WO2023000476A1 - 一种纳米材料改性水泥钙质砂及其制作方法 - Google Patents

一种纳米材料改性水泥钙质砂及其制作方法 Download PDF

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WO2023000476A1
WO2023000476A1 PCT/CN2021/118576 CN2021118576W WO2023000476A1 WO 2023000476 A1 WO2023000476 A1 WO 2023000476A1 CN 2021118576 W CN2021118576 W CN 2021118576W WO 2023000476 A1 WO2023000476 A1 WO 2023000476A1
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calcareous sand
nano
cement
modified cement
calcareous
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PCT/CN2021/118576
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French (fr)
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胡俊
曾晖
李健
佳琳
曾东灵
王志鑫
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海南大学
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    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B20/00—Use of materials as fillers for mortars, concrete or artificial stone according to more than one of groups C04B14/00 - C04B18/00 and characterised by shape or grain distribution; Treatment of materials according to more than one of the groups C04B14/00 - C04B18/00 specially adapted to enhance their filling properties in mortars, concrete or artificial stone; Expanding or defibrillating materials
    • C04B20/10—Coating or impregnating
    • C04B20/1055—Coating or impregnating with inorganic materials
    • C04B20/1077—Cements, e.g. waterglass
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B14/00—Use of inorganic materials as fillers, e.g. pigments, for mortars, concrete or artificial stone; Treatment of inorganic materials specially adapted to enhance their filling properties in mortars, concrete or artificial stone
    • C04B14/02—Granular materials, e.g. microballoons
    • C04B14/04—Silica-rich materials; Silicates
    • C04B14/06—Quartz; Sand
    • C04B14/068—Specific natural sands, e.g. sea -, beach -, dune - or desert sand
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02W—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT
    • Y02W30/00—Technologies for solid waste management
    • Y02W30/50—Reuse, recycling or recovery technologies
    • Y02W30/91—Use of waste materials as fillers for mortars or concrete

Definitions

  • the invention relates to the field of calcareous sand, in particular to a nano-material modified cement calcareous sand and a preparation method thereof.
  • nanomaterials are used in many fields by virtue of their excellent performance and particularity, and are known as the most promising materials in the 21st century. With the further development of nanotechnology and nanomaterial manufacturing process, there are more and more types of nanomaterials and the production mode begins to appear in industrialized production. This reduces the cost of using nanomaterials and makes it possible to modify the mechanical properties of cement-based materials with nanomaterials.
  • nanomaterials have been added to cement-based materials as external admixtures to improve the strength of cement-based materials. When nanomaterials are mixed into cement-based materials, they can act as the core of loose soil particles or sand particles to form a dense network structure, thereby achieving the purpose of improving the mechanical properties of cement-based materials.
  • Nanomaterials have a certain development prospect in the application engineering of modified cement-based materials.
  • calcareous sands are irregular and angular in shape, and are mainly divided into dendritic skeleton sand particles, massive sand particles, flaky sand particles, and biological debris such as shells and conchs.
  • Calcareous sand and terrigenous sand have huge differences in mechanical properties and engineering properties.
  • the strength of calcareous sand is often difficult to meet the needs of the South China Sea island reef reclamation project, so in-depth research on modified calcareous sand is needed.
  • CN104496337A discloses nano-clay modified fiber cement mortar and its preparation method
  • CN110218054A discloses a nano-clay modified high-performance concrete and its preparation method and application. These preparation methods are not suitable for calcareous sand.
  • the present invention proposes a nanomaterial-modified cement calcareous sand and a manufacturing method thereof to solve the above-mentioned technical problems.
  • a nanometer material modified cement calcareous sand is made of calcareous sand, cement, nano magnesia and water, and the added amount of the nano magnesia is 0.5-2.0% of the weight of the calcareous sand.
  • the particle diameter of the nano magnesium oxide is 40nm-60nm, and the purity is 99.9% (by mass percentage).
  • the calcareous sand has a particle size of 0.25 mm to 1 mm, a coefficient of inhomogeneity of 3.53, a coefficient of curvature of 1.45, an air-dried moisture content of 0.81%, and a specific gravity of 2.702.
  • the added amount of the nano magnesium oxide is 1.0-1.5%, preferably 1.5%, of the weight of the calcareous sand.
