Stability of Calcium Sulfate Base Course in a Wet Environment
Stability of Calcium Sulfate Base Course in a Wet Environment
复制标题
硫酸钙碱基在潮湿环境中的稳定性
DOI：
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发表时间：
2006
期刊：
影响因子：
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通讯作者：
Mingjiang Tao
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作者：
Zhongjie Zhang;Mingjiang Tao
混合硫酸钙（BCS）是氟石膏（FG）——一种工业副产品，与石灰或石灰石混合而成。美国每年大约产生90,000公吨（100,000吨）的氟石膏，这给环境处置带来了严重问题。路易斯安那州交通运输与发展部（LA DOTD）在过去15年中一直在路面建设中使用混合硫酸钙。虽然这种材料在施工后性能令人满意，但它对湿度的敏感性引起了LA DOTD工程师的关注，因为它在潮湿环境中给施工带来了困难。因此，有必要更好地了解混合硫酸钙在潮湿环境中的强度劣化情况，并通过使用各种合适的胶凝剂稳定混合硫酸钙来找到消除或减少这种劣化的方法。本研究分为两个主要部分：实验室测试和现场测试。进行实验室测试是为了确定显著影响未处理混合硫酸钙强度发展的因素，并寻求一种合适的稳定方案来改善未处理混合硫酸钙的水敏感性。从抗水性、强度以及稳定所引起的体积膨胀的角度评估了每种稳定方案的有效性。实验室测试还研究了稳定后的混合硫酸钙的回弹模量和永久变形特性。在实验室测试的样本包括在实验室中成型的以及在路易斯安那交通研究中心（LTRC）的路面研究设施（PRF）试验场试验区钻取的芯样。现场测试项目包括两部分：（1）根据拟定的施工规范在PRF试验场建造一个足尺试验段；（2）通过原位测试，如动力触探仪（DCP）、落锤式弯沉仪（FWD）和自动弯沉仪（DYNAFLECT）来评估稳定后的混合硫酸钙基层的性能，以表征其强度和结构特性。本研究使用等级为120的粒化高炉矿渣（GGBFS）来稳定混合硫酸钙以提高其抗水性。波特兰水泥、石灰和粉煤灰也作为添加剂以不同比例与粒化高炉矿渣一起使用，以改善粒化高炉矿渣稳定的混合硫酸钙的性能。本研究结果表明，含水量控制着未处理混合硫酸钙的强度，尽管干容重等其他因素也会影响结果。养护条件通过材料中含水量的变化影响未处理混合硫酸钙的强度。强度的损失和恢复通常是一个可逆过程，石膏晶体颗粒间存在自由水是这种现象的原因。按体积计用10%等级为120的粒化高炉矿渣稳定的混合硫酸钙可以作为一种良好的路面基层。它具有相当高的刚度，并且可以使用0.30的结构层系数用于路面设计。研究中使用的暂定施工规范（附录A）被证明对于现场施工是足够的。因此，它可以在稍加修改后用于未来的项目。研究人员建议LA DOTD考虑在不同交通和环境条件下使用粒化高炉矿渣稳定的混合硫酸钙作为路面基层建造几个现场试验段。
Blended Calcium Sulfate (BCS) is fluorogypsum (FG), an industrial by-product, blended with lime or limestone. Approximately 90,000 metric tons (100,000 tons) of FG are generated annually in the United States, posing a serious problem for environmental disposal. The Louisiana Department of Transportation and Development (LA DOTD) has been using BCS in pavement construction over the last 15 years. While this material has performed satisfactorily after construction, its moisture sensitivity has concerned LA DOTD engineers because it has presented construction difficulty in wet environments. Therefore, there is a need to better understand the strength deterioration of BCS in a wet environment, and find ways to eliminate or reduce such deterioration by stabilizing BCS with various suitable cementitious agents. This study was divided into two major parts: laboratory and field tests. Laboratory tests were conducted to identify factors that significantly affect the strength development of raw BCS and to seek a suitable stabilization scheme for ameliorating water susceptibility of raw BCS. The effectiveness of each stabilization scheme was evaluated from the perspective of water resistance, strength, and volumetric expansion incurred by stabilization. Laboratory tests also investigated the resilient modulus and permanent deformation characteristics of stabilized BCS. Samples tested in the laboratory included ones both molded in the laboratory and cored at the test section of the Pavement Research Facility (PRF) test site at the Louisiana Transportation Research Center (LTRC). The field test program included two parts: (1) building a full-scale test section at the PRF site according to proposed construction specifications; and (2) evaluating the performance of stabilized BCS base courses through in-situ tests, such as DCP, FWD, and DYNAFLECT to characterize their strength and structural properties. Ground granulated blast furnace slag (GGBFS) with a grade of 120 was used to stabilize BCS to improve its water resistance in this study. Portland cement, lime, and fly ash were also used as additives to GGBFS with different proportions to improve the properties of GGBFS-stabilized BCS. The results from this study indicate that moisture content controlled the strength of raw BCS, although other factors such as dry unit weight also influenced the result. Curing conditions affect the strength of raw BCS through the change of moisture content in the material. The loss and regaining of strength is generally a reversible process and the presence of free water among gypsum crystal particles is the reason for this phenomenon. BCS stabilized by 10 percent 120-grade GGBFS by volume can serve as a good pavement base. It achieved a fairly higher stiffness and a structural layer coefficient of 0.30 can be used for pavement design purpose. The tentative construction specifications (Appendix A) used in the study proved to be adequate for the field construction. Therefore, it can be used with minor modification for future projects. Researchers recommend that the LA DOTD consider building several field test sections in different traffic and environmental conditions using the GGBFS-stabilized BCS as pavement base course.