Concrete segregation degree evaluation method

Abstract

The invention belongs to the technical field of concrete performance testing, and discloses a concrete segregation degree evaluation method which comprises the following steps: firstly, placing a slump cone at the upper end of an inclined surface, then adding concrete into the slump cone, inserting and tamping, after the slump cone is filled with the concrete, lifting the slump cone along the vertical direction, and after the concrete stops flowing, taking out the slump cone; measuring a concrete expansion angle Ac; placing the truncated cone round die at the upper end of an inclined table top, preparing mortar according to the concrete mortar components, adding the mortar into the truncated cone round die, lifting the truncated cone round die after the truncated cone round die is filled with the mortar, and measuring the mortar expansion angle Am after the mortar stops flowing; and calculating the ratio of Am to Ac, and judging the stable state of the concrete according to the range of Am / Ac. According to the method, the flowing states of the concrete and the mortar on the inclined plane are measured on the inclined plane, the ratio of Am to Ac is obtained, and the segregation degree of the concrete can be judged according to the range of Am / Ac.

Description

Technical Field

[0001] The invention belongs to the technical field of concrete performance testing and relates to a method for evaluating the degree of concrete segregation. Background Art

[0002] Concrete is a multiphase composite material made of cement as a gelling material, sand and stone as aggregates, water, mineral admixtures and admixtures in a certain proportion. With the development of concrete engineering, the performance requirements for concrete are getting higher and higher, especially for modern buildings with complex geometric components or dense reinforcement, which require concrete to have excellent fluidity for construction. However, the segregation phenomenon of high-flow concrete has also become a key issue restricting the quality of engineering.

[0003] Concrete segregation is the phenomenon that aggregate and mortar do not flow in an orderly manner during the flow of fresh concrete and separate from each other. On the one hand, due to the difference in density between coarse aggregate and mortar, coarse aggregate tends to settle to the bottom; on the other hand, when the cohesion of mortar to coarse aggregate is insufficient, coarse aggregate and mortar separate due to inconsistent flow during the pouring of fresh concrete. Concrete segregation of different causes is manifested as uneven distribution of coarse aggregate in concrete. Therefore, the degree of concrete segregation can be characterized by measuring the difference in apparent density of concrete or volume fraction of coarse aggregate at different locations. However, when using these methods, the sample size obtained by local sampling is small, and there are subjective factors, which leads to a large discreteness of the test results. In order to improve the credibility of the test results, it is often necessary to increase the sample size, which greatly increases the time consumption, manpower investment and tediousness of the test. Summary of the invention

[0004] The present invention aims at the technical problems existing in the existing concrete segregation judgment and provides a method for evaluating the degree of concrete segregation. By measuring the flow state of concrete and mortar on the inclined plane, the mortar expansion angle A is obtained. m and concrete expansion angle A c ratio, and according to A m / A c The range in which the concrete is placed can be used to determine the degree of segregation of the concrete.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] The present invention provides a method for evaluating the degree of segregation of concrete, comprising the following steps:

[0007] a. First place the slump cone on the upper end of the inclined surface, prepare the concrete, then add the concrete into the slump cone, tamp it, and after the concrete fills the slump cone, lift the slump cone vertically within 10 seconds. The concrete flows downward along the inclined surface. After the flow stops, measure the angle formed by the edges of the concrete on both sides after it expands on the inclined surface, that is, the concrete expansion angle A. c ;

[0008] b. Place the truncated cone mold on the upper end of the inclined table, prepare mortar according to the concrete mortar composition in step a, add the mortar into the truncated cone mold, and after the mortar fills the truncated cone mold, lift the truncated cone mold within 3s to 5s. The mortar flows downward along the inclined table. After it stops flowing, measure the angle formed by the edges of the two sides of the mortar after it expands on the inclined surface, i.e., the mortar expansion angle A. m ;

[0009] c. Calculate the mortar expansion angle A m and concrete expansion angle A c ratio, and according to A m / A c The range determines the stability of the concrete.

