Method for simultaneously improving mechanical properties and water transport properties of high-volume fly ash mortar by using chemical admixtures

Abstract

This invention discloses a method for simultaneously improving the mechanical properties and moisture transport properties of high-volume fly ash mortar using chemical admixtures. The steps include: 1. Selecting multiple chemical admixtures, with their respective dosages as independent variables, and using response surface methodology to prepare multiple groups of high-volume fly ash mortar. 2. Testing their compressive strength, splitting tensile strength, first-stage water absorption coefficient, and second-stage water absorption coefficient after 28 days of curing, using these as dependent variables. 3. Establishing the mathematical relationship between the mechanical properties and moisture transport properties and influencing factors, predicting the optimal chemical admixture dosage, and preparing high-volume fly ash mortar based on this prediction. The accuracy of the match between the predicted and actual values ​​is then measured and verified. This invention addresses the difficulty of simultaneously improving the mechanical properties and moisture transport properties of high-volume fly ash mortar by applying experimental design and rationally using chemical admixtures to simultaneously improve both properties.

Description

Technical Field

[0001] This invention relates to the field of concrete materials, and in particular to a method for simultaneously improving the mechanical properties and moisture transport properties of high-volume fly ash mortar using chemical admixtures. Background Technology

[0002] Compared to ordinary cement mortar, high-volume fly ash mortar can exhibit similar or even higher later-stage strength, but its early-stage strength is often unsatisfactory, becoming a major reason limiting its further use in practical engineering. In addition, due to the large-scale use of fly ash, the unburned carbon particles in the fly ash can damage the pore structure of high-volume fly ash mortar, deteriorating its frost resistance and salt-frost resistance. Generally speaking, the frost resistance of mortar and concrete is closely related to their moisture transport properties; therefore, improving the moisture transport properties of high-volume fly ash mortar to enhance its frost resistance is a feasible approach.

[0003] Regarding moisture transport performance, it is generally believed that using a large amount of fly ash in concrete or mortar can fill the capillaries in the concrete or mortar through the additional CSH generated by the pozzolanic effect, reducing the number of capillaries, increasing the buckling of the capillary network, optimizing the pore size distribution, and ultimately reducing the possibility of moisture transport. However, optimizing the pore size distribution does not necessarily mean an improvement in the mechanical properties of concrete or mortar; the use of a large amount of fly ash can lead to a decrease in the mechanical properties of concrete or mortar. Currently, many improvement measures can be adopted to enhance the early mechanical properties of mortars with a large amount of fly ash, including reducing the water-cement ratio, using high-temperature curing regimes, adding activators, adding nanomaterials, adding ultrafine mineral admixtures or fibers, etc. However, these measures do not consider whether they can improve the moisture transport performance of mortars with a large amount of fly ash, which limits the practical application scenarios of mortars with a large amount of fly ash. Summary of the Invention

[0004] To overcome the difficulty of existing methods in simultaneously improving the mechanical properties and moisture transport properties of high-volume fly ash mortar, this invention proposes a method that uses experimental design to optimize the dosage of different types of chemical admixtures, thereby simultaneously improving the mechanical properties and moisture transport properties of high-volume fly ash mortar, ultimately broadening the application range of high-volume fly ash mortar.

[0005] To solve the aforementioned technical problems and achieve the above objectives, the present invention is implemented through the following technical solution:

[0006] A method for simultaneously improving the mechanical properties and moisture transport properties of high-volume fly ash mortar using chemical admixtures includes the following steps:

[0007] (1) Preparation of mortar with high fly ash content:

[0008] Using the dosage of various chemical admixtures as a factor, and different dosage values ​​of each chemical admixture as levels, a multi-factor, multi-level central composite experiment was designed using response surface methodology. Cementitious materials, sand, chemical admixtures, and mixing water were mixed and stirred evenly, then poured into molds, covered with plastic film, and cured at room temperature for 24 hours to obtain multiple groups of high-dosage fly ash mortars. The dosage of chemical admixtures was defined as the mass fraction of the chemical admixtures relative to the cementitious materials.

[0009] (2) Testing of mechanical properties and moisture transport properties:

[0010] The high-volume fly ash mortar was demolded and placed in a curing chamber for curing. After 28 days of curing, the compressive strength f of multiple groups of high-volume fly ash mortar was tested. c Splitting tensile strength f s Using the first-stage water absorption coefficient k1 and the second-stage water absorption coefficient k2 as four dependent variables, a mathematical model was established to establish the relationship between the dosage of chemical admixtures and the mechanical properties and moisture transport properties of high-dosage fly ash mortar. The influence of the dosage of different types of chemical admixtures on the mechanical properties and moisture transport properties of high-dosage fly ash mortar was analyzed.

