JPH0342571A - Method for measuring moisture adsorbed on aggregate - Google Patents

Abstract

PURPOSE:To easily and rapidly measure the moisture incorporated in aggregate without skill by adding an aq. soln. contg. the specific ion of a known concn. to the aggregate and mixing the same, then measuring the concn. of the specific ion and utilizing the calculated quantity of the moisture in the aggregate calculated from the difference in the concn. of the ion before and after the addition and the quantity of the moisture added to the aggregate. CONSTITUTION:A specified amt. of a aggregate sample which is previously adjusted in moisture content is drawn and a specified volume of the aq. soln. of the specific ion having the known concn. is added to the drawn aggregate sample, then both are mixed. The concn. of the specific ion in this aggregate sample after the mixing is measured. The quantity of the moisture of the aggregate sample is calculated from the difference in the concn. of the specific ion after the addition to the aggregate sample and before the addition. The quantity of the moisture incorporated in the aggregate is determined from the calculated quantity of the moisture and the quantity of the moisture added to the aggregate sample. The correction of the moisture incorporated in the aggregate and the determination of the moisture with high accuracy are possible in this way at the time of calculating the unit water quantity in the prepn. of concrete. The planned prepn. is thus attained.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a method for measuring the moisture content of aggregate.

[Conventional technology]

In recent years, as emphasis has been placed on managing the amount of water in fresh concrete, various methods for measuring the amount of water have been proposed. For example, one of them is a salt addition method previously filed by the present applicant (Japanese Patent Laid-Open No. 106368/1982).

This method involves adding a certain amount of a solution containing specific ions (Fl ions in this case), such as a salt aqueous solution with a known concentration, such as a NaF1 aqueous solution, to a sample of fresh concrete or mortar, and then mixing the mixture. Measure the concentration of specific ions inside.

Then, the amount of water in the sample is calculated from the difference between the concentration of the specific ion after mixing and the concentration of the ion before mixing. This salt addition method has the advantage that results with the required accuracy can be obtained quickly with a simple measuring instrument and without the need for special techniques.

[Problem to be solved by the invention]

In the conventional method of measuring the amount of water in concrete, etc. using the salt addition method, the measured value of ion concentration is affected by the moisture content of aggregate, which is a constituent material of concrete. This is because when an aqueous solution containing specific ions, such as a NaFf aqueous solution, is added to aggregates, the specific ions do not diffuse into all the water inside the aggregate and mix, and the water to which the specific ions do not diffuse remains inside the aggregate. This is to remain in the Hereinafter, the ratio of the weight of water contained inside the aggregate to the dry weight of the aggregate will be referred to as water content (%) of the aggregate.

In other words, by correcting the moisture content of the aggregate, it becomes possible to further improve the accuracy of moisture measurement by adding salt to Fresoch concrete, mortar, or the like.

However, when measuring the moisture content inside the aggregate, for example, when heat drying is applied, it takes a long time to heat and dry, and it also takes time and effort to conduct preliminary experiments, making it inappropriate to perform on-site. There was a problem.

The present invention has been made in view of these conventional problems, and its purpose is to provide a method for measuring the moisture content of aggregates that is simple, quick, and does not require special skill. The purpose of this invention is to solve the above-mentioned conventional problems.

[Means to solve the problem]

The present invention, which achieves the above object, collects a certain amount of aggregate sample whose water content has been adjusted in advance, adds a certain amount of an aqueous solution of specific ions of known concentration to the collected aggregate sample, and mixes the sample. The specific ion concentration is measured for the subsequent aggregate sample.

Then, the amount of water in the aggregate sample solution is calculated from the difference between the specific ion concentration after addition to the aggregate sample and the specific ion concentration before addition, and from the calculated water amount and the amount of water added to the aggregate sample. Determine the moisture content in the aggregate.

Then, a certain amount of water that does not contain the specific ions is added to another aggregate sample separately collected from the water content-adjusted aggregate, and the specific ion concentration is measured in the aggregate sample after the addition. By doing so, the concentration of the specific ion contained in the sample can be determined in advance as a blank value, and the concentration of the specific ion in the aqueous solution after the addition can be corrected using the blank value.

Here, the above-mentioned specific ions refer to those that meet the following conditions.

■ It is hardly contained in the aggregate sample, or even if it is contained, it is very small.

■ The aggregate sample does not react with or dissolve the ions.

■ When the ion is added to an aggregate sample, it is diluted by the water in the aggregate sample and the ion concentration changes quantitatively.

■ It has a certain degree of accuracy as a concentration measurement method, and the test method is simple.

Those that can generally satisfy these conditions can be selected from, for example, Fl-, r-, Br-, S''-, etc.

Various well-known methods can be applied to measure ion concentration, but potentiometric titration and coulometric titration methods, for example, are advantageous because they can use general-purpose measuring instruments and can be measured relatively easily and in a short time. It is.

