Model Prediksi Retak pada Beton Bertulang Akibat Korosi Tidak Seragam Karena Infiltrasi Klorida dengan Mempertimbangkan Siklus Basah dan Kering

Korosi merupakan salah satu permasalahan durabilitas yang dapat menyebabkan kerusakan pada struktur beton bertulang. Proses perbaikan dan perawatan struktur beton bertulang akibat korosi merupakan proses yang cukup sulit dan mahal untuk dilakukan. Oleh karena itu, diperlukan suatu metode yang dapat digunakan untuk memprediksi keretakan pada beton bertulang akibat korosi. Terdapat dua masalah utama dalam pengembangan pemodelan retak pada beton akibat korosi yaitu tidak dipertimbangkannya durasi basah dan kering serta masih digunakannya asumsi korosi seragam. Korosi pada daerah percikan memiliki mekanisme infiltrasi klorida yang berbeda bila dibandingkan pada daerah fully submerged. Pada daerah percikan, beton mengalami sikus basah dan kering sehingga mekanisme infiltrasi klorida sangat tergantung pada durasi basah dan kering. Penelitian yang ada selama ini terkait pemodelan korosi maupun keretakan akibat korosi belum mengakomodasi perbedaan konfigurasi durasi basah dan kering sebagai suatu variabel yang dapat mempengaruhi kecepatan masuknya klorida pada beton. Selain permasalahan terkait dengan siklus basah dan kering, permasalahan lain yang sering timbul pada pemodelan retak akibat korosi adalah persebaran karat. Pada penelitian sebelumnya, para peneliti mengasumsikan korosi terjadi secara merata disepanjang perimeter tulangan sehingga karat tersebar secara seragam atau uniform di sepanjang perimeter tulangan. Namun, pada kondisi sebenarnya karat tersebar secara tidak merata dengan kecenderungan bagian yang paling dekat dengan exposed surface memiliki ketebalan karat yang lebih besar bila dibandingkan dengan bagian lain. Dengan melihat dua permasalahan utama yang ada, penelitian ini berfokus untuk mengembangkan suatu model prediksi keretakan akibat korosi dengan mempertimbangkan ketidakseragaman persebaran karat dan adanya perbedaan konfigurasi durasi basah dan kering. Penelitian disertasi ini meliputi kegiatan eksperimental, pemodelan secara matematis dan numerik. Kegiatan eksperimental dilakukan dengan menggunakan dua metode yaitu metode galvanostatik dan metode wetting and drying. Pemodelan matematis dikembangkan untuk mendapatkan suatu model prediksi keretakan pada beton bertulang dengan pendekatan korosi tidak seragam dan mempertimbangkan efek dari siklus basah dan kering. Berdasarkan penelitian dan pengembangan model yang telah dilakukan dapat disimpulkan bahwa model yang dikembangkan secara keseluruhan dapat menggambarkan hasil eksperimental. Model infiltrasi klorida akibat siklus basah dan kering menghasilkan profil klorida yang sama dengan eksperimental dimana bagian yang lebih dekat dengan exposed surface menghasilkan konsentrasi yang lebih besar bila dibandingkan dengan bagian yang jauh dari exposed surface. Akan tetapi model yang dikembangkan masih menghasilkan konsentrasi yang sedikit lebih besar pada exposed surface. Rata-rata perbedaan konsentrasi yang dihasikan mencapai 6.24% bila dibandingkan dengan hasil eksperimetal. Selain model infiltrasi klorida akibat siklus basah dan kering, model keretakan akibat korosi juga dikembangkan dalam penelitian ini. Model keretakan beton akibat korosi dibagi menjadi tiga tahapan utama yaitu tahap inisiasi, tahap retak pertama dan tahapan propagasi retak hingga mencapai exposed surface. Model yang dikembangkan menggabungkan beberapa teori dasar yang kemudian dikembangkan menjadi suatu model prediksi. Pada tahapan inisiasi, hukum Faraday untuk kinematika korosi dan Gaussian Normal Function digunakan sebagai dasar pengembangan model. Pada tahapan retak pertama dan perambatan retak, teori thick walled cylinders digunakan untuk mensimulasikan proses keretakan akibat adanya korosi. Hasil pemodelan menunjukkan bahwa retak pertama terjadi 17.48 jam setelah pengujian dengan metode Galvanostatik dimulai. Selanjutnya retak tersebut berpropagasi dan mencapai exposed surface pada 80 jam setelah retak pertama mulai terjadi. Hasil ini lebih cepat bila dibandingkan dengan pengamatan eksperimental. Hal ini dikarenakan oleh ketebalan karat hasil perhitungan yang juga lebih besar dibandingkan pengukuran hasil eksperimental. Model ketebalan karat ini merupakan dasar dari