[0010] According to the above technical solution, when A m / A c When it is less than 1.5, the concrete is judged to be in a stable state without segregation risk; m / A c When it is between 1.5 and 2.0, the concrete is judged to be in an unstable state and has the risk of segregation. m / A c When it is greater than 2.0, the concrete is judged to be in a very unstable state and severe segregation occurs.

[0011] According to the above technical solution, the dimensions of the truncated cone circular mold are: height 60mm±0.5mm; upper inner diameter 70mm±0.5mm; lower inner diameter 100mm±0.5mm; lower outer diameter 120mm; and wall thickness greater than 5mm.

[0012] According to the above technical solution, the inclination angle of the inclined surface is 15° to 35°.

[0013] According to the above technical solution, when the slump of the concrete is greater than 180 mm, the inclination angle of the inclined surface is 15° to 25°.

[0014] Compared with the prior art, the present invention has the following beneficial effects:

[0015] The concrete segregation degree evaluation method proposed in the present invention only needs to measure the flow state of concrete and mortar on the inclined surface to obtain the mortar expansion angle A. m and concrete expansion angle Ac ratio, and according to A m / A c The segregation degree of concrete can be determined within the specified range, thus avoiding the test error caused by manual sampling and making the test results more scientific. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is the particle size distribution diagram of the fine aggregate of the present invention.

[0017] Figure 2 Schematic diagram of the testing and measurement process of the present invention.

[0018] Figure 3 It is a schematic diagram of the classification of concrete segregation levels according to the present invention. DETAILED DESCRIPTION

[0019] The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention. Unless otherwise specified, the technical means used in the examples are conventional means known to those skilled in the art. The test methods in the following examples are conventional methods unless otherwise specified.

[0020] Example 1

[0021] 1Raw materials

[0022] P·O42.5 grade cement was used to prepare concrete, and its chemical composition is shown in Table 1. Its physical properties were tested according to the standard GB / T1346-2011 "Test Methods for Water Consistency, Setting Time and Stability of Cement Standard Consistency", and the results are shown in Table 2 below, which is in line with the provisions of GB175-2007 "General Portland Cement".

[0023] Table 1 Main chemical composition of cement (unit: %)

[0024] Components <![CDATA[SiO2]]> <![CDATA[Al2O3]]> <![CDATA[Fe2O3]]> CaO MgO <![CDATA[SO3]]> other content 24 4.75 3.45 64.4 1.99 1.32 0.08

[0025] Table 2 Physical properties of cement

[0026]

[0027] This embodiment uses natural river sand as fine aggregate, and its technical indicators and gradation are shown in Table 3 and Figure 1 shown.

[0028] Table 3 Performance index of fine aggregate

[0029] Fineness modulus Apparent density Mud content Mud content 2.67 <![CDATA[2600kg / m 3 ]]> 0 2.8％

[0030] In this embodiment, crushed stone is used as coarse aggregate, and the particle size is 5-10 mm (CA1#) and 10-26.5 mm (CA2#). The apparent density and bulk density are shown in Table 4.

[0031] Table 4 Properties of coarse aggregate

[0032] Particle size range (mm) <![CDATA[Apparent density (kg / m 3 )]]> <![CDATA[Bulk density (kg / m 3 )]]> Void ratio (%) 5～10 2710 1450 46 10～26.5 2710 1420 48

[0033] The water reducer used in this embodiment is a high-performance polycarboxylate water reducer, and its indicators are shown in Table 5.

[0034] Table 5 Basic indicators of polycarboxylate water reducer

[0035] name Appearance Water reduction rate pH Polycarboxylate water reducer White powder 20％ 7.0-9.0

[0036] 2 Design of concrete with different mix proportions

[0037] In order to fully demonstrate the applicability of the inclined surface test, concrete mix proportions including different coarse aggregate volume fractions, coarse aggregate gradations, water-cement ratios, water-reducing agent dosages and cement-sand ratios were designed. The specific mix proportions are shown in Table 6.

