Đang tải... (xem toàn văn)
High performance concrete (HPC) and ultra high performance concrete (UHPC) have been increasingly attracting industry’s attention worldwide. Reinforced concrete projects with particular requirements like high rise buildings, long span bridges, tunnel linings, offshore oil platforms, and nuclear power plants have employed such materials due to their superior properties compared to its normal strength counterparts, such as high compressive strength, modulus of elasticity, density, and resistance to chemical and physical deterioration. Durability, economy of longterm maintenance, economy of construction, opportunity for ergonomical and better aesthetical solutions by engineers and architects are among the benefits of utilising HPC and UHPC, but with the penalty of more stringent quality control requirements. European Union through the harmonized regulations of the EUROCODES do not cover neither HPC nor UHPC, thus creating tremendous competitive limitations for the European Construction Industry. The European code of practice for the design of structures for earthquake resistance (EUROCODE 8, EN1998Part 1 for buildings and EN1998Part 2 for bridges) limits the strength of concrete to C4050, while EUROCODE 2 1992Part 1 for the design of concrete buildings (without earthquake resistance requirements) allow concrete strength of C90105. Both EUROCODES 2 and 8 limit the grade of reinforcing steel to 600 MPa, while the commonly used grade is 500 MPa (e.g. Greece). Therefore, whenever such materials are to be utilized in an infrastructure project, the mechanical properties need to be verified by carrying out relevant experimental tests thus leading to unavoidable delays and indirect cost increases. On the other hand, it is unrealistic to assume that the structural behavior of buildings and bridges made of high and ultra high strength concrete can be understood simply by extrapolating the knowledge of current normal strength counterparts. The proposal to include HPC and UHPC in the EN version of EUROCODE 8 was put forward, but the drafting committee decided against it at the time due to the scarcity of information regarding the performance of structures using these materials under seismic loading. From previous experience it is evident that development of concrete technology mostly relies on empirical approaches 1. The presented experimental work is part of a broader experimental program conducted on 120 column specimens to assess their performance under uniaxial and repeated loading. The scope of this study was to define the mixture design method to be used in the production of HPC and UHPC using locally available materials.
rd The Virtual Multidisciplinary Conference December, - 11 2015, www.quaesti.com Mix Proportions and Properties Assessment of HPC and UHPC Using Low Water/Binder ratios Dimirios Konstantindis Konstantinos Anagnostopoulos Department of Civil Engineering Alexander TEI of Thessaloniki Thessaloniki, Greece Department of Civil Engineering Alexander TEI of Thessaloniki Thessaloniki, Greece Georgios Sapidis Athanasios Valmis Department of Civil Engineering Alexander TEI of Thessaloniki Thessaloniki, Greece Department of Civil Engineering Alexander TEI of Thessaloniki Thessaloniki, Greece Angelos Patsios Grigorios Grigoriou Department of Civil Engineering Alexander TEI of Thessaloniki Thessaloniki, Greece Department of Civil Engineering Alexander TEI of Thessaloniki Thessaloniki, Greece Abstract—This paper presents the findings of a research program aimed at developing a mixture design for high strength and ultra high strength concrete using locally available materials Sixteen different concrete mix designs were examined containing varying water/binder and coarse/fine aggregate ratios Concrete mixes with smaller size aggregates exhibited slightly higher strengths at a given aggregate content level, while the reduction of water/binder ratio with a simultaneous increment of superplasticizer content resulted in a slightly higher strength Keywords- High performance concrete, Ultra high performance concrete, Mixture design I INTRODUCTION High performance concrete (HPC) and ultra high performance concrete (UHPC) have been increasingly attracting industry’s attention worldwide Reinforced concrete projects with particular requirements like high rise buildings, long span bridges, tunnel linings, offshore oil platforms, and nuclear power plants have employed such materials due to their superior properties compared to