JPS5810205B2 - Inspection method for water-cement ratio of ready-mixed concrete - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for testing the water-cement ratio of fresh concrete to determine whether the fresh concrete is blended according to its mix.

The mix of ready-mixed concrete delivered to the concrete pouring site is clearly stated on its mixing coat.

However, in reality, discrepancies may occur between the actual formulation and that of the formulation.

Ready-mixed concrete that is mixed according to the mixture will exhibit the desired strength after hardening, but ready-mixed concrete that is not mixed according to the mixture will not exhibit the desired strength after hardening, and will have defects. It is a quality product.

Whether or not the fresh concrete has been mixed according to the mixture can be determined by determining the water-cement ratio of the fresh concrete and comparing the water-cement ratio with that of the mixture.

By the way, conventional methods for determining the water-cement ratio of fresh concrete include the washing analysis method, the hydrochloric acid method, and the hydrometer method.

However, in the conventional washing analysis method, since it is necessary to measure the weight of the collected sample in water, a highly sensitive special weighing means is required to determine the weight of the sample in water, and its handling is difficult. Requires soaking.

Furthermore, the conventional hydrochloric acid method requires hydrochloric acid that must be handled with care, and the hydrometer method requires a hydrometer.

Furthermore, all of the above conventional methods require a working time of about 30 minutes or more.

For this reason, the conventional testing method requires special measuring means or chemicals, and cannot be easily implemented in a short time at a concrete placement site.

Therefore, an object of the present invention is to provide a method for testing the water-cement ratio of residential concrete easily and quickly, even at concrete placement sites, without using special measurements, one-stage weighing, or chemicals such as hydrochloric acid. Our goal is to provide the following.

The present invention basically involves determining the fine aggregate correction coefficient (a) using fine aggregate for ready-mixed concrete, and also determining the fine aggregate correction coefficient (a) using fine aggregate for ready-mixed concrete. A preliminary step of determining the cement moisture content (α) and fine aggregate moisture content (79) after dehydration treatment under predetermined conditions using The water weight (W) of the fresh concrete to be tested using the formula
) and the measured weight A, Wl of the fresh concrete in air to determine the cement weight (C).

and this step for measuring W2.

In the present invention, a preliminary step is performed in advance and once the a, α
, β have been determined, in this step, first and second mortar samples having approximately the same weight (5) are taken from the fresh concrete to be inspected, and the first mortar sample is subjected to the above-described method. After performing dehydration treatment under the same conditions, the weight W1 in the air was measured, and the second mortar sample was washed with water to remove cement from the second mortar sample, and the second mortar sample was After performing the dehydration treatment under the same conditions as described above, the weight W2 in the air was measured, and the measured weight A obtained by this step,
By substituting W, , W2 into the above equation, the water weight W and cement weight C of the fresh concrete to be inspected can be determined.
, and its water-cement ratio (W/C) can be obtained.

Therefore, according to the present invention, there is no need to use a special measuring means for determining the weight in water, a special measuring means such as a hydrometer for determining specific gravity, or a chemical agent such as hydrochloric acid, and the preliminary step By implementing the above a, α
, β have been determined, it is possible to easily calculate fresh concrete in a short time of about 15 minutes by carrying out this step for determining the measured weights A, Wl, and W2 in air at a concrete site, etc. The water-cement ratio can be tested.

The features of the present invention will become clearer from the following description with reference to the drawings showing the flow of procedures of the present invention.

The present invention includes a preliminary step and a main step, and in the main step, as shown in step 1 in FIG. .

This sampled ready-mixed concrete is
The fresh concrete collected through a mm sieve is separated into coarse aggregate and mortar by this sieve, and the mortar is collected.

In step 3, equal weight A of mortar is taken as first and second samples by weighing from this mortar.

In one example experiment, 2.2 kg of each sample was collected by weighing.

The first and second mortar samples can be taken directly from the fresh concrete to be tested without going through step 1 using a 5 mm sieve in step 2.

The first mortar sample is dewatered in step 4 and then weighed in step 5 according to Chart I.