  • the added amount of the cement is 10% of the weight of the calcareous sand.
  • the water content of the nano-material modified cement calcareous sand is 30%.
  • the preparation method of nanomaterial modified cement calcareous sand of the present invention comprises the following steps:
  • Calcareous sand preparation dry the calcareous sand after air-drying again, sieve, and set aside;
  • step (1) the size of the sieve is 2mm.
  • step (2) the mesh of the screen of the high-frequency vibrating screen is 0.1mm.
  • the first stirring time is 2-3 minutes
  • the second stirring time is 5-8 minutes
  • the third stirring time is 10-15 minutes.
  • the present invention adopts a certain amount of nano-magnesia modified cement calcareous sand to produce high-quality nanomaterial modified cement calcareous sand, and its compressive strength is significantly improved, and its internal friction angle, cohesion and peak stress It has been significantly improved, and the shear strength of the nano-material modified cement calcareous sand is improved, and the shear performance of the sample is improved.
  • the maintenance time can be significantly shortened, the construction period can be shortened, and the efficiency can be improved.
  • the CSH generated by the hydration reaction of cement can fill the pores on the surface of calcareous sand and improve the compactness of calcareous sand.
  • the present invention can promote cement hydration reaction by adding a certain amount of nano-MgO, and the fibrous CSH forms a dense network structure on the surface of calcareous sand particles.
  • the Mg(OH) 2 that can be generated by the hydrolysis of nano-MgO can also fill the pore structure of cement calcareous sand.
  • the calcareous sand used in the test of the present invention is taken from a certain area of Yongxing Island, Sansha City, Hainan province, and is loose and unbonded sand particles.
  • Embodiment 1 nano-magnesia modified cement calcareous sand
  • the particle size of calcareous sand is 0.25mm-1mm, the coefficient of inhomogeneity is 3.53, the coefficient of curvature is 1.45, the air-dried moisture content is 0.81%, and the specific gravity is 2.702.
  • element composition it mainly contains Ca and Mg elements.
  • the particle size of the selected nano magnesium oxide is 40nm-60nm, and the composition of the main compound (MgO) has a purity of 99.9% (by mass percentage).
  • the raw materials are composed of calcareous sand, cement, nano-magnesia and water, the amount of cement added is 10% of the weight of the calcareous sand, and the amount of added nano-magnesia is 0.5% of the weight of the calcareous sand.
  • Embodiment 2 nano-magnesia modified cement calcareous sand
  • the particle size of calcareous sand is 0.25mm-1mm, the coefficient of inhomogeneity is 3.53, the coefficient of curvature is 1.45, the air-dried moisture content is 0.81%, and the specific gravity is 2.702.
  • element composition it mainly contains Ca and Mg elements.
  • nano magnesium oxide 40nm-60nm, and the purity is 99.9%.
  • the raw materials are composed of calcareous sand, cement, nano-magnesia and water, the amount of cement added is 10% of the weight of the calcareous sand, and the amount of added nano-magnesia is 1.5% of the weight of the calcareous sand.
  • Embodiment 3 nano-magnesia modified cement calcareous sand
  • the particle size of calcareous sand is 0.25mm-1mm, the coefficient of inhomogeneity is 3.53, the coefficient of curvature is 1.45, the air-dried moisture content is 0.81%, and the specific gravity is 2.702.
  • element composition it mainly contains Ca and Mg elements.
  • nano magnesium oxide 40nm-60nm, and the purity is 99.9%.
  • the raw materials are composed of calcareous sand, cement, nano-magnesia and water, the amount of cement added is 10% of the weight of the calcareous sand, and the amount of added nano-magnesia is 2.0% of the weight of the calcareous sand.
  • Embodiment 4 nano-magnesia modified cement calcareous sand
  • the particle size of calcareous sand is 0.25mm-1mm, the coefficient of inhomogeneity is 3.53, the coefficient of curvature is 1.45, the air-dried moisture content is 0.81%, and the specific gravity is 2.702.
  • element composition it mainly contains Ca and Mg elements.
  • nano magnesium oxide 40nm-60nm, and the purity is 99.9%.
