CN113049791A - Plastic shrinkage cracking and reducing method for cement mortar - Google Patents
Plastic shrinkage cracking and reducing method for cement mortar Download PDFInfo
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- 239000004033 plastic Substances 0.000 title claims abstract description 77
- 238000005336 cracking Methods 0.000 title claims abstract description 62
- 239000011083 cement mortar Substances 0.000 title claims abstract description 58
- 238000000034 method Methods 0.000 title claims abstract description 29
- 230000001603 reducing effect Effects 0.000 title claims abstract description 26
- 239000004570 mortar (masonry) Substances 0.000 claims abstract description 53
- 239000004568 cement Substances 0.000 claims abstract description 48
- 239000000835 fiber Substances 0.000 claims abstract description 23
- 230000008020 evaporation Effects 0.000 claims abstract description 19
- 238000001704 evaporation Methods 0.000 claims abstract description 19
- 230000018044 dehydration Effects 0.000 claims abstract description 8
- 238000006297 dehydration reaction Methods 0.000 claims abstract description 8
- 238000011160 research Methods 0.000 claims abstract description 8
- 238000005259 measurement Methods 0.000 claims abstract description 4
- 230000002195 synergetic effect Effects 0.000 claims abstract 2
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 26
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims description 22
- 239000002023 wood Substances 0.000 claims description 15
- 229910052742 iron Inorganic materials 0.000 claims description 11
- 238000012360 testing method Methods 0.000 claims description 10
- 238000006073 displacement reaction Methods 0.000 claims description 9
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 claims description 8
- 230000005540 biological transmission Effects 0.000 claims description 8
- 239000010949 copper Substances 0.000 claims description 7
- 229910052802 copper Inorganic materials 0.000 claims description 7
- 239000002985 plastic film Substances 0.000 claims description 7
- 229920006255 plastic film Polymers 0.000 claims description 7
- 235000014121 butter Nutrition 0.000 claims description 3
- 239000011248 coating agent Substances 0.000 claims description 3
- 238000000576 coating method Methods 0.000 claims description 3
- 238000004026 adhesive bonding Methods 0.000 claims description 2
- 230000015271 coagulation Effects 0.000 claims description 2
- 238000005345 coagulation Methods 0.000 claims description 2
- 230000003111 delayed effect Effects 0.000 claims description 2
- 238000011049 filling Methods 0.000 claims description 2
- 238000004519 manufacturing process Methods 0.000 claims description 2
- 239000002002 slurry Substances 0.000 claims description 2
- 238000010276 construction Methods 0.000 claims 1
- 239000000463 material Substances 0.000 abstract description 27
- 239000002657 fibrous material Substances 0.000 abstract description 2
- 239000002344 surface layer Substances 0.000 description 4
- 238000002156 mixing Methods 0.000 description 3
- 239000002131 composite material Substances 0.000 description 2
- 238000007796 conventional method Methods 0.000 description 2
- 239000007788 liquid Substances 0.000 description 2
- 239000000203 mixture Substances 0.000 description 2
- QQONPFPTGQHPMA-UHFFFAOYSA-N propylene Natural products CC=C QQONPFPTGQHPMA-UHFFFAOYSA-N 0.000 description 2
- 125000004805 propylene group Chemical group [H]C([H])([H])C([H])([*:1])C([H])([H])[*:2] 0.000 description 2
- 239000004576 sand Substances 0.000 description 2
- 239000000758 substrate Substances 0.000 description 2
- 238000010998 test method Methods 0.000 description 2
- 241000537371 Fraxinus caroliniana Species 0.000 description 1
- 235000010891 Ptelea trifoliata Nutrition 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 239000004566 building material Substances 0.000 description 1
- 239000003795 chemical substances by application Substances 0.000 description 1
- 230000000052 comparative effect Effects 0.000 description 1
- 230000007797 corrosion Effects 0.000 description 1
- 238000005260 corrosion Methods 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 230000007613 environmental effect Effects 0.000 description 1
- 238000002474 experimental method Methods 0.000 description 1
- 239000010410 layer Substances 0.000 description 1
- 238000003756 stirring Methods 0.000 description 1
- 238000003786 synthesis reaction Methods 0.000 description 1
- 238000012546 transfer Methods 0.000 description 1
- 238000005303 weighing Methods 0.000 description 1
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- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