model retak yang dikembangkan. Apabila terdapat perbedaan ketebalan karat yang dihasilkan, maka waktu retak yang dihasilkan dari model dan eksperimental juga akan berbeda. Berdasarkan hasil pemodelan distribusi karat yang telah dilakukan, didapatkan bahwa ketebalan karat hasil dari model lebih besar bila dibandingkan dengan hasil eksperimental. Perbedaan yang terjadi mencapai 11.07% dan hal ini dimungkinkan karena adanya produk korosi yang masuk ke dalam celah retak sehingga tidak terukur pada saat eksperimental. =================================================== Corrosion is one of the durability problems which can lead to the collapse of the reinforced concrete structure. Repair and maintenance of the reinforced concrete structure due to corrosion are a process which quite difficult and expensive to do. For that reason, it needs a method to predict the cracking of the concrete due to corrosion accurately in accordance with actual conditions. There are two main problems in the cracking model development due to corrosion which are wetting and drying condition and uniform corrosion assumption. Corrosion in the splash zone has different chloride infiltration mechanism compared with the fully submerged area. Concrete in the splash zone exposed to wetting and drying environment. Hence, the transport mechanism should consider the variable related to wet and dry duration. Previous research related to chloride infiltration model did not consider the wetting and drying duration as one of variables which can affect the chloride profile in the concrete. Aside from the wetting and drying cycle problem, another problem which is critical to the corrosion induced cracking is the distribution of corrosion products. The previous studies assume that corrosion occurs uniformly along the perimeter of the steel bar. However, in fact, the rust is distributed non-uniformly along the perimeter of the steel bar. The part which has closets distance to the exposed surface tend to have thicker rust than the other parts. By looking the two main problems, this research is focused on the predictive model development of corrosion induced cracking by considering the effect of non-uniformed rust distribution and different configuration of wetting and drying cycle. This research includes experimental, mathematical and numerical modeling. The experimental activities were carried out by using two main methods which are galvanostatic and cyclic wetting and drying method. The two approaches were used to accommodate two problems which have been mentioned previously. Based on the research result, it can be concluded that the predictive models which have been developed were proven to have a good agreement with the experimental result. Model of chloride penetration due to cyclic wetting and drying produced a similar pattern of chloride profile. However, the exact value from the predictive model is still 6.24% higher than the experimental result. Model of corrosion induced cracking also developed in this research. The model divided into three main stage which are the initiation, first crack and cracks propagation stage. The corrosion induced cracking model combined several related theory. For the initiation stage, the Faraday’s Law for corrosion kinematics and Gaussian Normal Function were used. Furthermore, the thick walled cylinders theory was used in the first crack and crack propagation stage to simulate the cracking process due to corrosion. The predictive model showed that the first crack occurred 17.48 hours after the corrosion test with Galvanostatic method was started. The crack was propagated and reached the exposed surface 80 hours after the first crack. This result is faster when compared with experimental observations. This is because the calculated rust thickness is also greater than experimental results. The rust thickness is the basis of the crack model, so if there is a difference in the thickness of the rust, then the cracking time generated from the model and the experimental will also be different. The calculated rust thickness is thicker compared with the experimental results. The average difference reaches 11.07%. This condition is possible because there was corrosion product which infiltrates into the crack tip and did not measure during the experimental observation

