A cementitious material, ultra-high performance concrete and preparation method thereof

Abstract

The present invention belongs to the technical field of high-strength concrete, and specifically relates to a cementitious material and ultra-high performance concrete and a preparation method. The cementitious material is made by mixing and grinding lime, slag powder, fly ash, desulfurized gypsum, and an activator. The ultra-high performance concrete is made of the cementitious material and microbeads, machine-made sand, steel fiber, a water reducer, and water. The ultra-high performance concrete prepared by using the cementitious material has the advantages of low shrinkage and high compressive strength under natural curing conditions, and the cost is low. The ultra-high performance concrete is suitable for a variety of concrete construction engineering fields such as large-volume abutments and bridge heads.

Description

Technical Field

[0001] The invention belongs to the technical field of high-strength concrete, and specifically relates to a cementitious material and ultra-high performance concrete and a preparation method thereof. Background Art

[0002] Ultra-high performance concrete (UHPC) has super high mechanical properties and super durability. It has been adopted by many engineering projects in recent years. However, since its mix ratio is mainly composed of powder materials and quartz sand, and a large amount of steel fiber is added to improve its mechanical properties, although it has many advantages, it also has disadvantages that cannot be ignored. For example, its extremely low water-binder ratio causes its shrinkage to be much greater than that of ordinary concrete. Problems such as cracking and voiding caused by shrinkage have greatly restricted the promotion and application of UHPC. Therefore, shrinkage has become one of the focuses of UHPC research today, and has attracted much attention from scholars at home and abroad.

[0003] Although some research has been conducted on the shrinkage of UHPC at home and abroad, the current research is mainly based on the test results of steam-cured UHPC, and there are few studies on the shrinkage of UHPC under room temperature curing. In addition, in order to reduce the excessive shrinkage of UHPC under room temperature curing, compensating shrinkage components such as expansion agents are generally added to UHPC to compensate for the rapid development of UHPC's early self-shrinkage and reduce the risk of early shrinkage cracking of UHPC structures. However, the addition of compensating shrinkage components will change the internal microstructure of UHPC, thereby affecting its strength growth.

[0004] Patent documents CN201210126903.5 (CN102633525A), CN202410645646.9 (CN118529996A), CN202410340244.8 (CN118271058A) and the like provide a variety of concrete materials, but their strength is low or their shrinkage rate is large, which makes it difficult to meet the needs of large-volume buildings.

[0005] Therefore, the large shrinkage and easy cracking (and high cost) of UHPC materials after construction are the main bottlenecks for the large-scale promotion and application of UHPC materials. In the preparation process of UHPC, it is urgent to effectively reduce the shrinkage of concrete, improve the strength of concrete, reduce the amount of cement and material costs, and effectively solve the problem of large shrinkage deformation of traditional UHPC and reduce the risk of cracking of structures or components. Summary of the invention

[0006] In view of the above problems, the present invention provides a cementitious material and ultra-high performance concrete suitable for large-volume concrete building structures and a preparation method thereof, which can reduce the shrinkage rate of concrete, improve strength and reduce cost. The technical solution of the present invention is as follows:

[0007] First: A cementitious material made by mixing and grinding lime, slag powder, fly ash, desulfurized gypsum and activator.

[0008] Preferably, the weight ratio of lime, slag powder, fly ash, desulfurized gypsum and activator in the cementitious material is (1-2):70:(12-13):(15-16):1. Further preferably, the weight ratio of lime, slag powder, fly ash, desulfurized gypsum and activator in the cementitious material is 2:70:12:15:1.

[0009] Preferably, the lime is grade II quicklime.

[0010] Preferably, the slag powder is S95 grade slag.

[0011] Preferably, the fly ash is Class I fly ash, and the total content of silicon dioxide, aluminum oxide and iron oxide in the fly ash is >75 wt %.

[0012] Preferably, the desulfurized gypsum complies with the requirements of GB / T23456-2009 standard, the P2O5 content of the desulfurized gypsum is 0.6-0.8wt%, and the radioactivity of the desulfurized gypsum meets the requirements of GB6566 standard.

