Method to determine limit tensile strength of cement plastering compounds

FIELD: measurement equipment.

SUBSTANCE: invention relates to the field of tests of cement plastering compounds for tensile strength under static loading. Substance: the value of the limit tensile strength is defined by testing steel beams with applied plastering compound according to the scheme of the double-point bend with smooth loading by small steps and fixation of the loading step corresponding to the moment of cracking, and the value of the limit tensile strength is calculated using the formula.

EFFECT: simplified technology for testing, exclusion of the necessity to apply strain metering facilities, higher accuracy of detection of limit tensile strength and completion of tests on plaster layers with specifically small thickness from several mm to 2-3 cm.

1 tbl, 1 dwg

 

The invention relates to the field of testing cement plaster structures by the maximum elongation under static loading.

An important indicator for the façade plasters is the ability to perceive developing in them shrink and thermomechanical stress without cracking. The cracking of the plaster provides the aesthetic appearance of the facade and limits the ingress of moisture under the plaster, which can cause delamination of plaster layer and affect the durability of the wall.

There is a method of determining the conditional deformation of cement concrete εult(The crack resistance of concrete / Vol, Reitmanova. - M.: Energy, 1972. - P.57-59), in which this feature is calculated as the ratio of the strength of the samples tensile obtained by splitting cube or cylinder Rruskfor the dynamic modulus of elasticity EDeandetermined on samples of concrete of the same composition physical methods. Conditional maximum elongation εultdetermine from the relation εult=Rrusk/EDean.

The disadvantages of this method are the following: this method is indirect; each of the characteristics is determined with errors. In addition, when determining deformation by measuring the resistance at restiani the cleaving and dynamic modulus of elasticity tensile strength splitting R ruskusually 10-15% higher than the tensile strength Rpdetermined by direct testing of samples-eights of material on the axial extension, and dynamic modulus of elasticity higher than the static modulus of elasticity of about 20-25%. This leads to the fact that the thus obtained strain is actually more limiting elongation εultnot less than 15-20%.

Closest to the proposed a direct method for determining a deformation of concrete under tension on samples-eights (Crack resistance of concrete / Vol, Reitmanova. - M.: Energy, 1972. - P.55-56). In this method for determining definatively on samples-eights are bonded devices measure deformation (strain-gauge resistance, mechanical strain gauges), and the samples are tested for tensile strength. Based devices is the so-called zero method of measuring resistance wire sensors to ensure high accuracy of the readings. Such devices include devices series HADES-1M, AI-1, MS-3 and other

The disadvantage of this method is the difficulty of synchronizing data measuring deformation and breaking load, the following voltage.

In both the above methods are implemented test specimens of plaster composition sizes other than the real thickness of the plaster layer.

Object of the invention is the simplification of testing, eliminating the need for application of strain gauges, improving the accuracy of the determination of the maximum tensile and testing on the layers of plaster with a characteristically small in thickness from a few mm to 2-3 cm

The problem is solved in that in the method of determination of the maximum elongation of the cement plaster compounds, including testing of samples of material plaster composition tensile, according to the invention the minimum elongation shall be determined by testing samples of steel beams coated with a plaster composition according to the scheme of the two-point bending with a smooth loading of small steps and a fixation step of loading corresponding to the point of cracking, and the maximum elongation are calculated according to the formula:

where εultSh.R.the ultimate elongation of a plaster solution; P is the applied load is equal to two concentrated forces P/2, kN; and the distance from the support of balocchi to the point of application of concentrated force P/2, cm; Es- the modulus of elasticity of steel, 2·105MPa; b - width steel balocchi, cm; h - height of balocchi, see

By providing uniform loading cement plaster layer dostigaet the homogeneous stress state in the cross section of the specimen due to its alignment with the loading. Thus, technological simplicity in testing and improving the accuracy of determining the magnitude of the limiting stretch.

