AN APPROACH WITH CASE STUDIES ON UHPC (ULTRA HIGH PERFOMANCE CONCRETE)

Transcription

1 AN APPROACH WITH CASE STUDIES ON UHPC (ULTRA HIGH PERFOMANCE CONCRETE) RAHUL HRISHIKESH P II year B.E. Civil Engineering Sri Ramakrishna Engineering Cllege, Cimbatre, Tamilnadu hrishikeshrahul@gmail.cm Abstract: In the recent years f industrial and engineering advancements which have quite becme cmmn it is necessary that each f the advancement be studied and analysed fr future reference. Talking f Civil Engineering as a perspective f talk we have very advanced technlgies ccupying the stance f happenings. T state this papers aim at making a stand here, we have taken UHPC(ultra-high perfrmance cncrete).this new cncrete technlgy has the ptential t effect a majr change in the way engineers and technlgists cnceive and design precast systems. With cmpressive strength values f abut it is quite undubtedly a reliable way f paving way fr ur mega structures. UHPC is a leap frward in cncrete technlgy fr durable highway structures. These cncretes ffer dramatic imprvements in physical and mechanical prperties ver cnventinal cncretes and are virtually impermeable t the harsh envirnmental factrs that bridges thrughut the United States are expsed t every day. UHPC has imprtant advantages ver cnventinal and high-perfrmance cncretes, especially in the prductin f smaller and lighter sectins and the ptential eliminatin f passive mild steel reinfrcement. T sme ptential the faith in the lcal gvernment that it wuld bring a change in the develpmental aspects needs t be kindled with emerging prducts like the UHPC. It is als t be knwn that this technlgy has nt been very much implemented in INDIA whereas its usage has been mving t abundance in almst all the rest f the majr natins. It is als needed t be infrmed that the UHPC wns the freeze-thaw resistance which is much needed fr massive bridge cnstructins. In all, this paper majrly fcuses arund the advantages, disadvantages, mixing prcedure and the future aspects f UHPC as itself. And ecnmically it is always seen whether the prduct that is being talked abut is viable r nt, but with the verall ecnmic slwdwn shattering the hpes f develping natins, the UHPC des suck in a lt f investment but guarantees the nn-requirement f management csts. S, with this paper I wuld like t mainly cntribute ur part and awaken the public because TOGETHER, AN ADVANCEMENT IS NOTHING SHORT OF ACHIEVED. Keywrds: -UHPC, HIGH COMPRESSIVE SRENGTH, ECONOMIC VIABILITY INTRODUCTION: Cncrete is the mst widely used material in building cnstructin. Within the last few decades, research has been cnducted n what is knwn as Ultra High Perfrmance Cncrete (UHPC). The term includes a brad range f materials such as defectfree, dense particle, engineered cmpsite, multiscale particle, and fibre-reinfrced cementiusmaterials with enhanced prperties and characteristics. Cmmercial brands are available and many research mixtures have been develped t include lcal and green cnstituentsultra-high Perfrmance Cncrete (UHPC) is ne f the latest advances in cncrete technlgy and it addresses the shrtcmings f many cncretes tday: lw strength t weight rati, lw tensile strength, lw ductility, and vlume instability. In additin t achieving high cmpressive strengths in excess f 25,000 psi (smetimes greater than 30,000 psi), UHPC is als nearly impermeable. This very lw permeability allws UHPC t withstand many distresses nrmally assciated with NSC and HPC such as freeze-thaw deteriratin, crrsin f embedded steel, and chemical ingress. ADVANTAGES OF UHPC: UHPC is a family f cncretes ffering a cmbinatin f material and perfrmance characteristics that create prducts with: 1) Ductility: ability t supprt tensile lads even after initial cracking 2) Ultra high cmpressive strength (up t 200 MPa/29,000 psi) 3) Extreme durability; lw water t cementitius material (w/cm) rati 4) Self-cnslidating and highly muldable mixtures 5) High-quality surfaces 6) Flexural/tensile strength (up t 40 MPa/5,800 psi) thrugh fiber reinfrcement. 7) Thinner sectins; lnger spans; lighter weight 8) New graceful prduct gemetries 9) Chlride impermeability 10) Abrasin and fire resistance 11) N steel reinfrcing bar cages 12) Minimal creep and shrinkage after curing 13) Optimized mix prprtins 205