[0013] Preferably, the activator is a mixture of industrial-grade solid sodium silicate and aluminum sulfate, the weight ratio of the sodium silicate to the aluminum sulfate is 1:1, the soluble solid content of the sodium silicate is ≥98.5wt%, the modulus of the sodium silicate is 1.2~1.5, and the aluminum sulfate is in anhydrous powder form.

[0014] Second: an ultra-high performance concrete, made of the aforementioned cementitious material, microspheres, machine-made sand, steel fiber, water reducer, and water. The raw materials used in the ultra-high performance concrete include, by weight: 900-960 parts of cementitious material, 100-120 parts of microspheres, 920-970 parts of machine-made sand, 240-310 parts of steel fiber, 20-30 parts of water reducer, and 170-195 parts of water.

[0015] Preferably, the microbead sphericity is ≥ 0.95.

[0016] Preferably, the roundness of the machine-made sand is ≥0.85.

[0017] Preferably, the steel fiber has a diameter of 2 mm to 6 mm, a length of 32 mm to 38 mm, a compressive strength of >1100 MPa, and an elastic modulus of 200 GPa to 210 GPa; further preferably, the steel fiber is a steel fiber surface-modified with aminopropyltriethoxysilane (KH550) and nano-SiO2.

[0018] Preferably, the water reducing efficiency of the water reducing agent is ≥40%; further preferably, the water reducing agent is a polycarboxylate water reducing agent.

[0019] Third: The preparation method of the aforementioned ultra-high performance concrete comprises the following steps:

[0020] S1: Mix lime, slag powder, fly ash, desulfurized gypsum and activator and grind them to obtain a cementitious material;

[0021] S2: adding the gelling material and the micro beads into a mixer and dry mixing them to obtain a primary mixture;

[0022] S3: adding machine-made sand and steel fiber to the primary mixture of step S2, and stirring and mixing with a mixer to obtain a secondary mixture;

[0023] S4: dissolving the water reducing agent in water, and then adding the water reducing agent into the secondary mixture of step S3, and stirring the mixture with a mixer for ≥5 min to obtain ultra-high performance concrete.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] (1) The present invention uses an optimized cementitious material. Compared with cement, the cost of cementitious materials is relatively low, which can improve the shrinkage of concrete and further reduce the production cost of concrete. At the same time, it can also consume a large amount of solid waste materials such as slag and fly ash, and reduce the demand for raw materials such as cement and silica fume in engineering construction, which has important social and economic benefits in road engineering.

[0026] (2) The UHPC provided by the present invention has low hydration heat and small autogenous shrinkage value. The 7d autogenous shrinkage value is less than 100 μm / m, and the 28d autogenous shrinkage value is less than 200 μm / m, which is much lower than that of traditional UHPC.

[0027] (3) The mechanical properties and strength indexes of the UHPC of the present invention are comparable to those of conventional UHPC, and the 28d compressive strength is as high as 100MPa under normal curing conditions.

[0028] (4) The UHPC of the present invention can be used in various concrete construction engineering fields such as large-volume abutments and bridge heads. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a comparison diagram of the hydration heat of the concrete of the present invention and the comparative concrete. DETAILED DESCRIPTION

[0030] The technical scheme of the present invention is shown and described below in conjunction with the embodiments and drawings. It should be understood that the embodiments are for the purpose of illustrating some preferred examples, and are not intended to limit the scope of protection of the present invention. Without departing from the technical ideas of the present invention, other equivalent or improved schemes obtained without creative labor should belong to the scope of protection of the present invention.

[0031] Unless otherwise specified, the reagents and instruments used in the following examples are all commercially available products or can be prepared by yourself; the performance indicators and test methods are all conventional methods in the art.

[0032] The ultra-high performance concrete (UHPC) of the present invention is prepared by using the following raw materials: 900-960 parts by weight of cementitious material, 100-120 parts by weight of microspheres, 920-970 parts by weight of machine-made sand, 240-310 parts of steel fiber, 20-30 parts of water reducer, and 170-195 parts of water.

