Final Report - Assessment of Potential Phosphate Ion-Cementitious Materials Interactions

Abstract

The objectives of this limited study were to: (1) review the potential for degradation of cementitious materials due to exposure to high concentrations of phosphate ions; (2) provide an improved understanding of any significant factors that may lead to a requirement to establish exposure limits for concrete structures exposed to soils or ground waters containing high levels of phosphate ions; (3) recommend, as appropriate, whether a limitation on phosphate ion concentration in soils or ground water is required to avoid degradation of concrete structures; and (4) provide a "primer" on factors that can affect the durability of concrete materials and structures in nuclear power plants.An assessment of the potential effects of phosphate ions on cementitious materials was made through a review of the literature, contacts with concrete research personnel, and conduct of a "bench-scale" laboratory investigation. Results of these activities indicate that: no harmful interactions occur between phosphates and cementitious materials unless phosphates are present in the form of phosphoric acid; phosphates have been incorporated into concrete as set retarders, and phosphate cements have been used for infrastructure repair; no standards or guidelines exist pertaining to applications of reinforced concrete structures in high-phosphate environments; interactions of phosphate ions and cementitious materials has not been a concern of the research community; and laboratory results indicate similar performance of specimens cured in phosphate solutions and those cured in a calcium hydroxide solution after exposure periods of up to eighteen months. Relative to the "primer," a separate NUREG report has been prepared that provides a review of pertinent factors that can affect the durability of nuclear power plant reinforced concrete structures. iv v

The Effect of Exposure on the Autogenous Self-Healing of Ordinary Portland Cement Mortars

“…Those two processes, i.e., the adsorption of phosphates on cement grains and the formation of the HAP, were likely to contribute to the observed efficient crack closure of the samples in Exposure 2. In fact, both CSH as well as calcite present inside the crack were shown earlier to be efficient in the removal of phosphates from phosphate-contaminated solutions [41,42,43]. This could further support the hypothesis, assuming the formation of a calcium phosphate compound inside the crack.…”

Development, testing, and environmental impact assessment of glow‐in‐the‐dark concrete

“…The concentration ranges in GiD‐powder and GiD‐concrete were found in the order nitrate > chloride > sulfate > phosphate. The level of anions concentration in GiD‐powder and GiD‐concrete is within an acceptable range when compared to SCTLs for residential and commercial zones . Hence, based on the presented results it can be concluded that GiD‐concrete at 20% addition of GiD‐powder is considered safe with respect to human health and has a negligible negative impact on the surrounding soil.…”

Primer on Durability of Nuclear Power Plant Reinforced Concrete Structures - A Review of Pertinent Factors

“…46 Concrete exposed to a marine environment may deteriorate as a result of combined effects of chemical action of sea water constituents on cement hydration products, alkali-aggregate expansion if reactive aggregates are present, crystallization pressure of salts within concrete if one face of the structure is subject to wetting and others to drying conditions, frost action in cold climates, corrosion of embedded steel reinforcement, and physical erosion due to wave action or floating objects. 144 The data show that in an ordinary portland cement system the formation of calcium hydroxyapatite is capable of replacing free calcium hydroxide (Portlandite) and competes successfully for calcium in aluminosilicate matrices. In order to determine if this can lead to degradation of concrete through expansive reactions, a literature review and small-scale laboratory investigation was conducted.…”

“…Results of the literature review indicated that no harmful interactions of phosphate and cementitious materials occur unless the phosphates are present in the form of phosphoric acid. 144 The laboratory study involved casting cement paste cubes and prisms that were cured in solutions of calcium hydroxide (control), magnesium phosphate, and sodium phosphate. Periodically specimens were removed from each of the curing solutions and measured, weighed, evaluated for compressive strength, and examined by x-ray diffraction or scanning-electron microscope methods.…”