A low-drying-shrinkage alkali slag seawater sand concrete and its preparation method

Abstract

This invention discloses a low-drying-shrinkage alkali slag seawater sand concrete and its preparation method. The alkali slag seawater sand concrete is prepared by ball milling slag and anhydrous sodium silicate using mechanochemical force, followed by the addition of seawater and sea sand and stirring. This invention uses seawater sand instead of freshwater river sand as a raw material, improving the problems of high drying shrinkage and cracking in alkali slag concrete while maintaining its mechanical properties. Furthermore, the mechanochemical ball milling method is highly efficient and energy-saving, and it induces physicochemical changes in the alkali slag concrete material, improving its drying shrinkage performance.

Description

Technical Field

[0001] This invention belongs to the field of building materials technology, specifically relating to a low-drying-shrinkage alkaline slag seawater sand concrete and its preparation method. Background Technology

[0002] Approximately 70% of the Earth's surface is covered by water, of which freshwater accounts for only 3.5%, while seawater makes up 96.5%. To meet the demands of concrete production, the over-exploitation of river sand in my country has caused serious ecological problems, leading to the destruction of riverbank ecosystems and damage to the foundations of inland river bridges. Compared to river sand, sea sand resources are abundant, and given my country's vast sea area and long coastline, sea sand is gradually gaining attention as an alternative resource. Sea sand has advantages such as large reserves, low extraction difficulty, local sourcing, and low transportation costs. Therefore, researching the application of sea sand and seawater as substitutes for river sand and freshwater in concrete production not only has significant ecological benefits but also considerable economic value.

[0003] Alkali-activated cementitious materials, as a new type of green building cementitious material, are increasingly attracting the attention of researchers. Compared with ordinary Portland cement, the carbon dioxide emissions and energy consumption of producing the same unit mass of alkali-activated cementitious materials are only 20% and 40% of those of ordinary Portland cement, respectively. Using seawater and sea sand to prepare alkali-activated slag concrete can not only effectively alleviate the shortage of freshwater and river sand resources, but also play a positive role in protecting the environment and reducing environmental pressure, achieving two goals at once.

[0004] The high drying shrinkage rate of traditional cement often leads to cracks in building structures, increasing the risk of intrusion by corrosive substances and raising the likelihood of steel corrosion. Furthermore, the inherently high drying shrinkage of alkali-slag systems also limits their widespread application. Therefore, developing alkali-slag concrete with low drying shrinkage is of great significance for promoting its application in the construction field. Summary of the Invention

[0005] This invention is achieved through the following technical solution:

[0006] A method for preparing low-drying-shrinkage alkali slag seawater sand concrete: The steps are as follows: First, slag and activator are ball-milled by mechanical and chemical force to obtain powder, which is a single-component alkali slag cement. The slag is S95 grade granulated blast furnace slag, and the activator is anhydrous sodium silicate with an alkali modulus of 1.4. The mass of Na2O in the anhydrous sodium silicate accounts for 4% of the mass of slag and anhydrous sodium silicate. Then, the single-component alkali slag cement is mixed with sea sand and seawater to prepare alkali slag seawater sand concrete.

[0007] Furthermore, the sea sand, by mass percentage, has a moisture content of ≤6.0%, a mud content of ≤3.0%, a chloride ion content of ≤0.02%, and a shell content of ≤5.0%.

[0008] Furthermore, the seawater is prepared according to the concentration ratio of NaCl:MgCl2:Na2SO4:CaCl2:KCl:NaHCO3 = 24.53:5.2:4.09:1.16:0.695:0.201.

[0009] Furthermore, the sea sand has a particle size of less than 5 mm and a fineness modulus of 2.71, classifying it as medium sand in Zone II.

[0010] Furthermore, a method for preparing low-drying-shrinkage alkali slag seawater sand concrete includes the following steps:

[0011] (1) After drying and cooling the slag, it was mixed with anhydrous sodium silicate with an alkali modulus of 1.4 and ball-milled for 1 h. The ball milling speed was 75 r / min and the ball-to-material ratio was 7.5:1. After ball milling, the powder was sieved to obtain single-component alkali slag cement.

[0012] (2) Weigh seawater, sea sand and single-component alkali slag cement according to the proportion, and mix them with a mortar mixer to obtain seawater sea sand alkali slag concrete.

[0013] Furthermore, the mass ratio of seawater to single-component alkali slag cement is 0.43:1; the mass ratio of single-component alkali slag cement to sea sand is 1:2.

