Inventors Zongjin Li, Chung Kong Chau, Faming Li, and Baoguo Ma of Hong Kong designed an admixture from millet that makes concrete resistant to the effects of freezing and thawing.
The admixture incorporates a natural polymer made from millet. It also contains smaller quantities of naphthenic sulfate salt, triethanolamine, and formaldehyde.
An increasing percentage of natural polymer added to the concrete mix results in a corresponding reduction in compressive strength and Young's modulus (modulus of elasticity). Testing by the inventors has shown that the optimum amount of natural polymer additive is in the range of 0.1 percent to 2 percent of the solid content by weight of the cement.
Testing using mercury intrusion porosimetry measurements show significantly fewer surface cracks in the samples incorporating the new admixture. The results also show that the microstructure of the concrete modified with natural grain polymer is very stable, and both the pore sizes and amount of pores are similar whether or not the concrete is subjected to freeze-thaw exposure. In contrast, freeze-thaw cycles substantially alter the microstructure of ordinary concrete.