Experimental Investigation of UHPFRC Cube and Cylinder Compression Test at Elevated Temperature ()
1. Introduction
The UHPFRC is cement based composite material. The steel fibers are added to decrease the brittleness and increase compressive strength, the energy absorption capacity of the material increased by use of densified materials and special treatment, such as heat curing, pressure and extensive vibration, the structural geometry of hooked end steel fibers optimizing the matrix fiber interface properties and enhance the more compressive strength. Generally there are two types of test methods the cube and cylinder compression tests. In general cube compressive test is very common in Asian countries and cylinder test method in European countries in practice. The conventional concrete compressive strength of cube specimen is 20% higher than the cylindrical one. In UHPFRC the existence of steel fiber and exposure to temperature enhances the strength variation in ±5% in cube and cylinder ratio. During the past 30 years the use of steel fiber reinforcement in concrete has taken places a considerable development to achieve higher compressive strengths to carry heavier loads throughout the life of the structure, suitable for adverse environmental conditions, aesthetic requirements and architectural appearance is most required in construction sector. Structural safety and suitability of the structure is the global challenge in present day and increased continuous terrorist attack, with bullet impact velocity 800 m/sec, earthquake tremor on rector scale 9.0 and Tsunami wind velocity 240 km/hr to resist impacts a very high compressive strength, energy absorption capacity of concrete is necessary to minimize the loss of human life, valuable assets and structural failure. The researcher Yudenfreund et al. (1972) [1] investigated the high strength cement pastes with low w/c ratio ranges (0.20 - 0.30) and low porosity yielded high compressive strengths. Williamson (1974) [2] reported marginal change in compressive strength by use of steel fibers. Birchali et al. (1981) [3] achieved higher compressive strength of cement pastes, exceeding 200 Mpa by special material preparation. Fanella and Naaman (1985) [4] showed increased stress strain curve by addition of steel fibers in concrete in compression increased strain rate at peak stress, energy absorbing capacity and increment in toughness. Bache (1987) [5] developed a densified small particles (DSP) concept for densely compacted granular matrix approach by use of silica fume and super plasticizer based on the water solubility theory of polymers and fine particles mainly consists of silica to improve rheological properties of cement mixture with low water cement ratio. D. M. Roy (1992) [6] introduced Chemically Bonded Ceramics (CBC) a new class of cement based materials the chemical nature of the involvement of bond structure sub divided into two categories like DSP and MDF. Richard and Cheyrezy (1995) developed RPC (Refractive product concrete) enhancing compressive strengths by optimizing the granular particle mixture of cementitious Material PPD (Particle packing density). Collerpardi et al. (1998) [7] compared the RPC with the modified RPC and obtained the better results in strength, low porosity permeability and shrinkage, under steam curing, Jianxin Ma and Jorg Dietz (2002) [8] investigated the several properties of UHPC (Ultra high performance concrete) on work ability flow tests with percentage of admixture dosage to self compacting concrete and optimum 2% of powder mass to reduce air content for workable concrete. Resplendino. J. (2004) [9] observed UHPC with post peak stress response depends on alignment of fibers mixing placing, and compacting methodology the closer fiber accumulation at particular part due to gravitational orientation of steel fibers effect the compressive and tensile strength. Habel K. Denarie and Bruhwiler (2006) [10] adopted the probable possibilities usage of UHPFRC in rehabilitation of structural members time dependent based on the durability and proposed a numerical model and compared with the conventional concrete. Benjamin Graybeal and marshall Davis (2008) [11] investigated the UHPFRC alternative methods to compute compressive strengths of cube and cylinder ranging 100 - 200 N/mm2 and durability properties. Shihada S. and Arafa A. (2010) [12] studied the material properties in Gaza strip with addition of special materials, silica fume, quartz powder uniform mixing methodology to increase the dry density of UHPFRC optimum use of silica fume up to 15% mass of cement. Yang, Joh, and Kim (2011) [13] investigated in UHPFRC beams use of steel fibers 2% with replacement of coarse aggregates the behavior of compressive, flexural failure deflection and initial cracking pattern