Compressive Strength of Masonry Units in Cagayan's Heritage Churches: A Reference for Sustainable Preservation and Seismic Vulnerability Assessment

Abstract

This study addressed a critical data gap concerning the mechanical properties of Unreinforced Masonry (URM) materials used in Cagayan's Spanish colonial-era heritage churches, which are significant cultural assets highly susceptible to seismic activity. The Philippines is an earthquake-prone country, ranked second globally for exposure to natural hazards. While historical accounts confirm that Cagayan’s churches were extensively constructed with brick, a previous comprehensive national assessment of indigenous URM properties unintentionally missed collecting samples from this critical region, highlighting a continuing need for specific local scientific studies. Understanding the fundamental strength parameters of individual masonry units is crucial for accurate seismic vulnerability assessments, an indispensable first step in mitigation efforts for cultural heritage preservation. Therefore, this research aimed to comprehensively characterize the compressive strength of these masonry units to provide an essential reference for informed restoration measures and a proactive approach to mitigating the impact of possible earthquakes. By following minimal heritage protection guidelines, URM blocks were carefully retrieved as remnants from the ruins near St. Anne Church in Buguey, Cagayan. The gathered samples, taken from damaged areas, represent stonework that has been subjected to centuries of structural stress and environmental damage. Samples were subsequently prepared into 4'' x 4'' x 8'' blocks. For compressive testing, a uniaxial compressive force was applied perpendicular to the bed surface to simulate the compression loads experienced by the block in situ. The meticulous methodology was crucial for obtaining representative data concerning the materials’ structural integrity and seismic behaviour under axial stress. The analysed brick samples exhibited a mean compressive strength of 8.58 MPa, with individual strengths ranging from 8.44 MPa to 8.72 MPa. Critically, these measured values significantly exceed the ASCE. 41-17 default lower-bound strength of 1.96 MPa (285 lb/in²) typically specified for old unreinforced clay masonry with lime mortar. When compared to other indigenous URM materials found in the Philippines, the Cagayan bricks showed slightly higher strength than adobe (mean 7.49 MPa) and coralline limestone (mean 7.77 MPa), but were considerably weaker than sandstone (mean 37.12 MPa). These findings suggest that, if these bricks remain unreinforced, they would primarily limit structures to single stories, indicating a general need for further strengthening measures to sustain greater loads effectively. The study thus provides crucial foundational mechanical property data, essential for developing informed, low-invasive, and reversible conservation and retrofitting strategies for St. Anne Church and other heritage structures in Cagayan, contributing to their sustainable preservation and enhanced seismic resilience.