Neutron Activation Analysis of Mortars from Stone Houses Built in Canada During thc French Rkgirne

Abstract

The mortar used in the construction of stone houses and buildings in Canada during the French regime is known to have better properties, in particular better longevity, than even the modern mortars. However, the exact recipe for these mortars has been lost, as it was transferred verbally from the masons to their sons or successors. This paper covers part of a project attempting to find out the recipe of the ancient mortar from careful analysis of samples of ancient mortars provided graciously by the Quebec Ministry of Cultural Affairs. These samples come from the remains of three stone buildings in the old part of Quebec City: the second house of Champlain (1624), the Gervais-Beaudoin house (1682) and the "Magasin du Roy" (The King's Store)(l680-1700). For the sake of comparison, several mortar samples from buildings and houses in the Kingston area were also analyzed. The analysis work presented here was based on instrumental neutron activation analysis (INAA), using the SLOWPOKE-2 nuclear research reactor at Royal Military College. The main elements detected and measured with the JNAA technique were Ca, Al, Fe, K, Na, Ba, Mg, Ti, Cl and Mn. One of the difficulties with neutron activation analysis is that silicon has a (n,p) reaction with thermal neutrons, producing 28Al, the same radioisotope resulting from the (n, y) reaction with 27Al. Therefore, Si had to be determined by means other than nuclear. The results from INAA were quite surprising, because the French regime samples had significant differences in their elemental compositions. The samples from the second house of Champlain and the Gervais-Beaudoin house are quite similar, with 8-10% calcium, 6% aluminum, and 2% iron, for the most abundant isotopes (excluding silicon). However, the "Magasin du Roy" samples exhibited some 24% calcium, 25% aluminum, and negligible concentrations of iron and other elements. For this last set of samples, the relative concentrations are quite similar to those of the St. Mary's Cathedral and the modern mortars in Kingston. INAA produced results on the elemental content of the samples with a 5% accuracy, however, it cannot provide information on the molecular arrangement of the materials, and other, non-nuclear, methods are needed to obtain information here. The research is now performed using several conventional methods including infrared spectrometry, X-ray spectrometry, and other examination methods such as porosity, density and micro-hardness tests. Despite its limitations, INAA remains a key analysis method for this project since its high accuracy will be put to good use in the quantitative dosing of the various components of the French regime mortars.