  • the raw materials are composed of calcareous sand, cement, nano-magnesia and water, the amount of cement added is 10% of the weight of the calcareous sand, and the amount of added nano-magnesia is 1.5% of the weight of the calcareous sand.
  • Example 2 The main difference from Example 1 is that no nano magnesium oxide is added for modification. Specifically:
  • the particle size of calcareous sand is 0.25mm-1mm, the coefficient of inhomogeneity is 3.53, the coefficient of curvature is 1.45, the air-dried moisture content is 0.81%, and the specific gravity is 2.702.
  • element composition it mainly contains Ca and Mg elements.
  • the raw material is composed of calcareous sand, cement and water, and the amount of cement added is 10% of the weight of the calcareous sand.
  • Example 2 The main difference from Example 1 is that nano-clay is used instead of nano-magnesia. Specifically:
  • the calcareous sand is selected with a particle size of 0.25 mm to 1 mm, a coefficient of inhomogeneity of 3.53, a coefficient of curvature of 1.45, an air-dried moisture content of 0.81%, and a specific gravity of 2.702.
  • the nano-clay used in this test is a nano-scale derivative of montmorillonite.
  • the main components of nano-clay are SiO 2 and Al 2 O 3 . Produced by Hubei Jinxi Montmorillonite Technology Co., Ltd.,
  • the raw material is composed of calcareous sand, cement, nano-clay and water, the amount of cement added is 10% of the weight of the calcareous sand, and the amount of nano-clay added is 4% of the weight of the calcareous sand.
  • Example 3 The difference from Example 3 is that the amount of nano magnesium oxide added is adjusted to be 8% of the weight of the calcareous sand.
  • the raw materials are composed of calcareous sand, cement, nano-magnesia and water, the amount of cement added is 10% of the weight of the calcareous sand, and the amount of nano-magnesia added is 8% of the weight of the calcareous sand.
  • Raw material and preparation method are consistent with embodiment 1.
  • Example 4 optimizes the manufacturing method to further improve the compressive strength. It shows that under the same compressive strength requirement, the optimized manufacturing method of the present invention can obviously shorten the maintenance time, shorten the construction period and improve the efficiency.
  • the adjusting nano-clay mixing amount is 0.5%, 1.5%, 2%, 6%, 8%, 10%, the compressive strength of the same age All lower than Examples 1-4 and Comparative Example 3.
  • the shear strength is one of the important parameters to evaluate the shear performance of calcareous sand.
  • the samples obtained in the examples and the comparative examples have been subjected to the unconsolidated and undrained (UU) triaxial test to explore the influence on the shear performance of the product.
  • the curing ages were 7d, 14d and 28d, and samples were taken and tested respectively.
  • the results of internal friction angle are shown in Table 2 below, and the results of cohesion are shown in Table 3 below.
  • Example 4 optimizes the production method, further increases the internal friction angle and cohesion, and improves the shear strength of the nanomaterial modified cement calcareous sand.
  • the confining pressure is set to 100kPa, 200kPa, 300kPa and 400kPa respectively, and the curing age is set to 7d, 14d and 28d. Comparative analysis of peak stress, the results are as follows:
  • Fig. 1 is the scanning electron microscope picture of nanometer MgO modified cement calcareous sand
  • Fig. 1 (a) is that the embodiment 2 that curing age is 7d makes nano-magnesia modified cement calcareous sand magnified 100 times SEM figure;
  • Fig. 1 (b) is that the embodiment 2 that curing age is 28d makes nano-magnesia modified cement calcareous sand magnified 2000 times SEM figure;
  • Fig. 1 (c) is that the embodiment 3 that curing age is 7d makes nano-magnesia modified cement calcareous sand magnification 500 times SEM picture;
  • Figure 1(d) is a 2000-fold SEM image of the nano-magnesia modified cement calcareous sand prepared in Example 3 with a curing age of 28 days.
  • MCCS-1.5 is nano magnesium oxide modified cement calcium prepared by adding 1.5% magnesium oxide
  • MCCS-2.0 is nano magnesium oxide modified cement calcium prepared by mixing magnesium oxide 2.0%
  • CSH is cement Calcium silicate hydrate formed with calcareous sand
  • Mg(OH) 2 is magnesium hydroxide.
  • nano-MgO can fill the pore structure inside the cement calcareous sand.
