Nano-silica admixture tempers heat of hydration, boosts CSH formation

Sources: Silicone Solutions, Cuyahoga Falls, Ohio; CP staff

Adhesive, sealant, gel and coating specialist Silicone Solutions plans a 2018 World of Concrete launch for a nano-silica admixture that effectively converts Types I and II portland cement to a Type IV low heat binder. CoolCure skews hydration chemistry to calcium silicate hydrate or CSH, the principal binding agent in concrete, to the detriment of calcium hydroxide or Ca(OH)2, the heat of hydration source.

“Type I and Type II portland cements comprise both dicalcium and tricalcium silicates,” explains CoolCure developer and Silicone Solutions President David Brassard, who is commercializing the admixture through a subsidiary, New Technology Solutions LLC. “Tricalcium silicates are the most reactive, generating high heat of hydration or exotherm. In contrast, Type IV portland cement contains mostly dicalcium silicates, which are slower reacting than tricalcium silicates and generate less than one-third the heat during hydration.

“By mimicking a Type IV cement reaction in a Type I or Type II portland cement mixture, engineers and contractors will see more controlled, cooler hardening and curing phases compared to conventional concrete. Without high exotherms, they can eliminate or significantly reduce thermal cracking, curling and distortion. CoolCure’s balancing of hydration reactions also efficiently wets out the matrix and reduces bleed water.”

The admixture is dosed in two parts per cubic yard: a silica-rich liquid at up to 1 gal. plus a dry catalyst at up to 1 lb. per 100 lbs. of cement. The nano-silica in CoolCure bears the same basic chemical profile as silica sand or silicon dioxide (SiO2), but at one-millionth a typical grain’s gradation. At 1/1000th or smaller, nano-silicas likewise exhibit a sharp size contrast to portland cement or silica fume particles. When used in place of 1 lb. of sand, nano-silicas create as much as 100,000 times the prospective bonding surface in a concrete matrix.

New Technology Solutions has enlisted Ohio, Pennsylvania and West Virginia ready mixed producer Arrow Concrete, along with Essroc Cement and Lehigh Hanson, plus Intertek PSI of Cleveland in CoolCure trials. Conventional cylinder and 4-ft. square cube specimens have shown how the admixture—measured against plain controls—reduces heat of hydration; extends mixes’ working and placement window; and, increases compressive strength 40 to 100 percent in finished slabs and structures. Ca(OH)2 reduction results in finished concrete of under 12.4 pH, lowering the potential for delayed alkali silica reactivity observed in slabs or structures where pH is 12.5 or higher. —


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