水泥基材料约束收缩试验方法研究

发布时间：2018-05-10 21:39

本文选题：水泥基材料约束收缩试验 + 外方内圆偏心约束试验方法　；参考：《天津大学》2015年博士论文

【摘要】：混凝土裂缝产生的原因有很多,大致可分为荷载裂缝、次荷载裂缝和非荷载裂缝。在非荷载裂缝中,自由状态下的收缩对混凝土并无不良影响,但实际工程中,处于不同约束状态下的混凝土结构往往因收缩大而产生收缩裂缝,收缩裂缝会削弱混凝土的质量,影响其耐久性,甚至影响结构的整体性。检测水泥基材料收缩开裂性能的试验方法很多,其中圆环法使用最为广泛,被各国普遍采用,此法具有原理清晰和模具简单等特点,但是圆环法存在三个问题:(1)由于试件具有高度的对称性,使得收缩裂缝随机出现,不便于裂缝的观察;(2)混凝土圆环试件壁厚大多在30mm~35mm范围内,而粗骨料的最大粒径为10mm~15mm,这样的试件和骨料尺寸并不能真实的反应混凝土的收缩开裂性能;(3)砂浆圆环试件的最大壁厚为75mm,如果混凝土试件使用75mm的壁厚,则试件几乎是不开裂的,极大的降低了混凝土收缩开裂的时效性和敏感度。针对于以上三个问题,文中提出了外方内圆偏心约束试验方法和双圆偏心约束试验方法:通过数值分析确定了试验模具的尺寸,通过数理方法对试验结果(裂缝分布位置和开裂时间)做了统计分析,通过试验验证了外方内圆偏心约束试验方法的开裂敏感度,通过Weiss理论模型估算了混凝土试件的开裂应力。为了更直接和简单的检测试件收缩开裂时间,提出了一套水泥基材料收缩开裂时间检测装置,具体阐述如下:(1)净浆和砂浆外方内圆偏心约束收缩试验方法。外方内圆偏心约束试验方法是改变圆环法外边界的圆形为方形,同时将约束钢环沿其中两条对边的中线向一边移动,形成偏心,试件尺寸为170mm×170mm×35mm,最佳偏心距为20mm,通过对净浆和砂浆外方内圆偏心约束试件开裂时间和裂缝位置的数理统计发现:外方内圆偏心约束试件的平均开裂时间明显早于圆环试件,缩短了净浆和砂浆的收缩试验周期;98%的裂缝偏移量在预期开裂截面左右15.35mm以内,因此可以认为外方内圆偏心约束试验方法基本能起到限定收缩裂缝产生位置的作用。通过对比外方内圆试件和圆环试件在完全密封条件下收缩裂缝的发展路径发现,圆环试件从内侧先开裂而外方内圆偏心试件从外侧先开裂,验证了文中有限元计算结果的正确性,也说明外方内圆偏心约束试验方法提高了试件的开裂敏感度。(2)混凝土外方内圆偏心约束试验方法。混凝土外方内圆偏心约束试验方法与净浆(砂浆)外方内圆偏心约束试验方法原理相同,区别在于其尺寸,为了更真实的反映混凝土的收缩开裂性能,粗骨料最大尺寸选用25mm,试件尺寸为600mm×600mm×75mm,最狭窄处横截面尺寸为75mm×75mm,其中,约束钢环外直径为300mm,厚度为20mm,经过数值分析发现,外方内圆偏心约束试验方法能够形成一个预期的开裂位置,试验结果表明:0.5水灰比的混凝土外方内圆偏心约束试件不但开裂时间在两周之内,而且裂缝位置偏移量不大,而壁厚为75mm的圆环试件几乎是不开裂的。通过完全密封条件下外方内圆偏心约束试件的裂缝发展和开裂应力估算,证明了混凝土外方内圆偏心约束试验方法的开裂敏感度,以0.5水灰比的混凝土为例,混凝土外方内圆偏心约束试件在完全密封条件下依然能够开裂,而且裂缝从试件外侧向内侧发展,明显的提高了混凝土收缩开裂的敏感度。通过试件开裂应力估算可知,外方内圆偏心约束试件最大开裂应力大致为3.7MPa-4.2MPa。(3)双圆偏心约束试验方法。试件外边界为圆形,直径为600mm,高75mm,约束钢环直径为300mm,厚度为20mm,钢环沿模型直径向边框的某一点偏移,保证钢环外边缘与模具边框内边缘距离为75mm,双圆偏心约束试验方法同样能够有效的限制收缩裂缝的产生位置,通过试件开裂时间统计发现,双圆偏心约束试验方法能够提高混凝土收缩开裂的敏感度,但是效果不如外方内圆偏心约束试验方法。为了直接和简单地检测混凝土的收缩开裂时间,受到电路回路和断路的启发,提出了一套新的开裂时间检测装置,装置由导电性粘附材料、导线和指针型钟表组成,把导电性粘附材料涂抹在预期的开裂位置一定的范围内,导电材料干燥之后,与导线和钟表连接成回路,每12h观察一次钟表走动情况,如果试件开裂则电路由回路变为断路,钟表停止转动,此时钟表指针所指向的位置即为试件的开裂时刻,此方法能极大节省观察裂缝出现的时间,试验装置简单,操作方便,特别在净浆和砂浆试验中效果最为显著。
[Abstract]:There are many reasons for concrete cracks, which can be divided into load cracks, secondary load cracks and non load cracks. In non load cracks, the shrinkage of free state has no adverse effect on concrete, but in practical engineering, concrete structures in different confinement conditions often produce shrinkage cracks due to large shrinkage and shrink cracks. To weaken the quality of concrete, affect its durability and even influence the integrity of the structure. There are many testing methods for testing the shrinkage and cracking properties of cement based materials, in which the ring method is most widely used and is widely used by all countries. This method has the characteristics of clear principle and simple mold, but there are three problems in the ring method: (1) because the specimen is high The symmetry of the degree makes the shrinkage crack random and not easy to observe the crack; (2) the wall thickness of the concrete ring specimen is mostly in the range of 30mm~35mm, and the maximum size of the coarse aggregate is 10mm~15mm. The size of the specimen and aggregate can not reflect the shrinkage and cracking performance of the concrete; (3) the maximum wall thickness of the mortar ring specimen is 75mm, If the concrete specimen uses the wall thickness of 75mm, the specimen is almost no crack, which greatly reduces the aging and sensitivity of concrete shrinkage cracking. For the above three problems, the external eccentricity constraint test method and the double circle eccentric constraint test method are put forward in the paper. The size of the test die is determined by numerical analysis. Through the statistical analysis of the test results (the location of the crack distribution and the cracking time) through the mathematical method, the cracking sensitivity of the external eccentricity constraint test method is verified by the test. The cracking stress of the concrete specimen is estimated by the Weiss theoretical model. In order to more direct and simple single test specimen, a set of shrinkage cracking time is put forward. The testing device for shrinkage and cracking time of cement based materials is described as follows: (1) the test method of eccentric constriction of the inner circle and eccentricity of the mortar and mortar. The outer circle eccentric constraint test method is to change the circle of the outer boundary of the circular ring to the square, while the restrained steel ring moves along the middle line of the two sides to form the eccentric, and the specimen ruler is formed. The optimum eccentricity is 170mm x 170mm x 35mm, and the optimum