CN104374897A - Method for determining early-stage concrete crack resistance by adopting elliptical ring test specimen - Google Patents
Method for determining early-stage concrete crack resistance by adopting elliptical ring test specimen Download PDFInfo
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- CN104374897A CN104374897A CN201410686716.1A CN201410686716A CN104374897A CN 104374897 A CN104374897 A CN 104374897A CN 201410686716 A CN201410686716 A CN 201410686716A CN 104374897 A CN104374897 A CN 104374897A
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Abstract
The invention belongs to the field of research for early-stage concrete crack resistance, and relates to a method for determining the early-stage concrete crack resistance by adopting an elliptical ring test specimen. The method comprises the following steps: putting an internal steel ring with the thickness of 12.5mm into the inner side of an elliptical concrete ring with the thickness of 37.5mm, wherein the concrete ring closely attaches to the internal steel ring, the concrete ring and the internal steel ring have the heights of 75mm, the ratio of a long axis to a short axis of the outer ring of the elliptical internal steel ring is a/b=2, a=150mm, and b=75mm; putting strain gauges respectively at the part which is 50mm away from the long axis end of the inner ring of the internal steel ring horizontally, wherein the strain gauges are positioned on the same height of the internal steel ring, the height is at the middle part of the internal steel ring; connecting the strain gauges with a collecting system, and sealing the upper surface and the lower surface of the concrete ring with aluminum bands. According to the invention, compared with a circular ring testing method, not only is the crack time advanced, but also the crack position is more regular and is close to the long shaft of the elliptical ring, which is beneficial to the research for the early-stage concrete crack under limited contraction condition.
Description
Technical field
The invention belongs to early-age concrete fault analysis field, relate to the experimental technique adopting a kind of elliptical ring geometric parameter model determination early-age concrete splitting resistance, be specifically related to adopt elliptical ring test specimen to measure early-age concrete splitting resistance under restriction pinch condition.
Background technology
Concrete very easily produces crack because shrinking in length of time morning, the security of structure that what these cracks were serious have impact on, permanance and applicability, too increases maintenance cost, become one of main disease of xoncrete structure while reduction structure serviceable life.How to assess concrete splitting resistance, aobvious is very important.In the past few decades, engineering circles and academia are devoted to find a kind of simple effective method to assess concrete splitting resistance always.Although free shrink test can more different concrete volume change, be difficult to the cracking resistance of assessment material under outside effect of contraction.Therefore, can play the constraint strip test of confined shrinkage effect, the test of constraint template and confined shrinkage loop test obtain study and practice.
At present, recommend flat band method in China's " durability design and construction guidbook " and " Standard for test methods of longterm performance and durability of ordinary concrete standard " and assess concrete splitting resistance.But it can only part, uneven confined concrete drawdown deformation, and the result of test is very large to the dependence of the factors such as sample dimensions, material behavior, environmental aspect, and the generation in crack is irregular.These shortcomings make flat band method accurately to evaluate agent on crack resistance of concrete cracking behavior, are also unfavorable for comparing and standardizing.Owing to can providing enough constraint rigidity and being easy to laboratory operation, current confined shrinkage annulus is comparatively widely used in the splitting resistance of concrete under confined shrinkage condition and is assessed.In addition, confined shrinkage circle ring test by National Highway with transport association (AASHTO) and test material association of the U.S. (ASTM) be recommended as the standard test method assessing cracking of reinforced concrete, in China's " durability design and construction guidbook " also using confined shrinkage ring method as the recommend method testing cement-based gelling material splitting resistance.But circle ring test also has certain shortcoming, because steel loop constraining force deficiency such as to cause long at the time to be cracked, and this research tool for concrete fracture has a great impact, particularly for early-age concrete.The position of circle ring test cracking is not also fixed simultaneously, causes research relatively difficulty.He et al. (2004) proposes to adopt a kind of elliptical ring geometric model in the research that affect the cracking trend of mortar of evaluation alkali, and supposes that the cracking of elliptical ring occurs occurring that cracking is Zao than annulus.Also guess that the elliptical ring test specimen that affects due to physical dimension has stronger constraining force relative to annulus specimen, the crack location of elliptical ring test specimen is different with dry environment according to given concrete material feature, appears at the same fixed position of geometry ring simultaneously.But more than just conjecture, scientific basis does not support above speech, and does not do about the test of elliptical ring compared with annulus, and does not also provide concrete geometric parameter about elliptical ring.So for elliptical ring test specimen, current research is only confined to suppose that major axis may produce stress and concentrates and then shorten cracking time, and not for the proposition of the concrete geometric parameter of elliptical ring.For mensuration early-age concrete splitting resistance circle ring test, adopt U.S. test material association (ASTM) C1581/C1581M-09 standard test method, for ellipse ring test, identical with circle ring test method, change annulus into elliptical ring, and define geometric parameter.
