高强混凝土立方强度的尺寸效应

试验表明,高强混凝土立方强度的尺寸效应不同于普通混凝土。文章对55组高强混凝土立方强度实测数据作了分析,并给出计算表达式。     

高强混凝土柱小偏心受压性能尺寸效应试验研究

为了解高强混凝土柱小偏心受压性能的尺寸效应,进行了3组不同几何尺寸的高强混凝土柱小偏心受压破坏试验,其截面几何尺寸分别为200mm×200mm、400mm×400mm、800mm×800mm,对比分析了其破坏形态、承载力、变形能力及截面应变分布规律,揭示了其尺寸效应规律。研究结果表明,高强混凝土柱的小偏心受压破坏形态和横截面应变分布规律基本相同,其尺寸效应不明显;高强混凝土柱的小偏心受压承载力和变形能力存在明显尺寸效应,随着截面尺寸的增大,其极限承载力的安全储备量减小,变形能力减弱。     

钢筋混凝土梁的弯曲性能尺寸效应试验研究

进行了抗压强度为46.5～50.6MPa,截面高度为250～1 000mm的钢筋混凝土试件弯曲性能试验。与相同尺寸和配筋的高强混凝土试件(fcu=72.1～72.4MPa)的试验结果进行了对比分析,从受弯承载力和变形能力两个方面研究了钢筋混凝土试件的受弯性能尺寸效应。研究表明,截面尺寸的变化对钢筋混凝土构件的名义开裂弯矩、屈服弯矩和极限弯矩没有明显影响,对位移延性和塑性铰区塑性转动能力有显著影响,试件的位移延性系数和塑性铰转动能力随截面高度的减小而减小,并且普通混凝土试件和高强混凝土试件的尺寸效应规律基本相同,与混凝土强度无关。试验结果表明,不同混凝土强度和截面高度试件的塑性铰区长度均为1倍截面有效高度。     

高强度混凝土强度增长速度及强度增长机理的研究

本文探讨了高强高混凝土强度增长速率与水灰比之间的关系，并通过测试水化速率，孔结构分析了高强混凝土强度增长机理 。     

钢筋高强混凝土柱轴压性能尺寸效应试验

为揭示钢筋高强混凝土柱的尺寸效应规律,进行了不同几何尺寸、不配置箍筋的钢筋高强混凝土柱轴心受压性能试验,对比分析了不同几何尺寸试件的破坏特征、名义应力-应变曲线、承载力、变形及刚度.结果表明,未设置箍筋的钢筋高强混凝土柱轴心受压承载力、破坏特征和变形能力表现出一定的尺寸效应。     

不同类型混凝土弯曲强度尺寸效应

基于混凝土脆性的评价指标,采用Bazant提出的基于能量释放的尺寸效应律的方法,以普通混凝土、粉煤灰混凝土、轻骨料混凝土、纤维混凝土和聚合物改性混凝土为样本,对其弯曲强度的尺寸效应进行研究,定量表征不同类型混凝土的脆性.研究结果表明:Bazant提出的尺寸效应律适用于不同种类混凝土的弯曲强度的尺寸效应评价;从尺寸效应律曲线分析可知,轻骨料混凝土比其他混凝土呈现明显的脆性断裂行为,而纤维混凝土和聚合物改性混凝土的脆性断裂行为不明显,粉煤灰对于混凝土脆性的改善也具有一定的作用;线性断裂理论在一定尺寸范围内比非线性断裂理论更适用于混凝土断裂行为的评价.     

