CN114925987A - Grading method of concrete recycled macadam aggregate - Google Patents
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Abstract
The invention discloses a grading method of concrete recycled macadam coarse aggregate, which comprises the following steps: 1) according to the existing standard requirements, preliminarily determining an evaluation index for evaluating the performance of the regenerated broken stone coarse aggregate; then, determining the evaluation index after screening by adopting a statistical analysis method; 2) according to the screened evaluation indexes, further combining with a strength evaluation means, dividing the grade sections of different evaluation index types; 3) performing performance test of related evaluation indexes on the recycled crushed stone coarse aggregate according to the screened evaluation indexes to obtain performance evaluation parameters of the recycled crushed stone coarse aggregate; and realizing the rapid and efficient grading of the concrete recycled broken stone coarse aggregate according to the grade section obtained in the step 2). The combined grading standard for multi-level division of the quality of the recycled crushed stone coarse aggregate provided by the invention can effectively guide the rapid and efficient application of the recycled crushed stone coarse aggregate under each grade in the actual engineering.
Description
Technical Field
The invention belongs to the technical field of building solid waste regeneration application, and particularly relates to a grading method of recycled crushed stone aggregate.
Background
Since the middle of the twentieth century, the building and traffic industry in China has been rapidly developed, the demand of natural macadam is in an increasing state, meanwhile, a great amount of building solid waste is generated after the concrete facilities such as old buildings, roads, bridges and the like are dismantled, according to statistics of relevant data, the quantity of building waste generated in China per year exceeds 35 hundred million tons, and the quantity is increased by 10 percent per year. The construction industry in China faces two main problems: firstly, natural macadam resources are deficient; secondly, a large amount of construction waste is generated and is transported to the periphery of the city to be simply filled or treated in the open air, which brings serious pollution to the environment. The method has great significance for the research on the recycling of the waste concrete, can relieve the problem of resource fatigue, can also solve the problem of building garbage filling and stacking, and improves the ecological environment.
The foreign developed countries have relatively early research on recycling of waste concrete, have obtained better achievements on classification research of recycled aggregate, and have made relevant quality standards and specifications of recycled aggregate. (RILEM) international association of materials and structural research laboratories, grading the recycled coarse aggregate by measuring the water absorption, apparent density, organic matter content of the recycled coarse aggregate; japanese 'quality test regulations for recycled concrete materials' issued in 1994, which are graded by crushing index and water absorption; the regulation amendments issued by Denmark in 1990 are graded according to the strength of the recycled concrete; BS (British Standard) and ASTM also divide various indexes of recycled aggregates applied to different projects, and the main division indexes are the lowest apparent density, the highest water absorption, the highest needle-shaped content, the highest impact value, the highest chlorine content and the highest sulfate content.
The existing GB 25177-2010 concrete recycled coarse aggregate specification in China grades the recycled aggregate under each single index of micro powder and mud block content, water absorption, needle sheet content, harmful substance content, impurity content, firmness, crushing index, apparent density and porosity, but the indexes are too many, the operation is complex in actual grading, the operation is not beneficial to engineering practice, and no guidance is provided for the engineering application practice of the recycled coarse aggregate under each grade. In view of the above points, a set of grading method suitable for engineering practice, capable of screening and optimizing the recycled coarse aggregate and having a guiding effect on the application range of the recycled coarse aggregate is made to have great significance, the use of the recycled aggregate in concrete is further promoted, and the utilization level and the ratio of the recycled concrete are improved.
Disclosure of Invention
The invention mainly aims to provide a simple and efficient grading method for recycled crushed stone coarse aggregate, aiming at the problems and the defects that the existing grading method with the engineering guidance function is lack of the grading method with excessive indexes and indefinite interval division of the quality grade of the recycled crushed stone coarse aggregate, and the like.
In order to achieve the purpose, the invention adopts the technical scheme that:
a grading method of concrete recycled macadam coarse aggregate comprises the following steps:
1) according to the existing standard requirements, preliminarily determining an evaluation index for evaluating the performance of the regenerated macadam coarse aggregate; then, determining the evaluation index after screening by adopting a statistical analysis method;
2) according to the screened evaluation indexes, further combining with a strength evaluation means, dividing the grade sections of different evaluation index types;
3) carrying out related performance tests on the recycled crushed stone coarse aggregate according to the screened evaluation indexes to obtain performance evaluation actual measurement parameters of the recycled crushed stone coarse aggregate; and then according to the obtained actual measurement parameters and the grade section obtained in the step 2), realizing the rapid and efficient grading of the concrete recycled macadam coarse aggregate.
