JP3168911B2 - Evaluation method of water cement ratio of fresh concrete - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for evaluating the water-cement ratio of fresh concrete on site.

[0002]

BACKGROUND OF THE INVENTION Managing the quality of concrete involves:
This is an extremely important task in improving the reliability and economy of concrete work. At the site, various tests are conducted by collecting fresh concrete from a mixer or the like.

Of the management characteristics of concrete, it is needless to say that the compressive strength, particularly the compressive strength at the age of 28 days, is important. Not appropriate. As a method of determining the compressive strength in a short period,
28 hours accelerated strength test, 40 to 5 years of age with hot water curing
Although an accelerated strength test of 0 hours and an early strength test of 3 to 7 days of age at room temperature curing have been proposed, they also lack quickness and are not used for a management method before casting.

At present, the most effective method is to focus on the water cement ratio most closely related to the compressive strength, evaluate the water cement ratio of fresh concrete, and estimate the 28-day strength from the test results. It is said.

[0005]

However, as a method of testing the water-cement ratio of fresh concrete, JI
The “Test method for washing analysis of concrete that has not yet set) (JIS 1112), which is specified in S, requires not only tens of minutes even if the test procedure is complicated but also requires several people, but also requires a lot of labor. Had a problem that the accuracy was not sufficient.

[0006] Such a problem results in a situation in which fresh concrete of insufficient strength is cast, and in the worst case, hardened concrete must be removed and re-cast.

The present invention has been made in view of the above-mentioned circumstances, and quickly and accurately evaluates a water-cement ratio of fresh concrete in which the specific gravity and composition of a used material are known in advance as a W / C value for management. It is an object of the present invention to provide a method for evaluating a water-cement ratio of fresh concrete which can be performed.

[0008]

In order to achieve the above object, a method for evaluating a water-cement ratio of fresh concrete according to the present invention is as described in claim 1, wherein the air content A (%) and the unit volume of fresh concrete are defined. The weight W is measured, and the unit volume weight T not including air is calculated from the air amount A and the unit volume weight W by A = {(T−W) / T} · 100. The management W / C value is calculated using the obtained unit volume weight T. Management W / C value = (1000 / C _T ) ｛α- (α-1)
T / 1000｝ + β where α = 1 / (1-1 / ρ _A ) β = α (1 / ρ _A -1 / ρ _C ) ρ _A ; specific gravity of aggregate, etc. ρ _C ; specific gravity of cement C _T It is calculated according to the unit cement amount (kg / m ³ ).

In the method for evaluating the water-cement ratio of fresh concrete according to the present invention, since the specific gravity of the aggregate and the cement and the unit cement amount are known in advance, the air amount and the unit volume weight are measured by a simple test thereafter. The water / cement ratio of fresh concrete can be calculated as the W / C value for management alone.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a method for evaluating a water-cement ratio of fresh concrete according to the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a flowchart showing the flow of the water-cement ratio evaluation method according to the present embodiment. As can be seen from the figure, in the water-cement ratio evaluation method according to the present embodiment, first, fresh concrete is collected from a mixer, a hopper, a concrete transport device, a place where the concrete is poured, and the air amount A (%) is calculated. (Step 10
1). The air amount A (%) is determined, for example, by the air chamber pressure method (JI
SA1128).

Next, the unit weight W of the fresh concrete is measured (step 102). Here, in the case where a verified air volume measuring container whose volume and weight are known in advance is used in step 101, measurement is performed using a general-purpose balance having a sensitivity of 10 g while fresh concrete is kept in the container. By subtracting the weight of the container itself from the measured value and dividing by the volume of the container, the unit volume weight W of the fresh concrete can be easily measured.

Next, using the air volume A and the unit volume weight W measured in the above steps, the unit volume weight T that does not contain air is calculated as A (%) = {(T−W) / T}. 100 (1) That is, it is calculated by T = W / (1-A / 100) (1) '(step 103).

On the other hand, the specific gravity of the materials used, such as cement and aggregate, and the unit amount of the compound are investigated (step 104).

[0015] Next, when the weight of the water fresh concrete containing no air apparent to _{T w, T w = T-} ρ w (C T / ρ C + A T / ρ A + W T / ρ W) (2 ) T = C _T + A _T + W _T (3) T = T _W +1000 (4) where C _T ; mass of cement contained in concrete without air (kg / m ³ ) A _T ; does not contain air Mass of aggregates etc. contained in concrete (kg / m ³ ) W _T ; mass of water contained in concrete without air
(kg / m ³ ) ρ _A ; specific gravity of aggregate, etc. ρ _C ; specific gravity of cement ρ _W ; specific gravity of water. C value _{= (1000 / C T) {} α- (α-1) T / 1000} + β here, α = 1 / (1-1 / ρ A) β = α (1 / ρ A -1 / ρ C ) (5) can be calculated (step 105).