  • the invention can effectively improve the mechanical properties of the cement calcareous sand by adding an appropriate amount of nanometer MgO.
  • nano-MgO is a nanoscale particle that can fill the pores.
  • MgO is a basic oxide, and when exposed to air, it readily absorbs moisture and carbon dioxide to form basic magnesium carbonate.
  • MgO has hygroscopicity, which has a certain relationship with the size of the surface area, indicating that the larger the surface area, the higher the hygroscopicity.
  • nanoscale MgO is superhydrophilic, and the water adsorbed on its surface can be dissociated by reaction, which makes it easy to form chemisorbed water and form a physisorbed water layer. Therefore, nano-MgO mixed in cement can quickly absorb Ca 2+ in the liquid phase to form crystalline Ca(OH) 2 , accelerate the rate of hydration reaction of cement particles, and form a more compact hydrated calcium silicate gel structure.

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Abstract

一种纳米材料改性水泥钙质砂及其制作方法，由钙质砂、水泥、纳米氧化镁和水制成，所述纳米氧化镁的加入量为钙质砂重量的0.5～2.0％。采用一定量的纳米氧化镁改性水泥钙质砂，制得优质纳米材料改性水泥钙质砂，其抗压强度显著提高，内摩擦角、粘聚力和峰值应力得到明显提升，提高纳米材料改性水泥钙质砂的剪切性能。另外，在同一性能要求下，通过优化制作方法，能够明显缩短养护时间，缩短工期，提高效率。

Description

一种纳米材料改性水泥钙质砂及其制作方法 技术领域
本发明涉及钙质砂领域，特别涉及一种纳米材料改性水泥钙质砂及其制作方法。
背景技术
南海岛礁工程的建设对我国海洋事业和国防的发展具有重要战略意义，因此，近年来南海岛礁的基础设施建设工程逐渐增多。钙质砂(简称“CS”)广泛分布在我国南海海域，特殊的沉积环境使得钙质砂具有易破碎、高压缩性和强度低等特征，难以满足实际工程的需求。水泥作为常用的胶凝剂，可以提高钙质砂的强度，但水泥加固钙质砂(简称“CCS”)的强度提高有限。