In the scheme, the statistical analysis method in the step 1) comprises index correlation and significance analysis; the specific analysis steps are as follows:
1) normalizing the data of the preliminarily determined evaluation indexes, and eliminating the influence on the result caused by different index dimensions, wherein the reverse indexes are processed by adopting a formula (1):
and (3) processing the forward index by adopting a formula (2):
in the formula X (ij,min) 、X (ij,max) Respectively representing the minimum value and the maximum value of various preliminarily determined evaluation index values;
obtaining an index normalization matrix Z ij See formula (3):
2) analyzing the correlation between various preliminarily determined evaluation indexes (between every two evaluation indexes) and between the preliminarily determined evaluation indexes and the compressive strength by adopting a Pearson correlation coefficient, and screening and removing the evaluation indexes which are not related to the compressive strength (the Pearson correlation coefficient is less than 0.4); indexes with certain correlation are used as grading indexes, and when the recycled coarse aggregate is graded, the grading indexes have correlation, so that different grading indexes are favorable for falling into the same or adjacent grade intervals; wherein the Pearson correlation coefficient adopts a formula (4):
wherein z is i 、z j Respectively, normalized values of two sets of variables (two evaluation indexes or an evaluation index and compressive strength),
respectively representing normalized average values of two groups of variables;
3) respectively establishing a unary linear regression equation between the compressive strength and the residual evaluation indexes, and further deleting the evaluation indexes with lower regression coefficients (lower than 5), wherein the equation is shown as the formula (5):
y＝az ij +b (5)
wherein y is the compressive strength, z i Is the normalized value of the residual evaluation index, and a is the regression coefficient;
4) verifying the screened evaluation indexes by adopting weight calculation, and specifically comprising the following steps:
calculating the conflict T between the evaluation indexes according to the equations (6) and (7) ij And information amount C ij ：
In the formula, ρ i,j Is the correlation coefficient between indices, δ j Normalizing the standard deviation for the index; c j The larger the index is, the more important the index is.
Then, calculating the information weight of the evaluation index obtained by screening in the step 2) according to the formula (8):
and further screening the evaluation indexes with the information weight of more than 20% as the evaluation indexes adopted by the invention.
In the scheme, the specification requirements comprise the current specification GB 25177-2010 recycled coarse aggregate for concrete and the like.
In the scheme, the evaluation indexes preliminarily determined in the step 1) comprise micro powder and mud block content, water absorption, impurity content, firmness, crushing index, apparent density, porosity and the like.
In the scheme, the recycled crushed stone coarse aggregate is prepared by crushing and screening waste concrete to obtain a continuous gradation with the grain diameter of 4.75 (excluding 4.75mm) to 31.5mm (excluding 31.5mm) meeting the specification requirement; wherein the content of impurities is less than 1%, the content of needle sheets is less than 10%, and the content of harmful substances is less than the standard limit.
In the above scheme, the evaluation indexes after screening are apparent density, crush index and water absorption.
In the scheme, the compressive strength is the compressive strength after the specific strength grade (C20, C30, C40 or C50) corresponds to the standard concrete test piece and is subjected to standard curing for 28 d.
Preferably, the formula requirements of the standard concrete test block include:
(1) in the standard concrete of C20 grade, the components and the volume weight thereof comprise: 160-170 kg/m water 3 300 to 310kg/m of cement 3 The coarse aggregate is 1136-1186 kg/m 3 668.5-688.5 kg/m of sand 3 1.6-1.8 kg/m of water reducing agent 3 (ii) a The water-cement ratio is 0.54-0.56;
preferably: 166kg/m water 3 300kg/m cement 3 1136kg/m of coarse aggregate 3 668.5kg/m of sand 3 1.6kg/m of water reducing agent 3 (ii) a The water-cement ratio is 0.55;
(2) in the standard concrete of grade C30, the components and the occupied volume weight thereof comprise: 173-183 kg/m of water 3 375-385 kg/m cement 3 The coarse aggregate is 1136-1186 kg/m 3 668.5-688.5 kg/m sand 3 1.9-2.1 kg/m of water reducing agent 3 (ii) a The water-cement ratio is 0.46-0.48;
preferably, the following components are used: 178kg/m of water 3 375kg/m cement 3 1136kg/m of coarse aggregate 3 668.5kg/m of sand 3 1.9kg/m of water reducing agent 3 (ii) a The water-cement ratio is 0.47;
(3) in the standard concrete of C40 grade, the components and the volume weight thereof comprise: 163 to 173kg/m of water 3 450-460 kg/m cement 3 Coarse, coarseAggregate 1136-1186 kg/m 3 668.5-688.5 kg/m sand 3 2.1-2.3 kg/m of water reducing agent 3 (ii) a The water-cement ratio is 0.36-0.38;
preferably, the following components are used: 168kg/m of water 3 450kg/m of cement 3 1136kg/m of coarse aggregate 3 668.5kg/m of sand 3 2.1kg/m of water reducing agent 3 (ii) a The water-cement ratio is 0.37;
(4) in the standard concrete of grade C50, the components and the occupied volume weight thereof comprise: 155-165 kg/m water 3 485-495 kg/m cement 3 The coarse aggregate is 1136-1186 kg/m 3 668.5-688.5 kg/m of sand 3 3.1-3.3 kg/m of water reducing agent 3 (ii) a The water-cement ratio is 0.32-0.34;
preferably, the following components are used: 160kg/m water 3 485kg/m cement 3 The coarse aggregate is 1136kg/m 3 668.5kg/m of sand 3 3.1kg/m of water reducing agent 3 (ii) a The water-cement ratio was 0.33.
