水泥粉煤灰（CFG）增强的路基基床材料实验室评价
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摘要
从普通碎石路面到沥青路面再到混凝土路面,路面的结构性能不断地得到改善。通常天然地基不能承受车辆和其它交通荷载,所以一般需要在地基上面建筑路面。由于采用混凝土路面所需费用很高,故用稳定粒料路面代替。稳定路面的作用旨在改善土和路面的工程性能。稳定的形式有三种,即土工合成形式(土工布或土工格栅)、力学稳定(压实)和化学稳定(加入某些化学物质或者添加剂),本文主要研究化学稳定,特别是水泥和粉煤灰稳定的道路路面。基层和底基层的水泥稳定是最普通的化学稳定形式。这是因为与其他添加剂相比,水泥的掺入会使混合料的强度有很大的提高,并且具有优越的工程性能。但是过去用水泥处理的基层性能不好,使得基层和底基层出现过大的断层和收缩裂缝,当水泥含量提高时,这些现象更加明显。多年来,有很多研究致力于解决这些问题。将附加胶凝材料(SCM'S)如石灰、粒状高炉矿碴(BFS)、粉煤灰(FA)和非晶体硅石(AS)加入到土与水泥混合料中,可以减少或消除上述不利影响。在减少和消除这些不利影响的附加剂中,SCM'S附加剂可以改善混凝土的力学和结构性能,还可减少材料费用(因为SCM'S附加剂比水泥便宜)。但是这些附加胶凝材料随土或石的不同以及养护条件和养护时间的不同,作用效果也不相同,所以附加胶凝材料的类型与用量、土石类型、道路(现场条件)或试件养护条件与养护时间对道路或试件的强度、结构或力学性能有显著影响。
本文研究利用水泥掺粉煤灰稳定或加强路面的好处,以及象配合比设计、温度、湿度、时间这些因素是怎样影响稳定路面的结构和力学性能的。试验采用粘土、普通波特兰水泥和F级粉煤灰。对土的分类、密度、密实度及无侧限受压强度进行了试验,因为这些性能指标与其它工程力学特性如刚度和耐久性有关。在试验室制作了试件来模拟现场稳定过程。按不同比例的水泥和粉煤灰制作了试件并压实后在不同的养护条件下养护不同的时间。一共采用了十四个不同的配比,胶凝材料用量在碎石干重的0到20%范围内变化。养护条件分温度20℃和湿度100%、室内温度和湿度、温度60℃和湿度100%三种。养护时间为7天和28天两种。对于每一种配比制作了6个试件,在三种不同的养护条件下养护,在指定的养护时间结束后,对试件进行了无侧限受压试验,并记录了强度以备分析,从中找出哪一种配比最经济同时又有良好的力学和结构性能。
对得到的强度结果采用统计软件SPSS进行了理论与数值分析,在理论分析时,用excel绘制了直方图来表示强度随配比、温度、湿度以及龄期的变化规律。在数值分析中用SPSS软件进行了线性回归分析。统计结果表明强度与配比、温度、湿度和龄期的相关性以及它们的相关程度。理论分析与试验结果吻合良好。
两种分析表明,水泥掺粉煤灰提高了稳定或加强路面的力学和结构性能。对不同的混合物,掺粉煤灰的水泥试件脆性变小,而且配比设计、温度、湿度、时间对水泥-粉煤灰-碎石稳定路面的结构和力学性能有很大的影响。混合料的强度随水泥和粉煤灰用量的增加而增加,但是超过一定比例后,强度反而降低。在一定的养护条件和养护时间内,试件的强度随温度、湿度和时间的增加而增加,不掺粉煤灰和水泥掺量大于粉煤灰掺量的试件在前7天的强度增长较快,但是随后增长速放慢。相反,对于只掺粉煤灰和粉煤灰掺量大于水泥掺量的试件,前7天的强度增长慢,但随后强度增长加快。
Roads have developed from ordinary gravel roads to asphalt roads to concrete roads, each with increasing improvement in structural properties. Most of the time the natural subgrade is not strong enough to carry or support loads from vehicles and other traffic, so it is normally required to build a pavement on top of the subgrade (the in-situ soil). Instead of building a road exclusively made of concrete, which can be very expensive, pavement layers can be reinforced or stabilized. Reinforcement or stabilization is aimed at improving the engineering properties of the soil and subsequently that of the pavement. Reinforcement or stabilization can be in the form of geosynthetics (geotextiles or geogrids), mechanical (compaction) or chemical (addition of certain chemicals or additives). This research concentrates mainly on chemical stabilization, specifically cement and fly ash stabilization of pavement layers of a road. Cement stabilization of bases and subbases is the most common form of chemical stabilization; this is because cement when compared to other additives provides considerable strength to the mixture and has excellent engineering properties. However cement treated bases have shown poor performances in the past. Cement treated bases and subbases exhibit excessive pumping, faulting, and shrinkage cracking. These are thought to be more pronounced as the cement content is increased. A lot of research has been done over the years to help combat these problems. Supplementary cementitious materials (SCM's) like lime, granulated blast furnace slag (BFS), flyash (FA), and amorphous silica (AS) have been added to soil-cement mixtures to help reduce or eliminate the above mentioned undesirable effects on soil - cement mixes. In addition to reducing and eliminating such undesirable effects, addition of SCM's improves the mechanical and structural properties of the concrete and subsequently cut material costs (as some cement is replaced by SCM's, which are cheaper than cement). These supplementary cementitious materials however perform differently with different soils or rocks and also under different curing conditions and durations, so the type and amount of supplementary cementitious material used, type of soil or rock used, conditions under which the road (insitu) or the sample (laboratory) is cured and duration of curing are thought to grossly affect strength, structural and mechanical properties of the road or laboratory sample.
