Compliance Acceptance of Concrete Drying Shrinkage

In Australia, strength, and in particular compressive strength, has been used in AS 3600 and AS 1379 as a benchmark for structural performance, for durability and as a contractual basis for concrete supply. With tightening financial constraints and the ensuing need for increased construction efficiencies, there is a bigger emphasis on the provision of concrete quality. Contractually, quality provision is handled by measuring parameters such as compressive strength, flexural strength, chloride ion penetration by charge transfer (ASTM C1202-91), and concrete drying shrinkage. The correct assessment of such results, together with good concreting practices, will greatly increase the certainty of achieving desired quality in terms of design intent.Concrete drying shrinkage is recognised as important in the design process for maintaining serviceability requirements particularly on large horizontal structural elements, a common example being the limitation of cracking in large slabs. The compliance basis for compressive strength is well established in AS 3600 and AS 1379. Regarding concrete drying shrinkage, however, it is common to find in many design specifications average and absolute maximum values specified at 56 days. This can create immense constructional and contractual problems when individual samples fail to comply with the specified shrinkage limit.