1、PDF外文：http:/ 中文4550字外文原文二 Mechanical and thermal evaluation of Ultra High PerformanceFiberReinforced Concretes for engineering applications Valeria Corinaldesi, GiacomoMoriconi Department of Materials and Environment Engineering and Physics, UniversitPolitecnicadelle Marche, Via Br
2、ecceBianche, 60131 Ancona, Italy Abstract： Ultra High Performance Fiber Reinforced Concrete (UHPFRC) is a cement-based material, which behaveslike a low-porosity ceramic material with excellent mechanical performance. This work was aimed tostudy soft cast (flowable at casting time) UHPFRC s an
3、d, in particular, the time development of compressivestrength, flexural strength and elastic modulus was monitored for UHPFRC prepared by varying thewater to cement ratio from 0.20 to 0.32. Silica fume, steel fibers and acrylic-based superplasticizer wereemployed to prepare the UHPFRC mixtures. Opti
4、mum workability and mechanical performance wereobtained with a water to cement ratio of 0.24. Thermal conductivity was determined for the sameUHPFRC, in the presence and in the absence of steel fibers. The scope was to evaluate the effect of steelfibers on the thermal conductivity coefficient, in or
5、der to predict the UHPFRC capacity for heat loss. Thisinformation as well as its drilling characteristics, in order to test its suitability to be machined, could beessential for possible fields of application such as in mechanical engineering, where UHPFRC materialscan be employed as high abrasion-r
6、esistant dies in the molding process of metal and polymer products. Keywords： Machineworkability； Mechanicalperformance； UHPFRC Silica fume； Thermal conductivity 1.Introduction Ultra High Performance Fiber Reinforced Concrete is a specialcement-based material which b
7、ehaves like a low-porosity ceramicmaterial with excellent mechanical performance. In particular, it isa superplasticized silica fume concrete, often reinforced with fibers,with improved homogeneity because traditional aggregatesare replaced with very fine sand up to 400 lm 1. According toRichard and
8、 Cheyrezy 1, if soft cast and cured at room temperature,its compressive strength can achieve 200 MPa. In fact,UHPFRC representsthe highest development of High PerformanceConcrete (HPC) and its ultimate compressive strength depends onthe curing conditions (either standard curing or steam curing oraut
9、oclave curing 2,3), on possible thermal treatments 4,5 aswell as on themanufacturing technique adopted, and its valuecould rise up to 800 MPa in the case of compressive molding 6. Just to give an idea of the excellent mechanical performance ofUHPFRC, the stressstrain curves of an ordinary performanc
10、e concrete(OPC), of a High Performance Concrete (HPC) and of an UltraHigh Performance Fiber Reinforced Concrete (UHPFRC) are shownfor comparison in Fig. 1 7. In most industrial countries HPCmaterials are currently employedin infrastructural engineering works where heavy staticand dynamic stresses or
11、 severe environmental aggression have to be counteracted, such as in sea platforms for oil extraction, longspan bridges, undersea tunnels, andskyscrapers in seismic areas. However, UHPFRC materials show, although in an experimentalphase with some field tests, much higher performance than HPC.Particu
12、larly, besides extraordinary compressive and flexuralstrength (see Fig. 1), very high ductility as well as toughness andfracture energy 24 encourages new applications for these materials,competing with innovative ceramics and structural metals inthe field of mechanical and environmental engineering,
13、 as well ascivil and building engineering 7. The following applications are promising in relation to UHPFRCmaterials utilization 8. In environmental and chemical engineering,highly reliable containers can be advantageously produced tostore hazardous (toxic, inflammable, etc.) fluids or solids, since
14、the use of UHPFRC materials, in which negligible diffusion of ionicand molecular species occurs, can allow to make insignificant therelease of toxic or radioactive wastesfrom the container to theenvironment. In civil engineering, construction of extraordinary buildings,whose sizes or location requir
15、e very high performance in termsof both mechanical strength and ductility as well as toughness,may be realized with UHPFRC materials. As a matter of fact, in Tokyo,owing to a lack of available areas, plans of buildings as high as1000 m are being reliably studied.In mechanical engineering, high impac
16、t-resistant products,against burst or shot, or high abrasion-resistant dies in the moldingprocess of metal products, such as steel sheets, can besuccessfullydeveloped. Actual dies are characterized by very high unit costwhich, for theireconomic amortisation, need high volume productionlines. This fa
17、ct, for instance, prevents supply flexibility inrelation to coachwork changes in the car industry. The use ofUHPFRC materials, depending on the strength level requirements,can allow the production of cheaper prototypes, and mediumlowvolume dies. Remarkable interest is also emerging in theplastics in
18、dustry for the production of dies, whose requirementscould be easily met by adequately adjusting the mixture compositionand proportioning. This work was aimed to study soft cast UHPFRCs, in particulartheir mechanical performance, their thermal conductivity, in orderto predict UHPFRC capacity for hea
19、t loss, as well as their adaptabilityto machining processes. In fact, aim of this paper is also to investigatesome drilling characteristics of UHPFRC in order to assess thecapability of this material to be machined by conventional tools. In terms of UHPFRC mixture proportion optimization, the attent
20、ionwas focused on the effect of the type of superplasticizer usedand of the water to cement ratio (ranging from 0.20 to 0.32) onUHPFRC performances. In order to reduce the price of producingUHPFRC, local natural sand was used as replacement material forthe more expensive silica sand normally used to
21、 produce UHPFRC,similarly with the attempt made by Yang et al. 9. Generally, dueto the limited available resource and the high cost of silica fume,many authors also tried to reduce UHPFRC cost by searching forthe substitution of silica fume by other materials with similarfunctions such as ground gra
22、nulated blast furnace slag (GGBFS)24,10, ultra fine fly ash 2,4,10, rice husk ash 11. However,in this work the only mineral addition tried was silica fume,besides to cement. Concerning the kind of curing, standard curingat 20 _C was chosen (without thermal treatment), which representsthe cheapest way of producing soft cast UHPFRC.
