Here is a comprehensive explanation in English, based on international standards, regarding the maximum permissible temperature during concrete placing and the allowable time for concrete transport, along with solutions for temperature reduction and increasing transport time:
Maximum Permissible Temperature in Concrete Placing and Allowable Transport Time – According to International Standards
Maximum Permissible Temperature During Concrete Placing:
According to ACI (American Concrete Institute) and other international standards (such as ASTM C94), the maximum concrete temperature at the time of placement typically should not exceed 32°C (90°F). For mass concreting or critical structures, the maximum allowable temperature may be even lower (as per project specifications or client requirements), often set between 27°C to 30°C (80°F to 86°F) to prevent thermal cracking and unwanted rapid hydration.
Maximum Allowable Concrete Transport Time:
Based on ACI 318 and ASTM C94 standards, concrete should generally be delivered, discharged, and placed within 90 minutes after water is first added to the mix at the batching plant. In hot weather or long haul situations, the time may need to be further reduced unless the mix is specifically designed for extended working time.
Methods to Reduce Concrete Temperature:
Use Chilled Water or Ice: Replace part or all of the mixing water with chilled water or ice flakes.
Cool Aggregates: Store aggregates in shade or spray with water.
Shade Cement and Aggregates: Protect materials from direct sunlight.
Mix During Cooler Periods: Schedule concrete production and placement during early morning or at night.
Use Admixtures (Retarders): Add set-retarding admixtures to slow hydration and extend workability.
Reduce the Mixing Time: Reduce the duration between mixing and placement.
Use Insulated or Light-Colored Transport Vehicles: Prevent heat absorption.
Methods to Increase Allowable Transport Time:
Retarding Admixtures: Incorporate chemical admixtures that extend initial set time and concrete workability.
Use of Chilled Materials: Lower the concrete temperature to slow hydration and delay setting.
Insulation: Insulate the transport mixer and containers.
Rapid Transportation and Efficient Scheduling: Optimize logistics to minimize delay from batching plant to site.
Shorten Delivery Routes: If possible, use local batching facilities nearer to site.
References:
ACI 301: Specifications for Structural Concrete
ASTM C94: Standard Specification for Ready-Mixed Concrete
ACI 305R: Hot Weather Concreting
ACI 318: Building Code Requirements for Structural Concrete