This dehydration is carried out under the same conditions as the dehydration in the preliminary step, which will be described later. For example, the centrifugal dehydration device used in the preliminary step is used, and the device is operated for the same time as each dehydration period in the preliminary step.

In the experimental example, a 2000 r, p, m centrifugal dehydrator was used to dehydrate a 2.2 kg mortar sample.
After 3 minutes of dehydration using the centrifugal dehydrator, the weight W1 of the first mortar sample in air was measured by weighing.

Through this dehydration treatment, the fine aggregate contained in the first mortar sample is placed in a nearly surface-dry saturated state where it is not completely dry, and the cement is also placed in a similar state.

Therefore, the measured weight W1 is the sum of the cement weight C1 in the first mortar sample, the fine aggregate weight G, and the adhering water weights Wc and Wg contained in cement and fine aggregate, respectively, and the measured weight W1 is expressed by the following formula. .

W1= (C+Wc) + (G+Wg) ・-
”=(1) The second mortar sample was washed with water in step 4′ to remove cement, and then subjected to dehydration treatment in step 5′ under the same conditions as described above, in accordance with chart ①. is applied, and further step 6
' is weighed to determine its weight in air.

The water washing of the second mortar sample included 0.088 mm
A sieve is used to remove cement contained in the second sample.

Experiments have shown that it is preferable to use a 0.108 mm cloth sieve for this water washing.

The second mortar sample from which the cement has been removed is dehydrated in step 5' under the same conditions as in the dehydration of the first mortar sample in step 4, and then its weight W2 in air is measured by weighing. ing.

Therefore, this measured weight W2 is equal to the fine aggregate weight G' and the adhesion water weight W contained in the fine aggregate.

The measured weight W2 is expressed by the following formula.

W22e'+ wg ・・・・・・
...(2) By the way, the first mortar sample and the second
Since each of the mortar samples was taken in equal amounts from the same mortar and dehydrated under the same conditions, the sum of the fine aggregate weight G in the first measurement weight W1 and the adhering water weight Wg, and the second The sum of the fine aggregate weight G' and the adhering water weight W'g in the measured weight W2 is approximately equal.

However, since the second mortar sample is washed with water to remove cement, the mud, fine sand, etc. of the fine aggregate are removed along with the attached water.

Therefore, the value obtained by multiplying the measured weight W2 by the fine aggregate correction coefficient a determined in the preliminary step described later in order to correct this mud content, etc. is the measured weight W, the fine aggregate weight G and its adhering water weight. This relationship is expressed by the following formula:

As a result, the difference between the measured weight W1 and the value obtained by multiplying the measured weight W2 by the correction coefficient a is expressed by the following formula (% formula %) (3), and as mentioned above,
W & ), formula (3) is Wl-a X W2 = C+Wc..."
...It is expressed as (4).

Here, if α is the moisture content of the cement determined in the preliminary step described later and has undergone dehydration treatment under the same conditions as described above, then α is expressed as α=Wc/(C+Wc). Therefore, Wc is expressed by the following formula.

Wc = CXα/(1-α) ・・・・・・・
...(5) Therefore, by substituting equation (5) into equation (4), we get
W1aXW2-C10CX C1/(1cx)..."""
'(6) is obtained, and from equation (6), C=(1-α)(Wl-aXW2) ·--(force is obtained.

Therefore, a, α determined in advance in the preliminary step described later
By substituting the measured weights W1 and W2 obtained in this step into equation (7), the cement weight C of the fresh concrete to be inspected can be obtained.

In addition, since the weight A of the first or second mortar sample is the sum of the cement weight C1 in the mortar, the fine aggregate weight G, and the water weight W, the water weight W is expressed by the following formula % formula % (8) It will be done.

Here, if the moisture content of the fine aggregate determined in the preliminary step described later and after being dehydrated under the same conditions as described above is β, then β = Wg/( G+Wg).

Therefore, the fine aggregate weight G is G2(1-β), (G+Wg) It is indicated by.

Further, the weight of the fine aggregate and its adhering water (G+Wg) is equal to the product of the measured weight W2 and the correction coefficient a, as shown in equations (2) and (2').

