A research program was developed to investigate relative properties of three mortars containing lime-replacement additives compared to the properties of four traditional portland cement-lime mortars used in masonry construction. Plastic and hardened properties were determined using standard ASTM test methods. The test program indicates that, although the three lime-replacement mortars have comparable compressive strengths to portland cement-lime mortars, they have significantly different water retention and air content percentages and, as tested, the lime-replacement mortars do not meet specification requirements of either ASTM or ICBO. In addition, masonry walls constructed with the three lime-replacement mortars studied in this program were less resistant to water penetration than walls constructed with portland cement-lime mortars. It is suggested that ASTM specifications and test methods currently under development consider the essential properties of water retention, air content, and water penetration resistance in addition to compressive strength for acceptance of lime-replacement materials.
A mortar research program for the Public Works and Government Services of Canada was initiated in the late 1980's. This research program was a most comprehensive one on the Canadian level; more than 100 mortars were tested in the course of the last decade. Its primary objective was to identify durable repointing mortars which would be practical in their application and compatible with specific traditional stone masonry. For the first time physical and mechanical properties as well as frost resistance have been combined under the same research program. This research program was triggered and managed by practitioners to meet the need of major conservation projects carried out in Canada by the federal government. This paper presents an overview of the testing program, its performance criteria, and its key results. With respect to preservation standards, this paper provides an overview of the application of testing standards to this research program for repointing mortars in laboratory conditions and in-situ. It highlights situations where standards had to betailored to the preservation needs or developed as new testing procedures. The most important difficulties of this research program with respect to the development of preservation standards are as follows: 1) as the intent of modern masonry design is often different from traditional masonry, few existing standards are directly applicable; 2) there are no existing testing standards which specifically assess the durability of historic mortars; 3) some tests are too costly to be used in a testing program in practice; 4) excessive time is needed for some existing tests for quality control and site supervision. Practice currently suffers considerably from the lack of appropriate standards for the testing of traditional masonry mortars. There is a great need for preservation standards and only limited resources to address the situation. A well orchestrated and major collective effort is required to adjust and develop testing standards for the preservation of our masonry heritage.
Alone, neither a pozzolan nor hydrated lime is capable of setting under water. They are not hydraulic. When combined and mixed with water, however, the resulting reaction products are hydraulic. There is a renewed interest in pozzolan-lime binders, in particular for historic masonry. ASTM C593 provides a limited resource in defining suitable pozzolans to be used with lime for masonry mortars and exterior plasters. One of its limitations is that the specified pozzolan-lime weight ratio is not representative of a traditional volumetric ratio of one volume part binder to three volume parts sand. In addition, the standard requires accelerated curing, which is unrealistic for pozzolan-lime mortar. Preliminary results indicate that using specific ratios of pozzolan to lime and a vapor curing regime, as required by ASTM C593, does not necessarily promote the optimum pozzolanic reaction as tested by compressive strength. Results from ASTM C593 therefore do not represent the expected field behavior of pozzolan-lime mortars. The requirements of that standard should be modified with respect to pozzolan-lime ratios and curing conditions.
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