Effect of cement type and water-to-cement ( w / c ) ratio on characteristics of lightweight mortars produced with pumice: a comparative study on calcium aluminate (rapid hardening) and ordinary Portland cements

Over the last few decades there has been a growing interest in the use of blended or hybrid rapid hardening cements with optimized performance for use in a variety of applications. Blended cements can help decarbonize the construction industry and address the growing need for retrofitting the aging infrastructure. Among the most used cements, ordinary Portland cement (CEM) and calcium aluminate cements (CAC), from ordinary and rapid hardening family, are commonly on the list for use in many repair and rehabilitation applications. Using various grades of the mentioned cements, this study provides a detailed and comparative analysis of the influence of the type and content of the cement, compositions, and water-to-cement ( w / c ) ratio on the properties of lightweight mortars. Five types of ordinary and rapid hardening cements with different chemical compositions were used to produce a total of 20 mixes with w/c ratios ranging from 0.4 to 1.8. Samples have been tested for a variety of physical, mechanical, and thermal properties. Results show that CACs exhibit considerably higher sensitivity to water content due to stoichiometric water requirement that results in embedded cracks and structural defects, whereas the ordinary cements (CEM I) develop a more compact and crack free microstructures at longer ages, which can be the result of differences in the hydration phases. Finally, the results provide valuable information for the use based on physical–mechanical properties of lightweight mortars produced with a variety of cementitious compositions. Graphical abstract