WO2019053502A1

WO2019053502A1 - Probe for measuring conductivity of fresh concrete

Info

Publication number: WO2019053502A1
Application number: PCT/IB2018/000660
Authority: WO
Inventors: Akaki IROMASHVILI; Vano NATIDZE
Original assignee: Cst Corporation Limited
Priority date: 2017-09-14
Filing date: 2018-06-26
Publication date: 2019-03-21

Abstract

An apparatus for measurements on a flowable product, such as a cement/water mixture, comprises a data-processing device (2) and a single probe (4). The probe (4) has two terminals (28, 32) and conductors connected to them, for passing a measuring current therebetween through said flowable product.

Description

PROBE FOR MEASURING CONDUCTIVITY OF FRESH CONCRETE

The present invention relates to apparatus for use in and a method of measuring a characteristic of a fiowabie product.

It is known to measure and read electrical conductivity of a water- cement or water-concrete mixture by means of a hand-held battery powered instrument connected to two detection probes insertable into the mixture. The temperature of the mixture is measured by dipping a thermometer into it.

It is also known from SU 1695227(A1) and from WO2013/175246(A2) to base measurement of conductivity upon various formula?.

According to one aspect of the present invention, there is provided apparatus for use in measuring a characteristic of a fiowabie product, comprising a data-processing device and a single probe, the probe having two discrete terminals and conductors connected to the respective terminals for passing a measuring current therebetween through said product.

According to another aspect of the present invention, the^re is

provided a method of measuring a characteristic of a fiowabie product, comprising inserting into said product a single probe having two discrete terminals, passing an electric current between said terminals through said product and calculating said characteristic according to a signal produced by said current.

Owing to those aspects of the invention, it is possible to reduce the bulkiness of the apparatus and to make the method easier to

perform. The characteristic(s) and the flowable product may be the electrical conductivity, water/cement ratio or water content of a water-cement or water-concrete mixture.

According to a third aspect of the present invention, there is

provided a method comprising measuring a characteristic of a flowable product and employing the measurement value thereby obtained by calculating the value of a property of the product when set.

Advantageously, the characteristic is electrical conductivity, whilst the property may be the strength of the set product, particularly the compressive strength.

The flowable product may be a cement/water mix and the set product set cement. In that case, the Formula I hereinafter set forth is preferably employed in calculating the value of the property.

Alternatively, the flowable product may be a fresh mix concrete and the set product set concrete. In that case, the Formulae I tc V

hereinafter set forth are preferably employed in calculating the value of the property.

Owing to that aspect of the invention, a characteristic of the

produced, set cement, or set concrete, can be measured without having recourse to a lengthy setting procedure for a sample of the cement or concrete.

In order that this invention may be clearly and completely disclosed reference will now be made, by way of example, to the

accompanying drawings, in which: Figure 1 is a front view of apparatus for use in detecting the electrical conductivity and the temperature of a flowable product, e.g. a water- cement or water-concrete mixture;

Figure 2 shows an axial section through a probe included in the apparatus; and

Figure 3 is a graph illustrating the accuracy of the apparatus

compared with a European Standard "Cubes" test, for two differing cements used in respective concrete mixtures.

Referring to Figure 1, there are seen a hand-held, battery-powered instrument 2, a probe 4, a conductor cable 6 interconnecting the instrument 2 and the probe 4, and a graduated 600 ml. jug 8 for containing the flowable product sample.

The instrument 2 contains electrical circuitry for measuring the conductivity.

The conductivity and the temperature are indicated on a display screen 10 of the instrument 2.

The instrument 2 below the screen 10 has three buttons 2A, 2B and 2C for carrying out the method; the circuitry contained in the

instrument 2 calculates the flexural strength Rflex and the

compressive strength Rcomp, using the formulae downloaded into the software incorporated in the instrument and set out hereinafter and those parameters are also displayed on the screen 10.

The temperature measurement is performed to enable the user to check that the temperature of the sample mixture is of a value to provide an optimum measurement of the electrical conductivity. We have found that the temperature should be between 18 and 22 Celsius, advantageously as close to 20 Celsius as feasible. For

example, a suitable product in the jug 8 would be approximately, preferably exactly, 15 grams of cement mixed into 500 ml. of de- ionised water or 26 grams of freshly mixed concrete mixed into 500 ml of de-ionised water. Those proportions are important when using the formulae in question.