From this, formula (8) is W=A-(C+(1-β)×axW2)...
...It is shown by (9).

Therefore, the water weight W can be determined by substituting the measured weight W2 into equation (9), which includes a predetermined in a preliminary step to be described later and the concrete weight C obtained from equation (7).

As is clear from the above, according to the present invention,
The a, α, and β are determined in a preliminary step, and the a,
The measured weights A, Wl, and W2 obtained in this step are entered into equations (7) and (9) containing α and β.

By substituting, the water weight W and cement weight C of the fresh concrete to be inspected can be determined, and the water-cement ratio (W/C) can be calculated from this.

Next, prior to the above-described main step of the present invention.

Describe the preliminary steps taken.

In this preliminary step, the correction coefficient a1, the cement water content α and the fine aggregate water content β are determined.

The correction coefficient a is the weight ratio of the fine aggregate for ready-mixed concrete before and after removing mud, and a part of the fine aggregate used for the ready-mixed concrete is sampled.

The weight ratio of the fine aggregate before and after washing with water (Sa/Sb).

That is, after measuring the weight Sa of the collected fine aggregate in the air, the fine aggregate is washed with water under the same conditions as in this step, and dehydrated under the same conditions as in this step.

After this, the fine aggregate weight sb in the air after washing with water is measured, but since the mud etc. attached to the fine aggregate are removed by the water washing, as mentioned above, the weight sb of the fine aggregate in the air after washing with water is The ratio of the fine aggregate weight Sa to the fine aggregate weight sb after washing with water (Sa/Sb) can be set as the fine aggregate correction coefficient a.

However, it is preferable that the correction coefficient a is determined as follows through a procedure similar to that shown in FIG.

In other words, using pre-washed fine aggregate and unwashed fine aggregate, which are fine aggregates for ready-mixed concrete and have the same weight, the weight mixing ratio is equal to the weight mixing ratio according to the mixing light of the above-mentioned ready-mixed concrete. First and second ready-mixed test concretes are prepared at the same ratio.

Next, 5 m from the first and second ready-mixed concrete for testing.
first and second of equal weight, respectively, using m sieves.
Collect mortar samples.

Thereafter, each mortar sample is washed with water under the same conditions as in the main step, and further dehydrated under the same conditions as in the main step.

Thereafter, the first test mortar sample and the second
The weight of the test mortar sample in air is measured, but since both mortar samples have been washed with water, the measured values are the fine aggregate weight S1 of the first test mortar sample and the weight of the second test mortar sample, respectively. Fine aggregate weight S of mortar sample for testing
It becomes 2.

Moreover, since the fine aggregate of the second test mortar sample was not washed with water prior to test mixing, the measurement result S1 of the fine aggregate of the first mortar sample was different from that of the second mortar sample. The measurement result S2 of the fine aggregate is a value with a reduced weight due to mixing, etc.

Therefore, the measured weight S1 of both sets of aggregates mentioned above. S2 is the weight of the fine aggregate in the air before and after mud removal, and the ratio (S1/S2) can be used as the correction coefficient a.

The correction coefficient (St/S2) obtained in this way is
Compared to the above-mentioned correction coefficient (Sa/Sb), it is a more accurate correction value because it is determined by a procedure such as test practice that roughly follows the chart shown in FIG. 1, as described above.

The value of this correction coefficient a varies depending on the quality of the fine aggregate, but is approximately 1.
．． The value is about 01 to 1.02, and the value is 1.00 for fine aggregate with no adhesion of mud or the like.

The procedure for determining the cement water content α and the fine aggregate water content β in the preliminary step is as follows.

First, ready-mixed concrete for testing is prepared before mixing the ready-mixed concrete to be tested.

From this ready-mixed concrete for testing, approximately the volume (
Equivalent first and second test mortar samples of 1) are taken, and the weight (A') of one of them in air is measured.

Next, the first test mortar sample is subjected to dehydration treatment under the same conditions as the main step, in which the fine aggregate does not reach a completely dry state, and then its weight in air (w1') is measured.

The second mortar sample is washed with water using the same procedure as in this step, and after the cement is removed, it is dehydrated under the same conditions as described above.