- G01N33/38—Concrete; Lime; Mortar; Gypsum; Bricks; Ceramics; Glass
- G01N33/383—Concrete or cement
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B11/00—Measuring arrangements characterised by the use of optical techniques
- G01B11/02—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness
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Abstract
The invention relates to a plastic shrinkage cracking and crack reducing method for cement mortar. Belongs to the technical field of material science and engineering discipline. At a dehydration evaporation rate of 0.01 kg/(m)2·h)‑0.734kg/(m2H) measuring the restraint degree, the capillary shrinkage stress and the plastic tensile strength of the cement mortar, and then calculating the crack resistance index K of the cement mortar; the crack resistance index K obtained by measurement can be more than or equal to 1 by adjusting the constraint degree, the water-cement ratio and the ash collection ratio of the cement mortar; research results prove that under the condition of not doping fibers, the plastic shrinkage cracking of the cement mortar can be reduced or the cracking can be eliminated through the synergistic and consistent action of 3 parameters of the water-cement ratio, the ash collection ratio and the degree of constraint of the cement mortar. The invention can greatly reduce the plastic shrinkage cracking of the mortar, even reach the cracking-free degree, and is simple and economic compared with the crack resistance of the added fiber material.
Description
Technical Field
The invention relates to a plastic shrinkage cracking and crack reducing method for cement mortar. Can be used for reducing the plastic shrinkage cracking degree of cement mortar, and belongs to the technical field of material science and engineering discipline.
Background
The cement-based material has large demand and wide application, and is an essential component in the engineering of buildings, roads, bridges and the like. However, cement-based materials have the inevitable defect of easy shrinkage cracking due to their own reasons, and the shrinkage cracking has a great influence on the corrosion resistance, impermeability and service life of the cement-based materials, so that many researchers have conducted extensive research on the problem.
In view of this, the inventor has collected at 1 st stage 3/2000 pp48-52 "in the journal of building materialsThe propylene fiber cement-based composite material plastic shrinkage cracking mechanism is provided in the research (I) on the physical and mechanical properties of the propylene fiber cement-based composite material, namely the plastic shrinkage cracking resistance: after the cement-based material is cast and molded, due to the hydrophilicity of water and the cement-based material, a concave liquid surface is formed in a capillary tube of the surface layer material during water evaporation, the vertical component of the surface tension on the concave liquid surface forms the tensile stress of the material between tube walls, at the moment, the material is in a plastic stage, the plastic tensile strength of the material is lower, and if the tensile stress sigma generated by the dehydration shrinkage of the capillary tube on the surface layer of the material is lowercGreater than the plastic tensile strength f of the materialpI.e. sigmac>fpCracking of the surface layer of the material occurs, otherwise, if proper measures are taken to make sigma appearc≤fpThe cracking condition of the surface layer of the material is reduced or even disappears. Furthermore, the inventor also discloses a water loss evaporation rate test method in a plastic stage and a unitary constitutive equation of cement mortar without fiber in the early warning mechanism of plastic shrinkage cracking of cement mortar in the period 6 of 12 months in 2019 and pp839-845 in the building materials report, and designs and establishes capillary shrinkage stress sigmacMethod for testing plastic tensile strengthpThe two are combined to construct the plastic shrinkage cracking resistance index K ═ f of the cement-based materialp/σcThe following criteria are available:
cracking with K < 1
K is more than or equal to 1 and does not crack
The inventor carries out intensive research on shrinkage cracking of cement-based materials according to the technical path, and finds that the crack resistance index is reduced (and is less than 1) and the cracking condition is increased along with the increase of the dehydration evaporation rate (see the 2, 1.3 plastic stage dehydration evaporation rate test method and the 2.1.1 unary constitutive equation of fiber-free cement mortar in the article for details).