In the scheme, the evaluation index grades (quality grades of the recycled crushed stone coarse aggregate) in the step 2) are divided into: 5 grades of I grade, II grade, III grade, IV grade and V grade; the strength grade is divided according to the strength loss rate of the recycled concrete compared with common concrete, wherein the grade I is less than 5%, the grade II is less than 10%, the grade III is less than 20%, the grade IV is less than 30%, and the grade V is more than or equal to 30%.
In the foregoing solution, the index type rank section dividing method in step 2) includes the following steps: compared with the strength loss rate of natural concrete under the standard curing of 28d, the recycled concrete prepared under the condition of the percent substitution rate according to the recycled macadam coarse aggregates of each grade is divided into grade sections of different evaluation index types by adopting a probability statistical method; the formula system adopted by the recycled concrete and the natural concrete adopts the standard concrete test block requirement; the aggregate adopted by the recycled concrete is recycled broken stone coarse aggregate, and the aggregate adopted by the natural concrete is natural aggregate with the same gradation.
In the above solution, the step of dividing the level sections by using a probability statistical method includes: firstly, dividing the strength loss rate grade into four grades of 0-5% (grade I), 5-10% (grade II), 10-20% (grade III) and 20-30% (grade IV), and respectively testing the strength loss rate of the recycled concrete prepared by using recycled coarse aggregates with different evaluation indexes (apparent density, crushing index or water absorption) relative to the natural concrete to obtain corresponding scatter point data; and taking the numerical value (the upper limit value of the corresponding interval) corresponding to the evaluation index with the scatter point number ratio (percentage of the total scatter point number) between each evaluation index interval exceeding 60% for the first time as the corresponding grade section end value under the condition of different strength loss rate grades according to statistics.
In the foregoing solution, the step of classifying the rank segments specifically includes: firstly, aiming at the requirement of strength loss rate grade of 0-5%, taking the upper limit value of a water absorption interval corresponding to the condition that the ratio of the first accumulated scattered point quantity is more than 60% as the grade division end value of the I-grade evaluation index; sequentially determining grade division end values of the grade II to grade IV evaluation indexes, taking the grade division end value of the previous grade as a starting point, and taking the upper limit value of a corresponding water absorption interval when the sum of the subsequent scattered point quantity ratios exceeds 60% for the first time as the grade division end value of the grade evaluation index; and finally, taking the value requirement above the grade IV classification end value as the classification requirement of the grade V evaluation index.
Further, when the apparent density is graded, since the strength loss rate of the concrete as a whole decreases as the apparent density increases, the apparent density is graded in a tendency of decreasing the apparent density, and a grading requirement that a value smaller than an end value of the grading in the IV grade is set as a grading requirement for the evaluation of the apparent density in the V grade.
In the above scheme, the requirements of the different evaluation index types for the grade sections are as follows:
(1) an apparent density; class I, > 2600kg/m 3 (ii) a Class II-IV, 2450-2600 kg/m 3 (ii) a V grade, < 2450kg/m 3 ；
(2) A crush index; grade I, < 9%; grade II, < 12%; grade III, < 15%; grade IV, < 20%; grade V, not less than 20;
(3) water absorption; grade I, < 2%; grade II, < 3%; grade III, < 6%; grade IV, < 8%; v grade is more than or equal to 8.
