CN1181502A - Method for fast determining anti-permeability of concrete - Google Patents

Abstract

A method for quick evaluation of concrete's impervious power includes slicing concrete specimen, immersing in salt solution until saturation, applying low current to it, measuring current values at different voltages, finding out ion diffusivities by Nernst-Einstein formula, averaging the diffusivities to obtain average value Da, and finding out free ion diffusivity Df and apparent diffusity Dap by Df=f1Da and Dap=f2Da. The smaller the diffusity, the better the impervious power.

Description

A kind of method of fast determining anti-permeability of concrete

The present invention relates to evaluate the method for concrete permeability resistance, belong to concrete performance and measure.

The method that is used to estimate concrete permeability resistance now mainly contains following several: (1) osmometry comprises permeable method and air permeability method.This method is a kind of more traditional method of testing, is applicable to normal concrete, is unsuitable for high performance concrete; (2) coulometry comprises ASTMC1202 and modification method thereof.ASTMC1202 mainly is to be that 50mm, diameter are that the concrete sample of 100mm is under the 60V DC voltage by measuring thickness, the electric weight size that flows through in 6 hours is evaluated concrete impermeability, the electric weight that flows through is many more, illustrates that the passage in the concrete is many more, so impervious just poor more.This method also only is suitable for normal concrete, and is inapplicable to high performance concrete.Modification method mainly is to have reduced voltage, has prolonged the time, and its fatal shortcoming is the same with ASTMC1202, and evaluation high performance concrete time error is bigger; (3) electromigration, this method has multiple, Tang-Nilsson method that the most successful is (ACIMaterals Journal Vol.89, No.1,1992,49-53), promptly to being soaked in 3%NaCl-Ca (OH) ₂The concrete sample of solution applies the 30V DC voltage, and the energising certain hour is measured the length of penetration of chlorion with development process, uses a reduced equation afterwards

, obtain chloride diffusion coefficient, wherein D is a coefficient of diffusion, and a, b, c are known constant, and t is a time of penetration, and x is a length of penetration.The shortcoming of this method is comparatively complicated, data parsing needs certain galvanochemistry knowledge, and the civil engineering work personnel do not possess often, in addition, because the galvanization 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 not accurate enough.In addition, the same with coulometry, applied voltage is higher, causes the serious polarization of electrode and the composition of hole solution to change easily.So, also do not have preferably a kind ofly up to now, both be suitable for the rapid evaluation normal concrete, also be suitable for evaluating the method for high performance concrete impermeability.

The objective of the invention is electrochemical theory is applied to concrete,, provide a kind of method of new fast determining anti-permeability of concrete by the coefficient of diffusion of certain ion of fast measuring in concrete.

The method of fast determining anti-permeability of concrete of the present invention is that concrete is thinly sliced, under several (desirable 3 or 5) little DC voltage, measure by concrete current value with the saturated back of high salt concentration solution, try to achieve under each magnitude of voltage the coefficient of diffusion value of ion in concrete then by Nernst-Einstein equation (formula 1). $D_i=\frac{\mathrm{RT}}{Z_i^2{F}^2{C}_i}\·\frac{I\·l}{V\·S}------\left(1\right)$

D _Free=f ₁D _All(free coefficient of diffusion) (2)

D _Apparent=f ₂D _All(apparent diffusion coefficient) (3)

The coefficient of diffusion fluctuation that records is tried to achieve its mean value D 20% with each interior numerical value _AllTo be worth and to try to achieve ion free coefficient of diffusion and apparent (total) coefficient of diffusion in concrete in the substitution formula (2,3).The coefficient of diffusion bright concrete permeability resistance of novel more is good more.In the formula (1,2,3): D _iI ionic diffusion coefficient (cm in the-concrete ²/ s); R-gas law constant 8.314 J/molK; T-absolute temperature (K); Z _i-i ion combination valency; F-Faraday constant 96500 coul/mol; The DC voltage that V-applies (V); I-is corresponding to the measured current that applies voltage (A); 1-concrete sample thickness (cm); S-electrode area (cm ²); C _iI ion concentration (mol/cm in the-full salt solusion ³); f ₁, f ₂-correction factor, its size depends on concrete kind.