The basic principle of measurement according to the present invention will be explained below based on FIGS. 1 to 5.

(I) Adjustment of moisture content of aggregate and measurement of moisture content: After allowing the aggregate to absorb water for 24 hours, the water is drained and the moisture content is adjusted to a so-called wet state where the aggregate contains water above the water absorption rate.

A part of the wet aggregate whose moisture content has been adjusted is weighed, dried at 110° C. for 24 hours, and its dry weight is weighed to measure the moisture content α(χ).

Wet weight (n) Measurement of concentration of specific ions pre-contained in aggregate Aggregate sample S with adjusted water content. (g) is mixed with an aqueous solution W+(g) that does not contain specific ions, and the specific ion concentration R8 (int/wtX, hereinafter the same) in the sample after mixing is measured. The weight of specific ions contained in the aggregate is S = (g), and the amount of water contained in the aggregate is W4 (g).
)(W,=S,X (1-100/(100+α))
), the water content of the aggregate is F. (g), the specific ion concentration R6(χ) pre-existing in the aggregate can be expressed by the following formula.

The above is a blank test.

Note that if it is confirmed in advance that the aggregate does not contain any specific ions (that is, if R8=0), the blank test can be omitted.

(III) Measurement of specific ion concentration after adding an aqueous solution of specific ions to aggregates On the other hand, an aggregate sample whose water content was also adjusted was subjected to S. (g) Weigh it, and add an aqueous solution Wz (g) that does not contain specific ions to it.
) and a standard aqueous solution Wz(g) with a concentration R, (χ) are added and mixed, and the concentration R(X) of the specific ion after the mixing is measured. The concentration R(χ) of a specific ion is calculated using the following formula.In this case,
Some of the added specific ions diffuse through the surface water of the aggregate and into some of the internal saturated water near the surface of the aggregate, but they also diffuse into the water contained deeper inside the aggregate. Not done.

Therefore, the concentration of specific ions added to the aggregate together with water will change before and after addition depending on the amount of water contained in the aggregate. The method for measuring water content of the present invention utilizes this fact.

(IV) Calculation of water content in aggregate ■ Estimation of water content itFw (g) in aggregate Here, from equation (1) 00 From equation (2), X (Wz+W3+W4 Fw) 00 (4) - From (3) Rx (W, +W, +W4-F,) - RoX (W, +W
4-F,)-R,XWff -----------
----(5) is obtained.

This equation (5) expresses the mass balance for a specific a in a standard aqueous solution of known concentration.

Expanding this into the formula for FW(g), we get becomes.

The above is the basic principle. However, this basic principle has a second
There are four possible types shown in FIGS.

These methods differ in the formula for calculating the water content IFw(g) of the aggregate. This is shown below.

Case A (1) When measuring a blank (Figure 2) Aggregate sample S with adjusted moisture content. (g) is mixed with an aqueous solution WA (g) that does not contain specific ions, and the concentration of specific ions Ro (χ) after this mixing is measured.

On the other hand, aggregate sample S was also subjected to water content adjustment. (g) is mixed with an aqueous solution Wa (g) that does not contain specific ions.

Furthermore, a standard aqueous solution Ws (g) with a concentration Rs (R) is added and mixed, and the concentration R (X) of the specific ion after this mixing is measured.

Wa=Wz=W+, Ws=W3, so the basic principle (6
) F of the formula. (g) becomes as follows.

(2) When blank is not measured (Figure 3) Same as (1), but when blank test is not performed W, = 0, WA-W2
, W, = W3, Ro-o Note basic principle of formula (6)〇F
. (g) becomes as follows.

Case B (1) When measuring a blank (Fig. 4) An aqueous solution WA (g) that does not contain specific ions is mixed with the aggregate sample Sw (g) whose water content has been adjusted, and the concentration of specific ions after this mixing is Measure the concentration R(X).

Since W,=W,==W,,Wz=0, the basic principle (6)
F of the formula. (g) becomes as follows.

(2) When blank is not measured (Figure 5) Same as (1), but when blank test is not performed W + = O, W
z = Q, W a = W! , Ro = O. Sw(g) in equation (6) of the basic principle is as follows.

■ ■ Estimation of moisture content of aggregate The moisture content of the aggregate Fw (g) is determined by the absolute dry weight Sa of the aggregate sample.
(g) (Sa=S−X (100/(100+α))
) (moisture content Fc(χ) of the aggregate), the water content Fc(1) of the aggregate is obtained.

[Example 1] (1) Adjustment of moisture content of aggregate and measurement of moisture content: After immersing aggregate in water for 24 hours, the water was drained and the moisture content was adjusted to a wet state. A part of this aggregate was collected and 110″C1
It was dried for 24 hours and the moisture content was measured.

The obtained moisture content α was 2.32%.

