<p>Effect of triethanolamine and sulfate carriers on sulfate balance of ordinary Portland cement (OPC) and metakaolin blended cement (MKC) was investigated through calorimetry, compressive strength, XRD and pore solution analysis. Results show that anhydrite is better than hemihydrate for OPC to achieve sulfate balance with the addition of triethanolamine, while the opposite phenomenon is found for MKC. In OPC, fast dissolution of hemihydrate promotes the formation of ettringite, which in turn can consume hemihydrate rapidly and not have enough SO₄²⁻ left to passivate the hydration of aluminate-containing phase. While anhydrite can continuously supply SO₄²⁻ to maintain sulfate balance due to its low dissolution rate. In MKC, SO₄²⁻ released from hemihydrate can be adsorbed on MK’s surface instead of forming ettringite, leading MK to become another sulfate source to maintain sulfate balance after the depletion of hemihydrate. The activated MK’s dissolution by triethanolamine and slow supply of SO₄²⁻ from anhydrite benefit ettringite’s formation, leaving fewer SO₄²⁻ for adsorption, which makes anhydrite less effective than hemihydrate to maintain sulfate balance.</p>