Referring to Figure 2, the probe 4 comprises a tubular casing 12, a tubular outer insert 14 and a tubular inner insert 16, all of plastics. A proximal end 18 of the casing 12 is internally threaded at 20, for cooperation with external threading 22 of the insert 14. Fixed to and encircling co-axially the distal end of the insert 6 is an electrically conductive, stainless steel sleeve 28 spaced by a collar 30 of the insert 16 from another such sleeve 32. Each sleeve 28 and 32 firmly abuts the collar 30 and is fixed to the insert 16 by a suitable, water- resistant adhesive.

A lead 34 comprising three conductors 36, 38 and 40 insulted from each other enters the proximal end of the central bore of the insert 16. The conductor 36 extends and is electrically connected to the sleeve 28 through a hole 42 through the wall of the insert 16. The conductor 38 extends and is electrically connected to the sleeve 32 through a hole 44 through the wall of the insert 16, whilst the conductor 40 extends and is electrically connected to a digital thermometer 46 located in the tip of the insert 16. The conductors 36 and 38 are sealed into the insert 16. An air outlet hole 50 extends through the wall of the casing 12 at a level distally of the threading 22 and to the tip of the probe; which allows the air displaced by the mixture to escape. THE METHOD OF USE OF THE APPARATUS IS AS

FOLLOWS:

The jug 8 is filled with the de-ionised water and then the appropriate weight of cement or ready-mix concrete sample is mixed in the water and stirred for a given time, for example one minute.

The instrument 2 is switched on using the on-off button 2C.

The screen 10 displays a message as to whether the instrument is connected to the probe 4 and an instruction to insert the connected probe 4 into the mixture, which is then done.

The temperature measurement made by the thermometer 46 is displayed on the screen; if it is within the desired range, then the conductivity value is displayed on the screen 10. The button 2C is then pressed to accept the conductivity reading.

Button 2C is pressed again and an on-screen menu is displayed showing various icons including one for instruction to perform the test, which is then chosen.

The buttons 2A and 2B are used to select the desired icon, moving to and from among the icons. The test then proceeds.

For a cement test the type of cement is chosen from the display using buttons 2A and 2B. The button 2C is used to accept the selection. A similar process is used to select and accept other parameters, such as cement density, fineness, normal consistency of cement paste, particular additive size and quality, curing time and conditions. All of the finally selected parameters are displayed through pressing of the button 2C, pressing that button again displays the saveable test results.

For testing of freshly mixed concrete - need to select 26 grams of fresh concrete sample from the mass, filter it with 10 mm sieve to remove large particles of coarse aggregate. Conductivity of concrete sample mixture (26gr/ 500 ml deionised water) will be measured.

A similar process is used to select and accept each of a few

parameters of aggregate physical analyses such as:

Maximum particle sizes of coarse and fine aggregates in mm., aggregate mix ratio (by weight), slump test result determined by (British Standard) BS EN 12350-2, presence of any plasticizer or water reducer additives (type and amount in grams), curing time (days) and curing conditions (laboratory, ambient or hot steam curing conditions in degrees Celsius).

Finally, selected parameters are displayed on the screen 10 before processing to the test results, which could be saved to the

instrument's memory and transferred to a computer for further processing.

The spacing 19a between the sleeves 28 and 32 is important to give a fixed distance through which the given electric current has to flow in the mixture which has risen to just below the air hole 50. That spacing 19a is advantageously no more than 30 mm., since otherwise the current flow will not be reliable; for the formulae given

hereinafter, the spacing is substantially 20 mm.

The distal end of the casing 12 rests upon the bottom of the jug 8. The level of the hole 50 is above the mixture level. The radial spacing 17b between the external peripheral surface 52 of the insert 14 and the internal peripheral surface 54 of the casing 12 is advantageously between 4 and 6 mm.

For the formulae given hereinafter, if that spacing is higher than the 6mm. limit, it tends to make the final results of the test unreliable, because the volume of the mixture through which the current has to travel is increased, whilst lower than 4 mm. encourages clogging of the space between the two surfaces 52 and 54 with particulate matter. The spacing preferred is substantially 5 mm.

THE FORMULAE HEREINABOVE REFERRED TO

To calculate cement compressive and flexural strength using

characteristics of cement physical analyses as manually entered values:

FORMULA I

R_cem = Mdc² x _ln {(Y + KJ - ^)) JfhTc - VF + tf₂Z

Where:

X - hereinafter multiply d - density of cement (BS EN 196-2:2010) gr/cm² c - electrical conductivity value of water/cement mixture

Y - Approximate curing time (2 to 28 days) a - additive amount (according to EU [European Union] 197-1 cement composition, between 5 and 35 %) q - additive type (e.g. mineral additives such as GGBS [ground granulated blast furnace slag] or mineral/chemical additive, such as silica fume, and pozzolana, (according to EU 197-1 cement

composition) f - fineness (determined by 90-micron Mesh, BS EN 196-6:2010) h - consistency of normal paste (obtained by the "Vicat" apparatus, BS EN 196-1:2005) %

Z - water /cement ratio (by weight)

M - mineralogical/chemical composition of cement clinke r (10 - 20 % by weight) in - logarithmic function

A per se known master formula for calculating concrete compressive strength is: FORMULA II

Rconcr— AR_cem x sin²(¾ )T

Where:

A - mineralogical composition and quality of aggregates Rcem - cement compressive strength (Mpa).

