SBIR-STTR Award

In cold climates, concretes are susceptible to deterioration from the combination of the use of deicing salts and cyclic freezing and thawing cycles. The presence of salts is reported to exacerbate the susceptibility of concrete to freeze-thaw deterioration. IPANEX is an admixture that has been in use for nearly 30 years and has a long track record of compatibility with plasticizers and air entraining admixtures. The mechanism by which IPANEX functions, however, has only recently been established. With the development of the understanding of how it works has come greater insight into applications beyond the initial scope of its usage. IPANEX is composed of 5 to 20 nanometer-sized particles of C-S-H [hydrous calcium silicate] that in application, seed the growth of C-S-H from the hydration of tri-calcium silicate. Seeding with nanometer-sized seeds means that a small dose rate will result in a large number of seeds distributed throughout the mass concrete. These seeds have the effect of removing the supersaturation that occurs with tri-calcium silicate and providing a more homogeneous microstructure. As part of this refined microstructure, there are no large growths of calcium hydroxide crystals; not even at the aggregate low density zones. The controlled growth does not necessarily result in less pores but rather in a pore structure that is generally finer. IPANEX will impact any process that relies upon the movement of fluids [water or gases] through the pore system of a concrete. As water freezes, it draws additional fluids from the gel pores, if the critical concentration of water in capillary pores is less than 91.7%, or if water can not be drawn from the gel pores, freeze-thaw deterioration will not be a problem. Furthermore, because of the pore sizes, water will not freeze in capillary pores. One school of thought on freeze-thaw deterioration suggests that osmotic pressures which develop between the freezing water in large pores and the capillary porosity result in different alkali concentrations and hence different pressure is a more or less significant contribution to this mode of deterioration. It is however considered as a major factor in salt scaling. The objective of this SBIR will be to demonstrate that IPANEX is compatible with air-entraining admixtures and will improve the durability of the concrete to salt scaling through the improvement in the microstructural development of the concrete

Keywords:
PERMEABILITY, TORTUOSITY, DURABILITY, FREEZE THAW CYCLE, SALT SCALING

The phase I study of this sbir was completed in response to the need to enhance durability of chemical admixtures that will allow cold-weather concreteing to be conducted below freezing temperatures without the necessity of heating the form work and imbedded reinforcing steel. Under this study three ipanex-containing potential formulations where selected that exhibited promise for anti-freeze admixtures. The phase II SBIR proposal has as its objectives the optimization of the proportions of constituents in the three admixtures, carrying the optimized formulations into full-scale demonstrations of 8 to 12 yards, collecting pertinent early-age mechanical properties data on common grad a and aa concrete formulations and ultimately down selecting from three admixtures to two admixtures. The phase I studies have demonstrated that surface air flow (SAF) measurements developed as part of the fhwa's shrp program in the 1990's delineates the durability enhancing performance of concretes containing ipanex. Another component of this phase II study will be a redesign of the saf apparatus. Concurrent with the research program, data necessary for the development of an economic assessment and commercialization plan will be gather formulated into a business plan to market the developed admixtures and surface air flow apparatus.

Keywords:
Permeability, Tortuosity, Durability, Freeze Thaw Cycle, Salt Scaling