This study considers P.O42.5 cement from different sources and evaluates the related surplus coefficient(defined as the proportionality factor linking the measured compressive strength value of the cement after 28 day...This study considers P.O42.5 cement from different sources and evaluates the related surplus coefficient(defined as the proportionality factor linking the measured compressive strength value of the cement after 28 days to the“standard”value of cement strength).The needed tests have been conducted using a mixer,a pressure testing machine,a flexural testing machine,a vibrating table a ramming rod,a feeder and a metal ruler.The average value of the measured cement strength surplus coefficient of cement produced by five distinct cement manufacturers has been found to be 1.16.These results can be used as the basis to reduce the production cost and improve the performance of commercial concrete.展开更多
The mechanical properties of recycled aggregates concrete from demolition have been studied for several years. It has been documented that rheological properties of these concrete are generally affected by use of recy...The mechanical properties of recycled aggregates concrete from demolition have been studied for several years. It has been documented that rheological properties of these concrete are generally affected by use of recycled aggregates. They could present mechanical properties less affected by the presence of recycled aggregates if the initial concrete were of good quality. However, manufacturing problems, mainly attributed to the angular character of these aggregates and to the granulometry of recycled sand, limit their industrial use. The worth point of this study consists in the optimization of the concrete formulation using specific admixture, adapted to this aggregates in order to facilitate its manufacturing. It shows that the new generation of superplasticizers containing some copolymer polycarboxylate makes it possible to significantly improve the fluidity of the recycled aggregates concrete in its fresh state. The aim of this research is to control rheologica] properties of fresh recycled aggregates concrete with fine and coarse recycled aggregates to limit the negative influence of aggregates on mechanical properties of concrete.展开更多
在设计使用年限内,风力发电机组装配式预应力混凝土塔筒的疲劳问题非常突出,尤其在塔筒1/2高度以上区域。国内标准的疲劳验算公式是基于等幅疲劳2×10^(6)次的试验研究结果,而风力发电机组混凝土塔筒的疲劳次数在3×10^(8)以上...在设计使用年限内,风力发电机组装配式预应力混凝土塔筒的疲劳问题非常突出,尤其在塔筒1/2高度以上区域。国内标准的疲劳验算公式是基于等幅疲劳2×10^(6)次的试验研究结果,而风力发电机组混凝土塔筒的疲劳次数在3×10^(8)以上,故国内标准不适用风电机组混凝土塔筒的疲劳验算。而欧标Fib Model Code for Concrete Structures 2010(FIB规范)采用基于S-N曲线的Palmgren-Miner累积损伤方法进行混凝土疲劳验算,可以解决高次数的疲劳问题。介绍了FIB规范中混凝土塔筒常用的Ⅲ级和Ⅳ级设计方法,通过具体案例分析了混凝土塔筒疲劳承载力的影响因素。结果表明:提高混凝土强度等级和加大塔筒壁厚,可以有效提高塔筒的疲劳承载力。可为风力发电机组装配式预应力混凝土塔筒实际设计提供参考。展开更多
文摘This study considers P.O42.5 cement from different sources and evaluates the related surplus coefficient(defined as the proportionality factor linking the measured compressive strength value of the cement after 28 days to the“standard”value of cement strength).The needed tests have been conducted using a mixer,a pressure testing machine,a flexural testing machine,a vibrating table a ramming rod,a feeder and a metal ruler.The average value of the measured cement strength surplus coefficient of cement produced by five distinct cement manufacturers has been found to be 1.16.These results can be used as the basis to reduce the production cost and improve the performance of commercial concrete.
文摘The mechanical properties of recycled aggregates concrete from demolition have been studied for several years. It has been documented that rheological properties of these concrete are generally affected by use of recycled aggregates. They could present mechanical properties less affected by the presence of recycled aggregates if the initial concrete were of good quality. However, manufacturing problems, mainly attributed to the angular character of these aggregates and to the granulometry of recycled sand, limit their industrial use. The worth point of this study consists in the optimization of the concrete formulation using specific admixture, adapted to this aggregates in order to facilitate its manufacturing. It shows that the new generation of superplasticizers containing some copolymer polycarboxylate makes it possible to significantly improve the fluidity of the recycled aggregates concrete in its fresh state. The aim of this research is to control rheologica] properties of fresh recycled aggregates concrete with fine and coarse recycled aggregates to limit the negative influence of aggregates on mechanical properties of concrete.
文摘在设计使用年限内,风力发电机组装配式预应力混凝土塔筒的疲劳问题非常突出,尤其在塔筒1/2高度以上区域。国内标准的疲劳验算公式是基于等幅疲劳2×10^(6)次的试验研究结果,而风力发电机组混凝土塔筒的疲劳次数在3×10^(8)以上,故国内标准不适用风电机组混凝土塔筒的疲劳验算。而欧标Fib Model Code for Concrete Structures 2010(FIB规范)采用基于S-N曲线的Palmgren-Miner累积损伤方法进行混凝土疲劳验算,可以解决高次数的疲劳问题。介绍了FIB规范中混凝土塔筒常用的Ⅲ级和Ⅳ级设计方法,通过具体案例分析了混凝土塔筒疲劳承载力的影响因素。结果表明:提高混凝土强度等级和加大塔筒壁厚,可以有效提高塔筒的疲劳承载力。可为风力发电机组装配式预应力混凝土塔筒实际设计提供参考。
