Concrete Products covers the issues that attract producers of ready mixed and manufactured concrete focusing on equipment and material technology, market development and management topics.
Issue link: http://concrete.epubxp.com/i/923891
68 • January 2018 www.concreteproducts.com Ohio-based 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. The product is dosed in two parts per cubic yard: a silica-rich liquid at up to 1 gallon plus a dry catalyst at up to 1 lb. per 100 lbs. of cement. "Type I and Type II portland cements comprise both dicalcium and tricalcium silicates," explains CoolCure developer and Silicone Solu- tions President David Brassard, who is commercializing the admixture through a subsidiary, New Technology Solutions LLC. "Tricalcium sil- icates are the most reactive, generating high heat of hydration or exotherm. In contrast, Type IV portland cement contains mostly dical- cium 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 con- ventional 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." Since 2014, New Technology Solutions has enlisted Ohio and Pennsylvania 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. NANO FACTOR New Technology underscores CoolCure's potential to offset the use of fly ash, GGBF slag and aggregate- or mix-cooling methods geared to keeping in-transit or freshly placed mixes at or below target temperatures. It credits the admixture's capacity to impart Type IV portland cement performance to the use of a) nanotechnology, where silicon and other elements can be examined and manipulated at atomic level; b) a balancing of paste chemistry that minimizes hydration by-products; c) utilization of Ca(OH)2 to elevate CSH levels instead of heat; and, d) water and portland cement reaction efficiency, resulting in more cement paste and aggregate bonds. The nano-silicas in CoolCure bear the same basic chemical profile as silica sand or silicon dioxide (SiO 2 ), but at one millionth a typ- ical grain's gradation. At 1/1000 th or smaller, nano-silicas likewise exhibit a sharp size contrast to portland cement or silica fume particles. When used in place of one pound of sand, nano-silicas create as much as 100,000 times the prospective bonding surface in a concrete matrix. While the tiny particles are not new to concrete, CoolCure becomes the first agent in its class to be deployed for heat of hydration or exotherm control. In addition to the thermal aspect, the 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. INNOVATIONS REPORT BY DON MARSH ASTM C-39 test results Mix 7 days 14 days 21 days 28 days 6-bag control 4,560 psi 5,290 psi 5,325 psi 5,710 psi 6-bag CoolCure 3,445 psi 6,185 psi 7,745 psi 7,990 psi Tests performed at Intertek PSI, Cleveland for New Technology Solutions CEMENT HYDRATION REACTIONS Phase I — Hydration of tricalcium Tricalcium silicate + Water Calcium silicate hydrate + Calcium hydroxides + high heat 2 Ca 3 SiO 5 + 7 H 2 O 3 CaO 2SiO 2 4H 2 O + 3 Ca(OH) 2 + 173.6kJ Phase II — Hydration of dicalcium Dicalcium silicate + Water Calcium silicate hydrate + Calcium hydroxide + lower heat 2 Ca 2 SiO 4 + 5 H 2 O 3 CaO SiO 2 4H 2 O + Ca(OH) 2 + 58.6 kJ The CoolCure admixture's capacity to impart Type IV portland cement properties in concrete bearing Type I or II cement stems from its effect on the second of two reaction phases during hydration. A high rate of calcium silicate hydrate conversion observed in Phase II, coupled with lower heat of hydration or exotherm, yields a finished concrete of higher compressive strength and lower porosity. Dical- cium silicate-rich Type IV portland cement exhibits a low heat level akin to Type I/II cement Phase II hydration reaction. At cylinder break, uniform coarse aggregate fracture in a CoolCure specimen exhibits uniform, robust bonding the admixture imparts through increased matrix wetting and compres- sive strength development. Consultant Jim Render assists New Technology Solutions in a late-2017 CoolCure demonstration at Arrow Concrete. COMPRESSIVE STRENGTH DEVELOPMENT Admixture extracts CSH binding value, tempers heat-prone free lime