Summary of the invention
The object of the invention is to overcome the shortcoming existed in art methods, propose to adopt a kind of elliptical ring geometric parameter to measure the test method of early-age concrete splitting resistance.The method is for being 21-25 DEG C in temperature, relative humidity is under the environment of 48%-52%, the thickness of built-in steel loop and concrete ring is respectively 12.5mm and 37.5mm, concrete ring, built-in steel loop height are 75mm, the ratio of semi-minor axis length a/b=2 of steel elliptical ring outer shroud, size a=150mm, b=75mm, carry out mensuration early-age concrete splitting resistance.The method not only occurs that cracking time early, and crack location is substantially near elliptical ring major axis.The method is more conducive to the research of early-age concrete fracture.
Technical scheme of the present invention is: adopt elliptical ring test specimen to measure the method for early-age concrete splitting resistance, concrete steps are as follows:
Be 21-25 DEG C in temperature, relative humidity is under the environment of 48%-52%, and have thickness to be the built-in steel loop of 12.5mm in the inner side that thickness is 37.5mm oval concrete ring, concrete ring and built-in steel loop are close to; The height of built-in steel loop and concrete ring is 75mm; The ratio of semi-minor axis length a/b=2 of steel elliptical ring outer shroud, a=150mm, b=75mm.Four foil gauges are placed on the position of longitudinal end 50mm inside horizontal range steel elliptical ring respectively, and are all positioned at the sustained height of built-in steel loop, and this is highly the centre position of built-in steel loop; Be connected with acquisition system by above-mentioned four foil gauges, sealed by upper and lower for concrete ring surface aluminium strip, the external peripheral surface of concrete ring does not need sealing.Reaction when data acquisition system (DAS) display concrete cracking and unstability, steel loop strained.Along with concrete maintenance, there is crack because of built-in steel loop confined shrinkage in concrete ring.
The invention has the beneficial effects as follows:
One, elliptical ring geometric parameter model of the present invention, overcome the shortcoming causing cracking time longer because constraining force is not enough in circle ring test, increase cracking sensitivity, relative to circle ring test, there is the time of cracking comparatively early in the ellipse ring test first time adopted, thus test can be greatly reduced carry out the time, be conducive to evaluating cracking of reinforced concrete, for China's evaluation early-age concrete cracking resistance standard test method provides reference.Under Condition of Strong Constraint, the concrete cracking performance of the strong splitting resistance of mensuration is also seemed very important.
Two, elliptical ring geometric parameter model of the present invention, crack location is relatively fixing, and substantially near longitudinal end, early-age concrete splitting resistance under mensuration of being more convenient for restriction pinch condition, is conducive to the cracking behavior research of concrete fracture.
Accompanying drawing explanation
Accompanying drawing is elliptical ring test specimen structural representation.
In figure: 1 concrete ring; 2 built-in steel loops; 3 foil gauges; The built-in steel loop thickness of t;
A elliptical ring major axis radius; B elliptical ring minor axis radius; C foil gauge distance steel loop inner ring horizontal range.
Embodiment
Below in conjunction with accompanying drawing and technical scheme, further illustrate the specific embodiment of the present invention.
1. test prepares
Steel loop: the thickness of built-in steel loop is 12.5mm, is highly 75mm, the ratio of semi-minor axis length a/b=2 of steel elliptical ring outer shroud, size a=150mm, b=75mm (see figure).
Concrete: employing water cement ratio is the C30 concrete of 0.5, and the thickness of concrete ring is 37.5mm, is highly 75mm.
Foil gauge: four foil gauges, each foil gauge is wired to data acquisition system (DAS), is used for showing side strain development in steel loop.
Acquisition of information: data acquisition system (DAS) records the strain development of each foil gauge.The acquisition precision of acquisition system should be ± 0.0000005m/m.Acquisition system should record strain data in 30 minutes.
Platform: adopt epoxy coating plywood, or adopt other material platforms, its surface should not absorb, not react.
Test environment: temperature is 21-25 DEG C, relative humidity is in the environment of 48%-52%.