This thesis presents research on the benefits of adding flyash to cement mixes for stabilizing or reinforcing pavement layers and how factors like mix design, temperature, humidity and time affect the structural and mechanical properties of stabilized pavement layers. A cohesionless-frictional soil, ordinary Portland cement and Class F flyash was used. Soil classification, density and compaction and unconfined compressive strength tests were performed as these properties identify or relate to other engineering properties such as stiffness, durability etc. Samples were fabricated in the laboratory to simulate insitu stabilization process. Samples made of different proportions of cement and flyash where made, compacted and cured at different curing conditions and durations. Fourteen different mixes were used and cementitious material content was between 0% and 20% of dry weight of gravel. Curing conditions were 20°c and 100% humidity, room temperature and humidity and 60°c and 100% humidity. Curing durations were 7 days and 28 days. For each mix, six samples were made and cured at the three different curing conditions and the two different curing durations. After the specified curing durations, unconfined compressive tests (UCS) were done on the cured samples and strength results in Psi (pounds per square inch) were recorded for subsequent analysis, to see which one is the most economic (in terms of least cement or flyash content) but with good mechanical and structural properties.
The strength results got were analyzed theoretically and numerically (using Statistical Package for Social Scientists, SPSS). In the theoretical analysis, simple excel plots were drawn in the form of histograms to show how strength varies with respect to mix, temperature, humidity and number of days. In the numerical analyses, linear regression analyses were done using SPSS software. The statistical outputs showed how strength, mix, temperature, humidity and number of days are correlated and the extent of their correlation. The theoretical and numerical analyses agree with each other in every way.
From the two analyses, it was concluded that flyash enhances the mechanical and structural properties of cement mixes used in stabilizing or reinforcing pavement layers. For the different mixes, cement samples with flyash incorporated in them were less brittle and showed an increase in strength than their cement only counterparts. Also it can be concluded that factors like, mix design, temperature, humidity and time affect the structural and mechanical properties of cement-flyash-gravel (CFG) stabilized pavement layers greatly. For both cement and flyash, as cement and flyash content is increased, strength increases, but starts to decrease after a certain percentage is exceeded. Within the specified curing conditions and durations, as temperature, humidity and number of days increases, strength of samples increased. Cement only and more cement than flyash samples gain strength at a faster rate within the first 7 days but continue to gain strength at a slower rate afterwards. It is the opposite for flyash only and more flyash than cement samples, their rate of strength gain is slow within the first 7 days but increases afterwards.