After this, the weight W2' of the second mortar sample in air is measured.

The values obtained by dividing these measured weights &, W1', W2' by the volume (7) (, &/13, W177, W
2′/l) are A of the above formulas (7) and (9), respectively;
Wl and W2 are substituted into the equation, and the unit cement weight CT and unit water weight WT displayed before the mixing are further substituted into the equation as the W and C together with the fine aggregate correction coefficient (a).

By this substitution, the α and β are calculated, and as a result, in the preliminary step, the α and β are respectively determined together with the a.

These moisture contents α and β vary depending on the dehydration efficiency of the centrifugal dehydrator for dehydration after washing, but generally, 0.1≦α≦0.4, 0.01≦β≦0.04. range.

According to the present invention, as described above, the fine aggregate is corrected in advance by a preliminary step using fine aggregate for ready-mixed concrete and ready-mixed test concrete prepared in accordance with the preparation of the ready-mixed concrete to be tested. Once the coefficient a1 cement moisture content α and fine aggregate moisture content β have been determined, the measured weights A, Wl, and W2 of the fresh concrete to be investigated in this step are measured, and the measured values are used in the preliminary step. By substituting the determined a, α, and β into the equation (force) and (9), the cement weight C and water weight W of the fresh concrete to be investigated can be obtained, and the ratio W/C and the above By comparing the mixed water-cement ratio before mixing, it can be known whether the fresh concrete is mixed according to the ratio before mixing.

The above-mentioned cement weight C and water weight W are the respective weights in the mortar of weight A, and based on these values, the water-cement ratio It can be calculated.

Therefore, by substituting this water-cement ratio X into the following formula (% formula %) (K: cement strength), the mixed strength of fresh concrete can be calculated.

Further, the unit cement weight cT and unit water weight WT of the fresh concrete can be estimated by substituting the cement weight C and the water weight W into the following equations, respectively.

A comparison between the known mix values for fresh concrete and the estimated mix values for said fresh concrete estimated by the method according to the invention is shown in the following table.

Two mortar samples were taken from each fresh concrete as indicated by sample numbers A and B for fresh concrete samples 1, 2, and 5.6, respectively, and sample numbers A and B for fresh concrete samples 3 and 4, respectively. Three mortar samples were taken as shown in B and C, and the unit cement weight CT1 unit water weight WT and water-cement ratio W/C were determined for each mortar sample.

In addition, the fine aggregate correction coefficient a is 1 for samples 1 to 4.
．． 025 was used, for sample 5 1.015 and for sample 6 1.020.

Furthermore, cement moisture content α and fine aggregate moisture content β were 0.154 and 0.033, respectively, for each sample.

As is clear from this table, according to the present invention, the water-cement ratio, which is most important for knowing the mixed strength F of concrete, is within an error of about 2% with respect to the mixed water-cement ratio.

In order to clarify the comparison between this mixed water-cement ratio (Xl) and the water-cement ratio (X2) obtained by the present invention, Figure 2 shows the mixed water-cement ratio (Xl) and the water-cement ratio (X2) obtained by the present invention. A graph is shown with the cement ratio (x2) as the horizontal and vertical axes, respectively.

As is clear from the graph of FIG. 2, the water-to-cement ratio obtained by the present invention is considered to be within an error of 2%.

Therefore, the mixed strength F of concrete can be estimated very accurately based on the water-cement ratio obtained by the method according to the present invention.

In the above description, an example has been described in which a centrifugal dehydrator is used as the dehydrating means, but a heating device may also be used.

According to the present invention, as described above, fine details for correcting the cement moisture content α, fine aggregate moisture content β, and runoff such as mud due to water washing are adjusted according to the dewatering capacity of the dewatering means such as a centrifugal dehydrator. By predetermining the aggregate correction coefficient a in the preliminary step, the first and second mortar samples are taken from the fresh concrete to be inspected in this step, and the measured weights A and Wl of both mortar samples are .

By measuring W2 and substituting the measured value into a predetermined formula, the water weight W and cement weight can be determined, thereby determining the water-cement ratio W/C of the fresh concrete to be inspected.

