CN108503303B - VVTM design method for cement cold-recycling mixture - Google Patents

VVTM design method for cement cold-recycling mixture Download PDF

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CN108503303B
CN108503303B CN201810306744.4A CN201810306744A CN108503303B CN 108503303 B CN108503303 B CN 108503303B CN 201810306744 A CN201810306744 A CN 201810306744A CN 108503303 B CN108503303 B CN 108503303B
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CN108503303A (en
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蒋应军
易勇
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Changan University
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    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B28/00—Compositions of mortars, concrete or artificial stone, containing inorganic binders or the reaction product of an inorganic and an organic binder, e.g. polycarboxylate cements
    • C04B28/02—Compositions of mortars, concrete or artificial stone, containing inorganic binders or the reaction product of an inorganic and an organic binder, e.g. polycarboxylate cements containing hydraulic cements other than calcium sulfates
    • C04B28/04—Portland cements
    • G—PHYSICS
    • G05—CONTROLLING; REGULATING
    • G05D—SYSTEMS FOR CONTROLLING OR REGULATING NON-ELECTRIC VARIABLES
    • G05D11/00—Control of flow ratio
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B2111/00—Mortars, concrete or artificial stone or mixtures to prepare them, characterised by specific function, property or use
    • C04B2111/00034—Physico-chemical characteristics of the mixtures
    • C04B2111/00198—Characterisation or quantities of the compositions or their ingredients expressed as mathematical formulae or equations
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B2111/00—Mortars, concrete or artificial stone or mixtures to prepare them, characterised by specific function, property or use
    • C04B2111/00474—Uses not provided for elsewhere in C04B2111/00
    • C04B2111/0075—Uses not provided for elsewhere in C04B2111/00 for road construction
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B2201/00—Mortars, concrete or artificial stone characterised by specific physical values
    • C04B2201/50—Mortars, concrete or artificial stone characterised by specific physical values for the mechanical strength

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Abstract

The invention provides a VVTM design method of a cement cold-recycling mixture, which can quickly determine the doping amount of new aggregates and the cement dosage in the cement cold-recycling mixture, and the designed high-performance cement cold-recycling mixture has excellent pavement performance. The data of the examples show that the cement cold-recycling mixture designed by the invention can meet the design requirements.

Description

VVTM design method for cement cold-recycling mixture
Technical Field
The invention relates to the technical field of traffic civil engineering application, in particular to a design method of a cement cold-recycling mixture VVTM.
Background
At present, no universally accepted cement cold-recycling mixture design method is available on a global scale. No clear new aggregate mixing amount design method exists in the technical Specification for road asphalt pavement regeneration (JTG F41-2008) in China, and more new aggregates are mixed in cold regeneration pavement engineering to adjust the thickness of a regeneration layer rather than to optimally consider whether the performance is optimal or not; and determining that the optimal water content is larger and the maximum dry density is smaller by adopting a heavy compaction method.
The design method of the cement cold-recycling mixture in China generally adopts technical specification for highway pavement base course construction (JTGTF20-2015), and has the following limitations:
(1) mineral aggregate grading design: the inorganic binder stable cold-recycling mixture given in JTG F41-2008 has wide gradation range and can meet the requirement without design, so that the new aggregate mixing amount design in engineering practice is more considered to meet the requirement of the thickness of the recycling layer, and the influence degree of the aggregate specification on the performance of the cement cold-recycling mixture is different after neglecting. In addition, the new aggregate mixing amount is determined by experience, the design is not carried out by combining the milling thickness of the old pavement and the thickness of the regeneration layer, the new aggregate mixing amount is usually required to be adjusted for many times according to the actual compaction thickness of a field test section in engineering practice, the process is not only complicated, but also the engineering progress is influenced.
(2) The test piece design method comprises the following steps: the compaction action of wheels on the road surface cannot be accurately simulated by adopting a static compaction method and a heavy compaction test method for the inorganic binder stable material in JTG E51-2009, the density of a formed test piece cannot reflect the density of the road surface after many years of traffic, and the physical and mechanical properties of the test piece are not consistent with the actual road surface.
Disclosure of Invention
In view of the above, the present invention aims to provide a method for designing a cement cold-recycling mix VVTM. The design method provided by the invention can be used for quickly and accurately determining the doping amount, the optimal water content, the maximum dry density and the cement dosage of the new aggregate in the cement cold-recycling mixture, and the designed high-performance cement cold-recycling mixture has excellent pavement performance.
