CN104834771A - Method for establishing strength measurement curve of concrete with high-volume mineral admixtures - Google Patents

Abstract

The invention discloses a strength measuring curve and a method for establishing a large-volume mineral admixture concrete, wherein the establishment method includes the following steps: making a large-volume mineral admixture concrete test block according to the mineral content of 30%-50%; The prepared test block is subjected to natural maintenance; the rebound value of the test block is tested to obtain the rebound value; the compressive strength is obtained by applying the ultimate load of failure; the carbonization depth value is obtained by measuring the carbonization depth of the damaged test block; according to the measured rebound value, The compressive strength and carbonization depth values are obtained to obtain the strength curve equation. According to this strength curve, the compressive strength of concrete with large amount of mineral admixture can be detected. Compared with the national unified strength curve, the established rebound strength curve of large-volume mineral admixture concrete is more reliable and accurate. This is of great significance for the quality inspection and evaluation of concrete with large amount of mineral admixtures.

Description

Establishment Method of Strength Curve of Concrete with Large Amount of Mineral Admixture

technical field

The invention belongs to the technical field of concrete, and in particular relates to the establishment of a concrete compressive strength curve.

Background technique

In today's world, whether it is building structures or bridge engineering, concrete is one of the indispensable materials. It is widely used and has a long history. Various structures used in marine development. my country is the country with the largest amount of concrete. According to the "2013 China Land and Resources Bulletin" issued by the Ministry of Land and Resources of my country, the annual output of cement in 2013 in China has reached 2.42 billion tons, and the annual output of concrete has exceeded 2.196 billion cubic meters, of which commercial concrete has reached 1.17 billion cubic meters. , the annual steel consumption has reached 4,000 tons, and the annual output of cement and concrete ranks first in the world. However, in recent years, the poor durability of concrete has caused its premature failure and even destruction. Disasters caused by quality defects of concrete structures occur frequently, resulting in major property losses and even the safety of people's lives and property. Therefore, strengthening and perfecting the on-site inspection of concrete structures is an important means to ensure the safety of building structures.

The detection of concrete structure strength can be generally divided into destructive testing technology and non-destructive testing technology according to its different principles. Although the test result of destructive testing technology is relatively intuitive and reliable, it will cause local damage to the structure, and the tested structure needs to be repaired accordingly. It is not conducive to the development and maintenance of concrete components in the later stage. The on-site detection of concrete structure strength generally adopts non-destructive testing technology, which has become one of the evaluation and analysis methods of engineering accidents. play an important role in the process. The non-destructive testing technology of concrete structure refers to the detection technology that directly acts on the structure or components to measure one or some physical quantities without destroying the concrete structure, and speculates the strength and other indicators of concrete through the correlation between these physical quantities and strength. , including ultrasonic method, rebound method, ultrasonic rebound method, shock echo method, radar method, infrared imaging method, etc. Among them, the rebound method is due to the simple structure of the instrument, the convenience of carrying the instrument, the test method is easy to master, the detection efficiency is high, and the cost is low. The cost is relatively low, and the shape and size of the measured object are generally not limited, so it is widely used. Because it is especially suitable for random and large-scale inspections of the strength of structural concrete at the construction site, it has been recognized by the international academic community as One of the basic methods of non-destructive testing of concrete has become a common method for on-site structural concrete inspection and acceptance. After years of research and the accumulation of a large number of laboratory and field data, a national unified strength measurement curve has been established, and the "Technical Regulations for Testing the Compressive Strength of Concrete by Rebound Method" (JGJ/T23-2011) has been formed. It also researches and establishes the regional rebound strength curve suitable for local testing, which provides a basis for the quality testing and evaluation of physical projects.

In recent years, with the rapid development of the economy and the continuous advancement of the urbanization process, modern buildings or structures have shown a trend of high-rise and long-span development. The strength requirements of these projects are getting higher and higher, and ordinary concrete has gradually been unable to meet the needs of the project. For example, during the use of some civil facilities, such as the impact of waves on sea lines and offshore platforms, and the impact of aircraft on runways when taking off and landing, these projects require concrete materials with higher strength levels. At present, the water-to-binder ratio of concrete used in many civil projects and marine projects is less than 0.4; on the other hand, because the production of cement will produce a large amount of carbon dioxide, in order to protect the environment, it is replaced by large-volume mineral admixtures, etc. A large amount of cement can also achieve the same effect, so concrete with a large amount of mineral admixture and low water-binder ratio has developed rapidly. Therefore, the quality inspection and evaluation of these large-volume mineral admixture concretes are of great significance to ensure the safe service of structural engineering. The "Technical Regulations for Testing the Compressive Strength of Concrete by Rebound Method" (JGJ/T 23-2011) clearly states that the national unified strength measurement curve is suitable for ordinary concrete with a compressive strength within the range of (10.0-60.0) MPa. Concrete with a large amount of mineral admixture and low water-binder ratio is significantly different from ordinary concrete. With the promotion and application of its technology, the applicability of the national unified strength curve gradually decreases. Mainly manifested in the following aspects:

