An evaluation method for the interfacial enhancement of ultra-high performance concrete using limestone powder as a substitute for silica fume.

Abstract

This invention discloses a method for evaluating the interfacial reinforcement of ultra-high performance concrete using limestone powder as a substitute for silica fume, belonging to the technical field of cementitious composite material mix design and performance evaluation. The invention first establishes a reference cementitious material matrix system containing silica fume and sets up gradient substitution groups for silica fume using limestone powder. The strength of specimens with different substitution ratios is pre-screened based on the 28-day matrix compressive strength, selecting representative substitution groups. The 100-hour cumulative heat release, 28-day total porosity, peak pull-out load of a single steel fiber, and pull-out work of a single fiber are measured for the representative substitution groups. Hydration response coefficient, pore structure compactness coefficient, peak bearing capacity coefficient, and energy dissipation coefficient are constructed, and a coupled determination method of interfacial reinforcement index (IEI) and strength constraint coefficient (Kc) is established. Based on IEI and Kc, candidate reinforcement groups, optimal substitution groups, and corresponding substitution ratios are output. This invention can be used for the rapid screening and quantitative design of low-silica fume ultra-high performance concrete cementitious systems.

Description

Technical Field

[0001] This invention relates to the field of cement-based composite material mix design and performance evaluation technology, and in particular to an evaluation method for interface enhancement of ultra-high performance concrete using limestone powder as a substitute for silica fume. Background Technology

[0002] Silica fume is a commonly used highly active fine powder component in ultra-high performance concrete. It can significantly improve the density of the matrix and the structure of the interface transition zone through pozzolanic reaction and ultrafine filling effect. However, high silica fume content can also lead to problems such as high material cost, high slurry viscosity and increased construction sensitivity.

[0003] Limestone powder is widely available, inexpensive, and has flexible particle size distribution, making it a potential substitute for silica fume in low-silica ultra-high performance concrete systems. It can also regulate fine powder accumulation and reduce paste viscosity. When incorporated in appropriate amounts, limestone powder can improve the early structure formation process through filling, nucleation, and particle size distribution adjustments. However, excessively high substitution rates may weaken later gel formation and the interfacial reinforcement effect of steel fibers due to insufficient active silica sources.

[0004] Most existing designs for low-silica ultra-high performance concrete still rely on empirical mix design and a single strength index. There is a lack of a technical method that unifies and normalizes hydration response, pore structure densification, single fiber peak pull-out load and pull-out energy consumption, and uses it to determine the proportion of limestone powder to replace silica fume. As a result, it is difficult to accurately determine the optimal window for limestone powder to replace silica fume. Summary of the Invention

[0005] The purpose of this invention is to provide an evaluation method for the interface enhancement of ultra-high performance concrete using limestone powder as a substitute for silica fume, thereby solving the problem that the mix design of existing low-silica fume ultra-high performance concrete systems relies on experience-based trial mixing and is difficult to simultaneously consider matrix strength and fiber-matrix interface energy consumption.