In order to achieve the above object, the present invention provides the following technical solutions:
a design method of a cement cold-recycling mixture VVTM comprises the following steps:
(1) providing a cement cold recycling mixture according to the formula (1):
RCB: coarse aggregate: fine aggregate 1-C-X: c: x is a group represented by the formula (1),
in formula (1): c-the mass mixing amount of the coarse aggregate,
x-fine aggregate mass mixing amount;
the design method of the mass mixing amount of the coarse aggregate and the fine aggregate comprises the following steps:
(a) when (Y-1)/Yx 100% is more than or equal to 35%, C is (Y-1)/Yx 100% -20%, and X is 20%;
(b) when the content is more than or equal to 20 percent and less than or equal to (Y-1)/Y multiplied by 100 percent and less than 35 percent, C is 20 percent, and X is (Y-1)/Y multiplied by 100 percent to 20 percent;
(c) when (Y-1)/Y × 100% < 20%, C ═ Y-1)/Y × 100%, X ═ 0%;
wherein Y is the doping amount coefficient of the new aggregate,
Y＝0.875HR/hxthe compound of the formula (2),
in formula (2): y-new aggregate mixing amount coefficient;
HR-cold recycled structural layer design thickness, cm;
Hx-old road base milling thickness, cm;
(2) preparing mixtures with different cement dosages, and determining the optimal water content and the maximum dry density;
(3) respectively calculating the dry density of the mixed material test pieces with different cement dosages in the step (2) according to the base layer compaction degree of 98% or the subbase layer compaction degree of 97%, and forming VVT test pieces with different cement dosages according to the calculated dry density and the optimal water content obtained in the step (2);
(4) carrying out standard health maintenance on the VVTM test piece obtained in the step (3), and testing the 7d unconfined compressive strength and the 7d cleavage strength of the VVTM test piece after the standard health maintenance, wherein the 7d unconfined compressive strength and the 7d cleavage strength are independently calculated according to the formula (3) to obtain:
Figure GDA0002568341520000021
in formula (3): r0.95A representative value of the strength at a guarantee rate of 95%, MPa, wherein the representative value of the 7d unconfined compressive strength at a guarantee rate of 95% is denoted Rc0.95The 7d cleavage strength representative value of the 95% proof rate is represented as Ri0.95；
Figure GDA0002568341520000022
Average value of the test piece strength, MPa, where the average value of the unconfined compressive strength of test piece 7d is expressed as
Figure GDA0002568341520000023
The average value of the cleavage strength of the test piece 7d was represented by
Figure GDA0002568341520000024
S-standard deviation of specimen strength, MPa;
Cvcoefficient of variation of test piece strength,%, where the coefficient of variation of unconfined compressive strength of test piece 7d is denoted Cv,cThe coefficient of variation of the cleavage strength of the test piece 7d is represented by Cv,i；
Determining the cement dosage according to the strength standard shown in the table 1 and the cement dosage requirement shown in the table 2; if the obtained result can not reach the strength standard, readjusting the cement dosage or the new aggregate mixing amount for design;
TABLE 1 design criteria for strength of cement cold-recycled mixture
Horizon Degree of compaction (%) 7d cleavage Strength (MPa) 7d unconfined compressive strength (MPa)
Base layer ≥98 ≥0.40 ≥4.0
Sub-base layer ≥97 ≥0.35 ≥3.5
TABLE 2 Cement dosage design criteria for Cold Cement mix
Figure GDA0002568341520000031
Preferably, the grain size of the coarse aggregate in the step (1) is 15-30 mm or 10-25 mm, and the grain size of the fine aggregate is less than or equal to 2.36 mm.
Preferably, the step (2) includes: according to the method, cement dosages are set at intervals of 0.5% and 3-4.5% of base layer water-based additives and 2.5-4% of base layer cement additives, mixtures with different cement dosages are prepared, the moisture content is changed, a vibration compaction test is carried out, and when the maximum dry density is obtained, the moisture content of the mixture is the optimal moisture content.
Preferably, the vibration compaction test parameters include: the working frequency is 30 plus or minus 1Hz, the static eccentric moment is 7.6 plus or minus 0.02kN, the weight of the upper vehicle is 1.2 plus or minus 0.01kN, the weight of the lower vehicle is 1.8 plus or minus 0.01kN, and the vibration compaction time is 110 plus or minus 10 s.
Preferably, the step (3) is performed by molding: adopting vertical vibration compaction to form VVTM test pieces with different cement dosages, wherein the parameters of the vertical vibration compaction comprise: the working frequency is 30 plus or minus 1Hz, the static eccentric moment is 7.6 plus or minus 0.02kN, the weight of getting on the train is 1.2 plus or minus 0.01kN, and the weight of getting off the train is 1.8 plus or minus 0.01 kN.
Preferably, the VVTM specimen in the step (3) is a cylinder, the diameter of the cylinder is 150mm, and the height of the cylinder is 150 mm.
