue is 3.0%±0.8%; the raw material moisture content is ≤0.7%;

[0107] S3. Press the ground raw material into a test cake with a diameter of 10±2 cm and a thickness of 1±0.2 cm, calcine it at 1500~1600℃ for 20~30min, and cool it to room temperature to obtain cement.

[0108] The ratio of coal used at the head and tail of the kiln during the calcination process is controlled at 40%:60%; the clinker N value should match the kiln output; when clinker N = 3.50, the raw material input into the kiln is 241 tons / hour, and the clinker output is 3540 tons / day; when clinker N = 3.80, the raw material input into the kiln is 204 tons / hour, and the clinker output is 3250 tons / day; f-CaO is controlled at 0.5±0.3%; the clinker ignition loss is controlled within 0.6%. The specific surface area of ​​the cement is 400~500m 2 / kg.

[0109] The cement obtained by grinding the control group and the test group was mixed with water and standard sand to prepare an "8"-shaped cement mortar test block with a length, width and thickness of 80×50×25mm, where the width of the narrowest part of the "8"-shaped neck was 24mm. After 3 days, each control group and test group took a group of samples to soak in an alkaline solution (NaOH solution concentration 350g / L, temperature 25℃) for 2h, and tested the tensile strength values ​​of cement mortar test blocks of different ages. There were 5 test blocks in each group, and the average of their test values ​​was taken as the final test value of the group.

[0110] Table 1: Cement tensile strength performance data table for the experimental group and the control group

[0111]

[0112] The above data show that the modification of cement by cotton stalk fiber can enhance its reinforcement strength, but it reduces the density of cement and increases the voids, which reduces its strength. By modifying the cotton stalk fiber, its compatibility with cement and bonding strength are increased, the density and stiffness of the fiber are improved, the capillary channels and pores formed with cement are reduced, and at the same water-cement ratio, it provides more sufficient water for the cement hydration reaction, effectively improving its early compressive strength, flexural strength, and splitting tensile strength. However, under alkaline conditions, its long-term degradation durability is low. Figure 1As shown, during cement hardening, cotton stalk fiber and cement are tightly bonded, and there are not many capillary channels and pores under the electron microscope image, which can improve the tensile strength of cement. Wherein, the test group and control group of the present embodiment only tested the compression test, and in fact, compression resistance, flexural strength, and splitting tensile strength are all related, such as tensile strength is generally 10~20% of compressive strength, flexural strength and splitting tensile strength are all affected by tensile strength or the cement test block of its part of the test position is in a tensile state, and the core of the present embodiment is to improve the tensile performance of cement test block, and compressive strength, flexural strength, and splitting tensile strength are all in the case where tensile strength is improved, and the secondary performance effect that can be brought when other components or processes are unchanged is improved. Nano silicon dioxide is added to cement, and it reacts with it under alkaline conditions to generate silicon oxygen silicon bond, and self-assembles on the hydration phase surface to form a three-dimensional molecular film, reduces the damage of alkaline conditions to modified cotton stalk fiber, and improves the durability of cement. However, nano-silicon dioxide has low dispersibility in cement and is easy to agglomerate. Surface modification can make it have good dispersibility, greatly improve the performance of cement and facilitate construction. At the same time, the amide group grafted on the surface of modified nano-silicon dioxide reacts with the hydroxyl group on the surface of modified cotton stalk fiber to form a strong hydrogen bond, which further improves the tensile strength of cement and improves the mechanical properties of cement. Figure 2 As shown, the modified silica is assembled into a molecular film that is coated on the cotton stalk fiber, and the tensile strength of the cotton stalk fiber acting on cement is enhanced, while the contact effect of the alkaline environment on the cotton stalk fiber is reduced, thereby reducing the corrosion effect.

[0113] The above is an embodiment of the present invention. The above embodiments and the specific parameters in the embodiments are only for the purpose of clearly describing the invention verification process, and are not intended to limit the patent protection scope of the present invention. The patent protection scope of the present invention is still subject to its claims. Any equivalent structural changes made by using the contents of the description and drawings of the present invention should be included in the protection scope of the present invention.

