CN103149094B - The measuring method of tensile creep of early-age concrete - Google Patents
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Abstract
本发明涉及一种早期龄混凝土拉伸徐变的测量方法及装置。该测量装置包括同轴且水平设置的固定端组件和移动端组件、约束框架、及其支架，移动端组件通过加载轴与同轴线设置的穿心千斤顶相连接，且在移动端组件的外侧设置有位移传感器，用于测量试件移动端或/和加载轴在拉伸过程中的位移；本发明方法是对拉伸徐变试件施加徐变荷载进行主动约束试验；并记录施加的徐变荷载以及加载前后位移传感器的读数；同时利用补偿收缩试件按常规方法进行自收缩试验；到达试验设计龄期后终止试验，主动约束试验值减去自收缩试验值即为拉伸徐变变形值。本发明装置结构简单，其检测方法简便、检测成本低，且检测精度高。
The invention relates to a method and device for measuring tensile creep of early-age concrete. The measuring device includes a coaxial and horizontally arranged fixed-end assembly and a moving-end assembly, a constraining frame, and its support. A displacement sensor is provided for measuring the displacement of the moving end of the test piece or/and the loading shaft during the stretching process; the method of the present invention is to apply a creep load to the tensile creep test piece to carry out an active restraint test; and record the applied creep Change the load and the readings of the displacement sensor before and after loading; at the same time, use the compensating shrinkage specimen to perform the self-shrinkage test according to the conventional method; the test is terminated after the test design age is reached, and the active restraint test value minus the self-shrinkage test value is the tensile creep deformation value. The device of the invention has simple structure, simple and convenient detection method, low detection cost and high detection precision.
Description
技术领域 technical field
本发明涉及水工结构实验、观测与分析技术领域，具体涉及一种早期龄混凝土拉伸徐变的测量方法及装置。 The invention relates to the technical field of hydraulic structure experiment, observation and analysis, in particular to a method and device for measuring tensile creep of early-age concrete.
背景技术 Background technique
在混凝土大坝、厂房、泵站等水工建筑物中，混凝土裂缝是影响工程建设质量和耐久性的主要问题之一，非常突出，迄今防不胜防，为不争事实。为了深入探求混凝土的开裂机理，完善混凝土防裂仿真计算分析工作，这就需要深入关注混凝土早期的一些特性参量。在相关温控防裂仿真计算研究中发现，在水工大体积混凝土施工早期，采用不同徐变模型导致有20%～80%的差异，因而认为徐变对应力的结果是结构开裂不可忽略的主要影响因素之一。 In hydraulic structures such as concrete dams, workshops, pumping stations, etc., concrete cracks are one of the main problems affecting the quality and durability of engineering construction. In order to deeply explore the cracking mechanism of concrete and improve the simulation calculation and analysis of concrete crack prevention, it is necessary to pay close attention to some early characteristic parameters of concrete. In the related temperature control and anti-cracking simulation calculation research, it is found that in the early stage of hydraulic mass concrete construction, the use of different creep models leads to a difference of 20% to 80%. Therefore, it is believed that the result of creep versus stress is the main reason for structural cracking that cannot be ignored. one of the influencing factors.
早龄期混凝土拉伸徐变性能是决定混凝土早期开裂的关键问题之一。关于混凝土拉伸徐变的试验方法各国尚无统一标准，不同学者根据实际情况选择不同的测量方法，从而也发展出了一些测量混凝土拉伸徐变的方法，混凝土拉伸徐的测量方法可分为轴向拉伸、端部约束收缩和环向拉伸试验这三种方法。其中研究者们使用最多的方法是轴向拉伸试验和端部约束收缩试验两种方法，但所使用的拉伸徐变测量方法各有利弊。 The tensile and creep performance of early-age concrete is one of the key issues determining the early cracking of concrete. There is no uniform standard for the test method of concrete tensile creep in various countries. Different scholars choose different measurement methods according to the actual situation, and thus have developed some methods for measuring concrete tensile creep. The measurement methods of concrete tensile creep can be divided into These three methods are axial tension, end restraint shrinkage and hoop tension tests. Among them, the methods most used by researchers are the axial tensile test and the end-constrained shrinkage test, but the tensile creep measurement methods used have their own advantages and disadvantages.
