Investigation into lowering cement clinker content using available materials

Abstract

Reducing cement clinker with mineral addition has been considered an efficient way of saving energy, lowering CO2 footprint of cement and concrete industries. The trend of using limestone as mineral addition in cement production started in 1992s. Cement containing limestone additions up 35% have been used in European countries adopting the European Standard EN 197. Similar standards have been developed, such as Canadian Standard, CSA A3000, which has approved the limestone addition from 5% up to 15% by mass. In U.S., ASTM standard C595 for Portland blended cement needs to be changed to have a significant impact on sustainability. This research tested concrete fresh properties, strength development and durability properties made using different types of blended cement, a series of limestone addition rates, which changed from 5% to 18% by mass, and a series of ternary mixtures with limestone and fly ash combination at 20% replacement rate. Concrete mixtures using a type I/II cement was used as a baseline for comparison. Results showed that limestone addition decreased concrete workability while fly ash addition in ternary mixtures improved workability. Concrete made using cement with limestone addition showed improved early age strength. Fly ash addition in ternary mixtures showed lower early age strengths. Mortars with limestone addition to 18% and ternary mixtures showed no statistically significant difference on volume stability comparing to the control group which were prepared using ordinary Portland cement. Blended cement with limestone addition has less length changes when exposed to sulfates. Limestone additions up to 18% by mass showed improvement for sulfate resistance. The ternary mixtures also showed sulfate resistance improvement. Concrete permeability increased with increasing limestone addition. Fly ash showed significant decrease in permeability. Concrete freezethaw resistance is strongly related with air content. Limestone addition rates up to 18% had freeze-thaw resistance decreased. Results showed that the properties of blended cement such as particle size distribution, the quality and quantity of mineral addition can affect concrete fresh properties, harden properties and durability. Blend cement with limestone addition rate up to 18% have no significant negative effect on concrete performance.