CN1111737C - Rapid evaluation method for concrete permeability - Google Patents

Abstract

The present invention relates to a method for quickly evaluating the permeability of concrete. Concrete is cut into sheet samples which are then placed in a vacuum chamber dryly pumped, water or a salt solution is filled in the vacuum chamber wetly pumped, the concrete is saturated in water or salt, voltage is applied to the samples, and a current value is recorded. The diffusion coefficient of chlorine ions and the conductivity of concrete are calculated, and the permeability of concrete can be evaluated according to the values of the diffusion coefficient of chlorine ions and the conductivity of concrete. The method has the advantages of simple measurement and accurate and reliable data, and is suitable for common concrete and high-performance concrete.

Description

Rapid evaluation method for concrete permeability

Technical field

The present invention relates to a kind of fast appraisement method of concrete permeability, belong to the concrete technology field.

Background technology

The method that is used to estimate concrete permeability now mainly contains following several: (1) osmometry comprises permeable method and air permeability method.This method is traditional method of testing, is applicable to normal concrete, is unsuitable for high performance concrete; (2) coulometry comprises ASTM C1202 and improved method thereof.ASTM C1202 mainly be measure thickness be 50mm, diameter be the concrete sample of 95mm under the 60V DC voltage, the electric weight size of passing through in 6 hours is evaluated concrete perviousness, and is many more by electric weight, perviousness is big more.The method is applicable to normal concrete, for the applicability existence dispute of high performance concrete.Its improved method mainly is to have reduced voltage, has prolonged the time, and its fatal shortcoming is the same with ASTM C1202, and evaluation high performance concrete time error is bigger; (3) electromigration, this method has multiple, that the most successful is Tang-Nillsson method (ACI Materials Journal Vol.89, N0.1,1992,49-53), promptly by the concrete sample that is soaked in NaCl solution is applied appropriate voltage, by measuring the length of penetration of chlorion, utilize the Nernst-Plank equation of simplifying afterwards, obtain chloride diffusion coefficient.The shortcoming of this method is the method complexity, data parsing needs certain galvanochemistry knowledge, and the civil engineering work personnel do not possess often, in addition, because the measuring process time is longer, ion concentration in the concrete hole solution changes greatly, adds that the mean depth time error of measuring chloride permeability is also bigger, makes that the data that calculate at last are inaccurate.Therefore, also do not have a kind of normal concrete that both had been suitable for up to now, be suitable for the infiltrative fast appraisement method of high performance concrete yet.

The applicant once proposed a kind of rapid evaluation method for concrete permeability, the patent No. is: 97120246.X, its principle is by chlorion transport number in the concrete is converted into correction factor, solve the Nernst-Einstein equation and be difficult to use in an actual difficult problem, determined the feasibility and the reliability of chloride diffusion coefficient in the concrete with improved Nernst-Einstein equation.But do not provide concrete test technology, and the specimen preparation time is long, has influenced work efficiency.

Summary of the invention

The objective of the invention is to propose a kind of rapid evaluation method for concrete permeability, concrete is thinly sliced sample, full water of vacuum or full salt are handled then, carrying out dc conductivity afterwards measures, utilize improved Nernst-Einstein Equation for Calculating to go out chloride diffusion coefficient at last, by relatively fuller water or full salt conductivity, or the chloride diffusion coefficient under the full salt situation is estimated concrete perviousness height.

The rapid evaluation method for concrete permeability of the present invention's design comprises following each step:

(1) concrete is cut into the thin slice sample of 0.5～5cm;

(2) concrete thin slice sample is put into vacuum chamber, dry tap 1～8hrs under the vacuum tightness of 0.001～0.005MPa discharges water in vacuum chamber or salt solusion then, wets under the vacuum tightness of 0.001～0.005MPa and takes out 1～8hrs, makes full water of concrete or full salt:

(3) the concrete thin slice sample after full water or the full salt is applied the DC voltage of 1～10V, and write down the current value that respectively applies under the voltage;

(4) according to above-mentioned voltage, current value, with the chloride diffusion coefficient under the full salt situation of formula (1) computing machine, with the concrete electric conductance under full water of formula (2) calculating or the full salt situation, $D_{\mathrm{Cl}}=f\·\frac{\mathrm{RT}}{F^2{C}_{\mathrm{Cl}}}\·\mathrm{\σ}---\left(1\right)$ $\mathrm{\σ}=\frac{I\·l}{V\·S}---\left(2\right)$

In the following formula: D _ClBe chloride diffusion coefficient (cm ²/ s); R is gas law constant (8.314J/molK); T is absolute temperature (K); V applies DC voltage (V); I is the electric current of surveying corresponding to V (A); L is specimen thickness (cm); S is electrode area (cm ²); F is Faraday constant (96500Coul/mol); C _ClBe the chlorine ion concentration of solution in the concrete hole, often get the chlorine ion concentration (mol/cm in the full salt solusion ³); F is a correction factor, gets 1.0 usually; If desire is calculated free or apparent chloride diffusion coefficient, its value can be referring to table 1; σ is the concrete electric conductance, and unit is: 1/ (ohmcm).