In the scheme, one of the three types of evaluation indexes with the worst grade is used as the quality grade of the recycled coarse aggregate of the batch.
Furthermore, when the apparent density is 2450-2600 kg/m 3 And taking the worst one of the crushing index and the water absorption rate as the quality grade of the batch of the recycled coarse aggregate.
Further, according to the grade section obtained in the step 2), the range of engineering strength concrete suitable for the recycled crushed stone coarse aggregate can be further defined, and the concrete comprises the following concrete components: class I is applicable to C50 and below; class II is applicable to C40 and below; class III is applicable to C30 and below; grade IV applies to C20 and below; class V is suitable for non-structural concrete.
Compared with the prior art, the invention has the beneficial effects that:
1) the method comprises the steps of firstly, preliminarily determining an evaluation index for evaluating the performance of the coarse aggregate of the regenerated macadam based on the current standard, screening the evaluation index by adopting correlation and significance analysis and combining the distribution characteristics of the coarse aggregate of the regenerated macadam under each index, and screening the obtained evaluation index, so that the method not only accords with the practice, but also brings convenience to engineering practice;
2) on the basis of screening evaluation indexes, the invention further defines the grade interval of the recycled aggregate based on the strength loss rate of the recycled concrete with the same mixing proportion compared with the natural concrete and by combining a probability statistics dividing means, the divided grade interval is favorable for engineering practice, and the practical engineering application of the recycled aggregate can be simply, rapidly and efficiently guided;
3) the invention further provides the strength range of the concrete prepared from the recycled coarse aggregate under each grade, has important significance for guiding engineering practice, effectively promotes the efficient application of the recycled broken stone coarse aggregate in the concrete, and improves the utilization level and the ratio of the recycled concrete.
Drawings
FIG. 1 is a scatter diagram of water absorption of recycled coarse aggregate and cubic compressive strength of concrete;
FIG. 2 is a scatter diagram of the recycled coarse aggregate crushing index and the concrete cubic compressive strength;
FIG. 3 is a scatter diagram of the apparent density of recycled coarse aggregate and the cubic compressive strength of concrete;
FIG. 4 is a graph showing the relationship between the porosity of recycled coarse aggregate and the cubic compressive strength of concrete;
FIG. 5 is a graph showing the relationship between the solidity of recycled coarse aggregate and the compressive strength of concrete cubes;
FIG. 6 is a statistical scatter plot of the water absorption and strength loss of recycled coarse aggregate;
FIG. 7 is a statistical scatter plot of recycled coarse aggregate crush index and strength loss rate;
fig. 8 is a statistical scatter plot of apparent density and strength loss rate of recycled coarse aggregate.
Detailed Description
The technical solutions of the present invention will be described clearly and completely with reference to the following embodiments of the present invention, and it should be understood that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
In the following examples, the recycled coarse aggregates used were from 5 different batches (corresponding to batch 1, batch 2, batch 3, batch 4 and batch 5 in the examples respectively) of the building waste recycled material factory in hanyang district and Hubei Huidi renewable resource development and utilization Co., Ltd. and the particle size was 4.75-31.5 mm, and 5-25 mm continuous gradation was obtained by sieving in the laboratory;
the adopted cement is P.O 42.5.5-grade ordinary portland cement produced by Huaxin cement Ezhou limited company;
the adopted natural fine aggregate is continuous-graded natural river sand, and the particle size is 0.075-4.75 mm;
the adopted water reducing agent is a polycarboxylic acid high-efficiency water reducing agent, the solid content of the water reducing agent is 20 percent, the water reducing rate is 15 percent, and the water reducing agent is a light yellow liquid and is purchased from a new material company Limited in Wuhan city;
in the following examples, the method for grading the recycled concrete macadam coarse aggregate comprises the following steps:
1) crushing and screening the recycled crushed stone coarse aggregate to obtain a continuous gradation with the particle size of 4.75 (excluding 4.75mm) to 31.5mm (excluding 31.5 mm); wherein the content of impurities is less than 1%, the content of needle sheets is less than 10%, and the content of harmful substances is less than the standard limit;
2) according to the existing standard requirements, preliminarily determining evaluation indexes for evaluating the performance of the coarse aggregate of the regenerated macadam, wherein the preliminarily determined evaluation indexes comprise micro powder and mud block content, water absorption, impurity content, firmness, crushing index, apparent density and porosity; then, determining the evaluation indexes after screening as apparent density, crushing index and water absorption by adopting a statistical analysis method; the specific analysis steps comprise:
