Prediction of concrete final actual strength

FIELD: instrumentation.

SUBSTANCE: invention relates to prediction of final actual physical strength of concrete. This method comprises conductimetric measurement of specific electric resistance and temperature of mortars in their hardening in real time and evaluation of actual mechanical compression strength of preset type of concretes. The following process parameters are controlled: start of motor hardening and concrete specimen strength at 28-day age. Duration of measurements makes 100-125 min from mortar filling into container pickup till termination of hardening induction period. In said range parallel measurements of specific electric resistances of mortar specimens are performed for calibration and design minimum compositions. Correlation dependence between specific electric resistance and actual mechanical strength of concrete of preset type at design age is set. Results of analysis of variation in specific electric resistance in said range are used for control over of early hardening of said motor of preset concrete type to evaluate actual mechanical compression resistance of concrete.

EFFECT: higher quality of evaluation.

5 dwg, 6 tbl


The invention relates to methods of assessing the development status of cement-concrete mixtures in the process of curing and hardening in real time and predict the final actual concrete strength.

In the modern monolithic construction and wide application of precast concrete and concrete structures of buildings and structures non-destructive testing the ultimate strength of cement-concrete systems is one of the most important conditions for improving the quality of products based on mineral binders, as well as the intensification of their production for energy and resource saving technologies.

Methods of nondestructive testing of concrete systems, including the use for measurement of electrical quantities converted to direct evidence, defined in GOST 27005-86. These methods apply only for the control of products and structures made of concrete, under construction and durability, these methods are time-consuming (not earlier set of samples of examinees 28-day strength) and quite time consuming, which does not allow them to apply for quick adjustment of technological processes of casting.

From the description of the patent RU №1742702 A1, 24.07.1989 for "Device for measuring the potential of mass transfer material" known electrophysical method of controlling the solid�" binders using Akhmetzhanova sensor. In this method, produce a conductivity measurement the conductivity of the samples binders in liquid state, which can be downloaded in an electrolytic cell. In the process of measurement records the time of hardening and mass transfer potentials of the base and examined samples of Portland cement in a given time interval, but the resulting indicators of hardening in the first two hours of measurements is insufficient to predict the ultimate strength of concrete, because this method does not propose the establishment of a correlation between strength of concrete and the values of mass transfer.

In its technical essence and the achieved result is the closest analogue is the prototype of the present invention is a method of control of technological parameters and predict the final actual concrete strength, including conductometric measurement of electrical resistivity and temperature during the curing of the samples of concrete mixes in real time with the subsequent evaluation of the actual mechanical compressive strength of concrete samples of a given class (US No. 7225682 B2, 05.06.2007).

The known method, as proposed, based on the choice for measurements of electrical resistivity as an electro-physical quantity. In known�om method the interval of real time, which produce the necessary measurements is not less than 50 hours, i.e. more than one day. This circumstance given the fact that each cement concrete composition has its own special properties, defined by the set of process parameters (type of cement, concrete mixture, the conditions of transport), does not allow to create objective method of accelerated evaluation of process parameters and the actual ultimate compressive strength of samples of concrete of a given grade and structural concrete products.

The object of the invention is a rapid prediction of the actual ultimate strength of the concrete, the possibility of rapid adjustment of the technological process of casting, and prerequisites for the reduction of energy costs and material resources.

This problem is solved in that in the method of predicting final actual concrete strength, including conductometric measurement of electrical resistivity and temperature during the curing of the samples of concrete mixes in real time with the subsequent evaluation of the actual mechanical compressive strength of concrete samples of a given class, produce a parallel measurement of the specific electrical resistances of the samples of concrete mixtures calibration and calculation �ratings of compositions and establish the correlation between electrical resistivity and the actual mechanical strength of concrete of a given class in its design and age and the results of analysis of changes in electrical resistivity of the specimen concrete mix specified composition of a given class of concrete in a time interval equal to 100-125 minutes after pouring in the sensor container type specimens of both concrete mixes, provide control of early hardening of the samples of the concrete mix specified concrete grade and end-actual mechanical strength of concrete in compression.

The invention consists in the following.

