African Design Magazine ADM #40 May 2018 | Page 50

TECHNOLOGY THE INFLUENCE OF GROUND FLY ASH ON CEMENT HYDRATION AND MECHANICAL PROPERTY OF MORTAR In this study, the ground fly ash is made of ordinary grade I fly ash by grinding. Compared with grade I fly ash, the influence of ground fly ash on cement hydration and mechanical property of mortar was investigated. The results show that ground fly ash can improve the hydration of cement at all the ages compared with grade I fly ash, and not only does its pozzolanic reaction start earlier, but the reaction degree is higher and the speed is quicker. Jingjing Feng, 1  Jianwei Sun, 2,3  and Peiyu Yan 3 1 College of Hydraulic and Civil Engineering, Shandong Agricultural University, Tai’an, Shandong 271018, China 2 School of Mechanics and Civil Engineering, China University of Mining and Technology, Beijing 100083, China 3 Department of Civil Engineering, Tsinghua University, Beijing 100084, China Correspondence should be addressed to Jingjing Feng; [email protected] Academic Editor: Evangelos J. Sapountzakis Source: Advances in Civil Engineering, vol. 2018, Article ID 4023178, 7 pages, 2018.https://doi.org/10.1155/2018/4023178. B efore three days, the contribution of ground fly ash to the strength is mainly due to physical filling and microaggregate effect. After that, the contribution of pozzolanic effect to the strength becomes obvious and can significantly increase the compressive strength after 60 days and the flexural strength after 28 days. The ground fly ash is better than grade I fly ash to optimise the pore structure of hardened pastes. It can significantly reduce the number of harmful pores (>20 nm) and increase the number of harmless pores (<20 nm), which refines the pore structure and makes the structure denser. 1. Introduction Fly ash is a by-product from the residue of coal combustion, and it is a kind of pozzolana. Fly ash tends to be spherical with micrometres to millimetres particles 50 AFRICAN DESIGN MAGAZINE © | MAY 2018 and has a relatively high reactivity depending on the chemical formation of its individual particle [1]. These made the demand of fly ash grow steadily over the past 30 years [2, 3], especially in concrete and construction industries [3, 4]. Therefore, fly ash has become the most widely used mineral admixture in all kinds of concrete [5, 6]. The main chemical components of fly ash are Al2O3, SiO2, and Fe2O3 [7] and fly ash consists of a major amorphous phase and a small amount of crystalline phases [8, 9]. At early stages of hydration, fly ash particles often act as microaggregates to fill the pores of binders and nuclei for the hydration products [10], while at later stages, the chemical effect of fly ash works. Fly ash can react with Ca(OH)2, which is a product of cement hydration, to form C–S–H gel [11, 12]. This is the so-called pozzolanic reaction. The