Method for determining concrete grade as to freeze resistance

FIELD: test equipment.

SUBSTANCE: method relates to test methods of porous water-saturated bodies. It provides for production of a series of concrete specimens, saturation of specimens with water, measurement of specimens, determination of their initial volume, their frosting/defrosting to specified temperatures and recording of deformation. In addition, long-term strength limit of each specimen is determined by a non-destructive method under tension conditions. After defrosting, relative residual deformation of specimens is determined and energy dissipated in unit volume of each specimen is determined during its frosting/defrosting. Then, they are loaded under conditions of uniaxial compression to an extreme load meeting short-term strength limit; energy dissipated in unit volume of the specimen is determined during its compression to an extreme load, and as per the obtained results, grade is calculated as per freeze resistance of each specimen. Grade of concrete as to freeze resistance is determined as an arithmetic mean for grades of specimens.

EFFECT: increasing flexibility, reducing labour intensity and enlarging the number of hardware.

1 tbl

 

The invention relates to methods of testing water-saturated porous bodies and is intended to determine the grade on frost resistance of concrete, i.e. the number of standard cycles of freezing-thawing (for example, from +20 to -20°C for 4 hours) needed to reduce the tensile strength of the samples saturated with water by an amount specified by the standard, in particular for 5 or 15%, i.e. a relative reduction of tensile strength ΔR/R=0,05 0,15..., where R is the short-term tensile strength, ΔR is the absolute change in short-term tensile strength.

Known basic method for determination of frost resistance [GOST - 10060.1-95 Basic method for the determination of frost resistance"], including fabrication and testing of samples of the series. Saturate all samples of water, some of the specimens subjected to alternately repeated freezing and thawing. Destroy compression samples after different numbers of freeze-thawing and without freeze-thawing. Compare the average values of the tensile strengths of the samples of series tested as freeze-thawing, and without it. Determine the relative decrease of tensile strength under different numbers of freeze-thawing and as the mark on frost resistance of concrete accept the number of freeze-thawing needed to reduce the tensile strength in the limits, the agreed standard.

Significant random variation of tensile strength of concrete (coefficient of variation ρ=15...20%) at constant conditions of manufacture and testing of samples leads to a large scatter of the average values of tensile strength and requires a large amount of trials (the number of test samples 25...50) for evidence of the relative reduction of the tensile strength ΔR/R=0,05 0,15...in the freezing-thawing, where R is the short-term tensile strength, ΔR is the absolute change in short-term tensile strength. Thus, the main disadvantage of the basic ways - complexity and low efficiency.

Closest to the proposed method [GOST - 10060.3-95 "Dilatometric method for the rapid determination of frost resistance"]. It includes the manufacture of concrete samples, the measurement of samples, determination of the initial volume, the saturation of the samples with water, simultaneous freezing of each water-saturated sample and the standard sample in the dilatometer to standard temperature and measuring the difference of the values of the volumetric deformation of the concrete and standard samples (relative volume changes). Mark on frost resistance of concrete is determined by the maximum relative difference of the volumetric deformation of the concrete and standard samples is listed in the standard tables depending on the type of concrete, the shape and size of samples.

However, when you use the Guest tables, an acceptable result is obtained only for concrete Portland cement and slag Portland cement without surface-active additives (surfactants), such concrete is now used very rarely. And getting tables required for concretes with surfactants, requires a long time-consuming experiments using, for example, the first basic method.

The objective of the invention is the expansion of the Arsenal of methods for rapid determination of the brand on frost resistance of concrete.

The solution reached by the fact that, as in the prototype, made a series of samples from the same concrete mixture, the sample is saturated with water, measure samples frozen to the standard temperature. But unlike prototype: preliminary non-destructive method to determine the long-term strength of each sample in terms of stretching; the samples are thawed and establish the relative residual deformation of each sample; the values of the relative residual deformation of the sample and long-term strength of the sample in terms of stretching determine the energy scattered per unit volume of the sample in the process of freezing-thawing; load each sample under conditions of uniaxial compression to extreme loads that meet the short-term limit so the spine; when this register value of the axial load and the corresponding longitudinal deformation of each sample; on the obtained values of the axial load and the corresponding longitudinal deformations determine the energy scattered per unit volume of the sample during compression to extreme loads, find the value of the brand of each concrete sample frost as the magnitude is proportional to the ratio of the energy dissipated in the compression process to extreme loads, the energy dissipated in the process of freezing-thawing. Mark on frost resistance of concrete is defined as the average value found brands of concrete samples frost.