[0011] (3) Optimization of mechanical properties and moisture transport properties:

[0012] With compressive strength f c Splitting tensile strength f s The optimization indexes are maximizing the water absorption coefficient k2 in the second stage and minimizing the water absorption coefficient k1 in the first stage. This yields the optimal dosage of chemical admixtures for achieving the best mechanical properties and moisture transport performance of high-volume fly ash mortar. Furthermore, the optimal dosage of chemical admixtures can also be used to determine the compressive strength f when the compressive strength f is at its optimal level. c Splitting tensile strength f s The predicted values ​​of the first-stage water absorption coefficient k1 and the second-stage water absorption coefficient k2;

[0013] (4) Verification of the optimal dosage of chemical admixtures:

[0014] Based on the optimal dosage of chemical admixtures, high-volume fly ash mortar was prepared, and its mechanical properties and moisture transport properties were tested to obtain the compressive strength f. c Splitting tensile strength f s The measured values ​​of the first-stage water absorption coefficient k1 and the second-stage water absorption coefficient k2 are compared with the predicted values ​​to determine the accuracy of the optimal dosage of the chemical admixture.

[0015] Preferably, in step (1), the cementitious material includes fly ash and cement, wherein the fly ash accounts for 50-70 wt% and the cement accounts for 30-50 wt%.

[0016] Preferably, in step (1), the water-to-glue ratio is 0.3–0.4.

[0017] Preferably, in step (1), the mass ratio of sand to cementitious material is 1.5:1–2.5:1.

[0018] Preferably, in step (1), the chemical additive is selected from at least two of the following: tributyl phosphate, triethanolamine, propylene glycol, calcium stearate, aluminum sulfate, hydroxyl polysiloxane, asphalt emulsion, polyvinyl alcohol, hydroxypropyl methylcellulose, and ethylene-vinyl acetate copolymer.

[0019] Preferably, in step (1), the cementitious material, sand and solid chemical additives are first dry-mixed, and then the mixing water and liquid chemical additives are added.

[0020] Preferably, in step (2), the curing conditions inside the curing box are: temperature 22±2℃, relative humidity 98%.

[0021] Preferably, a fitting formula can be obtained between the dosage of chemical admixtures and the mechanical properties and moisture transport properties of high-volume fly ash mortar. Based on the fitting formula, a 3D visualization diagram of the response surface of different influencing factors and their interactions on the mechanical properties and moisture transport properties of high-volume fly ash mortar is obtained. Then, under the condition that the mechanical properties and moisture transport properties have the same optimization weight, the optimal dosage of chemical admixtures for simultaneously improving the mechanical properties and moisture transport properties of high-volume fly ash mortar is obtained.

[0022] Compared with the prior art, the advantages of the present invention are as follows:

[0023] This invention achieves simultaneous improvement in the mechanical properties and moisture transport properties of high-volume fly ash mortar through the rational use of chemical admixtures. It overcomes the limitations imposed on high-volume fly ash mortar in practical engineering due to its low early strength or poor frost resistance, thus broadening its application. Furthermore, response surface methodology experiments can be designed based on different chemical admixtures to predict the optimal chemical admixture dosage for achieving optimal mechanical and moisture transport properties. Attached Figure Description

[0024] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention, wherein:

[0025] Figure 1 The effect of the dosage of propylene glycol and aluminum sulfate on the splitting tensile strength f of mortar with high fly ash content is... s The influence surface plot.

[0026] Figure 2This is a surface plot showing the effect of the dosage of propylene glycol and calcium stearate on the first-stage water absorption coefficient k1 of high-dosage fly ash mortar. Detailed Implementation

[0027] The following disclosure provides many different embodiments or examples for implementing different structures of the invention. To simplify the disclosure, specific examples of components and arrangements are described below. Of course, these are merely examples and are not intended to limit the invention. Furthermore, reference numerals and / or letters may be repeated in different examples; such repetition is for simplification and clarity and does not in itself indicate a relationship between the various embodiments and / or arrangements discussed.

[0028] 1. Raw materials and test plan

[0029] 1.1 Raw materials

[0030] This invention uses a high-volume fly ash mortar as an example. The cementitious materials include P·II 42.5 type cement and Grade I fly ash, both with densities of 3.13 g / cm³. 3 and 2.56 g / cm 3 The aggregate in the mortar is silica sand, with a maximum particle size of 4.75 mm, a fineness modulus of 2.7, and an apparent density of 2618 kg / m³. 3 The aggregates should be brought to a saturated surface-dry state before use. Of the five chemical admixtures, triethanolamine, tributyl phosphate, and propylene glycol are liquids, while aluminum sulfate and calcium stearate are solids.