The inventors found that when the rate of water loss was further increased to 0.6 kg/(m)2H) the cracking is more severe, when the measured crack resistance index K is only about 0.58, when the conventional method of reducing the cracking of the doped fibers is adopted: mixing PVA fiber with high strength and high elastic modulus (tensile strength about 1600MPa, elastic modulus about 42GPa), fiber length of 18mm and fiber mixing amount of 1.5kg/m3The mortar is still openAnd the measured K value is about 0.69, although the value is larger than that of the fiber-free fiber, the value is still less than 1, and the mechanism and the criterion are met. In this case, if the fiber length is further increased, the fiber is easily bent, the effective length of the fiber in contact with the substrate is reduced, and the adhesion between the fiber and the substrate is reduced; if the fiber mixing amount is further increased, the fluidity of cement mortar is reduced, and the physical and mechanical properties of the cement mortar are affected. Thus, the problem of mortar plastic shrinkage cracking at the moment can not be solved by the traditional fiber-doped cracking reduction method.
The inventor considers the plastic shrinkage cracking of the cement-based material, and finds that factors influencing the plastic cracking of the cement-based material, such as the environmental dehydration evaporation rate and the material components, can be greatly related to the shrinkage restriction condition of the cement-based material. Therefore, a constraint degree measuring method is designed by self, and the research on the constraint degree (namely the constraint degree) suffered by the cement-based material during water loss shrinkage is developed.
Definition of degree of constraint:
the constraint degree is an index for measuring the constrained size in cement mortar, and the size is calculated by the formula (1):
method for measuring plastic shrinkage:
the testing method of the plastic shrinkage rate mainly adopts a self-built device for measurement, the testing device is formed by improving the sigma c measuring device, namely the sigma c measuring device is called as quasi-free shrinkage mortar without a connecting rod, the main device is called as constraint mortar with the connecting rod, the main device is the same as the testing device of the plastic shrinkage stress, the upper and lower layers of mortar are formed, then target blocks are placed in the long edge direction of a mould on the surface of the mortar, the distance between the two target blocks is about 335mm and is equal to the distance in the short edge direction of the mould, finally, the distance of the target blocks moving along with the shrinkage of the mortar is measured by a laser displacement sensor (adopting an LTC-025-04 laser displacement sensor) after the target blocks, the sum of the shrinkage distances of the target blocks at two ends, namely the total shrinkage distance of the mortar in a constrained state is recorded as delta l, and the plastic shrinkage rate is calculated:
and (3) measuring the degree of constraint:
the size of the mortar restraint degree is adjusted by the diameters of different connecting rods (common iron wires are adopted with the diameter of 0.6mm or more, and copper wires with different strands are adopted for synthesis with the diameter of less than 0.6 mm), and the corresponding relation between the restraint degree and the diameter of the connecting rods is determined through a large number of experiments, as shown in table 1:
TABLE 1 relationship table of constraint degree with diameter variation of connecting rod
On the basis, the inventor carries out a great deal of thinking and research, finds that the plastic shrinkage cracking of the cement-based material is not only greatly related to the dehydration evaporation rate, but also related to the composition (mainly water-cement ratio and ash collection ratio in terms of mortar) of the material and the degree of constraint of the material, finds out the combination of the influence factors of small water-cement ratio, large ash collection ratio and small constraint degree under the condition of not adding fibers through a great deal of experimental research, can effectively eliminate the problem of the plastic cracking of the mortar which cannot be solved by the traditional fiber adding cracking reducing method, and obtains the excellent effect of eliminating the plastic shrinkage cracking.
Disclosure of Invention
The invention aims to disclose a plastic shrinkage cracking and crack reducing method for cement mortar.