纳米材料作为新型材料，凭借其优异的性能和特殊性应用于多方面领域，被誉为21世纪最有发展前景的材料。随着纳米技术和纳米材料制作工艺的进一步发展，纳米材料的种类越来越多且生产模式开始出现工业化生产。这降低了纳米材料使用的成本，使得纳米材料的改性水泥基材料的力学性能成为可能。近年来，纳米材料作为外掺剂添加到水泥基材料中，改善水泥基材料的强度。纳米材料掺入到水泥基材料中，能够作为松散的土颗粒或砂颗粒的核心使其形成致密的网状结构，从而达到改善水泥基材料力学性能的目的。纳米材料在改性水泥基材料的应用工程中有一定的发展前景。与陆源砂相比，钙质砂形状不规则且多棱角，主要分为树枝状骨架砂颗粒、块状砂颗粒、片状砂颗粒和贝壳及海螺等生物碎屑。钙质砂和陆源砂在力学性能和工程性能都有着巨大的差异。钙质砂的强度往往难以满足南海岛礁吹填工程建设的需求，因此需要对改性钙质砂进行深入研究。CN104496337A公开纳米粘土改性纤维水泥砂浆及其制备方法，CN110218054A公开一种纳米粘土改性高性能混凝土及其制备方法与应用，这些制备方法均不适用于钙质砂。
发明内容
鉴于此，本发明提出一种纳米材料改性水泥钙质砂及其制作方法，解决上述技术问题。
本发明的技术方案是这样实现的：
一种纳米材料改性水泥钙质砂，由钙质砂、水泥、纳米氧化镁和水制成，所述纳米氧化镁的加入量为钙质砂重量的0.5～2.0％。
进一步的，所述纳米氧化镁的粒径为40nm～60nm，纯度为99.9％(按质量百分比计)。
进一步的，所述钙质砂的粒径为0.25mm～1mm，不均匀系数为3.53，曲率系数为1.45，风干含水率为0.81％，比重为2.702。
进一步的，所述纳米氧化镁的加入量为钙质砂重量的1.0-1.5％，优选1.5％。
进一步的，所述水泥的加入量为钙质砂重量的10％。
进一步的，所述纳米材料改性水泥钙质砂的含水率为30％。
本发明纳米材料改性水泥钙质砂的制作方法，包括以下步骤：
(1)钙质砂准备：对风干过后的钙质砂再次烘干，过筛，备用；
(2)先将纳米氧化镁与水泥加入搅拌锅内，于300-400r/min转速下进行第一次搅拌；再于800-1000r/min转速下进行第二次搅拌，第二次搅拌过程加入水，得到拌合料；然后利用高频振动筛将拌合料分成两个粒级级别，分别为大粒级和小粒级，将小粒级拌合料置于搅拌锅底部，再加入大粒级拌合料，于1100-1300r/min转速下进行第三次搅拌，置于模具中养护7-28d，得到纳米材料改性水泥钙质砂。
进一步的，在步骤(1)中，所述筛的规格为2mm。
进一步的，在步骤(2)中，所述高频振动筛的筛网的网孔为0.1mm。
进一步的，所述第一次搅拌时间为2-3min，第二次搅拌时间为5-8min，第三次搅拌时间为10-15min。
与现有技术相比，本发明的有益效果是：
(1)本发明采用一定量的纳米氧化镁改性水泥钙质砂，制得优质的纳米材料改性水泥钙质砂，其抗压强度显著提高，其内摩擦角、粘聚力和峰值应力得到明显提升，提高纳米材料改性水泥钙质砂的抗剪强度，提高样品剪切性能。
(2)另外，在同一性能要求下，通过本发明优化制作方法，能够明显缩短养护时间，缩短工期，提高效率。
(3)水泥掺入到钙质砂中，水泥的水化反应生成的C-S-H可以填充钙质砂表面的孔隙，提高钙质砂的密实度。一方面，本发明掺入一定量的纳米MgO可以促进水泥水化反应，纤维状的C-S-H在钙质砂颗粒的表面形成致密的网状结构。另一方面，纳米MgO水解可以生成的Mg(OH) 2也可以填充水泥钙质砂的孔隙结构。
具体实施方式
为了更好理解本发明技术内容，下面提供具体实施例，对本发明做进一步的说明。
本发明实施例所用的实验方法如无特殊说明，均为常规方法。
本发明实施例所用的材料、试剂等，如无特殊说明，均可从商业途径得到。
本发明试验使用的钙质砂取自海南省三沙市永兴岛某地区的钙质砂，为松散未胶结的砂颗粒。
实施例1纳米氧化镁改性水泥钙质砂
1原料准备
1.1选用钙质砂的粒径为0.25mm～1mm，不均匀系数为3.53，曲率系数为1.45，风干含水率为0.81％，比重为2.702，在元素组成方面，主要包含Ca和Mg元素。
1.2选用纳米氧化镁的粒径为40nm～60nm，主要化合物(MgO)组成为纯度为99.9％(按质量百分比计)。
2配合比
原料由钙质砂、水泥、纳米氧化镁和水组成，水泥掺入量为钙质砂重量的10％，纳米氧化镁掺入量为钙质砂重量的0.5％。
3制作方法
3.1钙质砂准备：对风干过后的钙质砂再次烘干，过2mm筛，备用；