The invention provides a VVTM design method of a cement cold-recycling mixture, which can quickly determine the doping amount of new aggregates and the cement dosage in the cement cold-recycling mixture, and the designed high-performance cement cold-recycling mixture has excellent pavement performance. The data of the examples show that the cement cold-recycling mixture designed by the invention can meet the design requirements.
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The present invention will be described in further detail with reference to the accompanying drawings and specific embodiments.
FIG. 1 is a graph showing the unconfined compressive strength relationship of the cement dosage of 7d of the cement cold recycling mixture prepared in example 1 of the invention;
FIG. 2 is a graph showing the relationship between the cement dose and the 7d cleavage strength of the cement cold-recycling mix prepared in example 1 of the present invention.
Detailed Description
The invention provides a design method of a cement cold-recycling mixture VVTM, which comprises the following steps:
(1) providing a cement cold recycling mixture according to the formula (4):
RCB: coarse aggregate: fine aggregate 1-C-X: c: x is a group represented by the formula (4),
in formula (4): c-the mass mixing amount of the coarse aggregate,
x-fine aggregate mass mixing amount;
the design method of the mass mixing amount of the coarse aggregate and the fine aggregate comprises the following steps:
(a) when (Y-1)/Yx 100% is more than or equal to 35%, C is (Y-1)/Yx 100% -20%, and X is 20%;
(b) when the content is more than or equal to 20 percent and less than or equal to (Y-1)/Y multiplied by 100 percent and less than 35 percent, C is 20 percent, and X is (Y-1)/Y multiplied by 100 percent to 20 percent;
(c) when (Y-1)/Y × 100% < 20%, C ═ Y-1)/Y × 100%, X ═ 0%;
wherein Y is the doping amount coefficient of the new aggregate,
Y＝0.875HR/hxthe compound of the formula (5),
in formula (5): y-new aggregate mixing amount coefficient;
HR-cold recycled structural layer design thickness, cm;
Hx-old road base milling thickness, cm;
(2) preparing mixtures with different cement dosages, and determining the optimal water content and the maximum dry density;
(3) respectively calculating the dry density of the mixed material test pieces with different cement dosages in the step (2) according to the base layer compaction degree of 98% or the subbase layer compaction degree of 97%, and forming VVT test pieces with different cement dosages according to the calculated dry density and the optimal water content obtained in the step (2);
(4) carrying out standard health maintenance on the VVTM test piece obtained in the step (3), and testing the 7d unconfined compressive strength and the 7d cleavage strength of the VVTM test piece after the standard health maintenance, wherein the 7d unconfined compressive strength and the 7d cleavage strength are independently calculated according to the formula (6) to obtain:
Figure GDA0002568341520000041
in formula (6): r0.95A representative value of the strength at a guarantee rate of 95%, MPa, wherein the representative value of the 7d unconfined compressive strength at a guarantee rate of 95% is denoted Rc0.95The 7d cleavage strength representative value of the 95% proof rate is represented as Ri0.95；
Figure GDA0002568341520000051
Average value of the test piece strength, MPa, where the average value of the unconfined compressive strength of test piece 7d is expressed as
Figure GDA0002568341520000052
The average value of the cleavage strength of the test piece 7d was represented by
Figure GDA0002568341520000053
S-standard deviation of specimen strength, MPa;
Cvcoefficient of variation of test piece strength,%, test piece 7d unconfined compressive strengthIs expressed as Cv,cThe coefficient of variation of the cleavage strength of the test piece 7d is represented by Cv,i；
Determining the cement dosage according to the strength standard shown in Table 3 and the cement dosage requirement shown in Table 4; if the obtained result can not reach the strength standard, readjusting the cement dosage or the new aggregate mixing amount for design;
TABLE 3 design criteria for strength of cement cold-recycled mixture
Horizon Degree of compaction (%) 7d cleavage Strength (MPa) 7d unconfined compressive strength (MPa)
Base layer ≥98 ≥0.40 ≥4.0
Sub-base layer ≥97 ≥0.35 ≥3.5
TABLE 4 Cement dosage design criteria for Cold Cement mix
Figure GDA0002568341520000054
In the invention, a cement cold-recycling mixture is provided according to the formula (7):
RCB: coarse aggregate: fine aggregate 1-C-X: c: x is a group represented by the formula (7),
in formula (7): c-the mass mixing amount of the coarse aggregate,
x-fine aggregate mass mixing amount;
the design method of the mass mixing amount of the coarse aggregate and the fine aggregate comprises the following steps:
(a) when (Y-1)/Yx 100% is more than or equal to 35%, C is (Y-1)/Yx 100% -20%, and X is 20%;
(b) when the content is more than or equal to 20 percent and less than or equal to (Y-1)/Y multiplied by 100 percent and less than 35 percent, C is 20 percent, and X is (Y-1)/Y multiplied by 100 percent to 20 percent;
(c) when (Y-1)/Y × 100% < 20%, C ═ Y-1)/Y × 100%, X ═ 0%;
wherein Y is the doping amount coefficient of the new aggregate,
Y＝0.875HR/hxthe compound of the formula (8),
in formula (8): y-new aggregate mixing amount coefficient;
HR-cold recycled structural layer design thickness, cm;
Hxold road base milled thickness, cm.