本文研究利用水泥掺粉煤灰稳定或加强路面的好处,以及象配合比设计、温度、湿度、时间这些因素是怎样影响稳定路面的结构和力学性能的。试验采用粘土、普通波特兰水泥和F级粉煤灰。对土的分类、密度、密实度及无侧限受压强度进行了试验,因为这些性能指标与其它工程力学特性如刚度和耐久性有关。在试验室制作了试件来模拟现场稳定过程。按不同比例的水泥和粉煤灰制作了试件并压实后在不同的养护条件下养护不同的时间。一共采用了十四个不同的配比,胶凝材料用量在碎石干重的0到20%范围内变化。养护条件分温度20℃和湿度100%、室内温度和湿度、温度60℃和湿度100%三种。养护时间为7天和28天两种。对于每一种配比制作了6个试件,在三种不同的养护条件下养护,在指定的养护时间结束后,对试件进行了无侧限受压试验,并记录了强度以备分析,从中找出哪一种配比最经济同时又有良好的力学和结构性能。
对得到的强度结果采用统计软件SPSS进行了理论与数值分析,在理论分析时,用excel绘制了直方图来表示强度随配比、温度、湿度以及龄期的变化规律。在数值分析中用SPSS软件进行了线性回归分析。统计结果表明强度与配比、温度、湿度和龄期的相关性以及它们的相关程度。理论分析与试验结果吻合良好。
两种分析表明,水泥掺粉煤灰提高了稳定或加强路面的力学和结构性能。对不同的混合物,掺粉煤灰的水泥试件脆性变小,而且配比设计、温度、湿度、时间对水泥-粉煤灰-碎石稳定路面的结构和力学性能有很大的影响。混合料的强度随水泥和粉煤灰用量的增加而增加,但是超过一定比例后,强度反而降低。在一定的养护条件和养护时间内,试件的强度随温度、湿度和时间的增加而增加,不掺粉煤灰和水泥掺量大于粉煤灰掺量的试件在前7天的强度增长较快,但是随后增长速放慢。相反,对于只掺粉煤灰和粉煤灰掺量大于水泥掺量的试件,前7天的强度增长慢,但随后强度增长加快。
Roads have developed from ordinary gravel roads to asphalt roads to concrete roads, each with increasing improvement in structural properties. Most of the time the natural subgrade is not strong enough to carry or support loads from vehicles and other traffic, so it is normally required to build a pavement on top of the subgrade (the in-situ soil). Instead of building a road exclusively made of concrete, which can be very expensive, pavement layers can be reinforced or stabilized. Reinforcement or stabilization is aimed at improving the engineering properties of the soil and subsequently that of the pavement. Reinforcement or stabilization can be in the form of geosynthetics (geotextiles or geogrids), mechanical (compaction) or chemical (addition of certain chemicals or additives). This research concentrates mainly on chemical stabilization, specifically cement and fly ash stabilization of pavement layers of a road. Cement stabilization of bases and subbases is the most common form of chemical stabilization; this is because cement when compared to other additives provides considerable strength to the mixture and has excellent engineering properties. However cement treated bases have shown poor performances in the past. Cement treated bases and subbases exhibit excessive pumping, faulting, and shrinkage cracking. These are thought to be more pronounced as the cement content is increased. A lot of research has been done over the years to help combat these problems. Supplementary cementitious materials (SCM's) like lime, granulated blast furnace slag (BFS), flyash (FA), and amorphous silica (AS) have been added to soil-cement mixtures to help reduce or eliminate the above mentioned undesirable effects on soil - cement mixes. In addition to reducing and eliminating such undesirable effects, addition of SCM's improves the mechanical and structural properties of the concrete and subsequently cut material costs (as some cement is replaced by SCM's, which are cheaper than cement). These supplementary cementitious materials however perform differently with different soils or rocks and also under different curing conditions and durations, so the type and amount of supplementary cementitious material used, type of soil or rock used, conditions under which the road (insitu) or the sample (laboratory) is cured and duration of curing are thought to grossly affect strength, structural and mechanical properties of the road or laboratory sample.