[0031] 1.2 Mix Design

[0032] This invention uses a fixed fly ash content (60 wt% of cementitious material), a fixed water-cement ratio (0.3), and a fixed bone-cement ratio (1.5:1) to prepare high-volume fly ash mortars with different chemical admixture contents (i.e., the mass fraction of chemical admixtures in cementitious material). The mechanical properties and moisture transport properties of high-volume fly ash mortars under different mix proportions are studied. Taking a five-factor, five-level central composite design as an example, the five factors are: X1, tributyl phosphate mass fraction of cementitious material (TBP / b); X2, triethanolamine mass fraction of cementitious material (TEA / b); X3, propylene glycol mass fraction of cementitious material (PD / b); X4, calcium stearate mass fraction of cementitious material (CS / b); and X5, aluminum sulfate mass fraction of cementitious material (AS / b). A total of 26 high-volume fly ash mortars are prepared, and the specific mix proportions are shown in Table 1.

[0033] High-volume fly ash mortar was prepared using a laboratory mortar mixer. Fly ash, cement, sand, and solid chemical admixtures (aluminum sulfate and calcium stearate) were first dry-mixed for 5 minutes, then mixing water and liquid chemical admixtures (triethanolamine, tributyl phosphate, and propylene glycol) were added and mixed for another 5 minutes to achieve better workability. After mixing, the freshly mixed mortar was poured into cylindrical molds with a diameter of 50.8 mm and a height of 101.6 mm. All samples were covered with a plastic film and cured at room temperature for 24 hours. Afterward, the samples were demolded and placed in a curing chamber (temperature 22±2℃, relative humidity 98%) for 28 days.

[0034] Table 1. Mix proportions of high-volume fly ash mortar

[0035]

[0036] 1.3 Test Methods

[0037] The compressive strength and splitting tensile strength of high fly ash mortar were tested according to standards ASTM C109 and C1006, respectively.

[0038] The water absorption of high-volume fly ash mortar mainly depends on the capillary porosity of the mortar and is determined by the rate of water absorption. Testing was conducted after appropriately modifying the specimen dimensions according to standard ASTM C1585. After curing, 10mm thick circular specimens were cut from the middle of the cylindrical specimens. The specimens were then placed in a drying oven at 60℃ and a vacuum of 84.6kPa for 24 hours to remove moisture. At a vacuum of 84.6kPa, the boiling point of water is 56℃, and setting the drying oven temperature to 60℃ ensures complete removal of moisture from the specimens. After the specimens cooled to room temperature, the upper and side surfaces were carefully sealed, and the specimens were then placed on an iron support in water, ensuring that only the lower surface could contact the water. The amount of water absorbed by the specimen was determined by its mass. The water absorption coefficient k (mm / s) was used. 1 / 2 It can be determined by the following formula:

[0039]

[0040] In the formula, I represents the water absorption per unit area (mm²). 3 / mm 2 );

[0041] m t —The mass (g) of the sample at time t;

[0042] a — Water absorption area of ​​the sample (cm²) 2 );

[0043] d — density of water (g / mm³) 3 ).

[0044] The first-stage water absorption coefficient of high-volume fly ash mortar reflects the rate of water absorption within the first 6 hours, while the second-stage water absorption coefficient reflects the rate of water absorption between the 2nd and 8th days.

[0045] 2. Test Results

[0046] 2.1 Mechanical properties and moisture transport properties of mortar with high fly ash content

[0047] Table 2 lists the 28-day compressive strength (f) of the 26 groups of high-volume fly ash mortars in Table 1. c ), splitting tensile strength (f) s ), first-stage water absorption coefficient (k1) and second-stage water absorption coefficient (k2).

