STRENGTH AND SORPTIVITY OF CONCRETE USING FLY ASH AND SILPOZZ IN MARINE ENVIRONMENT

Transcription

1 Journal of Engineering Science and Technology Vol. 13, No. 12 (2018) School of Engineering, Taylor s University STRENGTH AND SORPTIVITY OF CONCRETE USING FLY ASH AND SILPOZZ IN MARINE ENVIRONMENT T. JENA 1, *, K. C. PANDA 2 1 Civil Engineering Department, Siksha 'O' Anusandhan (Deemed to be University), Bhubaneswar, , Odisha, India 2 Civil Engineering Department, Government College of Engineering, Kalahandi, Bhawanipatna, , Odisha, India *Corresponding Author: trilochanjena1975@gmail.com Abstract This paper presents the strength and sorptivity study of concrete using Fly Ash (FA) and silpozz exposed to seawater. Conventional concrete made with 100% cement. First blended concrete series made with 0% FA and 10-30% replacement of silpozz with cement and second series made 10% FA and 10-30% silpozz replaced with cement. The studied parameters are compressive strength for 7, 28, 90, 180 and 365 days and flexural strength and split tensile strength for 7, 28 and 90 days of Sea Water Curing (SWC) and Normal Water Curing (NWC) samples. Modulus of elasticity and Strength Reduction Factor (SRF) in bond strength along with a slip of 28 days SWC samples are also studied. The chloride binding capacity, water absorption and sorptivity were observed as durability indicator. It reveals from the present investigation that incorporation of silpozz significantly improves the strength and reduces sorptivity of concrete against sea water. Keywords: Blended concrete, Compressive strength, Deterioration, Fly ash, Silpozz. 4310

2 Strength and Sorptivity of Concrete Using Fly Ash and Silpozz in Marine Introduction The growth of concrete technology is completely based on its strength but not only that should be considered but the coarseness degree of various environmental circumstances to which, concrete is being exposed for lifelong as should be considered and have given a great extent of importance. So, finally, both compressive strength and its nature of durability are considered clearly at the different design phase and its relationship also is taken into account. While estimating the conditions of present structures, concrete s durability is the most important consideration to be taken into account in designing new structures. Construction of concrete is gradually very cost effective as its durability has been higher so it is becoming one of the most complex things. When one understands the concrete s fundamental basic of durability, all start finding new methods to increase its service life of all the new and upcoming structures. Concrete s longtime durability potential is the key to knowledge as it consists of uncommon materials such as recycled aggregate and high silica aggregates with mineral admixtures. Although concrete is probably to get damaged up to some extent, ensuring good durability of concrete and minimizing the rate of damage. Kumar [1] reported that the deterioration mechanism in marine exposure condition studied the percentage decrease in compressive strength for the period of one year of exposure in both freshwater and seawater curing and concluded that the compressive strength decreases as the age of exposure increases. Menon et al. [2] investigated the effect of high strength concrete incorporated with Fly Ash (FA), silica fume (SF) and Ground Granulated Blast Furnace Slag (GGBS) with superplasticizer under severe exposure seawater tidal zone without serious deterioration. Wegian [3] reported that all forms of deterioration can be controlled by using higher cement content in seawater. Anwar and Roushdi [4] showed the improvement of mechanical properties of concrete containing OPC, FA and SF in artificial seawater and resist against environmental deterioration. Panda and Prusty [5] enhanced the strength properties using silpozz as a partial replacement of OPC. Jena and Panda [6-9] studied the development of mechanical properties in blended concrete made with silpozz to improve the durability of marine structures and diffusion of chloride and carbonation is minimized due to a replacement of FA and silpozz with ordinary Portland cement (OPC). Zareei et al. [10] investigated the compressive strength and water absorption with chloride ion penetration by using 5, 10, 15, 20 and 25% rice husk ash (RHA) incorporated with 10% micro silica (MS) and found 15% RHA with 10% MS gives optimized results. Kumar et al. [11] investigated the better strength and sorptivity of concrete by utilising the sugarcane bagasse ash and SF as a partial replacement of cement. Kartini et al. [12] studied the strength and sorptivity of blended concrete incorporating 20-30% of rice husk ash (RHA) replaced with OPC. The objective of this present work is to study the mechanical properties as well as water absorption and sorptivity of blended concrete incorporated with FA and silpozz with proper doses of superplasticizer in the marine environment and the utilization of eco-friendly materials in the construction industry.