The determination of the relative residual deformation of the sample and long-term strength of the sample, which begins the irreversible development of cracks in the concrete sample, allows us to estimate scattered in these processes the energy per unit volume of material in the process of freezing-thawing by the formula:

where WSCthe energy dissipated in a unit volume of the sample in the process of freezing-thawing;

θOST- relative residual deformation of the sample;

RDL- long-term strength of the sample in terms of stretching;

k - coefficient of proportionality.

p> k=1, because the development of water-filled cracks in concrete leads to the occupation of a nearby closed pores, stabilizing the pressure of the water inside the cracks around the value that causes the material tensile stress equal to the long-term strength of the sample in terms of stretching

Loading of the specimen in uniaxial compression to extreme loads, check the values of the axial load and the corresponding absolute longitudinal deformations allow numerical integration according to the axial load from the absolute longitudinal strains and the distribution of the last volume of the sample to find the value of the energy dissipated per unit volume of the sample during compression to extreme loads, i.e., before the passing of the concrete from damage, dispersed throughout the volume of the sample, the fragmentation of the main crack. The value of the energy dissipated per unit volume of the sample during compression to extreme loads, in proportion to the square of the short-term tensile strength [Overdiv I. N. Basic physics of concrete. - M, Stroiizdat, 1981, 464 S.; see S. 425 and the formula 11.16]:

where WSGthe energy dissipated in a unit volume of the sample during compression to extreme loads;

R short - time limit strongly the tee;

α is the coefficient of proportionality.

After taking the logarithm of the expression (2) and subsequent differentiation of the obtained dependence between relative reduction in the energy dissipated per unit volume of the sample during compression to extreme loads, and the relative decrease in short-term tensile strength:

where WSGthe energy dissipated in a unit volume of the sample during compression to extreme loads;

ΔW is the absolute change of the energy dissipated per unit volume of the sample;

R - short-term tensile strength;

ΔR is the absolute change in short-term tensile strength.

Equation (3) allows you to go from tolerable standard of the relative decline in short-term tensile strength for concrete valid for a test sample relative to reducing the energy dissipated per unit volume of the sample:

where WSGthe energy dissipated in a unit volume of the sample during compression to extreme loads;

[ΔW] is a valid absolute change in energy dissipated per unit volume of the sample;

R - short-term tensile strength;

ΔR is the absolute change in short-term tensile strength;

[ΔR/R] - tolerable standard the relative change to adobrinova strength.

This brand of concrete sample for frost resistance will be determined as the number of freeze-thawing, each of which requires an energy dissipated in a unit volume of the sample in the process of freezing-thawing, within the allowable absolute change of the energy dissipated per unit volume of the sample:

where Farr- brand concrete sample frost;

[ΔW] is a valid absolute change in energy dissipated per unit volume of the sample;

WSCthe energy dissipated in a unit volume of the sample in the process of freezing-thawing.

The method is implemented as follows. From the concrete mixture of the desired composition of the produced samples in the form of cylinders or cubes with an edge of 10 cm After curing under conditions close to the conditions of curing of concrete samples saturated with water, Oberau and for each sample non-destructive method, such as [rapid assessment methods for durability/materials of III MK "Popular concrete Sciences", February-March 2009, St. PETERSBURG: SPGU]* define in terms of stretching the largest non-destructive load Labout, without exceeding which the cracks in the sample have not yet developed. Tensile stresses in cylinders or cubes, it is advisable to create their grip on the lines of contact of the cylinder with the plane (rusk is ywaniem). Knowing Laboutyou can calculate the long-term strength for the tested sample:

where S is the cross-sectional area of the sample perpendicular to the plane of compression;

Labout- most non-destructive load the sample in terms of stretching;

RDL- long-term strength of the sample in terms of stretch.

After it is frozen and thawed sample to the standard temperature, determine the relative residual deformation of the sample and find the energy scattered per unit volume of the sample in the process of freezing-thawing by the formula (1):

WSC=kθOST·RDL,

where WSCthe energy dissipated in a unit volume of the sample in the process of freezing-thawing;

θOST- relative residual deformation of the sample;

RDL- long-term strength of the sample in terms of stretching;

k - coefficient of proportionality.

