JPS5810207B2 - 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 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 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. Caution is required.

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 an inspection method that can easily and quickly inspect the water-cement ratio of fresh concrete even at concrete placement sites, without using special measuring or measuring means or chemicals such as hydrochloric acid. It is about providing.

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

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, a single ready-mixed concrete sample is taken from the ready-mixed concrete to be inspected, the A of the ready-mixed concrete sample in air is measured, and the value of the ready-mixed concrete is measured. After dehydrating the sample under the same conditions as in the preliminary step described above, its weight W1 in air was measured, and after the measurement, the fresh concrete sample was washed with water to remove cement and mud from the fresh concrete sample. After removing the fresh concrete sample and subjecting it to the same treatment as described above, its weight W2 in air is measured, and the measured weight A obtained in this step is
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 the 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 can be easily calculated in 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 procedure of the present invention.

The present invention includes a preliminary step and a main step, in which, as shown in the flowchart in FIG.
A single fresh concrete sample is taken from the fresh concrete whose water-cement ratio is to be determined according to the present invention.

The amount of the concrete sample to be collected is preferably 11, taking into account the dehydration or washing treatment and conversion to a unit amount, which will be described later.

The fresh concrete sample is weighed and its weight A in air is measured.

The sample weight A is the cement weight in the sample, C is the water weight, W is the fine aggregate weight, and G is the coarse aggregate weight.
It can be thought of as the sum of these and can be related by a formula.

After this weighing, the sample is subjected to dehydration treatment under the same conditions as in the preliminary step described below.

The dehydration process can be carried out by blowing air, nitrogen gas, etc., using a heating device, etc., but a centrifugal dehydrator equipped with a rotary tank in which a filter material is removably installed and is driven and rotated at a constant rotation speed is preferred. It is preferable to use

A bag-shaped first filter material in the dehydration process is used as the filter material.
0 fabric was used.

The first 0 cloth is. Fabrics that block the passage of cement and aggregate and allow the passage of water, such as nylon taffeta (N-6
), one side of which was coated with acrylic fat (waterproofed) and formed into a bag shape.

The nylon taffeta has a thickness of 0.1 and is made by plain weaving 70 denier nylon threads with 107 ± 3 warp threads and 83 ± 5 weft threads per 2.54 cm (1 inch).
It is a cloth of 1±0.002 mm.

Also, the dehydrator was operated at about 200 Or, p, m for 3 minutes, so that the sample in the first mouth cloth was about 56
It is subjected to a centrifugal force of 0G.

As a result, the fine aggregate in the concrete sample is kept in a nearly surface-dry state that does not reach a completely dry state.

The concrete sample that has been dehydrated by the centrifugal dehydrator is weighed to determine its weight W1 in air.

The sample weight W1 is related by the following equation, where the weights of adhering water remaining in concrete and aggregates (fine aggregate and coarse aggregate), that is, water that has not been completely dehydrated, are Wc and Ws+G, respectively.

The fresh concrete sample whose sample weight W1 was measured is:
Next, the sample is washed with water to remove cement and mud from the sample.

It is preferable to use a second 0 cloth for the water washing.

That is, the second zero fabric is a fabric that blocks the passage of aggregate, ie, fine aggregate and coarse aggregate, and allows the passage of cement and water, for example, 30 denier nylon 15ON-6.
6, each 2.54 cm (1 inch) has 150 warp and weft threads and has a thickness of 0.11
A cloth woven to a thickness of 5 mm (net purpose: 108 μm) is formed into a bag shape, and the second zero cloth is attached to the rotating tank of the centrifugal dehydrator in place of the first zero cloth. It is considered possible.

The sample transferred into the second mouth cloth and washed with water is subjected to dehydration treatment under the same conditions as described above in the dehydrator, and then weighed to measure the sample weight W2 in air. .

The sample weight W2 is considered to be the aggregate of the sample and the moisture attached to the aggregate, that is, the moisture that could not be completely dehydrated, and is therefore related by the following equation.

By the way, regarding the sample weight W2 after washing with water,
Since cement is removed by washing the sample with water, as well as mud adhering to the aggregate, etc., it is necessary to introduce an aggregate correction coefficient a for this correction.

Therefore, instead of the measured weight W2 in equation (3), a value a×W2 obtained by multiplying the measured weight by the correction coefficient a is used.

That is, equation (3) can be replaced with the following equation.

Note that the aggregate correction coefficient a is a value obtained by a preliminary step described later.

Therefore, the following equation is derived from equations (2) and (4).

Further, if the moisture content of the cement after the dehydration treatment is α, then α is expressed as follows.

Therefore, the weight of water adhering to cement, that is, the weight of water Wc remaining in cement without being completely dehydrated by dehydration treatment, is expressed as follows, and by substituting equation (7) into equation (5), we get:
The following equation is derived.

The above-mentioned cement moisture content α is similar to the above-mentioned correction coefficient a,
This is a value obtained by a preliminary step described later.

Also, from equation (1), the water weight W is It is indicated by.

On the other hand, if the moisture content of the aggregate (fine aggregate and coarse aggregate) after the dehydration treatment is β, then β is expressed as follows.