In the invention, the particle size of the coarse aggregate is preferably 15-30 mm or 10-25 mm; the particle size of the fine aggregate is preferably less than or equal to 2.36 mm.
In the present invention, the specification of the coarse aggregate preferably satisfies the requirements shown in table 5:
TABLE 5 Specifications of coarse aggregates
Figure GDA0002568341520000061
In the present invention, the technical requirements of the coarse aggregate preferably satisfy the requirements shown in table 6:
TABLE 6 technical requirements of coarse aggregates
Technical index Apparent relative density Needle sheet content (%) Crush value (%)
Technical requirements ≥2.6 ≤20 ≤26
In the present invention, the technical requirements of the fine aggregate preferably satisfy the requirements shown in table 7:
TABLE 7 specification for fine aggregates
Test items Apparent relative density Sand equivalent (%) >0.3mm partial firmness (%) Angular character(s)
Technical requirements ≥2.5 ≥60 ≥12 ≥30
In the present invention, the technical requirements of the RCB preferably satisfy the requirements shown in table 8:
TABLE 8 technical requirements of RCB
Test items Water content (%) RCB grading Cement dosage (%) Sand equivalent (%)
Technical requirements Measured in fact Measured in fact Measured in fact >55
In the present invention, the RCB is preferably graded to meet the requirements shown in Table 9:
TABLE 9 RCB grading
Mesh size (mm) 37.5 31.5 26.5 19 9.5 4.75 2.36 0.6 0.075
Percent passage (%) 100 98.9 98.0 96.3 83.1 62 42.4 17.4 5.1
According to the invention, raw materials are provided according to the limitations of the aggregate gradation and the technical requirements, the obtained raw materials are prepared into the mixture with different cement dosages, and the optimal water content and the maximum dry density of the mixture are determined. In the present invention, the method of determining the optimum water content and the maximum dry density preferably includes: setting cement dosages at intervals of 0.5% according to the base cement additive amount of 3-4.5% and the subbase cement additive amount of 2.5-4%, preparing mixtures with different cement dosages, changing the water content, and performing a vibration compaction test, wherein when the maximum dry density is obtained, the water content of the mixture is the optimal water content; more preferably, the optimum water content and the maximum dry density of the mixture are determined by selecting the cement dosage of 3.0%, 3.5%, 4.0% and 4.5%.
In the present invention, the vibration compaction test parameters preferably include: the working frequency is 30 plus or minus 1Hz, the static eccentric moment is 7.6 plus or minus 0.02kN, the weight of the upper vehicle is 1.2 plus or minus 0.01kN, the weight of the lower vehicle is 1.8 plus or minus 0.01kN, and the vibration compaction time is 110 plus or minus 10 s.
In the present invention, the cement preferably meets the performance requirements shown in table 10:
TABLE 10 specification for cement
Figure GDA0002568341520000071
The invention respectively calculates the mixture with different cement dosages according to the base layer compaction degree of 98 percent or the subbase layer compaction degree of 97 percent to obtain the corresponding dry density of the test piece, and forms the VVT test piece of the mixture with different cement dosages according to the calculated dry density and the optimal water content. In the present invention, VVTM test pieces of different cement dosages are preferably formed by vertical vibratory compaction, and the parameters of the vertical vibratory compaction preferably include: the working frequency is 30 plus or minus 1Hz, the static eccentric moment is 7.6 plus or minus 0.02kN, the weight of getting on the train is 1.2 plus or minus 0.01kN, and the weight of getting off the train is 1.8 plus or minus 0.01 kN.
In the present invention, the VVTM specimen is preferably a cylinder, the diameter of the cylinder is preferably 150mm, and the height of the cylinder is preferably 150 mm.
In the present invention, the cement dosage in the VVTM test piece is preferably 3.0%, 3.5%, 4.0%, and 4.5%, respectively.