[0014] Furthermore, the mixing process involves adding seawater to the single-component alkali slag cement and mixing at low speed for 30 seconds, then adding sea sand within 30 seconds, mixing at high speed for 30 seconds, pausing for 90 seconds to mix the materials evenly, and then continuing to mix at high speed for 60 seconds.

[0015] This invention provides an optimal mix proportion for single-component alkali slag concrete. The beneficial effects of this invention are as follows:

[0016] (1) This invention uses seawater and sea sand as raw materials for engineering construction, which can save material transportation costs and has good economic benefits. On the other hand, it can save river sand resources and freshwater resources, promote the construction of the project, and has good social benefits.

[0017] (2) This invention uses seawater sand instead of deionized water river sand as raw material to prepare alkali slag concrete. Due to the chloride ions in seawater and the CaCO3, the main component of seashells in seawater, the drying shrinkage of alkali slag mortar is reduced. Its drying shrinkage performance is similar to that of ordinary silicate cement, effectively improving the problems of high drying shrinkage and easy cracking of alkali slag concrete. In addition, since seawater increases the pH value of concrete, and pH value is very important for the polymerization reaction of alkali-activated materials, it can promote the formation of more CSH gel in alkali slag materials. Therefore, the seawater sand alkali slag concrete obtained by this ratio also has good mechanical properties.

[0018] (3) This invention uses industrial waste residue as raw material to prepare alkali slag concrete. The alkali slag seawater sand concrete prepared by mechanochemical method has the advantages of high efficiency and energy saving. Furthermore, the mechanochemical method can induce alkali-activated cementitious materials to undergo physicochemical changes, thereby improving the drying shrinkage performance of single-component alkali-activated cementitious materials. Detailed Implementation

[0019] To make the content of this invention easier to understand, the technical solution of this invention will be further described below with reference to specific embodiments, but this invention is not limited thereto.

[0020] The experimental materials and their properties involved in the following examples are as follows:

[0021] (1) The slag is S95 grade granulated blast furnace slag from Yanxing Mineral Products Processing Plant in Lingshou County, Hebei Province. The basic physical properties of the slag are shown in Table 1. XRF analysis was performed on the slag samples, and the chemical composition analysis results are shown in Table 2.

[0022] (2) In the embodiments, three types of sand—sea sand, desalinated sea sand, and river sand—were used as aggregates. The sea sand and desalinated sea sand were both sourced from Zhangpu County, Zhangzhou City, Fujian Province. The desalinated sea sand was obtained by washing and drying sea sand. The river sand was sourced from Jinjing Town, Jinjiang City, Quanzhou City, Fujian Province, and was entirely undried river sand. The moisture content, mud content, chloride ion content, and shell content were determined according to GB / T14684-2022 "Construction Sand". The specific information for the three types of sand is shown in Table 3. The moisture content, sand content, chloride ion content, and shell content of the three types of sand all meet the requirements of the standard.

[0023] (3) The gradation of sea sand, desalinated sea sand, and river sand was determined according to the "Standard Methods for Quality and Inspection of Sand and Stone for Ordinary Concrete" (JCJ52-2006), and the cumulative sieve residues are shown in Table 4. Among them, A1, A2, A3, A4, A5, and A6 are the cumulative sieve residue percentages of 4.75mm, 2.35mm, 1.18mm, 500μm, 300μm, and 150μm sieves, respectively. The fineness modulus of the sand was calculated according to Formula 1-1. After calculation, the fineness modulus of sea sand is 2.71, which is medium sand in Zone II; the fineness modulus of desalinated sea sand is 1.86, which is fine sand in Zone III; and the fineness modulus of river sand is 3.03, which is medium sand in Zone II. Before use, particles with a diameter greater than 5mm in river sand were sieved out.

[0024] (4) Sodium chloride (NaCl), magnesium chloride (MgCl2), sodium sulfate (Na2SO4), calcium chloride (CaCl2), potassium chloride (KCl), and sodium bicarbonate (NaHCO3) are used. This invention mainly focuses on the influence of chloride ions and pH value in seawater on concrete performance. Therefore, only substances containing chloride ions (NaCl, MgCl2, etc.) and substances affecting pH (Na2SO4, etc.) are added. 4、 NaHCO3), artificial seawater was prepared according to the standard ASTM D1141-89, and the proportions are shown in Table 5. All water used in the tests was deionized water, and the seawater referred to in the examples was this artificial seawater.

