Projek ini dijalankan untuk menentukan jumlah optimum air redos kepada konkrit
segar untuk mengekalkan kebolehkerjaan konkrit tersebut dalam julat yang boleh
diterima selama 105 minit. Projek ini juga bertujuan untuk mengkaji kesan menambah
air kepada konkrit segar terhadap kekuatan mampatannya. Keputusan projek ini
diperoleh melalui kerja-kerja eksperimen. Tiga set eksperimen yang sama dijalankan
untuk mendapatkan hasil purata bagi mendapatkan hasil yang lebih tepat. Bagi setiap set
eksperimen, dua ujian dijalankan, iaitu ujian kericihan konkrit dan ujian kuib konkrit.
Ujian kericihan dijalankan pada T1 (0-45minit), T2 (45-90minit), T3 (90-105minit) dan
T4 (105minit). Sementara itu, kiub konkrit disediakan pada T1 (0-45minit), T2 (45-
90minit) dan T4 (105minit). Ujian kiub konkrit dijalankan pada hari ketiga dan hari ke
28. Penambahan air dijalankan pada 45 minit selepas 45 minit (T2). 0.3%
superplasticizer ditambah semasa pembancuhan konkrit untuk mendapatkan keruntuhan
sebanyak 80mm yang diperlukan. Dari hasil eksperimen, jumlah pengurangan air yang
meningkatkan nisbah w/c konkrit dari 0.45 hingga 0.50 dan 0.55 tidak mencukupi untuk
memulihkan dan mengekalkan kebolehkerjaan konkrit dalam lingkungan 75-100mm
dalam masa 105 minit. Kekuatan mampatan konkrit menurun selepas penambahan air,
tetapi jumlah kemerosotannya adalah kecil. Semua kiub konkrit mencapai kekuatan
mampatan melebihi keperluan minimum, iaitu 25MPa, tanpa mengira jumlah
penambahan air. Dari projek ini, jumlah air redos yang optimum tidak dapat ditentukan
kerana kebolehkerjaan konkrit yang mengalami kelewatan 105 minit tidak dapat
dipulihkan dan dikekalkan dalam lingkungan 75-100mm yang detetapkan.
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This project is carried out to determine the optimum amount of water redosage to
fresh concrete in order to maintain the workability of concrete within the acceptable
range for 105 minutes. This project is also aimed to study the effect of adding water to
the fresh concrete on its compressive strength. Results of this project are obtained via
experimental works. Three sets of the same experiments are carried out to obtain the
average result for a more accurate outcome. For each set of experiment, two tests are
conducted, namely slump test and concrete cube compression strength test. The slump
test was carried out at T1 (0-45mins), T2 (45-90mins), T3 (90-105mins) and T4
(105mins). Meanwhile, concrete cubes were prepared at T1 (0-45mins), T2 (45-90mins)
and T4 (105mins). Concrete cube compressive strength test was conducted at days 3 and
days 28. Water redosage was carried out at 45 minutes after batching (T2). 0.3% of
superplasticizer was added during the mixing of concrete in order to obtain a required
slump of 80mm. From the results of experiments, the amount of water redosage that
increased the w/c ratio of concrete from 0.45 to 0.50 and 0.55 is not sufficient to restore
and maintain the concrete workability within the range of 75-100mm over 105 minutes.
The compressive strength of the concrete decreased after water redosage, but the amount
of strength deteriorated are small. All of the concrete cubes achieved compressive
strength above the minimal requirement of 25MPa, regardless of the amount of water
redosage. From this project, the optimum amount of water redosage is unable to be
determined since the workability of concrete subjected to a delay of 105 minutes is
unable to be restored and maintained within the acceptable range of 75-100mm.
The effect of redosage of the water to cement ratio on roperties of concrete subjected to time lag in concreting / Bong Yack Huang