[0006] To achieve the above objectives, this invention provides an evaluation method for interface enhancement of ultra-high performance concrete using limestone powder as a substitute for silica fume, comprising the following steps: S1. Establish a reference cementitious material matrix system containing silica fume. The reference cementitious material matrix system includes cement, silica fume, quartz powder, water and water-reducing agent, wherein silica fume is used as the reference active fine powder component; limestone powder is used as the filler-nucleating fine powder component to replace silica fume; when used for single fiber pull-out test, a single steel fiber is embedded in the corresponding cementitious material matrix. S2. Keep the total amount of cementitious materials, water-cement ratio, water-reducing agent dosage, molding system and curing system consistent. Set up limestone powder to replace silica fume in equal mass ratios according to the predetermined ratio of silica fume mass, and prepare test specimen groups with different replacement ratios. S3. The 28-day matrix compressive strength fc of the specimen groups with different substitution ratios was measured respectively. 28And using the 0% replacement group without silica fume as the reference group, the strength constraint coefficient Kc=fc was calculated. 28 / fc 28,0 , of which fc 28,0 The 28-day matrix compressive strength is used as a reference group. S4. Based on the 28-day matrix compressive strength variation law, select representative substitution groups from the specimen groups with different substitution ratios. The representative substitution groups include the reference group, the low substitution group, the peak strength group, and the high substitution group. S5. Measure the cumulative heat release Q100 over 100 hours, total porosity P28 over 28 days, and peak pull-out load F of a single steel fiber for the representative alternative group. max And the single-fiber pull-out work W obtained by integrating the pull-out load-slip curve. p ; S6. Using the 0% substitution group (without silica fume) as the reference group, calculate the hydration response coefficient ηQ, pore structure compactness coefficient ηP, peak load-bearing capacity coefficient ηF, and energy dissipation coefficient ηW of the representative substitution group according to the following formula: ηQ=Q100 / Q0, ηP=P0 / P28, ηF=F max / F max,0 , ηW=W p / W p,0 ; Among them, Q0, P0, F max,0 W p,0 The values ​​are the cumulative heat release over 100 hours, total porosity over 28 days, peak pull-out load of a single steel fiber, and pull-out work of a single fiber, respectively, for the reference group. S7. Calculate the Interface Enhancement Index (IEI) based on ηQ, ηP, ηF, and ηW. The Interface Enhancement Index (IEI) is defined as IEI = a·ηQ + b·ηP + c·ηF + d·ηW, where the weighting coefficients a, b, c, and d are all greater than 0 and a + b + c + d = 1. S8. Determine the interface enhancement level of the representative substitution group based on the interface enhancement index IEI and the strength constraint coefficient Kc, and output the candidate enhanced substitution group, the optimal substitution group and the corresponding limestone powder to silica fume ratio.

[0007] Preferably, in S1, the mass of silica fume in the reference cementitious material matrix system accounts for 15% to 25% of the total mass of the cementitious material.

[0008] Preferably, in S2, the limestone powder replaces silica fume at a ratio of 0% to 60% of the silica fume mass.

[0009] Preferably, in S5, the cumulative heat release Q100 over 100 hours is determined by isothermal calorimetry, and the total porosity P28 over 28 days is determined by mercury porosimetry.

[0010] Preferably, in S5, the peak pull-out load F of the single steel fiber max And single fiber pull-out work W p The results were determined by a single fiber pull-out test; the conditions of the single fiber pull-out test included standardized control of the steel fiber embedding depth, pull-out angle, and loading rate.

[0011] Preferably, in S7, the weighting coefficients a, b, c, and d are allocated according to the contribution of hydration propulsion, pore structure densification, fiber interface peak load, and fiber interface energy dissipation to interface reinforcement, wherein the single fiber pull-out work W p The corresponding weight coefficient d is the largest.

[0012] Preferably, in S8, the rule for determining the interface enhancement level is: The alternative group with an interface enhancement index IEI ≥ 1.00 and a strength constraint coefficient Kc ≥ 1.00 was identified as the candidate enhancement group; When there are multiple candidate enhancement groups, the substitution group with the largest interface enhancement index (IEI) is determined as the optimal substitution group, and the limestone powder substitution ratio for silica fume corresponding to the optimal substitution group is determined as the optimal substitution ratio. The alternative groups with an interface enhancement index (IEI) < 1.00 or a strength constraint coefficient (Kc) < 1.00 were identified as the non-recommended groups.

[0013] The method is used to determine the design ratio of limestone powder to silica fume in a low-silica ultra-high performance concrete cementitious material system, and to prepare ultra-high performance concrete matrices for bridge engineering, marine engineering components, prefabricated connection components and thin-walled components.

[0014] Therefore, this invention adopts the above-mentioned evaluation method for interface enhancement of ultra-high performance concrete using limestone powder to replace silica fume, and introduces hydration advancement, pore structure refinement and fiber interface peak-energy consumption synergistic index; it realizes the quantitative comparison of substitution effect through interface enhancement index, outputs candidate enhancement group, optimal substitution group and non-recommended group, and uses the substitution ratio corresponding to the optimal substitution group as the design parameter of low silica fume ultra-high performance concrete matrix; it can serve the rapid design and engineering selection of low silica fume ultra-high performance concrete system.