measured. Barris et al. (2012) [14] studied performance of the concrete on different steel fibers based on orientation, content, material type and length. Ghafari E. et al. (2015) [15] based on statically mixture design (SMD) reported that the compressive strength is increased with higher dosage of micro silica by 1% - 5% by weight of cement. The mix design shows enormous improvements in material properties. Rong et al. (2015) [16] observed that addition of nanosilica reduces the corrosion rate of steel. and reduction in capillary porosity the improved mechanical properties shows 0% - 15% in compressive strength, 0% - 2% in flexural strength and 0% - 2.5% in splitting tensile strength, forming a denser, hardened cement material to carry heavier loads. Yuliarti Kusumawardaningsiha et al. [17] studied the compressive strength of UHPC and UHPFRC using cylinder and cube specimens and to determine its converting factors (ratio). The results show that the compressive strength relationships between specimens differ from those of conventional concrete. Hemraj R. Kumavat, Vikram J. Patel [18] experimental work carried out to investigate addition different size of aggregate and w/c ratio on the mechanical properties standard size of cube and cylinder. R. Yu. P Spiesz H.J.H. Brouwers (2014) [19] developed densely compacted concrete mix design based on Andersen and Andersen packing model with addition of steel fiber 1% - 2% by volume of concrete Kazemi and Lubell (2012) [20] observed that cube specimens exhibited higher compressive strength compared with cylinder specimens H. M. Al-Hassani et al. (2014) [21] indicated increasing the volume fraction of steel fibers from 0% to 1.0%, 2.0%, and 3.0% the cube compressive strength was increased by 3.72%, 8.36%, and 8.89% respectively, while the cylinder compressive strength was increased by 6.36%, 9.9%, and 11.54% respectively by Sudarshan N. M. and T. Chandrashekar Rao (2015) [22] .
From the literature survey it is clear that many researchers has done work only on variation in composition for the mix design. The high Compressive strength determination and development a great challenge in limited testing capability and availability of surface area preparation. The conversion factor is prime important to determine accurate compressive strength of the concrete in relationship with cube and cylinder to improve performance of the structure, safety and stability point of view. The Maintenance cost can be reduced. Here in this research work optimized the mix design developed for water binder ratio (w/b = 0.18) and cube, cylinder compressive tests conducted and compressive strengths determined for various days and In comparison of compressive strengths and mean conversion ratios ranges 0.98 - 1.05 for cube and cylinder in relationship to determine accurate compressive strength presented. The time and testing cost saving is beneficial in construction sector.
2. UHPFRC Material Properties
2.1. Cement
The Ultra-tech Portland cement of 53 Grade conforming to IS-12269 2013, particle size 1 - 100 μm normal consistency of 28% with specific gravity of 3:15 used. The physical and chemical properties as per standards in Table 1 and Table 2.
2.2. Micro Silica
The Elkemmicro Silica conforming to Grade 920-D with a grain size 0.2 microns, non combustible irregular shape fine particles and surface area (BET M2-gm < 15) specific gravity 2.25 was used as mineral admixture. The properties and standards in Table 3.
2.3. Sand
The locally available natural river sand free from impurities with less than 1 mm size sieved through, 1000 microns sieve analysis done as per IS 2386-1963 having specific gravity 2.63 conforming to IS 650 specifications. Particle size distribution as shown in Figure 1.
2.4. Quartz
The quartz sand was used from locally available source sized 150 - 1000 microns contained 99% silicon dioxide; the specific gravity of quartz sand is 2.59.
2.5. Steel Fibers
The Dura flex bright hard non glued, hook end steel fibers of dia. 0.6 mm and length 30 mm with modulus of elasticity 210 GPa tensile strength more than
1000 MPa having aspect ratio (a/r) = 50 The fiber properties and dimension in Table 4 are used.
2.6. Super Plasticizer
The addition of polymer based Sulphonated naphthalene conplast SP430 DIS admixture used to increases the liquid quantity and adequate workability of concrete to provide excellent acceleration of strength gain reducing water demand in a rheological behavior of concrete mix and its specific gravity is 1.00 confirms to ASTM-C494 type-F.
2.7. Water
The pure, drinkable water free from chemical, mineral impurities used for mixing & curing to improve the quality and strength of the material clean potable
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Table 3. Physical and chemical requirements.