After obtaining the VVTM test piece, the invention carries out standard health maintenance on the VVTM test piece, the 7d unconfined compressive strength and the 7d cleavage strength of the VVTM test piece after the standard health maintenance are tested, and the 7d unconfined compressive strength and the 7d cleavage strength are independently calculated according to the formula (9):
Figure GDA0002568341520000072
in formula (9): r0.95A representative value of the strength at a guarantee rate of 95%, MPa, wherein the representative value of the 7d unconfined compressive strength at a guarantee rate of 95% is denoted Rc0.95Protection ofThe representative 7d cleavage strength value showing 95% of the rate is represented as Ri0.95；
Figure GDA0002568341520000081
Average value of the test piece strength, MPa, where the average value of the unconfined compressive strength of test piece 7d is expressed as
Figure GDA0002568341520000082
The average value of the cleavage strength of the test piece 7d was represented by
Figure GDA0002568341520000083
S-standard deviation of specimen strength, MPa;
Cvcoefficient of variation of test piece strength,%, where the coefficient of variation of unconfined compressive strength of test piece 7d is denoted Cv,cThe coefficient of variation of the cleavage strength of the test piece 7d is represented by Cv,i；
Determining the cement dosage according to the strength criteria shown in Table 11 and the cement dosage requirements shown in Table 12; if the obtained result can not reach the strength standard, readjusting the cement dosage or the new aggregate mixing amount for design;
TABLE 11 design criteria for strength of cement cold-recycled mix
Horizon Degree of compaction (%) 7d cleavage Strength (MPa) 7d unconfined compressive strength (MPa)
Base layer ≥98 ≥0.40 ≥4.0
Sub-base layer ≥97 ≥0.35 ≥3.5
TABLE 12 design criteria for cement dosage for cold-recycling cement mixture
Figure GDA0002568341520000084
In the invention, the temperature of the standard curing is preferably 20 +/-2 ℃, the humidity of the standard curing is more than 95%, and the test piece of the standard curing is preferably 6 d.
In the invention, after standard curing, the test piece subjected to standard curing is preferably immersed in a constant-temperature water tank at 20 +/-2 ℃ for standby, and is used for detecting 7d unconfined compressive strength and 7d cleavage strength.
The following will describe the design method of the cement cold-recycling mix VVTM provided by the present invention in detail with reference to the examples, but they should not be construed as limiting the scope of the present invention.
Example 1
Selecting ordinary portland cement, coarse aggregate, fine aggregate and RCB. The technical property test result meets the requirements.
Old pavement base milling thickness hx13cm, the design thickness H of the cement cold regeneration structural layerR18 cm. Calculating to obtain a new aggregate mixing amount coefficient Y according to a formula (2):
Y＝0.875HR/hx＝0.875×18/13＝1.21
determining the mixing amount of coarse and fine aggregates
(Y-1)/Y×100％＝17％<20％
Therefore, the coarse aggregate content C is 17% and the fine aggregate content X is 0%.
Determination of cold-recycling mixture gradation of cement
The cold-recycling cement mixture is graded as follows:
RCB: coarse aggregate-1-C: c83: 17
The composition grade of the synthesized cement cold-recycling mixture is shown in Table 13.
TABLE 13 Cement Cold-recycled mixture Synthesis grading
Screen hole (mm) 37.5 31.5 26.5 19 9.5 4.75 2.36 0.6 0.075
Percent passage (%) 100 98.9 97.5 67.5 46.3 33.3 22.7 10.2 2.7
Selecting 3.0%, 3.5%, 4.0% and 4.5% of cement dosage, determining the optimal water content and the maximum dry density of the mixture by adopting a vertical vibration compaction method, and preferably selecting test parameters comprising: the working frequency is 30Hz, the static eccentric moment is 7.6kN, the weight of getting on the vehicle is 1.2kN, the weight of getting off the vehicle is 1.8kN, and the vibration compaction time is 110 s.
(1) 5 parts of dry mass m is prepared according to the requirement of synthesis gradations5500g of a sample;
(2) adding 1 part of dried sample into the sample with a predetermined mass ratio of (m)j+ms) ×, adding the corresponding cement, and mixing uniformly again to obtain wet mixture, wherein w isiAdding water content into the cement for the ith test, wherein the added cement quality for the first test is 1, 2, 3, 4 and 5;
(3) preparing a test piece by adopting a vibration compaction test method;
(4) drawing a density-water content relation curve according to the mixing water content and the density of 5 groups, wherein the vertical and horizontal coordinates of the peak of the hump-shaped curve are respectively the maximum density rhomaxAnd optimum water content ratio omega0。
The maximum dry density and the optimum water content of the cement cold-recycling mixture are shown in a table 14.