3.2先将纳米氧化镁与水泥加入搅拌锅内混合；于1000r/min搅拌20min，搅拌过程加入水，置于模具中养护28天，制成含水率为30％的纳米氧化镁改性水泥钙质砂。
实施例2纳米氧化镁改性水泥钙质砂
1原料准备
1.1选用钙质砂的粒径为0.25mm～1mm，不均匀系数为3.53，曲率系数为1.45，风干含水率为0.81％，比重为2.702，在元素组成方面，主要包含Ca和Mg元素。
1.2选用纳米氧化镁的粒径为40nm～60nm，纯度为99.9％。
2配合比
原料由钙质砂、水泥、纳米氧化镁和水组成，水泥掺入量为钙质砂重量的10％，纳米氧化镁掺入量为钙质砂重量的1.5％。
3制作方法
3.1钙质砂准备：对风干过后的钙质砂再次烘干，过2mm筛，备用；
3.2先将纳米氧化镁与水泥加入搅拌锅内混合；于1000r/min搅拌20min，搅拌过程加入水，置于模具中养护28天，制成含水率为30％的纳米氧化镁改性水泥钙质砂。
实施例3纳米氧化镁改性水泥钙质砂
1原料准备
1.1选用钙质砂的粒径为0.25mm～1mm，不均匀系数为3.53，曲率系数为1.45，风干含水率为0.81％，比重为2.702，在元素组成方面，主要包含Ca和Mg元素。
1.2选用纳米氧化镁的粒径为40nm～60nm，纯度为99.9％。
2配合比
原料由钙质砂、水泥、纳米氧化镁和水组成，水泥掺入量为钙质砂重量的10％，纳米氧化镁掺入量为钙质砂重量的2.0％。
3制作方法
3.1钙质砂准备：对风干过后的钙质砂再次烘干，过2mm筛，备用；
3.2先将纳米氧化镁与水泥加入搅拌锅内混合；于1000r/min搅拌20min，搅拌过程加入水，置于模具中养护28天，制成含水率为30％的纳米氧化镁改性水泥钙质砂。
实施例4纳米氧化镁改性水泥钙质砂
1原料准备
1.1选用钙质砂的粒径为0.25mm～1mm，不均匀系数为3.53，曲率系数为1.45，风干含水率为0.81％，比重为2.702，在元素组成方面，主要包含Ca和Mg元素。
1.2选用纳米氧化镁的粒径为40nm～60nm，纯度为99.9％。
2配合比
原料由钙质砂、水泥、纳米氧化镁和水组成，水泥掺入量为钙质砂重量的10％，纳米氧化镁掺入量为钙质砂重量的1.5％。
3制作方法
3.1钙质砂准备：对风干过后的钙质砂再次烘干，过2mm筛，备用；
3.2先将纳米氧化镁与水泥加入搅拌锅内，于350r/min转速下搅拌2min；再于900r/min转速下搅拌6min，该搅拌过程加入水，得到拌合料；然后利用高频振动筛(筛网网孔为0.1mm)将拌合料分成两个粒级级别，分别为+0.1mm大粒级和-0.1mm小粒级，将-0.1mm小粒级拌合料置于搅拌锅底部，再加入+0.1mm大粒级拌合料，最后于1200r/min转速下搅拌12min，置于模具中养护28d，制成含水率为30％的纳米氧化镁改性水泥钙质砂。
对比例1水泥钙质砂制作
与实施例1的主要区别在于，没有加入纳米氧化镁进行改性。具体为：
1原料准备
1.1选用钙质砂的粒径为0.25mm～1mm，不均匀系数为3.53，曲率系数为1.45，风干含水率为0.81％，比重为2.702，在元素组成方面，主要包含Ca和Mg元素。
2配合比
原料由钙质砂、水泥和水组成，水泥掺入量为钙质砂重量的10％。
3制作方法
3.1钙质砂准备：对风干过后的钙质砂再次烘干，过2mm筛，备用；
3.2将水泥加入搅拌锅内混合；于1000r/min搅拌20min，搅拌过程加入水，置于模具中养护28天，制成含水率为30％的水泥钙质砂。
对比例2纳米粘土改性水泥钙质砂
与实施例1的主要区别在于，采用纳米粘土替换纳米氧化镁。具体为：
1原料准备
1.1选用钙质砂的粒径为0.25mm～1mm，不均匀系数为3.53，曲率系数为1.45，风干含水率为0.81％，比重为2.702。
1.2选用纳米粘土，本试验所用的纳米粘土是蒙脱石的纳米级别衍生物，纳米粘土的主要成分为SiO 2和Al 2O 3。由湖北金细蒙脱石科技有限公司所生产，
