Cellulose ethers as water-retaining agents in natural hydraulic lime mortars

Cellulose ethers (CEs) are commonly used as viscosity enhancing, water retaining agents in cement-based mortars. Nevertheless, studies about the effect of CEs on the properties of natural hydraulic lime-based mortars (NHL) are absent, although the use of mortars with hydraulic lime is often preferred for renovation purposes. In this study, the behavior of NHL mortars modified by four different CEs is assessed. The fresh state of mortars was characterized by water retention, air content, density a consistency. Hardened mortars were submitted to strength determination, study of pore size distribution, and thermogravimetric analyses. Transport of liquid water in the studied materials was characterized by water absorption coefficient, sorptivity, and liquid water diffusivity. Durability of the prepared mortars was monitored by frost-resistance tests. The results revealed elevated air content and water retention in mortars with increasing dose of CEs resulting in decreased density of fresh mortars. The strengths of modified mortars surpassed the reference ones at age of 180 d despite the fact that the mortars showed higher open porosity and water absorption. Enhanced porosity of mortars resulted in improvement of their frost resistance and faster carbonation. From a practical and economical point of view, the CEs dosage of 0.5% by weight of the binder appears to be sufficient.