TABLE 14 maximum dry density and optimum moisture content of cold-recycling mixed materials with different cement mixing amounts
Figure GDA0002568341520000091
Selecting cement doses of 3.0%, 3.5%, 4.0% and 4.5%, and respectively manufacturing VVTM test pieces according to different cement doses;
measuring the cement dosage of each group of test pieces, carrying out 7d unconfined compressive strength test and 7d splitting strength test, and comprehensively determining the cement dosage by combining the technical requirements and engineering experience of tables 1 and 2;
preparing a test piece by adopting VVTM, carrying out standard health maintenance (temperature is 20 +/-2 ℃, humidity is more than 95%) for 6d, carrying out water saturation at 20 +/-2 ℃ for 24h, carrying out unconfined compressive strength test on the next day, and carrying out VVTM with different cement dosages
The unconfined compressive strength results of the test piece cold-recycling mixture 7d are shown in a table 15 and a figure 1, and the fracture strength results of the test piece cold-recycling mixture 7d of the VVTM cement with different cement dosages are shown in a table 16 and a figure 2. From the results in tables 15 and 16 and fig. 1-2, it can be seen that the cement cold-recycling mixture with a cement dosage of 3.5% can meet the design requirements, and the recommended cement dosage range is proved to be referred to herein.
TABLE 15 Cold-regenerated mixture VVTM test piece with different cement dosages and 7d unconfined compressive strength
Figure GDA0002568341520000101
TABLE 16 cold-recycling mixture VVTM test piece 7d splitting strength with different cement dosages
Figure GDA0002568341520000102
Example 2
Selecting ordinary portland cement, coarse aggregate, fine aggregate and RCB. The technical property test result meets the requirements.
Old pavement base milling thickness hx14cm, the design thickness H of the cement cold regeneration structural layerR20 cm. Calculating to obtain a new aggregate mixing amount coefficient Y according to a formula (2):
Y＝0.875HR/hx＝0.875×20/14＝1.25
determining the mixing amount of coarse and fine aggregates
20％≤(Y-1)/Y×100％＝31％<35％
Therefore, the coarse aggregate content C is 20%, and the fine aggregate content X is (Y-1)/yx 100-20 is 11%.
Determination of cold-recycling mixture gradation of cement
The cold-recycling cement mixture is graded as follows:
RCB: coarse aggregate: fine aggregate 1-C-X: c: x is 69:20:11
The composition grade of the synthesized cement cold-recycling mixture is shown in Table 17.
TABLE 17 Cement Cold-recycled mixture Synthesis grading
Screen hole (mm) 37.5 31.5 26.5 19 9.5 4.75 2.36 0.6 0.075
Percent passage (%) 100 98.5 97.8 78.5 63.4 48.3 30.7 14.2 4.6
Selecting 3.0%, 3.5%, 4.0% and 4.5% of cement dosage, determining the optimal water content and the maximum dry density of the mixture by adopting a vertical vibration compaction method, and preferably selecting test parameters comprising: the working frequency is 30Hz, the static eccentric moment is 7.6kN, the weight of getting on the vehicle is 1.2kN, the weight of getting off the vehicle is 1.8kN, and the vibration compaction time is 110 s.
(1) 5 parts of dry mass m is prepared according to the requirement of synthesis gradations5500g of a sample;
(2) adding 1 part of dried sample into the sample with a predetermined mass ratio of (m)j+ms) ×, adding the corresponding cement, and mixing uniformly again to obtain wet mixture, wherein w isiAdding water content into the cement for the ith test, wherein the added cement quality for the first test is 1, 2, 3, 4 and 5;
(3) preparing a test piece by adopting a vibration compaction test method;
(4) drawing a density-water content relation curve according to the mixing water content and the density of 5 groups, wherein the vertical and horizontal coordinates of the peak of the hump-shaped curve are respectively the maximum density rhomaxAnd optimum water content ratio omega0。
The maximum dry density and the optimum water content of the cement cold-recycling mixture are shown in the table 18.
TABLE 18 maximum dry density and optimum water content of cold-recycling mixed materials with different cement mixing amounts
Figure GDA0002568341520000111
Selecting cement doses of 3.0%, 3.5%, 4.0% and 4.5%, and respectively manufacturing VVTM test pieces according to different cement doses;
measuring the cement dosage of each group of test pieces, carrying out 7d unconfined compressive strength test and 7d splitting strength test, and comprehensively determining the cement dosage by combining the technical requirements and engineering experience of tables 1 and 2;
preparing a test piece by adopting VVTM, carrying out standard health maintenance (temperature is 20 +/-2 ℃, humidity is more than 95%) for 6d, carrying out water saturation at 20 +/-2 ℃ for 24h, carrying out unconfined compressive strength test on the next day, and carrying out VVTM with different cement dosages
The unconfined compressive strength results of the test piece cold recycled mixture 7d are shown in tables 19 and 20. From the results in tables 19 and 20, it can be seen that the cement cold-recycling mix with a cement dosage of 3.5% can meet the design requirements, and the cement dosage range suggested herein is proved to be available for reference.