[0015] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0016] Figure 1 This is a flowchart of the evaluation process for the interface enhancement of ultra-high performance concrete using limestone powder as a substitute for silica fume, as described in this invention. Figure 2 This is a graph showing the relationship between the proportion of limestone powder replacing silica fume and the compressive strength of 28-day neat cement paste in an embodiment of the present invention. Figure 3 This is a comparison chart of the cumulative heat release over 100 hours and the total porosity over 28 days for representative alternative groups in this embodiment of the invention. Figure 4 This is a comparison chart of peak single-fiber pull-out load and single-fiber pull-out work for a representative alternative group in this invention embodiment; Figure 5 This is a comparison chart of the Interface Enhancement Index (IEI) for representative alternative groups in embodiments of the present invention. Figure 6 This is a schematic diagram illustrating the mechanism by which limestone powder partially replaces silica fume to achieve interface enhancement in an embodiment of the present invention. Detailed Implementation

[0017] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0018] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning understood by one of ordinary skill in the art to which this invention pertains. The terms "first," "second," and similar terms used in this invention do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Terms such as "comprising" or "including" mean that the element or object preceding the word encompasses the elements or objects listed following the word and their equivalents, without excluding other elements or objects.

[0019] Example 1 This embodiment provides an evaluation method for interface enhancement of ultra-high performance concrete using limestone powder as a substitute for silica fume. The technical route and evaluation process are as follows: Figure 1 As shown, it includes the following steps: S1. Establish a reference cementitious material matrix system containing silica fume.

[0020] The reference cementitious material matrix system comprises cement, silica fume, quartz powder, water, and a water-reducing agent; for single fiber pull-out tests, a single steel fiber is embedded in the corresponding matrix; silica fume serves as the reference active fine powder component, and limestone powder serves as a substitute for silica fume as a filler-nucleating fine powder component. In this embodiment, the total mass of the cementitious material in the reference cementitious system is 100 parts, of which the mass fraction of silica fume is 20%.

[0021] S2, preparation of gradient substitution groups.

[0022] To maintain consistency in the total amount of cementitious materials, water-cement ratio, water-reducing agent dosage, molding regime, and curing regime, limestone powder was used to replace silica fume at a predetermined mass ratio to prepare specimen groups with different replacement ratios. Based on the baseline cementitious system, while keeping the masses of cement, quartz powder, water, and water-reducing agent constant, and maintaining the same total amount of cementitious materials and water-cement ratio, limestone powder was used to replace silica fume at equal mass ratios (by mass): 0%, 10%, 20%, 30%, 40%, 50%, and 60%, totaling seven groups. The group with a replacement ratio of 0% was designated as the baseline group, also known as the reference group. All specimens were cured under standard curing conditions to the specified age.

[0023] S3, Intensity Screening.

[0024] The 28-day matrix compressive strength fc was measured for seven gradient substitution groups (0%, 10%, 20%, 30%, 40%, 50%, and 60%). 28 When using neat cement paste specimens, the fc 28 To determine the 28-day compressive strength of the cementitious paste specimens, the strength constraint coefficient Kc=fc for each gradient substitution group was calculated, using the 0% substitution group as the reference group. 28 / fc 28,0 , of which fc 28,0 The matrix compressive strength at 28 days is the reference group.

[0025] For each of the seven complete gradients, neat cement paste specimens were molded and the 28-day matrix compressive strength fc was tested. 28 The result is as follows Figure 2 As shown in the figure, the results indicate that when the proportion of limestone powder replacing silica fume increased from 0% to 30%, the 28-day compressive strength of the cement paste gradually increased from 89.62 MPa in the reference group to 97.05 MPa; when the replacement ratio was further increased to 60%, the strength rapidly decreased to 63.15 MPa. This suggests that within the replacement range of 0% to 60%, partial replacement of silica fume with limestone powder can improve the 28-day matrix compressive strength to a certain extent, with the 30% replacement group exhibiting the highest strength, which can be used as the peak strength group in subsequent representative evaluations; excessively high replacement rates will weaken the overall mechanical properties.

