Machine-made sand high-performance concrete mix proportion design method for large-span high-pier continuous beam

Abstract

The invention relates to a high-performance concrete mix proportion design method, in particular to a machine-made sand high-performance concrete mix proportion design method for a large-span high-pier continuous beam. Comprising the following steps that (1) machine-made sand is detected, indexes such as the MB value, stone powder and the crushing value of the machine-made sand are strictly controlled, and the crushing index value is smaller than 25%; the MB value is strictly controlled within 1.0, and the stone powder content is not more than 13%; (2) addition of an additive: the compounding proportion of the selected compound slump retaining agent component is adjusted at any time according to various factors such as seasons, air temperature and construction modes, so that good adaptability between the compound slump retaining agent and concrete is ensured, and the state of the concrete can be ensured; (3) determining the preparation strength and the water-binder ratio of the concrete, determining the compact void ratio through a compact packing density test of coarse aggregate, setting the compact void ratio as the preliminary sand ratio of the mix proportion, adjusting the sand ratio according to + / -2% and + / -4 on the basis, detecting the workability and the mechanical property of the concrete under different sand ratios, and finally selecting the optimal mix proportion; the design method provided by the invention provides theoretical and data support for the design of the mix proportion of the machine-made sand high-performance concrete.

Description

Technical Field

[0001] The invention relates to a high-performance concrete mix ratio design method, in particular to a machine-made sand high-performance concrete mix ratio design method for large-span high-pier continuous beams. Background Art

[0002] With the continuous development of my country's social economy, the number of infrastructure construction projects has been increasing year by year, and the demand for construction sand has also been increasing. River sand is a short-term non-renewable resource, and its distribution in my country is uneven. In addition, it is not convenient for long-distance transportation. The contradiction between supply and demand of concrete sand has become increasingly prominent, which seriously affects the construction of projects. At the same time, illegal and disorderly mining of river sand has also caused damage to the environment. Therefore, it has become an inevitable trend to replace natural sand with machine-made sand and use it in large-scale civil engineering construction.

[0003] The mix design of high-performance concrete using machine-made sand is currently still based on experience and reference to previous similar projects. Although the use of machine-made sand in high-performance concrete is mentioned in the current national specifications and industry standards, only the limit ranges of several indicators such as the fineness modulus, methylene blue content, and stone powder content of machine-made sand are given, and there is no systematic mix design method. In addition, there are currently no application engineering examples of machine-made sand high-performance concrete used in the construction of large-span high-pier continuous beams in China, and the various performance indicators of the mix designed based on previous machine-made sand high-performance mix data cannot meet the requirements. Summary of the invention

[0004] The invention overcomes the shortcomings of the prior art, provides a method for designing the mix ratio of machine-made sand high-performance concrete for large-span high-pier continuous beams, and provides theoretical and data support for the mix ratio design of machine-made sand high-performance concrete.

[0005] In order to solve the above technical problems, the technical solution adopted by the present invention is: a method for designing the mix ratio of machine-made sand high-performance concrete for large-span high-pier continuous beams, comprising the following steps:

[0006] (1) Test the manufactured sand and strictly control its MB value, stone powder, crushing value and other indicators. The crushing index value should be less than 25%; the MB value should be strictly controlled within 1.0, and the stone powder content should not exceed 13%;

[0007] (2) Adding admixtures, such as compound collapse-preventing agents, the compounding ratio of the selected compound collapse-preventing agent components is adjusted at any time according to various factors such as season, temperature, and construction method to ensure good adaptability between the compound collapse-preventing agent and the concrete so that the concrete state can be guaranteed;

[0008] (3) Determine the concrete mix strength and water-cement ratio. Confirm the compact void ratio through the compact packing density test of coarse aggregate. Set the compact void ratio as the initial sand ratio of the mix ratio. Adjust the sand ratio by ±2% and ±4 on this basis. Test the workability and mechanical properties of concrete under different sand ratios, and finally select the optimal mix ratio.

[0009] As a further limitation of the technical solution of the present invention, the method for calculating the concrete mix strength in step (3) is:

[0010] f Cu·0 =f Cu·k +1.645σ

[0011] f Cu·0 -Concrete mix strength MPa;

[0012] f Cu·k -Concrete cube compressive strength standard value, 55MPa

[0013] σ-standard deviation of concrete strength, taken as 6MPa, obtained according to Table 4.0.2 in JGJ 55-2011.