As you know, the hardening of binders, in particular cement, included in the composition of concrete mixtures, during their interaction with water is based on the unique phenomenon of conversion of the starting material is hydrated in tumors of different composition. This dramatically increases the amount of the solid phase compared with the original volume of the binder (A. V. Volzhensky. Changes in absolute volumes of the phases in the interaction of inorganic binders with water and their influence on the properties of the formed structures. // Building materials, 1989, No. 8, p. 25). Hydration, i.e. the interaction of particles of the original substance with water, consists of physico-chemical dispersion (the actual chemical reaction of formation) hydrates complicated for polymineral binders real conditions of the processes, due to the mutual influence of mineral�in and phenomena of adsorption, diffusion, etc. and create patterns with defined physico-chemical properties.

The mechanism of hardening (hardening) of mineral binding materials and concretes - a series of successive stages-transitions of a system from one structural state to another.

The first stage of the hydration process is characterized by short exothermic reaction. The duration of this stage depends on the type of binder and includes several elementary acts (N. B. Ur'ev. Highly concentrated dispersed systems, M. ed. Chemistry, 1980, p. 320), which occur on the active sites of the surface of the original binder. The concentration and nature of active sites determine the intensity of the initial interaction of the binder with water (M. M. Sychev, Some questions chemistry interparticle condensation hardening cements. // Cement, 1982, No. 8, pp. 7-9).

The second stage of the hydrate formation induction period is characterized by the formation of capillary-porous colloidal body; in cement-concrete compositions of this period is determined by the development of the processes of setting and which is characterized by low rate of interaction of the binder with water (J. D. Birchall, A. J. Howard, Double D. D. Some general considerations of membrane/osmosis model for portland cement hydration // Cement and Concrete Research, 1980, V. 10, p.145-155). The duration of induction period from the start of mixing of the concrete mix before it is completed�message is usually from a half to two hours and it has the important practical significance because it allows the formation of products based on cement-concrete systems (Midgley H. G., Illstong M. Some comments on the micro structure of hardened cement pastes.// Cement and Concrete Research, 1983, v.13, No. 2, p.197-206).

Next after the induction period is the stage of acceleration of hydrate formation and the early stage of deceleration (the transition period) (S. I. Kontorovich and others Intergrowth of particles in supersaturated solutions during chemical modification of their surface // Hydration and hardening binding agents, Lviv, 1981, p. 60). At this stage forms a colloidal-crystal structure - quasi-solid capillary-porous body; this stage is characterized by the aging of the cement gel and development of crystallization hardening. Here mass formation of hydrates leads to the decrease of the reaction rate, which is limited by the diffusion of water molecules to the surface of the binder (Collepardi M. Low-slump-loss superhlasticized concrete. // Transp. Res. Rec, 1979, No. 720, p.7-12).

Final stage of hardening mechanism is the formation of capillary-porous structures - solid capillary-porous body whose status is determined by the laws of solid-phase interactions between the particles/aggregates of particles and intense growth of safety (L. B. Svatovo, etc. Dielectric measurements in the early stages of hardening of monomineral binders. // Russian journal of applied chemistry, 1973, vol. 46, No. 6, pp. 1219-1223, and takeem.M. Sychev. The role of electronic effects in the hardening of cements. // Cement, 1984, No. 7, pp. 10-13).

Data analysis of experimental measurements made on the basis of the same sample of concrete/mortar in the time interval 100-125 min, the corresponding end of the induction period of hardening of the concrete mix, confirms that the specified time interval is the most informative for the construction of kinetic curves "Strength - Time" and "Electric resistance - Time" on which to build the desired correlation between the electrical resistance of concrete mixture in two hours after pouring the concrete mix into the container sensor and the strength of concrete of a given class on the 28th day.

The method is as follows.

Research methodology structural hardening Portland cement concretes (hereinafter - the concretes) full range of classes from V7. 5 to B80 on the ability to predict their actual ultimate strength according to the claimed invention is the same, so the description of the implementation of the method is demonstrated on two examples - the choice of a concrete class B40 and class B15, as the most common in construction.

To study the solidification of heavy concrete class B40 were taken Portland cement M 500 TO Maltsov, Novorossiysk and Volsk cement plants, and for �of etona class B15 - Portland cement M 400 TO the Voskresensk cement plant and other components - sand, gravel, chemical additives and water, which was prepared concrete mix class B40 on the cements of different plants (table 1) and the composition of concrete mixtures at the Voskresensk cement plant (table 2). In tables 3 and 4 show respectively the performance of the concrete strength classes B40 and B15 in the interval of nine hours - 28 days".