混凝土双轴压缩强度尺寸效应机理

为了研究混凝土双轴强度尺寸效应产生的机理,考虑混凝土尺寸效应及其宏观力学非线性源于其材料组成的非均质性,结合混凝土细观结构形式,从细观角度将混凝土看作由骨料颗粒、砂浆基质和界面过渡区组成的三相复合材料,建立了尺寸分别为150 mm×150 mm、300 mm×300 mm和600 mm×600 mm的数值混凝土试件.首先通过对150 mm×150 mm方形混凝土试件进行单轴压缩力学特性模拟,采用反演法确定了界面过渡区的力学参数,进而对双轴压缩加载下混凝土的破坏行为及其尺寸效应进行了分析.研究结果表明:1)损伤破坏形式随试件尺寸发生变化,试件最终破坏消耗的断裂能不同是导致混凝土双轴压缩强度产生尺寸效应的主要原因;2)混凝土单、双轴压缩强度均存在明显的尺寸效应行为,并且Bazant尺寸效应律能够较好地描述混凝土在单、双轴压缩加载下的强度尺寸效应.     

RPC材料的抗折强度尺寸效应研究

为了研究活性粉末混凝土材料（RPC）的抗折强度尺寸效应，采用3种试块测量RPC材料抗折强度。通过统计分析、数据拟合，并应用Bazant断裂力学尺寸效应理论分析RPC材料尺寸效应现象。结果表明：RPC材料试块的尺寸越小，其抗折强度越大，具有明显的尺寸效应现象；基于Bazant能量释放的尺寸效应和无切口情况下的尺寸效应分别在一定的尺寸范围内与试验结果吻合良好，但是不适用于全尺寸范围；本文提出的修正公式在全尺寸范围内都能较好反映RPC抗折强度．     

高强混凝土柱滞回性能数值分析

目的通过在高强混凝土柱中配置强度超过1000MPa的纵向和横向高强钢筋的方法，改善柱的滞回性能，以提高其抗震能力．方法为定量研究配有高强钢筋的高强混凝土柱的滞回性能，利用“条带法”，在平截面假定的条件下，编制了非线性分析程序，该程序考虑了钢筋和混凝土应力应变关系的全过程，P-△效应，核芯混凝土的约束强化作用，保护层剥落影响及塑性铰影响等因素；利用该程序进行了柱在低周反复荷载作用下的强度和变形分析，绘出了P-△滞回曲线；将计算的结果与试验结果进行了比较研究．结果数值分析和试验结果之间的差异在合理范围之内；轴压比对高强钢筋高强混凝土柱的滞回性能影响较大．结论利用所提出构造处理方法可以明显提高柱子的延性；采用数值分析的方法，可以计算出配有高强钢筋的高强混凝土柱子的延性，为抗震设计提供了一种便捷的方法．     

高强混凝土回弹仪测强曲线研究

针对我国目前尚无高强混凝土无损检测技术规程这一现状，结合辽宁省实际特点，对强度等级为C50－C100的高强混凝土试块采用HT1000型回弹仪进行了回弹法检测强度的试验研究，知回弹法可以用于高强混凝土进行检测，通过采用多种回归模型进行分析比较，求得最佳高强混凝土回弹仪测强曲线公式fcu^e=2.461R-27.575,测试精度满足混凝土质量控制要求，以此作为辽宁地区强度分析曲线。通过误差传递理论分析可知，回归分析所用的反映散点离差规律的各种统计量主要反映了试块的强度离散性。     

湿排粉煤灰对混凝土性能的影响

通过实验室模拟研究不同湿法存放时间（1～60个月）的2种低钙粉煤灰的形貌、粒径和用于混凝土掺合料的性能变化。粉煤灰湿排后颗粒变粗,颗粒表面出现侵蚀,但颗粒形貌基本保持不变;湿排粉煤灰矿物减水效应明显降低,掺量为20％～40％的湿排粉煤灰混凝土坍落度比原状粉煤灰混凝土减少约20～40mm;掺加湿排粉煤灰的混凝土与外加剂适应性、抗渗和抗碳化无明显变化,坍落度经时损失有所降低;湿法存放3个月的粉煤灰掺量20％时混凝土28d和56d抗压强度比原状粉煤灰混凝土分别下降5．8％和3．7％,但掺量为20％的湿法存放36个月粉煤灰混凝土抗压强度比仍可以达到85％,湿法存放时间为3a和5a的粉煤灰混凝土强度无明显差别。研究结果表明,湿排低钙粉煤灰可以用作为混凝土掺合料。     

