PHYSICAL AND MECHANICAL PROPERTIES OF ULTRA-HIGH PERFORMANCE CONCRETES -Abstract-

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1 FACULTY OF CIVIL ENGINEERING Ing. Şoşa Pavel Ioan Ph.D. THESIS PHYSICAL AND MECHANICAL PROPERTIES OF ULTRA-HIGH PERFORMANCE CONCRETES -Abstract- Ph.D. Supervisor, Pro.dr.ing.Cornelia MĂGUREANU Scientiic evaluating committee: CHAIRMAN: MEMBERS: - Pro.dr.ing. Mihai Iliescu - Dean, Facultaty o Civil Engineering, Technical University o Cluj-Napoca. - Pro.dr.ing. Cornelia Măgureanu Ph.D. Supervisor, Facultaty o Civil Engineering, Technical University o Cluj-Napoca. - Pro.dr.ing. Marinela BărbuŃă Reviwer, Facultaty o Civil Engineering, Technical University Gheorghe Asachi o Iaşi; - Pro.dr. ing. Corneliu Bob - Reviewer, Faculty o Civil Engineering, University Politehnica o Timişoara; - Pro.dr.ing. Zoltan Kiss - Reviewer, Facultaty o Civil Engineering, Technical University o Cluj-Napoca. 1

2 PHYSICAL AND MECHANICAL PROPERTIES OF ULTRA-HIGH PERFORMANCE CONCRETES MOTIVATION Concrete is a well-known construction material. Taking into account the latest research on this ield, its true potential is just being revealed, as witnessed by the nearly kilometric high skyscrapers already built or to be built worldwide. One could say, rom this point o view, that high perormance concretes are the contemporary concretes, while the ultra-high perormance concretes (UHPC) are the uture. The studies related to UHPC became o worldwide interest with the publication o the Richard&Cheyrezy work in 1995 [1]. Since then, numerous scientiic researches and a ew structural applications emerged, but mainly using the commercially available concrete Ductal, developed by Laarge, Rhodia şi Bouygues. Using solely Ductal composition, it could be considered that both the researches and structures are limited and expansive. From this perspective and taking into account that in Romania there is no research regarding UHPC, an extensive experimental study was carried out using an original concrete composition made with locally available materials in order to study the physical and mechanical properties and the possibility o structural use o the experimental UHPC Objectives The main objectives o this thesis were the characterization o the physical, mechanical and durability properties o the Ultra High Perormance Concrete, including: - compression strength and behavior (stress-strain relationship) - lexural and splitting tensile strength and behavior - racture energy - concrete-rebar bond - creep in compression and tension - autogenous shrinkage, total shrinkage - thermal expansion - static and dynamic modulus o elasticity, Poisson coeicient - durability: reeze-thaw resistance, chloride penetration resistance Structure The thesis is structured in our Chapters: Chapter 1 comprises an introduction regarding the UHPC deinitions, reerences to the existing recommendations, technical reports on UHPC, and some o the main structural applications o UHPC. Chapter 2 is a state-o-the-art report on UHPC, in regard with speciic mechanical and physical properties. Chapter 3 presents the experimental program, results and discussions related to the research carried out on the UHPC compositions designed in this purpose. The research included experimental characterization o physical and mechanical properties as well as durability o the UHPC. The characterization o the above took into account inluence actors, such as: type and iber volume, concrete age, specimens geometry, test speed, test methodology and apparatus. Chapter 4 presents the conclusions, personal contributions to the studied domain, and uture objectives. Main remarks Compression strength The study o the compression strength took into consideration three inluencing actors, such as the curing regime, composition and testing methodology (apparatus, specimen geometry, test speed) The results revealed that all the compositions subject to thermal curing (T=90 C; RH=80-90%) developed a compression strength over 150 MPa. Maximum strength was obtained on a 2.55 Vol.-% ibre reinorced composition, ater 5 days o curing on a temperature o 140 C, without moisture control. The conclusions resulted are: - Compression strength o thermal cured specimens at temperature equal or above 90 C, with or without moisture (steam), was 46% to 91% higher than that o witness specimens cured in water or air at 20 C. - Compression strength increased linear with the curing temperatures. 2