TABLE 19 Cold-regenerated mixture VVTM test piece with different cement dosages and 7d unconfined compressive strength
Figure GDA0002568341520000121
TABLE 20 cold-recycling mixture VVTM test piece 7d splitting strength with different cement dosages
Figure GDA0002568341520000122
Example 3
Selecting ordinary portland cement, coarse aggregate, fine aggregate and RCB. The technical property test result meets the requirements.
Old pavement base milling thickness hx12cm, the design thickness H of the cement cold regeneration structural layerR18 cm. Calculating to obtain a new aggregate mixing amount coefficient Y according to a formula (2):
Y＝0.875HR/hx＝0.875×18/12＝1.31
determining the mixing amount of coarse and fine aggregates
(Y-1)/Y×100％＝41％≥35％
Therefore, the coarse aggregate content C is 21% (Y-1) × 100-20, and the fine aggregate content X is 20%.
Determination of cold-recycling mixture gradation of cement
The cold-recycling cement mixture is graded as follows:
RCB: coarse aggregate: fine aggregate 1-C-X: c: x59: 21:20
The composition grade of the synthesized cement cold-recycling mixture is shown in Table 21.
TABLE 21 Cement Cold-recycled mixture Synthesis grading
Screen hole (mm) 37.5 31.5 26.5 19 9.5 4.75 2.36 0.6 0.075
Percent passage (%) 100 98.4 97.0 69.4 52.3 43.3 29.4 13.2 3.7
Selecting 3.0%, 3.5%, 4.0% and 4.5% of cement dosage, determining the optimal water content and the maximum dry density of the mixture by adopting a vertical vibration compaction method, and preferably selecting test parameters comprising: the working frequency is 30Hz, the static eccentric moment is 7.6kN, the weight of getting on the vehicle is 1.2kN, the weight of getting off the vehicle is 1.8kN, and the vibration compaction time is 110 s.
(1) 5 parts of dry mass m is prepared according to the requirement of synthesis gradations5500g of a sample;
(2) adding 1 part of dried sample into the sample with a predetermined mass ratio of (m)j+ms) ×, adding the corresponding cement, and mixing uniformly again to obtain wet mixture, wherein w isiAdding water content into the cement for the ith test, wherein the added cement quality for the first test is 1, 2, 3, 4 and 5;
(3) preparing a test piece by adopting a vibration compaction test method;
(4) drawing a density-water content relation curve according to the mixing water content and the density of 5 groups, wherein the vertical and horizontal coordinates of the peak of the hump-shaped curve are respectively the maximum density rhomaxAnd optimum water content ratio omega0。
The maximum dry density and the optimum water content of the cement cold-recycling mixture are shown in a table 22.
TABLE 22 maximum dry density and optimum water content of cold-recycling mixed materials with different cement mixing amounts
Figure GDA0002568341520000131
Selecting cement doses of 3.0%, 3.5%, 4.0% and 4.5%, and respectively manufacturing VVTM test pieces according to different cement doses;
measuring the cement dosage of each group of test pieces, carrying out 7d unconfined compressive strength test and 7d splitting strength test, and comprehensively determining the cement dosage by combining the technical requirements and engineering experience of tables 1 and 2;
a test piece is prepared by adopting VVTM, standard health maintenance (temperature is 20 +/-2 ℃, humidity is more than 95%) is carried out for 6 days, water saturation is carried out for 24 hours at 20 +/-2 ℃, an unconfined compressive strength test is carried out the next day, and the unconfined compressive strength results of 7 days of VVTM test piece cold-recycling mixture with different cement dosages are shown in tables 23 and 24. From the results in tables 23 and 24, it can be seen that the cement cold-recycling mix with a cement dosage of 3.5% can meet the design requirements, and the cement dosage range suggested herein is proved to be available for reference.
TABLE 23 Cold-regenerated mixture VVTM test piece 7d unconfined compressive strength with different cement dosages
Figure GDA0002568341520000141
TABLE 24 cold-recycling mixture VVTM test piece 7d splitting strength with different cement dosages
Figure GDA0002568341520000142
The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.