The method is performed by the following sequence of operations: prepare pre-peeled (to improve adhesion) sample in the form of a steel fatless balocchi from soft carbon steel, the lower surface of which is applied a plaster layer of constant thickness. Next, the sample is incubated under normal conditions (temperature (20±2)°C and relative humidity (90±5)%) required time. After a period of storage under normal conditions balochku placed in natural conditions (temperature (20±2)°C, humidity (55±5)%) for 24 h to remove excess moisture. Next balochku mounted on support media with a mechanical system loading, and test the circuit point-to-point bending with a smooth loading of small steps. The magnitude of the steps taken small increase of the load relative to the maximum allowable, based on the yield strength of the steel sample. After application the next step of loading the plaster layer view (if necessary with the help of a magnifying glass) on the possibility of crack formation at this stage of loading. During the test, record the amount of steps corresponding to the moment of crack formation. The loading is performed in which the limits of 0.8 to 0.9 of the load level, corresponding to the yield strength of the steel balocchi. The ultimate elongation shall be determined based on strain compatibility conditions steel and plaster layer, assuming the absence of influence of a layer on the stress-strain state of the steel balocchi. The accuracy of the method is estimated by the deformation corresponding to1/2it increments one step prior to cracking. The maximum possible error in strain Δε respectively1/2stage load. Varying degrees increment of load, it is possible to obtain the required accuracy.

The drawing shows a diagram of the testing circuit point-to-point bending with a smooth loading of small steps.

In relation to the loading scheme of the two-point bending steel balocchi cross-section b×h, length (span) l bending moment in the pure bending zone will be

where P is the applied load is equal to two concentrated forces P/2, kN; and the distance from the fulcrum to the point of application of concentrated force P/2, cm; M is the bending moment, kN·cm;

where b is the width of the steel balocchi, cm; h - height of balocchi, cm; Wsthe moment resistance of the cross-section balocchi, cm3.

Normal stress in the extreme extended hair is not balocchi

when σsthe maximum allowable voltage is made relatively low yield strength steel σy10-20%, MPa.

From the compatibility conditions of deformation in the assumption that there is no influence of a layer on the stress-strain state of the steel balocchi get

where Es- the modulus of elasticity of steel, Es=2·105MPa; εsthe ultimate elongation of the steel balocchi; εultSh.R.the ultimate elongation of the plaster equal to

The proposed method can be used when estimating the limit of elasticity solutions and research on optimizing the composition of plasters to improve their fracture toughness.

Examples of implementation of the method

The proposed method for the determination of the maximum elongation of the plaster composition is substantiated by the experimental results.

Laboratory studies were carried out for different plaster compositions: Baumit StartContact, Baumit Artoplast, Fast OK Insulation, cement-sand mortar. The proposed method of preparing pre-peeled fat-free steel balocchi (steel grade S230) of size 7×10×200 mm, on the bottom surface which cause the thing is Horny layer of constant thickness. Further, these samples incubated under normal conditions (temperature (20±2)°C and relative humidity (90±5)%) required number of days. After a period of storage under normal conditions of balocchi placed in natural conditions (temperature (20±2)°C, humidity (55±5)%) for a day to remove excess moisture, and then install them on the support of the press with a mechanical system loading (mechanical press with a capacity of 5kN P-8), and test the circuit point-to-point bending with a smooth loading of small steps. Testing for compliance conducted at the age of 14 and 28 days.

The table shows the technique of the experiment and the results of the test beams coated with a plaster composition according to the scheme of the two-point bending on the ultimate elongation (see Annex).

The method of determination of the maximum elongation of the cement plaster compounds, including testing of samples of material plaster composition tensile, characterized in that the minimum elongation shall be determined by testing of steel beams coated with a plaster composition according to the scheme of the two-point bending with a smooth loading of small steps and a fixation step of loading corresponding to the point of cracking, and the maximum elongation calculated by the formula:

wherethe ultimate elongation of a plaster solution; P is the applied load is equal to two concentrated forces P/2, kN; and the distance from the support of balocchi to the point of application of concentrated force P/2, cm; Es- the modulus of elasticity of steel, 2·105MPa; b - width steel balocchi, cm; h - height of balocchi, see



 

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FIELD: technological processes.

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FIELD: technologies for testing properties of materials.

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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.

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EFFECT: enhanced accuracy of determining.

1 dwg, 1 ex

FIELD: construction.

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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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