2-1) normalizing the data of the preliminarily determined evaluation indexes by referring to the formula (1), the formula (2) and the formula (3), and eliminating the influence of different index dimensions on the result; then, analyzing the correlation between various preliminarily determined evaluation indexes (between every two evaluation indexes) and the correlation between the preliminarily determined evaluation indexes and the compressive strength by adopting a Pearson correlation coefficient according to a formula (4), and screening and removing the evaluation indexes which are not related to the compressive strength (the Pearson correlation coefficient is less than 4), wherein the evaluation indexes and a strength scatter diagram of the cubic concrete compressive strength are respectively shown in figures 1-5; the results of the correlation analysis between the evaluation indexes and the compressive strength are shown in table 1;
TABLE 1 analysis results of correlation between evaluation indexes and compressive strength
Table 1 shows that, from the correlation analysis, the water absorption and crush indexes have a large correlation with the compressive strength, followed by the bulk density, apparent density, and firmness; the content of the micro powder and the content of the mud blocks are not related to the compressive strength (the Pearson correlation coefficient is less than 0.4), and meanwhile, the content of the two indexes can be obviously reduced by washing the recycled coarse aggregate, so the two indexes are screened out;
2-2) then respectively establishing a unitary linear regression equation (formula 5) between the compressive strength and the residual evaluation indexes (water absorption, crushing index, compressive strength, bulk density, apparent density and firmness), and obtaining a regression coefficient matrix shown in table 2;
TABLE 2 regression coefficient matrix
The results in Table 2 show that the degree of influence of each evaluation index on the compressive strength is sequentially a crushing index, a water absorption rate, an apparent density, a firmness and a void ratio, wherein the regression coefficients of the void ratio and the firmness are less than 5 and obviously less than other indexes, so that the two indexes are further screened out; screening a crushing index, water absorption and apparent density as the evaluation indexes;
2-3) verification of evaluation index
The evaluation indexes obtained by screening are verified by adopting weight calculation and national standards respectively, and the method specifically comprises the following steps:
calculating the conflict T between the evaluation indexes according to the equations (6) and (7) ij And information amount C ij ：
In the formula, ρ i,j Is the inter-index correlation coefficient, δ j Normalizing the standard deviation for the index; c j The larger the index, the more important the index is.
Then, calculating the information weight of the residual evaluation index according to the formula (8); the specific calculation results are shown in table 3:
TABLE 3 weight calculation results
As can be seen from table 3; from the perspective of information content weight, the apparent density has a higher weight value, and other indexes are approximately equal and also have higher weight values;
by combining the points, the invention screens out the water absorption rate, the crushing index and the apparent density as grading indexes of the recycled coarse aggregate;
3) according to the screened evaluation indexes, compared with the compressive strength loss rate of natural C30-grade standard concrete (the specific formula is shown in table 8) under the standard curing of 28d, the recycled concrete prepared by the recycled crushed stone coarse aggregates of all grades under the condition of percent substitution rate is divided into the grade sections of different evaluation index types by adopting a probability statistical method, wherein the specific grade section dividing step comprises the following steps:
aiming at the water absorption index; firstly, respectively testing the corresponding relation between the water absorption rate and the strength loss rate of different recycled coarse aggregates according to the grade requirements of the strength loss rate of less than 5% (I grade), 5-10% (II grade), 10-20% (III grade) and 20-30% (IV grade) (a scatter diagram is shown in figure 6), counting the corresponding proportion information of the strength loss rate (ordinate) in each section (specifically shown in table 4), and the distribution proportion of the contained sample points in each section of the water absorption rate (abscissa): when the strength loss rate is less than 5%, the sample points are respectively 0%, 64%, 8%, 2, 0% and 0% in the intervals of (0,1), (1, 2), (2, 3), (7, 8) and (8), and the water absorption rate is less than 2% as the grade division end value for dividing the I-grade water absorption rate; when the strength loss rate is more than 5% and less than 10%, the included sample points respectively account for 0%, 62%, 5% and 0% of the intervals (0,1), (1, 2), (2, 3), (7, 8) and (8), (8) of the water absorption rate, the total account rate in the interval [2,3) exceeds 60% for the first time, and the water absorption rate is less than 3% for the grade division end value of the grade II water absorption rate; when the strength loss rate is more than 10% and less than 20%, the included sample points respectively account for 0%, 7%, 22%, 30%, 28%, 4%, 7%, 2% of the water absorption rate in (0,1), [1,2), [2,3),., [7,8), [8 ]), starting from the grade division end value of the II-class water absorption rate, the total account ratio in the [3,6) -interval firstly exceeds 60%, and the water absorption rate is less than 6% as the grade division end value for dividing the III-class water absorption rate; when the strength loss rate is more than 20% and less than 30%, the included sample points respectively account for 0%, 10%, 13%, 43%, 30% and 4% of the intervals (0,1), [1,2), [2,3),. -, [7,8), [8 ] -) of the water absorption rate, the total account for more than 60% for the first time in the interval [6,8) and the water absorption rate less than 8% as the grade division end value for dividing the grade IV water absorption rate; and finally, taking the residual water absorption requirement of more than or equal to 8 percent as the dividing requirement of the V-grade water absorption.
