JPS5810206B2 - 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 find out whether the fresh concrete is mixed according to its mixing light.

The mix of ready-mixed concrete delivered to the concrete placement site is clearly indicated on the mix light.

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

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

Whether fresh concrete has been mixed according to the mixing light can be determined by determining the water-cement ratio of the fresh concrete and comparing the water-cement ratio with that of the mixing light.

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 test method requires special measurement, measuring means, chemicals, etc., and cannot be easily implemented in a short time at a concrete pouring site.

Therefore, an object of the present invention is to provide a method for testing the water-cement ratio of fresh concrete easily and quickly even at a concrete casting site, without using special measuring or measuring means or chemicals such as hydrochloric acid. Our goal is to provide the following.

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 tested using the following equations, 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 mortar sample is taken from the fresh concrete to be inspected, the weight (A) of the mortar sample in air is measured, and After the dehydration treatment under the same conditions in the preliminary step described above, the weight W in air,
The measured diameter is washed with water to remove cement and mud from the mortar sample, and the mortar sample is subjected to dehydration treatment under the same conditions as described above, and then its weight in air W2 and the measured weights A, W, obtained through this step.

By substituting 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 have been determined, it is possible to easily calculate the weight of fresh concrete 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 invention will become clearer from the following description of the illustrated embodiments.

The present invention includes a preliminary step and a main step, and in the main step, as shown in FIG. A single mortar sample is taken from the fresh concrete.

The amount of the mortar sample to be collected is preferably about 200 cc, taking into consideration the dehydration treatment and washing treatment described later, and it is preferable to use a 5 mm sieve for the collection of the mortar sample, that is, the work of removing coarse aggregate from the fresh concrete. .

The mortar sample is weighed and its weight A in air is determined.

The sample weight A can be considered as the sum of the cement weight in the mortar sample, where C1 is the fine aggregate weight, S is the fine aggregate weight, and W is the water weight, and is related by the following formula.

A=W+C+S (1) After this measurement, the mortar sample is subjected to dehydration treatment under the same conditions as in the preliminary step described later.

The dehydration process can be performed by using a heating device or the like to blow air, nitrogen gas, etc., but it is also possible to use a rotating tank in which the filter material is a layered membrane and is driven and rotated at a constant rotation speed. Preferably, a centrifugal dehydrator is used.

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

The first zero fabric is a fabric that blocks the passage of cement and fine aggregate and allows the passage of water, such as nylon tack (N-
6), one side of which was coated with acrylic resin (waterproofed) and formed into a bag shape was used.

The nylon taffeta is made of 70 denier thick nylon threads with 107±3 warp threads per 2.54 cm (1 inch).
Thickness 0.11± plain woven with 83±5 same weft threads
It is a 0.02mm cloth.

Further, the dehydrator is operated at about 2900 r, p, m for 3 minutes, whereby the sample in the first mouth cloth is subjected to a centrifugal force of about 706 G.

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

The mortar 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 Wc and Wsa are the weights of adhering water remaining in concrete and fine aggregate, that is, water that has not been completely dehydrated.

W1=(C+Wc)+(S+Ws)・・・・・・(2
) The sample whose sample weight W1 has been measured is then washed with water to remove cement and mud from the sample.

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

That is, the second 0 cloth is a cloth that blocks the passage of fine aggregate but allows the passage of cement and mud, for example, a thread made of 30 denier nylon 15ON-66 with a length of 2.54 m (2.54 m).
It is a bag-shaped cloth (mesh purpose: 180 μm) woven so that each of the warp and weft threads are 150 per inch (1 inch) and the thickness is 0.115 mm.
The zero cloth can be attached to the rotating tank of the centrifugal dehydrator in place of the first zero cloth.

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 fine aggregate in the mortar sample and the moisture attached to the fine aggregate, that is, the moisture that has not been completely dehydrated, and is therefore related by the following equation.

W2=S+Ws ・・・・・・・・・(3
) By the way, regarding the sample weight W2 after washing with water, since washing the sample with water removes cement and dirt attached to the fine aggregate, an aggregate correction coefficient a is introduced to correct this. There is a need to.

Therefore, instead of the measured weight W2 in equation (3), a value aXW2 obtained by multiplying the measured weight by the correction coefficient a is used.

The formula (3) is the following formula a X W2= S + W
8-=-(4).

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

Therefore, from equations (2) and (4), the following equation W1-a
X W2 = C1W.

・・・・・・・・・(5) is derived.

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 water content α, like the aggregate correction coefficient a, is a value determined 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 fine aggregate after the dehydration treatment is β, then β is expressed as follows.

Therefore, the weight W8 of water adhering to the fine aggregate, that is, water remaining in the fine aggregate without being completely dehydrated by the dehydration process, is expressed as follows.

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

The moisture content β of the fine aggregate is a value obtained 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.
should be determined by 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 mortar 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 mortar sample can be determined.

