Production of Precast Items
Factory Quality Assurance Program
The main purpose of this program is to define minimum required practice for the production & erection of precast concrete units in conjunction with quality control program to attain an acceptable level of workmanship as desired & committed by the management. The factory shall implement and maintain this program in accordance with relevant standards.
a) Receiving inspection of materials:
The receiving inspection of the materials to use for production of concrete mixes is as follows:
- Cement: is received with test certificate and delivery order, once in six months, the cement will be tested in an independent testing laboratory for physical and chemical parameters.
- Aggregates & Sand: all the aggregates are received with a delivery note.
- Once a week sieve analysis (in house) will be carried out all Aggregates & sand.
- Once in four months, the following test will be carried out through an independent testing laboratory.
- Grading test including “ Passing 75 microns”
- Sulphate Content.
- Chloride Content.
- Specific Gravity.
- Water Absorption.
- Water: Normal water from Abu Dhabi Municipality will be used for concrete and will be tested for chemical analysis in an independent laboratory once in six months.
- Reinforcement:are received with delivery note and mill certificates.
- 3D construction panels: (comprised of EPS core, with varying thickness, sandwiched between two plane-paralleled welded wire mesh sheets positioned by uniformly distributed inclined “cross wires” that pierce through the EPS core and are welded at both mesh interfaces) are received from the supplier with all relevant test certificates. Visual inspections will be done on these panels prior to usage.
b) Inspection / Test of concrete Mixes & Cubes:
The concrete mixes as required by the design will be prepared in the in house batching plant. The sampling of fresh concrete, for Precast Elements is as follows:
- 2 test samples per week for each design mix, for concrete consumption of < 5 m3 per day.
- 1 test sample per day for each design mix, for concrete consumption > 5 m3 and < 50 m3 per day.
- 2 test samples per day for each design mix, for concrete consumption > 50 cubic meter per day
- Slump test will be done on every sampling of fresh concrete.
- Compressive strength will be tested in Abu Dhabi Precast’ laboratory as per BS 1881 part 116.
Test results will be recorded in appropriate form.
c) Production & Inspection Before Casting
- Inspection of Mould Fabrication: will be carried out on all new moulds & / or after a mould is change. As daily routine, quality controller checks the casting program / schedule for moulds to be inspected. Inspection will be carried out when mould fabrication completed. Heights are inspected on the highest side of the element & are inspected on three places. If any side is < 1000 mm, then only inspections are carried out, width is measured as height. Thickness is defined as height over table surface. Both diagonals are measured and the differences are recoded. Requirements / tolerances of the measurements are specified on the drawings & inspection forms.
- Inspection of Reinforcement: Any reinforcement shall be inspected. It will be carried out when it is place in the mould. Record of inspection is included in the precasting inspection form. Cast – in – parts is inspected for correct type, number & placement. Cover is inspected & measured at different locations. Cover requirements & tolerances are verified in the shop drawings.
- 3D Construction Panels: are placed in the mould as such the adequate thickness as mentioned in the design drawings will be achieved. Lifting hooks will be place with the 3D panels for the lifting and transportation purposes. The figure below shows a 3D panel and lifting hooks installed in it.
- Casting of Concrete after final inspection: Concrete is mixed in Automatic Batching plant as per the mix design to achieve the required strength as demanded by the structural design; the concrete is shifted to the casting yard by mean of motor van and poured into the mould. After pouring the concrete into the mould, vibrators are used for 3 minutes. Vibrators are permanent fixed under the steel casting tables. Exposed concrete face is troweled with the help of steel trowels to get smooth finish. In every mix, a slump is checked to control the workability. Moulds are released and units are lifted with the help of cranes after getting required strength for striping.
- Final Inspection after Casting: Final inspection is carried out on all precast elements & results will be recorded on post casting inspection form. Quality controller is responsible for the final inspection before the precast components are released for delivery. Quality controller inspect the precast elements for the, Cast – in – Parts, fixings, cut outs, lifting anchors & identification markings. When the quality controller is satisfied, he marks the element with “OK“ and signs it.
- Curing Of Precast Components: After casting, the precast concrete elements will be covered with polythene sheet. Soon after demoulding, the precast components will be taken to stockyard and covered with Asian Cloth. At least twice a day, water will be poured on the precast element till the surfaces are completely wet. Quality controller and stockyard foreman have to ensure that the element is covered well. The curing shall be done for three days before it can be sent for delivery.