The plastic shrinkage cracking and crack reducing method for cement mortar provided by the invention comprises the following steps:
at a dehydration evaporation rate of 0.01 kg/(m)2·h)-0.734kg/(m2H), water cement ratio of 0.35-0.55, cement collection ratio of 0.67-1.5, and degree of constraint of 0.24-0.82, and under the condition of not adding fiber, adopting parameter combination of low water cement ratio, high cement collection ratio and low degree of constraint to make cement mortar (adopting cement P.O.42.5, medium sand and running water)The mixture ratio is cement: sand: water 1: 1: 0.5) and measuring by using the conventional method for measuring the crack resistance index K, wherein the crack resistance index K can be increased to be more than 1 from less than 1, and the plastic shrinkage cracking state is changed to be a non-cracking state, so that the aim of eliminating the plastic shrinkage cracking of the mortar is fulfilled.
The application method of the plastic shrinkage cracking and crack reducing method of the cement mortar comprises the following steps:
the water cement ratio in the plastic shrinkage cracking and crack reducing method of cement mortar of the invention is smaller in the range of 0.35-0.55.
Secondly, the cement mortar plastic shrinkage cracking and crack reducing method of the invention uses a larger value for the cement-collecting ratio within the range of 0.67-1.5.
Thirdly, the restriction degree in the method for reducing plastic shrinkage cracking of cement mortar is smaller in the range of 0.24-0.82.
And fourthly, the 3 parameters can be combined by taking any value.
Weighing, stirring, transporting, pouring, plastering and the like according to the parameters by a common method for preparing the mortar, and measuring the crack resistance index K of the mortar by the method for measuring the crack resistance index K; and judging whether the mortar is cracked or not by taking K more than or equal to 1 as non-cracked and K less than 1 as cracked.
The invention can be widely used for mortar engineering of cement mortar wall surfaces, floors, roofs and the like to improve the performance of the cement mortar material such as plastic shrinkage cracking resistance and the like.
The invention has the following advantages:
1. by adopting the cracking reducing method, the plastic shrinkage cracking of the mortar can be greatly reduced, even the cracking can not be caused.
2. By adopting the crack reducing method, fiber crack reducing materials are not needed, and the plastic crack reducing cost can be greatly reduced.
3. The crack reducing method is convenient and simple to use and operate, for example, the water-cement ratio and the ash collection ratio in the mortar proportion are simply calculated, the constraint from the periphery of the mortar can be reduced by coating butter, an isolating agent and the like, and compared with crack resistance by adding a fiber material, the crack reducing method is simple and economical.
Drawings
FIG. 1 is a schematic view showing the structure of an apparatus for measuring a plastic shrinkage ratio in a quasi-free state according to the present invention.
FIG. 2 is a schematic side view of the apparatus for measuring the plastic shrinkage in a quasi-free state according to the present invention.
FIG. 3 is a schematic view showing the structure of an apparatus for measuring the plastic shrinkage rate in a constrained state according to the present invention.
FIG. 4 is a schematic side view of the apparatus for measuring plastic shrinkage in a constrained state according to the present invention.
In fig. 1, 2, 3 and 4:
the device comprises a wood mould 1, a laser displacement sensor 2, cement mortar 3, a fixed column 4, a cushion block 5, a support frame 6, a target block 7, a support bottom plate 8, a spring dynamometer 9, a plastic film 10, retarded mortar 11, a frame-shaped force transmission device 12 and a connecting rod 13.
Detailed Description
The degree of constraint is first determined.