[0025] Among them, NaCl (granular) is sourced from Tianjin Zhiyuan Co., Ltd., with a NaCl content of not less than 99.5%; MgCl2 (granular) is sourced from Fuchen Chemical Reagent Co., Ltd., with a MgCl2 content of not less than 98.0%; Na2SO4 is granular analytical grade, with a content of not less than 99.0%, produced by Tianjin Zhiyuan Co., Ltd.; CaCl2 is granular analytical grade, with a content of not less than 96.0%, produced by Tianjin Zhiyuan Co., Ltd.; potassium chloride is granular analytical grade, with a content of not less than 99.5%, produced by Sinopharm Chemical Reagent Co., Ltd.; and NaHCO3 (granular) is sourced from Tianjin Zhiyuan Co., Ltd., with a NaHCO3 content of not less than 99.5%.

[0026] (5) The alkali activator is analytical grade anhydrous sodium silicate (Na2SiO3), with a Na2SiO3 content of over 99% and a modulus of 1.4, produced by Tianjin Zhiyuan Co., Ltd.

[0027] Table 1 Basic physical quantities of slag

[0028]

[0029] Table 2 Chemical composition of slag

[0030]

[0031] Table 3 Physical properties of three types of sand

[0032]

[0033] Table 4. Cumulative sieve residue percentage of the three types of sand

[0034]

[0035]

[0036] Formula 1-1

[0037] Table 5 Chemical composition of seawater (unit: g / L)

[0038]

[0039] Example 1

[0040] Alkali slag concrete is prepared using slag, solid sodium silicate, seawater, and sea sand.

[0041] (1) Weigh 1828g of slag, dry it at 60℃ for 4h, cool it to room temperature, and then mix it with 173g of anhydrous sodium silicate with a modulus of 1.4;

[0042] (2) The above mixture was placed in a ball mill for ball milling. The slag and alkali were activated by ball milling. A WZM-15*2 Haoqiang Technology ball mill, 15L double-tank type, with an inner diameter of 26cm in the milling jar, was used. The steel balls had particle sizes of 30mm, 20mm, and 10mm, with a mass ratio of 1:1:1, totaling 15kg. The ratio of the total mass of the material to the total mass of the three types of steel balls was 1:7.5 (ball-to-material ratio), that is, the total mass of the slag and anhydrous sodium silicate was 2kg. After sealing, the mixture was placed in the ball mill and ball-milled at high speed (75r / min) for 1 hour.

[0043] (3) After ball milling, pour out the powder and sieve it to obtain the single-component alkali slag cement. Seal and store it at a temperature of 20°C-25°C.

[0044] (4) Add seawater and sea sand according to the mass ratio of seawater to single-component alkali slag cement of 0.43 (water-cement ratio) and the mass ratio of single-component alkali slag cement to sea sand of 1:2 (cement-sand ratio). Use a mortar mixer to mix the above mixture. The specific process is as follows: add 258g of seawater to 600g of single-component alkali slag cement and mix at low speed for 30s. Then automatically add 1200g of sea sand for 30s. Then mix at high speed for 30s, pause for 90s in the middle. During the pause, scrape off the material on the pot wall and the material settled at the bottom and mix it evenly. Finally, mix at high speed for 60s to obtain alkali slag concrete.

[0045] To verify the mechanical properties and drying shrinkage properties of the alkali slag concrete in this embodiment, an experiment was conducted on the alkali slag concrete prepared according to the above method.

[0046] Compressive and flexural strength tests were conducted according to GB / T 17671-2021, "Test Method for Strength of Cement Mortar". A 40mm×40mm×160mm triple mold was used. The concrete was poured into the mold in two stages, each stage vibrating 60 times. After smoothing and shaping, the mold was sealed with plastic wrap for one day before demolding. Nine specimens were prepared for each mix design, with three specimens of each mix. After demolding, the specimens were placed in a standard curing room (temperature 20±2℃, relative humidity above 95%) for curing. At the designated ages (3d, 7d, and 28d), the compressive and flexural strengths were measured using a fully automatic constant stress testing machine. Any values ​​exceeding ±10% of the average were discarded and recalculated.