[0026] S4. Selection of representative alternative groups.

[0027] Based on the 28-day matrix compressive strength variation pattern, four representative substitution groups (0%, 10%, 30%, and 60%) were selected for subsequent hydration, pore structure, and single-fiber interface performance tests. The 0% substitution group served as the reference group, the 10% substitution group as the low-substitution enhancement group, the 30% substitution group as the peak strength group, and the 60% substitution group as the high-substitution degradation group. These representative substitution groups covered four typical states: no substitution, low-substitution enhancement, peak strength enhancement, and high-substitution degradation.

[0028] S5. Determination of hydration, pore structure and single-fiber interface parameters of representative alternative groups.

[0029] For four representative substitution groups (0%, 10%, 30%, and 60%), the cumulative heat release (Q100) over 100 hours, the total porosity (P28) over 28 days, and the peak pull-out load (F) of a single steel fiber were measured. max And the single-fiber pull-out work W obtained by integrating the pull-out load-slip curve. p .

[0030] The cumulative heat release (Q100) over 100 hours was obtained using isothermal calorimetry, and the total porosity (P28) over 28 days was obtained using mercury intrusion porosimetry. The comparison results of the cumulative heat release over 100 hours and the total porosity over 28 days are as follows: Figure 3 As shown, the cumulative heat release of the 30% substitution group reached 153.83 J / g over 100 hours, higher than the 146.67 J / g of the reference group; meanwhile, its total porosity decreased to 5.07% over 28 days, significantly lower than the 9.21% of the reference group. This indicates that replacing silica fume with an appropriate amount of limestone powder did not weaken the reaction process of the system, but rather improved particle packing and promoted the densification of the hardened slurry structure to a certain extent.

[0031] Single fiber peak pull-out load F max And single fiber pull-out work W p The single-fiber pull-out test was conducted under the following conditions: steel fiber embedment depth 9±1 mm, pull-out angle 0°, and loading rate 0.1 mm / min. The comparison results of the peak pull-out load and pull-out work of a single fiber are as follows: Figure 4 As shown, compared to the reference group, the peak pull-out load of a single fiber in the 30% replacement group increased to 58.09 N, and the pull-out energy of a single fiber increased to 309.78 N·mm; while in the 60% replacement group, they decreased to 46.61 N and 169.85 N·mm, respectively, indicating that a high replacement rate will significantly weaken the peak load-bearing capacity of the fiber-matrix interface and the synergistic energy consumption throughout the process.

[0032] S6. Calculation of normalized response coefficients.

[0033] Using the 0% substitution group (without silica fume) as a reference group, the hydration response coefficient ηQ, pore structure compactness coefficient ηP, peak load-bearing capacity coefficient ηF, and energy dissipation coefficient ηW of representative substitution groups were calculated. According to the definitions, the coefficients for the four typical substitution groups (0%, 10%, 30%, and 60%) were calculated as follows: ηQ = Q100 / Q0, ηP = P0 / P28, ηF = F max / F max,0 ηW=W p / W p,0 ; Among them, Q0, P0, F max,0 Wp,0 The cumulative heat release over 100 hours, total porosity over 28 days, peak pull-out load per steel fiber, and pull-out work per fiber are respectively for the reference group (0% substitution group). The calculation results are summarized in Table 1.

[0034] Table 1 Key performance parameters, IEI and judgment results of typical alternative groups

[0035] S7. Calculate the interface reinforcement index (IEI) based on ηQ, ηP, ηF, and ηW. The weighting coefficients are allocated according to the contribution of hydration advancement, pore structure densification, fiber interface peak load, and fiber interface energy dissipation to interface reinforcement. The weighting coefficient corresponding to interface energy dissipation is the largest, and it satisfies a+b+c+d=1 and all coefficients are greater than 0. In this embodiment, the weighting coefficient corresponding to interface energy dissipation is the largest, at 0.30; specifically, IEI = 0.20·ηQ + 0.25·ηP + 0.25·ηF + 0.30·ηW. The strength constraint coefficient Kc in Table 1 is calculated from the 28d matrix compressive strength in S3.