[0048] Table 2 Mechanical properties and moisture transport properties of high-volume fly ash mortar

[0049]

[0050] Using the mechanical properties and moisture transport properties of high-volume fly ash mortar as dependent variables, fitting formulas can be established between significant factors and these properties:

[0051] f c -2.41 =1.285×10 -4 +1.672×10 -5 X3

[0052]

[0053]

[0054]

[0055] Based on the fitting formulas between the mechanical properties and moisture transport properties of high-volume fly ash mortar and their significant influencing factors, a 3D visualization of the response surface of the interaction between different influencing factors on the performance of high-volume fly ash mortar can be obtained, indicating possible directions for subsequent optimization of the mechanical properties and moisture transport properties of high-volume fly ash mortar. Figure 1 This study demonstrates the effects of propylene glycol and aluminum sulfate on the splitting tensile strength of mortar with high fly ash content. Figure 1 The dosages of propylene glycol and aluminum sulfate increased from -1 to +1 (coded value), while the dosages of other additives remained fixed at 0 (coded value). This means that the actual dosages of propylene glycol and aluminum sulfate increased from 0.2% to 0.8%, while the actual dosages of tributyl phosphate, triethanolamine, and calcium stearate remained fixed at 0.5%, 0.25%, and 1%, respectively. Figure 1 It can be seen that there is an interaction between propylene glycol and aluminum sulfate to affect the splitting tensile strength of mortar with high fly ash content. Figure 2 This indicates the influence of propylene glycol and calcium stearate on the first-stage water absorption coefficient of high-volume fly ash mortar. Figure 1 resemblance, Figure 2 This indicates that the interaction between propylene glycol and calcium stearate affects the first-stage water absorption coefficient of high-volume fly ash mortar. When the propylene glycol content is 0.8% (coded value +1), as the calcium stearate content increases from 0.4% to 1.6% (coded value from -1 to +1), the first-stage water absorption coefficient of the high-volume fly ash mortar increases from 0.0075 mm / s. 1 / 2 Reduced to 0.0047 mm / s 1 / 2 Calcium stearate, as a waterproofing agent, forms a hydrophobic layer around the cementitious particles inside the mortar, reducing the water absorption of mortar with a high content of fly ash.

[0056] 2.2 Optimization of Mechanical Properties and Moisture Transport Properties of High-Concentration Fly Ash Mortar

[0057] Based on the influence of different factors on the mechanical properties and moisture transport properties of high-volume fly ash mortar, the dosage of chemical admixtures was optimized with the objectives of maximizing compressive strength, splitting tensile strength, second-stage water absorption coefficient, and minimizing first-stage water absorption coefficient. During the optimization process, compressive strength, splitting tensile strength, first-stage water absorption, and second-stage water absorption coefficient were given equal weights. The optimization results are shown in Table 3.

[0058] As shown in Table 3, the optimal chemical admixture dosages for achieving the best mechanical and moisture transport properties in high-volume fly ash mortar are: triethanolamine 0.14%, propylene glycol 0.09%, aluminum sulfate 0.45%, and tributyl phosphate and calcium stearate 0%. Under these optimal dosages, the predicted compressive strength, splitting tensile strength, and first-stage water absorption coefficient of the high-volume fly ash mortar are 47.1 MPa and 4.1 MPa, respectively. 1 / 2 The predicted value of the water absorption coefficient for the second stage is 0.0007 mm / s. 1 / 2 .

[0059] Table 3 Performance optimization of high-volume fly ash mortar (%)

[0060]

[0061] 2.3 Verification of the optimal dosage of chemical admixtures for high-volume fly ash mortar

[0062] Based on the optimal dosage of chemical admixtures, high-volume fly ash mortar was prepared. After 28 days of standard curing, its mechanical properties and moisture transport properties were tested. The measured values ​​of compressive strength, splitting tensile strength, first-stage water absorption coefficient, and second-stage water absorption coefficient were 48.0 MPa, 4.0 MPa, and 0.0027 mm / s, respectively. 1 / 2 and 0.0007mm / s 1 / 2 The errors between the predicted and measured values ​​of the mechanical properties and moisture transport properties of high-volume fly ash mortar are all within 10%, indicating the accuracy of the optimal dosage of the selected chemical admixture.

[0063] Other embodiments of the invention will readily occur to those skilled in the art upon consideration of the specification and practice of the invention herein. This invention is intended to cover any variations, uses, or adaptations of the invention that follow the general principles of the invention and include common knowledge or customary techniques in the art. The specification and examples are to be considered exemplary only, and the true scope and spirit of the invention are indicated by the claims.

[0064] It should be understood that the present invention is not limited to the precise structure described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of the invention is limited only by the appended claims.