[0014] As a further limitation of the technical solution of the present invention, the calculation method of the water-binder ratio in step (3) is:

[0015]

[0016] W = B-concrete water-binder ratio;

[0017] α a -Regression coefficient, 0.53, obtained according to Table 5.1.2 in JGJ 55-2011;

[0018] a b -Regression coefficient, 0.2, obtained according to Table 5.1.2 in JGJ 55-2011;

[0019] f b -28d compressive strength of cementitious material (MPa), take 57.8MPa

[0020] f Cu·0 -Concrete mix strength MPa.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] Since machine-made sand has strong bonding with cement and other cementitious materials, the strength of concrete after using machine-made sand will be higher than that of concrete produced with river sand of the same sand ratio; the surface area of ​​machine-made sand is larger than that of river sand, which can increase the ratio of solid surface area to water volume in concrete, reduce water seepage and segregation, and improve the workability of concrete; in terms of green and low-carbon, since the production process of machine-made sand can realize the reuse of solid waste such as tailings and waste rock, it reduces the exploitation of natural resources and damage to the environment; at the same time, since the cost of machine-made sand is lower than that of river sand, preliminary statistics show that the use of machine-made sand can save about 80 yuan per cubic meter of concrete. In the face of such a large-scale infrastructure construction today, this will save huge costs.

[0023] The design method of the invention provides theoretical and data support for the mix design of high-performance concrete with machine-made sand. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a curve chart showing the relationship between MB value and water consumption.

[0025] Figure 2 This is the relationship curve between M stone powder content and mortar fluidity.

[0026] Figure 3 The relationship curve between sand ratio and slump

[0027] Figure 4 This is the relationship curve between sand ratio and 7d compressive strength.

[0028] Figure 5 This is the relationship curve between sand ratio and 28d compressive strength. DETAILED DESCRIPTION

[0029] The present invention is further described below in conjunction with specific embodiments.

[0030] Example 1

[0031] A method for designing a mix ratio of machine-made sand high-performance concrete for a large-span high-pier continuous beam comprises the following steps:

[0032] (1) Test the manufactured sand and strictly control its MB value, stone powder, crushing value and other indicators. Since the manufactured sand is mostly angular, it is concluded through a large number of concrete trials that medium sand with particle size distribution in zone I should be used. At the same time, in order to meet the mechanical properties of concrete, its crushing index value is required to be less than 25%. The MB value should be strictly controlled within 1.0 to prevent the state of concrete from being affected by excessive clay and other substances in the manufactured sand. The stone powder content can be relaxed to no more than 13%, because stone powder has a certain ball-bearing effect, so it can play a certain role in reducing friction in aggregate, which will greatly increase the slump of concrete and improve the working performance of concrete. In the hydration reaction process, stone powder can also play a certain role in micro-aggregate filling and crystal nucleation, which can effectively promote the crystallization of hydration products and fill the pores generated during the concrete construction process, greatly improving the density of concrete and effectively improving the strength and impermeability of concrete. For other technical indicators, they must comply with the provisions of the current "Technical Specifications for Highway Bridge and Culvert Construction" JTG / T 3650.

[0033] (2) Add admixtures. The admixtures should play a role in reducing water, reducing the cohesion of concrete, and improving the pumpability of concrete. In addition to the above functions, it is also necessary to add retarding components to the admixtures to reduce the cement hydration rate and hydration heat, and prolong the hardening time of concrete; the compound slump-preventing agent can effectively reduce the slump loss during concrete transportation and pouring, and improve the pumpability of concrete. At the same time, the compounding ratio of each component of the composite high-performance water-reducing agent needs to be adjusted at any time according to various factors such as season, temperature, and construction method to ensure good adaptability between it and concrete so that the state of the concrete can be guaranteed.

[0034] (3) First, calculate according to the "Ordinary Concrete Mix Design Code" JGJ 55-2011:

[0035] (3.1) Concrete mix strength

[0036] f Cu·0 =f Cu·k +1.645σ

[0037] f Cu·0 -Concrete mix strength (MPa);

[0038] f Cu·k -Concrete cube compressive strength standard value, 55MPa

[0039] σ-standard deviation of concrete strength, taken as 6MPa, obtained according to Table 4.0.2 in JGJ 55-2011.