常规的轴向拉伸徐变试验方法存在一些局限，如我国的水工混凝土试验规程DLT 5150-2001中建议适用的拉伸徐变的试验方法是端部通过预埋的拉力预埋件来施加拉力，混凝土变形的测量是通过预埋应变计来测量混凝土时间的变形，这种方法不宜保证位移传感器与混凝土试件的轴心重合；端部约束试验装置价格昂贵；环向拉伸徐变试验方法复杂，测量装置占用场地较大等等。 There are some limitations in the conventional axial tensile creep test method. For example, in my country’s hydraulic concrete test regulations DLT 5150-2001, the applicable tensile creep test method is to apply the pre-buried tension embedded parts at the end. Tensile force and concrete deformation are measured by pre-embedded strain gauges to measure the deformation of concrete over time. This method is not suitable to ensure that the axis of the displacement sensor coincides with the concrete specimen; the end restraint test device is expensive; the ring tensile creep test The method is complicated, and the measuring device takes up a lot of space and so on.
各研究者根据自己的研究目的及试验室条件等因素来设计不同的试验方法，尚有很大的研究空间。拉伸徐变测试中主要存在着混凝土端部的连接与测量仪器的选择和放置两方面的问题。 There is still a lot of research space for researchers to design different experimental methods according to their own research purposes and laboratory conditions and other factors. In the tensile creep test, there are mainly two problems: the connection of the concrete end and the selection and placement of the measuring instrument.
发明内容 Contents of the invention
本发明要解决的技术问题是提供一种结构简单、测量误差小、测试成本低廉的早期龄混凝土拉伸徐变的测量装置，并公开了一种操作方法简单、结果准确可靠的早期龄混凝土拉伸徐变的测量方法。 The technical problem to be solved by the present invention is to provide a measuring device for tensile creep of early-aged concrete with simple structure, small measurement error and low test cost, and discloses a tensile creep measuring device for early-aged concrete with simple operation method and accurate and reliable results. Measurement method of elongation creep.
为解决上述技术问题，本发明采用的技术方案是： In order to solve the problems of the technologies described above, the technical solution adopted in the present invention is:
设计一种早期龄混凝土拉伸徐变的测量装置,包括同轴且水平设置的固定端组件和移动端组件、约束框架、及其支架，所述移动端组件通过加载轴与同轴线设置的穿心千斤顶相连接，且在所述移动端组件的外侧设置有位移传感器，用于测量试件移动端或/和加载轴在拉伸过程中的位移。 Design a measuring device for tensile creep of early-age concrete, including coaxial and horizontally arranged fixed-end components and moving-end components, constraining frames, and their supports, and the moving-end components are set through the loading axis and the coaxial The through jacks are connected, and a displacement sensor is arranged outside the moving end assembly for measuring the displacement of the moving end of the test piece or/and the loading shaft during the stretching process.