[0036] S8, Interface Enhancement Level Determination.

[0037] The interface reinforcement level of representative substitution groups is determined based on the Interface Reinforcement Index (IEI) and the Strength Constraint Coefficient (Kc), outputting the candidate reinforcement groups, the optimal substitution group, and the optimal substitution ratio for limestone powder replacing silica fume. Specifically, the determination rules are as follows: substitution groups with an IEI ≥ 1.00 and a Kc ≥ 1.00 are identified as candidate reinforcement groups; when multiple candidate reinforcement groups exist, the substitution group with the highest IEI is identified as the optimal substitution group, and the corresponding limestone powder substitution ratio for this group is identified as the optimal substitution ratio; substitution groups with an IEI < 1.00 or a Kc < 1.00 are identified as unrecommended groups.

[0038] like Figure 5 As shown in Table 1, according to the above judgment rules, the IEI of both the SLP10 / S20LP10 group and the SLP30 / S20LP30 group is greater than 1.00, and their Kc values ​​are also greater than 1.00, therefore they are judged as candidate enhancement groups. Among them, the IEI of the SLP30 / S20LP30 group is the highest, reaching 1.322, so the SLP30 / S20LP30 group is determined as the optimal replacement group, and 30% is determined as the optimal replacement ratio of limestone powder for silica fume. The IEI and Kc of the SLP60 / S20LP60 group are both lower than 1.00, and it is judged as a non-recommended group.

[0039] This embodiment further explains the mechanism by which limestone powder partially replaces silica fume to achieve interface enhancement, such as... Figure 6As shown, systems with higher silica fume content are prone to problems such as silica fume agglomeration, increased local water demand, and insufficient fine powder packing efficiency. After partially replacing silica fume with limestone powder, the composite distribution of fine powder is improved, the particle packing is more compact, and the capillary pores are reduced. The optimization effect is transferred to the fiber-matrix interface zone of ultra-high performance concrete, making the interface transition zone more compact, and the peak pull-out load and pull-out work of a single steel fiber are simultaneously improved, achieving a balance between low silica fume and high performance.

[0040] Therefore, this invention adopts the above-mentioned evaluation method for interface enhancement of ultra-high performance concrete using limestone powder to replace silica fume. Based on hydration advancement, pore structure densification, and the peak-energy dissipation synergistic response of steel fiber interface, it constructs an interface enhancement index (IEI) and combines it with the strength constraint coefficient (Kc) for quantitative determination. This transforms empirical mix design into a quantifiable index screening process, reducing the blind spots in the research and development of low silica fume ultra-high performance concrete systems, and providing a unified evaluation basis for material design, engineering selection, and performance verification.

