Development of high-early-strength engineered cementitious composite with GGBS and nano-silica for bonding with self-compacting concrete

Engineered Cementitious Composites (ECC) exhibit exceptional ductility but often suffer from limited early-age strength, restricting their use in rapid repair applications. This study develops a ternary blended ECC incorporating Ground Granulated Blast Furnace Slag (GGBS) and nano-silica (NS) with hybrid polyvinyl alcohol (PVA) and steel fibers to enhance early-age strength and bonding with self-compacting concrete (SCC). A total of 12 ECC mixes with varying GGBS-to-cement ratios (0.8, 1.0, and 1.2) and NS-to-cement ratios (0, 0.05, 0.10, and 0.15) were evaluated. The experimental program included compressive strength, splitting tensile strength, direct tensile strength, split tensile bond strength, slant shear bond strength, and flexural behavior of layered ECC-SCC composite beams at curing ages of 3, 7, 28, and 90 days. The optimal mix (GGBS/cement = 1.0, NS/cement = 0.05) achieved a 22% increase in 7-day compressive strength (from 43.5 MPa to 53.2 MPa) and sustained tensile strain capacity exceeding 6% at 28 days. Bond strength between ECC and SCC improved by up to 78% at 90 days (from 1.87 MPa to 3.27 MPa) compared to the 3-day bond strength of control SCC. Composite beams incorporating the optimal ECC mix demonstrated enhanced first-crack load and ductility without interfacial de-bonding. These findings indicate that the developed GGBS-NS-modified ECC shows promise as a high-early-strength repair material with favorable bond characteristics to SCC substrates, although long-term durability performance requires further investigation.