[0038] Four kinds of concrete with coarse aggregate volume fractions are designed, and the numbers are respectively represented by Example 1 to Example 4, and the coarse aggregate volume fractions are 30%, 35%, 40% and 45% respectively. The coarse aggregate is selected from two particle sizes of 5-10mm (CA1#) and 10-26.5mm (CA2#), and the aggregate gradation is selected from 30% of 5-10mm crushed stone and 70% of 10-26.5mm crushed stone (i.e. CA1#: CA2#=3:7). The cement dosage of Example 1 is 618kg, polycarboxylate water reducer is 4.33kg, water is 204kg, fine aggregate is 763kg, and coarse aggregate is 813kg.

[0039] On the basis of the concrete of Example 2, three concretes with different gradations were designed, i.e., the content of 5-10 mm (CA1#) coarse aggregate in the overall coarse aggregate was adjusted up and down to 0%, 50% and 100%, corresponding to Examples 5-7 respectively.

[0040] On the basis of the concrete of Example 2, the properties of the mortar are changed by changing the water-cement ratio, the amount of water reducing agent, and the lime-sand ratio of the mortar. Examples 8 and 9 are concretes with different water-cement ratios, Examples 10 and 11 are concretes with different amounts of water reducing agent, and Examples 12 and 13 are concretes with different lime-sand ratios.

[0041] According to the corresponding mortar mix ratios of Examples 1 to 13, corresponding mortars (i.e., removing the coarse aggregate component) were prepared respectively, and recorded as M1 to M7.

[0042] Table 6 Concrete with different mix ratios

[0043]

[0044] 3 Experimental process

[0045] The inclination angle of the inclined surface is set to 20°. The dimensions of the slump cone are as follows: upper diameter: 100mm; lower diameter: 200mm; cone height: 300mm. The dimensions of the truncated cone mold are as follows: height 60mm±0.5mm; upper inner diameter 70mm±0.5mm; lower inner diameter 100mm±0.5mm; lower outer diameter 120mm; wall thickness greater than 5mm.

[0046] The test and measurement process diagram is as follows: Figure 2 As shown, the segregation degree evaluation index is determined according to the following steps:

[0047] a. First, fix the slump cone to the upper end of the inclined surface (the edge of the slump cone is flush with the edge of the inclined surface), and then add the concrete prepared in Examples 1 to 13 into the slump cone in three layers. After each layer of concrete is added, use a concrete tamping rod to tamp 15 times in a spiral shape along the wall of the cone toward the center. After the concrete fills the slump cone, lift the slump cone in a vertical direction within 10 seconds. The concrete flows downward along the inclined surface to form a shape that is narrow at the top and wide at the bottom. After the flow stops, measure and record the angle formed by the edges of the concrete on both sides of the inclined surface after expansion of each example, i.e., the concrete expansion angle A. c , the results are shown in Table 7;

[0048] b. Fix the truncated cone mold to the upper end of the inclined tabletop (the edge of the truncated cone mold is flush with the edge of the bevel), add mortars M1 to M7 into the truncated cone mold in two layers, and use a mortar tamping rod to spirally tamp along the side wall of the mold toward the center 10 times for each layer. After the mortar fills the truncated cone mold, lift the truncated cone mold within 3s to 5s, and the mortar flows downward along the inclined tabletop. After it stops flowing, measure and record the angle formed by the edges of the two sides of the mortar after it expands on the inclined surface, i.e., the mortar expansion angle A. m , the results are shown in Table 7;

[0049] c. Calculate the mortar expansion angle A m and concrete expansion angle A c The results are shown in Table 7, and according to A m / A c The range determines the stability of the concrete.

