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Bentonite is a mixture of clay and non-clay minerals. Montmorillonite clay mineral is a dominant mineral in bentonite. Silica and alumina bond in the crystal structure of montmorillonite. Therefore, they cannot contribute to the pozzolanic reaction. Heat treatment of bentonite leads to the destruction of the crystal structure of montmorillonite and converting silica and alumina to reactive phases. Thermally activated bentonite (TAB) is a relatively low reactive pozzolan when used as partial replacement of Portland cement modifies both fresh and hardened properties of cement paste, mortar, and concrete. The most desired effects of TAB are: improve segregation resistance, reduce the rate of strength gain, and enhance concrete durability against sulfates, chlorides, and acids, in addition to economic and ecological beneficiations. This paper provides information related to heat treatment of bentonite clays and montmorillonite minerals, and their effects on the paste, mortar, and concrete when used as a partial replacement of Portland cement.

• Reusing thermoactivated construction waste spoil (CSP) as a binder for durable concrete. • Effects of thermoactivated CSP content and particle size on the chloride transport in concrete. • Combine use of thermoactivated CSP and active admixture for more durable concrete. Construction and demolition waste is predominantly comprised of construction spoil. However, the proper recycling of this construction spoil in a manner that maximizes its value has historically received insufficient attention. Therefore, the objective of this study investigated the micro-structure and chloride transport of cement concrete including thermoactivated construction spoil powder (CSP) as a substitute for cement. The results highlights that the un-treated CSP consisted of massive inert components, and active metakaolin and amorphous components were generated in thermoactivated CSP after 800–1200 ℃ activation treatment. Mixing un-treated CSP negatively impacted the micro-structure and strength development of concrete, but the thermoactivated CSP blended paste had improved micro-structure and better strength than the un-treated CSP blended paste. Incorporating un-treated CSP raised the chloride transport in concrete. At the constant replacement ratio of CSP, the thermoactivated CSP blended concrete had lower chloride transport than the un-treated CSP blended concrete, and decreasing the particle size of thermoactivated CSP could further decline the chloride transport in thermoactivated CSP blended concrete. The concrete with 1200 ℃-activated CSP even had lower chloride transport than the reference concrete. The mix of un-treated CSP up to 30% reduced the chloride binding capacity of concrete, but the thermoactivated CSP blended concrete had superior chloride binding capacity to the un-treated CSP blended concrete. Particularly, the concrete with 20% thermoactivated CSP and 10% active metakaolin/silica fume had similar strength and lower chloride transport than reference concrete. By optimizing the thermoactivation temperature, replacement ratio, and particle size of CSP, it was possible to prepare a durable concrete with low chloride transport. [ABSTRACT FROM AUTHOR]

When concrete is placed in extreme climates, quality control of concrete is so difficult that cracking due to hydration heat easily occur. In the paper, new encapsulation technique is developed for control of cement hydration reaction through encapsulation of chemical admixtures. Lithium carbonate (LiCO) as accelerator and tartaric acid (CHO) as retarder are respectively selected for core material. For wall material of microcapsule, acrylic resin, silicon monoxide, and starch is synthesized. Several tests including chemical shrinkage, setting time, compressive strength, and adiabatic temperature are performed for evaluating an effect of the invented microcapsule on cement hydration behavior. Through encapsulation of accelerator and retarder, cement hydration behaviors like setting time, strength, shrinkage, and hydration heat are reasonably controlled. The developed encapsulation technique can be applied for manufacturing high durable concrete in harsh environmental condition avoiding cracking. [ABSTRACT FROM AUTHOR]