The effect of drying on early-age morphology of C–S–H as observed in environmental SEM

The morphology of early-age C–S–H, often referred to as outer product or low-density C–S–H, is generally accepted to be fibrillar and forms mainly during the early stages of hydration. This paper reports the effect of drying on the microstructure in young tricalcium silicate paste, which provides insight into the mechanism that leads to the fibrillar morphology. During the first few days after C3S is mixed with water, the morphology of C–S–H is more affected by drying rate than by relative humidity. This sensitivity is most apparent at partial pressures greater than 85%. During this time, the fibrillar C–S–H product can be suppressed by drying C3S paste samples very slowly prior to imaging. This approach is interpreted as evidence that this fibrillar morphology, which naturally form over time, grow as tiny colloidal particles that rearrange during the early stages of hydration, leading to well-established larger scale morphologies.