所述位移传感器为线性差动式位移传感器（LVDT），选用高精度（测量精度达1μm以上）的位移传感器LVDT（线性差动式位移传感器）进行位移测量。由于混凝土的拉伸徐变变形比压缩徐变变形要小的多，通常只有几十个至一百多个微应变，因而除了要求混凝土的变形测量仪器要有较高的精度外，还要求有稳定可靠的测量方法。目前徐变变形量测仪器主要有内埋差动式电阻应变计和钢弦式应变计法、粘贴电阻应变片法以及外置式的千分表或位移计法。内埋差动式电阻应变计和钢弦式应变计最明显的不足之处就是在浇筑试件时难以保证其最终位置与混凝土的纵向轴线重合。粘贴电阻应变片的方法，本发明技术方案亦不能，早龄期混凝土在拆模之后，其外表面湿度较大，不易粘贴电阻应变片。所以本发明装置中采用外置LVDT的方式测量早龄期混凝土试件的变形。该位移计相对简单、能在宽温度范围内工作、具有极精细的分辨率、可靠性高、不易损坏、非常适合从微米级至几个厘米内位移的测量。 The displacement sensor is a linear differential displacement sensor (LVDT), and a displacement sensor LVDT (linear differential displacement sensor) with high precision (measuring accuracy of more than 1 μm) is selected for displacement measurement. Since the tensile creep deformation of concrete is much smaller than the compressive creep deformation, usually only a few tens to more than one hundred microstrains, in addition to requiring high accuracy of concrete deformation measuring instruments, it is also required to have Stable and reliable measurement method. At present, creep deformation measurement instruments mainly include embedded differential resistance strain gauge and steel string strain gauge method, pasting resistance strain gauge method, and external dial gauge or displacement gauge method. The most obvious disadvantage of the embedded differential resistance strain gauge and the steel string strain gauge is that it is difficult to ensure that its final position coincides with the longitudinal axis of the concrete when pouring the specimen. The method for pasting the resistance strain gauges is also not possible in the technical scheme of the present invention. After the early-age concrete is removed from the formwork, the humidity of its outer surface is relatively large, so it is difficult to paste the resistance strain gauges. Therefore, the device of the present invention uses an external LVDT to measure the deformation of the early-age concrete specimen. The displacement meter is relatively simple, can work in a wide temperature range, has extremely fine resolution, high reliability, is not easy to damage, and is very suitable for measuring displacements from microns to several centimeters.
所述穿心千斤顶为自锁式穿心千斤顶。由于对混凝土的轴向拉伸试验的应力较大，而仅靠拧紧螺栓来施加拉应力不足以施加足够的应力，因此本发明装置采用穿心千斤顶进行加载，而普通的千斤顶随着时间的增长，可能出现卸载的现象，因此可进一步的采用自锁式穿心千斤顶进行加载。 The threaded jack is a self-locking threaded jack. Because the stress of the axial tensile test of concrete is relatively large, and the tensile stress is not enough to apply sufficient stress only by tightening the bolts, the device of the present invention uses a through-hole jack for loading, and the common jack increases with time. , the phenomenon of unloading may occur, so the self-locking through-hole jack can be further used for loading.
与所述移动端组件对应的承载构件通过滚动机构承载所述移动端。施加拉应力时，端部的移动端和下部的承载构件之间产生较大的摩擦力，如果不能有效的消除摩擦，施加的预加拉应力就不准确。为了减小摩擦力，采用的措施有：在测量装置的移动端组件的下部和承载构件的上部预留半圆形的槽，并在其上部放置钢球，这些钢球可以减小两者之间的摩擦。 The carrying member corresponding to the mobile end assembly carries the mobile end through a rolling mechanism. When tensile stress is applied, a large friction force is generated between the moving end of the end and the lower bearing member. If the friction cannot be effectively eliminated, the applied pre-tensioning stress will be inaccurate. In order to reduce the friction, the measures adopted are: reserve a semicircular groove on the lower part of the moving end assembly of the measuring device and the upper part of the bearing member, and place steel balls on the upper part, and these steel balls can reduce the friction between the two. friction between.