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Figure 1. Grain size particle distribution (μm).
water plays a vital role with super plasticizer to gain higher strengths. The typical range of materials shown in Table 5.
3. Mixture Proportions
The mixture proportions optimisation for the granular mix, designed by various researchers to achieve higher compressive strengths as shown in Table 6.
3.1. Binders
A Binder is a mixture of high proportion of cement and silica fume used va- rious mixtures by Rossi et al. 2008 (1318 Kg/m3), Magureanu et al. 2010 (754 Kg/m3), Katrin Habel et al. 2005 (1325 kg/m3), Eshan Ghafari et al. 2015 (1387 kg/m3), Hamdy K. Shehab Eldin et al. 2014 (935 Kg/m3), Prabhat Ranjan Prem et al. 2012 (985 Kg/m3), Alaa ABashandy 2013 (1042 Kg/m2) [23] - [29] to develop high compressive strength. In the present research work to improve workability and filling voids a suitable binder proportion of 1210 kg/m3 used.
3.2. Water/Binder Ratio
Avery low water binder ratio is used for achieving better results Rossi et al. 2004 (0.11) high percentage hooked end steel fibers 25 mm in length and 0.3 mm
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Table 5. Typical range of UHPFRC constituents in Kg/m3.
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Table 6. UHPFRC mixture components by mass of cement.
in diameter. Katrin Habel et al. 2005 (0.14), incorporated high percentage of straight steel fibers 10 mm in length and 0.2 mm in diameter. Shan Ghafari et al. 2015 (0.17) minimum content of hybrid steel fibers, Hamdy K. shehab Eldin et al. 2014 (0.13) addition straight steel fibers 50 mm in length and 1.0 mm in diameter, Prabhat ranjanprem et al. 2012 (0.17) chosen straight steel fibers 6 mm in length and 0.16 mm in diameter. Alaa A Bashandy 2013 (0.18) [23] - [29] steel fiber enhance the behavior of compressive strength with increased cement and super plasticizer (10%) percentage the water binder (w/b) ratio is very important parameter in increased compressive strength gaining. at elevated temperature. The various researchers UHPFRC mixture proportions shown in Figure 6. In this research work taking into consideration micro filler effect the water binder ratio maintained 0.18 with non glued hooked end steel fibers having aspect ratio 50 used to achieve highest compressive strength of the concrete.
3.3. Mix Design
A UHPFRC mix design material constituents are Cement, Fine sand, Micro silica, quartz sand, super plasticizer, with low water cement ratio with addition of 2.0% Hooked end steel fiber to resist crack expansion. The UHPFRC Composite is designed for ≥ 160 N/mm2.
1) Packing Density
The factors responsible for reduction of porosity and obtaining maximum packing density for conventional concrete studied by Fuller and Thomson [32] expressed by cumulative grain size distribution equation
where
―cumulative % of ith fraction,
―Diameter of the ith fraction in (mm),
―Diameter of Max grain size (mm) n―a constant value equal to 0.5.
Based on the research work Funk [33] adopted the Fullers curve for composite material similar to UHPFRC
―cumulative % of ith fraction,
―Diameter of the ith fraction in (mm),
―Diameter of Max grain size (μm) n―a constant value equal to 0.37. The detailed steps involved mixture design is shown in Flow diagram Figure 2.
2) The Mixing operation involves the following steps
i) The Dry cement, fine sand, micro silica and quartz powder per m3` put in a mixer machine as per the design proportions and mix is provided with a uniform blending, so as to form a homogeneous material.
ii) For a well mixed homogeneous mixture potable water is added until the materials have coagulated.
iii) Wait for few minutes to confirm the water is reacted properly to form a cement paste mixing was continued at low speed.
iv) Addition of super plasticizer to the coagulated mixture.
v) Hooked end steel fibers by spreading on the cement paste and mix it thoroughly to get consistent material. The stepwise preparation of UHPFRC materials shown in Figure 3 and blended mix material in Figure 4.
3.4. Casting
A three series of specimens cube are casted of sizes 150 × 150 × 150 mm and
cylinder 150 mm dia. 300 mm height with uniform vibrating the top surface were given with smooth finishing, the specimens demoulded after 24 hours. Casted specimens as shown in Figure 5.
