CN102183626B - Method for predicting plastic shrinkage cracking of cement mortar material - Google Patents
Method for predicting plastic shrinkage cracking of cement mortar material Download PDFInfo
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- CN102183626B CN102183626B CN 201110052018 CN201110052018A CN102183626B CN 102183626 B CN102183626 B CN 102183626B CN 201110052018 CN201110052018 CN 201110052018 CN 201110052018 A CN201110052018 A CN 201110052018A CN 102183626 B CN102183626 B CN 102183626B
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Abstract
The invention relates to a method for predicting plastic shrinkage cracking of a cement mortar material. The method comprises the following step of: substituting four cement-based material composition parameters comprising water cement ratio (Wc), cement sand ratio (Cs), fiber content (Fc) and fiber length (F1), water evaporation speed (Er) and demixing degree (Dd) and restraint degree (Rd) of the cement-based material into the following formula: K = 13.8822 - 14.0949Wc - 2.8247Cs + 0.5293Fc + 0.0022F1 - 17.0650Er + 0.2582Dd + 0.9436Rd, wherein the K is anti-cracking index. When the K value is more than 1.41, the cement-based material test piece is not cracked; when the K value is less than 0.99, the test piece is cracked; and when the K value is between 0.99 and 1.41, the test piece is cracked in certain probability. A multiplex constitutive equation of plastic shrinkage cracking of the mortar is constructed by using the parameters with great influence on the cement-based plastic shrinkage cracking, the tendency of early plastic shrinkage cracking of the cement-based material can be accurately predicted, and the method can be widely applied to early prediction of the plastic shrinkage cracking of the mortar.
Description
Technical field
The present invention relates to a kind of cement-based material plastic shrinkage cracking method.The early stage qualitative forecasting that can be used for plastic shrinkage cracking of cement mortar material trend.Belong to the Materials Science and Engineering ambit.
Technical background
Cement concrete is that consumption is maximum in the world, one of most popular building materials.Because cement concrete has applied widely, low price, easily moulding by casting is more durable, can effectively utilize some using industrial solid wastes to make the advantages such as energy saving and environment friendly building materials, will be the irreplaceable main building materials of China's modern construction within 21st century.
But undeniable, cement concrete exist from great, tensile strength is low, ultimate tensile strength is little, impact strength is poor, be easy to the shortcoming such as plasticity dehydration shrinkage cracking.When concrete is in free state, concrete causes because of certain reason what adverse consequences contraction can not cause, but in fact xoncrete structure is owing to the restrained condition that is in various degree that pins down of basis, reinforcing bar or inner adjacent part, concrete shrinkage can cause tension because suffering restraints, moreover concrete tensile strength is not high, thereby concrete shrinkage easily causes concrete cracking.Cement concrete was punctured into plastic shrinkage before condensing.General plastic shrinkage occurs in after the fresh concrete moulding in initial some hours, and when early stage moisture evaporation is faster, the plastic shrinkage performance is more obvious, and plastic shrinkage cracking also more easily occurs.
Horse one equality was once write articles the plastic shrinkage cracking mechanism of cement-based material was carried out Primary Study, think behind the cement-based material moulding by casting, because the affinity of water and cement-based material, form concave meniscus in the skin-material kapillary during moisture evaporation, the vertical component of its concave meniscus upper surface tension force has formed the tension to material between tube wall, this moment, material was in the plastic stage, and the plastic tensile strength of material self is lower, if the tensile stress sigma that produces is shunk in the dehydration of material surface kapillary
KapillaryWith material plasticity tensile strength f
MouldSatisfy formula (1):
σ
Kapillary＞f
Mould-----------------------------------------(1)
Then cracking phenomena appears in material surface.
When changing cement-based material composition and environmental baseline of living in thereof, the plastic tensile strength of material opposing cracking is changed, the capillary tension that also can make on the other hand the kapillary dehydration shrink formation changes, thereby makes σ
KapillaryWith f
MouldWhen satisfying formula (2):
σ
Kapillary≤ f
Mould----------------------------------------(2)
The cracking situation of material surface is alleviated, even disappears.
Sand-cement slurry plastic shrinkage cracking resistance criterion is being carried out showing after the preliminary research: the plasticity shrinkage stress of capillary should be set up in test specimen surface development, and according to the actual plasticity shrinkage stress of capillary in test specimen surface should greater than or when equaling plastic tensile strength at least test specimen just can ftracture and proposed critical depth of interaction h
CrWith cracking resistance index K, provided its computing formula:
K=f
Mould/ σ
Kapillary
On this theoretical foundation, the method for testings such as the plastic tensile strength of horse one equality designed, designed cement-based material, plastic contraction rate, plasticity kapillary constringency's pull should dint are carried out the research of cement-based material plastic shrinkage cracking problem.And the utilization mathematical method, substep makes up the monobasic constitutive equation of cement-based material plastic shrinkage cracking.Simultaneously by testing the cracking resistance index of accumulated water cement-based material plastic shrinkage cracking, the segmentation criterion of using logic analysis whether to be ftractureed.But, also do not have up to now to provide a polynary constitutive equation of plastic shrinkage cracking that comprises cement-based material composition, environmental baseline, initial configuration parameter and constraint condition, thereby expectation is used for the early prediction of mortar plastic shrinkage cracking.