By dividing the water weight W by the cement weight C and further multiplying that value by 100, the water in the fresh concrete,
The cement ratio (X) can be determined.

As is clear from the above, according to the present invention,
According to the present invention, the a, α, and β are determined in a preliminary step, and the formula (8) and (13) including the a, α, and β are
The measured weights A, Wl, obtained in the present step are expressed as:
By substituting W2, the water weight W and cement weight of the fresh concrete to be inspected can be determined, and the water-cement ratio (W/C) can thereby be calculated.

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 fine aggregate moisture content β are determined.

The aggregate correction coefficient a is calculated based on the weight (mlslm, G) of fresh concrete aggregate and coarse aggregate in air before removing mud, and the weight (mlslm, G) of fresh concrete aggregate and coarse aggregate in air after removing mud by washing with water. Weight (m2s+m2G)
can be obtained by substituting into the following equation.

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

The above formula (14) is the fine aggregate washout rate a according to JIS.
/3 is shown by the following formula, and the coarse aggregate washout rate a'G according to JIS
is expressed by the following formula, and the aggregate correction coefficient a is the value obtained by dividing the sum of the weight of fine aggregate including mud before washing with water and the mud content of coarse aggregate by the weight of fine aggregate after washing with water. Therefore, as a'G and a's in the following formula, the above formula (15), (
16) can be obtained by substituting.

Weight of the fine aggregate before and after removing mud m 1 s, m 2
As an example of determining s, for example, sample fine aggregate is collected from the fine aggregate for ready-mixed concrete, and the fine aggregate is once immersed in water and then dehydrated in this step as explained in FIG. undergo processing.

Weight of fine aggregate in air after dehydration treatment and before washing with water m
1s is measured.

Next, the sample whose weight m1s has been measured is washed with water in the same manner as in the present step, and then subjected to dehydration treatment under the same conditions as in the present step.

After that, the weight of fine aggregate in the air after washing with water In2
5 is measured.

Weight of the coarse aggregate before and after removing mud rn IQ + m
2Q can also be obtained by using the coarse aggregate for fresh concrete and following the same procedure as for determining the weight rT11s+r112s of the fine aggregate.

The measured weight In 1s+ 1712s+ rn IQ
+rn2Q can also be obtained as follows.

That is, test samples are taken separately from the fine aggregate for fresh concrete and the coarse aggregate.

The amount to be collected is preferably about 1000 J, and each sample is kept in a dry state (preferably an absolutely dry state) using a heating dryer.

Thereafter, a portion of each sample (preferably by quartering method) is kept dry for each of the fine and coarse aggregates.
About A is sampled, and the fine aggregate weight rn1s and the coarse aggregate weight m1G in air before washing with water are measured.

After being washed with water, the latter measurement samples are again placed in the same drying state as described above, and the fine aggregate weight m2s and coarse aggregate weight m2G of each sample after washing with water are measured.

As is clear from the above, the aggregate correction coefficient a is 1.0 when there is no mud attached to the coarse aggregate and fine aggregate for ready-mixed concrete, and its value varies depending on the aggregate used. However, for general aggregates, it is 1.0 to 1.0.
It is about 6.

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

First, as shown in FIG. 2a, ready-mixed concrete for testing is prepared in accordance with the mixing table of the ready-mixed concrete to be tested.

A single test mortar sample is taken from this test fresh concrete by a procedure similar to that described for this step in FIG. 1, and its volume l and weight in air (A') are measured.

After this measurement, the test mortar sample 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 (Wτ
) is measured.

Further, after this measurement, the mortar sample for the test was washed with water in the same way 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 mortar sample for the vaginal test. The weight (Wl2) in air is measured.

These measured weights A', WlX, Wl2 are expressed as the volume (A
) divided by (A'/13, W', /13, W
/l) are A in the above formulas (8) and (13), respectively.
, Wl, W2 are substituted into the formula, and the unit cement weight CT and unit water weight WT displayed in the formulation table are roughly substituted into the formula together with the aggregate correction coefficient (a) as W, C.
is assigned as .

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

In the preliminary step, instead of the ready-mixed concrete for testing, mortar with the same mixing ratio as the ready-mixed concrete (having the same water, cement ratio and slump as the ready-mixed concrete, and excluding coarse aggregate from the ready-mixed concrete) is used. The test can be carried out under the same conditions as in this step described in connection with FIG. 1 according to the procedure shown in FIG.

Each moisture content α described above. β increases or decreases depending on the dehydration efficiency of the dehydration treatment means, that is, the centrifugal dehydrator in the above example, but generally it is 0.1≦α≦04 and 0.01≦, respectively.
It is in the range β≦0.04.

Further, when blowing air or nitrogen gas is used as the dehydration treatment means, the range of each numerical value α and β varies slightly.