According to D _ClOr the value of σ, can estimate concrete perviousness.

The value of table 1 correction factor f

	Normal concrete	Flyash concrete	Slag concrete
				The free chloride ion coefficient of diffusion	0.6～1.0	0.7～1.0	0.7～1.0
Apparent chloride diffusion coefficient	2.0～2.4	2.1～2.7	2.4～2.9

On a large amount of experiment basis, obtained estimating the grade scale of concrete permeability with full salt conductivity or chloride diffusion coefficient, see Table 2.Have extraordinary linear relationship between concrete full water conductivity and the full salt conductivity, Fig. 1 is with saturated Ca (OH) ₂Full water conductivity that records during the saturated identical concrete of solution and 4M NaCl solution and the relation between the chloride diffusion coefficient can concern that associative list 2 estimates concrete perviousness according to this.

Table 2 is based on the concrete permeability split pole of chloride diffusion coefficient

Full salt concrete electric conductance (10 -4S/m)*	Chloride diffusion coefficient (10 -14m 2/s)	Concrete permeability is estimated
			＞2000 1000～2000 200～1000 100～200 10～100 ＜10	＞1000 500～1000 100～500 50～100 5～50 ＜5	Very high high, normal, basic very low ignoring

* be 25 ℃, with 4M or the saturated concrete conductivity of full salt of saturated NaCl solution

Method of testing of the present invention has been determined corresponding test technology fast, can provide correct data in 24hrs, is method of testing the most fast and accurately at present.Its reason mainly is by the full salt technology of the full water of vacuum, even make high-strength high-performance concrete in suitable sample thickness, also can finish the technical barrier of the full salt of full water in the time less than 24hrs.In fact the full asynchronism(-nization) of different concrete samples, can be implemented in full saturating concrete sample in 4～12hrs, for consideration to the working time, be decided to be the 24hrs one-period usually, the present invention shortens whole sense cycle greatly, test speed is fast, and data are accurate.Provided the concrete permeability grade scale simultaneously.The present invention has the following advantages: (1) device therefor can letter can be numerous, laboratory, scene all can possess.(2) measure simply, need not the work that operating personnel carry out large amount of complex, calculate easyly, do not need to understand galvanochemistry knowledge.(3) data are accurate, and are reliable, can be engineering technical personnel the simple forecast reinforced concrete structure chloride diffusion coefficient in serviceable life is provided.(4) both be applicable to normal concrete, also be applicable to high performance concrete.

Description of drawings

Fig. 1 is the graph of a relation between chloride diffusion coefficient of the present invention and full water conductivity.

Embodiment

Specimen preparation comprises two parts: the one, concret block is cut into the thin slice of suitable thickness, and the 2nd, satisfy water or full salt of concrete thin slice sample (being called for short sample later on) is handled.

The thickness of concrete sample depends on maximum diameter of aggrogate size in the concrete usually, and when accurately measuring chloride diffusion coefficient, sample thickness equals the maximum diameter of aggrogate size at least, gets 2～5cm usually; Carry out perviousness relatively or qualitative relatively the time, can cut thinly, get final product as 0.5～1cm is thick to shorten detection time.Attention concrete test block end 1～2cm concrete will be cast out to eliminate surface effect.

Full water treatment is applicable to the situation of estimating concrete permeability with full water conductivity, and full salt is handled the situation of estimating concrete permeability with full salt conductivity or chloride diffusion coefficient that is applicable to.The full salt method of full water can adopt the natural immersion method, is about to concrete sample and is soaked in certain hour in water or the salt solusion, is generally for 2～12 weeks; Also can adopt the full salt method of the full water of vacuum, this method can make thickness less than 5cm at present, the concrete of intensity in 120MPa is full saturating in 24 hours, concrete technology is: the concrete sample vertical codes is placed in the vacuum chamber, dry tap 1～8hrs under the vacuum tightness of 0.001～0.005MPa puts into water or salt solusion then then, the wetter 1～8hrs that takes out under the vacuum tightness of 0.001～0.005MPa, afterwards, keep vacuum or natural leak to end to 24hrs.Need to prove that dry tap and wet time length of taking out depend on the compactness extent and the thickness of concrete sample, sample is fine and close more, thick more, and the time that vacuumizes is corresponding long more; Otherwise, then short more.Full water can be used distilled water, tap water or saturated Ca (OH) ₂Clarified solution; Full salt can be with 4M or saturated NaCl solution, can by distilled water and to analyze pure NaCl formulated, and also can be by tap water and chemically pure reagent preparation.

