Abstract
Ternary blends of cementitious materials are investigated. A cement replacement level of 45% is used for all ternary mixtures consisting of 15% metakaolin and 30% slag replacements. Three metakaolin and two blast furnace slag, referred to as ‘slag’ for short, products commercially available are used to compare performance in ternary blends. A mixture with a 45% fly ash replacement is included to serve as a benchmark for performance. The control mixture contains 422 kg of cement per cubic meter of concrete, and a water-to-cementitious material ratio of 0.43 is used for all mixtures with varying dosages of superplasticizer to retain workability. Mixtures are tested for mechanical properties, durability, and volumetric stability. Mechanical properties include compression, split-cylinder tension, modulus of rupture, and dynamic Young’s modulus. Durability measures are comprised of rapid chloride-ion penetrability, sulfate resistance, and alkali–silica reactivity. Finally, the measure of dimensional stability is assessed by conducting drying shrinkage and coefficient of thermal expansion tests. Results indicate that ternary mixtures including metakaolin perform similarly to the control with respect to mechanical strength. It is concluded that ternary blends perform significantly better than both control and fly ash benchmark in tests measuring durability. Furthermore, shrinkage is reduced while the coefficients of thermal expansion are slightly higher than control and the benchmark.
Highlights
The use of supplementary cementitious materials (SCM) in ready-mixed concrete has seen rapid growth in North America since the 1970s [1]
Metakaolin has been present in concrete literature for decades, little work has been completed to explore its possible benefits inside ternary cementitious blends
All concrete mixtures incorporating MK as a replacement of cement require a high dosage of superplasticizer (≥4 mL/kg of cementitious material, or 6.1 oz./cwt)
Summary
The use of supplementary cementitious materials (SCM) in ready-mixed concrete has seen rapid growth in North America since the 1970s [1]. Two types of chemical reactions contribute to the performance of hardened concrete mixtures incorporating SCMs. The first is the hydraulic reaction, which is the reaction of free lime (CaO) with water produces heat, calcium silicate hydrates (C–S–H), and calcium hydroxide, Ca(OH) or CH. The second reaction is the pozzolanic reaction, which is exhibited by SCMs with high contents of glassy silica or alumina in the presence of CH and water In this reaction, amorphous (glassy) alumina or silica react with the CH created during hydration to produce additional C–S–H, calcium aluminate hydrates (C–A–H), or calcium aluminosilicate hydrates (C-A-S-H). Generation of heat from hydration of cement and associated volume change in mass concrete operations have historically been combatted by replacing a large portion of cement by supplementary cementitious materials. Binary replacements by either fly ash or slag are effective in mitigating high heat of hydration, this approach is susceptible to material shortages. Fly ash is an important SCM used in mitigating deleterious cracking due to the large thermal gradients in mass concrete, and the inability to obtain fly ash would have repercussions on mass concrete placements across the U.S It is important to evaluate alternative SCMs, as well as SCMs in ternary combinations
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