The C _T is preferably C _T = C / (100−A) (6) C, in consideration of the amount of air A, and C: the amount of cement blended (kg / m ³ ).

Further, as the aggregate or the like, in addition to the coarse aggregate and the fine aggregate, in some cases, different materials such as limestone fine powder material may be used in combination.
_A may be calculated by (ΣA _i ) / ρ _A = Σ (A _i / ρ _i ) (7). Here, A _i and ρ _i represent the unit volume weight and specific gravity of the i-th aggregate and the like, respectively, and Σ represents the total sum relating to i. Even when a plurality of types of cement are used, ρ _C may be calculated in the same manner.

FIG. 2 shows the evaluation of the W / C value for management of the fresh concrete mixed in various ways by the water-cement ratio evaluation method according to the present embodiment. As can be seen from the figure, the difference between the management W / C value and the blend W / C is
Regardless of the size of the blending W / C and the size of the air amount, the value is within about ± 2%.

As described above, according to the water-cement ratio evaluation method according to the present embodiment, since the specific gravity of the material used and the unit amount of the compound are generally known in advance, only the air amount and the unit volume weight are measured. Thus, the water-cement ratio of fresh concrete can be evaluated with high precision as a W / C value for management.

That is, the measurement of the air amount is an essential measurement item according to the construction specifications and JIS in the past, and the unit volume weight is also often measured at the time of the air amount measurement. It is not necessary to additionally perform another measurement to evaluate the working W / C value.

In the conventional method for determining W / C, for example, in the analytical test method specified in JISA1112, the Japan Society of Civil Engineers Standard Standard Specification (Standard Edition) [established in 1996]
As described in the example, the test result was 54.7% with respect to 50% of the indicated composition, and the difference was 4.7%, which was inferior in accuracy for the time-consuming test. If the evaluation method of the present embodiment is used, the blend W /
The difference from C is within about ± 2%, and it is possible to obtain more accurate data in a shorter time than before.

[0022] Therefore, when the W / C value for management is compared with the indication formula, failure of the air amount measuring device or the scale, mistake by the operator, abnormality of the aggregate surface water, measurement error, etc. can be detected at an early stage. In addition, the quality of fresh concrete can be effectively managed before casting.

[0023]

As described above, the method for evaluating the water-cement ratio of fresh concrete according to the present invention uses the air content A (%) and the unit volume weight W of fresh concrete.
Is measured, and the unit volume weight T not including air is calculated from the air amount A and the unit volume weight W by A = {(T−W) / T} · 100, and the unit not including the air is calculated. The W / C value for management is calculated using the volume weight T. The W / C value for management = (1000 / C _T ) ｛α- (α-1)
T / 1000｝ + β where α = 1 / (1-1 / ρ _A ) β = α (1 / ρ _A -1 / ρ _C ) ρ _A ; specific gravity of aggregate, etc. ρ _C ; specific gravity of cement C _T Calculating in accordance with the unit cement amount (kg / m ³ ), it is possible to efficiently and accurately evaluate the water-cement ratio of fresh concrete as a management W / C value.

[0024]

[Brief description of the drawings]

FIG. 1 is a flowchart showing a procedure of a method for evaluating a water-cement ratio of fresh concrete according to an embodiment.

FIG. 2 is a graph showing the W / C value for management of fresh concrete obtained according to the water-cement ratio evaluation method according to the present embodiment, wherein (a) shows the difference between the blending W / C value and the W / C value for management. A graph displayed for the blending W / C, and (b) is a graph also displayed for the air amount.

[Explanation of symbols]

100 Specific gravity of materials used,
Investigation process of unit amount of blending 101 Measurement process of air volume 102 Measurement process of unit volume weight 103 Calculation process of unit volume weight without air 104 Calculation process of management W / C value

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-2-276965 (JP, A) JP-A-4-295761 (JP, A) JP-A-7-244043 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) G01N 33/38

Claims (1)

(57) [Claims] 1. Air volume A of fresh concrete
(%) And a unit volume weight W, and a unit volume weight T containing no air from the air amount A and the unit volume weight W is calculated by A = {(T−W) / T} · 100, The management W / C value is calculated using the unit volume weight T that does not include the air. Management W / C value = (1000 / C _T ) ｛α− (α−1)
T / 1000｝ + β where α = 1 / (1-1 / ρ _A ) β = α (1 / ρ _A -1 / ρ _C ) ρ _A ; specific gravity of aggregate, etc. ρ _C ; specific gravity of cement C _T A method for evaluating the ratio of water cement to fresh concrete, wherein the method is calculated according to the unit cement amount (kg / m ³ ).