3 - Thermal treatment accelerated pozzolanic reactions and concrete reached the maximum strength ater the inalization o the treatment. Adjusted concrete age (concrete maturity) is 71 days, i the thermal treatment is applied or 5 days, starting at the age o 1 day. - The delay o the thermal treatment or curing temperature o T=140 C did not decrease the compression strength. - Compression strength was dimensionally dependent. Smaller specimens exhibited greater values o the compression strength with up to 20%. The resulted relationship or the inter-equivalence o the strengths relative to the specimen dimensions is: 0.84 c,cube50 = 0.94 c,cube70.7 = c,cube100 c,prisme100x100x300 - Experimental results on the concrete composition, made with aggregates smaller than 1.2 mm, suggested that an optimum base dimension or the testing specimens is smaller than or equal to 70.1mm. - Compression strength was not slenderness dependent, as both cube and prisms with the base length o 100 mm displayed similar values or strength. - Compression strength increased linear with the volume o ibers added in concrete composition, up to 15% or the maximum iber volumes (2.55 Vol.-%), compared to non-iber reinorced compositions. - Concrete reinorced only by long hooked end steel ibers displayed greater values o the compressive strength than compositions with hybrid reinorcement (50% long hooked end ibers + 50% straight short ibers). - Testing speed did not signiicantly inluence the concrete strength or test speeds between 0.15 MPa/s and 8 MPa/s. However, a testing speed o 2-3 MPa/s, may be considered as standard or UHPC. - Standard thermal treatment (T=90 C, RH=90%) stabilized the concrete, and no urther increases in concrete strength were observed ater the thermal treatment inalization at the age o 6 days. Elastic modulus o elasticity Elastic moduli were tested by static tests (longitudinal compression) and dynamic tests (resonant requency method). The conclusions are: - Secant static moduli between 0.05 cm and 0.4 cm o the ascendant and descendent branch, and the tangent modulus in origin were equal or the tested UHPC, both with or without ibers: E c =E ci =E cm. - Thermal treatment (T=90 C, without steam) did not play a major role or the elastic modulus. Elastic modulus was higher than that o untreated specimens with values o 3.8% (concrete without ibers) and 6.77% (OV, concrete with long hooked end ibers, 2.00 Vol.-%). - Concrete displayed only a small increase in the elastic modulus in time. For the concrete age interval o 6 28 days, the increase was less than 6.58%, depending on composition and curing regime. - Fiber addition did not signiicantly inluence the concrete modulus, conerring small enhancements o less than 6.28%, independent o type or iber volume. - As expected, longitudinal static modulus in compression had smaller values than dynamic longitudinal modulus. The static modulus represented o the equivalent dynamic modulus. - Untreated specimens presented a continuous increase o the dynamic modulus in the test interval 1 37 days, with the major values recorded until the age o 9 days (+16 18%). Aterwards, only a small evolution was observed. Predicting the relationship o the dynamic modulus evolution in time is equation: A E(t,t)=E(t ) t, whereas A depends on concrete composition The transverse dynamic modulus had similar time evolution with the dynamic longitudinal modulus. - Poisson coeicients experimentally determined by dynamic tests were , the higher values corresponding to thermal treated and iber reinorced specimens. - A relationship between static modulus and compression strength was also experimentally determined: E c =24900 ( c ) 0.15 (or W/B = 0.1 ) şi E c =7552 ( c ) 1/3 (or W/B = 0.2) Stress-strain relationship. σ-ε curves in compression The σ-ε curves (stress-strain) were determined at the concrete age o 6 days ater the thermal treatment inalization. The study was conducted on iber and non-reinorced compositions. The iber reinorced composition contained 1.50, 2.00 and 2.55 Vol.-% long hooked end ibers or hybrid ibers (long hooked end + short straight ibers) The conclusions o the study are: - Concrete with and without ibers, and with or without thermal treatment displayed dierent behaviors. - The stress-strain curves revealed small scatters on the ascendant branch, on the linear-elastic behavior branch, and large scatters or the iber reinorced concrete curves in post-peak behavior. - Non-reinorced concrete presented linear-elastic behavior until stress reached a magnitude o 0.95 c. -Fiber-reinorced concrete presented a linear-elastic behavior until stress reached 0.85 c. Curve delinearization was not signiicantly inluenced by the iber volume. 3