[0041] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for evaluating the interface enhancement of ultra-high performance concrete using limestone powder as a substitute for silica fume, characterized in that, Includes the following steps: S1. Establish a reference cementitious material matrix system containing silica fume. The reference cementitious material matrix system includes cement, silica fume, quartz powder, water and water-reducing agent, wherein silica fume is used as the reference active fine powder component; limestone powder is used as the filler-nucleating fine powder component to replace silica fume; when used for single fiber pull-out test, a single steel fiber is embedded in the corresponding cementitious material matrix. S2. Keep the total amount of cementitious materials, water-cement ratio, water-reducing agent dosage, molding system and curing system consistent. Set up limestone powder to replace silica fume in equal mass ratios according to the predetermined ratio of silica fume mass, and prepare test specimen groups with different replacement ratios. S3. The 28-day matrix compressive strength fc of the specimen groups with different substitution ratios was measured respectively. 28 Using the 0% replacement group (without silica fume) as the reference group, the strength constraint coefficient Kc=fc was calculated. 28 / fc 28,0 , of which fc 28,0 The 28-day matrix compressive strength is used as a reference group. S4. Based on the 28-day matrix compressive strength variation law, select representative substitution groups from the specimen groups with different substitution ratios. The representative substitution groups include the reference group, the low substitution group, the peak strength group, and the high substitution group. S5. Measure the cumulative heat release Q100 over 100 hours, total porosity P28 over 28 days, and peak pull-out load F of a single steel fiber for the representative alternative group. max And the single-fiber pull-out work W obtained by integrating the pull-out load-slip curve. p ; S6. Using the 0% substitution group (without silica fume) as the reference group, calculate the hydration response coefficient ηQ, pore structure compactness coefficient ηP, peak load-bearing capacity coefficient ηF, and energy dissipation coefficient ηW of the representative substitution group according to the following formula: ηQ=Q100 / Q0, ηP=P0 / P28, ηF=F max / F max,0 , ηW=W p / IN p,0 ; Among them, Q0, P0, F max,0 W p,0 The values ​​are the cumulative heat release over 100 hours, total porosity over 28 days, peak pull-out load of a single steel fiber, and pull-out work of a single fiber, respectively, for the reference group. S7. Calculate the Interface Enhancement Index (IEI) based on ηQ, ηP, ηF, and ηW. The Interface Enhancement Index (IEI) is defined as IEI = a·ηQ + b·ηP + c·ηF + d·ηW, where the weighting coefficients a, b, c, and d are all greater than 0 and a + b + c + d = 1. S8. Determine the interface enhancement level of the representative substitution group based on the interface enhancement index IEI and the strength constraint coefficient Kc, and output the candidate enhanced substitution group, the optimal substitution group and the corresponding limestone powder to silica fume ratio.

2. The evaluation method for interface enhancement of ultra-high performance concrete using limestone powder instead of silica fume according to claim 1, characterized in that, In S1, the mass of silica fume in the reference cementitious material matrix system accounts for 15% to 25% of the total mass of the cementitious material.

3. The evaluation method for interface enhancement of ultra-high performance concrete using limestone powder instead of silica fume according to claim 1, characterized in that, In S2, the limestone powder replaces silica fume at a ratio of 0% to 60% of the silica fume mass.

4. The evaluation method for interface enhancement of ultra-high performance concrete using limestone powder instead of silica fume according to claim 1, characterized in that, In S5, the cumulative heat release Q100 over 100 hours is determined by isothermal calorimetry, and the total porosity P28 over 28 days is determined by mercury porosimetry.

5. The evaluation method for interface enhancement of ultra-high performance concrete using limestone powder instead of silica fume according to claim 1, characterized in that, In S5, the peak pull-out load F of the single steel fiber max And single fiber pull-out work W p The results were determined by a single fiber pull-out test; the conditions of the single fiber pull-out test included standardized control of the steel fiber embedding depth, pull-out angle, and loading rate.

6. The evaluation method for interface enhancement of ultra-high performance concrete using limestone powder instead of silica fume according to claim 1, characterized in that, In S7, the weighting coefficients a, b, c, and d are allocated according to the contribution of hydration propulsion, pore structure densification, fiber interface peak load, and fiber interface energy dissipation to interface reinforcement. Among these, the single fiber pull-out work W... p The corresponding weight coefficient d is the largest.

7. The evaluation method for interface enhancement of ultra-high performance concrete using limestone powder instead of silica fume according to claim 1, characterized in that, In S8, the rule for determining the interface enhancement level is as follows: The alternative group with an interface enhancement index IEI ≥ 1.00 and a strength constraint coefficient Kc ≥ 1.00 was identified as the candidate enhancement group; When there are multiple candidate enhancement groups, the substitution group with the largest interface enhancement index (IEI) is determined as the optimal substitution group, and the limestone powder substitution ratio for silica fume corresponding to the optimal substitution group is determined as the optimal substitution ratio. The alternative groups with an interface enhancement index (IEI) < 1.00 or a strength constraint coefficient (Kc) < 1.00 were identified as the non-recommended groups.

8. The evaluation method according to any one of claims 1 to 7, characterized in that, The method is used to determine the design ratio of limestone powder to silica fume in a low-silica ultra-high performance concrete cementitious material system, and to prepare ultra-high performance concrete matrices for bridge engineering, marine engineering components, prefabricated connection components and thin-walled components.

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