3 4312 T. Jena and K. C. Panda 2. Methodology 2.1. Materials In this study, OPC 43 grade cement was used. The physical properties of OPC determined as per IS 8112: 2013 [13] such as initial setting time, final setting time, standard consistency, specific gravity and fineness are 165 min, 360 min, 34%, 3.15 and 333m2/kg respectively. Fineness modulus of coarse aggregates 7.0, specific gravity 2.86, impact value 24% and crushing value 23.3% was used. A specific gravity of fine aggregate 2.67 and fineness modulus 3.03 (zone-iii) was used. Normal water having ph value 6-8, seawater of Bay of Bengal, Puri beach and CERA HYPERPLAST XR-W40 high-end superplasticizer (SP) was used. The experimental value of coarse and fine aggregates is confirming to IS [14]. Silpozz contains amorphous silica, which is produced from rice husk burning in a controlled temperature of about 700 C. This ash produced is amorphous in nature. Silpozz is a very good super pozzolan and it is used in place of SF or micro silica at a lower cost without compromising the quality aspect. Physical properties FA and silpozz supplied by the supplier is presented in Table 1 and the chemical composition of cementitious materials is presented in Table 2. Table 1. Physical properties of FA and silpozz. Physical properties FA Silpozz Specific gravity Bulk density (gm/cc) Specific surface, m 2 /g Particle size (micron) Color Gray Gray black Physical state - Solid non-hazardous Table 2. Chemical composition of cementitious materials. Oxides (%) Cement Silpozz FA (OPC) SiO Al 2O Fe 2O Carbon CaO MgO K 2O Na 2O SO TiO Others Moisture content (%) Loss on ignition (%) Mix design and identity The mix design is targeted for M30 as it is the marine exposure condition as per IS [15]. The obtained material ratio was (1: 1.44: 2.91), water to binder ratio of The controlled specimen is prepared with 100% OPC without SP and there is no change of the quantity of materials. As SP is used in blended concrete mixes,

4 Strength and Sorptivity of Concrete Using Fly Ash and Silpozz in Marine the amount of water was reduced by 20% based upon the several trial mixes in order to maintain the slump in between mm. The strength properties and durability observations were studied and their percentage decrease in strength was evaluated. The mix identity MC100F0S0 means OPC 100%, FA 0% and silpozz 0% without SP. Similarly, the mix M1C90F0S10 means OPC 90%, FA 0% and silpozz 10% with SP 0.2% and so on. The details of mix identity along with their percentage of cementitious materials with SP are presented in Table 3 and details of concrete mix quantities in kg/m 3 along with slump value and compaction factor are shown in Table 4. Mix Identity Table 3. Details of cementitious materials with SP. Mix identity OPC (%) FA (%) Silpozz (%) SP (%) MC100F0S M1C90F0S M1C80F0S M1C70F0S M1C80F10S M1C70F10S M1C60F10S Cement (kg/m 3 ) Table 4. Details of mix quantity. Fine aggregate (kg/m 3 ) Coarse aggregate (kg/m 3 ) FA (kg/m 3 ) Silpozz (kg/m 3 ) Water SP (kg/m 3 ) MC100F0S M1C90F0S M1C80F0S M1C70F0S M1C80F10S M1C70F10S M1C60F10S Results and Discussions 3.1. Properties of fresh concrete Properties of fresh concrete were measured by slump value and compaction factor to know the workability. The dose of SP was added only to maintain the slump in between mm and the experimented slump ranged from 34 to 42 mm was observed. The compaction factor ranges from to 96.20%, which shows moderate workable concrete at all levels Properties of hardened concrete The hardened concrete properties were determined as per IS 516: 1959 [16]. The properties of hardened concrete are evaluated by their compressive strength up to 365 days curing period. The flexural strength and split tensile strength is evaluated up to 90 days of NWC and SWC. Modulus of elasticity was tested after 28 days of SWC samples. The decrease in strength depends upon the time of exposure, quality of materials, a concentration of CO 2, the diffusion rate of chloride into concrete samples and other harmful constituents present in the sea water.

