JP2001116748A - Method for measurement of water content per unit volume freshly mixed concrete by using apparatus for measuring salt content - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a test method in which various performances of concrete can be estimated precisely, quickly and simply in a state that the concrete is freshly mixed concrete in order to construct a good-quality building. SOLUTION: In order to judge various performances of concrete and to grasp the actual state of a change in the quality of freshly mixed concrete, it is optimum to measure a water content per unit volume freshly mixed concrete. As this method for the measurement of water content, two samples from an identical freshly mixed concrete sample are collected. A liquid which contains a salt content is mixed with one sample. A liquid which contains salt in an extremely small amount is mixed with the other sample. The concentration of the salt content is measured by an apparatus to which a salt content sensor is attached. Thereby, the concentration of the salt content can be measured with high accuracy and simply, and the content of a chloride can be measured simultaneously. Interfering ions which disturb the measurement of the salt content exist in the freshly mixed concrete. When the interfering ions are added in advance to the liquid to be used, the influence of the interfering ions can be prevented. When the apparatus is calibrated by the liquid mixed with the freshly mixed concrete or by a liquid whose salt content concentration is identical to that of the liquid, the error of the apparatus or an error due to the factor of the liquid is prevented, and the salt content can be measured precisely.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to quality control at a ready-mixed concrete plant, civil engineering, or construction site and to spot inspection for preventing defective construction.

[0002]

2. Description of the Related Art Inspection and quality control of ready-mixed concrete are performed by a slump test and an air volume test, and quality control of concrete is generally performed at a compressive strength of 28 days of age. In addition, a salt test has been carried out for more than ten years before the salt content of ready-mixed concrete began to be regarded as a problem, and more than ten types of measuring instruments are currently used as a salt meter for ready-mixed concrete. It has been said for several years that it has been necessary to measure the unit water volume of ready-mixed concrete for spot inspections and strength estimations, especially when defective structures built during the period of high economic growth have been regarded as a problem. The importance of measuring the amount of water has become important. Heat drying method, underwater mass method, alcohol specific gravity method, salt concentration method, neutron moisture meter method and capacitance method are considered as the test methods, but most of the test methods are still in the experimental stage, and the construction site There is no established method for easily performing the punching test. The method closest to the present invention is a titration analysis method in the salt concentration method, and there are a method using manual titration and a method using an automatic titrator.

[0003]

The conditions of good concrete are that the required strength is sufficiently satisfied, that dry shrinkage which causes cracking is small, that water tightness, durability and weather resistance are high. Among them, the strength that is highly important and easily expresses the performance of concrete as a numerical value is generally determined by the compressive strength of 28-year-old material. However, even if the required strength is not obtained and the concrete is rejected, it is extremely difficult to remove the cast concrete and it is often impossible to reconstruct the concrete.

[0004] From the standpoint of a ready-mixed concrete purchaser, the slump test that is currently being performed can measure the fluidity of ready-mixed concrete, but cannot determine whether or not it has the specified composition. In the case of ready-mixed concrete manufacturers, equipment such as slump monitors are used to check the change in quality of ready-mixed concrete due to the change in material quality.
The unit water amount may fluctuate depending on the amount of water adhering to the aggregate or the amount of water after slump adjustment, and it is very difficult to grasp the substance of the quality fluctuation of ready-mixed concrete.

[0005] Among the methods of measuring unit water content of ready-mixed concrete that are currently considered, the underwater mass method requires the density of material and the mix of ready-mixed concrete, and furthermore, the heat drying method, the neutron moisture meter method, and the capacitance method. Since it measures all the water in the ready-mixed concrete, it requires the water absorption of the aggregate and the mix of the ready-mixed concrete, and in some cases requires a power supply and a preliminary test, which is unsuitable for spot inspection at the construction site. The photorefractive method in the alcohol densitometer method and the salt concentration method cannot be measured accurately because it is affected by temperature and other dissolved substances. In the case of the salt concentration method by titration analysis, the measurement is accurate and can be performed without preliminary data such as aggregate and composition, but it is difficult to carry a delicate titrator to a construction site and work. There is also a problem of waste liquid treatment. When measuring the unit water amount by the salt concentration method, it is necessary to correct the salt content in the ready-mixed concrete.