2 An Apprach With Case Studies n UHPC (Ultra High Perfmance Cncrete) this material is a relatively new cncrete technlgy, particularly in the U.S. As American precast cncrete prducers becme mre familiar with UHPC and the nuances f its prductin, I believe we will see an increased use f this material, particularly in bridge applicatins. UHPC mixtures cntain prtland cement, silica fume, quartz flur, fine silica sand, high-range water reducer, water, and steel r rganic fibers. Materials are usually supplied t the precast cncrete prducer in three cmpnents: premix (blended, in-bulk bags); superplasticizer; and fibers. The micrstructural prperties f UHPC s mineral matrix prduce a highly cmpact, dense material within a lw prsity matrix. Other advantages may include: ability t cnstruct thin sectins and use cmplex structural frms, eliminatin f passive reinfrcement (reinfrcement bars), precise replicatin, use f cnventinalcncrete equipment, ability t cast by puring, injectin r extrusin techniques, selfcnslidatin, ff-sitemanufacturing, fast cnstructin, and reduced maintenance. Frm an aesthetic viewpint and als fr security purpses (such as disguising the appearance f the material), sme UHPC mixtures may have clr and texture ptins, surfaces can be sanded r plished and can even be made t lk similar t materials such as stne r marble. By reducing r eliminating the need fr steel reinfrcing bar cages, UHPC with steel r rganic (plyvinyl alchl) fibers can prduce bridge decks nt susceptible t chlride ingress (frm deicing salts) and the subsequent crrsin-induced deteriratin. UHPC ptimized designs and material prperties in bridge decks can mean lnger service life and lwer maintenance csts fr America s transprtatin infrastructure The applicatins are mainly as fllws: APPLICATIONS OF UHPC: 1) Use f UHPC by the Federal Highway Administratin: Since 2001 when the Federal Highway Administratin (FHWA) began its UHPC research prgram, tw bridge superstructures have been built with UHPC I-beams and mre are under cnstructin r in design. Benjamin A. Graybeal, Ph.D., P.E., research structural engineer with the FHWA, is an expert n UHPC research and its use in transprtatin infrastructure. The FHWA has made great strides in the past five years in beginning t use UHPC in the U.S. highway system, explains Graybeal, hwever, we still have a lng way t g. Currently, each prject using UHPC is still treated as a special case, because 206

3 Scraper paths in treatment plants. Bridges Narrw paths r supprts Thin slab-like cmpnents Buttresses fr high pressures Repair r strengthening f beams COMPOSITION: An Apprach With Case Studies n UHPC (Ultra High Perfmance Cncrete) In the remaining batch the fibres were nt included in the mix s that cmpressin test behaviur in unreinfrced UHPC culd be studied. A 2.0 ft3 capacity pan mixer was used fr nearly all f the UHPC mixing.a 0.3 ft3 mixer was used fr the tw batches that nly required A small vlume f material. Premix: Cnstituents Lb/yd3 %bywei g ht Prtland cement silica fume Grund quartz fine sand Metallic fiber Super plasticizer water Water/cement rati MIXING PROCEDURE: Inthemixing f UHPC premix, fibres, and liquids are used. The liquids that are mixed with the UHPC include water, acceleratr, and a high-range water-reducing admixture (HRWA). The fibres included in the UHPC were always unrefrmed cylindrical steel fibres that were 0.5 in. lng and had a in. diameter. These fibres are included in the mix at a cncentratin f 2% by vlume. The mix prprtins used thrughut this case study included the fllwing: Premix lb/ft3 f cncrete Water 6.81 lb/ft3 f cncrete HRWA 1.92 lb/ft3 f cncrete Acceleratr 1.87 lb/ft3 f cncrete Steel Fibres 9.74 lb/ft3 f cncrete These mix prprtins were fllwed fr all except three batches. In tw batches, the acceleratr was replaced by an additinal 1.80 lb/ft3 f water. The main prcedure basically cnstitutes the fllwing steps: 1. Weigh all cnstituent materials. Add ½ f HRWA t water. 2. Place premix in mixer pan, and mix fr 2 minutes. 3. Add water (with ½ f HRWA) t premix slwly ver the curse f 2 minutes. 4. Wait 1 minute then add remaining HRWA t premix ver the curse f 30secnds. 5. Wait 1 minute then add acceleratr ver the span f 1 minute. 6. Cntinue mixing as the UHPC changes frm a dry pwder t a thick paste. 7. The time fr this prcess will vary. 8. Add fibres t the mix slwly ver the curse f 2 minutes. 9. After the fibres have been added, cntinue running mixer fr 1 minute t ensure that the fibres are well dispersed. Csts, benefits and legal liabilities: UHPC ffers many benefits t perfrmance and design (see the Ptential f UHPC sectin), but as with ther advanced materials, the issues f initial cst and liability are currently f cncern and usually prvide impediments t the use f these materials in cnstructin. Fr UHPC, material csts may be high due t mix requirements and raw material availability; but research culd be cnducted t mdify the material mixtures, use reginal raw materials, and develp mre ecnmic, efficient, and green UHPC versins. There will be initial csts f mdificatin, cnversin, r purchase f equipment and facility csts. New methds and prcedures, training f wrkfrce, and familiarizatin with the material may be necessary and may result in high manufacturing, prcessing and cnstructin csts. It was suggested that sme f these csts may decrease as the technlgy matures, experience is gained, cmpetitin develps, and the market demands mass prductin. The cst f cncrete is usually given in terms f a cst f material per unit vlume basis, e.g., $/cubic yard r initial cnstructin cst and therefre, current UHPC csts are much higher than thse f cnventinal cncrete. Hwever, in many cases, the vlume f UHPC required t meet strength criteria 207