The constraint degree of the cement mortar is an index for measuring the constrained size in the cement mortar and is calculated by the following formula (1):
the plastic shrinkage in the quasi-free state was determined (see fig. 1, 2) as follows:
adopting the existing testing device for plastic shrinkage stress, manufacturing cement mortar according to the water cement ratio of 0.35-0.55 and the ash collection ratio of 0.67-1.5, pouring part of the cement mortar into a wood mould 1 with a plastic film 10 at the bottom to form delayed coagulation slurry 11, then covering the plastic film 10, then filling the rest of the cement mortar into the wood mould 1 to form mortar 3, arranging two support frames 6 at equal intervals between two long sides of the wood mould 1, placing a target block 7 on the surface of the mortar 3 along the long side direction of the wood mould 1, wherein the distance between the two target blocks is 335mm and is equal to the distance in the short side direction of the wood mould 1, then arranging a laser displacement sensor 2 behind the target block 7, measuring the distance of the target block 7 moving along with the shrinkage of the mortar 3 by using the laser displacement sensor 2, and recording the sum of the shrinkage distances of the two target blocks 7 as the total distance of plastic shrinkage under a quasi-free state as delta l, the plastic shrinkage in the quasi-free state is calculated according to the formula (2):
determination of plastic shrinkage in constrained state (see fig. 3, 4):
embedding two symmetrical frame-shaped force transmission devices 12 into mortar 3, wherein one frame-shaped force transmission device 12 is connected with a fixed column 4 through a connecting rod 13, and the fixed column 4 is fixedly connected with a supporting bottom plate 8 at one side of a wood mold 1 of the testing device for the plastic shrinkage stress through a cushion block 5; the other frame-shaped force transmission device 12 is connected with a spring dynamometer 9 through a connecting rod 13, and the spring dynamometer 9 is fixedly connected with a supporting bottom plate 8 at the other side of the wood mould 1 of the testing device of the plastic shrinkage stress through a cushion block 5; similarly, the distance of the target block 7 moving along with the shrinkage of the mortar is measured by using a laser displacement sensor, the sum of the shrinkage distances of the two target blocks, namely the total shrinkage distance of the cement mortar in a constrained state is recorded as delta l, and the plastic shrinkage rate in the constrained state is calculated according to the following formula (2):
the frame-shaped force transfer device 12 is a wire cage (500 mm x 40mm x 18mm in size) made of 3mm diameter wire.
The connecting rod 13 is made of 0.6mm-3mm common iron wires or 3-5 strands of copper wires with the diameter of 0.1-0.6 through gluing.
The cement-mortar ash collection ratio is 0.67-1.5.
The water cement ratio of the cement mortar is 0.35-0.55.
The degree of constraint is 0.24-0.82.
The reduction of the restraint degree can be realized by adopting connecting rods with different diameters, or by coating butter or other separant on the periphery of cement mortar, or paving a plastic film.
Reference mortar (used as reference for comparison in the following examples):
the standard mortar is adopted for proportioning, namely the water-cement ratio is 0.5, the ash collection ratio is 1, iron wires with the diameter of 3mm are adopted as connecting rods for constraint, and the water loss evaporation rate is about 0.60 kg/(m)2H) a cracking index K of about 0.58 (less than 1) is measured, and the mortar undergoes plastic shrinkage cracking.
Reference mortar doped with fibers (this is taken as another comparative reference for the inventive crack reduction method below):
the reference mortar proportion is adopted, namely the water cement ratio is 0.5, the ash collection ratio is 1, the PVA fiber is added, the fiber length is 18mm, and the fiber adding amount is 1.5kg/m3The iron wire with the diameter of 3mm is adopted as a connecting rod for constraint, and the water loss evaporation rate is about 0.60 kg/(m)2H) a cracking index K of about 0.69 (less than 1) is measured, and the mortar undergoes plastic shrinkage cracking.
Example 1
Adjusting the water-cement ratio of the mortar to 0.35, keeping the cement collecting ratio at 1, and constraining by using iron wires with the diameter of 3mm as connecting rods, wherein the water loss evaporation rate is about 0.60 kg/(m)2H), the measured crack resistance index K is about 1.3 (greater than 1), and the mortar does not have plastic shrinkage cracking.
Example 2
The mortar proportion is adjusted to a cement-collecting ratio, the water-cement ratio is still 0.5, the cement-collecting ratio is adjusted to 1.5, iron wires with the diameter of 3mm are used as connecting rods for constraint, and the water loss evaporation rate is about 0.33 kg/(m)2H), the measured crack resistance index K is about 3.0 (greater than 1), and the mortar does not show plastic shrinkage cracking.