its normal strength counterparts, such as high compressive strength, modulus of elasticity, density, and resistance to chemical and physical deterioration Durability, economy of long-term maintenance, economy of construction, opportunity for ergonomical and better aesthetical solutions by engineers and architects are among the benefits of utilising HPC and UHPC, but with the penalty of more stringent quality control requirements European Union through the harmonized regulations of the EUROCODES not cover neither HPC nor UHPC, thus creating tremendous competitive limitations for the European Construction Industry The European code of practice for the design of structures for earthquake resistance (EUROCODE 8, EN1998-Part for buildings and EN1998-Part for bridges) limits the strength of concrete to C40/50, while EUROCODE 1992-Part for the design of concrete buildings (without earthquake resistance requirements) allow concrete strength of C90/105 Both EUROCODES and limit the grade of reinforcing steel to 600 MPa, while the commonly used grade is 500 MPa (e.g Greece) Therefore, whenever such materials are to be utilized in an infrastructure project, the mechanical properties need to be verified by carrying out relevant experimental tests thus leading to unavoidable delays and indirect cost increases On the other hand, it is unrealistic to assume that the structural behavior of buildings and bridges made of high and ultra high strength concrete can be understood simply by extrapolating the knowledge of current normal strength counterparts The proposal to include HPC and UHPC in the EN version of EUROCODE was put forward, but the drafting committee decided against it at the time due to the scarcity of information regarding the performance of structures using these materials under seismic loading From previous experience it is evident that development of concrete technology mostly relies on empirical approaches [1] The presented experimental work is part of a broader experimental program conducted on 120 column specimens to assess their performance under uniaxial and repeated loading The scope of this study was to define the mixture design method to be used in the production of HPC and UHPC using locally available materials II Sixteen different mix proportions, with C1 to C16 notations were examined for producing HPC in the Concrete Laboratory at the department of Civil Engineering of the Alexander Technological Educational Institute of Thessaloniki The constituent materials were cement, silica fume, natural crushed stone sand, natural crushed stone aggregate with a maximum Civil engineering 10.18638/quaesti.2015.3.1.195 MATERIALS eISSN: 2453-7144, cdISSN: 1339-5572 - 279 - ISBN: 978-80-554-1170-5 rd The Virtual Multidisciplinary Conference December, - 11 2015, www.quaesti.com size of 12.5 mm, tap water for mixing and curing and superplasticizer The details of the mixing proportions are given in Table I Portland cement type CEM I 52.5 N according to EN-197-1 was supplied by TITAN cement producer The amount of the cement content in the mix ranged between 550 to 750 Kg/m3 Table II, shows the chemical composition of the cement used It has a specific gravity of 3.15 and a blaine fineness of approximately 4.66 m2/Kg Silica fume obtained from a ferro-chromite factory was used in all mix proportions It has a specific gravity of 2.3 and a blaine fineness of about 10000 m2/Kg Its’ chemical composition is shown in Table III The amount of Silica fume added in the mix ranged between 50 to 137.5 Kg/m3 In order to adjust concrete workability a polycarboxylate ether based superplasticizer provided by SIKA was selected as high range water reducer Its’ properties are summarized in Table IV The aggregates used to make HPC were brought from Mount Olympus Two size ranges of natural coarse aggregates were used, the first 12.5 to 6.3 mm and the second 6.3 to 4.75 mm Natural fine course aggregate of 4.75 to 0.425 mm was also used Table I, also summarizes the amount of water used in the mix, which ranged between 0.20 to 0.28, along with the water/binder ratio for each mix proportion, with the binder including cement and Silica fume The amount of water TABLE I Mix C1 C2 C3 C4 C5 C6 C7 C8 C9 C10 C11 C12 C13 C14 C15 C16 The mixing procedure was carried out very carefully in order to prevent agglomeration and also to promote uniform distribution of very fine particles First, all powders and aggregates were mixed for five minutes at low speed The mixing was continued