4 - The specimen s ailure was brittle or non-reinorced concrete and ductile or iber-reinorced concrete. - Fiber-reinorced concrete presented a pseudo-yielding plateau near the maximum stress (σ c / c = ). Strains corresponding to the pseudo-yielding plateau were (ibers 1.50Vol.- %, hybrid long) to (ibers 2.55 Vol.-%, hybrid long) - Fiber reinorced concrete had a descending branch o the stress-trains curve, with large plastic deormations or the concrete with 2.55 Vol.-% and smaller or the minimum volume used 1.50 Vol.-%. Post peak deormations (descending branch) presented two parts: the irst part, with a sudden drop o the stress, and the second part with almost constant stress and very large deormations (24 ). The second part developed when stress dropped to c, - Stress strain relationship o the experimental UHPFC (with ibers) was obtained by transorming an existing relationship in order to suite the descending branch o the curve. The relationship is σ c (a β η+1) = a β a β+η, where a and β are coeicients speciic to the composition used in experiments. cm Flexural and splitting tensile strength Tensile strength by lexural means was determined on 40x40x160 mm prismatic specimens, and by splitting on 100 mm cubes, at 6 days (ater the standard curing inalization, steam T=90 C). The conclusions are: - Non-iber concrete had the ollowing strengths: o splitting : 4.09 MPa o lexural: MPa -Fiber reinorced concrete had the ollowing strengths or the iber volumes 1.50Vol.-%, 2.00 Vol.-% and 2.55 Vol.-%: o Splitting : Hybrid ibers: 18.48, 17.12, MPa Long ibers: 18.58, 17.94, MPa o Flexure: Hybride ibers: 34.27, 32.32, MPa Long ibers: 39.43, 32.77, MPa - The casting direction had a major inluence on the lexural strength, horizontally cast prisms had a strength 46%...83% higher than that o vertically cast specimens. This is due to the iber tendency to orientate perpendicularly on the casting direction and parallel to the mould walls. Equivalence relationship between V H horizontally cast (H) and vertically cast (V) specimens is =, whereas K is 0.55 or long ibers and 0.61 hybrid ibers. - Flexural and splitting tensile strength developed proportionally to the iber volume, the proposed relationship or the evaluation o strength, as unction o the matrix strength (0 Vol.-%) and iber volume, are: =8.7 V + ibre H =10 V + ibre L =6 V + ibre H,L ct,sp 0 ibre 0 ibre 0 ibre ct,sp K - The splitting tensile strength represented a raction o the lexural strength. The raction value was or iber reinorced concrete and or non-reinorced concrete. - Specimen geometry did not have a major inluence on the lexural strength when a notch was applied at the bottom o the prisms. Otherwise, smaller specimens had strengths 60% to 110% higher than larger specimens. - The splitting tensile strength was inluenced by the specimens dimensions. 50 mm cubes had strength higher than 100 mm cubes (+50%) or non-reinorced concrete and approximately the same strength, independent on specimens dimension, or the iber reinorced concrete. -Equivalence between lexural and splitting tensile strength o dierent specimens geometry is obtained by the ollowing experimentally determined relationship: 100x100x300 4 = x40x x100x x70.7x x50x50 cil 90x100 =0.98 = = ct,sp ct,sp ct,sp ct,sp

5 - Thermal treatment increases lexural strength linearly with the curing temperature. The maximum increase was +65% when applying T=140 C compared to non-thermal treated specimens (T=20 C). The resulted predicting relationship o the lexural strength in terms o the applied curing temperature is: =T ( T-0.059)+0.8+ o T 20 C - Following the same trend as the compression and the elastic moduli, the tensile strength presented no time evolution ater thermal treatment inalization (age 6 days) - The lexural strength did not appear to be aected by the applied water-to-binder (W/B) ratios between 0.10 and Stress-displacement relationship or lexural and splitting tensile tests Behavior in lexure and splitting was studied using the σ - curves, stress-load point displacement (lexure), and σ ct,sp -, stress-cmod (split). The experimental results conducted to the ollowing conclusions: - The tensile behavior was essentially dierent between concrete with iber addition and concrete without iber addition - The irst cracks o the non-reinorced concrete emerged as the concrete reached the maximum stress, ollowed by the sudden ailure o the specimens. The exposed behavior was linear-elastic rom the start to the end o the test. - Ater the irst crack emerged, iber reinorced concrete continued to present stress and deormation increase, exposing a strain-hardening behavior with the development o the multi-micro cracks in the concrete matrix. - Fiber reinorced concrete also presented a pseudo-yielding plateau on the maximum stress zone. The pseudo-yielding plateau developed in the stress limits: σ ctl / ctl = Ater the maximum stress was attained, a dominant crack ormed, and the concrete displayed a plastic behavior with a descending branch on the stress-displacement curve. At this point, the measured load point displacements coincided with the progressive opening o the dominant crack, all the