Effects of PFA and GGBS on Early-Ages Engineering Properties of Portland Cement Systems

Abstract

A comprehensive study is presented on the effects of pulverised fly ash (PFA) and ground granulated blast furnace slag (GGBS) on early-age engineering properties of Portland cement (PC) systems. It has been found that partially replacing PC by PFA or GGBS resulted in longer setting times but better workability with PFA exhibiting more prominent effect than GGBS. As the replacement level increased, the setting of both PFA and GGBS pastes further delayed but workability of concrete was enhanced. PFA concretes exhibited consistently lower compression and splitting tensile strengths than PC ones. As the replacement level increased, strengths decreased. At the replacement level up to 30% by mass, GGBS concrete exhibited higher splitting tensile strength than PC concrete. However, as the replacement level further increased, it developed lower strength than PC concrete up to 21 days. Then, it managed to gain higher splitting tensile strength than PC concrete at the replacement levels up to 70% by mass at 28 days. Both PFA and GGBS can reduce drying shrinkage and the reduction effects became more significant as replacement level increased with GGBS performing better than PFA. Adding fibres into PFA concrete increased its splitting tensile strength and further reduced its drying shrinkage.

Evaluation of iron ore tailings as replacement for fine aggregate in concrete

“…The lower rates of drying shrinkage of IOT was attributed to the finer particle that fill the micro pore of the concrete and optimized the pore structure. This finding is clearly in agreement with Zhou et al [36]. Another factor for lower drying shrinkage of IOT could be attributed to the porous nature of IOT which would absorbed more water and release moisture slowly during the drying phase of concrete, like in the case of furnace bottom ash [37].…”

Shrinkage Cracking Resistance of Blast Furnace Slag Blended Cement Concrete - Influencing Factors and Enhancing Measures

“…The absolute value of the 6-month free shrinkage strain of BFS concrete showed an increase with increases in temperature, while that of the normal concrete showed the reverse tendency, resulting in larger or smaller values at 10°C and 30°C and vice versa, but nearly the same value at the temperature of 20°C. This behavior at 20°C agrees with the traditional understanding in which drying shrinkage of BFS concrete is not larger than that of normal concrete (e.g., Zhou et al 2012). It was reported that autogenous shrinkage of BFS concrete was greater when subjected to higher temperature history due to the liberation of hydration heat in massive concrete (JCI 2008), while under the condition of relatively low water-cement ratio and constant temperature, autogeneous shrinkage does not always increase with temperature (Lura et al 2001), though the mechanisms were unknown (Lura et al 2002).…”

Strength, Carbon Footprint and Cost Considerations of Mortar Blends with High Volume Ground Granulated Blast Furnace Slag

“…The slight difference could possibly be overcome at later ages considering GGBFS blends typically have better later strength due to the continuous hydration and some pozzolanic reaction [15]. A slight reduction in the 28 day compressive strength of concrete containing GGBFS at 30% replacement level or higher was also observed by Zhou et al [23]. Additionally, Gholampour and Ozbakkaloglu [24] similarly reported that use of 50% GGBS resulted in only about a 9% reduction in the 7 day compressive strength of concrete, and a strength improvement up to 6% was found after 28 days.…”