[0047] The test method was formulated in accordance with the "Standard for Test Methods of Basic Performance of Building Mortar" (JGJ / T 70-2009) and the "Test Method for Drying Shrinkage of Cement Mortar" (JC / T 603-2004). A 25mm×25mm×280mm shrinkage steel mold was used, with copper nails pre-installed at both ends. The mortar was poured in two layers, and after each pour, it was tamped back and forth 24 times with a tamping rod. After tamping, the surface was smoothed and covered with plastic wrap. To ensure the integrity of the specimens, the demolding time was extended to 48±2 hours from the time water was added. The specimens were then placed in water at (20±2)℃ for 24 hours for curing. After water curing, the specimens were removed, the surface was wiped clean, and then placed in a drying shrinkage curing chamber at (20±3)℃ and (50±4)% humidity for 4 hours at intervals. The length was then measured with a micrometer and taken as the initial length L0 of the specimen at 0d. The length L of the specimen was measured at 3d, 7d, 14d, 28d, 42d, 56d, 90d, and 180d of the aging period. t Calculate the drying shrinkage St of mortar at different ages according to the following formulas 1-2.

[0048]

[0049] Example 2

[0050] Alkali slag concrete was prepared by replacing sea sand with desalinated sea sand, and other conditions were the same as in Example 1. The specific material physical properties were the same as in Example 1, and the performance testing steps were the same as in Example 1.

[0051] Example 3

[0052] The sea sand was replaced with river sand, and other conditions were the same as in Example 1 to prepare alkali slag concrete. The specific material physical properties were the same as in Example 1, and the performance testing steps were the same as in Example 1.

[0053] Comparative Example 1

[0054] The seawater was replaced with deionized water, and other conditions were the same as in Example 1 to prepare alkali slag concrete. The specific material physical properties were the same as in Example 1, and the performance testing steps were the same as in Example 1.

[0055] Comparative Example 2

[0056] Alkali slag concrete is prepared using slag, solid sodium silicate, seawater, and sea sand.

[0057] (1) Weigh 548g of slag, dry it at 60℃ for 4h, cool it to room temperature, and then mix it with 52g of anhydrous sodium silicate with a modulus of 1.4. That is, the mass of Na2O accounts for 4% of the mass of slag and anhydrous sodium silicate.

[0058] (2) The mixture obtained is placed in a mortar mixer and stirred for 180 min to obtain a simple single-component alkali slag cement.

[0059] (3) Add seawater and sea sand according to the mass ratio of seawater to single-component alkali slag cement of 0.43 (water-cement ratio) and the mass ratio of single-component alkali slag cement to sea sand of 1:2 (cement-sand ratio). Use a mortar mixer to mix the above mixture. The specific process is as follows: add 258g of seawater to 600g of single-component alkali slag cement and mix at low speed for 30s. Then automatically add 1200g of sea sand for 30s. Then mix at high speed for 30s, pause for 90s in the middle. During the pause, scrape off the material on the pot wall and the material settled at the bottom and mix it evenly. Finally, mix at high speed for 60s to obtain alkali slag concrete. The performance test steps are the same as in Example 1.

[0060] Table 6 Mechanical properties of alkali slag concrete in the examples and comparative examples

[0061]

[0062] Table 7. Drying shrinkage rate of alkali slag concrete in the examples and comparative examples.

[0063]

[0064] Table 6 shows that the alkali slag concrete prepared by the mechanochemical method (Examples 1-3) exhibits better mechanical properties than the simple mixing method (Comparative Example 2). Under mechanochemical action, the compressive and flexural strengths of sea sand, desalinated sea sand, and river sand all show an increasing trend with age. The 3-day compressive strength of sea sand, desalinated sea sand, and river sand accounts for 64.5%, 68.8%, and 64.4% of the 28-day compressive strength, respectively. Therefore, the strength of alkali slag mortar develops rapidly in the early stages. It can be seen that the early compressive strengths of sea sand and desalinated sea sand are very similar, with sea sand showing a 13.16% increase in 28-day compressive strength compared to desalinated sea sand. The flexural strengths of sea sand and desalinated sea sand are almost identical. Compared to river sand, although sea sand affects the compressive strength of concrete, the compressive strength of Example 1 reaches 53.3 MPa and the flexural strength reaches 8.6 MPa at 28 days, meeting the basic requirements for application. Compared to Comparative Example 1 which used deionized water, seawater improved the compressive strength of alkali-slag concrete at different ages. The compressive strength of specimens at 3d, 7d, and 28d increased by 6.17%, 1.17%, and 18.44%, respectively. This is because seawater increased the pH value of the concrete, and pH is crucial for the polymerization reaction of alkali-activated materials. Seawater can promote the formation of more CSH gel in alkali-slag materials, leading to the increase in compressive strength. Flexural strength showed almost no difference.