other micro-crack widths being constant or even decreasing. - The matrix irst crack o the iber-reinorced concrete depended on the iber volume, revealing that higher the iber volume, the higher irst crack stress. - The ductile behavior was more pronounced when only long hooked end ibers where added than when the hybrid ibers where added (50% long hooked end ibers+50% short straight ibers). Flexural tests - Maximum stress (lexural strength) or iber reinorced concrete was 1.3 to 1.8 times higher than the irst crack stress. - Fiber reinorced concretes presented linear elastic behavior on the ascending branch o the stressdisplacement curve rom start to the irst crack appearance. The hybrid reinorced concretes re-linearized ater the irst crack appearance at σ / = (unction o iber volume), linear behavior being displayed up to a stress o σ / = Load point displacement when irst crack appeared was mm (0 Vol.-%) to 0.40 mm (2.55 Vol.- %), linearly increasing with the iber volume. - Pseudo-yielding plateau presented a load point displacement in the interval mm (0 Vol.-%) to mm (2.55 Vol.-%). Long iber addition seemed to be more avorable towards deormations than hybrid ibers. - Fiber-reinorced concrete displacement (at load point) was 0.600mm to mm, and depended (linearly) on the iber addition with a maximum increase o 1282% when compared to non-reinorced concrete. - Displacement growth rom the irst crack stress to the maximum stress, or iber reinorced concrete, was +66% to +187% (depending on the iber volume). Splitting tests - Maximum stress (splitting strength) was 2 to 3 times higher than matrix irst crack stress. - Fiber reinorced concrete displayed a linear-elastic behavior up to irst crack appearance. - Lateral displacement when irst crack emerged was mm to mm, depending linearly on the iber volume (0 Vol.-% to 2.55 Vol.-%). - Lateral displacement trough the pseudo-yielding plateau was mm to mm, depending linearly on the iber volume. - Lateral displacement at maximum stress (splitting strength) was or the iber reinorced concrete mm to mm, +1340% increase when compared to non-reinorced concrete. 5

6 Fracture energy Fracture energy is a measure o concrete ductility: higher the racture energy, higher the ductility o the concrete. Fracture energy (G) was determined using both F - (orce-load point displacement, LPD) and F - CMOD (Force crack mouth opening displacement, CMOD) curves in lexure and F ct,sp - (Force CMOD) or splitting tests. For the tested UHPC the racture energy obtained varied rom 31 N/m (or non-reinorced concrete) to N/m (or iber-reinorced concrete), depending on more parameters, such as the experimental curve used in calculus, the iber types and the iber volume. The conclusions resulted rom the experiments are: - Fracture energy o the concrete was 3 39% higher in splitting tests than in lexure tests. - Fracture energy o the iber reinorced concrete was 33 to 645 times higher than that o the nonreinorced concrete - Fracture energy o the horizontally cast prisms was 95% higher than that o vertically cast prisms, in lexure tests. - Fracture energy was % higher or thermally cured specimens than that o un-treated specimens The high values o racture energy or the iber reinorced concrete certiicates its capacity to absorb large quantities o energy, and consequently, the high ductility o this concrete. This very good characteristic recommends the ultra-high iber reinorced concrete or use in anti-seismic structures. Concrete bond The bond between reinorcement rebar (smooth surace) and UHPC was tested using traction tests. The maximum bond stress was MPa or all the compositions tested. The conclusions are: - Bond maximum stress (τ max ) depends on the casting direction. The bond in parallel cast direction towards the bar was % higher than that in perpendicular cast direction. This tendency was larger or iber reinorced concrete, where the parallel casting towards rebars corroborates with the avorable eect o ibers orientations. - Rebar slip o =0.1 mm was produced at bond stresses (τ 0.1 b) as high as τ max (maximum bond stress). -The rebar slip starts at =0.01 mm, produced at a stress o τ 0.01 b= ( )τ max. - For thermally treated specimens, with or without ibers, the ollowing relationships resulted: τ = ( ) τ b max or =0.01mm τ = (0.9 1) τ or =0.1mm b max - Concrete age did not play a major role in the bond stress development, the registered values being approximately the same in the concrete age interval 6 days to 28 days. - In the vast majority o the bond tests, ailure produced by the steel rebar yielding and solely in ew cases (exclusively or non-iber concrete) by the concrete split. - The maximum bond stress can be evaluated by the ollowing relationship resulted rom these experiments, using the splitting