Experimental study on the strength and durability-related properties of ordinary Portland and rapid hardening Portland cement mortar containing polyurethane binder

The durability of cement-based materials plays a significant role in controlling their life cycle. Bio-based polyurethane (Castor oil) was used to improve the durability and mechanical properties of two types of cement mortar, namely: Ordinary Portland cement (PCM-mortar) and rapid hardening Portland cement (RHPC-mortar). To investigate the effects of polyurethane (PU) binder; therefore, experimental tests, including flowability, rate of water absorption, early and dry restrained shrinkage properties, compressive strength, and flexural strength, were performed on the two mortar types. Moreover, the shrinkage properties were estimated using a restrained shrinkage eccentric ring device (RSERD) to improve cracks observation. The PU binder was added to the mortar mixture at 0 %, 15 %, and 25 % by cement weight. The result indicates that the optimum PU binder content (15 %) improves the flexural strength of PCM-mortar at 3 d, 7 d, and 28 d by 10.1 %, 0.93 %, and 10.62 %, respectively, and the flexural strength of RHPC-mortar at 3 d, 7 d, and 28 d was increased by 6.93 %, 1.78 %, and 1.74 %. However, a reduction in the compressive strength was observed. The workability of PU-cement mortar reduced with optimum PU binder content and increased with higher PU binder. The flow-ability percentage drop index revealed that PU-cement mortars containing 25 %PU from the PCM and RHPC-mortars showed lower FPI values of-3.57 % and-8.69 %, respectively. The RSERD mortar specimen controls the cracks propagation as expected crack occurred only on the eccentric side. None of the PU-cement mortar exhibited crack propagation for 182 d. The cracking time of PCM-PU0 and RHPC-PU0 are 104 h and 87.2 h, respectively. The water absorption capacity of PCM and RHPC-mortar was reduced by 67.97 % and 23.46 %, respectively. The PU could be regarded as a suitable candidate for improving cracking resistance and reducing the water absorption rate of cement-based composites.

Automated summary

The use of bio-based polyurethane improves the durability and mechanical properties of cement mortar. Experimental tests were conducted to investigate the effects of polyurethane binder on flowability, water absorption rate, shrinkage properties, compressive strength, and flexural strength. The results show that the addition of an optimal amount of polyurethane binder enhances the flexural strength of the mortar, but reduces compressive strength. The polyurethane also helps control crack propagation and reduce water absorption capacity of the cement mortar.