This thesis presents research on the benefits of adding flyash to cement mixes for stabilizing or reinforcing pavement layers and how factors like mix design, temperature, humidity and time affect the structural and mechanical properties of stabilized pavement layers. A cohesionless-frictional soil, ordinary Portland cement and Class F flyash was used. Soil classification, density and compaction and unconfined compressive strength tests were performed as these properties identify or relate to other engineering properties such as stiffness, durability etc. Samples were fabricated in the laboratory to simulate insitu stabilization process. Samples made of different proportions of cement and flyash where made, compacted and cured at different curing conditions and durations. Fourteen different mixes were used and cementitious material content was between 0% and 20% of dry weight of gravel. Curing conditions were 20°c and 100% humidity, room temperature and humidity and 60°c and 100% humidity. Curing durations were 7 days and 28 days. For each mix, six samples were made and cured at the three different curing conditions and the two different curing durations. After the specified curing durations, unconfined compressive tests (UCS) were done on the cured samples and strength results in Psi (pounds per square inch) were recorded for subsequent analysis, to see which one is the most economic (in terms of least cement or flyash content) but with good mechanical and structural properties.
The strength results got were analyzed theoretically and numerically (using Statistical Package for Social Scientists, SPSS). In the theoretical analysis, simple excel plots were drawn in the form of histograms to show how strength varies with respect to mix, temperature, humidity and number of days. In the numerical analyses, linear regression analyses were done using SPSS software. The statistical outputs showed how strength, mix, temperature, humidity and number of days are correlated and the extent of their correlation. The theoretical and numerical analyses agree with each other in every way.
From the two analyses, it was concluded that flyash enhances the mechanical and structural properties of cement mixes used in stabilizing or reinforcing pavement layers. For the different mixes, cement samples with flyash incorporated in them were less brittle and showed an increase in strength than their cement only counterparts. Also it can be concluded that factors like, mix design, temperature, humidity and time affect the structural and mechanical properties of cement-flyash-gravel (CFG) stabilized pavement layers greatly. For both cement and flyash, as cement and flyash content is increased, strength increases, but starts to decrease after a certain percentage is exceeded. Within the specified curing conditions and durations, as temperature, humidity and number of days increases, strength of samples increased. Cement only and more cement than flyash samples gain strength at a faster rate within the first 7 days but continue to gain strength at a slower rate afterwards. It is the opposite for flyash only and more flyash than cement samples, their rate of strength gain is slow within the first 7 days but increases afterwards.
引文
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[2] AASHTO. AASHTO Guide for Design of Pavement Structures. Washington, DC, 1986.
[3] Yoder, E. J., and Witczak, M.W. Principles of Pavement Design. John Wiley & Sons, New York, 1975.
[4] AASHTO. Interim Guide for the Design of Pavement Structures. American Association of State Highway and Transportation Officials, Washington, DC, 1972.
[5] Virginia DOT. Fundamental Concepts of Pavement Evaluation and Design. Chapter VI - Pavement Evaluation and Design. Sec. 601.01., 1995.
[6] Virginia DOT. Fundamental Concepts of Pavement Evaluation and Design. Division of Highways, 2006.
[7] Field Manual. Planning and Designs of Roads, Airfields, and Heliports un the Theater of Operations—Road Design. No. 5-430-00-1, Air Force Joint Pamphlet, No. 32-8013, Vol 1. Washington D.C, 1994.
[8] AASHTO. AASHTO Guide for Design of Pavement Structures. Washington, DC, 1993.
[9] McDonald R. Design and Implementation Aspects. Recycled Materials Relational Database, 2004.
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