Conductivity measurement can be adopted DC-method or AC method, can adopt manual method or automatic method in the operation.The present invention mainly carries out dc conductivity and measures.Manual measurement can adopt direct supply and multimeter to carry out, and the Special Automatic measuring system that automatic measurement can adopt us to develop is carried out, and this system is made up of computing machine, data collecting card (A/D, D/A plate) and the ADM software of writing specially.The measurement of dc conductivity can be carried out in less than the voltage range of 10V usually.The technology that detects with automatic measurement system is: the concrete sample that will satisfy is put between two electrodes that diameter is 5cm, in the scope of 1～10V, scan or apply single voltage then, utilize the ADM software that is provided to measure conductivity or chloride diffusion coefficient automatically.Can be a step-length with 1V in the scope of 2～5V generally, stabilization time, 10～30sec carries out linear sweep, after departing from bigger removal among the gained result, remainder data was on average got final product.Usually get the mean value of parallel sample more than three and estimate concrete perviousness height.This method can avoid because the measuring error that the serious polarization of electrode causes.

Test electrode commonly used is that diameter 5cm, thickness are 2.5cm, and surface smoothness is the red copper electrode of 7.Be to guarantee the excellent electric contact between electrode and test specimen, can be at pad between electrode and the test specimen one 80 orders commercially available standard copper mesh identical with electrode area.

Introduce embodiments of the invention below:

Embodiment one

Sample: Beijing metallurgical construction research institute sample, match ratio sees Table 3, and wherein B-23 is a normal concrete, all mixes 10% compacting agent among B-24, the B-25, has mixed 12.5% flyash among the B-25.

The rectangular end 20mm of concrete of 100 * 100 * 300mm of sending here is cut, be cut into the concrete thin slice sample that thickness is 20mm by maximum aggregate size 20mm then.Carry out the full salt of nature afterwards, full salt solusion is a 4M NaCl solution, and is formulated by distilled water and the pure NaCl of analysis.Natural immersion carries out conductivity measurement after 3 weeks.Manual method is adopted in conductivity measurement, the DH1720-4 bistable direct supply that promptly adopts big magnificent radio instrument factory to produce, and manual adjustments voltage, it is 10 that internal resistance is adopted in the measurement of electric current and voltage ⁷The digital multimeter of ohm.Apply 2,3,4,5V voltage, stablize 1～5 minute postscript picture recording induced current, calculate the concrete electric conductance then, calculate chloride diffusion coefficient by formula (1).The results are shown in Table 4, the impervious experiment in the table 4 oneself is finished by the JC492-94 standard by the smelting establishment.

Table 3: concrete sample match ratio

Specimen coding	Water cement ratio (W/C)	Tiger board 525 #Ordinary portland cement (kg/m 3)	Flyash (kg/m 3)	Sand (kg/m 3)	Stone (kg/m 3)	28d compressive strength (MPa)
							B-23	0.48	450	0	627	1067	40.5
B-24	0.35	405	0	627	1067	44.1
							B-25	0.35	405	58.5	627	1067	48.1

Table 4: the contrast of permeance property and chloride diffusion coefficient

Specimen coding	Infiltration height (mm)		Chloride diffusion coefficient (10 -9cm 2/s)	The perviousness rank
					W12	W21
	B-23 B-24 B-25	77.2 6.3 8.0					- 10.7 10.0	7.6 4.5 4.8	Low very low very low

Embodiment two

Sample: Beijing Research Institute of Building Materials Industry sample, match ratio does not provide, and only illustrates all to mix a certain amount of flyash and ground slag in every group of sample again, and maximum diameter of aggrogate is 20mm.

The concrete cube of 100 * 100 * 100mm of sending here is cut by method described in the embodiment one.The sample that cuts is carried out the full salt of vacuum.Full salt technology is: in vacuum tightness is dry tap 6hrs under the 0.001MPa, puts into then wetly under identical vacuum tightness again behind the 4MNaCl solution (by tap water and analytical reagent preparation) to take out 2hrs, closes vacuum pump afterwards, and the back of spending the night is taken out sample and carried out conductivity measurement.Automatic method is adopted in conductivity measurement, promptly by ADM software and Auto-Test System in 1～10V scope, with step-length 1V, stabilization time 10sec, automatically measure, chloride diffusion coefficient under each voltage is calculated automatically by ADM software, and wherein deviation on average promptly gets chloride diffusion coefficient value in the sample with remainder data after removing greater than 15% numerical value afterwards.Digital average close in three samples is promptly got the coefficient of diffusion value of chlorion in this group concrete.The testing result of three groups of Sample A, B, C sees Table 5.

