Compressive and Flexural Strength of Non-Hydraulic Lime Mortar with Slag (GGBS)

Mortar for masonry is important because it provides the bond between masonry units so enabling the composite to behave as a single material. The type of mortar used determines the flexural and compressive strength of the masonry. Currently, most mortars used in construction are cement based. However, due to the heavy energy-intensive processes that are involved in its production the cement industry is responsible for up to 10% of global CO2 emissions; therefore, there are serious environmental implications with the usage and application of cement mortars. A sustainable alternative are lime mortars which have 30% less embodied CO2. Lime mortars confer benefits in comparison to cement based mortars such as accommodating a greater degree of wall movement and improved damp resistance. The main disadvantage with lime mortars is the longer setting time which can take up to 91 days in addition to the low strength. A way to overcome this is to add cement replacements e.g pozzolans or slag. This paper investigates the properties of non-hydraulic (lime putty) lime mortar containing up to 20% ground granulated blastfurnace slag (GGBS). Findings show a minimal amount of GGBS addition of 2% doubles the mortar strength to 2 MPa within 91 days with an eventual strength of over 15 MPa achieved with 20% GGBS. Strengths satisfying minimum requirements for all four mortar designations were achieved with between 2 - 16% GGBS addition, all within 56 days ageing; with designations (i), (ii), (iii) & (iv) strengths being satisfied within 28 days. Therefore, non-hydraulic lime mortars with GGBS offer a more sustainable alternative to cement based mortars without compromising setting time or strength whilst offering improved flexibility and breathability.