Next, the sample is compressed in the uniaxial compression to extreme loads, i.e. up until the load begins to fall, and record the current values of the axial load and the corresponding values of the longitudinal deformation of the sample. Numerical integration according to the axial load from the absolute longitudinal strains and the distribution of the last volume is brazza allows you to find the energy scattered in a unit volume of material before reaching the extreme loads. According to the obtained results count mark frost for a specific sample:

where Farr- brand concrete sample frost;

WSCthe energy dissipated in a unit volume of the sample in the process of freezing-thawing;

WSGthe energy dissipated in a unit volume of the sample during compression to extreme loads;

R - short-term tensile strength;

ΔR is the absolute change in short-term tensile strength;

[ΔR/R] - admissible relative change in short-term tensile strength.

Mark on frost resistance of concrete is found as the average of the values of stamps on frost resistance for samples. Confidence interval marks on frost resistance of concrete is calculated by the dispersion of the values of stamps frost for a series of samples.

In particular, the method is implemented on 10 samples-cubes, edge 10 cm at the age of 88 days, made of concrete mixture of such composition: Portland cement 400-1 weight part, the sand - 2 weight parts, crushed granite 5...20 mm to 4.5 weight parts of water and 0.6 weight part. It was established experimentally in two different ways for this concrete at the age of 88 days after 105 freeze-R is storageware, the relevant stamp this on frost resistance of concrete, the average relative reduction in tensile strength is 0,142 according to the method of [civil Engineering journal, 2008, No. 2, pp. 40-44, St. PETERSBURG: SPBSPU] and 0.16 for the first basic method [GOST - 10060.1-95. Basic method for the determination of frost resistance"], that is, both values lie within the error of the used methods. The average relative reduction in tensile strength is 15%.

The samples were saturated with water under item 4 GOST 10060.0-95. "Methods for the determination of frost resistance. General requirements", omarali and record the volume. For each water-saturated cube-splitting on p. 5.4 GOST 10180-90. "Methods for determining the strength of the control samples (scheme II, app.9) was determined three times the maximum non-destructive load, without exceeding which the cracks in the sample have not yet developed irreversible. After each test changed plane compression of the sample perpendicular to the plane of the preceding compression. The definition of the greatest non-destructive load was performed using the acoustic emission method (AE)* using AE-complex AF-15 Kishinevskogo plant. Acoustic sensors with a frequency of 20-200 kHz was installed on the edge of the sample, parallel to the plane of compression. To create axial load used hydraulic press. Getting the value of the highest ner is prosaude load, hoped the corresponding value of long-term strength, and then the average value of the long-term strength shown in the table.

Water-saturated samples were placed in a measuring chamber of the differential volumetric dilatometer DOD-100-K, while the second camera was placed standard aluminum sample. Both chambers were filled with kerosene and have sealed. The dilatometer samples were placed in the freezer and after 30 min exposure started freezing with a speed of 0.3°C/min until a temperature (20±2)°C. On the basis of the index difference of the volumetric strain of concrete and aluminum sample were the value of the relative residual volumetric strain of the concrete sample and was calculated for each sample the energy scattered in the process of freezing-thawing by the formula (1):

where WSCthe energy dissipated in a unit volume of the sample in the process of freezing-thawing;

θOST- relative residual deformation of the sample;

RDL- long-term strength of the sample in terms of stretching;

k - coefficient of proportionality.

It was further determined the average value of the long-term strength of the sample in terms of stretchingRthe dlas the arithmetical mean of the values of RDLthe limits of long-term strength under conditions of strain.

Axial compression of the samples at the rate of 400 kg/sec was carried out on a hydraulic press equipped with a plotter according to the axial load from the longitudinal deformation. Values on the dynamometer are determined by the position of the slave and master gunner, which is part of a closed electronic circuit with indicator light. Smooth unloading of the sample started at the signal, the pilot lights, turn off the electrical contacts on the slave and master arrow of the dynamometer, as at the beginning of the destruction of the sample leading arrow opens with the guest that stays in the same position. The maximum load registers slave hand dynamometer press. Received on the plotter according to determined the area under it, i.e., the received energy scattered in the sample during compression to extreme loads. The energy scattered per unit sample, obtained by the formula (8):

where W is the energy dissipated in the sample volume during compression to extreme loads;

V - volume of sample;

WSGthe energy dissipated in a unit volume of the sample during its compressed what I'm up to extreme loads.