Effect of Polypropylene Fibers on the Long-term Tensile Strength of Concrete

The influence of low volume fraction of polypropylene(PP) fibers on the tensile properties of normal and high strength concretes was studied. The experimental results indicate that the addition of PP fibers in concrete leads to a reduction in tensile strength during the age of 28 d. Whereas, after 28 days, there is a notable effect in tensile strength due to PP fibers restraining the formation and growth of microcracks in concrete, which improves the continuity and integrality of concrete structure. Thus, a low volume fraction of PP fibers is beneficial to enhancing the long-term tensile strength of concrete materials and improving the durability of concrete structures.     

钢纤维对混凝土强度和韧性的影响

通过对234个钢纤维混凝土试件的力学性能试验,系统研究了钢纤维类型、体积分数、长径比和混凝土基体强度对钢纤维混凝土抗压强度、劈拉强度和弯曲韧性的影响.结果表明:钢纤维对混凝土抗压强度影响不大,但改变了受压破坏时的破坏形态;随钢纤维体积分数增大,混凝土劈拉强度和弯曲韧性显著提高,高强钢丝切断型钢纤维的改善效果最好,长径比越大,改善效果越明显.     

脉冲水气射流的破岩实验研究

利用脉冲水气射流喷嘴在振荡腔内引入空气,与自激脉冲射流掺混形成脉冲水气射流;当泵压为7．5MPa时,进行了2组冲蚀实验,冲蚀抗压强度为6．9MPa的混凝土,第一组实验分析了不同腔长对脉冲水气射流和脉冲射流冲蚀效果的影响,第二组实验分析了不同开孔孔径下脉冲水气射流的冲蚀效果。实验结果表明：泵压一定时,在合适的腔长下,脉冲水气射流比脉冲射流的破岩效果好,且存在一个最佳进气方式使脉冲水气射流的破碎体积最大。     

Effects of binder strength and aggregate size on the compressive strength and void ratio of porous concrete

To test the influence of binder strength, porous concretes with 4 binder strengths between 30.0-135.0 MPa and 5 void ra tios between 15%-35% were tested. The results indicated that for the same aggregate, the rates of strength reduction due to the in creases in void ratio were the same for binders with different strengths. To study the influence of aggregate size, 3 single size aggre gates with nominal sizes of 5.0, 13.0 and 20.0 mm (Nos. 7, 6 and 5 according to JIS A 5001) were used to make porous concrete. The strengths of porous concrete are found to be dependent on aggregate size. The rate of strength reduction of porous concrete with small aggregate size is found to be higher than that with larger aggregate size. At the same void ratio, the strength of porous concrete with large aggregate is larger than that with small aggregate. The general equations for porous concrete are related to compressive strength and void ratio for different binder strengths and aggregate sizes.     

再生骨料混凝土研究

采用正交实验研究了搅拌工艺，净水胶比、粗骨料种类对天然和再生骨料混凝土拌合物和易性，硬化混凝土力学性能的影响，结果表明，粗骨料种类对混凝土性能有很大影响，其程度不亚于水胶比对混凝土性能的影响，提出在进行混凝土配合比设计时，其强度公式中应考虑到粗骨料种类的影响，同时，若采用再生粗骨料配制混凝土，应采用较高的砂率和较低的水灰比，以保证混凝土拌合物的和易性，搅拌工艺因素中，水泥裹石工艺有助于改善拌合物和易性，硅灰裹石工艺有助于提高混凝土后期力学性能。     

Durability of concrete subjected to the combined actions of flexural stress,freeze-thaw cycles and bittern solutions

