Manufacturing
Cement concrete tiles are manufactured by in using wet casting methodology. The Concrete Mix Design /Concrete Proportions is based on the methodology presented in ACI 211.1 for normal weight concrete. The concrete proportions have been developed using white cement, coarse aggregates from Hub River and fine aggregate comprising of silica sand from Nooriabad. Mixing operations are carried out and produce by weigh batching for uniformity of strength, consistency, and appearance.
High performance concrete is achieved by using poly-carbo-xylate ether super-plasticizer with self-consolidating and easy compacting properties. Water cement ratios of approximately 0.45 is maintained
Concrete Mixing
Self-consolidating concrete are placed in a manner in which it flows and consolidates without segregation or air entrapment. The free fall of the concrete is kept to a minimum. Concrete is consolidated in such a manner that segregation of the concrete is minimized and honeycombed areas are kept to a minimum. Consolidation efforts are often not required when using self-consolidating concrete. Vibrators used to consolidate concrete have frequencies and amplitudes sufficient to produce well-consolidated concrete.
Testing
To test durability and performance requirements compressive strength test and concrete absorption test are conducted. Typical values are as follows
- Compressive Strength: ±3,500 psi
- Absorption: ±2%
Concrete Curing
Curing operations commences immediately following the initial set of the concrete and completion of surface finishing. Curing is carried out by moisture retention. Moisture is prevented from evaporating from exposed surfaces until adequate strength for stripping the pre-cast concrete unit from the forms is reached by one of the following methods as per ASTM C 171.
Patching And Repair
No repair is required to formed surfaces that are relatively free of air voids and honeycombed areas, unless the surfaces are required by the design to be finished.
Handling, Storage And Delivery
Pre-cast concrete units are handled and transported in a manner to minimize damage. Typically pre-cast units are delivered by packing pieces in the delivery truck. On customer requirement, independent shippers in wooden crates pack pre-cast units. Pre-cast concrete units shall be stored in a manner that will minimize potential damage.
Pre-cast concrete units shall be delivered to the site in accordance with the delivery schedule to avoid excessive build-up of units in storage at the site. Upon delivery to the jobsite all pre-cast concrete units shall be inspected by the customer or customer’s agent for quality and final acceptance at the time of delivery. For order outside Karachi, Client arranges shipper of their choice.
Upon final acceptance, the customer or customer’s agent acknowledges and understands the appropriate methods for handling the accepted pre-cast concrete unit(s). Upon acceptance by the customer or customer’s agent, the pre-cast concrete manufacture is not responsible for replacing damaged product resulting from improper handling practices on the job site.
Shipping Pre-Cast Concrete Units
Pre-cast concrete units are shipped after until they are at least 7 days old, unless it can be shown that the concrete strength has reached at least 75% of the specified 28-day strength, or that damage will not result, impairing the performance of the product.