Kajian rintangan kakisan ke atas keluli bar tetulang dalam pes geopolimer
Farah Farhana, Zainal
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This study has been conducted to understand corrosion resistance on reinforcement bar in geopolymer. Geopolymer paste has been used as a substitute for ordinary Portland cement (OPC) concrete structures. Geopolymer paste in this study was made from a mixture of fly ash and an alkaline activator of sodium hydroxide (NaOH) solution and sodium silicate (Na2SiO3) solution. For tests involving steel reinforcement bars, carbon steel is placed in the middle of the mixture and allowed to harden for 24 hours. Next, geopolymer paste placed in an oven for curing process for 24 hours. The temperature was 60˚C. Various tests were conducted to study the respect of geopolymer paste and study of corrosion on steel reinforcement bars in the paste. Among the tests conducted are phase analysis, type of bonding analysis, morphology analysis, water absorption test, porosity test, compressive strength test, pulse velocity test, immersion test, hardness test, electrical resistivity test, open circuit potential (OCP) measurements test and Tafel extrapolation test. For water absorption test, the percentage of water absorbed reduced from day 7 until day 90 which 4.65%, 4.27%, 4.16% and 3.81%. The percentage of porosity also reduced from 11.95%, 11.02%, 7.65% and 3.77% from day 7 until day 90. Vice versa, compressive strength value increased from day 7 until day 90 with the readings were 25.18 MPa, 26.76 MPa, 34.99 MPa and 56.50 MPa. The geopolymer electrical resistivity value at day 28 with electrode spacing 0.10 m and 0.01 mA current stated highest value of electrical resistivity with 61575 Ω.m however geopolymer at day 7 with electrode spacing 0.02 m and 0.95 mA current shows the lowest electrical resistivity with 537 Ω.m. It shows that the corrosion rate of geopolymer was low and too small. For OCP test before applying sacrificial anode cathodic protection (SACP), geopolymer stated minimum and maximum potential value with -0.120 V and 0.539 V respectively. From the tests, the corrosion rate of steel in geopolymer paste is still under controlled and located in the passive region. In the passive region, an oxide layer which is Iron (III) Oxide-Hydroxide (FeOOH) formed by the reaction between the steel, minerals and the air and protect the steel from corrosion agents. But this layer can only survive in the decades depends on the environment. The oxide layer will be destroyed if the paste or concrete cracks. Thus, the SACP method was implemented to protect the steel reinforcement bars in the geopolymer paste. Zinc anode is used as a sacrificial anode as the zinc has a higher electronegativity than iron in the electrochemical series. After running further analysis, it was found that the potential values located in the immunity region where the minimum potential value was -0.942 V and the maximum value was -0.704 V. In the immunity region, ferum (Fe) is stable and the reinforcement bar is not attacked by the corrosion.