Abstract
Owing to both shrinkage-reducing and water-reducing functions, shrinkage-reducing polycarboxylate admixture (SRPCA) has great advantages to mitigate shrinkage cracking of the low water-to-cement ratio cementitious materials. In this paper, cracking behavior of ultra-high strength mortar (UHSM) containing SRPCA and shrinkage reducing admixture (SRA) was evaluated by the temperature stress testing machine (TSTM) tests. To analyze the cracking reduction mechanism of SRPCA, mechanical properties, autogenous shrinkage, tensile creep and elastic modulus of UHSM with SRPCA and SRA were studied. Furthermore, the effect of SRPCA on the mechanical properties, autogenous shrinkage, tensile creep and elastic modulus was discussed by analyzing surface tension, hydration progress, portlandite content, pore structure and relative humidity. The results show that the addition of SRPCA significantly reduces autogenous shrinkage of UHSM mainly due to internal relative humidity reduction. The surface tension reduction and hydration regulation are key for the RH decrease. In addition, SRPCA can increase tensile creep and decrease elastic modulus of UHSM. As a result, incorporating SRPCA can improve cracking resistance of UHSM.
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