酸雨环境下老旧砖砌体的抗压性能

为研究酸雨环境下老旧砌体抗压力学性能退化规律,实验室配置了PH值分别为1.5、2.5和3.5的3种硫酸和硝酸混合溶液来模拟酸雨环境,采用完全浸泡加速腐蚀的试验方法对砖、砂浆和砖柱进行不同程度的腐蚀,并测定其抗压强度。试验表明,随着腐蚀时间的增加,砂浆试块抗压强度先增大后降低;砖试块抗压强度随腐蚀时间的增加而降低;模拟酸雨溶液PH值越小,砂浆和砖试块抗压强度降低程度也愈大;砖柱极限承载力和弹性模量均随腐蚀时间的增加而降低,且模拟酸雨溶液PH值越小,降低程度愈大;随着腐蚀时间的增加,砖柱初始刚度逐渐减小,极限破坏位移增大;模拟酸雨溶液PH值越小,砖柱在达到峰值荷载时的变形值越小,脆性愈大;基于试验结果,建立了酸雨环境下砖柱应力应变曲线上升段统一数学表达式及酸雨侵蚀后普通烧结粘土砖砌体剩余抗压强度回归公式。     

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。     

页岩烧结保温砌块砌体基本力学性能试验研究

通过对页岩烧结保温砌块砌体轴心抗压、沿通缝抗剪、剪压复合抗剪性能试验研究,分析其破坏特征和破坏机理。试验结果表明:页岩烧结保温砌块砌体受压破坏时,在竖向灰缝附近形成主裂缝,接近极限荷载时砌体出现表皮剥落现象;沿通缝抗剪破坏模式主要为单剪破坏,脆性明显;剪压破坏有剪磨、剪压和斜压3种类型;实测轴心抗压强度平均值高于规范值,沿通缝抗剪强度、复合抗剪强度平均值低于计算值,并分别给出砌体轴心抗压强度平均值、抗剪、剪压复合受力抗剪强度平均值建议公式;剪压复合抗剪强度随着压应力的增大而增大;建立了页岩烧结保温砌块砌体受压应力应变关系表达式;给出该类砌块的弹性模量和泊松比的建议值。     

高强钢绞线网加固混凝土粘结性能试验研究

通过高强钢绞线网聚合物砂浆加固层与混凝土结构的剥离破坏试验,对加固层与混凝土界面的剥离破坏特征进行了研究。探讨了单侧加固、植筋加固及U型加固等不同的加固方式对加固层抗剪承载力及抗剪强度的影响。试验结果表明,采用U型加固等增加粘结面积的方式能有效提高加固层粘结面抗剪承载力,但同时会削弱加固层的抗剪强度,而在界面上植入抗剪钢筋后,能同时提高聚合物砂浆加固层的抗剪承载力及抗剪强度。根据试验结果,提出了最小植筋率的建议值。     

再生粗骨料混凝土碳化分析的多场耦合模型及验证

再生粗骨料混凝土的碳化是一个复杂的物理扩散和化学反应过程,其分析和预测较为困难。鉴于此,基于再生粗骨料混凝土的碳化机理,结合再生粗骨料混凝土中CO₂的扩散定律和可碳化物质的质量守恒定律,综合考虑再生粗骨料混凝土中CO₂的有效扩散系数、碳化反应速率系数、可碳化物质的量、再生粗骨料的表面附着砂浆等重要参数的影响,建立了再生粗骨料混凝土碳化分析的多场耦合模型,并通过试验数据验证了模型的有效性和适用性。     

硫铝水泥和胶乳对水泥乳化沥青砂浆低温硬化性能的影响

通过分析水泥乳化沥青砂浆（CA砂浆）冬季低温病害的产生原因,研究了硫铝酸盐水泥、胶乳对CA砂浆低温凝结和灌注质量的影响。结果表明,低温导致CA砂浆超长缓凝,使体系稳定性变差,并引起泌水和揭板起皮等病害;掺入硫铝水泥能加快CA砂浆的低温凝结过程,随替代量增加,凝结时间逐渐缩短;随温度升高,胶乳水泥流态体系可搅拌时间呈降低趋势,选用低温稠化性能合适的的胶乳,可改善新拌CA砂浆的低温均匀稳定性;复掺10%硫铝水泥和8%胶乳的CA砂浆在24 h的强度和膨胀率符合要求,在实测0.5~7.7 ℃的低温环境中,揭板检查CA砂浆断面均匀、表面平整无起皮,符合上道要求。     

