Long-term shrinkage performance and anti-cracking technology of concrete under dry-cold environment with large temperature differences

Abstract

• The basic mechanical properties of long-age concrete under dry-cold environment with large temperature differences are analyzed. • The free shrinkage of long-age concrete under dry-cold environment with large temperature differences is analyzed. • The constrained shrinkage of long-age concrete under dry-cold environment with large temperature differences is analyzed. • The microstructure of long-age concrete under dry-cold environment with large temperature differences is analyzed. Shrinkage performance and anti-cracking technology of concrete in a dry-cold environment and large daily temperature differences (-20℃∼15℃) are investigated through environmental simulation tests. According to on-field practice, after 28-day standard curing, concrete specimens are placed in the simulated environment and under five different maintenance methods, which are natural exposure (NE) as reference, membrane curing (MC), coating curing (CC), curing with expansive agent (CE), and curing with both expansive and internal curing agent (CEI). A novel nano-ceramic coating is used in CC. The mechanical properties, free shrinkage rate, restrained shrinkage rate, and porosity by mercury intrusion porosimetry (MIP) of specimens after freezing age of 0 ∼ 56-d are measured. Both compressive strength ( f cu ) and tensile strength ( f t ) of NE and CE decrease evidently with freezing age, and f cu and f t for CC, MC, and CEI scenarios are slightly affected by freezing age. Both free shrinkage and restrained shrinkage are mainly due to the temperature deformation; the drying shrinkage takes only about 21 % of the total shrinkage. The cyclic temperature differences lead to accumulation of maximum restrained shrinkage stress in concrete. Shrinkage performances are highly dependent on curing methods; the order of anti-cracking performance from the best to worst is: CC, MC, CEI, CE, NE. Adding expansion agents alone (CE) is insignificant in reducing the shrinkage, which can be compensated by furthering adding internal curing agents (CEI). The moisturizing effect of internal curing agent, membrane, and coating contribute to better microstructure, strength development, and shrinkage mitigation. The thermal insulation and the bonding effect of CC further reduce the free shrinkage and restrained stress, thus presenting the strongest resistance to shrinkage and induced cracking. The porosity and most probable pore size (MPPS) from MIP tests are consistent with results of strength and shrinkage. Overall, specimens under CC show the best overall performances under simulated environment.