The method allows for the prediction (estimation) final actual strength concretes (S) at the age of 28 days based on the results of measurements of electrical resistivity (ℜ) WES in the early stage of curing of concrete in the induction period of hydrate formation (in the period from a half to two hours).

The prediction of strength is based on using the correlation S(τ)=ψ1(ℜ) (here S(τ) are the predicted values of strength in the desired age: τ=2, 3, 7, 14 and 28 days, ℜ* - base value WES).

Monitoring (assessment and development status of cement-concrete mixtures in the process of hardening a non-destructive method according to GOST R 53231-2008 in real time was used a device measuring parameters of cement-concrete mixtures ConTest-8, certified and listed in the State registry of measuring instruments, Registration No. 45346-10.

Measuring parameters (meter�traveler system) consists of multi-channel measuring unit, personal computer and container sensors to measure the electrical resistance of the material being tested.

In the personal computer of a measuring system incorporated a set of managers and manufacturing programme "Monitor". For the normal functioning of the meter was used, the operating system is Windows XP and the update tool NetFrame software update, which is the mandatory support of the program "Monitor". And if necessary the required elements of the software can be downloaded from Microsoft UpdateCenter (

The principle of operation of the meter is in continuous conductivity measurement method of the electrical resistance of the sample placed in the container sensor.

To obtain the dependence between the electrical resistance of the samples and their mechanical strength in accordance with GOST standard 22690-88 simultaneously with the filling of the container the sensor of the studied cement-concrete mixture control samples are manufactured according to GOST 10180-90. Further, the process of hardening of the samples and control samples is in the same terms.

In the recommended time standards are measured strength of the control specimens, and the measurement results are used to determine the calibration relationship between the electrical resistance�the pressure and strength of concrete, used for monitoring and forecasting the strength of the studied concrete.

In practice, the full range of concrete classes from v3. 5 to B80 correlation S(τ)=ψ1(ℜ) is defined on the results of the calibration tests specified compositions are usually concrete the basic range of classes V7,5-B40 design strength (normalized concrete strength at age of 28 days according to GOST 27006-86) taken from a statistically reliable number of batches of concrete, which are the most popular for jbk enterprises - manufacturers of concrete mixes using cement of the same brand.

To build correlation "Strength - WES" based on the same sample of concrete was experimentally establish the variation of the strength S and the electrical resistance ℜ, i.e. get the basic of kinetic curves S*=ƒ(τ) and ℜ*=φ(τ). The curve in the same moments of time τ (τ1, τ2...τndetermine the values of S and ℜ and build the required calibration curve S*(τ)=ψ (ℜ*).

For each concrete test batch to determine the value of ℜ* by sequentially measuring the resistance in a fixed moment of time τ from the start of curing of concrete in the induction period and after completion of the processes of setting - even at the stage of crystallizationsupernova, for example, at the age of 20 hours after the beginning of the hardening process of concrete hardening and at the same fixed time points in parallel for each test batch of concrete in the laboratory of the factory standard method to determine the strength of concrete S11),...Sn(τn)in a timely τ1...τn.

The obtained calibration compositions of concrete mixes based on cement from different manufacturers allow us to obtain statistical sets of values of electrical resistance ℜ* and accordingly the values of concrete strength that gives you the ability to graphically display coordinates "Strength (MPa) Time (h)" - "electrical resistivity (Ω·m)* - (h)". Next, the base rate ℜ* correlated with corresponding values of concrete strength S(τ) and receive correlation S(τ)=φ (ℜ*) in the form of a quadratic equation.

On the established correlation forecasting the strength measurement is carried out (ℜ) WES in the sample test batches of concrete at the age of 20 hours on the basis of cement of the same brand of cement from other suppliers with subsequent extrapolation of the obtained

Fig. 1-5 presents test data in the form of diagrams, curves which represent correlations between the electrical resistance of concrete mixture �through two hours after pouring into a container sensor and the strength of the concrete class B40 on the 28th day cements from different manufacturers, including concrete class B15.