The water absorption was finally classified into the class sections of (0,2), [2,3), [3,6), [6,8), [8, ] and (the corresponding statistical information is shown in table 5);
the steps of dividing the crushing index and the apparent density are the same as the water absorption index; specific statistical results are shown in tables 6 to 9. Wherein in the process of dividing the apparent density, the results of dividing the II level, the III level and the IV level are the same, so 2450-2600 kg/m 3 The interval of (A) is integrated into the grade requirements of II to IV, and finally, the ratio is less than 2450kg/m 3 The apparent density requirement of (2) is taken as a division requirement of the apparent density of class V.
Wherein, the formula system adopted by the recycled concrete and the natural concrete adopts the standard concrete test block requirement (see table 10); aggregate adopted by the recycled concrete is recycled gravel coarse aggregate, aggregate adopted by the natural concrete is natural aggregate with the same gradation, and the grade sections with different evaluation index types are divided, and the concrete is shown in table 11;
TABLE 4 probability statistics of Water absorption and Strength loss
As can be seen from FIG. 4, for the class conditions of strength loss (%) of <5, [5 to 10), [10 to 20) and [20 to 30), the values of the water absorption intervals at which the cumulative percentage of the water absorption reaches 60% or more are 2%, 3%, 6% and 8%, respectively; thus, a division scale of < 2, < 3, < 6, < 8, and ≧ 8;
TABLE 5 probability statistics for total percentage of 60% or more water absorption index section
TABLE 6 probability statistics of crush index and Strength loss Rate
TABLE 7 probability statistics of the corresponding index section of the crushing index with the total percentage of more than 60%
TABLE 8 probability statistics of apparent density and intensity loss rate
TABLE 9 probability statistics of total percentage up to 60% in the apparent density index section
TABLE 10 mixing ratio of different grades of standard concrete
Wherein, additional water should be added to each batch of recycled concrete according to the water absorption rate of the recycled coarse aggregate.
In the above scheme, the grade sections of different evaluation indexes are shown in table 1.
TABLE 11 grade sections of different evaluation indexes of the concrete recycled macadam coarse aggregate of the present invention
4) Carrying out related performance tests on the recycled crushed stone coarse aggregate by the screened evaluation indexes to obtain performance evaluation parameters of the recycled crushed stone coarse aggregate; according to the requirements of the grade sections in the table 1, the concrete recycled macadam coarse aggregate is classified quickly and efficiently; specific application examples are shown in examples 1 to 5.
Example 1
A grading method of concrete recycled broken stone coarse aggregate comprises the following steps:
1) detecting the crushing index, water absorption and apparent density of the recycled aggregate of batch 1; wherein the crushing index is carried out according to a corresponding test method in GB/T14685-2011 cobble and gravel for buildings, and the test result is 14.8%; the water absorption rate is 4.8% according to the corresponding test method in GB/T17431.2 lightweight aggregate and test method thereof, the apparent density is 2527kg/m according to the liquid specific gravity balance method in GB/T14685-2011 construction pebbles and macadam 3 ；
2) According to the comparison table 9, the crushing index of the recycled aggregate of the batch is III grade, the water absorption is III grade, and the apparent density is 2450-2600 kg/m 3 In the above, the classification is performed by the crushing index and the water absorption; and taking the worst grade in the grading indexes as the quality grade of the batch of recycled coarse aggregate, so that the quality grade of the batch of recycled coarse aggregate is grade III, and the applicable field range is C30 and below concrete.