Therefore, the weight of water adhering to the aggregate, that is, the weight of water Ws+G remaining in the fine aggregate and coarse aggregate without being completely dehydrated by the dehydration process, is expressed as follows.

Therefore, by substituting equation (11) into equation (4) and eliminating WG+s, the following equation is obtained, and the following equation is derived from equation (12) and equation (9).

The moisture content β of the aggregate is a value determined in a preliminary step, similar to the moisture content α of the cement and the aggregate correction coefficient a.

Therefore, each numerical value a, α and β is calculated in advance by a preliminary step.
, the sample weight W1 and the sample weight W
By substituting the value a×W2 obtained by multiplying 2 by the aggregate correction coefficient a into equation (8), the cement weight C in the fresh concrete sample can be determined.

Furthermore, by substituting the cement weight C1, the sample weight A, and the value aXW2 into equation (13), the water weight W in the concrete sample can be determined.

By dividing the water weight W by the cement weight C and then multiplying the value by 100, the water-cement ratio X of the ready-mixed concrete can be determined. By converting the weight C to that in 1 m3 of the concrete sample, the approximate amount of each unit in 1 m3 of fresh concrete can be found.

At this time, as described above, when the amount of concrete samples to be collected is 11, each unit amount can be easily determined by multiplying the determined cement weight C and water weight W by 1000, respectively.

Next, a preliminary step performed prior to the main step described above will be explained.

In this preliminary step, the aggregate correction coefficient a, the cement moisture content α and the aggregate moisture content β are determined.

The aggregate correction coefficient a is the weight of fine aggregate and coarse aggregate for ready-mixed concrete in the air before removing the mud (1s, m1G), and the weight in the air after removing the mud by washing with water. It is obtained by substituting the weight (m2s9m2G) into the following equation.

Here, ST. GT is the unit fine aggregate weight and unit coarse aggregate weight respectively indicated on the mix of ready-mixed concrete to be inspected.

The measured weight rnlsv rn2s+ rnlQ +
As an example of determining rn2Q, each of the fine aggregate and coarse aggregate for fresh concrete is sampled separately.

The amount of each sample to be collected is preferably about 1000 g, and each sample is once immersed in water and then separately subjected to dehydration treatment under the same conditions as in this step described with reference to FIG.

After the dehydration treatment, the fine aggregate weight m, B in the air and the coarse aggregate weight m1G in the air before washing with water are measured.

Each sample, that is, fine aggregate and coarse aggregate, for which the weight "ts + rnlQ" was measured, was washed with water in the same manner as in this step, and then subjected to dehydration treatment under the same conditions as in this step, and then , fine aggregate weight rn2s+coarse aggregate weight 'rn2G in air is measured.

The measured weight m1s1m2s1m1G1m2G can also be determined as follows.

That is, samples are taken separately from the fine aggregate and coarse aggregate for fresh concrete in the same manner as described above, and each sample is kept in a dry state (preferably in a dry state) using a heating dryer.

After that, about 1/2 of each of the fine aggregate and coarse aggregate is collected (preferably by the quartering method), and the fine aggregate weight m1s and the coarse aggregate weight m1 before washing with water are collected.
G is measured.

After the measurement, each sample was washed with water and dried again in the same manner as described above, and the fine aggregate weight m after washing was
2s and the coarse aggregate weight m2G are measured.

As is clear from the above, the correction coefficient a is 1.0 when there is no mud attached to the fine aggregate and coarse aggregate.
Although the value varies depending on the aggregate used, it is about 10 to 1.04 for general aggregates, and 1.0
It can also be used as a constant with a value of 2.

Next, a procedure for determining the cement moisture content α and the aggregate moisture content β in the preliminary step will be described.

First, as shown in FIG. 2, ready-mixed concrete for testing is prepared along the mixing light of the ready-mixed concrete to be inspected.

From this ready-mixed test concrete, a single test-ready concrete sample is taken by the same procedure as described for this step in Figure 1, and its volume (1) and weight in air (A') are measured. be done.

After this measurement, the fresh concrete sample for the test was subjected to dehydration treatment under the same conditions as in the main step, in which the fine aggregate did not reach a completely dry state, and then the weight in air (
Wl) is measured.

Further, the test mortar sample with this measured diameter was washed with water in the same manner as in the main step to remove cement and mud, and then subjected to dehydration treatment under the same conditions as described above, and then the fresh concrete sample for the test. The weight in air (Wl2) of is measured.

The value obtained by dividing these measured weights A', W;, W4 by the volume l) (A'#, W; /13, W',, /l
) are A and W in the above formulas (8) and (13), respectively.
The unit cement weight CT and the unit water weight WT displayed on the mixing light are substituted into the equation as W and C, together with the 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.

The moisture contents α and β vary depending on the dewatering efficiency of the dehydration treatment means and the type of aggregate used, but for the centrifugal dewatering device described above, α-0,169 to 0.202° β = 0.00.
4 to 0014 (for river sand and river gravel)
.

Therefore, when using the centrifugal dehydrator, α
−0,185, β−0,008.

Further, when blowing air, nitrogen gas, etc. is used as the dehydration means, the values α and β change slightly.

