冻融环境下钢筋与粉煤灰混凝土的粘结性能

通过对内贴应变片钢筋的直接拔出试验,分析冻融作用下粉煤灰掺量对钢筋与粉煤灰混凝土间粘结性能的影响,得出冻融循环作用对钢筋与粉煤灰混凝土之间粘结性能的影响规律。试验结果表明：钢筋与粉煤灰混凝土的粘结强度随粉煤灰掺量的增加而降低;当粉煤灰掺量一定时,随着冻融循环次数的增加,混凝土强度有所下降,钢筋与粉煤灰混凝土间极限粘结强度降低;当粉煤灰掺量较大,达到40%时,随冻融次数的增加,钢筋粉煤灰混凝土试件极限粘结强度的下降幅度明显减缓,极限粘结强度对应的滑移量增大。表明掺入较多粉煤灰可使试件的冻融损伤现象得到缓解,冻融环境下钢筋混凝土的粘结性能得到提高。     

再生混凝土与锈蚀钢筋间的粘结性能试验研究

为了探究再生混凝土结构的耐久性能,对5组不同钢筋锈蚀率(0~9%)的再生混凝土梁式试件进行加载试验。分析不同钢筋锈蚀率对再生混凝土梁式试件的钢筋应变、局部粘结应力、粘结滑移和极限粘结应力的影响。结果表明：钢筋锈蚀率大于3%时试件底部开始有细微锈胀裂缝出现;锈蚀率越大,荷载作用下钢筋应变沿锚固位置的变化曲线越平缓;局部粘结应力沿锚固段呈现出双峰分布,峰值主要集中在加载端和自由端附近;加载端附近位置滑移现象最先发生,远离加载端滑移现象延后;随着钢筋锈蚀率的增大,极限粘结强度先增加后降低,极限荷载下的滑移值增大。     

Bond properties of CFRP-high performance concrete subjected to freeze-thaw cycles

通过双面剪切试验,研究了冻融环境下CFRP-高性能混凝土界面粘结性能的发展规律。对比分析了未经冻融和经历25、50、100、150、200及300次冻融循环作用试件的破坏特征、剪应变分布、荷载滑移曲线、粘结承载力以及粘结破坏机理。结果表明,所有试件的界面破坏均发生在混凝土表层内,但随着冻融循环次数的增加,破坏界面有向胶层发展的趋势;经受冻融循环次数较少时(25、50次),界面的粘结强度、刚度及开裂荷载的变化不明显,甚至略微提高;但随着冻融循环次数的进一步增加,界面粘结性能有明显的变化,界面粘结强度、端部滑移量减小,刚度退化,初始开裂荷载水平降低,非线性特征增强。粘结极限承载力与混凝土立方体抗压强度均随冻融循环次数的增长存在先提高后下降的趋势,混凝土强度变化是界面粘结性能变化的最重要因素。     

油菜秸秆灰分混凝土与钢筋之间粘结性能研究

为了探究油菜秸秆灰分的掺入对钢筋-混凝土之间粘结性能的影响。对3种不同油菜秸秆灰分掺量的钢筋-油菜秸秆灰分混凝土试件进行中心拉拔试验,并与钢筋-普通混凝土粘结性能作对比试验。结果表明:钢筋-油菜秸秆灰分混凝土粘结强度与混凝土抗压强度呈正相关。当水胶比一定时,随着油菜秸秆灰分掺量的增加,钢筋-油菜秸秆灰分混凝土的粘结强度降低。水胶比为0.47时的钢筋-油菜秸秆灰分粘结性能与普通混凝土最为接近,为最优配合比。由试验结果可知,在承重要求较低的普通钢筋混凝土结构中,采用适量油菜秸秆灰分等量替代水泥,对于节省水泥生产能源和科学合理利用农业废弃物两方面均具有重要意义。     

冻融损伤喷射混凝土本构关系及微观结构

采用棱柱体试件,通过快速冻融试验方法,对冻融损伤后同配合比普通混凝土、喷射混凝土及钢纤维喷射混凝土单轴受压应力应变全曲线进行研究。对应力应变关系中相关参数进行回归分析,得出冻融循环后试件应力应变全曲线方程。结果表明：随着冻融循环次数增加,受压应力应变曲线趋于扁平;峰值应力降低,峰值应变增大,分别与冻融循环次数呈线性和指数变化。与普通混凝土相比,喷射混凝土峰值应力下降速率小,而钢纤维喷射混凝土的下降速率进一步减小。而后,采用扫描电子显微镜及压汞法,对损伤后试件微观结构和孔结构进行观察分析,发现随着冻融循环次数增加,在渗透压和冻胀压力综合作用下,试件内部微裂纹及气孔增多,孔径增大,试件密实度显著降低;而钢纤维喷射混凝土中仅出现少量连通毛细孔,这与宏观力学性能变化呈现一致性。     

