Testing properties governing the durability of lime-based repair mortars

Abstract

Lime-based mortars (LM(s)) seem to be preferred in repairing historic structures. The long-term performance of repair LM(s) is closely related to durability issues concerning the old structure substrate, the new repair mortars and interface between the two aforementioned materials, which is also much influenced by the technique of mortars application.
 Durability is a multifunctional property affected by a number of parameters, including local environmental conditions. However, experience showed that some of the characteristics of materials play a dominant role in assessing the durability of repair LM(s) and have a direct impact on longevity of the repaired structure.
 This paper presents review of research/case studies papers and Master/PhD theses supervised by the members of RILEM TC 277 LHS. Through the review and evaluation of research and common practice concerning durability challenges, we anticipate to find answers to questions arising in assessing durability of repair LM(s), such as:
 
 The most often encountered failures due to mortar durability inadequacy
 The mortar properties/characteristics that seem to be influential on durability
 The test methods used for testing the durability of LM(s) and comments related to their applicability and performance
 The importance of quality control and on site execution practices

Assessing the effect of a white Portland cement admixture on the early frost-thaw resistance of NHL-based masonry mortar

“…The related standard [28] provides a sample arrangement of stones and mortar primarily for flexural strength determination, which can be also used as composite specimen (see Fig. 3a), outlined as ideal configuration for an applied durability assessment [17,32]. Afterwards, we exposed them to the cold temperatures of the winter season 2019/20 in a comparative setting.…”

“…Parallel to this, we worked with three-stone test specimen as recommended by [17] as a ''hybrid'' testing series between the lab study and in-the-fieldapplications. These compound samples (mortar and natural stones) were exposed to real weathering conditions in the winter season.…”

Bond Properties of NHL-Based Mortars with Viscosity-Modifying Water-Retentive Admixtures

“…The frequency and the extent of repair may be influenced during the design and construction period and then again during any of the forthcoming repair periods by choosing the best-possible combination of materials. The course of durability is often approached on the basis of separate materials [4][5][6][7] and not the complex plaster-substrate system as recommended by several RILEM technical papers [8,9], whereas the separate material methods are widely accepted while studying the effects of specific mixture constituents, e.g., aggregate grading [9].…”

“…In particular, but not only for lime-based mortars, durability is closely linked to the water absorption capacity, and therefore the microstructure of the mortar [4,9]. Apart from binder type, the microstructure is mainly influenced by the water/binder ratio (w/b) and the aggregate properties.…”

“…Apart from binder type, the microstructure is mainly influenced by the water/binder ratio (w/b) and the aggregate properties. Growing w/b leads to an increase in the mean pore diameter, and thus the size of voids between the particles, and mainly to an increase in the capillary water coefficient, one of the properties detrimental for durability [9,10].…”