4 An Apprach With Case Studies n UHPC (Ultra High Perfmance Cncrete) will be less than that f cnventinal cncrete thereby reducing these csts. Furthermre, ifsustainability and resiliency requirements are t be mandated fr infrastructure, csts need t be viewed n a lifecycle basis. Bth cnventinal cncrete and UHPC wuld be subject t lng-term perfrmance evaluatin and this wuld include maintenance, inspectin, and mnitring and repair and replacement. On this basis, UHPC has cst advantages ver cnventinal cncrete. Green innvatin and the future f UHPC While the current LEED (Leadership in Energy and Envirnmental Design) rating system lacks credits fr ranking the numerus green benefits f precast cncrete, pints can ften be achieved thrugh the Innvatin in Design categry (see pages 4-9, Precast Slutins, May-June 2008 issue). UHPC can further prmte green benefits with CO2 emissin reductins. In additin, UHPC presents the pprtunity fr ptentially lwer embdied energy due t significant material reductin (up t 40 percent less weight) in ptimized members. Lng-term service life and expected minimal maintenance are material characteristics that lend themselves t reduced life cycle csts fr structures. This enhanced durability needs t be factred int sustainable slutins t ffset the currently higher csts f UHPC. UHPC is a leap frward in cncrete technlgy fr durable highway structures. These cncretes ffer dramatic imprvements in physical and mechanical prperties ver cnventinal cncretes and are virtually impermeable t the harsh envirnmental factrs that bridges thrughut the United States are expsed t every day. UHPC has imprtant advantages ver cnventinal and high-perfrmance cncretes, especially in the prductin f smaller and lighter sectins and the ptential eliminatin f passive mild steel reinfrcement. While UHPC s greatest ptential currently appears t be in transprtatin infrastructure, it is t early t predict what new slutins t design challenges will emerge as engineers and specifiers learn mre abut this new technlgy.legal liability issues are als a majr cncern when using a new material in cnstructin. Sme frm f suspensin f r limited liability may be required t prvide incentives fr prject participants.we will need t understand ptimal designs using this innvative material in a hst f ptential precast applicatins such as superstructures, substructures, sund barrier walls, crash and blast prtectin systems, precast pavements and hybrid systems. While design cdes can take several years t be apprved, interim recmmendatins are anticipated within the next few years. SOME IMPORTANT TESTS: 1. Structural cmpnent testing: 2.Perfrmance testing f lap splice cnnectin: 208

5 CONCLUSION: An Apprach With Case Studies n UHPC (Ultra High Perfmance Cncrete) REFERENCES: Hence, with all the case studies thathave been prvided abve we may reach t a cnclusin that the initiatin f usage f the UHPC and its prgress really is in need f an instigatin which can nly be derived frm sheer public participatin. S, pledging my part twards this strngly needed strategy, i request all my fellw civil engineers t kindle the future by abiding by yur cntributin twards a durable and strngerinfrastructural grwth. [1]. CHARACTERIZATION OF THE BEHAVIOUR OF ULTRA-HIGH PERFORMANCE CONCRETE,By Benjamin A. Graybeal [2]. CONCRETE JOURNALS [3]. INTERNET [4]. CONCRETE TECHNOLOGY, BY M.L GAMBHIR [5]. New Yrk State Department f Transprtatin *** 209