Summary of the invention
The object of the invention is to disclose a kind of polynary constitutive equation of plastic shrinkage cracking that comprises cement-based material material composition, environmental baseline, initial configuration parameter and constraint condition, be used for the early prediction of mortar plastic shrinkage cracking.
In order to achieve the above object, the present invention has made up the polynary constitutive equation of plastic shrinkage cracking that comprises cement-based material material composition, environmental baseline, initial configuration parameter and constraint condition on above-mentioned Research foundation:
K＝13.8822-14.0949Wc-2.8247Cs+0.5293Fc+0.0022F
1-17.0650Er+0.2582Dd+0.9436Rd
Wherein K refers to the cracking resistance index of cement-based material, judges in conjunction with following shrinkage cracking segmentation criterion whether cement-based material ftractures;
Wc refers to the water cement ratio of cement-based material, and Cs refers to the cement-sand ratio of cement-based material, and Fc refers to the fibers content in the cement-based material, F
1Refer to the fibre length in the cement-based material, the material that this four key element is cement-based material forms parameter;
Er refers to the moisture velocity of evaporation of cement-based material, is the parameter of the residing environmental baseline of cement-based material; (its assay method is studied foundation by present patent application person, the moisture velocity of evaporation of namely finding the massive plate mortar by research is approximated to linear relationship with the ratio of the moisture velocity of evaporation of small size mortar, can be obtained the linear equation of both sides relation by regretional analysis, can go out with the analog computation of small size mortar accordingly the moisture velocity of evaporation of actual plate mortar)
Dd refers to the delamination degree of cement-based material, is the parameter of cement-based material initial configuration parameter; Its measuring method is foundation that the present inventor studies: the denseness of at first measuring the mortar mixture, then the mortar mixture is once packed in the delamination degree cylinder and to knock gently under the 1-2 with wooden mallet around container distance four different places about equally afterwards wait filling, sink such as mortar and then should add at any time and then scrape off unnecessary mortar and floating with spatula to being lower than nozzle; After leaving standstill 30min, remove upper joint 200mm mortar, remaining mortar is poured out to be placed in the mix pot and is mixed 2min, surveys its denseness again.The difference of the denseness that front and back record is the stratification degree (cm) of this mortar.
Mortar for adjusting the initial configuration parameter after the mortar mixture stirs, in the slurry filling container and delamination degree cylinder of the mortar consistency tester of packing into immediately, all is positioned over slurry filling container and delamination degree cylinder on the homemade shaking table.At the uniform velocity fall the percussion vibration platform with the counterweight of constant weight from shaking table top fixed range, knock after certain number of times by fixed frequency, measure the denseness of mortar mixture in the container, be designated as initial value a1; After leaving standstill 30min, remove joint 200mm mortar on the delamination degree cylinder, remaining mortar is poured out to be placed in the mix pot and is mixed 2min, surveys its denseness again, is designated as a2.The stratification degree a=a1-a2 of mortar after then adjusting.)
Rd refers to the constraint degree of cement-based material, is the parameter of cement-based material constraint condition.(the constraint degree measuring method is foundation that present patent application person studies: then the plastic contraction rate under the accurate free state of measurement mortar and the plastic contraction rate under the mortar restrained condition are calculated as follows constraint degree:
Plastic contraction rate under the accurate free state of plastic contraction rate/mortar specimen under constraint degree=1-mortar specimen restrained condition)
The linearly dependent coefficient r=0.97 of this equation shows between this equation cracking resistance index and each parameter to have obvious linear dependence.
The segmentation criterion of sand-cement slurry plastic shrinkage cracking:
When the K value greater than 1.41 the time, test specimen does not ftracture;
When the K value less than 0.99 the time, the test specimen cracking;
When the K value was between 0.99 and 1.41, test specimen ftractureed with certain probability.
Advantage of the present invention:
Select the polynary constitutive equation that the larger parameter of cement based plastic shrinkage cracking impact has been made up the mortar plastic shrinkage cracking, can predict more exactly the trend of cement-based material early-age plastic shrinkage cracking.