利用上述测量装置进行早期龄混凝土拉伸徐变的测量方法，包括以下步骤： Utilize above-mentioned measuring device to carry out the measuring method of the tensile creep of early age concrete, comprise the following steps:
（1）制备狗骨型混凝土试件： (1) Preparation of dog-bone concrete specimens:
①在狗骨型的试模内部涂上脱模剂，然后再上面敷设一层聚乙烯薄膜，然后再涂上一层脱模剂； ① Apply a release agent to the inside of the dog-bone test mold, then lay a layer of polyethylene film on it, and then apply a layer of release agent;
②把拌制好的混凝土用铲刀装入试模内，经振捣密实抹平后用塑料薄膜密封，以防止水份蒸发，然后将混凝土徐变实验室中的温度控制在20±2℃； ②Put the mixed concrete into the test mold with a spatula, vibrate and smooth it, then seal it with a plastic film to prevent water from evaporating, and then control the temperature in the concrete creep laboratory at 20±2°C ;
③按上述方法同时制备出拉伸徐变试件和补偿收缩试件，试件成型养护20～24h后拆模，拆模后的拉伸徐变试件和补偿收缩试件立即用铝箔密封，以防止水分的散失，补偿收缩试件在龄期为24h时按常规方法开始测量混凝土的自收缩变形； ③Prepare the tensile creep test piece and the compensation shrinkage test piece at the same time according to the above method. After the test piece is formed and cured for 20-24 hours, the mold is removed. After the mold removal, the tensile creep test piece and the compensation shrinkage test piece are immediately sealed with aluminum foil. In order to prevent the loss of water, the shrinkage compensation specimens are measured in the conventional way when the age is 24h, and the autogenous shrinkage deformation of the concrete is measured;
④到达设计的加载龄期时，随机抽取一狗骨型混凝土试件按常规方法进行劈裂抗拉强度试验，以确定混凝土徐变试件施加荷载的大小； ④ When the designed loading age is reached, a dog-bone concrete specimen is randomly selected to conduct a splitting tensile strength test according to the conventional method, so as to determine the magnitude of the applied load on the concrete creep specimen;
（2）试验：将拉伸徐变试件安装在权利要求1所述早期龄混凝土拉伸徐变的测量装置上，将其位移传感器安装连接在加载轴上； (2) Test: install the tensile creep test piece on the measuring device for tensile creep of early-age concrete as claimed in claim 1, and install and connect its displacement sensor on the loading shaft;
（3）安装、加载：对拉伸徐变试件施加徐变荷载进行主动约束试验，即首先旋紧与穿心千斤顶配套使用的手动油泵上的放油阀，缓慢摇动油泵手柄对试件进行加载，整个过程在5min之内完成；并记录施加的徐变荷载以及加载前后位移传感器的读数；同时利用补偿收缩试件按常规方法进行自收缩试验；到达试验设计龄期后, 终止试验； (3) Installation and loading: Apply creep load to the tensile creep specimen to carry out the active restraint test, that is, first tighten the oil drain valve on the manual oil pump used with the through-hole jack, and slowly shake the handle of the oil pump to perform the active restraint test on the specimen. Loading, the whole process is completed within 5 minutes; and record the applied creep load and the readings of the displacement sensor before and after loading; at the same time, use the compensation shrinkage specimen to conduct the self-shrinkage test according to the conventional method; when the test design age is reached, the test is terminated;
（4）记录、计算： (4) Record and calculate:
采集、记录自收缩试验与主动约束试验的试验数据；主动约束试验值减去自收缩试验值即为拉伸徐变变形值。 Collect and record the test data of the autogenous shrinkage test and the active restraint test; the value of the active restraint test minus the autogenous shrinkage test value is the tensile creep deformation value.
本发明具有积极有益的效果： The present invention has positive and beneficial effects:
（1）采用水平放置混凝土试件的方式；早龄期的混凝土抗拉强度较低，可施加的预加拉力较小，自重对混凝土产生的应力较大，因此采用水平放置混凝土试件可以消除自重对混凝土试件不同位置处应力的影响； (1) The method of placing concrete specimens horizontally; the tensile strength of early-age concrete is low, the pre-loading force that can be applied is small, and the stress generated by its own weight on the concrete is relatively large, so placing concrete specimens horizontally can eliminate The effect of self-weight on the stress at different positions of concrete specimens;
（2）选择的测量标距较大，可以减小应变测量的误差；因混凝土的拉伸徐变变形相对较小，在同样位移测量误差的前提下，测量的标距越大，测量的应变误差就越小； (2) The selected measurement gauge length is larger, which can reduce the error of strain measurement; because the tensile creep deformation of concrete is relatively small, under the premise of the same displacement measurement error, the larger the measurement gauge length, the greater the measured strain the smaller the error;
（3）本发明装置结构简单，其检测方法操作简单，测试成本低，且检测精度高，能够应用于工程实践。 (3) The device of the present invention has simple structure, simple operation of the detection method, low test cost and high detection accuracy, and can be applied in engineering practice.
附图说明 Description of drawings
图1为一种早期龄混凝土拉伸徐变的测量装置的俯视图； Fig. 1 is a top view of a measuring device for tensile creep of early age concrete;
图2为一种早期龄混凝土拉伸徐变的测量装置的侧视图； Fig. 2 is a side view of a measuring device for early age concrete tensile creep;
图3为早期龄混凝土拉伸徐变的趋势图。 Figure 3 is a trend diagram of the tensile creep of early-age concrete.