for one more minute, while the required quantity of water was added, which already contained the superplasticiser After five minutes of stirring, the mixture became fluid The concrete mix produced was poured into steel molds and, 24 hours later the specimens were demoulded All specimens were cured in water immersion at 20o C until the day of the test The assessment of unconfined compressive strength of the different concrete mix proportions was performed at and 28 days of curing on cubic specimens (150mm x150mm x150mm) under a constant strain rate of 0.0043 mm/mm/sec For the same curing ages, splitting tensile strength tests were conducted following the instructions on cylindrical specimens with a height to diameter ratio of 300 mm/150 mm = The tests were performed on four specimens and the average values were recorded An Instron servohydraulic (model 4500 KPX J4 Static Hydraulic Universal Testing System) compression testing machine was used for all tests MIX PROPORTIONS AND NOTATION Water/ Binder ratio Water (Kg/m3) Cement (Kg/m3) Silica Fume (Kg/m3) 0.284 0.25 0.25 0.25 0.25 0.25 0.25 0.25 0.25 0.20 0.20 0.20 0.20 0.20 0.20 0.20 160 137.4 150 175 187.4 137.4 149 173.6 187.4 97 106.6 124 136 96.9 102 103.8 550 550 600 700 750 550 600 700 750 550 600 700 750 550 550 550 50 50 54.5 63.6 68.2 50 60 70 75 50 60 70 75 50 110 137.5 TABLE II Amount (%) included in the superplasticiser was taken into account in the water content [2] Coarse aggregates (Kg/m3) 12.5> d > 6.3 (mm) 430 430 421 411 402 430 430 430 Fine aggregates (Kg/m3) 4.75> d > 0.425 (mm) Superplasticizer (Kg/m3) 990 990 981 971 962 1710 1650 1540 1485 1710 1650 1540 1485 990 990 990 15 18 19.63 22.9 24.5 18 23.1 27 29 33 36.3 42.35 41.25 33 42.9 48.13 CHEMICAL COMPOSITION OF THE CEMENT SiO2 Al2O3 Fe2O3 CaO MgO SO3 K2O Na2O 19.38 4.28 3.24 61.56 3.43 3.09 0.57 0.72 TABLE III Amount (%) SiO2 91 Ignition loss 3.73 CHEMICAL COMPOSITION OF THE SILICA FUME Al2O3 1.2 Fe2O3 1.3 Civil engineering 10.18638/quaesti.2015.3.1.195 Coarse aggregates (Kg/m3) 6.3> d > 4.75 (mm) 290 290 281 271 262 290 290 290 CaO 0.35 MgO 1.9 SO3 0.95 K2O Na2O 1.3 eISSN: 2453-7144, cdISSN: 1339-5572 - 280 - ISBN: 978-80-554-1170-5 rd The Virtual Multidisciplinary Conference December, - 11 2015, www.quaesti.com Aspect Specific gravity pH Chloride ion content Solid content Molecular mass Recommended dosage* (% by cement weight) *by supplier III specimens with the fine aggregate’s and water/binder ratio of 0.25 in and 28 days of testing In Fig the same trend is depicted for specimens with water/binder ratios of 0.25 and 0.20 PROPERTIES OF THE SUPERPLASTISISER Polycarboxylate ether Slightly yellow 1.05 6.3 0.5 33 % 44,000 g/mol 0.6 – 1.4 115 110 TEST RESULTS AND DISCUSSION Table V, summarizes the mechanical properties for all concrete mix designs Mix C10, which contained only fine aggregates of 0.425 to 4.75 mm size, resulted in the highest compressive strength after 28 days equal to 120.2 MPa, as well as splitting tensile strength after and 28 days equal to 7.0 MPa and 8.2MPa The water/binder ratio in the mix was low and equal to 0.20 However, C13 mix was the one that attained the highest compressive strength of 104.5 MPa, as well as the highest splitting tensile strength of 7.2 after days C1 C2 C3 C4 C5 C6 C7 C8 C9 C10 C11 C12 C13 C14 C15 C16 Compressive strength (28 days) 85.0 91.7 82.2 79.4 81.5 97.8 97.3 93.3 86.6 101.1 98.0 93.0 104.5 96.4 93.5 92.8 98.0 106.0 99.0 97.4 95.1 110.0 107.2 102.0 99.4 120.2 115.0 110.0 116.4 111.7 108.7 104.7 Splitting tensile strength (7 days) 5.2 5.8 5.4 5.1 5.3 6.9 6.7 6.5 6.0 7.0 6.8 6.7 7.2 6.8 6.6 6.5 C8 C9 C6 100 C7 C8 95 90 C9 80 500 550 600 650 700 750 800 Cement content (Kg/m3) Splitting tensile strength (28 days) 6.6 6.7 6.2 5.9 5.8 7.7 7.4 7.1 6.9 8.2 7.9 7.7 8.0 7.6 7.4 7.2 Figure Effect of cement content on compressive strength 125 w/b = 0.25 - 28 days w/b = 0.20 - 28 days w/b = 0.25 - days w/b = 0.20 - days C6 120 C7 115 C6 110 C8 C9 C7 C8 105 C9 100 95 90 In general, concrete mixing proportions with smaller size aggregates exhibited slightly higher strengths at a given aggregate content level This is evident by comparing C2 - C5 mixes with C6 - C9 The increase of the cement content beyond 550 Kg/m3 appeared to result in a reduction of strength for all concrete mixes By comparing C2 with C3 - C5, this strength reduction is more evident in the case of concretes incorporating coarse aggregates than in the case of concretes containing finer aggregates (compare C10 with