Guide to Hot Weather Concreting

Description

Hot weather can create problems in mixing, placing, andcuring hydraulic-cement concrete that adversely affect theproperties and serviceability of the concrete. Most of theseproblems relate to the increased rate of cement hydration athigher temperature and increased evaporation rate of moisturefrom the freshly mixed concrete. The rate of cement hydrationdepends on ambient and concrete temperature, cementcomposition and fineness, amount and type of supplementarycementitious materials, and admixtures used.

A maximum as-placed concrete temperature is often specified in an effort to control rate of setting, strength, durability, plastic shrinkage cracking, thermal cracking, and drying shrinkage. The placement of concrete in hot weather ,however, is too complex to be dealt with by setting a maximum as-placed or as-delivered concrete temperature.

Concrete durability is defined as the ability of concrete toresist weathering action, chemical attack, abrasion, or anyother process of deterioration (ACI 201.2R). Generally, ifconcrete strengths are satisfactory and curing practices aresufficient to avoid undesirable drying of surfaces, the durability of hot weather concrete will not differ greatly from similar concrete placed at normal temperatures.

Where an acceptable record of field tests is not available, concrete proportions can be determined by trial batches (ACI301 and 211.1). Trial batches should be made at temperatures anticipated in the work and mixed following one of the procedures described in Section 4.10, Proportioning. The concrete supplier is generally responsible for determining concrete proportions to produce the required quality of concrete unless specified otherwise