According to the present invention, if each numerical value a, α, and β are determined in advance in the preliminary step described above, as described above, the measured weight A in air of the fresh concrete to be investigated in this step, By determining W and W2, the water-to-cement ratio (X) can be measured extremely quickly and easily.

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

The following table shows a comparison between the water-cement ratio 00 calculated from fresh concrete with a known mixing value and the water-cement ratio (Xi) actually measured for the fresh concrete by the method according to the present invention.

Three tests were conducted on each fresh concrete sample;
For sample a'-e, α-0,193, β=0.0
17, for sample f-j α=0.206β-0.0
16, α=0.180 for sample −0. β-0,
034 was adopted respectively.

Also, as the aggregate correction coefficient a, for samples a-e, α-
1,058, a=1.034 for sample f~'', and a=1.049 for sample k=o.

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 and cement ratio X. can do.

A graph is shown in FIG. 3 to clarify the comparison between the blended water and cement ratio X and the actual value Xi measured by the method according to the present invention.

The supplementary axis shows each sample shown in the above table, and the vertical axis shows the difference between the measured water/cement ratio Xi and the blended water/cement ratio X.

As is clear from the graph, the water-cement ratio determined by the method according to the present invention is within an error range of several percent;
Therefore, the mixed strength of concrete can be estimated very accurately based on the water-cement ratio determined by the method according to the present invention.

According to the present invention, as described above, the cement water content α, the fine aggregate water content β, and the bone water content for correcting the effluent 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 material correction coefficient a in the preliminary step, a single mortar sample is taken from the fresh concrete to be inspected in this step, and the measured weights A, Wl, W2 of the single mortar sample are By measuring and substituting the measured values 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.

Further, according to the present invention, since the mud content of fine aggregate and coarse aggregate is taken into consideration as the correction coefficient a, 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 takes a much shorter time than the conventional method, which takes about 15 minutes. The water-cement ratio can be determined by carrying out the following.

[Brief explanation of the drawing]

FIG. 1 is a flowchart showing the procedure of the main step according to the present invention, FIGS. 2a and b are flowcharts showing the procedure of the preliminary step according to the present invention, and FIG. It is a graph showing a comparison between cement ratio and blended 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 ratio, which method comprises: fine aggregate for ready-mixed concrete, coarse aggregate; Aggregate correction coefficient (a), cement moisture content (
Preliminary step to determine α) and fine aggregate water content (β); Main step to determine the water and cement weight of fresh concrete to be tested by the following formula including the determined a, α, and β; The preliminary step includes determining the weight in air of the fine aggregate and coarse aggregate for fresh concrete before mud removal (mls, m1G) and the weight in air after mud removal. (m2s9m2G), take a test mortar sample from the test fresh concrete and have a volume of l
) and its weight in air (A), after subjecting the test mortar sample to a dehydration treatment that does not allow the fine aggregate to reach a completely dry state, the test mortar sample's weight in air After measuring the weight (W1'), the test mortar sample is washed with water to remove cement and mud, and the test mortar sample is dehydrated under the same conditions as described above. This step includes measuring the weight in air (W'2) of the mortar sample for testing, and this step includes taking a mortar sample from the fresh concrete to be tested and measuring its weight in air 1 (A). measuring the weight (Wl) in air of a hindlimb mortar sample that has been dehydrated under the same conditions as described above; and washing the mortar sample with water to remove cement and mud. and measuring the weight in air (W2) of the test mortar sample after dehydrating the mortar sample under the same conditions as described above. Measured weight (11”11s+ [
Determine the aggregate correction coefficient (a) by substituting 112s+[1''11Q+m2G) into the formula (1) below, and calculate the aggregate correction coefficient (
Substituting a) into the following formulas (2) and (3), and assuming that the unit water weight (WT) and unit cement weight (CT) displayed on the blended batter are W and C, respectively, the above obtained in the preliminary step is The values (A'/l, W'X/l, W/l) obtained by dividing the measured weight (A'.
2, determine the cement moisture content (α) and the fine aggregate moisture content (β) by substituting them into the following formulas (2) and (3), and then calculate the following formula ( 2)・(3)
The measured weight (A, Wl,
Substituting W2) to find the water weight W and cement weight,
A method for inspecting the water-cement ratio of fresh concrete, the method comprising comparing the water-cement ratio (Xi=W/C) with the mixed water-cement ratio displayed on the mixing coat. Here, ST and GT are unit fine aggregate weight and unit coarse aggregate weight 2, respectively, which are displayed on the mixing coating.The mortar samples in the preliminary step and the main step are collected using a 5 mm sieve. An inspection method according to claim 1. 3 The above cement moisture content (α) and fine aggregate moisture content (β
) are 0, 1≦α≦04 and 001≦β≦00, respectively.
4. The testing method according to claim 1. 4. The inspection method according to claim 1, wherein the dehydration process is performed using a centrifugal dehydrator equipped with a filter.