[0006] Interfering ions such as calcium ions and sulfide ions are present in ready-mixed concrete, and errors may occur in the measurement of the salt concentration depending on the instrument.

At present, errors in measuring the chloride content of ready-mixed concrete with an instrument are recognized to be up to ± 10%. However, since it is desired to measure the unit water amount with an accuracy of about ± 1%, it is necessary to measure the salt content of ready-mixed concrete. They cannot be used in the same way. Further, even if the accuracy of the instrument is increased, the method of measuring the value of the salt concentration itself causes an error depending on the calibration state of the instrument and a factor of the liquid mixed with the ready-mixed concrete, and accurate measurement cannot be performed.

[0008]

[Means for Solving the Problems] In order to estimate the concrete strength, judge various properties such as water tightness, drying shrinkage, durability and weather resistance, and grasp the actual state of the quality fluctuation of the ready-mixed concrete, the unit water amount of the ready-mixed concrete is used. It is best to measure
High accuracy and simple measurement are possible by combining the principle that salt concentration is reduced by mixing water in the ready-mixed concrete when salt-containing liquid is mixed with the ready-mixed concrete, and the salt concentration measurement by an instrument equipped with a salt sensor.

[0009] By using a liquid having a very low salt content as one of the liquids to be mixed with the ready-mixed concrete, it is possible to correct an error in the measurement of the salt concentration due to the salt in the ready-mixed concrete, and simultaneously measure the chloride content in the ready-mixed concrete. it can. Until now, the chloride content was measured using the unit water amount at the time of mixing, but this method can use the actually measured unit water amount.

[0010] Depending on the instrument, there may be an error in the measurement of the salt concentration due to the effect of interfering ions in the ready-mixed concrete.
The effect of the interfering ions can be avoided by adding the interfering ions to the liquid used in advance.

Liquid mixed with ready-mixed concrete, or
The instrument is calibrated with a liquid with the same salt concentration as the liquid, and instead of measuring the actual salt concentration, the measurement is performed based on the liquid mixed with the ready-mixed concrete, so that errors due to the instrument and factors such as liquid Avoid errors.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described based on embodiments with reference to the drawings. First, a ready-mixed concrete sample 9 was prepared from the same ready-mixed concrete using the measuring containers 1 and 2.
Collect 10 Next, a liquid containing a certain concentration of salt is weighed using the measuring container 7, and a liquid having extremely low salt is weighed using the measuring container 8. The liquid weighed in the measuring container 7 is mixed into the ready-mixed concrete sample 9 and the ready-mixed concrete sample 10.
Is mixed with the liquid measured in the measuring container 8. Two sets of measuring containers for ready-mixed concrete and liquid having the same volume are required, and it is desirable that all materials have the same expansion and contraction due to temperature.

Calibrate the instrument.

The air content of the ready-mixed concrete is measured.

As shown in FIG. 3, the salt concentration of a ready-mixed concrete sample mixed with a liquid is measured. The unit water content of the ready-mixed concrete and the chloride content of the ready-mixed concrete are determined from the difference between the respective salt concentrations, the amount of liquid and the amount of air with respect to the ready-mixed concrete sample.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS As an example of an experiment, a description will be given using numerals.
Chlorine ion concentration of liquid mixed with ready-mixed concrete is 0.3
% And 0%, the calibration value of the instrument is 100 at 0.3% and 0 at 0%
And The amount of the ready-mixed concrete sample was 2500 ml, the amount of liquid mixed with the ready-mixed concrete sample was 400 ml (160 kg in terms of 1 cubic meter), and the target amount of ready-mixed concrete was 4.5% (absolute volume 955).
Liter). The measured value of the sample mixed with 0.3% chlorine ion liquid is 50.9 (the number of digits after the decimal point depends on the precision of the instrument), and the measured value of the sample mixed with 0% liquid is 2.6. If the air volume is 4.8% (absolute volume: 952 liters), the formula for calculating the unit water volume of ready-mixed concrete is Equation 1, and the formula for converting it to the unit water volume at the time of mixing with the air volume is Formula 2. The unit water quantity of ready-mixed concrete at the time of measurement is 172 kg. Formulas 1 and 2 are basic formulas, and if there is preliminary data such as the water absorption of aggregate, the water absorption by cement, and the mix of ready-mixed concrete, the shape of the formula changes due to the addition of coefficients, etc. There is also. The formula for calculating the chloride content of the ready-mixed concrete is Equation 3, and the value of the chloride content is 0.026 kg per cubic meter.