Embodiment
Embodiment 1
A certain sand-cement slurry water cement ratio Wc is 0.45, and cement-sand ratio is 1, and fibers content Fc is 0.9kg/m
3, fibre length F
1Be 12mm, the moisture velocity of evaporation that records this mortar under a certain environmental baseline is 0.250Kg/ (m
2H), delamination degree is 0.1cm, and constraint degree is 0.66, calculates K=1.60, and greater than 1.41, the prediction mortar can not ftracture under this environmental baseline.
The actual K value 1.82 that records, relative error 12.1%, mortar does not ftracture.
Embodiment 2
A certain sand-cement slurry water cement ratio Wc is 0.40, and cement-sand ratio is 0.67, and fibers content Fc is 0, fibre length F
1Be 0, the moisture velocity of evaporation that records this mortar under a certain environmental baseline is 0.296Kg/ (m
2H), delamination degree is 0.1cm, and constraint degree is 0.83, brings constitutive equation into and calculates K=2.11, and greater than 1.41, the prediction mortar can not ftracture under this environmental baseline.
The actual K value 2.33 that records, relative error 9.44%, mortar does not ftracture.
Embodiment 3
A certain sand-cement slurry water cement ratio Wc is 0.45, and cement-sand ratio is 1, and fibers content Fc is 0.9kg/m
3, fibre length F
1Be 6mm, the moisture velocity of evaporation that records this mortar under a certain environmental baseline is 0.30Kg/ (m2h), and delamination degree is 0.4cm, and constraint degree is 0.83, brings constitutive equation into and calculates K=0.97, and less than 0.99, the prediction mortar can ftracture in this environmental baseline.
The actual K value 1.07 that records, relative error 9.34%, mortar cracking.
Claims (1)
1. a prediction cement-based material plastic shrinkage cracking method is characterized in that: measure first the water cement ratio (Wc) that comprises cement-based material; Cement-sand ratio (Cs); The material of fibers content (Fc) and four kinds of cement-based materials of fibre length (Fl) forms parameter; Then, the parameter of the residing environmental baseline of mensuration cement-based material is that the parameter of moisture velocity of evaporation (Er), cement-based material initial configuration parameter is that the delamination degree (Dd) of cement-based material, the parameter of cement-based material constraint condition are the constraint degree (Rd) of cement-based material; At last, with above-mentioned seven following formula of parameter substitution, calculate:
K=13.8822-14.0949Wc-2.8247Cs+0.5293Fc+0.0022F
l-17.0650Er+0.2582Dd+0.9436Rd；
Described K is the cracking resistance index;
When the K value greater than 1.41 the time, the cement-based material test specimen does not ftracture; When the K value less than 0.99 the time, the test specimen cracking; When the K value was between 0.99 and 1.41, test specimen ftractureed with certain probability;
The unit of above-mentioned fibers content (Fc) is kg/m
3, the unit of fibre length (Fl) is mm, the unit of moisture velocity of evaporation (Er) is kg/m
2H, delamination degree (Dd) unit is cm.
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Families Citing this family (8)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN103163283B (en) * | 2013-02-05 | 2015-09-09 | 江苏苏博特新材料股份有限公司 | A kind of Forecasting Methodology of cement asphalt mortar compressive strength |
| CN106053329A (en) * | 2016-05-19 | 2016-10-26 | 扬州大学 | Method for testing air shrinkage resistant performance of plastering material |
| CN107589044B (en) * | 2017-09-07 | 2019-11-15 | 中国建筑土木建设有限公司 | The evaluation method of the ratio of mud after hydrated cement paste layering |
| CN109738618B (en) * | 2018-12-06 | 2021-07-06 | 同济大学 | Preliminary early warning method for plastic shrinkage cracking of cement-based material |
| CN109765355A (en) * | 2018-12-21 | 2019-05-17 | 内江师范学院 | A kind of cement concrete pavement of aerodrome splits mode prediction method |
| CN112257144B (en) * | 2020-09-29 | 2022-10-28 | 山西省交通科技研发有限公司 | Cement-based composite material elastic-plastic constitutive model and establishment method thereof |
| CN113049791A (en) * | 2021-02-08 | 2021-06-29 | 同济大学 | Plastic shrinkage cracking and reducing method for cement mortar |
| CN113158458B (en) * | 2021-04-20 | 2022-11-18 | 重庆大学 | Concrete change trend prediction method and system |
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| JP4593403B2 (en) * | 2005-08-26 | 2010-12-08 | 啓一 今本 | Method for predicting cracks in concrete |
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|---|---|---|---|---|
| WO2003006986A1 (en) * | 2001-07-13 | 2003-01-23 | HANSEN, Kirsten Højst | Apparatus and method for in situ measuring of evaporation from a surface |
| CN101122596A (en) * | 2007-09-04 | 2008-02-13 | 中交四航工程研究院有限公司 | Concrete cracking sensitivity test device and anti-crack ability evaluation method |
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