Chloride diffusion coefficient (10 in table 5 concrete ^-9Cm ²/ s) RT=34 ℃

Sample	The A group	The B group	The C group
				Water-cement ratio	0.54	0.36	0.30
28d compressive strength (MPa)	38.8	62.9	67
				Sample 1	9.10	8.12	5.07
Sample 2	7.19	5.92	6.60
				Sample 3	7.02	5.55	6.34

Binomial is average *	7.11	5.74	6.47
				The perviousness rank	Low	Low	Low

Annotate: binomial mean value be except that the italic numeral other two values on average.

Embodiment three

Sample: building materials teaching and research group of Tsing-Hua University sample, match ratio does not provide in detail.Specimen preparation is with embodiment two, and difference is that the vacuum tightness of full salt technology is 0.005MPa.Manual method is adopted in conductivity measurement, with embodiment one.Test result sees Table 6.

Table 6 chloride diffusion coefficient testing result

Sample	The A1-30-36 group	The A2-50-36 group	The B1-30-30 group	The B2-50-30 group
					Coefficient of diffusion (10 -9cm 2/s)	5.8	5.9	3.8	2.5
The perviousness rank	Low	Low	Very low	Very low

Annotate: east, A-30 (50)-36 Ji 525 cement, 2 grades of flyash of western high well mix 30% (50%), water cement ratio 0.36;

East, B-30 (50)-30 Ji 525 cement, 1 grade of flyash of first Golconda mixes 30% (50%), water cement ratio 0.30.

Embodiment four

Sample: Chinese architecture investigation of materials institute sample, match ratio does not provide.Specimen preparation is with embodiment two, and difference is that the vacuum tightness of full salt technology is 0.004MPa, and the dry tap time is 4hrs.Manual method is adopted in conductivity measurement, with embodiment one.Test result sees Table 7.

Table 7 chloride diffusion coefficient testing result

Specimen coding	Chloride diffusion coefficient (* 10 -9cm 2/s)	The perviousness grading
			JD	11	In
HA	8.4	Low
			HG	15	In
HG+0.7％FDN	12	In

Embodiment five

Sample: building materials teaching and research group of Tsing-Hua University sample, match ratio does not provide.Specimen preparation is with embodiment two, and difference is that the vacuum tightness of full salt technology is 0.001MPa, and wet finding time is 6hrs.Automatic method is adopted in conductivity measurement, with embodiment two.Test result sees Table 8.

Table 8 chloride diffusion coefficient test result

Sample	The F1 group	The F4 group
			28d compressive strength (MPa)	86	103
Chloride diffusion coefficient (10 -10cm 2/s)	30.5	4.8
			The perviousness rank	Very low	Can ignore

Claims (1)

1, a kind of rapid evaluation method for concrete permeability is characterized in that, this evaluation method comprises following each step:

(1) concrete is cut into the thin slice sample of 0.5～5cm;

(2) concrete thin slice sample is put into vacuum chamber, dry tap 1～8hrs under the vacuum tightness of 0.001～0.005MPa discharges water in vacuum chamber or salt solusion then, wets under the vacuum tightness of 0.001～0.005MPa and takes out 1～8hrs, makes full water of concrete or full salt;

(3) the concrete thin slice sample after full water or the full salt is applied the DC voltage of 1～10V, and write down the current value that respectively applies under the voltage;

(4) according to above-mentioned voltage, current value, with the chloride diffusion coefficient under the full salt situation of formula (1) computing machine, with the concrete electric conductance under full water of formula (2) calculating or the full salt situation, $D_{\mathrm{Cl}}=f\·\frac{\mathrm{RT}}{F^2{C}_{\mathrm{Cl}}}\·\mathrm{\σ}---\left(1\right)$ $\mathrm{\σ}=\frac{I\·l}{V\·S}---\left(2\right)$

In the following formula: D _ClBe chloride diffusion coefficient (cm ²/ s); R is gas law constant (8.314J/mol.K); T is absolute temperature (K); V applies DC voltage (V); I is the electric current of surveying corresponding to V (A); L is specimen thickness (cm); S is electrode area (cm ²); F is Faraday constant (96500Coul/mol); C _ClBe the chlorine ion concentration (mol/cm in the full salt solusion ³); F is a correction factor, gets 1.0; σ is the concrete electric conductance, and unit is: 1/ (ohmcm),

According to D _ClOr the value of σ, can estimate concrete perviousness.