水泥稳定三峡库区风化砂回弹模量试验及模型评估

以水泥稳定三峡库区风化砂的回弹模量值为研究对象,在风化砂中分别掺入3%、5%、7%、9%的水泥制作试样,然后各自养护7、14、21、28、35、56、70 d,开展室内回弹模量试验。试验结果表明:掺水泥能显著提高风化砂的回弹模量值。在相同的养护龄期下,随着水泥掺量的增加,回弹模量值逐渐增大,增长的幅度先大后小,二者呈现良好的对数函数关系;在相同的水泥掺量下,随着养护龄期的增长,回弹模量值也逐渐呈线性增大,且在最初养护的28 d内,回弹模量值的增长占整个测试期内的95%左右。通过回归分析,分别建立了水泥掺量与回弹模量值之间、养护龄期与回弹模量值之间的数学模型,再通过补充试验,进一步验证了所建数学模型的正确性及精确度。     

玉米堆的压缩弹塑性实验分析

利用LHT-1型粮食回弹模量测定仪对玉米堆在不同条件（预压力,水分）下的无侧向膨胀回弹模量进行了实验测定,分析了不同预压力（0、100kPa、200kPa）、不同水分（13.89%、15.12%、17.71%、18.74%）对玉米堆回弹模量的影响;弹塑性形变之比与预压力的关系以及每次加卸载时塑性形变的变化规律。实验结果表明：同一水分下,玉米堆的回弹模量随着预压力的增大而增大;同一预压力下,随着水分增大,玉米堆的回弹模量减小;第五圈的弹塑性形变之比随预压力的增大而减小;每次加卸载后塑性形变随加载次数的增加而减小。     

面向刚度曲线的汽车前保险杠缓冲块优化设计

以掺天然砂砾改良的红粘土为研究对象,采用室内承载板法测定回弹模量,通过不同初始干密度下的回弹模量试验,深入研究了天然砂砾改良红粘土的回弹模量随初始干密度的变化规律,建立了不同初始干密度下回弹模量的预估模型。试验结果表明:在同一天然砂砾掺量下,随着初始干密度的提高,红粘土的回弹模量逐渐增大。当初始干密度由低向最大干密度增大时,回弹模量增长速度较快,当初始干密度超过最大干密度继续增大时,回弹模量增长速度变缓;在同一初始干密度下,当天然砂砾掺量从0增至30%时,回弹模量的增长幅度较小,当天然砂砾掺量超过30%而继续增长时,回弹模量增长幅度较大;初始干密度由1.6 g·cm^-3增长至2.0 g·cm^-3时,回弹模量增长值随天然砂砾掺量的增加而逐渐增大。分别建立了回弹模量随初始干密度及天然砂砾掺量变化的预估模型,通过补充试验,验证了预估模型的准确性。     

未水化水泥颗粒后期水化对UHPC性能的影响

采用高温加速试验,并结合烧失量法、力学试验、测长法、电通量法、碳化等手段研究了不同养护温度和水胶比条件下未水化水泥颗粒后期水化对UHPC性能的影响。结果表明：60 ℃水养护能够有效加速UHPC中未水化水泥颗粒的后期水化,试块的结合水量在90 d内趋于稳定。随养护龄期的增长,UHPC试块先收缩后膨胀,90 d的抗折强度、抗氯离子渗透性和抗碳化性能均下降,抗压强度尚无明显损失。水胶比越低,UHPC试块90 d的结合水量增长率越大,膨胀值越大,抗折强度损失率也越高。     

Effect of the Carbonation on the Steelmaking Slag-Slaked Lime Mortar

The effect of the carbonation on the properties of the steelmaking slag-slaked lime (SmS-SL) mortar and its mechanism were mainly investigated. Furthermore, the environmental benefits of the SmS-SL mortar were discussed as well. Results indicated that carbonation could strengthen the SmS-SL mortar, reduce its drying shrinkage and improve its soundness. With the increase in the steel slag content, the strengthening effect of carbonation on the SmS-SL mortar is enhanced, but its dry shrinkage reduction effect is weakened. The SmS-SL mortar using steel slag exhibits significant environmental benefits. Its CO2 sequestration-efficiency and steel slag-recycle efficiency respectively reaches 6.4% and 27.8%.     

古代砖砌体风化性能分析及风化程度评定

自然界中气温、降水的长期作用导致古代砖砌体风化,风化损伤材料和砌体力学性能。实验采用大气环境实验舱实现自然风化作用人工模拟,根据不同饱水度和冻融次数,实验舱设定了7种非饱水冻融工况,对7种工况影响下的砖、灰浆、砌体抗压、砌体抗剪试件试件强度变化规律进行实验分析。实验表明,饱水度是反映材料冻融性能的重要指标;不同饱水度下的冻融试件强度呈现先升后降的趋势;试件在饱水度为53%的冻融作用下,砌体构件具有最佳抗力;提出古代砖砌体构件风化程度评定标准。实验对古砖砌体结构保护工作具有指导和应用价值,定期评定古塔砌体风化程度,时刻掌握古塔构件结构安全性能的变化规律,科学保护古塔。     

Image segmentation based on differential mutation bare bones particle swarm optimization and fuzzy entropy

