Radiocarbon Dating of Mortars with a Pozzolana Aggregate Using the Cryo2SoniC Protocol to Isolate the Binder

Abstract

To date, finding a technique able to effectively isolate the carbon signal from the binder of a mortar is still an open challenge. In this paper, the radiocarbon (14C) dating of one of the most challenging and diffuse types of mortar, the one with pozzolana aggregate, is investigated. Eight mortar samples from three archaeological sites near Rome (Italy) underwent a selection process called Cryo2SoniC. The selected fractions were analyzed by the accelerator mass spectrometry (AMS) 14C technique and compared to known historical references. Additional scanning electron microscopy analysis and petrographic investigations were done, respectively, to check the grain size of the fractions selected by Cryo2SoniC, and further, to characterize the original mortar samples. The masses of carbon yielded from the dated fractions were almost half of those released from some aerial mortars. The 14C dating results were accurate for pozzolana mortars, from buried and unburied structures, with calcination relics and small contamination of secondary calcite. A limitation in the purification protocol was observed on samples with a massive contamination of secondary calcite deposition of ground water origin, occluding porosity and substituting up to the 80% of the original binder matrix.

Radiocarbon Dating of Mortars and Charcoals from Novae Bath Complex: Sequential Dissolution of Historical and Experimental Mortar Samples with Pozzolanic Admixture

“…14 C measurements of mortar samples were based on the sequential dissolution methodology (Lindroos et al 2007) combined with sample characterization (Trąbska and Trybalska 2007;Michalska et al 2017). The mechanical and chemical separation of different grain fractions follows those described by Michalska and Czernik (2015) and preparation of suspension follows those described by Marzaioli et al (2013) and Nonni et al (2017).…”

A field guide to mortar sampling for radiocarbon dating*

“…For pozzolana that hardened in the presence of air, excess Ca(OH) 2 can react with atmospheric CO 2 to produce CaCO 3 , as described in equation ( 1) (Ringbom et al 2014). Lime lumps composed mainly of calcite are commonly found in pozzolana mortars, and pozzolana hardened in the presence of air has the potential for carbon dating (Stuiver and Smith 1965;Lindroos et al 2018;Nonni et al 2018).…”

“…Avoid drilling with drill-bits, as this will alter the grain distribution of the mortar. This obstructs the desired mechanical separation of the sample by gentle crushing, which is intended to separate the mortar binder from the aggregate without significant alteration of the grain size distribution of the sample (Heinemeier et al 1997;Nonni et al 2018;Ponce-Anton et al 2018).…”

“…The ancient bridge is located where the ancient road Via Emilia crossed the Parma stream in the city of Parma. In the laboratory, petrography can produce further information on the binder matrix and identify secondary calcite depositions (Hobbs and Siddall 2011;Nonni et al 2018).…”

“…Its purpose is to present sampling strategies to reduce the number of mortar samples affected by avoidable complications, and thereby increase the proportion of mortar samples with conclusive radiocarbon dating results. It also emphasizes the importance of multi-fraction dating (see the section Mortar dating studies below), without which complications can even lead to undetected errors (Stuiver and Smith 1965;Baxter and Walton 1970;Nonni et al 2018;Ponce-Anton et al 2018).…”