INVESTIGATION OF THE EFFECT OF SANDBLASTING WASTE TREATMENT METHOD AS NANO-SILICA ON THE COMPRESSIVE STRENGTH OF CONCRETE MORTAR

This study presents the effect of nano-silica (NS) from sandblasting waste as an additive on the mechanical properties of concrete mortar. The nano-silica was produced by using the sol-gel and mechanical grinding methods. In this research, nano silica material was added as an additive with a percentage varying from 0% to 5%. The results show that producing nano silica from sandblasting waste with a combination of sol-gel and mechanical grinding methods can produce an average size of 148.9 nm with 96.90% purities silica (SiO2). The compressive strength test also shows that adding NS can increase the compressive strength of the concrete. The highest compressive strength obtained from this research was. 29.76 MPa with the addition of 1% of nano-silica. This compressive strength is 37.5% higher than the control mixture

Strength reduction factor evaluation of the circular reinforced concrete column with varying eccentricity ratio (e/h)

This paper presents strength reduction factor evaluation of circular reinforced concrete column with varying eccentricity ratio (e/h) using the first-order-reliability-methods. The resistance properties of the reinforced concrete column is estimated using the monte-carlo simulation with random normally distributed material properties. Only dead and live load combination considered in the analysis. The parameters being investigated when evaluating the resistance of the reinforced concrete column are the concrete compressive strength, steel yield strength, coefficient of variation for both the concrete and steel materials, reinforced concrete column size, and the longitudinal reinforcement ratio. When evaluating the strength-reduction factor, the safety index values are 3.0, 3.5, and 4.0. From the analysis, it was found out that the strength reduction factor, for e/h higher than one and with safety index equal to 3.0, was equal to 0.9 which agrees well with the ACI 318 strength reduction factor for tension-controlled region. However, for e/h lower than one and safety index equal to 3.0, the strength reduction factor was equal to 0.6 which was lower than the ACI 318 strength reduction factor for compression-compression controlled region

SORPTIVITY AND CHLORIDE PENETRABILITY EVALUATION OF CONCRETE INCORPORATING FLY ASH AND SILICA FUME

Diffusion is believed to be the main mechanism of fluid ingress into the concrete. However, in partially saturated concrete, the fluid will mainly be absorbed by the capillary suction mechanism, which associates with the sorptivity properties of the concrete. This paper presents the results of an experimental program to investigate the influence of Portland cement substitution with Silica Fume (SF) and Type F Fly Ash (FA) on the rate of absorption, which also known as sorptivity, and chloride penetration of concrete. The sorptivity of the concrete was evaluated according to ASTM 1585, while the chloride penetration was evaluated according to ASTM C 1202. By substituting part of cement with FA and SF, it was found that the sorptivity of concrete is reduced. Furthermore, all type of concrete with supplementary material, including CFA, CSF and CSM, is confirmed to enhance the ability of concrete to resist chloride penetration compared yo normal concrete (NC)

Pemanfaatan Pasir Silika Limbah Sandblasting sebagai Substitusi Agregat Halus pada Structral Lightweight Foamed Concrete (SLFC)

Pasir silika limbah sandblasting dihasilkan dari proses blasting untuk mencegah terjadinya korosi pada permukaan logam. Berdasarkan Peraturan Pemerintah No 22 Tahun 2021 Lampiran IX, limbah sandblasting merupakan limbah B3 sehingga tidak dapat dibuang langsung ke lingkungan. Oleh karena itu, pada penelitian ini berfokus pada pemanfaatan limbah sandblasting sebagai material pengganti agregat halus pada Structural Lightweight Foamed Concrete (SLFC) dengan metode solidifikasi. Sampel beton yang digunakan yaitu tanpa pasir limbah sandblasting dan 100% dengan limbah sandblasting yang kemudian di uji kelayakan teknisnya dengan uji kuat tekan yang mengacupada ACI 357R-14 dan uji kelayakan lingkungan menggunakan TCLP berdasarkan PP No 22 Tahun 2021. Hasil pengujian kuat tekan pada beton penambahan limbah sandblasting sebesar 0% dan 100% menghasilkan kuat tekan sebesar 19,9 MPa dan 37,3 MPa diumur 28 hari. Berdasrkan hasil uji TCLP pada beton SLFC dengan konsentrasi limbah sandblasting 100% sebagai pengganti agregat halus terbukti layak teknis dan lingkungan