受火后钢-混凝土组合梁材料性能试验研究

为研究火灾高温后组合梁桥的基本材料力学性能与特征,共制作3片具有代表性的缩尺梁模型：简支T形梁、简支箱形梁及连续箱形梁,利用火灾试验炉进行局部三面受火试验,并给出详细的试验方案。通过受火后取样试件与未受火试件的材性试验结果对比,可以发现受火(最高温度在700～900 ℃)对钢板材料的屈服强度及极限强度均有一定程度的降低,降低幅度为10%～20%;而钢板材料弹性模量随温度升高略有变化,但变化值不大。火灾对混凝土强度材性的影响可以忽略不计,但对其冷却后的材料强度有一定影响,相对于常温混凝土其强度会降低5%左右。     

RC加气混凝土砌块组合墙加固框架抗震性能试验研究

RC加气混凝土砌块组合墙（简称组合墙）是由混凝土梁柱网格与加气混凝土砌块组合形成的一种轻型网格式抗震墙,可用于框架结构的抗震加固。笔者进行了1/2比例空框架试件、组合墙试件和组合墙加固框架试件的低周反复荷载试验,分析了各试件的主要破坏过程,对比了组合墙加固框架前后试件承载能力、刚度等抗震性能变化。试验结果及分析表明：组合墙加固框架后承载力、抗侧刚度有较大幅度提高,中大震及大震阶段其承载力、等效刚度约为空框架和组合墙单独受力之和的0.9倍,两者具有良好的协同工作性能;加固试件的破坏过程基本上遵循填充砌块混凝土框格外框架的破坏顺序,能够发挥组合墙多重抗震防线的特点,采用RC加气混凝土砌块组合墙加固框架是一种较为经济实用的加固方法。     

玉米粗缩病病情严重度分级标准及病情指数与产量损失率关系的研究

通过对农大108、郑单958和德玉18等3个玉米品种感染玉米粗缩病后株高与单株产量的测定,按病株相对健株株高的比值推导出了玉米粗缩病严重度分级标准,即病株相对健株株高的比依次为1,4/5,2/3,1/2,1/3,其对应病株的病级分别是0,1,2,3,4级;明确了0~4级玉米粗缩病病情严重度分级标准与产量损失的关系,即0,1,2,3,4级病株,产量损失率依次为0,25%,50%,75%和100%。利用该分级标准对10个生产品种的玉米粗缩病病情进行调查,构建了回归方程Y=-0.253 1.02X。利用16个生产品种对方程进行检验,检验准确率为:理论产量损失率与实际产量损失率没有显著差异。应用此方程,可预测玉米粗缩病导致的产量损失。     

Flexural toughness of hybrid fiber reinforced shotcrete

为了研究混杂纤维喷射混凝土的弯曲韧性,采用不同掺量的钢纤维和聚丙烯纤维混杂以及高炉微粉复合超叠加的方法制备600 mm×600 mm×100 mm混杂纤维喷射混凝土方板并置于刚性支撑架上,选用等位移控制对方板进行中心加载。通过生成的荷载挠度曲线及对其进行积分所得的能量吸收值综合评价各组方板的弯曲韧性,同时,通过破坏过程评价各板裂缝控制能力。试验结果表明：掺入1.2%钢纤维和0.11%聚丙烯纤维的喷射板试件的弯曲韧性优于掺入0.8%钢纤维和0.11%聚丙烯纤维的喷射板,其最大峰值荷载提高了18%,板中心挠度至25 mm时的能量吸收值也提高了25.6%;对于仅掺入0.8%单一钢纤维的板,混杂了0.11%聚丙烯纤维后,两种纤维间的正混杂效应使得板中心挠度至25 mm时的能量吸收值提高了28.5%;高炉微粉掺量的增加能提高混杂纤维喷射混凝土板的弯曲韧性;混杂纤维喷射混凝土板均展现出了良好的裂缝控制能力,板整体呈现裂而不断的延性破坏。     

T形板肋对预制带肋底板混凝土叠合板弯曲疲劳性能的影响

为研究T形板肋对预制带肋底板混凝土叠合板弯曲疲劳性能的影响,对3块T形肋底板叠合板和1块整浇板进行弯曲疲劳性能对比试验,主要考察T形板肋与疲劳荷载幅值对试件疲劳破坏形态及疲劳损伤程度的影响,得到了在不同疲劳循环加载次数下的跨中动位移、混凝土应变、预应力筋应变、残余变形等,分析了在不同疲劳循环加载次数下的刚度退化情况、荷载-应变分布规律、裂缝分布规律及剩余承载力等。研究结果表明,经历200万次疲劳循环加载后,T形肋底板叠合板无明显的刚度和强度退化,增设T形板肋的叠合板能达到与整浇板相同的弯曲疲劳性能;T形肋底板叠合板正截面弯曲疲劳强度计算可采用普通预应力混凝土受弯构件正截面疲劳应力验算的4个假定,最终以此建立了其正截面弯曲疲劳强度验算方法。     