Then for each sample was calculated (see table) mark concrete sample frost F15ias the number of freeze-thawing needed to reduce its tensile strength by 15% by the formula (7):

where F15i- brand concrete sample frost;

WSCthe energy dissipated in a unit volume of the sample in the process of freezing-thawing;

WSGthe energy dissipated in a unit volume of the sample during compression to extreme loads;

R - short-term tensile strength;

ΔR is the absolute change in short-term tensile strength;

[ΔR/R] - admissible relative change in short-term tensile strength.

Next expected averageF15for values of the brand F15iand standard deviation of results:

where S is the standard deviation of the results of experience;

F15i- mark i-th concrete sample frost is at the lower limit of its strength by 15%, obtained by the proposed method; where i is from 1 to 10;

F- brand on frost resistance of concrete equal to the arithmetical mean value of the marks of a series of concrete samples at the lower limit of their strength by 15%.

The standard deviation of the values of F15iwas equal to 16. With this in mind, the difference of the average values of the brand on frost resistance of concreteF15=99,7previously experimentally found the number of cycles 105 (mark F15) needed to reduce R by 15%, can be considered random, and the proposed method is correct.

Table
The number of the i-th sampleThe average value of the long-term strength of the sample in terms of stretchingRdl, MPaRelative residual deformation of the sample θOST·104The energy dissipated in a unit volume of the sample in the process of freezing-thawing Wt is ·104, MPaThe energy dissipated in a unit volume of the sample during compression to extreme loads WSG·10, MPaValid absolute change in energy dissipated per unit volume of the sample [ΔW]·102,MPaThe number of cycles required to reduce the tensile strength of each sample by 15% F15i
11,52,74,050,99902,99774
21,73,15,271,72155,16598
31,81,83,241,23123,694114
41,92,64,901,67965,039102
52,0 2,55,001,43334,30086
62,11,94,001,43644,309108
72,22,65,722,23086,692117
82,32,1a 4.831,38464,15486
92,91,85,221,60084,80292
103,11,54,651,86000,558120
Average2,152,14,69 1,557799,7

Thus it is shown that the proposed method expands the Arsenal of technical means rapid determination of the brand on frost resistance of concrete. The duration of the determination of frost resistance is determined, essentially, by the time of saturation of the sample with water (4 days on p. 4 GOST 10060.0. "Methods for the determination of frost resistance. General requirements").

The method of grade determination on frost resistance of concrete, including the manufacture of a series of concrete samples, the saturation of the water samples, the measurement of samples, determination of the initial volume, the suspension up to the standard temperature, wherein the pre-determined long-term strength of each sample non-destructively in terms of stretching, and after thawing determine the relative residual deformation of the sample and the energy scattered per unit volume of each sample in the process of freezing-thawing, then load the specimens in uniaxial compression to extreme loads that meet short-term tensile strength, determine the energy scattered per unit volume of each sample during compression to extreme loads, and the results I expect mark frost resistance of each sample as the magnitude proportional is optional to the ratio of the energy scattered per unit volume of the sample during compression to extreme loads, the energy dissipated per unit volume of the sample in the process of freezing-thawing, and mark on frost resistance of concrete is defined as the average of the grades of frost-series samples.



 

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20 ex

FIELD: technologies for testing properties of materials.

