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Abstract

We present the design and properties of combined air lime-cement structural injection grouts containing 17.5 % of hydrated lime, 7.5 % of cement as a binder, using white Portland cement of different strength classes and 75 % of limestone filler. The addition of a chemical admixture to prepare swelling grouts was tested as well. We have monitored the time evolution of the grout setting process during hydration from early to late stages by proton NMR spectroscopy, using the method of inverse Laplace processing of the spin-lattice relaxation data. The as-obtained “NMR hydration curves” of the grouts were compared to pure cement pastes. The NMR hydration curves reveal that the time evolution of the grout setting process is significantly slowed down (by more than 10 days) relative to the cement pastes. The fully set state of the grouts is not reached even after 35 days of hydration. The influence of the cement strength class on the grout hardening process was found to be minor, where higher strength class somewhat accelerates the grout hardening, but not drastically. The addition of the swelling agent neither speeds up nor slows down the setting process of the grouts and the cement pastes, i.e., the swelling agent does not chemically enter the reactions responsible for the hardening. We have determined the compressive strength of the set grouts in comparison to the set cement pastes. The compressive strength values of both types of materials increase systematically with the increasing cement strength class. For a given strength class, the compressive strength of the grout is by a factor of about 10 lower than that of the cement paste. The addition of the swelling agent lowers the compressive strength, with the strength of the grout being reduced much more (by about 50 %) than the strength of the cement paste (reduction by 8 %). The compressive strengths of our grouts are in the range of 1.5 to 2.5 MPa, so that the grouts appear as efficient materials for the repair and strengthening of historical and cultural-heritage buildings, where the compressive strength of historic mortars is seldom higher than 1 MPa.