5 4314 T. Jena and K. C. Panda Compressive strength Figures 1 and 2 show compressive strength versus curing time in days for both NWC and SWC samples respectively. The percentage decrease in compressive strength is limited to 8% for 12 months study but the sample having 10% FA and 20% silpozz replaced with OPC gives minimum 4.2%. It is observed from Fig. 2 that the normal mix shows higher percentage decrease in compressive strength at all ages of curing. The sodium chloride and some amount of CO 2 present in seawater react with Ca(OH) 2 and the formation of hydrochloric acid and CaCO 3 may reduce the strength gain in sea water. But FA and silpozz with proper doses of SP restricted the intrusion of chloride and CO 2, thus decrease in strength is minimizing. The percentage decrease in the compressive strength of sample having 0% FA and 20% silpozz replaced with OPC is 2% after 3 months of exposure and 4.8% after 12 months as compared to conventional concrete. From the above study, concrete works better in seawater with FA and silpozz having proper doses of SP. The percentage decrease in compressive strength for conventional concrete is 7% at 365 days of SWC curing compared with NWC samples. It is observed that the rate of deterioration is more in between 28 to 90 days and slowly reduces to 2% from 90 to 365 days. The silpozz based concrete without FA performed better in normal water at all ages but the blended sample containing 10% FA and 20% silpozz performed better in seawater in long-term basis at least for a period of one year, which is experimented from this study. The percentage reduction in strength seems to be very small for one year but the coastal structures are vulnerable to long-term exposure conditions. Therefore, it may be recommended that the resistance against concrete deterioration in a marine environment is significantly enhanced by using FA and micro silica present in silpozz with proper doses of high-end SP. Fig. 1. Compressive strength vs. curing time in days (NWC samples).

6 Strength and Sorptivity of Concrete Using Fly Ash and Silpozz in Marine Fig. 2. Compressive strength vs. curing time in days (SWC samples) Flexural strength Flexural strength versus curing time in days is shown in Figs. 3 and 4 for NWC and SWC respectively. After comparing between NWC and SWC samples, the percentage decrease in flexural strength is 2% at 90 days, 1.4% at 28 days and 0.8% at 7 days for 10% FA and 30% silpozz replaced with OPC. The minimum percentage decrease in flexural strength is 0.37%, 0.67% and 1% at 7, 28 and 90 days age for 10% FA and 20% silpozz replaced with OPC respectively. The decrease in flexural strength is limited to 1% at 7 days age for all samples and it is increased only after 28 days to 90 days. The rate of decrease in strength is directly proportional to the exposure conditions. The decrease in strength of sample containing 10% FA and 30% silpozz is 0.8% at 7 days, which is almost equal to the other samples except for M1C70F10S20 but the percentage decrease in flexural strength increases up to 2% at 90 days, which is the highest value in this study. As silpozz was replaced by 30% with OPC as a result of which, early strength gains may be the reason for increasing the strength at the age of 7 days. The percentage decrease in flexural strength for the sample having 0% FA and 20% silpozz is 0.86%, 0.94% and 1.22% at 7, 28 and 90 days of age respectively. It is observed from flexural strength results that the combined effect of FA and silpozz works better up to 30% replacement of OPC and more than that the DF increases.

7 4316 T. Jena and K. C. Panda Fig. 3. Flexural strength vs. curing time in days (NWC samples). Fig. 4. Flexural strength vs. curing time in days (SWC samples) Split tensile strength The split tensile strength versus curing time in days is shown in Figs. 5 and 6 for both SWC and NWC samples respectively. It is observed from Figs. 5 and 6 that some of the intermediate samples having almost equal split tensile strength at all ages. But the sample containing 10% FA and 20% silpozz showing 0.54%, 0.64% and 0.78% decrease in tensile strength at 7, 28 and 90 days age, which is the minimum value than the control specimen. After comparison, the maximum value of percentage decrease in tensile strength is 1.65% for 10% FA and 30% silpozz sample at the age of 90 days and it is equal to the value of control specimen for same curing periods. The percentage decrease in tensile strength is the same for M1C80F0S20 and M1C70F10S20 sample at the age of 90 days. The percentage decrease in tensile strength for the sample having 10% FA and 10% silpozz replaced with OPC is