Influences on Engineering Properties of AS Firming Agent Modified Soil by Freeze-thaw Cycles

To study the freeze-thaw durability of Aught-Set(AS) firming agent modified soil, a series of triaxial tests were conducted. The mutual relationships between stress-strain relationship, static strength, dynamic modulus and critical dynamic stress of AS firming agent modified soil and curing time, freeze-thaw cycles, cooling temperature were deeply analyzed. The results show that the unconfined compressive strength of 7 d is 75% than that of 28 d. The stress-strain curves of AS firming-agent modified soil are strain-softening and in brittle failure shape. The static strength, critical dynamic stress and resilient modulus decrease in exponential form with the increase of freeze-thaw cycles, and after 6 cycles of freezing and thawing, the trend is stable. Under the same dynamic stress, the cumulative plastic strain of samples develop from stable state to failure because of freezing and thawing. After many times of freeze-thaw cycles, the lower the negative temperature, the little influence on the mechanic properties.     

Rubber Powder Modified Frost Resistance of Recycled Aggregate Concrete

Utilizing relative dynamic elastic modulus and weight loss of concrete as evaluation indices, the frost resistance of concrete with 0.45 water-cement ratio and different recycled aggregate replacement proportions was studied in the water and 3.5% sodium chloride solution. The mass proportions of recycled aggregate are 25%, 50% and 75%, respectively. Furthermore, the frost resistance of the modified concrete with 5% and 10% rubber powder volume fractions replacing fine aggregates was studied. The results show that: the frost resistance of concrete decreases with the increase of recycled aggregate, when the recycled aggregate mass fractions are 25% and 50%, its influence on the frost resistance of concrete is little, and mixing rubber powders can effectively improve the frost resistance of concrete; when the recycled aggregate mass fraction reaches 75%, its effect on the frost resistance of concrete is significant, and mixing rubber powders has certain improvement effect, but compared with the benchmark group of concrete the maximum freeze-thaw cycles decreases more than 30%. In water frozen test, the weight loss is small and the relative dynamic elastic modulus loss is quite obvious. The frost resistance is better when adding 5% volume fraction of rubber powders. In salt frozen test, the main characteristic is the weight loss exceeds the requirements. The frost resistance is better when adding 10% volume fraction of rubber powders. The improvement effect of rubber powder to the frost resistance of concrete in salt solution is much better than that in water.     

Experiments on heat loss characteristics in a fully opened cylindrical cavity receiver

The climate has a great impact on highway bridge rubber bearings than on building rubber bearings. In order to study the change of the mechanical properties during the life of the plain chloroprene rubber bearings of highway bridge under freeze-thaw cycle condition, the plain chloroprene rubber bearings were processed 25, 50, 75, 100 times by freeze-thaw cycle in the standard freeze-thaw chamber, then the axial compression tests were carried. The changes of the performance indicators in the bearing capacity , the ultimate compressive strength, vertical stiffness, elastic modulus under different freeze-thaw cycles were analyzed comparatively. The results show that the plain chloroprene rubber bearings are more prone to brittle failure after the freeze-thaw cycle, and the failure phenomena of steel plate exposing or cracks is more serious than the phenomena of the standard specimen. With the increase of the number of freeze-thaw cycle, the ultimate bearing capacity, ultimate compressive strength and compressive elastic modulus of the plain chloroprene rubber bearings decrease. The attenuation formula and decay curve in 50 years of ultimate compressive strength and elastic modulus of compression are analyzed by least square method, the trends of change are both in line with the exponential function. The mechanical properties of plain chloroprene rubber bearings of highway bridge significantly decreased under freeze-thaw cycle condition. therefore, the temperature ranges of plain chloroprene rubber bearings of highway bridge should be strictly controlled, and some suggestions, such as increasing its minimum applicable temperature, usng the natural rubber bearings as much as possible in cold regions, have been given.     