2. test specimen makes and test foundation
1) on the position four foil gauges being placed in respectively longitudinal end 50mm inside horizontal range steel elliptical ring (see figure), and be all positioned at the sustained height of built-in steel loop, this is highly the centre position of built-in steel loop, and is connected with acquisition system by foil gauge.
2) platform for making, is bolted to the fixing outer shroud of steel annulus on platform, coats remover outside inner ring He inside outer shroud.Make three test specimens, and vibration compacting, cleaning concrete surface, builds rear test specimen and sent in experimental enviroment in 10 minutes, unclamp bolt, connect foil gauge and reading device, writing time in 2 minutes, reads first time data in 30 minutes.
3) maintenance: test specimen needs maintenance 24 hours at temperature is 21-25 DEG C, need first time shrink read after send to maintenance, if maintenance more than 24 hours, may remove outer shroud in 5 minutes.
3. start to measure front preparation (completing in 15 minutes)
1) take away outer shroud, take away polyethylene film.
2) loose material is picked from concrete surface.
3) by solid paraffin or gummed foil sealing test piece upper part.The two-layer aluminium strip in the upper and lower surface of concrete elliptical ring seals, and only allows external peripheral surface to keep dry state.
4. measure and record
Record cracking time and calculate average cracking time, recording the crack location of elliptical ring test specimen.
5. result
Employing water cement ratio is the C30 concrete of 0.5, and elliptical ring test specimen occurs that cracking was at 11 days, and crack appears near major axis all substantially.
The test of contrast annulus, annulus specimen occurs that cracking was at 18 days, and cracking does not have fixed position relative, compare, elliptical ring test occurs that cracking time is advanced by 7 days, occur that the position in crack is also more fixed, substantially near elliptical ring major axis, this provides better method of testing to mensuration early-age concrete splitting resistance.
Claims (1)
1. the method adopting elliptical ring test specimen to measure early-age concrete splitting resistance, it is characterized in that, step is as follows: be 21-25 DEG C in temperature, relative humidity is under the environment of 48%-52%, be that the built-in steel loop of 12.5mm is placed in inside the oval concrete ring that thickness is 37.5mm by thickness, concrete ring and built-in steel loop are close to, and the height of built-in steel loop and concrete ring is 75mm; The ratio of semi-minor axis length a/b=2 of oval built-in steel loop outer shroud, a=150mm, b=75mm; Four foil gauges are placed in the longitudinal end 50mm of the built-in steel loop inner ring of horizontal range respectively, and are all positioned at the sustained height of built-in steel loop, and this is highly the centre position of built-in steel loop; Be connected with acquisition system by above-mentioned four foil gauges, concrete ring upper surface and lower surface aluminium strip sealed, the external peripheral surface of concrete ring does not need sealing; The change of foil gauge on built-in steel loop when acquisition system display concrete cracking and unstability.
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN105738603A (en) * | 2016-02-26 | 2016-07-06 | 大连理工大学 | New test method for determining crack resistance of early-age concrete |
| CN105759017A (en) * | 2016-04-18 | 2016-07-13 | 天津大学 | Device and method for evaluating anti-crack performance of external squares and internal circles of cement-based materials |
| CN107923830A (en) * | 2014-10-03 | 2018-04-17 | 皮埃尔和玛丽居里大学（巴黎第六大学） | The characterizing method of the cracking mechanism of the break surface of material |
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| CN102680667A (en) * | 2012-05-11 | 2012-09-19 | 河海大学 | Concrete early-age crack resistance testing device capable of directly determining cracking position |
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2014
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| CN2583673Y (en) * | 2002-11-05 | 2003-10-29 | 武汉大学 | Oval ring restraining cracking automatic monitoring and testing device |
| CN102680667A (en) * | 2012-05-11 | 2012-09-19 | 河海大学 | Concrete early-age crack resistance testing device capable of directly determining cracking position |
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN107923830A (en) * | 2014-10-03 | 2018-04-17 | 皮埃尔和玛丽居里大学（巴黎第六大学） | The characterizing method of the cracking mechanism of the break surface of material |
| CN105738603A (en) * | 2016-02-26 | 2016-07-06 | 大连理工大学 | New test method for determining crack resistance of early-age concrete |
| CN105759017A (en) * | 2016-04-18 | 2016-07-13 | 天津大学 | Device and method for evaluating anti-crack performance of external squares and internal circles of cement-based materials |
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Application publication date: 20150225 |