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The present paper describes accelerated corrosion test results and the development of a probabilistic model to predict the depth and variability of pitting for pretensioned prestressing wires and strands subject to pitting corrosion. From the accelerated corrosion tests in a chloride-concrete environment the mode of wire failure is studied, and the spatial distribution of maximum pit depth along wires for various lengths is obtained. The analysis shows that the maximum pit-depth distribution of prestressing wires can be represented by the Gumbel extreme value distribution. This model can be extended to predict the distribution of maximum pit depth for any length of wire, corrosion rate and time of exposure in real concrete structures. This information can be used to predict minimum cross-sectional area of a corroded wire, wire capacity and the effect of pitting corrosion on the safety of pretensioned prestressed concrete structures.

Different types of corrosion may arise in steel reinforcement, such as general corrosion, pitting corrosion, hydrogen embrittlement, stress corrosion cracking and corrosion fatigue. However, corrosion of steel reinforcement in reinforced concrete (RC) structures can be classified into two categories: general (uniform) corrosion and pitting (localised) corrosion. In general, concrete researchers use uniform corrosion to study the effect of corrosion on RC structures. This approach is not accurate for concrete structures subjected to chloride attack, which usually experiences pitting corrosion. This paper describes an accelerated corrosion test used to obtain statistical parameters of maximum pit-depths distribution of corroded steel in a RC structure. Using probabilistic analysis, these statistical parameters are combined with statistical parameters of RC beams (i.e. beam dimensions, concrete strength, steel yield strength, cover thickness, workmanship quality, in situ strength factor, model error for flexure and shear and also corrosion rate) to determine the effect of corrosion on flexural and shear strength of RC beams. Using the proposed pitting corrosion model improves service life prediction of RC structures in a chloride environment.

Environmental issues resulted from cement production have become a major concern today. To develop a sustainable future it is encouraged to limit the use of this construction material that can affect the environment. Cement replacement material was proposed to partially replace cement portion in concrete. Geopolymer is a part of inorganic polymer material that has similar bonding function like cement in concrete. It consists of alkaline solutions and geological source material. Alkaline liquids used in this research are 8 M sodium hydroxide (NaOH) solution and sodium silicate (Na 2 SiO 3 ) solutions, while source materials are fly ash and microwave incinerated rice husk ash (MIRHA). Three different curing regimes, namely hot gunny curing, ambient curing, and external exposure curing, were applied to obtain suitable method that was suitable with cast in situ application. Geopolymer concrete samples were tested on their compressive strength and microstructure properties. It was found that external exposure curing had the highest compressive strength compared to other two curing methods. Scanning electron microscopy analysis also showed better improvement in interfacial transition zone for concrete sample with external exposure curing.Keywordsgeopolymer, sodium hydroxide, sodium silicate, fly ash, MIRHA AbstrakDampak terhadap lingkungan akibat produksi semen telah menjadi masalah yang besar pada saat ini. Untuk mengembangkan masa yang akan datang yang lebih berkelanjutan maka diperlukan usaha untuk membatasi penggunaan material konstruksi ini yang dapat mempengaruhi lingkungan. Material pengganti semen telah diusulkan untuk mengganti sebagian porsi semen dalam beton. Geopolimer adalah bagian dari polimer bukan organik yang mempunyai sifat mengikat seperti semen pada beton. Material tersebut terdiri dari cairan alkalin dan material dari sumber geologi. Cairan alkalin yang dipakai dalam penelitian ini adalah cairan 8 M Natrium Hidrosikda (NaOH) dan cairan Natrium silikat (Na 2 SiO 3 ), sementara material sumber geologi adalah Abu Terbang dan Abu Sekam Padi yang dibakar memakai gelombang-mikro (microwave incinerated rice husk ash/MIRHA). Tiga macam cara perawatan, yaitu perawatan memakai karung panas, perawatan suhu ruang dan perawatan di tempat terbuka tanpa perlindungan dari cahaya matahari, telah digunakan untuk mendapatkan metoda yang tepat untuk aplikasi cor setempat. Contoh beton geopolimer telah diuji kuat tekannya dan sifat-sifat struktur mikronya. Dari hasil uji tersebut ditemukan bahwa perawatan di tempat terbuka tanpa perlindungan dari cahaya matahari mempunyai kuat tekan tertinggi dibandingkan dengan dua cara perawatan lainnya. Analisa dengan cara pemindaian memakai mikrosokop elektron juga menunjukkan perbaikan zone transisi antar muka (interfacial transition zone) untuk beton dengan perawatan di tempat terbuka tanpa perlindungan dari cahaya matahari.

This paper presents a study of the flexural strength of geopolymer concrete beam using high calcium content fly ash (FA) in marine environment, without high heat curing. Two series of beam specimens were loaded to failure to study the effect of chloride environment on the flexural strength of geopolymer concrete beams. Series I specimens were subjected to sea environment, whereas series II were kept at room temperature. Tests performed on concrete cylinders show that the sea water has no effect on compressive and splitting tensile stress of high calcium content FA based geopolymer concrete. However, the ratio of splitting and compressive strength for both series was approximately 44%, almost double than that of normal concrete. In addition, the flexural test of concrete beams shows that the average cracking load for series I specimens was 275% higher than that of series II. However, the ultimate load, crack pattern and deflection characteristic for both series were very similar.