Example 2
A grading method of concrete recycled macadam coarse aggregate comprises the following steps:
1) the crushing index, water absorption and apparent density of the recycled aggregate of batch 2 were measured by the same method as in example 1. Wherein crushing means that the result is 17.9%; the water absorption was found to be 6.5% and the apparent density was found to be 2568kg/m 3 。
2) According to the comparison table 9, the crushing index of the recycled aggregate of the batch is IV grade, the water absorption rate is IV grade, and the apparent density is 2450-2600 kg/m 3 In the above, the classification is performed by the crushing index and the water absorption; and taking the worst grade in the grading indexes as the quality grade of the batch of recycled coarse aggregate, so that the quality grade of the batch of recycled coarse aggregate is grade IV, and the applicable field range is C20 and below concrete.
Example 3
A grading method of concrete recycled macadam coarse aggregate comprises the following steps:
1) the crushing index, water absorption and apparent density of the recycled aggregate of batch 3 were measured by the same method as in example 1. Wherein crushing means that the result is 9.5%; the water absorption was found to be 1.97%, and the apparent density was found to be 2685kg/m 3 。
2) Referring to table 9, the batch of recycled aggregate has a crush index of class II, a water absorption of class I, and an apparent density of class I. And taking the worst grade in the grading indexes as the quality grade of the batch of recycled coarse aggregate, so that the quality grade of the batch of recycled coarse aggregate is grade II, and the applicable field range is C40 and below concrete.
Example 4
A grading method of concrete recycled macadam coarse aggregate comprises the following steps:
1) the crushing index, water absorption and apparent density of the recycled aggregate of batch 4 were measured by the same method as in example 1. Wherein crushing means that the result is 12.9%; the water absorption was found to be 3.7%, and the apparent density was found to be 2560kg/m 3 。
2) According to the comparison table 9, the crushing index of the recycled aggregate of the batch is III grade, the water absorption rate is III grade, and the apparent density is 2450-2600 kg/m 3 In the above, the classification is performed based on the crushing index and the water absorption. The worst grade in the grading index is taken as the quality grade of the batch of recycled coarse aggregate, so that the quality grade of the batch of recycled coarse aggregate is grade III, and the applicable field range is C30 and below concrete.
Example 5
A grading method of concrete recycled macadam coarse aggregate comprises the following steps:
1) the crushing index, water absorption and apparent density of the recycled aggregate of batch 5 were measured by the same method as in example 1. Wherein crushing means that the result is 18.2%; the water absorption was found to be 4.9%, and the apparent density was found to be 2527kg/m 3 。
2) According to the comparison table 9, the crushing index of the recycled aggregate of the batch is IV grade, the water absorption is III grade, and the apparent density is 2450-2600 kg/m 3 In this connection, the crushing index and the water absorption rate are used for classification. The worst grade in the grading indexes is taken as the quality grade of the recycled coarse aggregate, so that the quality grade of the recycled coarse aggregate is grade IV, and the applicable field range is C20 and below concrete.
In order to further verify the scientificity and the rationality of the applicable field of the grading method for the recycled coarse aggregates for the divided concrete, the concrete test blocks with the strength of C30, C20, C40, C30, C30 and C20 are prepared by respectively designing the mixing ratios of batch 1, batch 2, batch 3, batch 4 and batch 5, the specific mixing ratios are shown in Table 8, and the strength of each batch of the recycled concrete test blocks is respectively 33.1MPa, 26.3MPa, 40.3MPa, 35.1MPa and 26.8MPa after 28d of standard curing, so that the grading method for the recycled coarse aggregates for the divided concrete is reasonable.
Further, comparing the grading method for dividing the recycled coarse aggregate for concrete with the existing standard grading method (GB 25177-2010 recycled coarse aggregate for concrete), the concrete grading method comprises the following specific steps:
according to the current standard classification method, aiming at the recycled aggregate of the batch 1, the water absorption and crushing indexes correspond to II-class aggregates, and the apparent density corresponds to I-class aggregates; the water absorption of batch 2 corresponds to class III aggregate, the crushing index corresponds to class II aggregate, and the apparent density corresponds to class I aggregate; batch 3 water absorption, crush index, apparent density all correspond to class I aggregate; batch 4 water absorption and crush indexes correspond to class II aggregate, and apparent density corresponds to class I; batch 5 water absorption, crush index correspond to class II aggregate, apparent density corresponds to class I. As can be seen, if batches of recycled coarse aggregate are divided according to specifications, the phenomenon that different indexes correspond to different grades is more likely to occur, and the span of grade difference is larger, so that grade division is not clear. The recycled coarse aggregate grading method for the divided concrete well solves the phenomenon, and compared with the standard, the divided grade evaluates the grade of the recycled coarse aggregate more conservatively, so that the reliability of the method in practical application is higher.