图中，1为自锁式穿心千斤顶，2为线性差动式位移传感器，3为移动端组件，4为底板，5为纵向加强筋，6为狗骨形混凝土试件，7为固定端组件，8为纵向工字钢件，9为横向工字钢件，10为纵向工字钢件，11为护栏，12为纵向加强筋，13为横向加强筋，14为横向工字钢件，15为支架，16为侧板。 In the figure, 1 is a self-locking core-through jack, 2 is a linear differential displacement sensor, 3 is a mobile end component, 4 is a bottom plate, 5 is a longitudinal rib, 6 is a dog-bone concrete specimen, and 7 is a fixed end Components, 8 is the vertical I-shaped steel part, 9 is the horizontal I-shaped steel part, 10 is the longitudinal I-shaped steel part, 11 is the guardrail, 12 is the longitudinal reinforcing rib, 13 is the transverse reinforcing rib, 14 is the horizontal I-shaped steel part, 15 is a support, and 16 is a side plate.
具体实施方式 Detailed ways
以下结合具体实施例进一步阐述本发明。 The present invention is further described below in conjunction with specific examples.
实施例1 一种早期龄混凝土拉伸徐变的测量装置,参见图1、图1，包括同轴且水平设置的固定端组件7和移动端组件3、约束框架（由纵向工字钢件8、10，纵向加强筋5、12，位于两端横向设置的横向工字钢件9、14，及底板4和侧板16构成，总体形变量≤1μm）、及支架15，所述移动端组件3通过加载轴与同轴线设置的自锁式穿心千斤顶1相连接，且在所述移动端组件3的外侧设置有线性差动式位移传感器（LVDT，测量精度达1μm）2，用于测量试件移动端在拉伸过程中的位移。在测量装置的移动端组件3的下部对应的承载构件的上部预留半圆形的槽，并在其上部放置钢球，以减小两者之间的摩擦。 Example 1 A measuring device for tensile creep of early-age concrete, referring to Fig. 1 and Fig. 1, includes a coaxial and horizontally arranged fixed end assembly 7 and a moving end assembly 3, and a constraining frame (made of longitudinal I-shaped steel parts 8 , 10, longitudinal ribs 5, 12, horizontal I-shaped steel parts 9, 14 located at both ends, and bottom plate 4 and side plate 16, the overall deformation is ≤ 1 μm), and bracket 15, the mobile end assembly 3. The loading shaft is connected to the self-locking type feed-through jack 1 set on the coaxial line, and a linear differential displacement sensor (LVDT, with a measurement accuracy of 1 μm) 2 is provided on the outside of the moving end assembly 3 for Measure the displacement of the moving end of the specimen during tension. A semicircular groove is reserved on the upper part of the bearing member corresponding to the lower part of the mobile end assembly 3 of the measuring device, and a steel ball is placed on the upper part to reduce the friction between the two.
