Title:
Effects of High Alkalinity on Cement Pastes
Author(s):
Maria C. Garci Juenger and Hamlin M. Jennings
Publication:
Materials Journal
Volume:
98
Issue:
3
Appears on pages(s):
251-255
Keywords:
alkali; cement; drying shrinkage; hydration; surface area.
DOI:
10.14359/10280
Date:
5/1/2001
Abstract:
Increasing the alkalinity of cement pastes by adding sodium hydroxide is known to increase the initial rate of hydration, thereby increasing early strength. The effects on the microstructure and other properties are unclear. The present study examines the influence of NaOH addition on the rate of cement hydration, surface area and porosity as measured by nitrogen (1 to 40 mm pore radius range), and drying shrinkage. While a 1M NaOH solution increases the rate of reaction prior to 1 day, hydration is retarded at later ages. The surface area is reduced when compared to samples without added NaOH, which is a reflection of a lower volume of small pores (1 to 4 nm radii). The rate of drying shrinkage appears to be slower when NaOH is added, but the total equilibrium value is unaffected. NaOH also increases the amount of cracking during drying shrinkage.