[0017]

According to the results of an experiment conducted by mixing and kneading ready-mixed concrete, the difference between the actual unit water amount and the measured value is within ± 1.5%, and 80% or more falls within the range of ± 1%. Also,
Preliminary data such as the water absorption of the aggregate, the water absorption by the cement, and the mix of the ready-mixed concrete allow for more accurate measurements. In the test using a salt meter for ready-mixed concrete, there is a large difference in performance depending on the instrument. However, by properly selecting the concentration of the liquid to be mixed with the ready-mixed concrete, ± 1.
Some models can measure at about 5%, and even with the existing salinity meter, there is a possibility that it can be used as a more accurate unit water volume meter without requiring significant performance improvement. In general, titration is considered to be accurate, but varies from individual to individual, and a well-tuned instrument is more likely to provide simple and accurate measurements. The effects of measuring the unit water volume of ready-mixed concrete are clues for estimating strength and judging water tightness, drying shrinkage, durability, weather resistance and management status. In the ready-mixed concrete factory, the quality control of one class can be achieved by introducing the measurement of the unit water amount into the process control. If you are a ready-mixed concrete purchaser, you can check the mixing and add water to the kneaded ready-mixed concrete, which is often a problem in poor construction work, and based on the difference between the value of the mix report and the measured value, It can also be used to evaluate technical capabilities.

[Brief description of the drawings]

FIG. 1 shows a measuring container for ready-mixed concrete and a liquid to be mixed with ready-mixed concrete.

FIG. 2 is a diagram in which a ready-mixed concrete sample and a liquid are mixed.

FIG. 3 is a diagram illustrating the measurement of the salt concentration of a ready-mixed concrete sample mixed with a liquid.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Ready-mixed concrete measuring container 2 Ready-mixed concrete measuring container 3 Tube connected to a measuring container 4 Tube connected to a measuring container 5 Cover of a tube connected to a ready-mixed concrete measuring container 6 Cover of a tube connected to a ready-mixed concrete measuring container 7 Liquid measuring container Reference Signs List 8 liquid measuring container 9 ready-mixed concrete sample 10 ready-mixed concrete sample 11 device for mixing liquid with ready-mixed concrete by rotating thing connected with 1, 3, 5, and 2, 4, 6 12 instrument for measuring salt content 13 salt content sensor

## EQU1 ## 100 ÷ (51.9-2.6) × 160-16
0 = 171.26 ...

## EQU2 ## 171.26... ÷ 952 × 955 = 171.
8

## EQU3 ## 0.3 × (171.8 + 160) × 2.6) ÷
10,000 = 0.02588

Claims (4)

[Claims] 1. The unit water content of ready-mixed concrete is measured by combining the principle of mixing salt-containing liquid into ready-mixed concrete and reducing the salt concentration by mixing water in the ready-mixed concrete, and the salt measurement using an instrument equipped with a salt sensor. Method. 2. The use of a liquid having a very low salt content as one of the liquids to be mixed with the ready-mixed concrete to correct errors caused by chlorides in the ready-mixed concrete on the measurement of salt concentration, Method for measuring the unit water content of ready-mixed concrete that can measure the content of materials. 3. The unit water content of the ready-mixed concrete is measured by using a liquid to which the interfering ions are added as a liquid to be mixed with the ready-mixed concrete in order to avoid errors due to the influence of interfering ions in the ready-mixed concrete. Method. 4. Calibrating the instrument with a liquid mixed with ready-mixed concrete or a liquid having the same salt concentration as the liquid mixed with ready-mixed concrete, and using the liquid mixed with the ready-mixed concrete as a reference, the error of the instrument and the liquid A method of measuring unit water content of ready-mixed concrete using an instrument for measuring salt content while avoiding errors due to factors such as