Reclamation of Abandoned Coal Mine Waste in Korea using Lime Cake By-Products

Abstract.  There are hundreds of abandoned coal mines in Korea's steep mountain valleys. Enormous amounts of coal waste from these mines were dumped on the slopes, contaminating streams with sediment and acid mine drainage. A limestone slurry by-product (lime cake), which is produced during the manufacture of soda ash, was investigated for its potential use in reclaiming the coal waste. The lime cake is fine grained, has low hydraulic conductivities (10^-8 to 10^-9 cm sec^-1), high pH, high electrical conductivity, and trace amounts of heavy metals. A field experiment was conducted; each plot was 20 x 5 m in size on a 56% slope. Treatments included a control (waste only), lime (CaCO₃), and lime cake. The lime requirement (LR) of the coal waste to pH 7.0 was determined; treatments consisted of adding 25, 50, and 100% of the LR. The lime cake and lime were applied either as a layer between the coal waste and topsoil or mixed into the topsoil and waste. Each plot was hydroseeded with grasses, and planted with trees. In each plot, soils, surface runoff, and subsurface water were collected and analyzed, and plant cover was measured. Lime cake treatments increased the pH of the coal waste from 3.5 to 6, and neutralized the pH of the runoff and leachate of the coal waste from 4.3 to 6.7. Moreover, the surface cover of seeded species was significantly increased; sufficient acidity in the coal waste was neutralized in the 25% LR plots to allow seed germination.     

黄土灰土地基的质量控制系统试验研究

对黄土灰土的物理力学性质和黄土灰土地基施工过程中的质量控制要点进行了试验研究。分析了各种因素的影响程度和影响结果 ,发现灰土不但有最优含水量而且有最佳含灰量问题。同时在施工过程中灰土地基的虚铺厚度、碾压过程及碾压间隔时间等都对施工质量产生一定的影响。     

灰土挤密桩在湿陷性黄土地基处理中的应用

结合工程实例 ,阐述了选用灰土挤密桩处理湿陷性黄土软弱地基的施工过程 ,介绍了灰土挤密桩的加固原理、施工工艺及质量检验 ,指出该工程造价低、工期短     

注浆联合石灰桩在岸坡挡墙地基加固中的应用

重力式挡土墙建立在桥台的下游护坡上,墙的基础由桩和筏板构成。在饱水时墙的稳定性未能满足规范要求,经用注浆联合石灰桩加固,取得了成功。     

谈深层搅拌石灰桩加固软弱地基

本文介绍深层搅拌石灰桩加固软弱地基的原理和设计方法,该方法具有设备简单、施工方便、经济效益好的特点。     

长寿命路面路床顶部土基处理技术研究

针对土基采用冲击压实机冲压后,路基表面容易形成薄层覆土,从而产生软弱层的问题,提出分别采用固化剂和石灰处理路基顶面20 cm土层,并提出施工注意事项,以供同类工程设计参考.     

加筋纤维石灰土的试验研究

试验结果表明,添加纤维可以改善石灰土的力学性能。若添加单丝纤维和短的网状纤维,其最佳含量为0.4%,而掺长网状纤维,最佳含量应为0.2%~0.3%;纤维石灰土的强度较石灰土有显著的增加,随龄期的增长,强度的增加大于弹性模量的增加,模强比较小,说明纤维石灰土不仅具有较高的抗压强度,而且具有一定的抗拉能力。应力应变曲线特征,主要表现在破坏后阶段,纤维含量越多,应力下降越小,龄期越长,应力下降越大;纤维石灰土的破坏特征基本符合莫尔-库伦剪切规律,但是随纤维含量的增多,剪切带增宽。     

混凝土收缩裂缝浅析

介绍了混凝土收缩的常见种类，对混凝土各收缩裂缝的形成原因进行了分析，从多方面提出了混凝土收缩裂缝的防治方法，从而避免或减少施工中的收缩裂缝。     

空军汉口新机场试验路段石灰改性膨胀土试验研究

空军汉口新机场试验路段石灰改性膨胀土（简称灰土）试验研究包括室内和现场试验研究。室内试验研究包括：天然膨胀土与击实膨胀土的基本物理特性和胀缩特性试验、灰土击实试验以及膨胀土掺石灰改性试验等。室内试验结果表明：击实膨胀土比天然膨胀土的膨胀潜势更大；在道面下一定范围内，填料不能采用膨胀土，而必须用灰土；石灰能有效地对场区内的膨胀土进行改性，最优石灰掺合比为6％～8％：不同灰土层的最大干密度与最佳含水量差异较大，现场施工填料不能混填。现场试验包括：碾压试验、压实灰土基本物理特性和胀缩特性试验、浸水载荷试验、测定路基回弹模量和回弹弯沉试验等。现场试验结果表明：在有效控制灰土的石灰掺量和含水量情况下，采用激振力为450kN的碾压机对松铺厚度为50和30cm的灰土进行碾压，分别需碾压8和6遍，路基压路度才能达到95％，表面沉降才趋于稳定；现场压实灰土的膨胀潜势很低，仍有明显失水收缩特性，在施工时应注意采取保水措施；压实灰土具有较高承载能力、强度特性和吸水稳定性。     

Deterioration and Recovery of Metakaolin Blended Concrete Subjected to High Temperature

The deterioration and spalling frequency of metakaolin (MK) blended concrete subjected to high temperature is analyzed and compared with the equivalent silica fume (SF), fly ash (FA) and pure OPC concretes. Normal and high strength concrete mixes incorporating 0–20% MK were prepared and exposed to a series of high temperatures till 800°C. The residual compressive strength, porosity and pore size distribution were determined. It was found that after an increase in compressive strength at 200°C, the MK concrete suffered a more severe loss of compressive strength and permeability-related durability than the corresponding SF, FA, and pure OPC concretes at higher temperatures. Explosive spalling was observed in both normal and high strength MK concretes, and the frequency increased with higher MK contents. It is concluded that the dense micro-structure and low porosity are the main reasons of the poor performance of MK concrete at high temperature. The effect of post-fire curing on the strength and durability recovery of fire-damaged concrete was also investigated. The test results indicated that the post-fire curing, results in substantial strength and durability recovery, and its extent depends upon the types of concrete, exposure temperature, method, and duration of re-curing.