Meanwhile, when the batches 1, 4 and 5 are classified according to the specification, the batches belong to the same grade, the C30 concrete is prepared from the three batches of recycled coarse aggregates according to the same mixing ratio in the table 8, and after 28d standard curing, the strength of each batch of recycled concrete test blocks is respectively 33.1MPa, 35.1MPa and 29.3MPa, so that the batches 1 and 4 have obvious quality difference compared with the batch 5.
The above embodiments are merely examples for clearly illustrating the present invention and do not limit the present invention. Other variants and modifications of the invention, which are obvious to those skilled in the art and can be made on the basis of the above description, are not necessary or exhaustive for all embodiments, and are therefore within the scope of the invention.
Claims (10)
1. A grading method of concrete recycled macadam coarse aggregate is characterized by comprising the following steps:
1) according to the existing standard requirements, preliminarily determining an evaluation index for evaluating the performance of the regenerated broken stone coarse aggregate; then, determining the evaluation index after screening by adopting a statistical analysis method;
2) according to the screened evaluation indexes, further combining with a strength evaluation means, dividing the grade sections of different evaluation index types;
3) testing the performance of the corresponding evaluation index of the recycled crushed stone coarse aggregate according to the screened evaluation index to obtain a performance evaluation actual measurement parameter of the recycled crushed stone coarse aggregate; and realizing the rapid grading of the concrete recycled macadam coarse aggregate according to the grade section obtained in the step 2).
2. The classification method according to claim 1, wherein the evaluation indexes preliminarily determined in step 1) include micropowder and clod contents, water absorption, impurity contents, solidity, crushing index, apparent density, and porosity.
3. The classification method according to claim 1, wherein the recycled crushed stone coarse aggregate is continuously graded by crushing and screening waste concrete to have a particle size of 4.75 to 31.5 mm.
4. The classification method according to claim 1, wherein the statistical analysis method of step 1) comprises index correlation and significance analysis, and evaluation indexes having a coefficient of correlation with compressive strength of less than 0.4 and a regression coefficient of less than 5 are screened out.
5. The grading method according to claim 4, wherein the compressive strength is the compressive strength of a standard concrete sample after standard curing for 28 d.
6. The classification method according to claim 1, wherein the evaluation indexes after the screening in step 1) are apparent density, crush index and water absorption.
7. The classification method according to claim 1, wherein the evaluation index grades are classified into 5 grades of I grade, II grade, III grade, IV grade, V grade in step 2); the strength grade is divided according to the strength loss rate of the recycled concrete compared with the common concrete, wherein the grade I is less than 5%, the grade II is less than 10%, the grade III is less than 20%, the grade IV is less than 30%, and the grade V is more than or equal to 30%.
8. The classification method according to claim 7, wherein the rating section division method of the evaluation index in step 2) includes the steps of: according to the strength loss rate of the recycled concrete prepared by the recycled crushed stone coarse aggregates of all grades under the condition of percent substitution rate compared with natural concrete under the standard curing of 28d, the grade sections of different evaluation index types are divided by adopting a probability statistical method; the formula system adopted by the recycled concrete and the natural concrete adopts the standard concrete test block requirement; the aggregate adopted by the recycled concrete is recycled broken stone coarse aggregate, and the aggregate adopted by the natural concrete is natural aggregate with the same gradation.
9. The ranking method according to claim 7, wherein the ranking section requirements for different evaluation index types are:
(1) an apparent density; class I, > 2600kg/m 3 (ii) a Class II-IV, 2450-2600 kg/m 3 (ii) a V grade, < 2450kg/m 3 ；
(2) A crush index; grade I, < 9%; grade II, < 12%; grade III, < 15%; grade IV, < 20%; grade V, not less than 20;
(3) water absorption; grade I, < 2%; grade II, < 3%; grade III, < 6%; grade IV, < 8%; grade V is more than or equal to 8.
10. The grading method according to claim 1, wherein the grade section obtained in step 2) is used for further defining the range of engineering strength concrete suitable for the recycled crushed stone coarse aggregate, and the method specifically comprises the following steps: class I is applicable to C50 and below; class II is applicable to C40 and below; class III is applicable to C30 and below; grade IV applies to C20 and below; class V is suitable for non-structural concrete.
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| CN116100703B (en) * | 2022-12-30 | 2023-11-14 | 玫瑰塑胶(昆山)有限公司 | Method and system for manufacturing plastic product by using recycled material |
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