8 Strength and Sorptivity of Concrete Using Fly Ash and Silpozz in Marine %, 0.65% and 1.01% at 7, 28 and 90 days of exposure in seawater respectively. The combined effect of FA and silpozz replaced with OPC up to 30% performed better DF as compared to control specimen up to 90 days.the deterioration of concrete increases as the percentage of replacement of cement increases more than 30%. The addition of SP plays an important role to decrease the deterioration of concrete in sea water. Fig. 5. Split tensile strength vs. curing time in days (NWC samples). Fig. 6. Split tensile strength vs. curing time in days (SWC samples) Modulus of elasticity The Young's modulus of elasticity, which is the function of concrete, which reveals its elastic nature mainly of aggregate and cement paste in proper relative ratio. It is relatively constant with keeping its stress at a low point because it develops a crack in concrete paste at a level of higher stress. Modulus of elasticity concrete ranges from 30 to 50 GPa. Figure 7 shows the modulus of elasticity (MPa) versus types of a mix for 28 days SWC samples from which, the mix

9 4318 T. Jena and K. C. Panda having 0% FA and 10-20% silpozz gives the same value of modulus of elasticity as compared to control sample. The sample containing 10% FA and 20% silpozz showing the highest value of elasticity as compared to other samples including a control sample. Silpozz based samples mixed with 10% FA giving a higher value of modulus of elasticity than the other samples after 28 days of SWC. There is no change up to 20% silpozz but suddenly modulus of elasticity increases when 10% FA and 20% silpozz replaced with OPC Bond strength Fig. 7. Modulus of elasticity vs. types of mix. The specimen size for pull out test is 150 mm 150 mm 150 mm with a reinforcing tor bar of 12 mm diameter. Total length of the bar is 120 mm with a bond length of 60 mm confirming to IS 2770 (Part 1): 1967 [17]. For all specimens the load rate was 0.1kN/s. The types of failure were identified for each test by recording the bond strength slip results measured at the free end with a dial micrometer an accuracy of mm. The ultimate bond strength was calculated from τ b = F max/πφl, where τ b is the bond strength, F max is the maximum pull out force, Φ is the diameter of the tor bar and L is the bond length. The SRF in bond strength versus types of mix is shown in Fig. 8. It observed from Fig. 8 that the lowest value of SRF is 10.35% for sample of 10% FA and 20% silpozz replaced with OPC. The highest value of SRF is 14.11% for control specimen at 28 days of curing. The combined samples having FA and silpozz performed better in sea water. The slip in mm versus types of mix is shown in Figs. 9 and 10. It is observed from Fig. 9 that slip is limited to 1.40 mm for normal concrete and minimum slip is 1 mm for silpozz based concrete. Slip is mainly depends upon the bond between cement concrete matrix and steel reinforcement. It was noted at the time of maximum applied load. When FA is added with silpozz the slip is controlled and less than the control specimen. It was observed that slip corresponding to bond strength decreases as the compressive increases. The sample 10% FA and 20% silpozz gives higher bond strength and compressive strength with minimum slip of 1 mm.

10 Strength and Sorptivity of Concrete Using Fly Ash and Silpozz in Marine Fig. 8. SRF (%) vs. types of mix. Fig. 9. Slip in mm vs. types of mix. Fig. 10. Slip in mm vs. types of mix.