2配合比
原料由钙质砂、水泥、纳米粘土和水组成，水泥掺入量为钙质砂重量的10％，纳米粘土掺入量为钙质砂重量的4％。
3制作方法
3.1钙质砂准备：对风干过后的钙质砂再次烘干，过2mm筛，备用；
3.2先将纳米粘土与水泥加入搅拌锅内混合；于1000r/min搅拌20min，搅拌过程加入水，置于模具中养护28天，制成含水率为30％的纳米粘土改性水泥钙质砂。
对比例3纳米氧化镁改性水泥钙质砂
与实施例3区别在于，调整纳米氧化镁掺入量为钙质砂重量的8％。
具体配合比：原料由钙质砂、水泥、纳米氧化镁和水组成，水泥掺入量为钙质砂重量的10％，纳米氧化镁掺入量为钙质砂重量的8％。原料以及制作方法与实施例1一致。
一、压缩性能
通过无侧限抗压强度试验，测试压缩性能。养护龄期为7d、14d和28d，分别取样测试。结果见下表1。
表1抗压强度对比
Figure PCTCN2021118576-appb-000001
结果显示，与对比例1相比，实施例1-4制得纳米材料改性水泥钙质砂的抗压强度显著提高，而且优于对比例2-3。其中，在实施例2的基础上，实施例4优化制作方法，进一步提高抗压强度。表明在同一抗压强度要求下，通过本发明优化制作方法，能够明显缩短养护时间，缩短工期，提高效率。
另外，在对比例2(纳米粘土掺入量4％)基础上，调整纳米粘土掺入量为0.5％、1.5％、2％、6％、8％、10％，同一龄期的抗压强度均低于实施例1-4以及对比例3。
二、抗剪强度指标分析
2.1抗剪强度是评价钙质砂剪切性能的重要参数之一。将实施例以及对比例得到样品进行了不固结不排水(UU)的三轴试验，探究对产品的剪切性能的影 响。养护龄期为7d、14d和28d，分别取样测试。内摩擦角结果见下表2，粘聚力结果见下表3。
表2内摩擦角对比
Figure PCTCN2021118576-appb-000002
表3粘聚力对比
Figure PCTCN2021118576-appb-000003
结果显示，与对比例1相比，实施例1-4制得纳米材料改性水泥钙质砂的内摩擦角和粘聚力得到明显提升，而且优于对比例2-3。其中，在实施例2的基础上，实施例4优化制作方法，进一步提高内摩擦角和粘聚力，提高纳米材料改性水泥钙质砂的抗剪强度。
2.2峰值应力对比分析
围压分别设置为100kPa、200kPa、300kPa和400kPa，养护龄期被设置为7d、14d和28d。对比分析峰值应力，结果如下：
表4峰值应力对比
Figure PCTCN2021118576-appb-000004
由上表可知，28d对比例2的峰值应力较对比例1提升了21％～25％，28d实施例2的峰值应力较对比例1提升了52％～71％。这表明纳米MgO促进水泥水化反应的能力优于纳米粘土。由上述的分析结果可知，掺入纳米MgO改性水泥钙质砂剪切性能明显优于纳米粘土。实施例提高峰值应力幅度明显优于对比例2，而且实施例4使用进一步优化后制作方法，其峰值应力得到进一步提升。
三、微观分析
图1为纳米MgO改性水泥钙质砂的电镜扫描图；
图1(a)为养护龄期为7d的实施例2制得纳米氧化镁改性水泥钙质砂放大100倍SEM图；
图1(b)为养护龄期为28d的实施例2制得纳米氧化镁改性水泥钙质砂放大2000倍SEM图；
图1(c)为养护龄期为7d的实施例3制得纳米氧化镁改性水泥钙质砂放大放大500倍SEM图；
图1(d)为养护龄期为28d的实施例3制得纳米氧化镁改性水泥钙质砂放大2000倍的SEM图。
图中，MCCS-1.5为掺入氧化镁1.5％所制备的纳米氧化镁改性水泥钙质，MCCS-2.0为掺入氧化镁2.0％所制备的纳米氧化镁改性水泥钙质，C-S-H为水泥和钙质砂形成的水化硅酸钙，Mg(OH) 2为氢氧化镁。
由图可知，掺入纳米MgO可以填充水泥钙质砂内部的孔隙结构。
