Influence of the Mechanical Properties of Lime Mortar on the Strength of Brick Masonry

Abstract

Abstract. This paper aims at improving the quality of lime mortar masonry by understanding the mechanics of mortars and masonry and their interaction. It investigates how the mortar's compressive and flexural strengths impact the compressive and bond strength of clay brick masonry bound with calcium lime (CL) and natural hydraulic lime (NHL) mortars. It concludes that the strength of the bond has a greater impact on the compressive strength of masonry than the mortar's strength. The masonry compressive strength increased proportionally to the strength of the bond up to 6 months. A regression analysis, giving a second order equation with coefficient of determination (R 2 ) of 0.918, demonstrates a strong and predictable relationship between bond strength and masonry compressive strength. It was noted that CL90s mortar masonry reaching a high bond value was stronger than that built with a stronger mortar but displaying a poorer bond. Finally, the mechanics of lime mortars and their masonry are similar. The predominantly elastic behaviour of the mortars of higher hydraulic strength compares well with the elastic and brittle behaviour of their masonry, with either little (NHL2) or non-existent plasticity (NHL3.5 and 5); in contrast, the CL90 mortar and masonry exhibit a plastic behaviour.

Bond-strength performance of hydraulic lime and natural cement mortared sandstone masonry

“…Mean bond strengths of all NHL masonry tested were within the range 0.07-0.33 MPa. This is lower than the range 0.2-0.61 MPa reported by Pavia and Hanley [6] utilising a richer 1:2.5 mix ratio (by mass) but within that of 0.05-0.63 MPa reported by Zhou et al [5] utilising a longer curing duration (91 days); it also lies within the 0.11-0.16 MPa range reported by Costigan and Pavia [7] utilising the same curing duration. An additional possible reason for the greater strength results found in previous studies [5,6] is their use of perforated bricks allowing mortar to flow in and bond to the perforation sides which may have led to overestimated bond strengths due to a greater bond area than that assumed.…”

“…The results of these tests indicate values that could be achieved in practice as the specimens were subjected to realistic site curing conditions over a 28-day period and using realistic mix proportions, albeit sheltered from rain. Previous studies on NHL mortars [7] have found substantial increases in bond strength between 28-days and 6-months therefore the values presented may thus represent less than half the expected long-term bond strength. The work presented in this paper has shown, however, that it is still practical to use 28-day data despite NHL mortars slow strength gain.…”

“…The work would also indicated that mortar strength testing, and NHL binder designation codes of practice [25,26], should relate to mix ratios commonly used in practice (as this study has used), for example, a 1:2.5 mix by volume rather than the 1:3 mix by mass. Despite the slow strength gain of NHL mortar, the work has shown that it is still practical to use 28-day data as prescribed in current codes of practice [26] but the strength obtained may represent less than half the expected long-term strength [7]. The work presented will also serve to promote awareness of hydraulic lime mortared sandstone masonry and to enable more confident design and assessment of this material.…”

“…Mean values of masonry flexural strength for NHL 2 and NHL 5 mortars ranged between these values and generally increased with greater mortar hydraulicity and flow. Costigan and Pavia [7] tested dry, medium suction, frogged clay bricks with hydraulic lime mortars of varying hydraulicity in a 1:3 mix ratio (by mass) for a range of curing periods. For a curing period of 28-days, mean values of masonry flexural strength were approximately 0.11 N/mm 2 for NHL 2 mortar, 0.16 N/mm 2 for NHL 3.5 and 0.15 N/mm 2 for NHL 5 mortar.…”

An experimental study on the effects of casein protein in unreinforced lime mortar specimens

“…While the strength comparison was the ultimate result, the mode of failure of the unreinforced lime mortar may be of interest. Costigan and Pavia [41] investigated the failure modes of lime mortar specimens. It was found that plastic deformation behaviour occurs with a lower-strength natural hydraulic lime mortar by itself (strengths of less than 2 MPa), while higher-strength mortars deform elastically to a brittle failure [41].…”