Example 3
The reference mortar is adopted for proportioning, namely the water cement ratio is 0.5, the ash collection ratio is 1, a copper wire with the diameter of 4 multiplied by phi 0.1mm is adopted as a connecting rod for constraint, and the water loss evaporation rate is about 0.60kg/(m2H), the measured crack resistance index K is about 1.03 (greater than 1), and the mortar does not show plastic shrinkage cracking.
Example 4
The mortar proportion is subjected to ash collection ratio and constraint degree adjustment, the water-ash ratio is still 0.5, the ash collection ratio is adjusted to 1.5, copper wires with the diameter of 4 x phi 0.1mm are used as connecting rods for constraint, and the water loss evaporation rate is about 0.60kg/(m2H), the measured crack resistance index K is about 1.17 (greater than 1), and the mortar does not show plastic shrinkage cracking.
Example 5
Adjusting the water-cement ratio and the ash collection ratio of the mortar, namely adjusting the water-cement ratio to be 0.35 and the ash collection ratio to be 1.5, and adopting an iron wire with the diameter of 3mm as a connecting rod for constraint, wherein the water loss evaporation rate is about 0.60kg/(m & lt/m & gt)2H), the measured crack resistance index K is about 1.5 (greater than 1), and the mortar does not have plastic shrinkage cracking.
Example 6
Adjusting the water-cement ratio and the constraint degree of the mortar, wherein the water-cement ratio is adjusted to be 0.35, the cement collection ratio is still 1, copper wires with the diameter of 4 x phi 0.1mm are used as connecting rods for constraint, and the water loss evaporation rate is about 0.60kg/(m2H), the measured crack resistance index K is about 2.3 (greater than 1), and the mortar does not have plastic shrinkage cracking.
Example 7
Adjusting the water-cement ratio, the ash collection ratio and the degree of constraint of the mortar, wherein the water-cement ratio is adjusted to be 0.35, the ash collection ratio is adjusted to be 1.5, copper wires with the diameter of 4 x phi 0.1mm are used as connecting rods for constraint, and the water loss evaporation rate is about 0.60kg/(m2H), the measured crack resistance index K is about 2.65 (greater than 1), and the mortar does not have plastic shrinkage cracking.
Example 8
Adjusting the water-cement ratio, the ash collection ratio and the degree of constraint of the mortar, wherein the water-cement ratio is adjusted to be 0.35, the ash collection ratio is adjusted to be 1.5, copper wires with the diameter of 4 x phi 0.1mm are used as connecting rods for constraint, and the water loss evaporation rate is about 0.33kg/(m2H), the measured crack resistance index K is about 11.5 (greater than 1), and the mortar does not have plastic shrinkage cracking.
Claims (6)
1. A plastic shrinkage cracking and crack reducing method for cement mortar is characterized in that:
first, at a dehydration evaporation rate of 0.01 kg/(m)2·h)-0.734kg/(m2H) measuring the restraint degree, the capillary shrinkage stress and the plastic tensile strength of the cement mortar in the environment of h), and then calculating the crack resistance index K of the cement mortar; then, the water-cement ratio, the ash collection ratio and the restraint degree of the cement mortar are adjusted, so that the crack resistance index K of the cement mortar obtained by measurement is more than or equal to 1; research results prove that under the condition of not doping fibers, the plastic shrinkage cracking of the cement mortar is reduced or the aim of eliminating cracking is fulfilled by the synergistic and consistent action of 3 parameters of the water-cement ratio, the ash collection ratio and the degree of constraint of the cement mortar, and the cement mortar can be directly applied to engineering construction;
the constraint degree meeting the crack reducing effect of the cement mortar is 0.24-0.82; the water-cement ratio is 0.35-0.55; the ash collection ratio is 0.67-1.5.