Claims (6)

1. A design method of a cement cold-recycling mixture VVTM comprises the following steps:
(1) providing a cement cold recycling mixture according to the formula (1):
RCB: coarse aggregate: fine aggregate 1-C-X: c: x is a group represented by the formula (1),
in formula (1): c-the mass mixing amount of the coarse aggregate,
x-fine aggregate mass mixing amount;
the design method of the mass mixing amount of the coarse aggregate and the fine aggregate comprises the following steps:
(a) when (Y-1)/Yx 100% is more than or equal to 35%, C is (Y-1)/Yx 100% -20%, and X is 20%;
(b) when the content is more than or equal to 20 percent and less than or equal to (Y-1)/Y multiplied by 100 percent and less than 35 percent, C is 20 percent, and X is (Y-1)/Y multiplied by 100 percent to 20 percent;
(c) when (Y-1)/Y × 100% < 20%, C ═ Y-1)/Y × 100%, X ═ 0%;
wherein Y is the doping amount coefficient of the new aggregate,
Y＝0.875HR/hxthe compound of the formula (2),
in formula (2): y-new aggregate mixing amount coefficient;
HR-cold recycled structural layer design thickness, cm;
Hx-old road base milling thickness, cm;
(2) preparing mixtures with different cement dosages, and determining the optimal water content and the maximum dry density;
(3) respectively calculating the dry density of the mixed material test pieces with different cement dosages in the step (2) according to the base layer compaction degree of 98% or the subbase layer compaction degree of 97%, and forming VVT test pieces with different cement dosages according to the calculated dry density and the optimal water content obtained in the step (2);
(4) carrying out standard health maintenance on the VVTM test piece obtained in the step (3), and testing the 7d unconfined compressive strength and the 7d cleavage strength of the VVTM test piece after the standard health maintenance, wherein the 7d unconfined compressive strength and the 7d cleavage strength are independently calculated according to the formula (3) to obtain:
Figure FDA0002568341510000011
in formula (3): r0.95A representative value of the strength at 95% proof, MPa, where the representative value of the 7d unconfined compressive strength at 95% proof is denoted Rc0.95The 7d cleavage strength representative value of the 95% proof rate is represented as Ri0.95；
Figure FDA0002568341510000012
Average value of the test piece strength, MPa, where the average value of the unconfined compressive strength of test piece 7d is expressed as
Figure FDA0002568341510000013
The average value of the cleavage strength of the test piece 7d was represented by
Figure FDA0002568341510000014
S-standard deviation of specimen strength, MPa;
Cvcoefficient of variation of test piece strength,%, where the coefficient of variation of unconfined compressive strength of test piece 7d is denoted Cv,cVariation of cleavage Strength of test piece 7dCoefficient is represented as Cv,i；
Determining the cement dosage according to the strength design standard of the cement cold-recycling mixture and the cement dosage design standard of the cement cold-recycling mixture; if the obtained result can not reach the strength standard, readjusting the cement dosage or the new aggregate mixing amount for design;
the strength design standard of the cement cold-recycling mixture is specifically as follows: the base layer has the compaction degree of more than or equal to 98 percent, the 7d cleavage strength of more than or equal to 0.40MPa, the 7d unconfined compressive strength of more than or equal to 4.0MPa, the subbase layer has the compaction degree of more than or equal to 97 percent, the 7d cleavage strength of more than or equal to 0.35MPa, and the 7d unconfined compressive strength of more than or equal to 3.5 MPa;
the design standard of the cement dosage of the cement cold-recycling mixture is as follows: the cement dosage of the base layer was 3.0% minimum and 4.5% maximum, and the cement dosage of the sub-base layer was 2.5% minimum and 4.0% maximum.
2. The design method according to claim 1, wherein the coarse aggregate in step (1) has a particle size of 15-30 mm or 10-25 mm, and the fine aggregate has a particle size of 2.36mm or less.
3. The design method of claim 1, wherein the step (2) comprises: setting cement dosages at intervals of 0.5% according to the base cement additive amount of 3-4.5% and the subbase cement additive amount of 2.5-4%, preparing mixtures with different cement dosages, changing the water content, and carrying out a vibration compaction test, wherein when the maximum dry density is obtained, the water content of the mixture is the optimal water content.
4. The design method according to claim 3, wherein the vibration compaction test parameters include: the working frequency is 30 plus or minus 1Hz, the static eccentric moment is 7.6 plus or minus 0.02kN, the weight of the upper vehicle is 1.2 plus or minus 0.01kN, the weight of the lower vehicle is 1.8 plus or minus 0.01kN, and the vibration compaction time is 110 plus or minus 10 s.
5. The design method according to claim 1, wherein the step (3) is formed by: adopting vertical vibration compaction to form VVTM test pieces with different cement dosages, wherein the parameters of the vertical vibration compaction comprise: the working frequency is 30 plus or minus 1Hz, the static eccentric moment is 7.6 plus or minus 0.02kN, the weight of getting on the train is 1.2 plus or minus 0.01kN, and the weight of getting off the train is 1.8 plus or minus 0.01 kN.
6. The designing method as claimed in claim 1 or 5, wherein the VVTM specimen in the step (3) is a cylinder having a diameter of 150mm and a height of 150 mm.
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