strength and the compressive strength parameters (common concrete quality parameters): τ max = 1.50 ha ct,sp τ = 1.50 h h max Time dependent deormations (shrinkage-swelling) The shrinkage (swelling) o the experimental concrete was determined using the ollowing methodology: - Autogenous shrinkage, determined on totally environmentally isolated specimens (using sel-adhesive aluminum oils and also polyethylene oils and surace oils). - Total shrinkage, measured on un-covered specimens that permitted ree humidity exchanges with the surrounding environment. The tests results conducted to the ollowing remarks: - Un-treated specimens revealed only autogenous shrinkage, and no drying shrinkage was observed. -The autogenous shrinkage o the un-treated specimens, that permitted humidity exchange with the environment (un-covered), was partially reduced by the swelling deormations, as the total measured deormations o this specimens (un-cover) were lower than that o the covered specimens (isolated). - The autogenuous shrinkage o the un-treated specimens developed with rapid rates rom the initiation at the approximately age o 4 hours (since casting) until 36 hours. A B c 6

7 -Autogenous shrinkage o the un-treated iber reinorced concrete stabilized at the age o 3 days, deormations measured at the time being 766 µm/m. No urther deormations were registered at the tests inalizations at 7 days. Instead, non-reinorced concrete continuously shrank rom the start to the end (7 days), although with lower rates ater the concrete age o 3 days. The inal autogenous shrinkage deormation o the non-reinorced concrete was 1011 µm/m (7 days), 32% higher than that o non-reinorced concrete. -Thermal treated specimens displayed no shrinkage ater the treatment inalization, but swelling. -The swelling measured ater the thermal treatment inalization was approximately 130 µm/m at concrete age 113 days (iber reinorced concrete). The deormations seemed to stabilize at this age. - The equation describing the autogenous shrinkage evolution o the un-treated specimens can be modeled using two equations. The irst one corresponds to the very early ages when evolution is rapid (4 hours...36 hours ater casting): ε ca = 590 t+ 25. The second equation describes the autogenous evolution in the interval 36 hours...7 days: εca = 65 ln( t) 656, whereas t represents the concrete age in days. - The swelling deormations that occurred ater the thermal treatment inalization (concrete age 6 days) can be described by the ollowing equation: ε cd = 45 ln( t) 80, whereas t is the concrete age in days (6 113 days). Concrete creep Concrete creep was determined in terms o compression creep and direct tensile creep. The stress, both in compression and tension, was 40% o the maximum stress, previously measured on similar specimens. Experiments conducted to the ollowing conclusions: Tensile creep - Test results showed that ater approximately 120 days o constant stress, the tensile creep coeicient was φ ct =0.544 or non-reinorced concrete, and φ ct =0.164 or iber reinorced concrete (hybrid ibers, 2.55 Vol.- %). - Creep coeicient o the iber reinorced specimens seemed to stabilize at the time o days ater loading. Aterwards, the creep coeicient increased less than 20% until the test inalization at 120 ater loading. The non-reinorced concrete presented 80% increase in the time interval 10 days.120 days ater loading. Compression creep - Creep coeicient in compression o the iber reinorced concrete was similar to that in tension, with a value o φ cc = Both in tension and compression, the creep coeicients were very small, especially or iber-reinorced concrete. The values were signiicantly reduced compared to normal strength concretes or even high strength concretes. Thermal expansion Thermal expansion was measured on prismatic specimens with a total length o 550 mm. The coeicients o thermal expansion determined on thermal cured specimens, at the age o 150 days, were µm/m/ C or ibre reinorced concrete and µm/m/ C or non-reinorced concrete. Concrete durability Durability tests were conducted towards: -Freeze-thaw resistance -Chloride penetration The results o the tests are: -No damage was observed in terms o compression strength or dynamic and static modulus o elasticity ater 1000 reeze-thaw cycles, when compared to witness specimens kept at constant temperature in water (T=20 ). The reeze-thaw specimens displayed an increase in both compression strength and static and dynamic moduli, i compared to witness specimens. - Chloride penetration tested by rapid tests (6 hours, ASTM C1202) and long-term tests (colorimetric method) showed no signs o chloride penetration into the tested concrete, independent o composition or curing regime. 7

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