[0033] The specific surface area of ​​the cementitious material in the UHPC of the present invention should be ≥400m 2 / kg, the specific surface area of ​​the gelling material can be adjusted by grinding and refining through a grinding process in the preparation of the gelling material, which is a conventional technology well known in the art.

[0034] In the embodiment, the water reducer adopts TK-101A polycarboxylate water reducer, but other water reducers meeting the water reduction rate requirements or other polycarboxylate water reducers meeting the water reduction rate requirements may also be adopted. In the embodiment, the microspheres adopt glass microspheres to fill the tiny gaps inside the concrete, thereby reducing the porosity and improving the density of the concrete. However, other microspheres meeting the sphericity requirements may also be adopted. The steel fiber used in the embodiment is obtained by surface modification of aminopropyltriethoxysilane (KH550) and nano-SiO2, and is end hook-shaped, with a diameter of 2mm~6mm, a length of 32mm~38mm, a compressive strength>1100MPa, and an elastic modulus of 200~210GPa. Commercially available products can be used or they can be prepared by themselves according to the literature method (Tian Jiefu, Yang Zhenjun, Yang Guojun, et al. Parameter optimization and mechanical properties of ultra-high performance concrete with silane-nano-SiO2 composite surface modified steel fiber [J]. Journal of Composite Materials, 2024, 42: 1-10.). The steel fiber in this study was prepared using the method in the literature.

[0035] The following are the raw material requirements and descriptions in the examples (Table 1):

[0036] Table 1 Raw material performance requirements and actual measured performance parameters of raw materials in the examples

[0037]

[0038] The following is a method for preparing UHPC in the embodiment, comprising the following steps:

[0039] S1: Take lime, slag powder, fly ash, desulfurized gypsum and activator, mix and grind to obtain a cementitious material;

[0040] S2: adding the gelling material and the micro beads into a mixer and dry mixing them to obtain a primary mixture;

[0041] S3: adding machine-made sand and steel fiber to the primary mixture of step S2, and stirring and mixing with a mixer to obtain a secondary mixture;

[0042] S4: dissolving the water reducing agent in water, and then adding it to the secondary mixture of step S3, stirring with a mixer for ≥5 min (the stirring time in Examples 1 and 2 is 5 min to 7 min) to obtain UHPC.

[0043] In Examples 1 and 2, the UHPC in the test group and the control group were prepared into concrete parts with the same specifications (150 cm 3 The cube was molded and cured under the same conditions (molding temperature 20±5℃, relative humidity ≥50%, standing for 36 hours after molding and then demolding and curing; curing temperature 20±2℃, relative humidity ≥95%) and tested.

[0044] Example 1 Preparation of cementitious materials and UHPC

[0045] Three kinds of cementitious materials and UHPC were prepared according to the ingredient list in Table 2. The specific surface area of ​​the cementitious materials was adjusted by a grinding process. Three kinds of cementitious materials and three kinds of UHPC were prepared in sequence according to the above steps S1 to S4, and the raw material performance parameters are shown in Table 1.

[0046] The weight ratio of lime, slag powder, fly ash, desulfurized gypsum and activator in the cementitious material of test group 1 is 2:70:12:15:1; the stirring time of the mixer in step S4 is 5 minutes.

[0047] In the cementitious material of test group 2, the weight ratio of lime, slag powder, fly ash, desulfurized gypsum and activator is 1:70:12:16:1; the stirring time of the mixer in step S4 is 6 minutes.

[0048] In the cementitious material of test group 3, the weight ratio of lime, slag powder, fly ash, desulfurized gypsum and activator is 1:70:13:15:1; the stirring time of the mixer in step S4 is 7 minutes.

