混凝土坝表层碳化及其危害性分析

随着时间的推移 ,混凝土坝表层碳化现象日益加重。许多工程实践表明 ,采用劣质材料和较差的混凝土配合比 ,施工质量差 ,未进行表面养护 ,以及环境相对湿度较小时 ,混凝土碳化速度较快 ;有的坝在混凝土龄期 30年以后碳化趋势尚未收敛稳定。混凝土坝的梁、柱构件因碳化引起钢筋锈蚀膨胀 ,产生顺筋裂缝和混凝土崩落的现象比较普遍。轻型平板坝因碳化严重 ,使面板挡水功能受到危害的问题 ,应引起高度重视 ,并应及时进行处理。

古田溪三级大坝老化病害及其治理

古田溪三级钢筋混凝土平板支墩坝,建成蓄水至今已40多年,随着岁月的流逝,坝基帷幕防渗能力逐渐衰减,迎水面遭受到严重风化侵蚀,面板渗漏溶蚀不断加剧,表层碳化深度日益累进,坝体裂缝增生或扩展,面板强度大幅度降低。为了遏制大坝进一步遭受到老化病害的危害,确保大坝安全运行,采取了一系列针对性防护和加固措施。对该坝老化症状坚持定期检测分析,并及时进行治理,对于其他大坝具有一定的借鉴意义。

Carbon and Nitrogen Transformations in Surface Soils Under Ermans Birch and Dark Coniferous Forests

Soil samples were taken from an Ermans birch （Betula ermanii）-dark coniferous forest （Picea jezoensis and Abies nephrolepis） ecotone growing on volcanic ejecta in the northern slope of Changbai Mountains of Northeast China, to compare soil carbon （C） and nitrogen （N） transformations in the two forests. The soil type is Umbri-Gelic Cambosols in Chinese Soil Taxonomy. Soil samples were incubated aerobically at 20℃ and field capacity of 700 g kg^-1 over a period of 27 weeks. The amount of soil microbial biomass and net N mineralization were higher in the Ermans birch than the dark coniferous forest （P 〈 0.05）, whereas the cumulative C mineralization （as CO2 emission） in the dark coniferous forest exceeded that in the Ermans birch （P 〈 0.05）. Release of the cumulative dissolved organic C and dissolved organic N were greater in the Ermans birch than the dark coniferous forest （P 〈 0.05）. The results suggested that differences of forest types could result in considerable change in soil C and N transformations.

Multilayer distribution of carbon dioxide system in surface water of the Yellow Sea in spring

Surface water can be divided into three layers from top downward： surface microlayer （SML, thickness≤50 μm）, subsurface layer （SSL, ≈25 cm） and surface layer （SL, l-5m）, among which the SML plays an important role on sea-air interaction because of its unique physical-chemical property. Carbon dioxide system including DIC （dissolved inorganic carbon）, Alk （alkalinity）, pH and pCO： （partial pressure of CO2） in multilayered waters of the Yellow Sea was studied for the first time in March and May 2005. The results show that： DIC and Alk are obviously enriched in SML. The contents ofDIC, Alk and pCO2 become lower in turn from SML, SSL to SL, higher in March and lower in May, whereas for pH it was opposite. The relationship between DIC and Alk is clearly positive, but negative between pH and pCO2. Meanwhile, pCO2 and temperature/salinity is also in positive relation, pCO2 decreases with latitude increase. DIC and Alk show a similar variation trend with the maximum at 02：00-03：00, but pH and pCO2 show an opposite pattern. In addition, the distribution patterns are similar to each other in the three layers. The Yellow Sea is shown to be a sink of atmospheric CO2 in spring by two methods： （1） comparing pCO2 in seawater and atmosphere; （2） turning direction of ＂pH-depth＂ curve. Calculation on the base of pCO2 data in SML in four models shows that carbon flux in spring in the area was about -6.96×10^6 t C.

Scaling and Removal of Calcium. Carbonate on Electroless Plating Surface

The scaling process of calcium carbonate on a low-energy heat transfer surface－electroless plating surface was investigated in a simulated cooling water system. Owing to the very low surface energy, the electroless plating surface exhibited less scaling susceptibility. A longer induction period and a lower scaling rate were obtained on the low-energy surface compared to copper surface under identical conditions. The calcite particles obtained on the electroless plating surface during the induction period were larger in size than those on copper surface because fewer crystals formed and grew at the same time on the low-energy surface. With increasing surface temperature, the induction period reduced and the scaling rate increased for the low-energy surface. When initial surface temperature was fixed, an increase in fluid velocity would reduce the induction period and increase the scaling rate due to the diffusion effect. However, when the heat flux was fixed, an increase in fluid velocity would decrease the surfacetemperature, and lead to a longer induction period and a lower scaling rate. The removal experiments of calcium carbonate scale indicated that during post induction period, the detachment was not obvious, while during the induction period, apparent removal of crystal particles was obtained on the electroless plating surface owing to the weak adhesion force. The more frequently the transient high hydrodynamic force acted, the more the detached crystal particles were.

Surface Soil Properties Influence Carbon Oxide Pulses After Precipitation Events in a Semiarid Vineyard Under Conventional Tillage and Cover Crops

In semiarid regions of the Mediterranean basin, a rainfall event can induce a respiratory pulse that releases a large amount of soil carbon dioxide （CO2） into the atmosphere; this pulse can significantly contribute to the annual ecosystem carbon （C） balance. The impacts of conventional tillage and two different cover crops, resident vegetation and Bromus catharticus L., on soil CO2 effiux were evaluated in a Vitis vinifera L. vineyard in La Rioja, Spain. Soil CO2 efflux, gravimetric water content, and temperature were monitored at a depth of 0-5 cm after rainfall precipitation events approximately every 10 d in the period from May 17 to July 27, 2012, during which the cover crops had withered. Additionally, on June 10, 2012, soil organic C, microbial biomass C, and I^-glucosidase activity were determined at soil depths of 0-2.5, 2.5-5, 5-15, and 15-25 cm. The results show that pulses of soil CO2 were related to the increase in soil water content following precipitation events. Compared to the conventional tillage treatment, both cover crop treatments had higher soil CO2 efflux after precipitation events. Both cover crop treatments had higher soil organic C, microbial biomass C, and β-glucosidase activity at the soil surface （0-2.5 cm） than the conventional tillage treatment. Each pulse of CO2 was related to the surface soil properties. Thus, this study suggests that the enhancement of soil organic C and microbiological properties at the soil surface under cover crops may increase soil CO2 efflux relative to conventional tillage immediately after precipitation events during the dry season.