SUBSTANCE: in method for determining compositions of friable systems of condensed-expanded type in fractions with core sizes D1>D2>D3>D4>D5 when D2/D1,…,D5/D4 greater than 0.155 volumes of fractions VD1, VD2, VD3, VD4 having core sizes D1, D2, D3, D4 respectively, m3, are determined, as well as core material denseness, average core size, value of emptiness VeD1 of fraction with core size D1, condensation grade coefficients Y1, Y2, Y3, of fraction with core size D1 by fraction with core size D2, mixture of condensed type on basis of fraction (D1+D2) with average sizes of cores Dav.sm2 by fraction with core size D3, mixture of condensed type on basis of fractions (D1+D2+D3) with average core size Dav.sm3 by fraction with core size D4 respectively, fractions with large core sizes are used for receiving mixtures of condensed type, condensed type mixtures volumes Vsm2, Vsm3, Vsm4,are determined on basis of fractions (D1+D2), (D1+D2+D3) and (D1+D2+D3+D4) respectively, m3, emptiness value Vemp2, Vemp3, of condensed type mixtures on basis of fraction (D1+D2) and (D1+D2+D3) respectively, separation of cores in condensed type mixture is performed by fractions with lesser core sizes, separation coefficient α1, α2, α3, value is determined, for mixture cores on basis of fractions (D1+D2) with core sizes D3, mixture cores on basis of fractions (D1+D2+D3) with core sizes D4, mixture cores on basis of fractions (D1+D2+D3+D4) with core sizes D5, respectively, and compositions of friable condensed-expanded type are determined from formulae in following order: composition of condensed type binary mixture on basis of fractions (D1+D2) from formulae m3, m3m3, Y1=1-D2/D1, 1 m3 of said condensed type binary mixture Vem2=VD1+VD2=1m3 for preparation of ternary condensed-expanded type mixture, composition of which is determined from formulae composition of ternary condensed type mixture is determined on basis of fractions (D1+D2+D3) from formulae 1 m3 of said ternary condensed type mixture is used for preparation of quaternary mixture of condensed-expanded type, composition of which is determined from formulae composition of quaternary condensed type mixture is determined on basis of fractions (D1+D2+D3+D4) from formulae Ysm3=1 m3, 1 m3 of quaternary condensed type mixture is used for preparation of quinary condensed-expanded type mixture, composition of which is determined from formulae

EFFECT: higher efficiency.

6 ex

FIELD: technologies for testing properties of materials.

SUBSTANCE: in method for determining compositions of bi-senary friable filled-separated type systems in fractions with core sizes d1>d2>…>d6 when d2/d1,…,d6/d5 less than 0.155 volumetric mass and denseness of core material is determined as well as emptiness value, empty spaces fill grade coefficient, volumetric separation coefficient, and fraction volumes are determined from formulae for binary systems V1=1 m31, m3,

V2=V11·Ve1 + α 1-1), m3, Y1=1-d2/d1, α 1=(1+d2/d1)3, Ve1=1-γ 11, for ternary systems V1=1 m31, m3, V2=V1((Y· Ve11-1)/α 2), m3, V3=V2(Y· Ve22-1), m3, y1=1-d2/d1,y2=1-d3/d2, α 1=1-d2/d1, α 2 =(1+(d2 + 2· d3)/d2)3, Ve1=1- γ 1/ρ 1 Ve2=1-γ 22, for quaternary systems V1=1m31, m3, V2=V1((Y1Ve11-1)/α 2), m3, V3 =V2((Y1Ve22-1)/α 3), m3, V4=V3(Y3 Ve33-1), m3, у1=1-d2/d1, y2=1-d3/d2, y3=1-d3/d3, α 1=(1+(d2+2· d3+4· d4)/d1)3, α 2=(1+(d3+2d4)/d2)3, α 3=(1+d4/d3)3, Ve1=1-γ 11,Ve2=1-γ 22, Ve3=1-γ 33, for quinary systems V1=1m31, m3, V2=V1((Y1Ve11,-1)/α 2), m3, V3=V2((Y2Ve22-1)/ α 3), mз, V4=V3((Y3Ye33-1)/α 4), m3, V5=V4(V4Ve44-l), m3, У1=1-d2/d1, y2=1-d3/d2, y3=1-d4/d3, y4=1-d5/d4, α 1=(1+(d2+2· d3+4· d4+8· d5)/d1)3, α 2=(1+(d3+· 2· d4+4· d5)/d2)3, α 3=(1+(d4+2· d5)/d3)3, α 4=(1+d5/d4)3, Ve1=1-γ l1, Ve2=1-γ 22, Ve3=1-γ 33, Ve4=1-γ 44, for senary friable systems V1=1 m31, m3, V2=V1((Y1Ve11-1)/α 2), m3,V3 =V2((Y2Ye22-1)/α 3), m3, Y4=Y3((Y3Ye33-1)/ α 4), m3, V5=V4((Y4Ve44-1)/α 5), m3, V6=V5(Y5Ve55-1), m3, Y1=1-d2/d1, Y2=1-d3/d2, Y3=1-d4/d3, Y4=1-d5/d4, Y5=1-d6/d5, α 1=(1+(d2+2· d3+4· d4+8· d5)/d1)3, α 2=(1+(d3+2· d4+4· d5)/d2)3, α 3=(1+(d4+2· d5)/d3)3, α 4=(1+d5/d4)3, α 5=(1+(d6/d5)3, Ve1=1-γ 11, Ve2=1-γ 22, Ve3=1-γ 33, Ve4=1-γ 44, Ve5=1-γ 55, where V1, V2, V3, V4, V5, V6 - volumes of fractions with cores sizes, respectively, d1, d2, d3, d4, d5, d6, m3; Y1, Y2, Y3, Y4, Y5 - coefficients for large core size fractions' empty spaces fill grade with fractions having lesser core sizes, dimensionless quantities; 0<Y<1; α1, α2, α3, α4, α5 - volumetric separation coefficients for fractions with large core sizes by all fractions with lesser core sizes, dimensionless quantities, in binary systems 1<α<8; Ve1, Ve2, Ve3, Ve4, Ve5 - values of fractions emptiness with core sizes, respectively, d1, d2, d3, d4, d5, dimensionless quantities (relation of emptiness' volume to fraction volume), ρ1, ρ2, ρ3, ρ4, ρ5 - denseness of cores material, kg/m3, γ1, γ2, γ3, γ4, γ5 - volumetric share of cores material, kg/m3.