The test process of fast determining anti-permeability of concrete method of the present invention is as follows:

1, concrete is cut into the thin slice test specimen of suitable thickness.

2, with the test specimen for preparing with the full fast salt of vacuum technique, or with the natural immersion method salt of satisfying.

3, will satisfy test specimen after the salt in (1～5V) time energising 1～5 minute of different little DC voltage.

4, record respectively applies the current value under the voltage.

5, calculate by formula (1), try to achieve the diffusion coefficient D under each voltage _i

6, the fluctuation that obtains under the different voltages is averaged with interior coefficient of diffusion 20%, try to achieve average

Value D _All

7, with the average diffusion coefficient value D of gained _AllThe substitution formula promptly gets free ionic diffusion coefficient and apparent ionic diffusion coefficient in (2,3).

Illustrate that embodiment is as follows:

With concrete formation is the test block of 100 * 100 * 300mm, and maintenance is after 28 days, is cut into the thick thin slice of 20mm (for eliminating the surface influence, first test specimen is not), with the 4MNaCl solution salt of satisfying; Electrode is the red copper electrode of diameter 50mm, thickness 25mm, and applying voltage is 2～5V (every 1V is an one-level), and the current stabilization time was generally 1～5 minute.

With current value substitution (1) formula that records under every magnitude of voltage, obtain corresponding diffusion coefficient D _Cl, with the fluctuation that obtains under the different voltages 20% with interior D _ClOn average, try to achieve mean value D _{Equal cl}This mean value substitution formula (2,3) is promptly got free chlorion and apparent chloride diffusion coefficient (being total chloride diffusion coefficient).The more for a short time concrete permeability resistance that shows of chloride diffusion coefficient is good more, otherwise poor more.F in the formula (2,3) ₁And f ₂Be respectively free and apparent chloride diffusion coefficient correction factor, its value depends on concrete mixture ratio and kind; To not mixing the Portland cement concrete (PCC) of mineral admixture, f ₁Between 0.6～1.0, get 0.80 usually, f ₂Between 2.0～2.4, get 2.20 usually; To Portland fly ash cement concrete, f ₁Between 0.7～1.0, get 0.85 usually, f ₂Between 2.1～2.7, get 2.40 usually.

Adopt the present invention to evaluate the method for concrete permeability resistance, can the concrete impermeability of rapid evaluation, and equipment is simple, and easy to operate, data are reliable.

Claims (1)

1, a kind of method of fast determining anti-permeability of concrete, it is characterized in that: concrete is thinly sliced, measure by concrete current value under several general desirable 3 or 5 little DC voltage with the saturated back of high salt concentration solution, press Nernst-Einstein equation (formula 1) then $D_i=\frac{\mathrm{RT}}{Z_i^2{F}^2{C}_i}\·\frac{I\·l}{V\·S}------\left(1\right)$

D _Free=f ₁D _All(free coefficient of diffusion) (2)

D _Apparent=f ₂D _All(apparent diffusion coefficient) (3)

Try to achieve under each magnitude of voltage, the coefficient of diffusion value of i ion in concrete tried to achieve its mean value D 20% with each interior numerical value with the coefficient of diffusion fluctuation that records again _AllTo be worth and can try to achieve i ion free coefficient of diffusion and apparent (total) coefficient of diffusion in concrete in the substitution formula (2,3), the coefficient of diffusion bright concrete permeability resistance of novel more is good more, in the formula (1,2,3): D _iCoefficient of diffusion (the cm of-concrete intermediate ion i ²/ s); R-gas law constant 8.314 J/molK; T-absolute temperature (K); Z _i-ion combination valency; F-Faraday constant 96500 coul/mol; The DC voltage that V-applies (V); I-is corresponding to the balanced balanced current (A) of executing voltage; 1-concrete sample thickness (cm); S-electrode area (cm ²); C _iI ion concentration (mol/cm in the-salt solusion ³); f ₁, f ₂-correction factor.