Sawdust, coal gangue and paper sludge were chosen as pore-forming agents of sintered shale brick. The pyrolysis behaviors of different forming agents were studied and the influences of the agents on bulk density, compressive strength, porosity, and water absorption properties of the shale brick were also investigated. It is shown that, with the increase of the dosage of sawdust, pore number of the sintered bricks and water-absorption increase, while the volume density and strength fall rapidly. Thus, the dosage of sawdust should be controlled within 6%. Because of poorer plasticity and lower ignition of coal gangue as well as low porosity rate of sintered bricks, the water-absorption of sintered bricks is poor, and decreases of density and strength are not obvious. In practical production, according to the requirements of brick-making heat and plasticity, a moderate amount of coal gangue can be added. The plasticity of the bricks improves as the dosage of paper sludge increases due to its good plasticity. However, excessive dosage of paper sludge will result in large shrinkage of sintered brick, low strength and high water absorption; therefore, the dosage should not exceed 7%.     

Carbonation Depth Prediction of Concrete Structures Based on Inspection Data

There are subjective uncertainty and randomness in concrete carbonation depth forecasting model and the model distribution parameters, which cause significant errors in application to practical engineering. Actual inspection data can not often be used to forecast concrete carbonation depth in the actual project due to its small sample size and lack of sufficient completeness. The weighted value of several model calculations was used to forecast the concrete carbonation depth. By using Bayesian approach, the inspection information and the prior prediction model were incorporated, and the prior model weights and model distribution parameters statistics were updated. It is more accurate to forecast the carbonation depth using the updated model weights and model distribution parameters. The procedure for updating the mechanical model selection and distribution parameter statistics was illustrated with a 10-year-long concrete carbonation test.     

E‐commerce,Transportation, and Economic Geography

ABSTRACT This paper explores possible ways in which growth in Internet retailing (e‐retailing) may affect the spatial distribution of economic activities. After a brief overview of e‐retailing, a categorization of possible spatial impacts is introduced. These include impacts on the retail industry, such as substitution of e‐retail for brick‐and‐mortar retail, impacts on transportation, such as substitution of freight transportation for personal transportation in goods delivery, and pervasive impacts that affect the whole economy. The latter category includes uniform delivered pricing, spatial leveling of accessibility, and marketing strategies that target individuals rather than regions. The question of whether e‐retailing and brick‐and‐mortar retailing are truly substitutes is taken up in the next section, along with potential implications of multi‐channel retailing. The final section of the paper defines some critical research directions.     

异质复合墙体日光温室的设计建造及保温性能的测定

针对河北省现有日光温室保温性能差、土地利用率低、抗自然灾害能力弱、使用年限短、标准化水平不高的问题,设计建造新型异质复合墙体日光温室及利用巡检仪测定其保温性能,筛选出页岩实心砖、页岩多孔砖作为墙体承重材料,酚醛板、HD-STP真空绝热板、水泥基复合保温砂浆作为墙体保温材料,挤塑聚苯板作为后屋面保温材料;设计建造了4种异质复合墙体日光温室,净跨度10m、矢高4.5m,内砌页岩实心砖或页岩多孔砖,外贴保温隔热材料的墙体结构;37cm厚的页岩实心红砖+5cm厚的酚醛板的墙体传热系数为0.05W/m₂.K,传热系数最小、保温性能最优;冬暖Ⅱ型日光温室墙体(底部2.9m、顶部1.5m厚的粘土碾压成型土墙)传热系数为0.12W/m₂.K,居第2位、保温性能居第2位;第3、4、5位依次为37cm厚的页岩多孔砖墙+5cm厚的酚醛板墙体0.53 W/m₂.K、37cm厚的页岩多孔砖墙+ 1cm厚的STP真空绝缘板墙体0.6 W/m₂.K、37cm厚的页岩实心红砖+5cm厚的保温砂浆墙体1.35W/m₂.K。本设计建造的异质复合墙体(37cm厚的页岩实心红砖+5cm厚的酚醛板)保温蓄热性能良好且优于冬暖Ⅱ型日光温室墙体,该温室可完全替代冬暖Ⅱ型日光温室。     

Deterioration Model and Reliability Analysis on Concrete Material at Stress States

According to the analysis of existing test data, the stress influence coefficient and water-cement ratio influence coefficient in the existing concrete carbonation depth forecasting models are modified and improved. Based on the reliability analysis, the rule of deterioration life is presented. The analysis shows that the rate of carbonation of concrete is accelerated or restricted at the status of tensile or compressive stress, respectively. Especially with the increase of the level of tensile stress, the carbonation rate of concrete will become faster and faster. According to the results of reliability analysis, the relation between probability and reliability of the concrete deterioration is one-to-one corresponsive, meanwhile, the concrete cover thicknesses and stress levels have great influences on the durability life of concrete structures. And with the same reliability, the time of deterioration of concrete decreases with a higher stress levels and a less cover thickness.