In addition, in the present invention, when measuring weight, it is not necessary to determine the weight of the object to be measured in water; it is sufficient to measure the weight in air; therefore, a special and highly sensitive scale is used to measure the weight in water. It is not necessary, and a commonly used spring balance that is easy to operate for measuring weight can be used.

Further, as a dewatering means, a centrifugal dehydrator or the like can be used, which is easy to operate and can be easily carried and installed at a concrete casting site.

Therefore, according to the present invention, there is no need to use special weighing means, ratio weighing and chemicals such as hydrochloric acid to determine the weight in water, and the preliminary steps are carried out in advance to
Once β has been determined, there is no need to repeat this preliminary step, and this step is a simpler operation compared to the conventional method described above, and is extremely short compared to the conventional method, which takes about 15 minutes. The water-cement ratio can be determined by carrying out the following.

[Brief explanation of drawings]

FIG. 1 is a flowchart showing the procedure of this step for the method for testing the water-cement ratio of fresh concrete according to the present invention, and FIG. 2 is a graph showing a comparison between the water-cement ratio determined in 1 and the mixed water-cement ratio.

Claims (1)

[Scope of Claims] 1. A method for inspecting the water-cement ratio of ready-mixed concrete in order to know whether the ready-mixed concrete is mixed according to its mixing table, the method comprising: A preliminary step for determining the fine aggregate correction coefficient a, cement moisture content α, and fine aggregate moisture content using the ready-mixed concrete for Test 1 prepared according to the table, and the determined aα and β. and a main step for determining the water and cement weight of the fresh concrete to be tested using the following formula, and the preliminary step includes determining the water and cement weight of the fresh concrete in the air before and after the removal of mud from the fine aggregate for fresh concrete. measuring the weight (Sa or s, , sb or S2) of the test mortar, taking first and second test mortar samples of approximately equal volume l from the test fresh concrete, and measuring the weight of at least one of the test mortar samples; Measuring the weight of the sample in the air, after subjecting the first test mortar sample to a dehydration treatment that does not allow the fine aggregate to reach a completely dry state, the first test mortar sample in the air; Weight at (W1'
), and in the second test, the test mortar sample is washed with water to remove cement, and the second test mortar sample is subjected to dehydration treatment under the same conditions as described above. This step includes measuring the weight in air (W2') of a test mortar sample of approximately equal weight (A) from the fresh concrete to be tested.
and collecting a second mortar sample, subjecting the first mortar sample to dehydration treatment under the same conditions as described above, and then measuring its weight in air (Wl); After removing cement from the second mortar sample by washing with water and subjecting the second mortar sample to dehydration treatment under the same conditions as described above, its weight in air (W2)
The measured weight of the fine aggregate for fresh concrete obtained in the preliminary step before mud removal (S
a or Sl) after its mud removal (sb or S
2), the fine aggregate correction coefficient (a=Sa/
Sb, or S1/S2) is determined, and the fine aggregate correction coefficient (
Substitute a) into the following formulas (1) and (2), and use the unit water weight (WT) and unit cement weight (CT) displayed in the recipe table as W and C, respectively, and the values obtained in the preliminary step. The value obtained by dividing the measured weight (A', W1', W2') by the volume (1) (R/l, W1'/
l. w, 7z) as A, Wl, W2, respectively, and the following formula (1
). (2) to determine the cement moisture content (α) and the fine aggregate moisture content (19), and the determined a, α
. The measured weights (A, W, , W2) obtained in this step are substituted into the following equations (1,) and (2) including β to determine the water weight W and cement weight C, and the water-cement ratio A method for inspecting the water-cement ratio of fresh concrete, the method comprising comparing (W/C) with the mixed water-cement ratio displayed on the mixing coat. C=(1-a)・(Wl-aXW2)-(1)
W=A-(C+(1-β) X a X W2 )
-''(2)2 The cement moisture content (a) and the fine aggregate moisture content (19) are o, i≦α≦0.4 and 0.01≦β≦0.04, respectively. Inspection method described in Section 1.