(II) Measurement of Cl ion concentration pre-existing in aggregate: 133.02 g of wet aggregate with adjusted moisture content was weighed into container 1 of the filtration device for moisture measurement shown in FIG.

Then, WA=36.98 g of water is added to this aggregate sample. The opening of the container 1 is covered with a lid 2, and the rotation speed knob 3 is turned to rotate the stirring blade 3A to thoroughly stir and mix the aggregate and water. After that, the stirring blade 3A is stopped, the lid 2 is removed, and the stirring blade 4. After filling the container 1 in the order of filtration 5, the container 1 is covered. Next, turn the vise 6 to push down the filter 5 to pressurize the mixture of aggregate and water. Moisture is filtered by filter paper 4, passes through hole 5A of filter exit 5, and accumulates in the upper part of container 1. . This filtrate was collected in a separate container, and the C1-concentration R0 was measured by a well-known potentiometric titration method. RO=0.0034%.

(II) C1 after adding NaCl aqueous solution to aggregate
Measurement of concentration: Weigh out <133.02g of the same aggregate with the same water content adjusted, add water (Wa = 36.98g) to this aggregate sample, and mix well in the filtration device for moisture measurement in the same manner as above. Stir. Then, add Rs""10.00% C1-?a degrees of N.
Ws = 2.0000 g of aC1 standard aqueous solution was added, stirred in container 1, and then filtered. CI in this filtrate! , -concentration R was determined by potentiometric titration method. R=0.491
It was 2%.

(IV) Calculation of moisture content of aggregate: ■ Calculation of moisture content of aggregate From equation (7) =1.01 ■ Calculation of moisture content of aggregate.

From the 00 formula, 30 = 0.78 In the above example, the value of the dry Itsd of the aggregate sample used to determine the moisture content FC of the aggregate is based on the moisture content obtained from the sample whose moisture content has been adjusted. This is the calculated value.

However, in order to further improve accuracy, the following may be used.

The remaining portion of the filtrate that was filtered after mixing the NaCl standard aqueous solution and used for concentration measurement is returned to the filtered aggregate. This is dried at 110°C and the dry weight of the aggregate is measured. The dry weight S4 of the aggregate is obtained by subtracting the previously added salt and the salt in the filtrate used for titration as correction values from the dry weight.

FIG. 7 is a graph showing the moisture content of a plurality of aggregate samples having different water absorption rates determined by the same procedure as above. As a result, it was found that the water content of the aggregate was lower than the water absorption rate.

Further, FIG. 8 shows the results of a test on the influence of the immersion time of the aggregate in the NaCl aqueous solution on the water content, that is, the change over time in the water content of the aggregate. This confirmed that the water content of the aggregate was not affected by the soaking time.

FIG. 9 compares the relationship between the planned unit water volume and estimated unit water volume in concrete mixing when the aggregate water content of the present invention is corrected and when it is not corrected. Through the correction, the planned unit water volume and estimated unit water volume were able to match well.

〔Effect of the invention〕

As explained above, according to the present invention, aggregate whose water content has been adjusted in advance is collected, a certain amount of an aqueous solution containing a specific ion at a known concentration is added thereto, and the mixture is mixed, and then the concentration of the specific ion is measured. Then, the amount of water in the aggregate solution is calculated from the difference in concentration of specific ions before and after addition. The moisture content of the aggregate is determined from the calculated moisture content and the moisture content added to the aggregate. Therefore, it is convenient.

The moisture content of aggregate can be measured quickly and without the need for special skill, and when calculating the unit water content in concrete, it is possible to correct the moisture content of aggregate and calculate it with high accuracy. The effect is that the blending can be carried out as planned.

[Brief explanation of drawings]

FIGS. 1 to 5 are conceptual diagrams of the measuring method of the present invention, FIG. 6 is a perspective view showing an example of the apparatus used for the measurement of the present invention, and FIGS. 7, 8, and 9 are diagrams of the present invention. It is a graph showing measurement results according to the invention.

Claims (2)

[Claims] (1) Collect a certain amount of aggregate sample whose water content has been adjusted in advance, add a certain amount of a specific ion aqueous solution of known concentration to the collected aggregate sample, and mix it. Measure the concentration, calculate the moisture content of the aggregate sample from the difference between the specific ion concentration after addition to the aggregate sample and the specific ion concentration before addition, and calculate from the calculated moisture content and the amount of water added to the aggregate sample. A method for measuring the moisture content of aggregate, characterized by determining the amount of moisture contained in the aggregate. (2) Adding a certain amount of water that does not contain the specific ions to another aggregate sample separately collected from the aggregate with adjusted water content, and measuring the specific ion concentration of the aggregate sample after the addition. The aggregate according to claim (1), wherein the concentration of the specific ion contained in the sample is determined in advance as a blank value, and the concentration of the specific ion in the aqueous solution after the addition is corrected using the blank value. How to measure the moisture content of.