eccentricity is 20mm. Through the mathematical statistics of the cracking time and the crack position of the eccentric confinement of the inner circle of the mortar and mortar, it is found that the average cracking time of the outer square eccentric restraint specimen is earlier than the ring specimen, and the shrinkage test period of the net pulp and the mortar is shortened; 98% of the crack offset is in the case. It is expected that the crack section is less than 15.35mm, so it can be considered that the outer inner circle eccentric constraint test method can basically play the role of limiting the position of the shrinkage crack. By comparing the development path of the contraction crack in the complete seal condition, the circular specimen and the circular specimen are cracked from the inside first and the outer square is round. The core specimen is cracked from the outside first, which verifies the correctness of the results of the finite element calculation in the article, and also shows that the external eccentricity constraint test method improves the cracking sensitivity of the specimen. (2) the eccentric constraint test method for concrete outer circle inner circle constraint test method and the external square eccentric constraint test of the concrete outer circle eccentric constraint test and the slurry (mortar) The method is the same, and the difference lies in its size. In order to reflect the shrinkage and cracking performance of concrete more truly, the maximum size of the coarse aggregate is 25mm, the size of the specimen is 600mm x 600mm x 75mm, the cross section size of the most narrow section is 75mm * 75mm, of which the outer diameter of the restrained steel ring is 300mm and the thickness is 20mm. Through numerical analysis, it is found that the outer circle is eccentric and eccentric. The test method can form a desired position of cracking. The test results show that the cracking time of 0.5 water cement concrete inner circle eccentricity restraint specimen is not only within two weeks, but the displacement of the crack position is small, and the circle specimen with the thickness of 75mm is almost not open. The crack development and the crack stress estimation of the restrained specimens prove the cracking sensitivity of the concrete outer circular eccentric constraint test method. Taking the concrete of 0.5 water cement ratio as an example, the concrete outer inner circular eccentric restraint test still can crack under the condition of complete seal, and the crack is developed from the outside of the specimen to the inside, and it is obviously improved. The sensitivity of concrete shrinkage cracking is estimated by the crack stress estimation of the specimen. It is found that the maximum crack stress of the outer inner circular eccentric constraint specimen is 3.7MPa-4.2MPa. (3) double circular eccentric constraint test method. The outer boundary of the specimen is round, the diameter is 600mm, the height is 75mm, the diameter of the restrained steel ring is 300mm, the thickness is 20mm, and the steel ring is along the model diameter to the frame. At a certain point, the distance between the outer edge of the steel ring and the inner edge of the die frame is 75mm, and the double circular eccentric constraint test method can also effectively limit the position of the shrinkage crack. The double circular eccentric constraint test method can improve the sensitivity of the shrinkage cracking of the coagulant soil, but the effect is not as good as the external side. In order to detect the shrinkage and cracking time of concrete directly and simply, inspired by circuit circuit and circuit breakage, a new set of cracking time detection device is put forward, which consists of conductive adhesive material, wire and pointer type clocks, and the conductive adhesive material is applied to the expected cracking position. Within the range, after the conductive material is dry, the circuit is connected with the wire and the clock, and every 12h watches a clock moving. If the specimen is cracked, the circuit turns from the circuit to the circuit breaker, the clock stops turning. At this time, the position of the clock pointer is the cracking time of the specimen. This method can greatly save the time for the observation of the crack. Test The device is simple and easy to operate, especially in the test of paste and mortar.

【学位授予单位】：天津大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TU528

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