11 4320 T. Jena and K. C. Panda 4. Durability Properties Deterioration of structural components in marine climate is generally associated with the chloride s penetration into concrete causing damage. The WSC was known as free chloride and ASC known as total chloride are determined as per IS 14959: 2001 (Part- 2) [18]. According to ASTM International [19], water absorption and sorptivity are done conforming to ASTM C The samples are tested for water absorption and sorptivity after curing 28 days in normal water and SWC pre-cast samples. The test procedures are described below for both water absorption and sorptivity test Chloride binding capacity The chloride binding capacity (P cb) can easily be evaluated using Eq. (1). P cb = ((C t - C f) / C t) 100 (1) where C t = Total chloride, C f = Free chloride. Figure 11 shows chloride binding capacity (%) versus concrete mix. It is observed that the chloride binding capacity in percentage is 24.44%, 23.91%, 23.95% and 24.15% for 28, 90, 180 and 365 days of SWC control samples respectively. At the instance, chloride binding capacity is more up to the age of 28 days but subsequently, the value obtained is less. Cheewaket et al. [20] observed the physical chloride binding in concrete. Due to a pozzolanic reaction, C-A-H, ettringite, C-S-H and monosulfate produced, which are responsible for physical chloride absorption. Luo et al. [21] commented that the physical adsorption and chemical reactions are two main reasons for the chloride binding capacity of concrete. In this study, FA contains aluminium oxide (Al 2O 3) at 31%, whereas OPC contains Al 2O 3 only 6.05%. After replacing FA in concreted, the amount of Al 2O 3 increases, as a result of which, chloride binding capacity increases. It is also observed that when the percentage of silpozz increases the chloride binding capacity (%) is increased. Yu et al. [22] explained that the amorphous silica in silpozz reacts with Ca(OH) 2 contains in cement and create more C-S-H gel (Ca1.5SiO 3.5 xh 2O) and less portlandite in comparison with OPC concrete, which mainly accounts for the improved resistance against chloride. Fig. 11. Chloride binding capacity (%) vs. types of mix.

12 Strength and Sorptivity of Concrete Using Fly Ash and Silpozz in Marine Water absorption The graphical plot between water absorption and concrete mixes is shown in Fig. 12. It is observed from Fig. 12, that the water absorption capacity for conventional concrete is 2.6% and 2.08% in both NWC and SWC pre-cast samples respectively. It is also observed that SWC pre-cast blended concrete samples have less absorption capacity as compared to NWC samples. It is clear from the observations that the pre-cast samples have already cured in normal water for 28 days and then they have been cured in seawater for the next 28 days. Therefore, absorption capacity decreases for the hardened matured stage. When the replacement percentage of silpozz increases, the absorption capacity decreases. When FA is replaced, again absorption capacity increases and after replacing silpozz, it counteracts the absorption capacity and reduces the rate of absorption. After replacing FA, the absorption capacity increases for both in NWC and SWC pre-cast samples. Silpozz based samples have higher resistivity than the composite samples having FA and silpozz. The absorption capacity depends on the porosity of concrete, particle size of FA and silpozz and their inner structural mechanism of concrete. The dense and compact structured concrete may give less absorption capacity Sorptivity Fig. 12. Water absorption (%) vs. types of mix. The comparison results of the sorptivity test between NWC and SWC pre-cast samples have shown in Fig. 13. It is observed from Fig. 13 that the conventional concrete has the highest sorptivity value among all mixes in both NWC and SWC pre-cast samples. The samples M1C70F10S20 and M1C60F10S30 have same sorptivity value for both in NWC and SWC. The value of sorptivity decreases by the partial replacement of silpozz and the value increases after partial replacement of FA. The result obtained from the silpozz based SWC samples is less than the NWC composite samples partially replaced with FA and silpozz. In normal water curing, a significant amount of calcium hydroxide migrates from specimen pores into surrounding water resulted less dense matrix hence sorptivity