Q - amount of cement in 1 M³ concrete mix (kg).

W - amount of water in 1 M³ concrete mix (litre).

T - coefficient for curing conditions:

FORMULA III

T= K₄e^~KSt x _ln(K₆Y^K7x e^K8t + ¾)

Where: t - approximate curing temperature Celsius

For the laboratory (20°C) conditions T =1

To calculate the amount of cement in 1 M³ concrete mix: FORMULA IV

Where:

C - Electrical Conductivity of cement/water mixture 2 gr/500 ml

C₂- Electrical Conductivity of cement/water mixture 6 gr/500 ml

C- Electrical Conductivity of concrete/water mixture 26 gr/500 ml

To calculate water content in a concrete mix there is used the formula:

FORMULA V

W = + ¾. Is - ¾n) e ¾₀flf x I + ¾ + K ₁(h - K₁₂) +

¾«? - ¾)P

Where:

,g - maximum size of coarse aggregate (mm.), s - sand grain module n - share of sand in aggregate (by ratio), e - Neper value h - consistency of normal paste (obtained by the Vicat apparatus BS EN 196-1:2005) %

Q - amount of cement in 1 M³ concrete mix - kg. p -plasticiser impact on compressive strength (1.0 - 3.0)

I - slump test result, according to BS EN 12390-2, cm.

Tests were carried out on the 3 June 2015 using the present probe in respect of cement/water mixture and concrete/water mixture, and the following results were obtained:-

Cement Tests Using the Present Probe

Since the length of the presentation of the results has required splitting into three parts, those are as follows:-

Part l

Event Date Time Cem Type Mix. temp. Conduct (c) Rcem

1 03/06/2017 15:35:54 NORMAL 18.4 27.59 48.84

2 03/06/2017 15:36:21 RAPID 18.4 27.59 41.52

Part 2

Density

R fl. oil R flex. (d) Fineness (f) Consist (h) Add. Am. (a) Add. Type (q)

12.29 5.16 2.8 4 22 0 1

10.44 4.39 2.8 4 22 15 1

Part 3

Cem.

W. Cem (Z) Curing (t) Curing Time (Y) Class EN R_cem

0.5 20 28 CEM I N 49.1

0.5 20 28 CEM II R 40.51 In the above results:-

- "R fl. oil" means flexural strength for cement used in oil wells

- "R flex." means flexural strength for cement used in construction

- "Mix. temp." means the temperature of the cement/water sample being tested

- "EN R_Cem" are values entered manually for comparison with the "Rcem" values and represent laboratory test results under the

European standard for the cement type in question after curing for 28 days.

Concrete Test Using the Present Probe

Again, since the length of the presentation of the results has required splitting into three parts, those are as follows:-

Part l

Event Date Time ^cem CI

1 24/05/2017 10:32 :46 52.5 16.1

2 24/05/2017 10:47:22 32.5 14.7

Part 2

Slump

g s n (1) P A h

30 3.5 0.3 1 0 1.5 28

30 3.5 0.3 1 0 1.5 30

Part 3

(t) (Q) (W)

temp Y Cem water ^concr

20 28 382.76 160.41 60.78

20 28 562.26 182.36 47.08 In the above tests, different cements were used, namely the standard cements CEMI 52.5, and CEMII/A-L 32.5R.