[0050] Table 7 Concrete properties

[0051] serial number Slump(mm) Slump extension (mm) <![CDATA[A c ]]> <![CDATA[A m ]]> <![CDATA[A m / A c ]]> Example 1 270 740 29 49 1.69 Example 2 250 660 32 49 1.53 Example 3 245 640 36 49 1.36 Example 4 210 610 38 49 1.29 Example 5 230 845 24 49 2.04 Example 6 245 765 30 49 1.63 Example 7 240 630 35 49 1.4 Example 8 230 825 22 45 2.05 Example 9 265 605 36 52 1.44 Example 10 240 725 29 46 1.59 Embodiment 11 255 635 36 50 1.39 Example 12 235 720 29 45 1.55 Embodiment 13 275 635 37 53 1.43

[0052] The visual inspection method in ASTM C1611 was used as a reference. Figure 3 As shown in Table 8, the segregation degree of fresh concrete can be divided into stable, unstable and very unstable states. m / A cWhen it is less than 1.5, the concrete is considered to be in a stable state and has no risk of segregation; A m / A c When the value is between 1.5 and 2.0, the concrete is in an unstable state and has the risk of segregation; A m / A c When it is greater than 2.0, the concrete is considered to be in a very unstable state and severe segregation occurs.

[0053] Table 8 Segregation classification of fresh concrete

[0054] Segregation degree Stablize Unstable Very unstable <![CDATA[A m / A c ]]> <1.5 1.5-2.0 >2.0

[0055] The embodiments described above are only preferred embodiments of the present invention and are only used to explain the present invention, not to limit the scope of implementation of the present invention. For those skilled in the art, other implementation methods can certainly be easily made by replacement or modification based on the technical contents disclosed in this specification. Therefore, all changes and improvements made on the principles of the present invention should be included in the scope of the patent application of the present invention.

Claims

1. A method for evaluating the degree of concrete segregation, characterized in that: The following steps are involved: a. First place the slump cone on the upper end of the inclined surface, prepare the concrete, then add the concrete into the slump cone, tamp it, and after the concrete fills the slump cone, lift the slump cone vertically within 10 seconds. The concrete flows downward along the inclined surface. After the flow stops, measure the angle formed by the edges of the concrete on both sides after it expands on the inclined surface, that is, the concrete expansion angle A. c ; b. Place the truncated cone mold on the upper end of the inclined table, prepare mortar according to the concrete mortar composition in step a, add the mortar into the truncated cone mold, and after the mortar fills the truncated cone mold, lift the truncated cone mold within 3s~5s. The mortar flows downward along the inclined table. After the flow stops, measure the angle formed by the edges of the two sides of the mortar after it expands on the inclined surface, that is, the mortar expansion angle A. m ; c. Calculate the mortar expansion angle A m and concrete expansion angle A c ratio, and according to A m / A c The range determines the stability of the concrete.

2. A method for evaluating the degree of concrete segregation according to claim 1, characterized in that: When A m / A c When it is less than 1.5, the concrete is judged to be in a stable state without segregation risk; m / A c When it is between 1.5 and 2.0, the concrete is judged to be in an unstable state and has the risk of segregation. m / A c When it is greater than 2.0, the concrete is judged to be in a very unstable state and severe segregation occurs.

3. A method for evaluating the degree of concrete segregation according to claim 1, characterized in that: The dimensions of the truncated cone circular die are: height 60 mm±0.5 mm; upper opening inner diameter 70 mm±0.5 mm; lower opening inner diameter 100 mm±0.5 mm; lower opening outer diameter 120 mm; and wall thickness greater than 5 mm.

4. A method for evaluating the degree of concrete segregation according to claim 1, characterized in that: The inclination angle of the inclined surface is 15°~35°.

5. A method for evaluating the degree of concrete segregation according to claim 4, characterized in that: When the slump of the concrete is greater than 180 mm, the inclination angle of the inclined surface is 15° to 25°.

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