Effects of exposure to elevated temperatures on the bond characteristics between normal concrete substrate and ultra high performance fiber reinforced cementitious composites
UHPFRCC kebiasaannya digunakan dalam pembinaan jambatan, pembaikan empangan, bangunan dan struktur konkrit yang lain. Kekuatan ikatan yang bagus antara konkrit lama dengan lapisan bahan pembaikan yang baru merupakan salah satu faktor dalam meningkatkan prestasi pembaikan konkrit. Walaubagaimanapun, konkrit akan terjejas apabila didedahkan kepada suhu yang tinggi dan jaminan kualiti kekuatan ikatan memerlukan kaedah yang boleh menilai kekuatan serta mengenal pasti jenis kegagalan. UHPFRCC hijau baru yang mana telah dipatenkan sebagai Universiti Sains Malaysia konkrit hijau bertetulang (GUSMRC) telah dicipta. Konkrit ini mengandungi 50 peratus jumlah simen dengan bahan pozolanik, iaitu POFA ultra halus (UPOFA). Objektif kajian ini iaitu untuk menyiasat ikatan antara muka apabila dikenakan pada suhu antara 100⁰C, 200⁰C, 300⁰C, 400⁰C and 500⁰C terhadap konkrit lama dan bahan baikpulih baru. GUSMRC telah digunakan sebagai bahan baik pulih baru dimana dua jenis kekasaran permukaan digunakan iaitu letupan pasir (sand blast) dan berlurah (grinding). Perubahan sifat-sifat kejuruteraan keatas sampel tunggal bahan baikpulih serta konkrit biasa juga dikaji selepas didedahkan pada suhu ternaik. Untuk pengujian sifat-sifat mekanikal dalam ikatan, ia diuji dengan menggunakan kaedah lereng ricih (slant shear), ujian ketegangan (splitting tensile), pull-off test dan ujian lenturan (flexural strength) untuk menentukan pengaruh kekasaran permukaan dan menguji kesan terhadap konkrit apabila dikenakan pada suhu yang tinggi. Keputusan menunjukkan lapisan konkrit hijau mencapai ikatan antara muka yang tinggi dan sesuai disamping konkrit biasa. Tekstur lapisan letupan pasir menunjukkan ikatan antara muka yang tinggi jika dibandingkan dengan jenis berlurah sebelum dan selepas dikenakan suhu yang tinggi. Kebanyakan mod kegagalan berlaku pada konkrit biasa dan secara automatik membuktikan ikatan antara dua muka adalah kuat. Kehilangan kekuatan konkrit yang kritikal untuk GUSMRC dicatatkan pada suhu 400⁰C and 500⁰C.
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UHPFRCC is usually applied to rehabilitation bridge of dam, building and other structures. Good bond strength between old concrete substrate and a newly overlaid repair material is a very important factor in assuring the performance of concrete repairs. However, the properties of concrete would be affected when it is exposed to high temperature. The quality assurance of the bond strength requires methods that can quantify the bond strength as well as identify the failure mode. A newly patented class of green UHPFRCC known as green Universiti Sains Malaysia reinforced concrete (GUSMRC) was developed. This concrete contains 50% of the cement total volume by pozzolanic material, ultra-fine POFA (UPOFA). The objective of this study is to evaluate the interfacial bonding characteristics between old concrete and new repair material after the composite is exposed to elevated temperatures of 100⁰C, 200⁰C, 300⁰C, 400⁰C and 500⁰C. GUSMRC was applied as the new repair material on the normal concrete substrate and the surface has been prepared / roughened either by sand blasting (SB) or grinding (GR). In addition, changes on the mechanical properties of the monolithic samples of the repair material as well as the normal concrete substrate were also evaluated after the exposure to the elevated temperatures. The characteristic of interfacial bond were assessed using the slant shear, pull-off, splitting tensile, and flexural strength test to evaluate the influence of two types of surface roughness and to evaluate the effect after the exposure to elevated temperatures. The results showed that the new green concrete overlay achieved good bond strength with the NC. Sand blasting surface treatment showed the excellent bonding properties compared to grinding before and after the exposure to the elevated temperatures. Mostly all the failure modes showed failures at NC substrate and automatically proved that the bondings between two layers are strong. The critical loss of strength for GUSMRC was recorded at 400⁰C and 500⁰C.
Effects of exposure to elevated temperatures on the bond characteristics between normal concrete substrate and ultra high performance fiber reinforced cementitious composites
Effects of exposure to elevated temperatures on the bond characteristics between normal concrete substrate and ultra high performance fiber reinforced cementitious composites / Nur Liyana Zainal