Comparative compressive strength tests under European standard EN 12390 had the following results for the respective concrete mixes as follows:-

Compressive Strength Test EN12390

CEMI 52.5 Compressive Strength (MPa)

Cube 1 57.9

Cube 2 58.9

Cube 3 58.5

Average 58.4

CEMII/A-L 32.5R Compressive Strength (MPa)

Cube 1 47.2

Cube 2 50.0

Cube 3 50.8

Average 49.3

The comparative results are illustrated in Figure 3, where the hatched columns are the results obtained with the present calculated values using the Formulae I to V and the plain columns are those obtained using the EN 12390 tests

In each sample, the concrete mix was as follows:

Concrete mix details

Gravel Water

Cement (kg) Sand (kg) (kg) (kg) 3.97 6.84 13.68 1.79

An example of Formula II is:-

FORMULA II

Rconcr = AR_cem x sin 2 (0.45— Q )xT

A = 1.5; Rcem = 52,5 Mpa;

Q = 387 kg; W=195ltr; T=l;

387

Thus, Rconcr = 1.5 x 52.5 x sin (0.45 x )

195⁷

= 78.75 x 0.606773 = 47.78 Mpa

An associated example of Formula III is:-

FORMULA III

T = 0.28e - ⁰⁰¹¹ x In (0.105Y¹⁵x e ^008t + 1) e = 2.718

Y = 28 days

t = 20 °Celsius

Thus, T = 0.28x2.718^~002 x In (0.105 x 28¹⁵ x 2.718¹⁶ + 1) = 0.23 x In (0.105 x 148x4.95 + 1) = 0.23 x In (77.923) = 0.23x4.356 = 1.0

Claims

1. Apparatus for use in measuring of a flowable product, comprising a data-processing device and a single probe, the probe having two discrete terminals and conductors connected to the respective terminals for passing a measuring current therebetween through said products.

2. Apparatus according to Claim 1, wherein the spacing between said terminals is no more than 30 mm.

3. Apparatus according to claim 2, wherein, for a method according to the formulae [?] hereinabove, said spacing is substantially 20 mm.

4. Apparatus according to any preceding Claim, wherein said

terminals are mounted on an insert, said insert is received in a casing and a gap between said terminals, on the one hand, and a facing, internal wall of said casing, on the other hand, is between 4 mm. and 6 mm.

5. Apparatus according to Claim 4, wherein said gap is substantially 5 mm.

6. Apparatus according to Claim 4 or 5, wherein said insert is cylindrical and each of said terminals is a ring co-axial with said insert and with said casing.

7. Apparatus according to any one of Claims 4 to 6, wherein said casing is provided with an air outlet for escape of air displaced by entry of said flowable product into said gap.

8. Apparatus according to any preceding Claim and further including in said probe an electrical thermometer, and a further conductor for supplying electric current to said thermometer.

9. Apparatus according to any preceding Claim and further

comprising a flexible cable lead including the conductors and

extending between said instrument and said probe and enabling moving of said probe relative to said instrument.

10. Apparatus according to Claim 7, or to Claim 8 or 9 as appended to Claim 7, and further comprising another insert, said other insert carrying at a distal end thereof the first-mentioned insert and being received with spacing in said casing, that spacing allowing said product to flow up to short of said air outlet.

11. Apparatus according to Claim 7 or 10, or Claim 8 or 9 as

appended to claim 7, and further comprising a measuring container for said product, the intended depth of product in said container being less than the distance between said air outlet and the distal extremity of said probe.

12. A method of measuring a characteristic of a flowable product, comprising inserting into said product a single probe having two discrete terminals, passing an electric current between said terminals through said product, and calculating said characteristic according to a signal produced by said current.

13. A method according to Claim 12, wherein said characteristic is the electrical conductivity of said flowable product.

14. A method according to Claim 13, wherein said product is a water/cement mixture or fresh concrete/water mixture.

15. A method according to Claim 14, wherein the cement-water ratio in said mixture is substantially up to 30 grams per litre and said calculating employs substantially the Formula I hereinabove.

16. A method according to Claim 13, wherein said product is a water- concrete mixture.

17. A method according to Claim 16, wherein the concrete-water ratio in said mixture is substantially 52 grams per litre and said calculating employs substantially the Formulae I to V hereinabove.

18. A method according to any one of Claims 12 to 17, wherein air displaced by entry of the product into said probe is allowed to escape from an air release hole.

19. A method comprising measuring a characteristic of a flowable product and employing the measurement value thereby obtained by calculating the value of a property of the product when set.

20. A method according to Claim 19, wherein said characteristic is electrical conductivity.

21. A method according to Claim 19 or 20, wherein said property is the strength of the set product.

22. A method according to Claim 21, wherein said strength is the compressive strength.

23. A method according to any one of Claims 19 to 22, wherein said flowable product is a cement/water mix and the set product is set cement.

24. A method according to any one of Claims 19 to 23, wherein the Formula I hereinbefore set forth is employed in said calculating.

25. A method according to any one of Claims 19 to 22, wherein said flowable product is a fresh mix concrete and said set product is set concrete.

26. A method according to Claim 25, wherein the Formulae I to V hereinbefore set forth are employed in said calculating.