Freeze-thaw durabilities of three types of concretesnormal portland cement concrete （OPC）, high strength concrete （HSC） and steel fiber reinforced high strength concrete （SFRHSC） were systemically investigated under the attacks of chemical solution, and combination of external flexural stress and chemical solution. Four kinds of bitterns from salt lakes in Sinkiang, Qinghai, Inner Mongolia and Tibet provinces of China were used as chemical attack solutions. The relative dynamic modulus （RDM） was used as an index for evaluating the damage degree during the course of chemical attack and stress corrosion. The experimental results show that the freeze-thaw durability of concrete is visibly reduced in the present of the flexural stress, i e, stress accelerates the damage process. In order to quantify the stress accelerated effect, a stress accelerating coefficient was proposed. The stress accelerating coefficient is closely related with the types of bitterns and the numbers of freeze-thaw cycles is. The more numbers of freeze-thaw cycles is, the greater the stress accelerating coefficient for various concretes will be. In addition, there also exists a critical ratio of external stress to the maximum flexural stress. If the stress ratio exceeds the critical one, the freeze-thaw durability of various concretes will be greatly decreased compared to the responding concretes without applied stress. The critical stress ratio of OPC, HSC and SFRHSC is 0.30, 0.40 and 0.40, respectively, indicating that HSC and SFRHSC have advantages over OPC and are suitable to use in the bittern erosion regions.     

Porosity,pore size distribution and chloride permeability of shotcrete modified with nano particles at early age

Nano particles have been found to be effective in enhancing many properties of regular concretes. However, there is little information on the effect of nano particles on shotcrete. In fact, if similar positive effect of nano particles can also appear in shotcrete, they will greatly benefit the wide application of shotcrete in more and more repair and strengthening of structures in civil engineering, especially in corrosive environments. In this study, through experiments on 70 specimens, the effects of nano SiO₂, CaCO₃ and Al₂O₃ particles on the early-age porosity, pore size distribution, compressive strength and chloride permeability of shotcrete were investigated.Test results indicated that nano SiO₂ particles significantly increased the compressive strength and chloride penetration resistance; nano Al₂O₃ and CaCO₃ particles had slight enhancing effect on the compressive strength; nano CaCO₃ particles were most effective in promoting the chloride penetration resistance of shotcrete. As a conclusion, nano SiO₂ particles were recommended when both early age compressive strength and chloride penetration resistance were crucial, and nano CaCO₃ particles were recommended when only chloride penetration resistance was concerned for their high cost-effectiveness.     

高性能混凝土早期开裂防治措施研究

早期开裂是当前混凝土施工应用中经常出现的质量通病,采取什么样的措施防止这种开裂成为当前研究热点.就掺入聚丙烯纤维、碳纤维、减缩剂及复合使用时混凝土的早期开裂、自收缩、抗渗性等进行了试验研究,并从扫描电镜照片进行微观结构分析.结果表明:纤维或减缩剂的加入都对混凝土早期开裂有一定抑制作用,但对混凝土抗压强度有一定降低.从综合性能看,各种措施对防止混凝土早期开裂的效果优劣次序为:减缩剂>减缩剂+聚丙烯纤维>碳纤维>聚丙烯纤维.     

Prediction of the residual strength for durability failure of concrete structure in acidic environments

According to the results of accelerated tests of acidification corrosion depth and compressive strength of concretes subjected to sulfuric acid environments, the acidification depth laws of concretes were predicted based on the grey system theory. Thus, the remaining compressive strength was calculated when the acidification depth reached the protection layer thickness of concrete structures, which indicates that the limit state of durability failure can be defined based on strength degradation, and the calculation process was illustrated by an example. The calculated results show that the remaining compressive strength values in the durability failure limit state for the concrete structures exposed to pH=2 and 3 sulfuric acid water environments and wet-dry cyclic sulfuric acid environment with pH=2 are 74%, 72%, and 80% of initial strength, respectively. The method provides references for the durability evaluation of concrete structure design under the acidic environments.