This paper reports the composition and properties of highly flowable selfconsolidating concrete (SCC) mixtures made of high proportions of cement replacement materials such as fly ash and pulverized limestone instead of high dosage of a plasticizing agent or viscosity-modifying chemical admixtures. Self-consolidating concrete mixtures 2 are being increasingly used for the construction of highly reinforced complex concrete elements and for massive concrete structures such as dams and thick foundation. In this study, by varying the proportion of portland cement, fly ash, and limestone powder, SCC mixtures with different strength values were produced, and the properties of both fresh and hardened concrete were determined. Sustainability criterion was assessed based on the life-cycle assessment (LCA) approach, which is particularly crucial for a methodical analysis and quantification of the overall environmental impacts of concrete production.This study quantifies the reduction in global warming potential based on a LCA of highvolume fly ash concrete.
TitleHigh-volume natural volcanic pozzolan and limestone powder as partial replacements for portland cement in self-compacting and sustainable concrete
a b s t r a c tA laboratory study demonstrates that high volume, 45% by mass replacement of portland cement (OPC) with 30% finely-ground basaltic ash from Saudi Arabia (NP) and 15% limestone powder (LS) produces concrete with good workability, high 28-day compressive strength (39 MPa), excellent one year strength (57 MPa), and very high resistance to chloride penetration. Conventional OPC is produced by intergrinding 95% portland clinker and 5% gypsum, and its clinker factor (CF) thus equals 0.95. With 30% NP and 15% LS portland clinker replacement, the CF of the blended ternary PC equals 0.52 so that 48% CO 2 emissions could be avoided, while enhancing strength development and durability in the resulting self-compacting concrete (SCC). Petrographic and scanning electron microscopy (SEM) investigations of the crushed NP and finely-ground NP in the concretes provide new insights into the heterogeneous fine-scale cementitious hydration products associated with basaltic ash-portland cement reactions.
Properties and characteristics of fly ash-or slag-based geopolymers have been extensively explored but comparatively less information is available for natural pozzolan-based geopolymers. The present work focuses on microstructural characteristics of natural pozzolan-based geopolymers activated by sodium hydroxide and a mixture of sodium hydroxide and sodium silicate. Synchrotron XRD and SEM-EDS studies combined with compressive strength tests successfully demonstrate the feasibility of the use of natural pozzolan for sustainable construction material. It is concluded that the geopolymers have sufficient strength as structural materials and matrices contain C-S-H like crystal as well as zeolites of hydroxysodalite and zeolite Y. Two zeolites of hydroxysodalite and zeolite Y are found as the main activation products in sodium hydroxide activation. Substitution with sodium silicate solution yields higher compressive strength and a denser microstructure with dominant activation products of C-S-H like crystal, zeolite Y, and phillipsite. It has been proposed that the crystal size of the activation products ranges from 10 nm to 1 μm. Different microstructural characteristics found herein provide a valuable information to develop natural pozzolan-based sustainable structural materials with improved properties.
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