[0040] After calculation according to the formula, the prepared strength is determined to be 64.9MPa.

[0041] (3.2) Water-cement ratio

[0042]

[0043] W = B-concrete water-binder ratio;

[0044] α a -Regression coefficient, 0.53, obtained according to Table 5.1.2 in JGJ 55-2011;

[0045] a b -Regression coefficient, 0.2, obtained according to Table 5.1.2 in JGJ 55-2011;

[0046] f b -The 28d compressive strength of cementitious material mortar (MPa) is 57.8MPa.

[0047] f Cu·0 -Concrete mix strength (MPa).

[0048] After calculation according to the formula, the water-binder ratio is 0.43. According to the requirements of the Code for Design of Concrete Structures (GB 50010-2010), the water-binder ratio of C55 concrete should not be greater than 0.32, so the initial water-binder ratio of the mix is ​​confirmed to be 0.32.

[0049] (3.3) Sand ratio

[0050] The difference from the conventional mix design is that the sand ratio in the mass method and the volume method is based on the empirical value obtained by looking up the table; the preparation concept of the present invention is to finally determine the mixing ratio with the smallest dense void ratio of the aggregate as the optimal sand ratio through a close packing density test on the aggregate, and the prepared concrete is more compact.

[0051] Through indoor tests, the tight void ratio of the coarse aggregate used on site was measured to be 43%. Therefore, the sand ratio was adjusted within the tight void ratio of ±2% and ±4, and the following data were obtained:

[0052]

[0053] According to the above five groups of mix ratio data, the mix ratio was tested and the corresponding performance tests were carried out. The following data were obtained through the tests:

[0054]

[0055] From the above data, we can find that although the performance of mix ratios 4 and 5 can meet the requirements, the 28d compressive strength does not reach the calculated adaptation strength, so they are discarded; mix ratio 1 is discarded because of its low sand ratio, resulting in a small slump; mix ratio 3 can meet the requirements, and the slump is within a reasonable range, but the 28d compressive strength just reaches the adaptation strength, and the surplus coefficient is low, so it is discarded. Finally, mix ratio 2 was determined to be used. The mix ratios are shown in the following table:

[0056]

Claims

1. A method for designing the mix ratio of machine-made sand high-performance concrete for large-span high-pier continuous beams, characterized in that: The following steps are involved: (1) Test the manufactured sand and strictly control its MB value, stone powder, crushing value and other indicators. The crushing index value should be less than 25%; the MB value should be strictly controlled within 1.0, and the stone powder content should not exceed 13%; (2) Adding admixtures, such as compound collapse-preventing agents, the compounding ratio of the selected compound collapse-preventing agent components is adjusted at any time according to various factors such as season, temperature, and construction method to ensure good adaptability between it and concrete so that the state of the concrete can be guaranteed; (3) Determine the concrete mix strength and water-cement ratio. Confirm the compact void ratio through the compact packing density test of coarse aggregate. Set the compact void ratio as the initial sand ratio of the mix ratio. Adjust the sand ratio by ±2% and ±4 on this basis. Test the workability and mechanical properties of concrete under different sand ratios, and finally select the optimal mix ratio.

2. The method for designing the mix ratio of machine-made sand high-performance concrete for long-span high-pier continuous beams according to claim 1 is characterized in that: The calculation method of concrete mix strength in step (3) is: f Cu·0 =f Cu·k +1.645s f Cu·0 -Concrete mix strength MPa; f Cu·k -Concrete cube compressive strength standard value, 55MPa σ-standard deviation of concrete strength, taken as 6MPa, obtained according to Table 4.0.2 in JGJ 55-2011.

3. The method for designing the mix ratio of machine-made sand high-performance concrete for long-span high-pier continuous beams according to claim 1 is characterized in that: The calculation method of water-binder ratio in step (3) is: W = B-concrete water-binder ratio; α a -Regression coefficient, 0.53, obtained according to Table 5.1.2 in JGJ 55-2011; a b -Regression coefficient, 0.2, obtained according to Table 5.1.2 in JGJ 55-2011; f b -28d compressive strength of cementitious material (MPa), take 57.8MPa f Cu·0 -Concrete mix strength MPa.

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