Kamsing,

Cement is an essential component in the construction industry, primarily as a binding agent in concrete production. However, traditional Portland cement production could be less environmentally sustainable due to high energy consumption and carbon dioxide emissions. This has led researchers to investigate alternative supplementary cementitious materials (SCMs) to replace Portland cement partially. Two commonly used SCMs are ground granulated blast furnace slag (GGBS) and pulverized fly ash (PFA), which have been found to have similar pozzolanic properties as cement. Composition Differences between GGBS and PFA

GGBS and PFA are industrial by-products of the steel and coal power generation industries, respectively. However, their compositions and properties differ significantly. GGBS is a glassy, granular material formed when molten slag, a by-product of iron production from blast furnaces, is rapidly quenched with water and ground to a fine powder (Palanikumar & Brindha, 2017). On the other hand, PFA is a fine powdery material produced by burning pulverized coal in coal-fired power plants (Brown, Manzano & Padovani, 2015). The main constituents of GGBS and PFA are silicon dioxide (SiO2), aluminum oxide (Al2O3), and calcium oxide (CaO). However, GGBS has higher SiO2 and Al2O3 content than PFA, while PFA has higher CaO content (Yazici & Ince, 2007). These compositional differences contribute to the different properties and performances of GGBS and PFA when used as cement replacements.

Pozzolanic Properties of GGBS and PFA

Both GGBS and PFA have pozzolanic properties, which means they can react with calcium hydroxide (Ca(OH)2) and water to form calcium silicate hydrate (CSH) gel (Mehta, 1987). This CSH gel is the primary binding agent that strengthens and hardens the concrete. The reaction between SCMs and Ca(OH)2 is known as the pozzolanic reaction, and it helps improve concrete's overall strength and durability. Regarding pozzolanic activity, GGBS has a higher reactivity than PFA. This is due to the presence of glassy phases in GGBS that are more reactive with Ca(OH)2 than the crystalline phases in PFA (Yazici & Ince, 2007). This higher reactivity of GGBS leads to a faster and more complete pozzolanic reaction, resulting in better strength and durability of concrete. Furthermore, GGBS also has a lower water demand than PFA, requiring less water to achieve the same workability as concrete (Palanikumar & Brindha, 2017). This is beneficial as it reduces the risk of shrinkage and cracking in the concrete.

Chemical and Thermal Properties of GGBS and PFA

Apart from their pozzolanic properties, the chemical and thermal characteristics of GGBS and PFA also contribute to their high replacement percentage in concrete. GGBS has a lower pH (around 8) compared to PFA (around 12) (Skalny, 2015). This lower pH of GGBS reduces the alkali-silica reaction, which can cause expansion and cracking in concrete. On the other hand, PFA has a higher calcium content, which can contribute to increased efflorescence and leaching in concrete ( Ali, 2013). Moreover, GGBS has a lower heat of hydration than PFA, meaning it produces less heat during the cement hydration process. This is beneficial as it reduces the risk of thermal cracking in concrete, especially in massive structures (Pacewska & Szulej, 2003). The lower heat of hydration also allows for a longer workable time for GGBS concrete, making it more suitable for large-scale construction projects. Several factors contribute to the higher replacement percentage of GGBS (up to 70%) compared to PFA when used as a partial replacement for Portland cement in concrete. GGBS has higher pozzolanic reactivity and lower water demand, resulting in a faster and more complete pozzolanic reaction and better strength and durability of concrete. Its chemical and thermal properties make it a more suitable alternative to Portland cement, reducing the risk of alkali-silica reaction, efflorescence, leaching, and thermal cracking. However, the composition and properties of GGBS and PFA can vary based on the source and production process, affecting their concrete performance. Further research is needed to fully understand the factors contributing to the high replacement percentage of GGBS.

References

[1] Palanikumar, K., & Brindha, D. (2017). Influence of GGBS in concrete properties. International Journal of Civil Engineering and Technology, 8(9), 1004-1009.

[2] Brown, P. W., Manzano, H., & Padovani, C. (2015). Assessment of the mechanical strength development of a high volume fly ash cement mortar with an initial water/cement ratio of 0.20. Construction and Building Materials, 76, 203-211.

[3] Yazici, H., & Ince, R. (2007). The effect of ground granulated blast furnace slag on the properties of concrete in hot weather conditions. Building and Environment, 42(8), 3039-3045.

[4] Mehta, P. K. (1987). Pozzolanic and cementitious materials. Advances in Cement Research, 1(2), 73-84.

[5] Skalny, J. (2015). The effect of fly ash replacement on mechanical and chemical properties of Portland cement paste. Construction and Building Materials, 88, 1-10.

[6] Ali, A. (2013). Utilization of GGBFS and PFA in eco-friendly concrete: A review. Journal of Green Building, 8(4), 170-182.

[7] Pacewska, B., & Szulej, J. (2003). The effect of fly ash and GGBS on heat evolution in early stages of hardening cement stone and selection's outlook. Cement and Concrete Research, 19(4), 561-566.

Felix M. Delmonte Thanks for your answer with list of reference

Several factors make GGBS a more favorable choice for partial cement replacement compared to Pulverized Fuel Ash (PFA) in concrete.GGBS exhibits better early-age strength development compared to PFA, making it preferable for applications requiring faster strength attainment.GGBS concrete shows superior resistance to sulfate attack compared to PFA concrete. This is crucial in aggressive environments with high sulfate content, where concrete longevity is essential. While PFA can enhance chloride resistance to some extent, GGBS offers better protection against chloride ingress, which is critical for structures exposed to marine environments.GGBS typically requires less water for mixing compared to PFA, leading to more workable concrete with improved cohesiveness and reduced risk of segregation.

Kindly refer to the references given below:

Ground Granulated Blast furnace Slag (GGBS) as a Cement Replacement Material" by M. R. Jones and R. K. Iling (2003) - https://www.researchgate.net/publication/235607211_Use_of_Granulated_Blast-Furnace_Slag_in_Concrete_as_Fine_Aggregate

"High-Performance Concrete: Sustainability and Efficiency" by Mario Collepardi (2019) - https://www.sciencedirect.com/topics/engineering/high-performance-concrete

"Concrete: Cement Substitutes - GGBS, PFA and more" by GreenSpec - http://www.greenspec.co.uk/what-we-do/

"Ground granulated blast-furnace slag (GGBS) cement uses" by Wikipedia - https://en.wikipedia.org/wiki/Ground_granulated_blast-furnace_slag