3.5. Curing
The curing regime of specimens includes exposing the specimens to thermal treatment to enhance material properties at a temperature of 90˚C for duration
of 24 hours the specimens are removed from the thermostat cabin and allowed to cool for about 3 hours.
3.6. Testing
Compressive test
In testing program compressive test on cube specimen size 150 × 150 × 150 mm, and 150 mm dia. Height 300 mm cylinder for 3, 7, 14, 28, days conducted as per ASTM C 39 standards on computer-controlled electromechanical servo hydraulic pressure Compression testing machine 3000 KN Figure 6 with standard procedures compression testing machine applied load at the rate 5 KN/sec, the ultimate load on the specimen recorded. The compressive strength is determined using Equation (1) A typical failure pattern is by crushing is shown in Figure 7 cube and Figure 8 cylinder
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(1)
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Figure 6. Automatic compression testing machine 3000 KN.
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= Compressive strength, P = Load, A = Cross sectional area.
The compressive strength of cube and cylinder fluctuates around 165 N/mm2 and 160 N/mm2 the difference between obtained compressive strength of cube and cylinder is relatively very small and the mean compressive strength, and
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Table 7. Experimental results for cube and cylinder.
cube, cylinder ratio tabulated in Table 7. From the experimental test results it shows the compressive strength is higher than Normal strength concrete (NSC), High strength concrete (HSC), Sudarshan N M and T Chandrashekar Rao [34] . The introduction of vibration during casting, mixing stage effects on the compressive strength and durability of concrete The addition of steel fibers results highest compressive strength and restricted in crack development and strain hardening capacity of the material.
4. Results and Discussions
The experimental test results shows compressive strength of cube is higher than the cylinder, due to the increased cube surface area 150 × 150 mm and that of cylinder 150 mm diameter, the absence of coarse aggregate less than 1 mm size fine aggregates use and hooked end steel fibers increase densely compactness and ductility of the matrix material atelevated temperature. In the present experimental conversion ratio of (ƒcu/ƒcy) cube compressive strength to at 28 day ranges between (0.95 - 1.04). The mean compressive strengths of 168.16 N/mm2 for cube specimen and 161.58 N/mm2 for cylinder 2% steel fibers. The mean compressive strength V/S mean ratio of cube and cylinder shown in Figure 9 and a comparison of mean compressive strength V/S Day shown in Figure 10 the higher compressive strength is obtained due to optimized granular mixture, silica fume pozzolanic reaction, compacted density and exposure to elevated temperature. It can be observed that the mean compressive strength conversion ratios of 3 series of between cube and cylinder namely (0.99) this ratio is ranges of UHPFRC is close to the conversion factors and by AMPA (2010) [35] which is 0.95 and by the Torsten Leutbecher (2014) [36] which is 0.96 these conversion ratios necessary to consider barring factors influence occurred by specimens Mansur and Islam (2004) [37] . Investigated compressive strength on cylinder and cube of 100 mm and 150 mm dia. the results shown almost similar with
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Figure 9. Mean compressive strength V/S mean ratio.
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Figure 10. Mean compressive strength V/S Days.
marginal increase in the cube strength Benjamin A Grabeal and Marshall Davis (2008) [38] concluded cube and cylinder of 100 and 102 mm diameter results the cube strength is higher than the cylinder.
5. Conclusion
The sample of specimens tested for cube and cylinder resulted compressive strengths obtained less than the design strength 180 N/mm2. It is noted that the compression strength of UHPFRC obtained using cube specimens is not precise uniaxial strength, thus converting its value to the cylinder specimen values is necessary. In order to determine the correct compression strength of UHPFRC, by considering barring factors occurred by the specimens the 0.99 conversion factor applied to cube strength equivalent cylinder strength in relationship, to determine accurate strength and development, the removal of coarse aggregates enhances homogeneity, steel fibers influence on mean strength ratio 1% - 5% for UHPFRC and 10% - 20% in normal concrete the difference decreases with increase in strength and failure occurs by rupture. The present studies conclude 5% increase in the cube strength higher than cylinder for UHPFRC mixture.