(1) The components of large-volume mineral admixture concrete are complex, and large-volume mineral admixture concrete is often mixed with a large amount of mineral admixture, resulting in a more complex composition. In addition, due to the relatively fast carbonation depth of fly ash in the early stage, the national uniform strength measurement curve is not applicable to large-volume mineral admixture concrete with a large amount of fly ash.

(2) The national unified strength measurement curve is only applicable to concrete with a strength below 60MPa, but it is helpless for the detection of high-performance concrete with a strength of 60MPa and above.

(3) Concrete with a large amount of mineral admixture has the characteristics of high fluidity, and its slump is often required to reach 140mm, or even more than 200mm, which is inconsistent with the requirements for fluidity in the national unified strength measurement curve, and its degree of influence There are many uncertainties.

It is urgent to start with the basic principle of rebound detection, explore the factors affecting the surface hardness of concrete with large amount of mineral admixtures, and establish the quantitative relationship of concrete strength. This will have important practical significance and engineering practical value for controlling engineering quality, preventing engineering accidents, solving concrete strength problems, promoting concrete development, and accurately evaluating engineering quality.

Contents of the invention

Purpose of the invention: The purpose of the invention is to establish a concrete strength measurement curve with a large amount of mineral admixture, improve the detection level of concrete compressive strength, and accurately evaluate the project quality.

Concrete technical scheme of the present invention is as follows:

The strength measurement curve of concrete with a large amount of mineral admixture, the mineral admixture includes fly ash and or slag, the amount of mineral admixture is 30%-50%, it is characterized in that the strength measurement curve The equation is:

${\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; cu</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; j</span>}}^{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0.049858</span>}{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}^{\mathrm{<span\; class="notranslate">\; 1.861617</span>}}{\mathrm{<span\; class="notranslate">\; 10</span>}}^{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 0.09947</span>}\mathrm{<span\; class="notranslate">\; Dm</span>}}$

In the formula: —Converted value of concrete compressive strength in the jth measurement area, unit MPa, accurate to 0.01MPa;

R _m — the average rebound value of the survey area, accurate to 0.1MPa;

D _m — the average carbonization depth of the survey area, in mm.

Among them, the fly ash is grade I fly ash, and the slag is grade S95.

Based on the low water-binder ratio of less than 0.35.

A method for establishing a strength curve of concrete with a large amount of mineral admixture is characterized in that it includes the following steps:

Step 1. According to the mineral content of 30%-50%, make a large-volume mineral admixture concrete test block:

Step 2, maintaining the prepared test block;

Step 3, perform a rebound value test on the test block to obtain the rebound value;

Step 4, obtain the compressive strength by applying the failure limit load;

Step 5, measuring the carbonization depth of the damaged test block to obtain the carbonization depth value;

Step 6. According to the measured rebound value, compressive strength and carbonization depth value, the strength measurement curve equation is obtained: $f_{\mathrm{cu},j}^c=0.049858R_m^{1.861617}{10}^{-0.09947\mathrm{Dm}}$

In the formula: —Converted value of concrete compressive strength in the jth measurement area, unit MPa, accurate to 0.01MPa;

R _m — the average rebound value of the survey area, accurate to 0.1MPa;

D _m — the average carbonization depth of the survey area, in mm.

Compared with the prior art, the present invention establishes the strength measuring curve of concrete with large amount of mineral admixture, through which, the compressive strength of concrete with different amount of admixture can be directly calculated without the need for different amounts of admixture Concrete samples are tested separately with high reliability and accuracy.

Description of drawings

Figure 1 is a comparison between the established strength curve of large-volume mineral admixture concrete and the national unified strength curve.