建筑垃圾细料生产流动化回填材料的性能

以灰砂比0.03、0.05和0.08,粉砂比0、0.05、0.1、0.15和0.2为设计参数,对建筑垃圾回填材料进行设计。通过试验对回填材料的流动性(流动度、泌水率)、无侧限抗压强度以及应力应变曲线、本构关系模型和弹性模量等进行研究。研究结果表明:回填材料的流动度受水固比影响较大,两者接近线性关系;流动度在200~250 mm范围,泌水率在4%~8%之间;回填材料抗压强度与灰砂比和水固比之间存在很好的幂指数关系;回填材料应力应变曲线形状与普通混凝土的相似,在此基础上提出回填材料的本构关系模型;回填材料无侧限抗压强度与弹性模量之间存在很好的指数关系。     

Stress Corrosion of Concrete Exposed to the Action of Freezing-thawing Cycles

Through the method of accelerated freezing-thawing and room-temperature corrosion, the stress corrosion of three kinds of concretes subjected to 5.0%MgSO4(in mass)solution was studied. The considered concretes include High Strength Concrete(HSC), High-Volume Mineral Admixture Concrete(HVMAC) and High Durable Concrete(HDC) added with high-volume mineral admixture, air-entraining agent, superplasticizer, fibers and expansion agent. The results showed that the relative dynamic elastic modulus of concrete went through strengthen and deterioration stages subjected to stress corrosion, whether the room temperature or freezing and thawing conditions. The length of time of these two stages are closely related with the experimental temperature. Freezing and thawing action significantly accelerated the process of sulphate stress corrosion damage. Under the action of freezing and thawing, stress corrosion strengthening the period length of HSC shorter 96%, deterioration section of the length of time shorter 88%, compared with the length of time at the corresponding room temperature. Deterioration section of the length of time of HVMAC is reduced by 98%, while the HDC reduced by 71%. The effect of freezing and thawing, HDC freezing-thawing cycles when the stress corrosion damage occurred were longer 1.5 times and 13 times than the HSC and HVMAC. Thus in the cold regions, HDC showed more resistance to sulfate stress corrosion.     

Experimental Research on Concrete Strength under Freeze-thaw Recycle Action with Ultra-low Temperature

The concrete structure has been used in low and ultra-low temperature environment. But few researches are experienced on its properties under freeze-thaw recycles with ultra-low temperature. Based on the standard for test methods of long-term performance and durability of ordinary concrete, considering the influence of the times and minimum temperature of recycles, water-cement ratio and the external environment humidity, compressive and tensile strength of cubic concrete and scanning electron microscopy on the residual sample are experimented to explore the impact of freezing and thawing cycles under ultra-low temperature on its strength and microstructure. The results show that the role of cryogenic temperature for freeze-thaw cycles has a greater effect on concrete performance. With the temperature decreasing and water-cement ratio increasing, the damage tends to grow up. Consistent with the results of the strength tests, electron microscopy tests show that the pore size of mortar increases and the material becomes looser.     

A THEORETICAL BASIS OF EQUATION OF CORRELATION BETWEEN STRENGTH AND ELASTIC MODULUS OF CONCRETE

The equation of correlation between compressive strength and elastic modulus of concrete is derived on the basis of modified Burger's model. The result shows that the derived equation is similar to the empirical equation of correlation between compressive strength and elastic moulus of concrete. So this empirical equation is confirmed by rheology theory of concrete.     

Three-dimensional Random Damage Prediction Model of Concrete Caused by Freeze-thaw

In order to effectively assess the damage of concrete in freeze-thaw condition, prediction model for concrete frost damage is presented based on damage mechanical theory and the experimental test. The degeneration of tension strength of air-entraining concrete is tested after freezing and thawing. Provided with the fact that the degeneration of concrete is an interior damage evolving process, freezing and thawing damage accumulation of concrete is analyzed based on the discrete grid with probability of stochastic method. And Three-dimensional multi-parameters Weibull distribution model about concrete damage evolutions is presented. Parameters are estimated based on gradient method, and the mathematical model is verified according to the tested data. Corresponding algorithm is designed and programming is completed by C + + programming language to establish concrete durability prediction model under freeze-thaw conditions. It is indicated that the damage of concrete develops in nonlinear way as the freezing and thawing increases.     

再生混凝土抗碳化性能试验研究及理论分析

通过快速碳化试验,以再生骨料掺量、水灰比、水泥用量、原始混凝土强度和矿物掺合料为影响因素,对再生混凝土的碳化性能进行研究。试验结果表明：再生混凝土的碳化深度随水灰比、再生骨料掺量的增加而减小,随原始混凝土强度的增大和水泥用量的增加而增大,适量添加矿物掺和料能降低再生混凝土的碳化深度,提升其抗碳化性能。在已有的普通混凝土碳化模型研究基础上,结合本试验和中国其他学者的试验数据,建立了再生混凝土碳化深度预测模型,模型预测结果与试验值吻合较好。