Claims

1. A method for simultaneously improving the mechanical properties and water transport properties of fly ash mortar with a large amount of fly ash by using chemical admixtures, characterized in that, Includes the following steps: (1) Preparation of mortar with high fly ash content: Using the dosage of various chemical admixtures as a factor, and different dosage values ​​of each chemical admixture as levels, a multi-factor, multi-level central composite experiment was designed using response surface methodology. Cementitious materials, sand, the aforementioned chemical admixtures, and mixing water were mixed and stirred evenly, then poured into molds and covered with plastic film. The mixtures were then cured at room temperature for 24 hours to obtain multiple groups of high-dosage fly ash mortars. The dosage of the chemical admixtures was defined as the mass fraction of the chemical admixtures relative to the cementitious materials. The factors are as follows: X1, the mass fraction of tributyl phosphate in the cementitious material (TBP / b); X2, the mass fraction of triethanolamine in the cementitious material (TEA / b); X3, the mass fraction of propylene glycol in the cementitious material (PD / b); X4, the mass fraction of calcium stearate in the cementitious material (CS / b); X5, the mass fraction of aluminum sulfate in the cementitious material (AS / b). The cementitious material includes fly ash and cement, wherein the fly ash accounts for 50-70 wt% and the cement accounts for 30-50 wt%. The water-cement ratio is 0.3–0.4; the mass ratio of the sand to the cementitious material is 1.5:1–2.5:1; (2) Testing of mechanical properties and moisture transport properties: The high-volume fly ash mortar was demolded and placed in a curing chamber for curing. After 28 days of curing, the compressive strength of multiple groups of the high-volume fly ash mortar was tested. f c Splitting tensile strength f s First stage water absorption coefficient k 1 and second stage water absorption coefficient k 2. As four dependent variables, a mathematical model was established between the dosage of the chemical admixture and the mechanical properties and moisture transport properties of the high-dosage fly ash mortar, and the influence of the variation of the dosage of different types of chemical admixtures on the mechanical properties and moisture transport properties of the high-dosage fly ash mortar was analyzed. The mathematical model is established as follows: a fitting formula can be obtained based on the relationship between the dosage of the chemical admixture and the mechanical properties and moisture transport properties of the high-dosage fly ash mortar. Based on the fitting formula, a 3D visualization of the response surface of different influencing factors and their interactions on the mechanical properties and moisture transport properties of the high-dosage fly ash mortar is obtained. Then, under the condition that the mechanical properties and moisture transport properties have the same optimization weight, the optimal dosage of the chemical admixture is obtained when the mechanical properties and moisture transport properties of the high-dosage fly ash mortar are improved simultaneously. The fitting formula is: ； X1 is selected from the mass fraction of tributyl phosphate in the cementitious material (TBP / b); X2 is selected from the mass fraction of triethanolamine in the cementitious material (TEA / b); X3 is selected from the mass fraction of propylene glycol in the cementitious material (PD / b); X4 is selected from the mass fraction of calcium stearate in the cementitious material (CS / b); X5 is selected from the mass fraction of aluminum sulfate in the cementitious material (AS / b). (3) Optimization of mechanical properties and moisture transport properties: the compressive strength f c the splitting tensile strength f s the second-stage water absorption coefficient k2 is maximized, and the first-stage water absorption coefficient k 1 is minimized as an optimization index, to obtain the optimal dosage of the chemical additive when the mechanical properties and moisture transport properties of the high-volume fly ash mortar are optimal; and to obtain the compressive strength f c the splitting tensile strength f s the first-stage water absorption coefficient k 1 and the second-stage water absorption coefficient k 2 are predicted values. (4) Verification of the optimal dosage of chemical admixtures: The high-volume fly ash mortar was prepared based on the optimal dosage of the aforementioned chemical admixture, and its mechanical properties and moisture transport properties were tested to obtain the compressive strength. f c The splitting tensile strength f s The first stage water absorption coefficient k 1 and the second stage water absorption coefficient k The accuracy of the optimal dosage of the chemical admixture is determined by comparing the predicted value with the measured value of 2.

2. The method for simultaneously improving the mechanical properties and moisture transport properties of high-volume fly ash mortar using chemical admixtures according to claim 1, characterized in that, In step (1), the chemical additive is selected from at least two of the following: tributyl phosphate, triethanolamine, propylene glycol, calcium stearate, aluminum sulfate, hydroxyl polysiloxane, asphalt emulsion, polyvinyl alcohol, hydroxypropyl methylcellulose, and ethylene-vinyl acetate copolymer.

3. The method for simultaneously improving the mechanical properties and moisture transport properties of high-volume fly ash mortar using chemical admixtures according to claim 1, characterized in that, In step (1), the cementitious material, the sand and the solid chemical additive are first dry-mixed, and then the mixing water and the liquid chemical additive are added.

4. The method for simultaneously improving the mechanical properties and moisture transport properties of high-volume fly ash mortar using chemical admixtures according to claim 1, characterized in that, In step (2), the curing conditions inside the curing chamber are: temperature 22°C. 2℃, relative humidity 98%.

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