[0049] Table 2 Ingredients of different UHPC (weight ratio)

[0050]

[0051] Example 2 Performance of UHPC

[0052] The comparative UHPC (control group) was prepared according to the ingredients in Table 2, in which the cementitious material used PI 42 5 reference cement (the specific surface area was adjusted by grinding process). Then the comparative UHPC was prepared according to steps S2-S4. The slump, shrinkage and compressive strength of the UHPC in test groups 1-3 and the control group were measured respectively, and the hydration heat reaction of the test group 1 and the control group was monitored. Both groups of tests used a water-binder ratio of 0.5 and were tested at a hydration temperature of 20°C. The total test time was 100 hours. After the test, the hydration heat reaction exotherm was drawn according to the hydration heat data.

[0053] Table 3 Performance parameters of different UHPC

[0054]

[0055] From Table 3, it can be found that the shrinkage of UHPC in test groups 1 to 3 is greatly reduced compared with that of the control UHPC. Under the same natural curing conditions, the compressive strength of 7 to 28 days is equivalent to that of the control UHPC. Figure 1 It can be seen from the hydration heat release diagram that as the hydration reaction proceeds, the hydration heat release of the early test group 1 UHPC is lower than that of the control UHPC. It can be seen that the use of the UHPC of the present invention can further reduce the production cost of concrete while improving the shrinkage of concrete, and can also consume a large amount of solid waste materials such as slag and fly ash, and can also reduce the demand for raw materials such as cement and silica fume in engineering construction, which will have important social and economic benefits in road engineering.

Claims

1. An ultra-high performance concrete suitable for large volumes prepared from a cementitious material, characterized in that: The raw materials used in the ultra-high performance concrete include, by weight: 900-960 parts of cementitious materials, 100-120 parts of microspheres, 920-970 parts of machine-made sand, 240-310 parts of steel fibers, 20-30 parts of water reducers, and 170-195 parts of water; the cementitious materials are prepared by mixing and grinding lime, slag powder, fly ash, desulfurized gypsum, and an activator; the weight ratio of lime, slag powder, fly ash, desulfurized gypsum, and an activator in the cementitious materials is (1-2):70:(12-13):(15-16):1; the lime is grade II quicklime; the slag powder is grade S95 slag; the fly ash is grade I fly ash, and the total content of silicon dioxide, aluminum oxide, and iron oxide in the fly ash is greater than 75wt%. ; the desulfurized gypsum complies with the requirements of GB / T23456-2009 standard, and the P2O5 content of the desulfurized gypsum is 0.6-0.8wt%; the activator is a mixture of industrial-grade solid sodium silicate and aluminum sulfate, the weight ratio of the sodium silicate to the aluminum sulfate is 1:1, the soluble solid content of the sodium silicate is ≥98.5wt%, and the modulus of the sodium silicate is 1.2-1.

5.

2. The ultra-high performance concrete according to claim 1, characterized in that: The sphericity of the micro-beads is ≥0.95; the sphericity of the machine-made sand is ≥0.85; and the water reducing efficiency of the water reducing agent is ≥40%.

3. The ultra-high performance concrete according to claim 1, characterized in that: The steel fiber has a diameter of 2 mm to 6 mm, a length of 32 mm to 38 mm, a compressive strength of >1100 MPa, and an elastic modulus of 200 GPa to 210 GPa.

4. The ultra-high performance concrete according to claim 1, characterized in that: The steel fiber is a steel fiber surface-modified with aminopropyltriethoxysilane and nano-SiO2; and the water reducer is a polycarboxylic acid water reducer.

5. The method for preparing ultra-high performance concrete according to claim 1, characterized in that: The steps include: S1: Mix lime, slag powder, fly ash, desulfurized gypsum and activator and grind them to obtain a cementitious material; S2: adding the gelling material and the micro beads into a mixer and dry mixing them to obtain a primary mixture; S3: adding machine-made sand and steel fiber to the primary mixture of step S2, and stirring and mixing with a mixer to obtain a secondary mixture; S4: dissolving the water reducing agent in water, and then adding the water reducing agent into the secondary mixture of step S3, and stirring the mixture with a mixer for ≥5 min to obtain ultra-high performance concrete.

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