Sodium silicate is widely used as a coagulation accelerator for oil-well cement. Adding a small amount of sodium hydroxide or sodium silicate to the sodium carbonate activator can significantly accelerate the reaction process, thus shortening the setting time and improving the mechanical properties.

Only 1% Na2O contribution from sodium hydroxide addition can lead to a 2-d compressive strength of 20 MPa for sodium carbonate-activated slag mixtures. In addition, the 28 days compressive strength was significantly higher than the sole sodium carbonate activator. The addition of sodium hydroxide or sodium silicate also considerably influenced the rheological behavior of the sodium carbonate-activated slag mixture, enhancing the structural build-up rate and transforming the shear-thinning behavior to Bingham or shear-thickening behavior. A more well-packed microstructure was observed in the mixtures with the addition of sodium hydroxide; however, more micro-cracks were observed in the mixtures with a small incorporation of sodium silicate.

However, some studies have reported the effect of adding sodium silicate on the setting time of oil well cement, and the results show that the addition of sodium silicate significantly delays the setting time of the cement paste with retarder. For oil well cements without retarder, the addition of sodium silicate shortened the setting time. On the contrary, for the oil well cement with retarder, the addition of sodium silicate prolonged the setting time and acted as a retarder. In addition, the mechanism of slowing down cement hydration with the addition of sodium silicate was investigated in detail by XRD, BET nitrogen adsorption and total organic carbon analysis. The results showed that the addition of sodium silicate delayed the hydration of tricalcium aluminate, thus prolonging the setting process of oil well cement.

References:

[1] XIAODI DAI. Accelerating the reaction process of sodium carbonate-activated slag mixtures with the incorporation of a small addition of sodium hydroxide/sodium silicate[J]. Cement & concrete composites, 2023, 141, 105-118.

[2] SHENGLAI GUO . Delaying the hydration of Portland cement by sodium silicate: Setting time and retarding mechanism[J]. Construction and Building Materials, 2019, 205: Pages 543-548. DOI:10.1016/j.conbuildmat.2019.02.041.