Therefore, in order to improve accuracy, it is preferable to determine α and β using a test sample prepared along the above-mentioned blended light as described above.

According to the present invention, by determining each numerical value a, α, and β in advance in the preliminary step described above, in this step, the sample weight A of the fresh concrete to be investigated is
By determining , W, and W2, the water weight W and cement weight C in the concrete sample can be determined extremely quickly and easily.

Furthermore, based on this water weight W and cement weight C, the water-cement ratio (X), unit water weight, and unit cement weight of the fresh concrete can be determined as described above.

The mixed strength F of fresh concrete can also be calculated by substituting the water-cement ratio (X) into the following equation.

The amount of cement in fresh concrete with a known mixing value (C
) and water-cement ratio (X), and the amount of cement (
A comparison with Ci) and water-cement ratio (Xi) is shown in the following table.

Six tests were conducted on each fresh concrete sample;
For sample (a), the cement moisture content is α-0,1
84, β-0012 as the aggregate moisture content, and a=1.0144 as the aggregate correction coefficient, respectively.

In addition, for sample (b), α-0,177° β-00
12 and a=1.0148, and for sample (c) α-0,179, β-0012 and a=1.
0145 is adopted, and for sample (d) α=0.1
82. β-0,010 and a=1.0149 were adopted.

As is clear from the above table, according to the present invention, the water-cement ratio Xi, which is the most important for knowing the mixed strength F of fresh concrete, can be measured within an error of about 3% with respect to the mixed water-cement ratio X. I can do it.

Therefore, the mixed strength of concrete can be estimated very accurately based on the water-cement ratio calculated from the cement weight and water weight determined by the method according to the present invention.

According to the present invention, as described above, the cement water content α, the aggregate water content β, and the aggregate for correcting the 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 correction coefficient a in the preliminary step, a single ready-mixed concrete sample is taken from the ready-mixed concrete to be inspected in this step, and the
The measured weight A, Wl for the fresh concrete sample.

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

Furthermore, according to the present invention, since the mud content of fine aggregate and coarse aggregate is taken into consideration as the correction coefficient a,
Since fresh concrete is used as the collected sample, the water-cement ratio can be determined with relatively high accuracy.

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, which is easy to operate, can be used to measure the weight.

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 the main step according to the present invention, and FIG. 2 is a flowchart showing the procedure of the preliminary step according to the present invention.

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 ratio, which method comprises: fine aggregate for ready-mixed concrete, coarse aggregate; Aggregate correction coefficient (a), cement moisture content (
α) and aggregate moisture content (β), and a main step to determine the water and cement weight of fresh concrete to be tested using the following formula including the determined a, α, and β. The preliminary step includes determining the respective weights (m, s, m1G) of the fine aggregate and coarse aggregate for fresh concrete in air before mud removal and their respective weights in air after mud removal. Weight (rn
2s'+ 1T12G), taking a test ready-mixed concrete sample from the test ready-mixed concrete, and measuring the volume [l) and its weight in air (A'); After subjecting the sample to a dehydration treatment that does not allow the fine aggregate to reach a completely dry state, measuring the weight (Wl) of the ready-mixed concrete sample for testing in air; After washing with water to remove cement and mud, and subjecting the test fresh concrete sample to dehydration treatment under the same conditions as described above,
The weight of the test fresh concrete sample in air (Wl2
), said step includes taking a ready-mixed concrete sample from said ready-mixed concrete to be tested, measuring the atmosphere in the atmosphere, and subjecting said ready-mixed concrete sample to the same conditions as mentioned above. Measuring the weight (Wl) in the air of a dehydrated hind leg fresh concrete sample; after the measurement, the fresh concrete sample is washed with water to remove cement and mud; After dehydration treatment under the same conditions, the weight (W2) of the fresh concrete sample in air is measured, and the measured weight (+7
11st I"112sI m1G, In2Q)
Determine the aggregate correction coefficient (a) by substituting into the formula (1) below,
Substitute the aggregate correction coefficient (a) into the following formulas (2) and (3), and set the unit water weight (WT) and unit cement weight (CT) displayed on the blended clothing as W and C, respectively, The measured weight (A',
Using the values (A'/l, W (/l. W12/l) obtained by dividing Wl, Wl2) by the volume (1), respectively, as A, Wl, W2, the following formula (2),
(3) to determine the cement moisture content (α) and aggregate moisture content (β), and enter the following equations (2) and (3) containing the determined a, α, and β in this step. The obtained measured weights (A, Wl, W2) are substituted to determine the water weight W and the cement weight C, and the water-cement ratio (W/C
) A method for inspecting the water-cement ratio of fresh concrete, the method comprising: comparing the mixed water-cement ratio displayed on the mixing coat. Here, sT and GT are the unit fine aggregate weight and unit coarse aggregate weight, respectively, which are displayed on the mixing coating.The cement moisture content (α) and the aggregate moisture content (b) are 01, respectively.
69≦α≦0.202 and 0.004≦β≦0.01
4. The testing method according to claim 1. 3. The inspection method according to claim 1, wherein the dehydration process is performed using a centrifugal dehydrator equipped with a filter.