Claims

1. A medium heat tensile cement, characterized in that: In parts by weight: comprising 160-190 parts of calcium oxide, 3-15 parts of calcium silicate, 10-20 parts of dicalcium silicate, 20-30 parts of tricalcium silicate, 15-30 parts of tricalcium aluminate, 8-13 parts of tetracalcium aluminoferrite, 20-35 parts of metakaolin, 6-12 parts of iron ore powder, 3-8 parts of modified cotton stalk fiber, 17-28 parts of modified nano silicon dioxide, 4-8 parts of sulfur trioxide, and 3-7 parts of magnesium oxide; The preparation of the modified cotton stalk fiber comprises the following steps: S11, drying and grinding cotton stalk fibers to obtain cotton stalk particles, wherein the moisture content of the cotton stalk particles is 7-10%; S12, soaking the cotton stalk particles in a sodium hydroxide solution for 3-5 hours, washing with water after the soaking, and drying after the washing, wherein the mass concentration of the sodium hydroxide solution is 11-13%; S13, spraying a sodium silicate solution onto the surface of the alkalized cotton stalk particles, drying the cotton stalk particles at 60-70° C. for 16-20 hours after the spraying, wherein the concentration of the sodium silicate solution is 1-2%, and the mass ratio of the sodium silicate solution to the cotton stalk particles is 2:3-4; The preparation of the modified nano silicon dioxide comprises the following steps: S21, grinding kaolin, calcining and keeping warm, and then cooling to room temperature; S22, adding 15% by mass of hydrochloric acid to the first calcined kaolin, stirring continuously for 2 to 3 hours under a constant temperature water bath, and then washing, drying, and filtering; S23, adding 20% ​​by mass sodium hydroxide solution to the kaolin treated by the first acidification, heating to 50-60° C., stirring continuously for 2-3 hours and then filtering; S24, adding 10% by mass of hydrochloric acid to the kaolin treated with the first alkali to adjust the pH to 6-7, and then centrifuging and drying; S25, calcining the kaolin subjected to the second acidification treatment at 500°C for 0.5-1h; S26, add ethanol solution to the silicon dioxide obtained by the second calcination treatment and stir; after dispersion is complete, add 8-10% by mass fraction of silane coupling agent solution dropwise thereto, and at the same time, heat to 120-140°C at a rate of 10-15°C / min, keep stirring for 1-2h, cool down, wash and dry; the ethanol solution ; S27. Dissolve sodium stearate in toluene, add silica powder modified by silane coupling agent, raise the temperature to 40-50°C and stir to react for 1-2 hours. After the reaction, centrifuge, wash, dry and grind to obtain modified nano-silica with a particle size of 16-20 nm; the amount of sodium stearate used is 12-15% of the amount of silica powder modified by silane coupling agent.

2. The medium heat tensile cement according to claim 1, characterized in that: The mass loss rate of the cotton stalk particles after alkalization treatment is 94-98%; Specific mass loss rate The calculation formula is , is the mass after soaking in sodium hydroxide, is the initial mass.

3. The medium heat tensile cement according to claim 1, characterized in that: The first calcination of kaolin comprises the following steps: S211, keeping the kaolin at 150-170° C. for 0.3-0.5 h to remove adsorbed water; S212. Keep the kaolin from which adsorbed water has been removed at 300-400°C for 0.3-0.5h, and then raise the temperature to 800-850°C at a rate of 10-20°C / min.

4. A method for preparing moderate heat tensile cement, applied to the moderate heat tensile cement according to any one of claims 1 to 3, characterized in that: The following steps are involved: S1. Prepare, by weight, 160-190 parts of calcium oxide, 3-15 parts of calcium silicate, 10-20 parts of dicalcium silicate, 20-30 parts of tricalcium silicate, 15-30 parts of tricalcium aluminate, 8-13 parts of tetracalcium aluminoferrite, 20-35 parts of metakaolin, 6-12 parts of iron ore powder, 3-8 parts of modified cotton stalk fiber, 17-28 parts of modified nano-silicon dioxide, 4-8 parts of sulfur trioxide, and 3-7 parts of magnesium oxide; S2, grinding the raw materials in step S1, the fineness of 0.08mm sieve residue is 19.0±1.5%, the 0.2mm sieve residue is 3.0%±0.8%; the raw material moisture content is ≤0.7%; S3. Press the ground raw material into a test cake with a diameter of 10±2 cm and a thickness of 1±0.2 cm, calcine it at 1500~1600℃ for 20~30min, and cool it to room temperature to obtain cement.

5. The method for preparing a moderately hot tensile cement according to claim 4, characterized in that: The ratio of coal used at the head and tail of the kiln during the calcination process is controlled at 40%:60%; the clinker N value must match the kiln output; when clinker N=3.50, the raw material feed into the kiln is 241 tons / hour and the clinker output is 3540 tons / day; when clinker N=3.80, the raw material feed into the kiln is 204 tons / hour and the clinker output is 3250 tons / day; control f-CaO=0.5±0.3%; and control the clinker loss on ignition within 0.6%.

6. The method for preparing moderate heat tensile cement according to claim 4, characterized in that: The specific surface area of ​​the cement is 400-500m 2 / kg.

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