图1(a)可以看出，7dMCCS-1.5的微观结构中出现了云雾状和纤维状的水化产物C-S-H以及片状Mg(OH) 2，颗粒主要以层状堆积存在，纤维状的胶凝物质在钙质砂颗粒之间起到了拉扯的作用。
当养护龄期为7d时，与MCCS-1.5相比，MCCS-2(图1(c))的微观结构中的纤维状水化产物减少，图中出现了更多的Mg(OH) 2晶体，排列松散。
当养护龄期为28d时，从图1(b)可以看出，MCCS-1.5的微观结构中出现了大量絮状和纤维状的水泥水化产物，纤维状的水泥水化产物在钙质砂颗粒的表面形成致密的网状结构。
本发明掺入适量纳米MgO可以有效提高水泥钙质砂的力学性能。原因可能是，一方面，纳米MgO是纳米级别的颗粒，可以填充孔隙。另一方面，MgO是一种碱性氧化物，当暴露在空气中时，它容易吸收水分和二氧化碳，生成碱式碳酸镁。MgO具有吸湿性，与表面积的大小有一定的关系，表明表面积越大，吸湿性越高。
纳米级MgO表面具有超亲水性，其表面吸附的水可以通过反应离解，这使得易于形成化学吸附的水，形成物理吸附的水层。因此，在水泥中混合的纳米MgO可以快速吸附液相中的Ca 2+，形成晶态Ca(OH) 2，加速水泥颗粒的水化反应的速率，形成更紧凑的水化硅酸钙凝胶结构。但是若纳米MgO的掺量过多，水泥的水化产物在纳米氧化镁改性水泥钙质砂的内部出现不均匀分布的现象，Mg(OH) 2局部的膨胀能力使得纳米氧化镁改性水泥钙质砂的内部出现微裂缝，从而使得水泥的水化产物不能较好地拉扯钙质砂颗粒，宏观变现为纳米氧化镁改性水泥钙质砂力学强度的下降。
以上所述仅为本发明的较佳实施例而已，并不用以限制本发明，凡在本发明的精神和原则之内，所做的任何修改、等同替换、改进等，均应包含在本发明的保护范围之内。

Claims (10)

  1. 一种纳米材料改性水泥钙质砂，其特征在于，由钙质砂、水泥、纳米氧化镁和水制成，所述纳米氧化镁的加入量为钙质砂重量的0.5～2.0％。
  2. 根据权利要求1所述的纳米材料改性水泥钙质砂，其特征在于，所述纳米氧化镁的粒径为40nm～60nm，纯度为99.9％。
  3. 根据权利要求1所述的纳米材料改性水泥钙质砂，其特征在于，所述钙质砂的粒径为0.25mm～1mm，不均匀系数为3.53，曲率系数为1.45，风干含水率为0.81％，比重为2.702。
  4. 根据权利要求1所述的纳米材料改性水泥钙质砂，其特征在于，所述纳米氧化镁的加入量为钙质砂重量的1.0-1.5％。
  5. 根据权利要求4所述的纳米材料改性水泥钙质砂，其特征在于，所述水泥的加入量为钙质砂重量的10％。
  6. 根据权利要求5所述的纳米材料改性水泥钙质砂，其特征在于，所述纳米材料改性水泥钙质砂的含水率为30％。
  7. 根据权利要求1-6任一项所述的纳米材料改性水泥钙质砂的制作方法，其特征在于，包括以下步骤：
    (1)钙质砂准备：对风干过后的钙质砂再次烘干，过筛，备用；
    (2)先将纳米氧化镁与水泥加入搅拌锅内，于300-400r/min转速下进行第一次搅拌；再于800-1000r/min转速下进行第二次搅拌，第二次搅拌过程加入水，得到拌合料；然后利用高频振动筛将拌合料分成两个粒级级别，分别为大粒级和小粒级，将小粒级拌合料置于搅拌锅底部，再加入大粒级拌合料，于1100-1300r/min转速下进行第三次搅拌，置于模具中养护7-28d，得到纳米材料改性水泥钙质砂。
  8. 根据权利要求7所述的纳米材料改性水泥钙质砂的制作方法，其特征在于，在步骤(2)中，所述高频振动筛的筛网的网孔为0.1mm。
  9. 根据权利要求7所述的纳米材料改性水泥钙质砂的制作方法，其特征在于，在步骤(1)中，所述筛的规格为2mm。
  10. 根据权利要求7所述的纳米材料改性水泥钙质砂的制作方法，其特征在于，所述第一次搅拌时间为2-3min，第二次搅拌时间为5-8min，第三次搅拌时间为10-15min。
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