EFFECT: higher efficiency, broader range of functional capabilities.

8 ex

FIELD: technologies for testing properties of materials.

SUBSTANCE: in method for determining compositions of friable condensed-filled-separated type systems in fractions with sizes of cores D1>D2>…>Dn-1>Dn when D2/D1, D3D2,…,Dn/Dn-1 greater than 0.155, d1>d2>…>dn-1>dn when d2/d1, d3/d2,…,dn/dn-1 less than 0.155, where Dn>d1, cores material denseness is determined, as well as volumetric mass, emptiness value and average fraction cores size, compaction level value is calculated, composition of mixture of condensed type is determined on basis of fractions with core sizes D, emptiness value and average cores size of said mixture, value of grade of filling of empty spaces of mixture with fractions with core sizes d is calculated, value of separation level of condensed mixture by fractions with core sizes d is calculated, and compositions of friable systems of condensed-filled-separate type are determined from formulae in following order: , m3, where Vmx - volume of mixture of condensed type on basis of fractions with core sizes D, m3; α - coefficient for condensed type mixture separation by fractions with core sizes d; Vd - volume of fraction with sizes of cores d, m3; Y - level of filling of empty spaces of compacted type by cores of fractions with sizes d, limits of value measurement being 0<Y≤1; Vemp - condensed type mixture emptiness value - relation of empty spaces volume to mixture volume, Dav.mx2 - average size of cores in a mixture.

EFFECT: higher precision, lower laboriousness.

4 ex

FIELD: nondestructive testing.

SUBSTANCE: method comprises drilling hole in concrete, securing anchor device inside the hole, and pulling out the anchor with applying destroying force. The strength of concreter is determined form the formula , where N is the destroying force, D is the diameter of the specimen, m, and d is the diameter of the hole, m.

EFFECT: enhanced accuracy of determining.

1 dwg, 1 ex

FIELD: construction.

SUBSTANCE: method comprises securing anchor device connected with the instrument in the concrete, applying breaking load, and determining the strength form the breaking load. The concrete is provided with hole and ring groove coaxial to the hole. The depth of the groove is equal to the height of the specimen. The anchor device is then secured in the hole and breaking force is applied by pressing the anchor device until the specimen is spalled. The strength is determined from the formula where N is the breaking load, in N, h is the height of the specimen, in m, D is the diameter of the specimen, in m, and d is the diameter of the hole.

EFFECT: decreased labor consumption.

1 dwg, 1 ex

FIELD: building, particularly to perform nondestructive testing of structure concrete strength.

SUBSTANCE: method involves drilling bore-hole in concrete body; cutting annular groove in concrete body coaxial to bore-hole; arranging metal cylindrical ferrule in annular groove, wherein cylindrical ferrule has dimension comparable with that of sample; securing anchoring head in bore-hole and pressing anchoring head into concrete body up to sample destruction. Concrete strength is determined from the following formula: R = (N·10-6)/2πdh, where R is concrete strength, MPa, N - destructive force, H, h is sample height, m.

EFFECT: possibility to determine physical and mechanical concrete characteristics directly in structure body.

1 dwg

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