[0065] Table 7 shows that the mechanochemical method produces alkali slag concrete with less drying shrinkage compared to the simple mixing method. This is likely because the ball milling process alters the internal pore size and capillary pressure of the material, resulting in a pore size distribution that favors drying shrinkage performance. Under mechanochemical action, the drying shrinkage rate of alkali slag concrete, from lowest to highest, is: Example 1 < Example 3 < Example 2. That is, the alkali slag concrete prepared with sea sand has the lowest drying shrinkage, and it is lower than that prepared with river sand. Compared to desalinated sea sand, the drying shrinkage of sea sand at 3d, 56d, and 180d is reduced by 26.84%, 22.82%, and 23.64%, respectively. This is because sea sand has a higher chloride ion content and a more vigorous hydration reaction than desalinated sea sand, resulting in higher compressive strength and thus reduced drying shrinkage. Compared to river sand, the drying shrinkage of sea sand at 3d, 56d, and 180d is reduced by 16.22%, 9.78%, and 9.28%, respectively. The reason is that sea sand has a lower evaporable water content compared to river sand and desalinated sea sand, produces the most CaCO3 crystals during hydration, and has the fewest microcracks in its microstructure. Therefore, using sea sand to prepare alkali slag concrete does not necessarily lead to increased drying shrinkage; using suitable sea sand can alleviate the problem of high drying shrinkage in alkali slag concrete. Within 180 days, the addition of seawater reduced the drying shrinkage of alkali slag concrete. Compared to deionized water, the drying shrinkage of seawater samples at 28 days, 56 days, and 180 days was reduced by 6.60%, 7.80%, and 8.90%, respectively. This is because chloride ions in seawater accelerate hydration products, resulting in more hydration products generated inside the alkali slag mortar prepared with seawater. The formation of hydration products refines some of the pore structure, hindering water loss and thus reducing shrinkage. In addition, chloride ions themselves have a water-absorbing and moisturizing effect, which also contributes to the reduction of drying shrinkage.

[0066] In summary, the alkali slag concrete prepared under mechanochemical conditions in this invention achieves a reduced drying shrinkage rate by replacing river sand with sea sand, approaching that of ordinary silicate cement. This effectively solves the problem of excessive drying shrinkage in alkali slag cementitious materials and provides data support for the further promotion and application of seawater-sand alkali slag concrete.

[0067] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made within the scope of the claims of the present invention should be included in the scope of the present invention.

Claims

1. A method for preparing low-drying-shrinkage alkali slag seawater sand concrete, characterized in that: First, the slag and activator are ball-milled using mechanochemical force to obtain powder, which is a single-component alkali slag cement. The slag is S95 grade granulated blast furnace slag, and the activator is anhydrous sodium silicate with an alkali modulus of 1.

4. The mass of Na2O in the anhydrous sodium silicate accounts for 4% of the mass of the slag and anhydrous sodium silicate. Then, the single-component alkali slag cement is mixed with sea sand and seawater to produce alkali slag seawater sea sand concrete. The sea sand, by mass percentage, has a moisture content ≤6.0%, a mud content ≤3.0%, a chloride ion content ≤0.02%, and a shell content ≤5.0%. The seawater was prepared according to the concentration ratio of NaCl:MgCl2:Na2SO4:CaCl2:KCl:NaHCO3 = 24.53:5.2:4.09:1.16:0.695:0.201; The sea sand has a particle size of less than 5 mm and a fineness modulus of 2.71, classifying it as medium sand in Zone II. The mass ratio of seawater to single-component alkali slag cement is 0.43:1; the mass ratio of single-component alkali slag cement to sea sand is 1:

2.

2. The method for preparing low-drying-shrinkage alkali slag seawater sand concrete according to claim 1, characterized in that, Includes the following steps: (1) After drying and cooling the slag, it was mixed with anhydrous sodium silicate with an alkali modulus of 1.4 and ball-milled for 1 h. The ball milling speed was 75 r / min and the ball-to-material ratio was 7.5:

1. After ball milling, the powder was sieved to obtain single-component alkali slag cement. (2) Weigh seawater, sea sand and single-component alkali slag cement according to the proportion, and mix them with a mortar mixer to obtain seawater sea sand alkali slag concrete.

3. The method for preparing low-drying-shrinkage alkali slag seawater sand concrete according to claim 2, characterized in that: The mixing process involves adding seawater to the single-component alkali slag cement and mixing at low speed for 30 seconds, then adding sea sand within 30 seconds, mixing at high speed for 30 seconds, pausing for 90 seconds to mix the materials evenly, and then continuing to mix at high speed for 60 seconds.

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