利用上述测量装置进行早期龄混凝土拉伸徐变的测量方法，包括以下步骤： Utilize above-mentioned measuring device to carry out the measuring method of the tensile creep of early age concrete, comprise the following steps:
（1）制备狗骨型混凝土试件（长度为1000mm, 截面大小100mm×100mm） (1) Preparation of dog-bone concrete specimens (length 1000mm, section size 100mm×100mm)
①在狗骨型的试模内部涂上脱模剂，然后再上面敷设一层聚乙烯薄膜，然后再涂上一层脱模剂； ① Apply a release agent to the inside of the dog-bone test mold, then lay a layer of polyethylene film on it, and then apply a layer of release agent;
②把拌制好的混凝土用铲刀装入试模内，经振捣密实抹平后用塑料薄膜密封，以防止水份蒸发，然后将混凝土徐变实验室中的温度控制在20±2℃； ②Put the mixed concrete into the test mold with a spatula, vibrate and smooth it, then seal it with a plastic film to prevent water from evaporating, and then control the temperature in the concrete creep laboratory at 20±2°C ;
③按上述方法同时制备出一定数量的拉伸徐变试件和补偿收缩试件，混凝土试件成型养护20～24h后拆模，拆模后拉伸徐变试件和补偿收缩试件立即用铝箔密封，以防止水分的散失，补偿收缩试件在龄期为24h时开始测量混凝土的自收缩变形； ③Prepare a certain number of tensile creep test pieces and compensation shrinkage test pieces at the same time according to the above method, remove the formwork after 20-24 hours of concrete forming and curing, and use the tensile creep test pieces and compensation shrinkage test pieces immediately after the formwork removal Sealed with aluminum foil to prevent the loss of moisture and compensate for the shrinkage. The specimen starts to measure the self-shrinkage deformation of the concrete when the age is 24h;
④到达设计的加载龄期时，进行劈裂抗拉强度试验，并确定混凝土徐变试件施加荷载的大小； ④ When the designed loading age is reached, the splitting tensile strength test shall be carried out, and the load applied to the concrete creep specimen shall be determined;
（2）试验：将拉伸徐变试件安装在权利要求1所述早期龄混凝土拉伸徐变的测量装置上，将其位移传感器（LVDT）的活动端连接安装于加载轴上； (2) Test: Install the tensile creep test piece on the measuring device for tensile creep of early-age concrete as claimed in claim 1, and connect and install the movable end of its displacement sensor (LVDT) on the loading shaft;
（3）安装、加载：对拉伸徐变试件施加徐变荷载进行主动约束试验，即首先旋紧与穿心千斤顶配套使用的手动油泵上的放油阀，缓慢摇动油泵手柄对试件进行加载，整个过程在5min之内完成；并记录施加的徐变荷载以及加载前后位移传感器的读数；同时利用补偿收缩试件按常规方法进行自收缩试验；到达试验设计龄期后, 终止试验； (3) Installation and loading: Apply creep load to the tensile creep specimen to carry out the active restraint test, that is, first tighten the oil drain valve on the manual oil pump used with the through-hole jack, and slowly shake the handle of the oil pump to perform the active restraint test on the specimen. Loading, the whole process is completed within 5 minutes; and record the applied creep load and the readings of the displacement sensor before and after loading; at the same time, use the compensation shrinkage specimen to conduct the self-shrinkage test according to the conventional method; when the test design age is reached, the test is terminated;
（4）记录、计算： (4) Record and calculate:
采集、记录自收缩试验与主动约束试验的试验数据；主动约束试验值减去自收缩试验值即为拉伸徐变变形值。 Collect and record the test data of the autogenous shrinkage test and the active restraint test; the value of the active restraint test minus the autogenous shrinkage test value is the tensile creep deformation value.
选取一种基准混凝土配合比，通过改变水灰比，按上述方法制备了5组配合比（如表1所示）的混凝土试件，配合比如下表。通过系列试验，获得随早龄期（7d）内徐变度数值，如图3所示，该试验曲线反应的值域及规律符合科学规律，与同类受拉徐变试验检测值的区间相符合，且试验精度得到较大提升。 A reference concrete mix ratio was selected, and by changing the water-cement ratio, 5 sets of concrete specimens with mix ratios (as shown in Table 1) were prepared according to the above method. The mix ratios are shown in the following table. Through a series of tests, the value of the creep degree with the early age (7d) was obtained, as shown in Figure 3, the value range and law of the test curve response conform to scientific laws, and are consistent with the range of detection values of similar tensile creep tests , and the test accuracy has been greatly improved.
表1 不同水灰比混凝土的配合比 Table 1 Mixing ratio of concrete with different water-cement ratios
虽然，上文中已经用一般性说明及具体实施方案对本发明作了详尽的描述，但在本发明基础上，可以对之作一些修改或改进，这对本领域技术人员而言是显而易见的。因此，在不偏离本发明精神的基础上所做的这些修改或改进，均属于本发明要求保护的范围。 Although the present invention has been described in detail with general descriptions and specific embodiments above, it is obvious to those skilled in the art that some modifications or improvements can be made on the basis of the present invention. Therefore, the modifications or improvements made on the basis of not departing from the spirit of the present invention all belong to the protection scope of the present invention.
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