2. The plastic shrinkage cracking and crack reducing method for cement mortar as claimed in claim 1, which is characterized in that: the constraint degree of the cement mortar is an index for measuring the constrained size in the cement mortar and is calculated by the following formula:
the plastic shrinkage in the quasi-free state is determined as follows:
adopting the existing testing device for plastic shrinkage stress, manufacturing cement mortar according to the water cement ratio of 0.35-0.55 and the ash collection ratio of 0.67-1.5, pouring part of the cement mortar into a wood mould (1) with a plastic film (10) at the bottom to form delayed coagulation slurry (11), then covering the plastic film (10), then filling the rest of the cement mortar into the wood mould (1) to form mortar (3), arranging two support frames (6) between two long sides of the wood mould (1) at equal intervals, placing a target block (7) on the surface of the mortar (3) along the long side direction of the wood mould (1), wherein the distance between the two target blocks is 335mm and is equal to the distance between the two short sides of the wood mould (1), then arranging a laser displacement sensor (2) behind the target block (7), and measuring the distance of the target block (7) moving along with the shrinkage of the mortar (3) by the laser displacement sensor (2), the sum of the shrinkage distances of the two target blocks (7) is the total plastic shrinkage distance in the quasi-free state, and is recorded as delta l, and the plastic shrinkage rate in the quasi-free state is calculated according to the following formula:
measurement of plastic shrinkage in restrained state:
embedding two symmetrical frame-shaped force transmission devices (12) into mortar (3), wherein one frame-shaped force transmission device (12) is connected with a fixed column (4) through a connecting rod (13), and the fixed column (4) is fixedly connected with a supporting bottom plate (8) on one side of a wood mold (1) of the testing device for the plastic shrinkage stress through a cushion block (5); the other frame-shaped force transmission device (12) is connected with a spring dynamometer (9) through a connecting rod (13), and the spring dynamometer (9) is fixedly connected with a supporting bottom plate (8) at the other side of the wood mould (1) of the testing device of the plastic shrinkage stress through a cushion block (5); similarly, measuring the distance of the target block (7) moving along with the shrinkage of the mortar by using a laser displacement sensor, recording the sum of the shrinkage distances of the two target blocks, namely the total shrinkage distance of the cement mortar in a constrained state as delta l, and calculating the plastic shrinkage rate in the constrained state according to the following formula:
the frame-shaped force transmission device 12 is an iron wire cage made of iron wires with the diameter of 3mm, and the size of the iron wire cage is 500mm multiplied by 40mm multiplied by 18 mm;
the connecting rod (13) is made of common iron wires with the diameter of 0.6mm-3mm or is formed by gluing 3-5 strands of copper wires with the diameter of 0.1-0.6.
3. The plastic shrinkage cracking and crack reducing method for cement mortar as claimed in claim 1, which is characterized in that: the cement-mortar collection ratio is 1-1.5.
4. The plastic shrinkage cracking and crack reducing method for cement mortar as claimed in claim 1, which is characterized in that: the water cement ratio of the cement mortar is 0.35-0.5.
5. The plastic shrinkage cracking and crack reducing method for cement mortar as claimed in claim 1, which is characterized in that: the degree of constraint is 0.31-0.82.
6. The plastic shrinkage cracking and crack reducing method for cement mortar as claimed in claim 1, which is characterized in that: the reduction of the restraint degree can be realized by adopting connecting rods with different diameters, or by coating butter or other separant on the periphery of cement mortar, or paving a plastic film.
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN114594239A (en) * | 2022-03-08 | 2022-06-07 | 信阳职业技术学院 | Cement-based material shrinkage stress detection device |
| CN116148452A (en) * | 2023-04-20 | 2023-05-23 | 山东高速明董公路有限公司 | Cement stabilized macadam volume shrinkage measuring device |
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| CN116148452A (en) * | 2023-04-20 | 2023-05-23 | 山东高速明董公路有限公司 | Cement stabilized macadam volume shrinkage measuring device |
| CN116148452B (en) * | 2023-04-20 | 2023-07-07 | 山东高速明董公路有限公司 | Cement stabilized macadam volume shrinkage measuring device |
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