E-modulus development of volcanic pozzolan concrete: A comparative investigation of digital image correlation and strain gauges

Concrete E-modulus ( E C ) relies heavily on accurate strain measurements. Strain gauge-based transducers provide high sensitivity but are limited by gauge placement, bonding quality, potential specimen disturbance, and localized readings. Digital image correlation (DIC) offers a promising non-contact, full-field alternative, but its use for E C —especially at early ages and for mixes with supplementary cementitious materials (SCMs)—remains limited. This study compares strain gauges and two-dimensional (2D) DIC in evaluating E C of three concrete mixes with varying amounts of a new SCM—Volcanic Pozzolan Iceland (VPI)—from 12 h to 91 days, emphasizing the early-age phase. Load-controlled uniaxial compression tests were conducted in two laboratories with different strain-gauge configurations and test set-ups, alongside two DIC postprocessing approaches: finite-element mesh and subset tracking. Key findings and contributions are: (i) variability from laboratory, test method, and concrete batch was quantified, with interlaboratory RMSE of 0.108 for compressive strength and 0.125 for E-modulus; (ii) subset tracking produced more accurate and robust DIC results, with average standard deviations (s = 0.6%) comparable to strain-gauge measurements; (iii) 2D DIC on cylindrical specimens was validated by low correlation residuals along the axis (mean = 2.0%, s = 2.2%) and over time (mean = 2.0%, s = 0.1%); (iv) the evolution of compressive strength and E C was compared with empirical models, highlighting parabolic hyperbolic and exponential models as the most accurate; (v) VPI showed reduced early-age reactivity followed by later-age recovery for both concrete properties, with higher overall reactivity than fly ash. • DIC matches strain gauge measurements for concrete E-modulus ( E C ) across ages. • Volcanic pozzolan: same E C development but higher reactivity than fly ash. • Robust intra/inter-laboratory scatter analysis with varied set-ups and EN methods.