NUMERICAL SIMULATION OF NON – UNIFORM CORROSION INDUCED CRACKING

This research is focused on modeling the damage of concrete due to corrosion. The load used in this paper is only focused on the internal load due to rust expansion. In this study, corrosion was modeled uniformly and non-uniformly to investigate the difference between these two configurations to the damage in concrete. The simulation in this study was carried out using the 3DNLFEA program. The results show that numerical simulation provides predictions that are in line with experimental and numerical modeling results performed by the previous study in terms of pressure and corrosion cracking patterns. From the crack analysis, the pattern found that a non-uniform corrosion model can be used to express a realistic rust corrosion development around the reinforcement. Meanwhile, uniform corrosion requires a larger loss of steel area to reach the damage stage. Therefore, for non-uniform corrosion, the corrosion rate cause cracks and reaches a limiting crack width at earlier times in the service life of the corroded part

Microstructural Investigation of Reinforced Concrete Exposed to Cyclic Wetting and Drying

Concrete which placed in an aggressive environment has a great chance to suffer from damage especially for concrete put in the marine environment. In this situation, damage process in concrete is mainly caused by chloride ingress. The chloride penetrates into the concrete by various mechanisms. For concrete submerged in seawater, the chloride solution penetrates into the concrete trough diffusion mechanism and cause damage over the time. However, in real life, reinforced concrete structure mostly placed in the partially saturated area and subjected to the repeated actions of the wetting and drying cycle. This condition makes the concrete structures more vulnerable to corrosion than structures in a fully saturated condition. Therefore, this study investigates the changes in concrete microstructures condition due to repeated actions of wetting and drying. The samples were exposed by 5% NaCl solution through the different configuration of wet and dry duration. The microstructural condition was observed by several methods such as XRF, SEM and EDX analysis. Major constituent phases of concrete and the differences in their distribution due to different duration of wet and dry were observed in this study. Finally, from the investigation, it was found that there were noticeable differences in chloride and magnesium percentage in the samples. This result acts as evidence that the duration of wet and dry can affect the formation of particular compounds such as chloroaluminate, quartz, brucite, and dolomite in the samples which plays roles in the damage process of concrete

Prediction of Rust Thickness in Reinforced Concrete Structures to Enhanced the Asset Management for Coastal Infrastructures

Corrosion in reinforced concrete structure is a serious problem, especially for coastal infrastructure. Managing the coastal infrastructure from corrosion is a really essential action to make sure that the infrastructure can be used properly throughout its service live. This research focused on analyzing the rust thickness on steel reinforcement due to corrosion. Series of corrosion test using galvanostatic was performed in this research. Furthermore, a predictive model based on Farraday’s Law with uniform corrosion assumption also developed in this research and compared with the experimental data. Based on the simulation result, it was found that the predictive model of rust thickness based on Farraday’s Law is capable to simulate the corrosion process and thickness of the rust

Pemanfaatan Limbah Padat Pasir Silika Limbah Sandblasting dan Fly Ash untuk Beton HVFA-SCC

Beton High Volume Fly Ash (HVFA) merupakan campuran beton yang menggunakan fly ash dengan persentase fly ash yang digunakan lebih dari 50%. Adanya kandungan bahan kimia silika dan alumina, yang membuat fly ash memiliki sifat pozzolanik seperti semen, sehingga dapat dimanfaatkan untuk menjadi material pengganti semen. Dalam penelitian ini metode yang digunakan adalah metode eksperimen dengan melakukan pembuatan beton high volume fly ash - self compacting concrete (HVFA-SCC) yang memanfaatkan limbah sandblasting sebagai pengganti agregat halus dan limbah fly ash sebagai pengganti semen yang akan dibandingkan dengan beton normal dan beton HVFA menggunakan pasir biasa. Hasil penelitian menunjukkan komposisi beton HVFA dengan variasi campuran 40% limbah fly ash dengan substitusi pasir silika limbah sandblasting menghasilkan kuat tekan sebesar 21,03 MPa pada usia beton 28 hari. Berdasarkan hal tersebut, pasir silika limbah sandblasting dapat berpotensi menjadi substitusi agregat halus pada beton HVFA dan termasuk ke dalam jenis beton mutu sedang yang dapat dimanfaatkan sebagai beton bertulang