HOW TO MAKE CEMENTS AND CONCRETES WITH LOWER CO_2 EMISSIONS - (PPT)

摘要

Finely ground homogenised mixture of raw materials (limestone, clay, etc.,) heated to >1400°C in rotary kiln to form nodules of "clinker": typically, ≈80% basic calcium silicates, plus ≈20% calcium aluminates and ferrites as "fluxing" phases. Cooled clinker is ground to fine powder with ≈5% gypsum to make "pure" Portland Cement. But most modern cements also contain other ingredients known as "supplementary cementitious materials" (SCMs) to reduce cost, energy requirements and CO_2 emissions. Portland cements harden when mixed with water because of hydration reactions that form mainly calcium silicate hydrates (C-S-H). SCMs vary in hydraulic reactivity and thus in their ability to substitute for PC clinker. The most effective are blast-furnace slags but their global supply is very limited. Coal fly ashes can be used but are less reactive. Other materials such as some limestones and volcanic rocks can be used but are even less reactive so substitution levels are lower.