Fig. 1 shows the correlation for the concrete mix at the Maltsov cement, Fig. 2 and 3, correlations for concrete mixes respectively at Novorossiysk and Volsky cements, Fig. 4 - consolidated graphic displays correlations for concrete class B40 in Fig. 5 - correlation for concrete class B15 resurrection on the cement.

During the execution of a series of experiments was a close correlation between the values of electrical resistance of concrete mixture in two hours after loading of the container sensor and the strength of the concrete class B40 28 days for example Maltsov cement (Fig. 1) and concrete strength class B15 on the 28th day example of Voskresensk cement cement (Fig. 5).

To describe the experimental data (increasing and decreasing in absolute value) was chosen polynomial trend line (polynomial of second degree). Close to unity, the value of reliability of approximation (>or = 0.97) indicates a good match curve with the experimental data; measuring the electrical resistance of concrete mixture in two hours after pouring the concrete mix into the container sensor, shown on the schedule or formula it is possible to estimate the ultimate strength of concrete.

This process can be simplified, using methods� standard deviations (C. O.). The method is based on determining a standard deviation (measure of dispersion in statistics, STDev) in technical analysis (V. P. Borovikov. Statistica-Statistical analysis and data processing in the Windows environment", Publishing house "Filin", St. Petersburg, 1997, 608 S.).

In particular, having a set of statistical values of electrical resistance of concrete mixture, on the one hand, and the set of values of ultimate concrete strength, on the other hand, with this analysis it is possible to establish communication between groups of measurements and to estimate the change of one parameter in a certain range depending on the change of another parameter in the appropriate range (for example concrete class B40 at the Maltsov cement (table 5) or for concrete class B15 on the resurrection cement (table 6).

The received data is easily used for practical evaluation of the predicted concrete strength by the values of electrical resistance as follows. When the gross valuation (Av+2STDev) for concrete class B40 in the range of resistivity of 50 Ω·m - 69 Ohm·m values of concrete strength will be in the range of 49.5 MPa to 56 MPa, and for concrete class B15 in the range of resistances 65-88 Ohm·m projected strength will be in the range of 20-28 MPa.

Thus, by measuring the electrical resistance of concrete mixture in two hours after pouring it into contact�enemy sensor, you can estimate the value of concrete strength at 28 days. A more accurate value of strength for a concrete class B40 can be calculated by the formula in Fig. 1, and for concrete class B15 - according to the formula in Fig. 5. The error of determination of concrete strength in this case (with standard deviation) does not exceed 3.5%.

It should be borne in mind that the final strength of concrete is determined according to the standard 28 days with a coefficient of variation (i.e., the error) equal to 13%. This means that based on the above the error is often inevitable overrun of cement, whereas the implementation of the present invention reduces the error by almost four times, thereby saving both material resources and energy consumption in concrete technology.

A method of predicting final actual concrete strength, including conductometric measurement of electrical resistivity and temperature during the curing of the samples of concrete mixes in real time with the subsequent evaluation of the actual mechanical compressive strength of concrete samples of a given class, Otley�audica, produce a parallel measurement of the specific electrical resistances of the samples of concrete mixtures calibration and calculation of the nominal compounds and establish the correlation between electrical resistivity and the actual mechanical strength of concrete of a given class in its design age and the results of analysis of changes in electrical resistivity of the specimen concrete mix specified composition of a given class of concrete in a time interval equal to 100-125 minutes after pouring in the sensor container type specimens of both concrete mixes, provide control of early hardening of the samples of the concrete mix specified concrete grade and end-actual mechanical strength of concrete in compression.


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3 dwg, 3 tbl

FIELD: servicing steel underground pipe lines; diagnosis of corrosion on pipe lines.

SUBSTANCE: pipe line under test is divided into sections and pit is made at boundaries; then electrical resistance is measured in section and at edge zones of these sections (in pits) by four-electrode scheme. Measured at edge zones are also thickness of pipe wall and its outer diameter. Specific resistance of pipe metal is calculated by these measurements. Electrical resistance of sections is calculated on basis of specific resistance and measured and specified magnitude are compared. Deviation of measured magnitude from specified ones is indicative of corrosion damage on these sections. Current and potential electrodes are located at distance no less than two diameters of pipe for enhancing measurement accuracy.

EFFECT: enhanced accuracy of measurement.

2 cl