13 4322 T. Jena and K. C. Panda is more but in pre-cast samples, which have already cured in normal water for 28 days and become hardened stage provides dense matrix. Then after the pre-cast samples were cured in seawater for 28 days and taken for testing, which gives less sorptivity. In case of higher water-cement ratio with 20% silpozz replacement, upon evaporation leaves voids spaces in concrete specimen leads to higher absorption but in lower water-cement ratio, doses of SP enhances the liquidity of silpozz concrete mixes and optimize the compaction results high impermeable concrete and less absorption capacity. 5. Conclusions Fig. 13. Sorptivity vs. types of mix. The following concluding remarks may be drawn from the present study: From the study, it reveals that concrete deterioration is not significantly changed. The SRF is found to be less than 3% and 8% for 10% FA up to 20% silpozz replaced with cement at 90 and 365 days of exposure respectively. The percentage decrease in flexural strength was found to be negligible but in long term, this may lead the vulnerability for coastal structures. It was found 1% for sample 10% FA and 20% silpozz replaced with OPC at 90 days SWC. The SRF in split tensile strength for sample 0% FA and 20% silpozz replaced with OPC is found 0.3%. 0.45% and 0.8% at 7, 28 and 90 days of age, which is less than the value for sample 10% FA and 20% silpozz. Here a different trend is observed in split tensile strength. And it may be due to 90 days test. Silpozz gives high strength at early ages. The higher value of young modulus of elasticity is found for the mix having 10% FA and 20% silpozz replaced with OPC because of higher compressive strength. The lowest value of SRF in bond strength is 10.35% for a sample of 10% FA and 20% silpozz replaced with OPC. The highest value of SRF is 14.11% for control specimen at 28 days of curing. The maximum and minimum slip is 1.40 mm and 1 mm for control specimen and the mix with 10% FA and 20%

14 Strength and Sorptivity of Concrete Using Fly Ash and Silpozz in Marine silpozz respectively in 28 days NWC. But the slip is observed mm and 1.19 mm for control specimen and 10% FA with 20% silpozz sample respectively in 28 days SWC. The SWC pre-cast samples have a better performance against water absorption. When the replacement percentage of silpozz increases, the absorption capacity decreases. After replacing FA the absorption capacity increases for both in NWC and SWC pre-cast samples. The SWC pre-cast samples are showing lower sorptivity value than the NWC samples after 28 days of curing. The conventional concrete has the highest sorptivity value among all mixes in both NWC and SWC pre-cast samples. The samples having 10% FA with 20% silpozz and 10% FA with 30% silpozz shown same sorptivity value for both in NWC and SWC pre-cast samples. One of the main reasons for the improvement in properties of concrete, such as strength and resistance to chloride penetration, by adding silpozz to concrete possibly may be attributed to the formation of more C-S-H gel and less portlandite in it due to the reaction occurring between silpozz and the Ca 2+ and OH - ions, or Ca(OH) 2 in hydrating cement. Acknowledgement Authors would like to thanks SM consultants, suppliers of FA and silpozz as well as SOA (Deemed to be University), Bhubaneswar, Odisha, for conducting the experimental work. Nomenclatures C f C t F max L P cb Free chloride Total chloride Pull out force Bond length Chloride binding capacity Greek Symbols τ b Bond Strength Φ Diameter of tor bar Abbreviations ASC Acid-Soluble Chloride FA Fly Ash GGBS Ground Granulated Blast Furnace Slag MS Micro Silica NWC Normal Water Curing OPC Ordinary Portland Cement RHA Rice Husk Ash SF Silica Fume SP Superplasticizer SRF Strength Reduction Factor SWC Sea Water Curing WSC Water Soluble Chloride

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16 Strength and Sorptivity of Concrete Using Fly Ash and Silpozz in Marine Bureau of Indian Standards. (1967). Methods of testing bond in reinforced concrete. Part 1 pull-out test. Indian Standards. IS 2770 (Part 1): Bureau of Indian Standards. (2001). Determination of water soluble and acid soluble chlorides in mortar and concrete methods of tests. Indian Standards. IS (Part 2): ASTM International. (2004). Standard test method for measurement of rate of absorption of water by hydraulic cement concretes. C Cheewaket, T.; Jaturapitakkul, C.; and Chalee, W. (2010). Long term performance of chloride binding capacity in fly ash concrete in a marine environment. Construction and Building Materials, 24(8), Luo, R.; Chai, Y.; Wang, C.; and Huang, X. (2003). Study of chloride binding and diffusion in GGBS concrete. Cement and Concrete Research, 33(1), Yu, Q.; Sawayama K.; Sujita, S.; Shoya, M.; and Isojima, Y. (1999). The reaction between rice husk ash and Ca(OH) 2 solution and the nature of its product. Cement and Concrete Research, 29(1),