Detailed ways

The present invention is described in detail below in conjunction with specific embodiment:

The method for establishing the strength measuring curve of the large-volume mineral admixture concrete of the present invention comprises the following steps:

Step 1. The production of concrete test blocks with large amount of mineral admixtures, P·Ⅱ52.5 grade cement and granite gravel produced by Onoda, continuous gradation, the maximum particle size is 20mm, and the fine aggregate is river sand. The apparent density is 2650kg/m ³ , and the fineness modulus is 2.96; tap water is used for concrete mixing. According to the characteristics of large-volume mineral admixture concrete, large-volume mineral admixtures, the use of functional admixtures, low water-binder ratio, and high fluidity are used to design mix ratios of different strength levels. Concrete of each strength grade is designed for X experimental ages and Y standard size test blocks are made. All test blocks of the same ratio shall be completed on the same day.

Step 2: Cover the concrete molding surface with a film after the test piece is formed to prevent the volatilization of moisture on the concrete surface. After 24 hours, remove the mold and put the test piece in the standard curing room for curing for one week. After one week, put the test piece To maintain in the natural environment, and stack the test blocks in a zigzag shape, the purpose is to fully simulate the actual engineering environment.

Step 3. Test the rebound value. Place the two opposite sides of the standard test block that has reached the design age between the bearing plates of the press, turn on the machine to make the pressure on the test block between 30KN-80KN, and then use the The rebound value of two opposite sides of the standard test block is measured horizontally by the elastic meter. Evenly select 8 points on each side, and the distance between each two points should not be less than 20mm. Remove 3 maximum values and 3 minimum values from the 16 rebound values of each test piece, and the remaining 10 values Take the average value R _a to get the rebound value of the test block at a certain age.

Step 4, strength test, and then continue to apply pressure to the test block on the press, and its failure limit load is the cubic compressive strength of high performance concrete.

Step 5. After the determination of the depth of carbonation and the concrete specimen compression test, after the destruction of the concrete specimen, drop 1% phenolphthalein alcohol solution (alcohol is anhydrous ethanol). When the boundary between carbonized and non-carbonized is clear, measure the carbonization depth with a carbonization measuring instrument.

Step 6. According to the measured rebound value, compressive strength value and carbonization depth value, computer analysis is carried out, and the regression strength curve equation is used Programming and fitting to establish the rebound strength curve of concrete with large amount of mineral admixture in this area.

Step 7, the obtained curve equation is $f_{\mathrm{cu},j}^c=0.049858R_m^{1.861617}{10}^{-0.09947\mathrm{Dm}}$

In the formula: —Converted value of concrete compressive strength in the jth measurement area, unit MPa, accurate to 0.01MPa;

R _m — the average rebound value of the survey area, accurate to 0.1MPa;

D _m — the average carbonization depth of the survey area, in mm.

Figure 1 is a schematic diagram of the comparison between the strength measurement curve of large-volume mineral admixture concrete established when the carbonation depth of concrete is 0 and the national unified strength-measurement curve. It can be seen from Figure 1 that when the carbonation depth is 0, the large-volume mineral admixture The strength measurement curve of raw material concrete is always higher than the national unified strength measurement curve, and with the increase of rebound value, the difference between the two tends to increase gradually.

Claims (4)

1. the concrete strength test curve of high content mineral admixtures, mineral admixture used comprises flyash and slag, and the volume of mineral admixture is 30%-50%, it is characterized in that, the equation of described strength test curve is:

$f_{\mathrm{cu},j}^c=0.049858R_m^{1.861617}{10}^{-0.09947\mathrm{Dm}}$

In formula: -jGe Ce district concrete crushing strength scaled value;

R _m-survey district's average rebound number;

D _m-survey the average carbonation depth value in district.

2. high content mineral admixtures concrete strength-detecting curve as claimed in claim 1, it is characterized in that, it is characterized in that, flyash is I grade of flyash, and slag is S95 level.

3. high content mineral admixtures concrete strength-detecting curve as claimed in claim 1, is characterized in that, is less than that the low water binder ratio of 0.35 sets up based on water-cement ratio.

4. a method for building up for high content mineral admixtures concrete strength-detecting curve, is characterized in that, comprises the steps:

Step one, according to mineral volume 30%-50%, make high content mineral admixtures concrete test block;

Step 2, to make test block carry out natural curing;

Step 3, test block carried out to rebound value test and obtain rebound value;

Step 4, obtain compressive strength by applying breaking limit load;

The carbonation depth that step 5, measurement destroy test block obtains carbonation depth value;

Step 6, the rebound value according to measuring, compressive strength and carbonation depth value, obtain strength test curve equation; $f_{\mathrm{cu},j}^c=0.049858R_m^{1.861617}{10}^{-0.09947\mathrm{Dm}}$

In formula: -jGe Ce district concrete crushing strength scaled value;

R _m-survey district's average rebound number;

D _m-survey the average carbonation depth value in district.