QUALITY CONTROL IN PRECAST PRODUCTION (Agus Dwi hariyanto, et al) Jurusan Teknik Arsitektur, Fakultas Teknik Sipil dan Perencanaan - Universitas Kristen Petra http://puslit.petra.ac.id/~puslit/journals/ 153 QUALITY CONTROL IN PRECAST PRODUCTION A case study on Tunnel Segment Manufacture Agus Dwi Hariyanto Lecturer Faculty of Civil and Planning Engineering, Architecture Department, Petra Christian University Hon Pui Kwan, Yee Weng Cheong Alumnt, Department of Building, National University of Singapore ABSTRACT Quality control forms an integral part of precast production. An efficient quality system is most critical in the mass production of precast components in any project. In this study, the quality control system implemented in a precast factory is discussed. The precast factory is set up for the manufacture of large quantity of tunnel segments under a contract. Processes in the precast manufacture are discussed with respect to the control procedures in the quality inspection plan. The standard tests involved, roles of inspectors and corrective actions on-site are highlighted. Critical issues pertaining to the productivity and quality of precast production are reviewed. These include the quality of staff and maintenance, which could potentially affect the efficiency of the quality system. Some considerations should also be given to improve the workflow and productivity of the plant. Keywords : precast, quality control. INTRODUCTION Merits of Precast The very existence of a precast concrete industry and the numerous successful building projects achieved using precast concrete, for the whole or just a part of the structure, is proof that the technique is practical and economical (Elliott, 2002). Structures with a high degree of modular coor- dination and repetitive grids are ideal for precast construction. Precast construction allows mass production. Better methods can be adopted in factories leading to speedy production and economic of scale. The advantages in productivity and lower unit price make precast construction welcomed in many recent projects. As precast modules are made under controlled conditions with close supervision, there can be a higher level of consistency, accuracy and quality. In addition, unique shapes and designs as well as various finishing effects can be achieved. Precast construction always groups similar work tasks for batch processing so that there is less material wastage as compared to conventional insitu construction methods. Since major fabricating pro- cesses are carried out off-site in precast construction, there is less wet trade in the construction area. The site can be neater and tidier, which is easier for site planning and space management. Reduction in site work also minimizes weather influence on the construction schedule. As a result, savings in construction time, manpower resources and a safer working environment can be achieved. Practical Limitations Precast construction seems to favour many large-scale projects. However, it does have some practical limitations. Generally, precast components are huge in size and require ample site space for loading and unloading, storage and maneuvering. Mechanical devices such as tower cranes are commonly used for the erection of precast compo- nents. The weight and size of the precast elements should match with the loading capacity of hoists and cranes, while sufficient working area is required to position the mechanical plants. A substantial amount of site co-ordination work and due care must be exercised during the on-site erection process. As it takes time for making precast components as well as delivery, professionals have to finalize their design at a comparatively early stage. Changes in design may lead to substantial abortive works and affect the construction programme. In comparison, precast construction may require longer design period, while in-situ construction method usually has longer site work period. Besides, precast emphasizes on unification and repetition, there is less flexibility in design and may be unfavourable from the aesthetical point of view. Precast construction may involve substantial amount of capital investment in the manufacturing factory and its cost effectiveness depends largely on the repetitiveness in the design. Consideration should always be given to the cost and risks involved in critical activities such as lifting, handling, transportation, plant mobilization and installation. Workmanship is always an important