C11-C13) Fig depicts the strength reduction due to the increase of cement content in 85 500 550 600 650 700 750 800 Cement content (Kg/m3) Figure Effect of cement content on compressive strength for different water/binder ratios Fig 3, shows the relation between concrete compressive strength and water binder ratio As the water binder ratio reduces concrete compressive strength increases for both and 28 days of testing The same trend was observed for splitting Civil engineering 10.18638/quaesti.2015.3.1.195 28 days 105 MECHANICAL PROPERTIES OF HPC AND UHPC Compressive strength (7 days) C7 85 Compressive strength (MPa) TABLE V days C6 Compressive strength (MPa) TABLE IV eISSN: 2453-7144, cdISSN: 1339-5572 - 281 - ISBN: 978-80-554-1170-5 rd The Virtual Multidisciplinary Conference December, - 11 2015, www.quaesti.com tensile strength as shown in Fig This is almost linear for specimens tested after days 115 C1 days Reduction of water/binder ratio with a simultaneous increment of superplasticizer content resulted in slightly higher strengths (Compare C1 with C2, C14 and C6-C9 with C10C13) 28 days C2 105 100 C14 C6 C1 Splitting tensile strength (MPa) Compressive strength (MPa) 110 from 78.9 to 91 % of the one obtained at 28 days In addition, the splitting tensile strength values of all concrete specimens at 28 days of curing ranged from to % of the compressive strength values 95 C2 90 C14 85 80 0.15 0.2 0.25 0.3 water/binder ratio days C7 7.5 28 days C8 C9 C6 C7 C8 6.5 C9 5.5 Figure Effect of w/b ratio on the compressive strength Splitting tensile strength (MPa) 500 days C1 600 650 700 750 800 Cement content (Kg/m3) 28 days 7.5 550 Figure Effect of cement content on splitting tensile strength C1 C2 IV C14 A comprehensive laboratory study was undertaken to investigate the effect of specific mix design parameters on the strength behavior of HPC and UHPC specimens Taking into account the data and results obtained in this study, the following conclusions can be drawn: 6.5 C2 0.15 Increasing the silica fume content beyond 10 % by weight of cement appeared to reduce compressive and splitting tensile strengths C14 5.5 CONCLUSIONS Reduction of water/binder ratio with a simultaneous incremental increase of superplasticizer content resulted in a slightly higher strengths 0.2 0.25 0.3 Concrete mixes with smaller size aggregates exhibited slightly higher strengths at a given aggregate content level water/binder ratio Figure Effect of w/binder ratio on splitting tensile strength The addition of silica fume in the mix (see C14, C15 and C16) in excess of 10 % by weight of cement resulted in the reduction of both compressive and splitting tensile strength The compressive strength development of all concrete mixes after days ranged from 81.4 to 91.4 % of that obtained after 28 days Similarly the splitting tensile strength ranged Increasing cement content beyond 550 Kg/m3 appeared to result in a reduction of strength for all concrete specimens The reduction of strength is more obvious in the case of concrete mixes incorporating coarse aggregates than in the case of concrete mixes containing finer aggregates The early strength development (7 days) of all concrete mixes did not seem to be affected by any of the aforementioned parameters It ranged from 81.4 to 91.4 % and from 78.9 to 91 % of the one obtained at 28 days for Civil engineering 10.18638/quaesti.2015.3.1.195 eISSN: 2453-7144, cdISSN: 1339-5572 - 282 - ISBN: 978-80-554-1170-5 rd The Virtual Multidisciplinary Conference December, - 11 2015, www.quaesti.com compressive strength and splitting tensile strength, respectively Splitting tensile strength values of all concrete mixes at 28 days of curing ranged from to % of the compressive strength values National Strategic Reference Framework (NSRF) - Research Funding Program: ARISTEIA (Excellence) II The authors would also like to thank the companies TITAN Cement, Sidenor S.A and SIKA Hellas for providing materials REFERENCES ACKNOWLEDGMENT [1] This research has been co-financed by the European Social Fund, European Union and Greek national funds through the Operational Program "Education and Lifelong Learning" of the [2] Civil engineering 10.18638/quaesti.2015.3.1.195 P – C Aitcin, High Performance Concrete E & FN SPON, London and NY, 1998 C A Anagnostopoulos, “Effect of superplasticiser type on the properties of cement grouts”, in Advances in Cement Research, Vol 27 (5), 2015, pp 297-307 eISSN: 2453-7144, cdISSN: 1339-5572 - 283 - ISBN: 978-80-554-1170-5